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  • 1
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    Facilitated crystal handling using a simple device for evaporation reduction in microtiter plates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-30
    Beschreibung: In the past two decades, most of the steps in a macromolecular crystallography experiment have undergone tremendous development with respect to speed, feasibility and increase of throughput. The part of the experimental workflow that is still a bottleneck, despite significant efforts, involves the manipulation and harvesting of the crystals for the diffraction experiment. Here, a novel low‐cost device is presented that functions as a cover for 96‐well crystallization plates. This device enables access to the individual experiments one at a time by its movable parts, while minimizing evaporation of all other experiments of the plate. In initial tests, drops of many typically used crystallization cocktails could be successfully protected for up to 6 h. Therefore, the manipulation and harvesting of crystals is straightforward for the experimenter, enabling significantly higher throughput. This is useful for many macromolecular crystallography experiments, especially multi‐crystal screening campaigns.
    Beschreibung: A simple and low‐cost device has been developed to minimize evaporation in microtiter plates for easy crystal handling and harvesting. image
    Schlagwort(e): 548 ; evaporation reduction ; crystal handling ; crystal harvesting ; crystallographic fragment screening
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  • 2
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    Cation distribution in Cu2ZnSnSe4, Cu2FeSnS4 and Cu2ZnSiSe4 by multiple‐edge anomalous diffraction (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-30
    Beschreibung: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Semiconductors from this group of materials are promising candidates for photovoltaic applications. Their properties strongly depend on point defects, in particular related to cation order–disorder. However, Cu+, Zn2+ and Fe2+ have very similar scattering factors and are all but indistinguishable in usual X‐ray diffraction experiments. Anomalous diffraction utilizes the dependency of the atomic scattering factors f′ and f′′ of the energy of the radiation, especially close to the element‐specific absorption edges. In the MEAD technique, individual Bragg peaks are tracked over an absorption edge. The intensity changes depending on the structure factor can be highly characteristic for Miller indices selected for a specific structural problem, but require very exact measurements. Beamline KMC‐2 at synchrotron BESSY II, Berlin, has been recently upgraded for this technique. Anomalous X‐ray powder diffraction and XAFS compliment the data. Application of this technique confirmed established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS). In contrast to the literature, cation distribution in Cu2ZnSiSe4 (CZSiSe) is shown to adopt a highly ordered wurtz‐kesterite structure type.
    Beschreibung: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Application of this technique confirms established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS), but in Cu2ZnSiSe4 (CZSiSe) the cation distribution is shown to adopt a highly ordered wurtz‐kesterite structure type in contrast to the literature. image
    Schlagwort(e): 548 ; synchrotron ; anomalous diffraction ; semiconductor ; MEAD
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  • 3
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    The copper(II)‐binding tripeptide GHK, a valuable crystallization and phasing tag for macromolecular crystallography (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-27
    Beschreibung: The growth of diffraction‐quality crystals and experimental phasing remain two of the main bottlenecks in protein crystallography. Here, the high‐affinity copper(II)‐binding tripeptide GHK was fused to the N‐terminus of a GFP variant and an MBP‐FG peptide fusion. The GHK tag promoted crystallization, with various residues (His, Asp, His/Pro) from symmetry molecules completing the copper(II) square‐pyramidal coordination sphere. Rapid structure determination by copper SAD phasing could be achieved, even at a very low Bijvoet ratio or after significant radiation damage. When collecting highly redundant data at a wavelength close to the copper absorption edge, residual S‐atom positions could also be located in log‐likelihood‐gradient maps and used to improve the phases. The GHK copper SAD method provides a convenient way of both crystallizing and phasing macromolecular structures, and will complement the current trend towards native sulfur SAD and MR‐SAD phasing.
    Beschreibung: A novel three‐residue tag containing the residues GHK that can be used to promote crystallization and in SAD phasing experiments using its tightly bound copper ion is described. image
    Schlagwort(e): 548 ; phasing ; crystallization ; GHK ; SAD
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  • 4
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    Determining paracrystallinity in mixed‐tacticity polyhydroxybutyrates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-30
    Beschreibung: Recently, the authors reported on the development of crystallinity in mixed‐tacticity polyhydroxybutyrates. Comparable values reported in the literature vary depending on the manner of determination, the discrepancies being partially attributable to scattering from paracrystalline portions of the material. These portions can be qualified by peak profile fitting or quantified by allocation of scattered X‐ray intensities. However, the latter requires a good quality of the former, which in turn must additionally account for peak broadening inherent in the measurement setup, and due to limited crystallite sizes and the possible presence of microstrain. Since broadening due to microstrain and paracrystalline order both scale with scattering vector, they are easily confounded. In this work, a method to directionally discern these two influences on the peak shape in a Rietveld refinement is presented. Allocating intensities to amorphous, bulk and paracrystalline portions with changing tactic disturbance provided internal validations of the obtained directional numbers. In addition, the correlation between obtained thermal factors and Young's moduli, determined in earlier work, is discussed.
    Beschreibung: A method to robustly determine paracrystalline contents from Rietveld‐refined powder X‐ray data is presented and discussed for the example of mixed‐tacticity polyhydroxybutyrates. image
    Schlagwort(e): 548 ; polyhydroxybutyrates ; mixed tacticity ; paracrystallinity ; Rietveld refinement ; thermal factors
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  • 5
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    Concepts for nondestructive and depth‐resolved X‐ray residual stress analysis in the near‐surface region of nearly single crystalline materials with mosaic structure (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-27
    Beschreibung: Two evaluation concepts for nondestructive depth‐resolved X‐ray residual stress analysis in the near‐surface region of materials with cubic symmetry and nearly single crystalline structure are introduced by simulated examples. Both concepts are based on the same data acquisition strategy, which consists in the determination of lattice‐spacing depth profiles along the ⟨hkl⟩ poles by stepwise sample rotation around the scattering vector. Segmentation of these profiles parallel to the sample surface provides the lattice strain state as a function of depth. The first evaluation concept extends the crystallite group method developed for materials with pronounced crystallographic texture by the feature of depth resolution and can be applied to samples with arbitrary orientation. The second evaluation concept, which adapts the linear regression approach of the sin2ψ method for the case of single crystalline materials, is restricted to samples with (001) orientation. The influence of the strain‐free lattice parameter a0 on residual stress analysis using both evaluation concepts is discussed on the basis of explicitly derived relations.
    Beschreibung: Two data evaluation concepts are proposed for nondestructive and depth‐resolved X‐ray residual stress analysis by means of energy‐dispersive diffraction on materials featuring cubic symmetry and a nearly single crystalline structure. image
    Schlagwort(e): 548 ; residual stress ; X‐ray diffraction ; depth‐resolved analysis ; mosaic crystals
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  • 6
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    X‐ray dichroism in polyimide caused by non‐resonant scattering (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-30
    Beschreibung: Dichroism is one of the most important optical effects in both the visible and the X‐ray range. Besides absorption, scattering can also contribute to dichroism. This paper demonstrates that, based on the example of polyimide, materials can show tiny dichroism even far from electronic resonances due to scattering. Although the effect is small, it can lead to a measurable polarization change and might have influence on highly sensitive polarimetric experiments.
    Beschreibung: Aligned molecules, for example in polyimide foils, lead to small dichroism even far from resonances, which can be revealed by high‐precision X‐ray polarimetry. image
    Schlagwort(e): 548 ; polyimide ; polarization ; X‐ray polarimetry ; wide‐angle scattering ; X‐ray dichroism
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  • 7
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    Elastic stiffness coefficients of thiourea from thermal diffuse scattering (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-27
    Beschreibung: The complete elastic stiffness tensor of thiourea has been determined from thermal diffuse scattering (TDS) using high‐energy photons (100 keV). Comparison with earlier data confirms a very good agreement of the tensor coefficients. In contrast with established methods to obtain elastic stiffness coefficients (e.g. Brillouin spectroscopy, inelastic X‐ray or neutron scattering, ultrasound spectroscopy), their determination from TDS is faster, does not require large samples or intricate sample preparation, and is applicable to opaque crystals. Using high‐energy photons extends the applicability of the TDS‐based approach to organic compounds which would suffer from radiation damage at lower photon energies.
    Beschreibung: The elastic stiffness coefficients of thiourea are determined from thermal diffuse scattering. image
    Schlagwort(e): 548 ; thermal diffuse scattering ; elastic stiffness ; thiourea
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  • 8
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    Fast fitting of reflectivity data of growing thin films using neural networks (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-07-03
    Beschreibung: X‐ray reflectivity (XRR) is a powerful and popular scattering technique that can give valuable insight into the growth behavior of thin films. This study shows how a simple artificial neural network model can be used to determine the thickness, roughness and density of thin films of different organic semiconductors [diindenoperylene, copper(II) phthalocyanine and α‐sexithiophene] on silica from their XRR data with millisecond computation time and with minimal user input or a priori knowledge. For a large experimental data set of 372 XRR curves, it is shown that a simple fully connected model can provide good results with a mean absolute percentage error of 8–18% when compared with the results obtained by a genetic least mean squares fit using the classical Parratt formalism. Furthermore, current drawbacks and prospects for improvement are discussed.
    Beschreibung: Artificial neural networks trained with simulated data are shown to correctly and quickly determine film parameters from experimental X‐ray reflectivity curves.
    Schlagwort(e): 548 ; X‐ray reflectivity ; machine learning ; organic semi‐conductors ; neural networks
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  • 9
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    Numerically stable form factor of any polygon and polyhedron (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-05
    Beschreibung: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Apparent singularities, all removable, are discussed in detail. Cancellation near the singularities causes a loss of precision that can be avoided by using series expansions. An important application domain is small‐angle scattering by nanocrystals.
    Beschreibung: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Series expansions are used to ensure numeric precision close to apparent singularities. image
    Schlagwort(e): 548 ; form factors ; polyhedra ; Fourier shape transform
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  • 10
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    ROBL‐II at ESRF: a synchrotron toolbox for actinide research (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-30
    Beschreibung: ROBL‐II provides four different experimental stations to investigate actinide and other alpha‐ and beta‐emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub‐p.p.m. range. The XES station with its five bent‐crystal analyzer, Johann‐type setup with Rowland circles of 1.0 and 0.5 m radii provides high‐energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The six‐circle heavy duty goniometer of XRD‐1 is equipped for both high‐resolution powder diffraction as well as surface‐sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X‐ray tomography experiments can be performed at a Pilatus 2M detector stage (XRD‐2). Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.
    Beschreibung: ROBL‐II at ESRF provides four experimental stations to investigate actinides with X‐ray absorption and emission spectroscopy, and with surface, high‐resolution powder, and single‐crystal X‐ray diffractometry.
    Schlagwort(e): 549 ; actinides ; EXAFS ; XANES ; HERFD‐XANES ; XAS ; XES ; RIXS ; XRD ; CTR ; RAXR ; surface diffraction
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  • 11
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    ATSAS 3.0: expanded functionality and new tools for small‐angle scattering data analysis (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-30
    Beschreibung: The ATSAS software suite encompasses a number of programs for the processing, visualization, analysis and modelling of small‐angle scattering data, with a focus on the data measured from biological macromolecules. Here, new developments in the ATSAS 3.0 package are described. They include IMSIM, for simulating isotropic 2D scattering patterns; IMOP, to perform operations on 2D images and masks; DATRESAMPLE, a method for variance estimation of structural invariants through parametric resampling; DATFT, which computes the pair distance distribution function by a direct Fourier transform of the scattering data; PDDFFIT, to compute the scattering data from a pair distance distribution function, allowing comparison with the experimental data; a new module in DATMW for Bayesian consensus‐based concentration‐independent molecular weight estimation; DATMIF, an ab initio shape analysis method that optimizes the search model directly against the scattering data; DAMEMB, an application to set up the initial search volume for multiphase modelling of membrane proteins; ELLLIP, to perform quasi‐atomistic modelling of liposomes with elliptical shapes; NMATOR, which models conformational changes in nucleic acid structures through normal mode analysis in torsion angle space; DAMMIX, which reconstructs the shape of an unknown intermediate in an evolving system; and LIPMIX and BILMIX, for modelling multilamellar and asymmetric lipid vesicles, respectively. In addition, technical updates were deployed to facilitate maintainability of the package, which include porting the PRIMUS graphical interface to Qt5, updating SASpy – a PyMOL plugin to run a subset of ATSAS tools – to be both Python 2 and 3 compatible, and adding utilities to facilitate mmCIF compatibility in future ATSAS releases. All these features are implemented in ATSAS 3.0, freely available for academic users at https://www.embl‐hamburg.de/biosaxs/software.html.
    Beschreibung: ATSAS is a comprehensive software suite for the processing, visualization, analysis and modelling of small‐angle scattering data. This article describes developments in the ATSAS 3.0 release, including new programs for data simulation and for the structural modelling of lipids, nucleic acids and polydisperse systems. image
    Schlagwort(e): 548 ; small‐angle scattering ; data analysis ; biological macromolecules ; structural modelling ; ATSAS
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  • 12
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    XGANDALF – extended gradient descent algorithm for lattice finding (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-27
    Beschreibung: Serial crystallography records still diffraction patterns from single, randomly oriented crystals, then merges data from hundreds or thousands of them to form a complete data set. To process the data, the diffraction patterns must first be indexed, equivalent to determining the orientation of each crystal. A novel automatic indexing algorithm is presented, which in tests usually gives significantly higher indexing rates than alternative programs currently available for this task. The algorithm does not require prior knowledge of the lattice parameters but can make use of that information if provided, and also allows indexing of diffraction patterns generated by several crystals in the beam. Cases with a small number of Bragg spots per pattern appear to particularly benefit from the new approach. The algorithm has been implemented and optimized for fast execution, making it suitable for real‐time feedback during serial crystallography experiments. It is implemented in an open‐source C++ library and distributed under the LGPLv3 licence. An interface to it has been added to the CrystFEL software suite.
    Beschreibung: A description and evaluation are given of XGANDALF, extended gradient descent algorithm for lattice finding, an algorithm developed for fast and accurate indexing of snapshot diffraction patterns. image
    Schlagwort(e): 548 ; indexing ; XGANDALF ; CrystFEL ; multiple lattices ; serial crystallography
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  • 13
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    pinkIndexer – a universal indexer for pink‐beam X‐ray and electron diffraction snapshots (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-27
    Beschreibung: A crystallographic indexing algorithm, pinkIndexer, is presented for the analysis of snapshot diffraction patterns. It can be used in a variety of contexts including measurements made with a monochromatic radiation source, a polychromatic source or with radiation of very short wavelength. As such, the algorithm is particularly suited to automated data processing for two emerging measurement techniques for macromolecular structure determination: serial pink‐beam X‐ray crystallography and serial electron crystallography, which until now lacked reliable programs for analyzing many individual diffraction patterns from crystals of uncorrelated orientation. The algorithm requires approximate knowledge of the unit‐cell parameters of the crystal, but not the wavelengths associated with each Bragg spot. The use of pinkIndexer is demonstrated by obtaining 1005 lattices from a published pink‐beam serial crystallography data set that had previously yielded 140 indexed lattices. Additionally, in tests on experimental serial crystallography diffraction data recorded with quasi‐monochromatic X‐rays and with electrons the algorithm indexed more patterns than other programs tested.
