bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic Analysis of Phospholipase C from Catharanthus roseus Transformed Roots Using Different Assays1
Authors: Hernández-Sotomayor S.M. Teresa , De Los Santos-Briones César , Muñoz-Sánchez J. Armando , Loyola-Vargas Victor M.
Published: July 2002

The properties of phospholipase C (PLC) partially purified from Catharanthus roseustransformed roots were analyzed using substrate lipids dispersed in phospholipid vesicles, phospholipid-detergent mixed micelles, and phospholipid monolayers spread at an air-water interface. Using [33P]phosphatidylinositol 4,5-bisphosphate (PIP2) of high specific radioactivity, PLC activity was monitored directly by measuring the loss of radioactivity from monolayers as a result of the release of inositol phosphate and its subsequent dissolution on quenching in the subphase. PLC activity was markedly affected by the surface pressure of the monolayer, with reduced activity at extremes of initial pressure. The optimum surface pressure for PIP2 hydrolysis was 20 mN/m. Depletion of PLC from solution by incubation with sucrose-loaded PIP2vesicles followed by ultracentrifugation demonstrated stable attachment of PLC to the vesicles. A mixed micellar system was established to assay PLC activity using deoxycholate. Kinetic analyses were performed to determine whether PLC activity was dependent on both bulk PIP2 and PIP2 surface concentrations in the micelles. The interfacial Michaelis constant was calculated to be 0.0518 mol fraction, and the equilibrium dissociation constant of PLC for the lipid was 45.5 μm. These findings will add to our understanding of the mechanisms of regulation of plant PLC.
Glucose Polyester Biosynthesis. Purification and Characterization of a Glucose Acyltransferase
Authors: Li Alice X. , Eannetta Nancy , Ghangas Gurdev S. , Steffens John C.
Published: July 2002

Glandular trichomes of the wild tomato species Lycopersicon pennellii secrete 2,3,4-O-tri-acyl-glucose (-Glc), which contributes to insect resistance. A Glc acyltransferase catalyzes the formation of diacyl-Glc by disproportionating two equivalents of 1-O-acyl-β-Glc, a high-energy molecule formed by a UDP-Glc dependent reaction. The acyltransferase was purified 4,900-fold from L. pennellii leaves by polyethylene glycol fractionation, diethylaminoethyl chromatography, concanavalin A affinity chromatography, and chromatofocusing. The acyltransferase possesses an isoelectric point of 4.8, a relative molecular mass around 110 kD, and is composed of 34- and 24-kD polypeptides as a heterotetramer. The 34- and 24-kD proteins were partially sequenced. The purified enzyme catalyzes both the disproportionation of 1-O-acyl-β-Glcs to generate 1,2-di-O-acyl-β-Glc and anomeric acyl exchange between 1-O-acyl-β-Glc and Glc.
Phosphatidylinositol 4-Kinase Associated with Spinach Plasma Membranes. Isolation and Characterization of Two Distinct Forms
Authors: Westergren Tomas , Ekblad Lars , Jergil Bengt , Sommarin Marianne
Published: July 2002

Highly purified plasma membranes from spinach (Spinacia oleracea L.) leaves contained phosphatidylinositol (PtdIns) kinase activity that was firmly associated with the membrane. The enzyme was solubilized by detergent treatment (2% [w/v] Triton X-100) and purified by heparin-Sepharose and Q-Sepharose chromatography. Two enzymically active fractions, QI and QII, both exhibiting PtdIns 4-kinase activity, were resolved and purified 100- to 300-fold over the plasma membrane. QI and QII shared similar high apparentK  m values for ATP (approximately 0.45 mm) and PtdIns (approximately 0.2 mm) and were insensitive to inhibition by adenosine. While Mg2+ was the preferred divalent cation, Mn2+ could partly substitute in the reaction catalyzed by the QII enzyme but not in that catalyzed by QI. Mn2+ acted synergistically with suboptimal Mg2+ concentrations to activate not only the QII enzyme, but also to some extent QI. Both enzymes were inhibited by millimolar concentrations of Ca2+ and micromolar concentrations of wortmannin. The apparent molecular mass for QI was 120 kD, which was determined by SDS-PAGE and western blotting using an antibody against a peptide unique for lipid kinases and the binding of3H-wortmannin, and for QII 65 kD as determined by immunodetection and renaturation of PtdIns kinase activity in the 65-kD region of polyacrylamide gels.
Directed Mutation of the Rubisco Large Subunit of Tobacco Influences Photorespiration and Growth
Authors: Whitney Spencer M. , von Caemmerer Susanne , Hudson Graham S. , Andrews T. John
Published: July 2002

The gene for the large subunit of Rubisco was specifically mutated by transforming the chloroplast genome of tobacco (Nicotiana tabacum). Codon 335 was altered to encode valine instead of leucine. The resulting mutant plants could not grow without atmospheric CO2 enrichment. In 0.3% (v/v) CO2, the mutant and wild-type plants produced similar amounts of Rubisco but the extent of carbamylation was nearly twice as great in the mutants. The mutant enzyme's substrate-saturated CO2-fixing rate and its ability to distinguish between CO2 and O2 as substrates were both reduced to 25% of the wild type's values. Estimates of these parameters obtained from kinetic assays with the purified mutant enzyme were the same as those inferred from measurements of photosynthetic gas exchange with leaves of mutant plants. The Michaelis constants for CO2, O2, and ribulose-1,5-bisphosphate were reduced and the mutation enhanced oxygenase activity at limiting O2concentrations. Consistent with the reduced CO2 fixation rate at saturating CO2, the mutant plants grew slower than the wild type but they eventually flowered and reproduced apparently normally. The mutation and its associated phenotype were inherited maternally. The chloroplast-transformation strategy surmounts previous obstacles to mutagenesis of higher-plant Rubisco and allows the consequences for leaf photosynthesis to be assessed.
Identification of a Hsp70 Recognition Domain within the Rubisco Small Subunit Transit Peptide
Authors: Ivey Robert A. , Subramanian Chitra , Bruce Barry D.
Published: July 2002

