bluuebunny/crossref_metadata_2025 huggingface dataset:
Turgor Regulation in Osmotically Stressed Arabidopsis Epidermal Root Cells. Direct Support for the Role of Inorganic Ion Uptake as Revealed by Concurrent Flux and Cell Turgor Measurements
Authors: Shabala Sergey N. , Lew Roger R.
Published: July 2002

Hyperosmotic stress is known to significantly enhance net uptake of inorganic ions into plant cells. Direct evidence for cell turgor recovery via such a mechanism, however, is still lacking. In the present study, we performed concurrent measurements of net ion fluxes (with the noninvasive microelectrode ion flux estimation technique) and cell turgor changes (with the pressure-probe technique) to provide direct evidence that inorganic ion uptake regulates turgor in osmotically stressed Arabidopsis epidermal root cells. Immediately after onset of hyperosmotic stress (100/100 mmmannitol/sorbitol treatment), the cell turgor dropped from 0.65 to about 0.25 MPa. Turgor recovery started within 2 to 10 min after the treatment and was accompanied by a significant (30–80 nmol m−2 s−1) increase in uptake of K+, Cl−, and Na+ by root cells. In most cells, almost complete (>90% of initial values) recovery of the cell turgor was observed within 40 to 50 min after stress onset. In another set of experiments, we combined the voltage-clamp and the microelectrode ion flux estimation techniques to show that this process is, in part, mediated by voltage-gated K+ transporters at the cell plasma membrane. The possible physiological significance of these findings is discussed.
Apoplastic Sugars, Fructans, Fructan Exohydrolase, and Invertase in Winter Oat: Responses to Second-Phase Cold Hardening
Authors: Livingston David P. , Henson Cynthia A.
Published: July 2002

Changes in apoplastic carbohydrate concentrations and activities of carbohydrate-degrading enzymes were determined in crown tissues of oat (Avena sativa L., cv Wintok) during cold hardening. During second-phase hardening (−3°C for 3 d) levels of fructan, sucrose, glucose, and fructose in the apoplast increased significantly above that in nonhardened and first-phase-hardened plants. The extent of the increase in apoplastic fructan during second-phase hardening varied with the degree of fructan polymerization (DP) (e.g. DP3 and DP4 increased to a greater extent than DP7 and DP > 7). Activities of invertase and fructan exohydrolase in the crown apoplast increased approximately 4-fold over nonhardened and first-phase-hardened plants. Apoplastic fluid extracted from nonhardened, first-phase-hardened, and second-phase-hardened crown tissues had low levels, of symplastic contamination, as determined by malate dehydrogenase activity. The significance of these results in relation to increases in freezing tolerance from second-phase hardening is discussed.
Genetic Interactions between Phytochrome A, Phytochrome B, and Cryptochrome 1 during Arabidopsis Development1
Authors: Neff Michael M. , Chory Joanne
Published: July 2002

Single, double, and triple null combinations of Arabidopsis mutants lacking the photoreceptors phytochrome (phy) A (phyA-201), phyB (phyB-5), and cryptochrome (cry) 1 (hy4-2.23n) were examined for de-etiolation responses in high-fluence red, far-red, blue, and broad-spectrum white light. Cotyledon unhooking, unfolding, and expansion, hypocotyl growth, and the accumulation of chlorophylls and anthocyanin in 5-d-old seedlings were measured under each light condition and in the dark. phyA was the major photoreceptor/effector for most far-red-light responses, although phyB and cry1 modulated anthocyanin accumulation in a phyA-dependent manner. phyB was the major photoreceptor in red light, although cry1 acted as a phyA/phyB-dependent modulator of chlorophyll accumulation under these conditions. All three photoreceptors contributed to most blue light deetiolation responses, either redundantly or additively; however, phyB acted as a modulator of cotyledon expansion dependent on the presence of cry1. As reported previously, flowering time in long days was promoted by phyA and inhibited by phyB, with each suppressing the other's effect. In addition to the effector/modulator relationships described above, measurements of hypocotyls from blue-light-grown seedlings demonstrated phytochrome activity in blue light and cry1 activity in a phyAphyB mutant background.
Barley Coleoptile Peroxidases. Purification, Molecular Cloning, and Induction by Pathogens1
Authors: Kristensen Brian Kåre , Bloch Helle , Rasmussen Søren Kjærsgaard
Published: July 2002

A cDNA clone encoding the Prx7 peroxidase from barley (Hordeum vulgare L.) predicted a 341-amino acid protein with a molecular weight of 36,515. N- and C-terminal putative signal peptides were present, suggesting a vacuolar location of the peroxidase. Immunoblotting and reverse-transcriptase polymerase chain reaction showed that the Prx7 protein and mRNA accumulated abundantly in barley coleoptiles and in leaf epidermis inoculated with powdery mildew fungus (Blumeria graminis). Two isoperoxidases with isoelectric points of 9.3 and 7.3 (P9.3 and P7.3, respectively) were purified to homogeneity from barley coleoptiles. P9.3 and P7.3 had Reinheitszahl values of 3.31 and 2.85 and specific activities (with 2,2′-azino-di-[3-ethyl-benzothiazoline-6-sulfonic acid], pH 5.5, as the substrate) of 11 and 79 units/mg, respectively. N-terminal amino acid sequencing and matrix-assisted laser desorption/ionization time-of-flight mass-spectrometry peptide analysis identified the P9.3 peroxidase activity as due to Prx7. Tissue and subcellular accumulation of Prx7 was studied using activity-stained isoelectric focusing gels and immunoblotting. The peroxidase activity due to Prx7 accumulated in barley leaves 24 h after inoculation with powdery mildew spores or by wounding of epidermal cells. Prx7 accumulated predominantly in the epidermis, apparently in the vacuole, and appeared to be the only pathogen-induced vacuolar peroxidase expressed in barley tissues. The data presented here suggest that Prx7 is responsible for the biosynthesis of antifungal compounds known as hordatines, which accumulate abundantly in barley coleoptiles.
Senescence-Associated Gene Expression during Ozone-Induced Leaf Senescence in Arabidopsis1
Authors: Miller Jennifer D. , Arteca Richard N. , Pell Eva J.
Published: July 2002

