Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Cubic

  • face-centered cubic

  • Terms modified by Cubic

  • cubic boron nitride
  • cubic cell
  • cubic core
  • cubic crystal
  • cubic crystal form
  • cubic element
  • cubic equation
  • cubic graph
  • cubic lattice
  • cubic metre
  • cubic perovskite
  • cubic perovskite structure
  • cubic phase
  • cubic spline
  • cubic structure
  • cubic symmetry

  • Selected Abstracts

    Homogeneous cubic cylinder packings revisited

    M. O'Keeffe
    A method of systematically enumerating homogeneous (i.e. symmetry-related) packings of equal cylinders is developed. 19 three-way packings with axes parallel to ,100, and 40 four-way packings with axes parallel to ,111, are described. Cubic 6-, 12- and 24-way packings are possible and examples are given with axes parallel to ,210, and ,421,. [source]

    Calcite microcrystals in the pineal gland of the human brain: First physical and chemical studies

    Simon Baconnier
    Abstract A new form of biomineralization has been studied in the pineal gland of the human brain. It consists of small crystals that are less than 20 ,m in length and that are completely distinct from the often observed mulberry-type hydroxyapatite concretions. A special procedure was developed for isolation of the crystals from the organic matter in the pineal gland. Cubic, hexagonal, and cylindrical morphologies have been identified using scanning electron microscopy. The crystal edges were sharp whereas their surfaces were very rough. Energy dispersive spectroscopy showed that the crystals contained only the elements calcium, carbon, and oxygen. Selected area electron diffraction and near infrared Raman spectroscopy established that the crystals were calcite. With the exception of the otoconia structure of the inner ear, this is the only known nonpathological occurrence of calcite in the human body. The calcite microcrystals are probably responsible for the previously observed second harmonic generation in pineal tissue sections. The complex texture structure of the microcrystals may lead to crystallographic symmetry breaking and possible piezoelectricity, as is the case with otoconia. It is believed that the presence of two different crystalline compounds in the pineal gland is biologically significant, suggesting two entirely different mechanisms of formation and biological functions. Studies directed toward the elucidation of the formation and functions, and possible nonthermal interaction with external electromagnetic fields are currently in progress. Bioelectromagnetics 23:488,495, 2002. © 2002 Wiley-Liss, Inc. [source]

    Nd2Ba2CaZn2Ti3O14.4: A New High Dielectric Constant Oxide Having a Disordered (Cubic) Perovskite Structure.

    CHEMINFORM, Issue 36 2003
    Pika Jha
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    The Structure of Twinned Ag4Mn3O8, a Novel Octahedral Framework with a Topology Related to the Archetype Cubic {10,3} Net.

    CHEMINFORM, Issue 42 2002
    S. Ahlert
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    Projective Texture Mapping with Full Panorama

    Dongho Kim
    Projective texture mapping is used to project a texture map onto scene geometry. It has been used in many applications, since it eliminates the assignment of fixed texture coordinates and provides a good method of representing synthetic images or photographs in image-based rendering. But conventional projective texture mapping has limitations in the field of view and the degree of navigation because only simple rectangular texture maps can be used. In this work, we propose the concept of panoramic projective texture mapping (PPTM). It projects cubic or cylindrical panorama onto the scene geometry. With this scheme, any polygonal geometry can receive the projection of a panoramic texture map, without using fixed texture coordinates or modeling many projective texture mapping. For fast real-time rendering, a hardware-based rendering method is also presented. Applications of PPTM include panorama viewer similar to QuicktimeVR and navigation in the panoramic scene, which can be created by image-based modeling techniques. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Viewing Algorithms; I.3.7 [Computer Graphics]: Color, Shading, Shadowing, and Texture [source]

