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Geometric Features (geometric + feature)
Selected AbstractsLaser-Assisted Machining of Damage-Free Silicon Nitride Parts with Complex Geometric Features via In-Process Control of Laser PowerJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006Yinggang Tian A methodology to achieve optimal operating conditions for laser-assisted machining (LAM) is developed for silicon nitride parts with complex geometric features by applying a three-dimensional, transient thermal model and in-process laser power control. Complex silicon nitride parts are successfully produced by the LAM operation, where the maximum and material removal temperatures are carefully designed and controlled to achieve good machining results and avoid thermal damage on the final part. On-line temperature and laser power measurements are conducted and compared with prescribed values to show the effectiveness of the power control scheme. Scanning electron microscopy examination reveals virtually no subsurface microcrack or thermal damage on the silicon nitride parts. The X-ray diffraction (XRD) study shows the preservation of the silicon nitride microstructure and no phase transformation of ,-Si3N4 during the LAM experiments. XRD residual stress measurements show moderate compressive residual stresses on the silicon nitride workpieces produced by the LAM operation. [source] Geometric features of the flame propagation process for an SI engine having dual-ignition systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2002Atilla Bilgin Abstract Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark-ignition engine, having cylindrical disc-shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark-ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd. [source] Perceptual 3D pose distance estimation by boosting relational geometric featuresCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2-3 2009Cheng Chen Abstract Traditional pose similarity functions based on joint coordinates or rotations often do not conform to human perception. We propose a new perceptual pose distance: Relational Geometric Distance that accumulates the differences over a set of features that reflects the geometric relations between different body parts. An extensive relational geometric feature pool that contains a large number of potential features is defined, and the features effective for pose similarity estimation are selected using a set of labeled data by Adaboost. The extensive feature pool guarantees that a wide diversity of features is considered, and the boosting ensures that the selected features are optimized when used jointly. Finally, the selected features form a pose distance function that can be used for novel poses. Experiments show that our method outperforms others in emulating human perception in pose similarity. Our method can also adapt to specific motion types and capture the features that are important for pose similarity of a certain motion type. Copyright © 2009 John Wiley & Sons, Ltd. [source] Adaptive and Feature-Preserving Subdivision for High-Quality Tetrahedral MeshesCOMPUTER GRAPHICS FORUM, Issue 1 2010D. Burkhart I.3.5 [Computer Graphics]: Curve, surface, solid, and object representations Abstract We present an adaptive subdivision scheme for unstructured tetrahedral meshes inspired by the, -subdivision scheme for triangular meshes. Existing tetrahedral subdivision schemes do not support adaptive refinement and have traditionally been driven by the need to generate smooth three-dimensional deformations of solids. These schemes use edge bisections to subdivide tetrahedra, which generates octahedra in addition to tetrahedra. To split octahedra into tetrahedra one routinely chooses a direction for the diagonals for the subdivision step. We propose a new topology-based refinement operator that generates only tetrahedra and supports adaptive refinement. Our tetrahedral subdivision algorithm is motivated by the need to have one representation for the modeling, the simulation and the visualization and so to bridge the gap between CAD and CAE. Our subdivision algorithm design emphasizes on geometric quality of the tetrahedral meshes, local and adaptive refinement operations, and preservation of sharp geometric features on the boundary and in the interior of the physical domain. [source] Alternative Mechanistic Paths in the Hetero-Diels,Alder Reaction of ,-Oxothiones: A Theoretical StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2007Laura Legnani Abstract DFT calculations at the B3LYP/6-311+G(d,p) level for the C, H, and O atoms and at the 6-311+G(2df,p) level for the S atom were used to study the hetero-Diels,Alder reactions between several ,-oxothiones and ethylene or methyl vinyl ether (MVE). All the transition states and the intermediates along the reaction pathways, as well as the reaction products, were located. The reactions with ethylene are all concerted though asynchronous whereas in the reactions with MVE the electron-releasing character of the methoxy substituent lowers the energy barriers and enhances the asynchronicity and the charge transfer process to such an extent that the reaction may become unconcerted and exhibit a two-step mechanism with a zwitterionic intermediate derived from nucleophilic attack of electron-rich MVE to the sulfur atom of the strongly electrophilically activated ,-oxothiones. The reactions are also favored by the conjugation of the newly formed C=C bond. Moreover, the geometric features of the diene exert a nonnegligible role, as dienes