上次对角双线性时间序列模型的近似三阶矩结构和双谱密度

本文讨论一类特殊的双线性时间序列模型，该模型中，每一个双线性项均为两个相关的随机变量的乘积，该模型的二阶结构(自协方差和谱)目前已经很清楚了，同线性ARMA模型类似，亦具有有理谱密度，理论上，为了识别该模型，通常是考虑三阶结构(三阶矩和双谱)，但由于该模型的复杂性，精确的三阶结构是无法求出的，本文给出一种计算近似三阶矩的公式，由此得到了近似的双谱密度，仿真计算验证了这种方法是有效的。     

正常人心动周期改变对房室传导间期心电频谱图的影响

通过正常人行心房食管调搏术来观察生理状态下心动周期 (RR)对房室传导时间 (PR)频谱图的影响 ,以期进一步了解心脏各间期心电频谱图的特征。 1 5例排除心血管疾病者行心房食管调搏术 ,逐步起搏 ,测定其各阶段连续心电信号 1 2 8个周期 ,经快速傅立叶 (FFT)转换后进行频谱分析。结果表明 ,正常情况下 ,随着起搏心率增加 (RR缩短 ) ,PR间期的频谱变化表现为低频逐渐升高 ,高频成分逐渐下降 ,低高比值升高 (P <0 0 5 )。本研究提示生理状态下 ,RR对PR心电频谱图的影响较大 ,这对于进一步探讨心电频谱图各影响因素的定量作用提供了一定的排除心率影响的依据 ,并有益于临床心血管疾病的诊疗     

Short duration gamma ray bursts

After a short review of gamma ray bursts (GRBs), we discuss the physical implications of strong statistical correlations seen among some of the parameters of short duration bursts (T ₉₀ < 2 s). Finally, we conclude with a brief sketch of a new unified model for long and short GRBs.     

使用共振多程光声池的CO_2和SF_6的无多普勒饱和吸收光谱

本文使用共振多程池的光声探测法对CO_2和SF_6分子的无多普勒饱和吸收光谱进行了实验研究.测量CO_2的吸收凹陷约为2.5MHz,实验中观察到5个SF_6的吸收凹陷、凹陷深率约为1.9MHz.两种情况的分辨率均大于10~7.     

Quantum chaos and fluctuation properties of regular and irregular spectra

Fluctuation properties of the regular and irregular energy levels for the Hénon-Heiles Hamiltonian are examined. The spacing distributions and the calculated values of the Δ₃-statistic show that there is no difference in the short range correlation properties of these spectra. Remarkably, the Δ₃ values agree with the results of random matrix theory. on leave of absence from P.R.L., Ahmedabad     

On the Γ-Convergence of Discrete Dynamics and Variational Integrators

Summary For a simple class of Lagrangians and variational integrators, derived by time discretization of the action functional, we establish (i) the Γ-convergence of the discrete action sum to the action functional; (ii) the relation between Γ-convergence and weak* convergence of the discrete trajectories in {itW{su1,℞}}({ofR};{ofr{sun}; and (iii) the relation between Γ-convergence and the convergence of the Fourier transform of the discrete trajectories as measured in the flat norm.     

Large‐eddy simulation with complex 2‐D geometries using a parallel finite‐element/spectral algorithm

A parallel stabilized finite‐element/spectral formulation is presented for incompressible large‐eddy simulation with complex 2‐D geometries. A unique discretization scheme is developed consisting of a streamline‐upwind Petrov–Galerkin/Pressure‐Stabilized Petrov–Galerkin (SUPG/PSPG) finite‐element discretization in the 2‐D plane with a collocated spectral/pseudospectral discretization in the out‐of‐plane direction. This formulation provides an efficient approach for solving 3‐D flows over arbitrary 2‐D geometries. Utilizing this discretization and through explicit temporal treatment of the non‐linear terms, the system of equations for each Fourier mode is decoupled within each time step. A novel parallelization approach is then taken, where the computational work is partitioned in Fourier space. A validation of the algorithm is presented via comparison of results for flow past a circular cylinder with published values for Re=195, 300, and 3900. Copyright © 2003 John Wiley & Sons, Ltd.     

Spectral analysis of the covariance of the almost periodically correlated processes

This paper deals with the spectrum of the almost periodically correlated (APC) processes defined on . It is established that the covariance kernel of such a process admits a Fourier series decomposition, K(s+t, s) , whose coefficient functions b are the Fourier transforms of complex measures m, , which are absolutely continuous with respect to the measure m_o. Considering the APC strongly harmonizable processes, the spectral covariance of the process can be expressed in terms of these complex measures m.

The usual estimators for the second order situation can be modified to provide consistent estimators of the coefficient functions b from a sample of the process. Whenever the measures m are absolutely continuous with respect to the Lebesgue measure, so m(dλ)=f(λ) dλ, the estimation of the corresponding density functions f is considered. Under hypotheses on the covariance kernel K and on the coefficient functions b, we establish rates of convergence in quadratic mean and almost everywhere of these estimators.     

氯霉素类兽药的三甲基硅衍生物的质谱特征及其残留测定

氯霉素(chloramphenicol,CAP)是20世纪50年代开发出来的一种广谱抗生素,因其对人体具有严重毒副作用而被禁止在食用动物源产品上使用。甲砜霉素(thiamphenicol,TAP)是人工合成的氯霉素类抗生素,结构与CAP类似,毒性较CAP小,但美国等发达国家也已禁止在食用动物上使用。氟甲砜(氯