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  • International Union of Crystallography (IUCr)  (8,517)
  • American Association for the Advancement of Science (AAAS)
  • American Chemical Society (ACS)
  • Springer Science + Business Media
  • 2020-2024  (21)
  • 1975-1979  (10,755)
  • 1960-1964  (1,792)
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  • 1
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    Global and regional temperature change over the past 4.5 million years (2024)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science, American Association for the Advancement of Science (AAAS), 383(6685), pp. 884-890, ISSN: 0036-8075
    Details
    Publication Date: 2024-03-21
    Description: Much of our understanding of Cenozoic climate is based on the record of δ18O measured in benthic foraminifera. However, this measurement reflects a combined signal of global temperature and sea level, thus preventing a clear understanding of the interactions and feedbacks of the climate system in causing global temperature change. Our new reconstruction of temperature change over the past 4.5 million years includes two phases of long-term cooling, with the second phase of accelerated cooling during the Middle Pleistocene Transition (1.5 to 0.9 million years ago) being accompanied by a transition from dominant 41,000-year low-amplitude periodicity to dominant 100,000-year high-amplitude periodicity. Changes in the rates of long-term cooling and variability are consistent with changes in the carbon cycle driven initially by geologic processes, followed by additional changes in the Southern Ocean carbon cycle. 〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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  • 2
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    Significant turning point: common buzzard (Buteo buteo) exposure to second-generation anticoagulant rodenticides in the United Kingdom (2024)
    American Chemical Society (ACS)
    In:  Environmental Science & Technology vol. 2024 no. 3c09052
    Details
    Publication Date: 2024-04-04
    Description: Second-generation anticoagulant rodenticides (SGARs) are widely used to control rodent populations, resulting in the serious secondary exposure of predators to these contaminants. In the United Kingdom (UK), professional use and purchase of SGARs were revised in the 2010s. Certain highly toxic SGARs have been authorized since then to be used outdoors around buildings as resistance-breaking chemicals under risk mitigation procedures. However, it is still uncertain whether and how these regulatory changes have influenced the secondary exposure of birds of prey to SGARs. Based on biomonitoring of the UK Common Buzzard (Buteo buteo) collected from 2001 to 2019, we assessed the temporal trend of exposure to SGARs and statistically determined potential turning points. The magnitude of difenacoum decreased over time with a seasonal fluctuation, while the magnitude and prevalence of more toxic brodifacoum, authorized to be used outdoors around buildings after the regulatory changes, increased. The summer of 2016 was statistically identified as a turning point for exposure to brodifacoum and summed SGARs that increased after this point. This time point coincided with the aforementioned regulatory changes. Our findings suggest a possible shift in SGAR use to brodifacoum from difenacoum over the decades, which may pose higher risks of impacts on wildlife.
    Keywords: apex predator ; conditional inference trees ; effectiveness evaluation ; regulatory changes ; seasonal fluctuation
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
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  • 3
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    Hotspots of Floating Plastic Particles across the North Pacific Ocean (2024)
    American Chemical Society (ACS)
    In:  EPIC3Environmental Science & Technology, American Chemical Society (ACS), 58(9), pp. 4302-4313, ISSN: 0013-936X
    Details
    Publication Date: 2024-03-28
    Description: The pollution of the marine environment with plastic debris is expected to increase, where ocean currents and winds cause their accumulation in convergence zones like the North Pacific Subtropical Gyre (NPSG). Surface-floating plastic (〉330 μm) was collected in the North Pacific Ocean between Vancouver (Canada) and Singapore using a neuston catamaran and identified by Fourier-transform infrared spectroscopy (FT-IR). Baseline concentrations of 41,600–102,700 items km–2 were found, dominated by polyethylene and polypropylene. Higher concentrations (factors 4–10) of plastic items occurred not only in the NPSG (452,800 items km–2) but also in a second area, the Papaha̅naumokua̅kea Marine National Monument (PMNM, 285,200 items km–2). This second maximum was neither reported previously nor predicted by the applied ocean current model. Visual observations of floating debris (〉5 cm; 8–2565 items km–2 and 34–4941 items km–2 including smaller “white bits”) yielded similar patterns of baseline pollution (34–3265 items km–2) and elevated concentrations of plastic debris in the NPSG (67–4941 items km–2) and the PMNM (295–3748 items km–2). These findings suggest that ocean currents are not the only factor provoking plastic debris accumulation in the ocean. Visual observations may be useful to increase our knowledge of large-scale (micro)plastic pollution in the global oceans.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    Direct Analysis of Marine Dissolved Organic Matter Using LC-FT-ICR MS (2024)
    American Chemical Society (ACS)
    In:  EPIC3Environmental Science and Technology, American Chemical Society (ACS), 58(10), pp. 4637-4647, ISSN: 0013-936X
    Details
    Publication Date: 2024-04-08
    Description: Marine dissolved organic matter (DOM) is an important component of the global carbon cycle, yet its intricate composition and the sea salt matrix pose major challenges for chemical analysis. We introduce a direct injection, reversed-phase liquid chromatography ultrahigh resolution mass spectrometry approach to analyze marine DOM without the need for solid-phase extraction. Effective separation of salt and DOM is achieved with a large chromatographic column and an extended isocratic aqueous step. Postcolumn dilution of the sample flow with buffer-free solvents and implementing a counter gradient reduced salt buildup in the ion source and resulted in excellent repeatability. With this method, over 5,500 unique molecular formulas were detected from just 5.5 nmol carbon in 100 μL of filtered Arctic Ocean seawater. We observed a highly linear detector response for variable sample carbon concentrations and a high robustness against the salt matrix. Compared to solid-phase extracted DOM, our direct injection method demonstrated superior sensitivity for heteroatom-containing DOM. The direct analysis of seawater offers fast and simple sample preparation and avoids fractionation introduced by extraction. The method facilitates studies in environments, where only minimal sample volume is available e.g. in marine sediment pore water, ice cores, or permafrost soil solution. The small volume requirement also supports higher spatial (e.g., in soils) or temporal sample resolution (e.g., in culture experiments). Chromatographic separation adds further chemical information to molecular formulas, enhancing our understanding of marine biogeochemistry, chemodiversity, and ecological processes.
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    Iron Promotes the Retention of Terrigenous Dissolved Organic Matter in Subtidal Permeable Sediments (2024)
    American Chemical Society (ACS)
    In:  EPIC3Environmental Science and Technology, American Chemical Society (ACS), ISSN: 0013-936X
    Details
    Publication Date: 2024-04-08
    Description: Marine permeable sediments are important sites for organic matter turnover in the coastal ocean. However, little is known about their role in trapping dissolved organic matter (DOM). Here, we examined DOM abundance and molecular compositions (9804 formulas identified) in subtidal permeable sediments along a near- to offshore gradient in the German North Sea. With the salinity increasing from 30.1 to 34.6 PSU, the DOM composition in bottom water shifts from relatively higher abundances of aromatic compounds to more highly unsaturated compounds. In the bulk sediment, DOM leached by ultrapure water (UPW) from the solid phase is 54 ± 20 times more abundant than DOM in porewater, with higher H/C ratios and a more terrigenous signature. With 0.5 M HCl, the amount of leached DOM (enriched in aromatic and oxygen-rich compounds) is doubled compared to UPW, mainly due to the dissolution of poorly crystalline Fe phases (e.g., ferrihydrite and Fe monosulfides). This suggests that poorly crystalline Fe phases promote DOM retention in permeable sediments, preferentially terrigenous, and aromatic fractions. Given the intense filtration of seawater through the permeable sediments, we posit that Fe can serve as an important intermediate storage for terrigenous organic matter and potentially accelerate organic matter burial in the coastal ocean.
