bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of Diastereomeric Mandelate Salts of Cinchonidine and the Relation to Their Quasidiastereomeric Analogues
Authors: Gjerløv A. , Larsen S.
Published: July 2002

The crystal structures have been determined for the diastereomeric salts formed by cinchonidine and the two enantiomers of mandelic acid using low-temperature [122 (1) K] X-ray diffraction data. The less soluble salt is cinchonidinium (S)-mandelate, C19H23N20O+.C8H7O3
−, M

r
= 446.53, monoclinic, C2, a = 21.400 (2), b = 6.2777 (6), c = 17.853 (2) Å3, \beta = 109.304 (8)°, V = 2263.6 (4) Å3, Z = 4, D

x
= 1.310 g cm−3, \lambda(Cu K\alpha = 1.54184 Å, Z = 7.08 cm−1, F(000) = 952, R
1 = 0.0259 for 2684 observed reflections. The cinchonidine salt with (R)-mandelic acid, C19H23N2O+.C8H7O3, has M

r
= 446.53, monoclinic, P21, a = 6.410 (3), b = 32.808 (11), c = 11.222 (2) Å, \beta = 100.67 (2)°, V = 2319.2 (13) Å3, Z = 4, D

x
= 1.279 g cm−3, \lambda(Cu K\alpha) = 1.54184 Å, \mu = 6.91 cm−1, F(000) = 952, R
1 = 0.0380 for 8951 observed reflections. The two salts have virtually identical hydrogen-bond patterns and similar herringbone stacking of the quinoline ring systems. The crystal packing of the two salts differ only with respect to the packing of the phenyl groups. The packing of the cinchonidinium mandelates is significantly different from the crystal packing in the corresponding mandelates of cinchonine. The lack of a quasidiastereomeric relationship between the two sets of salts can be attributed to the steric effects of the vinyl group. The similarities between the two cinchonidinium mandelate structures is a possible explanation to the similar solubilities of the salts. DSC and NMR measurements showed that the cinchonidinium salts undergo a chemical opening reaction in the solid state. The arrangement of hydrogen-bonded chains of alternating cations and anions appear to be important for the solid-state reaction to take place.
Crystal Engineering: Strategies and Architectures
Authors: Aakeröy C. B.
Published: July 2002

The area broadly described as crystal engineering is currently expanding at a brisk pace. Imaginative schemes for supramolecular synthesis, and correlations between molecular structure, crystal packing and physical properties are presented in the literature with increasing regularity. In practice, crystal engineering can be many different things; synthesis, statistical analysis of structural data, ab initio calculations etc. Consequently, we have been provided with a new playing field where chemists from traditionally unconnected parts of the spectrum have exchanged ideas, defined goals and made creative contributions to further progress not only in crystal engineering, but also in other disciplines of chemistry. Crystal engineering is delineated by the nature and structural consequences of intermolecular forces, and the way in which such interactions are utilized for controlling the assembly of molecular building blocks into infinite architectures. Although it is important to acknowledge that a crystal structure is the result of a subtle balance between a multitude of non-covalent forces, this article will focus on design strategies based upon the hydrogen bond and will present a range of approaches that have relied on the directionality and selectivity of such interactions in the synthesis of predictable one-, two- and three-dimensional motifs.
Distribution of the M-M Distances in the Rare Earth Oxides
Authors: Vegas A. , Isea R.
Published: July 2002

A systematic study of the distribution of the M—M distances in all the binary, ternary and quaternary oxides of the rare earth elements (RE = Sc, Y, La–Lu), contained in the Inorganic Crystal Structure Database (ICSD) has been carried out. The results indicate that the RE—RE distances are not distributed uniformly, but present maxima which are close to the corresponding distances in the pure metals. In some of the histograms (Y, Ce, Pr, Sm, Tb, Dy, Ho, Lu) two maxima appear which correspond to the nearest-neighbor (b.c.c., h.c.p.) and second-nearest neighbor (b.c.c.) distances of the elemental phases. As examples of this behavior, the cation arrays of the binary oxides, hydroxides and ternary oxides of both the delafossite and \alpha-NaFeO2 type are analyzed. In all of them the cations form aggregates whose topologies and distances can be related to the structure of the parent metals. The size of the metal aggregates seems to decrease with increasing oxygen content.
Electron density study of urea using TDS-corrected X-ray diffraction data: quantitative comparison of experimental and theoretical results
Authors: Zavodnik Valery , Stash Adam , Tsirelson Vladimir , de Vries Roelof , Feil Dirk
Published: July 2002

The electron-density distribution in urea, CO(NH2)2, was studied by high-precision single-crystal X-ray diffraction analysis at 148 (1) K. An experimental correction for TDS was applied to the X-ray intensities. R
merge(F
2) = 0.015. The displacement parameters agree quite well with results from neutron diffraction. The deformation density was obtained by refinement of 145 unique low-order reflections with the Hansen & Coppens [Acta Cryst. (1978), A34, 909–921] multipole model, resulting in R = 0.008, wR = 0.011 and S = 1.09. Orbital calculations were carried out applying different potentials to account for correlation and exchange: Hartree–Fock (HF), density-functional theory/local density approximation (DFT/LDA) and density-functional theory/generalized gradient approximation (DFT/GGA). Extensive comparisons of the deformation densities and structure factors were made between the results of the various calculations and the outcome of the refinement. The agreement between the experimental and theoretical results is excellent, judged by the deformation density and the structure factors [wR(HF) = 0.023, wR(DFT) = 0.019] and fair with respect to the results of a topological analysis. Density-functional calculations seem to yield slightly better results than Hartree–Fock calculations.
High-temperature phases of NaNbO3 and NaTaO3
Authors: Darlington C. N. W. , Knight K. S.
Published: July 2002

