共查询到20条相似文献,搜索用时 15 毫秒
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报道了用两个1.5W激光二极管偏振耦合端面泵浦的声光调Q内腔倍频Nd:YAG激光器。输出532nm绿光重复频率1KHz时,最大峰值功率为2.23KW,最窄脉宽为18ns,平均功率40mW。最高重复频率30KHz。重复频率15kHZ时,最高平均率128mW。对声光调Q内倍频Nd:YAG激光器的动态特性进行了理论分析及计算。 相似文献
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We perform a semi-analytical calculation of the field distributions of a conformal invisible device via mode expansions. For a discrete set of frequencies in the regime of wave optics, the conformal invisible device is perfectly transparent, which stems from the special conformal mapping and the refractiveindex profile of the Mikaelian lens. 相似文献
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序列脉冲倍频YAG激光器泵浦的氧气受激拉曼散射研究 总被引:2,自引:2,他引:0
对序列脉冲倍频YAG激光器泵浦的氧气受激拉曼散射进行了研究。对氧气的受激拉曼散射池的热传导过程进行了数值模拟计算,实验研究了序列脉冲倍频YAG激光器泵浦情况下氧气受激拉曼散射的热效应问题。 相似文献
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给出了满足电荷守恒的共形发射技术。首先阴极表面由三角网格共形描述, 发射带电粒子时, 根据电荷和电流线性分配方式和离散高斯定律, 带电粒子的初始位置设置在与三角面元处于同一个网格元胞内, 离三角面元最近且处于金属内部的网格点上。带电粒子的初始运动由两部分组成:一是由三角面上的法向场推进所产生的运动;二是使发射粒子在阴极面上分布呈随机性而设定的随机运动。运动产生的电流按照电荷守恒定律分配到离散网格中, 并且由于粒子的初始位置设置在整网格点上, 带电粒子的共形发射不会产生非物理的静电累加。最后通过同轴二极管模型来验证共形发射模型的正确性。 相似文献
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G. Felder 《Journal of Geometry and Physics》1993,11(1-4):397-407
These are three introductory lectures on the relation between representations of affine Kac-Moody algebras, homology of configuration spaces with local coefficient systems, and quantum groups. The first lecture contains background on highest weight representations of affine Kac-Moody algebras. In the second lecture, conformal blocks, the Friedan-Shenker connection and the Knizhnik-Zamolodchikov (KZ) equation are reviewed. In the third lecture, the case of slz is studied in more detail. Integral representations of solutions of the KZ equation are derived, and recent results, obtained in collaboration with C. Wieczerkowski, on the relation between integration cycles and representations of Uq (sl2) are explained. 相似文献
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Brandon Carter 《Journal of Geometry and Physics》1992,8(1-4):53-88
The differential geometry of an imbedded (e.g. string or membrane world sheet) surface in a higher-dimensional background is shown to be conveniently describable (except in the null limit case) in terms of what are designated as its first, second, and third fundamental tensors, which will have the respective symmetry properties ημν = η(μν) as a trivial algebraic identity, Kμνρ = K(μν)ρ as the “generalised Weingarten identity”, which is the (Frobenius type) integrability condition for the imbedding, and Ξλμνρ = Ξ(λμν)ρ as a “generalised Codazzi equation”, which depends on the background geometry being flat or of constant curvature, needing replacement by a more complicated expression for a generic value of the background curvature Bκλμν. The “generalised Gauss equation” expressing the dependence on this background curvature of the internal curvature tensor Rκλμν of the imbedded surface is converted into terms of the first and second fundamental tensors, and it is thereby demonstrated that the vanishing of the (conformally invariant) “conformation tensor”, i.e. the trace free part Cμνρ of the second fundamental tensor Kμvρ, is a sufficient condition for conformal flatness of the imbedded surface (and thus in particular for the vanishing of its (Weyl type) conformal curvature tensor Cκλμν) provided the background is itself conformally flat. In a trio of which the first two members are the generalised Gauss and Codazzi equations, the “third” member is shown to give an expression in terms of Cμνρ for the (trace free, conformally invariant) “outer curvature” tensor Ωκλμν whose vanishing is the condition for feasibility of the natural generalisation of the Walker frame transportation ansatz. The vanishing of Cμνρ is shown to be sufficient in a conformally flat background for the vanishing also of Ωκλμν. 相似文献
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Conformal transformations are frequently used tools in order to study relations between various theories of gravity and Einstein's general relativity theory. In this paper we discuss the rules of these transformations for geometric quantities as well as for the matter energy‐momentum tensor. We show the subtlety of the matter energy‐momentum conservation law which refers to the fact that the conformal transformation “creates” an extra matter term composed of the conformal factor which enters the conservation law. In an extreme case of the flat original spacetime the matter is “created” due to work done by the conformal transformation to bend the spacetime which was originally flat. We discuss how to construct the conformally invariant gravity theories and also find the conformal transformation rules for the curvature invariants R2, RabRab, RabcdRabcd and the Gauss‐Bonnet invariant in a spacetime of an arbitrary dimension. Finally, we present the conformal transformation rules in the fashion of the duality transformations of the superstring theory. In such a case the transitions between conformal frames reduce to a simple change of the sign of a redefined conformal factor. 相似文献