The expression patterns of senescence-related genes were determined during ozone (O3) exposure in Arabidopsis. Rosettes were treated with 0.15 μL L−1 O3 for 6 h d−1 for 14 d. O3-treated leaves began to yellow after 10 d of exposure, whereas yellowing was not apparent in control leaves until d 14. Transcript levels for eight of 12 senescence related genes characterized showed induction by O3. SAG13(senescence-associated gene), SAG21, ERD1(early responsive to dehydration), and BCB (blue copper-binding protein) were induced within 2 to 4 d of O3 treatment; SAG18, SAG20, and ACS6 (ACC synthase) were induced within 4 to 6 d; and CCH (copper chaperone) was induced within 6 to 8 d. In contrast, levels of photosynthetic gene transcripts,rbcS (small subunit of Rubisco) and cab(chlorophyll a/b-binding protein), declined after 6 d. Other markers of natural senescence, SAG12,SAG19, MT1 (metallothionein), andAtgsr2 (glutamine synthetase), did not show enhanced transcript accumulation. When SAG12promoter-GUS (β-glucuronidase) andSAG13 promoter-GUS transgenic plants were treated with O3, GUS activity was induced in SAG13-GUS plants after 2 d but was not detected in SAG12-GUS plants.SAG13 promoter-driven GUS activity was located throughout O3-treated leaves, whereas control leaves generally showed activity along the margins. The acceleration of leaf senescence induced by O3 is a regulated event involving many genes associated with natural senescence.
Lead mercaptides: materials useful as powder secondary standards and internal references for calibration of X-ray diffractometers at small and medium angles
Authors: Tiers George V. D. , Brostrom Myles L.
Published: July 2002

Heavy-atom alkanethiolates (mercaptides), especially of lead, provide a series of sharp first-order lines for calibrating both wide- and small-angle X-ray diffractometers (WAXD and SAXS), out to at least 60 Ådspacing. There is no reliance on published data or on externally validated substances other than silicon standard reference material (SRM); any preparation showing a large number of higher-order lines is a perfect standard. Well resolved lines extending beyond the 30th order are observed and provide an excellent statistical basis for calculating a reliable first-order spacing, and then for diffractometer calibration at all 2θ values. Owing to their very low solubility, the lead mercaptides may often be mixed into a sample without altering it, thus providing one or more internal references to bracket a line of interest, enabling interpolation. Simple high-yield preparations of finely divided long-chain mercaptides of lead (C8to C22), mercury, thallium and silver are reported, with first-orderdspacings. The mercaptides react readily with carbon disulfide to generate the corresponding metal alkyltrithiocarbonates in good yield; these also serve for WAXD/SAXS calibration, though the shorter-chain trithiocarbonates lack long-term stability.
A simple technique to control macromolecular crystal nucleation efficiently using a standard vapour-diffusion setup
Authors: Jovine Luca
Published: July 2002

Excessive nucleation often leads to a large number of small macromolecular crystals that are not useful for X-ray diffraction analysis. Crystals with dimensions suitable for data collection can be reproducibly obtained by releasing, for a discrete amount of time, the vapour pressure in both hanging- and sitting-drop experiments, set up at lower precipitant concentrations than those required for crystallization.
Using a prism to reject or select harmonic reflections in an X-ray monochromator
Authors: Zhong Z.
Published: July 2002

The angle by which an X-ray deviates from its original direction when it passes through a refractive prism is proportional to the square of the X-ray wavelength. This effect was used to discriminate between different harmonic orders of a two-crystal non-dispersive monochromator. Two cases are discussed. In the first case, a refractive prism allows tuning of the silicon 333 reflection to the peak of its double-crystal rocking curve while the higher-order harmonics are suppressed, with much of the harmonic rejection being controllable by the angle of the prism. In the second case, it is demonstrated that slightly tuning the second crystal of the monochromator allows the selection of a specific harmonic order from among reflections 333, 444 and 555.
Experimental determination of the instrumental transparency function of texture goniometers
Authors: Moras K. , Fischer A. H. , Klein H. , Bunge H. J.
Published: July 2002

