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Geometric Configuration (geometric + configuration)
Selected AbstractsInfluence of dynamic structure on the microstructure formation of a steel surface in the electrolyte in a steady magnetic fieldPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004Svetlana Gorobets Abstract The periodic microfabrication effect of metal element surfaces in an electrolyte solution in an external steady magnetic field was investigated. Authors have shown that corrosion velocity and periodic microstructure formation on the metal element surface can be controlled by magnetic field application. Geometric configuration of periodic microstructure depends on metal element characteristics, electrolyte solution, treatment time, magnetic field magnitude and other parameters. Investigation results have shown possibility of magnetic field influence on hydrodynamic conditions and metal surface structure under its etching in the nitric acid solution. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The stability of stars of triangular equilibrium plate elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2009E. A. W. Maunder Abstract Equilibrium models for finite element analyses are becoming increasingly important in complementary roles to those from conventional conforming models, but when formulating equilibrium models questions of stability, or admissibility of loads, are of major concern. This paper addresses these questions in the context of flat plates modelled with triangular hybrid elements involving membrane and/or flexural actions. Patches of elements that share a common vertex are considered, and such patches are termed stars. Stars may be used in global analyses as assemblies of elements forming macro-elements, or in local analyses. The conditions for stability, or the existence and number of spurious kinematic modes, are determined in a general algebraic procedure for any degree of the interpolation polynomials and for any geometric configuration. The procedure involves the determination of the rank of a compatibility matrix by its transformation to row echelon form. Examples are presented to illustrate some of the characteristics of spurious kinematic modes when they exist in stars with open or closed links. Copyright © 2008 John Wiley & Sons, Ltd. [source] Fundamentals of exergy analysis, entropy generation minimization, and the generation of flow architectureINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2002Adrian Bejan Abstract This paper outlines the fundamentals of the methods of exergy analysis and entropy generation minimization (or thermodynamic optimization,the minimization of exergy destruction). The paper begins with a review of the concept of irreversibility, entropy generation, or exergy destruction. Examples illustrate the accounting for exergy flows and accumulation in closed systems, open systems, heat transfer processes, and power and refrigeration plants. The proportionality between exergy destruction and entropy generation sends the designer in search of improved thermodynamic performance subject to finite-size constraints and specified environmental conditions. Examples are drawn from energy storage systems for sensible heat and latent heat, solar energy, and the generation of maximum power in a power plant model with finite heat transfer surface inventory. It is shown that the physical structure (geometric configuration, topology) of the system springs out of the process of global thermodynamic optimization subject to global constraints. This principle generates structure not only in engineering but also in physics and biology (constructal theory). Copyright © 2002 John Wiley & Sons, Ltd. [source] In vivo kinematics of total knee arthroplasty: Flat compared with concave tibial joint surfaceJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2000J. Uvehammer This study evaluated the influence of the geometric configuration of the tibial joint area on the kinematics of the knee. Twenty-two patients with noninflammatory arthritis and minor preoperative deformity were studied. They each received an AMK total knee replacement with retention of the posterior cruciate ligament. Eleven patients without any knee abnormalities were used as controls. The patients were stratified to either the flat (terminology of the manufacturer: standard) or concave (terminology of the manufacturer: constrained) polyethylene insert (n = 11 in each group). Knee kinematics were assessed 1 year after the operation by having the patient ascend a platform corresponding to an extension of the knee from 50 to 70° of flexion. During this motion, two film-exchangers simultaneously exposed six to 13 pairs of serial stereoradiographs. The concave geometric configuration of the tibial insert resulted paradoxically in increased anterior-posterior translations compared with the flat insect but no significant change of rotations and translations in the other directions. Compared with normal knees, the most obvious abnormality was increased anterior-posterior translations (p < 