    Beschreibung: pinkIndexer, an algorithm developed for indexing of snapshot diffraction patterns recorded with pink‐beam X‐rays, monochromatic X‐rays and electrons, is described and its use evaluated. image
    Schlagwort(e): 548 ; indexing ; pinkIndexer ; CrystFEL ; pink X‐ray beam ; serial electron diffraction
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  • 14
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    Crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-17
    Beschreibung: CRM1 is a nuclear export receptor that has been intensively targeted over the last decade for the development of antitumor and antiviral drugs. Structural analysis of several inhibitor compounds bound to CRM1 revealed that their mechanism of action relies on the covalent modification of a critical cysteine residue (Cys528 in the human receptor) located in the nuclear export signal‐binding cleft. This study presents the crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP at 2.58 Å resolution. The results demonstrate that buffer components can interfere with the characterization of cysteine‐dependent inhibitor compounds.
    Beschreibung: The covalent modification of human CRM1 by 2‐mercaptoethanol interferes with the characterization of cysteine‐dependent inhibitor compounds. image
    Schlagwort(e): 548 ; nuclear export ; cancer ; exportin 1 ; cysteine modification
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  • 15
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    Staircase array of inclined refractive multi‐lenses for large field of view pixel super‐resolution scanning transmission hard X‐ray microscopy (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-26
    Beschreibung: Owing to the development of X‐ray focusing optics during the past decades, synchrotron‐based X‐ray microscopy techniques allow the study of specimens with unprecedented spatial resolution, down to 10 nm, using soft and medium X‐ray photon energies, though at the expense of the field of view (FOV). One of the approaches to increase the FOV to square millimetres is raster‐scanning of the specimen using a single nanoprobe; however, this results in a long data acquisition time. This work employs an array of inclined biconcave parabolic refractive multi‐lenses (RMLs), fabricated by deep X‐ray lithography and electroplating to generate a large number of long X‐ray foci. Since the FOV is limited by the pattern height if a single RML is used by impinging X‐rays parallel to the substrate, many RMLs at regular intervals in the orthogonal direction were fabricated by tilted exposure. By inclining the substrate correspondingly to the tilted exposure, 378000 X‐ray line foci were generated with a length in the centimetre range and constant intervals in the sub‐micrometre range. The capability of this new X‐ray focusing device was first confirmed using ray‐tracing simulations and then using synchrotron radiation at BL20B2 of SPring‐8, Japan. Taking account of the fact that the refractive lens is effective for focusing high‐energy X‐rays, the experiment was performed with 35 keV X‐rays. Next, by scanning a specimen through the line foci, this device was used to perform large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy (PSR‐STHXM) with a 780 ± 40 nm spatial resolution within an FOV of 1.64 cm × 1.64 cm (limited by the detector area) and a total scanning time of 4 min. Biomedical implant abutments fabricated via selective laser melting using Ti–6Al–4V medical alloy were measured by PSR‐STHXM, suggesting its unique potential for studying extended and thick specimens. Although the super‐resolution function was realized in one dimension in this study, it can be expanded to two dimensions by aligning a pair of presented devices orthogonally.
    Beschreibung: A new X‐ray focusing device generates hundreds of thousands of line foci, periodically spaced in the sub‐micrometre range, with centimetre length. It enables to achieve large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy. image
    Schlagwort(e): 502.82 ; inclined refractive X‐ray multi‐lens array ; pixel super‐resolution ; scanning transmission hard X‐ray microscopy ; deep X‐ray lithography and electroplating
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  • 16
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    A new concept for temporal gating of synchrotron X‐ray pulses (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-07-02
    Beschreibung: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented. First experimental tests of the concept yield a diffraction efficiency of 0.18%; however, the calculations indicate a theoretical efficiency and contrast of 〉30% and 10−5, respectively. The full efficiency of the pulse picker has not been reached yet due to a long‐range thermal deformation of the sample after absorption of the excitation laser. This method can be implemented in a broad spectral range (100 eV to 20 keV) and is only minimally invasive to an existing setup.
    Beschreibung: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented.
    Schlagwort(e): 548 ; synchrotron ; time‐resolved ; thermal deformation ; transient grating ; pulse picking
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  • 17
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    The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP at BESSY II (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-06
    Beschreibung: The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP for optical pump/X‐ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four‐circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non‐linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time‐resolution of 17 ps is achieved with the `low‐α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X‐ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time‐resolved detection of the diffracted hard X‐ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields are presented.
    Beschreibung: The KMC‐3 XPP endstation of the synchrotron BESSY II is dedicated to time‐resolved studies of structural dynamics of matter upon optical and/or electrical excitation using hard X‐ray diffraction with an accessible time range from 17 ps to several microseconds. image
    Schlagwort(e): 548 ; beamline instrumentation ; time‐resolved X‐ray diffraction ; optical excitation ; thermal transport ; ferroelectric switching
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  • 18
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    Disordered sodium alkoxides from powder data: crystal structures of sodium ethoxide, propoxide, butoxide and pentoxide, and some of their solvates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publikationsdatum: 2021-03-27
    Beschreibung: The crystal structures of sodium ethoxide (sodium ethanolate, NaOEt), sodium n‐propoxide (sodium n‐propanolate, NaOnPr), sodium n‐butoxide (sodium n‐butanolate, NaOnBu) and sodium n‐pentoxide (sodium n‐amylate, NaOnAm) were determined from powder X‐ray diffraction data. NaOEt crystallizes in space group P421m, with Z = 2, and the other alkoxides crystallize in P4/nmm, with Z = 2. To resolve space‐group ambiguities, a Bärnighausen tree was set up, and Rietveld refinements were performed with different models. In all structures, the Na and O atoms form a quadratic net, with the alkyl groups pointing outwards on both sides (anti‐PbO type). The alkyl groups are disordered. The disorder becomes even more pronounced with increasing chain length. Recrystallization from the corresponding alcohols yielded four sodium alkoxide solvates: sodium ethoxide ethanol disolvate (NaOEt·2EtOH), sodium n‐propoxide n‐propanol disolvate (NaOnPr·2nPrOH), sodium isopropoxide isopropanol pentasolvate (NaOiPr·5iPrOH) and sodium tert‐amylate tert‐amyl alcohol monosolvate (NaOtAm·tAmOH, tAm = 2‐methyl‐2‐butyl). Their crystal structures were determined by single‐crystal X‐ray diffraction. All these solvates form chain structures consisting of Na+, –O− and –OH groups, encased by alkyl groups. The hydrogen‐bond networks diverge widely among the solvate structures. The hydrogen‐bond topology of the iPrOH network in NaOiPr·5iPrOH shows branched hydrogen bonds and differs considerably from the networks in pure crystalline iPrOH.
    Beschreibung: The crystal structures of NaOEt, NaOPr, NaOBu and NaOAm (Am = amyl = pentyl) were determined from powder data. These compounds crystallize in an anti‐PbO structure in the space groups P21m and P4/nmm. Additionally, solvates with the composition NaOEt·2EtOH, NaOPr·2PrOH, NaOiPr·5iPrOH and NaOtAm·tAmOH were synthesized, and their structures were determined from single crystals. They form interesting chain structures of different compositions and topologies. image
    Schlagwort(e): 548 ; sodium alkoxide ; powder data ; solvate ; isopropanol ; Bärnighausen tree ; PXRD
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  • 19
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    Small‐angle X‐ray scattering from GaN nanowires on Si(111): facet truncation rods, facet roughness and Porod's law (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-27
    Beschreibung: Small‐angle X‐ray scattering from GaN nanowires grown on Si(111) is measured in the grazing‐incidence geometry and modelled by means of a Monte Carlo simulation that takes into account the orientational distribution of the faceted nanowires and the roughness of their side facets. It is found that the scattering intensity at large wavevectors does not follow Porod's law I(q) ∝ q−4. The intensity depends on the orientation of the side facets with respect to the incident X‐ray beam. It is maximum when the scattering vector is directed along a facet normal, reminiscent of surface truncation rod scattering. At large wavevectors q, the scattering intensity is reduced by surface roughness. A root‐mean‐square roughness of 0.9 nm, which is the height of just 3–4 atomic steps per micrometre‐long facet, already gives rise to a strong intensity reduction.
    Beschreibung: The intensity of small‐angle X‐ray scattering from GaN nanowires on Si(111) depends on the orientation of the side facets with respect to the incident beam. This reminiscence of truncation rod scattering gives rise to a deviation from Porod's law. A roughness of just 3–4 atomic steps per micrometre‐long side facet notably changes the intensity curves. image
    Schlagwort(e): 548 ; nanowires ; Porod's law ; facet truncation rods ; small‐angle X‐ray scattering ; SAXS ; grazing‐incidence small‐angle X‐ray scattering ; GISAXS
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  • 20
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    The accuracy of protein models automatically built into cryo‐EM maps with ARP/wARP (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-28
    Beschreibung: Recent developments in cryogenic electron microscopy (cryo‐EM) have enabled structural studies of large macromolecular complexes at resolutions previously only attainable using macromolecular crystallography. Although a number of methods can already assist in de novo building of models into high‐resolution cryo‐EM maps, automated and reliable map interpretation remains a challenge. Presented here is a systematic study of the accuracy of models built into cryo‐EM maps using ARP/wARP. It is demonstrated that the local resolution is a good indicator of map interpretability, and for the majority of the test cases ARP/wARP correctly builds 90% of main‐chain fragments in regions where the local resolution is 4.0 Å or better. It is also demonstrated that the coordinate accuracy for models built into cryo‐EM maps is comparable to that of X‐ray crystallographic models at similar local cryo‐EM and crystallographic resolutions. The model accuracy also correlates with the refined atomic displacement parameters.
    Schlagwort(e): 548 ; ARP/wARP ; model building ; cryo‐EM ; model accuracy ; sequence assignment
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  • 21
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    Synthesis, crystal structure and structure–property relations of strontium orthocarbonate, Sr2CO4 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-05
    Beschreibung: Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single‐crystal X‐ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound.
    Beschreibung: A new orthocarbonate, Sr2CO4, was synthesized under extreme pressure and temperature conditions of 92 GPa and 2500 K, respectively. The crystal structure of the compound s fully characterized in situ by synchrotron single‐crystal X‐ray diffraction and DFT calculations were employed to provide insight into its equation of state, Raman and IR spectra, and bonding. image
    Schlagwort(e): 548 ; orthocarbonates ; crystal structure ; single‐crystal X‐ray diffraction ; high pressure ; Sr2CO4
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  • 22
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    Anomalous SAXS at P12 beamline EMBL Hamburg: instrumentation and applications (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-28
    Beschreibung: Small‐angle X‐ray scattering (SAXS) is an established method for studying nanostructured systems and in particular biological macromolecules in solution. To obtain element‐specific information about the sample, anomalous SAXS (ASAXS) exploits changes of the scattering properties of selected atoms when the energy of the incident X‐rays is close to the binding energy of their electrons. While ASAXS is widely applied to condensed matter and inorganic systems, its use for biological macromolecules is challenging because of the weak anomalous effect. Biological objects are often only available in small quantities and are prone to radiation damage, which makes biological ASAXS measurements very challenging. The BioSAXS beamline P12 operated by the European Molecular Biology Laboratory (EMBL) at the PETRA III storage ring (DESY, Hamburg) is dedicated to studies of weakly scattering objects. Here, recent developments at P12 allowing for ASAXS measurements are presented. The beamline control, data acquisition and data reduction pipeline of the beamline were adapted to conduct ASAXS experiments. Modelling tools were developed to compute ASAXS patterns from atomic models, which can be used to analyze the data and to help designing appropriate data collection strategies. These developments are illustrated with ASAXS experiments on different model systems performed at the P12 beamline.
    Schlagwort(e): 548 ; ASAXS ; biological SAXS ; metalloproteins ; gold nanoparticles ; anomalous scattering ; beamline development
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  • 23
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    Symmetry relations in wurtzite nitrides and oxide nitrides and the curious case of Pmc21 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-27
    Beschreibung: Binary III–V nitrides such as AlN, GaN and InN in the wurtzite‐type structure have long been considered as potent semiconducting materials because of their optoelectronic properties, amongst others. With rising concerns over the utilization of scarce elements, a replacement of the trivalent cations by others in ternary and multinary nitrides has led to the development of different variants of nitrides and oxide nitrides crystallizing in lower‐symmetry variants of wurtzite. This work presents the symmetry relationships between these structural types specific to nitrides and oxide nitrides and updates some prior work on this matter. The non‐existence of compounds crystallizing in Pmc21, formally the highest subgroup of the wurtzite type fulfilling Pauling's rules for 1:1:2 stoichiometries, has been puzzling scientists for a while; a rationalization is given, from a crystallographic basis, of why this space group is unlikely to be adopted.
    Schlagwort(e): 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
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  • 24
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    Comparison and evaluation of pair distribution functions, using a similarity measure based on cross‐correlation functions (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-20
    Beschreibung: An approach for the comparison of pair distribution functions (PDFs) has been developed using a similarity measure based on cross‐correlation functions. The PDF is very sensitive to changes in the local structure, i.e. small deviations in the structure can cause large signal shifts and significant discrepancies between the PDFs. Therefore, a comparison based on pointwise differences (e.g. R values and difference curves) may lead to the assumption that the investigated PDFs as well as the corresponding structural models are not in agreement at all, whereas a careful visual inspection of the investigated structural models and corresponding PDFs may reveal a relatively good match. To quantify the agreement of different PDFs for those cases an alternative approach is introduced: the similarity measure based on cross‐correlation functions. In this paper, the power of this application of the similarity measure to the analysis of PDFs is highlighted. The similarity measure is compared with the classical Rwp values as representative of the comparison based on pointwise differences as well as with the Pearson product‐moment correlation coefficient, using polymorph IV of barbituric acid as an example.
    Beschreibung: A novel approach to the quantification of the agreement between pair distribution functions by a similarity measure based on cross‐correlation functions is introduced and evaluated. image
    Schlagwort(e): 548 ; pair distribution functions ; similarity measures ; total scattering techniques ; cross‐correlation functions ; R values
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  • 25
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    Novel experimental setup for megahertz X‐ray diffraction in a diamond anvil cell at the High Energy Density (HED) instrument of the European X‐ray Free‐Electron Laser (EuXFEL) (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-26
    Beschreibung: The high‐precision X‐ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X‐ray Free‐Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump–probe X‐ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X‐ray heating and diffraction of Bi under pressure, obtained using 20 fs X‐ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC.
    Beschreibung: The high‐precision X‐ray diffraction (XRD) setup for work with diamond anvil cells (DACs) in Interaction Chamber 2 of the High Energy Density (HED) instrument of the European X‐ray Free‐Electron Laser is described. image
    Schlagwort(e): 548 ; diamond anvil cells ; X‐ray free‐electron lasers ; high‐precision X‐ray diffraction ; finite element modeling
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  • 26
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    The anisotropy in the optical constants of quartz crystals for soft X‐rays (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-26
    Beschreibung: The refractive index of a y‐cut SiO2 crystal surface is reconstructed from orientation‐dependent soft X‐ray reflectometry measurements in the energy range from 45 to 620 eV. Owing to the anisotropy of the crystal structure in the (100) and (001) directions, a significant deviation of the measured reflectance at the Si L2,3 and O K absorption edges is observed. The anisotropy in the optical constants reconstructed from these data is also confirmed by ab initio Bethe–Salpeter equation calculations for the O K edge. This new experimental data set expands the existing literature data for quartz crystal optical constants significantly, particularly in the near‐edge regions.