The high-temperature phases of the perovskites sodium niobate, NaNbO3, and sodium tantalate, NaTaO3, have been re-examined using the high-resolution powder diffractometer HRPD at the ISIS neutron spallation source; the two materials show the same sequence of phases with tilted octahedra. Diffraction patterns were measured every 5 K allowing structural changes with temperature within a single phase to be determined for the first time. Previous structure determinations within one phase had been performed at a single temperature only. The octahedra are tilted about pseudocubic \langle100\rangle directions and are also deformed; the magnitude of the deformation is shown to be proportional to the square of the angle of tilt as expected from a phenomenological theory applied to such transitions. The structures of NaNbO3 between 753 and 793 K and of NaTaO3 below 758 K are not as reported in the literature.
Single-crystal neutron diffraction study of β-Cs3(HSO4)2[H2−x
(S
x
P1−x
)O4] (x ≃ 0.5) at 15 K
Authors: Haile S. M. , Klooster W. T.
Published: July 2002

The structure of β-Cs3(HSO4)2[H2−x
(S
x
P1−x
)O4] has been examined by single-crystal neutron diffraction at 15 K. The compound crystallizes in space group C2/c and contains four formula units in the unit cell, with lattice parameters a = 19.769 (9), b = 7.685 (2), c = 8.858 (3) Å and β = 100.60 (4)°. Refinement of P, S and H site occupancies indicated that the value of x (in the stoichiometry) is 0.500 (6). This, together with the unit-cell volume of 1322.8 (14) Å3, implies a density of 3.463 Mg m−3. The structure contains zigzag rows of XO4 anions, where X = P or S, that alternate, in a checkerboard fashion, with zigzag rows of Cs cations. Moreover, there is one proton site, H(3), with an occupancy of 0.25 and one X-atom site, X(1), that is occupied by 0.5 P and 0.5 S. These features are in general agreement with a previous X-ray structure determination carried out at 298 K. In contrast to the X-ray study, however, it was found that two different structural models adequately fit the diffraction data. In the first model, the proton vacancies and the P atoms were assumed to be randomly distributed over the H(3) and X(1) sites, respectively, and to have no impact on the local structure. In the second model, several atoms were assigned split occupancies over two neighboring sites, to reflect the presence or absence of a proton vacancy, and the presence of P or S on the X(1) site. Refinement assuming the first model, in which anisotropic displacement parameters for 12 of 14 atom sites in the asymmetric unit were employed, yielded residuals w
R(F
2) = 0.084 and w
R(F) = 0.038. For the second model, in which anisotropic displacement parameters were utilized for only the five atoms that were not split relative to the first model, the residuals were w
R(F
2) = 0.081 and w
R(F) = 0.036.
A mediated hydrogen bond in an α-hydroxycarboxyl group: X-ray structure of (R,R)-N-methyltartramic acid monohydrate and an ab initio study of model systems
Authors: Rychlewska Urszula , Szarecka Agnieszka , Rychlewski Jacek , Motała Rafał
Published: July 2002

The crystal structure of (R,R)-N-methyltartramic acid monohydrate is presented and compared with that of the parent compound, (R,R)-tartaric acid. Despite some conformational differences between the two molecules the packing is very similar, as it is dictated by the carboxyl rather than the amide function. Particular attention is paid to a mediated three-centre hydrogen bond as one of the packing motifs involving the α-hydroxycarboxyl moiety. The stability and geometry of such structures in the gas phase and in solution are examined via theoretical ab
initio methods using the RHF/6-311++G** and RHF/6-311++G**/Onsager models, respectively. Liquid media, in particular those of high polarity, are found to stabilize the structures considerably.
What is the best crystal size for collection of X-ray data? Refinement of the structure of glycyl-L-serine based on data from a very large crystal
Authors: Görbitz Carl Henrik
Published: July 2002

The dipeptide Gly-L-Ser was crystallized as part of a study on hydrogen-bonding patterns in the structures of dipeptides. Hydrogen-bond donors and acceptors have been assigned ranks (1 is best, 2 is next best etc.), and the observed hydrogen-bond connectivity is compared with the hypothetical pattern in which the rank n donor associates with the rank n acceptor (n = 1, 2, . . .), and with the pattern observed in the retroanalogue L-Ser-Gly, which contains the same functional groups. Crystallization of the title compound produced very bulky crystals. Rather than reducing the size of one of these before data collection, three data sets with different exposure times were collected with a Siemens SMART CCD diffractometer on a very large specimen (2.2 × 2.0 × 0.8 mm). The crystal was subsequently shaped into a 0.30 mm-diameter sphere for collection of two additional data sets. The discussion of the refinement results focus on the effect of absorption correction for the various data sets, and a comparison of geometrical and thermal parameters. One advantage of using a large crystal, the great speed with which data can be obtained, has been exemplified by collection of a complete data set of good quality in less than 25 min.
Neutron powder diffraction study of orthorhombic and monoclinic defective silicalite
Authors: Artioli G. , Lamberti C. , Marra G. L.
Published: July 2002

