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  • Cell Press  (14,598)
  • International Union of Crystallography (IUCr)
  • 2020-2023  (7)
  • 1990-1994  (21,754)
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  • 1
    Publication Date: 2022-10-27
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Meaders, J. L., de Matos, S. N., & Burgess, D. R. A pushing mechanism for microtubule aster positioning in a large cell type. Cell Reports, 33(1), (2020): 108213, doi:10.1016/j.celrep.2020.108213.
    Description: After fertilization, microtubule (MT) sperm asters undergo long-range migration to accurately position pronuclei. Due to the large sizes of zygotes, the forces driving aster migration are considered to be from pulling on the astral MTs by dynein, with no significant contribution from pushing forces. Here, we re-investigate the forces responsible for sperm aster centration in sea urchin zygotes. Our quantifications of aster geometry and MT density preclude a pulling mechanism. Manipulation of aster radial lengths and growth rates, combined with quantitative tracking of aster migration dynamics, indicates that aster migration is equal to the length of rear aster radii, supporting a pushing model for centration. We find that dynein inhibition causes an increase in aster migration rates. Finally, ablation of rear astral MTs halts migration, whereas front and side ablations do not. Collectively, our data indicate that a pushing mechanism can drive the migration of asters in a large cell type.
    Description: We would like to thank Dr. Jesse Gatlin for sending us the Tau-mCherry fusion protein for imaging live MTs. We would also like to thank Dr. Timothy Mitchison, Dr. Christine Field, and Dr. James Pelletier for supplying us with CA4, p150-CC1, and EB1-GFP peptides, as well as for fruitful discussions. Finally, we would like to thank Dr. Charles Shuster and Leslie Toledo-Jacobo for constructive feedback when preparing the manuscript. We thank Bret Judson and the Boston College Imaging Core for infrastructure and support. This material is based upon work supported by NSF grant no. 124425 to D.R.B.
    Keywords: Dynein ; Aster ; Microtubule ; Centrosome ; Pronucleus ; Fertilization ; Aster position
    Repository Name: Woods Hole Open Access Server
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  • 2
    Publication Date: 2022-10-27
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Stolp, Z. D., Kulkarni, M., Liu, Y., Zhu, C., Jalisi, A., Lin, S., Casadevall, A., Cunningham, K. W., Pineda, F. J., Teng, X., & Hardwick, J. M. Yeast cell death pathway requiring AP-3 vesicle trafficking leads to vacuole/lysosome membrane permeabilization. Cell Reports, 39(2), (2022): 110647, https://doi.org/10.1016/j.celrep.2022.110647.
    Description: Unicellular eukaryotes have been suggested as undergoing self-inflicted destruction. However, molecular details are sparse compared with the mechanisms of programmed/regulated cell death known for human cells and animal models. Here, we report a molecular cell death pathway in Saccharomyces cerevisiae leading to vacuole/lysosome membrane permeabilization. Following a transient cell death stimulus, yeast cells die slowly over several hours, consistent with an ongoing molecular dying process. A genome-wide screen for death-promoting factors identified all subunits of the AP-3 complex, a vesicle trafficking adapter known to transport and install newly synthesized proteins on the vacuole/lysosome membrane. To promote cell death, AP-3 requires its Arf1-GTPase-dependent vesicle trafficking function and the kinase Yck3, which is selectively transported to the vacuole membrane by AP-3. Video microscopy revealed a sequence of events where vacuole permeability precedes the loss of plasma membrane integrity. AP-3-dependent death appears to be conserved in the human pathogenic yeast Cryptococcus neoformans.
    Description: Funding sources: National Institutes of Health, United States grants AI144373 and NS127076 (J.M.H.), AI115016 and AI153414 (K.W.C.), and AI052733, AI152078, and HL059842 (A.C.); National Natural Science Foundation of China 31970550; and the Priority Academic Program Development of the Jiangsu Higher Education Institutes (X.T.).
    Keywords: Yeast ; Programmed cell death ; Vesicle trafficking ; AP-3 ; Vacuole ; Cryptococcus ; Yck3 ; Regulated cell death ; Lysosome ; Vacuolar membrane permeabilization
    Repository Name: Woods Hole Open Access Server
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  • 3
    Publication Date: 2022-08-30
    Description: Most tropical corals live in symbiosis with Symbiodiniaceae algae whose photosynthetic production of oxygen (O2) may lead to excess O2 in the diffusive boundary layer (DBL) above the coral surface. When flow is low, cilia-induced mixing of the coral DBL is vital to remove excess O2 and prevent oxidative stress that may lead to coral bleaching and mortality. Here, we combined particle image velocimetry using O2-sensitive nanoparticles (sensPIV) with chlorophyll (Chla)-sensitive hyperspectral imaging to visualize the microscale distribution and dynamics of ciliary flows and O2 in the coral DBL in relation to the distribution of Symbiodiniaceae Chla in the tissue of the reef building coral, Porites lutea. Curiously, we found an inverse relation between O2 in the DBL and Chla in the underlying tissue, with patches of high O2 in the DBL above low Chla in the underlying tissue surrounding the polyp mouth areas and pockets of low O2 concentrations in the DBL above high Chla in the coenosarc tissue connecting neighboring polyps. The spatial segregation of Chla and O2 is related to ciliary-induced flows, causing a lateral redistribution of O2 in the DBL. In a 2D transport-reaction model of the coral DBL, we show that the enhanced O2 transport allocates parts of the O2 surplus to areas containing less chla, which minimizes oxidative stress. Cilary flows thus confer a spatially complex mass transfer in the coral DBL, which may play an important role in mitigating oxidative stress and bleaching in corals.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Reusch, S., Biswas, A., Hirst, W. G., & Reber, S. Affinity purification of label-free tubulins from xenopus egg extracts. STAR Protocols, 1(3), (2020): 100151, doi:10.1016/j.xpro.2020.100151.
    Description: Cytoplasmic extracts from unfertilized Xenopus eggs have made important contributions to our understanding of microtubule dynamics, spindle assembly, and scaling. Until recently, these in vitro studies relied on the use of heterologous tubulin. This protocol allows for the purification of physiologically relevant Xenopus tubulins in milligram yield, which are a complex mixture of isoforms with various post-translational modifications. The protocol is applicable to any cell or tissue of interest. For complete details on the use and execution of this protocol, please refer to Hirst et al. (2020).
    Description: This article was prompted by our stay at the Marine Biological Laboratory (MBL), Woods Hole, MA, in the summer of 2016 funded by the Princeton-Humboldt Strategic Partnership Grant together with the lab of Sabine Petry (Princeton University). We are grateful to the National Xenopus Resource (NXR) for supplying frogs. For mass spectrometry, we would like to acknowledge the assistance of Benno Kuropka and Chris Weise from the Core Facility BioSupraMol supported by the Deutsche Forschungsgemeinschaft (DFG). We thank the Protein Expression Purification and Characterization (PEPC) facility at the MPI-CBG; in particular, we thank Aliona Bogdanova and Barbara Borgonovo. We thank all former and current members of the Reber lab for discussions and helpful advice, in particular Christoph Hentschel and Soma Zsoter for technical assistance. S.R. acknowledges funding from the IRI Life Sciences (Humboldt-Universität zu Berlin, Excellence Initiative/DFG). W.H. was supported by the Alliance Berlin Canberra co-funded by a grant from the Deutsche Forschungsgemeinschaft (DFG) for the International Research Training Group (IRTG) 2290 and the Australian National University.