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    Heatwave responses of Arctic phytoplankton communities are driven by combined impacts of warming and cooling. (2024)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Sci Adv, American Association for the Advancement of Science (AAAS), 10(20), pp. eadl5904-eadl5904, ISSN: 2375-2548
    Details
    Publication Date: 2024-05-22
    Description: Marine heatwaves are increasing in frequency and intensity as climate change progresses, especially in the highly productive Arctic regions. Although their effects on primary producers will largely determine the impacts on ecosystem services, mechanistic understanding on phytoplankton responses to these extreme events is still very limited. We experimentally exposed Arctic phytoplankton assemblages to stable warming, as well as to repeated heatwaves, and measured temporally resolved productivity, physiology, and composition. Our results show that even extreme stable warming increases productivity, while the response to heatwaves depends on the specific scenario applied and is not predictable from stable warming responses. This appears to be largely due to the underestimated impact of the cool phase following a heatwave, which can be at least as important as the warm phase for the overall response. We show that physiological and compositional adjustments to both warm and cool phases drive overall phytoplankton productivity and need to be considered mechanistically to predict overall ecosystem impacts.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Driving forces of Antarctic krill abundance (2023)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science Advances, American Association for the Advancement of Science (AAAS), 9(50), ISSN: 2375-2548
    Details
    Publication Date: 2023-12-18
    Description: Antarctic krill, crucial to the Southern Ocean ecosystem and a vital fisheries resource, is endangered by climate change. Identifying drivers of krill biomass is therefore essential for determining catch limits and designating protection zones. We present a modeling approach to pinpointing effects of sea surface temperature, ice cover, chlorophyll levels, climate indices, and intraspecific competition. Our study reveals that larval recruitment is driven by both competition among age classes and chlorophyll levels. In addition, while milder ice and temperature in spring and summer favor reproduction and early larval survival, both larvae and juveniles strongly benefit from heavier ice and colder temperatures in winter. We conclude that omitting top-down control of resources by krill is only acceptable for retrospective or single-year prognostic models that use field chlorophyll data but that incorporating intraspecific competition is essential for longer-term forecasts. Our findings can guide future krill modeling strategies, reinforcing the sustainability of this keystone species.
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    High Levels of Microplastics in the Arctic Sea Ice Alga 〈i〉Melosira arctica〈/i〉, a Vector to Ice-Associated and Benthic Food Webs (2023)
    American Chemical Society (ACS)
    In:  EPIC3Environmental Science & Technology, American Chemical Society (ACS), 57(17), pp. 6799-6807, ISSN: 0013-936X
    Details
    Publication Date: 2023-08-16
    Description: Plastic pollution has become ubiquitous with very high quantities detected even in ecosystems as remote as arctic sea ice and deepsea sediments. Ice algae growing underneath sea ice are released upon melting and can form fast-sinking aggregates. In this pilot study, we sampled and analyzed the ice algaeMelosira arcticaand ambient sea water from three locations in the Fram Strait to assess their microplastic content and potential as a temporary sink and pathway to the deep seafloor. Analysis by μ-Raman and fluorescence microscopy detected microplastics (≥2.2 μm) in all samples at concentrations ranging from 1.3 to 5.7 × 104 microplastics (MP) m−3 in ice algae and from 1.4 to 4.5 × 103 MP m−3 in sea water, indicating magnitude higher concentrations in algae. On average, 94% of the total microplastic particles were identified as 10 μm or smaller in size and comprised 16 polymer types without a clear dominance. The high concentrations of microplastics found in our pilot study suggest thatM. arctica could trap microplastics from melting ice and ambient sea water. The algae appear to be a temporary sink and could act as a key vector to food webs near the sea surface and on the deep seafloor, to which its fast-sinking aggregates could facilitate an important mechanism of transport.
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    A Review of Arctic–Subarctic Ocean Linkages: Past Changes, Mechanisms, and Future Projections (2023)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Ocean-Land-Atmosphere Research, American Association for the Advancement of Science (AAAS), 2, ISSN: 2771-0378
    Details
    Publication Date: 2023-08-08
    Description: 〈jats:p〉Arctic Ocean gateway fluxes play a crucial role in linking the Arctic with the global ocean and affecting climate and marine ecosystems. We reviewed past studies on Arctic–Subarctic ocean linkages and examined their changes and driving mechanisms. Our review highlights that radical changes occurred in the inflows and outflows of the Arctic Ocean during the 2010s. Specifically, the Pacific inflow temperature in the Bering Strait and Atlantic inflow temperature in the Fram Strait hit record highs, while the Pacific inflow salinity in the Bering Strait and Arctic outflow salinity in the Davis and Fram straits hit record lows. Both the ocean heat convergence from lower latitudes to the Arctic and the hydrological cycle connecting the Arctic with Subarctic seas were stronger in 2000–2020 than in 1980–2000. CMIP6 models project a continuing increase in poleward ocean heat convergence in the 21st century, mainly due to warming of inflow waters. They also predict an increase in freshwater input to the Arctic Ocean, with the largest increase in freshwater export expected to occur in the Fram Strait due to both increased ocean volume export and decreased salinity. Fram Strait sea ice volume export hit a record low in the 2010s and is projected to continue to decrease along with Arctic sea ice decline. We quantitatively attribute the variability of the volume, heat, and freshwater transports in the Arctic gateways to forcing within and outside the Arctic based on dedicated numerical simulations and emphasize the importance of both origins in driving the variability.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    Chasing iron bioavailability in the Southern Ocean: Insights from Phaeocystis antarctica and iron speciation (2023)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science Advances, American Association for the Advancement of Science (AAAS), 9(26), pp. eadf9696-eadf9696, ISSN: 2375-2548
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    Publication Date: 2024-03-01
    Description: Dissolved iron (dFe) availability limits the uptake of atmospheric CO2 by the Southern Ocean (SO) biological pump. Hence, any change in bioavailable dFe in this region can directly influence climate. On the basis of Fe uptake experiments with Phaeocystis antarctica, we show that the range of dFe bioavailability in natural samples is wider (〈1 to ~200% compared to free inorganic Fe′) than previously thought, with higher bioavailability found near glacial sources. The degree of bioavailability varied regardless of in situ dFe concentration and depth, challenging the consensus that sole dFe concentrations can be used to predict Fe uptake in modeling studies. Further, our data suggest a disproportionately major role of biologically mediated ligands and encourage revisiting the role of humic substances in influencing marine Fe biogeochemical cycling in the SO. Last, we describe a linkage between in situ dFe bioavailability and isotopic signatures that, we anticipate, will stimulate future research.
    Repository Name: EPIC Alfred Wegener Institut
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  • 11
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    Improving Arctic sea-ice thickness estimates with the assimilation of CryoSat-2 summer observations (2023)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Ocean-Land-Atmosphere Research, American Association for the Advancement of Science (AAAS), 2, ISSN: 2771-0378
    Details
    Publication Date: 2024-02-13
    Description: 〈jats:p〉Rapidly shrinking Arctic sea ice has had substantial impacts on the Earth system. Therefore, reliably estimating the Arctic sea-ice thickness (SIT) using a combination of available observations and numerical modeling is urgently needed. Here, for the first time, we assimilate the latest CryoSat-2 summer SIT data into a coupled ice-ocean model. In particular, an incremental analysis update scheme is implemented to overcome the discontinuity resulting from the combined assimilation of biweekly SIT and daily sea-ice concentration (SIC) data. Along with improved estimates of sea-ice volume, our SIT estimates corrected the overestimation of SIT produced by the reanalysis that assimilates only SIC in summer in areas where the sea ice is roughest and experiences strong deformation, e.g., around the Fram Strait and Greenland. This study suggests that the newly developed CryoSat-2 SIT product, when assimilated properly using our approach, has great potential for Arctic sea-ice simulation and prediction.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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  • 12
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    Genomic evidence for West Antarctic Ice Sheet collapse during the Last Interglacial (2023)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science, American Association for the Advancement of Science (AAAS), 382(6677), pp. 1384-1389, ISSN: 0036-8075
    Details
    Publication Date: 2024-02-22
    Description: The marine-based West Antarctic Ice Sheet (WAIS) is considered vulnerable to irreversible collapse under future climate trajectories, and its tipping point may lie within the mitigated warming scenarios of 1.5° to 2°C of the United Nations Paris Agreement. Knowledge of ice loss during similarly warm past climates could resolve this uncertainty, including the Last Interglacial when global sea levels were 5 to 10 meters higher than today and global average temperatures were 0.5° to 1.5°C warmer than preindustrial levels. Using a panel of genome-wide, single-nucleotide polymorphisms of a circum-Antarctic octopus, we show persistent, historic signals of gene flow only possible with complete WAIS collapse. Our results provide the first empirical evidence that the tipping point of WAIS loss could be reached even under stringent climate mitigation scenarios.
