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81.
The junction conditions for a magnetohydrodynamic fluid sphere undergoing dissipative gravitational collapse in the form of
a radial heat flux with shear are obtained. These conditions extend particular results of earlier treatments. We demonstrate
that the pressure is proportional to the magnitude of the heat flux as is the case in shear-free models. However in our case
the gravitational potentials must be solutions of the Einstein-Maxwell system of equations. The mass function m(v) is increased by a factor related to the charge Q of the radiating star. Physical quantities relating to the local conservation of momentum and surface redshift are obtained. 相似文献
82.
It is common to schedule project activities first, then the utilization of equipment and its operating crew is planned based on such schedule. Real world experiences indicate that activity scheduling can be heavily impacted by the resources needed. In particular, if a project requires highly specialized and expensive equipment type, then one needs to take into account the schedule and cost of such resources in developing the project schedule. 相似文献
83.
This paper presents new bounds, heuristics, and an exact algorithm for the Pallet Loading Problem (PLP). PLP maximizes the number of boxes placed on a rectangular pallet. All boxes have identical rectangular dimensions and, when placed, must be located completely within the pallet. Boxes may be rotated 90° so long as they are placed with edges parallel to the pallet’s edges. The set of all PLP instances with an area ratio (pallet area divided by box area) less than 101 boxes can be represented by 3,080,730 equivalent classes. Our G5-heuristic finds optimal solutions to 3,073,724 of these 3,080,730 classes and in the remaining 7006 classes only differs from the best known bound by one box. We develop three other heuristics that solve another 54 instances. Finally, we solve the 6952 remaining classes with our exact HVZ algorithm. Only a subset of these classes has been solved previously. 相似文献
84.
强脉冲载荷作用下弹-塑性薄圆板的大挠度动力响应 总被引:3,自引:1,他引:2
利用有限变形弹塑性连续体的最小加速度原理 ,建立了分析圆板动力响应问题的数值方法 ,并通过对均匀分布的脉冲载荷作用下铰支圆板位移响应的细致分析 ,探讨了响应过程中的饱和冲量现象 ,指出对于高载范围内的脉冲载荷 ,相应于最大变形的饱和冲量确实是存在的。结果还表明 ,虽然圆板的弹塑性动力分析非常复杂 ,但基于最小加速度原理的数值计算方法却具有简单、直接的优点。 相似文献
85.
G. Teters 《Mechanics of Composite Materials》2005,41(5):461-466
Multicriteria optimization of the structure and geometry of a laminated anisotropic composite plate subjected to the thermal
and biaxial action is considered. From known properties of the monolayer and the given values of variable structural parameters,
the thermoelastic properties of the layered composite are determined. The criteria to be optimized—the transverse critical
load and the longitudinal thermal stresses—depend on two variable design parameters of composite properties and temperature.
In the space of the optimization criteria, the domain of allowable solutions and the Pareto-optimal subdomain are found.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 5, pp. 683–690, September–October, 2005. 相似文献
86.
Compromise optimization of a rectangular composite plate subjected to biaxial thermal loading and buckling under the action of shear 总被引:1,自引:1,他引:0
G. Teters 《Mechanics of Composite Materials》2008,44(4):325-330
The compromise optimization of the structure and geometry of a laminated anisotropic composite plate subjected to biaxial
thermal shear loading is considered. From the known properties of the monolayer and given values of a variable structural
parameter, the thermoelastic properties of the layered composite are determined. The optimization criteria — the critical
shear load and the longitudinal and transverse thermal stresses — depend on two variable design parameters of composite properties
and temperature. In the space of optimization criteria, the domain of allowable solutions and the Pareto-optimal subregion
are found.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 4, pp. 471–478, July–August, 2008. 相似文献
87.
Fabio Giannoni Antonio Masiello Paolo Piccione 《General Relativity and Gravitation》2001,33(3):491-514
We use a convexity condition to prove the finiteness of the number of light rays joining a pointlike source with a pointlike observer in a stationary relativistic spacetime. The result is extended to the case of conformally stationary metrics under suitable boundedness assumptions on the conformal factor. We discuss our hypotheses in some explicit examples of standard static and stationary Lorentzian manifolds. 相似文献
88.
The vibration and vibrational heating of a rectangular prism with copper and polyethylene layers is studied by solving numerically
a coupled problem of thermoelasticity. The cases of kinematic and mechanical harmonic shear loads on a section of the prism
surface are examined. Local heating regions are revealed. They are due to the stress fields in the neighborhood of the points
at which the type of boundary conditions changes. The temperature–time curves have preresonance, resonant, and postresonance
sections. The heating process reaches a steady thermal state under kinematic loading and may become avalanche-like (which
is typical of thermal instability) under mechanical loading
Translated from Prikladnaya Mekhanika, Vol. 45, No. 2, pp. 70–78, February 2009. 相似文献
89.
本文利用原位低场核磁共振(LF-NMR)技术在真实固液反应环境中对光催化还原Cr(Ⅵ)反应进行了定量研究,并对Ag纳米颗粒负载量不同的Ag担载石墨相氮化碳复合光催化剂(Ag/g-C3N4)在可见光照射下催化Cr(Ⅵ)还原为Cr(Ⅲ)的性能进行了研究.研究发现,Ag纳米颗粒负载(负载量分别为1 wt.%、2 wt.%、5 wt.%和10 wt.%)可以有效提高g-C3N4的光催化性能;且负载量为5 wt.%时光催化性能最优,为无Ag负载的g-C3N4的4倍.此外,本文还通过横向弛豫时间(T2)定量分析了反应体系中顺磁性Cr(Ⅲ)离子的浓度,证实了采用LF-NMR弛豫法评价光催化Cr(Ⅵ)还原反应性能的可行性. 相似文献
90.
Wael Zaki 《Journal of the mechanics and physics of solids》2007,55(11):2427-2454
The model in the first part of this paper is extended to account for SMA behavior under cyclic loading. To this end, three new state variables are introduced: internal stress B, residual strain ?r and cumulated martensite volume fraction ze. Several parameters of the extended model depend on ze, making them evolve with cyclic phase change. Cyclic SMA effects including training and two-way shape memory are accounted for and several numerical simulations are provided and validated in the case of cyclic superelasticity. 相似文献