bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of a Calmodulin-Regulated Ca2+-ATPase in the Endoplasmic Reticulum1
Authors: Hong Bimei , Ichida Audrey , Wang Yuwen , Scott Gens J. , Pickard Barbara G. , Harper Jeffrey F.
Published: July 2002

A unique subfamily of calmodulin-dependent Ca2+-ATPases was recently identified in plants. In contrast to the most closely related pumps in animals, plasma membrane-type Ca2+-ATPases, members of this new subfamily are distinguished by a calmodulin-regulated autoinhibitor located at the N-terminal instead of a C-terminal end. In addition, at least some isoforms appear to reside in non-plasma membrane locations. To begin delineating their functions, we investigated the subcellular localization of isoform ACA2p (ArabidopsisCa2+-ATPase, isoform 2 protein) in Arabidopsis. Here we provide evidence that ACA2p resides in the endoplasmic reticulum (ER). In buoyant density sucrose gradients performed with and without Mg2+, ACA2p cofractionated with an ER membrane marker and a typical “ER-type” Ca2+-ATPase, ACA3p/ECA1p. To visualize its subcellular localization, ACA2p was tagged with a green fluorescence protein at its C terminus (ACA2-GFPp) and expressed in transgenic Arabidopsis. We collected fluorescence images from live root cells using confocal and computational optical-sectioning microscopy. ACA2-GFPp appeared as a fluorescent reticulum, consistent with an ER location. In addition, we observed strong fluorescence around the nuclei of mature epidermal cells, which is consistent with the hypothesis that ACA2p may also function in the nuclear envelope. An ER location makes ACA2p distinct from all other calmodulin-regulated pumps identified in plants or animals.
Iron-Superoxide Dismutase Expression in Transgenic Alfalfa Increases Winter Survival without a Detectable Increase in Photosynthetic Oxidative Stress Tolerance
Authors: McKersie Bryan D. , Murnaghan Julia , Jones Kim S. , Bowley Stephen R.
Published: July 2002

To determine whether overexpression of Fe-superoxide (SOD) dismutase would increase superoxide-scavenging capacity and thereby improve the winter survival of transgenic alfalfa (Medicago sativa L.) plants, two genotypes were transformed with the vector pEXSOD10, which contains a cDNA for Arabidopsis Fe-SOD with a chloroplast transit peptide and cauliflower mosaic virus 35S promoter. A novel Fe-SOD was detected by native PAGE in both greenhouse- and field-grown transgenic plants, but activity varied among independent transgenic plants. The increased Fe-SOD activity was associated with increased winter survival over 2 years in field trials, but not with oxidative stress tolerance as measured by resistance of leaves to methyl viologen, a superoxide generator. Total shoot dry matter production over 2 harvest years was not associated with Fe-SOD activity. There was no detectable difference in the pattern of primary freezing injury, as shown by vital staining, nor was there additional accumulation of carbohydrates in field-acclimated roots of the transgenic alfalfa plants. We did not detect any difference in growth of one transgenic plant with high Fe-SOD activity compared with a non-transgenic control. Therefore, the improvement in winter survival did not appear to be a consequence of improved oxidative stress tolerance associated with photosynthesis, nor was it a consequence of a change in primary freezing injury. We suggest that Fe-SOD overexpression reduced secondary injury symptoms and thereby enhanced recovery from stresses experienced during winter.
Cryo-Scanning Electron Microscopy Observations of Vessel Content during Transpiration in Walnut Petioles. Facts or Artifacts?
Authors: Cochard Hervé , Bodet Christian , Améglio Thierry , Cruiziat Pierre
Published: July 2002

The current controversy about the “cohesion-tension” of water ascent in plants arises from the recent cryo-scanning electron microscopy (cryo-SEM) observations of xylem vessels content by Canny and coworkers (1995). On the basis of these observations it has been claimed that vessels were emptying and refilling during active transpiration in direct contradiction to the previous theory. In this study we compared the cryo-SEM data with the standard hydraulic approach on walnut (Juglans regia) petioles. The results of the two techniques were in clear conflict and could not both be right. Cryo-SEM observations of walnut petioles frozen intact on the tree in a bath of liquid nitrogen (LN2) suggested that vessel cavitation was occurring and reversing itself on a diurnal basis. Up to 30% of the vessels were embolized at midday. In contrast, the percentage of loss of hydraulic conductance (PLC) of excised petiole segments remained close to 0% throughout the day. To find out which technique was erroneous we first analyzed the possibility that PLC values were rapidly returned to zero when the xylem pressures were released. We used the centrifugal force to measure the xylem conductance of petiole segments exposed to very negative pressures and established the relevance of this technique. We then analyzed the possibility that vessels were becoming partially air-filled when exposed to LN2. Cryo-SEM observations of petiole segments frozen shortly after their xylem pressure was returned to atmospheric values agreed entirely with the PLC values. We confirmed, with water-filled capillary tubes exposed to a large centrifugal force, that it was not possible to freeze intact their content with LN2. We concluded that partially air-filled conduits were artifacts of the cryo-SEM technique in our study. We believe that the cryo-SEM observations published recently should probably be reconsidered in the light of our results before they may be used as arguments against the cohesion-tension theory.
A Terminal Flower1-Like Gene from Perennial Ryegrass Involved in Floral Transition and Axillary Meristem Identity
Authors: Jensen Christian S. , Salchert Klaus , Nielsen Klaus K.
Published: July 2002