    Repository Name: Woods Hole Open Access Server
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  • 5
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hirst, W. G., Kiefer, C., Abdosamadi, M. K., Schäffer, E., & Reber, S. In Vitro reconstitution and imaging of microtubule dynamics by fluorescence and label-free microscopy. STAR Protocols, 1(3), (2020): 100177, doi:10.1016/j.xpro.2020.100177.
    Description: Dynamic microtubules are essential for many processes in the lives of eukaryotic cells. To study and understand the mechanisms of microtubule dynamics and regulation, in vitro reconstitution with purified components has proven a vital approach. Imaging microtubule dynamics can be instructive for a given species, isoform composition, or biochemical modification. Here, we describe two methods that visualize microtubule dynamics at high speed and high contrast: (1) total internal reflection fluorescence microscopy and (2) label-free interference reflection microscopy.
    Description: We thank the AMBIO imaging facility (Charité, Berlin) and Nikon at MBL for imaging support. We thank all former and current members of the Reber lab for discussion and helpful advice, in particular Christoph Hentschel and Soma Zsoter for technical assistance. S.R. acknowledges funding by the IRI Life Sciences (Humboldt-Universität zu Berlin, Excellence Initiative/DFG). W.H. was supported by the Alliance Berlin Canberra co-funded by a grant from the Deutsche Forschungsgemeinschaft (DFG) for the International Research Training Group (IRTG) 2290 and the Australian National University. C.K. thanks the Deutsche Forschungsgesellschaft (DFG, JA 2589/1-1). C.K. and M.A. thank Steve Simmert and Tobias Jachowski former and current members of the Schäffer lab.
    Keywords: Biophysics ; Cell Biology ; Microscopy
    Repository Name: Woods Hole Open Access Server
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  • 6
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geisterfer, Z. M., Oakey, J., & Gatlin, J. C. . Microfluidic encapsulation of Xenopus laevis cell-free extracts using hydrogel photolithography. STAR Protocols, 1(3), (2020): 100221, doi:10.1016/j.xpro.2020.100221.
    Description: Cell-free extract derived from the eggs of the African clawed frog Xenopus laevis is a well-established model system that has been used historically in bulk aliquots. Here, we describe a microfluidic approach for isolating discrete, biologically relevant volumes of cell-free extract, with more expansive and precise control of extract shape compared with extract-oil emulsions. This approach is useful for investigating the mechanics of intracellular processes affected by cell geometry or cytoplasmic volume, including organelle scaling and positioning mechanisms. For complete details on the use and execution of this protocol, please refer to Geisterfer et al. (2020).
    Description: This work was made possible by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant no. 2P20GM103432. It was also supported by additional funding provided by the NIGMS under grant no. R01GM113028, the NSF Faculty CAREER Program under award no. BBBE 1254608, Whitman Center fellowships at the Marine Biological Laboratory, and the Biomedical Scholars program of the Pew Charitable Trusts. We thank Drs. Aaron Groen and Tim Mitchison for their intellectual contributions and involvement in some of the pioneering experiments that set the foundation for this approach.
    Keywords: Biophysics ; Cell Biology ; Cell isolation ; Microscopy ; Model Organisms
    Repository Name: Woods Hole Open Access Server
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  • 7
    Publication Date: 2022-11-18
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tian, Y., Liu, X., Li, J., Deng, Y., DeGiorgis, J. A., Zhou, S., Caratenuto, A., Minus, M. L., Wan, Y., Xiao, G., & Zheng, Y. Farm-waste-derived recyclable photothermal evaporator. Cell Reports Physical Science, 2(9), (2021): 100549, https://doi.org/10.1016./j.xcrp.2021.100549
    Description: Interfacial solar steam generation is emerging as a promising technique for efficient desalination. Although increasing efforts have been made, challenges exist for achieving a balance among a plethora of performance indicators—for example, rapid evaporation, durability, low-cost deployment, and salt rejection. Here, we demonstrate that carbonized manure can convert 98% of sunlight into heat, and the strong capillarity of porous carbon fibers networks pumps sufficient water to evaporation interfaces. Salt diffusion within microchannels enables quick salt drainage to the bulk seawater to prevent salt accumulation. With these advantages, this biomass-derived evaporator is demonstrated to feature a high evaporation rate of 2.81 kg m−2 h−1 under 1 sun with broad robustness to acidity and alkalinity. These advantages, together with facial deployment, offer an approach for converting farm waste to energy with high efficiency and easy implementation, which is particularly well suited for developing regions.
    Description: This project is supported by the National Science Foundation through grant no. CBET-1941743. This project is based upon work supported in part by the National Science Foundation under EPSCoR Cooperative Agreement no. OIA-1655221.
    Keywords: Biomass ; Recyclable ; Manure ; Farm waste ; Photothermal evaporation ; Desalination
    Repository Name: Woods Hole Open Access Server
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  • 8
    Electronic Resource
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 18-20 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Anomalous X-ray scattering terms for Rb+ near the K-edge measured in diffraction experiments with synchrotron radiation range up to 4.71 (6) for f′′ and down to −9.80 (11) for f′, in agreement with values derived from the absorption spectrum.
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  • 9
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 35-42 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The X-ray reflectivity of bent perfect crystals is calculated from a model where the crystal is approximated by a stack of perfect-crystal lamellae which have a gradually changing orientation. A computer program is developed for calculation of the reflectivity of the composite crystal from the dynamical theory of diffraction. An approximate solution is also given where an analytical formula for the reflectivity of a non-absorbing lamella is used and the effects of absorption are calculated separately. Typically, in the Bragg case, the reflectivity curve has a steep edge and an exponentially falling slope, while in the Laue case the curve is almost rectangular if the absorption is not too large. The width of the curve is inversely proportional to the bending radius in both cases. Reflectivity curves were measured for the 111 and 400 reflections of Si with Mo Kα1 radiation. The agreement with analytical and computer calculations is good, particularly at small bending radii where the kinematical limit is approached.
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  • 10
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 63-69 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method of measuring differences in lattice spacing with an accuracy of 1 part in 108 in a period as short as two minutes is described. The method uses one source of copper radiation and a triple-axis arrangement. Two of these axes are double-leaf silicon springs in monolithic crystal assemblies which achieve the high stability required by such measurements. Samples are easily changed and sequences of measurements are performed entirely under computer control. The method is demonstrated by a comparison of the lattice spacings of four samples which reveals differences of up to 60 parts in 108 between silicon crystals of different origins.
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  • 11
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 77-78 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 12
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 105-110 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Some experimental results are presented for an elastically bent perfect silicon crystal in a strongly asymmetric diffraction geometry as a neutron monochromator. The use of this unconventional geometry of the monochromator appears to be suitable for a wide (several centimetres) incident polychromatic beam, when, thanks to the spatial condensation of the diffracted neutrons (Fankuchen effect), a high monochromatic beam density may be obtained. Furthermore, when using focusing in real and in momentum space by adjusting an optimum bending radius, the intensity diffracted by a sample may be comparable even with the best mosaic monochromators such as highly oriented pyrolytic graphite (PG). A comparison is demonstrated on the rocking curves of a strongly mosaic Ni–Al(020) crystal obtained with the monochromatic beam from bent Si(111), Si(400) and from PG(002), Cu(220) mosaic monochromators.