The crystal structure of silicalite (SiO2) with a substantial amount of structural hydroxyl groups [Si(1−x)O(2−4x)(OH)4x
, with 0.08 < x < 0.10] has been refined from neutron powder diffraction data measured using the HRPD instrument at the ISIS pulsed neutron source. Powder data were collected on the as-synthesized orthorhombic sample at 298 K, and on the deuterated monoclinic sample at 100 K. Preferential location of Si-atom vacancies was found on four out of 12 independent T sites in the orthorhombic silicalite [Si(6), Si(7), Si(10) and Si(11)], although the H atoms of the substituting hydroxyl groups could not be located because of the low statistical site occupancy on multiple sites. No significant population of D atoms or of Si vacancies was found in the tetrahedral sites of the monoclinic sample. The detected long-range order of adjacent Si atoms in defective orthorhombic [MFI] structures is compatible with a mechanism of Si vacancy clustering and with the model of hydroxyl nests assumed in the literature on the basis of IR spectroscopic evidence. Crystal data: orthorhombic, Pnma, Z = 8, a = 20.0511 (1), b = 19.8757 (1), c = 13.36823 (9) Å, V = 5327.62 (5) Å3, D

x
= 1.798 g cm−3, M

r
= 721.01; monoclinic, P21/n, Z = 4, a = 19.8352 (2), b = 20.0903 (2), c = 13.3588 (1) Å, β = 90.892 (1)°, V = 5322.78 (6) Å3, D

x
= 1.799 g cm−3, M

r
= 1442.02.
Experimental charge density and electrostatic potential of glycyl-L-threonine dihydrate
Authors: Benabicha Farid , Pichon-Pesme Virginie , Jelsch Christian , Lecomte Claude , Khmou Ahmed
Published: July 2002

The experimental electron density distribution in glycyl-L-threonine dihydrate has been investigated using single-crystal X-ray diffraction data at 110 K to a resolution of (sin θ/λ) = 1.2 Å−1. Multipolar pseudo-atom refinement was carried out against 5417 observed data and the molecular electron density was analyzed using topological methods. The experimental electrostatic potential around the molecule is discussed in terms of molecular interactions. Crystal data: C6H12N2O4.2H2O, Mr
= 212.2, orthorhombic, P212121, Z = 4, F(000) = 456 e, T = 110 K, a = 9.572 (3), b = 10.039 (3), c = 10.548 (2) Å, V = 1013.6 (4) Å3, Dx
= 1.3 g cm−3, µ = 1.2 cm−1 for λMo = 0.7107 Å.
X-ray measurement of the thermal expansion of ammonium chloride
Authors: Sirdeshmukh D. B. , Deshpande V. T.
Published: July 2002

The lattice parameters of ammonium chloride have been measured at 31.5 and 54.0°C. The coefficient of linear expansion is found to be 58.5 × 10−6°C−1.
On the application of phase relationships to complex structures. XV. Magic determinants
Authors: Taylor D. J. , Woolfson M. M. , Main P.
Published: July 2002

A magic determinant is a Karle-Hauptman determinant in which the phases of reflexions forming the elements are expressed in magic-integer representation. By means of appropriate algorithms, which are described, magic determinants may be found, up to order 30, which have a high content of large E's. The value of the magic determinant depends on the values of the independent variables (usually two) in terms of which the magic-integer-represented phases are defined. Maxima are sought in a map of magic-determinant values and these give trial values for the constituent phases. These phases may be refined by maximizing one or more of the largest eigenvalues of the matrix of elements. Applications to five different structures are described and the usefulness and limitations of the magic-determinant concept are discussed. It is concluded that Karle-Hauptman determinants, chosen in the way described, provide a very discriminating figure of merit. However, the structure factors they contain usually provide a rather poor base for subsequent phase development and this limits the usefulness of the magic-determinant approach.
Some remarks on the `family tree' of Bärnighausen
Authors: Billiet Y.
Published: July 2002

Some comments are made on a recent paper of Bärnighausen [Acta Cryst. (1975), A31, S3]. A few improvements are suggested; these include a more detailed partial synopsis in relation to Landau theory, and a comparison between sequences of subgroups and physical transitions in real compounds.
Low-resolution phase information in multiple-wavelength anomalous solvent contrast variation experiments
Authors: Shepard W. , Kahn R. , Ramin M. , Fourme R.
Published: July 2002

The basic theory and principles of the multiple-wavelength anomalous solvent-contrast (MASC) method are introduced as a contrast-variation technique for generating low-resolution crystallographic phase information on the envelope of a macromolecule. Experimental techniques and practical considerations concerning the choice of anomalous scatterer, sample preparation and data acquisition are discussed. Test cases of crystals of three proteins of differing molecular weights from 14 kDa through to 173 kDa are illustrated. Methods for extracting the moduli of the anomalous structure factors from the MASC data are briefly discussed and the experimental results are compared with the known macromolecular envelopes. In all cases, the lowest resolution shells exhibit very large anomalous signals which diminish at higher resolution, as expected by theory. However, in each case the anomalous signal persists at high resolution, which is strong evidence for ordered sites of the anomalous scatterers. For the smaller two of these proteins the heavy-atom parameters could be refined for some of these sites. Finally, a novel method for phasing the envelope structure-factor moduli is presented. This method takes into account the relatively low number of observations at low resolution and describes the macromolecular envelope with a small number of parameters by presuming that the envelope is a compact domain of known volume. The parameterized envelope is expressed as a linear combination of independent functions such as spherical harmonics. Phasing starts from solutions of a sphere in the unit cell after positional refinement from random trials and the parameters describing the envelope are then refined against the data of structure-factor moduli. The preliminary results using simulated data show that the method can be used to reconstruct the correct macromolecular envelope and is able to discriminate against some false solutions.
Structural analysis of non-crystalline macromolecules: the ribosome
Authors: Orlova Elena V.
Published: July 2002

