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  • American Geophysical Union  (27,324)
  • Blackwell Publishing Ltd  (20,802)
  • Annual Reviews
  • International Union of Crystallography
  • 2020-2024  (370)
  • 2020-2022  (17,199)
  • 1980-1984  (45,238)
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  • 1
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    Millimeter wave spectroscopic measurements over the South Pole: 5. Morphology and evolution of HNO3vertical distribution, 1993 versus 1995 (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-21
    Description: We compare differences and similarities in the annual stratospheric HNO3 cycle derived from ground‐based measurements at the South Pole during 1993 and 1995, after correcting an error in earlier published profile retrievals for 1993 which led to under estimation of mixing ratios. The data series presented here provide profiling over the range ∼16–48 km, and cover the fall‐winter‐spring cycle in the behavior of HNO3 in the extreme Antarctic with a large degree of temporal overlap. With the exception of one gap of 20 days, the combined data sets cover a full annual cycle. The record shows an increase in HNO3 above 30 km occurring about 20 days before sunset, which appears to be the result of higher altitude heterogeneous conversion of NOx as photolysis diminishes. Both years show a strong increase in HNO3 beginning about polar sunset, in a layer peaking at about 25 km, as additional NOx is heterogeneously converted to nitric acid. When temperatures drop to the polar stratospheric cloud (PSC) formation range near the end of May, gas phase HNO3 is rapidly reduced in the lower stratosphere, although at least 2–3 weeks of temperatures ≤192 K appear to be required to complete most of the gas‐phase removal at the upper end of the depletion range (22–25 km). Despite a significant difference in residual sulfate loading from the explosion of Mount Pinatubo, there appears to be little gross difference in the timing and effects of PSC formation in removing gas phase HNO3 in these 2 years, though removal may be more rapid in 1995. Incorporation of gas phase HNO3 into PSCs appears to be nearly complete up to ∼25 km by midwinter. We also see a repeat of the formation of gas phase HNO3 in the middle stratosphere in early midwinter of 1995 with about the same timing as in 1993, suggesting that this phenomenon is driven by a repetition of dynamical transport and appropriate temperatures and pressures in the polar night, and not (as has been suggested) by ion‐based heterogeneous chemistry that requires triggering by large relativistic electron fluxes. High‐altitude HNO3 production peaks during a period of ∼20 days, but appears to persist for up to ∼40 days in the 40–45 km range, ceasing well before sunrise. This HNO3 descends rapidly throughout the production period, at a rate in good agreement with theoretically determined midwinter subsidence rates. As noted in earlier studies, later warming of this region above PSC evaporation temperatures does not cause reappearance of large amounts of HNO3, indicating that most PSCs gravitationally sink out of the stratosphere before early spring. We present evidence that smaller PSCs do evaporate to ∼1 to 3.5 ppbv of HNO3 in the lower stratosphere, however, working downward from ∼25 km as temperatures rise during the late winter. There is a delay of ∼15 days after sunrise before photolysis causes significant depletion in the altitude range below ∼30 km, where subsidence has carried virtually all higher‐altitude HNO3 by polar sunrise. Some continued subsidence and photolysis combine to keep mixing ratios less than ∼5 ppbv below 30 km until the final breakdown of the vortex in November brings larger amounts of HNO3 with air from lower latitudes.
    Description: Published
    Description: 17739-17750
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
    Keywords: ozone depletion ; HNO3 ; Antarctic stratosphere ; 01.01. Atmosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Probabilistic Seismic Hazard Analysis at Regional and National Scales: State of the Art and Future Challenges (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-01
    Description: Seismic hazard modeling is a multidisciplinary science that aims to forecast earthquake occurrence and its resultant ground shaking. Such models consist of a probabilistic framework that quantifies uncertainty across a complex system; typically, this includes at least two model components developed from Earth science: seismic source and ground motion models. Although there is no scientific prescription for the forecast length, the most common probabilistic seismic hazard analyses consider forecasting windows of 30 to 50 years, which are typically an engineering demand for building code purposes. These types of analyses are the topic of this review paper. Although the core methods and assumptions of seismic hazard modeling have largely remained unchanged for more than 50 years, we review the most recent initiatives, which face the difficult task of meeting both the increasingly sophisticated demands of society and keeping pace with advances in scientific understanding. A need for more accurate and spatially precise hazard forecasting must be balanced with increased quantification of uncertainty and new challenges such as moving from time‐independent hazard to forecasts that are time dependent and specific to the time period of interest. Meeting these challenges requires the development of science‐driven models, which integrate all information available, the adoption of proper mathematical frameworks to quantify the different types of uncertainties in the hazard model, and the development of a proper testing phase of the model to quantify its consistency and skill. We review the state of the art of the National Seismic Hazard Modeling and how the most innovative approaches try to address future challenges.
    Description: Published
    Description: e2019RG000653
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Assessment of earthquake locations in 3D deterministic velocity models: a case study from the Altotiberina Near Fault Observatory (Italy) (2020)
    American Geophysical Union
    Details
    Publication Date: 2021-07-14
    Description: An edited version of this paper was published by AGU. Copyright (2016) American Geophysical Union.
    Description: The accuracy of earthquake locations and their correspondence with subsurface geology depends strongly on the accuracy of the available seismic velocity model. Most modern methods to construct a velocity model for earthquake location are based on the inversion of passive source seismological data. Another approach is the integration of high-resolution geological and geophysical data to construct deterministic velocity models in which earthquake locations can be directly correlated to the geological structures. Such models have to be kinematically consistent with independent seismological data in order to provide precise hypocenter solutions. We present the Altotiberina (AT) seismic model, a three-dimensional velocity model for the Upper Tiber Valley region (Northern Apennines, Italy), constructed by combining 300 km of seismic reflection profiles, 6 deep boreholes (down to 5 km depth), detailed data from geological surveys and direct measurements of P- and S-wave velocities performed in situ and in laboratory. We assess the robustness of the AT seismic model by locating 11,713 earthquakes with a non-linear, global-search inversion method and comparing the probabilistic hypocenter solutions to those calculated in three previously published velocity models, constructed by inverting passive seismological data only. Our results demonstrate that the AT seismic model is able to provide higher-quality hypocenter locations than the previous velocity models. Earthquake locations are consistent with the subsurface geological structures and show a high degree of spatial correlation with specific lithostratigraphic units, suggesting a lithological control on the seismic activity evolution.
    Description: Published
    Description: 8113-8135
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
    Keywords: deterministic velocity model ; earthquakes ; nonlinear hypocenter location ; lithological control on seismicity ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    Intercomparison of stratospheric HNO3measurements over Antarctica: Ground-based millimeter-wave versus UARS/MLS Version 5 retrievals (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-21
    Description: [1] We present the first intercomparison between the two most comprehensive records of gas‐phase HNO3 profiles in the Antarctic stratosphere, covering the greater part of 1993 and 1995. We compare measurements by the Stony Brook Ground‐Based Millimeter‐wave Spectrometer (GBMS) at the South Pole with Version 5 HNO3 data from the Microwave Limb Sounder (MLS) aboard the Upper Atmospheric Research Satellite. Trajectory tracing was used to select MLS measurements in the 70°–80°S latitude band that sampled air observed by the GBMS during passage over the Pole. When temperatures were near the HNO3 condensation range, additional screening was performed to select MLS measurements that sampled air parcels within 1.5 K of the temperature they experienced over the Pole. Quantitative comparisons are given at 7 different potential temperature levels spanning the range ∼19–30 km. Agreement between the data sets is quite good between 465 and 655 K (∼20–25 km) during a large fraction of the year. Agreement is best during winter and spring, when seasonally averaged differences are generally within 1 ppbv below ∼25 km. At higher altitudes, and during summer and fall, the agreement becomes worse, and GBMS measurements can exceed MLS values by more than 3 ppbv. We provide evidence that differences occurring in the lower stratosphere during fall are due to lack of colocation between the two data sets during a period of strong poleward gradients in HNO3. Remaining discrepancies between GBMS and MLS V5 HNO3 measurements are thought to be due to instrumental or retrieval biases.
    Description: Published
    Description: id 4809
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
    Keywords: MLS ; Nitric acid ; polar stratosphere ; 01.01. Atmosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Tropical Rains Controlling Deposition of Saharan Dust Across the North Atlantic Ocean (2020)
    American Geophysical Union
    In:  EPIC3Geophysical Research Letters, American Geophysical Union, 47(5), ISSN: 0094-8276
    Details
    Publication Date: 2020-05-13
    Description: Mineral dust plays an important role in the atmospheric radiation budget as well as in the ocean carbon cycle through fertilization and by ballasting of settling organic matter. However, observational records of open‐ocean dust deposition are sparse. Here, we present the spatial and temporal evolution of Saharan dust deposition over 2 years from marine sediment traps across the North Atlantic, directly below the core of the Saharan dust plume, with highest dust fluxes observed in summer. We combined the observed deposition fluxes with model simulations and satellite observations and argue that dust deposition in the Atlantic is predominantly controlled by summer rains. The dominant depositional pathway changes from wet deposition in summer to dry deposition in winter. Wet deposition has previously been suggested to increase the release of dust‐derived nutrients and their bioavailability, which may be a key contributor to surface‐ocean productivity in remote and oligotrophic parts of the oceans.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 6
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    Arctic Continental Margin Sediments as Possible Fe and Mn Sources to Seawater as Sea Ice Retreats: Insights From the Eurasian Margin (2020)
    American Geophysical Union
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union, 34(8), ISSN: 0886-6236
    Details
    Publication Date: 2020-09-02
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Ice flow and the conditions of the ice-bed interface at the onset of the Northeast Greenland Ice Stream (2020)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2020 - Online Everywhere, Online, 2020-12-01-2020-12-17American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component contributing to the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The ice stream geometry and surface velocities in the onset region of the NEGIS are not yet sufficiently well reproduced by ice sheet models. We present an assessment of the basal conditions of the onset region in a systematic analysis of airborne ultra-wideband radar data. Our data yield a new detailed model of ice-thickness distribution and basal topography in the upstream part of the ice stream. We observe a change from a smooth to a rougher bed where the ice stream widens from 10 to 60 km, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. The observation of off-nadir reflections that are symmetrical to the bed reflection in the radargrams suggests that these structures are elongated subglacial landforms, which in turn indicate potential streamlining of the bed. Together with basal water routing pathways, our observations hint to two different zones in this part of the NEGIS: an accelerating and smooth upstream region, which is collecting water, with reduced basal traction, and in the further downstream part, where the ice stream is slowing down and is widening, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 8
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    Simulated Thermohaline Fingerprints in Response to Different Greenland‐Scotland Ridge and Fram Strait Subsidence Histories (2020)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 35, ISSN: 2572-4525
    Details
    Publication Date: 2021-02-16
    Description: Changes in ocean gateway configuration can induce basin‐scale rearrangements in ocean current characteristics. However, there is large uncertainty in the relative timing of the Oligocene/Miocene subsidence histories of the Greenland‐Scotland Ridge (GSR) and the Fram Strait (FS). By using a climate model, we investigate the temperature and salinity changes in response to the subsidence of these two key ocean gateways during early to middle Miocene. For a singular subsidence of the GSR, we detect warming and a salinity increase in the Nordic Seas and the Arctic Ocean. As convection sites shift to the north of Iceland, North Atlantic Deep Water (NADW) is formed at cooler temperatures. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface can cause a cooling in the southern high latitudes. These characteristic responses to the GSR deepening are independent of the FS being shallow or deep. An isolated subsidence of the FS gateway for a deep GSR shows less pronounced warming and salinity increase in the Nordic Seas. Arctic temperatures remain unaltered, but a stronger salinity increase is detected, which further increases the density of NADW. The increase in salinity enhances the contribution of NADW to the abyssal ocean at the expense of the colder southern source water component. These relative changes largely counteract each other and cause a negligible warming in the upwelling regions of the Southern Ocean.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 9
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    Planet Microbe: An Ontology-Enriched Cyberinfrastructure System for FAIR Marine ‘Omics Data (2020)
    American Geophysical Union
    In:  EPIC3Ocean Sciences Meeting 2020, 2020-02-16-2020-02-21American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    Antarctic Circumpolar Current Dynamics at the Pacific Entrance to the Drake Passage Over the Past 1.3 Million Years (2020)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 35(7), pp. e2019PA003773, ISSN: 2572-4525
    Details
    Publication Date: 2021-02-01
    Description: The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all three major basins of the global ocean. Our knowledge of glacial‐interglacial changes in ACC dynamics in the southeast Pacific is not well constrained and presently only based on reconstructions covering the last glacial cycle. Here we use a combination of mean sortable silt grain size of the terrigenous sediment fraction (10–63 μm, "Sortable Silt") and X‐ray fluorescence scanner‐derived Zr/Rb ratios as flow strength proxies to examine ACC variations at the Pacific entrance to the Drake Passage (DP) in the vicinity of the Subantarctic Front. Our results indicate that at the DP entrance, ACC strength varied by ~6–16% on glacial‐interglacial time scales, yielding higher current speeds during interglacial times and reduced current speeds during glacials. We provide evidence that previous observations of a reduction in DP throughflow during the last glacial period are part of a consistent pattern extending for at least the last 1.3 Ma. The orbital‐scale cyclicity follows well‐known global climate changes from prevailing ca. 41‐kyr cycles in the early part of the record (1.3 Ma to 850 ka; marine isotope stage 21) across the mid‐Pleistocene transition into the middle and late Pleistocene 100‐kyr world. A comparison to a bottom water flow record from the deep western boundary current off New Zealand (Ocean Drilling Program Site 1123) reveals anti‐phased changes between the two sites. The enhanced supply of deep water along the DP and into the Atlantic Ocean during interglacials corresponds to a weakened flow of the SW Pacific deep western boundary current.
    Repository Name: EPIC Alfred Wegener Institut
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  • 11
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    Evaluating learning spaces in flood risk management in Germany: Lessons for governance research (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-06-28
    Description: Efforts to collaboratively manage the risk of flooding are ultimately based on individuals learning about risks, the decision process, and the effectiveness of decisions made in prior situations. This article argues that much can be learned about a governance setting by explicitly evaluating the relationships through which influential individuals and their immediate contacts receive and send information to one another. We define these individuals as “brokers,” and the networks that emerge from their interactions as “learning spaces.” The aim of this article is to develop strategies to identify and evaluate the properties of a broker's learning space that are indicative of a collaborative flood risk management arrangement. The first part of this article introduces a set of indicators, and presents strategies to employ this list so as to systematically identify brokers, and compare their learning spaces. The second part outlines the lessons from an evaluation that explored cases in two distinct flood risk management settings in Germany. The results show differences in the observed brokers' learning spaces. The contacts and interactions of the broker in Baden‐Württemberg imply a collaborative setting. In contrast, learning space of the broker in North Rhine‐Westphalia lacks the same level of diversity and polycentricity.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: MWK Baden‐Württemberg
    Keywords: 333.91 ; brokerage ; collaborative water governance ; comanagement ; comparative analysis ; social networks
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  • 12
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    Facilitated crystal handling using a simple device for evaporation reduction in microtiter plates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: In the past two decades, most of the steps in a macromolecular crystallography experiment have undergone tremendous development with respect to speed, feasibility and increase of throughput. The part of the experimental workflow that is still a bottleneck, despite significant efforts, involves the manipulation and harvesting of the crystals for the diffraction experiment. Here, a novel low‐cost device is presented that functions as a cover for 96‐well crystallization plates. This device enables access to the individual experiments one at a time by its movable parts, while minimizing evaporation of all other experiments of the plate. In initial tests, drops of many typically used crystallization cocktails could be successfully protected for up to 6 h. Therefore, the manipulation and harvesting of crystals is straightforward for the experimenter, enabling significantly higher throughput. This is useful for many macromolecular crystallography experiments, especially multi‐crystal screening campaigns.
    Description: A simple and low‐cost device has been developed to minimize evaporation in microtiter plates for easy crystal handling and harvesting. image
    Keywords: 548 ; evaporation reduction ; crystal handling ; crystal harvesting ; crystallographic fragment screening
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  • 13
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    Cation distribution in Cu2ZnSnSe4, Cu2FeSnS4 and Cu2ZnSiSe4 by multiple‐edge anomalous diffraction (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Semiconductors from this group of materials are promising candidates for photovoltaic applications. Their properties strongly depend on point defects, in particular related to cation order–disorder. However, Cu+, Zn2+ and Fe2+ have very similar scattering factors and are all but indistinguishable in usual X‐ray diffraction experiments. Anomalous diffraction utilizes the dependency of the atomic scattering factors f′ and f′′ of the energy of the radiation, especially close to the element‐specific absorption edges. In the MEAD technique, individual Bragg peaks are tracked over an absorption edge. The intensity changes depending on the structure factor can be highly characteristic for Miller indices selected for a specific structural problem, but require very exact measurements. Beamline KMC‐2 at synchrotron BESSY II, Berlin, has been recently upgraded for this technique. Anomalous X‐ray powder diffraction and XAFS compliment the data. Application of this technique confirmed established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS). In contrast to the literature, cation distribution in Cu2ZnSiSe4 (CZSiSe) is shown to adopt a highly ordered wurtz‐kesterite structure type.
    Description: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Application of this technique confirms established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS), but in Cu2ZnSiSe4 (CZSiSe) the cation distribution is shown to adopt a highly ordered wurtz‐kesterite structure type in contrast to the literature. image
    Keywords: 548 ; synchrotron ; anomalous diffraction ; semiconductor ; MEAD
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  • 14
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    The copper(II)‐binding tripeptide GHK, a valuable crystallization and phasing tag for macromolecular crystallography (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: The growth of diffraction‐quality crystals and experimental phasing remain two of the main bottlenecks in protein crystallography. Here, the high‐affinity copper(II)‐binding tripeptide GHK was fused to the N‐terminus of a GFP variant and an MBP‐FG peptide fusion. The GHK tag promoted crystallization, with various residues (His, Asp, His/Pro) from symmetry molecules completing the copper(II) square‐pyramidal coordination sphere. Rapid structure determination by copper SAD phasing could be achieved, even at a very low Bijvoet ratio or after significant radiation damage. When collecting highly redundant data at a wavelength close to the copper absorption edge, residual S‐atom positions could also be located in log‐likelihood‐gradient maps and used to improve the phases. The GHK copper SAD method provides a convenient way of both crystallizing and phasing macromolecular structures, and will complement the current trend towards native sulfur SAD and MR‐SAD phasing.
    Description: A novel three‐residue tag containing the residues GHK that can be used to promote crystallization and in SAD phasing experiments using its tightly bound copper ion is described. image
    Keywords: 548 ; phasing ; crystallization ; GHK ; SAD
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  • 15
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    Determining paracrystallinity in mixed‐tacticity polyhydroxybutyrates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-30
    Description: Recently, the authors reported on the development of crystallinity in mixed‐tacticity polyhydroxybutyrates. Comparable values reported in the literature vary depending on the manner of determination, the discrepancies being partially attributable to scattering from paracrystalline portions of the material. These portions can be qualified by peak profile fitting or quantified by allocation of scattered X‐ray intensities. However, the latter requires a good quality of the former, which in turn must additionally account for peak broadening inherent in the measurement setup, and due to limited crystallite sizes and the possible presence of microstrain. Since broadening due to microstrain and paracrystalline order both scale with scattering vector, they are easily confounded. In this work, a method to directionally discern these two influences on the peak shape in a Rietveld refinement is presented. Allocating intensities to amorphous, bulk and paracrystalline portions with changing tactic disturbance provided internal validations of the obtained directional numbers. In addition, the correlation between obtained thermal factors and Young's moduli, determined in earlier work, is discussed.
