The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
J C Phillips - One of the best experts on this subject based on the ideXlab platform.
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is there a Lowest Upper Bound for superconductive transition temperatures
Journal of Physics: Conference Series, 2008Co-Authors: J C PhillipsAbstract:The values of superconductive transition temperatures Tc in conventional crystalline metallic superconductors are widely scattered, depend on the details of the Fermi surface (especially the density of states N(EF)), and are typically below 1 K. By far the highest Tc 's (~100 K) are found in the cuprates, and there Tc is apparently insensitive to the geometry of the Fermi surface, while it depends strongly on dopant density and configuration. For the cuprates there is a smooth master curve Tcmax( ) for the highest Tc's as a function of the average number of Pauling resonating bonds/atom in the parent (undoped) insulator. The existence of such an -dependent optimized Tc is suggested by analogies with the microscopic theory of optimized molecular glass networks (such as window glass), but it remains to derive a rigorous quantum theory of the origin of Tcmax( ).
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is there a Lowest Upper Bound for superconductive transition temperatures
Chemical Physics Letters, 2008Co-Authors: J C PhillipsAbstract:Abstract I show that for high temperature ceramic cuprates there is a smooth master curve T c max ( 〈 R 〉 ) for the highest superconductive transition temperatures T c ’s as a function of the average number 〈 R 〉 of Pauling resonating bonds/atom in the parent (undoped) insulator. The existence of such an 〈 R 〉-dependent optimized T c is suggested by analogies with the microscopic theory of optimized molecular glass networks (such as window glass). The chemical model is part of a larger nanoscopically mixed multiphase structural model that also explains the canonical cuprate phase diagrams, as well as recent dynamical fs pump/ps probe optical relaxation experiments.
S.k. Sahoo - One of the best experts on this subject based on the ideXlab platform.
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Upper Bound Analysis for Extrusion of T-section Bar from Square Billet Through Square Dies
Meccanica, 2000Co-Authors: S.k. SahooAbstract:The present study is devoted to the Upper Bound analysis of extrusion of T-section bars from square billets through square dies using the modified SERR (Spatial Elementary Rigid Region) technique. Optimized values of the non-dimensional average extrusion pressure at various area reductions have been computed and compared with experimental results available in literature. The optimization process in this study consisted of three stages: (i) optimization of the extrusion pressure with respect to appropriate system variables, (ii) determination of the optimum scheme of discretization of the deformation zone for each of the three formulations (single-point, double-point and triple-point), and (iii) identifying the formulation that gives the Lowest Upper Bound.
K.c. Singh - One of the best experts on this subject based on the ideXlab platform.
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Direct Upper Bound Solution to Rectangular-to-Polygonal Extrusion Through Square Die
Journal of Manufacturing Science and Engineering-transactions of The Asme, 1999Co-Authors: Susanta Kumar Sahoo, K.c. SinghAbstract:This paper is concerned with an attempt to find an Upper Bound solution for the problems of steady-state extrusion of asymmetric polygonal section bars through rough square dies. A class of kinematically admissible velocity fields is examined, reformulating the SERR technique, to get the velocity field that gives the Lowest Upper Bound. This velocity field is utilized to compute the non-dimensional average extrusion pressure at various area reductions for different billet aspect ratios.
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Upper-Bound analysis of the extrusion of a bar of channel section from square/rectangular billets through square dies
Journal of Materials Processing Technology, 1998Co-Authors: Susanta Kumar Sahoo, K.c. SinghAbstract:Abstract In this study, an Upper-Bound analysis is presented for the extrusion of bars of channel section from square/rectangular billets through rough square dies. A class of kinematically admissible discontinuous velocity fields, based on the reformulated SERR technique, is examined and the velocity field giving the Lowest Upper-Bound is identified. This velocity fields is used to compute the Upper-Bound extrusion pressure for various area reductions.
N.r. Chitkara - One of the best experts on this subject based on the ideXlab platform.
