bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of neutron double-crystal diffractometer scattering curves including multiple scattering
Authors: Staron P. , Bellmann D.
Published: July 2002

Double-crystal diffractometers (DCD) of the Bonse–Hart type are used for small-angle neutron scattering (SANS) experiments with very high resolution. Scattering from inhomogeneities in the size range of typically 100 nm to 10 µm can be detected with a DCD. The evaluation of DCD scattering curves is more complicated than for conventional SANS instruments with point collimation for two reasons: first, a DCD operates with a long-slit geometry, and second, owing to the high scattering power of large inhomogeneities, multiple small-angle scattering is likely to play a significant role in many DCD experiments. A numerical procedure is proposed for the determination of particle size distributions from DCD scattering curves influenced by multiple scattering. This procedure is based on ann-fold convolution of single-scattering cross sections, wherendepends on the degree of multiple scattering. It makes use of the indirect Fourier transformation method and thus, firstly, size distributions of arbitrary shape can be determined, and secondly, the calculation is fast, allowing an interactive analysis. The procedure is demonstrated with scattering from latex particles with different degrees of multiple scattering. The results show that the size and volume fraction of the latex spheres can be determined with a reasonable error even from scattering curves that are strongly influenced by multiple small-angle scattering.
SnBversion 2.2: an example of crystallographic multiprocessing
Authors: Rappleye Jason , Innus Martins , Weeks Charles M. , Miller Russ
Published: July 2002

The computer programSnBimplements a direct-methods algorithm, known asShake-and-Bake, which optimizes trial structures consisting of randomly positioned atoms. Although largeShake-and-Bakeapplications require significant amounts of computing time, the algorithm can be easily implemented in parallel in order to decrease the real time required to achieve a solution. By using a master–worker model,SnBversion 2.2 is amenable to all of the prevalent modern parallel-computing platforms, including (i) shared-memory multiprocessor machines, such as the SGI Origin2000, (ii) distributed-memory multiprocessor machines, such as the IBM SP, and (iii) collections of workstations, including Beowulf clusters. A linear speedup in the processing of a fixed number of trial structures can be obtained on each of these platforms.
Influence of neglected small-angle scattering in radial distribution function analysis
Authors: Cargill G. S.
Published: July 2002

Materials containing inhomogeneities (density-fluctuations) of much greater than atomic size produce scattering at very small angles, which may go unobserved in many X-ray, electron, and neutron scattering experiments. For liquids and for amorphous and polycrystalline solids composed of one atomic species, an approximate expression for the reduced radial distribution function obtained from intensity measurements which neglect the small-angle scattering is shown to be Gexp(r) = 4πr{ρ(r) − ρ0[1 + (\overline {\eta^2}η2(ω)/ρ0
2)γ(ω, r)]} where ρ(r) is the atomic distribution function, ρ0 is the average atomic density, \overline {\eta^2}(ω) is the average square of atomic density fluctuations, γ(ω,r) is the density fluctuation correlation function, and ω is a volume element larger than the average atomic volume but smaller than the scale of long-range density fluctuations. This expression is also valid for systems composed of more than one type of atom where ρ(r) is a weighted average of pair distribution functions and [\overline {\eta^2}(ω)/ρ0
2]γ(ω,r) for X-ray scattering describes electron density fluctuations The neglect of small-angle scattering gives rise to a G
exp(r) which appears, from its slope at small r, to correspond to a material of greater average atomic density ρ0,exp than that of the sample being studied. These results are illustrated by application to fluid argon (ρ0,exp/ρ0 = 1.17 near the critical point), to amorphous silicon (ρ0,exp/ρ0 = 1.13), and to phase separated PbO–B2O3 glasses (ρ0,exp/ρ0 = 1.07 for 24 wt. % PbO).
Small-angle X-ray scattering from helical macromolecules
Authors: Pringle O. A. , Schmidt P. W.
Published: July 2002

An earlier calculation of the intensity of small-angle X-ray scattering from helical filaments is extended to give an expression for the intensity from helical macromolecules with a finite cross section. The results are in quite good agreement with an experimental scattering curve for a solution of DNA molecules.
The development of the rolling texture in copper measured by neutron diffraction
Authors: Bunge H. J. , Tobisch J. , Sonntag W.
Published: July 2002

Three-dimensional orientation distribution functions of the crystallites in copper sheets, cold rolled to different degrees of reduction, have been determined using neutron diffraction pole figures. The main features of the textures may be represented by the orientation `tube' already described in prior publications. Two ranges of rolling reduction can be distinguished, a lower one (30 to 50%) and a higher one (70 to 95%) the texture changes of which correspond to those calculated after the Taylor theory. In an intermediate range (50 to 70%) a different deformation mechanism occurs which leads to an intermediate (001) [110] texture component. It is supposed that anisotropic hardening may have occurred in this range.
X-ray diffraction line broadening due to dislocations in non-cubic crystalline materials. III. Experimental results for plastically deformed zirconium
Authors: Kužel R. , Klimanek P.
Published: July 2002

Procedures of X-ray diffraction line profile analysis for the evaluation of the dislocation content in plastically deformed hexagonal materials were tested by means of conventional powder diffractometry on polycrystalline zirconium deformed under tension at 77 K. In order to obtain a representative picture of the dislocation-induced X-ray line broadening a series of reflections was measured. The integral breadths and the Fourier coefficients were evaluated by both direct profile-shape analysis and profile fitting with analytical functions. The results show a significant anisotropy of the line broadening. The 0001 reflections are clearly less broadened than most of the others. According to the theoretical calculations presented previously such a phenomenon can be expected if the plastic deformation favours generation of dislocations with Burgers vectors a/3 〈2{\bar 1} {\bar 1}0〉.
Observation of Periodic Domain Inversion in Periodically Poled LiNbO3 by High-Resolution Topography
Authors: Hu Z. W. , Thomas P. A. , Webjörn J.
Published: July 2002

