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991.
992.
An analysis is made on the absorption distribution within a cylindrical active medium lamp pumped by means of fused silica light-guides. The performances of the proposed pump cavities are analysed through a non-sequential 3D ray-trace program and are compared to those of three reflective chambers: an elliptical cavity, a close-coupled cavity and a diffusive close-wrap cavity. Two light-guides cavities with eight and nine guides, respectively, were built and tested. High coupling efficiency and a reasonable uniform absorption distribution were registered. An overall laser efficiency of 1% was measured. The proposed cavities have permitted the tailoring of the absorption distribution within the laser rod. 相似文献
993.
建立了S波段相对论速调管放大器双间隙输出腔开放腔的3维模型。采用时域有限差分法,通过监测激励电流源的响应计算了该双间隙输出腔的谐振频率、有载Q值、场分布以及特性阻抗,并分析了腔体结构尺寸对谐振频率、有载Q值和特性阻抗的影响。研究表明:腔体半径对开放腔的谐振频率影响很大,耦合孔尺寸对腔体谐振频率的影响较小;随着耦合孔张角增加,有载Q值逐渐减小;随着腔体半径增大、间隙的减小,腔体特性阻抗降低。研究结果可为S波段强流相对论速调管放大器双间隙输出腔的设计提供理论依据。 相似文献
994.
The goal in this work is to investigate the effectiveness of time-frequency representations for analysing dispersive waves by comparing the performance of three different methods. In particular, the smoothed pseudo-Wigner distribution, the continuous wavelet transform and the Hilbert-Huang transform are compared and evaluated in terms of their ability to analyse dispersive elastic waves. The waves under consideration are transient flexural ones generated by an impact in a beam. In view of the results of the comparative study, the advantages and shortcomings of each method are presented and discussed. 相似文献
995.
996.
《Journal of computational and graphical statistics》2013,22(2):281-294
By introducing auxiliary variables, the traditional Markov chain Monte Carlo method can be improved in certain cases by implementing a “slice sampler.” In the current literature, this sampling technique is used to sample from multivariate distributions with both single and multiple auxiliary variables. When the latter is employed, it generally updates one component at a time. In this article, we propose two variations of a new multivariate normal slice sampling method that uses multiple auxiliary variables to perform multivariate updating. These methods are flexible enough to allow for truncation to a rectangular region and/or exclusion of any n-dimensional hyper-quadrant. We present results of our methods and existing state-of-the-art slice samplers by comparing efficiency and accuracy. We find that we can generate approximately iid samples at a rate that is more efficient than other methods that update all dimensions at once. Supplemental materials are available online. 相似文献
997.
《Journal of computational and graphical statistics》2013,22(3):731-752
This article describes a reduction formula for the computation of multivariate normal probabilities first developed by Plackett. The method is recursive and, despite very promising results, seems not to have been implemented before. Extensive numerical results are given to compare the effectiveness of the approach to other methods from the literature. 相似文献
998.
Rui Qiao Hua Deng Karl W. Putz L. Catherine Brinson 《Journal of Polymer Science.Polymer Physics》2011,49(10):740-748
In this article, we utilize finite element modeling to investigate the effect of nanoparticle agglomeration on the glass transition temperature of polymer nanocomposites. The case of an attractive interaction between polymer and nanofiller is considered for which an interphase domain of gradient properties is developed. This model utilizes representative volume elements that are created and analyzed with varying degrees of nanoparticle clustering and length scale of interphase domain. The viscoelastic properties of the composites are studied using a statistical approach to account for variations due to the random nature of the microstructure. Results show that a monotonic increase in nanofiller clustering not only results in the loss of interphase volume but also obstructs the formation of a percolating interphase network in the nanocomposite. The combined impacts lead to a remarkable decrease of Tg enhancement of clustering nanofillers in comparison with a well‐dispersed configuration. Our simulation results provide qualitative support for experimental observations that clustering observed at high nanofiller concentrations negatively impacts the effects of the nanofiller on overall properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
999.
In this paper an asymptotic formula of Voronovskaja type for a multivariate extension of the Kantorovich generalized sampling
series is given. Moreover a quantitative version in terms of some moduli of smoothness is established. Finally some particular
examples of kernels are discussed, as the Bochner-Riesz kernel and the multivariate splines. 相似文献
1000.
Douglas Poland 《Journal of Polymer Science.Polymer Physics》2001,39(13):1513-1518
Using polypropylene as an example, we applied a method we have recently developed to calculate the probability distribution of enthalpy from the temperature dependence of the heat capacity. The method involves the use of local temperature expansions of the heat capacity to calculate a set of moments of the enthalpy distribution. Using the maximum‐entropy method, one can then construct the enthalpy distribution for the system. The method is completely model free. The enthalpy distribution so obtained is the analogue of the Maxwell–Boltzmann distribution of kinetic energies for a gas, and like that function, tells one the distribution of enthalpies that an average unit in the polymer chain can have, a quantity that is crucial to understanding the chemical and physical properties of a polymer. Given the enthalpy distribution, one can then calculate the Gibbs free energy and the density of states that correspond to a particular value of enthalpy, thus giving one an expanded thermodynamics of the system in addition to the usual average quantities. We illustrate the fact that the Gibbs free‐energy distribution for this system scales as a simple function of temperature and that the density‐of ‐states function yields a simple empirical partition function for the system giving both the average thermodynamics and the distribution functions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1513–1518, 2001 相似文献