    Repository Name: EPIC Alfred Wegener Institut
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  • 13
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    Caribbean salinity anomalies contributed to variable North Atlantic circulation and climate during the Common Era (2023)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science Advances, American Association for the Advancement of Science (AAAS), 9(44), pp. eadg2639-eadg2639, ISSN: 2375-2548
    Details
    Publication Date: 2024-04-24
    Description: Paleoceanographic reconstructions show that the strength of North Atlantic currents decreased during the Little Ice Age. In contrast, the role of ocean circulation in climate regulation during earlier historical epochs of the Common Era (C.E.) remains unclear. Here, we reconstruct sea surface temperature (SST) and salinity in the Caribbean Basin for the past 1700 years using the isotopic and elemental composition of planktic foraminifera tests. Centennial-scale SST and salinity variations in the Caribbean co-occur with (hydro)climate changes in the Northern Hemisphere and are linked to a North Atlantic SST forcing. Cold phases around 600, 800, and 1400 to 1600 C.E. are characterized by Caribbean salinification and Gulf of Mexico freshening that implies reductions in the strength of North Atlantic surface circulation. We suggest that the associated changes in the meridional salt advection contributed to the historical climate variability of the C.E.
    Repository Name: EPIC Alfred Wegener Institut
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  • 14
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    Structure-informed microbial population genetics elucidate selective pressures that shape protein evolution (2023)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science Advances, American Association for the Advancement of Science (AAAS), 9(8), pp. eabq4632-eabq4632, ISSN: 2375-2548
    Details
    Publication Date: 2024-04-03
    Description: 〈jats:p〉Comprehensive sampling of natural genetic diversity with metagenomics enables highly resolved insights into the interplay between ecology and evolution. However, resolving adaptive, neutral, or purifying processes of evolution from intrapopulation genomic variation remains a challenge, partly due to the sole reliance on gene sequences to interpret variants. Here, we describe an approach to analyze genetic variation in the context of predicted protein structures and apply it to a marine microbial population within the SAR11 subclade 1a.3.V, which dominates low-latitude surface oceans. Our analyses reveal a tight association between genetic variation and protein structure. In a central gene in nitrogen metabolism, we observe decreased occurrence of nonsynonymous variants from ligand-binding sites as a function of nitrate concentrations, revealing genetic targets of distinct evolutionary pressures maintained by nutrient availability. Our work yields insights into the governing principles of evolution and enables structure-aware investigations of microbial population genetics.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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  • 15
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    Finding the Balance between Research and Monitoring: When Are Methods Good Enough to Understand Plastic Pollution? (2023)
    American Chemical Society (ACS)
    In:  EPIC3Environmental Science and Technology, American Chemical Society (ACS), 57(15), pp. 6033-6039, ISSN: 0013-936X
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    Publication Date: 2024-04-17
    Description: Plastic pollution is an international environmental problem. Desire to act is shared from the public to policymakers, yet motivation and approaches are diverging. Public attention is directed to reducing plastic consumption, cleaning local environments, and engaging in citizen science initiatives. Policymakers and regulators are working on prevention and mitigation measures, while international, regional, and national bodies are defining monitoring recommendations. Research activities are focused on validating approaches to address goals and comparing methods. Policy and regulation are eager to act on plastic pollution, often asking questions researchers cannot answer with available methods. The purpose of monitoring will define which method is implemented. A clear and open dialogue between all actors is essential to facilitate communication on what is feasible with current methods, further research, and development needs. For example, some methods can already be used for international monitoring, yet limitations including target plastic types and sizes, sampling strategy, available infrastructure and analytical capacity, and harmonization of generated data remain. Time and resources to advance scientific understanding must be balanced against the need to answer pressing policy issues.
    Repository Name: EPIC Alfred Wegener Institut
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  • 16
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    Erratum to “A Review of Arctic–Subarctic Ocean Linkages: Past Changes, Mechanisms, and Future Projections” (2023)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Ocean-Land-Atmosphere Research, American Association for the Advancement of Science (AAAS), 2, ISSN: 2771-0378
    Details
    Publication Date: 2024-01-20
    Repository Name: EPIC Alfred Wegener Institut
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  • 17
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    A Call to Include Plastics in the Global Environment in the Class of Persistent, Bioaccumulative, and Toxic (PBT) Pollutants (2023)
    American Chemical Society (ACS)
    In:  EPIC3Environmental Science and Technology, American Chemical Society (ACS), 57(22), pp. 8185-8188, ISSN: 0013-936X
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    Publication Date: 2024-05-03
    Repository Name: EPIC Alfred Wegener Institut
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  • 18
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    Antarctic marine life under pressure (2022)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science, American Association for the Advancement of Science (AAAS), 378(6617), pp. 230-230, ISSN: 0036-8075
    Details
    Publication Date: 2023-05-10
    Description: 〈jats:p〉 Next week, the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) convenes in Hobart, Tasmania, to examine the state of marine life in the Southern Ocean. As part of the Antarctic Treaty System, this convention entered into force in 1982, and its focus on the region’s environmental integrity has never been more important, given the increasing effects of climate change and commercial fishing. An important focus over the past 40 years has been Antarctic krill, 〈jats:italic〉Euphausia superba〈/jats:italic〉 (hereafter krill), a keystone species that helps to hold this marine ecosystem together. Climate and fishing stresses should prompt the CCAMLR to address whether management of krill fishing is at a level that protects the Southern Ocean from losing its overall balance of marine life and the oceanic processes that regulate global climate. 〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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  • 19
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    Spatial heterogeneity and environmental predictors of permafrost region soil organic carbon stocks (2021)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science Advances, American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2024-04-22
    Description: Large stocks of soil organic carbon (SOC) have accumulated in the northern hemisphere permafrost region, but their current mounts and future fate remain uncertain. By analyzing an unprecedented dataset combining 〉2,700 soil profiles with environmental variables in a geospatial framework, we generated spatially explicit estimates of permafrost-region SOC stocks, quantified spatial heterogeneity, and identified key environmental predictors. We estimated 1014−175+194 Pg C are stored in the top 3 m of permafrost region soils. The greatest uncertainties occurred in circumpolar toe-slope positions and in flat areas of the Tibetan region. We found that soil wetness index and elevation are the dominant topographic controllers and surface air temperature (circumpolar region) and precipitation (Tibetan region) are significant climatic controllers of SOC stocks. Our results provide the first high-resolution geospatial assessment of permafrost region SOC stocks and their relationships with environmental factors, which are crucial for modeling the response of permafrost affected soils to changing climate.