Control of flowering and the regulation of plant architecture have been thoroughly investigated in a number of well-studied dicot plants such as Arabidopsis, Antirrhinum, and tobacco. However, in many important monocot seed crops, molecular information on plant reproduction is still limited. To investigate the regulation of meristem identity and the control of floral transition in perennial ryegrass (Lolium perenne) we isolated a ryegrassTERMINAL FLOWER1-like gene, LpTFL1, and characterized it for its function in ryegrass flower development. Perennial ryegrass requires a cold treatment of at least 12 weeks to induce flowering. During this period a decrease inLpTFL1 message was detected in the ryegrass apex. However, upon subsequent induction with elevated temperatures and long-day photoperiods, LpTFL1 message levels increased and reached a maximum when the ryegrass apex has formed visible spikelets. Arabidopsis plants overexpressing LpTFL1 were significantly delayed in flowering and exhibited dramatic changes in architecture such as extensive lateral branching, increased growth of all vegetative organs, and a highly increased trichome production. Furthermore, overexpression of LpTFL1 was able to complement the phenotype of the severe tfl1-14 mutant of Arabidopsis. Analysis of the LpTFL1 promoter fused to the UidA gene in Arabidopsis revealed that the promoter is active in axillary meristems, but not the apical meristem. Therefore, we suggest that LpTFL1 is a repressor of flowering and a controller of axillary meristem identity in ryegrass.
Salt-Induced Expression of the Vacuolar H+-ATPase in the Common Ice Plant Is Developmentally Controlled and Tissue Specific
Authors: Golldack Dortje , Dietz Karl-Josef
Published: July 2002

For salinity stress tolerance in plants, the vacuolar type H+-ATPase (V-ATPase) is of prime importance in energizing sodium sequestration into the central vacuole and it is known to respond to salt stress with increased expression and enzyme activity. In this work we provide information that the expressional response to salinity of the V-ATPase is regulated tissue and cell specifically under developmental control in the facultative halophyte common ice plant (Mesembryanthemum crystallinum). By transcript analysis of subunit E of the V-ATPase, amounts did not change in response to salinity stress in juvenile plants that are not salt-tolerant. In a converse manner, in halotolerant mature plants the transcript levels increased in leaves, but not in roots when salt stressed for 72 h. By in situ hybridizations and immunocytological protein analysis, subunit E was shown to be synthesized in all cell types. During salt stress, signal intensity declined in root cortex cells and in the cells of the root vascular cylinder. In salt-stressed leaves of mature plants, the strongest signals were localized surrounding the vasculature. Within control cells and with highest abundance in mesophyll cells of salt-treated leaves, accumulation of subunit E protein was observed in the cytoplasm, indicating its presence not only in the tonoplast, but also in other endoplasmic compartments.
Improvement of SAXS measurements on Kratky slit systems by Göbel mirrors and imaging-plate detectors
Authors: Bergmann Alexander , Orthaber Doris , Scherf Günther , Glatter Otto
Published: July 2002

Laboratory X-ray sources emit a highly divergent beam. The Kratky compact camera is constructed to maximize the intensity in the sample using a slit collimation system. The performance of this camera can be further increased if the primary beam is collimated from a divergent into a parallel beam. A recently developed device for this purpose is the so-called `Göbel mirror'. This mirror is made of parabolically bent multilayers, designed to collimate divergent X-rays from laboratory X-ray sources into a parallel and monochromatic beam of high brilliance. Modification of the block collimation system in combination with a Göbel mirror leads to a different beam geometry, resulting in an intensity increase by a factor of about 10. The gain in intensity implicates the use of imaging-plate detectors, which have a wide linear range in intensity and allow the full use of the increased intensity. Hence the quality of the SAXS data is improved by the higher intensity primary beam, the much lower background due to the exclusive use of CuKα radiation, and a detection unit which is linear in the measured intensity regime. All these advantages, such as intensity gain, lower background, better quality of the data, are demonstrated with some selected experimental results.
sasCIF: an extension of core Crystallographic Information File for SAS
Authors: Malfois M. , Svergun D.I.
Published: July 2002

Data acquisition packages developed at different small angle scattering facilities use different formats both for raw and processed data storage. To facilitate the data exchange between laboratories, a consensus in the small angle scattering community has been reached on an ASCII format for one-dimensional data which includes a self-describing header containing relevant information about the sample and instrumental conditions followed by raw or reduced data in a tabular form. This format called sasCIF was implemented as an extension of core CIF (Crystallographic Information File) dictionary.
Birefringence imaging of phase transitions: application to Na0.5Bi0.5TiO3
Authors: Geday M. , Kreisel J. , Glazer A. M. , Roleder K.
Published: July 2002

In recent years a number of imaging techniques to determine the optical properties of materials, either in reflection or in transmission, have been developed. Here the use of an imaging version of the so-called rotating-polarizer method in the study of phase transformations in crystals is demonstrated. This method creates false-coloured images representing the light transmissionI0, the extinction angle φ (orientationof the optical indicatrix) and |sin δ|, a function of the retardation resulting from the birefringence (and a measure of themagnitudeof optical anisotropy). When combined with a computer-controlled heating stage, this method provides an opportunity to createseparatemoving images oforientationandmagnitudeof optical anisotropy, showing the dynamics of twinning and domain-wall behaviour during temperature changes. It is believed that this is the first time that quantitative imaging of changes in birefringence has been used in this way to describe phase transitions. Two-phase transitions in a crystal of Na0.5Bi0.5TiO3(NBT) are presented as examples of the use of the system.
X-ray topographic determination of the granular structure in a graphite mosaic crystal: a three-dimensional reconstruction
Authors: Ohler M. , Sanchez del Rio M. , Tuffanelli A. , Gambaccini M. , Taibi A. , Fantini A. , Pareschi G.
Published: July 2002