that are planar or almost planar in their ground state show a lower energy barrier. Thus, both geometric and electronic features of the dienes as well as of the dienophiles play a significant role in the easiness of the reactions and in their mechanism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Application of the additive Schwarz method to large scale Poisson problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 3 2004K. M. Singh Abstract This paper presents an application of the additive Schwarz method to large scale Poisson problems on parallel computers. Domain decomposition in rectangular blocks with matching grids on a structured rectangular mesh has been used together with a stepwise approximation to approximate sloping sides and complicated geometric features. A seven-point stencil based on central difference scheme has been used for the discretization of the Laplacian for both interior and boundary grid points, and this results in a symmetric linear algebraic system for any type of boundary conditions. The preconditioned conjugate gradient method has been used as an accelerator for the additive Schwarz method, and three different methods have been assessed for the solution of subdomain problems. Numerical experiments have been performed to determine the most suitable set of subdomain solvers and the optimal accuracy of subdomain solutions; to assess the effect of different decompositions of the problem domain; and to evaluate the parallel performance of the additive Schwarz preconditioner. Application to a practical problem involving complicated geometry is presented which establishes the efficiency and robustness of the method. Copyright © 2004 John Wiley & Sons, Ltd. [source] Polygonal finite elements for topology optimization: A unifying paradigmINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2010Cameron Talischi Abstract In topology optimization literature, the parameterization of design is commonly carried out on uniform grids consisting of Lagrangian-type finite elements (e.g. linear quads). These formulations, however, suffer from numerical anomalies such as checkerboard patterns and one-node connections, which has prompted extensive research on these topics. A problem less often noted is that the constrained geometry of these discretizations can cause bias in the orientation of members, leading to mesh-dependent sub-optimal designs. Thus, to address the geometric features of the spatial discretization, we examine the use of unstructured meshes in reducing the influence of mesh geometry on topology optimization solutions. More specifically, we consider polygonal meshes constructed from Voronoi tessellations, which in addition to possessing higher degree of geometric isotropy, allow for greater flexibility in discretizing complex domains without suffering from numerical instabilities. Copyright © 2009 John Wiley & Sons, Ltd. [source] Constructal tree-shaped paths for conduction and convectionINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2003Adrian Bejan Abstract This lecture reviews a series of recent results based on the geometric minimization of the resistance to flow between one point (source, sink) and a volume or an area (an infinity of points). Optimization is achieved by varying the geometric features of the flow path subject to volume constraints. The method is outlined by using the problem of steady volume-point conduction. Optimized first is the smallest elemental volume, which is characterized by volumetric heat generation in a low-conductivity medium, and one-dimensional conduction through a high-conductivity ,channel'. Progressively larger volumes are covered by assemblies of previously optimized constructs. Tree-shaped flow structures spring out of this objective and constraints principle. Analogous problems of fluid flow, and combined heat and fluid flow (convection, trees of fins) are also discussed. The occurrence of similar tree structures in nature may be reasoned based on the same principle (constructal theory) (Bejan, 2000). Copyright © 2003 John Wiley & Sons, Ltd. [source] Geometric features of the flame propagation process for an SI engine having dual-ignition systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2002Atilla Bilgin Abstract Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark-ignition engine, having cylindrical disc-shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark-ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd. [source] Engineering functional materials by halogen bondingJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2007Pierangelo Metrangolo Abstract Engineering functional materials endowed with unprecedented properties require the exploitation of new intermolecular interactions, which can determine the characteristics of the bulk materials. The great potential of Halogen Bonding (XB), namely any noncovalent interaction involving halogens as electron acceptors, in the design of new and high-value functional materials is now emerging clearly. This Highlight will give a detailed overview on the energetic and geometric features of XB, showing how some of them are quite constant in most of the formed supramolecular complexes (e.g., the angle formed by the covalent and the noncovalent bonds around the halogen atom), while some others depend strictly on the nature of the interacting partners. Then, several specific examples of halogen-bonded supramolecular architectures, whose structural aspects as well as applications in fields as diverse as enantiomers' separation, crystal engineering, liquid crystals, natural, and synthetic receptors, will be fully described. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: PolymChem 45: 1,15, 2007 [source] Laser-Assisted Machining of Damage-Free Silicon Nitride Parts with Complex Geometric Features via In-Process Control of Laser PowerJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006Yinggang Tian A methodology to achieve optimal operating conditions for laser-assisted machining (LAM) is developed for silicon nitride parts with complex geometric features by applying a three-dimensional, transient thermal model and in-process laser power control. Complex silicon nitride parts are successfully produced by the LAM operation, where the maximum and material removal temperatures are carefully designed and controlled to achieve good machining results and avoid thermal damage on the final part. On-line temperature and laser power measurements are conducted and compared with prescribed values to show the effectiveness of the power control scheme. Scanning electron microscopy examination reveals virtually no subsurface microcrack or thermal damage on the silicon nitride parts. The X-ray diffraction (XRD) study shows the preservation of the silicon nitride microstructure and no phase transformation of ,-Si3N4 during the LAM experiments. XRD residual stress measurements show moderate compressive residual stresses on the silicon nitride workpieces produced by the LAM operation. [source] Evaluation of Digital Image Discretization Error in Droplet Shape Measurement Using SimulationPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5-6 2009Sina Ghaemi Abstract Droplet shape measurement using image based techniques can be conducted using shape parameters which consist of a number of geometric features of a droplet image. The accuracy of calculating these shape parameters and their capability in revealing shape deviation is considerably affected by the discretization of the image with a camera CCD. In this paper, a simulation of digital images is conducted to investigate the error caused by image discretization. The effect of this error on calculating area, perimeter, and also a selected number of shape parameters are investigated. Digital images of circular and elliptical discs at different image/pixel size ratio and locations relative to the pixel grid have been generated to simulate the projected view. Results show that the shape parameters demonstrate different levels of sensitivity to the desirable factor of shape deviation and the undesirable factor of image discretization. A "clearance factor" has been suggested and used to rank the shape parameters based on their compensation between sensitivity to shape deviation and image discretization. [source] Tris(4-bromophenyl)aminium hexachloridoantimonate (`Magic Blue'): a strong oxidant with low inner-sphere reorganizationACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Mauricio Quiroz-Guzman Both the radical cation tris(4-bromophenyl)aminium hexachloridoantimonate (`Magic Blue'), (C18H12Br3N)[SbCl6], (I), and neutral tris(4-bromophenyl)amine, C18H12Br3N, (II), show extremely similar three-bladed propeller structures with planar N atoms. Key geometric features, such as the C,N bond distances and the angles between the planes of the aryl groups and the central NC3 plane, are identical within experimental uncertainty in the two structures. This contrasts with the significant structural changes observed on oxidation of more electron-rich triarylamines, where resonance contributes to the stabilization of the radical cation, and suggests that, in general, more strongly oxidizing triarylaminium cations will have lower inner-sphere reorganization energies than their lower-potential analogues. [source] Hydrogen bonding in 2-(2-oxothiazolidin-3-yl)-4,5-dihydrothiazolium hydrogen sulfate monohydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008Rodrigo S. Corrêa The asymmetric unit of the title compound, C6H9N2OS2+·HSO4,·H2O, contains a heterocyclic cation, a hydrogen sulfate anion and a water molecule. There are strong hydrogen bonds between the hydrogen sulfate anions and water molecules, forming an infinite chain along the [010] direction, from which the cations are pendent. The steric, electronic and geometric features are compared with those of similar compounds. In this way, structural relationships are stated in terms of the influence of the sulfate group on the protonation of the heterocycle and on the tautomeric equilibrium in the solid state. [source] Very Long-Range Effects: Cooperativity between Anion,, and Hydrogen-Bonding InteractionsCHEMPHYSCHEM, Issue 13 2009Xavier Lucas Abstract The interplay between two important non-covalent interactions involving aromatic rings (namely anion,, and hydrogen bonding) is investigated. Very interesting cooperativity effects are present in complexes where anion,, and hydrogen bonding interactions coexist. These effects are found in systems where the distance between the anion and the hydrogen-bond donor/acceptor molecule is as long as ,11 Å. These effects are studied theoretically using the energetic and geometric features of the complexes, which were computed using ab initio calculations. We use and discuss several criteria to analyze the mutual influence of the non-covalent interactions studied herein. In addition we use Bader's theory of atoms-in-molecules to characterize the interactions and to analyze the strengthening or weakening of the interactions depending upon the variation of the charge density at the critical points. [source] | |||||||||||||||||||