    Beschreibung: The refractive index of a y‐cut SiO2 crystal surface is reconstructed from polarization‐dependent soft X‐ray reflectometry measurements in the energy range from 45 to 620 eV. The reconstructed anisotropy in the optical constants is also confirmed by ab initio Bethe–Salpeter equation calculations of the O K edge. image
    Schlagwort(e): 548 ; optical constants ; quartz ; anisotropy ; soft X‐ray reflectometry
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  • 27
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    Unravelling the crystal structure of Nd5.8WO12−δ and Nd5.7W0.75Mo0.25O12−δ mixed ionic electronic conductors (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-07-05
    Beschreibung: Mixed ionic electronic conducting ceramics Nd6−yWO12−δ (δ is the oxygen deficiency) provide excellent stability in harsh environments containing strongly reactive gases such as CO2, CO, H2, H2O or H2S. Due to this chemical stability, they are promising and cost‐efficient candidate materials for gas separation, catalytic membrane reactors and protonic ceramic fuel cell technologies. As in La6−yWO12−δ, the ionic/electronic transport mechanism in Nd6−yWO12−δ is expected to be largely controlled by the crystal structure, the conclusive determination of which is still lacking. This work presents a crystallographic study of Nd5.8WO12−δ and molybdenum‐substituted Nd5.7W0.75Mo0.25O12−δ prepared by the citrate complexation route. High‐resolution synchrotron and neutron powder diffraction data were used in combined Rietveld refinements to unravel the crystal structure of Nd5.8WO12−δ and Nd5.7W0.75Mo0.25O12−δ. Both investigated samples crystallize in a defect fluorite crystal structure with space group Fm3m and doubled unit‐cell parameter due to cation ordering. Mo replaces W at both Wyckoff sites 4a and 48h and is evenly distributed, in contrast with La6−yWO12−δ. X‐ray absorption spectroscopy as a function of partial pressure pO2 in the near‐edge regions excludes oxidation state changes of Nd (Nd3+) and W (W6+) in reducing conditions: the enhanced hydrogen permeation, i.e. ambipolar conduction, observed in Mo‐substituted Nd6−yWO12−δ is therefore explained by the higher Mo reducibility and the creation of additional – disordered – oxygen vacancies.
    Beschreibung: The crystal structures of non‐substituted and Mo‐substituted neodymium tungstates are described in detail through neutron diffraction and high‐resolution X‐ray diffraction. Combined X‐ray and neutron diffraction refinements and electron probe micro‐analysis were employed to locate Mo atoms in the crystal structure of Nd6−yW1−zMozO12−δ (z = 0, 0.25), while X‐ray absorption spectroscopy in the near‐edge regions confirmed no changes in the oxidation states of Nd and W.
    Schlagwort(e): 548 ; powder diffraction ; mixed conductors ; X‐ray absorption spectroscopy (XAS) ; Nd6−yWO12−δ
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  • 28
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    High‐temperature treatments of niobium under high vacuum, dilute air‐ and nitrogen‐atmospheres as investigated by in situ X‐ray absorption spectroscopy (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-30
    Beschreibung: Niobium metal foils were heat‐treated at 900°C under different conditions and in situ investigated with time‐resolved X‐ray absorption fine‐structure (EXAFS and XANES) measurements. The present study aims to mimic the conditions usually applied for heat treatments of Nb materials used for superconducting radiofrequency cavities, in order to better understand the evolving processes during vacuum annealing as well as for heat treatments in controlled dilute gases. Annealing in vacuum in a commercially available cell showed a substantial amount of oxidation, so that a designated new cell was designed and realized, allowing treatments under clean high‐vacuum conditions as well as under well controllable gas atmospheres. The experiments performed under vacuum demonstrated that the original structure of the Nb foils is preserved, while a detailed evaluation of the X‐ray absorption fine‐structure data acquired during treatments in dilute air atmospheres (10−5 mbar to 10−3 mbar) revealed a linear oxidation with the time of the treatment, and an oxidation rate proportional to the oxygen (air) pressure. The structure of the oxide appears to be very similar to that of polycrystalline NbO. The cell also permits controlled exposures to other reactive gases at elevated temperatures; here the Nb foils were exposed to dilute nitrogen atmospheres after a pre‐conditioning of the studied Nb material for one hour under high‐vacuum conditions, in order to imitate typical conditions used for nitrogen doping of cavity materials. Clear structural changes induced by the N2 exposure were found; however, no evidence for the formation of niobium nitride could be derived from the EXAFS and XANES experiments. The presented results establish the feasibility to study the structural changes of the Nb materials in situ during heat treatments in reactive gases with temporal resolution, which are important to better understand the underlaying mechanisms and the dynamics of phase formation during those heat treatments in more detail.
    Schlagwort(e): 548 ; in situ EXAFS ; high temperature ; time‐resolved EXAFS ; niobium
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  • 29
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    Pressure‐induced Pb–Pb bonding and phase transition in Pb2SnO4 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-03-27
    Beschreibung: High‐pressure single‐crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator‐to‐semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory‐based calculations show that at ambient conditions the channels in the structure host the stereochemically‐active Pb 6s2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.
    Beschreibung: The structure of Pb2SnO4 is found to strongly distort on compression and a structural phase transition with a change of space group from Pbam to Pnam occurs at ∼11 GPa. Our complementary DFT‐based calculations show that at ambient conditions, the channels in the structure host the stereochemically active Pb 6s2 lone electron pairs which form bonds between the Pb2+ ions with increasing pressure. image
    Schlagwort(e): 548 ; lead stannate (Pb2SnO4) ; density functional theory ; high‐pressure X‐ray diffraction ; pressure‐induced phase transition ; insulator–semiconductor transition
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  • 30
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    A discussion on `Domain formation and phase transitions in the wurtzite‐based heterovalent ternaries: a Landau theory analysis' (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-05
    Beschreibung: Heterovalent ternary nitrides are considered one of the promising classes of materials for photovoltaics, combining attractive physical properties with low toxicity and element abundance. One of the front‐runner systems under consideration is ZnSnN2. Although it is nominally a ternary compound, no clear crystallographic evidence for cation ordering has been observed so far. An attempt to elucidate this discrepancy [Quayle (2020). Acta Cryst. A76, 410–420] was the trigger for an intensive discussion between the authors, and an agreement was reached to elaborate on some points in order to set things in perspective. Rather than using a conventional comment–answer scheme, this is published in the form of a joint discussion to celebrate constructive criticism and collegiality.
    Beschreibung: A scientific exchange on an earlier paper [Quayle (2020). Acta Cryst. A76, 410–420] has led to the clarification of some of the points. image
    Schlagwort(e): 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
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  • 31
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    X‐SPEC: a 70 eV to 15 keV undulator beamline for X‐ray and electron spectroscopies (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-26
    Beschreibung: X‐SPEC is a high‐flux spectroscopy beamline at the KIT (Karlsruhe Institute of Technology) Synchrotron for electron and X‐ray spectroscopy featuring a wide photon energy range. The beamline is equipped with a permanent magnet undulator with two magnetic structures of different period lengths, a focusing variable‐line‐space plane‐grating monochromator, a double‐crystal monochromator and three Kirkpatrick–Baez mirror pairs. By selectively moving these elements in or out of the beam, X‐SPEC is capable of covering an energy range from 70 eV up to 15 keV. The flux of the beamline is maximized by optimizing the magnetic design of the undulator, minimizing the number of optical elements and optimizing their parameters. The beam can be focused into two experimental stations while maintaining the same spot position throughout the entire energy range. The first experimental station is optimized for measuring solid samples under ultra‐high‐vacuum conditions, while the second experimental station allows in situ and operando studies under ambient conditions. Measurement techniques include X‐ray absorption spectroscopy (XAS), extended X‐ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X‐ray PES (HAXPES), as well as X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS).
    Beschreibung: X‐SPEC is a high‐flux undulator beamline for electron and X‐ray spectroscopy with an energy range from 70 eV to 15 keV. It offers X‐ray absorption spectroscopy (XAS), extended X‐ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X‐ray PES (HAXPES), as well as X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS) for in vacuo, in situ and operando sample environments. image
    Schlagwort(e): 548 ; undulator beamline ; soft X‐ray ; tender X‐ray ; hard X‐ray ; in situ ; operando ; HAXPES ; RIXS ; XAS ; XES
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  • 32
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    Structure determination of organic compounds by a fit to the pair distribution function from scratch without prior indexing (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-06-26
    Beschreibung: A method for the ab initio crystal structure determination of organic compounds by a fit to the pair distribution function (PDF), without prior knowledge of lattice parameters and space group, has been developed. The method is called `PDF‐Global‐Fit' and is implemented by extension of the program FIDEL (fit with deviating lattice parameters). The structure solution is based on a global optimization approach starting from random structural models in selected space groups. No prior indexing of the powder data is needed. The new method requires only the molecular geometry and a carefully determined PDF. The generated random structures are compared with the experimental PDF and ranked by a similarity measure based on cross‐correlation functions. The most promising structure candidates are fitted to the experimental PDF data using a restricted simulated annealing structure solution approach within the program TOPAS, followed by a structure refinement against the PDF to identify the correct crystal structure. With the PDF‐Global‐Fit it is possible to determine the local structure of crystalline and disordered organic materials, as well as to determine the local structure of unindexable powder patterns, such as nanocrystalline samples, by a fit to the PDF. The success of the method is demonstrated using barbituric acid as an example. The crystal structure of barbituric acid form IV solved and refined by the PDF‐Global‐Fit is in excellent agreement with the published crystal structure data.
    Schlagwort(e): 548 ; pair distribution function analysis ; structure determination ; total scattering technique ; similarity measures ; PDF‐Global‐Fit
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  • 33
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    Structural basis of chitin utilization by a GH20 β‐N‐acetylglucosaminidase from Vibrio campbellii strain ATCC BAA‐1116 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-07-01
    Beschreibung: Vibrio species play a crucial role in maintaining the carbon and nitrogen balance between the oceans and the land through their ability to employ chitin as a sole source of energy. This study describes the structural basis for the action of the GH20 β‐N‐acetylglucosaminidase (VhGlcNAcase) in chitin metabolism by Vibrio campbellii (formerly V. harveyi) strain ATCC BAA‐1116. Crystal structures of wild‐type VhGlcNAcase in the absence and presence of the sugar ligand, and of the unliganded D437A mutant, were determined. VhGlcNAcase contains three distinct domains: an N‐terminal carbohydrate‐binding domain linked to a small α+β domain and a C‐terminal (β/α)8 catalytic domain. The active site of VhGlcNAcase has a narrow, shallow pocket that is suitable for accommodating a small chitooligosaccharide. VhGlcNAcase is a monomeric enzyme of 74 kDa, but its crystal structures show two molecules of enzyme per asymmetric unit, in which Gln16 at the dimeric interface of the first molecule partially blocks the entrance to the active site of the neighboring molecule. The GlcNAc unit observed in subsite −1 makes exclusive hydrogen bonds to the conserved residues Arg274, Tyr530, Asp532 and Glu584, while Trp487, Trp546, Trp582 and Trp505 form a hydrophobic wall around the −1 GlcNAc. The catalytic mutants D437A/N and E438A/Q exhibited a drastic loss of GlcNAcase activity, confirming the catalytic role of the acidic pair (Asp437–Glu438).
    Beschreibung: Crystal structures of a GH20 β‐N‐acetylglucosaminidase from V. campbellii reveal substrate specificity in chitin utilization.
    Schlagwort(e): 577.14 ; GH20 β‐N‐acetylglucosaminidase ; chitin recycling ; Vibrio spp ; marine bacteria
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  • 34
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    Resolution of a bent‐crystal spectrometer for X‐ray free‐electron laser pulses: diamond versus silicon (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-09-29
    Beschreibung: The resolution function of a spectrometer based on a strongly bent single crystal (bending radius of 10 cm or less) is evaluated. It is shown that the resolution is controlled by two parameters: (i) the ratio of the lattice spacing of the chosen reflection to the crystal thickness and (ii) a single parameter comprising crystal thickness, its bending radius, distance to a detector, and anisotropic elastic constants of the chosen crystal. The results allow the optimization of the parameters of bent‐crystal spectrometers for the hard X‐ray free‐electron laser sources.
    Beschreibung: The resolution function of a bent‐crystal spectrometer for pulses of an X‐ray free‐electron laser is evaluated. Under appropriate conditions, the energy resolution reaches the ratio of the lattice spacing to the crystal thickness. image
    Schlagwort(e): 548 ; X‐ray free‐electron lasers ; X‐ray spectroscopy ; bent crystals ; diamond crystal optics ; femtosecond X‐ray diffraction
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  • 35
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    Separation of the inelastic and elastic scattering in time‐of‐flight mode on the pinhole small‐angle neutron scattering diffractometer KWS‐2 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-09-29
    Beschreibung: To study and control the incoherent inelastic background in small‐angle neutron scattering, which makes a significant contribution to the detected scattering from hydrocarbon systems, the KWS‐2 small‐angle neutron scattering diffractometer operated by the Jülich Centre for Neutron Science (JCNS) at Heinz‐Maier Leibnitz Zentrum (MLZ), Garching, Germany, was equipped with a secondary single‐disc chopper that is placed in front of the sample stage. This makes it possible to record in time‐of‐flight mode the scattered neutrons in the high‐Q regime of the instrument (i.e. short incoming wavelengths and detection distances) and to discard the inelastic component from the measured data. Examples of measurements on different materials routinely used as standard samples, sample containers and solvents in the experiments at KWS‐2 are presented. When only the elastic region of the spectrum is used in the data‐reduction procedure, a decrease of up to two times in the incoherent background of the experimentally measured scattering cross section may be obtained. The proof of principle is demonstrated on a solution of bovine serum albumin in D2O.
    Beschreibung: A new chopper has been installed at the sample position in front of the sample stage at the KWS‐2 small‐angle neutron‐scattering diffractometer of the Jülich Centre for Neutron Science. The pulsed beam and the time‐of‐flight data acquisition enable the separation of elastic and inelastic scattering from hydrogenous samples.
    Schlagwort(e): 548 ; TOF‐SANS ; incoherent neutron scattering ; inelastic neutron scattering ; hydrocarbon systems
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  • 36
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    Czochralski growth of mixed cubic sesquioxide crystals in the ternary system Lu2O3–Sc2O3–Y2O3 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publikationsdatum: 2021-09-29
    Beschreibung: Cubic rare‐earth sesquioxide crystals are strongly demanded host materials for high power lasers, but due to their high melting points investigations on their thermodynamics and the growth of large‐size crystals of high optical quality remain a challenge. Detailed thermal investigations of the ternary system Lu2O3–Sc2O3–Y2O3 revealing a large range of compositions with melting temperatures below 2200°C and a minimum of 2053°C for the composition (Sc0.45Y0.55)2O3 are presented. These reduced temperatures enable for the first time the growth of high optical quality mixed sesquioxide crystals with disordered structure by the conventional Czochralski method from iridium crucibles. An (Er0.07Sc0.50Y0.43)2O3 crystal is successfully grown and characterized with respect to its crystallographic properties as well as its composition, thermal conductivity and optical absorption in the 1 µm range.
