Electrically induced flows in the vicinity of a dielectric stripe on a conducting plane

We report a theoretical and experimental study of the hydrodynamic flow induced by an a.c. electric field in the vicinity of a dielectric stripe deposited on a conducting plate. In the theoretical part, we model the stripe as a small change of the surface capacitance of the plate, and a perturbative approach is used to perform the calculations. This approach predicts an outwards rectified electro-osmotic slip along the surface that generates two steady counter-rotating rolls, the size of which decreases with the frequency. In the experimental section, we use tracers to determine the structure of the flow and investigate its dependence on the frequency and the amplitude of the applied voltage. The structure and amplitude of the observed flow compares satisfactorily with the theoretical analysis. This could guide the design of surface-controlled flows and help to understand the collective behavior of colloids near electrodes. Received 20 June 2002 RID="a" ID="a"e-mail: nadal@crpp.u-bordeaux.fr     

x强流相对论环形电子束在低磁场中传输分析

 用理论和粒子模拟相结合的方法分析了强流薄环形相对论电子束在低磁场导引下，在均匀波导，无箔二极管，以及锥形波导和渐减磁场位形条件下的传输过程，研究了束包络的波动和如何减少波动的问题。分析表明：在无箔二极管中一个适当渐增的磁场位形可以有效地抑制束电子的径向运动，从而减少电子在波导中的波动幅度；电子束在锥形波导和渐减磁场位形中运动，不会增加束电子的波动。因此适当的磁场位形可以降低微波器件对导引磁场的要求，有利于实现永磁包装微波器件。     

Detection of B-FSK signals using schmidt trigger

Possibility to record B-FSK signals with use of stochastic resonance is studied. A Schmidt trigger is employed as bistable stochastic resonator. A digital model of the detector is proposed and quantitative results are obtained by means of simulations. Dependence of the probability of correctly detected bits on the added noise power and on the low-pass filter cutoff frequency is studied. Also the stability of the detector with respect to channel-introduced phase shifts is revealed.     

Analysis of film strain and stress in a film-substrate cantilever system

The bending problem of a magnetic film-nonmagnetic substrate cantilever system is studied by using the principle of energy minimization. Emphasis is placed on the analysis of geometrical and physical parameter dependence of the neutral plane, internal film stress and strain of the cantilever system, and then the influence of such a parameter on the bending characteristic is presented. The results indicate, owing to the anisotropic expanding feature of the magnetostriction, that the neutral plane is generally anisotropic, and moves downwards rapidly with the increasing thickness ratio. Meanwhile, the bounding rigidity of substrate on the film will decrease with the increasing thickness ratio, and thus release the film stress, i.e., it decreases, but the film strain increases. The effect of Poisson’s ratio of the materials on the film strain, the stress and the neutral plane in the direction transverse to the magnetization is prominent. For the strain and the stress in the magnetization, however, the role of Poisson’s ratio is inconspicuous. This property is due to the initiative elongating (or contracting) feature of the magnetic film along its magnetization. Supported by the National Natural Science Foundation of China (Grant No. 10762001), the Key Project of the Chinese Ministry of Education (Grant No. 206024), and the Program for New Century Excellent Talents in University of China (Grant No. NCET-2005-0272)     

射频溅射法制备Pb_(1-x)Co_xSe薄膜及物性研究

利用复合靶共溅射法制备了半磁性半导体 Ｐｂ１－ ｘ Ｃｏｘ Ｓｅ 薄膜．研究了薄膜的成分结构以及电阻率温度特性和磁化率温度特性间的关系．结果表明：由于 Ｃｏ 离子介入, Ｐｂ１－ ｘ Ｃｏｘ Ｓｅ 发生了由金属特性向半导体特性的转变,在充分低的温度下,并伴有磁相转变．磁相转变温度与磁性离子浓度相关,磁化率的相对变化幅度与磁性离子浓度有关     

RL-C并联谐振态量与Q的几个关系式

对ＲＬ－Ｃ并联谐振电路中的几个谐振态量与Ｑ之间的关系作了详尽的推导。     

均匀磁场中带电粒子的四类升降算子

用因式分解法求出带电粒子在垂直于均匀磁场的平均面内运动体系的四类升降算子,并了相应的选择定则和守恒量子数。     

电、磁四极透镜问题

通过电四极透镜与磁四极透镜两个实例阐明中心反对称二维非均匀静电场静磁场及其应用。     

Spin concentration in a possible ESR dosimeter: An electron spin echo study on X-irradiated ammonium tartrate

Several single crystals and powder samples of ammonium tartrate, recently proposed as a possible ESR dosimeter, have been X-irradiated with different doses. The total radical concentration has been determined by quantitative cw ESR, by comparison with a standard. The samples have been studied by electron spin echo spectroscopy. The two-pulse echo decay has been obtained and simulated by a single exponential function for different values of the microwave power of the pulses and for different pulse lengths. The dependence of the phase memory time TM on the microwave power has been exploited to get information on the contribution of the instantaneous diffusion to spin dephasing. At room temperature in the range of radical concentrations of 10(18)-10(19) spins/cm3 the instantaneous diffusion is the dominant spin dephasing mechanism. The linear dependence of the instantaneous diffusion on the total concentration of the radicals is in agreement with the theory. From the latter result we conclude that the average radical-radical distance corresponds to a random distribution of the radicals in the matrix. A simple method of measuring the radical concentration by the ESE decays in powder samples of irradiated ammonium tartrate is described.     

Sensitivity-enhanced sim-CT HMQC PFG-HBHA(CO)NH and PFG-CBCA(CO)NH triple-resonance experiments

Short transverse relaxation times of Calpha and Cbeta single-quantum coherences reduce the sensitivity of triple-resonance experiments involving transfers of Calpha/Cbeta or Halpha/Hbeta coherences. Multiple-quantum line-narrowing techniques improve the relaxation properties of 13C coherences, thereby increasing the sensitivity of the experiment. In the present work, we describe PFG-CBCA(CO)NH and PFG-HBHA(CO)NH experiments that utilize heteronuclear multiple-quantum coherences in a simultaneous constant-time period to obtain completely decoupled spectra with improved sensitivity. Results indicate that approximately 30% of cross peaks show an average enhancement of approximately 15% in the CBCA(CO)NH experiment. In the related HBHA(CO)NH experiment, approximately 97% of the cross peaks show an average enhancement of approximately 40%.