Periodic domain inversion in an electric field poled LiNbO3 crystal has been studied using high-resolution multiple-crystal multiple-reflection X-ray diffraction topography. Fine linear contrast with spacings that correspond to the lateral dimensions of the periodic pattern has been observed by the choice of an appropriate diffraction mode to provide high spatial resolution and is shown to arise essentially from strains at the domain walls. The origin of the strain contrast at the domain walls is suggested primarily to be the result of the domain-inversion processing via the converse piezeoelectric effect. A structural model for the domain inversion that is based on a pseudosymmetry argument is invoked in order to quantify the ionic displacements for twinning. These results are compared with those obtained in a previous study employing a different diffraction mode [Hu, Thomas & Webjörn (1995). J. Phys. D, 28, A189–A194].
A Wide-Bandpass Multilayer Monochromator for Biological Small-Angle Scattering and Fiber Diffraction Studies
Authors: Tsuruta Hiro , Brennan Sean , Rek Zofia U. , Irving Thomas C. , Tompkins W. H. , Hodgson Keith O.
Published: July 2002

Many biological applications of small-angle X-ray scattering, in particular time-resolved studies, are often limited by the flux incident on the sample due to the smaller scattering cross section of biological specimens. The wider-energy bandpass of a monochromator that consists of a pair of synthetic multilayer microstructures can, in principle, provide a flux two orders of magnitude higher than that of an Si(111) double-crystal monochromator. Two types of multilayers have been installed in the standard monochromator tank of beamline 4-2 at the Stanford Synchrotron Radiation Laboratory; the multilayer beam has been characterized for studies of small-angle X-ray scattering/diffraction from biological materials. Reflectivity and topography measurements indicate that the multilayers are quite adequate for these applications and a pair of Mo/B4C multilayers provided a 10–30 times increase in flux, compared with the flux level obtained with an Si(111) double-crystal monochromator. The increased flux level is very useful in time-resolved scattering studies as well as for recording weak scattering at higher angles. Having carried out many solution scattering and fiber diffraction experiments, we conclude that the use of multilayer does not result in significant broadening of diffraction peaks nor does it have appreciable effects on small-angle resolution. No significant increase in background is observed.
A gentle vapor-diffusion technique for cross-linking of protein crystals for cryocrystallography
Authors: Lusty Carol J.
Published: July 2002

Protein crystals have been cross-linked by a gentle technique whereby glutaraldehyde is introduced by vapor diffusion into the crystallization droplet containing the crystals. Diffraction analyses of crystals of three different proteins show that cross-linking prevents, in a large part, the lattice disorder normally observed on rapid cooling of these crystals. The diffraction results suggest that this cross-linking procedure, performed as a simple extension of the standard vapor-diffusion crystallization experiment, may generally aid in the cooling of fragile protein crystals for which standard procedures of cryopreservation prove inadequate.
A maximum entropy method for determining column-length distributions from size-broadened X-ray diffraction profiles
Authors: Armstrong N. , Kalceff W.
Published: July 2002

We present a novel application of the maximum entropy (MaxEnt) method for solving the double-inverse problems of removing instrument broadening from X-ray diffraction profiles and calculating the column-length distribution of the crystallites. The MaxEnt approach is shown to have compelling advantages over the conventional methods it replaces: it is stable and robust, incorporates noise anda prioriinformation into the solution, preserves positivity of the solution, and can be applied successively. We also show how uncertainties in the derived profiles and column distributions can be determined and used in subsequent calculations, including integral breadth, Fourier coefficients, column-length distributions and apparent particle sizes. Calculations are performed on simulated X-ray diffraction profiles for a range of particle sizes, with a detailed study of the sensitivity of the results to background-level estimates and the use of an incorrect instrument response function.
SANS study of the structure and interaction of L64 triblock copolymer micellar solution in the critical region
Authors: Liao C. , Choi S.-M. , Mallamace F. , Chen S.-H.
Published: July 2002

Pluronic L64 triblock copolymer is soluble in water at room temperature up to more than 30 wt%, forming disordered spherical micellar phase above the cmc-cmt line. We investigate the structure and interaction between these micelles at temperature approaching the cloud point curve at approximate 57°C along isoconcentration lines. An extensive light scattering intensity measurement indicates that the critical concentration is about 5wt%. We use a previously developed cap-and-gown model for calculating the micellar structure factor and a sticky hard sphere model for the intermicellar structure factor. SANS intensity distribution is fitted with four parameters: the aggregation number of micelle N, the hydrophobic core radius a, the overall hard sphere volume fraction ϕ, and the stickiness between micelles 1/τ. The model is found to describe all SANS data satisfactorily in absolute scale. As one approaches the cloud point curve at constant weight fraction, the aggregation number increases, the micellar core becomes dryer, and the stickiness parameter increases. In particular, at weight fraction of 5%, the stickiness parameter approaches the critical value 10.2 at T=330.9 K. We thus conclude that there is a critical demixing point in this micellar solution where micelles interact strongly with each other by a short range temperature dependent attraction.
The estimation of triplet invariants from multi-wavelength data
Authors: Klop E. A. , Krabbendam H. , Kroon J.
Published: July 2002

