bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes of Dopamine Turnover in the Progression of Parkinson's Disease as Measured by Positron Emission Tomography: Their Relation to Disease-Compensatory Mechanisms
Authors: Sossi Vesna , de la Fuente-Fernández Raúl , Holden James E. , Schulzer Michael , Ruth Thomas J. , Stoessl Jon
Published: July 2004

An increase in dopamine turnover has been shown to occur early in Parkinson's disease (PD). This study investigated changes of dopamine turnover as a function of PD duration using the effective distribution volume (EDV) for dopamine, determined by positron emission tomography with 6-[18F]-fluoro-L-dopa, and compared them with changes in dopamine synthesis and storage ability, quantified with the fluorodopa uptake rate constant Ki. Six healthy subjects, 9 early PD patients (PD1), and 13 advanced PD patients (PD2) participated in the study. In the caudate, the Ki and EDV for PD1 were not significantly different from the normal values, whereas in the putamen Ki was 63% of normal and EDV was only 35%. Between PD1 and PD2 the decline in EDV was higher than that for Ki (caudate 44% and putamen 46% for EDV vs. 21% and 34%, respectively, for Ki). Turnover was higher in the caudate than the putamen in controls, whereas the PD patients exhibited the reverse pattern. This comparison of changes in Ki and EDV as a function of disease progression indicates that a relatively slower decrease in dopamine synthesis and a relatively faster increase in turnover in early disease likely act as compensatory mechanisms, and that the clinical onset of PD reflects a global failure of dopaminergic compensatory mechanisms.
Celecoxib Induces Functional Recovery after Intracerebral Hemorrhage with Reduction of Brain Edema and Perihematomal Cell Death
Authors: Chu Kon , Jeong Sang-Wuk , Jung Keun-Hwa , Han So-Young , Lee Soon-Tae , Kim Manho , Roh Jae-Kyu
Published: July 2004

The selective cyclooxygenase-2 (COX-2) inhibitor has been reported to have antiinflammatory, neuroprotective, and antioxidant effects in ischemia models. In this study, the authors examined whether a selective COX-2 inhibitor (celecoxib) reduces cerebral inflammation and edema after intracerebral hemorrhage (ICH), and whether functional recovery is sustained with longer treatment. ICH was induced using collagenase in adult rats. Celecoxib (10 or 20 mg/kg) was administered intraperitoneally 20 minutes, 6 hours, and 24 hours after ICH and then daily thereafter. Seventy-two hours after ICH induction, the rats were killed for histologic assessment and measurement of brain edema and prostaglandin E2. Behavioral tests were performed before and 1, 7, 14, 21, and 28 days after ICH. The brain water content of celecoxib-treated rats decreased both in lesioned and nonlesioned hemispheres in a dose-dependent manner. Compared with the ICH-only group, the number of TUNEL-positive, myeloperoxidase-positive, or OX42-positive cells was decreased in the periphery of hematoma and brain prostaglandin E2 level was reduced in the celecoxib-treated group. Celecoxib-treated rats recovered better by the behavioral tests at 7 days after ICH throughout the 28-day period, and the earlier the drug was administered, the better the functional recovery. Evidence of similar effects in an autologous blood–injected model showed that direct collagenase toxicity was not the major cause of inflammation or cell death. These data suggest that celecoxib treatment after ICH reduces prostaglandin E2 production, brain edema, inflammation, and perihematomal cell death in the perihematomal zone and induces better functional recovery.
X-ray diffraction analysis of stacking and twin faults in f.c.c. metals: a revision and allowance for texture and non-uniform fault probabilities
Authors: Velterop L. , Delhez R. , de Keijser Th. H. , Mittemeijer E. J. , Reefman D.
Published: July 2004

A revision is presented of the original description by Warren [X-ray Diffraction, (1969), pp. 275–298. Massachusetts: Addison-Wesley] of the intensity distribution of powder-pattern reflections from f.c.c. metal samples containing stacking and twin faults. The assumptions (in many cases unrealistic) that fault probabilities need to be very small and equal for all fault planes and that the crystallites in the sample have to be randomly oriented have been removed. To elucidate the theory, a number of examples are given, showing how stacking and twin faults change the shape and position of diffraction peaks. It is seen that significant errors may arise from Warren's assumptions, especially in the peak maximum shift. Furthermore, it is explained how to describe powder-pattern reflections from textured specimens and specimens with non-uniform fault probabilities. Finally, it is discussed how stacking- and twin-fault probabilities (and crystallite sizes) can be determined from diffraction line-profile measurements.
Assessment of different X-ray stress measuring techniques for thin titanium nitride coatings
Authors: Saerens A. , Van Houtte P. , Meert B. , Quaeyhaegens C.
Published: July 2004

Three different X-ray stress measuring techniques have been applied to thin titanium nitride coatings: the classicald–sin2ψ method, a low incident-beam-angle method and the crystallite-group method. The results are used for a comparison of the three methods. The influence of the crystallographic texture is studied by considering a set of coatings with a strong (111) fibre texture and another set with a weaker and mixed fibre texture. It is shown that no significant differences in the stresses in the latter coatings are found using the three methods, whereas the coatings with strong (111) fibre texture exhibit compressive stresses that are significantly higher, when the crystallite-group method is used. This is explained by the fact that (111)-oriented grains sustain stresses that are about 30% higher than those of the grains that show a deviation of 10° from this orientation. Non-linearities in thed–sin2ψ curves are reported that cannot be explained by means of linear elastic theories.
Solving crystal structures inP1: an automated procedure for finding an allowed origin in the correct space group
Authors: Burla Maria Cristina , Carrozzini Benedetta , Cascarano Giovanni Luca , Giacovazzo Carmelo , Polidori Giampiero
Published: July 2004