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  • 13
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 134-135 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Bhatia & Thornton [Phys. Rev. B. (1970), 2, 3004–3012] have derived the formula that relates the scattering intensity of a binary system to the Fourier transform of the local number density and concentration. For the intensity at the limit of zero scattering angle, the same formula can be derived by a much simpler process.
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  • 14
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 142-143 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 15
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 144-146 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 16
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 169-174 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Single-crystal synchrotron-radiation Laue photographs of protein crystals and viruses are densely populated and a considerable amount of spatial overlapping of spots often occurs on the films. An integration procedure which enables the efficient deconvolution of these spots in order to obtain their integrated intensity has been developed and implemented. Some results are given for glycogen phosphorylase b and tomato bushy stunt virus. A comparative study of reflections overlapped on one exposure and separated on another, taken from the same crystal at a longer crystal-to-film distance, gives merging statistics comparable to those from the treatment of spatially separated spots only. In all cases the majority of the spatially overlapped data is made available for subsequent analyses.
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  • 17
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 211-212 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Previous reports by Rosenzweig & Morosin [Acta Cryst. (1966). 20, 758–761], Liminga & Abrahams [J. Appl. Cryst. (1976). 9, 42–47] and Svensson, Albertsson, Liminga, Kvick & Abrahams [J. Chem. Phys. (1983). 78, 7343–7352], that the more steeply pointed ends of α-LiIO3 crystals grown from aqueous solution with 3 ≤ pH ≤ 7 have the apex of each pyramidal IO−3 ion pointing toward the direction which develops a positive polarity (d33 〉 0) under tensile stress applied along the polar hexagonal axis, have been confirmed contrary to the conclusion of Yang Hua-guang, Zhang Dao-fan, Chen Wan-chun & Li Yin-yuan [J. Appl. Cryst.(1989). 22, 144–149]. The error leading to the latter conclusion is identified.
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  • 18
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 223-223 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 19
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 222-223 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 20
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 228-233 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Synchrotron radiation has been used to measure the rocking curves from a (GaIn)(AsP) single layer grown on an InP (100)-oriented substrate. For angles of incidence ΦB = (ΘB − φ) ≤ 0.7° measured at the Bragg angle ΘB (φ is the angle between the diffracting lattice plane and the surface), the rocking curve (RC) is very strongly influenced by total external reflection (TER). This causes a decrease in the full width at half-maximum (FWHM) and an asymmetrical shape for the RC for small ΦB. Both of these effects are due to the Bragg-angle shift from the actual incident angle Φ which is not considered in the conventional dynamical theory. In this paper the essential influence of TER on any thin-layer rocking curve is investigated using a numerical solution of the extended dynamical theory. The pattern can be interpreted up to ΦB ≥ ΘC (ΘC is the angle of TER) by semiempirical incorporation of the results of the extended theory with the coupling formalism of Barrels, Hornstra & Lobeek [Acta Cryst. (1986). A42, 539–545].
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  • 21
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 277-281 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The ferroelectric ferroelastic phase transitions of tetramethylammonium tetrachlorozincate (HTMA) were observed by standard X-ray topography and by synchrotron topography. Observation of the phase boundary is possible in the latter case. The different kinds of domain walls observed in the ferroelastic phase cast doubts on the commonly assumed symmetry group of this phase.
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  • 22
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 180-185 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A theory is presented describing convolutional properties of the reduced intensity distribution (intensity divided by the square of the atomic factor and multiplied by the scattering-vector length). The approximation used, verified on model data, leads to a relation between the effect of the multiple running average routine applied to reduced intensity and both normalization constant and local atomic density in the neighbourhood of any given atom. This enables an estimate of the normalization constant and the local density to be made with a high degree of accuracy. The effect of the choice of adjustable parameters in the running average routine is discussed. The procedure to calculate the interference function in the presence of an unknown background varying slowly with the scattering vector is presented.
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  • 23
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 212-214 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper describes an instrumental artifact which has been observed in three Nicolet P3F diffractometers. In cases where the peaks are very sharp in ω, the artifact causes azimuthal or ψ scans to appear very noisy and to show a complex periodic variation of intensity with ψ. These intensity variations are reproducible. A simple correction is described which, when applied to the data, dramatically improves the appearance of these aberrant ψ scans. This correction is not limited to ψ scans and should improve the quality of all data collected on the machine.
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  • 24
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 225-227 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer-oriented procedure for the generation of the symmetry of the multiple implication function has been developed. The symmetry of the multiple implication function, referred to its own conventional unit cell, is tabulated for all space groups.
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  • 25
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 253-257 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is presented which indexes spots recorded on single oscillation images without any a priori knowledge of cell parameters. The strategy is similar to that used in four-circle diffractometry and the method works in a fully automatic manner. It is applicable to multiple oscillation images or multiple stills. A complementary method is also described to obtain orientation angles for the case where cell parameters have already been determined.
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  • 26
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 351-354 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A photographic Weissenberg camera has been constructed which can be mounted on the 2θ arm of a four-circle diffractometer. At a distance of 0.5 m from the sample the 2θ resolution for a 100 μm crystal is 0.2 mrad (0.01°), allowing a high-resolution mapping of reciprocal space at a synchrotron source in an efficient way. As sample experimental results, a study is presented of the streak system around the 111 reflection of a perfect germanium crystal and the detection of a minute phase transformation in a single-powder grain of a high-Tc superconductor.
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  • 27
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 378-386 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The accuracy of the Chebyshev expansion coefficients used for the calculation of attenuation correction factors for cylindrical samples has been improved. An increased order of expansion allows the method to be useful over a greater range of attenuation. It is shown that many of these coefficients are exactly zero, others are rational numbers, and others are rational fractions of π−1 The assumptions of Sears [J. Appl. Cryst. (1984), 17, 226–230] in his asymptotic expression of the attenuation correction factor are also examined.
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  • 28
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 397-400 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A single-crystal study on AlPO4 was performed at 2.90 (7) GPa with synchrotron radiation using a diamond-anvil cell with a beryllium gasket. For the data collection the radiation wavelength of only 0.54 Å, was chosen to minimize the absorption of X-rays in the pressure cell. The diffracted intensity was high enough to measure even weak reflections with sufficient counting statistics. The refined structural parameters are in good agreement with those determined from data collected with a conventional X-ray tube.
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  • 29
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    Applied crystallography online 23 (1990), S. 418-423 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: High-resolution transmission electron microscopy (HRTEM) was used for examining Cd(S,Se) nanocrystals grown in silicate glasses commercially available as optical filters. The lattice images of the nanocrystals were numerated and submitted to filtering through Fourier transformation in order to sweep off the background signal originating mainly from glass. Optical filters from several firms were examined. The nanocrystals have been identified with Cd(S,Se) compounds crystallized in the wurzite structure, as in bulk material. The lattice images indicate crystallites having the shape of hexagonal prisms a little elongated along the c axis. The distribution of grain size differs according to the filter: the smallest size being about 1.5 nm (threshold for detection), the largest size varies from 7 to 10 nm, the average size sa, from 3–4 to 5–6 nm and the characteristic size sc from 5–6 to 7–8 nm (sc is the size of grains occupying the main part of the crystallized volume).
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  • 30
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    Applied crystallography online 23 (1990), S. 430-432 
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    Notes: A photodiode X-ray detector was built to measure small-angle X-ray scattering (SAXS) at a synchrotron-radiation source in conjunction with a double-crystal diffractometer SAXS camera at photon energies between 5 and 11 keV. The photodiode detector response in this energy range is linear at photon counting rates up to 1012 photons s−1 and thus it was not necessary to attenuate the monochromatic X-ray beam with calibrated foils. SAXS data taken with a scintillation counter and the photodiode detector are compared, demonstrating marked improvement in counting statistics, rate of data acquisition and signal-to-noise ratio.
