Home About us Contact
|
Home About us Contact | ||
|
|
||
Domain Boundaries (domain + boundary)
Kinds of Domain Boundaries Selected AbstractsDirect Observation of Inversion Domain Boundaries of GaN on c -Sapphire at Sub-ångstrom Resolution,ADVANCED MATERIALS, Issue 11 2008Fude Liu Inversion domain boundaries (IDBs) of GaN are studied by a high-resolution technique. The IDB separates adjacent domains of opposite polarity. The image shows a GaN IDB in the [bar;2110] projection. The theoretical IDB structure fits the experimentally obtained structure well. The inset is an image acquired from a very thin region on the right side of the IDB. It can indicate the polarity of GaN directly. [source] Cation Ordering and Domain Boundaries in Ca[(Mg1/3Ta2/3)1,xTix]O3 Microwave Dielectric CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Mao Sen Fu Cation ordering and domain boundaries in perovskite Ca[(Mg1/3Ta2/3)1,xTix]O3 (x=0.1, 0.2, 0.3) microwave dielectric ceramics were investigated by high-resolution transmission electron microscopy (HRTEM) and Rietveld analysis. The variation of ordering structure with Ti substitution was revealed together with the formation mechanism of ordering domains. When x=0.1, the ceramics were composed of 1:2 and 1:1 ordered domains and a disordered matrix. The 1:2 cation ordering could still exist until x=0.2 but the 1:1 ordering disappeared. Neither 1:2 nor 1:1 cation ordering could exist at x=0.3. The space charge model was used to explain the cation ordering change from 1:2 to 1:1 and then to disorder. A comparison between the space charge model and random layer model was also conducted. HRTEM observations showed an antiphase boundary inclined to the (111)c plane with a projected displacement vector in the ,001,c direction and ferroelastic domain boundaries parallel to the ,100,c direction. [source] Secondary structure assignment of mouse SOCS3 by NMR defines the domain boundaries and identifies an unstructured insertion in the SH2 domainFEBS JOURNAL, Issue 23 2005Jeffrey J. Babon SOCS3 is a negative regulator of cytokine signalling that inhibits Janus kinase-signal transduction and activator of transcription (JAK-STAT) mediated signal tranduction by binding to phosphorylated tyrosine residues on intracellular subunits of various cytokine receptors, as well as possibly the JAK proteins. SOCS3 consists of a short N-terminal sequence followed by a kinase inhibitory region, an extended SH2 domain and a C-terminal suppressor of cytokine signalling (SOCS) box. SOCS3 and the related protein, cytokine-inducible SH2-containing protein, are unique among the SOCS family of proteins in containing a region of mostly low complexity sequence, between the SH2 domain and the C-terminal SOCS box. Using NMR, we assigned and determined the secondary structure of a murine SOCS3 construct. The SH2 domain, unusually, consists of 140 residues, including an unstructured insertion of 35 residues. This insertion fits the criteria for a PEST sequence and is not required for phosphotyrosine binding, as shown by isothermal titration calorimetry. Instead, we propose that the PEST sequence has a functional role unrelated to phosphotyrosine binding, possibly mediating efficient proteolytic degradation of the protein. The latter half of the kinase inhibitory region and the entire extended SH2 subdomain form a single ,-helix. The mapping of the true SH2 domain, and the location of its C terminus more than 50 residues further downstream than predicted by sequence homology, explains a number of previously unexpected results that have shown the importance of residues close to the SOCS box for phosphotyrosine binding. [source] P - and S -velocity images of the lithosphere,asthenosphere system in the Central Andes from local-source tomographic inversionGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2006Ivan Koulakov SUMMARY About 50 000 P and S arrival times and 25 000 values of t* recorded at seismic arrays operated in the Central Andes between 20°S and 25°S in the time period from 1994 to 1997 have been used for locating more than 1500 deep and crustal earthquakes and creating 3-D P, S velocity and Qp models. The study volume in the reference model is subdivided into three domains: slab, continental crust and mantle wedge. A starting velocity distribution in each domain is set from a priori information: in the crust it is based on the controlled sources seismic studies; in slab and mantle wedge it is defined using relations between P and S velocities, temperature and composition given by mineral physics. Each iteration of tomographic inversion consists of the following steps: (1) absolute location of sources in 3-D velocity model using P and S arrival times; (2) double-difference relocation of the sources and (3) simultaneous determination of P and S velocity anomalies, P and S station corrections and source parameters by inverting one matrix. Velocity parameters are computed in a mesh