    Description: A method to robustly determine paracrystalline contents from Rietveld‐refined powder X‐ray data is presented and discussed for the example of mixed‐tacticity polyhydroxybutyrates. image
    Keywords: 548 ; polyhydroxybutyrates ; mixed tacticity ; paracrystallinity ; Rietveld refinement ; thermal factors
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  • 16
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    Concepts for nondestructive and depth‐resolved X‐ray residual stress analysis in the near‐surface region of nearly single crystalline materials with mosaic structure (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-27
    Description: Two evaluation concepts for nondestructive depth‐resolved X‐ray residual stress analysis in the near‐surface region of materials with cubic symmetry and nearly single crystalline structure are introduced by simulated examples. Both concepts are based on the same data acquisition strategy, which consists in the determination of lattice‐spacing depth profiles along the ⟨hkl⟩ poles by stepwise sample rotation around the scattering vector. Segmentation of these profiles parallel to the sample surface provides the lattice strain state as a function of depth. The first evaluation concept extends the crystallite group method developed for materials with pronounced crystallographic texture by the feature of depth resolution and can be applied to samples with arbitrary orientation. The second evaluation concept, which adapts the linear regression approach of the sin2ψ method for the case of single crystalline materials, is restricted to samples with (001) orientation. The influence of the strain‐free lattice parameter a0 on residual stress analysis using both evaluation concepts is discussed on the basis of explicitly derived relations.
    Description: Two data evaluation concepts are proposed for nondestructive and depth‐resolved X‐ray residual stress analysis by means of energy‐dispersive diffraction on materials featuring cubic symmetry and a nearly single crystalline structure. image
    Keywords: 548 ; residual stress ; X‐ray diffraction ; depth‐resolved analysis ; mosaic crystals
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  • 17
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    X‐ray dichroism in polyimide caused by non‐resonant scattering (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-30
    Description: Dichroism is one of the most important optical effects in both the visible and the X‐ray range. Besides absorption, scattering can also contribute to dichroism. This paper demonstrates that, based on the example of polyimide, materials can show tiny dichroism even far from electronic resonances due to scattering. Although the effect is small, it can lead to a measurable polarization change and might have influence on highly sensitive polarimetric experiments.
    Description: Aligned molecules, for example in polyimide foils, lead to small dichroism even far from resonances, which can be revealed by high‐precision X‐ray polarimetry. image
    Keywords: 548 ; polyimide ; polarization ; X‐ray polarimetry ; wide‐angle scattering ; X‐ray dichroism
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  • 18
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    Elastic stiffness coefficients of thiourea from thermal diffuse scattering (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-27
    Description: The complete elastic stiffness tensor of thiourea has been determined from thermal diffuse scattering (TDS) using high‐energy photons (100 keV). Comparison with earlier data confirms a very good agreement of the tensor coefficients. In contrast with established methods to obtain elastic stiffness coefficients (e.g. Brillouin spectroscopy, inelastic X‐ray or neutron scattering, ultrasound spectroscopy), their determination from TDS is faster, does not require large samples or intricate sample preparation, and is applicable to opaque crystals. Using high‐energy photons extends the applicability of the TDS‐based approach to organic compounds which would suffer from radiation damage at lower photon energies.
    Description: The elastic stiffness coefficients of thiourea are determined from thermal diffuse scattering. image
    Keywords: 548 ; thermal diffuse scattering ; elastic stiffness ; thiourea
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  • 19
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    Fast fitting of reflectivity data of growing thin films using neural networks (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-03
    Description: X‐ray reflectivity (XRR) is a powerful and popular scattering technique that can give valuable insight into the growth behavior of thin films. This study shows how a simple artificial neural network model can be used to determine the thickness, roughness and density of thin films of different organic semiconductors [diindenoperylene, copper(II) phthalocyanine and α‐sexithiophene] on silica from their XRR data with millisecond computation time and with minimal user input or a priori knowledge. For a large experimental data set of 372 XRR curves, it is shown that a simple fully connected model can provide good results with a mean absolute percentage error of 8–18% when compared with the results obtained by a genetic least mean squares fit using the classical Parratt formalism. Furthermore, current drawbacks and prospects for improvement are discussed.
    Description: Artificial neural networks trained with simulated data are shown to correctly and quickly determine film parameters from experimental X‐ray reflectivity curves.
    Keywords: 548 ; X‐ray reflectivity ; machine learning ; organic semi‐conductors ; neural networks
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    Numerically stable form factor of any polygon and polyhedron (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-05
    Description: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Apparent singularities, all removable, are discussed in detail. Cancellation near the singularities causes a loss of precision that can be avoided by using series expansions. An important application domain is small‐angle scattering by nanocrystals.
    Description: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Series expansions are used to ensure numeric precision close to apparent singularities. image
    Keywords: 548 ; form factors ; polyhedra ; Fourier shape transform
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    ROBL‐II at ESRF: a synchrotron toolbox for actinide research (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-30
    Description: ROBL‐II provides four different experimental stations to investigate actinide and other alpha‐ and beta‐emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub‐p.p.m. range. The XES station with its five bent‐crystal analyzer, Johann‐type setup with Rowland circles of 1.0 and 0.5 m radii provides high‐energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The six‐circle heavy duty goniometer of XRD‐1 is equipped for both high‐resolution powder diffraction as well as surface‐sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X‐ray tomography experiments can be performed at a Pilatus 2M detector stage (XRD‐2). Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.
    Description: ROBL‐II at ESRF provides four experimental stations to investigate actinides with X‐ray absorption and emission spectroscopy, and with surface, high‐resolution powder, and single‐crystal X‐ray diffractometry.
    Keywords: 549 ; actinides ; EXAFS ; XANES ; HERFD‐XANES ; XAS ; XES ; RIXS ; XRD ; CTR ; RAXR ; surface diffraction
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    ATSAS 3.0: expanded functionality and new tools for small‐angle scattering data analysis (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: The ATSAS software suite encompasses a number of programs for the processing, visualization, analysis and modelling of small‐angle scattering data, with a focus on the data measured from biological macromolecules. Here, new developments in the ATSAS 3.0 package are described. They include IMSIM, for simulating isotropic 2D scattering patterns; IMOP, to perform operations on 2D images and masks; DATRESAMPLE, a method for variance estimation of structural invariants through parametric resampling; DATFT, which computes the pair distance distribution function by a direct Fourier transform of the scattering data; PDDFFIT, to compute the scattering data from a pair distance distribution function, allowing comparison with the experimental data; a new module in DATMW for Bayesian consensus‐based concentration‐independent molecular weight estimation; DATMIF, an ab initio shape analysis method that optimizes the search model directly against the scattering data; DAMEMB, an application to set up the initial search volume for multiphase modelling of membrane proteins; ELLLIP, to perform quasi‐atomistic modelling of liposomes with elliptical shapes; NMATOR, which models conformational changes in nucleic acid structures through normal mode analysis in torsion angle space; DAMMIX, which reconstructs the shape of an unknown intermediate in an evolving system; and LIPMIX and BILMIX, for modelling multilamellar and asymmetric lipid vesicles, respectively. In addition, technical updates were deployed to facilitate maintainability of the package, which include porting the PRIMUS graphical interface to Qt5, updating SASpy – a PyMOL plugin to run a subset of ATSAS tools – to be both Python 2 and 3 compatible, and adding utilities to facilitate mmCIF compatibility in future ATSAS releases. All these features are implemented in ATSAS 3.0, freely available for academic users at https://www.embl‐hamburg.de/biosaxs/software.html.
    Description: ATSAS is a comprehensive software suite for the processing, visualization, analysis and modelling of small‐angle scattering data. This article describes developments in the ATSAS 3.0 release, including new programs for data simulation and for the structural modelling of lipids, nucleic acids and polydisperse systems. image
    Keywords: 548 ; small‐angle scattering ; data analysis ; biological macromolecules ; structural modelling ; ATSAS
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    Synthetic resampling strategies and machine learning for digital soil mapping in Iran (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-07-04
    Description: Most common machine learning (ML) algorithms usually work well on balanced training sets, that is, datasets in which all classes are approximately represented equally. Otherwise, the accuracy estimates may be unreliable and classes with only a few values are often misclassified or neglected. This is known as a class imbalance problem in machine learning and datasets that do not meet this criterion are referred to as imbalanced data. Most datasets of soil classes are, therefore, imbalanced data. One of our main objectives is to compare eight resampling strategies that have been developed to counteract the imbalanced data problem. We compared the performance of five of the most common ML algorithms with the resampling approaches. The highest increase in prediction accuracy was achieved with SMOTE (the synthetic minority oversampling technique). In comparison to the baseline prediction on the original dataset, we achieved an increase of about 10, 20 and 10% in the overall accuracy, kappa index and F‐score, respectively. Regarding the ML approaches, random forest (RF) showed the best performance with an overall accuracy, kappa index and F‐score of 66, 60 and 57%, respectively. Moreover, the combination of RF and SMOTE improved the accuracy of the individual soil classes, compared to RF trained on the original dataset and allowed better prediction of soil classes with a low number of samples in the corresponding soil profile database, in our case for Chernozems. Our results show that balancing existing soil legacy data using synthetic sampling strategies can significantly improve the prediction accuracy in digital soil mapping (DSM). Highlights Spatial distribution of soil classes in Iran can be predicted using machine learning (ML) algorithms. The synthetic minority oversampling technique overcomes the drawback of imbalanced and highly biased soil legacy data. When combining a random forest model with synthetic sampling strategies the prediction accuracy of the soil model improves significantly. The resulting new soil map of Iran has a much higher spatial resolution compared to existing maps and displays new soil classes that have not yet been mapped in Iran.
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: German Research Foundation http://dx.doi.org/10.13039/501100001659
    Description: Soil and Water Research Institute, Agricultural Research, Education and Extension Organization, Karaj, Iran
    Keywords: 631.4 ; covariates ; imbalanced data ; machine learning ; random forest ; soil legacy data
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  • 24
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    XGANDALF – extended gradient descent algorithm for lattice finding (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: Serial crystallography records still diffraction patterns from single, randomly oriented crystals, then merges data from hundreds or thousands of them to form a complete data set. To process the data, the diffraction patterns must first be indexed, equivalent to determining the orientation of each crystal. A novel automatic indexing algorithm is presented, which in tests usually gives significantly higher indexing rates than alternative programs currently available for this task. The algorithm does not require prior knowledge of the lattice parameters but can make use of that information if provided, and also allows indexing of diffraction patterns generated by several crystals in the beam. Cases with a small number of Bragg spots per pattern appear to particularly benefit from the new approach. The algorithm has been implemented and optimized for fast execution, making it suitable for real‐time feedback during serial crystallography experiments. It is implemented in an open‐source C++ library and distributed under the LGPLv3 licence. An interface to it has been added to the CrystFEL software suite.
    Description: A description and evaluation are given of XGANDALF, extended gradient descent algorithm for lattice finding, an algorithm developed for fast and accurate indexing of snapshot diffraction patterns. image
    Keywords: 548 ; indexing ; XGANDALF ; CrystFEL ; multiple lattices ; serial crystallography
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    pinkIndexer – a universal indexer for pink‐beam X‐ray and electron diffraction snapshots (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: A crystallographic indexing algorithm, pinkIndexer, is presented for the analysis of snapshot diffraction patterns. It can be used in a variety of contexts including measurements made with a monochromatic radiation source, a polychromatic source or with radiation of very short wavelength. As such, the algorithm is particularly suited to automated data processing for two emerging measurement techniques for macromolecular structure determination: serial pink‐beam X‐ray crystallography and serial electron crystallography, which until now lacked reliable programs for analyzing many individual diffraction patterns from crystals of uncorrelated orientation. The algorithm requires approximate knowledge of the unit‐cell parameters of the crystal, but not the wavelengths associated with each Bragg spot. The use of pinkIndexer is demonstrated by obtaining 1005 lattices from a published pink‐beam serial crystallography data set that had previously yielded 140 indexed lattices. Additionally, in tests on experimental serial crystallography diffraction data recorded with quasi‐monochromatic X‐rays and with electrons the algorithm indexed more patterns than other programs tested.
    Description: pinkIndexer, an algorithm developed for indexing of snapshot diffraction patterns recorded with pink‐beam X‐rays, monochromatic X‐rays and electrons, is described and its use evaluated. image
    Keywords: 548 ; indexing ; pinkIndexer ; CrystFEL ; pink X‐ray beam ; serial electron diffraction
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    Crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-17
    Description: CRM1 is a nuclear export receptor that has been intensively targeted over the last decade for the development of antitumor and antiviral drugs. Structural analysis of several inhibitor compounds bound to CRM1 revealed that their mechanism of action relies on the covalent modification of a critical cysteine residue (Cys528 in the human receptor) located in the nuclear export signal‐binding cleft. This study presents the crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP at 2.58 Å resolution. The results demonstrate that buffer components can interfere with the characterization of cysteine‐dependent inhibitor compounds.
    Description: The covalent modification of human CRM1 by 2‐mercaptoethanol interferes with the characterization of cysteine‐dependent inhibitor compounds. image
    Keywords: 548 ; nuclear export ; cancer ; exportin 1 ; cysteine modification
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    Impact of biochar on nutrient supply, crop yield and microbial respiration on sandy soils of northern Germany (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-06-16
    Description: The application of biochar to agricultural soils to increase nutrient availability, crop production and carbon sequestration has gained increasing interest but data from field experiments on temperate, marginal soils are still under‐represented. In the current study, biochar, produced from organic residues (digestates) from a biogas plant, was applied with and without digestates at low (3.4 t ha−1) and intermediate (17.1 t ha−1) rates to two acidic and sandy soils in northern Germany that are used for corn (Zea mays L.) production. Soil nutrient availability, crop yields, microbial biomass and carbon dioxide (CO2) emissions from heterotrophic respiration were measured over two consecutive years. The effects of biochar application depended on the intrinsic properties of the two tested soils and the biochar application rates. Although the soils at the fallow site, with initially low nutrient concentrations, showed a significant increase in pH, soil nutrients and crop yield after low biochar application rates, a similar response was found at the cornfield site only after application of substantially larger amounts of biochar. The effect of a single dose of biochar at the beginning of the experiment diminished over time but was still detectable after 2 years. Whereas plant available nutrient concentrations increased after biochar application, the availability of potentially phytotoxic trace elements (Zn, Pb, Cd, Cr) decreased significantly, and although slight increases in microbial biomass carbon and heterotrophic CO2 fluxes were observed after biochar application, they were mostly not significant. The results indicate that the application of relatively small amounts of biochar could have positive effects on plant available nutrients and crop yields of marginal arable soils and may decrease the need for mineral fertilizers while simultaneously increasing the sequestration of soil organic carbon. Highlights A low rate of biochar increased plant available nutrients and crop yield on marginal soils. Biochar application reduced the availability of potentially harmful trace elements. Heterotrophic respiration showed no clear response to biochar application. Biochar application may reduce fertilizer need and increase carbon sequestration on marginal soils.
    Description: German Academic Exchange Service http://dx.doi.org/10.13039/501100001655
    Description: Institute Strategic Programme grants, “Soils to Nutrition”
    Keywords: 631.4 ; black carbon ; carbon sequestration ; corn ; digestate ; heterotrophic respiration ; marginal soils ; microbial biomass
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    Staircase array of inclined refractive multi‐lenses for large field of view pixel super‐resolution scanning transmission hard X‐ray microscopy (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: Owing to the development of X‐ray focusing optics during the past decades, synchrotron‐based X‐ray microscopy techniques allow the study of specimens with unprecedented spatial resolution, down to 10 nm, using soft and medium X‐ray photon energies, though at the expense of the field of view (FOV). One of the approaches to increase the FOV to square millimetres is raster‐scanning of the specimen using a single nanoprobe; however, this results in a long data acquisition time. This work employs an array of inclined biconcave parabolic refractive multi‐lenses (RMLs), fabricated by deep X‐ray lithography and electroplating to generate a large number of long X‐ray foci. Since the FOV is limited by the pattern height if a single RML is used by impinging X‐rays parallel to the substrate, many RMLs at regular intervals in the orthogonal direction were fabricated by tilted exposure. By inclining the substrate correspondingly to the tilted exposure, 378000 X‐ray line foci were generated with a length in the centimetre range and constant intervals in the sub‐micrometre range. The capability of this new X‐ray focusing device was first confirmed using ray‐tracing simulations and then using synchrotron radiation at BL20B2 of SPring‐8, Japan. Taking account of the fact that the refractive lens is effective for focusing high‐energy X‐rays, the experiment was performed with 35 keV X‐rays. Next, by scanning a specimen through the line foci, this device was used to perform large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy (PSR‐STHXM) with a 780 ± 40 nm spatial resolution within an FOV of 1.64 cm × 1.64 cm (limited by the detector area) and a total scanning time of 4 min. Biomedical implant abutments fabricated via selective laser melting using Ti–6Al–4V medical alloy were measured by PSR‐STHXM, suggesting its unique potential for studying extended and thick specimens. Although the super‐resolution function was realized in one dimension in this study, it can be expanded to two dimensions by aligning a pair of presented devices orthogonally.
    Description: A new X‐ray focusing device generates hundreds of thousands of line foci, periodically spaced in the sub‐micrometre range, with centimetre length. It enables to achieve large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy. image
    Keywords: 502.82 ; inclined refractive X‐ray multi‐lens array ; pixel super‐resolution ; scanning transmission hard X‐ray microscopy ; deep X‐ray lithography and electroplating
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    A new concept for temporal gating of synchrotron X‐ray pulses (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-02
    Description: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented. First experimental tests of the concept yield a diffraction efficiency of 0.18%; however, the calculations indicate a theoretical efficiency and contrast of 〉30% and 10−5, respectively. The full efficiency of the pulse picker has not been reached yet due to a long‐range thermal deformation of the sample after absorption of the excitation laser. This method can be implemented in a broad spectral range (100 eV to 20 keV) and is only minimally invasive to an existing setup.
    Description: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented.
    Keywords: 548 ; synchrotron ; time‐resolved ; thermal deformation ; transient grating ; pulse picking
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    The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP at BESSY II (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-06
    Description: The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP for optical pump/X‐ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four‐circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non‐linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time‐resolution of 17 ps is achieved with the `low‐α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X‐ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time‐resolved detection of the diffracted hard X‐ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields are presented.
    Description: The KMC‐3 XPP endstation of the synchrotron BESSY II is dedicated to time‐resolved studies of structural dynamics of matter upon optical and/or electrical excitation using hard X‐ray diffraction with an accessible time range from 17 ps to several microseconds. image
    Keywords: 548 ; beamline instrumentation ; time‐resolved X‐ray diffraction ; optical excitation ; thermal transport ; ferroelectric switching
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    Self‐stated recovery from flooding: Empirical results from a survey in Central Vietnam (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-06-27
    Description: Social inequalities lead to flood resilience inequalities across social groups, a topic that requires improved documentation and understanding. The objective of this paper is to attend to these differences by investigating self‐stated flood recovery across genders in Vietnam as a conceptual replication of earlier results from Germany. This study employs a regression‐based analysis of 1,010 respondents divided between a rural coastal and an urban community in Thua Thien‐Hue province. The results highlight an important set of recovery process‐related variables. The set of relevant variables is similar across genders in terms of inclusion and influence, and includes age, social capital, internal and external support after a flood, perceived severity of previous flood impacts, and the perception of stress‐resilience. However, women were affected more heavily by flooding in terms of longer recovery times, which should be accounted for in risk management. Overall, the studied variables perform similarly in Vietnam and Germany. This study, therefore, conceptually replicates previous results suggesting that women display slightly slower recovery levels as well as that psychological variables influence recovery rates more than adverse flood impacts. This provides an indication of the results' potentially robust nature due to the different socio‐environmental contexts in Germany and Vietnam.