The instrumental transparency functions of five commercially available texture goniometers were measured experimentally with six monocrystalline samples cut in different orientations from a large highly perfect silicon crystal with a rocking curve of less than 0.01°. Transparency functions were measured in steps of 0.02 to 0.2° in the pole-figure angles α, β. The window size Δα depends on the Bragg angle θ in the form 1/sinθ; the window size Δω is constant for each goniometer. The dominant instrumental parameter determining the long axis Δα of the pole-figure window is the axial width of the detector entrance slit. This parameter is smallest for area detectors (smaller by more than an order of magnitude compared with conventional scintillation detectors as well as one-dimensional position-sensitive detectors). The main features of the pole-figure window and their dependence on the instrumental parameters can be deduced fairly well from a simple geometrical model. The particular shapes of the transparency functions of the studied goniometers are markedly different. Particularly, they are not very well represented by Gauss functions. The two-dimensional transparency function can be fairly well characterized by its α and β profiles. The normalized profiles are virtually independent of the goniometer angles 2θ and α. The increasing size of the pole-figure window with decreasing θ puts a lower limit on the Bragg angle below which pole-figure measurement ceases to be meaningful.
Periodically poled KTA crystal investigated using coherent X-ray beams
Authors: Pernot-Rejmánková P. , Thomas P. A. , Cloetens P. , Lorut F. , Baruchel J. , Hu Z. W. , Urenski P. , Rosenman G.
Published: July 2002

The distribution of inverted ferroelectric domains on the surface and within the bulk of a periodically poled KTA (KTiOAsO4) single crystal has been observed using a simple X-ray diffraction imaging setup which takes advantage of the highly coherent beams available at a third-generation synchrotron source, such as the ESRF. This technique allows one to reveal the phase difference between the waves that are Bragg diffracted from adjacent domainsviafree-space propagation (Fresnel diffraction). The phase difference of the diffracted waves is mainly produced by the difference in phases of the structure factors involved, and contains precise structural information about the nature of the domain walls.
Response to Larsen & Thorkildsen's comments onExtinction-corrected mean thickness and integrated width used in the program UMWEG98
Authors: Rossmanith E.
Published: July 2002

Some additional comments are made concerning the asymptotic expressions for the primary-extinction factor for a perfect spherical crystal.
High-energy X-ray diffuse scattering using Weissenberg flat-cone geometry. Erratum
Authors: Butler B. D. , Haeffner D. R. , Lee P. L. , Welberry T. R.
Published: July 2002

In the paper by Butleret al.[J. Appl. Cryst.(2000),33, 1046–1050], Figures 3 and 4 on pages 1047 and 1048 reproduced poorly. Revised versions of these pages are available in the online version of this erratum, which is available throughCrystallography Journals Online.
A very simple and cheap greasing device for crystallization plates
Authors: Watanabe Nobuhisa
Published: July 2002

A device to grease a 24-well crystallization plate can be easily made with a disposable plastic syringe and a sample-retention vial from a centrifugal filter device. It takes only 2 min to grease one plate with the device.
String Fit: a new structurally oriented X-ray and neutron reflectivity evaluation technique
Authors: Politsch Erich
Published: July 2002

A novel method for the analysis of neutron and X-ray reflectivity measurements is presented. In contrast to existing methods, the new data fitting approach is structurally oriented and therefore only requires information about the chemical structure of studied molecules and no otherad hocassumptions. Apart from the inversion of reflectivity into scattering length density profile, the inversion of scattering length density profile into molecular arrangement is addressed systematically for non-trivial molecular conformations for the first time. This includes the calculation of structural characteristics, such as radius of gyration or chain order parameters, based on measured reflectograms. Another important option is the possibility to evaluate simultaneously neutron and X-ray reflectograms of a given sample. For better convergence, especially for complex simultaneous evaluations, an effective extension of the normally used least-squares deviation function is introduced. Different simulated molecular ensembles are used to illustrate the features of the new approach; typically, excellent agreement between the simulated starting and final deduced data sets is achieved.
Contribution to X-ray analysis of carbo-nitrided steel layers
Authors: Sprauel J. M. , Michaud H.
Published: July 2002

The non-destructive X-ray diffraction method is used to analyse carbo-nitrided steel layers after wear testing. These measurements are carried out on the two major phases of the material,i.e.the martensite and the retained austenite. Such measurements are particularly difficult for three reasons. First, strong gradients exist across the wear track. Second, the diffraction peaks obtained for the martensite are broadened, as a result of the overlap of different reflections of the tetragonal structure. Third, the studied material is multiphase. Its major phases are martensite and austenite, but it also contains carbide and nitride clusters, which lead to incoherent scattering of X-rays. A new quantitative phase analysis method is thus proposed to define the volume fractions of these different constituents of the material. This method accounts for the evolution of the background level during wear. A micro-mechanical model is then developed to process the diffraction peak positions obtained for the martensite and the retained austenite. This model defines the `true' stress and carbon content of both phases. It also allows separation of the reflections of the martensite. The true widths of the diffraction peaks, which characterize the plastic deformation, can thus be quantified. Results for wear-test specimens show a strong plastic deformation of the retained austenite during contact fatigue. This leads to a partial transformation of this phase into martensite. In the martensite, on the contrary, the plastic deformation remains low but the carbon content decreases. This is caused by a stress-induced precipitation of carbides.
On the diffractive determination of single-crystal elastic constants using polycrystalline samples
Authors: Matthies S. , Priesmeyer H. G. , Daymond M. R.
Published: July 2002

The diffractive determination of single-crystal elastic constants using polycrystalline samples represents the inverse problem to the (`direct') experiment of conventional diffractive residual-stress analysis. Both problems are rather sensitive to the quality of the experimental data and to the applied micro-mechanical models. This especially holds for the case of samples for which texture cannot be neglected. The current methods in the field are briefly described and specific difficulties are discussed. The key relations for the BPGeo micro-mechanical model (in which a texture-weighted geometric mean is applied in the stress analysis) are given for the general case. The necessity for careful analysis of the reliability of the results of planned experiments using theoretically modelled `experimental' data obtained with the applied micro-mechanical models is demonstrated for a set of line-shift data from a uniaxial tensile experiment on steel. The possibility of resolving the so-calledd0problem using the original line-position data for a structure refinement is demonstrated.
The derivation of non-merohedral twin laws during refinement by analysis of poorly fitting intensity data and the refinement of non-merohedrally twinned crystal structures in the programCRYSTALS
Authors: Cooper Richard I. , Gould Robert O. , Parsons Simon , Watkin David J.
Published: July 2002