    Beschreibung: The phase diagram of the ternary system Lu2O3–Sc2O3–Y2O3 is investigated and compositions with melting points below 2200°C are found. This allows for the first successful growth of the mixed cubic sesquioxide crystal (Er0.07Sc0.50Y0.43)2O3 by the Czochralski method from an iridium crucible. image
    Schlagwort(e): 548 ; crystal growth ; optical materials ; phase diagrams ; melting points ; rare earth sesquioxides
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  • 37
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    Cyclic thermal fluctuations can be burden or relief for an ectotherm depending on fluctuations’ average and amplitude (2021)
    British Ecological Society | Wiley
    In:  Functional Ecology, 35 (11). pp. 2483-2496.
    Details
    Publikationsdatum: 2021-11-10
    Beschreibung: Predicting the implications of ongoing ocean climate warming demands a better understanding of how short-term thermal variability impacts marine ectotherms, particularly at beyond-optimal average conditions during summer heatwaves. Using a globally important model species, the blue mussel Mytilus, in a 5-week-long experiment, we (a) assessed growth performance traits under 12 scenarios, consisting of four thermal averages (18.5, 21, 23.5 and 26℃) imposed as constant or daily fluctuating regimes with amplitudes of 2 or 4℃. Additionally, we conducted a short-term assay using different mussel individuals to (b) test for the species capacity for suppression and recovery of metabolic performance traits (feeding and aerobic respiration) when exposed to a 1-day thermal fluctuation regime (16.8–30.5℃). Using this high-resolution data, we (c) generated short-term thermal metabolic performance curves to predict and explain growth responses observed in the long-term experiment. We found that daily high-amplitude thermal cycles (4℃) improved mussel growth when fluctuations were imposed around an extreme average temperature of 26℃, representing end-of-century heatwaves. In contrast, thermal cycles negatively affected mussel growth at a less extreme average temperature of 23.5℃, resembling current peak summer temperature scenarios. These results suggest that fluctuations ameliorate heat stress impacts only at critically high average temperatures. The short-term assay demonstrated that during the warming phase, animals stopped feeding between 24 and 30℃ while gradually suppressing respiration. In the subsequent cooling phase, feeding and respiration partially and fully recovered to pre-heating rates respectively. Furthermore, nonlinear averaging of short-term feeding responses (upscaling) well-predicted longer term growth responses to fluctuations. Our findings suggest that fluctuations can be beneficial to or detrimental for the long-term performance of ectothermic animals, depending on the fluctuations' average and amplitude. Furthermore, the observed effects can be linked to fluctuation-mediated metabolic suppression and recovery. In a general framework, we propose various hypothetical scenarios of fluctuation impacts on ectotherm performance considering inter- or intra-species variability in heat sensitivity. Our research highlights the need for studying metabolic performance in relation to cyclic abiotic fluctuations to advance the understanding of climate change impacts on aquatic systems. A free Plain Language Summary can be found within the Supporting Information of this article
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  • 38
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    Comparative interevent time statistics of degassing and seismic activity at Villarrica Volcano (Chile) (2020)
    AGU (American Geophysical Union) | Wiley
    In:  (Submitted) Journal of Geophysical Research: Solid Earth .
    Details
    Publikationsdatum: 2021-01-07
    Beschreibung: It is generally assumed that seismic activity at volcanoes is closely connected to degassing processes. Intuitively, one would therefore expect a good correlation between degassing rates and seismic amplitude. However, both examples and counterexamples of such a correlation exist. In this study on Villarrica volcano (Chile), we pursued a different approach to relate gas flux and volcanic seismicity using 3 months of SO$_2$ flux rate measurements and 12 days of seismic recordings from early 2012.〈br /> We analyzed the statistical distributions of interevent times between transient seismic waveforms commonly associated with explosions and between peaks in the degassing time series.〈br /> Both event types showed a periodic recurrence with a mode of 20-25 s and around 1 h for transients and degassing, respectively. The normalized interevent times were fitted by almost identical log-normal distributions. Given the actually very different time scales, this similarity potentially indicates a scale-invariant phenomenon. We could reproduce these empirical findings by modelling the occurrence of transients as a renewal process from which the degassing events were derived recursively with increasing probability since the previous degassing event. In this model, the seismic transients could be either produced by degassing processes within the conduit or by gas release at the lava lake surface while the longer intervals of the degassing events may be explained by accumulation of gas either in the magma column or in the juvenile gas plume.〈br /> Additionally, we analyzed volcano-tectonic events, which behaved very differently from the transients. They showed the clustered occurrence of tectonic earthquakes.
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  • 39
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    Genus Blastochloris (2020)
    Wiley
    In:  In: Bergey's Manual of Systematics of Archaea and Bacteria (BMSAB). , ed. by Brenner, D. J., Krieg, N. R. and Staley, J. T. Wiley, New York, USA, pp. 506-507. ISBN 978-1-118-96060-8
    Details
    Publikationsdatum: 2020-11-27
    Beschreibung: Proteobacteria Alphaproteobacteria Rhizobiales Hyphomicrobiaceae Blas.to.chlo'ris. Gr. masc. n. blastos bud shoot; Gr. masc. adj. chloros green; N.L. fem. n. Blastochloris green bud shoot. Proteobacteria / Alphaproteobacteria / Rhizobiales / Hyphomicrobiaceae / Blastochloris Blastochloris species are anoxygenic phototrophic Alphaproteobacteria that have bacteriochlorophyll b in their photosynthetic reaction centers. Crystals of the photosynthetic reaction centers of Blastochloris viridis were the first that have been studied in high‐resolution structure analysis at 3 Å resolution. Internal photosynthetic membranes are present as lamellae underlying and parallel to the cytoplasmic membrane. Cells are rod shaped to ovoid and exhibit polar growth, budding, and asymmetric cell division and form rosette‐like cell aggregates. They are motile by means of subpolar flagella and stain Gram‐negative. Straight‐chain monounsaturated C18:1 is the predominant component of cellular fatty acids. Ubiquinones and menaquinones are present, and the lipopolysaccharides are characterized by a 2,3‐diamino‐2,3‐deoxy‐d‐glucose (DAG)‐containing, phosphate‐free lipid A with amide‐bound C14:0 3OH. DNA G + C content (mol%): 63.8–68.3. Type species: Blastochloris viridis (Drews and Giesbrecht 1966) Hiraishi 1997 (Rhodopseudomonas viridis Drews and Giesbrecht 1966).
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  • 40
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    Reply to Comment by A. Argnani on "Geometry of the Deep Calabrian Subduction from Wide‐Angle Seismic Data and 3‐D Gravity Modeling" (2020)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 21 (8). e2020GC009223.
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    Publikationsdatum: 2020-08-11
    Beschreibung: Keypoints This contribution is a reply on a comment submitted by A. Argnani. The alternate interpretation of the wide-angle seismic model is discussed. The Alfeo Fault system is proposed to be the current location of STEP fault. Abstract Andrea Argnani in his comment on Dellong et al., 2020 (Geometry of the deep Calabrian subduction (Central Mediterranean Sea) from wide‐angle seismic data and 3D gravity modeling), proposes an alternate interpretation of the wide-angle seismic velocity models presented by Dellong et al., 2018 and Dellong et al., 2020 and proposes a correction of the literature citations in these paper. In this reply, we discuss in detail all points raised by Andrea Argnani.
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  • 41
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    Effect on Subduction of Deeply Buried Seamounts Offshore of Kodiak Island (2020)
    AGU (American Geophysical Union) | Wiley
    In:  Tectonics, 39 (7). e2019TC005710.
    Details
    Publikationsdatum: 2021-01-08
    Beschreibung: Seamounts are ubiquitous on the oceanic plate; those situated near convergent margins will eventually undergo subduction. Using six prestack depth migrated MCS profiles transecting the Aleutian Trench, we investigate deeply buried seamounts offshore Kodiak Island, within 145–155°W and 55–58°N. A distinct sedimentary horizon exists in all six seismic profiles, at or above the average height of seamounts, which appears to be the preferred structural detachment zone. Where drilled, this horizon contains gravel‐sized debris interpreted to be ice rafted and marks the onset of intensification of Northern Hemisphere glaciation at ~2.7 Ma. Beneath this horizon, sediments prior to the Surveyor Fan development were deposited, all or the majority of these sediments will eventually be subducted. Despite the subducted seamounts being deeply buried, these features cause enhanced surface slope of the accretionary prism. Our observations lead us to propose a model for the stages of subduction for deeply buried seamounts. These stages include the following: (1) Prior to subduction, the protothrust zone undergoes enhanced shortening, (2) frontal thrust steepening and enhanced backthrusting occurs during subduction with a potential décollement step down seaward and a steeping outward of the deformation front to the limit of the protothrust zone, and (3) further subduction results in a pattern of uplift farther into the wedge resulting in enhanced out‐of‐sequence thrusting and persistence of the more seaward deformation front position. This pattern is distinct from the dominance of embayments and effective removal of prism material during seamount subduction described along margins with less deeply buried edifices.
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  • 42
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    Confronting Arctic Troposphere, Clouds, and Surface Energy Budget Representations in Regional Climate Models With Observations (2020)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Atmospheres, 125 (6). e2019JD031783.
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    Publikationsdatum: 2021-01-08
    Beschreibung: A coordinated regional climate model (RCM) evaluation and intercomparison project based on observations from a July–October 2014 trans‐Arctic Ocean field experiment (ACSE‐Arctic Clouds during Summer Experiment) is presented. Six state‐of‐the‐art RCMs were constrained with common reanalysis lateral boundary forcing and upper troposphere nudging techniques to explore how the RCMs represented the evolution of the surface energy budget (SEB) components and their relation to cloud properties. We find that the main reasons for the modeled differences in the SEB components are a direct consequence of the RCM treatment of cloud and cloud‐radiative interactions. The RCMs could be separated into groups by their overestimation or underestimation of cloud liquid. While radiative and turbulent heat flux errors were relatively large, they often invoke compensating errors. In addition, having the surface sea‐ice concentrations constrained by the reanalysis or satellite observations limited how errors in the modeled radiative fluxes could affect the SEB and ultimately the surface evolution and its coupling with lower tropospheric mixing and cloud properties. Many of these results are consistent with RCM biases reported in studies over a decade ago. One of the six models was a fully coupled ocean‐ice‐atmosphere model. Despite the biases in overestimating cloud liquid, and associated SEB errors due to too optically thick clouds, its simulations were useful in understanding how the fully coupled system is forced by, and responds to, the SEB evolution. Moving forward, we suggest that development of RCM studies need to consider the fully coupled climate system.
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  • 43
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    Biology of Green Sulfur Bacteria (2020)
    Wiley
    In:  In: eLS (Encyclopedia of Life Sciences). Wiley, Chichester, UK, pp. 21-33.
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    Publikationsdatum: 2020-10-02
    Beschreibung: Green sulfur bacteria, the Chlorobiaceae, have gained much attention because of unique structures of the photosynthetic apparatus and the presence of chlorosomes as very powerful light antenna that can capture minute amounts of light. This has important ecological consequences, because the efficient light‐harvesting determines the ecological niche of these bacteria at the lowermost part of stratified environments where the least of light is available. The oxidation of sulfide as their outmost important photosynthetic electron donor involves the deposition of elemental sulfur globules outside the cells and separates the process of sulfide oxidation to sulfate into two parts. This is the basis for stable syntrophic associations between green sulfur bacteria and sulfur‐ and sulfate‐reducing bacteria in which the sulfur compounds are recycled. The green sulfur bacteria are distantly related to other bacteria and systematically members of the Chlorobiaceae family with Chlorobium, Chlorobaculum, Prosthecochloris and Chloroherpeton as representative genera. Green sulfur bacteria depend on light for life due to their obligate phototrophic metabolism. Green sulfur bacteria are most efficient in photosynthesis due to the presence of light‐harvesting organelles, the chlorosomes, which are filled with bacteriochlorophyll molecules. Green sulfur bacteria are offsprings of one of the most ancient bacterial lineages performing biosynthesis of bacteriochlorophyll and photosynthesis. Green sulfur bacteria inhabit the lowermost light‐receiving part of the chemocline in the stratified environment due to their high sensitivity to oxygen, high tolerance to the toxic sulfide and highly efficient light capture. Green sulfur bacteria are important drivers of oxidation of reduced sulfur compounds in the stratified, sulfide‐containing environment receiving low irradiation.
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  • 44
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    Athleten des Meeres Zur Ökophysiologie pelagischer Kalmare (1994)
    Wiley
    In:  Biologie in unserer Zeit, 24 (4). pp. 192-199.
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    Publikationsdatum: 2020-06-05
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  • 45
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    Morphological variation in shallow-water octopuses (Mollusca: Cephalopoda) (1994)
    Wiley-Blackwell
    In:  Journal of Zoology, 232 (3). pp. 491-504.
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    Publikationsdatum: 2020-07-17
    Beschreibung: Whether the study of external morphology can increase our knowledge of shallow-water octopuses and their biology is tested by multivariate morphometric analyses. The extent of morphological variation among 20 species from the Atlantic and eastern tropical Pacific Oceans is explored, and four hypotheses are addressed: (1) that octopuses show secondary sexual dimorphism; (2) that remote, ostensibly conspecific populations are morphologically distinct; (3) that morphometric characters contribute to resource partitioning among sympatric species; and (4) that morphology is predictably associated with habitat. Results of principal components analysis show most species to be very similar in shape. Arm length contributes most shape variation; other characters contribute little. Principal components and size-free discriminant analyses refute each of the hypotheses considered. The morphological similarity of isolated Atlantic populations may be a symplesiomorphy, but information on the planktonic phase of the octopus lire cycle supports the possibility of dispersal across the Atlantic Ocean. Size, not directly treated here, may significantly affect some aspects of octopus biology. Increased female size may evolve due to selection for increased fecundity and intraspecific niche partitioning. Size may also indicate interaction within and among species. Characters of shape, deemed essential to species descriptions, do not appear to be able to identify most specimens, nor to increase our understanding of octopus biology.
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  • 46
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    The Use of Bacteriological Variables for the Characterization of Different Water Bodies (1994)
    Wiley
    In:  Internationale Revue der gesamten Hydrobiologie und Hydrographie, 79 (4). pp. 605-619.