The interaction between SStp, the transit peptide of the precursor protein to the small subunit of Rubisco (prSSU) and two Hsp70 molecular chaperones, Escherichia coli DnaK and pea (Pisum sativum) CSS1, was investigated in detail. Two statistical analyses were developed and used to investigate and predict regions of SStp recognized by DnaK. Both algorithms suggested that DnaK would have high affinity for the N terminus of SStp, moderate affinity for the central region, and low affinity for the C terminus. Furthermore, both algorithms predicted this affinity pattern for >75% of the transit peptides analyzed in the chloroplast transit peptide (CHLPEP) database. In vitro association between SStp and these Hsp70s was confirmed by three independent assays: limited trypsin resistance, ATPase stimulation, and native gel shift. Finally, synthetic peptides scanning the length of SStp and C-terminal deletion mutants of SStp were used to experimentally map the region of greatest DnaK affinity to the N terminus. CSS1 displayed a similar affinity for the N terminus of SStp. The major stromal Hsp70s affinity for the N terminus of SStp and other transit peptides supports a molecular motor model in which the chaperone functions as an ATP-dependent translocase, committing chloroplast precursor proteins to unidirectional movement across the envelope.
The BtpA Protein Stabilizes the Reaction Center Proteins of Photosystem I in the Cyanobacterium Synechocystis sp. PCC 6803 at Low Temperature
Authors: Zak Elena , Pakrasi Himadri B.
Published: July 2002

Specific inhibition of photosystem I (PSI) was observed under low-temperature conditions in the cyanobacteriumSynechocystis sp. strain PCC 6803. Growth at 20°C caused inhibition of PSI activity and increased degradation of the PSI reaction center proteins PsaA and PsaB, while no significant changes were found in the level and activity of photosystem II (PSII). BtpA, a recently identified extrinsic thylakoid membrane protein, was found to be a necessary regulatory factor for stabilization of the PsaA and PsaB proteins under such low-temperature conditions. At normal growth temperature (30°C), the BtpA protein was present in the cell, and its genetic deletion caused an increase in the degradation of the PSI reaction center proteins. However, growth ofSynechocystis cells at 20°C or shifting of cultures grown at 30°C to 20°C led to a rapid accumulation of the BtpA protein, presumably to stabilize the PSI complex, by lowering the rates of degradation of the PsaA and PsaB proteins. A btpAdeletion mutant strain could not grow photoautotrophically at low temperature, and exhibited rapid degradation of the PSI complex after transfer of the cells from normal to low temperature.
Distinct Abscisic Acid Signaling Pathways for Modulation of Guard Cell versus Mesophyll Cell Potassium Channels Revealed by Expression Studies in Xenopus laevisOocytes
Authors: Sutton Fedora , Paul Sunil S. , Wang Xi-Qing , Assmann Sarah M.
Published: July 2002

Regulation of guard cell ion transport by abscisic acid (ABA) and in particular ABA inhibition of a guard cell inward K+current (I  Kin) is well documented. However, little is known concerning ABA effects on ion transport in other plant cell types. Here we applied patch clamp techniques to mesophyll cell protoplasts of fava bean (Vicia faba cv Long Pod) plants and demonstrated ABA inhibition of an outward K+ current (I  Kout). When mesophyll cell protoplast mRNA (mesophyll mRNA) was expressed in Xenopus laevisoocytes, I  Kout was generated that displayed similar properties to I  Kout observed from direct analysis of mesophyll cell protoplasts.I  Kout expressed by mesophyll mRNA-injected oocytes was inhibited by ABA, indicating that the ABA signal transduction pathway observed in mesophyll cells was preserved in the frog oocytes. Co-injection of oocytes with guard cell protoplast mRNA and cRNA for KAT1, an inward K+ channel expressed in guard cells, resulted in I  Kin that was similarly inhibited by ABA. However, oocytes co-injected with mesophyll mRNA and KAT1 cRNA produced I  Kin that was not inhibited by ABA. These results demonstrate that the mesophyll-encoded signaling mechanism could not substitute for the guard cell pathway. These findings indicate that mesophyll cells and guard cells use distinct and different receptor types and/or signal transduction pathways in ABA regulation of K+ channels.
Effects of Elevated [CO2] and Nitrogen Nutrition on Cytokinins in the Xylem Sap and Leaves of Cotton
Authors: Yong Jean W.H. , Wong S. Chin , Letham D. Stuart , Hocart Charles H. , Farquhar Graham D.
Published: July 2002

We measured the level of xylem-derived cytokinins (CKs) entering a cotton leaf, and the CK levels in the same leaf, thus enabling xylem sap and foliar CKs to be compared concurrently. Although zeatin was the dominant CK in xylem sap, zeatin, dihydrozeatin, and N6-(2-isopentenyl) adenine were present in approximately equimolar levels in leaves. Elevated [CO2] (EC) has an effect on the levels of cytokinins in sap and leaf tissues. This effect was modulated by the two levels of root nitrogen nutrition (2 and 12 mm nitrate). Growth enhancement (70%) in EC over plants in ambient [CO2] (AC) was observed for both nitrogen nutrition treatments. Low-nitrogen leaves growing in EC exhibited photosynthetic acclimation, whereas there was no sign of photosynthetic acclimation in high-nitrogen grown leaves. Under these prevailing conditions, xylem sap and leaf tissues were obtained for CK analysis. Higher nitrogen nutrition increased the delivery per unit leaf area of CKs to the leaf at AC. EC caused a greater increase in CK delivery to the leaf at low nitrogen conditions (106%) than at high nitrogen conditions (17%). EC induced a significant increase in CK content in low-nitrogen leaves, whereas CK content in leaf tissues was similar for high-nitrogen leaves growing in AC and EC.
Dielectric Relaxation of Water and Water-Plasticized Biomolecules in Relation to Cellular Water Organization, Cytoplasmic Viscosity, and Desiccation Tolerance in Recalcitrant Seed Tissues
Authors: Sun Wendell Q.
Published: July 2002

