Geometry

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Geometry

  • acquisition geometry
  • active site geometry
  • arbitrary geometry
  • basin geometry
  • bipyramidal geometry
  • bone geometry
  • cell geometry
  • channel geometry
  • cis geometry
  • complex geometry
  • complicated geometry
  • confined geometry
  • contact geometry
  • coordination geometry
  • device geometry
  • die geometry
  • different geometry
  • diffraction geometry
  • distorted octahedral geometry
  • distorted square-planar geometry
  • distorted square-pyramidal geometry
  • distorted tetrahedral geometry
  • distorted trigonal bipyramidal geometry
  • epipolar geometry
  • equilibrium geometry
  • experimental geometry
  • femoral geometry
  • field geometry
  • fractal geometry
  • general geometry
  • good geometry
  • ground-state geometry
  • hydrogen-bond geometry
  • inclusion geometry
  • internal geometry
  • ligand geometry
  • local geometry
  • lv geometry
  • magnetic field geometry
  • mesh geometry
  • molecular geometry
  • octahedral coordination geometry
  • octahedral geometry
  • optimized geometry
  • planar geometry
  • pore geometry
  • pyramidal geometry
  • reflection geometry
  • rigid geometry
  • sample geometry
  • scattering geometry
  • scene geometry
  • screw geometry
  • similar geometry
  • simple geometry
  • site geometry
  • specimen geometry
  • spherical geometry
  • square-planar coordination geometry
  • square-planar geometry
  • square-pyramidal geometry
  • state geometry
  • structural geometry
  • substrate geometry
  • surface geometry
  • tetrahedral geometry
  • three-dimensional geometry
  • tool geometry
  • transmission geometry
  • trigonal bipyramidal geometry
  • vane geometry
  • various geometry
  • ventricular geometry

  • Terms modified by Geometry

  • geometry catalyst
  • geometry change
  • geometry effects
  • geometry optimization
  • geometry parameter

  • Selected Abstracts


    OSCILLATING VANE GEOMETRY FOR SOFT SOLID GELS AND FOAMS

    JOURNAL OF TEXTURE STUDIES, Issue 6 2002
    C. SERVAIS
    ABSTRACT Several relationships between the torque and the stress exist for the vane geometry, but only a few equations have been proposed for the relationship between angular displacement and strain. In this study, an expression based on the infinite gap approximation for concentric cylinders is used and well-defined reference data are compared to oscillating vane data to validate the assumptions used. Gelatin gels are used for their property to stick to the wall and carrageenan gels are used to show that wall slip does not occur with oscillating vanes in serrated cup geometries. Shaving foams are used as a model low density, time and shear stable foam, which resists irreversible damage when loaded between serrated parallel plates. Results show that the assumptions used for the determination of stress and strain with the vane provide material viscoelastic properties that are not significantly different from reference values as obtained with concentric cylinders and parallel plates. [source]


    Geometries, vibrational frequencies, and electron affinities of X2Cl (X=C,Si,Ge) clusters

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2007
    Feng-You Hao
    Abstract Ab initio quantum chemical calculations have been performed on X2Cl, and X2Cl (X = C, Si, Ge) clusters. The geometrical structures, vibrational frequencies, electronic properties and dissociation energies are investigated at the Hartree,Fock (HF), Møller,Plesset second- and fourth-order (MP2, MP4), CCSD(T) level with the 6-311+G(d) basis set. The X2Cl (X = C, Si, Ge) and X2Cl, (X = Si, Ge) take a bent shape obtained at the ground state, while C2Cl, has a linear structure. The impact on internal electron transfer between the X2Cl and the corresponding anional clusters is studied. The three different types of electron affinities (EAs) at the CCSD(T) are reported. The most reliable adiabatic electronic affinities, obtained at the CCSD(T)/cc-pvqz level of theory, are predicted to be 3.30, 2.62, and 1.98 eV for C2Cl, Si2Cl, and Ge2Cl, respectively. The calculated EAs of C2Cl and Ge2Cl are in good agreement with theoretical results reported. The correlation effects and basis sets effects on the geometrical structures and dissociation energies are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]


