bluuebunny/crossref_metadata_2025 huggingface dataset:
A selective, multiple-criteria method for handling constraint
violations in well-defined design problems
Authors: DENTSORAS ARGIRIS J.
Published: July 2002

A selective, multiple-criteria method is proposed
for handling constraint violations in well-defined design
problems. First, the types of design problems upon which
the method may apply are presented and a graph topology
is adopted for representing the problem decomposition in
the level of design parameter interrelations (design parameter
graphs). Next, the problem of constraint violations for
the design parameters is discussed. It is shown that these
violations can be resolved by modifying the values of the
primary design parameters and recalculating the values
of the violated parameters. Any “blind” attempt
of modifying the values of the primary design parameters
for resolving occurring violations may, eventually, create
additional violations. The proposed method guides the designer
toward those primary design parameters that present the
least possibility of creating more violations when their
values are modified. This is achieved by applying multiple
criteria and by producing a final, sorted list of primary
design parameters. The designer may then choose the first
element of this list to handle efficiently the violations
of the design parameters. Two examples are given on a design
space where constraint violations occur. Through these
examples, the capability of the proposed method in helping
the designer to handle constraint violation is shown. The
concluding remarks, except for summarizing the potential
of the method, determine its boundaries and include a reference
on relative work currently under investigation.
CALL FOR PAPERS
Journal of Functional Programming
Special Issue on Theorem Provers and Functional Programming
Authors: Melham Tom
Published: July 2002

A special issue of the Journal of Functional Programming will
be devoted to the use of functional programming in theorem proving. The submission
deadline is 31 August 1997.

The histories of theorem provers and functional languages have been deeply
intertwined since the advent of Lisp. A notable example is the ML family of
languages, which are named for the meta language devised for the LCF theorem
prover, and which provide both the implementation platform and interaction facilities
for numerous later systems (such as Coq, HOL, Isabelle, NuPrl). Other examples
include Lisp (as used for ACL2, PVS, Nqthm) and Haskell (as used for Veritas).

This special issue is devoted to the theory and practice of using functional
languages to implement theorem provers and using theorem provers to reason about
functional languages. Topics of interest include, but are not limited to:

– architecture of theorem prover implementations

– interface design in the functional context

– limits of the LCF methodology

– impact of host language features

– type systems

– lazy vs strict languages

– imperative (impure) features

– performance problems and solutions

– problems of scale

– special implementation techniques

– term representations (e.g. de Bruijn vs name carrying vs BDDs)

– limitations of current functional languages

– mechanised theories of functional programming
Clinical comparison of selective serotonin reuptake inhibitors in the treatment
of geriatric depression: a review of literature
Authors: Patel Richard Marc
Published: July 2002

Introduction

With their ease of administration, relatively benign side-effect profile and safety
in overdose, in the United States the selective serotonin reuptake inhibitors (SSRIs)
have become de facto first choice in the treatment of geriatric depression, displacing
tricyclic antidepressants (TCAs). In this paper, the relevant literature regarding
neurochemistry, kinetics, dosing, efficacy and differential side-effect profiles
of citalopram, fluvoxamine, fluoxetine, sertraline, and paroxetine, the five currently
available SSRIs in the USA, will be reviewed with special emphasis on geriatric data.
Of late, considerable controversy has been generated regarding whether SSRIs are
as effective as TCAs in severe and melancholic depressive subtypes. This important
issue will be explored and the relative utility of all the SSRIs in the elderly patient
compared and contrasted. Finally, reasons for difficulties in comparing results across
studies will be elucidated.
Adult aural rehabilitation
Authors: Mackenzie IJ
Published: July 2002

The epidemiology of hearing loss in the elderly has been well documented in the UK by Davis and in the USA by Gates. Both studies confirm that presbyacusis is common. Hearing loss results in significant disability in social communication. Davis based his conclusions on a cohort of 2910 subjects while Gates looked at 1475 subjects six years apart. Both studies carried out detailed audiological examinations.
Public Opinion and International Policy Choices: Global Commitments for Japan and Its Peers?
Authors: Bobrow Davis B. , Boyer Mark A.
Published: July 2002

To understand the prospects for global order and progress in the coming years, we explore the joint implications of three premises: (1) states advantaged by the current international order have stakes in its regularity and predictability, and thus in moving to counter or prevent threats to those stakes; (2) along impure public and club goods lines, they are more likely to make efforts to do so when some private or club benefits result; and (3) public opinion provides a bounded policy acceptance envelope offering incentives and disincentives to national political elites to act as envisioned by the first two premises. We present a mosaic of public opinion in major OECD countries (the US, Japan, and major EU members) on three policy areas – foreign aid, UN peace-keeping operations, and environmental quality – that contain international public goods elements. Actual contribution tendencies in those areas found in our previous work largely conform to the public opinion patterns reported here. Within the limits of available data, domestic political incentives as represented by public opinion warrant neither extreme optimism nor pessimism about the prospects for continuing contributions by OECD states to sustaining orderly functioning of the current world system.
Photoresponses of Transgenic Arabidopsis Overexpressing the Fern Adiantum capillus-veneris PHY1
Authors: Okamoto H. , Sakamoto K. , Tomizawa K. I. , Nagatani A. , Wada M.
Published: July 2002