Crystal structure solution inP1 may be particularly suitable for complex crystal structures crystallizing in other space groups. However, additional efforts and human intervention are often necessary to locate correctly the structural model so obtained with respect to an allowed origin of the actual space group. An automatic procedure is described which is able to perform such a task, allowing the routine passage to the correct space group and the subsequent structure refinement. Some tests are presented proving the effectiveness of the procedure.
Kinematical intensity profiles obtained for single and multiple diffraction in perfect spherical crystals
Authors: Rossmanith Elisabeth
Published: July 2004

The `intensity' (power) profiles obtained with the rotating-crystal method are derived in the framework of the kinematical theory for a spherically shaped crystal bathed in a parallel monochromatic incident beam. It is shown that in the case of the ψ scanning technique, the `particle size effect' can cause appreciable broadening of the Bragg intensity profiles.
Extinction-corrected mean thickness and integral width used in the programUMWEG98
Authors: Rossmanith Elisabeth
Published: July 2004

The kinematical upper limit of the extinction-corrected mean thickness as well as the corresponding integral width of the intensity profiles are estimated for spherical crystals. The new expression for the primary-extinction correction is compared with expressions given recently in the literature as well as with those widely used in crystal structure analysis.
How theRfactor changes as molecules become larger
Authors: Krebs Frederik C.
Published: July 2004

TheRfactors and the numbers of independent atoms for the entire set of molecular organic structures contained in the Cambridge Structural Database were retrieved and analysed. The averageRfactor for all structures containing the same number of independent atoms was plotted against the number of independent atoms. A clear correlation was observed. The plot is suggested to give a graphical overview of how values of theRfactor for large-molecule structures with 200–1000 independent atoms increase as the number of independent atoms increases.
Modeling radial collimators for use in stress and texture measurements with neutron diffraction
Authors: Wang D.-Q. , Wang X.-L. , Robertson J. L. , Hubbard C. R.
Published: July 2004

Radial collimators have been recently introduced to define the sampling volume during neutron diffraction stress and texture mapping experiments. This paper presents both analytical and Monte Carlo numerical models for the calculation of the spatial distribution of neutron transmission through a radial collimator. It is shown that the effective size of the scattered neutron beam as seen by detectors behind the collimator is quite sensitive to the collimator length and the number of blades. For a given radius of a collimator, the effective beam width increases sharply as the length is shortened. Due to the finite blade thickness, the center of gravity of the sampling volume is shifted away from the collimator. In contrast, attenuation of the neutron beam by the sample brings the center of gravity of the sampling volume closer to the collimator.
Polar potassium rare earth nitrates K2[RE(NO3)5(H2O)2] (RE = La, Ce, Pr and Nd). I. Crystal growth and crystal structures
Authors: Held P. , Hellwig H. , Rühle S. , Bohatý L.
Published: July 2004

Using a standard evaporation technique at 311 K, large single crystals of the polar orthorhombic potassium rare earth nitrates K2RE(NO3)5.2H2O, where RE = La, Ce, Pr or Nd, of optical quality and dimensions up to 5 × 5 × 4 cm, were grown from aqueous solutions containing a stoichiometric ratio of potassium and rare earth ions (K:RE = 2:1) and a surplus of nitric acid. Detailed structural and crystal chemical analyses of all four isomorphic compounds based on single-crystal X-ray diffraction data were carried out [space groupFdd2;Z= 8; La compound:a= 11.2814 (6),b= 21.480 (1),c= 12.2589 (4) Å,R= 0.94%; Ce compound:a= 11.263 (3),b= 21.404 (3),c= 12.230 (4) Å,R= 1.92%; Pr compound:a= 11.213 (2),b= 21.392 (4),c= 12.204 (2) Å,R= 1.58%; Nd compound:a= 11.197 (1),b= 21.378 (1),c= 12.195 (1) Å,R= 1.55%]. The main structural feature is the diaquapentanitratolanthanide(III) group, [RE(NO3)5(H2O)2]2−, as stated earlier by Eriksson, Larsson, Niinistö & Valkonen [Acta Chem. Scand. Ser. A, (1980),34, 567–572] for the La compound. The rare earth atoms are surrounded by 12 O atoms, two of which belong to water molecules, the remaining ten belonging to five bidentate nitrate groups. The coordination polyhedron [REO12] is a distorted icosahedron; its geometry is discussed using a simple hard-sphere model.
Polar potassium rare earth nitrates K2[RE(NO3)5(H2O)2] (RE = La, Ce, Pr and Nd). II. Linear and nonlinear optical properties
Authors: Hellwig H. , Rühle S. , Held P. , Bohatý L.
Published: July 2004