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    Publikationsdatum: 2018-06-19
    Beschreibung: Studies on the Mediterranean Undercurrent in the Gulf of Cádiz showed that bacterial abundance and biomass as well as heterotrophic activity were higher in the water of Mediterranean origin in 500–800 m depth than in the adjacent Atlantic water. Upwelling processes off Mauretania and Portugal were accompanied by high bacterial numbers (bacterial plate counts) in the mixed surface layer. Changes in the qualitative composition of the bacterial flora in the waters off West Africa and in the Arabian Gulf were explained by the introduction of dust from desert regions into the sea by aeolian transport. In the Western Baltic migration of fish was detected by the presence of special bacteria, which normally live on or in these animals. Regions with complex hydrographic structures such as the Western and Central Baltic Sea revealed interesting relationships between bacteriological abundance and activity on the one hand and characteristic physical and chemical properties, such as origin, salinity and O2/H2S‐content, on the other. The importance of bacteriological variables for the characterization of different water bodies is discussed.
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  • 47
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    Speciation by Reinforcement of Premating Isolation (1994)
    Wiley
    In:  Evolution, 48 (5). p. 1451.
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    Publikationsdatum: 2015-11-23
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  • 48
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    North Atlantic volcanic margins: Dimensions and production rates (1994)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 99 (2). pp. 2955-2968.
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    Publikationsdatum: 2020-06-02
    Beschreibung: Early Tertiary lithospheric breakup between Eurasia and Greenland was accompanied by a transient (∼3 m.y.) igneous event emplacing both the onshore flood basalts of the North Atlantic Volcanic Province (NAVP) and huge extrusive complexes along the continent‐ocean transition on the rifted continental margins. Seismic data show that volcanic margins extend 〉2600 km along the early Eocene plate boundary, in places underlain by high‐velocity (7.2–7.7 km/s) lower crustal bodies. Quantitative calculations of NAVP dimensions, considered minimum estimates, reveal an areal extent of 1.3×106 km2 and a volume of flood basalts of 1.8×106 km3, yielding a mean eruption rate of 0.6 km3/yr or 2.4 km3/yr if two‐thirds of the basalts were emplaced within 0.5 m.y. The total crustal volume is 6.6×106 km3, resulting in a mean crustal accretion rate of 2.2 km3/yr. Thus NAVP ranks among the world's larger igneous provinces if the volcanic margins are considered. The velocity structure of the expanded crust seaward of the continent‐ocean boundary differs from standard oceanic and continental crustal models. Based on seismic velocities this “volcanic margin” crust can be divided into three units of which the upper unit corresponds to basaltic extrusives. The regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust, including the high‐velocity lower crust which extends some distance landward of the continent‐ocean boundary, was emplaced during and subsequent to breakup. The volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling, probably reflecting the interaction of a mantle plume and a lithosphere already extending.
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  • 49
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    Population dynamics of Black-browed and Grey-headed Albatrosses Diomedea melanophris and D. chrysostoma at Bird Island, South Georgia (1994)
    Wiley
    In:  Ibis, 136 (1). pp. 50-71.
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    Publikationsdatum: 2021-04-26
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  • 50
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    Effects of a floating fish farm in Kiel Fjord on the sediment (1994)
    Wiley
    In:  Journal of Applied Ichthyology, 10 (4). pp. 353-361.
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    Publikationsdatum: 2018-08-17
    Beschreibung: The effects of a floating fish farm in Kiel Fjord, Western Baltic, have been studied in the summer 1991 by underwater video, sediment and benthos samples. Significant alterations of the benthos and sediment geochemistry as compared to control stations were documented. The sediment under the farm is anoxic, organically enriched (1.5 to 3.5 fold), covered by sulfur bacteria, and almost free of benthic macro fauna. Rates of decay of organic carbon and oxygen uptake (derived from porewater profiles) are high and account for 100–150 mmol m‐2 d‐1 in summer.
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  • 51
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    Parasiten haben's schwer (1994)
    Wiley
    In:  Biologie in unserer Zeit, 24 (2). p. 82.
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    Publikationsdatum: 2018-08-13
    Beschreibung: Nicht leicht haben es die Vertreter einer wenig beschriebenen Terordnung, nach denen wir diesmal fragen. Birgt doch ihr Parasitendasein mit mehrfachem Wirtswechsel in den Weiten der Ozeane nicht wenige Gefahren.
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  • 52
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    Terminal spawning in the deepwater squid Moroteuthis ingens (Cephalopoda: Onychoteuthidae) (1994)
    Wiley-Blackwell
    In:  Journal of Zoology , 234 . pp. 189-201.
    Details
    Publikationsdatum: 2020-11-09
    Beschreibung: Maturation in the onychoteuthid squid Moroteuthis ingens was found to be irreversible, with death following shortly after sexual maturation and spawning. Both males and females were found with spent gonads. The ovary reaches very large sizes in mature females and probably prevends feeding by constricting the caecum. There was also a marked difference in the tissue with an inelastic, gelantinous appearence. Histological examination of the mantle wall revealed that the tissue breakdown was due to a drastic histolysis of muscle tissue and, to a lesser extent, collagen fibres. Mature males also showed some tissue breakdown and loss of muscle fibres but this was not as dramatic as in the females. These features are considered in relation to processes contributing to terminal maturation in M. ingens.
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  • 53
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    The influence of room temperature deformation on porosity and permeability in calcite aggregates (1994)
    AGU (American Geophysical Union) | Wiley
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    Publikationsdatum: 2022-02-15
    Beschreibung: Changes in permeability and porosity during shortening deformation of Carrara marble and hot-pressed calcite aggregates were measured under high pressure at room temperature using argon as pore fluid. At effective pressures of 30 and 50 MPa, the permeability of Carrara marble increased by up to 2 orders of magnitude with less than 2% strain during which the connected porosity increased by only 0.005. The permeability increased more slowly with further strain up to 18%, during which the connected porosity increased by a further 0.05 to 0.06. At effective pressures of 100 MPa to 200 MPa, these effects were much less marked. In hot-pressed calcite aggregates, deformed at an effective pressure of 50 MPa, the permeability increased by about 2 orders of magnitude after about 12% strain and an increase in connected porosity of about 0.03. Microstructural studies indicate that, in the coarse-grained Carrara marble specimens, both transgranular and grain boundary cracks are present after room temperature deformation. For a given strain, the average length and the linear density of transgranular cracks decrease with increasing effective pressure. In fine-grained, hot-pressed calcite aggregates, dilatancy is mainly due to opening of grain boundary cracks. The very marked increase in permeability with small strain at low effective pressure can be correlated with the proliferation of connected microcracks of relatively large apertures, deduced on the basis of theoretical models.
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  • 54
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    Ecotoxicity testing of heavy metals using methods of sediment microbiology (1993)
    Wiley
    In:  Environmental Toxicology & Water Quality, 8 (3). pp. 299-311.
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    Publikationsdatum: 2018-03-22
    Beschreibung: Current measures of microbe‐mediated biogeochemical processes in sediments were examined for their potential use as indicators of heavy metal ecotoxicity in both river sediments and bacterial cultures. Assays were carried out with HgCl2, CuSO4, and 3CdSO4 · 8H2O added to sediment samples and bacterial cell suspensions at concentrations ranging from 0.1 to 10 mM and 0.1 μM to 1 mM, respectively. Chemoautotrophic CO2 fixation by Elbe River sediment microbiota was most sensitive to Hg2+ and Cd2+, but not to Cu2+. Among the estimates of heterotrophic productivity, incorporation of leucine into cellular protein showed clearer dose responses than incorporation of thymidine into bacterial DNA. Thymidine incorporation was highly resistant to and even stimulated by metal ions, particularly in starved and anaerobic cultures of a test strain of Vibrio anguillarum. Similar metal ion induced “overshoot” responses beyond the levels of untreated controls were noted for mineralization of 14C‐glucose by V. anguillarum and, in the case of Cd2+, also in sediment. As a less complex measure of microbial respiratory activity, succinate dehydrogenase (SDH) showed normal dose responses without stimulatory effects, as long as bacterial cell homogenates were assayed. Despite this result, it is concluded that levels of SDH in natural sediment microbiota are inevitably affected by metal‐induced processes of selection and enzyme synthesis, and would thus fail to provide an appropriate measure of metal ecotoxicity. The final conclusion is that current parameters of microbial production and activity often reveal dose responses that do not fulfill basic requirements of ecotoxicity testing in metal‐polluted sediments.
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  • 55
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    The δ13C in benthic foraminiferal tests of Fontbotia wuellerstorfi (Schwager) Relative to the δ13C of dissolved inorganic carbon in Southern Ocean Deep Water: Implications for glacial ocean circulation models (1993)
    Wiley
    In:  Paleoceanography, 8 (5). pp. 587-610.
    Details
    Publikationsdatum: 2015-10-05
    Beschreibung: On a transect between 20° and 70°S in the eastern Atlantic Ocean and Weddell Sea, water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon (δ13CΣCO2). These measurements were compared to δ13C values determined on live specimens of the benthic foraminifer Fontbotia wuellerstorfi and closely related genera from the same stations. In addition, at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured. General deepwater and bottom-water mass circulation patterns as inferred from the δ13CΣCO2 are in close agreement with those known from other nonconservative tracers. Very low δ13C values of upper Circumpolar Deep Water (〈0.3‰ Pee Dee belemnite (PDB)) in the Polar Front region and the eastern limb of the Weddell gyre coincide with nutrient maxima. However, a significant decoupling of the dissolved phosphate signal from the δ13CΣCO2 signal is indicated in the abyssal Weddell Sea. We attribute this to temperature-dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom-water formation. Multiple corer water from the sediment/water interface is slightly δ13C depleted relative to deepwater and bottom-water δ13ΣCO2. The surface sediment organic carbon δ13C is 3 to 4‰ lower south of the Polar Front than north of it, and the δ13Corg in freshly accumulated phytodetritus is 3 to 4‰ lower than surface sediment organic carbon δ13C. Comparison of live F. wuellerstorfi δ13C and related genera with bottom-water δ13CΣCO2 exhibits at most stations between the Subtropical Front (≈41°S) and the southern boundary of the Antarctic Circumpolar Current (≈55°S) a significant lowering of foraminiferal δ13C values. Compilation of a mean last glacial/interglacial δ13C amplitude (Δδ13C) from six published southern ocean cores results in a shift of −0.99± 0.13‰ PDB; this shift is greater than that in all other regions. However, all of these cores are from positions close to Recent oceanic fronts. Thus, for these peripheral areas of the southern ocean, we suggest about half of the glacial/interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production.
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  • 56
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    Diatom extracellular polymeric stubstances: function, fine structure, chemistry, and physiology (1993)
    Wiley
    In:  Journal of Phycology, 29 (5). pp. 537-566.
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    Publikationsdatum: 2020-07-20
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  • 57
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    Growth of the Mediterranean GorgonianLophogorgia ceratophyta(L., 1758) (1993)
    Wiley-Blackwell
    In:  Marine Ecology, 14 (4). pp. 329-340.
    Details
    Publikationsdatum: 2016-02-04
    Beschreibung: Growth of the shallow-water gorgonian Lophogorgia ceratophyta was investigated in an infralittoral station located in La Spezia Gulf, Ligurian Sea. Mean annual height growth rate was estimated to be 2.57 cm · a-1. The fractal dimension of the colonies was found to gradually evolve in complexity, exhibiting a simpler branching pattern in younger specimens. The maintenance of a low, invariable ramification complexity as an optimal choice in managing relationships between water and the colony's living tissues is also discussed.
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  • 58
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    Induction of specific proteins in eukaryotic algae grown under iron, phosphorus and nitrogen deficient conditions (1993)
    Wiley
    In:  Journal of Phycology, 29 . pp. 767-777.
    Details
    Publikationsdatum: 2018-04-26
    Beschreibung: What limits phytoplankton growth in nature? The answer is elusive because of methodological problems associated with bottle incubations and nutrient addition experiments. We are investigating the possibility that antibodies to proteins repressed by a specific nutrient can be used as probes to indicate which nutrient limits photosynthetic carbon fixation in the ocean. The diatom Phaeodactylum tricornutum Bohlin and the chlorophyte Dunaliella tertiolecta Butcher were grown in batch cultures in artificial seawater and f/2 nutrient lacking either phosphorus, iron, or nitrogen. Chlorosis was induced by nutrient limitation in both species with the exception of phosphorus‐limited D. tertiolecta. The synthesis and appearance of specific proteins were followed by labeling with 14C‐bicarbonate. Nutrient limitation in general leads to a decrease in the quantum efficiency of photosystem II, suggesting that deficiency of any nutrient affects the photosynthetic apparatus to some degree: however, the effect of nitrogen and iron limitation on quantum efficiency is more severe than that of phosphorus. A crude fractionation of the soluble and membrane proteins demonstrated that the large proteins induced under limitation by phosphorus and iron were associated with the membranes. However, small iron‐repressible proteins were located in the soluble fraction. Isolation with anion‐exchange chromatography and N‐terminal sequencing of iron‐repressible, 23‐kDa Proteins from D. tertiolecta, P. tricornutum, and Chaetoceros gracilis revealed that these small soluble proteins have strong homology with the N‐terminal sequence of flavodoxins from Azotobacter and Clostridium. The identity of the flavodoxin from D. tertiolecta was confirmed by immunodetection using antiflavodoxin raised against Chlorella. Flavodoxin was detected only under iron deprivation and was absent from nitrogen‐and phosphorus‐limited algae. Flavodoxin is a prime candidate for a molecular probe of iron limitation in the ocean. The requirements to confirm its utility in nature are discussed.
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  • 59
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    Das Kohlenstoffrätsel (1993)
    Wiley
    In:  Biologie in unserer Zeit, 23 (2). pp. 97-101.
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    Publikationsdatum: 2016-06-17
    Beschreibung: Etwa ein Drittel des von Menschen freigesetzten Treibhausgases Kohlendioxid (CO2) reichert sich in der Atmosphäre an und verstärkt dort den Treibhauseffekt. Zwei Drittel dieses Eintrags werden der Atmosphäre wieder entzogen und an anderer Stelle deponiert. Doch nur für etwa die Hälfte des wieder gebundenen Kohlendioxids kennen wir bisher die Senken. Wo bleibt der Rest? Um Aussagen über den Verbleib weiterer CO2-Emissionen und damit über die zukünftige Entwicklung des Treibhauseffektes machen zu können, bedarf es der Lösung des Kohlenstoffrätsels.
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  • 60
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    Benthic standing stock and metabolic activity in the bathyal Red Sea from 17°N to 27°N (1993)
    Wiley-Blackwell
    In:  Marine Ecology, 14 . pp. 67-79.
    Details
    Publikationsdatum: 2017-10-05
    Beschreibung: To study the impact of the gradient of primary production between the southern, central, and northern Red Sea, benthic metabolism and standing stocks were investigated in the axial trough between 17°N and 27°N. Data on sediment chloroplastic pigments, macrofauna and meiofauna abundance, particulate adenylate, protein and carbohydrate biomass, as well as electron transport activity of the sediment community give evidence for an enhanced benthic standing stock and activity in the southern Red Sea south of 18°N; this is related to the increased primary productivity in the area south 16°N. Despite a large primary production only small benthic standing stocks were found in all areas investigated; they are much smaller than in other parts of the world's deep oceans with comparable primary production. The low benthic biomass is caused by two factors: a large proportion of particulate organic carbon is remineralized in the water column, while only a relatively small amount sediments to the sea floor; nearly all sedimented particulate organic matter is respired by the benthic community of the deep Red Sea and only a minute proportion is used for the production of benthic biomass.