The phytochrome gene (PHY1) cDNA from the fern Adiantum capillus-veneris encodes an amino acid sequence that shows equal similarity (50–60%) to all five Arabidopsis phytochromes (PHYAE). The A. capillus-veneris PHY1 cDNA was transformed into Arabidopsis ecotype Landsberg erecta to investigate its activity in angiosperms. Three of the resulting lines contained at least 8 times more spectrally active phytochrome than the wild type, indicating that A. capillus-veneris phytochrome can incorporate the chromophore of the host plants. Hypocotyl growth inhibition of these transgenic lines was investigated under red and far-red light. The results indicated dominant negative activity of A. capillus-veneris phy1 on the phytochrome A response in the host plants under continuous far-red light. However, the fern phytochrome did not interfere with the red-light repression of hypocotyl growth mediated by endogenous phytochrome B, and it failed to complement a phyB mutant phenotype. These observations suggest that the phy1 phytochrome molecule is too diverged from those of Arabidopsis to be fully functional.
Dynamics of dense, charge-stabilized suspensions of colloidal silica studied by correlation spectroscopy with coherent X-rays
Authors: Grübel G. , Abernathy D. L. , Riese D. O. , Vos W. L. , Wegdam G. H.
Published: July 2002

The dynamics of concentrated, charge-stabilized colloidal silica suspensions was studied over a wide range of wave-vectors. The short-time diffusion coefficient, D(Q), was measured for concentrated suspensions up to their solidification points by photon correlation spectroscopy with coherent X-rays and compared to free particle diffusion D0, studied by Dynamic Light Scattering (DLS) in the dilute case. Small angle X-ray scattering (SAXS) was used to determine the static structure factor S(Q). D0/D(Q) peaks for Q values corresponding to the maximum of the static structure factor showing that the mostly likely density fluctuations decay the slowest. The data allow one to estimate the diffusion coefficient D(Q) in the Q → 0 and Q → ∞ limits. Thus, hydrodynamic functions can be derived free from any modeling of the static or dynamic properties. The effects of hydrodynamic interactions on the diffusion coefficient in charge-stabilized suspensions are presented for volume fractions 0.075 < Φ < 0.28.
Kinematical two-dimensional multiple-diffraction intensity profiles. Application to ω–ψ scans of silicon and diamond obtained with synchrotron radiation
Authors: Rossmanith E. , Hupe A , Kurtz R. , Schmidt H. , Krane H.-G.
Published: July 2002

In a previous paper by Rossmanith [J. Appl. Cryst.(2000),33, 1405–1414], expressions for the calculation of multiple-diffraction patterns observed in ω–ψ scans of Bragg reflections were derived within the framework of the kinematical theory, taking into account the divergence and wavelength spread of the incident beam, as well as the mosaic structure of the crystal sample. Agreement with CuKα experiments was demonstrated. In this paper, it is shown that the theoretical expressions are also suitable for synchrotron radiation experiments.
Optimization and planning of experiments in single-crystal diffractometry with a zero-dimensional detector
Authors: Nekrasov Yu.
Published: July 2002

An algorithm for the optimization of data collection is described. The algorithm ensures optimum quality of measurements at the set survey rate and operates efficiently and simply by the flexible distribution of time between first and second measurements of a reflection.
Determination of displacements from nanoprecipitates in a Cu–Ni–Fe single crystal using anomalous small-angle and large-angle X-ray scattering
Authors: Lyon O. , Guillon I. , Servant C.
Published: July 2002

Single crystals of Cu–41.5 at.% Ni–16 at.% Fe have been studied by small-angle and large-angle X-ray scattering in order to determine the displacements induced by the disc-like precipitates formed during decomposition. The small-angle X-ray scattering (SAXS) patterns gave information on the size and the organization of the precipitates, while the scattering near Bragg peaks allows a determination of the distortions of the lattice created by these precipitates. The variations of the atomic scattering factors of Fe, Ni and Cu (for the large-angle measurements) were used to determine both the partial structure functions (`chemical' data) and the partial displacements. The precipitates were found to be enriched in Fe and Ni, which induced a contraction of the lattice, while the depleted matrix (mainly Cu) was dilated. This succession of compressed and dilated regions is very stable and prevents a single precipitate from growing much in this direction during coarsening. This can explain why a single precipitate tends to grow mainly in the orthogonal directions, where the extension of the displacements is smaller than the precipitated region.
A random procedure for the decomposition of a powder pattern inEXPO
Authors: Altomare Angela , Giacovazzo Carmelo , Moliterni Anna Grazia Giuseppina , Rizzi Rosanna
Published: July 2002

The main obstacle toab initiocrystal structure solution by powder data is the lack of accuracy in the single Bragg integrated intensity estimates. The two-stage method proves powerful for solving crystal structures from powder data: in the first stage, the integrated intensities and, consequently, the structure-factor moduli, are extracted from the pattern for each reflection; in the second stage, direct methods may be applied to estimate the phases of the structure factors. The greater the accuracy of the integrated intensities, the more efficient the phasing procedure. A new procedure is described, aiming at overcoming the tendency of the Le Bail algorithm [Le Bailet al.(1988).Mater. Res. Bull.23, 447–452] to equipartition the intensities of strongly overlapping reflections. It proves to be efficient for lowering the phase error in the phasing process. The procedure has been implemented in theEXPOprogram [Altomareet al.(1999).J. Appl. Cryst.32, 339–340].
Orthorhombic lattice deformation of CuAlBe shape-memory single crystals under cyclic strain
Authors: Tidu A. , Eberhardt A. , Bolle B. , Moreau F. , Heizmann J.-J.
Published: July 2002