A two-step procedure is presented for the estimation of triplet invariants from multi-wavelength data. In the first step wavelength-independent structure-factor magnitudes of both the total structure and the light-atom substructure, together with associated structure-factor phase differences, are calculated explicitlyviaa modified Singh & Ramaseshan [Acta Cryst. (1968), B24, 35-40] procedure. In the second step these quantities are employed as conditional information in the probability distribution of a triplet invariant which can be derived from Hauptman's [Acta Cryst.(1982), A38, 289-294] joint probability distribution for an isomorphous pair of structures. Test calculations on the structure of the iron-containing protein ferredoxin show the feasibility of the procedure.
Structure of the alloy Ti50Ni48.7Co1.3
Authors: Lekston Z. , Naish V. E. , Novoselova T. V. , Sagaradze I. V.
Published: July 2002

The structure of the R phase of the alloy Ti50Ni48.7Co1.3 was determined by the crystallogeometric analysis of martensitic transformations in titanium nickelide. This analysis is based on the concept of cooperative thermal vibrations of the (110)-like planes in the b.c.c. and B2 structures and their freezing (transformation to static displacements) at the point of the phase transition. The space group of the R phase is trigonal P31m with a hexagonal Bravais lattice. The validity of the R-phase structure determination is confirmed by an X-ray diffraction pattern that was obtained at room temperature using Cu Kα radiation. The Rietveld procedure was used to compare the calculated and experimental X-ray diffraction patterns. The proposed structural model of the R phase agrees satisfactorily with the experimental data.
Investigation of the structure and phase transitions in the novel A-site substituted distorted perovskite compound Na0.5Bi0.5TiO3
Authors: Jones G. O. , Thomas P. A.
Published: July 2002

Rietveld neutron powder profile analysis of the compound Na0.5Bi0.5TiO3 (NBT) is reported over the temperature range 5–873 K. The sequence of phase transitions from the high-temperature prototypic cubic structure (above 813 K), to one of tetragonal (673–773 K) and then rhombohedral structures (5–528 K) has been established. Coexisting tetragonal/cubic (773–813 K) and rhombohedral/tetragonal (with an upper temperature limit of 145 K between 528 and 673 K) phases have also been observed. Refinements have revealed that the rhombohedral phase, space group R3c, with a
H = 5.4887 (2), c
H = 13.5048 (8) Å, V = 352.33 (3) Å3, Z = 6 and D

x
= 5.99 Mg m−3, exhibits an antiphase, a
−
a
−
a
− oxygen tilt system, ω = 8.24 (4)°, with parallel cation displacements at room temperature. The tetragonal phase, space group P4bm, with a

T
= 5.5179 (2), c

T
= 3.9073 (2) Å, V = 118.96 (1) Å3, Z = 2 and D

x
= 5.91 Mg m−3, possesses an unusual combination of in-phase, a
0
a
0
c
+ oxygen octahedra tilts, ω = 3.06 (2)°, and antiparallel cation displacements along the polar axis. General trends of cation displacements and the various deviations of the octahedral network from the prototypic cubic perovskite structure have been established and their systematic behaviour with temperature is reported. An investigation of phase transition behaviour using second harmonic generation (SHG) to establish the centrosymmetric or non-centrosymmetric nature of the various phases is also reported.
Hydrogen-Bonded Urea–Anion Host Lattices. 6. New Inclusion Compounds of Urea with Tetra-n-propylammonium Halides
Authors: Li Q. , Mak T. C. W.
Published: July 2002

New inclusion complexes tetra-n-propylammonium fluoride–urea–water (2/7/3), 2(n-C3H7)4N+F−.7(NH2)2CO.3H2O (1), tetra-n-propylammonium chloride–urea (1/2), (n-C3H7)4N+Cl−.2(NH2)2CO (2), tetra-n-propylammonium chloride–urea (1/3), (n-C3H7)4N+Cl−.3(NH2)2CO (3), tetra-n-propylammonium bromide–urea–water (1/3/1), (n-C3H7)4N+Br−.3(NH2)2CO.H2O (4), and tetra-n-propylammonium iodide–urea–water (1/3/1), (n-C3H7)4N+I−.3(NH2)2CO.H2O (5), have been prepared and characterized by X-ray crystallography. Crystal data, Mo Kα radiation: (1), space group P21/c, Z = 4, a = 8.560 (2), b = 16.301 (3), c = 37.004 (7) Å, β = 92.31 (3)°, R

F
= 0.075 for 3945 observed data; (2), space group P21/n, Z = 4, a = 9.839 (2), b = 15.160 (3), c = 14.583 (3) Å, β = 108.82 (3)°, R

F
= 0.058 for 1770 observed data; (3), space group P21/c, Z = 4, a = 9.866 (2), b = 16.274 (3), c = 15.277 (3) Å, β = 103.36 (3)°, R

F
= 0.060 for 2272 observed data; (4), space group P1¯, Z = 2, a = 8.857 (2), b = 10.639 (2), c = 15.115 (3) Å, α = 88.01 (3), β = 75.02 (3), γ = 66.72 (3)°, R

F
= 0.064 for 2694 observed data; (5), space group P1¯, Z = 2, a = 9.045 (2), b = 10.781 (2), c = 15.169 (3) Å, α = 87.98 (3), β = 76.00 (3), γ = 65.73 (3)°, R

