四极磁透镜的边缘场研究

本文对四极磁透镜的磁场分布和电子的输运问题进行了研究和计算。文中阐述了四极磁透镜边缘场的三种处理方法,用这三种方法计算了透镜的输运矩阵。相互比较表明,四极磁透镜的边缘场采用传统的直角边近似就可以很好地解决问题。     

谐振腔链色散关系及场分布的解析研究

从圆柱坐标系下的Borgnis位函数的齐次标量Helmholtz方程出发,引入慢波驻波概念及其场 表达式,利用Borgnis位函数的边界条件及相邻子区公共界面上的场匹配条件,导出了整腔 结尾的谐振腔链内角向均匀TM模的色散关系及场分布的解析表达式.运用该解析法对实际器 件——四腔渡越管振荡器进行了求解,求得的谐振频率与实验中测得的微波频率一致,求得 的场分布与数值法得到的场分布十分符合.关键词：谐振腔链色散关系场分布解析法     

固体中半整数四极核的自旋扩散

首先介绍固态中自旋扩散的一般理论,包括半经典描述和建立在投影算子理论上的密度矩阵描述. 接着以丰核环境中相互偶合的自旋-1/2系统以及自旋-3/2系统为典型列举了自旋扩散速率的计算. 最近藉助多量子魔角旋转(MQMAS)方法实现半整数四极核的多量子谱自旋扩散实验,可以测量固体粉末中半整数四极核体系四极张量相对方向. 结合作者最近的计算机模拟和实验测量结果对这一新兴方向作了重点介绍,尤其指出了射频
脉冲强度、宽度及样品旋转速度对交叉峰线型的影响.     

超短沟道MOSFET电势的二维半解析模型

本文根据超短沟道MOSFET的工作原理, 在绝缘栅和空间电荷区引入两个矩形源, 提出了亚阈值下电势二维分布的定解问题. 通过半解析法和谱方法相结合, 首次得到了该定解问题的二维半解析解, 解的结果是一个特殊函数, 为无穷级数表达式. 该模型的优点是避免了数值分析时的方程离散化, 表达式不含适配参数、运算量小、精度与数值解的精度相同, 可直接用于电路模拟程序. 文中计算了沟道长度是45—22 nm的MOSFET电势、表面势和阈值电压. 结果表明, 新模型与Medici数值分析结果相同.关键词：半解析法电势阈值电压MOSFET     

解薄圆板动力响应的DQ半解析方法

直接从薄圆板的控制微分方程出发，在空间域采用ＤＱ法在时间域取级数，采用时域配点得到求位移场全部待定参数的线性方程组，解一次方程组即得全域的响应位移场。     

分离作用射频四极场加速器的结构和工艺设计

 介绍了北京大学分离作用射频四极场(RFQ)加速器的结构特点,包括膜片式电极、支撑环式电极支撑系统、水冷系统、调谐系统及其工艺实现;介绍了基于该分离作用RFQ加速腔进行的调谐测试、高功率实验和束流实验。结果表明:调谐系统的频率调节范围及品质因数完全满足实验要求;分离作用RFQ加速腔的输入功率可以达到33 kW以上,满足高功率下稳定运行的条件;在束流实验中,把1.03 MeV的O⁺入射束流加速到1.65 MeV,半高宽能散小于3%。加速器结构满足物理设计要求,加速系统运行稳定。     

分离作用射频四极场加速器的结构和工艺设计

介绍了北京大学分离作用射频四极场(RFQ)加速器的结构特点,包括膜片式电极、支撑环式电极支撑系统、水冷系统、调谐系统及其工艺实现;介绍了基于该分离作用RFQ加速腔进行的调谐测试、高功率实验和束流实验。结果表明:调谐系统的频率调节范围及品质因数完全满足实验要求;分离作用RFQ加速腔的输入功率可以达到33 kW以上,满足高功率下稳定运行的条件;在束流实验中,把1.03 MeV的O+入射束流加速到1.65 MeV,半高宽能散小于3%。加速器结构满足物理设计要求,加速系统运行稳定。     

分离作用射频四极场加速器中动力学参数与极限流强的探讨

系统分析了粒子在分离作用射频四极场(RFQ)加速结构中的运动,导出了极限流强与动力学参数的关系. 存在于分离作用RFQ膜片加速间隙处的加速电场,较传统的RFQ能更加有效地加速带电粒子.四杆电极之间的射频四极场,对粒子的横向具有聚焦或者散焦作用,通过适当选取粒子动力学参数可以保证粒子在分离作用RFQ中横向和纵向运动的稳定性. 关键词：分离作用射频四极场加速器稳定性反场极限流强     