    Keywords: 333.7 ; flood recovery ; resilience ; societal equity ; vulnerability
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    Disordered sodium alkoxides from powder data: crystal structures of sodium ethoxide, propoxide, butoxide and pentoxide, and some of their solvates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: The crystal structures of sodium ethoxide (sodium ethanolate, NaOEt), sodium n‐propoxide (sodium n‐propanolate, NaOnPr), sodium n‐butoxide (sodium n‐butanolate, NaOnBu) and sodium n‐pentoxide (sodium n‐amylate, NaOnAm) were determined from powder X‐ray diffraction data. NaOEt crystallizes in space group P421m, with Z = 2, and the other alkoxides crystallize in P4/nmm, with Z = 2. To resolve space‐group ambiguities, a Bärnighausen tree was set up, and Rietveld refinements were performed with different models. In all structures, the Na and O atoms form a quadratic net, with the alkyl groups pointing outwards on both sides (anti‐PbO type). The alkyl groups are disordered. The disorder becomes even more pronounced with increasing chain length. Recrystallization from the corresponding alcohols yielded four sodium alkoxide solvates: sodium ethoxide ethanol disolvate (NaOEt·2EtOH), sodium n‐propoxide n‐propanol disolvate (NaOnPr·2nPrOH), sodium isopropoxide isopropanol pentasolvate (NaOiPr·5iPrOH) and sodium tert‐amylate tert‐amyl alcohol monosolvate (NaOtAm·tAmOH, tAm = 2‐methyl‐2‐butyl). Their crystal structures were determined by single‐crystal X‐ray diffraction. All these solvates form chain structures consisting of Na+, –O− and –OH groups, encased by alkyl groups. The hydrogen‐bond networks diverge widely among the solvate structures. The hydrogen‐bond topology of the iPrOH network in NaOiPr·5iPrOH shows branched hydrogen bonds and differs considerably from the networks in pure crystalline iPrOH.
    Description: The crystal structures of NaOEt, NaOPr, NaOBu and NaOAm (Am = amyl = pentyl) were determined from powder data. These compounds crystallize in an anti‐PbO structure in the space groups P21m and P4/nmm. Additionally, solvates with the composition NaOEt·2EtOH, NaOPr·2PrOH, NaOiPr·5iPrOH and NaOtAm·tAmOH were synthesized, and their structures were determined from single crystals. They form interesting chain structures of different compositions and topologies. image
    Keywords: 548 ; sodium alkoxide ; powder data ; solvate ; isopropanol ; Bärnighausen tree ; PXRD
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    The potential of ryegrass as cover crop to reduce soil N2O emissions and increase the population size of denitrifying bacteria (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-07-05
    Description: Nitrogen (N) fertilization is the major contributor to nitrous oxide (N2O) emissions from agricultural soil, especially in post‐harvest seasons. This study was carried out to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size. A microcosm experiment was conducted with soil planted with perennial ryegrass (Lolium perenne L.) and bare soil, each with four levels of N fertilizer (0, 5, 10 and 20 g N m−2; applied as calcium ammonium nitrate). The closed‐chamber approach was used to measure soil N2O fluxes. Real‐time PCR was used to estimate the biomass of bacteria and fungi and the abundance of genes involved in denitrification in soil. The results showed that the presence of ryegrass decreased the nitrate content in soil. Cumulative N2O emissions of soil with grass were lower than in bare soil at 5 and 10 g N m−2. Fertilization levels did not affect the abundance of soil bacteria and fungi. Soil with grass showed greater abundances of bacteria and fungi, as well as microorganisms carrying narG, napA, nirK, nirS and nosZ clade I genes. It is concluded that ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions in soils with moderate or high NO3− concentrations. This highlights the importance of cover crops for the reduction of N2O emissions from soil, particularly following N fertilization. Future research should explore the full potential of ryegrass to reduce soil N2O emissions under field conditions as well as in different soils. Highlights This study was to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size; Plant reduced soil N substrates on one side, but their root exudates stimulated denitrification on the other side; N2O emissions were lower in soil with grass than bare soil at medium fertilizer levels, and growing grass stimulated the proliferation of almost all the denitrifying bacteria except nosZ clade II; Ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions.
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: The National Science Project for University of Anhui Province
    Keywords: 551.9 ; 631.4 ; denitrification ; perennial ryegrass (Lolium perenne L.) ; soil bacteria ; soil CO2 emissions ; soil N2O emissions
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    Small‐angle X‐ray scattering from GaN nanowires on Si(111): facet truncation rods, facet roughness and Porod's law (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: Small‐angle X‐ray scattering from GaN nanowires grown on Si(111) is measured in the grazing‐incidence geometry and modelled by means of a Monte Carlo simulation that takes into account the orientational distribution of the faceted nanowires and the roughness of their side facets. It is found that the scattering intensity at large wavevectors does not follow Porod's law I(q) ∝ q−4. The intensity depends on the orientation of the side facets with respect to the incident X‐ray beam. It is maximum when the scattering vector is directed along a facet normal, reminiscent of surface truncation rod scattering. At large wavevectors q, the scattering intensity is reduced by surface roughness. A root‐mean‐square roughness of 0.9 nm, which is the height of just 3–4 atomic steps per micrometre‐long facet, already gives rise to a strong intensity reduction.
    Description: The intensity of small‐angle X‐ray scattering from GaN nanowires on Si(111) depends on the orientation of the side facets with respect to the incident beam. This reminiscence of truncation rod scattering gives rise to a deviation from Porod's law. A roughness of just 3–4 atomic steps per micrometre‐long side facet notably changes the intensity curves. image
    Keywords: 548 ; nanowires ; Porod's law ; facet truncation rods ; small‐angle X‐ray scattering ; SAXS ; grazing‐incidence small‐angle X‐ray scattering ; GISAXS
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    The accuracy of protein models automatically built into cryo‐EM maps with ARP/wARP (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-28
    Description: Recent developments in cryogenic electron microscopy (cryo‐EM) have enabled structural studies of large macromolecular complexes at resolutions previously only attainable using macromolecular crystallography. Although a number of methods can already assist in de novo building of models into high‐resolution cryo‐EM maps, automated and reliable map interpretation remains a challenge. Presented here is a systematic study of the accuracy of models built into cryo‐EM maps using ARP/wARP. It is demonstrated that the local resolution is a good indicator of map interpretability, and for the majority of the test cases ARP/wARP correctly builds 90% of main‐chain fragments in regions where the local resolution is 4.0 Å or better. It is also demonstrated that the coordinate accuracy for models built into cryo‐EM maps is comparable to that of X‐ray crystallographic models at similar local cryo‐EM and crystallographic resolutions. The model accuracy also correlates with the refined atomic displacement parameters.
    Keywords: 548 ; ARP/wARP ; model building ; cryo‐EM ; model accuracy ; sequence assignment
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    Synthesis, crystal structure and structure–property relations of strontium orthocarbonate, Sr2CO4 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-05
    Description: Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single‐crystal X‐ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound.
    Description: A new orthocarbonate, Sr2CO4, was synthesized under extreme pressure and temperature conditions of 92 GPa and 2500 K, respectively. The crystal structure of the compound s fully characterized in situ by synchrotron single‐crystal X‐ray diffraction and DFT calculations were employed to provide insight into its equation of state, Raman and IR spectra, and bonding. image
    Keywords: 548 ; orthocarbonates ; crystal structure ; single‐crystal X‐ray diffraction ; high pressure ; Sr2CO4
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  • 37
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    Anomalous SAXS at P12 beamline EMBL Hamburg: instrumentation and applications (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-28
    Description: Small‐angle X‐ray scattering (SAXS) is an established method for studying nanostructured systems and in particular biological macromolecules in solution. To obtain element‐specific information about the sample, anomalous SAXS (ASAXS) exploits changes of the scattering properties of selected atoms when the energy of the incident X‐rays is close to the binding energy of their electrons. While ASAXS is widely applied to condensed matter and inorganic systems, its use for biological macromolecules is challenging because of the weak anomalous effect. Biological objects are often only available in small quantities and are prone to radiation damage, which makes biological ASAXS measurements very challenging. The BioSAXS beamline P12 operated by the European Molecular Biology Laboratory (EMBL) at the PETRA III storage ring (DESY, Hamburg) is dedicated to studies of weakly scattering objects. Here, recent developments at P12 allowing for ASAXS measurements are presented. The beamline control, data acquisition and data reduction pipeline of the beamline were adapted to conduct ASAXS experiments. Modelling tools were developed to compute ASAXS patterns from atomic models, which can be used to analyze the data and to help designing appropriate data collection strategies. These developments are illustrated with ASAXS experiments on different model systems performed at the P12 beamline.
    Keywords: 548 ; ASAXS ; biological SAXS ; metalloproteins ; gold nanoparticles ; anomalous scattering ; beamline development
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    Symmetry relations in wurtzite nitrides and oxide nitrides and the curious case of Pmc21 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-27
    Description: Binary III–V nitrides such as AlN, GaN and InN in the wurtzite‐type structure have long been considered as potent semiconducting materials because of their optoelectronic properties, amongst others. With rising concerns over the utilization of scarce elements, a replacement of the trivalent cations by others in ternary and multinary nitrides has led to the development of different variants of nitrides and oxide nitrides crystallizing in lower‐symmetry variants of wurtzite. This work presents the symmetry relationships between these structural types specific to nitrides and oxide nitrides and updates some prior work on this matter. The non‐existence of compounds crystallizing in Pmc21, formally the highest subgroup of the wurtzite type fulfilling Pauling's rules for 1:1:2 stoichiometries, has been puzzling scientists for a while; a rationalization is given, from a crystallographic basis, of why this space group is unlikely to be adopted.
    Keywords: 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
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  • 39
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    Comparison and evaluation of pair distribution functions, using a similarity measure based on cross‐correlation functions (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-20
    Description: An approach for the comparison of pair distribution functions (PDFs) has been developed using a similarity measure based on cross‐correlation functions. The PDF is very sensitive to changes in the local structure, i.e. small deviations in the structure can cause large signal shifts and significant discrepancies between the PDFs. Therefore, a comparison based on pointwise differences (e.g. R values and difference curves) may lead to the assumption that the investigated PDFs as well as the corresponding structural models are not in agreement at all, whereas a careful visual inspection of the investigated structural models and corresponding PDFs may reveal a relatively good match. To quantify the agreement of different PDFs for those cases an alternative approach is introduced: the similarity measure based on cross‐correlation functions. In this paper, the power of this application of the similarity measure to the analysis of PDFs is highlighted. The similarity measure is compared with the classical Rwp values as representative of the comparison based on pointwise differences as well as with the Pearson product‐moment correlation coefficient, using polymorph IV of barbituric acid as an example.
    Description: A novel approach to the quantification of the agreement between pair distribution functions by a similarity measure based on cross‐correlation functions is introduced and evaluated. image
    Keywords: 548 ; pair distribution functions ; similarity measures ; total scattering techniques ; cross‐correlation functions ; R values
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  • 40
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    Novel experimental setup for megahertz X‐ray diffraction in a diamond anvil cell at the High Energy Density (HED) instrument of the European X‐ray Free‐Electron Laser (EuXFEL) (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: The high‐precision X‐ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X‐ray Free‐Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump–probe X‐ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X‐ray heating and diffraction of Bi under pressure, obtained using 20 fs X‐ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC.
    Description: The high‐precision X‐ray diffraction (XRD) setup for work with diamond anvil cells (DACs) in Interaction Chamber 2 of the High Energy Density (HED) instrument of the European X‐ray Free‐Electron Laser is described. image
    Keywords: 548 ; diamond anvil cells ; X‐ray free‐electron lasers ; high‐precision X‐ray diffraction ; finite element modeling
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  • 41
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    The anisotropy in the optical constants of quartz crystals for soft X‐rays (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: The refractive index of a y‐cut SiO2 crystal surface is reconstructed from orientation‐dependent soft X‐ray reflectometry measurements in the energy range from 45 to 620 eV. Owing to the anisotropy of the crystal structure in the (100) and (001) directions, a significant deviation of the measured reflectance at the Si L2,3 and O K absorption edges is observed. The anisotropy in the optical constants reconstructed from these data is also confirmed by ab initio Bethe–Salpeter equation calculations for the O K edge. This new experimental data set expands the existing literature data for quartz crystal optical constants significantly, particularly in the near‐edge regions.
    Description: The refractive index of a y‐cut SiO2 crystal surface is reconstructed from polarization‐dependent soft X‐ray reflectometry measurements in the energy range from 45 to 620 eV. The reconstructed anisotropy in the optical constants is also confirmed by ab initio Bethe–Salpeter equation calculations of the O K edge. image
    Keywords: 548 ; optical constants ; quartz ; anisotropy ; soft X‐ray reflectometry
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  • 42
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    Unravelling the crystal structure of Nd5.8WO12−δ and Nd5.7W0.75Mo0.25O12−δ mixed ionic electronic conductors (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-05
    Description: Mixed ionic electronic conducting ceramics Nd6−yWO12−δ (δ is the oxygen deficiency) provide excellent stability in harsh environments containing strongly reactive gases such as CO2, CO, H2, H2O or H2S. Due to this chemical stability, they are promising and cost‐efficient candidate materials for gas separation, catalytic membrane reactors and protonic ceramic fuel cell technologies. As in La6−yWO12−δ, the ionic/electronic transport mechanism in Nd6−yWO12−δ is expected to be largely controlled by the crystal structure, the conclusive determination of which is still lacking. This work presents a crystallographic study of Nd5.8WO12−δ and molybdenum‐substituted Nd5.7W0.75Mo0.25O12−δ prepared by the citrate complexation route. High‐resolution synchrotron and neutron powder diffraction data were used in combined Rietveld refinements to unravel the crystal structure of Nd5.8WO12−δ and Nd5.7W0.75Mo0.25O12−δ. Both investigated samples crystallize in a defect fluorite crystal structure with space group Fm3m and doubled unit‐cell parameter due to cation ordering. Mo replaces W at both Wyckoff sites 4a and 48h and is evenly distributed, in contrast with La6−yWO12−δ. X‐ray absorption spectroscopy as a function of partial pressure pO2 in the near‐edge regions excludes oxidation state changes of Nd (Nd3+) and W (W6+) in reducing conditions: the enhanced hydrogen permeation, i.e. ambipolar conduction, observed in Mo‐substituted Nd6−yWO12−δ is therefore explained by the higher Mo reducibility and the creation of additional – disordered – oxygen vacancies.
    Description: The crystal structures of non‐substituted and Mo‐substituted neodymium tungstates are described in detail through neutron diffraction and high‐resolution X‐ray diffraction. Combined X‐ray and neutron diffraction refinements and electron probe micro‐analysis were employed to locate Mo atoms in the crystal structure of Nd6−yW1−zMozO12−δ (z = 0, 0.25), while X‐ray absorption spectroscopy in the near‐edge regions confirmed no changes in the oxidation states of Nd and W.
    Keywords: 548 ; powder diffraction ; mixed conductors ; X‐ray absorption spectroscopy (XAS) ; Nd6−yWO12−δ
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  • 43
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    ogs5py: A Python‐API for the OpenGeoSys 5 Scientific Modeling Package (2021)
    Blackwell Publishing Ltd | Malden, US
    Details
    Publication Date: 2021-07-04
    Description: High‐performance numerical codes are an indispensable tool for hydrogeologists when modeling subsurface flow and transport systems. But as they are written in compiled languages, like C/C++ or Fortran, established software packages are rarely user‐friendly, limiting a wider adoption of such tools. OpenGeoSys (OGS), an open‐source, finite‐element solver for thermo‐hydro‐mechanical–chemical processes in porous and fractured media, is no exception. Graphical user interfaces may increase usability, but do so at a dramatic reduction of flexibility and are difficult or impossible to integrate into a larger workflow. Python offers an optimal trade‐off between these goals by providing a highly flexible, yet comparatively user‐friendly environment for software applications. Hence, we introduce ogs5py, a Python‐API for the OpenGeoSys 5 scientific modeling package. It provides a fully Python‐based representation of an OGS project, a large array of convenience functions for users to interact with OGS and connects OGS to the scientific and computational environment of Python.
    Description: German Federal Environmental Foundation http://dx.doi.org/10.13039/100007636
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: 551.49 ; hydrogeology ; subsurface flow ; modeling ; software
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  • 44
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    High‐temperature treatments of niobium under high vacuum, dilute air‐ and nitrogen‐atmospheres as investigated by in situ X‐ray absorption spectroscopy (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-30
    Description: Niobium metal foils were heat‐treated at 900°C under different conditions and in situ investigated with time‐resolved X‐ray absorption fine‐structure (EXAFS and XANES) measurements. The present study aims to mimic the conditions usually applied for heat treatments of Nb materials used for superconducting radiofrequency cavities, in order to better understand the evolving processes during vacuum annealing as well as for heat treatments in controlled dilute gases. Annealing in vacuum in a commercially available cell showed a substantial amount of oxidation, so that a designated new cell was designed and realized, allowing treatments under clean high‐vacuum conditions as well as under well controllable gas atmospheres. The experiments performed under vacuum demonstrated that the original structure of the Nb foils is preserved, while a detailed evaluation of the X‐ray absorption fine‐structure data acquired during treatments in dilute air atmospheres (10−5 mbar to 10−3 mbar) revealed a linear oxidation with the time of the treatment, and an oxidation rate proportional to the oxygen (air) pressure. The structure of the oxide appears to be very similar to that of polycrystalline NbO. The cell also permits controlled exposures to other reactive gases at elevated temperatures; here the Nb foils were exposed to dilute nitrogen atmospheres after a pre‐conditioning of the studied Nb material for one hour under high‐vacuum conditions, in order to imitate typical conditions used for nitrogen doping of cavity materials. Clear structural changes induced by the N2 exposure were found; however, no evidence for the formation of niobium nitride could be derived from the EXAFS and XANES experiments. The presented results establish the feasibility to study the structural changes of the Nb materials in situ during heat treatments in reactive gases with temporal resolution, which are important to better understand the underlaying mechanisms and the dynamics of phase formation during those heat treatments in more detail.
    Keywords: 548 ; in situ EXAFS ; high temperature ; time‐resolved EXAFS ; niobium
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  • 45
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    High‐Resolution Integrated Transport Model for Studying Surface Water–Groundwater Interaction (2021)
    Blackwell Publishing Ltd | Malden, US
    Details
    Publication Date: 2021-06-27
    Description: Transport processes that lead to exchange of mass between surface water and groundwater play a significant role for the ecological functioning of aquatic systems, for hydrological processes and for biogeochemical transformations. In this study, we present a novel integral modeling approach for flow and transport at the sediment–water interface. The model allows us to simultaneously simulate turbulent surface and subsurface flow and transport with the same conceptual approach. For this purpose, a conservative transport equation was implemented to an existing approach that uses an extended version of the Navier–Stokes equations. Based on previous flume studies which investigated the spreading of a dye tracer under neutral, losing and gaining flow conditions the new solver is validated. Tracer distributions of the experiments are in close agreement with the simulations. The simulated flow paths are significantly affected by in‐ and outflowing groundwater flow. The highest velocities within the sediment are found for losing condition, which leads to shorter residence times compared to neutral and gaining conditions. The largest extent of the hyporheic exchange flow is observed under neutral condition. The new solver can be used for further examinations of cases that are not suitable for the conventional coupled models, for example, if Reynolds numbers are larger than 10. Moreover, results gained with the integral solver provide high‐resolution information on pressure and velocity distributions at the rippled streambed, which can be used to improve flow predictions. This includes the extent of hyporheic exchange under varying ambient groundwater flow conditions.