Linear and nonlinear optical properties of the four isomorphic orthorhombic (point groupmm2) potassium rare earth nitrates K2[RE(NO3)5(H2O)2], with RE = La, Ce, Pr or Nd, have been investigated. Refractive indices in a wavelength range from 0.35 to 2.5 µm and the transmission spectra between 0.25 to 3.0 µm were measured. Using the Maker fringe technique, the d_{ijk}^{\rm\, SHG} coefficients of second-harmonic generation for a fundamental of the Nd–YAP laser (λ = 1079.5 nm) were determined for all four compounds. The d_{ijk}^{\rm\, SHG} coefficients of all four substances are about three times larger than those of KDP, as was first published by Ebberset al.[IEEE J. Quantum Electron.(1993),29, 497–507] for K2[La(NO3)5(H2O)2]. These nitrates are promising materials for application to nonlinear optics (e.g.second-harmonic generation of Nd laser radiation). The nonlinear optical properties of these compounds seem to have their origin mainly in the nitrate groups, as indicated by a simple model (summing the molecular hyperpolarizabilities of the NO3group). Neglecting local field effects, the hyperpolarizability of the NO3group was calculated as β222= 2.52 × 10−40 m4 V−1.
The Huber G670 imaging-plate Guinier camera tested on beamline I711 at the MAX II synchrotron
Authors: Ståhl Kenny
Published: July 2004

A Huber G670 imaging-plate Guinier powder diffraction camera has been tested at an X-ray synchrotron source. It was found to be a very potent tool, offering an unusual combination of high angular resolution and short data collection time, while using very small amounts of sample. Specifically, it was found that: (i) the angular resolution (full width at half-maximum) varies between 0.07 and 0.15° in 2θ without focusing,i.e.relying on a parallel synchrotron beam; (ii) with a readout and erasure cycle time of 15 s, it is possible to obtain Rietveld-refinable data within less than a minute for a low-symmetry zeolite refined with 82 parameters; (iii) special attention has to be given to calibration of the detector and some general geometrical correction factors should be included in the data reduction.
A correction for anisotropic line broadening due to structural defects in powder diffraction structure analysis
Authors: Solovyov Leonid A.
Published: July 2004

An anisotropic line-broadening correction allowing for the presence of structural defects in crystals is developed for powder diffraction full-profile structure analysis. The approach is based on the statistical consideration of diffraction from a crystal composed of two types of unit cells differing in atomic arrangement and/or content, but not in shape and size. The correction is incorporated into a computer program for powder diffraction structural analysis. The application of this correction in crystal structure investigations oftrans- and β-trans-[Pd(NH3)2X2] (X= Cl, Br, I) overcame the problem of selective anisotropic peak broadening and allowed precise and self-consistent information about the structure and the microstructure of these compounds to be obtained.
Use of a crystallization robot to set up sitting-drop vapor-diffusion crystallization andin situcrystallization screens
Authors: Snook Christopher F. , Purdy Michael D. , Wiener Michael C.
Published: July 2004

A commercial crystallization robot has been modified for use in setting up sitting-drop vapor-diffusion crystallization experiments, and for setting up protein crystallization screensin situ. The primary aim of this effort is the automated screening of crystallization of integral membrane proteins in detergent-containing solutions. However, the results of this work are of general utility to robotic liquid-handling systems. Sources of error that can prevent the accurate dispensing and mixing of solutions have been identified, and include local environmental, machine-specific and solution conditions. Solutions to each of these problems have been developed and implemented.
In situX-ray crystallography
Authors: McPherson Alexander
Published: July 2004

A method is proposed, and preliminary experiments are described, for collection of X-ray data from macromolecular crystalsin situ. The usual processes of mounting for either room-temperature or cryogenic X-ray data collection are eliminated by growing crystals, using vapor diffusion, on small supports or films that can be either frozen or treated before transfer directly to the X-ray beam. The approach has the advantage that individual crystals are never manipulated and it is not necessary to isolate single crystals. Furthermore, crystals fixed to the surface on which they grow provides a positive advantage, small and otherwise problematic crystals become serviceable, and robotic or automated data collection becomes simplified.
ROD: a program for surface X-ray crystallography
Authors: Vlieg Elias
Published: July 2004

A brief description is given of the C-programRODwith which surface structures can be refined on the basis of X-ray data. All main features one encounters on surfaces, like roughness, relaxations, reconstructions and multiple domains, are taken into account. The program has proven to be a useful tool over the past ten years.
X-ray study of the light-induced metastable state of a spin-crossover compound
Authors: Kusz Joachim , Spiering Hartmut , Gütlich Philipp
Published: July 2004

Iron(II) complexes exhibiting thermal spin crossover may be converted from the1A1low-spin (LS) state to the5T2high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST). The lifetime of the metastable LIESST state may be sufficiently long for X-ray diffraction study. The lattice parameters of a single crystal of [Fe(ptz)6](BF4)2(ptz = propyltetrazole) were measured between 300 and 10 K, while the crystal changed from the HS to the LS state near 135 K. Using the green light (514 nm) of an argon-ion laser, the crystal was quantitatively converted to the metastable LIESST state at 10 K; its lattice parameters were measured up to 50 K, at which point the LIESST state begins to decay on a minute timescale. The change of the lattice parameters can be interpreted by a superposition of a normal temperature dependence, for which the isostructural zinc compound served as a reference, and an almost temperature-independent part which is proportional to the fraction of molecules in the HS state.
A non-linear positive method to reconstruct the parent textures from the inherited textures in phase transformation
Authors: Humbert M. , Gey N. , Esling C.
Published: July 2004