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  • 61
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    Response of the photosynthetic apparatus of Phaeodactylum tricornutum (Bacillariophyceae) to nitrate, phosphate or iron starvation. (1993)
    Wiley
    In:  Journal of Phycology, 29 . pp. 755-766.
    Details
    Publikationsdatum: 2018-04-26
    Beschreibung: The effects of nitrate, phosphate, and iron starvation and resupply on photosynthetic pigments, selected photosynthetic proteins, and photosystem II (PSII) photochemistry were examined in the diatom Phaeodactylum tricornutum Bohlin (CCMP 1327). Although cell chlorophyll a (chl a) content decreased in nutrient‐starved cells, the ratios of light‐harvesting accessory pigments (chl c and fucoxanthin) to chl a were unaffected by nutrient starvation. The chl a‐specific light absorpition coefficient (a*) and the functional absorption cross‐section of PSII (σ) increased during nutrient starvation, consistent with reduction of intracellular self‐shading (i.e. a reduction of the “package effect”) as cells became chlorotic. The light‐harvesting complex proteins remained a constant proportion of total cell protein during nutrient starvation, indicating that chlorosis mirrored a general reduction in cell protein content. The ratio of the xanthophylls cycle pigments diatoxanthin and diadinoxanthin to chl a increased during nutrient starvation. These pigments are thought to play a photo‐protective role by increasing dissipation of excitation energy in the pigment bed upstream from the reaction centers. Despite the increase in diatoxanthin and diadinoxanthin, the efficiency of PSII photochemistry, as measured by the ration of variable to maximum fluorescence (Fv/Fm) of dark‐adapted cells, declined markedly under nitrate and iron starvation and moderately under phosphate starvation. Parallel to changes in Fv/Fm were decreases in abundance of the reaction center protein D1 consistent with damage of PSII reaction centers in nutrient‐starved cells. The relative abundance of the carboxylating enzyme, ribulose bisphosphate carboxylase/oxygenase (RUBISCO), decreased in response to nitrate and iron starvation but not phosphate starvation. Most marked was the decline in the abundance of the small subunit of RUBISCO in nitrate‐starved cells. The changes in pigment content and fluorescence characteristics were typically reversed within 24 h of resupply of the limiting nutrient.
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  • 62
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    Diatom demography in winter – simulated by the Lagrangian Ensemble method (1993)
    Wiley
    In:  Fisheries Oceanography, 2 (3-4). pp. 202-222.
    Details
    Publikationsdatum: 2017-01-06
    Beschreibung: According to Sverdrup's (1953) model of the spring bloom, phytoplankton biomass decreases in winter when the mixed layer depth exceeds the critical depth. We have used a one-dimensional mathematical model integrated by the Lagrangian Ensemble method to simulate a population of diatoms during the winter between two growing seasons off the Azores. The model allows us to diagnose the demographic changes in the simulated diatom population from a variety of perspectives. The total population falls to a minimum of 70 million diatoms m-2 at the end of February. The vertical distribution of the population dynamics is first analysed in terms of daily Eulerian averages over 1 m depth intervals. Growth starts in February when the diurnal thermocline becomes shallower than 50 m, but while the mixed layer is still 200 m deep. The natural mortality has a minimum in winter because it is reduced (in the model) with temperature and population density. Eulerian analysis suggests that in winter, diatoms have a life expectancy of more than 3 months, so a significant number will survive the months of December, January and February when there is very little growth. Losses to grazing are negligible in winter. Lagrangian analysis shows how an individual diatom responds to its changing ambient environment caused by variation in depth (due to turbulent mixing) and the diurnal and seasonal changes in the photosynthetically active radiance. The different trajectories followed by the thousands of plankton particles simulated by the model produce diversity in growth rate ranging over several orders of magnitude, so care has to be taken in statistical analysis. The paper ends with a re-assessment of the value of the critical depth and compensation depth as predictors for onset of the spring bloom. The compensation depth was computed by Eulerian averaging over 1 m depth inter-vals each day. For 1 month after the vernal equinox the compensation depth follows the ascent of the mixed layer as it rises from a depth of 100 m to 40 m. Lagrangian analysis reveals that this is due to the photo-adaptation better matching the ambient irradiance experienced by diatoms in the mixed layer compared with those at the same depth in the seasonal thermo-cline. By mid-April the spring bloom has already ad-vanced so far that self shading influences the compensation depth, which then rises into the mixed layer. We conclude that Sverdrup's criterion is not useful for predicting changes in the diatom population simulated by our model.
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  • 63
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    Analysis of the demersal community of fish and cephalopods on the Agulhas Bank, South Africa (1993)
    Wiley
    In:  Journal of Fish Biology, 43 (Suppl. A). pp. 169-191.
    Details
    Publikationsdatum: 2021-05-05
    Beschreibung: The demersal fish and cephalopod communities of the continental shelf and upper slope from 17 to 395m deep were studied during five annual cruises between Cape Agulhas and Port Alfred, South Africa. The cruises showed a consistent pattern of an inshore community (〈100m), a shelf community (c. 90–190m) and a shelf‐edge/upper slope fauna (〉200m). These groups were identified by dendrograms and multidimensional scaling cluster analysis, which supported on‐board observations of catch variation with depth. Although the boundaries are not clearly defined, examination of physical features at the clustered stations suggests that depth, temperature and, to a lesser extent, oxygen concentration are important in the grouping. Occasional, apparently anomalous associations of inshore stations suggested that water temperature and oxygen may over‐ride the normal depth distributions of the species groups. This intimates that patterns offish and cephalopod distribution may be dynamic and in part related to the physical parameters of the water body.
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  • 64
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    Population Densities of Juvenile Trout (Salmo trutta) in Five Upland Streams and Their Effects Upon Growth, Survival and Dispersal (1993)
    Wiley
    In:  Journal of Applied Ecology, 30 (4). pp. 759-771.
    Details
    Publikationsdatum: 2020-04-22
    Beschreibung: 1. Survival, growth and downstream dispersal of trout (especially 0 group) and the relationships of these variables to initial stocking density were studied in north Pennine streams. 2. Two methods were used. First, electrofishing censuses were made in a marked reach of each of four streams over a period of about 20 years. Second, downstream moving trout were trapped in two streams over a 10-year period. Each stream upstream of the trap was experimentally stocked with `swim-up' trout fry, using a different population density each year. 3. Before 1970 the four census reaches showed very large year-upon-year variations in August trout parr densities, with local failures of recruitment in some years. Population densities after completion of Cow Green Reservoir (1970) were generally higher but still showed wide fluctuations. 4. Survival (including the effects of losses by dispersal) from swim-up to early August, for starting population densities of 0-10 fry m-2, was about 10% regardless of initial density. Estimates of survival from August to early October were 30-50% for the census reaches and 55-65% for the areas upstream of the traps. However, for August 0 group densities of 0-0.9 m-2, estimated instantaneous loss rate from August of the first year of life up to age 40-65 months showed a positive curvilinear relationship to population density in the first year of life. Loss rate was, therefore, density-dependent during this period. 5. Estimated instantaneous growth rate day-1 of 0 group fish from swim-up to August and from swim-up to October was inversely related to the natural logarithm of August population density and this was most apparent for August densities of 〈0.15 fish m-2. 6. Although survival from swim-up to August was proportional (about 10%, at starting densities of 10 m-2 or less), the percentages of the total loss attributable to mortality and to downstream dispersal varied considerably with starting density. At starting densities around 4-5 fish m-2 dispersal was negligible. As initial density rose above 4-5 fish m-2 and towards 10 fish m-2 the percentage of loss attributable to dispersal rose towards 30%. As initial densities decreased from 4 to 1.4 fish m-2, the percentage rose to around 20%. Below a starting density of 1.4 fish m-2 the percentage decreased.
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  • 65
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    National Systematics Laboratory: The NSL works toward healthy marine biodiversity (1993)
    Wiley
    In:  Fisheries, 19 (11). p. 26.
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    Publikationsdatum: 2020-11-04
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  • 66
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    A reexamination of the flexural deformation beneath the Hawaiian Islands (1993)
    Wiley | AGU (American Geophysical Union)
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    Publikationsdatum: 2024-01-08
    Beschreibung: Seismically derived depth estimates to the top of the oceanic crust beneath the Hawaiian Islands indicate that the curvature of the deflected lithosphère is much larger than commonly believed. The conservative and model-independent curvature estimates exceed 10−7 m−1 and are comparable in magnitude to curvatures at trenches and outer rise systems. The depth estimates are used to constrain both two-dimensional (2-D) and three-dimensional (3-D) flexural models. The curvature constraints require a 2-D variable elastic thickness that decreases from 35 km in areas away from the volcanic load to 25 km directly beneath the load. In an attempt to understand the nature of the yielding beneath the Hawaiian Islands we introduce two new 3-D models. The first model combines a realistic yield strength based rheology with a new technique for 3-D flexure calculations in which the elastic plate thickness is curvature-dependent. The new variable rigidity model predicts an undeformed (mechanical) plate thickness of 44 km, decreasing to 33 km beneath the big island of Hawaii. The best-fitting mechanical thickness corresponds approximately to the depth to the 600 °C isotherm in 90-m.y.-old lithosphere. The second model uses a broken plate, but here the crack is oriented along the weak Molokai fracture zone rather than along the island chain trend. This unconventional flexure model can explain the observed asymmetry in the depth data across the fracture zone without requiring the excessively large elastic thickness of more conventional broken plate models. Both the proposed models imply that modeling with constant thickness plates may underestimate the true mechanical plate thickness by being unduly influenced by the weak zone beneath the seamounts.
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  • 67
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    Culture studies on the life history of Chordaria Linearis (Phaeophyceae) from Tierra del Fuego, South America (1992)
    Wiley
    In:  Journal of Phycology, 28 (5). pp. 678-683.
    Details
    Publikationsdatum: 2018-03-09
    Beschreibung: Studies of laboratory cultures of Chordaria linearis (Hooker et Harvey) Cotton from southernmost South America revealed that this species has an obligate sexual life history in which a macroscopic sporophyte alternates with a monoecious microscopic gametophyte. Sexual reproduction is isogamous and under photoperiodic control. Gametes are produced only in short days, whereas in long days, asexual zoospores are formed that recycle the gametophyte generation. Unfused gametes develop into gametophytes, and sporophytes originate only from zygotes. Unlike other sexual members of the Chordariales, gametes of C. linearis have a reduced stigma and do not show phototaxis. They are released at the beginning of the night, not in the morning. In nature, C. linearis seems to be regularly infected by a dictyosiphonalean epiphyte resembling the rare arctic species Trachynema groenlandicum (Lund) Pedersen. The epiphyte is responsible for previous contradictory results obtained in laboratory cultures of C. linearis. This is the first record of Trachynema in the southern hemisphere.
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  • 68
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    Dyar's rule and multivariate allometric growth in nine species of waterstriders (Heteroptera: Gerridae) (1992)
    Wiley
    In:  Journal of Zoology, 227 (3). pp. 453-464.
    Details
    Publikationsdatum: 2018-03-16
    Beschreibung: The constancy of postmoult/premoult ratios of measures of linear size during ontogeny in insect and other arthropods is widely known as Dyar's rule. We tested this rule in nine species of the waterstrider genera Gerris and Aquarius (Heteroptera: Gerridae), using two size variables: head width and a multivariate measure derived from the pattern of multivariate allometry common to the species considered. Allometric patterns were similar in two independent datasets of laboratory-reared and field-caught specimens. Although our data strictly followed Dyar's rule injust a few instances, all growth ratios varied within a limited range only. Growth ratios for head width differed more between moults than those for multivariate size. The relationship between growth ratios for the two size measures conformed to the predictions based on allometry. We discuss hypotheses of the possible adaptive significance of growth ratios, such as their relation to mobility and systematic differences between hemimetabolous and holometabolous insects, and emphasize the importance of allometry. Since Dyar's rule is consistent with available evidence of physiological mechanisms underlying growth and moulting control of insects and crustaceans, it can be used as a general frame of reference to test alternative growth models.
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  • 69
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    The cause of the Late Cenozoic Northern Hemisphere glaciations: a climate change enigma (1992)
    Wiley
    In:  Terra Nova, 4 (3). pp. 305-311.
    Details
    Publikationsdatum: 2018-02-06
    Beschreibung: The ultimate cause of the onset of glaciations remains elusive, but in the case of northem hemisphere glaciation it is probable that several factors acted in combination. General global cooling resulted from reduction of atmospheric C02 by weathering of silicate rocks exposed by erosion of late Cenozoic uplifts. Uplifts in south Asia, southwestern North America and Scandinavia occurred at distances appropriate for the generation of quasi-permanent Rossby waves in the atmosphere. The resulting winds, given suitable moisture sources, were favourable for causing large-scale precipitation at mid-latitudes on the northern continents. Moisture sources were provided by the closure of the Central American isthmus. Gulf Stream flow increased, carrying warm subtropical waters to high latitudes. The Denmark Strait deepened permitting greater outflow of deep water from the Norwegian-Greenland Sea. The relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies.
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  • 70
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    Diving Behavior and Energetics During Foraging Cycles in King Penguins (1992)
    Wiley
    In:  Ecological Monographs, 62 (1). pp. 143-163.
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    Publikationsdatum: 2017-04-19
    Beschreibung: King Penguins are the second largest of all diving birds and share with their congener, Emperor Penguins, breeding habits strikingly different from other penguins. Our purpose was to determine the feeding behavior, energetics of foraging and the prey species, and compare these to other sympatric species of subantarctic divers. We determined: (1) general features of foraging behavior using time—depth recorders, velocity meters, and radio transmitters, (2) energetics by doubly labeled water, (3) food habits and energy content from stomach lavage samples, and (4) resting and swimming metabolic rate by oxygen consumption measurements. The average foraging cycle was ≈6 d, during which the mass gain of 30 birds was ≈2 kg. When at sea, the birds exhibit a marked pattern of shallow dives during the night, whereas deep dives of 〉100 m only occurred during the day. Maximum depth measured from 34 birds and 18 537 dives was 304 m, and maximum dive duration from 23 birds and 11 874 dives was 7.7 min. The frequency distribution of dive depth was bimodal, with few dives between 40 and 100 m. Overall, swim velocities when a bird was at sea averaged 2.1 m/s (N = 5), while descent and ascent rates of change in depth averaged 0.6 m/s for dives 〈60 m (N = 74) and 1.4 m/s for dives 〉150 m (N = 90). Night feeding dives occurred at a rate of ≈20 dives/h, and deep dives occurred at a rate of ≈5 dives/h. The energy consumption rate while resting ashore was 3.3 W/kg (N = 3) or 1.6 times the predicted standard metabolic rate (SMR). The average energy consumption rate while away from the colony was 10 W/kg (N = 8) or 4.6 x SMR, compared to 4.3 x SMR estimated from a time—energy budget. The latter value is based on an average metabolic rate of 4.2 W/kg for three birds while resting in 5°C water and 9.6 W/kg while swimming at 2 m/s, which was extrapolated from the average of three birds swimming at 1 m/s. The average energy intake based on 9 stomach content samples was nearly 24.6 kJ/g dry mass. The main prey by number are myctophid fish of the species Krefftichthys anderssoni and Electrona carlsbergi. It was concluded that: (1) feeding begins ≈28 km from the colony, (2) prey is pursued night and day through its vertical movements, (3) vertical distribution of the prey is reflected closely by diving habits of the birds, (4) deep—diving, for unknown reasons, is an important component of foraging success, (5) diving capacities of King Penguins are remarkable compared to other birds and many pinnipeds, and (6) calculated foraging energetics can be closely estimated from time—energy budgets.