with the density of nodes proportional to the ray density with double-sided nodes at the domain boundaries. The next iteration is repeated with the updated velocity model and source parameters obtained at the previous step. Different tests aimed at checking the reliability of the obtained velocity models are presented. In addition, we present the results of inversion for Vp and Vp/Vs parameters, which appear to be practically equivalent to Vp and Vs inversion. A separate inversion for Qp has been performed using the ray paths and source locations in the final velocity model. The resulting Vp, Vs and Qp distributions show complicated, essentially 3-D structure in the lithosphere and asthenosphere. P and S velocities appear to be well correlated, suggesting the important role of variations of composition, temperature, water content and degree of partial melting. [source] Magnetically Tunable Metal,Insulator SuperlatticesADVANCED MATERIALS, Issue 4 2010Masao Nakamura Design and control of nanometer-scale electronic phase separation are demonstrated in high-quality manganite superlattices composed of a ferromagnetic metal and an antiferromagnetic insulator (see figure). Bicritical competition of these phases sensitively controls the magnetic and electronic properties of the superlattices as a whole. A magnetic field can effectively tune the volume fraction of each phase and consequently the position of the phase domain boundaries. [source] A new fast hybrid adaptive grid generation technique for arbitrary two-dimensional domainsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2010Mohamed S. Ebeida Abstract This paper describes a new fast hybrid adaptive grid generation technique for arbitrary two-dimensional domains. This technique is based on a Cartesian background grid with square elements and quadtree decomposition. A new algorithm is introduced for the distribution of boundary points based on the curvature of the domain boundaries. The quadtree decomposition is governed either by the distribution of the boundary points or by a size function when a solution-based adaptive grid is desired. The resulting grid is quaddominant and ready for the application of finite element, multi-grid, or line-relaxation methods. All the internal angles in the final grid have a lower bound of 45° and an upper bound of 135°. Although our main interest is in grid generation for unsteady flow simulations, the technique presented in this paper can be employed in many other fields. Several application examples are provided to illustrate the main features of this new approach. Copyright © 2010 John Wiley & Sons, Ltd. [source] Shape optimization of piezoelectric devices using an enriched meshfree methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2009C. W. Liu Abstract We present an enriched reproducing kernel particle method for shape sensitivity analysis and shape optimization of two-dimensional electromechanical domains. This meshfree method incorporates enrichment functions for better representation of discontinuous electromechanical fields across internal boundaries. We use cubic splines for delineating the geometry of internal/external domain boundaries; and the nodal coordinates and slopes of these splines at their control points become the design parameters. This approach enables smooth manipulations of bi-material interfaces and external boundaries during the optimization process. It also enables the calculation of displacement and electric-potential field sensitivities with respect to the design parameters through direct differentiation, for which we adopt the classical material derivative approach. We verify this implementation of sensitivity calculations against an exact solution to a variant of Lamé's problem, and also, finite-difference approximations. We follow a sequential quadratic programming approach to minimize the cost function; and demonstrate the utility of the overall technique through a model problem that involves the shape optimization of a piezoelectric fan. Copyright © 2008 John Wiley & Sons, Ltd. [source] Imposing Dirichlet boundary conditions in the extended finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2006Nicolas Moës Abstract This paper is devoted to the imposition of Dirichlet-type conditions within the extended finite element method (X-FEM). This method allows one to easily model surfaces of discontinuity or domain boundaries on a mesh not necessarily conforming to these surfaces. Imposing Neumann boundary conditions on boundaries running through the elements is straightforward and does preserve the optimal rate of convergence of the background mesh (observed numerically in earlier papers). On the contrary, much less work has been devoted to Dirichlet boundary conditions for the X-FEM (or the limiting case of stiff boundary conditions). In this paper, we introduce a strategy to impose Dirichlet boundary conditions while preserving the optimal rate of