F
= 0.052 for 4973 observed data. In the crystal structure of (1) an alternate crisscross arrangement of urea ribbons, which are cross-bridged by other urea molecules, water molecules and fluoride ions, generates a three-dimensional host lattice containing an open-channel system running parallel to the b axis, with the (n-C3H7)4N+ cations accommodated in a zigzag column within each channel. In the crystal structure of (2) the cations are sandwiched between puckered layers resulting from parallel urea ribbons that are cross-bridged by chloride anions. In (3) the (n-C3H7)4N+ cations are accommodated in a channel-type host lattice built of planar arrays of twisted ribbons constructed from three independent urea molecules, which are cross-linked by bridging chloride ions. Complexes (4) and (5) are isomorphous with the same channel host framework built of parallel corrugated urea layers that are interlinked by cyclic (H2O.X
−)2 tetramers.
Conformation-Related Reaction Efficiency of Glutarimides with Phenyllithium. Structures of 3,3,5,5-Tetramethylglutarimide and 2-Hydroxy-2-phenyl-3,3,5,5-tetramethyl-6-piperidone. X-ray and Theoretical Study
Authors: Maurin J. K. , Czarnocki Z. , Paluchowska B. , Winnicka-Maurin M.
Published: July 2002

Crystal structures of 3,3,5,5-tetramethylglutarimide [3,3,5,5-tetramethylazacyclohexane-2,6-dione] (8) and the product of its reaction with phenyllithium, 2-hydroxy-2-phenyl-3,3,5,5-tetramethyl-6-piperidone (9), have been determined by X-ray structural methods [(8), monoclinic, P21/c, a = 7.715 (2), b = 11.136 (2), c = 11.707 (2) Å, \beta = 105.63 (3)°; (9), triclinic, P\overline 1, a = 6.1685 (6), b = 11.1475 (10), c = 11.526 (2) Å, \alpha = 117.100 (10), \beta = 103.390(10), \gamma = 91.288 (7)°]. Molecular structures of three different glutarimides are discussed. Their energy optimal structures were determined with the use of ab initio calculations. The results of crystallographic and theoretical studies show that the conformational changes in glutarimide introduced by substitution with methyl groups resulted in electron-charge distribution changes. These differences in charge distribution are the reason for the observed variation in yields of the reaction of glutarimides with phenyllithium.
Distribution of the M-M Distances in the Oxides of the Group 13 Elements and their Spinels and Delafossites
Authors: Isea R. , Vegas A. , Ramos-Gallardo A.
Published: July 2002

An analysis of the distribution of the M—M distances (M = Al, Ga, In, Tl) in all their binary, ternary and quaternary oxides, contained in the Inorganic Crystal Structure Database (ICSD95), shows that the M—M distances are not distributed uniformly, but present maxima at values which are near the corresponding distances in pure metals. As for boron, this feature reflects the tendency of these elements to form aggregates in their compounds. These metal aggregates maintain distances and, in many instances, also the topology of the elemental structures, as is illustrated here with two families of structures, i.e. spinels and delafossites. In spinels, the group 13 cations form a 3D (three-dimensional) network of truncated tetrahedra, which are also found in the Zintl phases of these elements. In MgAl2O4 the Al subnet is identical, in topology and dimensions, to that of CaAl2 and both reproduce exactly half of the f.c.c. (face-centred cubic) net of Al metal.
Solid-State Modeling. VI. 2,3-Diketopiperazine: the Integration of Crystallographic and Spectroscopic Evidence
Authors: Lenstra A. T. H. , Bracke B. , van Dijk B. , Maes S. , Van Alsenoy C. , Desseyn H. O. , Perlepes S. P.
Published: July 2002

2,3-Diketopiperazine (2,3-piperazinedione) crystallizes in the monoclinic space group P21/c with a = 5.941 (3), b = 10.080 (3), c = 8.282 (2) Å and β = 95.87 (3)°. The six-membered ring adopts a skew-boat conformation with Q = 0.467 (3) Å, θ = 64.6 (3)° and φ = 269.8 (4)°. Ab initio calculations show that the perfect skew-boat with its C
2 symmetry is broken by the formation of two intermolecular N—H...O bonds, involving only one of the C=O groups of the 2,3-diketopiperazine molecule. Vibrational spectra were recorded in solution and in the solid state. The assignment of the normal vibrations is proposed based on comparison with spectra of similar molecules and spectral changes due to deuteration. Ab initio calculations for the isolated molecule and the solid-state structure were used to calculate differences in the molecular geometry in the gas phase and crystalline state. Using these reference structures we calculated the stretching frequencies for the C=O groups. We predict an IR shift for C=O of 130 cm−1, when the molecule goes from the gas phase to the solid state. The observed shift is 110 cm−1. The differences between the C=O moieties in the solid state produce a calculated Δν of 55 cm−1, which matches satisfactorily the observed value of 49 cm−1.
An Unusual Hydrogen-Bonded Network Associated with Metal-Organic Chains: Structure and Crystal Packing of the Coordination Polymer [Cd(terephthalate)(H2O)3].4H2O
Authors: Michaelides O. A. , Tsaousis D. , Skoulika S. , Raptopoulou C. P. , Terzis A.
Published: July 2002

Single crystals of [Cd(terephthalate)(H2O)3].4H2O (1), triaquo(1,4-benzenecarboxylato-κO)cadmium tetrahydrate, are grown in a silica gel column. Crystal structure analysis shows that (1) is a polymer with metal-organic chains stacked along the a axis forming layers parallel to the ab plane. These layers are linked by an unusual hydrogen-bonded network formed by the water molecules (both `free' and coordinated ones) and the carboxylate O atoms. This network comprises tridymite-like O8 cages which `propagate' in the direction of the a axis, mimicking the way they `propagate' along the c axis in hexagonal ice.
More Space-Group Corrections: From Triclinic to Centred Monoclinic and to Rhombohedral; Also From P1 to P-1 and From Cc to C2/c
Authors: Herbstein F. H. , Marsh R. E.
Published: July 2002