    Description: Technische Universität Berlin, Germany
    Description: German Research Foundation http://dx.doi.org/10.13039/501100001659
    Keywords: 551.4 ; aquatic systems ; sediment-water interface ; transport model
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  • 46
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    Pressure‐induced Pb–Pb bonding and phase transition in Pb2SnO4 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: High‐pressure single‐crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator‐to‐semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory‐based calculations show that at ambient conditions the channels in the structure host the stereochemically‐active Pb 6s2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.
    Description: The structure of Pb2SnO4 is found to strongly distort on compression and a structural phase transition with a change of space group from Pbam to Pnam occurs at ∼11 GPa. Our complementary DFT‐based calculations show that at ambient conditions, the channels in the structure host the stereochemically active Pb 6s2 lone electron pairs which form bonds between the Pb2+ ions with increasing pressure. image
    Keywords: 548 ; lead stannate (Pb2SnO4) ; density functional theory ; high‐pressure X‐ray diffraction ; pressure‐induced phase transition ; insulator–semiconductor transition
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  • 47
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    Iron isotope fractionation in soil and graminaceous crops after 100 years of liming in the long‐term agricultural experimental site at Berlin‐Dahlem, Germany (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-07-05
    Description: Sustainable arable cropping relies on repeated liming. Yet, the associated increase in soil pH can reduce the availability of iron (Fe) to plants. We hypothesized that repeated liming, but not pedogenic processes such as lessivage (i.e., translocation of clay particles), alters the Fe cycle in Luvisol soil, thereby affecting Fe isotope composition in soils and crops. Hence, we analysed Fe concentrations and isotope compositions in soil profiles and winter rye from the long‐term agricultural experimental site in Berlin‐Dahlem, Germany, where a controlled liming trial with three field replicates per treatment has been conducted on Albic Luvisols since 1923. Heterogeneity in subsoil was observed at this site for Fe concentration but not for Fe isotope composition. Lessivage had not affected Fe isotope composition in the soil profiles. The results also showed that almost 100 years of liming lowered the concentration of the HCl‐extractable Fe that was potentially available for plant uptake in the surface soil (0–15 cm) from 1.03 (standard error (SE) 0.03) to 0.94 (SE 0.01) g kg−1. This HCl‐extractable Fe pool contained isotopically lighter Fe (δ56Fe = −0.05 to −0.29‰) than the bulk soil (δ56Fe = −0.08 to 0.08‰). However, its Fe isotope composition was not altered by the long‐term lime application. Liming resulted in relatively lower Fe concentrations in the roots of winter rye. In addition, liming led to a heavier Fe isotope composition of the whole plants compared with those grown in the non‐limed plots (δ56FeWholePlant_ + Lime = −0.12‰, SE 0.03 vs. δ56FeWholePlant_‐Lime = −0.21‰, SE 0.01). This suggests that the elevated soil pH (increased by one unit due to liming) promoted the Fe uptake strategy through complexation of Fe(III) from the rhizosphere, which favoured heavier Fe isotopes. Overall, the present study showed that liming and a related increase in pH did not affect the Fe isotope compositions of the soil, but may influence the Fe isotope composition of plants grown in the soil if they alter their Fe uptake strategy upon the change of Fe availability. Highlights Fe concentrations and stocks, but not Fe isotope compositions, were more heterogeneous in subsoil than in topsoil. Translocation of clay minerals did not result in Fe isotope fractionation in the soil profile of a Luvisol. Liming decreased Fe availability in topsoil, but did not affect its δ56Fe values. Uptake of heavier Fe isotopes by graminaceous crops was more pronounced at elevated pH.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Keywords: 551.9 ; liming ; plant‐available Fe pool in soil ; winter rye ; δ56Fe
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    A discussion on `Domain formation and phase transitions in the wurtzite‐based heterovalent ternaries: a Landau theory analysis' (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-05
    Description: Heterovalent ternary nitrides are considered one of the promising classes of materials for photovoltaics, combining attractive physical properties with low toxicity and element abundance. One of the front‐runner systems under consideration is ZnSnN2. Although it is nominally a ternary compound, no clear crystallographic evidence for cation ordering has been observed so far. An attempt to elucidate this discrepancy [Quayle (2020). Acta Cryst. A76, 410–420] was the trigger for an intensive discussion between the authors, and an agreement was reached to elaborate on some points in order to set things in perspective. Rather than using a conventional comment–answer scheme, this is published in the form of a joint discussion to celebrate constructive criticism and collegiality.
    Description: A scientific exchange on an earlier paper [Quayle (2020). Acta Cryst. A76, 410–420] has led to the clarification of some of the points. image
    Keywords: 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
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  • 49
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    X‐SPEC: a 70 eV to 15 keV undulator beamline for X‐ray and electron spectroscopies (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: X‐SPEC is a high‐flux spectroscopy beamline at the KIT (Karlsruhe Institute of Technology) Synchrotron for electron and X‐ray spectroscopy featuring a wide photon energy range. The beamline is equipped with a permanent magnet undulator with two magnetic structures of different period lengths, a focusing variable‐line‐space plane‐grating monochromator, a double‐crystal monochromator and three Kirkpatrick–Baez mirror pairs. By selectively moving these elements in or out of the beam, X‐SPEC is capable of covering an energy range from 70 eV up to 15 keV. The flux of the beamline is maximized by optimizing the magnetic design of the undulator, minimizing the number of optical elements and optimizing their parameters. The beam can be focused into two experimental stations while maintaining the same spot position throughout the entire energy range. The first experimental station is optimized for measuring solid samples under ultra‐high‐vacuum conditions, while the second experimental station allows in situ and operando studies under ambient conditions. Measurement techniques include X‐ray absorption spectroscopy (XAS), extended X‐ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X‐ray PES (HAXPES), as well as X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS).
    Description: X‐SPEC is a high‐flux undulator beamline for electron and X‐ray spectroscopy with an energy range from 70 eV to 15 keV. It offers X‐ray absorption spectroscopy (XAS), extended X‐ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X‐ray PES (HAXPES), as well as X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS) for in vacuo, in situ and operando sample environments. image
    Keywords: 548 ; undulator beamline ; soft X‐ray ; tender X‐ray ; hard X‐ray ; in situ ; operando ; HAXPES ; RIXS ; XAS ; XES
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  • 50
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    Structure determination of organic compounds by a fit to the pair distribution function from scratch without prior indexing (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: A method for the ab initio crystal structure determination of organic compounds by a fit to the pair distribution function (PDF), without prior knowledge of lattice parameters and space group, has been developed. The method is called `PDF‐Global‐Fit' and is implemented by extension of the program FIDEL (fit with deviating lattice parameters). The structure solution is based on a global optimization approach starting from random structural models in selected space groups. No prior indexing of the powder data is needed. The new method requires only the molecular geometry and a carefully determined PDF. The generated random structures are compared with the experimental PDF and ranked by a similarity measure based on cross‐correlation functions. The most promising structure candidates are fitted to the experimental PDF data using a restricted simulated annealing structure solution approach within the program TOPAS, followed by a structure refinement against the PDF to identify the correct crystal structure. With the PDF‐Global‐Fit it is possible to determine the local structure of crystalline and disordered organic materials, as well as to determine the local structure of unindexable powder patterns, such as nanocrystalline samples, by a fit to the PDF. The success of the method is demonstrated using barbituric acid as an example. The crystal structure of barbituric acid form IV solved and refined by the PDF‐Global‐Fit is in excellent agreement with the published crystal structure data.
    Keywords: 548 ; pair distribution function analysis ; structure determination ; total scattering technique ; similarity measures ; PDF‐Global‐Fit
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  • 51
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    Structural basis of chitin utilization by a GH20 β‐N‐acetylglucosaminidase from Vibrio campbellii strain ATCC BAA‐1116 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-01
    Description: Vibrio species play a crucial role in maintaining the carbon and nitrogen balance between the oceans and the land through their ability to employ chitin as a sole source of energy. This study describes the structural basis for the action of the GH20 β‐N‐acetylglucosaminidase (VhGlcNAcase) in chitin metabolism by Vibrio campbellii (formerly V. harveyi) strain ATCC BAA‐1116. Crystal structures of wild‐type VhGlcNAcase in the absence and presence of the sugar ligand, and of the unliganded D437A mutant, were determined. VhGlcNAcase contains three distinct domains: an N‐terminal carbohydrate‐binding domain linked to a small α+β domain and a C‐terminal (β/α)8 catalytic domain. The active site of VhGlcNAcase has a narrow, shallow pocket that is suitable for accommodating a small chitooligosaccharide. VhGlcNAcase is a monomeric enzyme of 74 kDa, but its crystal structures show two molecules of enzyme per asymmetric unit, in which Gln16 at the dimeric interface of the first molecule partially blocks the entrance to the active site of the neighboring molecule. The GlcNAc unit observed in subsite −1 makes exclusive hydrogen bonds to the conserved residues Arg274, Tyr530, Asp532 and Glu584, while Trp487, Trp546, Trp582 and Trp505 form a hydrophobic wall around the −1 GlcNAc. The catalytic mutants D437A/N and E438A/Q exhibited a drastic loss of GlcNAcase activity, confirming the catalytic role of the acidic pair (Asp437–Glu438).
    Description: Crystal structures of a GH20 β‐N‐acetylglucosaminidase from V. campbellii reveal substrate specificity in chitin utilization.
    Keywords: 577.14 ; GH20 β‐N‐acetylglucosaminidase ; chitin recycling ; Vibrio spp ; marine bacteria
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  • 52
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    Resolution of a bent‐crystal spectrometer for X‐ray free‐electron laser pulses: diamond versus silicon (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-09-29
    Description: The resolution function of a spectrometer based on a strongly bent single crystal (bending radius of 10 cm or less) is evaluated. It is shown that the resolution is controlled by two parameters: (i) the ratio of the lattice spacing of the chosen reflection to the crystal thickness and (ii) a single parameter comprising crystal thickness, its bending radius, distance to a detector, and anisotropic elastic constants of the chosen crystal. The results allow the optimization of the parameters of bent‐crystal spectrometers for the hard X‐ray free‐electron laser sources.
    Description: The resolution function of a bent‐crystal spectrometer for pulses of an X‐ray free‐electron laser is evaluated. Under appropriate conditions, the energy resolution reaches the ratio of the lattice spacing to the crystal thickness. image
    Keywords: 548 ; X‐ray free‐electron lasers ; X‐ray spectroscopy ; bent crystals ; diamond crystal optics ; femtosecond X‐ray diffraction
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  • 53
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    Separation of the inelastic and elastic scattering in time‐of‐flight mode on the pinhole small‐angle neutron scattering diffractometer KWS‐2 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-09-29
    Description: To study and control the incoherent inelastic background in small‐angle neutron scattering, which makes a significant contribution to the detected scattering from hydrocarbon systems, the KWS‐2 small‐angle neutron scattering diffractometer operated by the Jülich Centre for Neutron Science (JCNS) at Heinz‐Maier Leibnitz Zentrum (MLZ), Garching, Germany, was equipped with a secondary single‐disc chopper that is placed in front of the sample stage. This makes it possible to record in time‐of‐flight mode the scattered neutrons in the high‐Q regime of the instrument (i.e. short incoming wavelengths and detection distances) and to discard the inelastic component from the measured data. Examples of measurements on different materials routinely used as standard samples, sample containers and solvents in the experiments at KWS‐2 are presented. When only the elastic region of the spectrum is used in the data‐reduction procedure, a decrease of up to two times in the incoherent background of the experimentally measured scattering cross section may be obtained. The proof of principle is demonstrated on a solution of bovine serum albumin in D2O.
    Description: A new chopper has been installed at the sample position in front of the sample stage at the KWS‐2 small‐angle neutron‐scattering diffractometer of the Jülich Centre for Neutron Science. The pulsed beam and the time‐of‐flight data acquisition enable the separation of elastic and inelastic scattering from hydrogenous samples.
    Keywords: 548 ; TOF‐SANS ; incoherent neutron scattering ; inelastic neutron scattering ; hydrocarbon systems
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    The ‘Flood Resilience Rose’: A management tool to promote transformation towards flood resilience (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-09-29
    Description: Coping with the growing impacts of flooding in EU countries, a paradigm shift in flood management can be observed, moving from safety‐based towards risk‐based approaches and holistic perspectives. Flood resilience is a common denominator of most of the approaches. In this article, we present the ‘Flood Resilience Rose’ (FRR), a management tool to promote harmonised action towards flood resilience in European regions and beyond. The FRR is a result of a two‐step process. First, based on scientific concepts as well as analysis of relevant policy documents, we identified three ‘levels of operation’. The first level refers to the EU Floods Directive and an extended multi‐layer safety approach, comprising the four different layers of protection, prevention, preparedness and recovery, and related measures to be taken. This level is not independent but depends both on the institutional (second level) and the wider (third level) context. Second, we used surveys, semi‐structured interviews and group discussions during workshops with experts from Belgium, Denmark, Germany, the Netherlands and the United Kingdom to validate the definitions and the FRR's practical relevance. The presented FRR is thus the result of rigorous theoretical and practical consideration and provides a tool capable to strengthen flood risk management practice.
    Description: European Regional Development Fund http://dx.doi.org/10.13039/501100008530
    Keywords: 551.48 ; flood defence measures ; governance and institutions ; integrated flood risk management ; resilience
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    Czochralski growth of mixed cubic sesquioxide crystals in the ternary system Lu2O3–Sc2O3–Y2O3 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-09-29
    Description: Cubic rare‐earth sesquioxide crystals are strongly demanded host materials for high power lasers, but due to their high melting points investigations on their thermodynamics and the growth of large‐size crystals of high optical quality remain a challenge. Detailed thermal investigations of the ternary system Lu2O3–Sc2O3–Y2O3 revealing a large range of compositions with melting temperatures below 2200°C and a minimum of 2053°C for the composition (Sc0.45Y0.55)2O3 are presented. These reduced temperatures enable for the first time the growth of high optical quality mixed sesquioxide crystals with disordered structure by the conventional Czochralski method from iridium crucibles. An (Er0.07Sc0.50Y0.43)2O3 crystal is successfully grown and characterized with respect to its crystallographic properties as well as its composition, thermal conductivity and optical absorption in the 1 µm range.
    Description: The phase diagram of the ternary system Lu2O3–Sc2O3–Y2O3 is investigated and compositions with melting points below 2200°C are found. This allows for the first successful growth of the mixed cubic sesquioxide crystal (Er0.07Sc0.50Y0.43)2O3 by the Czochralski method from an iridium crucible. image
    Keywords: 548 ; crystal growth ; optical materials ; phase diagrams ; melting points ; rare earth sesquioxides
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    Methane Emissions from Northern Wetlands During the Holocene : A Synthesis Approach to Account for Wetland Expansion and Fen-Bog-Permafrost Transitions (Invited) (2021)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, New Orleans, LA, USA, 2021-12-13-2021-12-17American Geophysical Union
    Details
    Publication Date: 2021-12-23
    Description: Methane emissions from northern high latitude wetlands constitute a major uncertainty in the atmospheric methane (CH4) budget during the Holocene. To reconstruct northern wetland methane emissions, we used an empirical model based on syntheses of observations of peat initiation from more than 3600 radiocarbon-dated basal peat ages, plant-macrofossil-derived peatland type from more than 250 peat cores from sites across the northern high latitudes, and observed CH4 emissions averaged from modern-day wetland types in order to explore the effects of wetland expansion and changes in wetland type. Peatland basal ages and plant macrofossil records showed the widespread formation of fens in major northern wetland complexes before 8000 BP. After 8000 BP, new fen formation continued, but widespread peatland succession (to bogs) and permafrost aggradation also occurred. Reconstructed CH4 emissions from peatlands increased rapidly between 10,600 BP and 6900 BP due to fen formation and expansion, then stabilized after 5000 BP at 42 ± 25 Tg CH4 y-1, as high methane-emitting fens transitioned to lower methane-emitting bogs and permafrost peatlands. Permafrost formation in northern peatlands after 1000 BP decreased CH4 emissions by 20% to 34 ± 21 Tg y-1 by the present day. Warming temperatures, changes in peatland hydrology, and permafrost thaw will likely change the magnitude of northern peatland emissions in the future.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev , info:eu-repo/semantics/conferenceObject
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    Monitoring the human footprint across the Arctic coastal region in the context of climate change impact assessment (2021)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2021, Online, 2021-12-13-2021-12-17American Geophysical Union
    Details
    Publication Date: 2021-12-26
    Description: Infrastructure and anthropogenic impacts are expanding across the Arctic. A consistent record of human impact is required in order to quantify the changes and to assess climate change impacts on the communities. We derived a first panarctic satellite-based record of expanding infrastructure and anthropogenic impacts along all permafrost affected coasts (100 km buffer) within the H2020 project Nunataryuk based on Sentinel-1/2 satellite imagery. C-band synthetic aperture radar and multi-spectral information is combined through a machine learning framework. Depending on region, we identified up to 50% more information (human presence) than in OpenStreetMap. The combination with satellite records on vegetation change (specifically NDVI from Landsat since 2000) allowed quantification of recent expansion of infrastructure. Most of the expanded human presence occurred in Russia related predominantly to oil/gas industry. The majority of areas with human presence will be subject to thaw by mid-21st century based on ground temperature trends derived from the ESA CCI+ Permafrost time series (1997-2019). Of specific concern in this context are also settlements located directly at permafrost affected coasts. An efficient erosion rate monitoring scheme needs to be developed and combined with settlement records in order to assess the risk for local communities and infrastructure. Relevant progress in the framework of the ESA EO4PAC project will be discussed.
    Repository Name: EPIC Alfred Wegener Institut
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    Evaluating a deep-learning approach for mapping retrogressive thaw slumps across the Arctic (2021)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2021, Online, 2021-12-13-2021-12-17American Geophysical Union
    Details
    Publication Date: 2021-12-26
    Description: Retrogressive thaw slumps (RTS) are typical landforms indicating processes of rapid thawing and degrading permafrost. Their abundance is increasing in many regions and quantifying their dynamics is of high importance for assessing geomorphic, hydrologic, and biogeochemical impacts of climate change in the Arctic. Here we present a deep-learning (DL) based semantic segmentation framework to detect RTS, using high-resolution multi-spectral PlanetScope, topographic (ArcticDEM elevation and slope), and medium-resolution multi-temporal Landsat Trend data. We created a highly automated processing pipeline, which is designed to allow reproducible results and to be flexible for multiple input data types. The processing workflow is based on the pytorch deep-learning framework and includes a variety of different segmentation architectures (UNet, UNet++, DeepLabV3), backbones and includes common data transformation techniques such as augmentation or normalization. We tested (training, validation) our DL based model in six different regions of 100 to 300 km² size across Canada, and Siberia. We performed a regional cross-validation (5 regions training, 1 region validation) to test the spatial robustness and transferability of the algorithm. Furthermore, we tested different architectures, backbones and loss-functions to identify the best performing and most robust parameter sets. For training the models we created a database of manually digitized and validated RTS polygons. The resulting model performance varied strongly between different regions with maximum Intersection over Union (IoU) scores between 0.15 and 0.58. The strong regional variation emphasizes the need for sufficiently large training data, which is representative of the diversity of RTS types. However, the creation of good training data proved to be challenging due to the fuzzy definition and delineation of RTS. We are further continuing to improve the usability and the functionality to add further datasets and classes. We will show first results from the upscaling beyond small test areas towards large spatial clusters of extensive RTS presence e.g. Peel Plateau in NW Canada.