    Theoretical study of the reactions BF3 + BX, where X = H or N

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005
    Patrícia R. P. Barreto
    Abstract This work presents the rate constant for the gas-phase reaction BF3 + BX, where X = H or N, over the temperature range of 200,4,000 K. Conventional transition state theory (TST) is used to study these reactions. Geometries, frequencies, and the potential energy for reactant, products, and saddle point are obtained from accurate electronic structure calculations performed with the GAUSSIAN 98 program. The reaction rate for these reactions are determined using a simple code developed for this task. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source]


    QM/MM calculation of solvent effects on absorption spectra of guanine

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2010
    Maja Parac
    Abstract Electronic spectra of guanine in the gas phase and in water were studied by quantum mechanical/molecular mechanical (QM/MM) methods. Geometries for the excited-state calculations were extracted from ground-state molecular dynamics (MD) simulations using the self-consistent-charge density functional tight binding (SCC-DFTB) method for the QM region and the TIP3P force field for the water environment. Theoretical absorption spectra were generated from excitation energies and oscillator strengths calculated for 50 to 500 MD snapshots of guanine in the gas phase (QM) and in solution (QM/MM). The excited-state calculations used time-dependent density functional theory (TDDFT) and the DFT-based multireference configuration interaction (DFT/MRCI) method of Grimme and Waletzke, in combination with two basis sets. Our investigation covered keto-N7H and keto-N9H guanine, with particular focus on solvent effects in the low-energy spectrum of the keto-N9H tautomer. When compared with the vertical excitation energies of gas-phase guanine at the optimized DFT (B3LYP/TZVP) geometry, the maxima in the computed solution spectra are shifted by several tenths of an eV. Three effects contribute: the use of SCC-DFTB-based rather than B3LYP-based geometries in the MD snapshots (red shift of ca. 0.1 eV), explicit inclusion of nuclear motion through the MD snapshots (red shift of ca. 0.1 eV), and intrinsic solvent effects (differences in the absorption maxima in the computed gas-phase and solution spectra, typically ca. 0.1,0.3 eV). A detailed analysis of the results indicates that the intrinsic solvent effects arise both from solvent-induced structural changes and from electrostatic solute,solvent interactions, the latter being dominant. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 [source]


    Toward direct determination of conformations of protein building units from multidimensional NMR experiments VI.

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2005
    Chemical shift analysis of his to gain 3D structure, protonation state information
    Abstract NMR,chemical shift structure correlations were investigated by using GIAO-RB3LYP/6-311++G(2d,2p) formalism. Geometries and chemical shifts (CSI values) of 103 different conformers of N,-formyl-L-histidinamide were determined including both neutral and charged protonation forms. Correlations between amino acid torsional angle values and chemical shifts were investigated for the first time for an aromatic and polar amino acid residue whose side chain may carry different charges. Linear correlation coefficients of a significant level were determined between chemical shifts and dihedral angles for CSI[1H,]/,, CSI[13C,]/,, and CSI[13C,]/,. Protonation of the imidazole ring induces the upfield shift of CSI[13C,] for positively charged histidines and an opposite effect for the negative residue. We investigated the correspondence of theoretical and experimental 13C,, 13C,, and 1H, chemical shifts and the nine basic conformational building units characteristic for proteins. These three chemical shift values allow the identification of conformational building units at 80% accuracy. These results enable the prediction of additional regular secondary structural elements (e.g., polyProlineII, inverse ,-turns) and loops beyond the assignment of chemical shifts to ,-helices and ,-pleated sheets. Moreover, the location of the His residue can be further specified in a ,-sheet. It is possible to determine whether the appropriate residue is located at the middle or in a first/last ,-strand within a ,-sheet based on calculated CSI values. Thus, the attractive idea of establishing local residue specific backbone folding parameters in peptides and proteins by employing chemical shift information (e.g., 1H, and 13C,) obtained from selected heteronuclear correlation NMR experiments (e.g., 2D-HSQC) is reinforced. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1307,1317, 2005 [source]


    Theoretical investigation of electron transfer transition in tetracyanoethylene-contained organic complexes