convergence. The key aspect is the construction of the correct Lagrange multiplier space on the boundary. As an application, we suggest to use this new approach to impose precisely zero pressure on the moving resin front in resin transfer moulding (RTM) process while avoiding remeshing. The case of inner conditions is also discussed as well as two important practical cases: material interfaces and phase-transformation front capturing. Copyright © 2006 John Wiley & Sons, Ltd. [source] Direct Observation of Inversion Domain Boundaries of GaN on c -Sapphire at Sub-ångstrom Resolution,ADVANCED MATERIALS, Issue 11 2008Fude Liu Inversion domain boundaries (IDBs) of GaN are studied by a high-resolution technique. The IDB separates adjacent domains of opposite polarity. The image shows a GaN IDB in the [bar;2110] projection. The theoretical IDB structure fits the experimentally obtained structure well. The inset is an image acquired from a very thin region on the right side of the IDB. It can indicate the polarity of GaN directly. [source] The HUDSEN Atlas: a three-dimensional (3D) spatial framework for studying gene expression in the developing human brainJOURNAL OF ANATOMY, Issue 4 2010Janet Kerwin Abstract We are developing a three-dimensional (3D) atlas of the human embryonic brain using anatomical landmarks and gene expression data to define major subdivisions through 12 stages of development [Carnegie Stages (CS) 12,23; approximately 26,56 days post conception (dpc)]. Virtual 3D anatomical models are generated from intact specimens using optical projection tomography (OPT). Using mapaint software, selected gene expression data, gathered using standard methods of in situ hybridization and immunohistochemistry, are mapped to a representative 3D model for each chosen Carnegie stage. In these models, anatomical domains, defined on the basis of morphological landmarks and comparative knowledge of expression patterns in vertebrates, are linked to a developmental neuroanatomic ontology. Human gene expression patterns for genes with characteristic expression in different vertebrates (e.g. PAX6, GAD65 and OLIG2) are being used to confirm and/or refine the human anatomical domain boundaries. We have also developed interpolation software that digitally generates a full domain from partial data. Currently, the 3D models and a preliminary set of anatomical domains and ontology are available on the atlas pages along with gene expression data from approximately 100 genes in the HUDSEN Human Spatial Gene Expression Database (http://www.hudsen.org). The aim is that full 3D data will be generated from expression data used to define a more detailed set of anatomical domains linked to a more advanced anatomy ontology and all of these will be available online, contributing to the long-term goal of the atlas, which is to help maximize the effective use and dissemination of data wherever it is generated. [source] Different models for the polar nanodomain structure of PZN and other relaxor ferroelectricsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2008T. R. Welberry Computer simulations have been carried out to test the recently proposed model for the nanodomain structure of relaxor ferroelectrics such as lead zinc niobate (PZN). In this recent model it was supposed that the polar nanodomains are three-dimensional, that the observed diffuse rods of scattering originate from the boundaries between domains and that the Pb displacements may be directed along , or . This is in marked contrast to a previously published model, which described the polar domains as thin plates with Pb displacements confined to the directions within the essentially two-dimensional domains. The present results confirm that and types of Pb displacement are viable possibilities, but the number of domain boundaries required to produce sufficiently strong diffuse rods of scattering means that individual domains cannot be described as three-dimensional and must still be relatively thin. The current work has been carried out with no direct involvement of the B -site cation ordering, which many workers assume is necessary to understand the formation of the polar nanodomains. While it may be true that the B -site cation distribution could provide an underlying perturbation field that might ultimately limit the extent of any polar domain, it is certainly not necessary to produce the observed scattering effects. [source] Cation Ordering and Domain Boundaries in Ca[(Mg1/3Ta2/3)1,xTix]O3 Microwave Dielectric CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Mao Sen Fu Cation ordering and domain boundaries in perovskite Ca[(Mg1/3Ta2/3)1,xTix]O3 (x=0.1, 0.2, 0.3) microwave dielectric ceramics were investigated by high-resolution transmission electron microscopy (HRTEM) and Rietveld analysis. The variation of ordering structure with Ti substitution was revealed together with the formation mechanism of ordering domains. When x=0.1, the ceramics