0.004). At 50° of flexion, the implants with the flat tibial polyethylene insert had displaced 2 times and the concave ones had displaced 2.5 times more posteriorly than the normal knees (p , 0.001). Less internal tibial rotation was also recorded in the flexed positions for both types of inserts compared with the normal knees (p < 0.02). Four knees in four patients, who reported symptoms of instability and abnormal knee function, showed significantly increased proximal displacement of the center of the tibial plateau in the flexed position. The findings suggest that current prosthetic designs and surgical technique do not restore normal knee kinematics and indicate that design improvements should rely on in vivo kinematic studies. [source] Synthesis of N -alkoxybenzimidoyl azides and their reactions in electrophilic mediaJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2010Debra D. Dolliver Abstract A new general route to N -alkoxybenzimidoyl azides [ArC(N3)=NOR] from a reaction of N -alkoxybenzimidoyl bromide [ArC(Br)=NOR] with sodium azide in DMSO is described. These reactions result in the Z -geometric configuration. These compounds show a moderate degree of thermal stability as assessed by differential scanning calorimetry, and lack reactivity in traditional 1,3-dipolar cycloaddition ,click' reactions. Upon exposure to electrophilic compounds (trifluoroacetic acid or acetyl chloride), these azide compounds can react by two pathways: a Schmidt-type rearrangement to form an N -alkoxyurea or an isomerization,cyclization reaction pathway to form an N -alkoxytetrazole. The route of the reaction has no dependence on solvent polarity and appears to depend upon the electrophile (H+vs. CH3CO+): reaction of the azide with trifluoroacetic acid results predominantly in the urea; reaction with acetyl chloride results solely in the tetrazole. Calculations indicate that the urea product is thermodynamically favored over the tetrazole product. They also indicate that both reaction conditions result in an equilibration between the starting azide and the tetrazole with the tetrazole being the major component in this equilibrium mixture. The fact that the azide also undergoes a Schmidt-type rearrangement to form an N -alkoxyurea when treated with trifluoroacetic acid appears to indicate that the barrier for aromatic ring migration is lower in the protonated azide produced on reaction with trifluoroacetic acid than in the acetylated azide produced on reaction with acetyl chloride. Copyright © 2009 John Wiley & Sons, Ltd. [source] Solids Circulation Flux and Gas Bypassing in a Pressurized Spout-fluid Bed with a Draft TubeTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2002Rui Xiao Abstract An experimental study on solids circulation flux and gas bypassing of a spout-fluid bed with a draft tube at elevated pressures up to 600 kPa was performed in a 200 mm diameter cylindrical steel column with a 608 conical distributor. Glass beads with mean diameter 2.067 mm were used as bed materials to investigate the effect of operating conditions and geometric configuration on the solids circulation flux and the gas distribution between the annulus and the draft tube. A novel technique has been developed to measure the solids fluxes under pressure, and gas (CO2) traces have been employed to investigate gas bypassing characteristics. The solids circulation flux is greatly enhanced when operating pressure and auxiliary gas flowrate are increased, and it is also strongly influenced by geometric configuration. Two experimental relations are proposed for predicting solids circulation flux enhancement factors. Une étude expérimentale sur le flux de circulation des solides et la dérivation du gaz d'un lit jaillissant muni d'un tube d'aspiration à des pressions élevées jusqu'à 600 kPa, a été réalisée dans une colonne d'acier cylindrique de 200 mm de diamètre avec un distributeur conique à 608. Des billes de verre d'un diamètre moyen de 2,067 mm ont été utilisées comme matériaux de lit pour étudier l'effet des conditions opératoires et de la configuration géométrique sur le flux de circulation des solides et la distribution du gaz entre l'espace annulaire et le tube d'aspiration. Une nouvelle technique a été élaborée pour mesurer les flux de solides sous pression et les caractéristiques de la dérivation du gaz ont été étudiées à l'aide de gaz traceurs (CO2). Le flux de circulation des solides est grandement amélioré lorsque la pression de fonctionnement et le débit de gaz auxiliaire sont augmentés, et il est également fortement influencé par la configuration géométrique. Deux relations expérimentales sont proposées pour la prédiction des facteurs d'amélioration du flux de circulation des solides. [source] A parallel Galerkin boundary element method for surface radiation and mixed heat transfer calculations in complex 3-D geometriesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2004X. Cui Abstract This paper presents a parallel Galerkin boundary element method for the solution of surface radiation exchange problems and its coupling with the