    Repository Name: EPIC Alfred Wegener Institut
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    Evaluating the Effects of Tundra Fires on Soil Microtopography and Hydrologic Surface Networks in Polygonal Permafrost Landscapes (2021)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2021, Online, 2021-12-13-2021-12-17American Geophysical Union
    Details
    Publication Date: 2021-12-26
    Description: With the Earth’s climate rapidly warming, the Arctic represents one of the most vulnerable regions to environmental change. These northern high latitude regions experience intensified fire seasons and especially tundra fires are projected to become more frequent and severe. Fires in permafrost regions have extensive impacts, including the initiation of thermokarst (rapid thaw of ice-rich ground), as they combust the upper organic soil layers which provide insulation to the permafrost below. Rapid permafrost thaw is, thus, often observable in fire scars in the first years post-disturbance. In polygonal ice-wedge landscapes, this becomes most prevalent through melting ice wedges and degrading troughs. The further these ice wedges degrade, the more troughs will likely connect and build an extensive hydrological network with changing patterns and degrees of connectivity that influences hydrology and runoff. While subsiding troughs over melting ice wedges may host new ponds, an increasing connectivity may also subsequently lead to more drainage of ponds, which in turn can limit further thaw and help stabilize the landscape. To quantify the changes in such dynamic landscapes over large regions, highly automated methods are needed that allow extracting information on the geomorphic state and changes over time of ice-wedge trough networks from remote sensing data. We developed a computer vision algorithm to automatically derive ice-wedge polygonal networks and the current microtopography of the degrading troughs from very high resolution, airborne laserscanning-based digital terrain models. We represent the networks as graphs (a concept from the computer sciences to describe complex networks) and apply methods from graph theory to describe and quantify hydrological network characteristics of the changing landscape. In fire scars, we especially observe rapidly growing networks and fast micromorphological change in those degrading troughs. In our study, we provide a space-for-time substitution comparing fire scars throughout the Alaskan tundra of up to 70 years since the fire disturbance, to show how this type of disturbed landscape evolves over time.
    Repository Name: EPIC Alfred Wegener Institut
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    How to discover an unknown mega-landslide in the Siberian far-east (2021)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2021, Online, 2021-12-13-2021-12-17American Geophysical Union
    Details
    Publication Date: 2021-12-26
    Description: Using our custom visualization tool for multitemporal Landsat satellite imagery we discovered, to our knowledge, an undocumented mega-landslide in far-east Siberia, which occurred in summer 2017 (https://bit.ly/2WYRLM1; 61.55°N; 170.01°E). To create and visualize this unique dataset, we processed temporal trends of multispectral indices of 〉100,000 Landsat images for a period from 2000-2019 using the freely available Google Earth Engine cloud processing platform (https://ingmarnitze.users.earthengine.app/view/hotspottcvisapp). The megaslide has a size of 3.66 km² and using the ArcticDEM data we estimate a volume movement of ~20 Mm³. With this size and volume, the landslide is among the largest globally known in recent decades. The landslide is accompanied by a smaller one (0.31 km², 1 Mm³) about 600 m further east, which already occurred in summer 2015. The large landslide caused the formation of several small lakes by blocking two valleys with debris and within newly formed crevasses near the hilltop, which are still persisting as of August 2021. As this event occurred in a remote valley far from any settlement, no visible damage to infrastructure or human livelihoods was detected. The remoteness has likely led to being not detected, like many similar, albeit a lot smaller, erosion features in the Arctic permafrost region. In this presentation we will show the main properties of the landslide, potential trigger mechanisms in the traditional sense. As this region is located along the fringes of permafrost presence we will discuss its potential connection to the rapidly warming climate in the high latitudes. Further, we will discuss how such a large event remained undetected for several years. We discuss and highlight the value of our landscape change visualization tool based on Landsat trend analysis (see Nitze et al., AGU 2020), which helped us to identify this extreme event. With more and more available data sources, this tool in addition to automated image analysis (e.g. deep-learning) or seismic analysis will help to uncover the hidden processes and dynamics of the Earth’s surface.
    Repository Name: EPIC Alfred Wegener Institut
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    The future of community- and policy- relevant thermokarst research: Lessons learned and a call to action (2021)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2021, Online, 2021-12-13-2021-12-17American Geophysical Union
    Details
    Publication Date: 2021-12-26
    Description: Several decades of research have provided insight into patterns of and controls on thermokarst initiation and expansion, yet studies tend to focus on individual types of thermokarst (i.e., thaw lake formation and subsequent drainage) in particular regions. Today, we are left with uneven knowledge about abrupt permafrost thaw both conceptually and regionally. The goal of this presentation is to summarize recent advancements in monitoring thermokarst and its impact on soil, vegetation, and water while also framing a call to action for the next decade of research. Over the next decade, permafrost researchers must align their efforts on several fronts to not only increase our knowledge about changing permafrost but to align this knowledge with key community and policy needs. To support climate change planning and adaptation, northern communities need future thaw vulnerability mapped at scales relevant to their needs, which will require a suite of downscaled and new mapping and remote sensing products. Thermokarst predisposition maps based on circumpolar datasets greatly overestimate the area vulnerable to thermokarst, which can lead to poor planning and climate anxiety. In some situations, existing mapping products may be useful for downscaling with more detailed input data. In other situations, entirely new approaches may be required to support local action. A second key need for community relevant research is the ability to detect and monitor early warning indicators of thermokarst. Such information is needed to support scenario planning and to help mitigate the risks to social, cultural, and physical infrastructure created by permafrost change. We are evaluating the potential for using changes in vegetation, wetting/drying and topography as early warning indicators of thermokarst, all of which can be remotely sensed. Finally, integrating fine-scale disturbances such as thermokarst into large scale models remains a key challenge but critical for supporting sound climate policy. While a diversity of permafrost modeling approaches is necessary, we outline guiding principles that will help enhance model comparisons, assimilation of simulated data across spatiotemporal scales, and the ability for policy decisions to be rapidly informed by emerging science on permafrost change.
    Repository Name: EPIC Alfred Wegener Institut
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    Skillful long-lead prediction of summertime heavy rainfall in the US Midwest from sea surface salinity (2022)
    American Geophysical Union
    Details
    Publication Date: 2023-01-07
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(13), (2022): e2022GL098554, https://doi.org/10.1029/2022GL098554.
    Description: Summertime heavy rainfall and its resultant floods are among the most harmful natural hazards in the US Midwest, one of the world's primary crop production areas. However, seasonal forecasts of heavy rain, currently based on preseason sea surface temperature anomalies (SSTAs), remain unsatisfactory. Here, we present evidence that sea surface salinity anomalies (SSSAs) over the tropical western Pacific and subtropical North Atlantic are skillful predictors of summer time heavy rainfall one season ahead. A one standard deviation change in tropical western Pacific SSSA is associated with a 1.8 mm day−1 increase in local precipitation, which excites a teleconnection pattern to extratropical North Pacific. Via extratropical air-sea interaction and long memory of midlatitude SSTA, a wave train favorable for US Midwest heavy rain is induced. Combined with soil moisture feedbacks bridging the springtime North Atlantic salinity, the SSSA-based statistical prediction model improves Midwest heavy rainfall forecasts by 92%, complementing existing SSTA-based frameworks.
    Description: This study is supported by the NSF PREEVENTS program under ICER-1663138 (LL) and ICER-1663704 (RWS and CCU).
    Description: 2023-01-07
    Keywords: Sea surface salinity ; Midwest precipitation ; Heavy rainfall ; Long-lead prediction
    Repository Name: Woods Hole Open Access Server
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    Digitization of imaging plates from Guinier powder X‐ray diffraction cameras (2022)
    Nasir, Jamal ; Steinbrück, Nils ; Xu, Ke ; [et al.]
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-01-15
    Description: A Guinier camera equipped with an imaging plate is used to investigate and eliminate the sources of instrumental errors affecting the quality of the obtained scanned Guinier data. A program with a graphical user interface is presented which converts the data of the scanned images into different standard file formats for powder X‐ray patterns containing intensities, their standard deviations and the diffraction angles. The program also allows for manual and automatic correction of the 2gθ scale against a known reference material. It is shown using LaB6 that the exported X‐ray diffraction patterns provide a 2gθ scale reproducible enough to allow for averaging diffractograms obtained from different exposures of the imaging plate for the same sample. As shown on a mixture of NaCl and sodalite, the quality of the produced data is sufficient for Rietveld refinement. The software including source code is made available under a free software license.
    Description: A program for the digitization of Guinier powder diffraction images is described, which works with images from both optical and laser scanners. Thus, processing of data from storage‐phosphor‐based imaging plates and Ag‐based photographic films is possible.
    Keywords: ddc:548 ; IPreader software ; Guinier cameras ; imaging plates (IPs) ; diffraction pattern conversion into data columns ; powder X‐ray diffraction ; data processing ; Guinier method
    Language: English
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    Contributions of different sea-level processes to high-tide flooding along the US coastline (2022)
    American Geophysical Union
    Details
    Publication Date: 2023-01-14
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(7), (2022): e2021JC018276, https://doi.org/10.1029/2021JC018276.
    Description: Coastal communities across the United States (U.S.) are experiencing an increase in the frequency of high-tide flooding (HTF). This increase is mainly due to sea-level rise (SLR), but other factors such as intra- to inter-annual mean sea level variability, tidal anomalies, and non-tidal residuals also contribute to HTF events. Here we introduce a novel decomposition approach to develop and then analyze a new database of different sea-level components. Those components represent processes that act on various timescales to contribute to HTF along the U.S. coastline. We find that the relative importance of components to HTF events strongly varies in space and time. Tidal anomalies contribute the most along the west and northeast coasts, where HTF events mostly occur in winter. Non-tidal residuals are most important along the Gulf of Mexico and mid-Atlantic coasts, where HTF events mostly occur in fall. We also quantify the minimum number of components that were required to cause HTF events in the past and how this number changed over time. The results highlight that at present, due to SLR, fewer components are needed to combine to push water levels above HTF thresholds, but tidal anomalies alone are still not sufficient to reach HTF thresholds in most locations. Finally, we explore how co-variability between different components leads to compounding effects. In some places, positive correlation between sea-level components leads to significantly more HTF events than would be expected if sea-level components were uncorrelated, whereas in other places negative correlation leads to fewer HTF events.
    Description: his work was supported by NASA's Sea Level Change Team award number 80NSSC20K1241. S.L. also acknowledges support by the China Scholarship Council (no. 201904910413) and the Ministry of Science and Technology of the People's Republic of China (grant no. 2011YQ120045).
    Description: 2023-01-14
    Repository Name: Woods Hole Open Access Server
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    Non‐exchangeable stable hydrogen isotope ratios in clay minerals and soil clay fractions: A method test (2022)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-01-20
    Description: Stable hydrogen isotope ratios (δ2H values) in structural hydroxyl groups of pedogenic clay minerals are inherited from the surrounding water at the time of their formation. Only non‐exchangeable H preserves the environmental forensic and paleoclimate information (δ2Hn value). To measure δ2Hn values in structural H of clay minerals and soil clay fractions, we adapted a steam equilibration method by accounting for high hygroscopicity. Our δ2Hn values for USGS57 biotite (−95.3 ± SD 0.9‰) and USGS58 muscovite (30.7 ± 1.4‰) differed slightly but significantly from the reported δ2H values (−91.5 ± 2.4‰ and −28.4 ± 1.6‰), because the minerals contained 1.1%–4.4% of exchangeable H. The low SD of replicate measurements (n = 3) confirmed a high precision. The clay separation method including destruction of Fe oxides, carbonates and soil organic matter, and dispersion did not significantly change the δ2Hn values of five different clay minerals. However, we were unable to remove all organic matter from the soil clay fractions resulting in an estimated bias of 1‰ in two samples and 15‰ in the carbon‐richest sample. Our results demonstrate that δ2Hn values of structural H of clay minerals and soil clay fractions can be reliably measured without interference from atmospheric water and the method used to separate the soil clay fraction. Highlights We tested steam equilibration to determine stable isotope ratios of structural H in clay. Gas‐tight capsule sealing in Ar atmosphere was necessary to avoid remoistening. Our steam equilibration method showed a high accuracy and precision. The clay separation method did not change stable isotope ratios of structural H in clay.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:549 ; controlled isotope exchange technique ; deuterium ; montmorillonite ; soil clay separation ; soil organic matter removal ; steam equilibration ; structural H ; USGS57 biotite ; vermiculite ; δ2H
    Language: English
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    Crystal diffraction prediction and partiality estimation using Gaussian basis functions (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-04
    Description: The recent diversification of macromolecular crystallographic experiments including the use of pink beams, convergent electron diffraction and serial snapshot crystallography has shown the limitations of using the Laue equations for diffraction prediction. This article gives a computationally efficient way of calculating approximate crystal diffraction patterns given varying distributions of the incoming beam, crystal shapes and other potentially hidden parameters. This approach models each pixel of a diffraction pattern and improves data processing of integrated peak intensities by enabling the correction of partially recorded reflections. The fundamental idea is to express the distributions as weighted sums of Gaussian functions. The approach is demonstrated on serial femtosecond crystallography data sets, showing a significant decrease in the required number of patterns to refine a structure to a given error.
    Description: Reflection position, size and shape prediction and partiality estimation of crystal diffraction by integrating using a Gaussian basis are described.
    Keywords: ddc:548 ; partiality estimation ; diffraction prediction ; merging ; serial snapshot crystallography
    Language: English
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    Small‐angle neutron scattering of long‐wavelength magnetic modulations in reduced sample dimensions (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-04
    Description: Magnetic small‐angle neutron scattering (SANS) is ideally suited to providing direct reciprocal‐space information on long‐wavelength magnetic modulations, such as helicoids, solitons, merons or skyrmions. SANS of such structures in thin films or micro‐structured bulk materials is strongly limited by the tiny scattering volume vis a vis the prohibitively high background scattering by the substrate and support structures. Considering near‐surface scattering just above the critical angle of reflection, where unwanted signal contributions due to substrate or support structures become very small, it is established that the scattering patterns of the helical, conical, skyrmion lattice and fluctuation‐disordered phases in a polished bulk sample of MnSi are equivalent for conventional transmission and near‐surface SANS geometries. This motivates the prediction of a complete repository of scattering patterns expected for thin films in the near‐surface SANS geometry for each orientation of the magnetic order with respect to the scattering plane.
    Description: Near‐surface SANS is discussed for its potential as a probe of long‐wavelength magnetic modulations in specimens with reduced sample dimensions.
    Keywords: ddc:548 ; small‐angle neutron scattering ; near‐surface SANS ; magnetism ; non‐collinear magnetism ; thin films ; skyrmions ; MnSi
    Language: English
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    In situ neutron diffraction for analysing complex coarse‐grained functional materials (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-10-24
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Complex functional materials play a crucial role in a broad range of energy‐related applications and in general for materials science. Revealing the structural mechanisms is challenging due to highly correlated coexisting phases and microstructures, especially for 〈italic〉in situ〈/italic〉 or 〈italic〉operando〈/italic〉 investigations. Since the grain sizes influence the properties, these microstructural features further complicate investigations at synchrotrons due to the limitations of illuminated sample volumes. In this study, it is demonstrated that such complex functional materials with highly correlated coexisting phases can be investigated under 〈italic〉in situ〈/italic〉 conditions with neutron diffraction. For large grain sizes, these experiments are valuable methods to reveal the structural mechanisms. For an example of 〈italic〉in situ〈/italic〉 experiments on barium titanate with an applied electric field, details of the electric‐field‐induced phase transformation depending on grain size and frequency are revealed. The results uncover the strain mechanisms in barium titanate and elucidate the complex interplay of stresses in relation to grain sizes as well as domain‐wall densities and mobilities.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉This work reports 〈italic〉in situ〈/italic〉 neutron diffraction experiments on a broad range of grain sizes of barium titanate. The study reveals the grain‐size‐dependent strain mechanisms and shows the competitiveness of neutron diffraction with high‐resolution synchrotron diffraction.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005767:jcr2vb5054:jcr2vb5054-fig-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:550.724 ; ddc:548 ; neutron diffraction ; in situ ; applied electric fields ; barium titanate ; strain mechanisms ; grain sizes ; complex functional materials ; microstructures ; coexisting phases
    Language: English
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  • 69
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    Using diffraction losses of X‐rays in a single crystal for determination of its lattice parameters as well as for monochromator calibration (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-12-04
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉A way has been developed to measure the unit‐cell parameters of a single crystal just from an energy scan with X‐rays, even when the exact energy of the X‐rays is not well defined due to an error in the pitch angle of the monochromator. The precision of this measurement reaches 〈italic〉da〈/italic〉/〈italic〉a〈/italic〉 ∼ 1 × 10〈sup〉−5〈/sup〉. The method is based on the analysis of diffraction losses of the beam, transmitted through a single crystal (the so‐called `glitch effect'). This method can be easily applied to any transmissive X‐ray optical element made of single crystals (for example, X‐ray lenses). The only requirements are the possibility to change the energy of the generated X‐ray beam and some intensity monitor to measure the transmitted intensity. The method is agnostic to the error in the monochromator tuning and it can even be used for determination of the absolute pitch (or 2gθ) angle of the monochromator. Applying the same method to a crystal with well known lattice parameters allows determination of the exact cell parameters of the monochromator at any energy.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Diffraction losses (glitches) at certain energies of the X‐ray beam, transmitted through a single crystal, can be used for lattice parameters determination as well as for calibrating the monochromator (absolute pitch angle and the unit‐cell parameter).〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005775:jsy2ay5590:jsy2ay5590-fig-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:548 ; X‐ray glitches ; diffraction losses ; unit‐cell parameter ; single‐crystal X‐ray optics ; monochromator calibration
    Language: English
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    Seismic imaging of Dante’s Domes oceanic core complex from streamer waveform inversion and reverse time migration (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-25
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 127(8), (2022): e2021JB023814, https://doi.org/10.1029/2021jb023814.
    Description: Early arrival traveltime tomography and full waveform inversion were conducted on downward continued streamer seismic data at Dante's Domes oceanic core complex (OCC), providing unprecedented details of shallow P wave velocity structure. Together with reverse time migration images, seafloor morphology, in situ geological samples, magnetic and gravity data, the seismic constraints are used to infer the lithological distribution along the seismic profiles. Based on the striking similarity in velocity structure beneath the corrugated domes with other OCCs and drilling results from Atlantis Massif, we confidently reconfirmed the Southern Dome as dominantly gabbroic rocks, and the Northern Dome as serpentinized peridotites. A series of isolated gabbroic bodies embedded in the diabase and basaltic layers is observed in the breakaway zone, suggesting that the initiation of Dante's Domes OCC occurred over a long period during which there were several failed attempts to form a long-lived detachment fault. This early development of the OCC probably occurred under a regime of alternating magma starvation and magma replenishment. The predominantly gabbroic section, beneath the Southern Dome and extending to termination, indicates the OCC has been created with relatively high magma flux. We also imaged distinct shallow subseafloor reflections which are also termed as D reflectors underneath the corrugated domes. The location of the D reflectors is similar to those in the Atlantis Massif, with depths well correlated with the top of exhumed gabbroic bodies and the discontinuities in the D reflectors between gabbroic bodies. Our findings contribute to the understanding of processes controlling the OCCs initiation and evolution at slow spreading ridges.
    Description: This research was supported by the National Natural Science Foundation of China (91858207), Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (GML2019ZD0205), and Guangdong Basic and Applied Basic Research Foundation (2021B1515020023). M. X. acknowledges support from Special Foundation for National Science and Technology Basic Research Program of China (2018FY100505), Guangdong NSF research team project (2017A030312002), K. C. Wong Education Foundation (GJTD-2018-13), and the Chinese Academy of Sciences (Y4SL021001, QYZDY-SSWDQC005, 133244KYSB20180029, 131551KYSB20200021, and ISEE2021PY03). J. P. C. acknowledges support from the Independent Research and Development Program at WHOI.
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  • 71
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    Spatial variability of movement, structure, and formation of Warm Core Rings in the Northwest Atlantic Slope Sea (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-25
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 127(8),(2022): e2022JC018737, https://doi.org/10.1029/2022jc018737.