Although non-merohedrally twinned crystal structures can normally be solved without difficulty, problems usually arise during refinement. Careful analysis of poorly fitting data reveals that they belong predominantly to certain distinct zones in which |Fo|2is systematically larger than |Fc|2. In the computer programROTAX, a set of data with the largest values of (|F_{o}^{\,2}| − |F_{c}^{\,2}|)/u(|F_{o}^{\,2}|) is identified and their indices transformed by rotations or roto-inversions about possible direct- and reciprocal-lattice directions. Matrices that transform the indices of the poorly fitting data to integers are identified as possible twin laws.
Phasing possibilities using different wavelengths with a xenon derivative
Authors: Panjikar Santosh , Tucker Paul A.
Published: July 2002

Xenon derivatives are generally expected to be isomorphous with the native; however, theK- andL-absorption edges are not easily accessible on most synchrotron beamlines, which might limit their usefulness in phase determination. Various phasing procedures for xenon-derivatized porcine pancreatic elastase have been investigated using data sets measured at three generally accessible wavelengths. The importance of highly redundant data in measuring precise anomalous differences is highlighted and it is shown that, after such measurements, a single isomorphous replacement anomalous scattering (SIRAS) procedure yields a better phase set than those generated by single anomalous scattering (SAS) or multiwavelength anomalous diffraction (MAD) procedures.
Bridging the gap – structure determination of the red polymorph of tetrahexylsexithiophene by Monte Carlo simulated annealing, first-principles DFT calculations and Rietveld refinement
Authors: Neumann Marcus A. , Tedesco Consiglia , Destri Silvia , Ferro Dino R. , Porzio William
Published: July 2002

The crystal structure of the red polymorph of tetrahexylsexithiophene (THST) is solved from X-ray powder diffraction data by a direct-space Monte Carlo simulated-annealing approach. First-principles density functional theory (DFT) calculations are used to distinguish between three nearly identical solutions in the space groupsC2/m,C2 andP\bar{1} and to improve the overall accuracy of the crystal structure. The correct space group is found to beC2/m. In all space groups, the thiophene backbone is planar and the hexyl side chains assume an all-transconformation except for two terminal methyl residues, which adopt agaucheorientation. The ability of first-principles DFT calculations to provide atomic coordinates of single-crystal quality is demonstrated by lattice-energy minimization of the known crystal structure of the yellow polymorph of THST. The combination of Monte Carlo simulated annealing, first-principles DFT calculations and Rietveld refinement presented in this paper is generally applicable. It provides a powerful alternative to standard approaches in cases where the information content of the powder diffraction pattern alone is insufficient to distinguish between different structure solutions. DFT calculations can also provide invaluable guidance in Rietveld refinement.
The temperature dependence of the long-range order parameter of Ni3Al
Authors: Pope D. P. , Garin J. L.
Published: July 2002

The macroscopic yield stress of Ni3Al increases rapidly with temperature, reaching a maximum at about 700°C. Such anomalous behavior has been observed in other ordered alloys which undergo partial disordering with increasing temperature, e.g. Cu3Au. The long-range order parameter, S, of stoichiometric Ni3Al powder was measured over the temperature range 25°C to 1000°C and great care was taken to ensure a fine particle size and thus avoid extinction effects. The results of this study showed that, in Ni3Al, S remains constant at about 0.93 over the entire temperature range investigated. This means that theories relating the strength of ordered alloys to S are not applicable to Ni3Al.
On the determination of the metastable miscibility gap in ternary alloys from small-angle measurements. I. Theoretical background
Authors: Gerold V.
Published: July 2002

Metastable precipitation as the formation of GP zones is governed by a metastable miscibility gap. It is shown that the limits of this gap in a ternary system can be determined from combined analysis of the small-angle scattering (SAS) of X-rays and of neutrons. The necessary condition is a significantly different ratio β = (bC
−bA
)/(bB
−bA
) of the atomic scattering amplitudes b of the components A, B and C for both the X-rays and the neutrons. This difference enables one to determine the slope of the tie-line passing through an individual alloy by comparing the integrated SAS intensities of the two types of radiation. Thereafter, the determination of the gap limits follows the same procedure as already known for binary alloys. The change of the mean atomic volume with composition influences the result, but this can be taken into account provided the same Vegard's law is valid for both the depleted matrix and the precipitate.
The problem of white radiation in the measurement of intensities with a solid-state detector: erratum
Authors: Howard C. J. , Jones R. D. G.
Published: July 2002

In Howard & Jones [J. Appl. Cryst. (1976), 9, 235] the first author's initials should be C.J. and not H.J.
Flat-cone diffractometer utilizing a linear position-sensitive detector
Authors: Prince E. , Wlodawer A. , Santoro A.
Published: July 2002