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  • 31
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    Applied crystallography online 23 (1990), S. 441-443 
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    Notes: The X-rays emitted from a laser-produced plasma have been used to obtain powder diffraction patterns with exposures of less than a nanosecond. The X-rays were produced by focusing approximately 50 J of 0.53 μm laser light in a 600 ps (FWHM) pulse to a tight (1̃00 μm diameter) spot on a solid titanium target. The spectral brightness of the resonance line of the helium-like titanium thus produced was sufficient to record diffraction from LiF powder in a single exposure using the Seemann–Bohlin geometry. These results indicate that time-resolved measurements of the lattice parameters of polycrystalline materials can be made with sub-nanosecond temporal resolution.
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  • 32
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    Applied crystallography online 23 (1990), S. 446-446 
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  • 33
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    Applied crystallography online 23 (1990), S. 476-484 
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    Notes: The use of a one-dimensional position-sensitive detector for diffuse X-ray scattering measurements is described. Calibration procedures for scattering angle and intensity measurements are discussed. Some nonuniformities have been found in the counting efficiency as a function of distance along the detector. A procedure is described for measuring the diffuse scattering in a section of reciprocal space.
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  • 34
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    Applied crystallography online 23 (1990), S. 497-508 
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    Notes: The elastic diffuse neutron scattering of an NbC0.73 single-crystal has been measured at room temperature on two different spectrometers, the four-circle D10 at the HFR–ILL (Grenoble), and the two-axis G44 with time-of-flight analysis at the Laboratoire Léon Brillouin (Saclay). The data were treated either by Fourier transformations or by least-squares fit. The short-range-order parameters and the interatomic static displacements obtained by the various experiments and/or data treatment are in good agreement: carbon vacancies tend to be third neighbours in the f.c.c. metalloid sublattice and metal atoms relax away from the vacancy first neighbours by 0̃.05 Å. It is shown that the treatment of diffuse scattering data limited to two reciprocal planes [(001) and (1{\bar 1}0)] gives satisfactory results.
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  • 35
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    Applied crystallography online 23 (1990), S. 526-534 
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    Notes: Following the profile decomposition of CeO2 X-ray powder data into individual structure factors, the maximum-entropy method (MEM) has been used to obtain an electron-density-distribution map. In the profile decomposition process, it is impossible to avoid the problems of overlapping peaks which have the same magnitude of reciprocal vectors, such as d*(511) and d*(333), for a cubic crystal, or very severely overlapping reflections. The formalism to treat such overlapping reflections in the MEM analysis is to introduce combined structure factors. The maximum value of the scattering vector, 4π(sinθ)/λ, which was used in the present analysis is small (about 7.8 Å−1) but the resulting electron-density-distribution map is of a high quality and much superior to the conventional map. As a consequence, the ionic charge of Ce and O ions can be obtained with reasonable accuracy from the MEM density map. Furthermore, the map reveals the existence of electrons around the supposedly vacant site surrounded by eight O atoms, which is probably related to the high ionic conductivity of this substance.
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    Applied crystallography online 23 (1990), S. 558-558 
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    Applied crystallography online 23 (1990), S. 560-560 
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  • 38
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    Applied crystallography online 24 (1991), S. 18-29 
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    Notes: A previously described method of synthesizing a real-space distribution of scattering points which will give rise to virtually any required diffraction pattern has been investigated from the point of view of trying to establish the rôle that the phase of individual modulations plays in determining the real-space structure. For an object involving continuous random variables, the choice of phase cannot affect the diffracted intensity and phases can be chosen freely. Although such variation of phases does not affect the diffracted intensity, the real-space amplitudes are no longer normally distributed and the structures will in general contain non-zero multisite correlations. For an object involving binary variables (such as site occupancy), it is shown that the phases of individual elementary volumes of reciprocal space not only contain information about multisite correlations, but also contain the information that the object is binary. It is also shown that the information concerning multisite correlations can be, at least partially, transferred to an object giving a different diffraction pattern by using a known set of phases with a different set of amplitudes.
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  • 39
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    Applied crystallography online 24 (1991), S. 63-63 
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    Notes: Establishment of absolute structures requires measurement of Bijvoet differences with a right-handed set of axes. There can be pitfalls in the satisfaction of this requirement, and a very simple method of assessing this hand is described.
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  • 40
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    Applied crystallography online 24 (1991), S. 66-70 
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    Notes: Restraint equations suitable for incommensurate (IC) structure refinement by least squares are defined. Other quantities used in the final results analysis are reviewed. The main purpose of such a restrained refinement is to prevent high local variations of stereochemical parameters (e.g. bond lengths and/or angles), leaving the corresponding average values to be refined. The method is a natural generalization of that commonly used for commensurate structures and in some cases does not require user-supplied parameters.
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  • 41
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    Applied crystallography online 24 (1991), S. 78-78 
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    Applied crystallography online 24 (1991), S. 96-101 
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    Notes: Accurate measurement of the deviation from coincidence orientation for grain boundaries allows the intergranular dislocation structure to be predicted. For hexagonal symmetry, the deviation may generally be split into two components: a pure rotation and a deformation. This rotation may be determined directly by measuring the displacement of rational common zone axes across the grain boundary plane, independently of any coincidence site lattice (CSL). The precision on the elements of the rotation – axis and angle – depends strongly on the sharpness of the Kikuchi lines. For deformed and annealed magnesium, a precision of 10° on the axis position and of 0.2° on the rotation angle has been obtained.
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    Applied crystallography online 24 (1991), S. 196-196 
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    Applied crystallography online 24 (1991), S. 197-202 
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    Notes: A complex standardless mineral-analysis method is described which determines both the concentrations and the chemistry of minerals in a batch of m ≤ w + t suitable rock samples, where w and t are the numbers of crystalline and amorphous minerals, respectively. The method is based on data from X-ray diffractometry and the bulk chemistry of the samples. Analytical examples are given. The problem of the accuracy of the analysis is discussed.
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    Applied crystallography online 24 (1991), S. 30-37 
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    Notes: The design and operation of a new small-angle X-ray scattering instrument, optimized for high throughput at a synchrotron source, high angular and wavelength resolution, large sample cross-sectional area, accurate energy tuning, excellent signal-to-noise ratio and harmonic rejection are presented. The principles of design and implementation are given, as are the details of primary calibration of absolute intensity and experimental desmearing. The instrument has been tested for application to anomalous-scattering measurements near the chromium K edge. Preliminary results on samples of a heat-treated steel are presented as a demonstration of the capability of this experiment to separate the microstructure evolution as a function of temperature of a chromium-rich precipitate from the thermal behavior of other precipitates in the steel.
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    Applied crystallography online 24 (1991), S. 61-63 
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    Notes: A new powder diffractometer has been designed which can be used for various experimental geometries such as the long-arm Bragg–Brentano method, Guinier method and parallel-beam method. The X-ray source, goniometer and scintillation counter are placed on rails so that the source-to-monochromator, monochromator-to-sample and sample-to-counter distances can be changed arbitrarily. A FWHM of 0.07° for the Kα1 peak of the silicon 111 reflection was obtained by lengthening the counter arm in the Bragg-Brentano method. Rather high angular resolution was achieved by the Guinier and parallel-beam methods for organic samples having poor crystallinity and low absorption.
