bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopaminergic influences beyond extraversion
Authors: Derryberry Douglas , Reed Marjorie A.
Published: July 2002

Studies of human performance indicate that extraverts show
enhanced motivation in relation to reward signals, but not in relation
to safety signals under defensive conditions. When it occurs under
defensive conditions, enhanced motivation may be related to
neuroticism. While extraverts show some attentional skills consistent
with frontal dopaminergic facilitation, other frontal capacities
may be related to conscientiousness. These findings suggest that
dopaminergic influences on response and attentional processes may
contribute to additional personality dimensions such as neuroticism
and conscientiousness.
Assessing the Benefit of Innovations in ATC
Authors: Ratcliffe S.
Published: July 2002

Recent advances in technology have encouraged proposals
for new approaches to ATC in Europe
and elsewhere. Two such proposals, both rather loosely framed,
are for ‘free flight’ or for
‘seamless contracts’; otherwise ‘tubes of
flight’. These concepts, and variations on them, aim
to increase the traffic capacity of the airspace. They have been the subject
of numerous
published papers. Given the declared objects of these systems, it is surprising
that, nearly
without exception, these papers discuss the proposals only in qualitative
terms. The present
paper discusses idealised versions of these systems on the basis of quantitative
studies. It is
concluded that the ‘seamless contract’ is
very probably unworkable in Europe. ‘free flight’
is workable in principle, but there is a need for investigation of possible
mechanisms by which
last-minute problems may be resolved.
Reduced glutamate uptake by retinal glial cells under ischemic/hypoxic
conditions
Authors: NAPPER GENEVIEVE A. , PIANTA MICHAEL J. , KALLONIATIS MICHAEL
Published: July 2002

The high-affinity uptake of glutamate by glial
cells and neurons of the central nervous system, including
the retina, serves to inactivate synaptically released
glutamate and maintains glutamate at low concentrations
in the extracellular space. This uptake prevents accumulation
of glutamate extracellularly and thus minimizes the possibility
of glutamate neurotoxicity secondary to ischemic insult.
One mechanism whereby glutamate neurotoxicity may occur
in ischemic/hypoxic insult is through increased extracellular
K+ reversing the electrogenic glutamate uptake
into retinal glial (Müller) cells. We investigated
glial uptake of the amino acids glutamate, GABA, and D-aspartate
in the intact isolated rat retina under high extracellular
K+ conditions and under conditions simulating
ischemia. Immunocytochemical findings showed that uptake
of glutamate and GABA by Müller cells in the intact
isolated rat retina continues under conditions simulating
ischemia and high extracellular K+ conditions,
and uptake of D-aspartate also continues under high K+
conditions. However, under high K+ conditions,
the glutamate uptake system saturates at a lower concentration
of exogenous glutamate than in the normal K+
condition. These findings provide evidence that disruption
of glutamate uptake by Müller cells is likely to be
a significant contributing factor to excess glutamate accumulation
in the extracellular space which can lead to neurotoxicity.
Phonetic realisation of downstep in Bimoba
Authors: Snider Keith L.
Published: July 2002

Few phonological phenomena have so captured the attention of theorists
and continued to baffle them as the phenomenon of tonal downstep.
Downstep is the lowering of the tonal register that sometimes occurs
between adjacent, otherwise identical tones. It is cumulative, and successive
occurrences of the phenomenon result in ever lower settings of the
tonal register. The present work reports on an instrumental study of
downstep in Bimoba, a Gur language spoken in the Northern Region of
Ghana. So far as I am aware, the present work is the only description in
existence of tone in Bimoba.

Bimoba is a good candidate for a study of downstep, because it is a
‘three-tone’ language in which both Low tones (floating and
non-floating)
and Mid tones cause High tones to be downstepped. A number of
phonological studies (based on auditory impressions only) of three-tone
languages with downstep of High tone have claimed that the difference in
pitch between a High and a following Mid is equivalent to that between
a High and a following downstepped High. These include Supyire
(Carlson 1983), Babanki (Hyman 1979), Moba (Russell 1986) and Kagoro
(van de Kolk 1992). This issue is important to tone theorists because a
number of proposals on the theory of downstep formally equate a
downstepped High with one type of Mid tone. These include Clements
(1983), Hyman (1986, 1993), Inkelas (1987) and Snider (1990). On the
other hand, a number of other proposals account for downstep with
phonetic implementation rules. These include Pierrehumbert (1980),
Poser (1984), Beckman & Pierrehumbert (1986) and Pierrehumbert &
Beckman (1988). ‘If register shift is indeed a rule of phonetic implementation,
there is no reason, a priori, for the interval of register shift
to be equivalent to that found between two phonemic tones’ (Snider
1990:
470). So far as I am aware, no instrumental study has ever addressed this
issue. The present study therefore undertakes to help fill this lacuna,
and
concludes that in Bimoba a Mid tone is phonetically indistinguishable
from a downstepped High tone in comparable environments.
Rehabilitation after minor fractures in elderly patients
Authors: MacLennan WJ , Currie CT
Published: July 2002