The recent development of linear position-sensitive detectors for neutrons and X-rays leads to the possibility of large improvements in the efficiency of data collection in single-crystal diffractometers. In order to take advantage of the properties of a linear position-sensitive detector it is desirable to use a diffraction geometry which causes the diffracted beams from many different reflecting planes to lie in a common plane. A design for a diffractometer utilizing the flat-cone geometry is described, and the relevant mathematical formulas are summarized. An instrument using this design has been constructed as a modification to an existing four-circle diffractometer and is now operating. Practical details of its construction, of the collection and handling of data, and of data rates are discussed.
Comparison of two numerical methods for the integration of the Takagi–Taupin equations
Authors: Nourtier C. , Taupin D.
Published: July 2002

Two methods for the numerical resolution of the Takagi-Taupin equations are compared. It is shown that for a small integration step Taupin's [Acta Cryst. (1967), 23, 25–35] extension to two dimensions of the one-dimensional Runge–Kutta third-order method is more accurate than the algorithm of Authier, Malgrange & Tournarie [Acta Cryst. (1968), A24, 126–136] but, for a given precision, Authier, Malgrange & Tournarie's method is faster than Taupin's so the former will usually be preferred for numerical calculation.
Phase assignment to diffraction patterns based on the analytic properties of scattered fields applied to the structure of nerve myelin
Authors: Burge R. E. , Fiddy M. A.
Published: July 2002

An analysis of published X-ray diffraction data from nerve myelin is given based on the properties of analytic functions. Functions defined by a finite Fourier transform may be described by their distribution of zeros. This description allows a phase function to be determined from real data, which is unique in principle. A solution to the phase assignment is given and compared with corresponding published solutions derived by other methods. The strong measure of agreement for the phases of the first nine diffraction orders, and the stability of this agreement against the efforts of experimental error, leads to the conclusion that these phases are probably correct.
Crystal data for the monoclinic form of the lanthanide molybdoperrhenates Ln(MoO4)(ReO4)
Authors: Argelès D. , Quarton M. , Silvestre J.-P.
Published: July 2002

Nd(MoO4) (ReO4) is monoclinic, space group P21/c; the cell dimensions are a = 6.169 (1), b = 9.822 (1), c = 13.139 (2) Å and β = 111.65 (1)°. The monoclinic compounds in the series Ln(MoO4) (ReO4), with Ln = Ce to Lu (Pm compound is not examined), are isotypic. Crystal parameters and powder diffraction data are given.
Crystal data for tris (1, 10-phenanthroline)–bis(sulfuric acid) dihydrate, 3C12H8N2.2H2SO4.2H2O, and 1, 10-phenanthroline–bis(sulfuric acid), C12H8N2.2H2SO4
Authors: Thevenet G. , Souleau C. , Montagu M. , Ceolin R.
Published: July 2002

The powder data for the title compounds are reported. They are monoclinic, Bb or B2/b, with, for 3C12H8N2.2H2SO4.2H2O, a = 20.87 (1), b = 14.581 (9), c = 11.458 (7) Å, γ = 108.32 (6)°, Z = 4, Dm
= 1.58, Dc
= 1.55 Mg m−3, and, for C12H8N2.2H2SO4, a = 17.39 (3), b = 15.38 (4), c = 6.85 (1) Å, γ = 124.9 (1)°, Z = 4.
Données cristallographiques sur les composés M
II2TlIIIOH(XO4)2: M=K, Rb, Tl, NH4 et X=S, Se
Authors: Abraham F. , Jolibois B. , Laplace G. , Nowogrocki G. , Tudo J.
Published: July 2002

Tl2TlOH(SO4)2 is monoclinic, space group Cc or C2/c. The cell parameters are a = 7.758 (3), b = 17.587 (9), c = 7.356 (3) Å, β = 119.91 (3)°, Z = 4. Compounds in the series M
I
2
M
IIIOH(X O4)2 (with M
I= K, Rb, Tl, NH4; M
III = Tl, In; X = S, Se) are isotypic. Crystal parameters and powder diffraction data are given.
Crystal data of branched-chain derivatives of D-psicose
Authors: Sharafi N. , Donnay G. , Herve du Penhoat P. C. M. , Perlin A. S.
Published: July 2002

Crystal data are reported for six derivatives of 1,2-O-isopropylidene-3-C-(pyridin-2-yl)-β-D-psicopyranose, C14H19NO6, previously studied in solution by NMR spectroscopy. Molecules that differ only by the replacement of H by CH3 on one non-ring oxygen atom, converting an alcohol to an ether molecule, show no similarity in cell dimensions, and have different numbers of molecules per cell. All six phases belong to non-centrosymmetric space groups, four to P212121 and two to P21; in agreement with previously reported optical activity of these molecules in solution, it is concluded that only molecules of one-and-the-same handedness are present in any one of the crystalline phases.
Crystallographic computing on an array processor
Authors: Furey W. , Wang B. C. , Sax M.
Published: July 2002

To date, six computationally intense but frequently needed crystallographic applications programs have been developed for an array processor (Floating Point Systems model AP 190L) driven by a DEC 10 computer. In all of the applications attempted, it was possible to reduce the required processing time to at least an order of magnitude below that required by a large university scale computer (DEC 10) for the same problem. In fact, the rate-determining step in full-matrix least-squares refinement can be made to run 20–30 times faster in the array processor. For the refinement of proteins, one cycle with a space-group-general algorithm executes faster in the array processor than a typical small-molecule refinement cycle executes on the DEC 10. We conclude that many of the time-consuming operations frequently encountered in crystallographic computer programs can be handled very efficiently on an inexpensive array processor attached to a host computer.
Lattice modulation in the hexagonal-type antiphase domain structure of Au–33at.%Cd alloy
Authors: Watanbe Y. , Iwasaki H.
Published: July 2002