The orientation distribution function (ODF) of the parent phase is reconstructed from the inherited ODF of the transformed phase, provided that the lattice symmetry of the parent phase is higher than that of the inherited one and that the orientation relation between both phases is known. In the cases of experimental errors or variant selections, the positivity of the ODF of the parent phase is ensured by assuming that it is of quadratic form.
X-ray investigation and discussion of the magnetostriction of Gd3T(T= Ni, Rh, Irx) single crystals
Authors: Kusz J. , Böhm H. , Talik E.
Published: July 2004

The variations of the lattice parameters of Gd3T(T= Ni, Rh, Irx) single crystals with temperature were measured in the range 10–300 K. The compounds with Ni and Rh crystallize in the orthorhombic space groupPnma, but the compound with Ir crystallizes as Gd5Ir2in the monoclinic space groupA2/a. The three compounds exhibit an anomalous anisotropic spontaneous magnetostriction below the magnetic ordering temperature.
ShakePSD: automatic phase solver covering heavy-atom methods and direct methods for Windows PCs
Authors: Okada Sachiko , Okada Kenji
Published: July 2004

A new computer program,ShakePSD(filtering using the Patterson function, search procedures and direct methods), has been developed to solve the structures of organic compounds automatically on personal computers (PCs) operating under Windows.ShakePSDis a single program that can discriminate whether a heavy-atom is included or not and can employ heavy-atom methods (Patterson function and search for all remaining atoms) or direct methods (tangent formula and/or minimal function). A new subroutine,MINIMAL, adopts the Karle recycling method based on the minimal-function theory. The input data are cell constants, space group, number of atoms with atomic types and observed structure factorsFo(h). Compared to theTANGENTprocedure (employing the tangent formula),MINIMALis able to obtain the same or a larger number of atoms in a run set and the number of run sets is distinctly larger in a single computer execution.MINIMALis a powerful procedure, but it takes a considerable amount of processing time on a Windows PC. The output is in the form of two-dimensional projection diagrams of the molecules in a unit cell.ShakePSDis an automatic general phase solver, being able to handle both heavy-atom methods and direct methods within a single program, and determines, with certainty, molecular fragments.
SAXS experiments on absolute scale with Kratky systems using water as a secondary standard
Authors: Orthaber Doris , Bergmann Alexander , Glatter Otto
Published: July 2004

For small-angle scattering, of X-rays (SAXS) and neutrons (SANS), the importance of absolute calibration has been recognized since the inception of the technique. The work reported here focuses on SAXS measurements using Kratky slit systems. In former days, only molecular weights or scattering per particle were determined, but today absolute calibration implies the use of the unit of cm−1for the scattering curve. It is necessary to measure the so-called absolute intensity, which is the ratio of the scattering intensity to the primary intensityP0. Basically there are two possible ways to determine the absolute intensity. The first one is the direct method, which involves the mechanical attenuation of the primary beam by a rotating disc or a moving slit. The second is the indirect method, using secondary standards. Water is well suited as a calibration standard because of the angle-independent scattering. The essential advantage is that the scattering of water only depends on the physical property of isothermal compressibility. Before presenting an example of the practical performance of this method, the most important theoretical equations for an SAS experiment on the absolute scale are summarized. With the slit collimation system, the scattering curve of water can be measured with high enough statistical accuracy. As a first example, the scattering curve of the protein lysozyme on the absolute scale is presented. The second example is the determination of the aggregation number of a triblock copolymer P94 (EO17–PO42–EO17). Taking into account that at least 10% of the polymer sample consists of diblocks, the accuracy of around 10% for the determined aggregation number is rather good. The data of P94 are also considered on the particle scale in order to obtain the radial scattering-length density distribution.
Parallel-beam X-ray diffractometry using X-ray guide tubes
Authors: Yamanoi Toyoko , Nakazawa Hiromoto
Published: July 2004

A parallel-beam X-ray diffraction geometry using X-ray guide tubes is proposed to eliminate preferred-orientation effects in powder X-ray diffraction (XRD) patterns and for new applications of XRD. A bundle of X-ray guide tubes (polycapillaries) is used to provide an intense quasi-parallel (approximately 0.2° divergence) and large-diameter (approximately 20 mm) beam of X-rays needed for parallel-beam diffractometry. Mica and silicon particles were agitated inside a cylindrical chamber by a steady flow of N2gas so that they were randomly oriented. The quasi-parallel incident X-ray beam passed through the cloud of floating particles. The diffracted X-rays were detected using a standard 2θ diffractometer. The integrated intensities observed agree well with those calculated from the known model of the crystal structure. This result demonstrates that this type of diffractometry is capable of avoiding preferred-orientation effects and of collecting XRD data for moving powder samples.
Elimination of extrinsic components overlapping lattice distortion variations of a silicon single crystal obtained by double-crystal X-ray topography
Authors: Kudo Y. , Liu K.-Y. , Kawado S. , Hirano K.
Published: July 2004

Variations in lattice plane spacing and lattice plane orientation,i.e.Δd/dand Δα, reflect variations in lattice distortion in a single crystal. Double-crystal X-ray topography (DCT) using synchrotron radiation can be used to measure Δd/dand Δα of a silicon single crystal. However, both Δd/dand Δα measured using DCT are always overlapped by extrinsic components, showing particular long-range variations. The extrinsic components should be eliminated from the measured Δd/dand Δα for quantitative characterization of silicon single crystals. A sample-rotation and area-detector-traverse (RT) method, applicable to X-ray optics for DCT, has been newly developed. The extrinsic components are eliminated by modification of the intensity distribution on the X-ray topographs using the RT method. From theoretical considerations, it is confirmed that the extrinsic components are mainly due to the (+,−) non-parallel setting between the monochromator and the collimator, and a minute bend in the sample due to its physical restraint.
Deconvolution of X-ray diffraction profiles by using series expansion
Authors: Sánchez-Bajo F. , Cumbrera F. L.
Published: July 2004