    Repository Name: EPIC Alfred Wegener Institut
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  • 20
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    A global environmental crisis 42,000 years ago (2021)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2024-02-07
    Description: Geological archives record multiple reversals of Earth’s magnetic poles, but the global impacts of these events, if any, remain unclear. Uncertain radiocarbon calibration has limited investigation of the potential effects of the last major magnetic inversion, known as the Laschamps Excursion [41 to 42 thousand years ago (ka)]. We use ancient New Zealand kauri trees (Agathis australis) to develop a detailed record of atmospheric radiocarbon levels across the Laschamps Excursion. We precisely characterize the geomagnetic reversal and perform global chemistry-climate modeling and detailed radiocarbon dating of paleoenvironmental records to investigate impacts. We find that geomagnetic field minima ~42 ka, in combination with Grand Solar Minima, caused substantial changes in atmospheric ozone concentration and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record.
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  • 21
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    Post-2020 goals overlook genetic diversity (2020)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2023-02-08
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  • 22
    Electronic Resource
    Electronic Resource
    Curve analysis of small-angle scattering by triaxial body models using a graphic display device (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 628-628 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An interactive program using a graphic display device for the analysis of small-angle scattering has been developed. It includes the curve fitting of experimental data to theoretical results calculated through a triaxial body approximation.
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    X-ray television area detectors for macromolecular structural studies with synchrotron radiation sources (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 1-9 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two-dimensional X-ray diffraction patterns may be recorded quantitatively by means of X-ray-to-electron converters which are scanned in a television-type raster scan. Detectors of this type are capable of operating over the whole range of counting rates from very low to higher than those with which other types of converters can deal. The component parts of an X-ray television detector are examined and the limits to the precision of the measurements are analysed.
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    On the possibility of utilizing holographic schemes in X-ray microscopy (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 19-24 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray holography schemes are analyzed. It is shown that they have a very low aperture ratio, and this limits the size of objects from which a hologram can be recorded. It is indicated that holography schemes can be constructed on the basis of the methods of X-ray diffraction optics.
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    Small-angle X-ray data processing for planar multilayered structures. I. Theory (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 42-48 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Fourier transform values are obtained by multiplying the integrated intensities by the correction factor C(h). The problem of calculating the correction factor for biological specimens which have a multilayered structure is treated. Allowance is made for the transverse size of the specimen, the disorientation in the specimen (ω), the divergence of the X-ray beam (ε), the size of the repeating unit and the curvature of the sphere of reflection. The correction factor C(h) is given by C(h) = Ω[1 + 2γh2]1/2 exp (πδ2)exp (−Ω2[1 + 2γh2]), where γ = (ω2 + ε2)/2(Ω2d2) and where Ω is the diameter of the hth order disc when ω = ε = 0. The formula for C(h) applies to specimens which remain stationary during the X-ray experiment.
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    Pyroelectric temperature analysis as a method for study of ferroelectric transitions in polycrystalline materials (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 54-56 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The transition temperature of ferro- and antiferroelectric crystals can be simply determined by continuous pyroelectric temperature analysis (PTA) of unsintered pressed powder. In order to avoid excessive stored charge the samples were not previously treated by a polarizing electric field. Experiments performed with (NH4)2SO4, KH2PO4 and NH4H2PO4 showed the transition points with a precision of 1°C.
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    Five new polytypes and polytypic change in PbI2 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 57-59 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Five new PbI2 polytypes, 8H(1232), 10H(11112112), 10H(112222), 22H[11(22)5] and 30R[111313]3, were solved by the X-ray diffraction method. It was found on polytypic change that (a) the 2H polytype is changed into various polytypes on heating at 130°C and most of these further change to 12R[13]3 on heating at 260°C; (b) the polytypes 4H, faulted 4H, 14H, 22H, 26H and 30R with layer structures similar to the 12R[13]3 are fairly stable at high temperatures; (c) the 2H-30R [111313]3 transformation occurs reversibly.
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    Orientations mutuelles observées sur des cristaux d'hématite (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 66-69 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The reactivity of hematite depends among other factors on the morphology of the crystal. The choice of the orientation of the reference axes has been made with the help of stereographic projection combined with the morphology of the etch figures on the different faces of the crystal. That the most stable face of a crystal corresponds to the composition plane is shown for crystals of hematite from Elba.
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    Etude des défauts dans des monocristaux naturels de béryl. I. Observations des dislocations (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 70-77 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The lattice defects of beryl single crystals from Brazil and Madagascar have been studied by X-ray topography. Two types of linear defects are observed: channels and grown-in dislocations. Slip systems and Burgers-vector moduli are determined. Some calculations of directions of minimum dislocation energy are given and they are in quite good agreement with the observations.
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    FN: A criterion for rating powder diffraction patterns and evaluating the reliability of powder-pattern indexing (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 60-65 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: At present, over 30 000 powder diffraction patterns are available as references. It is proposed that the patterns on file as well as new patterns submitted for publication be assigned quantitative quality factors. A simple-to-use figure of merit, FN, covering both accuracy in the measurement of the positions of the diffraction lines and completeness of the pattern, has been derived: FN = (1/|{\bar \Delta 2 \theta}|) (N/Nposs), where Nposs is the number of independent diffraction lines possible up to the Nth observed line and |{\bar \Delta 2 \theta}| is the average absolute discrepancy between observed and calculated 2θ values. This figure of merit provides a rapid evaluation of powder patterns, in much the same way as the R factor provides a rating for single-crystal structure determinations. This figure of merit also provides a means to assess the reliability of a unit derived solely from powder data. At present FN ranking scheme is shown to be superior to de Wolff's M20 for ranking patterns. It is recommended that use of the latter be discontinued for that purpose. Guidelines are given on the use and implementation of the FN rating of powder diffraction patterns.
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    Gandolfi attachment for a Debye–Scherrer camera (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 126-126 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A standard Debye–Scherrer camera can be readily converted to operate in the Gandolfi mode by the addition of a simple attachment. The attachment replaces the usual camera cover; no changes to the original powder camera are required and its inherent accuracy is preserved.
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    New crystal data for silver sulphide sulphate, Ag8S3SO4 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 129-130 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The title compound was recognized from the new and unexpected powder pattern of aged precipitates obtained by mixing solutions of excess silver nitrate and sodium thiosulphate under specified conditions. The possible crystalline impurities were identified and conditions were established to yield a pure product. The brown microcrystalline material is tetragonal with a = b = 7.201; c = 10.220 Å. It is a solid electrolyte, has an irreversible transition point at 246°C and melts at 405°C. Method of preparation and powder data are given.
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    Computer-generated standard stereographic projections (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 133-134 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two Fortran programs have been written. The first determines the coordinates of points on a standard stereographic projection, and the second plots these points. The programs may also be used to draw pole figures of so-called `ideal' sheet textures.
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    Crystal data for calcium fluoride silicon oxide (CaF2.SiO2), a dehydration product of fluorapophyllite (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 131-132 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Powder data for a previously unreported dehydration product of fluorapophyllite (KCa4Si8O20F.8H2O) are presented. The reflexions are indexed on the basis of a tetragonal cell with a = 6.937 ± 0.003 and c = 8.488 ± 0.004 Å, (c/a = 1.2235 ± 0.0008). The d spacings and intensities correspond to the unindexed data for CaF2.SiO2 in the JCPDS file (Card No. 20-1050) and the refined cell dimensions are identical, to within the experimental error. Single-crystal data have not yet been obtained for this phase.
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    Profile analysis of diffractometer data (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 134-134 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A computer program has been written for the evaluation of integrated intensities from X-ray diffractometer data. It has been compiled for IBM 360/65 and HP 2100A. The Lehmann–Larsen profile-analysis method [Lehmann & Larsen (1974). Acta Cryst. A30, 580–584] has been used. For weak reflections, profiles obtained from well defined, neighbouring reflections are employed.