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The conformal charge is an important quantity which characterizes the nature of the two-dimensional phase transition. We report a first attempt to use a new numerical method to calculate the conformal charge. In this paper, we apply our method to the 2-dimensional,
4, continuous-spin Ising model. By varying the parameters in the Hamiltonian, one can change continuously from the known Gaussian limit to the Ising limit. It is well known that the critical points for these two systems are not in the same universality class. We study this behavior for the Gaussian model, the single-well 4 model, the border model, and the double-well
4 model for a large lattice. Our results, while giving a good general picture, are not so far sufficient to differentiate whether the non-Gaussian cases studied belong to the Ising model universality class or not. Further studies of other lattice sizes should serve to improve greatly our conclusions. 相似文献
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Naresh Dadhich 《Pramana》1997,49(4):417-420
We prove the theorem: A necessary and sufficient condition for a spacetime to represent an isothermal fluid sphere (linear
equation of state with density falling off as inverse square of the curvature radius) without boundary is that it is conformal
to a spacetime of zero gravitational mass (‘minimally’ curved). 相似文献
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A period of rapidly accelerating expansion is expected in the early Universe implemented by a scalar field slowly rolling down along an asymptotically flat potential preferred by the current data. In this paper, we point out that this picture of the cosmic inflation with an asymptotically flat potential could emerge from the Palatini quadratic gravity by adding the matter field in such a way to break the local gauged conformal symmetry in both kinetic and potential terms. 相似文献
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Uniform stable conformal convolutional perfectly matched layer for enlarged cell technique conformal finite-difference time-domain method 下载免费PDF全文
Based on conformal construction of physical model in a three-dimensional Cartesian grid,an integral-based conformal convolutional perfectly matched layer(CPML) is given for solving the truncation problem of the open port when the enlarged cell technique conformal finite-difference time-domain(ECT-CFDTD) method is used to simulate the wave propagation inside a perfect electric conductor(PEC) waveguide.The algorithm has the same numerical stability as the ECT-CFDTD method.For the long-time propagation problems of an evanescent wave in a waveguide,several numerical simulations are performed to analyze the reflection error by sweeping the constitutive parameters of the integral-based conformal CPML.Our numerical results show that the integral-based conformal CPML can be used to efficiently truncate the open port of the waveguide. 相似文献
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Talbot效应是一种近场自成像效应,通常只有周期光栅可以产生Talbot效应,而环形光栅无法产生.本文通过引入保角变换,发现可以在环形光栅外部设计适当的折射率渐变层介质,使得其中也能够产生严格的Talbot效应,并计算了对应的自成像半径表达式.本文利用FDTD软件分别将一个环形光栅放置在真空中以及人工设计的折射率渐变层中进行了模拟,并对二者的结果进行了比较分析,发现这种折射率渐变层介质确实对点光源入射的环形光栅的自成像情况有着很好的改善.希望这一工作能够推广Talbot效应的应用范围. 相似文献
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共形光学系统瞬时视场外杂散光的分析及处理 总被引:1,自引:0,他引:1
针对空间成像光学系统的像质容易受到瞬时视场外杂散辐射的影响,利用杂散光分析软件建立一个共形光学系统光学机械结构模型,并对其进行反向光线追迹,从而确定出该系统中对瞬时视场外杂散辐射光的聚集贡献较大的关键表面及视场外杂散辐射光的主要传递路径.采用在系统中加入多级挡光环辅助结构的方式获得了100%的瞬时视场外杂散光屏蔽效果.该设计方案具有简单易行的特点. 相似文献
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时域有限差分(FDTD)算法求解电磁问题时,如果目标结构不能和传统网格体系共形,往往采用局部共形网格或非正交网格算法。详细讨论了二维圆柱坐标系中五角形共形网格算法,该算法能方便地对倾斜薄层媒质或电导率不均匀的倾斜媒质等复杂结构建模,并以锥形电磁脉冲天线为例,验证了该算法的有效性。 相似文献
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An analytical model for coplanar waveguide on silicon-on-insulator substrate with conformal mapping technique 下载免费PDF全文
In this paper, the authors present an analytical model for coplanar waveguide on silicon-on-insulator substrate. The four-element topological network and the conformal mapping technique are used to analyse the capacitance and the conductance of the sandwich substrate. The validity of the model is verified by the full-wave method and the experimental data. It is found that the inductance, the resistance, the capacitance and the conductance from the analytical model show they are in good agreement with the corresponding values extracted from experimental S-parameter until 10 GHz. 相似文献
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共形整流罩像差特性分析及校正方法 总被引:2,自引:1,他引:2
共形结构不仅具有良好的空气动力学性能,且不存在由于表面不连续造成的热梯度等问题,因而采用该结构的导弹整流罩更有利于导弹系统作战性能的提高。但共形结构中采用的非球面罩曲面使整流罩表现出许多不同于球形结构的动态特性,这给导引头中光学系统的设计带来很多困难。在分析共形结构一阶特性的基础上,利用矢量像差理论详细分析该结构中初级像差产生的原因及特点,并提出通过控制元件的倾斜和偏心来平衡所有观察视场中像差的方法。软件分析结果表明:加入倾斜偏心元件后可适当放大小观察视场中的像差,共形整流罩在各观察视场中具有较为稳定的像差特性,有效地改善了该结构的成像质量。 相似文献