The deconvolution of X-ray diffraction profiles is a basic step in order to obtain reliable results on the microstructure of crystalline powder (crystallite size, lattice microstrain,etc.). A procedure for unfolding the linear integral equationh=g finvolved in the kinematical theory of X-ray diffraction is proposed. This technique is based on the series expansion of the `pure' profile,f. The method has been tested with a simulated instrument-broadened profile overlaid with random noise by using Hermite polynomials and Fourier series, and applied to the deconvolution of the (111) peak of a sample of 9-YSZ. In both cases, the effects of the `ill-posed' nature of this deconvolution problem were minimized, especially when using the zero-order regularization combined with the series expansion.
A beam-stop mount designed for use with area detectors
Authors: Bertok Alexander , Allen Jr John W. , Li Wen-jeng , Sheriff Steven
Published: July 2004

A beam-stop holder is described that allows for easy removal of the beam stop during alignment and calibration measurements and then for precise repositioning prior to data collection.
Next-near-neighbour interactions with Al in Li+- and Rb+-exchanged Na+β-aluminas, detected by synchrotron X-ray absorption spectroscopy
Authors: Marcelli Augusto , Mottana Annibale , Cibin Giannantonio
Published: July 2004

Synchrotron X-ray absorption near-edge structure (XANES) spectroscopy studies have been carried out on the electronic and crystal structure environments around the Al atom in Na+β-alumina and in two β-aluminas with Na+exchanged by Li+and Rb+. The aim is to define the type of interaction, if any, existing between the Al located in the `spinel block' and the fast-conducting cations in the `conduction plane'. Na+β′′-alumina has also been studied for comparison. All β-alumina spectra differ from that of α-alumina (corundum) by showing additional features due to the presence of tetrahedral Al. Moreover, they all show a much greater degree of local disorder. There are definite, but small, interactions between tetrahedral Al (and, possibly, also octahedral Al) in the `spinel block' and the Na+and Rb+cations in the `conduction plane'; Na+and Rb+β-aluminas have similar AlK-edge XANES features, but with intensities that change in relation to the weight of the `conduction plane' atom. Despite differences in composition and structure, Na+β′′-alumina shows the same behaviour, thus confirming the substantial similarity of the Al local environments. Li+-exchanged β-alumina has an AlK-edge XANES spectrum that apparently differs from all others, but actually conveys the same basic information. Indeed, interaction between Al and Li is much greater than in any other β-alumina because Li+moves laterally off the `conduction plane' to become close to a facing tetrahedral Al, and strongly interacts with it. Thus, this study also draws attention to the fact that β-aluminas react differently to alkali exchange.
Multiple CCD detector for macromolecular X-ray crystallography
Authors: Phillips Walter C. , Stanton Martin , Stewart Alexander , Qian Hua , Ingersoll Charles , Sweet Robert M.
Published: July 2004

A charge-coupled device (CCD)-based detector designed for macromolecular crystallography is described. The detector has an area of 200 × 200 mm, a readout time of 1.6 s, and total noise equivalent to approximately three 12 keV X-ray photons per pixel. The detector is constructed from a 2 × 2 array of four identical units, each unit consisting of a 4.1:1 demagnifying fiber-optic taper bonded to a 1 k × 1 k, 24 µm pixel, CCD sensor. Each CCD is read out in parallel though four channels and digitized to 16 bits. A Gd2O2S phosphor X-ray-to-light converter bonded to an aluminized-plastic film is held in contact with the input surfaces of the fiber-optic tapers with an air pillow. The full width at half-maximum (FWHM) of the point response function is 120 µm, the response is linear to better than 1% over the entire range of intensity from background to nearly full well, the gain is 3.4 e per 8 keV incident X-ray photon, the noise is 12.6 e per pixel for a 10 s integration time, the modulation transfer function (MTF) is 0.35 at 5 line pairs (lp) mm−1(the Nyquest frequency), and the measured detective quantum efficiency (DQE) is 0.74 for relatively strong Bragg peaks. Data collected from crystallographic studies with synchrotron radiation are presented. In an anomalous difference Patterson map for a data set collected in 40 min on a monoclinic myoglobin crystal, the magnitude of the Fe–Fe peaks is 18 times the standard uncertainty of the map.
Crystallization bench
Authors: Cabric B. , Pavlovic T.
Published: July 2004

An air cooler (`cold bench'), installed in a laboratory tube furnace, which allows regulation and simultaneous crystallization of several substances at different temperature gradients and rates is presented. It may be used for preparing single crystals in a school laboratory. A description of how the crystals are formed and conditions for the crystallization of some substances are given. This method can also be applied in crucible and chamber furnaces.
Reconstruction of low-resolution three-dimensional density maps from one-dimensional small-angle X-ray solution scattering data for biomolecules
Authors: Walther Dirk , Cohen Fred E. , Doniach Sebastian
Published: July 2004