A great deal of attention has been devoted to the ever-increasing incidence of fractures of the proximal femur in elderly patients and the impact which this has had upon their life expectancy and quality of life. The condition has also made heavy demands on the Health Service, and much effort has been devoted to increasing hospital throughput by effective programmes of rehabilitation. In these circumstances, it is not surprising that much less has been written about the issues involved in treating elderly patients with less serious forms of fracture. Nonetheless, closer attention to this group reveals that it also makes heavy demands on the Health Service. An example is that, in 1995, out of 1771 elderly patients admitted to the acute orthopaedic wards at Edinburgh Royal Infirmary, only 47% had fractures related to the proximal femur or displacement of a hip prosthesis (Figure 1) (CT Currie, unpublished data, 1996). Most of the remainder had fractures at other sites, while 8% had soft tissue injuries. The percentage of fractures involving more common sites in old people was 2.5% for the neck of humerus, 3% for the shaft of humerus, and 7% for the wrist. The low proportion of vertebral fractures emphasizes that this condition rarely leads to admission to an acute unit, so that the size of the problem is usually underemphasized.
Time-resolved small angle scattering: kinetic and structural data from proteins in solution
Authors: Roessle M. , Manakova E. , Lauer I. , Nawroth T. , Holzinger J. , Narayanan T. , Bernstorff S. , Amenitsch H. , Heumann H.
Published: July 2002

Using the high flux of a third generation synchrotron sources at ESRF and ELETTRA, structural changes of the chaperonin system GroE were analyzed by time-resolved small angle scattering. A fast mixing device were established which permits determination of the solution scattering parameters of the E.coli chaperonin system GroE in time slices of 300msec. Using this device, the r eaction pathway of the two component system, GroEL and GroES was analyzed.
A modified Pinkerton-type helium gas-flow system for high-accuracy data collection at the X3 SUNY synchrotron beamline at NSLS
Authors: Ribaud Lynn , Wu Guang , Zhang Yuegang , Coppens Philip
Published: July 2002

As the combination of high-intensity synchrotron sources and area detectors allows collection of large data sets in a much shorter time span than previously possible, the use of open helium gas-flow systems is much facilitated. A flow system installed at the SUNY X3 synchrotron beamline at the National Synchrotron Light Source has been used for collection of a number of large data sets at a temperature of ∼16 K. Instability problems encountered when using a helium cryostat for three-dimensional data collection are eliminated. Details of the equipment, its temperature calibration and a typical result are described.
A new version of the method for analysing peak broadening caused by local tilt distribution in double-crystal X-ray diffraction measurements. Erratum
Authors: Nakashima Kiichi
Published: July 2002

As a result of a printer's error, Fig. 9 of the paper by Nakashima [J. Appl. Cryst.(2000),33, 1376–1385] was incorrectly printed. The correct figure is given here.
Prediction of hydrodynamic and small-angle scattering parameters from crystal and electron microscopic structures
Authors: Zipper P. , Durchschlag H.
Published: July 2002

Hydrodynamic multibody models (bead models) of selected proteins were derived from crystal, SAXS and electron microscopic structures, by using various data reduction procedures. Pair distance distribution functions and scattering curves of initial and reduced models were calculated in order to check the maintainance of the structural characteristics of the molecules. Hydrodynamic calculations were performed by using a novel concept for handling overlaps between unequal beads. Predicted hydrodynamic parameters were found to be in good accord with observed data, provided hydration contributions were taken into account appropriately.
Robust Rietveld refinement in the presence of impurity phases
Authors: David W. I. F.
Published: July 2002

A modified least-squares analysis is presented that allows reliable structural parameters to be extracted from a powder diffraction pattern even in the presence of a substantial unmodelled impurity contribution. The algorithm is developed within the context of Bayesian probability theory. Experimental points that fall above those calculated, and are thus more probably from impurity peaks, are systematically down-weighted. This approach is illustrated with a two-phase example.
Optical properties of synthetic and mineral chlorapatites
Authors: Elliott J. C.
Published: July 2002

The birefringence and orientation of the indicatrix for acicular and prismatic habits of monoclinic flux-grown chlorapatite (ClAp), Ca5(PO4)3Cl, have been measured. There are slight differences in birefringence between the habits due to compositional changes, which, because the indicatrix is very nearly spherical, cause the optic axial plane (OAP) to change its orientation by 90°, although the direction of the axes of the indicatrix do not change. The acicular crystals are the purer and are biaxial (−), γ − β = 2.9 × 10−5, β − α = 8.2 × 10−5, mean refractive index (n) = 1.6672 and have the unique c axis normal to the OAP. ClAp is uniaxial (+) above its monoclinic-to-hexagonal transition. Hydrothermally grown monoclinic ClAp has optical properties that can be understood from the results for the flux-grown crystals. Synthetic monoclinic F,ClAp and monoclinic ClAp from Bob's Lake, Ontario, is biaxial (+) with the unique axis lying in the OAP and n = 1.6635.
Crystal data for an adduct of orthotelluric acid and urea, Te(OH)6.2CO(NH2)2
Authors: Loub J. , Dušek M.
Published: July 2002

The crystal data of the title compound have been determined from single-crystal data [Loub, Haase & Mergehenn (1979). Acta Cryst. B35, 3039–3041]: C2/c, a = 14.828(8), b = 8.891(6), c = 10.023(7) Å, β = 129.13(3)°, V = 1025.0(9) Å3, Z = 4, Dm
= 2.31(3), Dx
= 2.27 Mg m−3. Power data obtained with powder diffractometer, θ–2θ scan, T = 295 K, Cu Kα radiation are presented. Infrared and Raman spectra are given. Thermal decomposition is reported [Fábry, Loub & Feltl (1982). J. Therm. Anal.
24, 95–100]. The JCPDS Diffraction File No. for C2H8N4O2Te(OH)6 is 36-1470.
X-ray diffraction line broadening due to dislocations in non-cubic materials. I. General considerations and the case of elastic isotropy applied to hexagonal crystals
Authors: Klimanek P. , Kužel R.
Published: July 2002

