X波段重复频率GW级超辐射相对论返波管

运用超辐射机理,通过粒子模拟设计了X波段超辐射相对论返波管,并在小型Tesla脉冲源平台上开展了实验研究。通过空间功率积分和直接对辐射微波时域波形的分析得到实验结果:在束压350 kV、束流4.8 kA、脉宽3.1 ns、引导磁场2.2 T条件下,产生的微波辐射功率1.4 GW,中心频率9.36 GHz,脉宽500~700 ps,辐射模式为TE11,能在重复频率100 Hz下稳定运行。功率转换效率超过80%。实验结果与粒子模拟结果比较吻合,成功实现了在短脉冲条件下产生重复频率、亚纳秒脉宽、GW级微波辐射。     

弱吸收基底上弱吸收薄膜的光学常数计算方法

采用一种相对简单而又精确的光度法来计算弱吸收基底上弱吸收薄膜的光学常数,为低损耗紫外薄膜的设计与实现提供了理论基础。采用JGS1型熔融石英基底,制备了MgF2与LaF3材料的单层膜,获得了JGS1型熔融石英基底及MgF2与LaF3薄膜的光学常数色散曲线。结果显示:在200 nm左右处,JGS1型熔融石英基底的吸收已经比较明显,消光系数在10-8量级,因此,应考虑基底的弱吸收,以提高薄膜光学常数的计算精度。     

退火对B掺杂纳米金刚石薄膜微结构和电化学性能的影响

采用热丝化学气相沉积法制备B掺杂纳米金刚石薄膜,并对薄膜进行真空退火处理,系统研究了不同退火温度对B掺杂纳米金刚石薄膜的微结构和电化学性能的影响.结果表明,当退火温度升高到800 ℃后,薄膜的Raman谱图中由未退火时在1157,1346,1470,1555 cm^-1处的4个峰转变为只有D峰和G峰,说明晶界上的氢大量解吸附量减少,并且D峰和G峰的积分强度比I_D/I_G值变为最小,即sp²相团簇     

Broadening of Cr nanostructures in laser-focused atomic deposition

This paper presents the experimental progress of laser-focused Cr atomic deposition and the experimental condition.The result is an accurate array of lines with a periodicity of 212.8±0.2 nm and mean full-width at half maximum as approximately 95 nm.Surface growth in laser-focused Cr atomic deposition is modeled and studied by kinetic Monte Carlo simulation including two events:the one is that atom trajectories in laser standing wave are simulated with the semiclassical equations of motion to obtain the deposition position;the other is that adatom diffuses by considering two major diffusion processes,namely,terrace diffusion and step-edge descending.Comparing with experimental results(Anderson W R,Bradley C C,McClelland J J and Celotta R J 1999 Phys.Rev.A 59 2476),it finds that the simulated trend of dependence on feature width is in agreement with the power of standing wave,the other two simulated trends are the same in the initial stage.These results demonstrate that some surface diffusion processes play important role in feature width broadening.Numerical result also shows that high incoming beam flux of atoms deposited redounds to decrease the distance between adatoms which can diffuse to minimize the feature width and enhance the contrast.     

二维变系数对流扩散问题的特征配置法

1引言 在多种问题的数值模拟中均涉及抛物型对流扩散方程的数值求解问题.由于配置法 无需计算数值积分，计算简便，收敛阶高等优点，使之在工程技术和计算数学的许多领域 得到广泛的应用，但范围一般局限在一维常系数{1，21和二维常系数问题降，4]，90年代[s] 提出了二维变系数     

Study of intrinsic localized vibrational modes in micromechanical oscillator arrays

Intrinsic localized modes (ILMs) have been observed in micromechanical cantilever arrays, and their creation, locking, interaction, and relaxation dynamics in the presence of a driver have been studied. The micromechanical array is fabricated in a 300 nm thick silicon-nitride film on a silicon substrate, and consists of up to 248 cantilevers of two alternating lengths. To observe the ILMs in this experimental system a line-shaped laser beam is focused on the 1D cantilever array, and the reflected beam is captured with a fast charge coupled device camera. The array is driven near its highest frequency mode with a piezoelectric transducer. Numerical simulations of the nonlinear Klein-Gordon lattice have been carried out to assist with the detailed interpretation of the experimental results. These include pinning and locking of the ILMs when the driver is on, collisions between ILMs, low frequency excitation modes of the locked ILMs and their relaxation behavior after the driver is turned off.     

Numerical differentiation from a viewpoint of regularization theory

In this paper, we discuss the classical ill-posed problem of numerical differentiation, assuming that the smoothness of the function to be differentiated is unknown. Using recent results on adaptive regularization of general ill-posed problems, we propose new rules for the choice of the stepsize in the finite-difference methods, and for the regularization parameter choice in numerical differentiation regularized by the iterated Tikhonov method. These methods are shown to be effective for the differentiation of noisy functions, and the order-optimal convergence results for them are proved.

     

A New Gradient Method with an Optimal Stepsize Property

The gradient method for the symmetric positive definite linear system is as follows

Mn和N共掺ZnO稀磁半导体薄膜的研究

使用对Zn₂N₃:Mn薄膜热氧化的方法成功制备了高含N量的Mn和N共掺ZnO的稀磁半导体薄膜.在没有N离子共掺的情况下,ZnO:Mn薄膜的铁磁性非常微弱;如果进行N离子的共掺杂,就会发现ZnO:Mn薄膜在室温下表现出非常明显的铁磁性,饱和离子磁矩为0.23 μ_B—0.61 μ_B.这说明N的共掺激发了ZnO:Mn薄膜中的室温铁磁性,也就是受主的共掺引起的空穴有利于ZnO中二价Mn离子的铁磁性耦合,这和最近的相关理论研究符合很好. 关键词： 磁性半导体 受主掺杂 空穴媒介的铁磁性     

BCK-代数中子集的次极大理想

在BCK-代数中引入子集的次极大理想的概念,研究了它的基本特性,将极大理想和次极大理想的某些结果进行了推广.