X-ray diffraction experiments were carried out to prove that X-ray methods can be used to assess strain-induced fatigue in CuAlBe shape-memory alloys. The pseudoelastic fatigue behaviour of CuAlBe single crystals presents a strong decrease of the critical stress of the martensitic transformation. During the fatigue test, the austenitic lattice exhibits a lattice distortion. This lattice distortion evolves during the fatigue test: the austenitic cubic lattice (β1) tends to transform gradually towards an orthorhombic one. Various hypotheses concerning this lattice distortion are proposed.
Analysis of powder diffraction patterns of monoclinic and triclinic crystals
Authors: Ishida T. , Watanabe Y.
Published: July 2002

Based upon the published methods of indexing powder data of triclinic crystals, a systematic method of computerizing the procedures is devised and the ways of conveniently treating various errors are discussed. For monoclinic crystals, a new function, R'(i,h,k), is introduced and its efficacy of deriving lattice parameters is shown. The merits and demerits of the present methods are compared with those of methods previously reported.
Correction of integrated Bragg intensities for anisotropic thermal scattering
Authors: Merisalo M. , Kurittu J.
Published: July 2002

A readily applicable procedure is presented for calculating the contribution of one-phonon scattering (TDS) to measured integrated intensities for single crystals of any symmetry under conventional experimental situations. The anisotropy of the scattering is included correctly within the continuum elasticity approximation. A computer program is presented for the calculation of TDS contribution for cubic, tetragonal, orthorhombic, hexagonal and trigonal crystal structures. The procedure is applied to the calculation of the one-phonon contribution for the hexagonal and tetragonal crystal structures.
Crystal data for 2-nitroso-2-bromo-3,3-dimethylbutane
Authors: Newton M. G. , Pantaleo N. S. , Galobardes M. , Pinnick H. W.
Published: July 2002

Crystals of the title compound crystallize in a body-centered cubic cell with a = 7.697 (3) Å and Z = 2. This substance belongs to a class of highly disordered hexasubstituted ethanes, and is a rare example of a solid-state monomeric nitroso compound.
Crystal data for NH(CH3)3GeCl3
Authors: Möller A. , Felsche J.
Published: July 2002

NH(CH3)3GeCl3, C3H10N+.Ge2+.3Cl−, crystallizes at room temperature in an orthorhombic modification with a = 9.537(2), b = 8.235(2), c = 12.138(2) Å, Z = 4, space group Cmc21. These cell parameters correspond to a derivative of the cubic perovskite structure type, with a≃b≃\sqrt{2} a
cubic and c≃ 2a
cubic. Unlike other chlorogermanates(II) there is not a phase change to an ionically conducting cubic high-temperature form.
X-ray guide tube for diffraction experiments
Authors: Nakazawa H.
Published: July 2002

For diffraction experiments with an extremely small crystal or with very long distance from X-ray source to detecting instrument, the use of an `X-ray guide tube' (XGT) is proposed on the basis of a simple consideration and experiment with a Pyrex-glass tube. X-ray intensities through an XGT of glass and also through a pin hole were measured as a function of photon energy and compared to derive the gain by use of XGT. At wavelengths between Cu Kα and Mo Kα radiations, the observed gain in brightness is about thirty to twenty for the present setup, corresponding to about 50 to 80% of the maximum possible gain calculated on the assumption that the reflectivity of X-ray total external reflection is 1.0.
A new magnesium aluminium zirconium oxide, Mg5+x
Al2.4−x
Zr1.7+0.25x
O12 with -0.4≲x≲0.4
Authors: Tassot P. , Konig G. , Liebau F. , Seifert F.
Published: July 2002

The title compound has been synthesized by sintering oxide mixtures between 1975 and 2175 K. It decomposes at or below ca 1875 K. Quenched to room temperature, the phase is trigonal with ao
= 3.2496(1), c0
= 25.221(1) Å, V = 230.65(2) Å3, Z = 1, Dm
= 3.95(1) g cm−3, refraction indices ∊

D

293 K = 1.805(5), ω

D

293 K = 1.855 (5) and birefringence Δ′ = 0.05. The JCPDS File No. for magnesium aluminium zirconium oxide is 34-1495.
Background removal in X-ray fiber diffraction patterns
Authors: Millane R. P. , Arnott S.
Published: July 2002

Background can be a major source of error in measurement of diffracted intensities in fiber diffraction patterns. Errors can be large when poorly oriented less-crystalline specimens give diffraction patterns with little uncontaminated background. A method for estimating and removing a general global background in such cases is described and illustrated with an example.
On the estimation of the unit-cell volume from powder diffraction data
Authors: Paszkowicz W.
Published: July 2002