    Artistic Surface Rendering Using Layout of Text

    Tatiana Surazhsky
    An artistic rendering method of free-form surfaces with the aid of half-toned text that is laid-out on the given surface is presented. The layout of the text is computed using symbolic composition of the free-form parametric surface S(u, v) with cubic or linear Bézier curve segments C(t) = {cu (t), cv (t)}, comprising the outline of the text symbols. Once the layout is constructed on the surface, a shading process is applied to the text, affecting the width of the symbols as well as their color, according to some shader function. The shader function depends on the surface orientation and the view direction as well as the color and the direction or position of the light source. [source]

    In-situ TiC precipitation in molten Fe-C and their characterisation

    K. I. Parashivamurthy
    Abstract TiC particles were formed in liquid iron solution by the reaction between pure titanium and carbon available in molten iron. TiC particles have been precipitated in steels with four different carbon contents by in situ reactions during melting. The influence of titanium and carbon concentration on the precipitation of TiC was studied. The samples were studied by means of optical microscopy, scanning electron microscopy and X-ray microanalysis. The morphology of the obtained crystals was studied and correlated with carbon and titanium. It was found that TiC crystallises as primary crystals at 1600°C during solidification of the Fe-Ti-C melt. The obtained crystals were of cubic, rectangle and had maximum size of 18.7 µm. The size and shape of the carbides increases with increasing carbon and titanium in molten iron. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Biophysical characterization of the interaction of Limulus polyphemus endotoxin neutralizing protein with lipopolysaccharide

    FEBS JOURNAL, Issue 10 2004
    Jörg Andrä
    Endotoxin-neutralizing protein (ENP) of the horseshoe crab is one of the most potent neutralizers of endotoxins [bacterial lipopolysaccharide (LPS)]. Here, we report on the interaction of LPS with recombinant ENP using a variety of physical and biological techniques. In biological assays (Limulus amebocyte lysate and tumour necrosis factor-, induction in human mononuclear cells), ENP causes a strong reduction of the immunostimulatory ability of LPS in a dose-dependent manner. Concomitantly, the accessible negative surface charges of LPS and lipid A (zeta potential) are neutralized and even converted into positive values. The gel to liquid crystalline phase transitions of LPS and lipid A shift to higher temperatures indicative of a rigidification of the acyl chains, however, the only slight enhancement of the transition enthalpy indicates that the hydrophobic moiety is not strongly disturbed. The aggregate structure of lipid A is converted from a cubic into a multilamellar phase upon ENP binding, whereas the secondary structure of ENP does not change due to the interaction with LPS. ENP contains a hydrophobic binding site to which the dye 1-anilino-8-sulfonic acid binds at a Kd of 19 µm, which is displaced by LPS. Because lipopolysaccharide-binding protein (LBP) is not able to bind to LPS when ENP and LPS are preincubated, tight binding of ENP to LPS can be deduced with a Kd in the low nonomolar range. Importantly, ENP is able to incorporate by itself into target phospholipid liposomes, and is also able to mediate the intercalation of LPS into the liposomes thus acting as a transport protein in a manner similar to LBP. Thus, LPS,ENP complexes might enter target membranes of immunocompetent cells, but are not able to activate due to the ability of ENP to change LPS aggregates from an active into an inactive form. [source]

    Biophysical characterization of the interaction of high-density lipoprotein (HDL) with endotoxins

