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71.
This paper presents a computer-based method for optimally sizing members of planar steel frameworks using commercially available standard sections. For first-order behavior and static loads, a minimum-weight structure is found while simultaneously ensuring stress and displacement performance conditions under applied service loads. Architectural conditions are imposed on section sizes to satisfy fabrication requirements related to member continuity and structure symmetry. The design method presented is iterative in nature and remarkably efficient. The number of iterations is generally quite small and almost totally independent: of the complexity of the structure. Designs are presented for two steel frameworks that are typical of those encountered in professional practise. 相似文献
72.
73.
V. A. Tkachenko Z. D. Kvon O. A. Tkachenko D. G. Baksheev O. Estibals J. -C. Portal 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):469
An AlGaAs/GaAs lateral quantum dot of triangular shape with a characteristic size L<100 nm containing less than ten electrons was studied. Single-electron oscillations of the conductance G of this dot were measured at G<e2/h. When going from Ge2/h to G≈0.5e2/h, a decrease was found not only in the amplitude but also in the period of the oscillations. A calculation of the 3D-electrostatics demonstrated that this effect is due to a change in the dot size produced by control voltages. 相似文献
74.
75.
利用快分子离子与固体的相互作用,依靠一套高分辨装置,测量了H2+,HD+和D2+的结构,得到其核间距分别为1.19±0.003 nm、1.25±0.003 nm和1.32±0.003 nm.通过对比,证实了分子离子结构中同位素效应的存在,分析了实验值和理论值存在差别的原因,讨论了实验结果中同位素效应产生的缘由. 相似文献
76.
We use the concept of the exchange hole introduced by Slater to bound the energy of atoms, molecules, and other systems interacting by Coulomb forces from below by one-particle Hamiltonians with an effective screening potential and an exchange hole around each electron. Interestingly enough the optimal size of the exchange hole is smaller than Slater proposed: the best lower bound is obtained when the exchange hole carries charge 1/2 instead of 1. To highlight the quality of our estimate we show that the Dirac exchange energy with a slightly different constant bounds the exchange–correlation energy from below, an estimate previously derived by Lieb and later improved by Lieb and Oxford.
Acknowledgements The authors thank Walter Farkas and Christian Hainzl for helpful discussions. Financial support by the European Union under its IHP network program, grant HPRN-CT-2002-00277, is gratefully acknowledged.© By the authorsThe author A.M. Klaus Müller is deceased 相似文献
77.
Using low-fugacity expansions, we study the exact behavior of the Kosterlitz-Thouless critical line near the zero-density critical point. We show that the critical temperature deviates from its zero-density value by a term proportional to the square root of the density. 相似文献
78.
We solve analytically for the perimeter-area generating functions for two models of vesicles. While from the solution of the first model, staircase polygons, one can easily extract the asymptotic scaling behavior, the exact solution of the second, column-convex polygons, is difficult to analyze. This leads us to apply a recently developed method for deriving the scaling behavior indirectly, utilizing a set of nonlinear differential equations. One result of this work is a nontrivial confirmation of the scaling/universality hypothesis. 相似文献
79.
80.
Jari M. Kinaret Mats Jonson Robert I. Shekhter Sebastian Eggert 《Physica E: Low-dimensional Systems and Nanostructures》1998,1(1-4)
We consider a mesoscopic ring connected to external reservoirs by tunnel junctions. The ring is capacitively coupled to an external gate electrode and may be pierced by a magnetic field. Due to strong electron–electron interactions within the ring the conductance shows Coulomb blockade oscillations as a function of the gate voltage, while Aharonov–Bohm interference effects lead to a dependence on the magnetic flux. The Hamiltonian of the ring is given by a Luttinger model that allows for an exact treatment of both interaction and interference effects. We conclude that the positions of conductance maxima as a function the external parameters can be used to determine the interaction parameter
, and the shapes of conductance peaks are strongly affected by electron correlations within the ring. 相似文献