Single-particle analysis using cryo-electron microscopy has emerged recently as a tool for elucidating the structure of biological macromolecules and their assemblies. A prerequisite for single-particle analysis is an ensemble of images of structurally identical particles in different orientations. There are a variety of techniques used for image processing of this type of object in electron microscopy. The paper gives an overview of the general philosophy of image analysis of single particles in electron microscopy. It has been shown that multivariate statistical analysis of large data sets in conjunction with angular reconstitution is capable of yielding a structural resolution approaching that of X-ray structural analysis of large macromolecules. Structure preservation during specimen preparation for electron microscopy is crucial for high-resolution studies. Nowadays, cryo-electron microscopy is a beneficial method for studying biological macromolecules in their natural environment, allowing their rapid freezing in a particular functional state. The processing of images of 50S Escherichia coli ribosomal subunits embedded in vitreous ice is used as an example of image analysis of single particles at 7.5 Å resolution.
Crystallization and preliminary X-ray analysis of a member of a new family of pectate lyases, PeIL from Erwinia chrysanthemi
Authors: Shevchik Vladimir , Scott Mandy , Mayans Olga , Jenkins John
Published: July 2002

PeIL, a pectate lyase (E.C. 4.2.2.9) from E. chrysanthemi 3937 that is not homologous to the lyases with known structures, has been purified and crystallized by the hanging-drop method using a variety of organic solvents as precipitant. Elongated lathes grown from poly(ethylene glycol) plus isopropanol belong to the space group P212121 with cell dimensions a = 55.5, b = 58.2, c = 16.4 Å with a single molecule in the asymmetric unit. Although complete data sets have been collected to 2.3 Å resolution, these crystals diffract to at least 1.9 Å resolution and are suitable for structure determination. Chunky plates grown using other organic solvents as the precipitant diffracted to 3 Å resolution and were partially characterized as a second orthorhombic crystal form with space group P21212 and cell dimensions a = 119.1, b = 140.5 and c = 105.4 Å, suggesting four molecules in the asymmetric unit.
Structures of ruthenium-modified Pseudomonas aeruginosa azurin and [Ru(2,2′-bipyridine)2(imidazole)2]SO4·10H2O
Authors: Faham Salem , Day Michael W. , Connick William B. , Crane Brian R. , Di Bilio Angel J. , Schaefer William P. , Rees Douglas C. , Gray Harry B.
Published: July 2002

The crystal structure of Ru(2,2′-bipyridine)2(imidazole)(His83)azurin (RuAz) has been determined to 2.3 Å resolution by X-ray crystallography. The spectroscopic and thermodynamic properties of both the native protein and [Ru(2,2′-bipyridine)2(imidazole)2]2+ are maintained in the modified protein. Dark-green RuAz crystals grown from PEG 4000, LiNO3, CuCl2 and Tris buffer are monoclinic, belong to the space group C2 and have cell parameters a = 100.6, b = 35.4, c = 74.7 Å and β =  106.5°. In addition, [Ru(2,2′-bipyridine)2(imidazole)2]SO4·10H2O was synthesized, crystallized and structurally characterized by X-ray crystallography. Red–brown crystals of this complex are monoclinic, space group P21/n, unit-cell parameters a = 13.230 (2), b = 18.197 (4), c = 16.126 (4) Å, β = 108.65 (2)°. Stereochemical parameters for the refinement of Ru(2,2′-bipyridine)2(imidazole)(His83) were taken from the atomic coordinates of [Ru(2,2′-bipyridine)2(imidazole)2]2+. The structure of RuAz confirms that His83 is the only site of chemical modification and that the native azurin structure is not perturbed significantly by the ruthenium label.
σ2

R
, a reciprocal-space measure of the quality of macromolecular electron-density maps
Authors: Terwilliger Thomas C.
Published: July 2002

It has previously been shown that the presence of distinct regions of solvent and protein in macromolecular crystals leads to a high value of the standard deviation of local r.m.s. electron density and that this can in turn be used as a reliable measure of the quality of macromolecular electron-density maps [Terwilliger & Berendzen (1999a). Acta Cryst. D55, 501–505]. Here, it is demonstrated that a similar measure, \sigma_{R}^{2}, the variance of the local roughness of the electron density, can be calculated in reciprocal space. The formulation is suitable for rapid evaluation of macromolecular crystallographic phases, for phase improvement and for ab initio phasing procedures.
Dynamic light-scattering and preliminary crystallographic studies of the sensor domain of the haem-based oxygen sensor FixL from Rhizobium meliloti
Authors: Miyatake Hideyuki , Kanai Manabu , Adachi Shin-ichi , Nakamura Hiro , Tamura Koji , Tanida Hajime , Tsuchiya Terumasa , Iizuka Tetsutaro , Shiro Yoshitsugu
Published: July 2002