    FEBS JOURNAL, Issue 23 2002
    Klaus Brandenburg
    The interaction of bacterial endotoxins [lipopolysaccharide (LPS) and the ,endotoxic principle' lipid A], with high-density lipoprotein (HDL) from serum was investigated with a variety of physical techniques and biological assays. HDL exhibited an increase in the gel to liquid crystalline phase transition temperature Tc and a rigidification of the acyl chains of the endotoxins as measured by Fourier-transform infrared spectroscopy and differential scanning calorimetry. The functional groups of the endotoxins interacting with HDL are the phosphates and the diglucosamine backbone. The finding of phosphates as target groups is in accordance to measurements of the electrophoretic mobility showing that the zeta potential decreases from ,50 to ,60 mV to ,20 mV at binding saturation. The importance of the sugar backbone as further target structure is in accordance with the remaining negative potential and competition experiments with polymyxin B (PMB) and phase transition data of the system PMB/dephosphorylated LPS. Furthermore, endotoxin binding to HDL influences the secondary structure of the latter manifesting in a change from a mixed ,-helical/,-sheet structure to a predominantly ,-helical structure. The aggregate structure of the lipid A moiety of the endotoxins as determined by small-angle X-ray scattering shows a change of a unilamellar/inverted cubic into a multilamellar structure in the presence of HDL. Fluorescence resonance energy transfer data indicate an intercalation of pure HDL, and of [LPS],[HDL] complexes into phospholipid liposomes. Furthermore, HDL may enhance the lipopolysaccharide-binding protein-induced intercalation of LPS into phospholipid liposomes. Parallel to these observations, the LPS-induced cytokine production of human mononuclear cells and the reactivity in the Limulus test are strongly reduced by the addition of HDL. These data allow to develop a model of the [endotoxin]/[HDL] interaction. [source]

    Low-Temperature Superionic Conductivity in Strained Yttria-Stabilized Zirconia

    Michael Sillassen
    Abstract Very high lateral ionic conductivities in epitaxial cubic yttria-stabilized zirconia (YSZ) synthesized on single-crystal SrTiO3 and MgO substrates by reactive direct current magnetron sputtering are reported. Superionic conductivities (i.e., ionic conductivities of the order ,1 ,,1cm,1) are observed at 500,°C for 58-nm-thick films on MgO. The results indicate a superposition of two parallel contributions , one due to bulk conductivity and one attributable to conduction along the film,substrate interface. Interfacial effects dominate the conductivity at low temperatures (<350,°C), showing more than three orders of magnitude enhancement compared to bulk YSZ. At higher temperatures, a more bulk-like conductivity is observed. The films have a negligible grain-boundary network, thus ruling out grain boundaries as a pathway for ionic conduction. The observed enhancement in lateral ionic conductivity is caused by a combination of misfit dislocation density and elastic strain in the interface. These very high ionic conductivities in the temperature range 150,500,°C are of great fundamental importance but may also be technologically relevant for low-temperature applications. [source]

    Scattering of charged tensor bosons in gauge and superstring theories

    I. Antoniadis
    Abstract We calculate the leading-order scattering amplitude of one vector and two tensor gauge bosons in a recently proposed non-Abelian tensor gauge field theory and open superstring theory. The linear in momenta part of the superstring amplitude has identical Lorentz structure with the gauge theory, while its cubic in momenta part can be identified with an effective Lagrangian which is constructed using generalized non-Abelian field strength tensors. [source]

    Analysis of Nanostructuring in High Figure-of-Merit Ag1,xPbmSbTe2+m Thermoelectric Materials

    Bruce A. Cook
    Abstract Thermoelectric materials based on quaternary compounds Ag1,xPbmSbTe2+m exhibit high dimensionless figure-of-merit values, ranging from 1.5 to 1.7 at 700,K. The primary factor contributing to the high figure of merit is a low lattice thermal conductivity, achieved through nanostructuring during melt solidification. As a consequence of nucleation and growth of a second phase, coherent nanoscale inclusions form throughout the material, which are believed to result in scattering of acoustic phonons while causing only minimal scattering of charge carriers. Here, characterization of the nanosized inclusions in Ag0.53Pb18Sb1.2Te20 that shows a strong tendency for crystallographic orientation along the {001} planes, with a high degree of lattice strain at the interface, consistent with a coherent interfacial boundary is reported. The inclusions are enriched in Ag relative to the matrix, and seem to adopt a cubic, 96 atom per unit cell Ag2Te phase based on the Ti2Ni type structure. In-situ high-temperature synchrotron radiation diffraction studies indicated that the inclusions remain thermally stable to at least 800,K. [source]