Section topographs recorded at different spatial locations and at different rocking angles of a highly oriented pyrolytic graphite (HOPG) crystal allow three-dimensional maps of the local angular-dependent scattering power to be obtained. This is performed with a direct reconstruction from the intensity distribution on such topographs. The maps allow the extraction of information on local structural parameters such as size, form and internal mosaic spread of crystalline domains. This data analysis leads to a new method for the characterization of mosaic crystals. Perspectives and limits of applicability of this method are discussed.
X-ray diffraction from perfect silicon crystals distorted by surface acoustic waves
Authors: Tucoulou R. , Pascal R. , Brunel M. , Mathon O. , Roshchupkin D. V. , Schelokov I. A. , Cattan E. , Remiens D.
Published: July 2002

High-resolution X-ray diffraction measurements were carried out on ZnO/Si devices under surface acoustic wave excitation and revealed some very clear satellite diffraction peaks that are obtained from the sinusoidal modulation of the near-surface region. This experiment shows that the propagation of a Rayleigh surface acoustic wave in a perfect crystal acts as a dynamical diffraction grating. The variation of the acoustic velocity has been followed across the crystal surface from the acoustic source region (beneath the ZnO film) to the far field region (not covered by the ZnO film).
X-ray determination of dislocation density and arrangement in plastically deformed copper
Authors: Breuer D. , Klimanek P. , Pantleon W.
Published: July 2002

Using the kinematical theory of X-ray scattering by crystals with dislocations as developed by Krivoglazet al.and Wilkens, the dislocation content of compressed copper single and polycrystals was investigated by means of profile analysis of selected diffraction peaks. Measurements of radial intensity distributionsI(2θ) were performed with a double-crystal spectrometer in the case of the single crystals and with conventional polycrystal diffractometers in the case of the polycrystals. Additionally, the misorientations Θ occurring within the dislocation cell structure because of the accumulation of excess dislocations of one sign were investigated by means of rocking curves of the single-crystal reflections and by evaluation of electron backscattering patterns (EBSPs). Within a wide deformation range, the mean total dislocation density ρdcan be related well to the flow stressviathe Taylor relationship. Assuming a random distribution of the misorientations Θ between adjacent dislocation cells, the evaluation of the rocking curves gives mean values 〈|Θ|〉 much smaller than those determined by EBSP analysis. For this reason, a model of a dislocation cell structure with restrictedly correlated misorientations, which leads to better agreement of the X-ray and the EBSP data, is proposed.
X-ray diffraction line broadening from thermally deposited gold films
Authors: Cheary R. W. , Dooryhee E. , Lynch P. , Armstrong N. , Dligatch S.
Published: July 2002

Diffraction profiles were analysed from thermally deposited 111-oriented gold films, ranging in thickness from 300 to 1900 Å. The data were collected using the high-resolution powder diffractometer on beamline BM16 at the European Synchrotron Research Facility (ESRF) set at a wavelength of 0.3507 Å. The profiles were measured under conventional symmetric θ–2θ reflection conditions and by asymmetric transmission diffraction to ensure that only crystallites oriented normal to the substrate contribute to the diffraction. An analysis of the instrument profile shape of the diffractometer was undertaken using the SRM 660 LaB6line profile standard. A parallel study of the films using atomic force microscopy and transmission electron microscopy was also undertaken to provide information on the dimensions of the crystallite columns in the films and the presence of dislocations. All the films displayed diffraction broadening arising from both crystallite-size effects and dislocation-induced strain effects. Analysis of the magnitude and anisotropy of the dislocation-induced broadening withhklindicates that the dislocations have a mixed screw/edge character and tend to form primarily on (111) slip planes parallel to the substrate at densities of ∼1015to 1016 m−2.
CHOOCH: a program for deriving anomalous-scattering factors from X-ray fluorescence spectra
Authors: Evans Gwyndaf , Pettifer Robert F.
Published: July 2002

A Fortran programCHOOCH, which derives experimental values of the anomalous-scattering factorsf′′ andf′ from X-ray fluorescence spectra, is described. The program assumes knowledge of theoretical values for the imaginary term,f′′, of the anomalous-scattering factor away from the absorption edge to scale the experimental fluorescence spectrum and thus derive values off′′ near the absorption edge, where tabular data are inappropriate. The Kramers–Kronig relation is used to calculate the real part,f′, of the anomalous-scattering factor. The program aids the decision-making process in macromolecular crystallographic experiments where optimal wavelength selection is required. Magnitudes off′ andf′′ at selected wavelengths can later be used as starting values for heavy-atom refinement with crystallographic phasing programs.
Clear strategy screens for macromolecular crystallization
Authors: Brzozowski Andrzej Marek , Walton Julia
Published: July 2002