FixL is a transmitter protein in a two-component system which acts as an oxygen sensor when the symbiotic Rhizobia resides in root nodules of host plants. The oxygen-sensor domain of Rhizobium meliloti FixL (RmFixLH) was purified by His-tag affinity and isoelectronic focusing chromatographies, without the use of gel-filtration chromatography. Dynamic light-scattering measurements of RmFixLH thus obtained revealed it to be monodispersive and present as a homodimer in solution. A single crystal of RmFixLH in the met (Fe3+) form was grown in 100 mM acetic acid/NaOH buffer at pH 4.6 in the presence of 200 mM ammonium acetate, using 40%(w/v) PEG 4000 as a precipitant. A crystal of the ferrous CO form of RmFixLH was also prepared by reduction of the met crystal with Na2S2O4 in an atmosphere of CO. The crystals (0.2 × 0.05 × 0.01 mm) belong to the monoclinic system (C2) with unit-cell parameters a = 60.94, b = 37.44, c = 54.14 Å, β = 115.29° and diffract X-rays to 1.7 Å resolution at station BL44B2 of SPring-8, Japan. Bijvoet difference Patterson maps show a clear peak corresponding to the haem iron in RmFixLH.
Crystallization of the 10-23 DNA enzyme using a combinatorial screen of paired oligonucleotides
Authors: Nowakowski Jacek , Shim Peter J. , Joyce Gerald F. , Stout C. David
Published: July 2002

One of the most difficult steps in the X-ray crystallography of nucleic acids is obtaining crystals that diffract to high resolution. The choice of the nucleotide sequence has proven to be more important in producing high-quality crystals than the composition of the crystallization solution. This manuscript describes a systematic procedure for identifying the optimal sizes of a multi-stranded nucleic acid complex which provide high-quality crystals. This approach was used to crystallize the in vitro evolved 10-23 DNA enzyme complexed with its RNA substrate. In less than two months, 81 different enzyme–substrate complexes were generated by combinatorial mixing and annealing of complementary oligonucleotides which differed in length, resulting in duplexes of varying length, with or without nucleotide overhangs. Each of these complexes was screened against a standard set of 48 crystallization conditions and evaluated for crystal formation. The screen resulted in over 40 crystal forms, the best of which diffracted to 2.8 Å resolution when exposed to a synchrotron X-ray source.
A two-dimensional histogram-matching method for protein phase refinement and extension
Authors: Nieh Yeu-Perng , Zhang Kam Y. J.
Published: July 2002

A new method has been developed for protein phase improvement using the joint distribution of the electron density and its gradient (two-dimensional histogram) as a constraint in a density-modification procedure. Matching the two-dimensional (2D) histogram of a given map to that of an ideal 2D histogram was achieved through alternating applications of one-dimensional (1D) histogram matching on electron density and on density gradient. The 2D histogram-matching method was compared with the 1D density histogram-matching method for phase refinement and extension starting from either medium-resolution or high-resolution data on three different types of phases. These included phase refinement and extension using MIR phases of T6 insulin and phases with randomly generated errors. The test results demonstrated significant improvement of the phases and the overall map quality using the 2D histogram-matching method compared with the 1D density histogram-matching method in each of the three test cases.
Phase imaging using highly coherent X-rays: radiography, tomography, diffraction topography
Authors: Baruchel José , Cloetens Peter , Härtwig Jürgen , Ludwig Wolfgang , Mancini Lucia , Pernot Petra , Schlenker Michel
Published: July 2002

Several hard X-rays imaging techniques greatly benefit from the coherence of the beams delivered by the modern synchrotron radiation sources. This is illustrated with examples recorded on the `long' (145 m) ID19 `imaging' beamline of the ESRF. Phase imaging is directly related to the small angular size of the source as seen from one point of the sample (`effective divergence' ≃ microradians). When using the `propagation' technique, phase radiography and tomography are instrumentally very simple. They are often used in the `edge detection' regime, where the jumps of density are clearly observed. The in situ damage assessment of micro-heterogeneous materials is one example of the many applications. Recently a more quantitative approach has been developed, which provides a three-dimensional density mapping of the sample (`holotomography'). The combination of diffraction topography and phase-contrast imaging constitutes a powerful tool. The observation of holes of discrete sizes in quasicrystals, and the investigation of poled ferroelectric materials, result from this combination
Structural characterization of W-Ni-Al2O3 catalysts
Authors: Jordão M. H. , Assaf J. M. , Nascente P. A. P. , Mastelaro V. R.
Published: July 2002

A series of W/Ni/Al2O3 catalysts was prepared by coprecipitation of nickel and aluminum and impregnation of tungsten. The samples were characterized by XRD, XPS and XAS techniques. XRD measurements detected two phases: NiO as the main phase and NiAl2O4 in lower amount; no phase containing tungsten was detected. XPS measurements indicated the presence of Al2O3, NiAl2O4, and Al2(WO4)3 phases on the catalyst surfaces. The XANES spectra of catalysts were rather similar for all of the samples. According to the EXAFS results, at the short range level, tungsten does not form any bound with Ni atoms. The nickel first coordination shell in the catalysts containing tungsten is similar to that encountered in COP 1 catalyst without tungsten. The lower Ni-Ni coordination number observed for all catalysts, when compared to the NiO phase, can be attributed to the nickel-aluminum interaction.
Theory of spin-polarized optical potential
Authors: Hatada Keisuke , Tanaka Hisashi , Fujikawa Takashi , Hedin Lars
Published: July 2002