A Monte Carlo type reconstruction algorithm (Saxs3D) to yield low-resolution three-dimensional structures from one-dimensional small-angle X-ray scattering data (SAXS) is presented. It is demonstrated thatSaxs3Dreliably reproduces the shape of several test protein structures, with their respective SAXS profiles calculated theoretically from their known high-resolution atomic coordinate sets. A reconstruction for experimentally obtained scattering data for GroEL, a molecular chaperone, correctly reproduced the gross structural features of GroEL. Compared to other reconstruction methods described in the literature,Saxs3Dhas the advantage of allowing for any topology of the target structure, does not require any prior estimation of its dimensions, is fast and conceptually very simple.
Refinement of free structure parameters of a thin film when only one reflection is available
Authors: Meyer Dirk C. , Paufler Peter
Published: July 2004

A procedure is described to exploit measurements for the refinement of free structure parameters if only a few (or even only one) reflections are available. The method is illustrated taking an epitaxial layer of Ga0.5In0.5P deposited on (001)GaAs as an example, where the number of accessible reflections is limited by geometrical conditions. Another complication with this material arises from the well known ordering phenomenon, which occurred in a small part of the layer only. It is shown that the energy dependence of DAFS (diffraction anomalous fine structure) intensity is still sufficiently sensitive to values of free structure parameters when the oscillating part of the DAFS/XAFS (X-ray absorption fine structure) structure factor is ignored for evaluation of intensity. This facilitates evaluation of DAFS intensities considerably by avoiding time-consuming analysis of fine structure.
Accuracy of XRPD QPA using the combined Rietveld–RIR method
Authors: Gualtieri Alessandro F.
Published: July 2004

QPA (quantitative phase analysis) of polycrystalline materials using XRPD (X-ray powder diffraction) can be performed using the combined Rietveld and reference intensity ratio (RIR) methods, providing an estimate of both the crystalline and the amorphous phase in a mixture. Although the accuracy of estimates of the phase composition of simple ternary or quaternary mixtures is generally very good, uncertainties remain and bias the accuracy of phase determinations in complex systems such as pyroclastic rocks, which may contain two or more zeolite species, a number of other phases (generally up to four or five), and glass. The contribution of the incoherent scattering, biasing accuracy, in the glass determination has been discussed in an earlier work on the modal analysis of pyroclastic rocks [Gualtieri (1996).Powder Diffr.11, 97–106]. In this work, the assumption of the crystal structure, the influence of the spike addition, background and atomic (thermal) displacement parameters are discussed. It is shown that the structure-model assumption no longer holds for systems containing complex phases such as zeolites, as the accuracy is degraded and, as far as the influence of the added spike is concerned, there is an underestimation of the glass content with increasing amounts of added spike.
Measurement of single-crystal elastic constants by neutron diffraction from polycrystals. Addendum and erratum
Authors: Howard C. J. , Kisi E. H.
Published: July 2004

Correction is made to an equation in a paper by Howard & Kisi [J. Appl. Cryst.(1999),32, 624–633] and additional references are cited.
Phase transitions in ReO3studied by high-pressure X-ray diffraction
Authors: Jørgensen J.-E. , Staun Olsen J. , Gerward L.
Published: July 2004

ReO3has been studied at pressures up to 52 GPa by X-ray powder diffraction. The previously observed cubicIm3¯ high-pressure phase was shown to transform to a monoclinic MnF3-related phase at about 3 GPa. All patterns recorded above 12 GPa could be indexed on rhombohedral cells. The compressibility was observed to decrease abruptly at 38 GPa. It is therefore proposed that the oxygen ions are hexagonally close packed above this pressure, giving rise to two rhombohedral phases labelled I and II. The zero-pressure bulk moduliBoof the observed phases were determined and the rhombohedral phase II was found to have an extremely large value of 617 (10) GPa. It was found that ReO3transforms back to thePm3¯mphase found at ambient pressure.
Application of high-energy synchrotron radiation for texture studies
Authors: Mishin O. V. , Lauridsen E. M. , Krieger Lassen N. C. , Brückner G. , Tschentscher T. , Bay B. , Juul Jensen D. , Poulsen H. F.
Published: July 2004

A novel experimental technique that employs high-energy synchrotron radiation is used for the investigation of through-thickness texture gradients in two aluminium plates, cold-rolled 40% with either intermediate or small draughts. In these two plates, crystallographic textures are inspected in a large number of layers. Texture maps of pole densities throughout the sample thickness are presented. A texture of the rolling type is developed through the plate thickness after intermediate draught rolling. Pronounced inhomogeneities associated with the shear texture are observed in the sample rolled with small draughts. For selected layers, direct pole figures are compared with those obtained by traditional low-energy X-ray diffraction and by the electron backscattering pattern technique using a scanning electron microscope. A good qualitative agreement between textures measured using the three different techniques is obtained. Experimental aspects and potentials of the new technique are discussed.
Performance of a multi-wavelength monochromator system for neutron single-crystal and powder diffraction
Authors: Ahmed F. U. , Tanaka I. , Niimura N.
Published: July 2004