were composed of 1:2 and 1:1 ordered domains and a disordered matrix. The 1:2 cation ordering could still exist until x=0.2 but the 1:1 ordering disappeared. Neither 1:2 nor 1:1 cation ordering could exist at x=0.3. The space charge model was used to explain the cation ordering change from 1:2 to 1:1 and then to disorder. A comparison between the space charge model and random layer model was also conducted. HRTEM observations showed an antiphase boundary inclined to the (111)c plane with a projected displacement vector in the ,001,c direction and ferroelastic domain boundaries parallel to the ,100,c direction. [source] Distribution of Cerium Ions in Cerium-Doped ,,-SiAlON and Its Effect on Grain MorphologyJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002Fang-Fang Xu Cerium-doped ,,-SiAlON material was prepared by spark plasma sintering at 1750°C under 30 MPa pressure for 10 min. Yttrium ,,-SiAlON seeds (1 wt%) were added to the starting powder mixture. Recent work showed that up to 45 wt% of ,,-SiAlON phases are formed in the present sintered ceramics. The material presented a microstructure, containing rodlike cerium-doped ,,-SiAlON crystals. In this paper, transmission electron microscopy and energy dispersive spectroscopy examinations of the ,,-SiAlON grains are reported. The structural analyses revealed a high density of domain boundaries, within which larger amounts of cerium ions were segregated than in the matrix. The density of the domain boundaries was proportional to the amount of incorporated cerium ions. These structural defects eventually dominated the growth habits of the ,,-SiAlON crystals, by modifying the structure of the interstices at the boundary sites. The role of yttrium ,,-SiAlON seeds also is discussed in this paper. [source] Microstructure Characterizations in Calcium Magnesium NiobateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2001Hwack Joo Lee Microstructural studies on the domain boundaries in Ca(Mg1/3CNb2/3)O3 (CMN) complex perovskite compound were conducted using X-ray diffractometry and transmission electron microscopy. The 1:2 chemical ordering of B-site cations and the tilting of oxygen octahedra were involved in the CMN microstructure, as inferred from the presence of two types of domain boundaries. One type was the antiphase boundaries (APBs), which did not lie on a specific set of crystallographic planes. These boundaries were caused by the chemical 1:2 ordering of B-site cations, magnesium and niobium. The other type was the ferroelastic domain boundaries, which were parallel to a certain crystallographic plane. Therefore, CMN had the 1:2 ordered monoclinic unit cell distorted by the antiphase or in-phase tilting of oxygen octahedra. CMN had the mixed phases rather than the homogeneous phase. [source] The Hall,Petch law investigated by means of in situ straining experiments in lamellar TiAl and deformed AlMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2009Daniel Caillard Abstract Dislocation-boundary interactions are studied in TiAl and Al by means of in situ straining experiments in transmission electron microscopes (TEM). The results in TiAl allow us to measure the strength of domain boundaries against the motion of ordinary dislocations and twins. The results in Al are used to analyze the interaction between dislocations and cell walls. Parameters involved in the Hall-Petch law are then deduced from these observations. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] Inversion domain boundaries in GaN studied by X-ray microprobePHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1-2 2010Gema Martínez-Criado Abstract In this study, we report on the application of synchrotron spectro-microscopic techniques to the examination of inversion domain boundaries formed intentionally in a GaN-based lateral polarity heterostructure. Using X-ray sub-microbeams, no evidence of field-driven electrodiffusion effects has been observed on spatially separated inversion domain boundaries. In addition, XANES data around the Ga K-edge strongly supported hexagonal Ga site configurations, suggesting high local order reconstruction. Based on inner-shell excited luminescence on the micrometer scale, the uniform spectral distribution of the radiative centers was discussed. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Inhomogeneous surface electronic properties and charge ordering in epitaxial Fe3O4 films on MgO(001)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007A. Subagyo Abstract We report scanning tunneling microscopy (STM) study of surface electronic properties and charge ordering of epitaxially grown magnetite, Fe3O4, (001) films exhibiting high density of antiphase domain boundaries (APBs). STM measurements using a W tip reveal surface termination at B-sites. Fe ions with a 0.3 nm periodicity, i.e., a single atomic distance are observed. Current imaging tunneling spectroscopy reveals the alternation of two kinds of current peaks with a 0.6 nm periodicty indicating the presence of charge ordering consisted of Fe dimers with different charge states. STM measurements using a magnetic Ni tip provide higher contrast of the charge ordering. The APBs can modify the charge ordering as ordered and disordered areas are observed on adjacent domains separated by an APB. These strongly indicate that APBs can induce inhomogeneous properties on the surface of Fe3O4(001) films. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Soft X-ray absorption spectroscopy and magnetic circular dichroism study of electroless-deposited CoNiFe ternary alloy soft magnetic filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006Masahito Tanaka Abstract We studied microscopic magnetic properties of each consistent atom in boron added CoNiFe electroless-deposited soft magnetic films, which is a promising candidate for the soft magnetic underlayer of the perpendicular magnetic recording medium, by X-ray absorption spectra (XAS) and magnetic circular dichroism (MCD) measurement. It was found that various monoxides and Fe sesquioxide coexisted with the metals at the upper part of the films. The results of MCD sum rule showed the expected values of orbital angular moment ,Lz, for the film with macroscopic magnetic domain boundaries were larger than those of without domains at Co and Ni atoms and smaller at Fe atom. The appearance of macroscopic magnetic domain boundaries probably originated from the increase in ,Lz, of Co and/or Ni atoms. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Polycrystalline GaN: Analysis of the DefectsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003G. Nouet Abstract GaN polycrystalline layers were grown by ECR molecular beam epitaxy on quartz glass substrate. Strong photoluminescence emission was observed. Analysis of these layers was carried out by high resolution transmission electron microscopy. It is shown that the microstructure is characterised by a columnar growth with the ,0001, direction parallel to the growth direction. The mean size of the grains is in the range 30,50 nm. Sphalerite, cubic, and wurtzite, hexagonal, phases are observed, thus some defects such as basal stacking faults are present. Inversion domain boundaries are also formed. However, no threading dislocations within the grains are visible. [source] The disulfide bond pattern of catrocollastatin C, a disintegrin-like/cysteine-rich protein isolated from Crotalus atrox venomPROTEIN SCIENCE, Issue 7 2000Juan J. Calvete Abstract The disulfide bond pattern of catrocollastatin-C was determined by N-terminal sequencing and mass spectrometry. The N-terminal disintegrin-like domain is a compact structure including eight disulfide bonds, seven of them in the same pattern as the disintegrin bitistatin. The protein has two extra cysteine residues (XIII and XVI) that form an additional disulfide bond that is characteristically found in the disintegrin-like domains of cellular metalloproteinases (ADAMs) and PIII snake venom Zn-metalloproteinases (SVMPs). The C-terminal cysteine-rich domain of catrocollastatin-C contains five disulfide bonds between nearest-neighbor cysteines and a long range disulfide bridge between CysV and CysX. These results provide structural evidence for a redefinition of the disintegrin-like and cysteine-rich domain boundaries. An evolutionary pathway for ADAMs, PIII, and PII SVMPs based on disulfide bond engineering is also proposed. [source] Orogenic Gold Mineralization in the Qolqoleh Deposit, Northwestern IranRESOURCE GEOLOGY, Issue 3 2007Farhang Aliyari Abstract The Qolqoleh gold deposit is located in the northwestern part of the Sanandai-Sirjan Zone, northwest of Iran. Gold mineralization in the Qolqoleh deposit is almost entirely confined to a series of steeply dipping ductile,brittle shear zones generated during Late Cretaceous,Tertiary continental collision between the Afro-Arabian and the Iranian microcontinent. The host rocks are Mesozoic volcano-sedimentary sequences consisting of felsic to mafic metavolcanics, which are metamorphosed to greenschist facies, sericite and chlorite schists. The gold orebodies were found within strong ductile deformation to late brittle deformation. Ore-controlling structure is NE,SW-trending oblique thrust with vergence toward south ductile,brittle shear zone. The highly strained host rocks show a combination of mylonitic and cataclastic microstructures, including crystal,plastic deformation and grain size reduction by recrystalization of quartz and mica. The gold orebodies are composed of Au-bearing highly deformed and altered mylonitic host rocks and cross-cutting Au- and sulfide-bearing quartz veins. Approximately half of the mineralization is in the form of dissemination in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in quartz,sulfide microfractures, microveins and veins. Only low volumes of gold concentration was introduced during ductile deformation, whereas, during the evident brittle deformation phase, competence contrasts allowed fracturing to focus on the quartz,sericite domain boundaries of the mylonitic foliation, thus permitting the introduction of auriferous fluid to create disseminated and cross-cutting Au-quartz veins. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification and sulfidation zone (major ore body); sericite and carbonate alteration zone; and sericite,chlorite alteration zone that may be taken to imply wall-rock interaction with near neutral fluids (pH 5,6). Silicified and sulfide alteration zone is observed in the inner parts of alteration zones. High gold grades belong to silicified highly deformed mylonitic and ultramylonitic domains and silicified sulfide-bearing microveins. Based on paragenetic relationships, three main stages of mineralization are recognized in the Qolqoleh gold deposit. Stage I encompasses deposition of large volumes of milky quartz and pyrite. Stage II includes gray and buck quartz, pyrite and minor calcite, sphalerite, subordinate chalcopyrite and gold ores. Stage III consists of comb quartz and calcite, magnetite, sphalerite, chalcopyrite, arsenopyrite, pyrrhotite and gold ores. Studies on regional geology, ore geology and ore-forming stages have proved that the Qolqoleh deposit was formed in the compression,extension stage during the Late Cretaceous,Tertiary continental collision in a ductile,brittle shear zone, and is characterized by orogenic gold deposits. [source] Ferroelastic phase transitions: structure and microstructureACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2005Ekhard K. H. Salje Landau-type theories describe the observed behaviour of phase transitions in ferroelastic and co-elastic minerals and materials with a high degree of accuracy. In this review, the derivation of the Landau potential G = ½A,S [coth(,S/T) , coth(,S/TC)]Q2 + ¼BQ4 + , is derived as a solution of the general ,4 model. The coupling between the order parameter and spontaneous strain of a phase transition brings the behaviour of many phase transitions to the mean-field limit, even when the atomistic mechanism of the transition is spin-like. Strain coupling is also a common mechanism for the coupling between multiple order parameters in a single system. As well as changes on the crystal structure scale, phase transitions modify the microstructure of materials, leading to anomalous mesoscopic features at domain boundaries. The mesostructure of a domain wall is studied experimentally using X-ray diffraction, and interpreted theoretically using Ginzburg,Landau theory. One important consequence of twin mesostructures is their modified transport properties relative to the bulk. Domain wall motion also provides a mechanism for superelastic behaviour in ferroelastics. At surfaces, the relaxations that occur can be described in terms of order parameters and Landau theory. This leads to an exponential profile of surface relaxations. This in turn leads to an exponential interaction energy between surfaces, which can, if large enough, destabilize symmetrical morphologies in favour of a platelet morphology. Surface relaxations may also affect the behaviour of twin walls as they intersect surfaces, since the surface relaxation may lead to an incompatibility of the two domains at the surface, generating large strains at the relaxation. Landau theory may also be extended to describe the kinetics of phase transitions. Time-dependent Landau theory may be used to describe the kinetics of order,disorder phase transitions in which the order parameter is homogeneous. However, the time-dependent Landau theory equations also have microstructural solutions, explaining the formation of microstructures such as tweed. [source] Definition of domain boundaries and crystallization of the SMN Tudor domainACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2003Remco Sprangers Spinal muscular atropy (SMA) is the major genetic disease leading to childhood mortality and is caused by mutations in or deletions of the smn1 gene. The human survival of motor neurons (SMN) protein encoded by this gene plays an important role in the assembly of snRNPs (small nuclear ribonucleoprotein complexes) via binding to the spliceosomal Sm proteins. The tails of these Sm proteins contain symmetrically dimethylated arginines that are recognized by the central SMN Tudor domain. To gain insight in the molecular basis of this specific interaction, the SMN Tudor domain has been crystallized. The rapid crystallization of the protein and the high stability of the crystals is facilitated by redefinition of domain boundaries based on NMR relaxation experiments and the previously determined solution structure. The crystals diffract to high resolution (1.8,Å) and a complete data set has been collected from a hexagonal crystal form (P61/P65), with unit-cell parameters a = b = 27.65, c = 110.30,Å, , = , = 90, , = 120°. Crystal soaks and