    Description: Gulf Stream Warm Core Rings (WCRs) have important influences on the New England Shelf and marine ecosystems. A 10-year (2011–2020) WCR dataset that tracks weekly WCR locations and surface areas is used here to identify the rings' path and characterize their movement between 55 and 75°W. The WCR dataset reveals a very narrow band between 66 and 71°W along which rings travel almost due west along ∼39°N across isobaths – the “Ring Corridor.” Then, west of the corridor, the mean path turns southwestward, paralleling the shelfbreak. The average ring translation speed along the mean path is 5.9 cm s−1. Long-lived rings (lifespan 〉150 days) tend to occupy the region west of the New England Seamount Chain (NESC) whereas short-lived rings (lifespan 〈150 days) tend to be more broadly distributed. WCR vertical structures, analyzed using available Argo float profiles indicate that rings that are formed to the west of the NESC have shallower thermoclines than those formed to the east. This tendency may be due to different WCR formation processes that are observed to occur along different sections of the Gulf Stream. WCRs formed to the east of the NESC tend to form from a pinch-off mechanism incorporating cores of Sargasso Sea water and a perimeter of Gulf Stream water. WCRs that form to the west of the NESC, form from a process called an aneurysm. WCRs formed through aneurysms comprise water mostly from the northern half of the Gulf Stream and are smaller than the classic pinch-off rings.
    Description: AS and AG are grateful for financial support from NOAA (NA11NOS0120038), NSF (OCE-1851242 and OCE-2123283), SMAST, and UMass Dartmouth. GG was supported by NSF under grant OCE-1657853. MA was supported by NSF under grant OCE-2122726 and by ONR under grant N00014-22-1-2112.
    Keywords: Gulf Stream ; Warm core rings ; Trajectories ; Eddies ; Aneurysm ; Ring formation
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  • 72
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    Eruption rates, tempo, and stratigraphy of Paleocene flood basalts on Baffin Island, Canada (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-25
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biasi, J., Asimow, P., Horton, F., & Boyes, X. Eruption rates, tempo, and stratigraphy of Paleocene flood basalts on Baffin Island, Canada. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2021GC010172, https://doi.org/10.1029/2021gc010172.
    Description: High-temperature melting in mantle plumes produces voluminous eruptions that are often temporally coincident with mass extinctions. Paleocene Baffin Island lavas—products of early Iceland mantle plume activity—are exceptionally well characterized geochemically but have poorly constrained stratigraphy, geochronology, and eruptive tempos. To provide better geologic context, we measured seven stratigraphic sections of the volcanic deposits and collected paleomagnetic data from 38 sites in the lavas and underlying Cretaceous sediments (Quqaluit Fm.). The average paleomagnetic pole from this study does not overlap with the expected pole for a stable North American locality at 60 Ma, yet the data have sufficient dispersion to average out secular variation. After ruling out other possibilities, we find that the picrites were probably erupted during a polarity transition, over less than 5 kyr. If so, the average eruption interval was ∼67 years per flow for the thickest sequence of exposed lavas. We also calculate that the flood basalts had a minimum total volume of ∼176 km3 (excluding submerged lavas in Baffin Bay). This implies a minimum eruption rate of ∼0.035 km3 yr−1, which is similar to rates found in West Greenland lavas but less than rates found in larger flood basalts. Despite this, the Baffin and West Greenland lavas temporally correlate with the “End C27n event” (a period of ∼2°C global warming) and may be its underlying cause.
    Description: his work was supported by the National Science Foundation (award #1911699 to F. Horton and award #2052963 to J. Biasi), Woods Hole Oceanographic Institution (WHOI) Andrew W. Mellon Foundation Endowed Fund for Innovative Research, a National Geographic Society grant (#CP4-144R-18), and internal funding from the Caltech Geological and Planetary Sciences Division.
    Keywords: Baffin island ; North Atlantic ; Flood basalt ; Paleomagnetism ; Volcanology ; Secular variation
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  • 73
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    Carbonation of serpentinite in creeping faults of California (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-21
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 49(15), (2022): e2022GL099185, https://doi.org/10.1029/2022gl099185.
    Description: Several large strike slip faults in central and northern California accommodate plate motions through aseismic creep. Although there is no consensus regarding the underlying cause of aseismic creep, aqueous fluids and mechanically weak, velocity-strengthening minerals appear to play a central role. This study integrates field observations and thermodynamic modeling to examine possible relationships between the occurrence of serpentinite, silica-carbonate rock, and CO2-rich aqueous fluids in creeping faults of California. Our models predict that carbonation of serpentinite leads to the formation of talc and magnesite, followed by silica-carbonate rock. While abundant exposures of silica-carbonate rock indicate complete carbonation, serpentinite-hosted CO2-rich spring fluids are strongly supersaturated with talc at elevated temperatures. Hence, carbonation of serpentinite is likely ongoing in parts of the San Andres Fault system and operates in conjunction with other modes of talc formation that may further enhance the potential for aseismic creep, thereby limiting the potential for large earthquakes.
    Description: This work was supported by National Science Foundation (NSF) grants NSF-EAR-1220280 to F. K. and J. L., NSF-EAR-1219908 to D. G., and NSF-OCE-2001728 to J. L.
    Keywords: Mineral carbonation ; Serpentinite ; Talc ; CO2 ; Aseismic creep ; San Andreas Fault
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    Does sea spray aerosol contribute significantly to aerosol trace element loading? a case study from the US GEOTRACES Pacific Meridional Transect (GP15) (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-21
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marsay, C. M., Landing, W. M., Umstead, D., Till, C. P., Freiberger, R., Fitzsimmons, J. N., Lanning, N. T., Shiller, A. M., Hatta, M., Chmiel, R., Saito, M., & Buck, C. S. Does sea spray aerosol contribute significantly to aerosol trace element loading? a case study from the US GEOTRACES Pacific Meridional Transect (GP15). Global Biogeochemical Cycles, 36(8), (2022): e2022GB007416. https://doi.org/10.1029/2022GB007416.
    Description: Atmospheric deposition represents a major input for micronutrient trace elements (TEs) to the surface ocean and is often quantified indirectly through measurements of aerosol TE concentrations. Sea spray aerosol (SSA) dominates aerosol mass concentration over much of the global ocean, but few studies have assessed its contribution to aerosol TE loading, which could result in overestimates of “new” TE inputs. Low-mineral aerosol concentrations measured during the U.S. GEOTRACES Pacific Meridional Transect (GP15; 152°W, 56°N to 20°S), along with concurrent towfish sampling of surface seawater, provided an opportunity to investigate this aspect of TE biogeochemical cycling. Central Pacific Ocean surface seawater Al, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb concentrations were combined with aerosol Na data to calculate a “recycled” SSA contribution to aerosol TE loading. Only vanadium was calculated to have a SSA contribution averaging 〉1% along the transect (mean of 1.5%). We derive scaling factors from previous studies on TE enrichments in the sea surface microlayer and in freshly produced SSA to assess the broader potential for SSA contributions to aerosol TE loading. Maximum applied scaling factors suggest that SSA could contribute significantly to the aerosol loading of some elements (notably V, Cu, and Pb), while for others (e.g., Fe and Al), SSA contributions largely remained 〈1%. Our study highlights that a lack of focused measurements of TEs in SSA limits our ability to quantify this component of marine aerosol loading and the associated potential for overestimating new TE inputs from atmospheric deposition.
    Description: This research was supported by the National Science Foundation (NSF) grants OCE-1756103 to C. S. Buck, OCE-1756104 to W. M. Landing, OCE-1737024 to A.M. Shiller, OCE-1736906 to M. Hatta, OCE-1736875 to C. P. Till, OCE-1737167 to J. N. Fitzsimmons, and OCE-1736599 to M. Saito. In addition, N. T. Lanning was supported by the NSF Graduate Research Fellowship Program award 1746932.
    Keywords: Aerosols ; Trace elements ; GEOTRACES ; Sea spray aerosol ; Pacific Ocean
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  • 75
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    Using misorientation and weighted burgers vector statistics to understand intragranular boundary development and grain boundary formation at high temperatures (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-21
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 127(8), (2022): e2022JB024497, https://doi.org/10.1029/2022JB024497.
    Description: During plastic deformation, strain weakening can be achieved, in part, via strain energy reduction associated with intragranular boundary development and grain boundary formation. Grain boundaries (in 2D) are segments between triple junctions, that connect to encircle grains; every boundary segment in the encircling loop has a high (〉10°) misorientation angle. Intragranular boundaries terminate within grains or dissect grains, usually containing boundary segments with a low (〈10°) misorientation angle. We analyze electron backscatter diffraction (EBSD) data from ice deformed at −30°C (Th≈ 0.9). Misorientation and weighted Burgers vector (WBV) statistics are calculated along planar intragranular boundaries. Misorientation angles change markedly along each intragranular boundary, linking low- (〈10°) and high-angle (10–38°) segments that exhibit distinct misorientation axes and WBV directions. We suggest that these boundaries might be produced by the growth and intersection of individual intragranular boundary segments comprising dislocations with distinct slip systems. There is a fundamental difference between misorientation axis distributions of intragranular boundaries (misorientation axes mostly confined to ice basal plane) and grain boundaries (no preferred misorientation axis). These observations suggest during progressive subgrain rotation, intragranular boundaries remain crystallographically controlled up to large misorientation angles (〉〉10°). In contrast, the apparent lack of crystallographic control for grain boundaries suggests misorientation axes become randomized, likely due to the activation of additional mechanisms (such as grain boundary sliding) after grain boundary formation, linking boundary segments to encircle a grain. Our findings on ice intragranular boundary development and grain boundary formation may apply more broadly to other rock-forming minerals (e.g., olivine, quartz).
    Description: This work was supported by a NASA fund (Grant No. NNX15AM69G) to David L. Goldsby and two Marsden Funds of the Royal Society of New Zealand (Grant Nos. UOO1116, UOO052) to David J. Prior. Sheng Fan was supported by the University of Otago doctoral scholarship, the Antarctica New Zealand doctoral scholarship, a research grant from New Zealand Ministry of Business, Innovation and Employment through the Antarctic Science Platform (ANTA1801) (Grant No. ASP-023-03), and a New Zealand Antarctic Research Institute (NZARI) Early Career Researcher Seed Grant (Grant No. NZARI 2020-1-5). Open access publishing facilitated by University of Otago, as part of the Wiley – University of Otago agreement via the Council of Australian University Librarians.
    Keywords: High temperature deformation ; Misorientation ; Weighted Burgers vector ; Intragranular boundary ; Grain boundary ; Boundary geometry
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    Energy‐dispersive X‐ray stress analysis under geometric constraints: exploiting the material's inherent anisotropy (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-09-12
    Description: Two data evaluation concepts for X‐ray stress analysis based on energy‐dispersive diffraction on polycrystalline materials with cubic crystal structure, almost random crystallographic texture and strong single‐crystal elastic anisotropy are subjected to comparative assessment. The aim is the study of the residual stress state in hard‐to‐reach measurement points, for which the sin2ψ method is not applicable due to beam shadowing at larger sample tilting. This makes the approaches attractive for stress analysis in engineering parts with complex shapes, for example. Both approaches are based on the assumption of a biaxial stress state within the irradiated sample volume. They exploit in different ways the elastic anisotropy of individual crystallites acting at the microscopic scale and the anisotropy imposed on the material by the near‐surface stress state at the macroscopic scale. They therefore complement each other, in terms of both their preconditions and their results. The first approach is based on the evaluation of strain differences, which makes it less sensitive to variations in the strain‐free lattice parameter a0. Since it assumes a homogeneous stress state within the irradiated sample volume, it provides an average value of the in‐plane stresses. The second approach exploits the sensitivity of the lattice strain to changes in a0. Consequently, it assumes a homogeneous chemical composition but provides a stress profile within the information depth. Experimental examples from different fields in materials science, namely shot peening of austenitic steel and in situ stress analysis during welding, are presented to demonstrate the suitability of the proposed methods.
    Description: The single‐crystal elastic anisotropy and the anisotropy of the near‐surface (residual) stress state of polycrystalline materials with random texture are exploited in energy‐dispersive X‐ray stress analysis to study samples under constrained measurement conditions.
    Keywords: ddc:548 ; X‐ray stress analysis ; energy‐dispersive diffraction ; polycrystalline materials ; single‐crystal elastic anisotropy
    Language: English
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    Use of electron backscatter diffraction patterns to determine the crystal lattice. Part 3. Pseudosymmetry (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-20
    Description: A pseudosymmetric description of the crystal lattice derived from a single wide‐angle Kikuchi pattern can have several causes. The small size (〈15%) of the sector covered by an electron backscatter diffraction pattern, the limited precision of the projection centre position and the Kikuchi band definition are crucial. Inherent pseudosymmetries of the crystal lattice and/or structure also pose a challenge in the analysis of Kikuchi patterns. To eliminate experimental errors as much as possible, simulated Kikuchi patterns of 350 phases have been analysed using the software CALM [Nolze et al. (2021). J. Appl. Cryst.54, 1012–1022] in order to estimate the frequency of and reasons for pseudosymmetric crystal lattice descriptions. Misinterpretations occur in particular when the atomic scattering factors of non‐equivalent positions are too similar and reciprocal‐lattice points are systematically missing. As an example, a pseudosymmetry prediction depending on the elements involved is discussed for binary AB compounds with B1 and B2 structure types. However, since this is impossible for more complicated phases, this approach cannot be directly applied to compounds of arbitrary composition and structure.
    Description: Distinguishing between actual and apparent pseudosymmetry in electron backscatter diffraction patterns is nearly impossible, even for simulated patterns. However, the resulting lattice is always a superlattice as long as the signal is not a superposition of multiple patterns.
    Keywords: ddc:548 ; Bravais lattices ; pseudosymmetry ; lattice point density ; ordered/disordered structures ; lattice distortion ; electron backscatter diffraction ; backscattered Kikuchi diffraction patterns ; lattice parameters ; Funk transform
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  • 78
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    Combining reverse Monte Carlo analysis of X‐ray scattering and extended X‐ray absorption fine structure spectra of very small nanoparticles (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-21
    Description: Finite size effects in partial pair distribution functions generate artefacts in the scattering structure factor and scattering intensity. It is shown how they can be overcome using a binned version of the Debye scattering equation. Accordingly, reverse Monte Carlo simulations are used for very small nanoparticles of LaFeO3 with diameters below 10 nm to simultaneously analyse X‐ray scattering data and extended X‐ray absorption fine structure spectra at the La K and Fe K edges. The structural information obtained is consistent regarding local structure and long‐range order.
    Description: Computing scattering intensity using the Debye scattering equation after binning interatomic distances avoids finite size artefacts and is efficient enough for simultaneous refinement of scattering data and extended X‐ray absorption spectra by reverse Monte Carlo simulations.
    Keywords: ddc:548 ; extended X‐ray absorption fine structure ; EXAFS ; wide‐angle X‐ray scattering ; WAXS ; reverse Monte Carlo ; RMC ; nanocrystals ; LaFeO3
    Language: English
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  • 79
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    Use of electron backscatter diffraction patterns to determine the crystal lattice. Part 2. Offset corrections (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-21
    Description: A band width determination using the first derivative of the band profile systematically underestimates the true Bragg angle. Corrections are proposed to compensate for the resulting offset Δa/a of the mean lattice parameters derived from as many Kikuchi band widths as possible. For dynamically simulated Kikuchi patterns, Δa/a can reach up to 8% for phases with a high mean atomic number Z, whereas for much more common low‐Z materials the offset decreases linearly. A predicted offset Δa/a = f(Z) is therefore proposed, which also includes the unit‐cell volume and thus takes into account the packing density of the scatterers in the material. Since Z is not always available for unknown phases, its substitution by Zmax, i.e. the atomic number of the heaviest element in the compound, is still acceptable for an approximate correction. For simulated Kikuchi patterns the offset‐corrected lattice parameter deviation is Δa/a 〈 1.5%. The lattice parameter ratios, and the angles α, β and γ between the basis vectors, are not affected at all.
    Description: Automatically determined band widths in simulated backscatter Kikuchi patterns exhibit differences from the double Bragg angles that correlate with the scatterer density. Corrections are proposed to compensate for this.
    Keywords: ddc:548 ; mean atomic number ; Kikuchi patterns ; lattice parameters ; automated Bragg angle determination ; lattice parameter determination ; dynamical theory of electron diffraction ; electron backscatter diffraction ; Funk transform
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    POWTEX visits POWGEN (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-21
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The high‐intensity time‐of‐flight (TOF) neutron diffractometer POWTEX for powder and texture analysis is currently being built prior to operation in the eastern guide hall of the research reactor FRM II at Garching close to Munich, Germany. Because of the world‐wide 〈sup〉3〈/sup〉He crisis in 2009, the authors promptly initiated the development of 〈sup〉3〈/sup〉He‐free detector alternatives that are tailor‐made for the requirements of large‐area diffractometers. Herein is reported the 2017 enterprise to operate one mounting unit of the final POWTEX detector on the neutron powder diffractometer POWGEN at the Spallation Neutron Source located at Oak Ridge National Laboratory, USA. As a result, presented here are the first angular‐ and wavelength‐dependent data from the POWTEX detector, unfortunately damaged by a 50〈italic〉g〈/italic〉 shock but still operating, as well as the efforts made both to characterize the transport damage and to successfully recalibrate the voxel positions in order to yield nonetheless reliable measurements. Also described is the current data reduction process using the 〈italic〉PowderReduceP2D〈/italic〉 algorithm implemented in 〈italic〉Mantid〈/italic〉 [Arnold 〈italic〉et al.〈/italic〉 (2014). 〈italic〉Nucl. Instrum. Methods Phys. Res. A〈/italic〉, 〈bold〉764〈/bold〉, 156–166]. The final part of the data treatment chain, namely a novel multi‐dimensional refinement using a modified version of the 〈italic〉GSAS‐II〈/italic〉 software suite [〈ext-link ext-link-type="uri" xlink:href="http://scripts.iucr.org/cgi-bin/paper?aj5212"〉Toby & Von Dreele (2013). 〈italic〉J. Appl. Cryst.〈/italic〉〈bold〉46〈/bold〉, 544–549〈/ext-link〉], is compared with a standard data treatment of the same event data conventionally reduced as TOF diffraction patterns and refined with the unmodified version of 〈italic〉GSAS‐II〈/italic〉. This involves both determining the instrumental resolution parameters using POWGEN's powdered diamond standard sample and the refinement of a friendly‐user sample, BaZn(NCN)〈sub〉2〈/sub〉. Although each structural parameter on its own looks similar upon comparing the conventional (1D) and multi‐dimensional (2D) treatments, also in terms of precision, a closer view shows small but possibly significant differences. For example, the somewhat suspicious proximity of the 〈italic〉a〈/italic〉 and 〈italic〉b〈/italic〉 lattice parameters of BaZn(NCN)〈sub〉2〈/sub〉 crystallizing in 〈italic〉Pbca〈/italic〉 as resulting from the 1D refinement (0.008 Å) is five times less pronounced in the 2D refinement (0.038 Å). Similar features are found when comparing bond lengths and bond angles, 〈italic〉e.g.〈/italic〉 the two N—C—N units are less differently bent in the 1D results (173 and 175°) than in the 2D results (167 and 173°). The results are of importance not only for POWTEX but also for other neutron TOF diffractometers with large‐area detectors, like POWGEN at the SNS or the future DREAM beamline at the European Spallation Source.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The first real‐world neutron diffraction data have been collected with one of the POWTEX detectors (FRM II, Garching, Germany) mounted for testing at the Spallation Neutron Source (Oak Ridge National Laboratory, USA). They allow for angular‐ and wavelength‐dispersive Rietveld refinement using a modified version of 〈italic〉GSAS‐II〈/italic〉.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005767:jcr2tu5033:jcr2tu5033-fig-0001"〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:548 ; neutron detectors ; POWGEN beamline ; POWTEX detector ; DREAM beamline ; time‐of‐flight diffraction ; angular‐dispersive refinement ; wavelength‐dispersive refinement ; powder diffraction ; Rietveld refinement ; multi‐dimensional refinement
    Language: English
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    A note on the wedge reversion antisymmetry operation and 51 types of physical quantities in arbitrary dimensions (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-21
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The paper by Gopalan [〈ext-link ext-link-type="uri" xlink:href="http://scripts.iucr.org/cgi-bin/paper?ib5086"〉(2020). 〈italic〉Acta Cryst.〈/italic〉 A〈bold〉76〈/bold〉, 318–327〈/ext-link〉] presented an enumeration of the 41 physical quantity types in non‐relativistic physics, in arbitrary dimensions, based on the formalism of Clifford algebra. Gopalan considered three antisymmetries: spatial inversion, 〈overline〉1〈/overline〉, time reversal, 1′, and wedge reversion, 1〈sup〉†〈/sup〉. A consideration of the set of all seven antisymmetries (〈overline〉1〈/overline〉, 1′, 1〈sup〉†〈/sup〉, 1′〈sup〉†〈/sup〉, 〈overline〉1〈/overline〉〈sup〉†〈/sup〉, 〈overline〉1〈/overline〉′, 〈overline〉1〈/overline〉′〈sup〉†〈/sup〉) leads to an extension of the results obtained by Gopalan. It is shown that there are 51 types of physical quantities with distinct symmetry properties in total.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉It is shown that there are 51 types of physical quantities in arbitrary dimensions with distinct transformations by wedge reversion symmetry. In the paper by 〈ext-link ext-link-type="uri" xlink:href="http://scripts.iucr.org/cgi-bin/paper?ib5086"〉Gopalan [(2020). 〈italic〉Acta Cryst.〈/italic〉 A〈bold〉76〈/bold〉, 318–327]〈/ext-link〉 only 41 types were enumerated.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:20532733:aya2ib5117:aya2ib5117-fig-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:548 ; multivectors ; wedge reversion ; antisymmetry ; Clifford algebra
    Language: English
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  • 82
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    Use of electron backscatter diffraction patterns to determine the crystal lattice. Part 1. Where is the Bragg angle? (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-19
    Description: The derivation of a crystal structure and its phase‐specific parameters from a single wide‐angle backscattered Kikuchi diffraction pattern requires reliable extraction of the Bragg angles. By means of the first derivative of the lattice profile, an attempt is made to determine fully automatically and reproducibly the band widths in simulated Kikuchi patterns. Even under such ideal conditions (projection centre, wavelength and lattice plane traces are perfectly known), this leads to a lattice parameter distribution whose mean shows a linear offset that correlates with the mean atomic number Z of the pattern‐forming phase. The consideration of as many Kikuchi bands as possible reduces the errors that typically occur if only a single band is analysed. On the other hand, the width of the resulting distribution is such that higher image resolution of diffraction patterns, employing longer wavelengths to produce wider bands or the use of higher interference orders is less advantageous than commonly assumed.
