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排序方式: 共有142条查询结果,搜索用时 15 毫秒
51.
平均跟踪与伪轨跟踪 总被引:4,自引:0,他引:4
赵俊玲 《高校应用数学学报(A辑)》2004,19(3):311-314
证明了紧致度量空间中有伪轨跟踪的distal同胚不具有平均跟踪性,并给出了有平均跟踪性的同胚是极小的一个充分条件。 相似文献
52.
The complete optical transmittance for a polarized light passing through the magnetic fluids is investigated theoretically and experimentally, when the externally magnetic field is applied along the propagation direction of the incident light. Hybrid effects due to the geometric shadowing and Faraday rotation are considered simultaneously. The Langevin-like functions are employed to describe the magnetic-field-dependent volume concentration of the particle-aggregation (φ′) and the approximate number of magnetic nanoparticles in the particle-aggregation (βN0). Based on the experiments on the geometric shadowing effect of our magnetic fluid sample, the analytical expression for the total transmitted power with externally magnetic field after an analyzer is derived. Theoretical simulations disclose the influence of certain critical parameters of the magnetic fluids on the field-dependent optical transmittance. For the entire polarized light transmittance, qualitative agreement between the calculations and the experiments is achieved. Applications of magnetic fluids to several polarized devices operating in longitudinal field arrangement are proposed and discussed. The results presented in this work may be useful for designing the corresponding magnetic-fluid-based optical devices. 相似文献
53.
In this paper, the J/ψ nuclear absorption effect is studied at RHIC and LHC energies with the EKS98 shadowing parameterizations. By assuming that the J/ψ absorption cross section, σ abs , increases with the charmonium-nucleon (J/ψ-N) center of mass energy, s J/ψN , it is found that σ abs should depend on x F (or y) at a certain center of mass energy per nucleon pair,s , especially at LHC energies. The theoretical results with the x F (or y)-dependence of the absorption effect are in good agreement with the experiment data from PHENIX in d-Au collisions and the predicted results will be examined by the forthcoming experimental data from LHC in d-Pb collisions. Finally, we also present baseline calculations of cold nuclear matter effects on J/ψ production in nucleus-nucleus (A-A) collisions and find that the x F (or y)-dependence of absorption effect is very small at both RHIC and LHC energies in A-A collisions. 相似文献
54.
WANG Hong-Min SUN Xian-Jing ZHANG Ben-Ai 《理论物理通讯》2008,50(7):175-179
Having studied the initial state energy loss versus nuclear shadowing for the Drell- Yan dimuon pair production in the color string model, the inhomogeneous shadowing effect is considered in this paper. We find that the inhomogeneous shadowing effect does amend the rate of energy loss per unit path length, -dE/ dz. Finally, the theoretical results for the Drell Yan differential cross-section ratios are compared with the E772 and E866 data. It is found that the theoretical results are in good agreement with the experimental data. 相似文献
55.
The medium modifications of J/ψ production in d-Au collisions at √SNN= 200 GeV are studied in the Glauber model. By means of the c.m. energy loss parameter per collision studied in Drell-Yan process,taking account of the inhomogeneous shadowing effect, we find that the initial-state energy loss effect can be ignored in d-Au collisions at mid-rapidity. Then, the final-state J/ψ absorption effect is also considered and the theoretical results are in good agreement with the recent experimental data given by PHENIX. Finally,the experimental results of J/ψ production in d-Pb collisions are also predicted at RHIC and LHC energies respectively. 相似文献
56.
57.
页岩气藏压裂缝网扩展数值模拟 总被引:4,自引:1,他引:4
为探究页岩气藏水力压裂复杂裂缝网络的形成机理,开展了缝网扩展的数值模拟研究.考虑应力阴影和天然裂缝作用,建立了井筒和裂缝中流体流动模型,利用位移不连续方法求解应力与位移不连续量,然后构建了压力与裂缝宽度的迭代方程,并采用牛顿迭代法求解.通过比较数值解经典模型解析解,验证了模型和迭代解法的正确性.多簇裂缝同步扩展时裂缝间距越小,压裂液分配到各条裂缝越不均匀,靠近井筒跟部的裂缝的分流量越大,从而裂缝宽度越大;考虑天然裂缝作用时,逼近角越小或者应力各向异性越弱,水力裂缝越容易发生转向扩展,裂缝网络越复杂. 相似文献
58.
59.
最小二乘跟踪方法是近几年提出的一种计算动力系统跟踪轨迹的方法.基于最小二乘跟踪的灵敏度分析算法可以有效避免传统的非线性系统灵敏度分析方法中的病态初值问题,因此其在混沌系统灵敏度分析方面有着重要的应用.针对非线性的最小二乘跟踪问题,首先将其重新描述为带有约束的非线性最优控制问题,引入协态变量并将系统的哈密顿函数表示为关于状态变量和协态变量的函数.然后将目标函数的积分时间离散化,根据对偶变量变分原理,以离散区间两端的状态变量作为独立变量,用Lagrange插值多项式近似离散区间内的状态变量和协态变量,进而将非线性最优控制问题转化为求解非线性方程组问题.这种算法无需对原问题做线性化处理,避免了复杂的线性化过程以及可能因此造成的误差,同时为求解非线性最小二乘跟踪问题提供了新的思路.根据最小二乘方法可以得到两条设计参数有微小变化的状态轨迹,基于这两条状态轨迹可进一步计算出系统关于设计参数的灵敏度,范德波振子作为数值算例验证了该方法在求解最小二乘跟踪问题以及计算非线性系统灵敏度时的有效性. 相似文献
60.
When a random rough surface is viewed obliquely by an imaging system, the position of a viewed point fluctuates with surface displacements. This fluctuation introduces an additional blur to the images that are mapped on the average surface. A new class of spread function, which represents the resolution associated with the randomness of an imaging object, is introduced to treat this problem and an analytical expression of the function is obtained for a Gaussian random surface under the presence of shadowing effects. This spread function is useful in understanding the loss in resolution of images of a random surface such as the thermal imagery of an ocean surface in the near horizon. 相似文献