To understand the relationship between the organization of cellular water, molecular interactions, and desiccation tolerance, dielectric behaviors of water and water-plasticized biomolecules in red oak (Quercus rubra) seeds were studied during dehydration. The thermally stimulated current study showed three dielectric dispersions: (a) the relaxation of loosely-bound water and small polar groups, (b) the relaxation of tightly-bound water, carbohydrate chains, large polar groups of macromolecules, and (c) the “freezing in” of molecular mobility (glassy state). Seven discrete hydration levels (water contents of 1.40, 0.55, 0.41, 0.31, 0.21, 0.13, and 0.08 g/g dry weight, corresponding to −1.5, −8, −11, −14, −24, −74, and −195 MPa, respectively) were identified according to the changes in thermodynamic and dielectric properties of water and water-plasticized biomolecules during dehydration. The implications of intracellular water organization for desiccation tolerance were discussed. Cytoplasmic viscosity increased exponentially at water content < 0.40 g/g dry weight, which was correlated with the great relaxation slowdown of water-plasticized biomolecules, supporting a role for viscosity in metabolic shutdown during dehydration.
Pathogenesis of the Human Opportunistic PathogenPseudomonas aeruginosa PA14 in Arabidopsis
Authors: Plotnikova Julia M. , Rahme Laurence G. , Ausubel Frederick M.
Published: July 2002

The human opportunistic pathogen Pseudomonas aeruginosa strain PA14 is a multihost pathogen that can infect Arabidopsis. We found that PA14 pathogenesis in Arabidopsis involves the following steps: attachment to the leaf surface, congregation of bacteria at and invasion through stomata or wounds, colonization of intercellular spaces, and concomitant disruption of plant cell wall and membrane structures, basipetal movement along the vascular parenchyma, and maceration and rotting of the petiole and central bud. Distinctive features of P. aeruginosa pathogenesis are that the surface of mesophyll cell walls adopt an unusual convoluted or undulated appearance, that PA14 cells orient themselves perpendicularly to the outer surface of mesophyll cell walls, and that PA14 cells make circular perforations, approximately equal to the diameter of P. aeruginosa, in mesophyll cell walls. Taken together, our data show that P. aeruginosa strain PA14 is a facultative pathogen of Arabidopsis that is capable of causing local and systemic infection, which can result in the death of the infected plant.
Identification of Mutator Insertional Mutants of Starch-Branching Enzyme 2a in Corn
Authors: Blauth Susan L. , Yao Yuan , Klucinec Jeffery D. , Shannon Jack C. , Thompson Donald B. , Guiltinan Mark J.
Published: July 2002

Starch-branching enzymes (SBE) break the α-1,4 linkage of starch, re-attaching the chain to a glucan chain by an α-1,6 bond, altering starch structure. SBEs also facilitate starch accumulation by increasing the number of non-reducing ends on the growing chain. In maize (Zea mays), three isoforms of SBE have been identified. To examine the function of the SBEIIa isoform, a reverse genetics polymerase chain reaction-based screen was used to identify a mutant line segregating for a Mutator transposon withinSbe2a. To locate the insertion within the second exon ofSbe2a, the genomic sequence of Sbe2acontaining the promoter and 5′ end was isolated and sequenced. Plants homozygous for sbe2a::Mu have undetectable levels of Sbe2a transcripts and SBEIIa in their leaves. Characterization of leaf starch from sbe2a::Mumutants shows reduced branching similar to yet more extreme than that seen in kernels lacking SBEIIb activity. Characterization of endosperm starch from sbe2a::Mu mutants shows branching that is indistinguishable from wild-type controls. These mutant plants have a visible phenotype resembling accelerated senescence, which was correlated with the Mutator insertion withinSbe2a. This correlation suggests a specific role for SBEIIa in leaves, which may be necessary for normal plant development.
Regulation of psbA and psaE Expression by Light Quality in Synechocystis Species PCC 6803. A Redox Control Mechanism
Authors: Bissati Kamal El , Kirilovsky Diana
Published: July 2002

We investigated the influence of light of different wavelengths on the expression of the psbA gene, which encodes the D1 protein of the photosystem II and the psaE gene, which encodes the subunit Psa-E of the photosystem I, inSynechocystis sp PCC 6803. In an attempt to differentiate between a light-sensory and a redox-sensory signaling processes, the effect of orange, blue, and far-red light was studied in the wild-type and in a phycobilisome-less mutant. Transferring wild-type cells from one type of illumination to another induced changes in the redox state of the electron transport chain and inpsbA and psaE expression. Blue and far-red lights (which are preferentially absorbed by the photosystem I) induced an accumulation of psbA transcripts and a decrease of the psaE mRNA level. In contrast, orange light (which is preferentially absorbed by the photosystem II) induced a large accumulation of psaE transcripts and a decrease of psbA mRNA level. Transferring mutant cells from blue to orange light (or vice versa) had no effect either on the redox state of the electron transport chain or on the levels of psbAand psaE mRNAs. Thus, light quality seems to regulate expression of these genes via a redox sensory mechanism inSynechocystis sp PCC 6803 cells. Our data suggest that the redox state of one of the electron carriers between the plastoquinone pool and the photosystem I has opposite influences onpsbA and psaE expression. Its reduction induces accumulation of psaE transcripts, and its oxidation induces accumulation of psbA mRNAs.
Proteomic Analysis of Arabidopsis Seed Germination and Priming
Authors: Gallardo Karine , Job Claudette , Groot Steven P.C. , Puype Magda , Demol Hans , Vandekerckhove Joël , Job Dominique
Published: July 2002