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2002
    Xiang-Yuan Li
    Abstract In this work, the authors use complete active space self-consistent field method to investigate the photoinduced charge-separated states and the electron transfer transition in complexes ethylene-tetracyanoethylene and tetramethylethylene-tetracyanoethylene. Geometries of isolated tetracyanoethylene, ethylene, and tetramethylethylene have been optimized. The ground state and the low-lying excited states of ethylene and tetracyanoethylene have been optimized. The state energies in the gas phase have been obtained and compared with the experimentally observed values. The torsion barrier of tetracyanoethylene has been investigated through the state energy calculation at different conformations. Attention has been particularly paid to the charge-separated states and the electron transfer transition of complexes. The stacked conformations of the donor,acceptor complexes have been chosen for the optimization of the ground and low-lying excited states. Equilibrium solvation has been considered by means of conductor-like screening model both in water and in dichloromethane. It has been found that the donor and tetracyanoethylene remain neutral in complexes in ground state 1A1 and in lowest triplet state 3B1, but charge separation appears in excited singlet state 1B1. Through the correction of nonequilibrium solvation energy based on the spherical cavity approximation, ,,,* electron transfer transition energies have been obtained. Compared with the experimental measurements in dichloromethane, the theoretical results in the same solvent are found higher by about 0.5 eV. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 874,886, 2002 [source]


    Geometries and Electronic Structures of Co-Oligomers and Co-Polymers Based on Tricyclic Nonclassical Thiophene: A Theoretical Study

    MACROMOLECULAR THEORY AND SIMULATIONS, Issue 7-8 2008
    Yangwu Fu
    Abstract The geometries and electronic properties of four copolymers based on tricyclic nonclassical thiophene were studied using DFT at the B3LYP/6-31G(d) level. Bond lengths and their alternation, electron densities at BCPs, NICS, and WBIs were analyzed and correlated with the energy gap. The results show that the degree of conjugation increases upon main chain extension. The energy gap decreased steadily with increasing degree of polymerization. Conjugation is stronger in the central than in the outer section. The results suggest that the narrow HOMO/LUMO separation of tricyclic nonclassical thiophenes can be carried over to their co-polymers by using them as building blocks for the co-polymers. [source]


    Models of S/, interactions in protein structures: Comparison of the H2S,benzene complex with PDB data

    PROTEIN SCIENCE, Issue 10 2007
    Ashley L. Ringer
    Abstract S/, interactions are prevalent in biochemistry and play an important role in protein folding and stabilization. Geometries of cysteine/aromatic interactions found in crystal structures from the Brookhaven Protein Data Bank (PDB) are analyzed and compared with the equilibrium configurations predicted by high-level quantum mechanical results for the H2S,benzene complex. A correlation is observed between the energetically favorable configurations on the quantum mechanical potential energy surface of the H2S,benzene model and the cysteine/aromatic configurations most frequently found in crystal structures of the PDB. In contrast to some previous PDB analyses, configurations with the sulfur over the aromatic ring are found to be the most important. Our results suggest that accurate quantum computations on models of noncovalent interactions may be helpful in understanding the structures of proteins and other complex systems. [source]


    Structuring Strategies for Complex Geometries

    ARCHITECTURAL DESIGN, Issue 4 2010
    Wolf Mangelsdorf
    Abstract Over the last couple of decades, computation has proved a great facilitator for design, allowing far greater scope for analysis and generative design. Intelligent engineering, though, can only be truly set apart by the pursuit of the right design strategy, as outlined here by Wolf Mangelsdorf of Buro Happold. Mangelsdorf highlights four different models that enable the generation and engineering of geometrically complex forms and describes how they have been applied by Buro Happold in four very diverse projects with different architect collaborators. Copyright © 2010 John Wiley & Sons, Ltd. [source]


    A Density Functional Study of Phosphorus Nitride P3N5: Refined Geometries, Properties, and Relative Stability of ,-P3N5 and ,-P3N5 and a Further Possible High-Pressure Phase ,-P3N5 with Kyanite-Type Structure.

