http://journals.iucr.org/j/issues/2009/02/00/isscontsbdy.html Journal of Applied Crystallography covers a wide range of crystallographic topics from the viewpoints of both techniques and theory. The journal presents papers on the application of crystallographic techniques and on the related apparatus and computer software. For many years, the Journal of Applied Crystallography has been the main vehicle for the publication of small-angle scattering papers and powder diffraction techniques. The journal is the primary place where crystallographic computer program information is published. Recent additions are a Cryocrystallography Papers section and a Software Reviews section. en Copyright (c) 2009 International Union of Crystallography 2009-04-01 International Union of Crystallography International Union of Crystallography http://journals.iucr.org urn:issn:0021-8898 Journal of Applied Crystallography covers a wide range of crystallographic topics from the viewpoints of both techniques and theory. The journal presents papers on the application of crystallographic techniques and on the related apparatus and computer software. For many years, the Journal of Applied Crystallography has been the main vehicle for the publication of small-angle scattering papers and powder diffraction techniques. The journal is the primary place where crystallographic computer program information is published. Recent additions are a Cryocrystallography Papers section and a Software Reviews section. text/html Journal of Applied Crystallography, Volume 42, Part 2, 2009 text yearly 6 2002-02-01T00:00+00:00 2 42 2009-04-01 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography 153 urn:issn:0021-8898 med@iucr.org April 2009 2009-04-01 http://journals.iucr.org/logos/rss10j.gif http://journals.iucr.org/j/issues/2009/02/00/isscontsbdy.html Still image http://scripts.iucr.org/cgi-bin/paper?ks5195 Selected compositions of the Ba–Sr–Co–Fe–O system were synthesized from powders by the solid-state reaction method. Samples were equilibrated at 1273 K for 36 000 s in air. The resulting powders were characterized by X-ray diffraction (XRD) at room temperature and by high-temperature in situ XRD. The phases present in the BaxSr1−xCoyFe1−yO3−δ system are outlined for 1273 K in air. For most of the quaternary compositions, the cubic perovskite is formed, except for the compositions with x = 1 (excluding y = 0.4), y = 1 and x, y = 0.8, where the phases mainly show hexagonal distortions, and x, y = 0, for which a predominant cubic phase is mixed with other phases. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Yáng, Z. Harvey, A.S. Infortuna, A. Gauckler, L.J. 2009-02-03 doi:10.1107/S0021889809002040 International Union of Crystallography An isothermal phase map for the Ba–Sr–Co–Fe–O system is proposed. en BSCF perovskites mixed ionic–electronic conductors solid oxide fuel cell cathodes ceramic materials Selected compositions of the Ba–Sr–Co–Fe–O system were synthesized from powders by the solid-state reaction method. Samples were equilibrated at 1273 K for 36 000 s in air. The resulting powders were characterized by X-ray diffraction (XRD) at room temperature and by high-temperature in situ XRD. The phases present in the BaxSr1−xCoyFe1−yO3−δ system are outlined for 1273 K in air. For most of the quaternary compositions, the cubic perovskite is formed, except for the compositions with x = 1 (excluding y = 0.4), y = 1 and x, y = 0.8, where the phases mainly show hexagonal distortions, and x, y = 0, for which a predominant cubic phase is mixed with other phases. text/html Phase relations in the Ba–Sr–Co–Fe–O system at 1273 K in air text 2 42 2009-02-03 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 153 160 http://scripts.iucr.org/cgi-bin/paper?ko5075 Small-angle neutron scattering (SANS) analysis was performed to investigate the miscibility of blends of metallocene-catalyzed octene linear low-density polyethylene (octene-mLLDPE) and low-density polyethylene (LDPE). The quantitative SANS analysis found that the blends are miscible in both the melt and the quenched states. Moreover, this analysis confirmed that the radii of gyration of octene-mLLDPE(D) and LDPE(H) remain unchanged in the quenched state and that the two polymer components cocrystallize via fast crystallization from the melt state. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Shin, T.J. Lee, B. Lee, J. Jin, S. Sung, B.S. Han, Y.S. Lee, C.-H. Stein, R.S. Ree, M. 2009-02-07 doi:10.1107/S0021889809002854 International Union of Crystallography The miscibility of octene-mLLDPE(D)/LDPE(H) blends was studied with small-angle neutron and X-ray scattering techniques. It was found that the blends are miscible in both the melt and the quenched states, and two polymer components are cocrystallized via fast crystallization from the melt state. en small-angle neutron scattering (SANS) small-angle X-ray scattering (SAXS) octene-mLLDPE/LDPE blends melt state solid state miscibility radius of gyration cocrystallization Small-angle neutron scattering (SANS) analysis was performed to investigate the miscibility of blends of metallocene-catalyzed octene linear low-density polyethylene (octene-mLLDPE) and low-density polyethylene (LDPE). The quantitative SANS analysis found that the blends are miscible in both the melt and the quenched states. Moreover, this analysis confirmed that the radii of gyration of octene-mLLDPE(D) and LDPE(H) remain unchanged in the quenched state and that the two polymer components cocrystallize via fast crystallization from the melt state. text/html Small-angle neutron scattering study of the miscibility of metallocene-catalyzed octene linear low-density polyethylene and low-density polyethylene blends text 2 42 2009-02-07 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 161 168 http://scripts.iucr.org/cgi-bin/paper?kk5028 In vivo, some proteins exist as monomers (single polypeptide chains) and others as oligomers. The latter are composed of two or more chains (subunits) that are associated with each other through noncovalent interactions and, occasionally, disulfide bonds. Oligomers can be further classified into homo-oligomers (formed by identical subunits) and hetero-oligomers (formed by different subunits), and they form the structural basis of various biological functions such as cooperative effects, the allosteric mechanism and ion-channel gating. Therefore, it would be of less interest or of low priority for crystallographic scientists to crystallize a single protein chain and determine its three-dimensional structure if it is already known as part of an oligomer. However, it is both time-consuming and laborious to acquire such information on the quaternary structure attribute purely by experiment. In particular, with the avalanche of protein sequences generated in the post-genomic age, it is highly desirable to develop an automated method by which crystallographic scientists can rapidly and effectively identify which quaternary attribute a particular protein chain has according to its sequence information. In view of this, a computational method has been developed by hybridizing the approaches of functional domain composition and pseudo amino acid composition. For the convenience of crystallographic scientists, a user-friendly web server, PQSA-Pred, has been established at http://218.65.61.89:8080/bioinfo/pqsa-pred, by which the desired information can be easily obtained. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Xiao, X. Wang, P. Chou, K.-C. 2009-02-14 doi:10.1107/S0021889809002751 International Union of Crystallography A user friendly web server, called PQSA-Pred, has been established at http://218.65.61.89:8080/bioinfo/pqsa-pred, by which one can predict the quaternary structural attributes of proteins according to their sequence information alone. en PQSA-Pred SMART FunD composition PseAA composition complexity measurement factors nearest neighbor algorithms jackknife test In vivo, some proteins exist as monomers (single polypeptide chains) and others as oligomers. The latter are composed of two or more chains (subunits) that are associated with each other through noncovalent interactions and, occasionally, disulfide bonds. Oligomers can be further classified into homo-oligomers (formed by identical subunits) and hetero-oligomers (formed by different subunits), and they form the structural basis of various biological functions such as cooperative effects, the allosteric mechanism and ion-channel gating. Therefore, it would be of less interest or of low priority for crystallographic scientists to crystallize a single protein chain and determine its three-dimensional structure if it is already known as part of an oligomer. However, it is both time-consuming and laborious to acquire such information on the quaternary structure attribute purely by experiment. In particular, with the avalanche of protein sequences generated in the post-genomic age, it is highly desirable to develop an automated method by which crystallographic scientists can rapidly and effectively identify which quaternary attribute a particular protein chain has according to its sequence information. In view of this, a computational method has been developed by hybridizing the approaches of functional domain composition and pseudo amino acid composition. For the convenience of crystallographic scientists, a user-friendly web server, PQSA-Pred, has been established at http://218.65.61.89:8080/bioinfo/pqsa-pred, by which the desired information can be easily obtained. text/html Predicting the quaternary structure attribute of a protein by hybridizing functional domain composition and pseudo amino acid composition text 2 42 2009-02-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 169 173 http://scripts.iucr.org/cgi-bin/paper?fe5049 With the demand for higher rates of discovery in the materials field, characterization techniques that are capable of rapidly and reliably surveying the characteristics of large numbers of samples are essential. A chemical combinatorial approach using thin films can provide detailed phase diagrams without the need to produce multiple, individual samples. This is achieved with compositional gradients forming high-density libraries. Conventional raster scanning of chemical or structural probes is subsequently used to interrogate the libraries. A new, alternative approach to raster scanning is introduced to provide a method of high-throughput data collection and analysis using an X-ray diffraction probe. Libraries are interrogated with an extended X-ray source and the scattering data collected using an area detector. A simple technique of `partitioning' this scattering distribution enables determination of information comparable to conventional raster scanned results but in a dramatically reduced collection time. The technique has been tested using synthetic X-ray scattering distributions and those obtained from contrived samples. In all cases, the partitioning algorithm is shown to be robust and to provide reliable data; discrimination along the library principal axis is shown to be ∼500 µm and the lattice parameter resolution to be ∼10−3 Å mm−1. The limitations of the technique are discussed and future potential applications described. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Roncallo, S. Karimi, O. Rogers, K.D. Lane, D.W. Ansari, S.A. 2009-02-27 doi:10.1107/S0021889809003227 International Union of Crystallography An initial report is presented of a high-throughput X-ray diffraction method, combining simultaneous data collection of multiple diffraction patterns with the electronic partitioning required to calculate lattice parameter information for the individual samples. en X-ray diffraction high throughput combinatorial techniques thin films With the demand for higher rates of discovery in the materials field, characterization techniques that are capable of rapidly and reliably surveying the characteristics of large numbers of samples are essential. A chemical combinatorial approach using thin films can provide detailed phase diagrams without the need to produce multiple, individual samples. This is achieved with compositional gradients forming high-density libraries. Conventional raster scanning of chemical or structural probes is subsequently used to interrogate the libraries. A new, alternative approach to raster scanning is introduced to provide a method of high-throughput data collection and analysis using an X-ray diffraction probe. Libraries are interrogated with an extended X-ray source and the scattering data collected using an area detector. A simple technique of `partitioning' this scattering distribution enables determination of information comparable to conventional raster scanned results but in a dramatically reduced collection time. The technique has been tested using synthetic X-ray scattering distributions and those obtained from contrived samples. In all cases, the partitioning algorithm is shown to be robust and to provide reliable data; discrimination along the library principal axis is shown to be ∼500 µm and the lattice parameter resolution to be ∼10−3 Å mm−1. The limitations of the technique are discussed and future potential applications described. text/html An approach to high-throughput X-ray diffraction analysis of combinatorial polycrystalline thin film libraries text 2 42 2009-02-27 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 174 178 http://scripts.iucr.org/cgi-bin/paper?db5056 The implementation of a new soft chemical constraint for the reverse Monte Carlo (RMC) program RMCProfile, based on bond valence sum (BVS) calculations, is described and its advantages for the analysis of `total scattering' diffraction data collected from disordered crystalline systems discussed. The inclusion of the BVS formalism proves particularly valuable in the early stages of the RMC fitting procedure, by avoiding the formation of regions containing chemically unreasonable local configurations which can become frozen in. Furthermore, this approach provides the fitting procedure with additional chemical information to differentiate between cation species that share the same crystallographic sites within the averaged unit cell and possess similar neutron scattering lengths. These issues are illustrated using total neutron scattering data collected at room temperature on the oxide-ion conductor Zr2Y2O7 and the nonlinear optical material KTiOPO4. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Norberg, S.T. Tucker, M.G. Hull, S. 2009-02-27 doi:10.1107/S0021889809004981 International Union of Crystallography The implementation and demonstration of a soft chemical constraint, based on bond valence calculations, for the reverse Monte Carlo program RMCProfile is reported. en reverse Monte Carlo techniques RMCProfile bond valence sums soft chemical constraints total scattering local crystalline disorder The implementation of a new soft chemical constraint for the reverse Monte Carlo (RMC) program RMCProfile, based on bond valence sum (BVS) calculations, is described and its advantages for the analysis of `total scattering' diffraction data collected from disordered crystalline systems discussed. The inclusion of the BVS formalism proves particularly valuable in the early stages of the RMC fitting procedure, by avoiding the formation of regions containing chemically unreasonable local configurations which can become frozen in. Furthermore, this approach provides the fitting procedure with additional chemical information to differentiate between cation species that share the same crystallographic sites within the averaged unit cell and possess similar neutron scattering lengths. These issues are illustrated using total neutron scattering data collected at room temperature on the oxide-ion conductor Zr2Y2O7 and the nonlinear optical material KTiOPO4. text/html Bond valence sum: a new soft chemical constraint for RMCProfile text 2 42 2009-02-27 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 179 184 http://scripts.iucr.org/cgi-bin/paper?ko5074 The stress–strain relation presented by Tanaka, Akiniwa, Ito & Inoue [Jpn Soc. Mech. Eng. Int. J. Ser. A, (1999), 42, 224–234] for X-ray stress analysis for polycrystalline specimens with fibre texture is re-examined. By introducing the symmetry of reciprocal lattices for constituent crystallites, the physical meaning of taking an average of the strains observed by X-ray diffraction and the validity of the approximation used are made clear. By applying the present treatment to a cubic specimen in the m{\overline 3}m point group, hkl Bragg reflections with h ≠ k ≠ l split into doublets owing to the existence of crystallites with two different orientations. The formulae derived for cubic polycrystalline specimens with 〈111〉 fibre texture in the biaxial state in the Reuss model are in good agreement with those given previously. This technique is applicable to polycrystalline specimens of any symmetry with fibre texture. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Yokoyama, R. Harada, J. 2009-03-05 doi:10.1107/S0021889809003409 International Union of Crystallography The stress–strain relation used in X-ray stress analysis for polycrystalline specimens with fibre texture is re-examined by taking into account the symmetry of the reciprocal lattice (Laue class) of the constituent crystallites. The treatment is applicable to any polycrystalline specimen in any Laue class. en residual stress fibre texture Laue classes The stress–strain relation presented by Tanaka, Akiniwa, Ito & Inoue [Jpn Soc. Mech. Eng. Int. J. Ser. A, (1999), 42, 224–234] for X-ray stress analysis for polycrystalline specimens with fibre texture is re-examined. By introducing the symmetry of reciprocal lattices for constituent crystallites, the physical meaning of taking an average of the strains observed by X-ray diffraction and the validity of the approximation used are made clear. By applying the present treatment to a cubic specimen in the m{\overline 3}m point group, hkl Bragg reflections with h ≠ k ≠ l split into doublets owing to the existence of crystallites with two different orientations. The formulae derived for cubic polycrystalline specimens with 〈111〉 fibre texture in the biaxial state in the Reuss model are in good agreement with those given previously. This technique is applicable to polycrystalline specimens of any symmetry with fibre texture. text/html Re-evaluation of formulae for X-ray stress analysis in polycrystalline specimens with fibre texture text 2 42 2009-03-05 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 185 191 http://scripts.iucr.org/cgi-bin/paper?cg5091 A method is outlined that allows the determination of one-dimensional stress gradients at length scales greater than 0.2 mm. By using standard four-circle X-ray diffractometer equipment and simple aperture components, length resolutions down to 0.05 mm in one direction can be achieved through constant orientation of a narrow, line-shaped beam spot. Angle calculations are given for the adjustment of goniometer angles, and for the effective azimuth and tilt of the scattering vector for general angle settings in a four-circle goniometer. The latter is necessary for the computation of stresses from lattice strain measurements. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Gnäupel-Herold, T. 2009-03-05 doi:10.1107/S0021889809004300 International Union of Crystallography This work presents angle calculations necessary for orienting line-shaped beam spots and for calculating effective azimuth and tilt angles for residual stress determination in a four-circle goniometer. en stress gradients beam-spot orientation angle calculation A method is outlined that allows the determination of one-dimensional stress gradients at length scales greater than 0.2 mm. By using standard four-circle X-ray diffractometer equipment and simple aperture components, length resolutions down to 0.05 mm in one direction can be achieved through constant orientation of a narrow, line-shaped beam spot. Angle calculations are given for the adjustment of goniometer angles, and for the effective azimuth and tilt of the scattering vector for general angle settings in a four-circle goniometer. The latter is necessary for the computation of stresses from lattice strain measurements. text/html Formalism for the determination of intermediate stress gradients using X-ray diffraction text 2 42 2009-03-05 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 192 197 http://scripts.iucr.org/cgi-bin/paper?ks5167 The microstructural characteristics of solid solutions, prepared by heating dried gel precursors with nominal compositions VxZr1−xO2 (0 ≤ x ≤ 0.1) at 723 and 1573 K, were determined from X-ray diffraction patterns. The crystalline microstructure of the resulting specimens, characterized by a prevalent crystallite shape, a volume-weighted crystallite size distribution and a second-order lattice strain distribution, was found to depend on the vanadium content. A characteristic feature of all size distributions was their bimodality, explained as a result of transformations between tetragonal and monoclinic phases during thermal treatment. A comparative study of the microstructure of both zirconia phases has been carried out, enabling reconstruction of a probable course of crystallization of both pure and vanadium-doped zirconias: on heating a sample, nucleation and the early growth stages involve crystallites of both phases; then on annealing and cooling, the crystallites of one phase transform into the other, depending on the thermal treatment temperature. Each logarithmic normal component of the crystallite size distribution of the resulting phase can be attributed to one of these processes. The limit of solubility of vanadium in tetragonal and monoclinic zirconia is estimated from the microstructural characteristics. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Kojdecki, M.A. Ruiz de Sola, E. Serrano, F.J. Amigó, J.M. Alarcón, J. 2009-03-14 doi:10.1107/S0021889809005135 International Union of Crystallography Thermal treatment of gel precursors with initial compositions VxZr1−xO2 (0 ≤ x ≤ 0.1), with a final annealing temperature of 723 or 1573 K, resulted in a major tetragonal or pure monoclinic zirconia phase. Each pure or vanadium-doped zirconia specimen is characterized by a prevalent crystallite shape, a volume-weighted crystallite size distribution and a second-order crystalline lattice strain distribution. en vanadium-doped zirconium dioxide crystalline microstructure powder pattern analysis line profile analysis volume-weighted crystallite size distribution second-order crystalline lattice strain distribution crystallite shape The microstructural characteristics of solid solutions, prepared by heating dried gel precursors with nominal compositions VxZr1−xO2 (0 ≤ x ≤ 0.1) at 723 and 1573 K, were determined from X-ray diffraction patterns. The crystalline microstructure of the resulting specimens, characterized by a prevalent crystallite shape, a volume-weighted crystallite size distribution and a second-order lattice strain distribution, was found to depend on the vanadium content. A characteristic feature of all size distributions was their bimodality, explained as a result of transformations between tetragonal and monoclinic phases during thermal treatment. A comparative study of the microstructure of both zirconia phases has been carried out, enabling reconstruction of a probable course of crystallization of both pure and vanadium-doped zirconias: on heating a sample, nucleation and the early growth stages involve crystallites of both phases; then on annealing and cooling, the crystallites of one phase transform into the other, depending on the thermal treatment temperature. Each logarithmic normal component of the crystallite size distribution of the resulting phase can be attributed to one of these processes. The limit of solubility of vanadium in tetragonal and monoclinic zirconia is estimated from the microstructural characteristics. text/html Comparative X-ray diffraction study of the crystalline microstructure of tetragonal and monoclinic vanadium–zirconium dioxide solid solutions produced from gel precursors text 2 42 2009-03-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 198 210 http://scripts.iucr.org/cgi-bin/paper?ko5078 The diffraction intensity distributions for orthorhombic crystals containing the ordered twin boundaries of the system (110), 〈1{\overline 1}0〉 were calculated in the kinematic approach using the Monte Carlo computer simulation technique. A simple model of short-range order in the arrangement of the twin boundaries was assumed to generate the nano-twinned structure. Analysis of the intensity distributions showed that such a twin boundary distribution results in the formation of extra peaks along the reciprocal lattice rods that are perpendicular to the close-packed planes. These extra peak intensities and positions are dependent on the most probable distances between the twin boundaries and on the degree of short-range order. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Ustinov, A. Olikhovska, L. Glavatska, N. Glavatskyy, I. 2009-03-14 doi:10.1107/S0021889809007171 International Union of Crystallography The intensity distributions from an orthorhombic single crystal containing twin boundaries (110), 〈1{\overline 1}0〉 that tend to short-range order were simulated in the reciprocal lattice space using Monte Carlo techniques. en Ni–Mn–Ga modulated structures nano-twins diffraction The diffraction intensity distributions for orthorhombic crystals containing the ordered twin boundaries of the system (110), 〈1{\overline 1}0〉 were calculated in the kinematic approach using the Monte Carlo computer simulation technique. A simple model of short-range order in the arrangement of the twin boundaries was assumed to generate the nano-twinned structure. Analysis of the intensity distributions showed that such a twin boundary distribution results in the formation of extra peaks along the reciprocal lattice rods that are perpendicular to the close-packed planes. These extra peak intensities and positions are dependent on the most probable distances between the twin boundaries and on the degree of short-range order. text/html Diffraction features due to ordered distribution of twin boundaries in orthorhombic Ni–Mn–Ga crystals text 2 42 2009-03-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 211 216 http://scripts.iucr.org/cgi-bin/paper?do5044 The successful use is reported of a particle-swarm optimization algorithm to design a focusing, multi-channel neutron guide for the measurement of millimetre- and sub-millimetre-sized samples. For a 5 Å incident neutron wavelength on an IN5-type instrument, this results in a ninefold gain in the peak neutron count rate, and around an eightfold average gain in the count rate over the crucial 3–6 Å wavelength range, averaged over a 2 × 2 mm sample. A particle swarm method and a genetic algorithm were compared for simple neutron flux maximization, and the particle swarm was found to be faster for these kinds of problems. The focusing device was then designed by coupling the particle swarm algorithm to a full Monte Carlo neutron ray-tracing system. This realizes the `holy grail' of autonomous, self-optimizing virtual neutron devices based on life processes. The end result is superior to the manual (human) design of a focusing guide, and the design can be entirely re-optimized within a few days if the design requirements for a specific instrument should change. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Bentley, P.M. Andersen, K.H. 2009-02-14 doi:10.1107/S0021889809003483 International Union of Crystallography The design and optimization of focusing neutron guide elements using swarm intelligence are described. A large gain in performance is observed compared with the best human designs for complex devices. en neutron instrumentation focusing neutron guide elements artificial intelligence The successful use is reported of a particle-swarm optimization algorithm to design a focusing, multi-channel neutron guide for the measurement of millimetre- and sub-millimetre-sized samples. For a 5 Å incident neutron wavelength on an IN5-type instrument, this results in a ninefold gain in the peak neutron count rate, and around an eightfold average gain in the count rate over the crucial 3–6 Å wavelength range, averaged over a 2 × 2 mm sample. A particle swarm method and a genetic algorithm were compared for simple neutron flux maximization, and the particle swarm was found to be faster for these kinds of problems. The focusing device was then designed by coupling the particle swarm algorithm to a full Monte Carlo neutron ray-tracing system. This realizes the `holy grail' of autonomous, self-optimizing virtual neutron devices based on life processes. The end result is superior to the manual (human) design of a focusing guide, and the design can be entirely re-optimized within a few days if the design requirements for a specific instrument should change. text/html Optimization of focusing neutronic devices using artificial intelligence techniques text 2 42 2009-02-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 217 224 http://scripts.iucr.org/cgi-bin/paper?he5429 Vaterite is one of three polymorphs of calcium carbonate (CaCO3) found in nature, the others being calcite and aragonite. Here the formation of vaterite from decomposition of ikaite (CaCO3·6H2O) was investigated using synchrotron powder diffraction and scanning electron microscopy. The crystallite sizes of vaterite (∼40 nm) were found to be much smaller than those of the precursor ikaite (∼0.5–1.0 µm) as a result of vaterite nucleating as ikaite dehydrates. The rate of decomposition to vaterite increases with temperature, indicating kinetic control of this transformation. It is postulated that the structural arrangement of the hydration sphere around Ca2+ in ikaite determines the orientation of Ca2+ and CO32− ions such that vaterite nucleates upon dehydration. This implies that the dehydration of a precursor hydrated phase such as ikaite is required for vaterite nucleation. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Tang, C.C. Thompson, S.P. Parker, J.E. Lennie, A.R. Azough, F. Kato, K. 2009-02-27 doi:10.1107/S0021889809005810 International Union of Crystallography The ikaite–vaterite transformation was observed in polycrystalline samples during dehydration. Although the original ikaite morphology is retained following dehydration, development of domain structure is observed in individual crystallites. A structural model is developed to describe the transformation to vaterite. en vaterite ikaite calcium carbonate Vaterite is one of three polymorphs of calcium carbonate (CaCO3) found in nature, the others being calcite and aragonite. Here the formation of vaterite from decomposition of ikaite (CaCO3·6H2O) was investigated using synchrotron powder diffraction and scanning electron microscopy. The crystallite sizes of vaterite (∼40 nm) were found to be much smaller than those of the precursor ikaite (∼0.5–1.0 µm) as a result of vaterite nucleating as ikaite dehydrates. The rate of decomposition to vaterite increases with temperature, indicating kinetic control of this transformation. It is postulated that the structural arrangement of the hydration sphere around Ca2+ in ikaite determines the orientation of Ca2+ and CO32− ions such that vaterite nucleates upon dehydration. This implies that the dehydration of a precursor hydrated phase such as ikaite is required for vaterite nucleation. text/html The ikaite-to-vaterite transformation: new evidence from diffraction and imaging text 2 42 2009-02-27 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 225 233 http://scripts.iucr.org/cgi-bin/paper?cg5097 Electron backscatter diffraction (EBSD) is a scanning electron microscope-based technique principally used for the determination and mapping of crystal orientation. This work describes an adaptation of the EBSD technique into a potential tool for crystal phase determination. The process can be distilled into three steps: (1) extracting a triclinic cell from a single EBSD pattern, (2) identifying the crystal symmetry from an examination of the triclinic cell, and (3) determining the lattice parameters. The triclinic cell is determined by finding the bands passing through two zone axes in the pattern including a band connecting the two. A three-dimensional triclinic unit cell is constructed based on the identified bands. The EBSD pattern is indexed in terms of the triclinic cell thus formed and the crystal orientation calculated. The pattern indexing results in independent multiple orientations due to the symmetry the crystal actually possesses. By examining the relationships between these multiple orientations, the crystal system is established. By comparing simulated Kikuchi bands with the pattern the lattice parameters can be determined. Details of the method are given for a test case of EBSD patterns obtained from the hexagonal phase of titanium. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Dingley, D.J. Wright, S.I. 2009-01-24 doi:10.1107/S0021889809001654 International Union of Crystallography A novel method for extracting the crystal symmetry and unit-cell parameters from electron backscatter diffraction patterns is described. en electron backscatter diffraction unit-cell determination Electron backscatter diffraction (EBSD) is a scanning electron microscope-based technique principally used for the determination and mapping of crystal orientation. This work describes an adaptation of the EBSD technique into a potential tool for crystal phase determination. The process can be distilled into three steps: (1) extracting a triclinic cell from a single EBSD pattern, (2) identifying the crystal symmetry from an examination of the triclinic cell, and (3) determining the lattice parameters. The triclinic cell is determined by finding the bands passing through two zone axes in the pattern including a band connecting the two. A three-dimensional triclinic unit cell is constructed based on the identified bands. The EBSD pattern is indexed in terms of the triclinic cell thus formed and the crystal orientation calculated. The pattern indexing results in independent multiple orientations due to the symmetry the crystal actually possesses. By examining the relationships between these multiple orientations, the crystal system is established. By comparing simulated Kikuchi bands with the pattern the lattice parameters can be determined. Details of the method are given for a test case of EBSD patterns obtained from the hexagonal phase of titanium. text/html Determination of crystal phase from an electron backscatter diffraction pattern text 2 42 2009-01-24 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 234 241 http://scripts.iucr.org/cgi-bin/paper?hx5080 Odd electron diffraction patterns (EDPs) have been obtained by transmission electron microscopy (TEM) on silicon nanowires grown via the vapour–liquid–solid method and on silicon thin films deposited by electron beam evaporation. Many explanations have been given in the past, without consensus among the scientific community: size artifacts, twinning artifacts or, more widely accepted, the existence of new hexagonal Si phases. In order to resolve this issue, the microstructures of Si nanowires and Si thin films have been characterized by TEM, high-resolution transmission electron microscopy (HRTEM) and high-resolution scanning transmission electron microscopy. Despite the differences in the geometries and elaboration processes, the EDPs of the materials show great similarities. The different hypotheses reported in the literature have been investigated. It was found that the positions of the diffraction spots in the EDPs could be reproduced by simulating a hexagonal structure with c/a = 12(2/3)1/2, but the intensities in many EDPs remained unexplained. Finally, it was established that all the experimental data, i.e. EDPs and HRTEM images, agree with a classical cubic silicon structure containing two microstructural defects: (i) overlapping Σ3 microtwins which induce extra spots by double diffraction, and (ii) nanotwins which induce extra spots as a result of streaking effects. It is concluded that there is no hexagonal phase in the Si nanowires and the Si thin films presented in this work. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Cayron, C. Den Hertog, M. Latu-Romain, L. Mouchet, C. Secouard, C. Rouviere, J.-L. Rouviere, E. Simonato, J.-P. 2009-01-24 doi:10.1107/S0021889808042131 International Union of Crystallography Anomalous extra spots visible in electron diffraction patterns of silicon nanowires and silicon thin films are explained by the presence of micro- and nanotwins. en silicon nanowires silicon thin films artifacts twinning Odd electron diffraction patterns (EDPs) have been obtained by transmission electron microscopy (TEM) on silicon nanowires grown via the vapour–liquid–solid method and on silicon thin films deposited by electron beam evaporation. Many explanations have been given in the past, without consensus among the scientific community: size artifacts, twinning artifacts or, more widely accepted, the existence of new hexagonal Si phases. In order to resolve this issue, the microstructures of Si nanowires and Si thin films have been characterized by TEM, high-resolution transmission electron microscopy (HRTEM) and high-resolution scanning transmission electron microscopy. Despite the differences in the geometries and elaboration processes, the EDPs of the materials show great similarities. The different hypotheses reported in the literature have been investigated. It was found that the positions of the diffraction spots in the EDPs could be reproduced by simulating a hexagonal structure with c/a = 12(2/3)1/2, but the intensities in many EDPs remained unexplained. Finally, it was established that all the experimental data, i.e. EDPs and HRTEM images, agree with a classical cubic silicon structure containing two microstructural defects: (i) overlapping Σ3 microtwins which induce extra spots by double diffraction, and (ii) nanotwins which induce extra spots as a result of streaking effects. It is concluded that there is no hexagonal phase in the Si nanowires and the Si thin films presented in this work. text/html Odd electron diffraction patterns in silicon nanowires and silicon thin films explained by microtwins and nanotwins text 2 42 2009-01-24 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 242 252 http://scripts.iucr.org/cgi-bin/paper?cg5086 This paper reports the accurate measurement of the ReO3 cell parameter as a function of temperature. The thermal expansion is confirmed to be negative over most of the temperature range from 5 to 300 K. The main problems with the measurements are the very small variations (in the range of 10−5 Å) in the cell parameter at each temperature, requiring tight control of the stability and reliability of instrumental effects. In particular, achieving monochromator stability over time might be challenging with the high energy and high beam current variations of a third-generation synchrotron facility. On the other hand, such effects are usually checked by the addition of silicon as an internal standard, but the accuracy (and precision) of the published thermal expansion (which is not certified) might not be sufficient for its use when dealing with very small cell parameter variations. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Dapiaggi, M. Fitch, A.N. 2009-02-03 doi:10.1107/S002188980804332X International Union of Crystallography The very small negative thermal expansion of ReO3 below room temperature has been confirmed from careful high-resolution powder diffraction measurements. The systematic errors that can arise when using synchrotron radiation for such studies are considered. en low thermal expansion instrumental errors rhenium(VI) oxide This paper reports the accurate measurement of the ReO3 cell parameter as a function of temperature. The thermal expansion is confirmed to be negative over most of the temperature range from 5 to 300 K. The main problems with the measurements are the very small variations (in the range of 10−5 Å) in the cell parameter at each temperature, requiring tight control of the stability and reliability of instrumental effects. In particular, achieving monochromator stability over time might be challenging with the high energy and high beam current variations of a third-generation synchrotron facility. On the other hand, such effects are usually checked by the addition of silicon as an internal standard, but the accuracy (and precision) of the published thermal expansion (which is not certified) might not be sufficient for its use when dealing with very small cell parameter variations. text/html Negative (and very low) thermal expansion in ReO3 from 5 to 300 K text 2 42 2009-02-03 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 253 258 http://scripts.iucr.org/cgi-bin/paper?he5417 Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the program GASBOR at 5 Å resolution (qmax = 1.25 Å−1) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8 Å resolution from the correctly positioned envelope; four distinct peaks at the 3.2σ level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (qmax = 0.25 Å−1). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination of FSEARCH and WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Hong, X. Hao, Q. 2009-02-07 doi:10.1107/S0021889809003094 International Union of Crystallography Molecular envelopes determined from SAXS/WAXS solution scattering can be used to locate the heavy-atom sites in the crystallographic unit cell. en molecular replacement small-angle X-ray scattering (SAXS) wide-angle X-ray scattering (WAXS) molecular envelopes heavy-atom location Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the program GASBOR at 5 Å resolution (qmax = 1.25 Å−1) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8 Å resolution from the correctly positioned envelope; four distinct peaks at the 3.2σ level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (qmax = 0.25 Å−1). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination of FSEARCH and WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement. text/html Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sites text 2 42 2009-02-07 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 259 264 http://scripts.iucr.org/cgi-bin/paper?db5051 It is demonstrated that high-intensity illumination with an Ar-ion laser beam can generate domain-inversion patterning in KNbO3 crystals. With a special laser-assisted micro-manipulation platform, direct patterning of domain-inversion structures without applying any external electric field can be carried out. The domain-nucleation process has been observed, and the process is purely optical, localized, and potentially controllable both in size and in orientation. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Chen, Y. Lu, Z. Xiao, M. 2009-02-14 doi:10.1107/S0021889809003987 International Union of Crystallography It is demonstrated that high-intensity illumination with an Ar-ion laser beam can generate domain-inversion patterning in KNbO3 crystals. en photosensitive materials domain inversion ferroelectricity It is demonstrated that high-intensity illumination with an Ar-ion laser beam can generate domain-inversion patterning in KNbO3 crystals. With a special laser-assisted micro-manipulation platform, direct patterning of domain-inversion structures without applying any external electric field can be carried out. The domain-nucleation process has been observed, and the process is purely optical, localized, and potentially controllable both in size and in orientation. text/html Observation of light-induced localized domain-inversion pattern formation in KNbO3 text 2 42 2009-02-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 265 267 http://scripts.iucr.org/cgi-bin/paper?do5043 A numerical method for computing the Fourier transform of an arbitrary space curve is described. The method is applicable to all sufficiently smooth curves and relies on the local geometric parameters describing a curve. The numerical results for a helical curve are compared with the exact analytical theory for the transform of a helix. It is shown that the transform of a filamentary density distribution radially symmetric around a curve is equivalent to the transform of that curve scaled by an appropriately defined weight function. These filamentary density distributions in conjunction with the numerical transform evaluation method can be used for simulating low-resolution diffraction data for protein crystals. Crystallographic structure factors obtained from a filament model representing a simple three-helix-bundle protein are compared with those calculated from conventional coordinate models. At low resolution, the filamentary representation provides an excellent approximation of the structure factors obtained from the standard coordinate model, but requires far fewer independent parameters. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Hausrath, A.C. Goriely, A. 2009-02-14 doi:10.1107/S0021889809002544 International Union of Crystallography A numerical method for the evaluation of the Fourier transform of a general space curve is described and its application to low-resolution crystallographic data analysis is presented. en Fourier transforms protein structures space curves A numerical method for computing the Fourier transform of an arbitrary space curve is described. The method is applicable to all sufficiently smooth curves and relies on the local geometric parameters describing a curve. The numerical results for a helical curve are compared with the exact analytical theory for the transform of a helix. It is shown that the transform of a filamentary density distribution radially symmetric around a curve is equivalent to the transform of that curve scaled by an appropriately defined weight function. These filamentary density distributions in conjunction with the numerical transform evaluation method can be used for simulating low-resolution diffraction data for protein crystals. Crystallographic structure factors obtained from a filament model representing a simple three-helix-bundle protein are compared with those calculated from conventional coordinate models. At low resolution, the filamentary representation provides an excellent approximation of the structure factors obtained from the standard coordinate model, but requires far fewer independent parameters. text/html The Fourier transforms of curves and filaments and their application to low-resolution protein crystallography text 2 42 2009-02-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 268 278 http://scripts.iucr.org/cgi-bin/paper?he5431 Orthorhombic crystals of the enzyme aspartyl-tRNA synthetase (AspRS) were prepared in agarose gel, a chemical alternative to microgravity or nano-volume drops. Besides providing a convection-free medium, the network of the polysaccharide improved the stability of the crystalline lattice during soaking with l-aspartol adenylate, a synthetic and non-hydrolysable analog of the catalytic intermediate aspartyl adenylate. When crystals were embedded in the polysaccharide matrix the ligand reached their surfaces more uniformly. Gel-grown crystals exhibited well defined reflections even at high resolution and low mosaicity values, despite their fairly high solvent content and the relatively harsh flash cooling procedure. By contrast, soaked AspRS crystals prepared in solution broke apart within 10–30 s after the ligand was introduced into the mother liquor, and subsequently these fragments became an amorphous precipitate. A general objection to the use of gels in protein crystallization is that chemical interactions may occur between the polysaccharide matrix and proteins or ligands. The example of AspRS shows that this is not a major concern. This method may be generally applicable to crystal soaking with other small molecules or heavy atoms. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Sauter, C. Balg, C. Moreno, A. Dhouib, K. Théobald-Dietrich, A. Chênevert, R. Giegé, R. Lorber, B. 2009-02-14 doi:10.1107/S0021889809003446 International Union of Crystallography Agarose gel stabilizes the AspRS enzyme crystal lattice for soaking with a catalytic intermediate analog. By contrast, AspRS crystals prepared in solution broke apart within 10–30 s after the ligand was introduced into the mother liquor, and subsequently these fragments became an amorphous precipitate. en proteins crystallization agarose gel ligands inhibitors soaking Orthorhombic crystals of the enzyme aspartyl-tRNA synthetase (AspRS) were prepared in agarose gel, a chemical alternative to microgravity or nano-volume drops. Besides providing a convection-free medium, the network of the polysaccharide improved the stability of the crystalline lattice during soaking with l-aspartol adenylate, a synthetic and non-hydrolysable analog of the catalytic intermediate aspartyl adenylate. When crystals were embedded in the polysaccharide matrix the ligand reached their surfaces more uniformly. Gel-grown crystals exhibited well defined reflections even at high resolution and low mosaicity values, despite their fairly high solvent content and the relatively harsh flash cooling procedure. By contrast, soaked AspRS crystals prepared in solution broke apart within 10–30 s after the ligand was introduced into the mother liquor, and subsequently these fragments became an amorphous precipitate. A general objection to the use of gels in protein crystallization is that chemical interactions may occur between the polysaccharide matrix and proteins or ligands. The example of AspRS shows that this is not a major concern. This method may be generally applicable to crystal soaking with other small molecules or heavy atoms. text/html Agarose gel facilitates enzyme crystal soaking with a ligand analog text 2 42 2009-02-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 279 283 http://scripts.iucr.org/cgi-bin/paper?ko5080 The crystal structure of monoclinic Lu2SiO5 (LSO) crystals, grown by the Czochralski method, was determined at room temperature by X-ray diffraction. The unit-cell parameters are a = 10.2550 (2), b = 6.6465 (2), c = 12.3626 (4) Å, β = 102.422 (1)° in space group I2/a. The linear thermal expansion tensor was determined along the a, b, c and c* directions over the temperature range from 303.15 to 768.15 K, and the principal coefficients of the thermal expansion tensor are found to be αI = −1.0235 × 10−6 K, αII = 4.9119 × 10−6 K and αIII = 10.1105 × 10−6 K. The temperature dependence of the cell volume and monoclinic angle were also evaluated. In addition, the specific heat and the thermal diffusivity were measured over the temperature ranges from 293.15 to 673.15 K and from 303.15 to 572.45 K, respectively. As a result, the anisotropic thermal conductivity could be calculated and is reported for the first time, to the best of the authors' knowledge. The specific heat capacity of LSO is 139.54 J mol−1 K−1, and the principal components of the thermal conductivity are kI = 2.26 W m−1 K−1, kII = 3.14 W m−1 K−1 and kII = 3.67 W m−1 K−1 at 303.15 K. A new structure model was proposed to better understand the relationships between the crystal structure and anisotropic thermal properties. In comparison with other laser matrix crystals, it is found that LSO possesses relatively large anisotropic thermal properties, and owing to its small heat capacity it has a moderate thermal conductivity, which is similar to those of the tungstates but lower than those of the vanadates. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Cong, H. Zhang, H. Wang, J. Yu, W. Fan, J. Cheng, X. Sun, S. Zhang, J. Lu, Q. Jiang, C. Boughton, R.I. 2009-02-27 doi:10.1107/S0021889809004269 International Union of Crystallography The novel laser matrix Lu2SiO5 (LSO) presents a structure consisting of two interpenetrating frameworks, Lu1O6 and Lu2O7. The material shows a maximum thermal expansion of 10.1105 × 10−6 K and thermal conductivity of 3.67 W m−1 K−1 at 303.15 K, while exhibiting relatively large anisotropic thermal properties. en laser matrix crystals thermal properties The crystal structure of monoclinic Lu2SiO5 (LSO) crystals, grown by the Czochralski method, was determined at room temperature by X-ray diffraction. The unit-cell parameters are a = 10.2550 (2), b = 6.6465 (2), c = 12.3626 (4) Å, β = 102.422 (1)° in space group I2/a. The linear thermal expansion tensor was determined along the a, b, c and c* directions over the temperature range from 303.15 to 768.15 K, and the principal coefficients of the thermal expansion tensor are found to be αI = −1.0235 × 10−6 K, αII = 4.9119 × 10−6 K and αIII = 10.1105 × 10−6 K. The temperature dependence of the cell volume and monoclinic angle were also evaluated. In addition, the specific heat and the thermal diffusivity were measured over the temperature ranges from 293.15 to 673.15 K and from 303.15 to 572.45 K, respectively. As a result, the anisotropic thermal conductivity could be calculated and is reported for the first time, to the best of the authors' knowledge. The specific heat capacity of LSO is 139.54 J mol−1 K−1, and the principal components of the thermal conductivity are kI = 2.26 W m−1 K−1, kII = 3.14 W m−1 K−1 and kII = 3.67 W m−1 K−1 at 303.15 K. A new structure model was proposed to better understand the relationships between the crystal structure and anisotropic thermal properties. In comparison with other laser matrix crystals, it is found that LSO possesses relatively large anisotropic thermal properties, and owing to its small heat capacity it has a moderate thermal conductivity, which is similar to those of the tungstates but lower than those of the vanadates. text/html Structural and thermal properties of the monoclinic Lu2SiO5 single crystal: evaluation as a new laser matrix text 2 42 2009-02-27 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 284 294 http://scripts.iucr.org/cgi-bin/paper?ks5201 On the basis of the concept of Polanyi [Z. Phys. (1921), 7, 149–180], the mapping of fiber diffraction patterns into reciprocal space is revisited. The result is a set of concise mapping relations that does not contain any approximations. This set permits the design of a direct method that, in principle, does not require refinement of mapping parameters even for patterns of tilted fibers. The method is unsuitable for diffuse scattering patterns. If inaccuracies of two pixels can be tolerated, a pattern is automatically mapped into reciprocal space in real time. The method is proposed for the processing of the extensive sets of patterns that are recorded in time-resolved wide-angle X-ray diffraction investigations of polymer materials. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Stribeck, N. Nöchel, U. 2009-02-27 doi:10.1107/S0021889809004713 International Union of Crystallography For application in time-resolved wide-angle X-ray diffraction studies, a method for the automatic mapping of fiber diffraction patterns into reciprocal space has been designed. en wide-angle X-ray diffraction (WAXD) polymers fiber diffraction patterns mapping reciprocal space On the basis of the concept of Polanyi [Z. Phys. (1921), 7, 149–180], the mapping of fiber diffraction patterns into reciprocal space is revisited. The result is a set of concise mapping relations that does not contain any approximations. This set permits the design of a direct method that, in principle, does not require refinement of mapping parameters even for patterns of tilted fibers. The method is unsuitable for diffuse scattering patterns. If inaccuracies of two pixels can be tolerated, a pattern is automatically mapped into reciprocal space in real time. The method is proposed for the processing of the extensive sets of patterns that are recorded in time-resolved wide-angle X-ray diffraction investigations of polymer materials. text/html Direct mapping of fiber diffraction patterns into reciprocal space text 2 42 2009-02-27 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 295 301 http://scripts.iucr.org/cgi-bin/paper?he5430 Data resolution limits the information carried by diffraction data and is therefore the most critical limit for the success of ab initio crystal structure solution. To overcome this limit, two methods have recently been proposed, namely the correction of resolution bias in electron-density maps and extrapolation of the structure factors beyond the data resolution limit. The first method has successfully been applied to powder data and the second to protein data. Neither of them has been applied to single-crystal data from small or medium-sized molecules. A third technique, the active use of the PSI-0 triplets in a tangent procedure, was applied to small molecules in the early days of crystallography, but it soon became obsolete because of the great success of methods combining reciprocal and direct space techniques. This paper explores the role of data resolution for small-to-medium-sized molecules and studies the usefulness of three auxiliary techniques, i.e. active use of the PSI-0 triplets, resolution bias correction and extrapolation of the structure factors. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Caliandro, R. Carrozzini, B. Cascarano, G.L. Giacovazzo, C. Mazzone, A. Siliqi, D. 2009-03-05 doi:10.1107/S0021889809004051 International Union of Crystallography Phasing of small and medium-sized molecules is attempted at different data resolutions via different algorithms. en phasing algorithms small molecules medium-sized molecules data resolution Data resolution limits the information carried by diffraction data and is therefore the most critical limit for the success of ab initio crystal structure solution. To overcome this limit, two methods have recently been proposed, namely the correction of resolution bias in electron-density maps and extrapolation of the structure factors beyond the data resolution limit. The first method has successfully been applied to powder data and the second to protein data. Neither of them has been applied to single-crystal data from small or medium-sized molecules. A third technique, the active use of the PSI-0 triplets in a tangent procedure, was applied to small molecules in the early days of crystallography, but it soon became obsolete because of the great success of methods combining reciprocal and direct space techniques. This paper explores the role of data resolution for small-to-medium-sized molecules and studies the usefulness of three auxiliary techniques, i.e. active use of the PSI-0 triplets, resolution bias correction and extrapolation of the structure factors. text/html Crystal structure solution of small-to-medium-sized molecules at non-atomic resolution text 2 42 2009-03-05 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 302 307 http://scripts.iucr.org/cgi-bin/paper?cg5103 Grain boundaries are frequently classified into tilt, twist and mixed-type boundaries. However, the classification (into tilt and twist) is not a dichotomy; due to crystal symmetries, some boundaries may be concurrently tilt and twist boundaries. Formal conditions for a planar homophase boundary between crystals with m3m symmetry to be a tilt as well as a twist boundary are determined, and a procedure for verification of whether a boundary has such dual character is given. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Morawiec, A. 2009-03-14 doi:10.1107/S0021889809006979 International Union of Crystallography Conditions for a planar homophase grain boundary to be concurrently a tilt and a twist boundary are given. en tilt grain boundaries twist grain boundaries mixed-type grain boundaries Grain boundaries are frequently classified into tilt, twist and mixed-type boundaries. However, the classification (into tilt and twist) is not a dichotomy; due to crystal symmetries, some boundaries may be concurrently tilt and twist boundaries. Formal conditions for a planar homophase boundary between crystals with m3m symmetry to be a tilt as well as a twist boundary are determined, and a procedure for verification of whether a boundary has such dual character is given. text/html Tilt and twist grain boundaries text 2 42 2009-03-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 308 311 http://scripts.iucr.org/cgi-bin/paper?ks5204 Nanocomposite films consisting of Au and/or Cu nanoclusters embedded in amorphous carbon matrices were characterized by anomalous grazing incidence small-angle X-ray scattering (AGISAXS) using synchrotron radiation. Whenever relative intensities can be measured with precision, it is shown that AGISAXS, being element specific, is a powerful method for separating the scattering contributions of two types of metallic nanoclusters. Two methodologies to analyse AGISAXS data are compared; the differential method appears the most efficient since it permits separation of the scattering from one type of nanocluster from the other contributions including other types of nanocluster, surface roughness or defects. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Simon, J.-P. Babonneau, D. Drouet, M. Lyon, O. 2009-03-14 doi:10.1107/S0021889809007316 International Union of Crystallography Methodologies to separate different signals in anomalous grazing incidence small-angle X-ray scattering are presented for well characterized samples: two binary nanocomposite films with Au or Cu nanoclusters encapsulated in amorphous carbon and one ternary film including both Au and Cu nanoclusters within the carbon matrix. The differential method appears the most efficient since the anomalous signal is well separated from that of the non-anomalous contributions, whatever their scattering profiles. en GISAXS anomalous scattering AGISAXS methodology metallic clusters in glassy carbon Nanocomposite films consisting of Au and/or Cu nanoclusters embedded in amorphous carbon matrices were characterized by anomalous grazing incidence small-angle X-ray scattering (AGISAXS) using synchrotron radiation. Whenever relative intensities can be measured with precision, it is shown that AGISAXS, being element specific, is a powerful method for separating the scattering contributions of two types of metallic nanoclusters. Two methodologies to analyse AGISAXS data are compared; the differential method appears the most efficient since it permits separation of the scattering from one type of nanocluster from the other contributions including other types of nanocluster, surface roughness or defects. text/html Anomalous grazing incidence small-angle X-ray scattering of carbon-encapsulated Au and Cu clusters text 2 42 2009-03-14 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography research papers 312 322 http://scripts.iucr.org/cgi-bin/paper?ks5186 A comparison between the resonant scattering curve obtained by anomalous small-angle X-ray scattering at the X-ray absorption edge of Ni and the complementary small-angle neutron scattering curve from an Al89Ni6La5 alloy sample is reported. The sample does not comply with the two-phase approximation. The two resulting scattering curves are approximately proportional to each other in this particular case. The anomalous small-angle X-ray scattering resonant curve at the Ni absorption edge equals the Ni–Ni partial structure factor and, owing to the favourable neutron scattering lengths of Ni, La and Al, the neutron scattering curve is also proportional to that partial structure factor. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Hoell, A. Tatchev, D. Haas, S. Haug, J. Boesecke, P. 2009-01-24 doi:10.1107/S0021889808042453 International Union of Crystallography A comparison between the resonant scattering curve obtained by anomalous small-angle X-ray scattering at the X-ray absorption edge of Ni and the small-angle neutron scattering curve from an Al89Ni6La5 alloy sample is reported. It is shown that the two curves are proportional to each other and to the Ni–Ni partial structure factor. en small-angle scattering partial structure factors anomalous small-angle X-ray scattering A comparison between the resonant scattering curve obtained by anomalous small-angle X-ray scattering at the X-ray absorption edge of Ni and the complementary small-angle neutron scattering curve from an Al89Ni6La5 alloy sample is reported. The sample does not comply with the two-phase approximation. The two resulting scattering curves are approximately proportional to each other in this particular case. The anomalous small-angle X-ray scattering resonant curve at the Ni absorption edge equals the Ni–Ni partial structure factor and, owing to the favourable neutron scattering lengths of Ni, La and Al, the neutron scattering curve is also proportional to that partial structure factor. text/html On the determination of partial structure functions in small-angle scattering exemplified by Al89Ni6La5 alloy text 2 42 2009-01-24 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography short communications 323 325 http://scripts.iucr.org/cgi-bin/paper?ce5046 Based on explicit formulas of chord length density functions (CLDs) for a regular pentagon and a hexagon, the CLDs of infinitely long regular homogeneous pentagonal/hexagonal cylinders are discussed. Characteristic properties of the small-angle scattering of these cylinders are studied. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Gille, W. Aharonyan, N.G. Harutyunyan, H.S. 2009-01-24 doi:10.1107/S0021889809002143 International Union of Crystallography Chord length density functions and characteristic details of the small-angle scattering of infinitely long cylinders with pentagonal/hexagonal right section are analyzed. en chord length density functions small-angle scattering Based on explicit formulas of chord length density functions (CLDs) for a regular pentagon and a hexagon, the CLDs of infinitely long regular homogeneous pentagonal/hexagonal cylinders are discussed. Characteristic properties of the small-angle scattering of these cylinders are studied. text/html Chord length distribution of pentagonal and hexagonal rods: relation to small-angle scattering text 2 42 2009-01-24 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography short communications 326 328 http://scripts.iucr.org/cgi-bin/paper?he5427 A rapid and simple X-ray fluorescence-based method is reported for characterizing heavy atom derivatives of proteins for protein crystallography using multiple isomorphous replacement (MIR). MIR is a widely used technique for solving protein crystallographic structures which requires that a `heavy atom' be incorporated into the protein to provide a strong signal in the diffraction pattern. Current methods for determining the effectiveness of these protein–heavy atom reactions are not always successful. In contrast, X-ray fluorescence quickly determines the presence of heavy atom modifications of proteins and the stoichiometry of these modifications. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Colip, L.A. Koppisch, A.T. Broene, R.D. Berger, J. Baldwin, S.M. Harris, M.N. Peterson, L.J. Warner, B.P. Birnbaum, E.R. 2009-01-24 doi:10.1107/S0021889809000077 International Union of Crystallography A method is described for using X-ray fluorescence for determining the solution phase reaction stoichiometry of heavy atom incorporation reactions. en protein crystallography multiple isomorphous replacement heavy atom derivatization X-ray fluorescence A rapid and simple X-ray fluorescence-based method is reported for characterizing heavy atom derivatives of proteins for protein crystallography using multiple isomorphous replacement (MIR). MIR is a widely used technique for solving protein crystallographic structures which requires that a `heavy atom' be incorporated into the protein to provide a strong signal in the diffraction pattern. Current methods for determining the effectiveness of these protein–heavy atom reactions are not always successful. In contrast, X-ray fluorescence quickly determines the presence of heavy atom modifications of proteins and the stoichiometry of these modifications. text/html A rapid method for quantifying heavy atom derivatives for multiple isomorphous replacement in protein crystallography text 2 42 2009-01-24 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography short communications 329 332 http://scripts.iucr.org/cgi-bin/paper?kk5040 X-ray fluorescence (XRF) measurements on solutions or crystals of biological macromolecules provide additional information that can be used in structure determination and/or refinement protocols. Here details are presented of an experimental setup, employed on all the ESRF Macromolecular Crystallography Group beamlines, that allows the online collection and qualitative analysis of XRF spectra. This experimental setup uses a highly attenuated beam and short exposures, meaning it is minimally destructive but retains high sensitivity. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Leonard, G.A. Solé, V.A. Beteva, A. Gabadinho, J. Guijarro, M. McCarthy, J. Marrocchelli, D. Nurizzo, D. McSweeney, S. Mueller-Dieckmann, C. 2009-02-03 doi:10.1107/S0021889809001721 International Union of Crystallography This paper describes the implementation of an online tool for the collection and qualitative analysis of X-ray fluorescence spectra that allows the identification of ions in a crystal or a solution of a biological macromolecule. en X-ray fluorescence macromolecular crystallography X-ray fluorescence (XRF) measurements on solutions or crystals of biological macromolecules provide additional information that can be used in structure determination and/or refinement protocols. Here details are presented of an experimental setup, employed on all the ESRF Macromolecular Crystallography Group beamlines, that allows the online collection and qualitative analysis of XRF spectra. This experimental setup uses a highly attenuated beam and short exposures, meaning it is minimally destructive but retains high sensitivity. text/html Online collection and analysis of X-ray fluorescence spectra on the macromolecular crystallography beamlines of the ESRF text 2 42 2009-02-03 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography short communications 333 335 http://scripts.iucr.org/cgi-bin/paper?he5421 Sequence–structure correlation studies are important in deciphering the relationships between various structural aspects, which may shed light on the protein-folding problem. The first step of this process is the prediction of secondary structure for a protein sequence of unknown three-dimensional structure. To this end, a web server has been created to predict the consensus secondary structure using well known algorithms from the literature. Furthermore, the server allows users to see the occurrence of predicted secondary structural elements in other structure and sequence databases and to visualize predicted helices as a helical wheel plot. The web server is accessible at http://bioserver1.physics.iisc.ernet.in/cssp/. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Gupta, A. Deshpande, A. Amburi, J.K. Sabarinathan, R. Senthilkumar, R. Sekar, K. 2009-01-24 doi:10.1107/S0021889808043847 International Union of Crystallography A web-based computing server for consensus prediction of secondary structure was developed. It is available on the World Wide Web at http://bioserver1.physics.iisc.ernet.in/cssp/. en computer programs CSSP protein sequences consensus secondary structure prediction sequence–structure correlation Sequence–structure correlation studies are important in deciphering the relationships between various structural aspects, which may shed light on the protein-folding problem. The first step of this process is the prediction of secondary structure for a protein sequence of unknown three-dimensional structure. To this end, a web server has been created to predict the consensus secondary structure using well known algorithms from the literature. Furthermore, the server allows users to see the occurrence of predicted secondary structural elements in other structure and sequence databases and to visualize predicted helices as a helical wheel plot. The web server is accessible at http://bioserver1.physics.iisc.ernet.in/cssp/. text/html CSSP (Consensus Secondary Structure Prediction): a web-based server for structural biologists text 2 42 2009-01-24 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography computer programs 336 338 http://scripts.iucr.org/cgi-bin/paper?kk5042 New software, OLEX2, has been developed for the determination, visualization and analysis of molecular crystal structures. The software has a portable mouse-driven workflow-oriented and fully comprehensive graphical user interface for structure solution, refinement and report generation, as well as novel tools for structure analysis. OLEX2 seamlessly links all aspects of the structure solution, refinement and publication process and presents them in a single workflow-driven package, with the ultimate goal of producing an application which will be useful to both chemists and crystallographers. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Dolomanov, O.V. Bourhis, L.J. Gildea, R.J. Howard, J.A.K. Puschmann, H. 2009-01-24 doi:10.1107/S0021889808042726 International Union of Crystallography The program OLEX2 provides tools for the determination, visualization and analysis of molecular crystal structures. en computer programs visualization and analysis graphical user interfaces metadata data harvesting OLEX2 New software, OLEX2, has been developed for the determination, visualization and analysis of molecular crystal structures. The software has a portable mouse-driven workflow-oriented and fully comprehensive graphical user interface for structure solution, refinement and report generation, as well as novel tools for structure analysis. OLEX2 seamlessly links all aspects of the structure solution, refinement and publication process and presents them in a single workflow-driven package, with the ultimate goal of producing an application which will be useful to both chemists and crystallographers. text/html OLEX2: a complete structure solution, refinement and analysis program text 2 42 2009-01-24 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography computer programs 339 341 http://scripts.iucr.org/cgi-bin/paper?aj5117 DAMMIF, a revised implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented. The program was fully rewritten, and its algorithm was optimized for speed of execution and modified to avoid limitations due to the finite search volume. Symmetry and anisometry constraints can be imposed on the particle shape, similar to DAMMIN. In equivalent conditions, DAMMIF is 25–40 times faster than DAMMIN on a single CPU. The possibility to utilize multiple CPUs is added to DAMMIF. The application is available in binary form for major platforms. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Franke, D. Svergun, D.I. 2009-01-24 doi:10.1107/S0021889809000338 International Union of Crystallography DAMMIF, an enhanced and significantly faster implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented. en computer programs DAMMIF DAMMIN small-angle scattering particle shape determination DAMMIF, a revised implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented. The program was fully rewritten, and its algorithm was optimized for speed of execution and modified to avoid limitations due to the finite search volume. Symmetry and anisometry constraints can be imposed on the particle shape, similar to DAMMIN. In equivalent conditions, DAMMIF is 25–40 times faster than DAMMIN on a single CPU. The possibility to utilize multiple CPUs is added to DAMMIF. The application is available in binary form for major platforms. text/html DAMMIF, a program for rapid ab-initio shape determination in small-angle scattering text 2 42 2009-01-24 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography computer programs 342 346 http://scripts.iucr.org/cgi-bin/paper?ce5049 Irena, a tool suite for analysis of both X-ray and neutron small-angle scattering (SAS) data within the commercial Igor Pro application, brings together a comprehensive suite of tools useful for investigations in materials science, physics, chemistry, polymer science and other fields. In addition to Guinier and Porod fits, the suite combines a variety of advanced SAS data evaluation tools for the modeling of size distribution in the dilute limit using maximum entropy and other methods, dilute limit small-angle scattering from multiple non-interacting populations of scatterers, the pair-distance distribution function, a unified fit, the Debye–Bueche model, the reflectivity (X-ray and neutron) using Parratt's formalism, and small-angle diffraction. There are also a number of support tools, such as a data import/export tool supporting a broad sampling of common data formats, a data modification tool, a presentation-quality graphics tool optimized for small-angle scattering data, and a neutron and X-ray scattering contrast calculator. These tools are brought together into one suite with consistent interfaces and functionality. The suite allows robust automated note recording and saving of parameters during export. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Ilavsky, J. Jemian, P.R. 2009-02-03 doi:10.1107/S0021889809002222 International Union of Crystallography Irena, a tool suite of scientific software for analysis of small-angle scattering data, is presented. Models, the graphical user interface and user support tools included in the package as well as software distribution are described. en computer programs small-angle scattering modeling size distribution pair-distance distribution function Irena, a tool suite for analysis of both X-ray and neutron small-angle scattering (SAS) data within the commercial Igor Pro application, brings together a comprehensive suite of tools useful for investigations in materials science, physics, chemistry, polymer science and other fields. In addition to Guinier and Porod fits, the suite combines a variety of advanced SAS data evaluation tools for the modeling of size distribution in the dilute limit using maximum entropy and other methods, dilute limit small-angle scattering from multiple non-interacting populations of scatterers, the pair-distance distribution function, a unified fit, the Debye–Bueche model, the reflectivity (X-ray and neutron) using Parratt's formalism, and small-angle diffraction. There are also a number of support tools, such as a data import/export tool supporting a broad sampling of common data formats, a data modification tool, a presentation-quality graphics tool optimized for small-angle scattering data, and a neutron and X-ray scattering contrast calculator. These tools are brought together into one suite with consistent interfaces and functionality. The suite allows robust automated note recording and saving of parameters during export. text/html Irena: tool suite for modeling and analysis of small-angle scattering text 2 42 2009-02-03 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography computer programs 347 353 http://scripts.iucr.org/cgi-bin/paper?ko5079 A program for instrumental drift correction by nonparametric statistics using a point-detector diffractometer is described. The correction improves structural results such as merging and refinement R factors. The kernels available are as follows: uniform, Epanechnikov, quartic, octic, Gaussian. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Dudka, A. 2009-02-07 doi:10.1107/S0021889809002271 International Union of Crystallography Instrumental drift correction by nonparametric statistics is described. en data reduction instrumental drift nonparametric statistics computer programs A program for instrumental drift correction by nonparametric statistics using a point-detector diffractometer is described. The correction improves structural results such as merging and refinement R factors. The kernels available are as follows: uniform, Epanechnikov, quartic, octic, Gaussian. text/html Instrumental drift correction by nonparametric statistics text 2 42 2009-02-07 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography computer programs 354 355 http://scripts.iucr.org/cgi-bin/paper?db5053 The simulated annealing approach to structure solution from powder diffraction data, as implemented in the DASH program, is easily amenable to parallelization at the individual run level. Very large scale increases in speed of execution can therefore be achieved by distributing individual DASH runs over a network of computers. The GDASH program achieves this by packaging DASH in a form that enables it to run under the Univa UD Grid MP system, which harnesses networks of existing computing resources to perform calculations. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Griffin, T.A.N. Shankland, K. van de Streek, J. Cole, J. 2009-03-05 doi:10.1107/S0021889809006840 International Union of Crystallography A program that exploits a commodity grid to accelerate crystal structure solution from powder diffraction data, using the DASH program, is described. en distributed computing structure solution from powder diffraction data DASH The simulated annealing approach to structure solution from powder diffraction data, as implemented in the DASH program, is easily amenable to parallelization at the individual run level. Very large scale increases in speed of execution can therefore be achieved by distributing individual DASH runs over a network of computers. The GDASH program achieves this by packaging DASH in a form that enables it to run under the Univa UD Grid MP system, which harnesses networks of existing computing resources to perform calculations. text/html GDASH: a grid-enabled program for structure solution from powder diffraction data text 2 42 2009-03-05 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography computer programs 356 359 http://scripts.iucr.org/cgi-bin/paper?db5054 The simulated annealing approach to structure solution from powder diffraction data, as implemented in the DASH program, is easily amenable to parallelization at the individual run level. Modest increases in speed of execution can therefore be achieved by executing individual DASH runs on the individual cores of CPUs. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Griffin, T.A.N. Shankland, K. van de Streek, J. Cole, J. 2009-03-05 doi:10.1107/S0021889809006852 International Union of Crystallography A program that exploits the increasing availability of computers with more than one CPU or with CPUs with multiple cores to accelerate structure solution from powder diffraction data, using the DASH program, is described. en distributed computing structure solution from powder diffraction data multi-core CPUs DASH The simulated annealing approach to structure solution from powder diffraction data, as implemented in the DASH program, is easily amenable to parallelization at the individual run level. Modest increases in speed of execution can therefore be achieved by executing individual DASH runs on the individual cores of CPUs. text/html MDASH: a multi-core-enabled program for structure solution from powder diffraction data text 2 42 2009-03-05 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography computer programs 360 361 http://scripts.iucr.org/cgi-bin/paper?kk5034 The widely used restraint-based approach to structural analysis using diffraction data is critiqued. The convenience of using rigid constraints, through the use of internal coordinates, is discussed. Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Immirzi, A. 2009-02-07 doi:10.1107/S0021889808044142 International Union of Crystallography The restraint-based procedure in least-squares refinement is critiqued and the advantages of using internal coordinates are discussed. en constraints restraints crystal structure analysis The widely used restraint-based approach to structural analysis using diffraction data is critiqued. The convenience of using rigid constraints, through the use of internal coordinates, is discussed. text/html Constraints and restraints in crystal structure analysis text 2 42 2009-02-07 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography letters to the editor 362 364 http://scripts.iucr.org/cgi-bin/paper?kk5041 Copyright (c) 2009 International Union of Crystallography urn:issn:0021-8898 Helliwell, J.R. 2009-02-03 doi:10.1107/S0021889809002775 International Union of Crystallography en lecture demonstrations crystallographic teaching text/html Lecture demonstrations in a public lecture on `X-ray crystal structure analysis: from W. L. Bragg to the present day' text 2 42 2009-02-03 Copyright (c) 2009 International Union of Crystallography Journal of Applied Crystallography notes and news 365 365