co-crystallization with peptides derived from the Sm protein tails have been initiated. Molecular replacement with the NMR coordinates is under way. [source] Simultaneous untangling and smoothing of moving gridsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2008Ezequiel J. López Abstract In this work, a technique for simultaneous untangling and smoothing of meshes is presented. It is based on an extension of an earlier mesh smoothing strategy developed to solve the computational mesh dynamics stage in fluid,structure interaction problems. In moving grid problems, mesh untangling is necessary when element inversion happens as a result of a moving domain boundary. The smoothing strategy, formerly published by the authors, is defined in terms of the minimization of a functional associated with the mesh distortion by using a geometric indicator of the element quality. This functional becomes discontinuous when an element has null volume, making it impossible to obtain a valid mesh from an invalid one. To circumvent this drawback, the functional proposed is transformed in order to guarantee its continuity for the whole space of nodal coordinates, thus achieving the untangling technique. This regularization depends on one parameter, making the recovery of the original functional possible as this parameter tends to 0. This feature is very important: consequently, it is necessary to regularize the functional in order to make the mesh valid; then, it is advisable to use the original functional to make the smoothing optimal. Finally, the simultaneous untangling and smoothing technique is applied to several test cases, including 2D and 3D meshes with simplicial elements. As an additional example, the application of this technique to a mesh generation case is presented. Copyright © 2008 John Wiley & Sons, Ltd. [source] Numerical simulation of vortical ideal fluid flow through curved channelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2003N. P. Moshkin Abstract A numerical algorithm to study the boundary-value problem in which the governing equations are the steady Euler equations and the vorticity is given on the inflow parts of the domain boundary is developed. The Euler equations are implemented in terms of the stream function and vorticity. An irregular physical domain is transformed into a rectangle in the computational domain and the Euler equations are rewritten with respect to a curvilinear co-ordinate system. The convergence of the finite-difference equations to the exact solution is shown experimentally for the test problems by comparing the computational results with the exact solutions on the sequence of grids. To find the pressure from the known vorticity and stream function, the Euler equations are utilized in the Gromeka,Lamb form. The numerical algorithm is illustrated with several examples of steady flow through a two-dimensional channel with curved walls. The analysis of calculations shows strong dependence of the pressure field on the vorticity given at the inflow parts of the boundary. Plots of the flow structure and isobars, for different geometries of channel and for different values of vorticity on entrance, are also presented. Copyright © 2003 John Wiley & Sons, Ltd. [source] Mathematical modeling of boundary conditions for laser-molecule time-dependent Schrödinger equations and some aspects of their numerical computation,One-dimensional caseNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 1 2009Emmanuel Lorin Abstract This article deals with boundary conditions for time-dependent Schrödinger equations for molecules excited by intense and ultrashort electric fields. On the basis of Volkov wavefunctions, we propose an original boundary condition design that allows to reduce spurious reflections at the domain boundary and allows to take at least partially, plasma effects into account. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009 [source] Structural analysis of pyramidal defects in Mg-doped GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006A. Pretorius Abstract Pyramidal defects in GaN:Mg grown by metalorganic vapour phase epitaxy are studied by high resolution transmission electron microscopy, energy dispersive X-ray analysis and scanning transmission electron microscopy. High resolution transmission electron microscopy images were simulated using the multislice approach in order to analyse the basal plane of the pyramidal defects. The simulated images were compared quantitatively with the experimental images. Two structural models for the basal plane inversion domain boundary containing antibixbyite-type layers are presented which show the best observed agreement with the experimentally found inversion domain boundary. Nevertheless, both models still do not match the experimental images satisfactorily, indicating that some other structure than antibixbyite is present at the boundary. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||