    Description: The lattice parameters of more than 350 phases have been determined from simulated backscatter Kikuchi patterns. The deviations correlating with the mean atomic number correspond to those observed previously for experimental electron backscatter diffraction patterns.
    Keywords: ddc:548 ; Bragg angles ; Kikuchi bands ; Kikuchi patterns ; first derivative ; lattice parameters ; lattice parameter determination ; Bravais lattice type ; electron backscatter diffraction ; Radon transform
    Language: English
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  • 83
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    Data reduction for X‐ray serial crystallography using machine learning (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-19
    Description: Serial crystallography experiments produce massive amounts of experimental data. Yet in spite of these large‐scale data sets, only a small percentage of the data are useful for downstream analysis. Thus, it is essential to differentiate reliably between acceptable data (hits) and unacceptable data (misses). To this end, a novel pipeline is proposed to categorize the data, which extracts features from the images, summarizes these features with the `bag of visual words' method and then classifies the images using machine learning. In addition, a novel study of various feature extractors and machine learning classifiers is presented, with the aim of finding the best feature extractor and machine learning classifier for serial crystallography data. The study reveals that the oriented FAST and rotated BRIEF (ORB) feature extractor with a multilayer perceptron classifier gives the best results. Finally, the ORB feature extractor with multilayer perceptron is evaluated on various data sets including both synthetic and experimental data, demonstrating superior performance compared with other feature extractors and classifiers.
    Description: A machine learning method for distinguishing good and bad images in serial crystallography is presented. To reduce the computational cost, this uses the oriented FAST and rotated BRIEF feature extraction method from computer vision to detect image features, followed by a multilayer perceptron (neural network) to classify the images.
    Keywords: ddc:548 ; serial crystallography ; data reduction ; machine learning ; feature extraction
    Language: English
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  • 84
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    Towards joint in situ determination of pressure and temperature in the large volume press exclusively from X‐ray diffraction (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-19
    Description: Since high‐pressure devices have been used at synchrotron facilities, accurate determination of pressure and temperature in the sample has been a crucial objective, particularly for experiments that simulate the Earth's interior. However, in some cases using a thermocouple may have a high likelihood of failure or is incompatible with a high‐pressure assembly. To address these challenges and similar issues, we aim to expand a previously proposed solution: to jointly estimate pressure and temperature (〈italic〉PT〈/italic〉) through 〈italic〉in situ〈/italic〉 X‐ray diffraction, to cover a wider range of internal 〈italic〉PT〈/italic〉 calibrants tested over larger 〈italic〉PT〈/italic〉 ranges. A modifiable Python‐based software is offered to quickly obtain results. To achieve these aims, 〈italic〉in situ〈/italic〉 large volume press experiments are performed on pellets of intimately mixed powders of a halide (NaCl, KCl, KBr, CsCl) or MgO and a metal (Pt, Re, Mo, W, Ni) in the pressure range 3–11 GPa and temperature range 300–1800 K. Although the pressure range was chosen for practical reasons, it also covers an equally important depth range in the Earth (down to 350 km) for geoscience studies. A thermocouple was used to validate the 〈italic〉PT〈/italic〉 conditions in the cell assemblies. The key results show that choosing the appropriate calibrant materials and using a joint 〈italic〉PT〈/italic〉 estimation can yield surprisingly small uncertainties (〈italic〉i.e.〈/italic〉 〈±0.1 GPa and 〈±50 K). This development is expected to benefit current and future research at extreme conditions, as other materials with high compressibility or high thermal pressure, stable over large 〈italic〉PT〈/italic〉 ranges, may be discovered and used as 〈italic〉PT〈/italic〉 calibrants.〈/p〉
    Description: Research in high‐pressure devices, such as the diamond anvil cell and the large volume press, requires knowledge of the pressure and temperature in the sample. Here, a large volume press and an internal resistive heater were used to generate high load and heat to various combinations of intimately mixed powders of materials. X‐ray diffraction and custom software were used to jointly estimate the pressures and temperatures in the samples and establish calibrants for 〈italic〉in situ〈/italic〉 experiments at extreme conditions.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005775:jsy2vl5008:jsy2vl5008-fig-0001"〉
    Description: https://gitlab.desy.de/robert.farla/eoscross
    Keywords: ddc:548 ; equations of state ; X‐ray diffraction ; large volume press ; high pressure ; resistive heating
    Language: English
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  • 85
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    Monitoring volcanic activity through combined measurements of CO2 efflux and (222Rn) and (220Rn) in soil gas: an application to Mt. Etna (Italy) (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-07
    Description: We present measurements of soil CO2 effluxes combined with soil (222Rn) and (220Rn) from two high-degassing areas on the lower flanks of Mt. Etna volcano (ZE-SV on the E flank and PAT on the SW flank). Measurements were conducted periodically from June 2006 to January 2009 in the ZE-SV area and January 2007 to January 2009 in the PAT area. The results showed significant variations in discharge activity and style. Log values of (220Rn)/(222Rn) and CO2 efflux generally follow a negative correlation, herein parameterized as the Soil Gas Disequilibrium Index (SGDI). Deviations of the SGDI from this negative correlation provide insight into variance of localized and shallow system conditions, namely rock fracturing, residual magma degassing, and near surface interactions between magmatic gases and groundwater. Statistical analysis highlighted signal anomalies, both negative and positive, that were modeled according to the physical properties and the modes of transport for each of the SGDI gas components. The revealed anomalies show correspondence with episodes of magma ascent and eruption, thereby demonstrating the potential of using the SGDI as another instrument for forecasting volcanic activity. An important strength of the SGDI, compared to other magma gas proxies like CO2 or SO2, is that the very short and very different half-lives of 222Rn (t1/2 = 3.85 days) and 220Rn (t1/2 = 55 seconds) provide unique information on the timescales of soil gas transport. Coupling the SGDI with other pre-eruptive proxies enhances the volcanological community’s response capabilities, which is critical for effective hazard mitigation.
    Description: Published
    Description: 167-202
    Description: 4V. Processi pre-eruttivi
    Keywords: Soil gases ; radon ; carbon dioxide ; volcano monitoring ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 86
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    Relative timing of off‐axis volcanism from sediment thickness estimates on the 8°20’N seamount chain, East Pacific Rise (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-16
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fabbrizzi, A., Parnell‐Turner, R., Gregg, P., Fornari, D., Perfit, M., Wanless, V., & Anderson, M. Relative timing of off‐axis volcanism from sediment thickness estimates on the 8°20’N seamount chain, East Pacific Rise. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2022GC010335, https://doi.org/10.1029/2022gc010335.
    Description: Volcanic seamount chains on the flanks of mid-ocean ridges record variability in magmatic processes associated with mantle melting over several millions of years. However, the relative timing of magmatism on individual seamounts along a chain can be difficult to estimate without in situ sampling and is further hampered by Ar40/Ar39 dating limitations. The 8°20’N seamount chain extends ∼170 km west from the fast-spreading East Pacific Rise (EPR), north of and parallel to the western Siqueiros fracture zone. Here, we use multibeam bathymetric data to investigate relationships between abyssal hill formation and seamount volcanism, transform fault slip, and tectonic rotation. Near-bottom compressed high-intensity radiated pulse, bathymetric, and sidescan sonar data collected with the autonomous underwater vehicle Sentry are used to test the hypothesis that seamount volcanism is age-progressive along the seamount chain. Although sediment on seamount flanks is likely to be reworked by gravitational mass-wasting and current activity, bathymetric relief and Sentry vehicle heading analysis suggest that sedimentary accumulations on seamount summits are likely to be relatively pristine. Sediment thickness on the seamounts' summits does not increase linearly with nominal crustal age, as would be predicted if seamounts were constructed proximal to the EPR axis and then aged as the lithosphere cooled and subsided away from the ridge. The thickest sediments are found at the center of the chain, implying the most ancient volcanism there, rather than on seamounts furthest from the EPR. The nonlinear sediment thickness along the 8°20’N seamounts suggests that volcanism can persist off-axis for several million years.
    Description: This work was supported by National Science Foundation awards OCE-1356610, OCE-1356822, OCE-1357150, OCE-1754419, OCE-1834797, OCE-2001314, and OCE-2001331.
    Keywords: Off-axis seamounts ; East Pacific Rise ; Sediment thickness ; Seafloor morphology ; Autonomous underwater vehicle ; Eruption history
    Repository Name: Woods Hole Open Access Server
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  • 87
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    Potential erodibility of semi‐arid steppe soils derived from aggregate stability tests (2022)
    Koza, Moritz ; Pöhlitz, Julia ; Prays, Aleksey ; [et al.]
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-01-26
    Description: Erosion is a severe threat to the sustainable use of agricultural soils. However, the structural resistance of soil against the disruptive forces steppe soils experience under field conditions has not been investigated. Therefore, 132 topsoils under grass‐ and cropland covering a large range of physico‐chemical soil properties (sand: 2–76%, silt: 18–80%, clay: 6–30%, organic carbon: 7.3–64.2 g kg−1, inorganic carbon: 0.0–8.5 g kg−1, pH: 4.8–9.5, electrical conductivity: 32–946 μS cm−1) from northern Kazakhstan were assessed for their potential erodibility using several tests. An adjusted drop‐shatter method (low energy input of 60 Joule on a 250‐cm3 soil block) was used to estimate the stability of dry soil against weak mechanical forces, such as saltating particles striking the surface causing wind erosion. Three wetting treatments with various conditions and energies (fast wetting, slow wetting, and wet shaking) were applied to simulate different disruptive effects of water. Results indicate that aggregate stability was higher for grassland than cropland soils and declined with decreasing soil organic carbon content. The results of the drop‐shatter test suggested that 29% of the soils under cropland were at risk of wind erosion, but only 6% were at high risk (i.e. erodible fraction 〉60%). In contrast, the fast wetting treatment revealed that 54% of the samples were prone to become “very unstable” and 44% “unstable” during heavy rain or snowmelt events. Even under conditions comparable to light rain events or raindrop impact, 53–59% of the samples were “unstable.” Overall, cropland soils under semi‐arid conditions seem much more susceptible to water than wind erosion. Considering future projections of increasing precipitation in Kazakhstan, we conclude that the risk of water erosion is potentially underestimated and needs to be taken into account when developing sustainable land use strategies. Highlights Organic matter is the important binding agent enhancing aggregation in steppe topsoils. Tillage always declines aggregate stability even without soil organic carbon changes. All croplands soil are prone to wind or water erosion independent of their soil properties. Despite the semi‐arid conditions, erosion risk by water seems higher than by wind.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Keywords: ddc:631.4 ; climate change ; land use ; soil organic carbon ; soil texture ; water erosion ; wind erosion
    Language: English
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  • 88
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    Size-differentiated export flux in different dynamical regimes in the ocean (2021)
    American Geophysical Union
    Details
    Publication Date: 2023-02-17
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(3), (2021): e2020GB006764, https://doi.org/10.1029/2020GB006764
    Description: Export of Particulate Organic Carbon (POC) is mainly driven by gravitational sinking. Thus, traditionally, it is thought that larger, faster-sinking particles make up most of the POC export flux. However, this need not be the case for particles whose sinking speeds are comparable to the vertical velocities of a dynamic flow field that can influence the descent rate of particles. Particles with different settling speeds are released in two process-oriented model simulations of an upper ocean eddying flow in the Northeast Pacific to evaluate the impact of (1) ocean dynamics on the respective contribution of the different sinking-velocity classes to POC export, and (2) the particle number size-spectrum slope. The analysis reveals that the leading export mechanism changes from gravitationally driven to advectively driven as submesoscale dynamics become more active in the region. The vertical velocity associated with submesoscale dynamics enhances the contribution of slower-sinking particles to POC export flux by a factor ranging from 3 to 10, especially where the relative abundance of small particles is large (i.e., steep particle size-spectrum slope). Remineralization generally decreases the total amount of biomass exported, but its impact is weaker in dynamical regimes where submesoscale dynamics are present and export is advectively driven. In an advectively driven export regime, remineralization processes counter-intuitively enhance the role of slower-sinking particles to the point where these slower-sinking velocity classes dominate the export, therefore challenging the traditional paradigm for POC export. This study demonstrates that slow-sinking particles can be a significant contribution, and at times, even dominate the export flux.
    Description: The work was funded by NASA grant NNX16AR48 G, to complement the EXport Processes in the global Ocean from RemoTe Sensing (EXPORTS) program.
    Description: 2021-08-17
    Keywords: Export ; Flux ; Particulate organic carbon ; Sinking rates ; Submeso-scales ; Vertical velocities
    Repository Name: Woods Hole Open Access Server
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  • 89
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    The influence of ocean topography on the upwelling of carbon in the Southern Ocean (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-17
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(19), (2021): e2021GL095088, https://doi.org/10.1029/2021GL095088.
    Description: The physical circulation of the Southern Ocean sets the surface concentration and thus air-sea exchange of CO2. However, we have a limited understanding of the three-dimensional circulation that brings deep carbon-rich waters to the surface. Here, we introduce and analyze a novel high-resolution ocean model simulation with active biogeochemistry and online Lagrangian particle tracking. We focus our attention on a subset of particles with high dissolved inorganic carbon (DIC) that originate below 1,000 m and eventually upwell into the near-surface layer (upper 200 m). We find that 71% of the DIC-enriched water upwelling across 1,000 m is concentrated near topographic features, which occupy just 33% of the Antarctic Circumpolar Current. Once particles upwell to the near-surface layer, they exhibit relatively uniform pCO2 levels and DIC decorrelation timescales, regardless of their origin. Our results show that Southern Ocean bathymetry plays a key role in delivering carbon-rich waters to the surface.
    Description: Riley X. Brady was supported by the Department of Energy's Computational Science Graduate Fellowship (DE-FG02-97ER25308), and particularly benefited from the fellowship's summer practicum at Los Alamos National Lab. Nicole S. Lovenduski and Riley X. Brady were further supported by the U.S. Department of Energy Biological and Environmental Research program (DE-SC0022243) and by the National Science Foundation (NSF-PLR 1543457; NSF-OCE 1924636; NSF-OCE 1752724; NSF-OCE 1558225). Mathew E. Maltrud and Phillip J. Wolfram were supported as part of the Energy Exascale Earth System Model (E3SM) project, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. This research used resources provided by the Los Alamos National Laboratory Institutional Computing Program, which is supported by the U.S. Department of Energy National Nuclear Security Administration under Contract No. 89233218CNA000001.
    Keywords: Southern Ocean ; Carbon cycle ; Upwelling ; Lagrangian modeling ; Ocean biogeochemistry ; Climate modeling
    Repository Name: Woods Hole Open Access Server
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  • 90
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    X‐ray diffraction with micrometre spatial resolution for highly absorbing samples (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-01-21
    Description: X‐ray diffraction with high spatial resolution is commonly used to characterize (poly)crystalline samples with, for example, respect to local strain, residual stress, grain boundaries and texture. However, the investigation of highly absorbing samples or the simultaneous assessment of high‐Z materials by X‐ray fluorescence have been limited due to the utilization of low photon energies. Here, a goniometer‐based setup implemented at the P06 beamline of PETRA III that allows for micrometre spatial resolution with a photon energy of 35 keV and above is reported. A highly focused beam was achieved by using compound refractive lenses, and high‐precision sample manipulation was enabled by a goniometer that allows up to 5D scans (three rotations and two translations). As experimental examples, the determination of local strain variations in martensitic steel samples with micrometre spatial resolution, as well as the simultaneous elemental distribution for high‐Z materials in a thin‐film solar cell, are demonstrated. The proposed approach allows users from the materials‐science community to determine micro‐structural properties even in highly absorbing samples.
    Description: A demonstration of high‐resolution micro X‐ray diffraction at high photon energies for highly absorbing samples.
    Keywords: ddc:548 ; X‐ray diffraction ; high spatial resolution ; high photon energy ; X‐ray fluorescence ; goniometers
    Language: English
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  • 91
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    Vertical SOC distribution and aromatic carbon in centuries old charcoal‐rich Technosols (2022)
    Bonhage, Alexander ; Raab, Thomas ; Schneider, Anna ; [et al.]