General formulae allowing estimation of the unit-cell volume are derived. They are valid for all Bravais lattices. The precision of the estimation is discussed. The examples illustrate the application of the method.
Critical temperatures of superconductivity and neutron diffraction studies at 293 and at 10 K of molybdenum–iridium single crystals of A15 structure
Authors: Koksbang R. , Rasmussen S. E. , Hazell R. G.
Published: July 2002

A crystal of dimensions 2.5 × 2.5 × 1.8 mm and of composition Mo3.25Ir was examined by neutron diffraction at 293 and 10 K. It has the A15 structure for which the space group is Pm3n and the ideal composition would be Mo3Ir. Least-squares refinements gave R(F) values of 0.013 and 0.017 for the 293 and the 10 K data, respectively. No structural phase transition was observed at 10 K. The lattice constants found were a = 4.967 (2) Å at 293 K and 4.958 (2) Å at 10 K. The transition temperature to superconductivity of the crystal was measured by an inductive method. An onset of superconductivity was found at 9.25 (5) K and a main transition at 9.10 (5) K. Another, approximately cylindrical, sample of volume 117 mm3 showed an onset at 8.6 (1) K and a main transition at 8.0 (1) K. About two thirds of this sample was a single-crystal.
An X-ray diffractometer for studying the effect of external fields on the structure and electron distribution of single crystals
Authors: Aslanov L. A. , Trunov V. A. , Fetisov G. V. , Priemyshev V. A. , Rybakov V. B. , Kasman Ya. A. , Bulkin A. P.
Published: July 2002

A new four-circle X-ray diffractometer (RMD) for single crystals is described that has only one (horizontal) axis of specimen rotation and a movable X-ray tube and detector. The diffractometer is characterized by the equatorial geometry. The equatorial plane rotates about the χ axis lying in this plane whereas the φ axis is fixed. This permits the use of various external (electromagnetic, magnetic etc.) fields applied to specimens along the φ axis. The angles between this direction and all the other crystallographic directions in the specimen remain constant in the course of intensity measurements. The designed RMD diffractometer allows the study of structural changes and electron distribution variations in a crystal subjected to external actions. The geometry and the design of the goniometer are considered in detail. Experiments carried out on the RMD diffractometer have demonstrated its efficiency for precision X-ray structure analysis.
Characterization of nematic lyomesophases by X-ray diffraction
Authors: Amaral L. Q.
Published: July 2002

Procedures for an independent characterization of lyotropic nematics by X-ray diffraction (XD) are presented. Nc
(cylindrical micelles) and Nd
(discotic micelles) can be distinguished on the basis of surface orientation alone by a method of sample scanning through the X-ray beam. The sign of the diamagnetic anisotropy susceptibility can also be independently obtained. The differences between optical and XD information for such a characterization are discussed.
Some practical features for calculating the polycrystalline elastic properties from texture
Authors: Humbert M. , Diz J.
Published: July 2002

The prediction of the elastic properties of a polycrystalline material requires the knowledge of its orientation density function (ODF), which represents mathematically the crystallographic texture. The real piece of texture information needed for such calculations depends on the modelling and is obtained from pole figures, the number of which is determined by crystal symmetry. According to these features different methods have been used to calculate (mean values, self-consistent approach) the elastic properties of low-symmetry materials with minimal texture information. Calculation of these properties for hexagonal materials becomes very simple and can be achieved directly from 00.1 pole figures.
The application of the neutron time-of-flight technique for real-time diffraction studies
Authors: Balagurov A. M. , Mironova G. M. , Novozchilov V. E. , Ostrovnoy A. I. , Simkin V. G. , Zlokazov V. B.
Published: July 2002

Real-time neutron powder diffraction and small-angle scattering techniques have been developed on the TOF diffractometer DN-2 at the IBR-2 pulsed reactor at JINR (Dubna) with a total flux on the sample of 107 neutrons cm−2 s−1 and a resolution of about 1%. A special arrangement of the detector system ensures a high counting rate of diffracted neutrons. Depending upon sample type and experimental conditions, the measuring time ts
of one neutron pattern varies from a few minutes to several seconds. The performance of the diffractometer is discussed and typical data are shown to demonstrate current achievements using real-time techniques at a pulsed reactor.
Determination of crystal imperfection by X-ray diffraction in a strong acoustic field
Authors: Zolotoyabko E. , Polikarpov I. , Panov V. , Schvarkov D.
Published: July 2002

A study of X-ray diffraction in single silicon and quartz crystals in a strong ultrasonic field has been carried out. The dependence of diffraction intensity I(w) on sound amplitude w has been obtained right up to the kinematical limit Ik
= I(∞). It is shown that the ratio η = I(∞)/I(0) depends on the crystal quality. Experimental data for different reflections, sound frequencies and X-ray wavelengths are compared with the model calculations for several lattice-distortion mechanisms.
Resolution of a protein sequence ambiguity by X-ray crystallographic and mass spectrometric methods
Authors: Keefe L. J. , Lattman E. E. , Wolkow C. , Woods A. , Chevrier M. , Cotter R. J.
Published: July 2002