We present 14 examples of crystal structures that were originally described as triclinic, but are properly described as either C-centred monoclinic (ten examples) or rhombohedral (four examples). There is also one example each of changes from P1 to P1¯ and from Cc to C2/c.
Structure of uranium(VI) oxide dihydrate, UO3·2H2O; synthetic meta-schoepite (UO2)4O(OH)6·5H2O
Authors: Weller Mark. T. , Light Mark E. , Gelbrich Thomas
Published: July 2002

The structure of uranium oxide dihydrate, also known as meta-schoepite (UO2)4O(OH)6·5H2O, has been determined from a synthetic single crystal. The structure, at 150 K, space group Pbcn, lattice constants a = 14.6861 (4), b = 13.9799 (3) and c = 16.7063 (5) Å, consists of layers of stoichiometry (UO2)4O(OH)6, formed from edge-sharing UO7 pentagonal bipyramids, interleaved with hydrogen-bonded water molecules. Three of the layer hydroxyl groups are linked through hydrogen bonding to single water molecules and the three remaining OH units form interactions with water molecules that each act as acceptors in two hydrogen bonds. One of the water molecules in the inter-layer region is disordered over two symmetry-related sites and forms hydrogen-bonded interactions only within the layer and with the uranyl O atoms. The relationship of the structure of meta-schoepite to that of schoepite is discussed in detail.
Phasing from an envelope
Authors: Hao Quan
Published: July 2002

Solution of the phase problem is central to crystallographic structure determination. Conventional molecular-replacement methods are ineffective in the absence of knowledge of the structure of a homologous protein. A recent method utilizing the low-resolution molecular shape determined from solution X-ray scattering data has been shown to be successful in locating the molecular shape within the crystallographic unit cell for the cases of the trimeric nitrite reductase (AxNiR, 105 kDa) and the dimeric superoxide dismutase (SOD, 32 kDa). This was achieved by performing a direct real-space search for orientation and translation using the orientation of the non-crystallographic axis obtained by performing a self-rotation on the crystallographic data. This effectively reduces the potential six-dimensional search to a four-dimensional one (Eulerian angle γ and three translational parameters). The program FSEARCH incorporating this method has been generalized to handle molecules from all space groups. The program can also be used in general six-dimensional cases for a molecular-replacement solution given a predetermined envelope from any source, such as electron-microscopic images or solution scattering, provided that the envelope can be converted to the standard CCP4 map format or expressed in terms of spherical harmonics. It is hoped that this method will greatly facilitate the ab initio structure determination of proteins and provide a good foundation for further structure refinement.
Implementation of molecular replacement in AMoRe
Authors: Navaza Jorge
Published: July 2002

An account is given of the molecular replacement method as implemented in the package AMoRe. The overall strategy of the method is presented and the main functions used in the package are described. The most important features of AMoRe are the quality of the fast rotation and translation functions and the facility of multiple inputs to translation and rigid-body refinement functions, which allow for a fast multiple exploration of crystal configurations with a high level of automation.
Patterson correlation methods: a review of molecular replacement with CNS
Authors: Grosse-Kunstleve R. W. , Adams P. D.
Published: July 2002

This paper presents a review of the principles of molecular replacement with the audience of the CCP4 Study Weekend in mind. A complementary presentation with animated Patterson maps is available online (http://cci.lbl.gov/~rwgk/ccp4sw2001/). The implementation of molecular-replacement methods in the Crystallography and NMR System (CNS) is presented and discussed in some detail. The three principal components are the direct rotation function, Patterson correlation refinement and the fast translation function. CNS is available online and is free of charge for academic users.
Crystallization and preliminary diffraction studies of the extracellular region of human p58 killer cell inhibitory receptor (KIR2)
Authors: Maenaka Katsumi , Juji Takeo , Tadokoro Kenji , Harlos Karl , Stuart David I. , Jones E. Yvonne
Published: July 2002

Molecules of the human killer cell inhibitory receptor (KIR) family, which belong to the immunoglobulin superfamily (IgSF), are expressed on the surface of natural killer (NK) cells and some subsets of T cells. These receptors function to mediate the inhibition or activation of cytotoxic activity by recognizing HLA class I molecules on the target cell. The extracellular region of a p58 KIR specific for HLA-Cw1,3,7 (KIR2) has been overproduced in Escherichia coli and purified. The recombinant KIR2 has been crystallized in 9–10% poly(ethylene glycol) methyl ether (average Mr
= 8000), 50mM HEPES, 8% ethylene glycol, 0.5% octyl-β-glucoside, pH 7.5, at 294 K using the sitting-drop vapour-diffusion method. Preliminary X-ray diffraction studies reveal the space group to be hexagonal (P6122 or P6522) with lattice constants a = b = 95.3, c = 130.8 Å. A native data set (3 Å resolution) has been collected at the Photon Factory (λ = 1.0 Å).
Crystallization and preliminary X-ray diffraction analysis of cytochrome P450sca-2 from Streptomyces carbophilus involved in production of pravastatin sodium, a tissue-selective inhibitor of HMG-CoA reductase
Authors: Ito Shuichiro , Matsuoka Tatsuji , Watanabe Ichiro , Kagasaki Takeshi , Serizawa Nobufusa , Hata Tadashi
Published: July 2002