In order to improve significantly data collection efficiency, the advantages of using multi-wavelengths in single-crystal neutron diffraction as well as in powder neutron diffraction were established by experiments using a stacked monochromator assembly of two elastically bent perfect Si(111) and Si(220) crystals. The TAS-2 spectrometer on JRR-3M at JAERI (Japan Atomic Energy Research Institute) was employed for these experiments. Each crystal was elastically bent in order to increase the flux density at the sample position. Two wavelengths, λ1= 1.80 Å for Si(220) and λ2= 2.94 Å for Si(111), were selected. The alignment of the stacked monochromator was successful and a well defined rocking curve of approximately 0.3° full width at half-maximum (FWHM) was obtained. Diffraction patterns of Si powder were collected using the TAS-2 point detector as well as a neutron imaging plate (NIP) detector to compare the relative performance of the two detector systems. With the NIP detector, it was possible to acquire multiple reflections simultaneously with better intensity, better statistics and higher spatial resolution with an open geometry. The NIP detector was used to obtain the diffraction pattern of a single crystal of the organic compound piperidine cobaloxime. For the systems investigated in this study, it was possible to assign unambiguously rings or spots to diffraction by λ1or by λ2in the case of powder and single-crystal diffraction.
Small-angle X-ray scattering analysis of the periodic tricontinuous network structure of symmetricABCtriblock copolymers
Authors: Seki Motohiro , Suzuki Jiro , Matsushita Yushu
Published: July 2004

The periodic tricontinuous network structure (TNS) of symmetric isoprene (I)–styrene (S)–2-vinylpyridine (P) triblock copolymers has been studied by small-angle X-ray scattering (SAXS). The observed SAXS profiles were compared with the calculated diffraction intensities based on the model electron density distributions constructed for a pair of surfaces parallel to the infinite periodic minimal surface. In the model, an imaginary minimal surface exists at the centre of the styrene labyrinth and both I/S and S/P interfaces are on the parallel surfaces, powder orientation of the model structure being assumed. The experimental SAXS patterns for the samples with different styrene volume fractions,i.e.0.48 and 0.66, which are the lower and higher extremes for tricontinuous network structure, are well explained by the model calculation for surfaces parallel to the Gyroid minimal surface.
Twinning and defects in N-Nb2O5
Authors: Rohrer Franziska E. , Larsson Ann-Kristin
Published: July 2004

N-Nb2O5 [C2/m (No. 12), a = 28.51, b = 3.830 and c = 17.48 Å, and β = 124.8°] has been investigated by means of selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). N-Nb2O5 is domain twinned, with the twin plane perpendicular to the c* axis. The domains are rather small and the domain twinning can sometimes be best explained as stacking faults. A second type of coherent twinning at an angle of 90° to the other two domain directions was also found. These domains are linked together by areas containing blocks of different sizes, similar to the disordered block arrangement observed in M-Nb2O5.
Intramolecular hydrogen bonds: common motifs, probabilities of formation and implications for supramolecular organization
Authors: Bilton Clair , Allen Frank H. , Shields Gregory P. , Howard Judith A. K.
Published: July 2004

A systematic survey of the Cambridge Structural Database (CSD) has identified all intramolecular hydrogen-bonded ring motifs comprising less than 20 atoms with N and O donors and acceptors. The probabilities of formation Pm
of the 50 most common motifs, which chiefly comprise five- and six-membered rings, have been derived by considering the number of intramolecular motifs which could possibly form. The most probable motifs (Pm
> 85%) are planar conjugated six-membered rings with a propensity for resonance-assisted hydrogen bonding and these form the shortest contacts, whilst saturated six-membered rings typically have Pm
< 10%. The influence of intramolecular-motif formation on intermolecular hydrogen-bond formation has been assessed for a planar conjugated model substructure, showing that a donor-H is considerably less likely to form an intermolecular bond if it forms an intramolecular one. On the other hand, the involvement of a carbonyl acceptor in an intramolecular bond does not significantly affect its ability to act as an intermolecular acceptor and thus carbonyl acceptors display a substantially higher inclination for bifurcation if one hydrogen bond is intramolecular.
Isomorphism and pseudosymmetry in 2,6-dichloro- and 2,6-dibromobenzonitrile
Authors: Britton Doyle , Noland Wayland E. , Pinnow Matthew J.
Published: July 2004

The title compounds are isomorphous, with two half-molecules in the asymmetric unit of a monoclinic unit cell in the space group C2/m. For the chloro compound: a = 18.0525 (8), b = 20.7374 (10), c = 3.8334 (2) Å, β = 101.143 (1)°; for the bromo compound: a = 18.2269 (15), b = 21.349 (2), c = 3.9663 (3) Å, β = 101.446 (2)°. The dominant intermolecular interactions are between halogen atoms rather than between halogen and nitrile, as is the case in the corresponding 2,4,6-trihalobenzonitriles. The molecules pack into layers with a fourfold pseudosymmetry. The pseudosymmetry appears to be the consequence of halogen–halogen intermolecular interactions.
Packing modes of (R,R)-tartaric acid esters and amides
Authors: Rychlewska Urszula , Warżajtis Beata
Published: July 2004