Ambiguities in amino acid sequences are a potential problem in X-ray crystallographic studies of proteins. Amino acid side chains often cannot be reliably identified from the electron density. Many protein crystal structures that are now being solved are simple variants of a known wild-type structure. Thus, cloning artifacts or other untoward events can readily lead to cases in which the proposed sequence is not correct. An example is presented showing that mass spectrometry provides an excellent tool for analyzing suspected errors. The X-ray crystal structure of an insertion mutant of Staphylococcal nuclease has been solved to 1.67 Å resolution and refined to a crystallographic R value of 0.170 [Keefe & Lattman (1992). In preparation]. A single residue has been inserted in the C-terminal α helix. The inserted amino acid was believed to be an alanine residue, but the final electron density maps strongly indicated that a glycine had been inserted instead. To confirm the observations from the X-ray data, matrix-assisted laser desorption mass spectrometry was employed to verify the glycine insertion. This mass spectrometric technique has sufficient mass accuracy to detect the methyl group that distinguishes glycine from alanine and can be extended to the more common situation in which crystallographic measurements suggest a problem with the sequence, but cannot pinpoint its location or nature.
Determination of texture inhomogeneity in near-surface layers. Experimental verification
Authors: Bonarski J. , Morawiec A.
Published: July 2002

An experimental verification of the method of investigating texture inhomogeneity in the near-surface layers of a flat sample using the X-ray technique is presented. The investigations were performed on deformed aluminium. The results show that this method can be applied when finding the texture of the layers in the material is essential. Some limitations in the application of this method are due to its sensitivity to measurement errors.
A simple method for determining orientation and misorientation of the cubic crystal specimen
Authors: Liu Q.
Published: July 2002

With the aid of a double-tilt holder, a simple method for determining orientation and misorientation of a cubic crystal specimen in a transmission electron microscope is developed. To use this method, a recognizable zone axis from one grain needs to be aligned along the beam direction, the corresponding tilt positions (α
0, β
0) of the two rotation axes must be obtained from the meter reading of the holder and the rotation position of the Kikuchi pattern around the beam direction must be measured on the fluorescent screen with the aid of apparatus for the direct measurement of a diffraction-pattern position on screen. After the input of (α
0, β
0) and the rotation positions, the orientation of the grain can be calculated using a computer program. The misorientation matrix R, rotation angle Θm
, axis I

m
and sense can then be calculated for any selected set of two grains. The accuracy of determination of the orientation of any particular grain is about 1° and, in the case of the determination of misorientation angles between two grains within a sample, the precision is within 0.1°. This method is considered to be much simpler and more rapid than previous methods because no photographs of Kikuchi patterns need to be taken and only one zone-axis orientation needs to be adjusted along the beam direction.
Computer simulation of local atomic displacements in alloys. Application to Guinier–Preston zones in Al–Cu
Authors: Kyobu J. , Murata Y. , Morinaga M.
Published: July 2002

A new computer program has been developed for the simulation of local atomic displacements in alloys with face-centered-cubic and body-centered-cubic lattices. The combined use of this program with the Gehlen–Cohen program for the simulation of chemical short-range order completely describes atomic fluctuations in alloys. The method has been applied to the structural simulation of Guinier–Preston (GP) zones in an Al–Cu alloy, using the experimental data of Matsubara & Cohen [Acta Metall. (1985), 33, 1945–1955]. Characteristic displacements of atoms have been observed around the GP zones and new structural models including local displacements have been proposed for a single-layer zone and several multilayer zones.
A Spreadsheet Approach to Automated Protein Crystallization
Authors: Andersen G. R. , Nyborg J.
Published: July 2002

To design and analyse a large number of protein crystallization experiments, a set of macros running in Excel 4.0 has been developed. The macros are designed to work in a multiuser environment. An interface for a crystallization robot based on two Gilson autosamplers is included.
Advances in Texture Analysis from Diffraction Spectra
Authors: Matthies S. , Lutteroti L. , Wenk H. R.
Published: July 2002

The orientation distribution of a textured polycrystal has been traditionally determined from a few individual pole figures of lattice planes hkl, measured by X-ray or neutron diffraction. A new method is demonstrated that uses the whole diffraction spectrum, rather than extracted peak intensities, by combining ODF calculation with Rietveld crystal structure refinement. With this method, which is illustrated for a synthetic calcite texture, it is possible to obtain quantitative texture information from highly incomplete pole figures and regions of the diffraction spectrum with many overlapping peaks. The approach promises to be advantageous for low-symmetry compounds and composites with complicated diffraction spectra. The method is particularly elegant for time-of-flight neutron diffraction, saving beam time by using small pole-figure regions and many diffractions.
Absolute Calibration of Small-Angle Neutron Scattering Data of a Double-Crystal Diffractometer
Authors: Carsughi F. , Bellmann D. , Kulda J. , Magnani M. , Stefanon M.
Published: July 2002

Small-angle neutron scattering (SANS) experiments generally provide the absolute SANS cross sections and this allows quantitative results to be obtained; however, data collected at double-crystal diffractometers are frequently not normalized to absolute cross sections and they are used only for qualitative analysis. In point-geometry diffractometers, the normalization is done by comparing the scattered intensities to those of samples of known cross sections or by measuring the direct-beam intensity; in the double-crystal diffractometer, the incident flux information is contained in the rocking curve measured without a sample and this feature can therefore be used to normalize the scattered intensities to the SANS cross sections. A sample of thickness 1 mm of the Ni-based superalloy UDIMET 520 was analyzed at a double-crystal diffractometer; the SANS cross section obtained by the proposed procedure compares well with the SANS cross section found for similar materials by using conventional point-geometry diffractometers and calibrated by light water.
Studying the Microstructure of Unaged and Aged PVDF by Small- and Wide-Angle X-ray Scattering
Authors: Stribeck N. , Buchner S.
Published: July 2002