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    A semiautomatic coordinate measuring device for molecular models (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 135-135 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    A status monitor for the Elliott rotating-anode X-ray source (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 136-136 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Model drawing programs: manufacture of masks to produce optical transforms (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 135-136 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    A low-cost Richards box for superimposing molecular models on three-dimensional electron density maps (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 137-137 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Synchrotron Radiation Symposium, European Physical Society Fourth General Conference, York, England, 25–29 September 1978 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 137-138 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Union Office, Change of Address (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 138-138 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Crystallographers (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 138-138 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Teaching Crystallography for Today's Sciences, Summer School, Erice, Sicily, Italy, 6–16 September 1977 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 138-138 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Copying Fees and Copyright Law (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 138-139 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Determination of intersubunit distances and subunit shape parameters in DNA-dependent RNA polymerase by neutron small-angle scattering (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 176-185 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: In all organisms the multi-subunit enzyme DNA-dependent RNA polymerase catalyses the first basic step in gene expression, the transcription of DNA into RNA. The neutron small-angle scattering effects were studied in the Guinier region by applying the contrast-matching technique. Isotopic labelling was realised by culturing fully deuterated E. coli cells in a heavy-water medium containing deuterated substrates. One or two completely deuterated components (subunits) of polymerase holoenzyme (composition formula α2ββ′σ, molecular weight 497000) were recombined with the remaining natural (`hydrogenated') subunits for these neutron measurements. Measurements are presented of radii of gyration R, overall shapes, and pair distances d, of three components (subunits α2β,β′) in RNA polymerase of E. coli. The subunits β′, β and α2 are obviously rather elongated in situ and exhibit (as scattering-equivalent prolate ellipsoids) axial ratios of about 7:1 up to 9:1. The intersubunit centre of gravity distances were analysed to be 7.3 ± 0.8 nm for β−β′, 8.2 ± 1.2 nm for α2−β′ and 7.0 ± 1.7 nm for α2−β.
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    A perfect-crystal neutron polarizer as an application of magnetic prism refraction (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 186-191 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: It is demonstrated experimentally that the well known spin-selective deflection of neutrons transmitted through a static magnetic field region with triangular geometric boundaries combined with the high angular resolution of a non-dispersive double-crystal arrangement can be used to polarize a thermal neutron beam to a degree close to unity at reasonably low laboratory fields of 1.0 to 1.5 T.
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    The small-angle neutron scattering facility at the SAFARI-1 reactor (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 192-200 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A long-wavelength neutron scattering facility at the SAFARI-1 reactor is described. Neutrons of wavelength between 5 and 15 Å can be selected. Features of the facility are the use of microwave guides as neutron conductors, flexible guide-pipe configuration and automatic sequential sample changing. Examples are given of measurements on radiation-induced voids in copper, aluminium, Al-0.4%Si and Al-0.1%In after neutron irradiation and magnetic scattering in US and in 80US-10UC-10UC2.
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    The use of nuclear emulsions in X-ray topography: improvement of the development methods (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 201-204 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The development is critical in recording X-ray topographs since it takes a long time and determines the final quality of the pictures. It is shown that, in most cases, it is possible to decrease both exposure time and development time and still obtain pictures of good quality. Standard conditions of development should be used to achieve higher resolution only. This new standard may be of great use with the modern high-power sources.
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    The doping method in quantitative X-ray diffraction phase analysis (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 205-208 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The doping method in quantitative X-ray diffraction phase analysis is described. The method involves the addition to the investigated system of known amounts of the components, the weight fractions of which are to be simultaneously determined. The weight fraction of a component is related to the intensities diffracted by that component and by any non-added component, before and after doping. The method can also be applied to systems containing unidentified components by analysing for only those components of interest, as well as for amorphous-content determination.
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    Determination of strain distribution in elastically bent materials by X-ray intensity measurement (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 209-220 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A method for quantitative determination of local curvature in elastically bent perfect crystals is described. The method is based on X-ray intensity measurements, and a comparison of experimentally determined values with those derived from diffraction theory gives satisfactory agreement. The method was applied to determine the strain gradient and strain concentration in the vicinity of the notch of an elastically bent crystal. The experimental results were compared with those derived from a similar model based on continuum mechanics. Possible applications of the X-ray method are discussed to obtain experimental solutions to strain analyses which, when approached by continuum mechanics, pose formidable mathematical obstacles.
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    A solid-state transformation in 1,5-dichloroanthraquinone (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 239-239 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: 1,5-Dichloroanthraquinone undergoes a solid-state transformation at 470 K. The two modifications are very similar, except that a is greater than b above the transition temperature and the inverse is true at room temperature.
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    A high-temperature focusing X-ray powder camera with new features (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 221-224 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A film-type X-ray high-temperature (up to about 2250 K) powder camera using the Guinier focusing principle in transmission is described. Use is made of a germanium monochromator. The powder specimen is spread without adhesive on a horizontal supporting film of refractory material, and rotates about a vertical axis. The support is surrounded by a cylindrical furnace of thin tantalum sheet enclosed in a chamber which can be evacuated or filled with an inert gas. The X-radiation enters and leaves the chamber through beryllium windows. The film holder is situated outside the chamber. The sample temperature is measured by thermocouples and optical pyrometry. Problems due to the coating by evaporated material of the silica glass window used to observe the specimen are obviated by the use of a transparent shield which can be rotated to give fresh surfaces when needed.
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    Crystal data for isotypic Cs2[M(CN)4].H2O compounds, M=Pt, Pd and Ni (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 241-242 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Cs2[Pd(CN)4].H2O and Cs2[Ni(CN)4].H2O were found to be isotypic with the known hexagonal Pt compound which shows an unusual helical chain of six [Pt(CN)4]2− groups in the unit cell, space group P61 or P65. The crystal data are a = 9.559 (2) and c = 19.308 (4) Å, Dm = 2.87 (4), Dx = 2.912 Mg m−3 for the Ni compound, and a = 9.704 (2), c = 19.388 (4) Å, Dm = 3.12 (4), Dx = 3.115 Mg m−3 for the Pd compound. X-ray powder data are given.
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    Crystal data for Na3Mg2P5O16 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 244-244 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Na3Mg2P5O16 is monoclinic, P21/c, Z = 2, with unit-cell parameters a = 5.177 (1), b = 6.853 (1), c = 18.628 (5) Å, β = 90.00 (4)°.
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    Semi-metals & narrow-bandgap semiconductors by D. R. Lovett (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 262-262 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Comparison and optimization of smoothing procedures for small-angle X-ray scattering curves. Polynomial fitting and modified frequency filtering (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 267-274 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The filter theory allows one to compare the efficiencies of smoothing procedures widely used in the field of small-angle X-ray scattering. This method is demonstrated for polynomial fitting and modified frequency filtering. Optimized and objective smoothing parameters are determined for both procedures through the knowledge of variance reduction factors, transfer functions of the filters, the largest value of the spatial frequencies of the scattering curve and the distortions caused by the smoothing procedures. The comparison of the efficiency of polynomial fitting and frequency filtering clearly shows the superiority of the latter; therefore, this method has to be preferred.
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    Détermination expérimentale de la fonction d'orientation – son application dans le calcul des bandes de diffraction (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 332-338 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The influence of orientation on the powder diagrams produced by lamellar structure systems is studied in the case where the bidimensional lattice is very limited and where the layer structure is complex. The orientation distribution must be included in the numerical integration which leads to the line diffraction profile. The technical measurement of the real experimental orientation is discussed. An example is given showing the influence of the orientation on the interference function in the absolute scale.
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    Geometrical problems with a position-sensitive detector employed on a diffractometer, including its use in the measurement of stress (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 339-345 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Defocusing errors associated with the use of a one-dimensional position-sensitive proportional counter on a powder diffractometer are considered. These errors are small in the measurement of residual stress and it is not necessary to apply mathematical corrections, especially if the X-ray tube is aligned properly. Correspondingly, these errors are small for high-angle peaks in any reflection experiment compared with the present detector resolution. The equations presented allow for an evaluation of this error in most equipment configurations.