To better understand seed germination, a complex developmental process, we developed a proteome analysis of the model plant Arabidopsis for which complete genome sequence is now available. Among about 1,300 total seed proteins resolved in two-dimensional gels, changes in the abundance (up- and down-regulation) of 74 proteins were observed during germination sensu stricto (i.e. prior to radicle emergence) and the radicle protrusion step. This approach was also used to analyze protein changes occurring during industrial seed pretreatments such as priming that accelerate seed germination and improve seedling uniformity. Several proteins were identified by matrix-assisted laser-desorption ionization time of flight mass spectrometry. Some of them had previously been shown to play a role during germination and/or priming in several plant species, a finding that underlines the usefulness of using Arabidopsis as a model system for molecular analysis of seed quality. Furthermore, the present study, carried out at the protein level, validates previous results obtained at the level of gene expression (e.g. from quantitation of differentially expressed mRNAs or analyses of promoter/reporter constructs). Finally, this approach revealed new proteins associated with the different phases of seed germination and priming. Some of them are involved either in the imbibition process of the seeds (such as an actin isoform or a WD-40 repeat protein) or in the seed dehydration process (e.g. cytosolic glyceraldehyde-3-phosphate dehydrogenase). These facts highlight the power of proteomics to unravel specific features of complex developmental processes such as germination and to detect protein markers that can be used to characterize seed vigor of commercial seed lots and to develop and monitor priming treatments.
Molsee: a Tcl/Tk-based program to controlRasmol
Authors: Mao Fenglou , Lai Luhua
Published: July 2002

Rasmolis a widely used program for visualizing molecules. In order to make it more user-friendly,Molsee, a Tcl/Tk-based graphical user interface front end for controllingRasmol, has been developed.
Characterization of H defects in the aluminium–hydrogen system using small-angle scattering techniques
Authors: Buckley C. E. , Birnbaum H. K. , Lin J. S. , Spooner S. , Bellmann D. , Staron P. , Udovic T. J. , Hollar E.
Published: July 2002

Aluminium foils (99.99% purity) and single crystals (99.999% purity) were charged with hydrogen using a gas plasma method and electrochemical methods, resulting in the introduction of a large amount of hydrogen. X-ray diffraction measurements indicated that within experimental error there was a zero change in lattice parameter after plasma charging. This result is contradictory to almost all other face-centred cubic (f.c.c.) materials, which exhibit a lattice expansion when the hydrogen enters the lattice interstitially. It is hypothesized that the hydrogen does not enter the lattice as an interstitial solute, but instead forms an H–vacancy complex at the surface that diffuses into the volume and then clusters to form H2bubbles. Small- and ultra-small-angle neutron scattering (SANS, USANS) and small-angle X-ray scattering (SAXS) were primarily employed to study the nature and agglomeration of the H–vacancy complexes in the Al–H system. The SAXS results were ambiguous owing to double Bragg scattering, but the SANS and USANS investigation, coupled with results from inelastic neutron scattering, and transmission and scanning electron microscopy, revealed the existence of a large size distribution of hydrogen bubbles on the surface and in the bulk of the Al–H system. The relative change in lattice parameter is calculated from the pressure in a bubble of average volume and is compared with the experimentally determined value.
Estimation of cobalt coating layer thickness on acicular Fe3O4powder using HR-TEM
Authors: Sakai Keitarou , Saguchi Hiroto , Nishimura Tadashi
Published: July 2002

The thicknesses of cobalt coating layers grown on four different types of acicular Fe3O4particles were estimated from the analysis of lattice images and from the determination of the Co depth profile using high-resolution transmission electron microscopy (HR-TEM) coupled with an energy dispersive X-ray (EDX) analysis system. It was observed that the coating thickness might vary with the crystallite size resulting from the growth mechanism of the coating layer. In this study, two different layer thicknesses, 40 Å and less than 10 Å, were evidenced for crystallite sizes of 390 Å and 350 Å, respectively.
Human tissue analysis by small-angle X-ray scattering
Authors: Avtandilov G. , Dembo A. , Komardin O. , Lazarev P. , Paukshto M. , Shkolnik L. , Zayratiyants O.
Published: July 2002

Molecular structure of pathologically changed biological tissue differs greatly from the normal one. It gives the opportunity to diagnose different diseases by using methods of structural tissue analysis. The present paper is based on Ultra-Low Angle X-ray (ULAX) coherent scattering data from 1000 paired samples of mammary gland tissue dissected during the surgical treatment from 500 patients with different types of breast tumours (malignant or benign) and tumour-like formations (fibrocystic change). The medical data (histological and histostereometrical analysis) and the digital scattering information have been compared by regression analysis to produce the scattering pattern recognition code that demonstrates the high sensitivity of the ULAX method.
An optimum design for a time-of-flight neutron diffractometer for measuring engineering stresses
Authors: Johnson Michael W. , Daymond Mark R.
Published: July 2002