    CHEMINFORM, Issue 41 2002
    Peter Kroll
    No abstract is available for this article. [source]


    NMR Parameters and Geometries of OHN and ODN Hydrogen Bonds of Pyridine,Acid Complexes

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004
    Hans-Heinrich Limbach Prof.
    Abstract In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine,acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors are proposed which take into account anharmonic zero-point energy vibrations. The correction factors are different for OHN and ODN hydrogen bonds and depend on whether a double or a single well potential is realized in the strong hydrogen-bond regime. One correction factor was determined from the known experimental structure of a very strong OHN hydrogen bond between pentachlorophenol and 4-methylpyridine, determined by the neutron diffraction method. The remaining correction factors which allow one also to describe H/D isotope effects on the NMR parameters and geometries of OHN hydrogen bond were determined by analysing the NMR parameters of the series of protonated and deuterated pyridine- and collidine,acid complexes. The method may be used in the future to establish hydrogen-bond geometries in biologically relevant functional OHN hydrogen bonds. [source]


    Inclusion Behavior of ,-Cyclodextrin with Bipyridine Molecules: Factors Governing Host-Guest Inclusion Geometries

    CHEMISTRY - AN ASIAN JOURNAL, Issue 3 2009
    Yan-Li Zhao Dr.
    Abstract Guest Effect: The differences of nitrogen atom positions and the bridge bonds linked to two pyridine rings of some bipyridine guests can significantly affect the binding abilities and inclusion geometries of ,-cyclodextrin with the guests in both the solution and solid states. The 1:1 complexation of ,-cyclodextrin (,-CD) with structurally similar bipyridine guests which lead to the formation of six inclusion complexes (1,6) of ,-CD with 4,4,-vinylenedipyridine, 2,2,-vinylenedipyridine, 1-(2-pyridyl)-2-(4-pyridyl)ethylene, 4,4,-ethylene-dipyridine, 4,4,-dithiodipyridine, and 2,2,-dithiodipyridine has been investigated comprehensively by X-ray crystallography in the solid state and by 1H,NMR spectroscopy and microcalorimetric titration in aqueous solution. The complex formation constants (KS) for the stoichiometric 1:1 host,guest inclusion complexation of ,-CD with the bipyridine derivatives were determined in aqueous solution by microcalorimetry and the host,guest inclusion geometries of the complexes were deduced from 1H ROESY NMR spectroscopy. It transpires that the guest bipyridine molecules are included in the ,-CD cavity with a range of different inclusion geometries. In the solid state, the crystal superstructures for the ,-CD complexes 1, 4, and 5 are characterized by the triclinic crystal system (space group P1) commensurate with AAAA type supramolecular aggregation. By contrast, the ,-CD complexes 2, 3, and 6 display either monoclinic (space group P21) or orthorhombic (space group C2221) crystal systems, characteristic of ABAB type supramolecular aggregation. The results demonstrate that the relative locations of the nitrogen atom positions and the bridge-bond links between the two pyridine rings in these bipyridine guests, not only lead to distinct crystal systems and space groups, but also to different binding geometries and thermodynamical parameters on complexation of the bipyridines with ,-CD. The knowledge obtained from this research improves our understanding of the molecular recognition and self-assembly processes exhibited by ,-CD, both in the solid state and in aqueous solution. [source]


    On the Importance of CP-corrected Gradient Optimization in the Study of Hydrogen Bonded Systems

    CHINESE JOURNAL OF CHEMISTRY, Issue 12 2003
    Wei-Zhou Wang
    Abstract Geometries, harmonic vibrational frequencies and interaction energies of the water-hydrogen sulfide dimer, hydrogen fluoride dimer and glycine zwitterion-water dimer were determined by the counterpoise-corrected (CP-corrected) gradient optimization that explicitly corrects for the basis set superposition error (BSSE) and CP-uncorrected (normal) gradient optimization respectively at the B3LYP and MP2 levels of theory, employing the popular Pople's standard 6,31G(d), 6,31G(d, p) and 6,311 + + G(d, p) basis sets in order to assess the importance of CP-corrected gradient optimization in the study of hydrogen bonded systems. The normal optimization of these three H-bonded systems obtained using these popular basis sets all yielded erratic results, whereas use of CP-corrected gradient optimization led to consistent results with those from larger basis sets. So this CP receipt becomes useful and necessary to correctly describe large systems, where the use of small basis sets may be necessary. [source]