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  • 71
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    Factors influencing routine oxygen consumption in turbot, Scophthalmus maximus (1992)
    Wiley
    In:  Journal of Applied Ichthyology, 8 (1-4). pp. 62-71.
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    Publikationsdatum: 2018-03-09
    Beschreibung: Routine oxygen consumption of turbot, Scophthalmus maximus, was determined in relation to temperature, salinity, body wet weight, and time of day. The highest routine oxygen consumption rates measured roughly followed a arabolic curve over the temperature range tested (8 to 24°C). The lowest rates showed a more linear refationship over the same temperature range. It is argued that lowest rates correspond to the standard oxygen consumption. Between 16 and 19°C, routine oxygen consumption reached a maximum. It is suggested that these temperatures correspond to the preferred ternerature of the species and are within the range of optimum temperature for growth of specimens weigkng about 100 g. Salinity effect on oxygen consumption rates was studied in five groups acclimated over 4 weeks to 8, 15, 22, 29, and 35%. salinity. Routine oxygen consumption rates were lowest at 8% salinity with no significant differences in higher acclimation salinities. Routine respiration of turbots showed conspicuous daily fluctuations. During spring, summer, and autumn, oxygen Consumption was higher during morning hours and at night. In winter, higher rates were measured only once (during morning and early afternoon). The relationship between routine oxygen consumption and body weight of turbots followed an exponential function with a slope of 0.7, which was lower compared to the slope of 0.8 usually given for roundfish-species.
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  • 72
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    Distinction of South American Haplogloia Andersonii and Chordaria Linearis (Phaeophyceae) based on differences in sexual reproduction, morphology, ecophysiology, and distribution (1992)
    Wiley
    In:  Journal of Phycology, 28 (5). pp. 684-693.
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    Publikationsdatum: 2018-03-13
    Beschreibung: Haplogloia andersonii (Farlow) Levring is an anti-tropical species that occurs on cold and warm-temperate Pacific coasts of both Americas. In its habit it resembles the subantarctic species Chordaria linearis (Hooker et Harvey) Cotton. Culture studies show that the species differ in morphology and ecophysiology of their microscopic gametophytes and in gamete behavior. Details of sporophyte anatomy are presented that also allow the distinction of field plants. In South America, H. andersonii occurs only on the Pacific coast, from central Perú (14°S) to southern Chile (50°S). Chordaria linearis occurs on the Pacific coast from Chiloé Island (43°S) to Cape Horn (56°S). In the shared area the species may co-occur. On the Atlantic coast, C. linearis was newly collected at a locality in northern Patagonia (41°S). In addition, C. linearis occurs in Antarctica. Haplogloia moniliformis Richer, recently described from Macquarie Island, is probably synonymous with Chordaria linearis.
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  • 73
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    Temperature responses of disjunct temperate brown algae indicate long-distance dispersal of microthalli across the tropics (1992)
    Wiley
    In:  Journal of Phycology, 28 (4). pp. 428-438.
    Details
    Publikationsdatum: 2018-03-13
    Beschreibung: We examined the temperature tolerance of microscopic phases from geographically disjunct isolates of eight species or closely related, putatively conspecific taxa of temperate brown algae with disjunct distributions. Maximum within-taxon differences were small and ranged from 1.6° to 4.3° C. Desmarestia aculeata and Sphaerotrichia divaricata, both with northern hemisphere amphioceanic distributions, showed little or no significant intraspecific variation between the mean upper survival limits (USL) of Atlantic and Pacific strains (δUSL ≤ 1.4°C), which would agree with a relatively recent separation of the respective populations. Among the plants with bipolar distributions, there was likewise very little difference (δUSL 0–1.1°C) between northern and southern hemisphere strains in Striaria attenuata and in the species pair Desmarestia viridis/D. willii. In Desmarestia ligulata, and in the species pairs Desmarestia firma/D. munda, Dictyosiphon foeniculaceus/D. hirsutus, and Scytothamnus australis/Scytothamnus sp., significant differences occurred, which indicate longer divergence times. δUSL in these cases ranged from 1.7° to 2.7°C, without overlap between strains from the northern and southern hemispheres. All species that passed the equator during cooler epochs had a USL of 26–27°C, at least in some geographical isolates. The NE Asian kelp Undaria pinnatifida, which passed the equator in recent times, had a USL of 29.6°C. We hypothesize that the mechanism of spreading in the amphipolar species studied was migration of vegetative microthalli. The more unlikely alternative hypothesis of continuous populations through the tropics during a cooler epoch would imply a drop in seawater temperatures to approximately 20° C in summer and 15° C in winter, which is not supported by paleoclimatic evidence.
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  • 74
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    Prey species and nutritive value of food fed during summer to King Penguin Aptenodytes patagonica chicks at Possession Island, Crozet Archipelago (1992)
    Wiley-Blackwell
    In:  Ibis, 134 (2). pp. 118-127.
    Details
    Publikationsdatum: 2020-07-29
    Beschreibung: The diet of King Penguins Aptenodytes patagonica at Possession Island was studied in February 1989 by analysis of 20 stomach contents collected from adult birds, just before they fed their single chicks. The mean mass of the samples was 1.84 kg, equivalent to 15% of the unladen adult body-mass. Fish accounted for 99.8% and squids for 0.2% by mass. The main prey were mesopelagic myctophid fish which live in dense shoals and perform a daily vertical migration. Subadults/adults of Electrona carlsbergi and juveniles and subadults/adults of Krefftichthys anderssoni represented 73.7 and 13.4% of the diet by mass, respectively. No difference was found in the diet of male and female King Penguins. Comparison of individual samples suggests that these birds catch a large quantity of fish from only a limited number of shoals. The mean caloric content of the food was 7 kJ/g wet mass. The total energy requirement of each chick during its initial period of growth was estimated to amount to 328,000 kJ, equivalent to 55 kg of food. The rate at which energy was delivered to the chick was calculated to be 50 W during this period.
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  • 75
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    A histological study of the accessory reproductive organs of femaleLoligo forbesi(Cephalopoda: Loliginidae) (1992)
    Wiley-Blackwell
    In:  Journal of Zoology, 226 (3). pp. 469-490.
    Details
    Publikationsdatum: 2020-07-17
    Beschreibung: In Loligo forbesi Steenstrup, the female reproductive system consists of the ovary and accessory reproductive organs which include the oviducal gland, the nidamental gland, the accessory nidamental gland and seminal receptacle. Histological studies were made on the accessory reproductive organs of female L. forbesi. The various changes observed during maturation are described and the functional significance discussed. The secretions produced by the oviducal gland and nidamental gland apparently form the egg coats. The seminal receptacle serves to store spermatozoa after mating. The function of the accessory nidamental gland is unknown.
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  • 76
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    The oxygen requirements of three fish species from the German Bight: cod Gadus morhua, plaice Pleuronectes platessa, and dab Limanda limanda (1992)
    Wiley
    In:  Journal of Applied Ichthyology, 8 (1-4). pp. 72-76.
    Details
    Publikationsdatum: 2018-03-15
    Beschreibung: The survival of cod Gadus morhua, plaice Pleuronectes platessa, and dab Limanda limanda was determined in relation to ambient oxygen saturation at 8° C and 35% m salinity. Mortalit rates were observed in fish exposed to constant oxygen levels for 24h. First mortality occurred around 60 % oxygen saturation in cod and around 30% oxygen saturation in dab and plaice. Below these thresholds mortality increased linearly with decreasing oxygen levels. If cod were infested with 1 or 2 individuals of Lernaeocera branchialis (Copepoda), their tolerance was significantly lower; under such circumstances the incipient lethal oxygen saturation was 66 %.
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  • 77
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    Deep-sea cephalopods of the north-western Mediterranean: indications of up-slope ontogenetic migration in two bathybenthic species (1992)
    Wiley-Blackwell
    In:  Journal of Zoology, 227 (2). pp. 267-276.
    Details
    Publikationsdatum: 2020-07-17
    Beschreibung: The cephalopod fauna collected during six surveys carried out in the bathyal basin of the north-western Mediterranean is discussed. Samples were taken at depths mainly between 1000 and 2000 m. Ten species were identified. Bathypolypus sponsalis and Neorossia caroli were the commonest species. Small individuals of both these species occurred at greater depths than did larger individuals, suggesting up-slope ontogenetic migration. The depth ranges recorded for all species collected are discussed and compared to the results of previous studies found in the literature.
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  • 78
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    The influence of salinity and temperature covariation on the photophysiological characteristics of Antarctic sea ice microalgae (1992)
    Wiley
    In:  Journal of Phycology, 28 (6). pp. 746-756.
    Details
    Publikationsdatum: 2017-11-29
    Beschreibung: The responses of sea ice microalgae to variation in ambient irradiance (0 to 150 μE · m−2· s−1), temperature (–6° to + 6° C), and salinity (0 to 100 ppt) were tested to determine whether these variables act independently or in concert to influence rates of microalgal photosynthesis. The photosynthetic efficiency and maximum photosynthetic rate for sea ice microalgae increased as a function of incubation temperature between -6° and + 6° C. Furthermore, photosynthetic efficiency, maximum photosynthetic rate, and quantum yield were greatest at salinities between SO and 50 ppt. In contrast, the mean specific absorption coefficients were lowest near seawater salinities, and the saturating irradiance, Is, appeared to be inversely proportional to salinity. Results also suggest that the effects of salinity on the growth of sea ice microalgae are independent of those elicited by temperature or light, and that the functional relationship between salinity and light or temperature is multiplicative. This information is essential to the proper formulation of algorithms used to describe algal growth in environments where light, temperature, and salinity are changing simultaneously, such as within sea ice or within the water column at the marginal ice edge zone.
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  • 79
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    Antimicrobial Procecces (1992)
    Wiley
    In:  Water environment research, 64 . pp. 391-398.
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    Publikationsdatum: 2020-04-28
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  • 80
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    Effects of variation in temperature. II. On the fatty acid composition of eight species of marine phytoplankton (1992)
    Wiley
    In:  Journal of Phycology, 28 (4). pp. 488-497.
    Details
    Publikationsdatum: 2020-07-20
    Beschreibung: Eight species of marine phytoplankton showed significant variation in the relative amount of some fatty acids (FAs) in response to variation in temperature. Large changes in relative amounts of certain FAs occurred as a result of a 15° C change in growth temperature. For example, 14:0 increased from ≃4% of total FAs at 10° C to 〉 20% at 25° C for Chaetoceros simplex and Isochrysis aff. galbana but decreased for Phaeodactylum tricornutum. The percentage of the polyunsaturated fatty acid (PUFA) 16:ω1 was consistently greater at 10° C than at 25° C, and the converse was usually true for 16: 4ω3. Calculated over all eight species, there was a modest but significant inverse relationship between the percentage of PUFAs and temperature. Only for Thalassiosira pseudonana was the percentage of either of the PUFAs and nutritionally essential fatty acids (EFAs) also an inverse function of temperature. For T. pseudonana, the percentage of the EFA 22:6ω3 decreased linearly with increasing temperature over the range from 10 to 25° C. For three species, the ratio of unsaturated/saturated FAs was correlated with growth rate when growth rate was controlled by variation in irradiance and temperature. Only for Thalassiosira pseudonana was the ratio of unsaturated/saturated FAs also an inverse function of temperature alone.
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  • 81
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    Use and misuse of the seafloor : report of the Dahlem Workshop on Use and Misuse of Seafloor, Berlin 1991, March 17 - 22 (1992)
    Wiley
    In:  , ed. by Hsü, K. J. and Thiede, J. Wiley, Chicester, XV, 440 S pp. ISBN 0-471-93191-8
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    Publikationsdatum: 2015-03-10
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  • 82
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    Structure of extracellular polysaccarides produced by a soil Cryptomonas Sp. (Cryptophyceae) (1992)
    Wiley
    In:  Journal of Phycology, 28 (1). pp. 61-63.
    Details
    Publikationsdatum: 2020-07-20
    Beschreibung: The Hindak strain of a Cryptomonas species (Cryptophyceae) produces extracellular polysaccharides. Because there is no information on the structure of these compounds in the Cryptophyceae we conducted structural studies. Gas–liquid chromatographic analyses showed that the polysaccharide is composed of fucose, rhamnose, xylose, mannose, glucose, galactose, galacturonic acid, glucuronic acid, and traces of 3-O-methyl galactose. The polysaccharide was separated into two subtractions by ion-exchange chromatography. Fraction A consisted mainly of 1,3-linked galactose units and 1,4-linked galacturonic acid. Unlike fraction B, fraction A did not have xylose, 3-O-methyl galactose, or glucuronic acid. Also, its degree of branching was low compared to that of fraction B. Only traces of sulfate were present infraction A, but fraction B was 10–15% sulfated. Protein was approximately 1% in both fractions. These polysaccharides appear to be a novel type of polymer in algae.
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  • 83
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    Heterochronic Developmental Plasticity in Larval Sea Urchins and Its Implications for Evolution of Nonfeeding Larvae (1992)
    Society for the Study of Evolution | Wiley
    In:  Evolution, 46 (4). p. 972.
    Details
    Publikationsdatum: 2020-07-31
    Beschreibung: Preexisting developmental plasticity in feeding larvae may contribute to the evolutionary transition from development with a feeding larva to nonfeeding larval development. Differences in timing of development of larval and juvenile structures (heterochronic shifts) and differences in the size of the larval body (shifts in allocation) were produced in sea urchin larvae exposed to different amounts of food in the laboratory and in the field. The changes in larval form in response to food appear to be adaptive, with increased allocation of growth to the larval apparatus for catching food when food is scarce and earlier allocation to juvenile structures when food is abundant. This phenotypic plasticity among full siblings is similar in direction to the heterochronic evolutionary changes in species that have greater nutrient reserves within the ova and do not depend on particulate planktonic food. This similarity suggests that developmental plasticity that is adaptive for feeding larvae also contributes to correlated and adaptive evolutionary changes in the transition to nonfeeding larval development. If endogenous food supplies have the same effect on morphogenesis as exogenous food supplies, then changes in genes that act during oogenesis to affect nutrient stores may be sufficient to produce correlated adaptive changes in larval development.
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  • 84
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    Movement, injuries and growth of members of a natural population of the Pacific pygmy octopus, Octopus digueti (1992)
    Wiley
    In:  Journal of Zoology, 228 (2). pp. 247-264.