Use is made of the theory of dislocation-induced X-ray diffraction line broadening in the form presented by Krivoglaz, Martynenko & Ryaboshapka [Fiz. Metall. Metalloved. (1983), 55, 5–171 to express the so-called orientation factors occurring in the relations of diffraction profile parameters (e.g. Fourier coefficients, line widths) in a form which systematically takes into account both the lattice geometry and the elastic behaviour of the scattering crystals. The formalism can be used, in principle, for any materials and types of dislocations. In the case of elastically isotropic media the orientation factors can be described by analytical expressions. The application of the formalism is demonstrated in some detail for various slip systems in hexagonal polycrystals with random orientation of grains.
Absolute calibration of small-angle neutron scattering data
Authors: Wignall G. D. , Bates F. S.
Published: July 2002

Absolute calibration forms a valuable diagnostic tool in small-angle neutron scattering (SANS) experiments, and allows the parameters of a given model to be restricted to the set which reproduces the observed intensity. Discrepancies between the observed and calculated intensities may arise from potential artifacts or even new physical processes and absolute calibration methods are useful in delineating these circumstances. General methods which are available for absolute scaling are discussed along with estimates of the degree of internal consistency which may be achieved between the various standards. In order to minimize the time devoted to calibration in a given experimental program, emphasis is placed on developing a set of precalibrated strongly scattering standards which may be run in the chosen experimental geometry. Comparison of such a set developed at the National Center for Small-Angle Scattering Research (Oak Ridge) with independent determinations by SANS users indicates consistency to within ± 5%.
Stress distribution and lattice curvature determinations in multilayer structures by simulation of X-ray rocking curves
Authors: Cembali F. , Servidori M.
Published: July 2002

A mechanical model is presented for the calculation of the stress depth distribution and the curvature radius in multilayer crystalline structures. The model is compatible with the perpendicular strain and thickness determined for each lamella by simulation of a double-crystal X-ray rocking curve, and is suitable for coherence at all the interfaces as well as for coherence loss at one interface. An example of an application to a hypothetical practical case shows that the comparison between experimental and calculated curvatures and asymmetric rocking curves allows one to determine if loss of coherence occurred at an interface as a consequence of sample processing, and to determine the amount of incoherence and the depth position of the incoherent interface.
X-ray diffractometry of AlGaAs/GaAs superlattices and GaAs in the temperature range 5–295 K
Authors: Clec'h G. , Calvarin G. , Auvray P. , Baudet M.
Published: July 2002

The temperature dependence of the lattice constants of Al
x
Ga1 − x
As/GaAs superlattices MBE-grown on (001) oriented GaAs substrates was determined by X-ray diffractometry. The thermal expansion coefficients of these materials become negative at low temperatures, like that of GaAs and other tetrahedrally bonded covalent solids. The temperature dependence of the stress in these structures was also studied; although its value increases as temperature decreases, strain remains elastic down to 5 K.
Magnetically coupled crystal holder and liquid-helium cryostat for X-ray four-circle diffractometer studies between 5 and 300 K
Authors: Argoud R. , Muller J.
Published: July 2002

A new low-temperature system for X-ray four-circle diffractometer studies down to 5 K has been developed. The crystal is mounted on a new holder which is magnetically coupled to the diffractometer. This coupling is achieved by mounting a master magnet in place of the classical goniometer head. This master magnet drives a slave magnet fixed on the new crystal holder, and therefore the crystal is indirectly oriented by the master magnet. This magnetically coupled crystal holder (MCCH) is enclosed in a helium-flow cryostat which remains stationary during the φ, χ and to movements. The χ value is limited to ±65° and ω to 40° for a 150 mm diameter χ circle. All the tests and data collections (from 5 to 15 d) gave accuracies on the intensities, cell parameters and atomic positions identical to those obtained with a classical goniometer head. No frost problem occurs with this apparatus. The MCCH may also have applications in controlled-atmosphere, high-pressure or vacuum investigations.
A high-resolution Weissenberg camera for X-ray synchrotron radiation
Authors: Hohlwein D. , Axe J. D.
Published: July 2002

A photographic Weissenberg camera has been constructed which can be mounted on the 2θ arm of a four-circle diffractometer. At a distance of 0.5 m from the sample the 2θ resolution for a 100 μm crystal is 0.2 mrad (0.01°), allowing a high-resolution mapping of reciprocal space at a synchrotron source in an efficient way. As sample experimental results, a study is presented of the streak system around the 111 reflection of a perfect germanium crystal and the detection of a minute phase transformation in a single-powder grain of a high-Tc
superconductor.
Modernization of the Philips PW1100 single-crystal diffractometer computer control system
Authors: Grigg M. W. , Barnea Z.
Published: July 2002

Modifications are described to the Philips PW1100 single-crystal diffractometer control system whereby the minicomputer control system and part of its associated hardware interface have been replaced by an IBM AT-compatible computer with a custom interface.
A fundamental parameters approach to X-ray line-profile fitting
Authors: Cheary R. W. , Coelho A.
Published: July 2002