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    Applied crystallography online 24 (1991), S. 266-266 
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    Applied crystallography online 24 (1991), S. 286-292 
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    Notes: The crystal structure of magnesium boron nitride in the low-pressure phase, Mg3BN3(L), has been solved ab initio from X-ray powder data. The cell is hexagonal (space group P63/mmc, Z = 2) with a = 3.54453 (4), c = 16.03536 (30) Å. Initial positional parameters for the Mg atoms were obtained from Patterson functions generated by 50 integrated intensities derived from a whole-powder pattern decomposition. The remaining atoms were located by trial-and-error model building, followed by Rietveld refinements (Rwp = 8.5%). The structure can be described as consisting of ABB′BACC′CA... layers perpendicular to the c axis with linear N=B=N molecular anions at position A, Mg2+ at positions B and C and Mg2+ with three coordinating N atoms at positions B′ and C′, although Mg3BN3(L) is not a layer compound. A very similar structure has also been obtained by applying standard direct methods to the same intensity data. A high-quality electron-density map has been calculated from the structure factor data using the maximum-entropy method.
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    Applied crystallography online 24 (1991), S. 316-323 
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    Notes: Measurements of lattice distortion due to a slip band were carried out and compared with the theoretically estimated values. A simple model of a single-slip system with uniformly distributed dislocations in a narrow planar slip band was adopted. It was shown that both the effect of all dislocations in the slip band and the surface relaxation must be taken into account.
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    Applied crystallography online 24 (1991), S. 365-368 
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    Notes: A method is presented for indexing the powder diffraction lines from incommensurate structures by a systematic search of reciprocal space, choosing a propagation vector length derived from a satellite reflection in the powder diagram. An interactive computer program gives a graphical display of the direction of the propagation vector which gives the best fit to the pattern.
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    Applied crystallography online 24 (1991), S. 190-193 
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    Notes: The application of single-board microcomputers as programmable interfaces simplifies the construction of complex diffractometer control units. The amount of hardware components of the control units is reduced and the structure of the circuits is easy to survey. These intelligent multipurpose single-board microcomputers unburden the personal computer and simplify the development of the diffractometer measuring program. The presented solution is based on an Atari 1040 STF. The concept, however, can be applied to any type of personal computer.
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    Applied crystallography online 24 (1991), S. 193-195 
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    Notes: A Fortran computer program is described which performs three-dimensional electron-density cage contouring together with atomic structure model display on a Tektronix-4100 command graphics terminal hosted to a VAX/VMS computer. The program also supports ball-and-stick visualization of the model, on-line manipulation of the display and convenient hard-copy output. Such a program is useful in a research environment where an expensive graphics workstation is not readily available and hard copies of publication quality are often desired.
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    Applied crystallography online 24 (1991), S. 212-221 
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    Notes: The principles of the monolithic X-ray magnifier based on two successive asymmetric non-coplanar diffractions from the same crystal are analyzed from the geometrical point of view. The conditions of the distortion-free two-dimensional pattern magnification are formulated by means of matrix formalism. The general solution of the problem of determination of the crystal surface planes satisfying the conditions of distortion-free magnification is derived in the closed form. The calculation is performed on the basis of the kinematical theory of diffraction. It is shown that the number of solutions is infinite for any given pair of diffraction vectors and magnification. General properties of the solution are illustrated by some examples. The effect of the refraction of X-rays on the pattern distortion is estimated. The results suggest that the refractive index correction has a negligible influence on the distortion of the magnified pattern. The results presented enable us to prepare monolithic X-ray magnifiers or demagnifiers that can be used in various fields of X-ray optics, especially in X-ray topography and X-ray lithography.
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    Applied crystallography online 24 (1991), S. 232-238 
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    Notes: Triple junctions in polycrystalline silicon for solar cell applications have been studied by TEM (transmission electron microscopy). The typical characteristic of these junctions is the existence of high-symmetry interfaces, i.e. twins of different order. Whenever the triple junction contains two such interfaces, the intersection axis is a CSL (coincidence site lattice) symmetry axis. In this case the mutual relation of the grain boundaries of the triple junctions is revealed by symmetry rules, since the boundaries are described by symmetry elements of the corresponding CSL which do not belong to the symmetry group of the parent lattice. Therefore, the different variant orientations of these CSL symmetry elements, implied by the symmetry of the lattice, are used for the study of triple junctions. A junction is geometrically characterized by the point-group-symmetry properties. The observations concern symmetrically different triple junctions of the same type of macroscopically stable grain boundaries and faceted and microfaceted interfaces. It is shown that in silicon the thermodynamically favored twins are combined by specific symmetry rules. The results are discussed in accordance with the possible growth mechanisms.
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    Applied crystallography online 24 (1991), S. 243-254 
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    Notes: The theoretical predictions of the triple isotopic substitution (TIS) method in small-angle neutron scattering have been confirmed experimentally. A unique advantage of the method, namely the possibility to make part of a complex particle `invisible' in normal (H2O) buffer, is demonstrated. Particle association, the addition of `small' molecules (such as glycerol) or `large' molecules (such as pyruvate kinase) in the solutions under study have been shown not to influence the difference scattering curve obtained. The possibility of extracting normalized interparticle interference functions from the TIS data is discussed. This enables the detection of the presence of aggregates (e.g. dimers) in the solution, even in cases where the molar mass of a particle and/or its concentration are unknown. A simple internal test is suggested which checks whether or not sufficient conditions for the applicability of the method are fulfilled.
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    Applied crystallography online 24 (1991), S. 264-264 
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    Applied crystallography online 24 (1991), S. 267-277 
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    Notes: The efficiency of data collection using the Laue technique varies with the wavelength range, the crystal symmetry, the orientation of the crystal in the X-ray beam, the crystal-to-film distance and the acceptance angle of the detector. By optimizing these parameters and by taking advantage of the diffraction symmetry represented by the Laue class, it is often possible to collect a nearly complete data set in one or two exposures. This paper discusses general strategies for data collection and presents results from a computer survey to find optimal crystal orientations for the eleven Laue classes.
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    Applied crystallography online 24 (1991), S. 293-297 
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    Notes: A method for empirical determination of TDS (thermal diffuse scattering) corrections in X-ray structure analysis is developed. Thermal diffuse scattering is introduced into the model suggested earlier [Chulichkov et al. (1987). Sov. Phys. Crystallogr. 32, 649–653; Laktionov, Chulichkov, Chulichkova, Fetisov, Pyt'ev & Aslanov (1989). J. Appl. Cryst. 22, 315–320] for measuring the Bragg reflection intensity profile with a four-circle diffractometer. The improved model in combination with the mathematical reduction method enables the extraction of TDS and background intensity values from the experimental intensity profile. Thus the problem of TDS correction in crystal structure refinement is solved without knowledge of the sample's elasticity constants. The comparison of TDS corrections obtained by this method with those calculated from elasticity constants for hexamethylenetetramine, C6H2N4, and sulfur, S8, crystals shows good agreement.
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    Applied crystallography online 24 (1991), S. 324-330 
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    Notes: The lattice distortion due to the head of the slip band at the grain boundary is measured by double-crystal topography. The head of the slip band is approximated by a macrodislocation situated at the grain boundary. To interpret the topographs, the relaxation due to the free surface is included. The Burgers vectors of macrodislocations, i.e. the number of accumulated dislocations, are found.