    Details
    Publikationsdatum: 2021-05-11
    Beschreibung: Sampling inadequacies and an inability to distinguish age classes have limited our knowledge of octopus biology in nature. Using an artificial shelter sampling technique (Voight, 1988a), and defining mature males by the presence of enlarged suckers (Voight, In press), an intertidal population of Octopus digueti was monitored for one year. In total, 803 octopuses were narcotized; the mass, sex, arm injuries and reproductive condition of each octopus were recorded. Captures were more frequent in lower intertidal areas offering higher shelter availability and a more moderate environment. Capture rates, assumed to indicate octopus movement, correlated with sea temperature except during full moon periods when they were reduced. Over 26%, of the octopuses handled had damaged arms or arm tips, with dorsal arm pairs more often injured. The overall sex ratio was significantly male biased, probably due to maturity‐linked mobility differences between the sexes. Reproduction occurred throughout the year; reproductively competent adults, brooding females and juveniles were present every month. However, annual temperature oscillations synchronize spring hatching of eggs spawned from winter to early spring, creating a clear spring cohort. Growth and age at maturity of males in the spring and autumn cohorts were estimated. Variance was too high for these parameters to be estimated in the winter cohort. Growth rates of males over 12 weeks of age did not differ from those reported in laboratory rearing studies. Estimated average age at maturity ranged from 20 to 32 weeks, depending on temperature.
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  • 85
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    The breeding biology and population dynamics of King Penguins Aptenodytes patagonica on the Crozet Islands (1992)
    Wiley
    In:  Ibis, 134 (2). pp. 107-117.
    Details
    Publikationsdatum: 2021-04-26
    Beschreibung: Among King Penguins Aptenodytes patagonica at Possession Island, one of the Crozet Islands, the length of the moult period, pre‐laying period, incubating and brooding shifts were highly variable according to the year and to the stage of the breeding season. The moulting period was shorter in late breeders than in early breeders. Only half of the birds which successfully reared a chick bred the following cycle, but late in the season. Almost all these late breeders were unsuccessful. The reasons for the high variability in the breeding pattern observed in this species between years, as well as between colonies and between individuals are discussed. Breeding success was on average 30.6% and survival during the first year at sea could reach 50%. The survival of adult birds has increased during the past 10 years from 90.7% to 95.2% per annum. Despite an almost biennial breeding frequency and a very high rate of chick loss during the winter fast, the King Penguin population of Possession Island has doubled between 1966 and 1985 due to a high survival rate of adult and immature birds. The increase during the last decade in adult survival and in adult and chick condition suggests that the population increase could be the result of an improvement in food availability.
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  • 86
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    On the structure of the Ivrea‐Verbano Zone (northern Italy) and its implications for present‐day lower continental crust geometry (1992)
    Wiley
    In:  Terra Nova, 4 (1). pp. 34-40.
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    Publikationsdatum: 2020-11-02
    Beschreibung: The Ivrea‐Verbano Zone in northern Italy represents a section through the lower continental crust which has been tilted and emplaced into its present position during the Alpine orogeny. Recent and on‐going structurally‐oriented geological mapping in this region is providing new information about the geometry of the complex. The central part of the zone is dominated by a large basic complex (the ‘mafic formation') which is intrusive into the surrounding gneisses. The foliation within the envelope of gneisses is deflected around the intrusive complex as if by ballooning, but in the region south‐west of Monte Capio both units are folded together into a tight to isoclinal steeply plunging fold with an amplitude of c. 10 km. This fold locally inverts the stratigraphy of the layered basic group of the complex, and is thought to be the result of gravitational collapse following intrusion and inflation of a large magma body into the lower crust. Several high‐temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body. Close parallels can be drawn between the observed structure in the Ivrea‐Verbano Zone (after removing the effects of late, low‐temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and Range province.
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  • 87
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    Egg development in the octopus Eledone cirrhosa (1992)
    Zoological Society of London | Wiley
    In:  Journal of Zoology, 227 . pp. 623-638.
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    Publikationsdatum: 2020-11-05
    Beschreibung: The development of egg/follicular cell complexes is described in maturing females of the octopus Eledone cirrhosa. Follicle cells proliferate to enclose the oocyte in a single epithelial layer which becomes deeply infolded. Active cell division of the follicle cells and recruitment of cells from an outer (thecal) layer generate this expansion of follicle cell epithelium. The onset of the main phase of vitellogenesis, secretion of protein yolk, occurs when eggs reach about 2mm in length and is marked by the columnar appearance of the follicle cells and an increased number of larger and more complex nuclei. A significant proportion of the egg population fails to develop beyond 2-3mm in length and these eggs subsequently degenerate.
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  • 88
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    Shear strength of the Great Pacific Fracture Zones (1992)
    Wiley | AGU (American Geophysical Union)
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    Publikationsdatum: 2024-01-08
    Beschreibung: Shipboard bathymetry and gravity data from 30 crossings of 6 great Pacific fracture zones (FZs), the Mendocino, Murray, Molokai, Clarion, Clipperton, and Udintsev, are compared with the predictions of a model in which FZs are locked beyond the ridge-transform intersection, such that no vertical motion occurs on the fault in response to differential thermal subsidence. At least some sections of all of these FZs, except the Molokai, are consistent with this model and sustain shear stresses as high as 20 MPa. However, none of the FZs is locked along its entire length, as inferred from observed shear stresses dropping below 75% of the value necessary to maintain a locked fault. There is some suggestion that the unlocking may be related to excess volcanism.
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  • 89
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    The giant squid Architeuthis in southern African waters (1991)
    Wiley-Blackwell
    In:  Journal of Zoology, 224 (3). pp. 431-477.
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    Publikationsdatum: 2020-07-17
    Beschreibung: Three specimens of the rare giant squid (genus Architeuthis, 18 nominal species) are described from the waters around southern Africa. Consideration of their internal and external morphology, including beaks, radula, statocyst and statolith give no reason to suppose that the three specimens do not pertain to the same species. A standardized data collection form and a summary of existing morphometric data are presented for the first time and the morphology and systematics of the genus are discussed. The value of various systematic characters is examined and certain guidelines are proposed, with an appeal for a more scientific approach to Architeuthis studies. Features of the internal anatomy, including the female reproductive tract, are described and illustrated and the beak dimensions are used to evaluate existing regression formulae for beak and body parameters. The statocyst and statolith are described and illustrated in full, the statolith for the first time, and are compared with those of other squids. The value of recent data from trawl-caught specimens, as well as indirect evidence, is cited to replace speculation in discussions on distribution and habitat. Our specimens suggest that the waters off the south-western coast of Africa may be one of the natural habitats of Architeurhis, during both feeding and spawning periods of the life cycle.
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  • 90
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    A note on the eggs of Benthoctopus piscatorum (Cephalopoda: Octopoda) (1991)
    Wiley-Blackwell
    In:  Journal of Zoology, 223 (3). pp. 499-500.
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    Publikationsdatum: 2020-07-17
    Beschreibung: Benthoctopus piscatorum appears to be a multiple spawner. In the ovary of one specimen about 50 eggs were found at various stages of development.
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  • 91
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    Structure of the reproductive system of the squid Thysanoteuthis rhombus (Cephalopoda: Oegopsida) (1991)
    Wiley-Blackwell
    In:  Journal of Zoology, 224 (2). pp. 271-283.
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    Publikationsdatum: 2020-07-17
    Beschreibung: The structure of the reproductive systems of mature males and females of the nektonic, oceanic squid Thysanoteuthis rhombus are described. The main peculiarities of the female system are relatively low capacity oviducts, set in a tight spiral, and hypertrophically developed oviducal glands with a very large second section. The male reproductive system is characterized by a long, narrow Needham's sac containing 10–15 large spermatophores 80–100 mm in length. The mesentery supporting the gonad, and protruding into it dorsally, is a characteristic feature in both sexes. The hectocotylus structure differs markedly from that in other squids and resembles that of sepiids. The reproductive system of T. rhombus possesses primitive features (pattern of gonad attachment and hectocotylus) but mostly secondary characters (small oviducts, very large oviducal glands and ovary). The complex morpho-ecological adaptations of T. rhombus are reflected in the distinctive features of the reproductive system.
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  • 92
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    Seasonal variation in the diet of common seals (Phoca vitulina) in the Moray Firth area of Scotland (1991)
    Wiley-Blackwell
    In:  Journal of Zoology, 223 (4). pp. 641-652.
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    Publikationsdatum: 2020-07-17
    Beschreibung: Seasonal variation in the diet of common seals (Phoca vitulina) in the Moray Firth, north-east Scotland, was determined from analysis of faecal samples collected at haul-out sites during each month of 1988. Data on diet of common seals in 1987 are also presented. Limitations of the methods available for quantification of diet are discussed. Although some of the observed variation in diet from month to month may reflect changes in the sampling regime, a clear seasonal pattern was apparent, with clupeids predominating in the winter and sandeels in the summer. The trends observed are consistent with opportunistic feeding on the most abundant Prey.
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  • 93
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    Identification of fish otoliths and bones in faeces and digestive tracts of seals (1991)
    Wiley-Blackwell
    In:  Journal of Zoology, 224 (2). pp. 320-328.
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    Publikationsdatum: 2020-07-17
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  • 94
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    Digestive tract contents of seals in Scottish waters: comparison of samples from salmon nets and elsewhere (1991)
    Wiley-Blackwell
    In:  Journal of Zoology, 225 (4). pp. 670-676.
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    Publikationsdatum: 2020-07-17
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  • 95
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    Tackling the Sulfide Gradient: A Novel Strategy Involving Marine Nematodes and Chemoautotrophic Ectosymbionts (1991)
    Wiley-Blackwell
    In:  Marine Ecology, 12 (3). pp. 261-279.
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    Publikationsdatum: 2015-08-31
    Beschreibung: The Stilbonemutinue (marine free-living nematodes) arc remarkable for cctosymbiotic bacteria, which cover the greatest part of their body in a highly ordered and species specific pattern. Using SEM we describe the main types of symbiotic cover and give evidence for the role of the bacteria in the nutrition of their host on the basis of stable carbon isotope ratios. In experimental systems the worms migrated repeatedly across a sulfide gradient during 12 h when sulfide concentrations were low, but stayed above the sulfide maximum at high concentrations. The migration across the chemocline exposes the symbionts alternately to reduced sulfur compounds and oxygen; this constitutes an alternative strategy to the ventilation/circulation systems in symbiotic macrofauna from sulfidic habitats
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  • 96
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    Ihering's hypothesis in the light of foraminiferological data (1991)
    Wiley-Blackwell
    In:  Lethaia, 24 (2). pp. 191-198.
    Details
    Publikationsdatum: 2020-07-15
    Beschreibung: The presence of several typically northern hemisphere foraminiferal species in the upper Miocene and Recent deposits of the Río de la Plata, Paraná river and adjacent areas, and their absence along the Brazilian coast strongly suggests that in the late Miocene the Caribbean and the Southern Atlantic were linked by a marine connection. This connection was first envisioned by H. von Ihering, who called it the ‘Arm of the Tethys’. It was represented by a very broad strait which ran meridionally across the South American continent. In the Pliocene it shrank considerably and its salinity was lowered by Andean river runoff. At the end of the Pliocene - beginning of the Pleistocene it gave rise to the Paraná river, a series of brackish water lakes and lagoons, and the Río de la Plata. □Foraminifera, arm of the Tethys, South America.
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  • 97
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    Lagotoside: A New Phenylpropanoid Glycoside from Lagotis stolonifera (1991)
    Wiley
    In:  Helvetica Chimica Acta, 74 (6). pp. 1273-1277.
    Details
    Publikationsdatum: 2020-07-29
    Beschreibung: From the aerial parts of Lagotis stolonifera (Scrophulariaccae), a new phenylpropanoid glycoside, lagotoside (8), and the three known glycosides ehrenoside (5), verbascoside (= acteoside; 6), and plantamajoside (7) were isolated, together with the four known iridoid glucosides aucubin (1), catalpol(2), globularin (4), and lythantosalin (3). The structure of the new compound 8 was elucidated on the basis of chemical and spectral data as 2-(3-hy-droxy-4-methoxyphenyl)ethyl O-[α-L-arabinopyranosyl-(1 [RIGHTWARDS ARROW] 2)]-O-[α-L-rhamnopyranosyl-(1 [RIGHTWARDS ARROW] 3)]-4-O-feruloyl-β-D-glucopyranoside.
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  • 98
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    Cephalopods in the diet of the South African fur seal (Arctocephalus pusillus pusillus) (1990)
    Wiley-Blackwell
    In:  Journal of Zoology, 221 (3). pp. 359-374.
    Details
    Publikationsdatum: 2020-07-17
    Beschreibung: The stomach contents of 1522 adult seals (Arctocephalus pusillus pusillus) and 673 pups, which were collected around the West and South Coasts of Southern Africa, were examined and cephalopod prey identified. About 20 cephalopod species (some identifications were uncertain) were found in the stomachs, of which only six were significant: Loligo vulgaris reynaudii. Sepia spp., Octopus sp., Todaropsis eblanae, Todarodes angolensis and Ocythoe tuberculata. This list suggests that A. pusillus feeds exclusively on the continental shelf, frequently on or near the bottom. Among adults, cephalopod prey varied in importance around the coast. It was most important on the South Coast of South Africa where it comprised 35.0% of the weight of all prey, of which L. v. veynaudii constituted about 88%. On the West Coast cephalopods comprised about 26.6% by weight of all prey, and Octopus sp. predominated, whereas in Namibian waters cephalopods were least important, constituting only 3.4% by weight of all prey, with Todarodes angolensis and Octopus sp. being most significant. Among pups (aged 8–10 months) in the Lüderitz (Namibia) area, cephalopods were about 16.9% of prey by weight, of which Ocythoe tuberculata, small Sepia spp. and Octopoda were most important.
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  • 99
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    On the nonuniqueness of receiver function inversions (1990)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 95 (B10). pp. 15303-15318.
    Details
    Publikationsdatum: 2021-02-01
    Beschreibung: To study the resolving power of teleseismic P waveforms for receiver structure, we model synthetic waveforms using a time domain waveform inversion scheme beginning with a range of initial models to estimate the range of acceptable velocity structures. To speed up the waveform inversions, we implement Randall's (1989) efficient algorithms for calculating differential seismograms and include a smoothness constraint on all the resulting velocity models utilizing the “jumping” inversion technique of Shaw and Orcutt (1985). We present the results of more than 235 waveform inversions for one‐dimensional velocity structures that indicate that the primary sensitivity of a receiver function is to high wavenumber velocity changes, and a depth‐velocity product, not simply velocity. The range of slownesses in a typical receiver function study does not appear to be broad enough to remove the depth‐velocity ambiguity; the inclusion of a priori information is necessary. We also present inversion results for station RSCP, located in the Cumberland Plateau, Tennessee. Our results are similar to those from a previous study by Owens et al. (1984) and demonstrate the uncertainties in the resulting velocity estimate more clearly.
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  • 100
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    The Food of Grey-Faced Petrels (Pterodroma macroptera gouldi (Hutton)), with Special Reference to Diurnal Vertical Migration of their Prey (1973)
    Wiley-Blackwell
    In:  Journal of Animal Ecology, 42 (3). pp. 645-662.
    Details
    Publikationsdatum: 2020-07-27
    Materialart: Article , PeerReviewed
    Format: text
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