    Design and use of a multimedia trainer for the subject Descriptive Geometry

    COMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 1 2009
    Máximo Pérez Morales
    Abstract Less and less time is being dedicated to Descriptive Geometry in Technical Careers. For that reason, a multimedia application that allows us improve and optimize the teaching,learning process in the resolution of typical problems of this subject has been designed. Easy of use, interactiveness or efficiency are characteristics that can be related to this application. In this article, we describe the more important aspects of the developed Multimedia Trainer, as well as the results obtained in an experience with students with the purpose of evaluating its possibilities of use. © 2008 Wiley Periodicals, Inc. Comput Appl Eng Educ 17: 13,24, 2009; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae20164 [source]


    Hierarchical Structure Recovery of Point-Sampled Surfaces

    COMPUTER GRAPHICS FORUM, Issue 6 2010
    Marco Attene
    I.3 COMPUTER GRAPHICS; I.3.5 Computational Geometry and Object Modeling,Object hierarchies Abstract We focus on the class of ,regular' models defined by Várady et al. for reverse engineering purposes. Given a 3D surface,,represented through a dense set of points, we present a novel algorithm that converts,,to a hierarchical representation,. In,, the surface is encoded through patches of various shape and size, which form a hierarchical atlas. If,,belongs to the class of regular models, then,,captures the most significant features of,,at all the levels of detail. In this case, we show that,,can be exploited to interactively select regions of interest on,,and intuitively re-design the model. Furthermore,,,intrinsically encodes a hierarchy of useful ,segmentations' of,. We present a simple though efficient approach to extract and optimize such segmentations, and we show how they can be used to approximate the input point sets through idealized manifold meshes. [source]


    Fast Inverse Reflector Design (FIRD)

    COMPUTER GRAPHICS FORUM, Issue 8 2009
    A. Mas
    I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism; I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling , Physically based modeling; I.3.1 [Hardware architecture]: Graphics processors Abstract This paper presents a new inverse reflector design method using a GPU-based computation of outgoing light distribution from reflectors. We propose a fast method to obtain the outgoing light distribution of a parametrized reflector, and then compare it with the desired illumination. The new method works completely in the GPU. We trace millions of rays using a hierarchical height-field representation of the reflector. Multiple reflections are taken into account. The parameters that define the reflector shape are optimized in an iterative procedure in order for the resulting light distribution to be as close as possible to the desired, user-provided one. We show that our method can calculate reflector lighting at least one order of magnitude faster than previous methods, even with millions of rays, complex geometries and light sources. [source]


    Multiresolution Random Accessible Mesh Compression

    COMPUTER GRAPHICS FORUM, Issue 3 2006
    Junho Kim
    This paper presents a novel approach for mesh compression, which we call multiresolution random accessible mesh compression. In contrast to previous mesh compression techniques, the approach enables us to progressively decompress an arbitrary portion of a mesh without decoding other non-interesting parts. This simultaneous support of random accessibility and progressiveness is accomplished by adapting selective refinement of a multiresolution mesh to the mesh compression domain. We present a theoretical analysis of our connectivity coding scheme and provide several experimental results. The performance of our coder is about 11 bits for connectivity and 21 bits for geometry with 12-bit quantization, which can be considered reasonably good under the constraint that no fixed neighborhood information can be used for coding to support decompression in a random order. Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling [source]


    Sweep-based Freeform Deformations

    COMPUTER GRAPHICS FORUM, Issue 3 2006
    Seung-Hyun Yoon
    We propose a sweep-based approach to the freeform deformation of three-dimensional objects. Instead of using a volume enclosing the whole object, we approximate only its deformable parts using sweep surfaces. The vertices on the object boundary are bound to the sweep surfaces and follow their deformation. Several sweep surfaces can be organized into a hierarchy so that they interact with each other in a controlled manner. Thus we can support intuitively plausible shape deformation of objects of arbitrary topology with multiple control handles. A sweep-based approach also provides important advantages such as volume preservation. We demonstrate the effectiveness of our technique in several examples. Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computational Geometry and Object Modeling]: Curve, surface, solid, and object representations [source]


