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排序方式: 共有47条查询结果,搜索用时 15 毫秒
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非线性涡黏性系数模型和代数应力模型联系了线性涡黏性系数湍流模型和完整的微分 雷诺应力模型.随着它们受到日益关注,其形式也越来越多样化.本篇综述的目的是对这些模 型加以总结并比较它们之间的共同点及不同之处,指出它们与完整微分雷诺应力模型之间的 关系,以及相对于线性涡黏性系数模型而言它们在预报流场上所具有的优势.  相似文献   
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高温超导线圈在大电流下稳定性的数值仿真   总被引:2,自引:0,他引:2  
在电力应用中,超导磁体可能会因为线圈工作于过流状态而失超,也可能会因为交流损耗而导致失超.为此,我们模拟了一个磁体在大电流过载下的稳定性情况.我们使用了一个建立在热传导方程和麦克斯韦方程基础上的差分数值计算方法来得出磁体内部的温度分布.我们对各种不同的电流冲击情况进行了考察,我们的模型可以使磁体设计者在实际制作之前能够估计一个比较安全的操作电流水平,有着广泛的实用价值.  相似文献   
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本实验利用动态~(95)Mo NMR监测Mo-Cu系列化合物的形成过程,对反应CuCl+NaR_2dtc+MoO_nS,摩尔比3:3:1,溶剂为DMF;R=Et,n=0(Ⅰ);R=Me,n=0(Ⅱ);R=Et,n=2(Ⅲ)进行了研究,观察到具有不同簇骼的多种中间产物的存在及随反应进程相互转化等现象。  相似文献   
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An extended F?rster theory (EFT) on electronic energy transfer is presented for the quantitative analysis of time-resolved fluorescence lifetime and depolarisation experiments. The EFT, which was derived from the stochastic Liouville equation, yields microscopic information concerning the reorientation correlation times, the order parameters, as well as inter chromophoric distances. Weakly interacting donor and acceptor groups, which reorient and interact in a pair wise fashion, are considered, under isotropic and anisotropic conditions. For the analysis of experiments it is shown that not only do we need to consider the orientational distributions of the transition dipoles, but the internal reorienting molecular dynamics within the pair which is of even greater importance. The latter determines the shape as well as the rate of the observed donor fluorescence and depolarisation decays, which are most often not mono-exponential functions. It is shown that the commonly used F?rster theory is a special case of the EFT. Strategies are presented for applying the EFT, which makes use of Brownian dynamics simulation.  相似文献   
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This paper discusses the process of energy migration transfer within reorientating chromophores using the stochastic master equation (SME) and the stochastic Liouville equation (SLE) of motion. We have found that the SME over-estimates the rate of the energy migration compared to the SLE solution for a case of weakly interacting chromophores. This discrepancy between SME and SLE is caused by a memory effect occurring when fluctuations in the dipole-dipole Hamiltonian (H(t)) are on the same timescale as the intrinsic fast transverse relaxation rate characterized by (1/T(2)). Thus the timescale critical for energy-transfer experiments is T(2) approximately 10(-13) s. An extended SME is constructed, accounting for the memory effect of the dipole-dipole Hamiltonian dynamics. The influence of memory on the interpretation of experiments is discussed.  相似文献   
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A mathematical framework for translational Brownian motion on hypersurfaces is presented, using an imbedding of the surface and Ito diffusions in the ambient space. This includes a survey of Ito calculus and differential geometry. Computational methods for time correlation functions relevant to spin relaxation studies on curved interfaces are given, and explicit calculations of time correlation functions and order parameters for a Rippled surface are presented.  相似文献   
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A generalization of the modified SBM theory is developed in closed analytical form. The theory is applied to describe the paramagnetically enhanced water proton spin-lattice relaxation rates of the aqueous-systems containing a gadolinium(S=7/2) complex(MS-325) in the presence or absence of human serum albumin (HSA). MS-325 binds to HSA: in the absence of the protein the reorientational time, tauR, is short, but when HSA is added tauR becomes much longer. In this way, the effect of reorientational motion, static (Delta s), and transient (Delta t) zero-field splitting (ZFS) interactions on both the water proton relaxivity and the Gd ESR lineshapes are investigated. Two dynamic models of electron spin relaxation are presented, characterized by transient and static ZFS-interactions. X-, Q-, and W-bands ESR spectra of MS-325+HSA are analyzed in order to describe the effect on the electron spin system upon binding to a macromolecule. A computer program based on this theory is developed which calculates solvent water proton T1 NMRD profiles and the corresponding X-, Q-, U-, and W-bands ESR lineshapes.  相似文献   
10.
有优先权的光突发交换中光缓存的性能分析   总被引:6,自引:6,他引:0  
张民  张帆  王建  叶培大 《光子学报》2002,31(10):1190-1195
分析了配置有限数量光纤时延线(FDLs)和优先权机制的光突发交换(pOBS)网络性能,建立了pOBS的网络模型和排队模型;并以模型为基础,比较了各级别数据包的排队等延时与FDLs单位、负荷强度比例的关系;比较了有和无FDLs时,包丢失率与FDLs单位、FDLs深度、系统负荷强度以及波长数的关系.研究发现;高优先级数据包的平均延时远小于其它数据包,负荷强度越大平均延时也越大,高优先级数据包的比例越大则低优先级数据包的延时越大且丢失率越高,加入有限数量和适当深度的FDLs、减小FDLs最小单位、增加波长数都能减小数据包的平均排队延时和丢失率.  相似文献   
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