A convolution approach to X-ray powder line-profile fitting is developed in which the line shape is synthesized from the Cu Kα emission profile, the dimensions of the diffractometer and the physical variables of the specimen. In addition to the integrated intensities and 2θ positions of the line profiles, the parameters that may be fitted include the receiving-slit width, the receiving-slit length, the X-ray-source size, the angle of divergence of the incident beam, the X-ray attenuation coefficient of the specimen and the crystallite size. This is a self-consistent approach to fitting as the instrumental parameters are usually known by direct measurement. To minimize correlation between refined instrumental parameters, profiles at high and low 2θ values should be fitted simultaneously. The Cu Kα emission profile used in this work is based on recent monolithic double-crystal spectrometer measurements that have identified a doublet structure in both the Kα
1 and Kα
2 components. Fast and accurate convolution procedures have been developed and a mixture of multilinear regression and Gauss–Newton non-linear least squares with numerical differentials is used for fitting the profiles. The method is evaluated by fitting powder diffraction data from well crystallized specimens of MgO and Y3Al5O12 (YAG). Testing has also been carried out by examining the changes in the fitted values after altering various instrumental parameters (e.g. receiving-slit width, detector defocus, receiving-slit length and inclusion of a monochromator).
The iterative series-expansion method for quantitative texture analysis. II. Applications
Authors: Dahms M.
Published: July 2002

The orientation distribution function (ODF) of the crystallites of polycrystalline materials can be calculated from experimentally measured pole density functions (pole figures). This procedure, called pole-figure inversion, can be achieved by the series-expansion method (harmonic method). As a consequence of the (hkl)-({\bar h}{\bar k}{\bar l}) superposition, the solution is mathematically not unique. There is a range of possible solutions (the kernel) that is only limited by the positivity condition of the distribution function. The complete distribution function f(g) can be split into two parts, \tilde {f}(g) and \tildes {f}(q), expressed by even- and odd-order terms of the series expansions. For the calculation of the even part \tilde {f}(g), the positivity condition for all pole figures contributes essentially to an `economic' calculation of this part, whereas, for the odd part, the positivity condition of the ODF is the essential basis. Both of these positivity conditions can be easily incorporated in the series-expansion method by using several iterative cycles. This method proves to be particularly versatile since it makes use of the orthogonality and positivity at the same time. In the previous paper in this series [Dahms & Bunge (1989) J. Appl. Cryst.
22, 439–447] a general outline of the method was given. This, the second part, gives details of the system of programs used as well as typical examples showing the versatility of the method.
Correcting spatial distortions and nonuniform response in area detectors
Authors: Stanton M. , Phillips W. C. , Li Y. , Kalata K.
Published: July 2002

Software and hardware methods have been developed to correct images for spatial and intensity distortions produced by optical and electro-optical components in X-ray area detectors. Spatial distortions are divided into two types: gross distortions produced by the inherent properties of the detector components and local distortions formed by irregularities in the components. Intensity distortions are separated into three types: those caused by background nonuniformity; those resulting from pixel-dependent nonuniform intensity response; and those resulting from time-dependent variations in background and incident beam intensity. From background, flat-field, reference and mask images, `forward' and `reverse' interpolation tables are generated to correct for spatial distortions and a lookup table is generated to correct for nonuniform sensitivity. The routines have been used successfully on four different area detectors to correct entire images or to correct intensities of individual Bragg peaks. The spatial-distortion correction is good to within 0.1 pixels and the nonuniformity correction to ≲ 2%.
The effect of the shape function on small-angle scattering analysis by the maximum-entropy method
Authors: Jemian P. R. , Allen A. J.
Published: July 2002

Analysis of small-angle scattering data to obtain a particle-size distribution is dependent upon the shape function used to model the scattering. From a maximum-entropy analysis of small-angle scattering data, the effect of shape-function selection on the obtained size distribution is demonstrated using three different shape functions to describe the same scattering data from each of two alloys. The alloys have been revealed by electron microscopy to contain a distribution of randomly oriented and mainly noninteracting irregular ellipsoidal precipitates. A comparison is made between the different forms of the shape function. The effect of an incident-wavelength distribution is also shown. The importance of testing appropriate shape functions and validating these against other microstructural studies is discussed.
Lysozyme solubility in H2O and D2O solutions as a function of sodium chloride concentration
Authors: Broutin I. , Riès-Kautt M. , Ducruix A.
Published: July 2002

Some spectroscopic methods require solubilization or crystallization of proteins in heavy water because of the large difference in neutron scattering properties between protons and deuterons. In order to quantify the impact of slightly different physical properties of D2O and H2O, lysozyme solubility curves have been measured for these solvents, using 0.2 to 3.0 M sodium chloride in 0.050 M sodium acetate buffer (pH 4.5) at 291 K. After four months of crystallization, solubility data were measured within 9% error and showed that the lysozyme solubility in H2O is 1.3 times that in D2O.
A Small-Angle X-ray Scattering Study of the Lyotropic Nematic Phase of Vanadium Pentoxide Gels
Authors: Davidson P. , Bourgaux C. , Sergot P. , Livage J.
Published: July 2002