    Applied Geometry:Discrete Differential Calculus for Graphics

    COMPUTER GRAPHICS FORUM, Issue 3 2004
    Mathieu Desbrun
    Geometry has been extensively studied for centuries, almost exclusively from a differential point of view. However, with the advent of the digital age, the interest directed to smooth surfaces has now partially shifted due to the growing importance of discrete geometry. From 3D surfaces in graphics to higher dimensional manifolds in mechanics, computational sciences must deal with sampled geometric data on a daily basis-hence our interest in Applied Geometry. In this talk we cover different aspects of Applied Geometry. First, we discuss the problem of Shape Approximation, where an initial surface is accurately discretized (i.e., remeshed) using anisotropic elements through error minimization. Second, once we have a discrete geometry to work with, we briefly show how to develop a full- blown discrete calculus on such discrete manifolds, allowing us to manipulate functions, vector fields, or even tensors while preserving the fundamental structures and invariants of the differential case. We will emphasize the applicability of our discrete variational approach to geometry by showing results on surface parameterization, smoothing, and remeshing, as well as virtual actors and thin-shell simulation. Joint work with: Pierre Alliez (INRIA), David Cohen-Steiner (Duke U.), Eitan Grinspun (NYU), Anil Hirani (Caltech), Jerrold E. Marsden (Caltech), Mark Meyer (Pixar), Fred Pighin (USC), Peter Schröder (Caltech), Yiying Tong (USC). [source]


    Progressive Hulls for Intersection Applications

    COMPUTER GRAPHICS FORUM, Issue 2 2003
    Nikos Platis
    Abstract Progressive meshes are an established tool for triangle mesh simplification. By suitably adapting the simplification process, progressive hulls can be generated which enclose the original mesh in gradually simpler, nested meshes. We couple progressive hulls with a selective refinement framework and use them in applications involving intersection queries on the mesh. We demonstrate that selectively refinable progressive hulls considerably speed up intersection queries by efficiently locating intersection points on the mesh. Concerning the progressive hull construction, we propose a new formula for assigning edge collapse priorities that significantly accelerates the simplification process, and enhance the existing algorithm with several conditions aimed at producing higher quality hulls. Using progressive hulls has the added advantage that they can be used instead of the enclosed object when a lower resolution of display can be tolerated, thus speeding up the rendering process. ACM CSS: I.3.3 Computer Graphics,Picture/Image Generation, I.3.5 Computer Graphics,Computational Geometry and Object Modeling, I.3.7 Computer Graphics,Three-Dimensional Graphics and Realism [source]


    Deferred, Self-Organizing BSP Trees

    COMPUTER GRAPHICS FORUM, Issue 3 2002
    Sigal Ar
    Abstract bsptrees and KD trees are fundamental data structures for collision detection in walkthrough environments. A basic issue in the construction of these hierarchical data structures is the choice of cutting planes. Rather than base these choices solely on the properties of the scene, we propose using information about how the tree is used in order to determine its structure. We demonstrate how this leads to the creation ofbsptrees that are small, do not require much preprocessing time, and respond very efficiently to sequences of collision queries. Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling I.3.6 [Computer Graphics]: Graphics data structures and data types, Interaction techniques I.3.7 [Computer Graphics]: Virtual reality [source]


    Semi-Automatic 3D Reconstruction of Urban Areas Using Epipolar Geometry and Template Matching

    COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 7 2006
    José Miguel Sales Dias
    The main challenge is to compute the relevant information,building's height and volume, roof's description, and texture,algorithmically, because it is very time consuming and thus expensive to produce it manually for large urban areas. The algorithm requires some initial calibration input and is able to compute the above-mentioned building characteristics from the stereo pair and the availability of the 2D CAD and the digital elevation model of the same area, with no knowledge of the camera pose or its intrinsic parameters. To achieve this, we have used epipolar geometry, homography computation, automatic feature extraction and we have solved the feature correspondence problem in the stereo pair, by using template matching. [source]


    Application of the 3D Finite Difference Scheme to the TEXTORDED Geometry

    CONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006
    R. Zagórski
    First page of article [source]


    Good Geometry for Effective Science Education

    CURATOR THE MUSEUM JOURNAL, Issue 2 2005
    Dennis Liu
    First page of article [source]