We develop an approximation for the non-local spin-polarized optical potential theory for atoms in solids at intermediate and high energy. The present approximation for the optical potential builds on the GW-expression. We separate the RPA polarization propagator into a core electron and a valence electron part, and can then achieve a corresponding separation of the optical potential. For the valence electron optical potential we use a local density approximation because the charge density changes fairly slowly, whereas we use a non-local optical potential for the core electron part. Both of them depend on the spin-polarization. We apply this method to electron-Fe elastic scattering in solid, and discuss the results.
Studies on corrosion inhibitors for oil‐well tubular material in acid environments
Authors: Jeyaprabha C. , Muralidharan S. , Jayaperumal D. , Venkatachari G. , Rengaswamy N.S.
Published: July 2002

To reduce the corrosion of oil‐ and gas‐well equipment during acid treatment, the acid must be inhibited. The behaviour of N‐80 oilfield material in 15 per cent hydrochloric acid solution inhibited by different inhibitor formulations containing amine, ester and a quaternary ammonium compound was studied at 303K for five hours by the mass loss method. The corrosion rates were obtained by polarisation. Impedance studies were carried out to evaluate the performance of the inhibitor formulations. It was found that the formulation containing 3,000ppm amine, 1,000ppm ester and 1,000ppm quaternary ammonium compound was effective for the specific oil‐well tubular material.
Kite flying: the role of marketing in the post‐BSE British beef export industry
Authors: Baines Paul R. , Harris Phil
Published: July 2002

Outlines the role of the Meat Livestock Commission in dealing with the BSE/CJD crisis in the UK meat industry. It covers the re‐launch of British beef, the history of the BSE crisis, the decline of the export market for beef and the increasingly political nature of the world beef and meat markets. In addition, the article assesses the impact of supermarkets, government and environmental concerns and the development of this key industry. The issue of reputation alongside natural products is considered and the complexities of a fragmented market. Suggests that there is no quick and easy fix to the re‐establishment of UK roast beef as a premier brand.
Numeracy and employment
Authors: Parsons Samantha , Bynner John
Published: July 2002

Uses National Child Development Study (NCDS) data to examine the employment experiences of men and women assessed with poor numeracy compared with those with good numeracy skills at age 37. To uncover the extent of negative effects of having poor numeracy skills, the sample is restricted to those whose poor or good numeracy was accompanied by good literacy skills. As a further control, much of the analysis is also restricted to those who had left full‐time education at age 16. Maps the proportions in full‐time employment between ages 17 to 37 and demonstrates the very different labour market experiences of the two skills groups in the areas of occupation, training, promotion and income. Concludes that poor numeracy reduces employment opportunities and progress in jobs.
Automating agricultural vehicles
Authors: Callaghan Victor , Chernett Paul , Colley Martin , Lawson Tony , Standeven John , Carr‐West Malcolm , Ragget Malcolm
Published: July 2002

Describes the design and construction of TROWEL ‐ a test bed for experimental agricultural vehicles. The vehicle will be used to explore ways of increasing the productivity of expensive agricultural mobile machinery by taking over some of the tasks of the operator, allowing him to drive faster or for longer; and by allowing a single operator to control several machines simultaneously. In some cases machines may be able to operate entirely autonomously without operator intervention.
Barriers to the development of self‐organizing teams
Authors: Balkema Ageeth , Molleman Eric
Published: July 2002

We studied the barriers to the development of self‐organization in three teams by means of questionnaires and observations. We found that the level of self‐organization pertaining to “routine work” is rather high. With respect to “machine‐related tasks”, the opportunities provided by the maintenance support group, and the complexity of some of these tasks are the main barriers to delegating more of these tasks. “Shift‐related tasks” are delegated to the team, but actually are done by the group coordinator only. “Communication tasks” have not been delegated to the teams, although the need to do so is high. Barriers lay in the shift system and in the skills of the workers. With respect to “sophisticated tasks” and the “tasks directed to the environment”, we conclude that the requisite of delegating them to the team is low. A moderate level of participation, however, seems appropriate here.
Mitigation and response planning in a bio‐terrorist attack
Authors: Fischer Henry W.
Published: July 2002

With the emergence of biological weapons of mass destruction as potential tools of terrorism, Presidential Decision Directive 39 initiated US plans to enhance mitigation and response activity. Anecdotal information suggests many of the likely behavioral and organizational response challenges are not being addressed. The current paper applies the disaster research literature to identify the likely behavioral and organizational response challenges a community or nation would encounter in a bio‐terrorist attack on a metropolitan area. Mitigation and response planning, it is argued, would be enhanced if these likely challenges were actually taken into account.
The contributions of Chester Barnard to strategic management theory
Authors: McMahon Dave , Carr Jon C.
Published: July 2002

Chester Barnard’s The Functions of the Executive (1938) represents a book of historical significance to the study of management. Using the fundamental principles that Barnard outlines, an application of these principles is made to the area of strategic management. The analysis focuses specifically on two main areas: the movement from a static to a dynamic model and the role of the environment. Highlights the importance of returning to the work of early writers and their contribution to the future development of management disciplines.
Unusual evolutionary history of the tRNA splicing endonuclease EndA: Relationship to the LAGLIDADG and PD‐(D/E)XK deoxyribonucleases
Authors: Bujnicki Janusz M. , Rychlewski Leszek
Published: July 2002