The development of high-throughput crystallography combined with the wealth of already accumulated information about protein crystallization properties requires constant revision of current crystallization screening procedures. Two complementary 6 × 4 matrix `clear strategy screens' (CSS) have been developed and tested on a number of previously non-crystallized proteins. The screens yielded diffraction-quality crystals of a wide range of proteins (enzymes, transcription factors, structural proteins,etc.) in cases where the applications of commercially available screens were unsuccessful. Both their inherently simple design and their flexible nature provide an experimenter with a logical platform for further modification and optimization. Furthermore, the screens facilitate cryoprotection and potential incorporation of anomalous scatterers for multiple/single-wavelength anomalous dispersion (MAD/SAD) experiments.
A perdeuterated cryoprotectant for neutron studies and a demonstration of its use for neutron powder diffraction onL-(−)-ephedrine hemihydrate
Authors: Krebs Frederik C. , Jørgensen Mikkel , Lebech Bente , Frydenvang Karla
Published: July 2002

The use of perdeuteropolyethylpropylene (d-PEP) as a cryoprotectant for neutron studies of molecular organic solids is demonstrated by the solution of the structure of L-(−)-ephedrine hemihydrate from neutron powder diffraction data on a sample containing 20 wt% d-PEP. It is demonstrated that no contribution from d-PEP to the scattering is observed. Neutron diffraction studies of solvent-containing molecular crystals that require a perdeuterated cryoprotectant oil are thus possible.
Biosynthetic deuteration of Thermus thermophilus ribosomes for SANS
Authors: Shcherbakova I.V. , Serdyuk I.N.
Published: July 2002

The extreme thermophilic bacterium, Thermus thermophilus, was cultivated in a fully deuterated medium. Two-step adaptation of the strain HB8 Thermus thermophilus to the fully deuterated medium was used. The synthetic medium described by Findling et al. [Findling K.L., Yoshida T., Fee J.A. (1984). J. Biol. Chem.
259, 123–125] was used with ND4Cl as the nitrogen source and deuterated glycerol and succinate as carbon sources. Batch cultivation (maximal optical density of the culture was 1.7 optical units at 590 nm, biomas yield was about 2 g wet cell/L) pr eceded fed-batch cultivation (optical density was about 9 optical units at 590 nm, biomass yield was above 15 g wet cell/L) followed by continuous cultivation. It allowed to obtain deuterated biological material in large quantities. The approach for selective deuteration of RNA component of E.coli ribosomes without reconstitution stage was extended to Thermus thermophilus cultivation. However, the approarch did not produce the results obtained for E.coli. Fully deuterated ribosomes and hybrid ribosomes, where one subunit was protonated and the other one was deuterated, were obtained and their neutron scattering data were collected. The data are useful for interpreting the SANS experiments in the terms of a four-component model of the ribosome at low resolution, which may be a preliminary model to interpret X-ray diffraction data.
A general approach in multilayer optical system design for SAXS
Authors: Jiang L. , Verman B. , Joensen K.D.
Published: July 2002

An approach to using multilayer optics for SAXS is discussed. The approach consists of employing a two-dimensional multilayer focusing optic to monochromatize and intensify the x-ray beam, and a pinhole system to further shape the beam. Depending on the sample scattering power, different pinhole systems can be used. With a two-pinhole system, high flux can be achieved but with nonblocked parasitic scattering from the pinholes and scattering from multilayer reflectors. With a three-pinhole system, parasitic scattering and scattering from multilayer are completely shielded beyond certain angular range for weak scattering samples. Using ray-tracing method, the performances of the proposed systems are compared to the most commonly used graphite-pinhole system and found to provide a factor 10 more flux for similar resolution and background requirements.
Focusing cold neutrons with multiple biconcave lenses for small-angle neutron scattering
Authors: Choi S.-M. , Barker J.G. , Glinka C.J. , Cheng Y.T. , Gammel P.L.
Published: July 2002

The focusing of a cold neutron beam by multiple biconcave lenses has recently been proposed as a practical means of extending the lower limit of Q in conventional, long flight-path small-angle neutron scattering (SANS) instruments. To test the feasibility of this approach, we have carried out extensive measurements on one of the 30 m SANS instruments at NIST of the focusing characteristics of a set of 28 biconcave MgF2 lenses. The focused beam profile has been measured over several orders of magnitude using high resolution neutron auto-radiography. The focusing lens configuration outperforms the pinhole collimation at Q
min lower than 0.004 Å−1. At Q
min = 0.001 Å−1, the intensity gain of the lens configuration over the pinhole collimation is greater than one order of magnitude.
Three-dimensional small-angle neutron scattering (3D-SANS) and its application
Authors: Suzuki J.-I.
Published: July 2002

Three-dimensional small-angle neutron scattering (3D-SANS) analysis is derived. This analysis using neutrons, which can penetrate matter easily, is a powerful technique to investigate the anisotropic nanoscale structures in single crystal bulk materials, although it takes a long time to get a complete data set. This technique is applied to the analysis of the anisotropic neutron scattering from a superconductor CeRu2. It suggests that planar defects correlate well with the lattice symmetry of the crystal and influence superconducting properties as pinning centers. It is also shown by simulation that the 3D-SANS analysis is useful even at intense short pulse spallation sources that give a wider band width of neutron wavelength, if the SANS profile is highly anisotropic.
Temperature dependence of lattice constants of the rare-earth hexaborides EuB6and GdB6
Authors: Takahashi Yasuhiko , Fujimoto Masayoshi , Tsuchiko Masashi , Ohshima Ken-Ichi
Published: July 2002