    Participatory Governance in Urban Management and the Shifting Geometry of Power in Mumbai

    DEVELOPMENT AND CHANGE, Issue 5 2009
    Marie-Hélène Zérah
    ABSTRACT This article questions the participatory dimension of urban governance in Mumbai. Based on surveys of a number of participatory projects for urban services, it compares the differentiated impacts of participation in middle-class colonies with those in slums. Results demonstrate that changing citizen,government relationships have led to the empowerment of the middle and upper middle class who harness the potential of new ,invited space' to expand their claims on the city and political space. In contrast, the poor end up on the losing side as NGOs function more as contracted agents of the State than as representatives of the poor. Direct community participation empowers influential community members, small private entrepreneurs and middlemen, and contributes to labour informalization. Ultimately, these processes consolidate a form of ,governing beyond the State' that promotes a managerial vision of participation and leads to double standards of citizenship. [source]


    Structural and biophysical simulation of angiogenesis and vascular remodeling ,

    DEVELOPMENTAL DYNAMICS, Issue 4 2001
    Ralf Gödde
    Abstract The purpose of this report is to introduce a new computer model for the simulation of microvascular growth and remodeling into arteries and veins that imitates angiogenesis and blood flow in real vascular plexuses. A C++ computer program was developed based on geometric and biophysical initial and boundary conditions. Geometry was defined on a two-dimensional isometric grid by using defined sources and drains and elementary bifurcations that were able to proliferate or to regress under the influence of random and deterministic processes. Biophysics was defined by pressure, flow, and velocity distributions in the network by using the nodal-admittance-matrix-method, and accounting for hemodynamic peculiarities like Fahraeus-Lindqvist effect and exchange with extravascular tissue. The proposed model is the first to simulate interdigitation between the terminal branches of arterial and venous trees. This was achieved by inclusion of vessel regression and anastomosis in the capillary plexus and by remodeling in dependence from hemodynamics. The choice of regulatory properties influences the resulting vascular patterns. The model predicts interdigitating arteriovenous patterning if shear stress-dependent but not pressure-dependent remodeling was applied. By approximating the variability of natural vascular patterns, we hope to better understand homogeneity of transport, spatial distribution of hemodynamic properties and biomass allocation to the vascular wall or blood during development, or during evolution of circulatory systems. © 2001 Wiley-Liss, Inc. [source]


    Diagrammatic Representation in Geometry

    DIALECTICA, Issue 4 2006
    Dennis Potter
    In this paper I offer a theory about the nature of diagrammatic representation in geometry. On my view, diagrammatic representaiton differs from pictorial representation in that neither the resemblance between the diagram and its object nor the experience of such a resemblance plays an essential role. Instead, the diagrammatic representation is arises from the role the components of the diagram play in a diagramatic practice that allows us to draws inferences based on them about the ojbects they represent. [source]


    Overestimation of Left Ventricular Mass and Misclassification of Ventricular Geometry in Heart Failure Patients by Two-Dimensional Echocardiography in Comparison with Three-Dimensional Echocardiography

    ECHOCARDIOGRAPHY, Issue 3 2010
    Dmitry Abramov M.D.
    Background: Accurate assessment of left ventricular hypertrophy (LVH) and ventricular geometry is important, especially in patients with heart failure (HF). The aim of this study was to compare the assessment of ventricular size and geometry by 2D and 3D echocardiography in normotensive controls and among HF patients with a normal and a reduced ejection fraction. Methods: One hundred eleven patients, including 42 normotensive patients without cardiac disease, 41 hypertensive patients with HF and a normal ejection fraction (HFNEF), and 28 patients with HF and a low ejection fraction (HFLEF), underwent 2DE and freehand 3DE. The differences between 2DE and 3DE derived LVM were evaluated by use of a Bland,Altman plot. Differences in classification of geometric types among the cohort between 2DE and 3DE were determined. Results: Two-dimensional echocardiography overestimated ventricular mass compared to 3D echocardiography (3DE) among normal (166 ± 36 vs. 145 ± 20 gm, P = 0.002), HFNEF (258 ± 108 vs. 175 ± 47gm, P < 0.001), and HFLEF (444 ± 136 vs. 259 ± 77 gm, P < 0.001) patients. The overestimation of mass by 2DE increased in patients with larger ventricular size. The use of 3DE to assess ventricular geometry resulted in reclassification of ventricular geometric patterns in 76% of patients with HFNEF and in 21% of patients with HFLEF. Conclusion: 2DE overestimates ventricular mass when compared to 3DE among patients with heart failure with both normal and low ejection fractions and leads to significant misclassification of ventricular geometry in many heart failure patients. (Echocardiography 2010;27:223-229) [source]