Aqueous suspensions of vanadium pentoxide (V2O5) ribbons, also called Zocher phases, are known to display a lyotropic nematic phase. In this paper, it is shown how the small-angle X-ray scattering (SAXS) technique can provide useful information on the building blocks and their organization in this phase. SAXS experiments were performed either on unoriented samples or on samples aligned by a magnetic field or by shear flow. The scattering is comparable to that of the other classic lyotropic nematic phases displayed by stiff organic rod-like particles such as the tobacco mosaic virus. Scattering studies show that the building blocks have a ribbon shape, that their thickness is 9 (1) Å and indirectly that their width is several 100 Å. Their length is known to be around a few thousand Å and therefore could not be measured by SAXS. By following the average distance between the ribbons as a function of concentration, it is shown that the swelling of the phase is one-dimensional at large concentrations and two-dimensional at low concentrations. Finally, estimates of the nematic order parameter of a single domain sample and of samples sheared in a Couette cell have been obtained.
Small-Angle X-ray Scattering from Blends of PE and SBS. Observation of a Novel Kind of Deviation from Porod's Law
Authors: Stribeck N. , Ghioca P. , Buzdugan E.
Published: July 2002

In a study of technical blends from poly(ethylene) and poly(styrene)–poly(butadiene) star block copolymers, reproducibility of the blending process and of the structural analysis is tested. A peculiar and reproducible deviation in the angular interval of the scattering curve is observed, which is governed by a decay according to Porod's law. The notion of a faint electron-density undulation in space with a wavelength of 5 nm, an amplitude of 1 e.u. nm−3 and a range of 40 nm could explain the triangular peak observed in a plot which otherwise linearizes the scattering curve in the Porod regime.
The Influence of the Available Scattering Vector Range on the Retrieval of Particle-Size Distributions from Small-Angle Scattering Intensity Data
Authors: Mulato M. , Tygel D. , Chambouleyron I.
Published: July 2002

The determination of the particle-size distribution [D(r)] from small-angle scattering intensity data is discussed. The influence of the maximum available scattering vector h
max on D(r) retrieval is investigated with the help of numerical experiments with previously known solutions. The numerical corrector method provides a good answer even in cases where h
max is much smaller than those values necessary with other retrieval methods.
Use of Image-Processing Tools for Texture Analysis of High-Energy X-ray Synchrotron Data
Authors: Fisker R. , Poulsen H. F. , Schou J. , Carstensen J. M. , Garbe S.
Published: July 2002

The introduction of synchrotron beamlines for high-energy X-ray diffraction raises new possibilities for texture determination of polycrystalline materials. The local texture can be mapped out in three dimensions and texture developments can be studiedin situin complicated environments. However, it is found that a full alignment of the two-dimensional detector used in many cases is impractical and that data-sets are often partially subject to geometric restrictions. Estimating the parameters of the traces of the Debye–Scherrer cones on the detector therefore becomes a concern. Moreover, the background may vary substantially on a local scale as a result of inhomogeneities in the sample environmentetc. A set of image-processing tools has been employed to overcome these complications. An automatic procedure for estimating the parameters of the traces (taken as ellipses) is described, based on a combination of a circular Hough transform and nonlinear least-squares fitting. Using the estimated ellipses the background is subtracted and the intensity along the Debye–Scherrer cones is integrated by a combined fit of the local diffraction pattern. The corresponding algorithms are presented together with the necessary coordinate transform for pole-figure determination. The image-processing tools may be useful for the analysis of noisy or partial powder diffraction data-sets in general, provided flat two-dimensional detectors are used.
High-resolution Neutron Diffraction using Larmor Precession
Authors: Kraan W. H. , Kaiser C. T. , Rekveldt M. Th.
Published: July 2002

A polarized neutron beam travels through a precession coil with fieldBand the intensity in a detector behind the analyser is recorded as a function ofB. Fourier transformation of the intensity signal gives the wavelength spectrum of the beam entering the detector. Any (diffraction) experiment can be set up in the optical pathway between the analyser and detector. This technique is applied in an array of high-resolution diffraction experiments along the path of the neutron beam through a bent Al strip. The detector intensities are measured only over a small range ofBaway from B=0. The phase shift between the intensity signals from compressed/extended regions, relative to the signal from a reference region in the strip, reveals the deformation of the Al lattice.
Quantitative treatment for extracting coherent elastic scattering from X-ray scattering experiments
Authors: Laaziri Khalid , Robertson J. L. , Roorda S. , Chicoine M. , Kycia S. , Wang J. , Moss S. C.
Published: July 2002

A fitting procedure for separating the inelastic and elastic contributions to the total scattering in diffuse-scattering experiments at high energy using energy-dispersive X-ray techniques is presented. An asymmetric peak function is used to model the elastic peak. The inelastic scattering peak is modeled using a theoretical Compton profile, calculated using the impulse approximation (Hartree–Fock wave functions were used), convoluted with the detector resolution. This procedure, which requires only two free parameters, is shown to be extremely effective in extracting the integrated elastic intensity of coherent scattering at each wave vector, even at low scattering angles where the Compton scattering is not well resolved.
Application of silver behenate powder for wavelength calibration of a SANS instrument – a comprehensive study of experimental setup variations and data processing techniques
Authors: Keiderling U. , Gilles R. , Wiedenmann A.
Published: July 2002