The temperature dependences of the lattice constants of single crystals of the rare-earth hexaborides EuB6and GdB6were determined by analysing the low-temperature X-ray patterns. The lattice constant decreases monotonously with decreasing temperature. The linear thermal expansion coefficients for the two compounds were also obtained by analysing the temperature dependence of the lattice constants.
Structural and morphological investigation of amorphous hydrogenated silicon carbide
Authors: Prado R. J. , Fantini M. C. A. , Pereyra I. , Odo G. Y. , Lepienski C. M.
Published: July 2002

Amorphous hydrogenated silicon carbide thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) at temperatures ranging from 573 to 623 K, with different concentrations of silane and methane, exploring two deposition parameters: the radio frequency (r.f.) power and the hydrogen dilution. The aim of the work was to induce, predominantly, the formation of Si—C heteronuclear bonds in a homogeneous network. The composition was determined by Rutherford backscattering and the chemical bonding by Fourier transform infrared spectrometry. The local structural order was analyzed by means of extended X-ray absorption fine structure at the SiKedge. The morphology was investigated by small-angle X-ray scattering in order to determine the possible presence of voids in the amorphous matrix. The morphological investigation was completed by transmission electron microscopy. Better-structured films were obtained for a composition close to stoichiometry, grown with an r.f. power of 100 W and with 300 s.c.c.m. (standard cubic centimeter per minute) of hydrogen dilution.
Combination of oils and gels for enhancing the growth of protein crystals
Authors: Moreno Abel , Saridakis Emmanuel , Chayen Naomi E.
Published: July 2002

This note focuses on two different ways of enhancing the use of gels in protein crystallization by applying oils to the trials. Using a five-channel motorized syringe setup, crystals were grown in gelled microbatch drops under oil and compared with those grown under similar conditions in standard microbatch drops. The advantage of this technique over existing gel techniques is that numerous trials can be dispensed automatically, while consuming very small quantities of protein. The application of oil to improve the gel acupuncture technique was also investigated; crystal growth in the presence of an oil barrier was slower than in its absence, giving rise in each case to a single large crystal with no precipitation nor smaller crystals in the capillary.
Direct detection of the protein quaternary structure and denatured entity by small-angle scattering: guanidine hydrochloride denaturation of chaperonin protein GroEL
Authors: Hiragi Yuzuru , Seki Yasutaka , Ichimura Kaoru , Soda Kunitsugu
Published: July 2002

A change in the higher-order structure of an oligomeric protein is directly detectable by small-angle scattering. A small-angle X-ray scattering (SAXS) study of the denaturation process of the chaperonin protein GroEL by guanidine hydrochloride (GdnHCl) showed that the disappearance of the quaternary structure can be monitored by using a Kratky plot of the scattered intensities, demonstrating the advantage of the SAXS method over other indirect methods, such as light scattering, circular dichroism (CD), fluorescence and sedimentation. The collapse of the quaternary structure was detected at a GdnHCl concentration of 0.8 Mfor a solution containing ADP (adenosine diphosphate)/Mg2+(2 mM)/K+. From pairwise plots of the change in forward scattering intensityJ(0)/C(weight-average molecular weight) and thez-average (root mean square) radius of gyration against the GdnHCl concentration, the stability and nature of the denatured protein can be determined. The SAXS results suggest that the GroEL tetradecamer directly dissociates to the unfolded coil without going through a globular monomer state. The denatured ensemble is not a single unfolded monomer coil particle, but some mixture of entangled aggregates and a monomer of the coil molecules. Small-angle scattering is a powerful method for the detection and study of changes in quaternary and higher-order structures of oligomeric proteins.
Use of dry paraffin oil and Panjelly in the xenon derivatization of protein crystals
Authors: Panjikar Santosh , Tucker Paul A.
Published: July 2002

Crystals of porcine pancreatic elastase have been used to demonstrate that cryoprotection using dry paraffin oil or using Panjelly allows, with equal or better efficacy compared with conventional cryoprotectants, derivatization with xenon under a xenon atmosphere prior to shock cooling.
Attainment of near-hydrostatic compression conditions using the Paris–Edinburgh cell
Authors: Marshall William G. , Francis Duncan J.
Published: July 2002

By means of a straightforward modification to the Paris–Edinburgh cell gasket configuration, it is now possible to utilize fluid pressure-transmitting media up to at least 9 GPa. Test data on various representative samples are presented, discussed and contrasted with typical results obtained using the earlier gasket arrangement and Fluorinert pressure-transmitting medium. For the case of deuterated urea, the significant improvement in compression conditions revealed the existence of two new structural phases (IV and V) which are first observed at 3.0 GPa and 7.5 GPa. Future development possibilities for the technique of sample encapsulation are presented and discussed.
Some goemetrical problems related to the rotation camera. II. Dimensions of integration domains for intensity measurements
Authors: Zelwer C. , Taupin D.
Published: July 2002

The dimensions of spot integration domains are generally computed using an expansion scheme that takes account of the effects of the oblique incidences of the incident beam on the crystal and of the diffracted beam on the film. Since large cells result in diffraction spots very close to each other, it is necessary to predict their size accurately in order to avoid both the inclusion of parts of neighbouring spots and the non-inclusion of part of the spot under evaluation. General formulae are given for overall spot sizes in the case of a parallelepipedic crystal having two pairs of faces parallel to the spindle axis of the camera.
An energy-dispersive X-ray diffraction study of mean-square atom displacements in highly oriented pyrolytic graphite
Authors: Metzger T. H.
Published: July 2002