Cytochrome P450sca-2 from Streptomyces carbophilus catalyzes the hydroxylation of ML-236B sodium salt to pravastatin sodium, a tissue-selective inhibitor of 3-hydroxy-3-methylglutaryl-coenzymeA (HMG-CoA) reductase. HMG-CoA reductase is a key enzyme in cholesterol biosynthesis. Crystals of the protein were obtained by the vapour-diffusion method, using ammonium sulfate as a precipitant. The crystals belong to the trigonal space group P3121 (or its enantiomorph, P3221) with unit-cell dimensions a = 103.5, c = 79.8 Å. Assuming the presence of one molecule in the asymmetric unit, the calculated value of Vm
is 2.68 Å3 Da−1. A native data set was collected to a resolution of 2.2 Å.
Crystallization and preliminary X-ray diffraction study of the endo-polygalacturonase from Fusarium moniliforme
Authors: Federici Luca , Mattei Benedetta , Caprari Claudio , Savino Carmelinda , Cervone Felice , Tsernoglou Demetrius
Published: July 2002

Endo-polygalacturonases catalyze the fragmentation and solubilization of the homogalacturonan of the plant cell wall. These enzymes are extracellularly targeted glycoproteins produced by a number of organisms such as fungi, bacteria and plants, and are involved in both pathological and physiological processes. Single crystals of the endo-polygalacturonase from the phytopathogenic fungus Fusarium moniliforme were obtained by the vapour-diffusion method at 294 K. The starting material as well as the crystal consist of three forms with different degrees of glycosylation. The crystals belong to the orthorhombic space group P212121 and diffract to 1.9 Å resolution on a synchrotron-radiation source under cryocooling conditions.
Crystallization and preliminary X-ray diffraction analysis of restriction endonuclease EcoRII
Authors: Karpova Elisavetta A. , Meehan Edward , Pusey Marc L. , Chen Liqing
Published: July 2002

Crystals of the restriction endonuclease EcoRII have been obtained by the vapor-diffusion technique in the presence of ammonium sulfate or polyethylene glycol. The best crystals were grown with ammonium sulfate as a precipitant. Crystals with dimensions of up to 0.6 × 0.6 × 0.6 mm have been observed. The crystals diffract to about 4.0 Å resolution at a cryo-temperature of 100 K using a rotating-anode X-ray source and a Rigaku R-AXIS IV imaging-plate detector. The space group has been determined to be either I23 or I213, with unit-cell parameters a = b = c = 160.3 Å, α = β = γ = 90°. The crystal asymmetric unit contains two protein molecules, and self-rotation function analysis shows a pseudo-twofold symmetry relating the two monomers. Attempts to improve the resolution of crystal diffraction and to search for heavy-atom derivatives are under way.
Crystallization and preliminary X-ray diffraction studies of undecaprenyl diphosphate synthase from Micrococcus luteus B-P 26
Authors: Fujihashi Masahiro , Shimizu Naoto , Zhang Yuan-Wei , Koyama Tanetoshi , Miki Kunio
Published: July 2002

Undecaprenyl diphosphate synthase from Micrococcus luteus B-P 26, one of the Z-prenyl chain-elongating enzymes, was crystallized using the sitting-drop vapour-diffusion method with ammonium sulfate and lithium sulfate as precipitants. The crystals belong to the monoclinic space group C2, with unit-cell parameters a = 127.2, b = 60.2, c = 75.7 Å, β = 105.6°. The crystals diffract X-rays to at least 2.2 Å resolution using synchrotron radiation and are suitable for high-resolution crystal structure analysis.
Calculation of rare-earth 4d giant-absorption spectra with multiplet effects and decay processes
Authors: Ogasawara Haruhiko , Kotani Akio
Published: July 2002

The total and partial photoelectron yield spectra of all the trivalent rare-earth ions in the 4d giant resonance region are calculated with full multiplet effects. The decay processes are treated as coherent processes following photoexcitation. The results reproduce the over all features of experiments. It is obtained that the character of the giant-absorption is different between the light and heavy rare-earths. The multiplet effects play an essential role in the decay processes.
Studies of the magnetic structure at the ferromagnet–antiferromagnet interface
Authors: Scholl A. , Nolting F. , Stöhr J. , Lüning J. , Seo J. W. , Locquet J.-P. , Fompeyrine J. , Anders S. , Ohldag H. , Padmore H. A.
Published: July 2002

Antiferromagnetic layers are a scientifically challenging component in magnetoelectronic devices, such as magnetic sensors in hard-disk heads, or magnetic random-access memory (RAM) elements. In this paper, it is shown that photoelectron emission microscopy (PEEM) is capable of determining the magnetic structure at the interface of ferromagnets and antiferromagnets with high spatial resolution (down to 20 nm). Dichroism effects at the L edges of the magnetic 3d transition metals, using circularly or linearly polarized soft X-rays from a synchrotron source, give rise to a magnetic image contrast. Images, acquired with the PEEM2 experiment at the Advanced Light Source, show magnetic contrast for antiferromagnetic LaFeO3, microscopically resolving the magnetic domain structure in an antiferromagnetically ordered thin film for the first time. Magnetic coupling between LaFeO3 and an adjacent Co layer results in a complete correlation of their magnetic domain structures. From field-dependent measurements, a unidirectional anisotropy resulting in a local exchange bias of up to 30 Oe in single domains could be deduced. The elemental specificity and the quantitative magnetic sensitivity render PEEM a perfect tool to study magnetic coupling effects in multilayered thin-film samples.
Hartree–Fock study of orbital magnetic moments in 3d and 5f magnets and X-ray magnetic circular dichroism
Authors: Jo T.
Published: July 2002