    Concentric Sub-micrometer-Sized Cables Composed of Ni Nanowires and Sub-micrometer-Sized Fullerene Tubes,

    F. Tao
    Abstract Highly ordered arrays of submicrometer-sized coaxial cables composed of submicrometer-sized C60 and C70 tubes filled with Ni nanowires are successfully prepared by combining a sol,gel method with an electrodeposition process. The wall thickness of the submicrometer-sized tubes can be adjusted by the concentration of fullerenes and the immersion time. The thermal stability of the submicrometer-sized C60 tubes is studied by Raman spectroscopy and it is found that these structures can be easily decomposed to form carbon nanotubes at relatively low temperatures (above 573,K) in an alumina template. These novel coaxial cable structures have been characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), field-emission SEM (FESEM), Raman spectroscopy, elemental mapping, energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), vibrating sample magnetometer (VSM) experiments, and superconducting quantum interference device (SQUID) measurements. Magnetic measurements show that these submicrometer-sized cables exhibit enhanced ferromagnetic behavior as compared to bulk nickel. Moreover, submicrometer-sized C70/Ni cables show uniaxial magnetic anisotropy with the easy magnetic axis being parallel to the long axis of the Ni nanowires. C70/Ni cables also exhibit a new magnetic transition at ca.,10,K in the magnetization,temperature (M,T) curve, which is not observed for the analogous C60/Ni structures. The origin of this transition is not yet clear, but might be related to interactions between the Ni nanowires and C70 molecules. There is no preferred magnetization axis in submicrometer-sized C60/Ni cables, which implies that the Ni nanocrystals have different packing modes in the two composites. These different crystalline packing modes lead to different magnetic anisotropy in the two composites, although the Ni nanocrystals have the same face-centered cubic (fcc) structure in both cases. [source]

    Mechanisms Controlling Crystal Habits of Gold and Silver Colloids

    C. Lofton
    Abstract Examples of gold and silver anisotropic colloids, such as prisms and rods, have appeared in the literature for many years. In most cases, the morphologies of these thermodynamically unfavorable particles have been explained by the particular reaction environment in which they were synthesized. The mechanisms used to explain the growth generally fall into two categories, one in which chemically adsorbed molecules regulate the growth of specific crystal faces kinetically, and the other where micelle-forming surfactants physically direct the shape of the particle. This paper raises questions about the growth of anisotropic metal colloids that the current mechanisms cannot adequately address, specifically, the formation of multiple shapes in a single homogeneous reaction and the appearance of similar structures in very different synthesis schemes. These observations suggest that any growth mechanism should primarily take into consideration nucleation and kinetics, and not only thermodynamics or physical constrictions. The authors suggest an alternative mechanism where the presence and orientation of twin planes in these face-centered cubic (fcc) metals direct the shape of the growing particles. This explanation follows that used for silver halide crystals, and has the advantage of explaining particle growth in many synthesis methods. In this mechanism, twin planes generate reentrant grooves, favorable sites for the attachment of adatoms. Shape and structural data are presented for gold and silver particles synthesized using several different techniques to support this new model. Triangular prisms are suggested to contain a single twin plane which directs that growth of the initial seed in two dimensions, but limits the final size of the prism. Hexagonal platelets are suggested to contain two parallel twin planes that allow the fast growing edges to regenerate one another, allowing large sizes and aspect ratios to form. Rods and wires were found to have a fivefold symmetry, which may only allow growth in one dimension. It is expected that a superior mechanistic understanding will permit shape-selective synthesis schemes to be developed. [source]

    Synthesis of Indium and Indium Oxide Nanoparticles from Indium Cyclopentadienyl Precursor and Their Application for Gas Sensing,