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    Applied crystallography online 24 (1991), S. 369-402 
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    Applied crystallography online 24 (1991), S. 406-408 
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    Applied crystallography online 24 (1991), S. 624-634 
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    Notes: Small-angle neutron scattering (SANS) provides a powerful tool in the non-destructive characterization of statistically representative microstructures in technologically important disordered materials. While qualitative microstructural models must be provided by other methods such as transmission electron microscopy (TEM), SANS quantifies the microstructural parameters and can characterize scale-invariant (fractal) disordered materials such as cements, clays and porous rocks. H2O/D2O contrast-variation methods have proved particularly useful for investigating the accessibility of different parts of the pore structure and in differentiating between pore-volume access (measured by other methods) and pore-surface accessibility (likely to control sorption and leaching processes). This paper describes SANS studies of disordered porous materials, particularly the hydration of cement and the real-time permeation of water in clay minerals. Other microstructural effects are also considered.
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    Applied crystallography online 24 (1991), S. 638-644 
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    Notes: The microstructure of a coating deposited onto a tungsten carbide layer by cathodic sputtering assisted by chemical vapour deposition (CVD) has been analysed by small-angle scattering of X-rays (SAXS) with a conventional laboratory set-up specially adapted for grazing incidence. Anomalous-scattering measurements have also been performed at LURE, the French synchrotron-radiation facility at Orsay with the aim of characterizing the structure of phases present in the coating. SAXS results reveal the existence of very small precipitates; the size of these precipitates determined from the use of the Guinier approximation is about 16 Å, the correlation length deduced from the position of the peak in the small-angle scattering pattern is about 36 Å. The value of the experimental integrated intensity and the variation of the observed intensities with photon energy lead to the conclusion that these nanocrystals are highly enriched in tungsten and embedded in a carbon-based matrix having a weak electronic density. Electron diffraction results support the assumption of the presence of β-WC1 − x, an unstable high-temperature phase. Furthermore, the low electronic density of the matrix is in agreement with face-centred-cubic carbon recently proposed in the literature.
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  • 64
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    Applied crystallography online 24 (1991), S. 679-684 
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    Topics: Geosciences , Physics
    Notes: Lamellar microdomains formed in the solvent-cast films of a poly[styrene-block-(ethylene-alt-propylene)] (SEP) diblock polymer were studied by small-angle X-ray scattering (SAXS). The SAXS profiles, displaying a series of peculiar scattering maxima which cannot be ascribed to the higher-order diffraction maxima from a regular lamellar spacing, were analyzed based on a model of the one-dimensional paracrystal with a preferential orientation. The results suggest that these maxima are due to higher-order scattering maxima from single lamellar microdomains. The maxima suggest that the relative standard deviation for the distribution of the polystyrene lamellar size is much smaller than that of the lamellar spacing, giving rise to a situation in which the oscillation of the particle factor with scattering vector h persists up to high h values while that of the lattice factor damps to unity at low h values. The SAXS result was interpreted as being due to a bending distortion of the polystyrene lamella with a smaller thickness and a narrower thickness distribution than those of the poly(ethylene-alt-propylene) lamella. A study by transmission electron microscopy tends to support this result.
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  • 65
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    Applied crystallography online 24 (1991), S. 436-443 
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    Topics: Geosciences , Physics
    Notes: A survey is given of recent work on the use of small-angle neutron scattering to examine colloidal dispersions. Particular attention is given to the determination of particle size and polydispersity, the determination of particle morphology and the behaviour of concentrated colloidal dispersions, both at rest and under the influence of an applied shear field.
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  • 66
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    Applied crystallography online 24 (1991), S. 910-912 
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    Notes: The results of intensity profile analysis of Bragg reflections are used for the calculation of the reflectivity Q(Δθij, σij) = W(Δθij, σij)(|F|2Lp)ij in the energy transfer equation for multiwave X-ray diffraction in crystals. The diffraction profiles in the profile analysis are fitted by different analytical functions and the fitting results are used for modelling the multiwave diffraction. The results of modelling multiwave diffraction in Si and V3Si crystals with different grades of perfection demonstrate that the method suggested here is sensitive to the content of defects in crystals and can be used not only for simultaneous reflection correction in X-ray structure analysis but also for estimation of single-crystal perfection.
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  • 67
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    Applied crystallography online 24 (1991), S. 928-930 
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    Notes: While the deviations from linearity of ε−sin2ψ curves in the case of two welded hot-rolled C40 steel bars were being studied, this paper was prompted by the observation that, at ψ = 0°, the diffraction angle 2θ depends on φ, the inclination angle of the diffraction plane with respect to an arbitrarily chosen reference plane attached to the specimen. This result is unexpected and cannot be explained by bulk structural or microstructural factors. A surface effect is offered as a possible explanation.
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  • 68
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    Applied crystallography online 24 (1991), S. 946-950 
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    Notes: The MOLSCRIPT program produces plots of protein structures using several different kinds of representations. Schematic drawings, simple wire models, ball-and-stick models, CPK models and text labels can be mixed freely. The schematic drawings are shaded to improve the illusion of three dimensionality. A number of parameters affecting various aspects of the objects drawn can be changed by the user. The output from the program is in PostScript format.
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  • 69
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    Applied crystallography online 24 (1991), S. 961-962 
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    Notes: Modifications to the high-stability mounting device for the closed-cycle helium cryostat as developed by Henriksen, Larsen & Rasmussen [J. Appl. Cryst. (1986). 19, 390–394] are described. They allow use of the cryostat on the smaller Huber 511.1 diffractometer circle with a smaller source-to-sample distance and reduced blind and collision zones.
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    Applied crystallography online 24 (1991), S. 972-973 
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  • 71
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    Applied crystallography online 23 (1990), S. 1-5 
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    Notes: The small-angle neutron scattering technique is applied to a hot stretched 5% perdeuterated polystyrene sample in order to investigate the residual macromolecular orientation at various length scales. The observed orientation is left over after fast quenching (in ice water) of the hot stretched sample. Previous investigations focused on how much polymer chains follow the external stretching. It is found that, even when macromolecules follow the external stretching affinely on the average, they do not deform uniformly. Moreover, over the time scale of the temperature quench, small chain portions relax more rapidly than large ones.
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  • 72
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    Applied crystallography online 23 (1990), S. 21-25 
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    Notes: Anisotropic diffuse scattering of the one-dimensional conductor K-hollandite has been measured at a synchrotron source and compared with measurements with a rotating anode. The intensity gain of more than one order of magnitude and the ability to adjust the wavelength provide the counting statistics in a few hours that are necessary for a quantitative analysis of diffuse phenomena. The main advantage of a synchrotron source is the high resolution throughout reciprocal space (low and high Q). Thus, commensurate/incommensurate positions of diffuse layers may be distinguished, weak diffuse maxima become detectable and small peak shifts of diffuse modulations clearly visible. Correlation functions may be determined directly from the diffuse profiles without tedious resolution corrections. These features are essential for a dedicated instrument at a storage ring.
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  • 73
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    Applied crystallography online 23 (1990), S. 73-76 
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    Notes: A new computer program MINREF has been developed for the refinement of neutron powder diffraction patterns as well as single-crystal data corresponding to incommensurate structures. The program is written in VAX Fortran 77 and is of modular construction. The program allows user-desired modifications and permits in the present version simultaneous refinement of the structures of three phases: one commensurate and two incommensurate.