The spin (M

s
) and orbital magnetic moments (M

o
) of the uranium 5f state in the ferromagnetic compound uranium sulfide (US) and of the cobalt 3d state in various transition-metal superlattices are calculated on the basis of a tight-binding model, in which the intra-atomic f–f or d–d multipole interaction is taken into account using the Hartree–Fock (HF) approximation. The parameters in the model are determined on the basis of available first-principles calculations. For US, the calculated ratio M

o
/M

s
and magnetic circular dichroism spectrum for U M
4,5 absorption are in good agreement with the experimental results. Inclusion of the expectation values of the spin-off-diagonal operators in addition to the number operators in the 5f state is found to be crucially important when describing the 5f magnetic state. A difference in enhancement of M

o
of the Co atom between the Co/Pd and Co/Cu superlattices is discussed on the basis of a semi-quantitative calculation, assuming ferromagnetism.
Surface EXAFS study of metastable magnetic thin films
Authors: Chandesris D. , Le Fèvre P. , Magnan H. , Jaffrès H.
Published: July 2002

Epitaxial thin films provide new opportunities to explore the relationship between structure and magnetism. The bidimensionnal character of magnetic films deposited on single-crystal substrates and the occurrence of singular crystallographic structures often confer on these systems electronic and magnetic properties that cannot be found in the bulk solids. Although shape anisotropy would favour an in-plane easy axis of magnetization for thin films, Ni layers deposited on Cu(001) present a perpendicular magnetic anisotropy in a very wide thickness range. It is shown that this can be explained by a distorted structure of Ni, originating from the strain induced by the epitaxy on the Cu substrate. In the field of low-dimensional magnetism, nanostructures with a reduced lateral dimension are now being widely investigated in view of their technological applications. Thin Fe layers on MgO(001) can be cut into strips by the `atomic saw' method: a compression of the substrate induces a dislocation slipping which `saws' both the substrate and the Fe film into regular and separated ribbons. The observed magnetic anisotropy, with the easy axis perpendicular to the strips, is explained by a structural relaxation occurring during the structuration process. In these two studies, a precise structural characterization and simple magnetoelastic models allow the magnetic behaviour of the systems to be described. The structure of the films can be described as an elastic deformation of the bulk structure.
Structural properties of Y1–x
Yb
x
Ni2B2C synthesized at high pressure: EXAFS data analysis
Authors: Menushenkov A. P. , Konarev P. V. , Tsvyashchenko A. V. , Meyer-Klaucke W. , Cortes R.
Published: July 2002

Local structure of Y1–x
Yb
x
Ni2B2C series synthesized at high pressure 8 GPa has been studied using EXAFS. Measurements were performed at the Ni K-edge in temperature range 5-300 K. The results show that the Debye-Waller factor for Ni-Ni bond in the parent YNi2B2C compound is characterized by the Einstein temperature Θ
E
= 350 K, while a minimum value of Θ
E
= 300 K is reached for the compound with x = 0.025, which has the highest critical temperature T

c
= 12.5 K of the superconductive transition. This correlates with the further suppressing of superconductivity and with the appearance of the local magnetic moments in the investigated Y1–x
Yb
x
Ni2B2C series for x ≥ 0.05 compounds. Observed changes in the local electronic and the local crystal structure of this system as a function of Yb concentration and of temperaturre were explained in the frame of the band filling effect.
Polarized Cu K edge XANES spectra of CuO – theory and experiment
Authors: Sipr Ondrej , Simunek Antonin , Bocharov Sergey , Kirchner Thomas , Dräger Günther
Published: July 2002

Polarized Cu K edge X-ray absorption near-edge structure (XANES) spectra of CuO are analyzed. Partial spectral components reflecting both dipole and quadrupole transitions are resolved from the experiment. Theoretical spectra were obtained using the real-space multiple-scattering technique and by calculating the band structure via the pseudopotential method. We demonstrate that the pre-peak is of a quadrupole character and find its decomposition into individual d components. The self consistent pseudopotential calculation, free from any constraints on the form of the potential, improves the agreement between theory and experiment in those areas where real-space calculation, based on non-self-consistent muffin-tin potential, fails. Therefore we argue that the most significant contributions to the Cu K edge XANES come from one-electron processes.
Deglitching procedure for XAFS
Authors: Zhuchkov Konstantin N. , Shuvaeva Victoria A. , Yagi Kenichiro , Terauchi Hikaru
Published: July 2002

A computer program for eliminating artifacts such as glitches and Bragg peaks of the polarized XAFS spectra is presented. It permits to easily locate and to eliminate from the EXAFS spectra the additional signals originated from the Bragg scattering by crystalline samples. The test of the procedure on the spectra with specially introduced artifacts and on the experimental polarized XAFS spectra showed its high effectiveness.
Anomalous Wide-Angle X-ray Scattering Apparatus on the GILDA Beamline at the ESRF
Authors: Meneghini C. , Balerna A. , Boscherini F. , Pascarelli S. , Mobilio S.
Published: July 2002

The experimental apparatus for anomalous wide-angle X-ray scattering (AWAXS) on the GILDA beamline at the ESRF is described. The main features are the high beam stability and reproducibility which allow anomalous scattering effects to be resolved also on dilute elements, the large spectral range which allows AWAXS experiments at the K edges of heavy elements, and the use of a high-efficiency detection system. The apparatus has been tested in extreme conditions by performing AWAXS experiments at the Eu K edge in Eu-doped Sr metaphosphate glasses.
Electrochemical behaviour of AISI‐316 stainless steels in sulphuric/nitric acid mixtures
Authors: Singh Inder , Bhattamishra A.K. , Basu D.K.
Published: July 2002