A method is described for optimizing the design of a time-of-flight neutron diffractometer designed to measure lattice parameters. Such diffractometers are now used extensively by engineers and materials scientists for measuring strain within metallic and ceramic components. The method presented relies on the identification of a figure of merit (FOM) that accurately describes the performance of such an instrument. For the first time, an FOM for an instrument exhibiting non-Gaussian peak shapes is described, and the methods by which this FOM may be maximized are described. Although the instrument described is based on the time-of-flight technique, the FOM derived may equally well be used to optimize a reactor-based instrument. While measuring peak position is a straightforward example, it is shown that similar figures of merit may be found for other peak shape parameters, and thus other types of instrumentation.
A comparative study of single-line and Rietveld strain–size evaluation procedures using MgO ceramics
Authors: Pratapa Suminar , O'Connor Brian , Hunter Brett
Published: July 2002

Strain–size evaluations from diffraction line broadening for MgO ceramic materials have been compared using single-line integral-breadth and Rietveld procedures with the Voigt function. Diffraction data were measured by Bragg–Brentano X-ray diffractometry (XRD), without incident beam monochromatization, and neutron diffractometry (ND) to encompass near-surface and bulk effects, respectively. The specimens consisted of sets of MgO ceramics and MgO–Y2O3ceramic composites sintered over a range of temperatures. An MgO ceramic sintered at 1723 K for 2 h exhibited slightly less XRD broadening than the standard LaB6NIST 660 SRM, and was therefore selected to make instrument profile corrections for both XRD and ND data. It was found for both data types that: (a) sintering initially relieves residual strain present in the MgO powder used to sinter the ceramics and also promotes grain growth; (b) residual strain of the MgO ceramic minimizes as the sintering temperature increases, and then increases with further rise in the sintering temperature, presumably as a result of intragranular interactions associated with grain growth; and (c) introduction of the second phase (Y2O3) increases strain and inhibits crystal growth. The single-line and Rietveld methods gave similar strain values from both the XRD and ND data within the limits of experimental error, but there were substantial differences between the single-line and Rietveld size estimates determined with the XRD and ND data.
Mallard's law recast as a Diophantine system: fast and complete enumeration of possible twin laws by [reticular] [pseudo] merohedry
Authors: Le Page Y.
Published: July 2002

Mallard's law of observation states that known twins by reticular pseudomerohedry have low twin indexmand low obliquity δ between a lattice row and a lattice plane. Crystals in the twin are related by exact reflection in the lattice plane, exact rotation by π about the perpendicular to the lattice plane, or by exact rotation about the lattice row by 2kπ/q, withq= 2, 3, 4 or 6, and 1 ≤k<q. In known cases,mis up to five or six, and δ is up to five or six degrees. Mallard's converse problem is then about finding all pairs of indices for rows and planes leading to twin indices not larger thanmand to obliquities that are at most δ. Mallard's law is recast as the Diophantine pair constituted by the equalityh · u=nand the inequality |h × u| <n tan δ. If a primitive reference system is used, the integernis eitherm, 2mor 3m. A direct general solution of this system forugivenn,h, δ and lattice data is detailed. That straightforward solution involves a tiny two-dimensional grid foru, considerably reducing the number of permutations to be considered. If the primitive reference system is Buerger-reduced, then moduli for indices of solutionshcannot exceed 3m, thus establishing a simple way to produce complete solutions. A program calledOBLIQUEwas designed on such principles. An implementation is available for free execution at http://ylp.icpet.nrc.ca/oblique/.OBLIQUEis also an interactive tool in Toth Information Systems'Materials Toolkit(http://www.tothcanada.com/), an exploitation framework currently operating on CRYSTMET and ICSD crystal structure data. The example of quartz cell data is described withmmax= 3 and δmax= 6°.
Abinitiostructure determination of triphenyl phosphite by powder synchrotron X-ray diffraction
Authors: Hernandez Olivier , Hédoux Alain , Lefebvre Jacques , Guinet Yannick , Descamps Marc , Papoular Robert , Masson Olivier
Published: July 2002

The crystal structure of the glass-forming molecular liquid triphenyl phosphite [TPP, P(OC6H5)3, six torsional degrees of freedom] has been solvedab initioat 110 K from powder synchrotron X-ray diffraction data by real-space methods (simulated annealing) followed by rigid-body Rietveld refinements. The symmetry is trigonal, with a rhombohedral lattice, space group R\bar{3}. The associated hexagonal cell, which is a sixfold multiple of the previously published less-symmetric monoclinic cell [Hédouxet al.(1999).Phys. Rev. B,60, 9390–9395], is unusually large [V= 7075.7 (4) Å3,Z= 18] and displays a noteworthy platelet-like shape [a= 37.766 (1) andc= 5.7286 (2) Å]. The TPP molecule does not exhibit the idealC3symmetric propeller shape, its conformation being on the contrary almost mirror-symmetric, with the pseudo-mirror plane passing through the P—O1 bond and two carbon atoms inparaposition with respect to the O1 atom. The hitherto unknown topological features of crystalline TPP, including unusual intermolecular weak C—H...O hydrogen-bonding networks, are presented and discussed in the scope of the `glacial state' problem.
Background subtraction and moments of the microscopic density fluctuation
Authors: Sobry Roger , Ciccariello Salvino
Published: July 2002

Some models of microscopic density fluctuations are numerically analysed in order to study the behaviour of the related background contribution. The results suggest that this contribution can be described by an algebraic expression depending on only the moments of the microscopic density fluctuation. In this way, the parameter values, determined by a best-fit procedure to account for background contributions in the case of real samples, acquire a definite physical meaning. The procedure is applied to the small-angle X-ray intensities of a polymer sample analysed at different temperatures and yields satisfactory results.
A new film instrument for the exploration of reciprocal space
Authors: Wölfel E. R.
Published: July 2002