The measurement of the mean-square thermal displacement 〈u
2〉 of carbon atoms in highly oriented pyrolytic graphite (HOPG) in the hexagonal c direction is reported. Energy-dispersive X-ray diffraction (EDXD) has been used to study the integrated intensity of all Bragg reflections 004 through 0′0′14 as a function of temperature. It is demonstrated that the correction of the Bragg intensities due to thermal diffuse scattering contributions is very important for HOPG, when EDXD is used. The Debye temperature ΘD
= 554 (30) K is obtained.
Structural changes associated with solid-state reactions in Al–Ag–Mg alloys
Authors: Cousland S. M. , Tate G. R.
Published: July 2002

The structural changes associated with the precipitation of metastable and equilibrium phases during decomposition of three supersaturated Al-rich Al–Ag–Mg alloys at 393, 456 and 508 K have been established by analysing the diffraction of monochromatic X-radiation by single-crystal alloy plates. Precipitated phases observed were: (a) in the Al–0.54 at.% Ag–4.49 at.% Mg alloy, type 1 Guinier–Preston zones, T′ phase, T phase; (b) in the Al–0.87 at.% Ag–1.80 at.% Mg alloy, type 1 Guinier–Preston zones, type 2 Guinier–Preston zones (a newly observed body-centred tetragonal compound, a = 4.13, c = 8.60 Å, space group I 41/amd), T′ phase, η phase; (c) in the Al–1.30 at.% Ag–1.05 at.% Mg alloy, type 1 Guinier–Preston zones, type 2 Guinier–Preston zones, γ phase. Volume fractions of the precipitated phases, sizes of the precipitates and orientations of cell axes relative to the axes of the Al lattice are given for various stages of each decomposition sequence.
The processing of diffraction data taken on a screenless Weissenberg camera for macromolecular crystallography
Authors: Higashi T.
Published: July 2002

A method has been developed based on Rossmann's [J. Appl Cryst. (1979). 12, 225–238] treatment of oscillation camera data for processing of X-ray diffraction data collected on a screenless Weissenberg camera for macromolecular crystals [Sakabe (1983). J. Appl. Cryst.
16, 542–547]. Crystal orientation parameters and film orientation parameters are refined by minimizing the discrepancies between the calculated and observed positions of reflections on a film. A data processing example is presented. Intensities were collected using a synchrotron radiation source and the imaging plate as a detector. The results show that the quality of the data is good, as judged by the agreement of the equivalent reflections. An absorption correction based on the use of the empirical Fourier expansion method reduced the R value and improved the correlations between Bijvoet differences observed on the different imaging plate exposures.
Layer thickness determinations with X-ray diffraction
Authors: Anderson D. E. , Thomson W. J.
Published: July 2002

A new equation involving an absorption coefficient is presented for calculating the thickness of a layer of a crystalline specimen deposited on a crystalline substrate. This new equation is particularly applicable to in situ X-ray diffraction studies of diffusion-limited kinetics; it is demonstrated that the practical difficulty of optimally partitioning count time between the peak of the substrate and peak of the layered specimen is overcome by making use of all available data in this single equation. This can result in more precise thickness determinations for intermediate specimen thicknesses than would be possible with either of the existing methods.
A profile-fitting procedure for analysis of broadened X-ray diffraction peaks. I. Methodology. Erratum
Authors: Enzo S. , Fagherazzi G. , Benedetti A. , Polizzi S.
Published: July 2002

Equation (18) of the paper by Enzo, Fagherazzi, Benedetti & Polizzi [J. Appl. Cryst. (1988). 21, 536–542] is in error. The correct equation is: A(2θ) = exp [−a|(2θ − 2θ
0)/cot 2θ
0|].
Some consideration of data corrections for a SAXS system employing a linear PSPC
Authors: Li H. , Chen H.
Published: July 2002

When a one-dimensional position-sensitive proportional counter (PSPC) is employed in a small-angle X-ray scattering (SAXS) system, detector-related problems might be encountered, such as nonuniformity of the detector, resolution function defined by the geometry of the receiving slit etc., all of which could cause distortion to the measured intensity profile. A set of experiments has been performed to test the significance of some of these problems, and corrections have been worked out to circumvent them. To obtain an optimized condition between flux and resolution, a wedge-shaped receiving slit is recommended.
A fast algorithm for macromolecular packing calculation
Authors: Mande S. C. , Suguna K.
Published: July 2002

An algorithm to improve the computation time of packing calculations for macromolecules is presented. This is achieved by reducing the three-dimensional search to a small set of two-dimensional searches.
MORGUE, a neutron powder diffraction profile refinement program with control-file facility to include structural and rigid-body thermal-motion constraints
Authors: Byrom P. G. , Hoffmann S. E. , Lucas B. W.
Published: July 2002

A neutron powder profile refinement program, MORGUE, has been written to facilitate the (possible) inclusion of both structural and rigid-body thermal-motion constraints. MORGUE results from major code modification to the program EDINP [Pawley (1980). J. Appl. Cryst.
13, 630–633] to allow the introduction of constraint conditions from an input parameter file in most practical situations. This replaces the previous need to write constraint-specific sub-routines for each structural and thermal-motion model refined, with the consequent repeated requirement for some recompilation and linkage of the modular parts to form the new executable program. The code is written in (VAX/VMS) Fortran77 and the program has been run on a VAX 11/750 computer. Examples of its use are included.
Improvements to the Chebyshev expansion of attenuation correction factors for cylindrical samples
Authors: Mildner D. F. R. , Carpenter J. M.
Published: July 2002