    K. Soulantica
    Abstract Decomposition of the organometallic precursor [In(,5 -C5H5)] in toluene in the presence of methanol (8 vol.-%) at room temperature leads to the immediate formation of aggregates of indium nanoparticles of 15,±,2 nm mean diameter. The aggregates are roughly spherical with a mean size of 400,±,40 nm. The particles were characterized by means of transmission electron and high-resolution transmission electron microscopies (TEM and HRTEM), and X-ray diffraction (XRD) studies indicate that the powder consists of the tetragonal phase of indium. The thermal oxidation in air of these nanoparticles yields well-crystallized nanoparticles of In2O3 with unchanged morphology (aggregates of nanoparticles of 16.6,±,2 nm mean diameter with aggregate mean size of 400,±,40 nm) and without any sign of coalescence. XRD pattern shows that the powder consists of the cubic phase of In2O3. The electrical conductivity measurements demonstrate that this material is highly sensitive to an oxidizing gas such as nitrogen dioxide and barely sensitive to a reducing gas such as carbon monoxide. Its association with SnO2 -based sensors allows the selective detection of carbon monoxide (30 ppm) and sub-ppm amounts of nitrogen dioxide (400 ppb) in a mixture at 21,°C and at a relative humidity of 60,%. [source]

    Competitive Abnormal Grain Growth between Allotropic Phases in Nanocrystalline Nickel

    ADVANCED MATERIALS, Issue 10 2010
    L. N. Brewer
    Electron backscatter diffraction-generated phase map showing the distribution of the abnormally grown grains for both the face centered cubic (red) and hexagonal close packed (blue) phases. Annealing condition was 17,h at 548,K. [source]

    An augmented Lagrange multiplier approach to continuum multislip single crystal thermo,elasto,viscoplasticity

    C. C. Celigoj
    Abstract The material and structural behaviour of single crystals is going to be investigated. On the constitutive level the concept of ,generalized standard materials (gsm)' is used to set up the equations for finite deformation multislip single crystal thermo,elasto,viscoplasticity within a continuum slip theory. The only two scalar quantities needed are a thermodynamic potential and a dissipation potential. The resulting evolution equations for the internal (viscoplastic) variables are discretized in time and solved via a backward Euler scheme, using an ,augmented Lagrange multiplier method' for satisfying the multiple constraints, thus circumventing the cumbersome and less robust ,active set strategies'. As a computational reference frame serves the Eulerian setting. The structural behaviour (non-linear coupled thermomechanics) is solved in a staggered algorithm: in an isothermal mechanical phase via q1(displacements)/p0(pressure)/j0(jacobian)-finite elements and in an isogeometric thermal phase via q1(temperatures)-finite elements, followed by an isogeometric and isothermal update phase of the internal variables. Numerical results of the simple isothermal shear test of a single face-centred cubic (fcc) crystal and of the thermomechanical behaviour of a geometrically imperfect strip consisting of initially equally oriented (0/45/30 in Euler angles) fcc-crystals under tension and plane strain conditions are given. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    A meshfree thin shell method for non-linear dynamic fracture

    T. Rabczuk
    Abstract A meshfree method for thin shells with finite strains and arbitrary evolving cracks is described. The C1 displacement continuity requirement is met by the approximation, so no special treatments for fulfilling the Kirchhoff condition are necessary. Membrane locking is eliminated by the use of a cubic or quartic polynomial basis. The shell is tested for several elastic and elasto-plastic examples and shows good results. The shell is subsequently extended to modelling cracks. Since no discretization of the director field is needed, the incorporation of discontinuities is easy to implement and straightforward. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Fully-automated hex-dominant mesh generation with directionality control via packing rectangular solid cells