The crystal structure of an ordered Au–33at.%Cd alloy has been reinvestigated by X-ray diffraction. Least-squares refinement using single-crystal intensity data collected by photographic methods has shown that mixed occupation by the two kinds of atoms preferentially occurs in the atomic sites located near the boundaries of the hexagonal antiphase domains, confirming the results obtained by electron diffraction [Hirabayashi, Yamaguchi, Hiraga, Ino, Sato & Toth (1970). d. Phys. Chem. Solids, 31, 77–94]. The refinement has also shown that many of the atoms are periodically displaced from the normal positions of the fundamental h.c.p. lattice. The physical significance of the occupancy and displacement modulations is discussed. The latter bears a resemblance to the motion of cations in the transition-metal dichalcogenides and the direction of the displacements in the alloy can be explained if charge-density waves synchronizing with the occupancy waves are assumed to exist.
A low-temperature X-ray Weissenberg goniometer with closed-cycle cooling to about 28 K
Authors: Adlhart W. , Huber H.
Published: July 2002

A low-temperature camera for single-crystal X-ray investigation between 28 and 350 K has been developed for a modified Weissenberg goniometer. Cooling is provided by a double-stage cryorefrigerator which is firmly attached to the low-temperature camera. Stranded copper cables ensure a flexible heat transfer between crystal and cold finger allowing a crystal rotation of 180°. Compared to the usual Weissenberg technique almost no further limitation is given on the accessible angular range of the scattered radiation.
A method for collection of step-scan data on a CAD4 diffractometer, homogeneity of the monochromated primary X-ray beam
Authors: Birknes B. , Hansen L. K.
Published: July 2002

A procedure for collecting protein data by a simulated step-scan method is described for a CAD4 diffractometer. The method allows one to collect 100–150 reflections per hour without any significant loss in accuracy, thus reducing the time spent on each reflection by a factor of 2–3 compared with the ω–2θ scan technique. A comparison between data collected for the protein phospholipase C by the present method and by the ω–2θ technique gives a reliability factor of 2%. Prior to this work the homogeneity of the X-ray beam from a graphite monochromator was determined, and the intensity cross section of the monochromatized X-ray beam showed that the total X-ray illumination of the crystal is practically unchanged regardless of the orientation of the crystal in the primary beam.
Powder diffraction by layered minerals containing different layers and/or stacking defects. Comparison between Markovian and non-Markovian models
Authors: Plançon A. , Drits V. A. , Sakharov B. A. , Gilan Z. I. , Brahim J. B.
Published: July 2002

The models used up to now for the calculation of powder patterns of layer minerals containing defects have adopted a Markovian hypothesis for the law of defect occurrence. One consequence of this hypothesis is that in a powder obeying this law the particles differ in their contents (chemical composition and/or abundance of stacking defects). Another model can be considered in which the particles have identical contents of each type of layers or stacking defects. This is denoted here by the `identical contents crystal model' (ICC model). In this article are described: (i) the calculation of diffracted intensities for the ICC model and its comparison with that of the Markovian one, and (ii) the application of this calculation to a two-component mixed-layer system. It is shown which kind of modification of intensities or peak positions occur with the ICC model for thin crystals.
Le tétrabromomercurate(II) de monométhylammonium
Authors: Ben Salah A.
Published: July 2002

Bis(monomethylammonium) tetrabromomercurate, (CH3NH3)2HgBr4, 2CH6N+.Hg2+.4Br−, is monoclinic, space group P21/c. Unit-cell dimensions are: a = 7.979(4), b = 13.351(4), c = 11.289(4) Å, β = 96.36(2)°, Z = 4, Dm
= 3.25, Dx
= 3.24 Mgm−3. The compound undergoes a phase transition at low temperature. The JCPDS Diffraction File No. of this compound is 33-1997.
X-ray measurement of the static Debye–Waller factor of NbH
x
Authors: Behr H. , Metzger H. , Peisl J.
Published: July 2002

Integrated X-ray Bragg intensities from Nb single crystals have been measured as a function of H concentration and scattering vector along high-symmetry directions. The observed attenuation can be described in terms of a static Debye–Waller factor (DWF) due to the static displacements of the Nb lattice atoms around the dissolved H. The crystals were loaded with H in situ on the X-ray diffractometer. The static DWF was determined from the ratio of the intensities from a crystal with and without H. Corrections are necessary for several magnitudes which change with the lattice-parameter change and the change of the thermal displacements upon the uptake of H. The measured static DWF is proportional to the H concentration c(H/Nb) for c≤0.30 and the square of the scattering vector K
2 for small K, as expected from theory. From analysis of the static DWF the static displacements of the Nb atoms closest to the H impurity u
1 = 0.1 Å were determined.
A rapid and precise method of measuring Kendrew-model coordinates with theodolites
Authors: Lebioda L. , Hatada M. H. , Tulinsky A.
Published: July 2002

The Kendrew-model coordinates of KDPG aldolase have been measured with the use of two theodolites which are improved versions of a conventional surveyor's transit. The four angular measurements are converted to Cartesian coordinates and a minimum-error estimate with a minicomputer interfaced to the theodolites. The positions of 1677 atoms of the asymmetric unit of KDPG aldolase were measured by two of the authors in four working days or at the rate of about 60 atoms h−1. The standard deviations of the bond distances and angles of the model obtained were ± 0.04 Å and about 7°, respectively. The mathematics of the various conversions are presented.
Crystal data for 2-(4-methyl-2-pyridyliminomethyl)phenol and 2-(4,6-dimethyl-2-pyridyliminomethyl)phenol
Authors: Escobar C. , Garland M. T. , Spodine E.
Published: July 2002