The accuracy of the Chebyshev expansion coefficients used for the calculation of attenuation correction factors for cylindrical samples has been improved. An increased order of expansion allows the method to be useful over a greater range of attenuation. It is shown that many of these coefficients are exactly zero, others are rational numbers, and others are rational fractions of π
−1 The assumptions of Sears [J. Appl. Cryst. (1984), 17, 226–230] in his asymptotic expression of the attenuation correction factor are also examined.
Mounting of crystals for macromolecular crystallography in a free-standing thin film
Authors: Teng T.-Y.
Published: July 2002

A method for mounting single crystals in macromolecular crystallographic studies is described in which the crystal is suspended in a thin film. The film is formed from a mixture of the crystallization buffer and a hydrophilic viscous material, confined within a thin-wire loop by surface tension. Compared with conventional crystal mounting methods, this method greatly simplifies and speeds the mounting procedure, is well suited to shock freezing and to optical monitoring of the crystals, deforms fragile crystals less and gives a lower and more uniform background in the X-ray diffraction patterns.
A position-sensitive detector system for the measurement of diffuse X-ray scattering
Authors: Osborn J. C. , Welberry T. R.
Published: July 2002

The use of a one-dimensional position-sensitive detector for diffuse X-ray scattering measurements is described. Calibration procedures for scattering angle and intensity measurements are discussed. Some nonuniformities have been found in the counting efficiency as a function of distance along the detector. A procedure is described for measuring the diffuse scattering in a section of reciprocal space.
Crystal structure determination by neutron powder diffraction using structural and packing constraints
Authors: Byrom P. G. , Lucas B. W.
Published: July 2002

In the past, crystal structure determination of solids consisting of molecules (or atom groups) whose geometry and size are known approximately has often been attempted using neutron powder diffraction profile refinement techniques, but without inclusion of this information. A method of structure solution has therefore been developed to include it. The proposed method does not require a set of structure factors and thus avoids the problems encountered in separating peaks in a powder diffraction scan. A successful test was conducted with a previously determined (yet treated as unknown) crystal structure, where direct methods had failed to solve the structure due to incorrect peak separation. Two computer programs, MODEL and PARAM, that implement the method are described.
Phase Transition of KNO3 Monitored by Synchrotron X-ray Powder Diffraction
Authors: Christensen A. , Norby P. , Hanson J. C. , Shimada S.
Published: July 2002

The solid-state phase transitions of KNO3 were studied at atmospheric pressure in the temperature range 303 to 533 K by synchrotron X-ray powder diffraction. The detectors used were (i) a curved position-sensitive detector and (ii) a moving imaging-plate system built for time-, temperature- and wavelength-dependent powder diffraction. On heating, the transition from α-KNO3 to β-KNO3 occurs at 401 K. On cooling with a cooling rate of 7 K min−1, the transition from β-KNO3 to γ-KNO3 was observed at 388 K. The phase transition from γ-KNO3 to α-KNO3 occurred at temperatures that strongly depended upon the cooling rate. With a high cooling rate of 15 K min−1 from 403 to 303 K, the γ-KNO3 phase was obtained as a pure phase at 303 K, but it was eventually transformed to α-KNO3 at this temperature, and the phase transition at 303 K was complete within 15 min. With a slow cooling rate of 0.5 K min−1 from 403 to 303 K, the γ-KNO3 phase was formed at 391 K and transformed at 370 K to α-KNO3. With a cooling rate of 7 K min−1 from 403 to 303 K, the γ-KNO3 phase transformed to α-KNO3 in a temperature range between 377 and 353 K. The two phases could exist simultaneously in temperature ranges that were apparently dependent upon the thermal history of the sample. The unit-cell parameters of γ-KNO3 from 383 K to room temperature are reported.
Optimized Schedule for Large Crystallography Meetings
Authors: Le Page Y.
Published: July 2002

International crystallography meetings like the International Union of Crystallography, European Crystallographic Meetings and American Crystallographic Association ones currently offer very comprehensive programs with four parallel sessions or more over a week or so. Proper scheduling of these sessions is nearly as important for the scientific success of these meetings as the selection of topics. In order to tackle this problem objectively, it is proposed here to poll crystallographers about the sessions they most wish to attend, and to accept that schedule which minimizes the sum of residual conflicts calculated from the results of the poll and also respects a number of constraints. A novel semi-automated optimization in four steps, based on the existence of major interest profiles among participants, was applied to the scheduling of the American Crystallographic Association 1995 Annual Meeting: a simple rearrangement of a `conflict matrix' to produce clusters of sessions with large conflicts, followed by application of constraints within clusters in step 2, then a small number of permutations within clusters only, each of them lowering the sum of conflicts while respecting constraints, and finally assignment of sessions to rooms. Without necessarily producing the absolute best solution, solutions very superior to those from intuition and respecting constraints can be built in this way with limited computing power. The experimental data were taken from 102 replies to an e-mail poll of crystallographers at large. Only 20 permutations were performed in step 3. The solution respected all constraints but one, which was relaxed in order to avoid a bad conflict. At the meeting, the room assignments turned out to be mostly verified, with just a few surprises, all having to do with outstanding contributed talks at sessions with no invited speakers. The total attendance at sessions remained high for the whole duration of the meeting. Calculations were programmed in Fortran and performed on a 386 PC clone.
Grazing-Incidence Small-Angle Scattering. Morphology of Deposited Clusters and Nanostructure of Thin Films
Authors: Naudon A. , Thiaudiere D.
Published: July 2002