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-01-21
    Description: Charcoal‐rich Technosols on century‐old relict charcoal hearths (RCHs) are the subject of ongoing research regarding potential legacy effects that result from historic charcoal production and subsequent charcoal amendments on forest soil properties and forest ecosystems today. RCHs consist mostly of Auh horizons that are substantially enriched in soil organic carbon (SOC), of which the largest part seems to be of pyrogenic origin (PyC). However, the reported range of SOC and PyC contents in RCH soil also suggests that they are enriched in nonpyrogenic SOC. RCH soils are discussed as potential benchmarks for the long‐term influence of biochar amendment and the post‐wildfire influences on soil properties. In this study, we utilised a large soil sample dataset (n = 1245) from 52 RCH sites in north‐western Connecticut, USA, to quantify SOC contents by total element analysis. The contents of condensed highly aromatic carbon as a proxy for black carbon (BC) were predicted by using a modified benzene polycarboxylated acid (BPCA) marker method in combination with diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy‐based partial least square regression (r2 = 0.89). A high vertical spatial sampling resolution allowed the identification of soil organic matter (SOM) enrichment and translocation processes. The results show an average 75% and 1862% increase in TOC and BPCA‐derived carbon, respectively, for technogenic Auh horizons compared to reference soils. In addition to an increase in aromatic properties, increased carboxylic properties of the RCH SOC suggest self‐humification effects of degrading charcoal and thereby the continuing formation of leachable aromatic carbon compounds, which could have effects on pedogenic processes in buried soils. Indeed, we show BPCA‐derived carbon concentrations in intermediate technogenic Cu horizons and buried top/subsoils that suggest vertical translocation of highly aromatic carbon originating in RCH Auh horizons. Topmost Auh horizons showed a gradual decrease in total organic carbon (TOC) contents with increasing depth, suggesting accumulation of recent, non‐pyrogenic SOM. Lower aliphatic absorptions in RCH soil spectra suggest different SOM turnover dynamics compared to reference soils. Furthermore, studied RCH soils featured additional TOC enrichment, which cannot be fully explained now. Highlights BC to TOC ratio and high resolution vertical SOC distribution in 52 RCH sites were studied. RCH soils non‐BC pool was potentially different to reference soils. RCH soils feature TOC accumulation in the topmost horizon. There is BC translocation into buried soils on RCH sites.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:631.4 ; benzene polycarboxylated acid marker (BPCA) ; black carbon ; charcoal degradation ; charcoal kiln ; pyrogenic carbon ; relict charcoal hearth ; biochar
    Language: English
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  • 92
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    Domain Auto Finder (DAFi) program: the analysis of single‐crystal X‐ray diffraction data from polycrystalline samples (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-01-21
    Description: This paper presents the Domain Auto Finder (DAFi) program and its application to the analysis of single‐crystal X‐ray diffraction (SC‐XRD) data from multiphase mixtures of microcrystalline solids and powders. Superposition of numerous reflections originating from a large number of single‐crystal domains of the same and/or different (especially unknown) phases usually precludes the sorting of reflections coming from individual domains, making their automatic indexing impossible. The DAFi algorithm is designed to quickly find subsets of reflections from individual domains in a whole set of SC‐XRD data. Further indexing of all found subsets can be easily performed using widely accessible crystallographic packages. As the algorithm neither requires a priori crystallographic information nor is limited by the number of phases or individual domains, DAFi is powerful software to be used for studies of multiphase polycrystalline and microcrystalline (powder) materials. The algorithm is validated by testing on X‐ray diffraction data sets obtained from real samples: a multi‐mineral basalt rock at ambient conditions and products of the chemical reaction of yttrium and nitrogen in a laser‐heated diamond anvil cell at 50 GPa. The high performance of the DAFi algorithm means it can be used for processing SC‐XRD data online during experiments at synchrotron facilities.
    Description: This paper presents the Domain Auto Finder (DAFi) program and its application to the analysis of single‐crystal X‐ray diffraction (SC‐XRD) data from multiphase mixtures of microcrystalline solids and powders. The DAFi algorithm is designed to quickly find subsets of reflections from individual domains in a whole set of SC‐XRD data and neither requires a priori crystallographic information nor is limited by the number of phases or individual domains.
    Keywords: ddc:548 ; single‐crystal domain auto finder ; DAFi ; single‐crystal X‐ray diffraction ; polycrystalline samples ; multiphase mixtures
    Language: English
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  • 93
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    Submarine groundwater discharge in the northern Bohai Sea, China: Implications for coastal carbon budgets and buffering capacity (2022)
    American Geophysical Union
    Details
    Publication Date: 2023-01-20
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 127(8), (2022): e2022JG006810, https://doi.org/10.1029/2022jg006810.
    Description: Submarine groundwater discharge (SGD) has been widely recognized as an important source of dissolved nutrients in coastal waters and affects nutrient biogeochemistry. In contrast, little information is available on SGD impacts on coastal carbon budgets. Here, we assessed the SGD and associated carbon (dissolved inorganic carbon [DIC] and total alkalinity [TA]) fluxes in Liaodong Bay (the largest bay of the Bohai Sea, China) and discussed their border implications for coastal DIC budget and buffering capacity. Based on 223Ra and 228Ra mass balance models, the SGD flux was estimated to be (0.92–1.43) × 109 m3 d−1. SGD was the largest contributor of DIC, accounting for 55%–77% of the total DIC sources. The low ratio (〈1) of SGD-derived TA to DIC fluxes and negative correlation between radium isotopes and pH in seawater implied that SGD would potentially reduce seawater pH in Liaodong Bay. Combining the groundwater carbon data in Liaodong Bay with literature data, we found that the SGD-derived DIC flux off China was 4–9 times greater than those from rivers. By analyzing the TA/DIC ratios in groundwater along the Chinese coast and related carbon fluxes, SGD was thought to partially reduce the CO2 buffer capacity in receiving seawater. These results obtained at the bay scale and national scale suggest that SGD is a significant component of carbon budget and may play a critical role in modulating coastal buffering capacity and atmospheric CO2 sequestration.
    Description: his research was supported by National Natural Science Foundation of China (Grant Nos. 42130703, 42007170) and the Science, Technology and Innovation Commission of Shenzhen (Grant No. 20200925174525002.
    Description: 2023-01-20
    Keywords: Submarine groundwater discharge ; Radium isotopes ; Dissolved inorganic carbon ; Total alkalinity ; Carbon budgets ; Buffering capacity
    Repository Name: Woods Hole Open Access Server
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  • 94
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    High‐resolution XEOL spectroscopy setup at the X‐ray absorption spectroscopy beamline P65 of PETRA III (2022)
    Levcenko, S. ; Biller, R. ; Pfeiffelmann, T. ; [et al.]
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-01-25
    Description: A newly designed setup to perform steady‐state X‐ray excited optical luminescence (XEOL) spectroscopy and simultaneous XEOL and X‐ray absorption spectroscopy characterization at beamline P65 of PETRA III is described. The XEOL setup is equipped with a He‐flow cryostat and state‐of‐the‐art optical detection system, which covers a wide wavelength range of 300–1700 nm with a high spectral resolution of 0.4 nm. To demonstrate the setup functioning, low‐temperature XEOL studies on polycrystalline CuInSe2 thin film, single‐crystalline GaN thin film and single‐crystalline ZnO bulk semiconductor samples are performed.
    Description: X‐ray excited optical luminescence (XEOL) spectroscopy is increasingly important to understand the interplay between the optical properties, structure and chemical composition, providing insights into the mechanism of radiative recombination for a wide range of materials. This study demonstrates a newly implemented setup to perform steady‐state XEOL and simultaneous XEOL and XAFS characterizations at beamline P65 of PETRA III.
    Keywords: ddc:550.2 ; XEOL ; XAS ; CuInSe2 ; ZnO ; GaN
    Language: English
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  • 95
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    Retrieving a “Weather Balloon” from the last Ice Age (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-28
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Seltzer, A. M., & Tyne, R. L. Retrieving a “Weather Balloon” from the last Ice Age. AGU Advances, 3(4), (2022): e2022AV000747, https://doi.org/10.1029/2022AV000747.
    Description: “How cold was the last ice age?” is a question that paleoclimate scientists have been trying to answer for decades. Constraining the magnitude of climate change since the Last Glacial Maximum (∼20,000 years ago) can help improve our understanding of Earth's climate sensitivity and, therefore enhance our ability to predict future change (Tierney et al., 2020). Of course, there is no single answer to this question: there is spatial structure to LGM temperature change that is linked to fundamental climate system properties and processes. Consequently, paleoclimate scientists have focused on variations of this question, like “What was the latitudinal gradient of LGM temperature change?” (Chiang et al., 2003), “What was the land-sea contrast?” (Rind & Peteet, 1985) or “What was the change in ocean heat content?” (Bereiter et al., 2018). These questions inform large-scale atmospheric and oceanic circulation, the intensity of the water cycle, and planetary energy balance; the answers to these questions come from proxies like planktic and benthic foraminifera, speleothems, ice cores, pollen records, ancient groundwater, lake sediments, and glacial moraines, to name a few. In short, the paleoclimate community has developed a proxy “tool kit” equipped to map changes across the Earth's surface and into the ocean interior; but, until now, no “tool” existed for the upper atmosphere.
    Repository Name: Woods Hole Open Access Server
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    The Arctic Ocean’s Beaufort Gyre (2023)
    Annual Reviews
    Details
    Publication Date: 2023-02-28
    Description: © The Author(s), 2023. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Timmermans, M.-L., & Toole, J. The Arctic Ocean’s Beaufort Gyre. Annual Review of Marine Science, 15(1), (2023): 223-248, https://doi.org/10.1146/annurev-marine-032122-012034.
    Description: The Arctic Ocean's Beaufort Gyre is a dominant feature of the Arctic system, a prominent indicator of climate change, and possibly a control factor for high-latitude climate. The state of knowledge of the wind-driven Beaufort Gyre is reviewed here, including its forcing, relationship to sea-ice cover, source waters, circulation, and energetics. Recent decades have seen pronounced change in all elements of the Beaufort Gyre system. Sea-ice losses have accompanied an intensification of the gyre circulation and increasing heat and freshwater content. Present understanding of these changes is evaluated, and time series of heat and freshwater content are updated to include the most recent observations.
    Description: Support was provided by the National Science Foundation Office of Polar Programs and the Office of Naval Research.
    Keywords: Arctic Ocean ; Beaufort Gyre ; Circulation ; Sea ice ; Freshwater ; Ocean heat content
    Repository Name: Woods Hole Open Access Server
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  • 97
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    Sediments in sea ice drive the Canada Basin surface Mn maximum: insights from an Arctic Mn Ocean model (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-28
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 36(8), (2022): e2022GB007320, https://doi.org/10.1029/2022GB007320.
    Description: Biogeochemical cycles in the Arctic Ocean are sensitive to the transport of materials from continental shelves into central basins by sea ice. However, it is difficult to assess the net effect of this supply mechanism due to the spatial heterogeneity of sea ice content. Manganese (Mn) is a micronutrient and tracer which integrates source fluctuations in space and time while retaining seasonal variability. The Arctic Ocean surface Mn maximum is attributed to freshwater, but studies struggle to distinguish sea ice and river contributions. Informed by observations from 2009 IPY and 2015 Canadian GEOTRACES cruises, we developed a three-dimensional dissolved Mn model within a 1/12° coupled ocean-ice model centered on the Canada Basin and the Canadian Arctic Archipelago (CAA). Simulations from 2002 to 2019 indicate that annually, 87%–93% of Mn contributed to the Canada Basin upper ocean is released by sea ice, while rivers, although locally significant, contribute only 2.2%–8.5%. Downstream, sea ice provides 34% of Mn transported from Parry Channel into Baffin Bay. While rivers are often considered the main source of Mn, our findings suggest that in the Canada Basin they are less important than sea ice. However, within the shelf-dominated CAA, both rivers and sediment resuspension are important. Climate-induced disruption of the transpolar drift may reduce the Canada Basin Mn maximum and supply downstream. Other micronutrients found in sediments, such as Fe, may be similarly affected. These results highlight the vulnerability of the biogeochemical supply mechanisms in the Arctic Ocean and the subpolar seas to climatic changes.
    Description: This work was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) Climate Change and Atmospheric Research Grant: GEOTRACES (RGPCC 433848-12) and VITALS (RGPCC 433898), an NSERC Discovery Grant (RGPIN-2016-03865) to SEA, and by the University of British Columbia through a four year fellowship to BR. Computing resources were provided by Compute Canada (RRG 2648 RAC 2019, RRG 2969 RAC 2020, and RRG 1541 RAC 2021).
    Keywords: GEOTRACES ; Arctic Ocean ; Trace elements ; Canadian Arctic Archipelago ; Ocean modeling ; Micronutrients
    Repository Name: Woods Hole Open Access Server
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    WISTFUL: whole‐rock interpretative seismic toolbox for ultramafic lithologies (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-28
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Shinevar, W., Jagoutz, O., & Behn, M. WISTFUL: whole‐rock interpretative seismic toolbox for ultramafic lithologies. Geochemistry, Geophysics, Geosystems, 23(8), (2022): e2022GC010329, https://doi.org/10.1029/2022gc010329.
    Description: To quantitatively convert upper mantle seismic wave speeds measured into temperature, density, composition, and corresponding and uncertainty, we introduce the Whole-rock Interpretative Seismic Toolbox For Ultramafic Lithologies (WISTFUL). WISTFUL is underpinned by a database of 4,485 ultramafic whole-rock compositions, their calculated mineral modes, elastic moduli, and seismic wave speeds over a range of pressure (P) and temperature (T) (P = 0.5–6 GPa, T = 200–1,600°C) using the Gibbs free energy minimization routine Perple_X. These data are interpreted with a toolbox of MATLAB® functions, scripts, and three general user interfaces: WISTFUL_relations, which plots relationships between calculated parameters and/or composition; WISTFUL_geotherms, which calculates seismic wave speeds along geotherms; and WISTFUL_inversion, which inverts seismic wave speeds for best-fit temperature, composition, and density. To evaluate our methodology and quantify the forward calculation error, we estimate two dominant sources of uncertainty: (a) the predicted mineral modes and compositions, and (b) the elastic properties and mixing equations. To constrain the first source of uncertainty, we compiled 122 well-studied ultramafic xenoliths with known whole-rock compositions, mineral modes, and estimated P-T conditions. We compared the observed mineral modes with modes predicted using five different thermodynamic solid solution models. The Holland et al. (2018, https://doi.org/10.1093/petrology/egy048) solution models best reproduce phase assemblages (∼12 vol. % phase root-mean-square error [RMSE]) and estimated wave speeds. To assess the second source of uncertainty, we compared wave speed measurements of 40 ultramafic rocks with calculated wave speeds, finding excellent agreement (Vp RMSE = 0.11 km/s). WISTFUL easily analyzes seismic datasets, integrates into modeling, and acts as an educational tool.
    Description: Funding for this study was provided by NSF Grants EAR-17-22935 (OJ) and EAR-18-44340 (MB).
    Keywords: Seismic velocity ; Seismic wave speed ; Thermodynamic modeling ; Density ; Composition ; Elastic moduli
    Repository Name: Woods Hole Open Access Server
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  • 99
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    Can we estimate air‐sea flux of biological O2 from total dissolved oxygen? (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-02
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 36(9), (2022): e2021GB007145, https://doi.org/10.1029/2021gb007145.
    Description: In this study, we compare mechanistic and empirical approaches to reconstruct the air-sea flux of biological oxygen (F[O2]bio-as) by parameterizing the physical oxygen saturation anomaly (ΔO2[phy]) in order to separate the biological contribution from total oxygen. The first approach matches ΔO2[phy] to the monthly climatology of the argon saturation anomaly from a global ocean circulation model's output. The second approach derives ΔO2[phy] from an iterative mass balance model forced by satellite-based physical drivers of ΔO2[phy] prior to the sampling day by assuming that air-sea interactions are the dominant factors driving the surface ΔO2[phy]. The final approach leverages the machine-learning technique of Genetic Programming (GP) to search for the functional relationship between ΔO2[phy] and biophysicochemical parameters. We compile simultaneous measurements of O2/Ar and O2 concentration from 14 cruises to train the GP algorithm and test the validity and applicability of our modeled ΔO2[phy] and F[O2]bio-as. Among the approaches, the GP approach, which incorporates ship-based measurements and historical records of physical parameters from the reanalysis products, provides the most robust predictions (R2 = 0.74 for ΔO2[phy] and 0.72 for F[O2]bio-as; RMSE = 1.4% for ΔO2[phy] and 7.1 mmol O2 m−2 d−1 for F[O2]bio-as). We use the empirical formulation derived from GP approach to reconstruct regional, inter-annual, and decadal variability of F[O2]bio-as based on historical oxygen records. Overall, our study represents a first attempt at deriving F[O2]bio-as from snapshot measurements of oxygen, thereby paving the way toward using historical O2 data and a rapidly growing number of O2 measurements on autonomous platforms for independent insight into the biological pump.
    Description: N. Cassar was supported by the “Laboratoire d'Excellence” LabexMER (ANR-10-LABX-19) and co-funded by a grant from the French government under the program “Investissements d'Avenir.” Y. Huang was supported by grants from the China NSF (Nos. 42130401 and 42141002). Y. Huang was also partly supported by Chinese State Scholarship Fund to study at Duke University as a joint PhD student (No. 201806310052). R. Eveleth was supported by the NSF GRFP under grant (No. 1106401). D. Nicholson was supported by the NSF OCE-1129973 and OCE-1923915.
    Keywords: Air-sea gas biological oxygen flux ; Physical oxygen saturation anomaly ; Total dissolved oxygen ; Mechanistic and empirical models
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    Accuracy and reproducibility of coral Sr/Ca SIMS timeseries in modern and fossil corals (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-08
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sayani, H., Cobb, K., Monteleone, B., & Bridges, H. Accuracy and reproducibility of coral Sr/Ca SIMS timeseries in modern and fossil corals. Geochemistry, Geophysics, Geosystems, 23(9), (2022): e2021GC010068, https://doi.org/10.1029/2021gc010068.
    Description: Coral strontium-to-calcium ratios (Sr/Ca) provide quantitative estimates of past sea surface temperatures (SST) that allow for the reconstruction of changes in the mean state and climate variations, such as the El Nino-Southern Oscillation, through time. However, coral Sr/Ca ratios are highly susceptible to diagenesis, which can impart artifacts of 1–2°C that are typically on par with the tropical climate signals of interest. Microscale sampling via Secondary Ion Mass Spectrometry (SIMS) for the sampling of primary skeletal material in altered fossil corals, providing much-needed checks on fossil coral Sr/Ca-based paleotemperature estimates. In this study, we employ a set modern and fossil corals from Palmyra Atoll, in the central tropical Pacific, to quantify the accuracy and reproducibility of SIMS Sr/Ca analyses relative to bulk Sr/Ca analyses. In three overlapping modern coral samples, we reproduce bulk Sr/Ca estimates within ±0.3% (1σ). We demonstrate high fidelity between 3-month smoothed SIMS coral Sr/Ca timeseries and SST (R = −0.5 to −0.8; p 〈 0.5). For lightly-altered sections of a young fossil coral from the early-20th century, SIMS Sr/Ca timeseries reproduce bulk Sr/Ca timeseries, in line with our results from modern corals. Across a moderately-altered section of the same fossil coral, where diagenesis yields bulk Sr/Ca estimates that are 0.6 mmol too high (roughly equivalent to −6°C artifacts in SST), SIMS Sr/Ca timeseries track instrumental SST timeseries. We conclude that 3–4 SIMS analyses per month of coral growth can provide a much-needed quantitative check on the accuracy of fossil coral Sr/Ca-derived estimates of paleotemperature, even in moderately altered samples.
    Description: We'd also like to thank Yolande Berta and Georgia Tech's Center for Nanostructure Characterization for providing access to their SEM facilities, and the Khaled bin Sultan Living Ocean Foundation and The Nature Conservancy for financial and logistical support for field excursions to Palmyra. Funding for this work was provided by the National Science Foundation (Award Numbers 1502832 and 2002458 to K.M.C) and the National Oceanic and Atmospheric Administration (Award Number: NA11OAR4310165 to K.M.C).
    Repository Name: Woods Hole Open Access Server
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