Crystal data for the Schiff bases 2-(4-methyl-2-pyridinyliminomethyl)phenol (salampy) and 2-(4,6-dimethyl-2-pyridyliminomethyl)phenol (saladimpy) are reported. Salampy: C13H12N2O, Mr
= 212.0, P21/c, a = 11.772(4), b = 7.5386(7), c = 15.154(5) Å, β = 124.89 (2)°, V = 1103.1(4) Å3, Dm
= 1.24, Dx
= 1.28 g cm−3, Z = 4; saladimpy: C14H14N2O, Mr
= 226.0, P212121, a = 21.585(5), b = 8.8285(8), c = 6.2952(6) Å, V = 1199.6(3) Å3
Dm
= 1.22, Dx
= 1.25 g cm−3, Z = 4. The JCPDS Diffraction File No. for C13H12N2O is 33-1999, for C14H14N2O 33-1998.
Qualitative and quantitative morphological study on α and β phases of ammonium pentaborate tetrahydrate
Authors: Solans X. , Font-Altaba M. , Aguiló M. , Solans J. , Domenech M. V.
Published: July 2002

A qualitative and quantitative morphological study on the α and β phases of ammonium pentaborate tetrahydrate has been carried out. Crystals of the two phases were obtained by slow evaporation from aqueous solutions. Usually the α phase was obtained with {101}; {\bar 101}; {011} and {110} as crystal forms, a high percentage of the crystals (99%) were twins, with a twofold axis parallel to c as the twin law. When MgCl2.6H2O was added to the solution, the β phase was obtained as prismatic crystals elongated along [\bar 110] with {111}, {\bar 111 } and {001} as crystal forms. Generally, these crystals were also twins, with a twofold axis parallel to [110] as twin law. A qualitative and quantitative morphological study showed the α-phase crystals to have the theoretical growth forms, while the crystal forms of the β phase were explained by the presence in the solution of (H2O)6Mg2+ and Cl− ions.
Diffuse scattering measurements with synchrotron radiation: instrumentation and techniques
Authors: Matsubara E. , Georgopoulos P.
Published: July 2002

The analysis of diffuse scattering from single crystalline specimens in the reflection mode has generally been acknowledged as a very powerful means of obtaining structural information on local atomic arrangements in disordered alloys, intermetallics and ceramics. However, owing to the low intensities encountered and the large number of measurements required for such an analysis, experiments have been extremely time consuming and few have been attempted. Synchrotron radiation makes it possible to conduct such experiments in a matter of hours and much higher quality data can be obtained than in the laboratory. This paper describes the experimental procedures and methods applied to a study of Al–Cu age hardening alloys conducted at the Cornell Synchrotron Source (CHESS).
X-ray position-sensitive detectors
Authors: Arndt U. W.
Published: July 2002

The physical processes are examined which can be used for the detection of X-rays in the range between about 3 and about 20 keV and for the positional localization of the incident photons. The criteria for choosing a detector for particular purposes are discussed in general terms. Specific examples of one- and two-dimensional detectors are then considered with particular emphasis on devices which are still in a state of development, and an attempt is made to summarize the nature, performance and suitability for different experiments of available detectors.
X-ray determination of static displacements of atoms in alloyed Ni3Al
Authors: Morinaga M. , Sone K. , Kamimura T. , Ohtaka K. , Yukawa N.
Published: July 2002

Single crystals of Ni3(Al, M) were grown by the Bridgman method, where M is Ti, V, Cr, Mn, Fe, Nb, Mo and Ta. The composition was controlled to be about Ni75Al20
M
5 so that the alloying element, M, substitutes mainly for Al. With these crystals conventional X-ray structural analysis was performed. The measured static displacements of atoms from the average lattice points depended largely on the alloying elements and varied in the range 0.00–0.13 Å for Ni atoms and 0.09–0.18 Å for Al atoms. It was found that these atomic displacements correlated well with the atomic radius of the alloying element, M. For example, when the atomic radius of M is larger than that of Al, the static displacements are large for the atoms in the Al sublattice but small for the atoms in the Ni sublattice. By contrast, when the atomic radius of M is smaller than that of Al, the displacements are more enhanced in the Ni sublattice than in the Al sublattice. Thus, there is an interesting correlation between the atomic displacements in both the Al and Ni sublattices in the presence of alloying elements. This seems to be one of the characteristics of alloyed compounds with several sublattices.
Experiences with a new translation-function program
Authors: Fujinaga M. , Read R. J.
Published: July 2002

The development of a new translation-function program is reported. It is one that uses a linear correlation coefficient to determine the correct position of an oriented molecule in the crystal cell. The method has been implemented in a computer program called BRUTE. The program can also refine the orientation of the model and accept a set of atoms with fixed positions. Comparison of the correlation coefficient with other translation functions indicates that it is comparable to or slightly better than the rest. The most important feature of the program is its ability to adjust the orientation of the model. This allows for errors in the orientation obtained from the rotation function to be corrected.
A toolkit for computational molecular biology. III. MICRYFON – a (fairly) general program for input of protein coordinate files
Authors: Lesk A. M.
Published: July 2002