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    Determination of local atomic configurations for binary substitutional alloys (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 351-356 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A method is described whereby the complete distribution of first-nearest-neighbor atomic configurations can be determined from experimental short-range order coefficients for binary substitutional f.c.c. alloys. The process involves the computer simulation of the structure represented by the experimental αi by a Gehlen–Cohen-type procedure, followed by the classification of each atom of a given species in the model as one of the 144 crystallographically distinct nearest-neighbor types. These simulation and searching procedures are then used to demonstrate the consistency of the information one can expect to obtain from a given set of αi by `close fitting' to different numbers of coordination shells. It is shown, for example, that a six-shell close fit to a selected set of αi can yield a solution with a mean relative deviation of about five per cent for the nearest-neighbor configuration concentrations.
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    Simple methods of aligning four-circle diffractometers with crystal reflections (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 357-359 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Simple methods of aligning four-circle diffractometers with crystal reflections are devised. They provide the methods to check (1) perpendicularity of χ plane to the incident beam, (2) zero point of 2θ and linearity of focus-χ center-receiving aperture and (3) zero point of χ.
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    Total thermal neutron cross sections of Al, Si, Cu, Zn, Ge, Pb and Bi single crystals (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 399-400 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Experimental values of the cross sections of Al, Si, Cu, Zn, Ge, Pb and Bi at room temperature for several neutron energies between 2 × 10−3 and 10−1 eV, are reported. The measurements were repeated for a Bi single crystal at T = 80 K.
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    Absorption correction and normalization of X-ray small-angle scattering data for materials producing intense scattering at extremely low angles (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 401-402 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Some materials of low absorption that contain particles in the several thousand Å range can produce an intensity of small-angle scattering that is a significant fraction of that of the transmitted beam. This is quite apparent in the range of a few s scattering angle when a Bonse–Hart small-angle scattering diffractometer is used. A method was developed that allows an accurate absorption correction to be calculated when the scattering by the sample can be approximated by an exponential function in the range of 0 to 5 s double Bragg angle 2θ. Variation of sample thickness allows the correction method to be checked.
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    Crystal data for Na4Mg2Si3O10 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 405-406 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: An indexed powder pattern is reported for Mg2Na4O10Si3. The unit cell is orthorhombic, a = 10.584 (7), b = 14.328 (7), c = 10.457 (7) Å. Transition to a cubic phase, a = 7.440 Å, occurs at 918 K. A Na-deficient tetragonal phase was also observed.
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    A simple furnace for neutron diffraction studies (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 403-404 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A simple yet effective high temperature furnace for heating crystals or powder specimens for neutron diffraction studies on a θ/2θ diffractometer is described. The furnace can maintain samples at temperatures up to 1573 K, in air, with a stability of ± 4 K for periods of many hours. Specimen temperature is uniform within 12 K, or much less with the use of a silica sleeve.
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    Powder diffraction data for compounds in the series Nax(Ca3±xNax)Al2O6 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 407-410 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Indexed powder diffraction data are presented for Ca3Al2O6 and its sodium-containing solid solutions. Powder patterns of the cubic and orthorhombic phases calculated from the crystal structure data are compared with the observed patterns. Indexed data are presented for the monoclinic phase, which is stabilized by sodium and silicon. The so-called tetragonal phase is shown by electron diffraction to be orthorhombic, pseudo-tetragonal. It probably has the symmetry Pcaa with a = b = 10.8599 (9), c = 15.1234 (20) Å.
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    Crystal data and molecular packing of drug charge-transfer complexes. I. Promethazine picrate (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 413-413 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Crystal data for promethazine picrate (C23H23N5O7S) complex are: triclinic P1 or P{\bar 1}, Z = 2, a = 18.49 (1), b = 7.77 (1), c = 7.79 (1) Å, α = 70.9 (2), β = 90.0 (2), γ=83.0 (2)°.
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    Crystal data of tris(2-cyanoethyl)phosphine oxide, tris(2-cyanoethyl)phosphine sulphide and tris(2-cyanoethyl)phosphine selenide (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 414-415 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Tris(2-cyanoethyl)phosphine oxide, OP(C2H4CN)3, C9H12N3OP, is hexagonal (rhombohedral), space group R3c, with a = 13.484 (1) and c = 10.162 (1) Å. The sulphide and selenide are triclinic, space group P{\bar 1}. Cell dimensions for SP(C2H4CN)3, C9H12N3PS, are a = 8.363 (8), b = 9.026 (4), c = 9.777 (6) Å; α = 98.75 (4), β = 107.31 (5), γ = 115.85 (5), and for SeP(C2H4CN)3, C9H12N3PSe, a = 8.497 (5), b = 9.148 (2), c = 9.972 (8) Å; α = 98.85 (2), β = 107.20 (6), γ = 116.96 (3)°. X-ray powder diffraction data are quoted.
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    Radiation Leakage around X-ray Tube Shields (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 488-488 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Advances in X-ray analysis. Vol. 21. Proceedings of 26th Annual Conference on Application of X-ray Analysis, Aug. 3-5, 1977 edited by C. S. Barrett, D. E. Leyden, J. B. Newkirk and C. O. Ruud (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 488-488 
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    Etude d'un systeme micellaire de type inverse par diffusion centrale des neutrons (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 502-510 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The study by neutron small-angle scattering of reverse-type micellar solutions of the ternary system water–OT aerosol–n-heptane is reported. The contrast variation method used both on the water inside the micelle and on the solvent makes it possible to determine some structural parameters of the micelle and to propose two micellar models.
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    The influence of multiaxial stress states, stress gradients and elastic anisotropy on the evaluation of (Residual) stresses by X-rays (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 489-501 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: In recent years, nonlinear d versus sin2 ψ distributions have been observed in stressed materials which cannot be explained by the classical fundamentals of X-ray stress measurement, d is the interplanar spacing measured and ψ is the angle between the surface normal of the sample and the measuring direction. This paper reviews treatments for these nonlinear distributions, including stress gradients, shear stresses and anisotropic X-ray elastic constants. Methods for the evaluation of stresses are reported, and recommendations are given for the practical application of X-ray stress measurement.
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    Pressure-induced tetrahedral tilting and deformation in Ge2N2O (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 511-516 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: High-pressure time-of-flight neutron diffraction studies have been carried out on orthorhombic Ge2N2O to 25.4 × 108 Pa and by X-ray diffraction to 49 × 108 Pa. The zero-pressure axial compressibility coefficients are Ka = 33 (2), Kb = 41 (2), Kc = 28 (2), and volume Kv = 99 (5) × 10 −13 Pa−1. The changes in bond angles and bond lengths at pressures from 105 to 25.4 × 108 Pa have been measured. The structure of Ge2N2O consists of GeN3O tetrahedra linked along the a direction by Ge–O–Ge bonds and along the b and c directions by three coordinated Ge–N bonds. This structural framework adjusts to applied pressure by tetrahedra tilting in a cooperative fashion, the biggest change being observed in the Ge–O–Ge angle which decreases by 12.4°. The behavior of Ge2N2O is very similar to its isomorph Si2N2O, though the tetrahedra deform somewhat more for Ge2N2O. The pressure changes in the lattice parameters of Ge2N2O up to 8̃ × 108 Pa are very similar to those of Si2N2O up to 2̃4 × 108 Pa, supporting the contention that germanates behave as high-pressure models for silicates.
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    Determination of inter-element effects through Monte Carlo simulation of X-ray fluorescence (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 517-524 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A Monte Carlo model is developed to simulate the X-ray fluorescence process within a homogeneous multi-element mixture. Validation of the model is obtained through comparison of the model's predictions with experimental data for the iron–nickel–chromium system, for which the inter-element effects are severe. The results indicate that the Monte Carlo model is an excellent simulator and may be used in place of a set of standards to determine the influence coefficients for analysis of fluorescence data.