Silver behenate powder [CH3(CH2)20COOAg] is one of the very few materials featuring cold neutron Bragg reflections in the angular range of 4–26° (2θ) accessible to small-angle neutron scattering (SANS) instruments. These reflections can be analysed with Bragg's law to determine the wavelength of the primary beam produced by the monochromator of the SANS instrument. Compared with the usual time-of-flight (TOF) method for wavelength calibration, this method does not require any additional time-resolving equipment for the instrument. An extensive study has been performed to determine the optimum parameters for the experimental setup and for the data processing procedure. The results of wavelength calibrations using silver behenate and TOF measurements are compared.
Angle calculations for a six-circle κ diffractometer
Authors: Thorkildsen Gunnar , Mathiesen Ragnvald H. , Larsen Helge B.
Published: July 2002

By parametrizing the conic surfaces spanned by the reciprocal-lattice vector under the action of the rotation axes, a new procedure for angle calculations for a κ diffractometer is presented. It is applied to obtain angle settings in various modes for a newly developed six-circle diffractometer.
Parallel-slit analyzer developed for the purpose of lowering tails of diffraction profiles
Authors: Fujinawa Go , Toraya H. , Staudenmann J.-L.
Published: July 2002

A parallel-slit analyzer (PSA) has been developed for the purpose of lowering tails in diffraction profiles from powders and thin films. In the present work, four different materials were used for the foils: sintered and hot-pressed tungsten (W), cold-worked stainless steel (SUS), beryllium bronze (Cu98Be2) and chemically surface-processed beryllium bronze (CuOx). The PSAs were tested in a parallel-beam geometry using CuKα radiation collimated with a gradedd-spacing parabolic multilayer mirror. The W and CuOx PSAs gave pseudo-Voigt profiles of ∼80% Gaussian in the direct-beam case. Textured and roughened surfaces of W and CuOx foils are considered effective for depressing total-reflection effects from the surfaces of the foil materials, and consequently for lowering the tails of diffraction peaks.
pH dependent self assembly of β-amyloid(10-35) and β-amyloid(10-35)-PEG3000
Authors: Thiyagarajan P. , Burkoth T.S. , Urban V. , Seifert S. , Benzinger T.L.S. , Morgan D.M. , Gordon D. , Meredith S.C. , Lynn D.G.
Published: July 2002

Small angle neutron and x-ray scattering (SANS/SAXS) studies were conducted on the structure of the aggregates formed from both the truncated model peptide β-Amyloid(10-35) (Aβ10-35) and a block copolymer β-Amyloid(10-35)-PEG3000 (Aβ10-35-PEG) in D2O at pHs from 3.0 to 7.0. These studies indicate that Aβ10-35 aggregates into rod-like particles (fibril) and their radii are strongly dependent on the pH of the solution. The fibril-fibril association in Aβ10-35 solutions is less at pH < 5.6, but becomes larger at higher pH. Aβ10-35-PEG also assembles into rod-like particles whose radius is larger by about 30 Å than that for Aβ10-35 fibril at pH 4.2, while it is about 23 Å larger at higher pH. Contrast matching SAXS/SANS experiments that eliminate the coherent scattering from PEG reveal that PEG moiety is located at the periphery of the fibril. Also the mass per unit length of the peptide portion is similar for both Aβ10-35 and Aβ10-35 fibrils at pH 5.6. The mass per unit length of the rods from SANS provides key information on the packing of Aβ10-35 peptides in the fibril.
Crystallography of quasi-crystals
Authors: Janssen T.
Published: July 2002

The symmetry of quasi-crystals, a class of materials that has recently aroused interest, is discussed. It is shown that a quasi-crystal is a special case of an incommensurate crystal phase and that it can be described by a space group in more than three dimensions. A number of relevant three-dimensional quasi-crystals is discussed, in particular dihedral and icosahedral structures. The symmetry considerations are also applied to the two-dimensional Penrose patterns.
Bloch waves and multislice in transmission and reflection diffraction
Authors: Ma Y. , Marks L. D.
Published: July 2002

The consistency between Bloch-wave and multislice approaches to calculating high-energy electron diffraction is investigated in both transmission and reflection cases, the emphasis being upon the latter. It is first shown, in more detail than previously published, that in transmission the two yield identical results. Next, the Bloch-wave approach for reflection is shown to yield a stationary solution in multislice, except for a small effect from the surface truncation. It is pointed out that the multislice approach can be exploited to solve exactly for the reflected wave for an arbitrary surface potential by using it as a Picard iteration solution of the Schrödinger equation. The surface potential scattering is not incidence-angle related and is not significant as might be expected. The introduction of absorption improves the consistency between the two methods. Finally, the stationary solutions are compared with solutions obtained using a top-hat incident wave. The latter approach leads to partially stationary solutions, although it is very hard to identify these.
Moiré patterns in electron microscopy with atomic focuser crystals
Authors: Cowley J. M. , Ooi Newton , Dunin-Borkowski R. E.
Published: July 2002

The periodic array of very fine cross-overs formed at the exit face of a thin `atomic focuser' crystal, illuminated by a parallel electron beam, may be used to form moiré patterns with a specimen crystal such that the structure of the specimen crystal may be derived with a resolution of better than 0.5 Å. Computer simulations of the moiré pattern formation have been made for the simple idealized case of two parallel gold-like lattices having a 10% difference in lattice constant. Moiré images are shown for the case of a small objective aperture in the viewing electron microscope such that the individual crystal lattices are not resolved and for a larger objective aperture for which the individual crystal lattices are resolved and the intensity is measured at the positions of the atoms of the atomic focuser crystal. The latter case confirms the viability of the scheme for ultra-high-resolution imaging of general specimens by use of a thin-crystal periodic atomic focuser, as previously proposed.
Quantitative zone-axis convergent-beam electron diffraction (CBED) studies of metals. II. Debye–Waller-factor measurements
Authors: Saunders M. , Fox A. G. , Midgley P. A.
Published: July 2002