A layer from plasticized poly(vinylidene fluoride) (PVDF) was aged by exposing one of its faces to an aggressive fluid at elevated temperature and pressure. From visual inspection the aged material appeared not to be homogeneous. Therefore, samples from three distinguishable regions were compared with a sample cut from the virgin material by studying their small- and wide-angle X-ray scattering (SAXS and WAXS). The results show that plasticizer has vanished from the aged material, the crystalline layer thickness distribution has narrowed, amorphous lamellae are collapsed and voids have been created. Within the aged material the number of voids varies: there are more at the inner surface and fewer at the outer surface beneath the rods of a supporting metal grid. Based on the results of this study and theoretical considerations, a method for the quantitative description of the ageing process is proposed, which only requires a simple kind of SAXS measurement.
Polarized Neutron Scattering from Polarized Nuclei Near Paramagnetic Centers
Authors: Stuhrmann H. B. , van den Brandt B. , Hautle P. , Konter J. A. , Niinikoski T. O. , Schmitt M. , Willumeit R. , Zhao J. , Mango S.
Published: July 2002

Polarized neutron scattering from dynamically polarized targets has been used for the study of hydrogenous materials in several laboratories. A new variant, which is less dependent on specific deuteration, is proposed. This is based on the observation that a radio frequency (RF) field swept over a selected part of an NMR line depolarizes the spins depending on their spatial distribution in and around paramagnetic molecules. An RF field swept over a narrow frequency interval has little effect on polarized nuclear spins in the paramagnetic centers, whereas remote nuclear spins can be depolarized. When applying the sweep over a much larger frequency range, all spins are depolarized. This was observed both by NMR and by polarized neutron scattering after selective depolarization of the proton spins in a solid solution of protonated EHBA–CrV, Na(C12H20O7CrV).D2O, in a mixture of deuterated glycerol and water. The decay time of proton spin polarization in domains associated with the paramagnetic centers varies between 5 h in a deuterated solvent and less than 1 min in a protonated solvent. The size of such a domain is barely larger than 1 nm. The same observation is also made when the nuclear polarization is reversed by adiabatic fast passage. If the RF sweep is limited to frequencies close to the central peak of the proton NMR line, the proton spins far away from the paramagnetic centers are reversed, whereas those of EHBA–CrV and close to the centers maintain their original polarization. This method may become a useful tool in neutron scattering once the paramagnetic centers can be fixed as spin labels to well defined sites in a macromolecule, preferably in a crystal lattice.
Shear-Induced Structures in Concentrated Surfactant Micellar Phases
Authors: Penfold J. , Staples E. , Tucker I. , Tiddy G. J. T. , Khan Lodhi A.
Published: July 2002

Constant and oscillatory Couette shear flow have been used in combination with small-angle neutron scattering to observe the shear-induced ordering in concentrated surfactant micellar phases. For the lamellar phase of hexaethylene glycol monohexadecyl ether, C16
E
6, two distinct lamellae orientations have been identified. At low shear gradients the lamellae are ordered parallel to the flow–vorticity plane, whereas at higher shear gradients the lamellae order parallel to the flow-shear gradient plane, corresponding to a rotation through 90° of the axis of orientation. At intermediate values of constant shear and for oscillatory shear, both lamellae orientations are simultaneously observed for the first time in a surfactant lamellar phase. For the lamellar phase, a dispersion of the binary surfactant mixtures of dioleyl cationic and 2-ethyl hexaglycerol monoether surfactants, a high degree of alignment, in the direction parallel to the flow–vorticity plane, is observed at zero and low shear. With time, during the application of a shear gradient of 25 s−1, the lamellar phase transforms to a highly ordered solution of monodisperse multilamellar vesicles.
Ba6CoNb9O30 and Ba6FeNb9O30: Two New Tungsten-Bronze-Type Ferroelectrics. Centrosymmetry of Ba5.2K0.8U2.4Nb7.6O30 at 300 K
Authors: Foster M. C. , Brown G. R. , Nielson R. M. , Abrahams S. C.
Published: July 2002

Ba6CoNb9O30 and Ba6FeNb9O30 in space group P4bm are shown to satisfy the structural criteria for ferroelectricity. Ba6CoNb9O30 undergoes a diffuse phase transition at 660 (11) K, as observed calorimetrically, in addition to a dielectric permittivity anomaly with an onset temperature of 685 (10) K. The demonstration of dielectric hysteresis at room temperature under the application of a varied DC field reaching a maximum of ± 300 kV m−1, corresponding to a spontaneous polarization of 1.2 (5) × 10−2C m−2, provides unambiguous verification that it is a new ferroelectric. Ba6FeNb9O30 also undergoes a diffuse phase transition at 605 (16) K, with a dielectric anomaly at 583 (5) K, and exhibits dielectric hysteresis at room temperature under a varied DC field ranging to ± 310 kV m−1 corresponding to a spontaneous polarization of 2.2(5) × 10−2Cm−2; it too is demonstrably a new ferroelectric. Although Ba5.2K0.8U2.4Nb7.6O30 has also been reported in space group P4bm, all atomic displacements from the corresponding centrosymmetric positions are less than their refined root-mean-square thermal or static amplitudes. Such an arrangement is likely to be thermodynamically unstable. Either its space group has been incorrectly assigned, and reinvestigation will show the space group is P4/mbm, or the structural refinement is incomplete.
Influence of miscut on crystal truncation rod scattering
Authors: Munkholm A. , Brennan S.
Published: July 2002