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    Quantitative structural studies by means of the energy-dispersive method with X-rays from a storage ring (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 531-536 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Test experiments were made using the X-ray energy-dispersive method at the storage ring DORIS (Hamburg) working in the single-bunch mode. It is shown that the spectral distribution of the incident beam calculated from the storage-ring parameters is in very good agreement with that derived from measured diffraction patterns of known substances, and thus it can be used for structural studies. This is illustrated with results of profile-fitting refinement applied to urea (CH4N2O) and naphthalene (C10H8). It is also shown that because of an improved detector system and the time structure of the radiation emitted from the storage ring one is able to record 7 × 104 photons per second and obtain reliable patterns in times of the order of 1 s.
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    The determination of crystallite dimensions using synchrotron-radiation X-ray diffraction photographs (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 525-530 
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    Notes: Synchrotron-radiation Laue patterns give valuable information on the sizes and shapes of grains in a polycrystalline material even if these are too small for synchrotron topography. A calculation, based on kinematic theory, is presented for the radial and lateral broadening of the diffraction spots obtained with white radiation. The most conspicuous broadening is to be expected when the dimensions of the reflecting planes are small and not their number; this is at variance with the conditions leading to broadening with conventional monochromatic methods. Quantitative assessment of the crystal dimensions is possible if auxiliary spectral information is obtained by using selectively absorbing filters. The theory was applied to the analysis of Laue photographs of xenon and krypton crystallites condensed on a cooled beryllium substrate. Crystal dimension down to a few nanometers could be determined. The method is, in principle, applicable to the determination of the grain size and shape distribution of fine-grained polycrystalline samples of any material. Changes during crystallization and recrystallization can be easily followed by virtue of the simple experimental set-up and short exposure times involved.
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    A liquid-helium cryostat for collection of three-dimensional X-ray intensity data down to 20 K. The crystal structure of D(+)-tartaric acid at 35, 105, 160 and 295 K (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 537-544 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A Be-walled conduction cooling He(l) cryostat intended for the interval 20–80 K and the κ geometry of the CAD4 X-ray diffractometer is described. Three-dimensional X-ray intensity data can be collected in the interval − 45 〈 χ 〈 45° with the temperature stability maintained within ± 1 K. The experimental problems caused by centering an unseen crystal and by the absorption and scattering in the Be walls are discussed. D(+)-tartaric acid, C4H6O6, was chosen as a test compound. Only minor differences occur in its crystal and molecular geometry between 295 and 35 K.
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    X-ray diffraction profiles from single crystals of Cu–Ge alloy containing heavily faulted regions (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 545-550 
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    Notes: Intensity profiles of diffuse streaks along [111] were accurately measured for heavily faulted regions in deformed specimens. They often showed two or three broad peaks and differ remarkably from Paterson's [J. Appl. Phys. (1952). 23, 805–811] profiles (Reichweite s = 1), but are in fairly good agreement with Kakinoki's [Acta Cryst. (1967). 23, 875–885] profile of s = 2 with the sequence probabilities α1 = 0.45–0.85 and α2 = 0–0.1. This means that the deformation (intrinsic) faults are produced more easily on every other (111) plane than on successive planes. A model which shows the distribution of the deformation faults is constructed by a computer simulation. A detailed study using Kakinoki's theory with s = 3 shows a better fit with the experimental profile.
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    Analysis of two-dimensional reflections from a fine-particle carbon (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 551-553 
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    Notes: The intensities of two-dimensional reflections from a non-graphitic carbon were correctly calculated by using the general Debye scattering equation and the hypothesis of small (about 12 Å in diameter) domains diffracting incoherently with respect to one another.
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    A texture goniometer with variable radius and collimation for analysis of textures in rocks (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 564-569 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A texture goniometer has been built specifically for geologic applications. Features include (1) a large and variable radius, (2) a variable collimation system that is simple to use and which permits excellent resolution, (3) a wide main circle that allows large specimens to be analysed, (4) partial vacuum paths for the incident and diffracted beams, (5) a θ:2θ drive that allows 2θ scans. The performance of the goniometer is assessed by determining resolution and count rate for various collimations and radii.
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    An analysis of the Rietveld refinement method (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 554-563 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An analysis of the Rietveld profile refinement method used in the interpretation of neutron or X-ray powder diffraction patterns has been carried out. It is shown that the values obtained for the structural parameters are not exactly the same as those obtained from an integrated intensity refinement of the same data and that the standard deviations of the parameters are determined incorrectly. Whilst the differences in the values of the parameters may not be statistically significant, the fact that their standard deviations are estimated incorrectly severely limits their usefulness. These conclusions are confirmed by refinement of a number of data sets using both methods and in most of these cases the standard deviations are found to be underestimated by the profile refinement method by a factor of at least two. Discussions based on the results of profile refinement must therefore be reconsidered and the relative value of powder diffraction techniques must be reviewed.
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  • 81
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    Etude cristallographique des monophosphates acides du type MII(H2PO4)2.2H2O pour MII=MnII, FeII, CoII (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 609-610 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Acid monophosphates MII(H2PO4).2H2O with MII = Mn, Fe and Co are isotypic with the corresponding Cd and Zn salts. Crystal data and powder diffraction data for these three salts are given.
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  • 82
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    Crystal data for ammonium magnesium carbonate tetrahydrate [(NH4)2Mg(CO3)2.4H2O] (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 611-611 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Ammonium magnesium carbonate tetrahydrate crystallizes with an orthorhombic unit cell, a = 7.697, b = 10.287, c = 6.639 Å, Z = 2; Dx = 1.595, DM = 1.61 ± 0.01 Mg m−3. An indexed powder pattern is given.
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  • 83
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    Crystal data for pipemidic acid trihydrate C14H17N5O3.3H2O (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 612-612 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The powder data for pipemidic acid trihydrate are reported. This compound is triclinic with a = 8.570 (3), b = 8.514 (3), c = 15.208 (6) Å, α = 105.14 (4), β = 110.84 (5), γ = 113.96 (5)°. Z = 2.
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  • 84
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    Crystal data for sodium propanoate: C2H5COONa (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 613-614 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Indexed powder patterns of three monoclinic phases of sodium propanoate, Na+.C3H5O2−, are given. The cell dimensions are a = 3.624 (3), b = 5.338 (4), c = 11.414 (8) Å, β = 90.84 (3)° at 507.7 K; a = 3.622 (3), b = 5.359 (5), c = 11.400 (10) Å, β = 90.58 (2)° at 489.8 K and a = 3.569 (3), b = 5.306 (4), c = 11.188 (9) Å, β = 92.86 (2)° at 298.1 K. For the room temperature phase III, smoothing equations are given to describe the thermal expansion.
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  • 85
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    Données crystallographiques sur la forme basse température de (NH4)3In(SO4)3 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 615-615 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The low-temperature modification of (NH4)3In(SO4)3 is monoclinic, space group P21/c. The lattice constants are a = 8.963 (7), b = 15.644 (15), c = 9.131 (6) Å, β = 108.28 (5)° (Z = 4). The indexed powder diagram is given.
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  • 86
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    New crystal data for Ca, Cu, UO2 hydrated carbonate: voglite (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 616-616 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Voglite, Ca2Cu(UO2)(CO3)4.6H2O (?) is monoclinic with a = 25.97, b = 24.50, c = 10.70 Å, β = 104.0°, Z = 16. Probable space group P21 or P21/m. Powder diffraction data are given.
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  • 87
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    Crystal data for N(CH3)4GeCl3 (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 617-618 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The ionic conductor N(CH3)4GeCl3 shows a phase transition at 424 K. The high-temperature modification is cubic with a = 6.552 (2)Å, space group Pm3m. At 293 K the compound is orthorhombic with unit-cell parameters a = 13.096 (2), b = 8.911 (1), c = 9.128 (2) Å, space group Pna21.