finite element method for mixed mode heat transfer computations in general 3-D geometries. The computational algorithm for surface radiation calculations is enhanced with the implementation of ideas used for 3-D computer graphics applications and with data structure management involving creating and updating various element lists optimized for numerical performance. The algorithm for detecting the internal third party blockages of thermal rays is presented, which involves a four-step procedure, i.e. the primary clip, secondary clip and adaptive integration with checking. Case studies of surface radiation and mixed heat transfer in both simple and complex 3-D geometric configurations are presented. It is found that a majority of computational time is spent on the detection of foreign element blockages and parallel computing is ideally suited for surface radiation calculations. Results show that the decrease of the CPU time approaches asymptotically to an inverse rule for parallel computing of surface radiation exchanges. For large-scale computations involving complex 3-D geometries, an iterative procedure is a preferred approach for the coupling of the Galerkin boundary and finite elements for mixed mode heat transfer calculations. Copyright © 2004 John Wiley & Sons, Ltd. [source] First principles study of small palladium cluster growth and isomerizationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2007Chen Luo Abstract Structures and physical properties of small palladium clusters Pdn up to n = 15 and several selected larger clusters were studied using density functional theory under the generalized gradient approximation. It was found that small Pdn clusters begin to grow 3-dimensionally at n = 4 and evolve into symmetric geometric configurations, such as icosahedral and fcc -like, near n = 15. Several isomers with nearly degenerate average binding energies were found to coexist and the physical properties of these clusters were calculated. For several selected isomers, relatively moderate energy barriers for structural interchange for a given cluster size were found, implying that isomerization could readily occur under ambient conditions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Effect of Sample Configuration on the Morphology of Foamed LDPE/PP Blends Injection Molded by a Gas Counterpressure ProcessMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2007Georgi Kotzev Abstract Blends of isotactic poly(propylene) and low-density polyethylene with different composition ratios were prepared through direct melt compounding on a twin-screw extruder. The specimens with various geometric configurations were injection-molded using a gas counterpressure process, using blends to which 0.5 wt.-% of a blowing agent was added. The influence of blend composition and specimen geometry on the structure and morphology of the samples was investigated by SEM and WAXS. The thermal behavior of the blends was analyzed by DSC. It was found that the morphology of each region depended on the composition ratio and specimen geometry. [source] Kinetics Approximation Considering Different Reactivities of the Structural Units Formed by the Anionic Copolymerization of 1,3-Butadiene and Styrene Using Al/Li/Ba as InitiatorMACROMOLECULAR REACTION ENGINEERING, Issue 8 2009José. A. Tenorio López Abstract The copolymerization reaction of butadiene and styrene copolymers prepared by anionic living polymerization using an initiator composed of alkyl aluminum, n -butyl lithium, and barium alkoxide is studied using a kinetic model that considers the reactivity of active sites to be different; this assumption is justified by the varying geometric configurations. With the first-order Markov model, the expressions for the fraction of active sites and dyad distribution are obtained. The rate constants are determined by fitting to the conversion and Bernoulli dyad data using the nonlinear least squares method. The conversion and dyad sequence distribution are correctly predicted, and the experimental results indicate that the microstructure and sequence distribution do not change with the conversion and temperature. [source] Kinetics of the Anionic Polymerization of Buta-1,3-diene Considering Different Reactivities of the cis, trans and vinyl Structural UnitsMACROMOLECULAR REACTION ENGINEERING, Issue 5 2008José A. Tenorio López Abstract The anionic solution polymerization of buta-1,3-diene was modeled, considering the reactivity of the active sites to be different due to varying geometric configurations. With the first-order Markov model, expressions for the fraction of active sites and dyad distribution were obtained. The rate constants were determined by fitting to the conversion and dyad experimental data using the nonlinear least squares method. The kinetic model shows that the microstructure and the dyads do not depend on initiator and butadiene concentration but only on rate constants. Without a modifier, the butadiene addition mechanism is entropic; with a modifier, the mechanism changes to entropic-enthalpic. [source] | ||||||||||||||||