A new film instrument has been built which permits exploration and undistorted photography of nearly all of reciprocal space with a single mounting of the crystal. To accomplish this both the Buerger precession and the de Jong–Bouman arrangements are combined in the one instrument. The principles, technique for optimum use, and some applications of the instrument are described.
Profile separation in complex powder patterns
Authors: Naidu S. V. N. , Houska C. R.
Published: July 2002

Diffraction patterns from multi-element alloys, composite materials, enriched ores and other materials involving a mix of several phases often contain regions of overlapping diffraction peaks. In many cases, the peaks can be separated by a combination of numerical differentiation of the data and non-linear least-squares curve-fitting techniques. The derivative provides a powerful but simple technique for distinguishing the number of peaks and their locations within a scramble. These results are required as input to a least-squares curve-fitting routine. The end result of this two-step procedure is a set of parameters that define the positions, shape, width and areas of the separate peaks. A statistical analysis of the data requirements indicates that a good second derivative can be obtained with a peak count in the ~ 105 range using raw data, and the ~ 104 range with digital smoothing. The use of less accurate analog scans is also discussed. Examples are given with overlapping peaks in a 2θ range of less than 1° . The theoretical results describing the data requirements, resolution, distortion effects, and peak enhancement are based upon a Pearson VII function which is capable of describing all shapes continuously between the Cauchy, modified Lorentzian and the Gaussian.
Laue photography of fine crystalline particles
Authors: Steinberger I. T. , Asaf U. , Graeff W. , Kalman Z. H.
Published: July 2002

An experimental method is described for the determination of crystallite dimensions in polycrystalline materials. It is based on studying the geometry of streaks that appear in powder photographs taken with white X-ray radiation. A detailed analysis is presented that includes a differentiation between these streaks and somewhat similar streaks due to asterism. Results by synchrotron radiation from powder samples of various materials are discussed and compared with the crystallite dimensions obtained by other methods. It is demonstrated that the method is largely complementary to measurements by electron microscopy and that it is particularly useful for the determination of the thickness distribution of thin (0.005–0.5 μm) platelets, oriented parallel to the substrate.
Kα2 elimination algorithm for Cu, Co and Cr radiations
Authors: Platbrood G.
Published: July 2002

It is well known that the extraneous Kα
2 line complicates the interpretation of X-ray diffraction spectra. Experience has shown that the arms and weights calculated by Ladell's method [Laddell, Parrish & Taylor (1959). Acta Cryst. 12, 561–567] have to be determined for each user's X-ray diffractometer, rather than using the published coefficients, for an accurate Kα
2 elimination. When different materials are analyzed, the signal/noise ratio can be optimized by choosing a suitable target material. Kα
2 correction coefficients have been calculated for Cu, Co and Cr radiations using a fast Fourier calculation method.
A new optical method and apparatus `HAUP' for measuring simultaneously optical activity and birefringence of crystals. I. Principles and construction
Authors: Kobayashi J. , Uesu Y.
Published: July 2002

A new and accurate method has been developed by which all the components of the anisotropy of the optical susceptibilities can be determined. The apparatus based on this method has been constructed, and named as HAUP (High-Accuracy Universal Polarimeter). The basic principle is to measure the intensity of the light beam, which is propagated successively through a polarizer, a specimen, and an analyser, as functions of azimuth and deflecting angle from the crossed-Nicols condition. Thus the method is characterized by its extreme simplicity, which prevents systematic errors. Considerations and tests of inevitable systematic errors are made. The systematic errors originating in the parasitic ellipticities of the polarizer and analyser are found to be serious for the measurements of optical activity; appropriate solutions to remove them are devised here. Sensitivities of measurements of optical activity and birefringence by the HAUP method reach 4.8 × 10−8 and 2.2 × 10−6 respectively, the accuracy being 4.2 × 10−3 and 2.2 × 10−3 respectively. By using HAUP it has become possible to measure simultaneously all the components of optical activity, birefringence and rotation of optical indicatrix of any crystals, including those belonging to the monoclinic and triclinic systems. These measurements can be made from about 400 K down to 10 K. Also, simultaneous determinations of electrogyration and electrooptic coefficients have become feasible by applying electric fields to crystals.
Oscillation photography of radiation-sensitive crystals using a synchrotron source
Authors: Rossmann M. G. , Erickson J. W.
Published: July 2002

A method is described to determine the accurate setting of a crystal placed in an unknown orientation on an oscillation camera. This avoids time-consuming setting operations during which the crystal is subject to continuous radiation damage initiated by the first setting photograph. It also ensures maximal use of synchrotron radiation time as there is no need for any prior setting and developing periods. The method is dependent on measuring the lengths and orientations of the major axes of the ellipses on two, preferably approximately orthogonal, `still' photographs.
Four-circle angle calculations for surface diffraction
Authors: Mochrie S. G. J.
Published: July 2002

It is shown how the angles of incidence and exit may be controlled in a surface diffraction experiment using a four-circle diffractometer. The procedure may be readily incorporated into existing diffractometer control programs.
X-ray powder spectroscopy to determine easy axis in colloidal magnetic particles
Authors: Briggs E. , Nunes A. C.
Published: July 2002

Non-interacting suspended colloidal single-domain magnetic particles can be expected to acquire a preferred orientation in a magnetic field. Their direction is determined by the easy magnetization axes of the particle and the applied field to a degree determined by the Langevin equation governing paramagnetic phenomena. The magnitudes of resulting changes in powder line intensities have been calculated and found to be of the order of 5 to 25% for ferrite particles near the critical size (where anisotropy energy ≥ kT), the larger for larger particles. The pattern of line intensity changes allows one to distinguish between (1,0,0) and (1,1,1) easy axes.
Optical transforms of disordered systems displaying diffuse intensity loci
Authors: Welberry T. R. , Withers R. L.
Published: July 2002