Stainless steels are very unique in that they offer a wide range and combination of resistance to corrosion, resistance to oxidation at high temperature and good mechanical properties at room temperature. With rapid industrialization all over the world, these very properties have led to extensive use of stainless steels in different industries. Austenitic stainless steels containing molybdenum exhibit corrosion resistance in both sulphuric acid and nitric acid. Stainless steel undergoes severe attack in sulphuric acid having concentrations in the range of 20‐85 per cent, whereas they are immune to nitric acid in any concentration. However, sensitized stainless steels are prone to intergranular attack in acids, even in nitric acid. Further, the attack is aggravated in the presence of aggressive ions. Study of the behaviour of stainless steels in a mixture of acids (nitric and sulphuric acid) is lacking in the literature. This paper, therefore, discusses the performance of AISI‐316 and 316‐L in sulphuric acid and nitric acid and a mixture thereof at room temperature. It is observed that the steels are quite resistant to sulphuric acid and nitric acid, but in the acid mixture they are not so resistant, especially in AISI‐316 SS in respect of corrosion resistance, even in acid mixture containing C1‐ and Cu++ ions.
Protective ebonite coatings on the base of oligobutadienes
Authors: Pushkarev Yury N. , Figovsky Oleg L.
Published: July 2002

Explores the possibility of preparing elastic and hard ebonite coatings, utilizing the properties of oligobutadienes without ending functional groups. Examines the vulcanization processes leading to formation of rubberizing ebonite coatings on samples of oligobutadienes. Finds that the most effective bonding material for non‐solution compositions is ebonite coatings.
Supporting open and distance learners: practice and policy across further and higher education libraries
Authors: Gibson Andrew , Newton Robert , Dixon David
Published: July 2002

This paper reviews provision for open and distance learners across further and higher education libraries in the UK, focusing in particular on developments in Scotland. After offering a critical review of the literature which pays particular attention to international examples of best practice, the paper reports on the findings of a questionnaire survey conducted among all Scottish FE and HE libraries and selected English institutions and on a short programme of structured interviews conducted with HE librarians working at universities within the Glasgow area. Evidence from the review of literature, the questionnaire survey and the programme of interviews is drawn together and analysed in order to indicate the key areas which have to be addressed by libraries in institutions which are aspiring to offer open and distance learning education.
Nutrition in older people
Authors: Wynne Amanda
Published: July 2002

A new National Diet and Nutrition Survey was published in October 1998, by the Ministry of Agriculture, Fisheries and Food and the Department of Health, which reported on the dietary intake and nutritional status of people over 65 years of age in the UK. This survey provided data on 1,275 free‐living people and 412 people in residential care. Along with the information on diet and nutritional status are data on anthropometric and biochemical parameters. A second related survey looked at dental health in this age group. The key findings of these surveys and the public health implications for older people are discussed.
A competence approach to the assessment of student placements
Authors: Fowler Gillian , Tietze Susanne
Published: July 2002

Discusses sandwich placements and their importance at Sheffield Hallam University. Outlines the Business Studies degree programme and the assessment procedure of work placements, mentioning its role in final degree assessment. Lists problems of assessment, and criticisms from the employers’ points of view. Finally, provides a framework for a new programme based on both the competence approach and a survey of placement companies.
Students’ expectations from their cooperative education placements in the hospitality industry: an international perspective
Authors: Waryszak Robert Z.
Published: July 2002

Four groups of students from the following institutions participated in a study to assess the expectations from their cooperative education placements’ work environment: Victoria University of Technology, Melbourne, N = 80; Hotel School, The Hague, N = 107; Oxford Brookes University, Oxford, N = 50; University of Strathclyde, Glasgow, N = 50. In all, 287 students responded to a mail questionnaire (Work Environment Scale, Moos, 1994) before their cooperative education placements. Overall, all four samples including the Melbourne students had moderate to high expectations from their organisations’ work environment. Specifically, Melbourne students expected higher involvement, greater peer cohesion, more task orientation, more work pressure and greater control when compared with the The Hague students. They also expected less autonomy on the job as compared with the Strathclyde students. The Hague students had overall lower expectations on most of the social climate dimensions. It is suggested however that the above findings be verified by replication with a greater variety of populations and institutions.
Current models and innovative strategies in management education in China
Authors: Wang Zhong‐Ming
Published: July 2002

With the rapid development of economic reform and organizational change, management education and development has become an increasingly important topic among Chinese universities, governmental departments as well as industrial organizations. The transformation of the Chinese state‐owned management systems into a market‐oriented shareholding system, the nationwide organizational reform and downsizing movement among state enterprises, the development of international joint ventures and wholly‐owned companies, and the increasingly urgent needs for professional training call for innovative approaches to management education in China. This article presents some current models of management education and innovative strategies for facilitating training and development in Chinese enterprises.
Key ingredients for the effective implementation of statistical process control
Authors: Antony Jiju , Balbontin Alejandro , Taner Tolga
Published: July 2002

Continuous improvement of product, process and service quality is important for today’s organisations to remain competitive in global marketplaces. Statistical process control (SPC) is an important and powerful technique for the continuous improvement of product and process quality. The control chart is the familiar tool used within SPC for determining out‐of‐control situations and thereby eliminating or reducing variation in processes. However, a control chart is by no means the only ingredient – nor necessarily the most important – for the successful application of SPC. This paper identifies and discusses these key ingredients for the successful application of SPC in both manufacturing and service organisations.