    Soji Yamakawa
    Abstract A new fully automatic hex-dominant mesh generation technique of an arbitrary 3D geometric domain is presented herein. The proposed method generates a high-quality hex-dominant mesh by: (1) controlling the directionality of the output hex-dominant mesh; and (2) avoiding ill-shaped elements induced by nodes located too closely to each other. The proposed method takes a 3D geometric domain as input and creates a hex-dominant mesh consisting mostly of hexahedral elements, with additional prism and tetrahedral elements. Rectangular solid cells are packed on the boundary of and inside the input domain to obtain ideal node locations for a hex-dominant mesh. Each cell has a potential energy field that mimics a body-centred cubic (BCC) structure (seen in natural substances such as NaCl) and the cells are moved to stable positions by a physically based simulation. The simulation mimics the formation of a crystal pattern so that the centres of the cells provide ideal node locations for a hex-dominant mesh. Via the advancing front method, the centres of the packed cells are then connected to form a tetrahedral mesh, and this is converted to a hex-dominant mesh by merging some of the tetrahedrons. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Three-dimensional transient free-surface flow of viscous fluids inside cavities of arbitrary shape

    Kyu-Tae Kim
    Abstract The three-dimensional transient free-surface flow inside cavities of arbitrary shape is examined in this study. An adaptive (Lagrangian) boundary-element approach is proposed for the general three-dimensional simulation of confined free-surface flow of viscous incompressible fluids. The method is stable as it includes remeshing capabilities of the deforming free-surface, and thus can handle large deformations. A simple algorithm is developed for mesh refinement of the deforming free-surface mesh. Smooth transition between large and small elements is achieved without significant degradation of the aspect ratio of the elements in the mesh. The method is used to determine the flow field and free-surface evolution inside cubic, rectangular and cylindrical containers. These problems illustrate the transient nature of the flow during the mixing process. Surface tension effects are also explored. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    A Petrov,Galerkin finite element model for one-dimensional fully non-linear and weakly dispersive wave propagation

    Seung-Buhm Woo
    Abstract A new finite element method is presented to solve one-dimensional depth-integrated equations for fully non-linear and weakly dispersive waves. For spatial integration, the Petrov,Galerkin weighted residual method is used. The weak forms of the governing equations are arranged in such a way that the shape functions can be piecewise linear, while the weighting functions are piecewise cubic with C2 -continuity. For the time integration an implicit predictor,corrector iterative scheme is employed. Within the framework of linear theory, the accuracy of the scheme is discussed by considering the truncation error at a node. The leading truncation error is fourth-order in terms of element size. Numerical stability of the scheme is also investigated. If the Courant number is less than 0.5, the scheme is unconditionally stable. By increasing the number of iterations and/or decreasing the element size, the stability characteristics are improved significantly. Both Dirichlet boundary condition (for incident waves) and Neumann boundary condition (for a reflecting wall) are implemented. Several examples are presented to demonstrate the range of applicabilities and the accuracy of the model. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    One-Nanometer-Thick Seed Layer of Unilamellar Nanosheets Promotes Oriented Growth of Oxide Crystal Films,

    ADVANCED MATERIALS, Issue 2 2008
    T. Shibata
    Room-temperature fabrication of an ultimately thin seed layer using 2D oxide nanosheets is demonstrated. Flat nanosheets are tiled to form a highly organized monolayer with a thickness of ca. 1 nm on a glass substrate (see figure). Monolayer films of nanosheets such as Ca2Nb3O10 (2D square lattice) and MnO2 (2D hexagonal) successfully promote oriented film growth of oxide crystals such as SrTiO3 (cubic), TiO2 (tetragonal), and ZnO (hexagonal). [source]

    Synthesis and Self-Assembly of Triangular and Hexagonal CdS Nanocrystals,

    ADVANCED MATERIALS, Issue 24 2005
    H. Warner
    CdS nanocrystals with cubic, triangular, and hexagonal geometries have been synthesized using simple wet-chemistry techniques. Analysis of the crystal structures revealed that the cubic nanocrystals have a zinc-blende crystal structure whilst the triangular and hexagonal CdS nanocrystals have a wurtzite crystal structure. When dried, these CdS nanocrystals self-assemble to form complex structures such as linear rods (see Figure), nanoarrows and dimers. [source]