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  • 74
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    Applied crystallography online 23 (1990), S. 78-78 
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    Applied crystallography online 23 (1990), S. 94-98 
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    Notes: A computational method of absorption correction in X-ray diffractometry for single crystals in the shape of convex polyhedra bathed in an inhomogeneous and in a homogeneous X-ray beam is suggested. An absorption correction is calculated for each reflection of the data set using the measured coordinates of the specimen vertices and the experimentally measured intensity distribution in the primary beam. The program ABSCOR is written in Fortran and may be readily adopted to any four-circle diffractometer and data format. The results of the method described for crystals of different dimensions and different absorption coefficients are given. It is shown that beam inhomogeneity strongly influences the reflection intensity of large non-isometric crystals.
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  • 76
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    Applied crystallography online 23 (1990), S. 99-104 
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    Notes: Two computer programs – one for calculation and graphical representation of the azimuthal angle ψ of all possible multiple reflections versus the wavelength λ (PSILAM) and one for the simulation of the Umweganregung-intensity variation during rotation of the crystal about the scattering vector of a `forbidden' or very weak reflection (PSIINT) – have been developed on the basis of the program UMWEG [Rossmanith (1985). Z. Kristallogr. 171, 253–254; (1986). Acta Cryst. A42, 344–348] with emphasis on suitability for inexpensive hardware. Examples of the excellent agreement between measurements and calculations and of the necessity of the combined application of both programs are given.
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    Applied crystallography online 23 (1990), S. 136-137 
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    Notes: A computer program has been written for the determination of crystal-size distribution in a direction perpendicular to an (hkl) crystal plane, from a digitized XRD peak. It implements an information theory approach devised by Guérin, Alvarez, Rebollo Neira, Plastino & Bonetto [Acta Cryst. (1986), A42, 30–35] and Alvarez, Bonetto, Guérin, Plastino & Rebollo Neira [Powder Diffr. (1987), 2, 220–224]. The program has a fully automated operation mode and owing to the very restricted amount of input data this program is specially suited to users with a limited knowledge of crystal-size-determination methods.
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    Applied crystallography online 23 (1990), S. 144-144 
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    Applied crystallography online 23 (1990), S. 151-160 
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    Notes: The thermal and light-induced high-spin (HS: 5T2g) low-spin (LS: 1A1g) transitions of [Fe(ptz)6](BF4)2 (ptz = 1-propyltetrazole) are investigated by X-ray powder diffractometry in the range between ambient temperature and 1̃5 K. The anisotropic lattice deformation caused by variation of the HS fraction and by temperature change was calculated directly from the differences in peak positions of the powder diagrams measured at different temperatures. An analytical expression for the dependence of peak shifts and splittings on the deformation tensor elements was derived. The differences of the lattice deformations accompanying the thermal and light-induced spin transitions are discussed.
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    Applied crystallography online 23 (1990), S. 175-179 
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    Notes: A one-stage He refrigerator (Displex CS1003) has been modified and installed on a quarter-circle Eulerian cradle of 250 mm diameter (AED Siemens) and has been operated down to 50 K. The mechanical interface, which can easily be mounted, is described as well as some alignment problems. The device is suitable for any Eulerian cradle 250 mm or larger. Structure redeterminations of two organic compounds were carried out at 52 K. R values of 2.2 and 3.6% were obtained and proved the quality of this set up.
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    Applied crystallography online 23 (1990), S. 218-221 
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    Notes: A procedure has been developed to incorporate stereo-chemical restraints information for new groups into the dictionary of ideal groups used by the program PROTIN which prepares the input file needed by the reciprocal-space least-squares refinement program PROLSQ. It requires the availability of Cartesian coordinates for the group to be added to the dictionary, usually obtained from crystallographic analysis of crystals of the compound. If no such information is available these coordinates can be generated by an ancillary program, MOLBLD, which makes use of specified bond lengths, bond angles and dihedral angles to produce the required coordinates. The program is written in standard Fortran 77 and has been used in the refinement of several structures.
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    Applied crystallography online 23 (1990), S. 223-224 
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    Applied crystallography online 23 (1990), S. 234-240 
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    Notes: The reproducibility of data collected on a Seimens/ Nicolet area detector has been tested with respect to crystal orientation, X-ray collimation and scaling procedure. In addition, a comparison between area detector data and diffractometer data was made in order to determine the accuracy of the area detector data. The reproducibility of the area detector data, although acceptable, is somewhat affected by crystal orientation (shape effect) and appears to be insensitive to X-ray collimation, contrary to what would be expected. The scaling procedures used in the tests were XENGEN [Howard, Gilliland, Finzel, Poulos, Ohlendorf & Salemme (1987). J. Appl. Cryst. 20, 383–387] (one, two and three parameters), FBSCALE [Weissman (1982). In Computational Crystallography, edited by D. Sayre, pp. 56–63. Oxford: Clarendon Press] and SIMPLAD [Takusagawa (1987). J. Appl. Cryst. 20, 243–245]. It was found that, although these procedures do an adequate job of scaling area detector data, none can totally correct for crystal-shape effects. From our experience, XENGEN multi-parameter or SIMPLAD scaling on data sets having low redundancy must be used with care. When compared to diffractometer data, area detector data scaled by any of the above procedures is in good agreement, with merging R-factors (on F) in the range 3.45 to 4.55%. A plot of 〈Fad〉 versus 〈Fd〉 shows a straight line with slope of 1(3)%. No saturation problems were observed.
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    Applied crystallography online 23 (1990), S. 258-262 
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    Notes: An autoclave cell has been designed for performing time-resolved neutron diffraction analyses of the dynamic processes occurring during hydrothermal syntheses under hostile (corrosive and explosive) conditions: such conditions include those of hot NaOH/NaOD solutions and pressurized steam. The cell is also capable of measuring differential pressures and accurate sample temperatures as required for the study of reactions which are temperature sensitive. The cell is described and examples of its successful use are given illustrating the synthesis of basic zeolites and a layered calcium silicate hydrate. This technique has considerable potential for studying a variety of synthesis processes of industrial importance, such as in the production of catalysts and the hydration of cements.
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    Applied crystallography online 23 (1990), S. 282-285 
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    Notes: A straightforward method for the systematic peak-shift correction using the standard reference material is proposed for the least-squares determination of unit-cell parameters. It requires no pre-determined angle-calibration curve, and the peak-shift correction can be applied simultaneously during the least squares. The procedure, programmed with Fortran 77 statements, has been tested with powder diffractometer data of an α-SiO2 + Si mixture. Advantages of the procedure are: (i) all reflection data from both sample and standard reference material contribute to determining the angle-dependent calibration curve, and (ii) one reflection from the standard reference material suffices for the correction of systematic errors.
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    Applied crystallography online 23 (1990), S. 303-314 
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    Notes: A previously described method of synthesizing a real-space distribution of scattering points which will give rise to virtually any required diffraction pattern has been extended to include the possibility of multiple symmetry-related sites per unit cell. The distribution may be used in the form of an optical diffraction screen to give an immediate visual check on both the real-space and reciprocal-space distributions. The method has been applied successfully to two examples which exhibit strong diffuse X-ray scattering effects: a molecular crystal sample, 1,3-dibromo-2,5-diethyl-4,6-dimethylbenzene (BEMB2), in which disorder occurs because the molecule can take up two different orientations in any given molecular site, and a mineral mullite, Al2(Al2 + 2xSi2 − 2x)O10 − x⊗x, where disorder diffuse scattering occurs as a result of the oxygen vacancies ⊗ and the accompanying cation displacements.