A method is described of synthesizing a real-space distribution of scattering points which will give rise to virtually any required diffraction pattern. The distribution may be used in the form of an optical diffraction screen to give an immediate visual check on both the real-space and reciprocal-space distributions. The method is applied to two examples which exhibit electron diffraction patterns with diffuse intensity distributed in the form of complex loci in reciprocal space: certain transition-metal niobium sulfide intercalates in which ordering of metal ions and vacancies occurs; and the high-temperature phase of 1T tantalum disulfide in which phenomena due to charge-density waves (CDW) and accompanying periodic lattice distortions (PLD) are observed. It is shown how useful statistical information concerning the local ordering may be obtained from the resulting lattice realizations.
The primitive function for slit-height desmearing in SAXS
Authors: Deutsch M. , Luban M.
Published: July 2002

The recursive method of Schmidt & Fedorov [J. Appl. Cryst. (1978). 11, 411–416] allows for calculation of the correction function g(t) for slit-height smearing in terms of the slit transmission function f(t). In this method, if the primitive function g(t) = g
0(t) is known for the interval 0 ≤ t ≤ t
0, then g(t) = gn
(t) can be calculated recursively, for the intervals n
½
t
0 ≤ t ≤ (n + 1)½
t
0. A general method is presented for calculating g
0(t) in powers of t. To illustrate the utility of our method, three numerical examples are examined, indicating rapid convergence to a level of accuracy of 1 in 106.
A powder diffractometer for a synchrotron source
Authors: Sabine T. M.
Published: July 2002

A design is given for a powder diffractometer on a synchrotron source. A reasonable balance between resolution and luminosity is achieved by making the effective mosaic spread parameters of the monochromator and analyser crystal equal to the vertical divergence of the synchrotron beam. A monochromator with a Bragg angle of 60° should be used. Care is necessary in preparing specimens for data collection to avoid the hazards of particle-size broadening on one hand and extinction on the other. The conclusions are compared with recent experimental work.
Crystal data for p-chloroiodobenzene and p-bromochlorobenzene/p-chloroiodobenzene mixed crystals at 293 K
Authors: Alcobé X. , Estop E. , Haget Y. , Cuevas M. A. , Labrador M. , Calvet T. , Tauler E.
Published: July 2002

The powder data for p-chloroiodobenzene and p-bromochlorobenzene/p-chloroiodobenzene mixed crystals [pBCB]
x
[pCIB]1 − x
at 293 K are reported; their stability at 293 K is given. The cell dimensions have been refined by least squares from accurate powder diffractometer data recorded at T = 293 (1) K (quartz as internal standard). Vertical diffractometer, graphite monochromator, Cu Kα
1−Cu Kα
2 correction so that λ = 1.54056 Å. They are all isomorphous, monoclinic, P21/a with Z = 2. a = 15.818(4), b = 5.912(2), c = 4.214(2) Å, β = 113.61(1)°, V = 361.1 Å3, Dx
= 2.193 Mg m−3 for pCIB; JCPDS No. 37–2000. a = 15.210(5), b = 5.860(3), c = 4.091(2) Å, β = 112.64(2)°, V = 336.5 Å3, Dx
= 1.936 Mg m−3 for [pBCB]0.90[pCIB]0.10; JCPDS No. 37–1989. a = 15.287(6), b = 5.870(3), c = 4.111(2) Å, β = 112.78(2)°, V = 340.1 Å3, Dx
= 1.961 Mg m−3 for [pBCB]0.80[pCIB]0.20; JCPDS No. 37–1990. a = 15.360(5), b = 5.880(2), c = 4.126(1) Å, β = 112.87(2)°, V = 343.3 Å3, Dx
= 1.988 Mg m−3 for [pBCB]0.70[pCIB]0.30; JCPDS No. 37–1991. a = 15.424(5), b = 5.889(3), c = 4.137(2) Å, β = 112.99(2)°, V = 346.0 Å3, Dx
= 2.018 Mg m−3 for [pBCB]0.60[pCIB]0.40; JCPDS No. 37–1992. a = 15.493(4), b = 5.896(2), c = 4.155(2) Å, β = 113.09(2)°, V= 349.1 Å3, Dx
= 2.045 Mg m−3 for [pBCB]0.50[pCIB]0.50; JCPDS No. 37–1993. a = 15.566(5), b = 5.901(3), c = 4.168(2) Å, β = 113.20(2)°, V = 351.9 Å3, Dx
= 2.073 Mg m−3 for [pBCB]0.40[pCIB]0.60; JCPDS No. 37–1994. a = 15.623(5), b = 5.904(3), c = 4.178(3) Å, β = 113.26(2), V = 354.0 Å3, Dx
= 2.105 Mg m−3 for [pBCB]0.30[pCIB]0.70; JCPDS No. 37–1995. a = 15.691(4), b = 5.913(3), c = 4.195(2)Å, β = 113.43(2)°, V = 357.1 Å3, Dx
= 2.130 Mg m−3 for [pBCB]0.20[pCIB]0.80; JCPDS No. 37–1996. a = 15.759(4), b = 5.906(2), c = 4.204(2) Å, β = 113.55(2)°, V = 358.7 Å3, Dx
= 2.164 Mg m−3 for [pBCB]0.10[pCIB]0.90; JCPDS No. 37–1999.
Integration of Bragg reflections with an Anger camera area detector
Authors: Wilkinson C. , Schultz A. J.
Published: July 2002