X-rays can be used to measure the roughness of a surface by the study of crystal truncation rod scattering. It is shown that for a simple cubic lattice the presence of a miscut surface with a regular step array has no effect on the scattered intensity of a single rod and that a distribution of terrace widths on the surface is shown to have the same effect as adding roughness to the surface. For a perfect crystal without miscut, the scattered intensity is the sum of the intensity from all the rods with the same in-plane momentum transfer. For all real crystals, the scattered intensity is better described as that from a single rod. It is shown that data-collection strategies must correctly account for the sample miscut or there is a potential for improperly measuring the rod intensity. This can result in an asymmetry in the rod intensity above and below the Bragg peak, which can be misinterpreted as being due to a relaxation of the surface. The calculations presented here are compared with data for silicon (001) wafers with 0.1 and 4° miscuts.
A strengthened zero-scattering-alloy pressure cylinder for neutron powder diffraction
Authors: Knorr K. , Annighöfer B. , Depmeier W.
Published: July 2002

A strengthened pressure cylinder for piston/cylinder devices is presented for use in angle-dispersive high-pressure neutron powder diffraction. It is shown that these cylinders, manufactured from Ti52/Zr48zero-scattering alloy and strengthened by the shrink-fit method, allow the extension of the accessible pressure range of the Kiel–Berlin Cell I to 22 kbar.
X-ray diffraction in disordered paraelectric crystal structures with polar clusters and thegparameter
Authors: Łukaszewicz K.
Published: July 2002

In the crystal structure analysis of disordered structures consisting of randomly distributed polar lattice cells, additional information on the range of order can be obtained by introducing thegparameter in the structure-factor equationF(h) =A(h) +igB(h). In the case of perfect disorder, the parametergtends to zero; however, in the case of local order, the crystal structure contains small polar clusters and thegparameter becomes greater than zero (0 <g< 1). The physical meaning of thegparameter is explained in terms of the peculiar features of X-ray diffraction in disordered structures.
Combined method forab initiostructure solution from powder diffraction data
Authors: Putz H. , Schön J. C. , Jansen M.
Published: July 2002

A new direct-space method forabinitiosolution of crystal structures from powder diffraction diagrams is presented. The approach consists of a combined global optimization (`Pareto optimization') of the difference between the calculated and the measured diffraction pattern and of the potential energy of the system. This concept has been tested successfully on a large variety of ionic and intermetallic compounds.
Correction of zero shift in powder diffraction patterns using the reflection-pair method
Authors: Dong C. , Wu F. , Chen H.
Published: July 2002

Zero shifts of 2θ usually represent one of the most serious systematic errors in powder patterns obtained by diffractometers, and they cannot be readily diagnosed and corrected. Frequently, large zero shifts hinder indexing of the patterns. Programs exist to refine the lattice constants and calculate the zero shift, but they need the indexing results. We have derived an equation, based on the reflection-pair method, to calculate and correct the zero shift before indexing. The equation has been tested on many experimental data and the effectiveness of the method has been confirmed. The method is very useful inabinitiocrystal structure determination using powder data.
CRUNCH: a phase refinement program for high-resolution macromolecular structures
Authors: Langs David A. , Blessing Robert H. , Smith G. David
Published: July 2002

A phase refinement program for high-resolution macromolecular structures is described. The mean phase error of an initial structural solution can often be as large as 60° prior to attempting a refinement, but theCRUNCHprogram procedure may allow one to reduce this phase error to 10 or 20° for all data prior to actually inspecting any map to see how well it may fit a structural model. The procedure is similar to the real/reciprocal space refinement loop incorporated in thehalf-bakedalgorithm described by Sheldrick [Sheldrick & Gould (1995).Acta Cryst.B51, 423–431.] Refinement results are presented for nine different structures which diffract to better than 1.2 Å resolution. The program and test data are availableviaanonymous ftp (nexus.hwi.buffalo.edu).
Long-range interactions in insulating fluids probed by SANS
Authors: Magli R. , Bafile U. , Barocchi F. , Casanova G. , Formisano F. , Guarini E.
Published: July 2002

The study of the microscopic interaction law represents a centraltopic in the physics of the fluid state of matter. Particular interest has been devoted in the past decades to the long-range part of the interatomic force. We review here some recent results, obtained investigating the low-q part of the static structure factor S(q) of insulating fluids, which provide a direct and unambiguous demonstration of the r
−6 dispersion tail of the potential and allow an experimental determination of the strengths of the long-range double and triple dipole interactions.
Space groups rare for organic structures. III. Symmorphism and inherent molecular symmetry
Authors: Wilson A. J. C.
Published: July 2002