The tRNA splicing endoribonuclease EndA from Methanococcus jannaschii is a homotetramer formed via heterologous interaction between the two pairs of homodimers. Each monomer consists of two α/β domains, the N‐terminal domain (NTD) and the C‐terminal domain (CTD) containing the RNase A‐like active site. Comparison of the EndA coordinates with the publicly available protein structure database revealed the similarity of both domains to site‐specific deoxyribonucleases: the NTD to the LAGLIDADG family and the CTD to the PD‐(D/E)XK family. Superposition of the NTD on the catalytic domain of LAGLIDADG homing endonucleases allowed a suggestion to be made about which amino acid residues of the tRNA splicing nuclease might participate in formation of a presumptive cryptic deoxyribonuclease active site. On the other hand, the CTD and PD‐(D/E)XK endonucleases, represented by restriction enzymes and a phage λ exonuclease, were shown to share extensive similarities of the structural framework, to which entirely different active sites might be attached in two alternative locations. These findings suggest that EndA evolved from a fusion protein with at least two distinct endonuclease activities: the ribonuclease, which made it an essential “antitoxin” for the cells whose RNA genes were interrupted by introns, and the deoxyribonuclease, which provided the means for homing‐like mobility. The residues of the noncatalytic CTDs from the positions corresponding to the catalytic side chains in PD‐(D/E)XK deoxyribonucleases map to the surface at the opposite side to the tRNA binding site, for which no function has been implicated. Many restriction enzymes from the PD‐(D/E)XK superfamily might have the potential to maintain an additional active or binding site at the face opposite the deoxyribonuclease active site, a property that can be utilized in protein engineering.
Solution structure of the DNA‐binding domain of the TyrR protein of Haemophilus influenzae
Authors: Wang Yunjun , Zhao Shimin , Somerville Ronald L. , Jardetzky Oleg
Published: July 2002

The TyrR protein of Haemophilus influenzae is a 36‐kD transcription factor whose major function is to control the expression of genes important in the biosynthesis and transport of aromatic amino acids. Using 1H and 15N NMR spectroscopy, we have determined the 3D solution structure of the TyrR C‐terminal DNA‐binding domain (DBD) containing residues from 258 to 318 (TyrR[258–318]). The NMR results show that this segment of TyrR consists of a potential hinge helix at its N terminus (residues 263–270) as well as three well‐defined α‐helices extending from residues 277–289 (HR‐2), 293–300 (HR‐1), and 304–314 (HR). Helix HR‐1 and HR fold in a typical helix–turn–helix (HTH) motif. The three helices and the hinge helix are tightly bound together by hydrophobic interaction and hydrogen bonds. Several hydrophilic residues whose side chains may directly interact with DNA are identified. A hydrophobic patch that may be part of the interaction surface between the domains of TyrR protein is also observed. Comparisons with the structures of other HTH DNA‐binding proteins reveal that in terms of the spatial orientation of the three helices, this protein most closely resembles the cap family.
Multiple regulation by external ATP of nifedipine‐insensitive, high voltage‐activated Ca2+ current in guinea‐pig mesenteric terminal arteriole
Authors: Morita Hiromitsu , Sharada Thapaliya , Takewaki Tadashi , Ito Yushi , Inoue Ryuji
Published: July 2002

We investigated the receptor‐mediated regulation of nifedipine‐insensitive, high voltage‐activated Ca2+ currents in guinea‐pig terminal mesenteric arterioles (ImVDCC) using the whole‐cell clamp technique. Screening of various vasoactive substances revealed that ATP, histamine and substance P exert modulatory effects on ImVDCC. The effects of ATP on ImVDCC after complete P2X receptor desensitization exhibited a complex concentration dependence. With 5 mm Ba2+, ATP potentiated ImVDCC at low concentrations (∼1–100 μm), but inhibited it at higher concentrations (>100 μm). The potentiating effects of ATP were abolished by suramin (100 μm) and PPADS (10 μm) and by intracellular application of GDPβS (500 μm), whereas a substantial part of ImVDCC inhibition by milimolar concentrations of ATP remained unaffected; due probably to its divalent cation chelating actions. In divalent cation‐free solution, ImVDCC was enlarged and underwent biphasic effects by ATPγS and ADP, while 2‐methylthio ATP (2MeSATP) exerted only inhibition, and pyrimidines such as UTP and UDP were ineffective. ATP‐induced ImVDCC potentiation was selectively inhibited by anti‐Gαs antibodies or protein kinase A (PKA) inhibitory peptides and mimicked by dibutyryl cAMP. In contrast, ATP‐induced inhibition was selectively inhibited by Gαq/11 antibodies or protein kinase C (PKC) inhibitory peptides and mimicked by PDBu. Pretreatment with pertussis toxin was ineffective. The apparent efficacy for ImVDCC potentiation with PKC inhibitors was: ATPγS > ATP≥ADP and for inhibition with PKA inhibitors was: 2MeSATP > ATPγS > ATP > ADP. Neither ImVDCC potentiation nor inhibition showed voltage dependence. These results suggest that ImVDCC is multi‐phasically regulated by external ATP via P2Y11‐resembling receptor/Gs/PKA pathway, P2Y1‐like receptor/Gq/11/PKC pathway, and metal chelation.
Repeated ischaemic isometric exercise increases muscle fibre conduction velocity in humans: involvement of Na+‐K+‐ATPase
Authors: Rongen G. A. , van Dijk J. P. , Ginneken E. E. van , Stegeman D. F. , Smits P. , Zwarts M. J.
Published: July 2002