Quantitative CBED techniques, such as the ZAPMATCH zone-axis pattern-matching method [Bird & Saunders (1992). Ultramicroscopy, 45, 241–251], have been applied with great success to the accurate refinement of low-order structure factors. The major limitation on the accuracy of the structure-factor measurements is uncertainty in the Debye–Waller factors describing the temperature-dependent atomic vibrations. While X-ray and neutron diffraction techniques are both capable of accurate measurements of Debye–Waller factors, the frequent use of liquid-nitrogen-cooled samples in CBED experiments means that previous measurements are rarely available at the temperatures required. This has prompted attempts to determine Debye–Waller factors from electron diffraction data obtained under experimental conditions that match those used for the quantitative CBED work. In this paper, the possibility of extracting accurate Debye–Waller factors from the low-order reflections of a zone-axis CBED pattern is investigated. In this way, the Debye–Waller factors and structure factors could be obtained from the same data set. With this new approach, it is shown that errors lower than ±0.02 Å2 can be obtained for the measurement of Debye–Waller factors from room- and liquid-nitrogen-temperature nickel and copper 〈110〉 zone-axis data. The results obtained are compared with previous measurements and theoretical predictions.
X-ray diffraction study of copper(I) thiourea complexes formed in sulfate-containing acid solutions
Authors: Piro O. E. , Piatti R. C. V. , Bolzán A. E. , Salvarezza R. C. , Arvia A. J.
Published: July 2002

The formation of three different copper(I) thiourea complexes in sulfate-containing acid solutions was observed. The ratio between CuI and thiourea (tu) in these complexes depends on the amount of thiourea and copper sulfate in the solution. The crystal and molecular structure of a new complex, [Cu_2(tu)_6](SO_4)\cdotH_2O, was determined, and the formation and structures of [Cu_2(tu)_5](SO_4)\cdot3H_2O and [Cu_4(tu)_7](SO_4)_2\cdotH_2O were confirmed. The compound [Cu_2(tu)_6](SO_4)\cdotH_2O crystallizes in the P\overline 1 space group, with a = 11.079 (2), b = 11.262 (1), c = 12.195 (2) Å, \alpha = 64.84 (1), \beta = 76.12 (1), \gamma = 66.06 (1)°, and Z = 2. The Cu-thiourea complex is arranged as a CuI tetranuclear ion, [Cu_4(tu)_{12}]^{4+}, sited on a crystallographic inversion center. All copper ions are in a tetrahedral coordination with thiourea ligands and located at alternate sites on an eight-membered, crown-like ring.
Anharmonicity of potentials of atoms in potassium hydrogensulfide (KDS) determined by neutron single-crystal diffraction
Authors: Haarmann Frank , Jacobs Herbert , Reehuis Manfred , Loose Anja
Published: July 2002

Potassium hydrogensulfide (KHS) is an ionic compound with an anionic molecular group HS^-. The fast reorientational disorder of the anions was determined for the ambient temperature modification [R\bar 3m; Jeffrey (1974). Can. J. Phys.
52, 2370–2378]. Single crystals are available now as protonated or deuterated specimens. With neutron single-crystal diffraction at room temperature, a considerable anharmonicity of the atom potential of the H or D atoms was observed. Even the thermal motions of K and S atoms show small deviations from an isotropic probability density function, which can be modelled using anharmonic temperature factors. The temperature factors of the atoms were expanded into a Gram–Charlier series [Kuhs (1992). Acta Cryst. A48, 80–98] in order to evaluate the anharmonicity quantitatively. Parameters up to a fourth-order approximation are relevant for the D atoms. Results from neutron single-crystal diffraction are compared with split-atom models extracted from neutron powder diffraction patterns of fully deuterated samples.
Dopant positions in strontium/chromium- and barium-doped KTP, determined with synchrotron X-radiation
Authors: Norberg Stefan T. , Streltsov Victor A. , Svensson Göran , Albertsson Jörgen
Published: July 2002

Structure factors for strontium/chromium- (Sr/Cr) and barium- (Ba) doped potassium titanyl phosphate (KTiOPO4, KTP) were measured with focused synchrotron X-radiation [0.75000 (9) Å] using a fast avalanche photodiode counter. Space group Pna21, Z = 8, a = 12.786 (2), b = 6.3927 (8), c = 10.5585 (9) Å, T = 293 (1) K, R = 0.028 (SrCrKTP); a = 12.851 (6), b = 6.418 (3), c = 10.620 (5) Å, T = 120 (1) K, R = 0.031 (BaKTP). The refinement of the dopant positions showed that Ba2+ is positioned in the larger of the two K cavities of KTP, while the smaller Sr2+ ion is located in both. Split positions are found for the strontium dopant in both cavities and they are located in the positive c direction from the potassium cation. The chromium dopant has two different oxidation states, namely +III and +VI; in both states the dopant is located inside the TiO6 octahedra. The two structures show slightly less distorted TiO6 octahedra than pure KTP.
X-ray and neutron structure of 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol (P326); some pitfalls of automatic data collection
Authors: Palmer Rex A. , Potter Brian S. , Lisgarten John N. , Fenn Ruth H. , Mason Sax A. , Mills Owen S. , Robinson Peter M. , Watt C. Ian F.
Published: July 2002