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Extrusion of non-symmetric U- and I-shaped sections through ruled-surface dies: numerical simulations and some experiments
International Journal of Mechanical Sciences, 2002Co-Authors: Kemal Celik, N.r. ChitkaraAbstract:Abstract In this paper, previously developed analytical approach (Chitkara NR, Celik KF. Int J Mech Sci 2000; 42:273) based on the Upper-Bound theory was applied to analyse the mechanics of the extrusion of non-symmetric U- and I-shaped sections and the symmetric ones from initially round billets through the ruled-surface dies. To investigate the optimum shape of the designed extrusion dies, that yield the Lowest Upper-Bound for a given reduction in area, die length, off-centric positioning and frictional conditions a computer program was developed. Computations were carried out for various cases and some of the results compared with the experimental verifications. Curvature of the extruded product and simulated deforming grid patterns were also predicted and compared. A sophisticated CAD/CAM package was used in conjunction with the CNC and EDM processes to design and manufacture the streamlined dies for the extrusion of some non-symmetric U- and I-shaped sections. The theoretical predictions were observed to be in good agreement with the experimental results.
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Extrusion of non-symmetric T-shaped sections, an analysis and some experiments
International Journal of Mechanical Sciences, 2001Co-Authors: N.r. Chitkara, K.f. CelikAbstract:Abstract In the present study, previously developed analytical approach (Int. J. Mech. Sci. 42 (2000) 273), based on the Upper-Bound theory, for the design of three-dimensional off-centric extrusion of arbitrarily shaped dies was applied to the extrusion of T-shaped sections from initially round billets with the experimental verifications. Here, non-symmetric T-shaped sections as well as symmetric ones were considered. A computer program was written to obtain optimum die design which yield the Lowest Upper-Bound for a given reduction in area, die length, its off-centric positioning and the frictional conditions. Computations were carried out both for the converging (ruled-surface) and the smooth curved (advanced-surface) dies. Curvature of the extruded product and simulated deforming grid pattern were also predicted. A sophisticated CAD/CAM package was used in conjunction with the CNC and EDM processes to manufacture the streamlined dies for the extrusion of T-shaped sections. The theoretical predictions were observed to be in good agreement with the experimental results.
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Application of an Upper Bound method to off-centric extrusion of square sections, analysis and experiments
International Journal of Mechanical Sciences, 2000Co-Authors: Kemal Celik, N.r. ChitkaraAbstract:Abstract In the present study, previously developed analytical approach (Chitkara and Celik) which was based on the Upper-Bound theory, for the design of three dimensional off-centric extrusion of arbitrarily shaped dies was applied to the off-centric extrusion of square sections from initially round billets with experimental verifications. A computer program was written to obtain optimum die design which yield the Lowest Upper-Bound for a given reduction in area, die length, off-centric positioning and frictional conditions. Computations were carried out both for the converging (ruled-surface) and smooth curved (advancedsurface) dies. Curvature of the extruded product and simulated deforming grid pattern were also predicted. A sophisticated CAD/CAM package was used in conjunction with the CNC and EDM processes to manufacture the streamlined dies for the off-centric extrusion of square section rods. The theoretical predictions were observed to be in good agreement with the experimental results.
Kentaro Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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Seismic bearing capacity of shallow foundations near slopes using the Upper-Bound method
International Journal of Geotechnical Engineering, 2010Co-Authors: Kentaro YamamotoAbstract:AbstractThe seismic bearing capacity factors of spread and embedded foundations near slopes have been analytically investigated. The pseudo-static approach was used and the seismic forces consisted of a horizontal load applied to the foundation and the inertia of the soil mass. The Upper-Bound method of limit analysis was employed and a non-symmetrical failure mechanism was proposed. This mechanism comprises a triangular active wedge, a logarithmic spiral shear zone and a passive wedge. The shear transfer coefficient was introduced to calculate the seismic bearing capacity of spread foundations with variable shear transfer at the base of foundations. The validity of the results from the present analysis was confirmed by comparing with the results proposed by other investigators. Finally, the Lowest Upper-Bound solutions of the seismic bearing capacity factors of shallow foundations near slopes were presented in the form of design charts for practical use in geotechnical engineering. It has been shown that...