This study was performed to test two hypotheses: (1) ischaemic preconditioning (development of tolerance to ischaemia) influences muscle fibre conduction velocity (MFCV) during repeated ischaemic isometric exercise and (2) the increase in MFCV to supranormal levels during recovery from ischaemic exercise is caused by activation of Na+−K+‐ATPase. For this purpose, MFCV was measured with surface electromyography (sEMG) during repeated ischaemic isometric exercise of the brachioradial muscle (2 min at 30 % of maximal voluntary contraction). The involvement of ischaemic preconditioning was tested by changing the duration of ischaemia and by intra‐arterial infusion of adenosine (brachial artery, 50 μg min−1 dl−1). The role of Na+−K+‐ATPase was explored using ouabain (0.2 μg min−1 dl−1). During the exercise, MFCV decreased from 4.4 ± 0.2 m s−1 to 3.7 ± 0.2 m s−1 (P < 0.01, n= 13). Similar reductions in MFCV were observed during repeated exercise, irrespective of the reperfusion time (10 min vs. 18 min) or duration of the ischaemia (2 vs. 10 min). However, initial MFCV gradually increased for each subsequent contraction when contractions were repeated at 10 min intervals (4.4 ± 0.2 m s−1vs. 4.9 ± 0.2 m s−1 for the first and fourth contraction respectively; P < 0.01; n= 13). This increase was not observed when contractions were performed at 18 min intervals, nor when additional ischaemia was applied. Intra‐arterial adenosine did not affect MFCV. Intra‐arterial ouabain did not affect the reduction in MFCV during exercise but completely prevented the increase in MFCV during recovery: from 4.7 ± 0.2 m s−1 to 5.2 ± 0.2 m s−1vs. 4.5 ± 0.1 m s−1 to 4.5 ± 0.1 m s−1 in the absence and presence of ouabain respectively (P < 0.05 for ouabain effect; n= 6). In conclusion, ischaemic preconditioning is not involved in changes in MFCV during repeated ischaemic isometric exercise. The increase in MFCV during recovery from repeated ischaemic isometric exercise is caused by rapid activation of Na+−K+‐ATPase.
Modeling and Feedback Structural Acoustics Control of a Flexible Plate
Authors: Seto Kazuto , Ren Mingzhang , Doi Fumio
Published: July 2002

A lumping method via an inverse modal analysis approach is proposed in this paper for creating a lumped parameter model for a structure with distributed parameters. On the basis of the lumped parameter model, the formulation of an optimal controller in physical state space is presented and, furthermore, the design of a reduced-order controller is described. The method is demonstrated and verified by the vibration and noise control experiments carried out on a clamped plate. Several modes of the plate with high sound radiating efficiencies are well controlled by using three sensors and one actuator, based on a 9 degree-of-freedom (DOF) lumped parameter model of the plate.
A Simultaneous Variable Solution Procedure for Laminar and Turbulent Flows in Curved Channels and Bends
Authors: Wang Jianrong , Shirazi Siamack A.
Published: July 2002

Direct Numerical Simulation of turbulent flow requires accurate numerical techniques for solving the Navier-Stokes equations. Therefore, the Navier-Stokes equations in general orthogonal and nonorthogonal coordinates were employed and a simultaneous variable solution method was extended to solve these general governing equations. The present numerical method can be used to accurately predict both laminar and turbulent flow in various curved channels and bends. To demonstrate the capability of this numerical method and to verify the method, the time-averaged Navier-Stokes equations were employed and several turbulence models were also implemented into the numerical solution procedure to predict flows with strong streamline curvature effects. The results from the present numerical solution procedure were compared with available experimental data for a 90 deg bend. All of the turbulence models implemented resulted in predicted velocity profiles which were in agreement with the trends of experimental data. This indicates that the solution method is a viable numerical method for calculating complex flows. [S0098-2202(00)01803-4]
Comparison of Algorithms for Unsteady Flow Calculations in Inlet and Exhaust Systems of IC Engines
Authors: Vandevoorde M. , Vierendeels J. , Sierens R. , Dick E. , Baert R.
Published: July 2002

A comparison of different numerical algorithms used in commercial codes for the calculation of the one-dimensional unsteady flow in the pipes of the inlet and exhaust systems of internal combustion engines is presented in this work. The comparison is made between the Method Of Characteristics (MOC), different Lax-Wendroff schemes, first order upwind schemes and the newest TVD (Total Variation Diminishing) schemes. These algorithms are representative for the complete evolution noticed in the computer codes from the beginning of their use to the present state of the art. Two models of realistic problems in engine simulation tasks are considered: the shock tube calculation (so called Sod’s problem) and the calculation in a tapered pipe. The first test case simulates the exhaust valve opening and releasing a pressure (shock)wave in the exhaust manifold while the other test case covers any gradual variation in the cross section of the manifold pipes. For both test cases computed results are compared with an exact solution and computer time and accuracy are evaluated. None of the examined schemes is completely satisfactory. They either show too much overshoots (for the first test case), or they have local discretization errors (at the section changes of the second test case). A new TVD scheme is proposed that does not introduce any of the foregoing inaccuracies. With this scheme overshoots and dips are eliminated and mass balances are fulfilled, while maintaining high accuracy. [S0742-4795(00)00304-5]
Simplex Based Sliding Mode Control of an Underwater Gripper
Authors: Bartolini G. , Coccoli M. , Punta E.
Published: July 2002

In this paper the sliding mode control theory is applied to a particular underwater gripper actuated by linear motors which, acting on a hydraulic circuit, generate mono-directional forces. In practical realizations actuators often show imprecise relationships between electrical input signals and mechanical output; such a situation constitutes a source of uncertainties. A sliding mode control methodology based on the use of a simplex of constant control vectors is presented. The proposed approach is general enough to also work with different applications. [S0022-0434(00)01204-1]