A variable-size `box' method is described which optimizes the precision with which integrated intensities of neutron Bragg reflections are measured with an Anger camera. The consequent improvements in the least-squares-fitted crystallographic structural parameters and R-factors in test experiments on MnF2 and Cr3Si are substantial.
Orientational disorder in ammonium chloride: elastic diffuse neutron scattering with a new technique
Authors: Born R. , Hohlwein D. , Eckold G.
Published: July 2002

Elastic diffuse neutron scattering intensity due to orientational disorder in ND4Cl at room temperature, space group Pm3m, is studied with a single crystal. By a novel `vertical' energy analysis on the one hand and the `flat-cone' technique on the other, the intensity is obtained in a large three-dimensional region of reciprocal space in a reasonable time. The data are analysed with short-range-order and interaction-potential parameters. The two parameter sets are consistent. Local chlorine displacements of 0.16 Å, along 〈111〉 directions are determined.
Easy derivation of the formula relating the fluctuations of a binary system to the X-ray scattering intensity extrapolated to s = 0
Authors: Hayashi H. , Nishikawa K. , Iijima T.
Published: July 2002

Bhatia & Thornton [Phys. Rev. B. (1970), 2, 3004–3012] have derived the formula that relates the scattering intensity of a binary system to the Fourier transform of the local number density and concentration. For the intensity at the limit of zero scattering angle, the same formula can be derived by a much simpler process.
High-pressure single-crystal study on AlPO4 with synchrotron radiation
Authors: Sowa H. , Reithmayer K. , Macavei J. , Rieck W. , Schulz H. , Kupčik V.
Published: July 2002

A single-crystal study on AlPO4 was performed at 2.90 (7) GPa with synchrotron radiation using a diamond-anvil cell with a beryllium gasket. For the data collection the radiation wavelength of only 0.54 Å, was chosen to minimize the absorption of X-rays in the pressure cell. The diffracted intensity was high enough to measure even weak reflections with sufficient counting statistics. The refined structural parameters are in good agreement with those determined from data collected with a conventional X-ray tube.
Characterization of a chromia–alumina catalyst using small-angle neutron scattering
Authors: Acharya D. R. , Crowley T. L. , Hughes R. , Koon C. L. , Menendez M. , Rieutord F.
Published: July 2002

Neutron scattering has been employed to study the pore structure of a chromia–alumina catalyst. The results indicated the existence of three distinct scattering regimes with distinct slopes corresponding to the values of the wavevector, Q. The analysis of the scattering in these regions suggested that the large-Q region corresponds to Porod's law scattering and provides information on the specific surface area. The intermediate Q region arises from scattering from hollow capillaries and provides information on the dimension of the capillaries. The small-Q behaviour arises from the relative spatial arrangement of capillaries, which appear to form a `fractal' network.
A furnace for in situ synchrotron Laue diffraction and its application to studies of solid-state phase transformations
Authors: Bhat H. L. , Clark S. M. , El Korashy A. , Roberts K. J.
Published: July 2002

The design of a new microfurnace for use for Laue diffraction studies of solid-state transformations is described. The furnace operates in the temperature range 298–573 K with a thermal stability of about ± 0.1 K. The potential of the synchrotron-radiation Laue diffraction technique for studies of structural phase transitions is demonstrated. Experimental data on phase transitions in caesium periodate, potassium tetrachlorozincate and pentaerythritol are presented.
Short-range-order determination in quenched NbC0.73 by elastic diffuse neutron scattering
Authors: Beuneu B. , Priem T. , de Novion C. H. , Lefebvre S. , Chevrier J. , Christensen A. N.
Published: July 2002

The elastic diffuse neutron scattering of an NbC0.73 single-crystal has been measured at room temperature on two different spectrometers, the four-circle D10 at the HFR–ILL (Grenoble), and the two-axis G44 with time-of-flight analysis at the Laboratoire Léon Brillouin (Saclay). The data were treated either by Fourier transformations or by least-squares fit. The short-range-order parameters and the interatomic static displacements obtained by the various experiments and/or data treatment are in good agreement: carbon vacancies tend to be third neighbours in the f.c.c. metalloid sublattice and metal atoms relax away from the vacancy first neighbours by ~0.05 Å. It is shown that the treatment of diffuse scattering data limited to two reciprocal planes [(001) and (1{\bar 1}0)] gives satisfactory results.
Absolute polarity of α-lithium iodate. Erratum
Authors: Abrahams S. C. , Liminga R. , Albertsson J.
Published: July 2002

A typsetting error in the paper by Abrahams, Liminga & Albertsson [J. Appl. Cryst. (1990). 23, 211–222] is corrected. On page 212, the first sentence of the second paragraph should read: However, the Miller indices given by Rosenzweig & Morosin's (1966) coordinates result in an opposite sense assignment for the polar c-axis direction and Yang Hua-guang et al. (1989) hence confused (hk.l) with ({\bar h}{\bar k}.{\bar l}).
Valence-contrast studies by resonant diffraction with synchrotron radiation; the rôle of X-ray absorption measurements
Authors: Wilkinson A. P. , Cheetham A. K.
Published: July 2002

The X-ray absorption spectra of GaCl2, GaAlCl4 and GaCl3 have been measured in the vicinity of the Ga K edge and values of f′′ and f′ estimated for GaI and GaIII from the latter two spectra by using the optical theorem and the Kramers–Kronig relation. The resulting f′ values are compared with those previously determined from anomalous-scattering measurements with synchrotron X-rays on the compound GaCl2 [Wilkinson, Cheetham & Cox (1991). Acta Cryst. B47, 155–161] and found to be in good agreement. The use of anomalous scattering methods for distinguishing oxidation states is discussed in the light of these results and others found in the literature.