    Hexagonal and cubic TiOF2

    Samuel Shian
    The chemical, electrochemical, optical and electro-optical properties of titanium oxyfluoride, TiOF2, have led to interest in this compound for a number of applications. Prior analyses have indicated that TiOF2 possesses a simple cubic structure (space group Pmm) at room temperature. Three-dimensional nanostructured assemblies of polycrystalline TiOF2 have recently been synthesized via chemical conversion of intricate SiO2 structures by metathetic reaction with TiF4(g). Rietveld analysis has been used to evaluate the structure of the TiOF2 product formed by such reaction at 623,K. Unlike prior reports, this TiOF2 product possessed a hexagonal structure (space group Rc) at room temperature. Upon heating through 333,338 K, the hexagonal TiOF2 polymorph converted into cubic (Pmm) TiOF2. Differential scanning calorimetry and X-ray diffraction analyses have been used to evaluate this thermally induced phase transformation. [source]

    Pressure-induced high-density amorphous ice in protein crystals

    Chae Un Kim
    Crystal cryocooling has been used in X-ray protein crystallography to mitigate radiation damage during diffraction data collection. However, cryocooling typically increases crystal mosaicity and often requires a time-consuming search for cryoprotectants. A recently developed high-pressure cryocooling method reduces crystal damage relative to traditional cryocooling procedures and eases or eliminates the need to screen for cryoprotectants. It has been proposed that the formation of high-density amorphous (HDA) ice within the protein crystal is responsible for the excellent diffraction quality of the high-pressure cryocooled crystals. This paper reports X-ray data that confirm the presence of HDA ice in the high-pressure cryocooled protein crystallization solution and protein crystals analyzed at ambient pressure. Diffuse scattering with a spacing characteristic of HDA ice is seen at low temperatures. This scattering then becomes characteristic successively to low-density amorphous, cubic and hexagonal ice phases as the temperature is gradually raised from 80 to 230,K, and seems to be highly correlated with the diffraction quality of crystals. [source]

    Effects of cryoprotectant concentration and cooling rate on vitrification of aqueous solutions

    Naji S. Husseini
    Vitrification of aqueous cryoprotectant mixtures is essential in cryopreservation of proteins and other biological samples. Systematic measurements of critical cryoprotective agent (CPA) concentrations required for vitrification during plunge-cooling from T = 295,K to T = 77,K in liquid nitrogen are reported. Measurements on fourteen common CPAs, including alcohols (glycerol, methanol, 2-propanol), sugars (sucrose, xylitol, dextrose, trehalose), polyethylene glycols (ethylene glycol, PEG 200, PEG 2000, PEG 20000), glycols [dimethyl sulfoxide (DMSO), 2-methyl-2,4-pentanediol (MPD)], and salt (NaCl), were performed for volumes ranging over four orders of magnitude from ,1,nl to 20,µl, and covering the range of interest in protein crystallography. X-ray diffraction measurements on aqueous glycerol mixtures confirm that the polycrystalline-to-vitreous transition occurs within a span of less than 2% w/v in CPA concentration, and that the form of polycrystalline ice (hexagonal or cubic) depends on CPA concentration and cooling rate. For most of the studied cryoprotectants, the critical concentration decreases strongly with volume in the range from ,5,µl to ,0.1,µl, typically by a factor of two. By combining measurements of the critical concentration versus volume with cooling time versus volume, the function of greatest intrinsic physical interest is obtained: the critical CPA concentration versus cooling rate during flash-cooling. These results provide a basis for more rational design of cryoprotective protocols, and should yield insight into the physics of glass formation in aqueous mixtures. [source]