由卷积型变分原理求解瞬态热传导问题的半解析法

主要针对二维问题，基于卷积型变分原理，提出了求解瞬态热传导问题的半解析法，该方法在空间域内作分区域插值离散，在时间域上采用解析函数。     

532nm长脉冲激光致GaAs热分解损伤的半解析法分析

考虑到GaAs具有受热分解的特性,采用热传导理论和半解析法研究了波长532nm的毫秒量级长脉冲激光致GaAs的表面热分解损伤．首先,建立了激光辐照GaAs的二维轴对称瞬态温度场及表面热分解损伤阈值的计算模型,模拟了吸收率不同时,GaAs的瞬态温度场分布及热分解损伤阈值．计算结果表明：较高的吸收率引起GaAs表面的温升较高,但所需的热分解损伤阈值较低;增加作用激光能量密度,GaAs表面发生热分解损伤随之提前．本文研究结果对激光与GaAs相互作用及其损伤机理的研究具有指导意义和实用价值．     

Comments on the Paper astro-ph/0103335 by C. Rubano and P. Scudellaro

We briefly comment on a paper by Rubano and Scudellaro [Gen. Rel. Grav. 34 (2002) 307, astro-ph/0103335] where they found general exact solutions for two classes of exponential potentials in a scalar field model for quintessence. In that paper the authors were led to some interesting conclusions after a proper choice of the integration constants. By using dimensionless variables we show that the integration constants can be found explicitly without additional assumptions. In consequence we revise some results and conclusions in that paper. We also reproduce observations for Type-Ia supernovae with good accuracy.     

Non commuting quantum cosmology with scalar matter

We study noncommutative quantum and classical cosmology with a scalar field by means of deforming the minisuperspace. We analyze the homogeneous and isotropic model and compare our results with the usual commutative case. In particular the classical behaviour of the scalar field can dramatically change due to the presence of noncommutativity.We dedicate this work to Michael P. Ryan on the occasion of his sixtieth birthday. Around 30 years ago, Mike patiently introduced us to Quantum Cosmology. Since that time, we have had rich and friendly discussions and fruitful collaborations.     

Baryogenesis in Fresh Inflation

I study the possibility of baryogenesis can take place in fresh inflation. I find that it is possible that violation of baryon number conservation can occur during the period out-of-equilibrium in this scenario. Indeed, baryogenesis could be possible in the range of times (10⁹ – 10¹²) G^1/2, before the thermal equilibrium is restored at the end of fresh inflation.     

Bessel光束的矢量分析及其能流密度的特征

通过比较自由空间Besssel光束标量解E(r,t)满足的方程和光场矢量E(r,t)与矢量势A(r,t)之间的关系表达式,利用Bessel的特点,合理构造了矢量势A(r,t)的具体形式,推导出电场量E(r,t)的磁场量B(r,t)各分量满足的具体形式。通过数值计算,给出电场E(r,t)在不同参数θ,φ下与径向坐标ρ之间的关系图线(图1,图2),发现由方程(6)描述的标量解仅是矢量场E(r,t)(方程15描述)在小θ下的近似。通过对能量传输特性的讨论,说明“超光速”的提法是不恰当的。     

Role of Brans-Dicke Theory with?or?without?Self-Interacting Potential in?Cosmic?Acceleration

In this work we have studied the possibility of obtaining cosmic acceleration in Brans-Dicke theory with varying or constant ω (Brans-Dicke parameter) and with or without self-interacting potential, the background fluid being barotropic fluid or Generalized Chaplygin Gas. Here we take the power law form of the scale factor and the scalar field. We show that accelerated expansion can also be achieved for high values of ω for closed Universe.     

Polarization of line radiation in the presence of external electric quadrupole and uniform magnetic fields: II. Arbitrary orientation of magnetic field

In continuation of our earlier investigation (referred to hereafter as part I) where we considered the mathematically simple case of magnetic field orientation along the Z-axis of the principal axes frame (PAF) of the electric quadrupole field, we take up here the general problem of arbitrary orientation of the magnetic field with respect to the PAF, and investigate the nature of polarized line spectra of an atom making a transition from an upper level with spin J_u to a lower level with spin J_l. Explicit formulae for the emitted Stokes parameters are obtained and we discuss their physical significance by computing numerically the cases of transitions J_u=1→J_l=0 and . Specific features or signatures of the polarized line spectra are discussed as functions of the relevant physical parameters. The Stokes parameters are also analyzed in terms of the Zeeman term contributions and the cross-term contributions (which arise due to quantum interference).     

Acceleration of the universe with a simple trigonometric potential

In this paper, we investigate the quintessence model with a minimally coupled scalar field in the context of recent supernovae observations. By choosing a particular form of the deceleration parameter q, which gives an early deceleration and late time acceleration for the dust dominated model, we show that this sign flip in q can be obtained by a simple trigonometric potential. The early matter dominated model expands with q = 1/2 as desired and enters a negative q phase quite late during the evolution.     

Brane world cosmology in Jordan-Brans-Dicke theory

We consider the embedding of 3+1 dimensional cosmology in 4+1 dimensional Jordan-Brans-Dicke theory. We show that exponentially growing and power law scale factors are implied. Whereas the 4+1 dimensional scalar field is approximately constant for each, the effective 3+1 dimensional scalar field is constant for exponentially growing scale factor and time dependent for power law scale factor.