    Relationship between Left Ventricular Geometry and Left Ventricular Systolic and Diastolic Functions in Patients with Chronic Severe Aortic Regurgitation

    ECHOCARDIOGRAPHY, Issue 6 2008
    Murat Çayli M.D.
    Background: Chronic aortic regurgitation (AR) is a form of volume overload inducing left ventricle (LV) dilatation. Myocardial fibrosis, apoptosis, progressive LV dilatation, and eventually LV dysfunction are seen with the progression of disease. The aim of the study was to assess the relation between LV geometry and LV systolic and diastolic functions in patients with chronic severe AR. Methods: The study population consisted of 88 patients with chronic severe AR and 42 healthy controls. The LV ejection fraction (LVEF) was calculated. Subjects were divided as Group I (controls, n = 42), Group II (LVEF > 50%, n = 47), and Group III (LVEF < 50%, n = 41). Transmitral early and late diastolic velocities and deceleration time were measured. The annular systolic (Sa) and diastolic (Ea and Aa) velocities were recorded. Diastolic function was classified as normal, impaired relaxation (IR), pseudonormalization (PN), and restrictive pattern (RP). Results: The LVEF was similar in Group I and II, while significantly lower in Group III. Sa velocity was progressively decreasing, but LV long- and short-axis diameters were increasing from Group I to Group III. Forty-six, 31 and 11 patients had IR, PN, and RP, respectively. LV long-axis systolic and diastolic diameters were significantly increasing, while LVEF and Sa velocity were significantly decreasing from patients with IR to patients with RP. The LV long-axis diastolic diameter is independently associated with LV systolic and diastolic functions. Conclusions: The LV long-axis diastolic diameter is closely related with LV systolic and diastolic functions in patients with chronic severe AR. [source]


    Local Dysfunction and Asymmetrical Deformation of Mitral Annular Geometry in Ischemic Mitral Regurgitation: A Novel Computerized 3D Echocardiographic Analysis

    ECHOCARDIOGRAPHY, Issue 4 2008
    Masao Daimon M.D.
    Objective: Most studies of the pathogenesis of functional mitral regurgitation (MR) have focused on alterations in ventricular function and geometry. We used a novel 3D echocardiographic method to assess abnormalities in mitral annular (MA) geometry and motion in patients with ischemic MR (IMR) and compared these data to those obtained from normal subjects and from patients with MR caused by dilated cardiomyopathy (DMR). Methods: Real time 3D echo was performed in 12 normal subjects, 25 with IMR, and 14 with DMR. Eight points along the saddle-shaped MA were identified using our software at systole and diastole. From these eight points, four annular diameters at each cardiac phase were determined. Annular motion was assessed by measuring local displacement (LD) of a given point between systole and diastole. Results: Annular motion was different between groups: IMR had smaller LD in posterior MA segments than did normals (2.6 ± 1.1 vs 4.8 ± 1.9 mm, P < 0.01), while DMR had globally reduced LD. In IMR systolic MA dilatation was striking in the anterior,posterior (diameter; IMR vs controls, 28.3 ± 3.5 vs 22.5 ± 2.2 mm, P< 0.05) and anterolateral,posteromedial (31.7 ± 3.5 vs 25.1 ± 2.2 mm, P < 0.05) directions; in IMR, systolic MA diameters in these two directions correlated with MR severity(P = 0.02). MA dilatation occurred globally in DMR. Conclusion: This novel 3D echo method demonstrated that MA motion and dilatation were asymmetric in IMR and symmetric in DMR. These differences in MA geometry and motion may aid in the development of distinct new therapies for IMR and DMR. [source]