    Synchrotron texture analysis with area detectors

    H.-R. Wenk
    The wide availability of X-ray area detectors provides an opportunity for using synchrotron radiation based X-ray diffraction for the determination of preferred crystallite orientation in polycrystalline materials. These measurements are very fast compared to other techniques. Texture is immediately recognized as intensity variations along Debye rings in diffraction images, yet in many cases this information is not used because the quantitative treatment of texture information has not yet been developed into a standard technique. In special cases it is possible to interpret the texture information contained in these intensity variations intuitively. However, diffraction studies focused on the effects of texture on materials properties often require the full orientation distribution function (ODF) which can be obtained from spherical tomography analysis. In cases of high crystal symmetry (cubic and hexagonal) an approximation to the full ODF can be reconstructed from single diffraction images, as is demonstrated for textures in rolled copper and titanium sheets. Combined with area detectors, the reconstruction methods make the measurements fast enough to study orientation changes during phase transformations, recrystallization and deformation in situ, and even in real time, at a wide range of temperature and pressure conditions. The present work focuses on practical aspects of texture measurement and data processing procedures to make the latter available for the growing community of synchrotron users. It reviews previous applications and highlights some opportunities for synchrotron texture analysis based on case studies on different materials. [source]

    The calculation of a parent grain orientation from inherited variants for approximate (b.c.c.,h.c.p.) orientation relations

    N. Gey
    The orientations of parent , grains are evaluated from several , variants inherited from the same parent during the body-centred cubic (b.c.c.) to hexagonal close packed (h.c.p.) phase transformation. The proposed calculation, based on orientation correlating and orientation averaging, is particularly useful when the inherited variants are not strictly related to the parent orientation by a strict Burgers orientation relation or when the orientations of the inherited volumes vary slightly at different locations of the variant. This method of parent identification from variant orientations is an improvement of a previously published method. [source]

    Thermal expansion and atomic displacement parameters of cubic KMgF3 perovskite determined by high-resolution neutron powder diffraction

    I. G. Wood
    The structure of KMgF3 has been determined by high-resolution neutron powder diffraction at 4.2,K, room temperature and at 10,K intervals from 373,K to 1223,K. The material remains cubic at all temperatures. The average volumetric coefficient of thermal expansion in the range 373,1223,K was found to be 7.11,(3) × 10,5,K,1. For temperatures between 4.2 and 1223,K, a second-order Grüneisen approximation to the zero-pressure equation of state, with the internal energy calculated via a Debye model, was found to fit well, with the following parameters: ,D = 536,(9),K, Vo = 62.876,(6),Ĺ3, = 6.5,(1) and (VoKo/,,) = 3.40,(2) × 10,18,J, where ,D is the Debye temperature, Vo is the volume at T = 0, is the first derivative with respect to pressure of the incompressibility (Ko) and ,, is a Grüneisen parameter. The atomic displacement parameters were found to increase smoothly with T and could be fitted using Debye models with ,D in the range 305,581,K. At 1223,K, the displacement of the F ions was found to be much less anisotropic than that in NaMgF3 at this temperature. [source]

    High-pressure properties of TiP2O7, ZrP2O7 and ZrV2O7

    Stefan Carlson
    High-pressure synchrotron X-ray powder diffraction studies of TiP2O7, ZrP2O7 and ZrV2O7 have been performed. The ZrV2O7 structure undergoes a reversible transition at 1.38,1.58,GPa from cubic ,- to pseudo-tetragonal ,-ZrV2O7 that displays an orthorhombic 2 × 3 × 3 supercell. At pressures above 4,GPa, ZrV2O7 becomes irreversibly X-ray amorphous. No such transformations are observed for TiP2O7 and ZrP2O7, which compress smoothly up to the highest investigated pressures (40.3 and 20.5,GPa, respectively). These differences in high-pressure properties are discussed in terms of the negative thermal expansion of ZrV2O7. The bulk moduli at ambient pressure (B0) for TiP2O7, ZrP2O7, ,-ZrV2O7 and ,-ZrV2O7 were estimated to be 42,(3), 39,(1), 17.0,(7) and 20.8,(10),GPa, respectively. [source]