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    Applied crystallography online 23 (1990), S. 334-339 
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    Notes: An automatic diffraction data collection system with an imaging plate has been developed for protein crystallography. The system works in a similar way to the conventional rotation camera method, but in full online mode. After exposure to the X-ray beam, the imaging plate (100 mm radius) rotates whilst a reading head scans across the plate to measure the stimulated luminescence in a record-player-like manner. During the next period of exposure, the image taken immediately before is processed in parallel. The system has been tested using both peptide and protein crystals and has been proven to work successfully.
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    Applied crystallography online 23 (1990), S. 347-348 
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    Notes: TEXCAM is an interactive program designed for IBM PC/XT/AT or compatible personal computers. It constructs schematic simulations which represent diffraction patterns produced by the texture camera. The program can be used to produce patterns from samples which are both polycrystalline and epitaxic in nature. Patterns from polycrystalline samples containing uniaxial texture may also be calculated. An installation program facilitates scaling of the on-screen image allowing texture camera films to be directly superimposed upon the simulation.
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    Applied crystallography online 23 (1990), S. 374-377 
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    Notes: This paper contains information about the Riemannian structure of orientation space which is necessary for the analysis of the rotation rate field, which in turn describes some aspects of the plastic deformation of textured polycrystalline materials. The components of the metric tensor and the connection coefficients in the coordinates used in quantitative texture analysis are given. The relation between the vector components at symmetrically equivalent points and the relation between the frequently used vectors of infinitesimal rotations are presented. The solution of the continuity equation is given for the case of a constant rotation rate field during the deformation process.
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    Applied crystallography online 23 (1990), S. 387-391 
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    Notes: A method for mounting single crystals in macromolecular crystallographic studies is described in which the crystal is suspended in a thin film. The film is formed from a mixture of the crystallization buffer and a hydrophilic viscous material, confined within a thin-wire loop by surface tension. Compared with conventional crystal mounting methods, this method greatly simplifies and speeds the mounting procedure, is well suited to shock freezing and to optical monitoring of the crystals, deforms fragile crystals less and gives a lower and more uniform background in the X-ray diffraction patterns.
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    Applied crystallography online 23 (1990), S. 406-411 
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    Notes: Assessment of the hand of chiral molecular compounds by least-squares refinement of a chirality parameter with all reflections is not statistically robust and can lead to incorrect answers due to a single, unnoticed, gross intensity-measurement error. An alternative is described in which the most easily observable Bijvoet differences are derived from the solved structure and remeasured at slow speed and possibly longer wavelength. Errors due to absorption, multiple reflections and anisotropic extinction can be cancelled out in the measurement for the sense of Bijvoet pairs with the proper experimental technique. An estimate of the probability of having derived the wrong hand, based exclusively on the number of remeasurements and the number of contradictions, and therefore insensitive to individual measurement errors, is developed. With this estimate, determination of the hand of compounds with oxygen as the heaviest scatterer is statistically unambiguous with Cu Kα intensity data, and feasible even with Mo Kα data. Consequently, the method can be applied to Cu Kα data for molecules with carbon as the heaviest scatterer. This approach has been automated as the utility BIVOET in the NRCVAX system of programs.
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    Applied crystallography online 23 (1990), S. 430-430 
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    Notes: A typsetting error in the paper by Abrahams, Liminga & Albertsson [J. Appl. Cryst. (1990). 23, 211–222] is corrected. On page 212, the first sentence of the second paragraph should read: However, the Miller indices given by Rosenzweig & Morosin's (1966) coordinates result in an opposite sense assignment for the polar c-axis direction and Yang Hua-guang et al. (1989) hence confused (hk.l) with ({\bar h}{\bar k}.{\bar l}).
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    Applied crystallography online 23 (1990), S. 439-440 
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    Notes: With the recent improvement of high-pressure technology, in particular the diamond-anvil cell, an ever-increasing number of studies are appearing which relate unit-cell parameters (as measured by X-ray diffraction) to the applied pressure.
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    Applied crystallography online 23 (1990), S. 445-445 
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    Applied crystallography online 23 (1990), S. 447-457 
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    Notes: This paper is a review of the symmetry and connectivity of composite materials with particular emphasis on the effect that these have on composite properties. Analogies are drawn between composites and crystal structures to demonstrate the similarities between microscopic and macroscopic connectivity. A notation for composite transitions which can be used to describe changes in symmetry and connectivity is also presented.
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    Applied crystallography online 23 (1990), S. 469-475 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small- and intermediate-angle neutron scattering studies have been undertaken on mixtures of deuterated and protonated poly(ethylene terephthalate) (PET) molecules with a wide range of concentration. The samples were converted to random copolymers by transesterifying in the melt, thus removing the coherent component of the intensity associated with single-chain scattering. The transesterified samples were used to determine the level of incoherent scattering associated with each isotopic mixture which was compared with estimates from established background-correction techniques based on extra-polating from the scattering of fully protonated or deuterated blanks. Scaling via the measured sample transmission works well for predominantly protonated mixtures but fails when the fraction of deuterated polymer exceeds φD 0̃.6. Scaling via the component of the sample transmission attributable to the incoherent scattering from H nuclei works well over the whole concentration range. This method involves calculations of the sample transmission via the bound-atom cross section and this is a good approximation at the wavelength employed (λ 4̃.75 Å), where the hydrogen incoherent cross section is close to the bound-atom cross section (σH 8̃0 × 10−28 m2). However, σH is a strong function of wavelength and the method cannot be used where the measured and calculated transmissions diverge. A recently developed theory describing the scattering from random copolymers was used to analyze the residual coherent cross section of the copolymers and led to a statistical segment length b = 14.3 ± 1 Å, in good agreement with existing values for PET.
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  • 97
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 515-519 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The phase transformation from NaCl structure (B 1) to CsCl structure (B2) in actinide compounds has been studied using X-ray powder diffraction in the pressure range up to about 60 GPa. It is shown that the transition is sluggish, has a strong hysteresis and is accompanied by a volume change in the range 8–12%. These features are similar to those of the corresponding transition in the alkali halides and other B1 compounds, indicating a common mechanism for the transformation as concerns the lattice geometry.
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  • 98
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 545-549 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The design of a new microfurnace for use for Laue diffraction studies of solid-state transformations is described. The furnace operates in the temperature range 298–573 K with a thermal stability of about ± 0.1 K. The potential of the synchrotron-radiation Laue diffraction technique for studies of structural phase transitions is demonstrated. Experimental data on phase transitions in caesium periodate, potassium tetrachlorozincate and pentaerythritol are presented.
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  • 99
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 558-559 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 554-557 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: MXD is a new least-squares program for non-standard crystallographic refinement. It uses an original procedure of formula management that is derived from up-to-date compiler programming techniques. While still offering all the least-squares possibilities of most traditional programs, e.g. SHELX, SDP, XRAY etc., MXD has been fully designed for complex crystallographic, magnetic and/or modulated structure refinement. The user enters all the specific formulae describing his own problem into the input data file. Thus, MXD is very convenient when dealing with very complex problems including fitting of modulated structures (magnetic and/or charge density wave), twin or magnetic domain distribution and severe secondary extinction correction. Moreover, if the experimental data are accurate enough (especially from using polarized neutrons), form-factor fitting is accessible. Independently collected data, using various wavelengths, powder or/and single-crystal data, polarized and unpolarized neutron information etc., can be treated simultaneously.
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