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  • 88
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    Crystal data for a second polymorph (β) of C.I. Pigment Red 1,1-[(4-nitrophenyl)azo]-2-naphthol (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 626-627 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The preliminary single-crystal data and powder pattern are given for a second polymorph of C.I. Pigment Red 1, C16H11N3O3. The powder pattern has been indexed using the single-crystal dimensions; the problems of multiple indexing have been reduced by comparison with single-crystal intensities.
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  • 89
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    A review of my papers on crystal optics 1912 to 1968 (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 1-9 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The theory of the diffraction of X-rays by crystals was developed by Ewald as part of a unified study of the interaction of light of all wavelengths with crystals, beginning with the work for his 1912 thesis and extending to his papers in 1968. The formulation of the problem in terms of the interaction of electromagnetic radiation with a periodic array of dipoles is placed in its historical perspective and is compared with Laue's version based on the assumption of a continuous electron density distribution. The Borrmann effect, hinted at in 1917, is derived readily from consideration of the dispersion surface.
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  • 90
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    A solution of the X-ray `phase problem' (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 17-21 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The phases of X-ray reflections are lost in the diffraction process in conventional two-beam diffraction. It is shown that the phases are not lost when three beams diffract simultaneously, and that phase information can be extracted from knowledge of the spatial distribution of the diffracted intensities about the three-beam point. In centrosymmetric crystals, the distribution is a sensitive function of the invariant phase of the product of the structure factors involved in simultaneous diffraction. High-resolution divergent-beam photographs illustrating the intensity differences associated with positive and negative triplet-phase products are shown.
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  • 91
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    Tensorial covariants for the 32 crystal point groups (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 83-95 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The recently published tables of Clebsch-Gordan products are applied to derive the tensorial covariants (bases of irreducible or physically irreducible representations) for the 32 crystal point groups. Tensors of the following intrinsic symmetries in Jahn notation are considered: &egr; (pseudoscalar), V (polar vector), [V2], V[V2], [[V2]2], [V2]2, &egr;[V2], and &egr;V[V2]. With this choice the most important tensors of optical and other properties are covered. Explicit lists of covariants in components of these tensors are given for the non- centrosymmetric groups; with the use of parity arguments the lists also apply to centrosymmetric groups. Applications, especially for phase transitions with reduction of the point symmetry, are briefly discussed.
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  • 92
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    Ferroelastic transformations in lead orthophosphate and its structure as a function of temperature (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 108-114 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In Pb3(PO4)2 there are in general triplets of crystallographically independent atoms of the same kind that are pseudosymmetrically related by a pseudo-threefold rotation and interchange identity in ferroelastic transformations. By means of a rotation of axes that takes into account the distortion of the real monoclinic lattice, the atomic coordinates in the ferroelastic transformations of Pb3(PO4)2 are calculated. The results of the refinement of the structure by means of the Rietveld technique, at several temperatures below and above the phase transition, are reported, as well as the atomic displacements involved in the ferroelastic switching as a function of temperature.
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  • 93
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    Conditional phase probability distributions of structure factors in a Karle–Hauptman matrix (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 105-107 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: From the joint probability distribution of all structure factors in a Karle-Hauptman matrix new phase probability distributions are obtained. These calculations lead to a reformulation of the maximum-determinant rule for phase determination. In addition a new function is derived whose maximum corresponds to the most probable values for the phases of an arbitrary subset of the structure factors in a Karle-Hauptman matrix. This function accounts for the interaction among phases in a Karle-Hauptman matrix through triple products and quartets simultaneously.
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  • 94
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    Use of the neutron time-of-flight technique for structure investigations (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 131-136 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The application of a time-of-flight neutron diffractometer for crystallographic investigations, designed on the basis of a pulsed neutron source, is discussed. The procedure for obtaining integrated intensities and introducing corrections is described. The results of a test experiment with perdeuteronaphthalene are given. The deuterium atom positions in the structure of La2Mg3(NO3)12.24D2O are also refined and compared with those obtained using X-ray diffraction techniques. The observed systematic differences in bond lengths and valence angles are explained by the differences between the 'X-ray' and 'neutron' coordinates of the light atoms.
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  • 95
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    Experimental electronic valence charge density of NaCl and SrCl2 along the nearest-neighbour axis (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 140-142 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Valence-electron charge distributions have been calculated by difference Fourier inversion of experimental structure factors. The contribution of core electrons has been subtracted by using a one-term Gaussian representation. The results are in agreement with theoretical charge distributions obtained by the local-orbitals Hartree-Fock method.
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  • 96
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    Transformations to optimize the superposition of similar structures (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 158-163 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A simple, efficient and general method is described for finding the linear orthogonal transformation to superpose two similar structures given by sets of equivalent points, usually atomic position vectors. Formulae are also given for extracting the independent variables of rotation from the resulting transformation matrix. In addition, general transformations are derived, both in the case of proper rotation and in the case of rotatory inversion, to convert to a molecular frame of reference based on the superposition axis of symmetry.
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  • 97
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    Diffraction profiles from small crystallites (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 171-176 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The diffraction profile for a small crystallite has been obtained as the orientational average of the diffraction intensity given by Ino & Minami [Acta Cryst. (1979), A35, 163-170]. The formula obtained is a type of Debye interference function modified by a function {cal V}(r) (the self-convolution of a crystal shape function) and is expressed as a sum over all the atomic distance vectors in the crystal structure. Since the set of the vectors has Laue symmetry (the order of the group: L), the summation can be simplified to a sum over a reduced range corresponding to 1/L of the original range, while the {cal V}(r) is changed to {\bar v}(r) = ΣLp = 1= {cal V}(Rpr)/(LVt) (Vt: volume of the crystal; R1, . . . , RL: element of Laue symmetry group). Once the {\bar v} function is determined, the profile for a complicated crystal of any size and any crystal system can be systematically and efficiently calculated.
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  • 98
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    The structure of ordered Ag3Mg: an ordinary long-period alloy as opposed to periodically antiphased alloys (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 181-188 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A necessary distinction is established between two kinds of long-period ordered structures: (1) periodic antiphases (PAP), whose principal characteristic feature is a continuous variation of antiphase half-period M as the composition changes; (2) 'ordinary' long-period structures, which show, as the composition changes, a series of phases stable in small composition ranges, every phase displaying a different, but well-defined, crystallographic structure. It is shown, through electron diffraction studies, that the ordered Ag3Mg alloy belongs to the second kind, unlike standard PAP alloys such as AuCu, AuCu3, Au3Cu, Cu3Pt and Cu3Pd. It is stressed that standard PAP structures can always be obtained by heating, above some transition temperature, a L 12 (or L 10) phase which always exists at lower temperature. This is not the case for ordered Ag3Mg. In this connection, the theory about stabilization of long-period structures is discussed [Sato & Toth (1965). Alloying Behaviour and Effects in Concentrated Solid Solutions, pp. 295-419. New York: Gordon & Breach].
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    A hard-disc system: structures of a close-packed thin layer (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 194-196 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The possible structural transitions between n and (n - 1) thin layers of hard discs are considered. The apparently obvious homogeneous transition postulated on the basis of n = 2 is shown by an analogue experiment not to be the general solution. It is argued that the maximum density is retained by a 'Δ-form' transition which minimizes the density deficit at the boundary walls, and can be referred to different sections of a two-dimensional close packing.
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  • 100
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    Structural changes in β-FeOOH caused by radiation damage (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 197-200 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A high-resolution electron-microscope study of β-FeOOH (akaganéite) has been carried out. Examination of intact crystals and ultrathin sections provided no evidence for the hollow-rod structure proposed by earlier workers. It was found also that features, such as mottling and striations, previously thought to be indicative of a porous structure, were due to radiation damage. It is concluded that the β-FeOOH crystals are not porous, but are, in fact, crystallographically homogeneous.
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