It is shown that grazing-incidence small-angle X-ray scattering (GISAXS) is a new experimental technique that combines both grazing incidence and scattering at low angles. The experiments are carried out at or near the critical angle: the result is a considerably enhanced surface sensitivity. It allows morphological characterization of aggregates deposited or gathered on a flat substrate, such as silicon wafer or Coming glass. The full potential of this technique is realized when using a synchrotron source (flux, collimation and choice of wavelength in order to avoid fluorescence or to perform anomalous measurements) and when patterns are recorded with two-dimensional detectors: gas detectors or imaging plates (IPs). It is then possible to study the anisotropic shape of the scattering pattern and to determine the sizes of the aggregates. Results are presented for gold clusters deposited on a silicon wafer covered by a carbon sublayer in order to make a comparison with transmission electron microscopy and with scanning probe microscopy. Other examples are presented in order to highlight the advantages of such a technique applied to small inclusions in thin surface layers.
The Use of Partial Reflections for Scaling and Averaging X-ray Area-Detector Data
Authors: Bolotovsky Robert , Steller Ingo , Rossmann Michael G.
Published: July 2002

Frozen crystals of proteins, nucleic acids or other biological macromolecules often have mosaic spreads comparable to the maximum useful oscillation angles. It is, therefore, necessary to develop scaling methods that are independent of the exclusive use of full reflections. The Hamilton, Rollett and Sparks [Acta Cryst(1965),18, 129–130] procedure for scaling frames of X-ray area-detector data has been generalized to utilize partial reflections by adding intensities of partial reflections from consecutive frames (method 1) or by correcting intensities of partial reflections, using a model to calculate the reflection partiality (method 2). Both methods have been applied to scaling and averaging of data-sets collected on crystals of biological macromolecules. The agreement factors of the scaled data are better when using method 1, although it often fails when there are rotation gaps between successive images or when the data redundancy is low. Method 2 is more stable and versatile, allowing scaling of data-sets with incompletely measured reflections and low redundancy. The major drawback of method 2 is its sensitivity to inaccuracy in calculated partiality. The actual values of the scale factors obtained with the two methods are within 5%. However, when the true value of the scale factor changes dramatically between consecutive frames (e.g.due to beam dumps and refills at a synchrotron source), the results of the two methods can differ by as much as 15% because method 1 produces physically wrong results. The scaling algorithm implemented in the commercially available programSCALEPACKis vulnerable to the same problems as method 1.
Focusing Mirrors for Use with Microfocus X-ray Tubes
Authors: Arndt U. W. , Duncumb P. , Long J. V. P. , Pina L. , Inneman A.
Published: July 2002

Several different types of X-ray mirrors suitable for use with a microfocus X-ray tube and intended principally for single-crystal diffractometry are discussed and compared. The construction and performance of ellipsoidal mirrors made by an electroforming method are described in detail. The intensity at the mirror focus is comparable with the flux obtained with conventional arrangements with X-ray tubes dissipating more than 100 times the power of the microfocus tube.
Crystal structures of a solvated and unsolvated sulfone cyclic oligomer
Authors: Kaduk J. A. , Cahill P. J. , Venkateshwaran L. N.
Published: July 2002

The structure of the DMSO (dimethyl sulfoxide) solvate of the macrocyclic [2+2] dimer, 17,17,37,37-tetramethyl-2,12,22,32-tetraoxa-7,27-dithianonacyclo[36.2.2.2^{3,6}.-2^{8,11}.2^{13,16} .2^{18,21} .2^{23,26} .2^{28,31} .2^{33,36} ]hexapentaconta-3,5,8,-10,13,15,18,20,23,25,28,30,33,35,38,40,41,43,45,47,49,51,53,55-tetracosaene 7,7,27,27-tetraoxide, formed from 4,\!4'-dichlorodiphenyl sulfone and bisphenol-A has been determined by single-crystal techniques and the structure of the unsolvated dimer refined using X-ray powder diffraction data. The molecular conformations are similar and phenyl–phenyl stacking interactions are apparently important in determining the molecular conformation in the solid state. {\rm C_{54}H_{44}O_8S_2} .{\rm C_2H_6OS} (1)cyclo-[p\hbox{-}{\rm C_6H_4)SO_2(}p\hbox{-}{\rm C_6H_4)O(}p{\rm \hbox{-}C_6H_4){\rm C(CH_3)_2(}p{\rm \hbox{-} {\rm C_6H_4)O]_2}.{\rm C_2H_6OS}: molecular weight 963.2, monoclinic, P2_1/c,a=9.702  (2), b=18.623  (3), c=13.676  (2) Å, \beta =91.18 (1)^\circ , V=2470.5  (7) Å^3,Z=2 .{\rm C_{54}H_{44}O_8S_2} (2),cyclo-[(p{\rm \hbox{-} C_6H_4)SO_2(}p{\rm \hbox{-} {\rm C_6H_4)O(}p{\rm \hbox{-} C_6H_4)C(CH_3)_2(}p{\rm \hbox{-} {\rm C_6H_4)O]_2} : molecular weight 885.06, monoclinic, P2_1/c , a=9.5703  (15), b=18.7582  (18), c=13.3945  (12) Å, \beta =92.684 (11)^\circ , V=2402.0  (5) Å^3,Z=2 .