The molecular packing modes of a series of mono- and diamides of (R,R)-tartaric acid are discussed on the basis of their crystal structures. Derivatives include combinations of methylester, amide, N-methylamide and N,N-dimethylamide groups, both symmetrically and asymmetrically substituted. The symmetrically substituted derivatives do not utilize their C
2 symmetry in the crystal. The packing of primary tartramides seems to be driven by NH...O=C hydrogen bonds and supplemented by strong OH...O=C and weak NH...OH bonds. On the other hand, in derivatives containing methylester and/or methylamide groups OH...OH...O=C hydrogen-bond patterns seem to dominate. Types of aggregates, characteristic for the investigated derivatives, include cyclic dimers and ring systems analogous to the dimers, but formed by two different although complementary functional groups, as well as sets of chains aligned in a manner resembling the helical arrangement of peptides. The helices are formed along the screw axis with an identity period of approximately 5 Å. In tartramic acids, containing in one molecule both carboxyl and amide functions, in competition between the two groups to control the molecular arrangement, the latter dominates, unless it is N-substituted tartramide, in which case the carboxyl group predominates. Problems with packing, which occur in some of the structures owing to the steric bulk of the methyl groups, are overcome by changes in conformation (esters) or by co-crystallization with solvent water molecules (methylamides and dimethylamides). These derivatives are also more likely to crystallize with multiple asymmetric units.
Crystal structure and charge distribution of YbFeMnO4
Authors: Nespolo Massimo , Isobe Mitsumasa , Iida Junji , Kimizuka Noboru
Published: July 2004

The structure of synthetic YbFeMnO4 has been refined by single-crystal X-ray diffraction. Space group R\bar 3m, a = 3.4580 (1), c = 25.647 (3) Å, V = 265.59 (3) Å3, Z = 3. Yb is in octahedral coordination, whereas Fe and Mn are disordered on a single crystallographic type of trigonal bipyramid, in which the cation is off-centred from the basal plane. Assuming perfect stoichiometry, R
1 = 0.0195, but the charge distribution (CD) analysis suggests incomplete occupation of the Yb site. Refinement of the occupancy lowers R
1 to 0.0175, resulting in s.o.f.(Yb) = 0.963 (3), with a significant improvement of the Fourier difference. The electroneutrality is likely preserved through incomplete occupancy of one of the two oxygen sites: the compound is thus non-stoichiometric, with the formula Yb0.963FeMnO3.945. Another mechanism for preserving the electroneutrality is the oxidation of a small amount of Mn2+ to Mn3+, which is, however, less probable because of the reduction conditions in which the sample was synthesized. Both models give a satisfactorily CD result, but they cannot be definitively distinguished by X-ray data.
N-(6-Amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl) derivatives of glycine, valine, serine, threonine and methionine: interplay of molecular, molecular–electronic and supramolecular structures
Authors: Low J. N. , López M. D. , Arranz Mascarós P. , Cobo Domingo J. , Godino M. L. , López Garzón R. , Gutiérrez M. D. , Melguizo M. , Ferguson G. , Glidewell C.
Published: July 2004

In each of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)valine, C10H15N5O4 (3) (orthorhombic, P212121), N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)serine monohydrate, C8H11N5O5·H2O (4) (orthorhombic, P212121), and N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)threonine, C9H13N5O5(5) (monoclinic, P21), the C-nitroso fragments exhibit almost equal C—N and N—O bond lengths: the C—N range is 1.315 (3)–1.329 (3) Å and the N—O range is 1.293 (3)–1.326 (3) Å. In each compound there are also very short intermolecular O—H...O hydrogen bonds, in which carboxyl groups act as hydrogen-bond donors to the nitrosyl O atoms: the O...O distances range from 2.440 (2) to 2.504 (4) Å and the O—H...O angles lie between 161 and 163°. An interpretation of the relationship between the unusual intramolecular bond lengths and the very short intermolecular hydrogen bonds has been developed based on database analysis and computational modelling. In each of (3)–(5) there is an extensive network of intermolecular hydrogen bonds, generating three-dimensional frameworks in (3) and (5), and two-dimensional sheets in (4).
Conformational transformation coupled with the order–disorder phase transition in 2-methyl-1,3-cyclohexanedione crystals
Authors: Katrusiak Andrzej
Published: July 2004

The half-chair conformation of the dynamically disordered molecular ring of 2-methyl-1,3-cyclohexanedione, C_7H_{10}O_2, transforms to a sofa below T_c = 244 K, when the crystal undergoes a continuous phase transition induced by the onset of halting large-amplitude vibrations of methylene groups C(4)H_2 and C(5)H_2. The temperature dependence of the crystal structure has been investigated by X-ray diffraction. The Ibam symmetry of the crystal reduces below T_c to space group Pccn. The mechanism of the phase transition and of the conversion of the ring conformation is discussed.
Synchrotron X-ray analysis of RbTiOAsO4
Authors: Streltsov Victor A. , Nordborg Jenni , Albertsson Jörgen
Published: July 2004

Structure factors for rubidium oxotitanium arsenate, RbTiOAsO4, were measured at 293 K with focused synchrotron X-radiation [λ = 0.7500 (9) Å] using a fast avalanche photodiode counter. The accurate synchrotron single-crystal data are of sufficient quality and resolution to detect the splitting positions of the Rb cations at room temperature. Strong accumulation of the Δρ difference charge density near the Rb atoms at a distance of ∼0.5 Å in the −c direction can be attributed to the partial occupancy of additional sites related by pseudosymmetry. This type of static and/or dynamic disorder is temperature-dependent and seems to be universal for the KTiOPO4 family of compounds. The best modelling of the experimental data was obtained with the Rb atom in split positions described within the harmonic approximation and the multipole functions for the other atoms. The Δρ density features in the Ti—O and As—O covalent bonds can be related to the linear and non-linear susceptibility using bond-polarization theory. The charge-density maps reflect the anisotropy of non-linear susceptibility, which is larger for directions where locally antisymmetric components of Δρ are strong.