The structure of the crown ether 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol, C24H30O6·H2O (1), code name P326, the parent compound for a series of derivatives, has been determined by both X-ray diffraction at room temperature and neutron diffraction at very low temperature. The unit cells are very similar at both temperatures and in both cases the crystals exhibit P21 symmetry with Z = 4 (two molecules, A and B, respectively, per asymmetric unit) and pseudosymmetry P21/c. The higher symmetry is broken mainly by the two independent water molecules in the unit cell, some reflections which would be absent in P21/c having strong intensities in both the X-ray and neutron data. In both molecules A and B hydrogen bonds involving the water molecule stabilize the macrocyclic ring structure, one involving the macrocyclic O(9) as a donor. Close contacts between the water and macrocyclic O atoms in each molecule also suggest the presence of two bifurcated hydrogen bonds, involving water HW2 to both O(16) and O(18), and water HW1 to both O(18) and O(20), respectively, with considerable variation in the geometry being present. Both molecules A and B exhibit very close pseudosymmetry across a plane perpendicular to the molecular plane and through atoms C(9) and O(18), and in addition are predominantly planar structures. The X-ray analysis failed to reveal one H atom per water molecule, each being subsequently included after location and refinement in the neutron analysis.
Non-covalent interactions in the crystallization of the enantiomers of 1,7-dioxaspiro[5.5]undecane (olive fly sex pheromone) by enantiospecific cyclodextrin hosts, hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin
Authors: Makedonopoulou Stella , Yannakopoulou Konstantina , Mentzafos Demetrios , Lamzin Victor , Popov Alexander , Mavridis Irene M.
Published: July 2002

The enantiomers of racemic olive fly sex pheromone 1,7-dioxaspiro[5.5]undecane (1) have been isolated by crystallization with enantiospecific cyclodextrin hosts: (S)-(1) crystallizes with heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TMβCD) and (R)-(1) with hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin (TMαCD). The crystal structure of TMβCD/(S)-(1) from synchrotron radiation data at 100 K, determined for the first time, proves that TMβCD crystallizes with only the (S)-enantiomer from the racemic mixture. Comparison with the 100 K structure of TMαCD/(R)-(1) redetermined with synchrotron data has provided insight into the interactions between each of the hosts with the corresponding enantiomeric guests. Owing to the high resolution of the data and the unusually high quality of the crystals, localization of the H atoms has been achieved, a rare accomplishment for cyclodextrin X-ray structures. This made possible, apart from the geometry of the complexes, the detailed description of a five-membered-ring water cluster with very well ordered hydrogen bonding. The enantiospecificity exhibited by the described systems reveals the subtle differences of the weak intermolecular forces involved in the selective binding of the two optical antipodes by the two hosts. The binding geometry in the two complexes is different, but it is effected in both by numerous host–guest C—H...O interactions, resulting from induced fit of the hosts toward each of the enantiomeric guests. In TMαCD/(R)-(1) two of these H...O host–guest distances, directed toward the acetal O atoms defining the chirality of the guest, are much shorter than the rest and also shorter than all the H...O distances in TMβCD/(S)-(1). Moreover, (R)-(1) interacts not only with the enclosing host, but with other hosts in the crystal lattice, in contrast to (S)-(1) in the TMβCD/(S)-(1) complex which is isolated inside channels formed by the host molecules. The above differences are reflected in the much higher binding constant of TMαCD/(R)-(1) compared with that of TMβCD/(S)-(1) (∼6800 and ∼935 M−1, respectively), determined by NMR in aqueous solution, and the ability of TMαCD to selectively precipitate (R)-(1) from racemic (1) in much higher yield than TMβCD precipitates (S)-(1).
X-ray studies on crystalline complexes involving amino acids and peptides. XXXVII. Novel aggregation patterns and effect of chirality in the complexes of DL- and L-lysine with glutaric acid
Authors: Saraswathi N. T. , Manoj N. , Vijayan M.
Published: July 2002

The complexes of glutaric acid with DL-lysine contain singly positively charged zwitterionic lysinium ions and singly negatively charged semi-glutarate ions. Both the ions exhibit different conformations in the two complexes. The structures contain head-to-tail sequences of amino acids. However, the aggregation patterns in the two complexes are entirely different, demonstrating the effect of chirality on molecular aggregation. These patterns also turn out to be different from those so far observed, in structures containing amino acids. The structures contain characteristic interaction patterns involving linear arrays of alternating amino and carboxylate groups.
Study of rare-earth π-complexes by means of Voronoi–Dirichlet polyhedra
Authors: Blatova O. A. , Blatov V. A. , Serezhkin V. N.
Published: July 2002

An investigation of 135 π-complexes of rare-earth atoms (Ln) was carried out with Voronoi–Dirichlet polyhedra. A novel method for the evaluation of the sizes of polyatomic ligands and steric effects in the structure of organometallic compounds was developed. The dependence of the domain size for Ln atoms on their nature, coordinating number and oxidation state was studied. The reasons for the occurrence of agostic Ln—H contacts were considered with a geometrical–topological analysis.