The Sensitivity Analysis of Full Digital Compensatory MMW Radiometer

The digital compensatory millimeter wave radiometer is a new type of radiometer, which uses the digital compensatory operator to compensate gain and receiver noise fluctuation. This paper aims at the full digital compensatory 8 MMW radiometer which was designed, proposing the analysis method of its sensitivity, obtaining the mathematical formulae of its equivalent integration time and the best sensitivity adjustment method by software. Supported by the National High-Tech Research and Development Program (863 Program No.2006AA09Z143)of China, and the Science and Technology Committee of HuBei Province (No. 2006ABA069).     

KAHAN'S INTEGRATOR AND THE FREE RIGID BODYDYNAMICS

1.IntroductionAmongotherunconventionalnumericalmethods,Kahanll]hassuggestedadiscretizationofasimpleLotka-Volterasystemwiththepropertythatthecomputed.pointsdonotspiral.ThemotivationofthisbehaviourwasgivenrecentlybySanzSerna[3]byshowingthatKahan'sintegratorisasymplecticone.Thegoalofourpaperistostudysomepropertiesofthisintegratorintheparticularcaseofthefreerigidbody.2.TheFreeRigidBodyLetSO(3)betheLiegroupofall3x3orthogonalmatriceswithdeterminantoneandso(3)itsLiealgebra.Itcanbecanonicallyide…     

基于开关电容的双积分环SC振荡器

介绍了开关电容电路及由此构成的SC积分器和SC振荡器。     

A parallel time integrator for solving the linearized shallow water equations on the rotating sphere

With the stagnation of processor core performance, further reductions in the time to solution for geophysical fluid problems are becoming increasingly difficult with standard time integrators. Parallel‐in‐time exposes and exploits additional parallelism in the time dimension, which is inherently sequential in traditional methods. The rational approximation of exponential integrators (REXI) method allows taking arbitrarily long time steps based on a sum over a number of decoupled complex PDEs that can be solved independently massively parallel. Hence, REXI is assumed to be well suited for modern massively parallel super computers, which are currently trending. To date, the study and development of the REXI approach have been limited to linearized problems on the periodic two‐dimensional plane. This work extends the REXI time stepping method to the linear shallow‐water equations on the rotating sphere, thus moving the method one step closer to solving fully nonlinear fluid problems of geophysical interest on the sphere. The rotating sphere poses particular challenges for finding an efficient solver due to the zonal dependence of the Coriolis term. Here, we present an efficient REXI solver based on spherical harmonics, showing the results of a geostrophic balance test, a comparison with alternative time stepping methods, an analysis of dispersion relations indicating superior properties of REXI, and finally, a performance comparison on the Cheyenne supercomputer. Our results indicate that REXI not only can take larger time steps but also can be used to gain higher accuracy and significantly reduced time to solution compared with currently existing time stepping methods.     

Numerical integrators based on modified differential equations

Inspired by the theory of modified equations (backward error analysis), a new approach to high-order, structure-preserving numerical integrators for ordinary differential equations is developed. This approach is illustrated with the implicit midpoint rule applied to the full dynamics of the free rigid body. Special attention is paid to methods represented as B-series, for which explicit formulae for the modified differential equation are given. A new composition law on B-series, called substitution law, is presented.

     

Solving Hamiltonian systems arising from ODE eigenproblems

This paper presents an algorithm for solving a linear Hamiltonian system arising in the study of certain ODE eigenproblems. The method follows the phase angles of an associated unitary matrix, which are essential for correct indexing of the eigenvalues of the ODE. Compared to the netlib code SL11F [11] the new method has the property that on many important problems – in particular, on matrix–vector Schrödinger equations – the cost of the integration is bounded independently of the eigenparameter λ. This allows large eigenvalues to be found much more efficiently. Numerical results show that our implementation of the new algorithm is substantially faster than the netlib code SL11F.     

Vacation models in discrete time

A class of single server vacation queues which have single arrivals and non-batch service is considered in discrete time. It is shown that provided the interarrival, service, vacation, and server operational times can be cast with Markov-based representation then this class of vacation model can be studied as a matrix–geometric or a matrix-product problem – both in the matrix–analytic family – thereby allowing us to use well established results from Neuts (1981). Most importantly it is shown that using discrete time approach to study some vacation models is more appropriate and makes the models much more algorithmically tractable. An example is a vacation model in which the server visits the queue for a limited duration. The paper focuses mainly on single arrival and single unit service systems which result in quasi-birth-and-death processes. The results presented in this paper are applicable to all this class of vacation queues provided the interarrival, service, vacation, and operational times can be represented by a finite state Markov chain.An erratum to this article can be found at     

测量软X射线脉冲信号的门控积分器

 研制了满足ICF诊断中软X射线能量测量精度要求的具有限定时间积分功能的门控积分器。测试结果表明, 门控积分器的门有效导通时间约为7.8ns; 用信号源做被积信号, 门控积分器与示波器同时测量, 积分非线性小于3%; 门控积分器与示波器测量对比, 最大误差小于门控积分器满量程的5%。     

MCP选通X射线皮秒分幅相机在ICF中的应用

在上海“神光”装置上，首次将我国研制的首台ＭＣＰ（微通道板）选通Ｘ射线皮秒分幅相机样机用于ＩＣＦ（惯性约束聚变）激光等离子体物理诊断，在１．２ｎｓ内连续拍摄到激光注入孔等离子体辐射随时间变化的１２福二维空间分布图像，观测到等离子体喷射空间尺度随时间的变化过程．本文就该相机结构、测量原理和方法以及实验中获得的典型结果进行了分析讨论．     

宽频带无源积分器的设计和实验

 为获得宽频带的无源积分器,建立了考虑杂散参数的等效电路并进行了电路仿真。结果表明无源积分器的频响上限由杂散参数决定。对于相同结构的积分器,增大RC积分常数,会使杂散参数的影响加剧,导致积分器的高频响应变差。使用同轴结构可以减小电容的杂散电感,提高积分器的带宽。对制作的RC常数为10 μs的同轴式积分器进行了频响实验。实验结果表明：在偏差小于5％的范围内,同轴式积分器带宽为50 kHz～80 MHz。在D-dot电压探头线下标定实验和初级试验平台(PTS)单路样机激光触发开关输出电压测量中,使用该同轴积分器获取的测量波形没有波形畸变和高频干扰。