To a close approximation, the relative frequency of the space groups of molecular organic compounds is determined by ease of packing. When the molecules are in general Wyckoff positions, the relative frequency anticorrelates with the degree of symmorphism. Somewhat different considerations apply if the molecule possesses and uses some inherent symmetry (\overline 1, 2, m, 2/m, 222, mm, ...) [Kitaigorodskii (1955); Kitaigorodskii (1961). Organic Chemical Crystallography. New York: Consultants Bureau]. The observed frequencies are analysed in the light of the degree of symmorphism and molecular symmetry.
Holographic methods in X-ray crystallography. III. First numerical results
Authors: Maalouf G. J. , Hoch J. C. , Stern A. S. , Szöke H. , Szöke A.
Published: July 2002

The holographic method for the completion of crystal structures, described in paper II [Szöke (1993). Acta Cryst. A49, 853–866], is implemented numerically. The purpose of these modest calculations is to show that the holographic method can handle real crystallographic data in easy problems and to test various algorithms for its implementation. Both synthetic and experimental data are used and sources of error are systematically introduced. The numerical experiments support the theory presented in paper II and show that the holographic method may be a potentially viable alternative to conventional methods for the completion of crystal structures.
Algebraic expressions for symmetry-adapted functions of the icosahedral group in spinor space
Authors: Fan Peng-Dong , Chen Jin-Quan , Draayer J. P.
Published: July 2002

Algebraic expressions for projection operators and symmetry-adapted functions (SAFs) of the icosahedral group for spinor (double-valued) representations are found by using the double-induced technique and eigenfunction method. The SAFs are functions of the angular momentum j, the quantum numbers \lambda, \nu, \mu of the group chain I \supset D_5 \supset C_5, and the multiplicity label \bar m. By this procedure, SAFs for the group I are provided once for all instead of one j value at a time.
How precise are measurements of unit-cell dimensions from single crystals?
Authors: Herbstein Frank H.
Published: July 2002

The results of single-site and many-site measurements of cell dimensions from single crystals are compared for Bond and four-circle diffractometers using samples of corundum (essentially pure rhombohedral α-Al2O3, aluminum oxide) of high diffraction quality, where the effects of small changes in temperature and composition (Cr2O3, chromium oxide, in solid solution) can be taken into account. Similar comparisons are made for four-circle diffractometer measurements on ruby (α-Al2O3, with 0.46 wt % Cr in solid solution). The precisions are some parts in 105. There is partial support for the Taylor–Kennard [Acta Cryst. (1986), B42, 112–120] dictum that standard uncertainties (s.u.s) of cell parameters from routine four-circle diffractometer measurements are less than those for many-site measurements by factors of 5 for cell lengths and 2.5 for cell angles. For organic crystals, independent repetitions of adequate quality for comparison and analysis of routine four-circle diffractometer measurements are available only for α-oxalic acid dihydrate and anthracene. The experimental standard uncertainties given for these two crystals agree reasonably well with the sample s.u.s at room temperature, but appreciably less well at ∼100 K, again giving partial support to the Taylor–Kennard dictum. The relation between specimen characteristics and attainable precision is emphasized; the precisions for routine measurements on good quality organic crystals are some parts in 104. Area-detector measurements of cell dimensions have also been appraised; currently published s.u.s from such measurements appear to be highly unreliable, and this is supported by a recent analysis of the operation of such diffractometers [Paciorek et al. (1999). Acta Cryst. A55, 543–557]. Formulation of a standard protocol for such measurements is badly needed. The dangers inherent in high degrees of replication are illustrated by recounting Kapteyn's Parable of the Chinese Emperor. Attention is drawn to the fact that there has been little improvement in claimed precisions over the past 40–60 years.
Asymmetric hydrogen bonds in centrosymmetric environment: neutron study of very short hydrogen bonds in potassium hydrogen dichloromaleate
Authors: Olovsson I. , Ptasiewicz-Bak H. , Gustafsson T. , Majerz I.
Published: July 2002

The structure of the title compound has been studied by neutron diffraction at 30 and 295 K, with the emphasis on the location of the protons. There are two crystallographically independent H atoms in two very short hydrogen bonds, 2.437 (2) and 2.442 (2) Å at 30 K. The structure could be refined successfully in the centrosymmetric space group P\bar 1, with the H atoms located at the centres of symmetry. However, the form of the thermal ellipsoids of hydrogen indicated either asymmetric hydrogen bonds or overlap of two closely spaced, partially occupied positions around the centres of symmetry. Several different types of refinements have then been applied, including unconventional models; with all atoms except hydrogen constrained in P\bar 1, but with hydrogen allowed to refine without any constraints in P1, anisotropic refinement of all atoms resulted in clearly off-centred hydrogen positions. Significance tests clearly showed that the results from this constrained refinement give the most satisfactory description of the structure. This structure may be described as `pseudo-centrosymmetric with non-centred protons'. The results demonstrate that it is very important to also include refinement models with non-centrosymmetric hydrogen in a centrosymmetric environment when studying very short hydrogen bonds. The shifts of the two H atoms from the centres of symmetry are 0.15 (1) and 0.12 (1) Å, respectively, at 30 K, and 0.15 (1) Å for both H atoms at room temperature. At 30 K: R(F) = 0.036 for 1485 reflections; at 295 K: R(F) = 0.035 for 1349 reflections.