The large number and variety of formats in use for storing protein coordinate data sets make it difficult to integrate the operation of programs from different laboratories. To ameliorate this situation a general input program, called MICRYFON, has been designed and written. MICRYFON will analyze and interpret many common protein coordinate formats without the specification of any `option' indicating which format the program is to expect.
A standardless X-ray diffraction method for the quantitative analysis of multiphase mixtures
Authors: Rius J. , Plana F. , Palanques A.
Published: July 2002

An X-ray diffraction method is described that determines calibration constants using only diffracted intensities and calculated phase absorption coefficients through a least-squares procedure. The conditions necessary for the application of this method are that the qualitative analysis be complete, that sufficient samples with essential differences in the quantitative phase composition be available and that the chemical compositions of the phases be known approximately. It does not require the use of pure phases or the measuring of the sample absorption coefficients. It allows the easy introduction of known calibration constants, thus reducing the number of samples needed and increasing the versatility of the method.
Crystal data for ternary compounds of the system Cu–As2Se3
Authors: Majid C. A. , Hussain M. A.
Published: July 2002

Structural studies of polycrystalline CuAsSe2, Cu3AsSe4 and Cu3AsSe3 are reported. These were found to be cubic with space group Pm{\bar 3}m and lattice parameters as follows: (1) CuAsSe2: a = 5.513(4) Å, V = 167.47(1) Å3, Z = 2; Dm
= 5.56(6), Dx
= 5.88 g cm−3. (2) Cu3AsSe4: a = 5.530(5) Å; V = 169.11(2) Å3; Z = 1; Dm
= 5.51(5), Dx
= 5.75 g cm−3. (3) Cu3AsSe3: a = 5.758(9) Å, V = 190.87(3) Å3, Z = 1, Dm
= 5.03(9), Dx
= 4.45 g cm−3. X-ray diffraction data using a Rigaku DMAX-IIIA diffractometer and Cu Kα radiation.
Easy-to-use indirect Fourier transformation routines for evaluation of slit-length-smeared SAXS curves of polystyrene in solution
Authors: Kube O. , Springer J.
Published: July 2002

Two easy-to-use indirect Fourier-transformation routines for the evaluation of slit-length-smeared SAXS curves of polystyrene in solution are demonstrated. For approximation of the SAXS curve, analytically transformable Gaussian and Lorentzian functions are chosen. The nonlinear least-squares fit is transformed to a linear one by specifying fixed non-linear coefficients. The fit is constrained by allowing only positive linear coefficients. The range over which nonlinear coefficients have to be specified can be easily obtained from the SAXS curve. An exact specification of this range is unnecessary for the fit. The method allows direct and clear control of the indirect Fourier transformation.
X-ray diffraction study of anharmonic thermal vibrations in β-AgI
Authors: Piltz R. O. , Barnea Z.
Published: July 2002

Intensity data were collected at room temperature from an extended-face crystal of AgI using Mo Kα radiation. Least-squares refinement indicates that the thermal motion of the Ag+ ions is large with a considerable anharmonic component. The wurtzite positional parameter, u, was found to be 0.3748(2). The proportion of point defects was determined to be no greater than 0.9%. The proportion of random staking faults was determined by two experimental techniques to be no greater than 2%.
A multiple-slit collimator for synchrotron white-beam section topography
Authors: Stock S. R. , Chung Y. H. , Rek Z. U.
Published: July 2002

A multiple slit for simultaneously recording up to ten section topographs is described for use with synchrotron white radiation. Two collimators were fabricated from a GaAs crystal and a Ta sheet by laser machining; the spacing was 1 mm between each of the ten parallel 50 μm × 10 mm slits. The longest dimension of the slits was in the horizontal plane, and rotations of the multiple slit between 20 and 25° from normal to the incident beam (i.e. about an axis parallel to slits) produced the sharpest Pendellösung fringe patterns from a dislocation-free Si crystal. The Ta multiple slit proved to be much superior to the GaAs slits, but background levels were somewhat higher than for single slits.
On the use of a small two-dimensional position-sensitive detector in neutron diffraction
Authors: Lehmann M. S. , Kuhs W. F. , McIntyre G. J. , Wilkinson C. , Allibon J. R.
Published: July 2002

A small position-sensitive 3He gas detector has been developed for diffraction studies using short-wavelength neutrons. It covers 32 × 32 pixels with a 2 mm resolution, which in the present set up corresponds to 0.25°, and the efficiency is 75% at a wavelength of 0.8 Å. The detector has been used for standard data collection, as well as for studies of twinned crystals and measurements involving parasitic reflections. In all cases it has improved the mode and speed of the measurement, with gain factors compared with single detectors which range from more than two in standard measurements to several hundred for the study of details of the Bragg peak(s). The computation time in data analysis and the storage of the data are no major limitations, partly due to the smallness of the data array, and partly due to efficient packing routines.
The properties of anisotropic small-angle scattering
Authors: Svetogorsky D. A.
Published: July 2002

It is shown that the cross section of small-angle neutron scattering (SANS) on an anisotropic system of point scatterers is determined by a symmetric tensor (R). The mean square radius of gyration of the system is the trace of R. A simple method is proposed for experimental determination of the tensor R by small-angle measurements with rotation of a sample.
N-beam interactions examined with the help of the computer programs PSIINT and PSILAM
Authors: Rossmanith E. , Kumpat G. , Schulz A.
Published: July 2002

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.