Spectral analysis of the semi-relativistic Pauli-Fierz hamiltonian

We consider a charged particle, spin , with relativistic kinetic energy and minimally coupled to the quantized Maxwell field. Since the total momentum is conserved, the Hamiltonian admits a fiber decomposition as H(P), P∈R³. We study the spectrum of H(P). In particular we prove that, for non-zero photon mass, the ground state is exactly two-fold degenerate and separated by a gap, uniformly in P, from the rest of the spectrum.     

On the Cauchy problem for a generalized Boussinesq equation

In this paper, we consider the Cauchy problem for a generalized Boussinesq equation. We show that, under suitable conditions, a global solution for the initial value problem exists. In addition, we derive the sufficient conditions for the blow-up of the solution to the problem.     

Speciation and instrumental neutron activation analysis for arsenic in water samples

Ground water samples obtained from West Bengal, India were analyzed for total arsenic and its inorganic species contents by instrumental neutron activation analysis (INAA). Two anion exchange separation methods using Dowex 1X8 in chloride and acetate forms were standardized for the speciation of As(III) and As(V) using radiotracers. The method by Dowex 1X8 in the acetate form was validated using synthetic mixtures of As(III) and As(V), and applied to water samples; the species concentrations were determined by INAA. The accuracy of the INAA method was evaluated by analyzing the NRCC CRM DORM-2 for total arsenic.     

(AgI)n团簇熔化行为的分子动力学模拟

用遗传算法结合经验势搜索了(AgI)n(n=3-15)团簇的可能稳定结构, 并用微正则分子动力学方法研究了它们的熔化行为. (AgI)n团簇的稳定结构主要以四元环和六元环相接的笼状结构为主. 大多数(AgI)n会在一个较大的温度范围内随温度升高结构不断扭曲, 原子间距涨落及动能涨落不断增大, 直到在某个温度下熔化, 结构变得完全无序. (AgI)6的结构具有很高的对称性, 熔化发生在一个较窄的温度范围. 对于(AgI)5, 会在熔化前较大的温度范围内发生最稳定结构与能量较高的环状异构体之间的转化, 并可能出现负热容现象.     

联苯桥联的聚对苯乙烯撑齐聚物基态、激发态的结构与光电性能

用密度泛函理论(DFT)和单激发(CIS)方法分别对几种联苯桥联的聚对苯乙烯撑(PPV)齐聚物分子的基态结构和激发态结构进行全优化, 得到基态与激发态分子的最优几何构型和前线分子轨道, 并用半经验ZINDO(Zerner's intermediate neglect of differential overlap)和含时密度泛函(TD-DFT)方法分别计算了各自的吸收光谱和发射光谱, 分析了随着联苯链的增长前线分子轨道能级和能隙的变化以及对光电性能的影响. 结果表明, 联苯链的加长对吸收和发射性质影响不大, 但在分子结构上由于PPV 齐聚物(发光中心)链间交叉链内扭曲的构象越来越明显, 降低了分子的平面性和对称性, 减弱了这类共轭分子在固体中的π-π堆积作用, 这可能是减少荧光猝灭效应, 提高固体发光器件荧光量子效率的主要原因.     

On asymptotic stability in energy space of ground states of NLS in 2D

We transpose work by K. Yajima and by T. Mizumachi to prove dispersive and smoothing estimates for dispersive solutions of the linearization at a ground state of a Nonlinear Schrödinger equation (NLS) in 2D. As an application we extend to dimension 2D a result on asymptotic stability of ground states of NLS proved in the literature for all dimensions different from 2.     

Predicting noise from aircraft operated on the ground

Averaged data for sound levels due to aircraft engine testing out to a distance of 3 km obtained under low wind speed conditions are presented. Predictions of standard analytical approximations are compared with these averaged data. The measured average sound levels are shown to be consistent with the predicted influence of ground effect including impedance discontinuities. There is a noticeable influence of directionality also.     

探地雷达高功率高稳定度脉冲源设计

 对于探地雷达，脉冲源的功率和稳定度直接影响其作用距离和探测精度，对目标成像时进行相干积累有着重要意义。采用雪崩三极管设计的全固态脉冲源具有很高的稳定度指标，但输出功率较低，使用Marx电路可以提高其输出峰值电压幅度。梳状PCB(印刷电路板)电路是一种结构紧凑具有自相似性的电路形式，有利于进一步提高脉冲源的稳定度指标，也有利于脉冲源的小型化设计。根据某探地雷达要求，采用梳状PCB电路形式，实现了12级Marx电路的脉冲源，采用欠电荷法对脉冲波形进行了优化设计，其输出峰值电压大于400 V(50 Ω负载)，脉冲宽度为600 ps，重复频率大于25 kHz；并且具有良好的时基稳定度和波形稳定度，脉冲宽带抖动小于1%，峰值抖动小于1%。     

Why do the second row transition metal atoms prefer 5s14dm+1 to 5s24dm?

Numerical Hartree-Fock (NHF) calculations have been performed for 332 ground and low-lying excited states of the fifth period atoms Rb through Xe, with our special interest in the states arising from the 5s ²4d ^m , 5s ¹4d ^m +1, and 5s ⁰ 4d ^m +2 configurations of the second row transition metal atoms. Among various properties, orbital energies and mean values ofr of the outermost orbitals of each symmetry are presented as well as total energies. It is discussed in some detail why the second row transition metal atoms have a tendency to prefers ¹ d ^m +1 as the ground configuration in contrast to the preferreds ² d ^m configuration in the first row transition metal atoms. Our systematic NHF computations reported in this and the previous papers conclude that the Hartree-Fock method correctly predicts the experimental ground state of the atoms He through Xe with the sole exception for Zr.