Influence of surface heterogeneity in electroosmotic flows—Implications in chromatography, fluid mixing, and chemical reactions in microdevices

We analyze the influence of surface heterogeneity, inducing a random ζ-potential at the walls in electroosmotic incompressible flows. Specifically, we focus on how surface heterogeneity modifies the physico-chemical processes (transport, chemical reaction, mixing) occurring in microchannel and microreactors. While the macroscopic short-time features associated with solute transport (e.g. chromatographic patterns) do not depend significantly on ζ-potential heterogeneity, spatial randomness in the surface ζ-potential modifies the spectral properties of the advection-diffusion operator, determining different long-term properties of transport/reaction phenomena compared to the homogeneous case. Examples of physical relevance (chromatography, infinitely fast reactions) are addressed.     

Numerical resolution of the modified Langevin equation using a differential expression: Application to the Jiles magnetostriction law of approach

The Langevin equation is classically used to model the anhysteretic magnetization curve. A modified version of this equation has been introduced by Jiles to take into account the effects of magnetostriction on the anhysteretic magnetization behavior when a ferromagnetic material undergoes mechanical stresses. The numerical resolution of the modified Langevin equation is usually performed with a root-finding algorithm. In this paper, a differential form of the modified Langevin equation is proposed, allowing a faster numerical resolution.     

Scheme for direct measurement of Wigner function in two-mode cavity QED driven by classical fields

We propose a scheme for the direct measurement of Wigner function in two-mode cavity QED.The atoms are sent to resonantly interact with two orthogonally polarized cavity modes in the presence of strong classical field.The probability of measuring the atom in the ground state directly gives the useful information of the cavity field.This method can be used for quantum non-demolition measurement of the photon number.     

The magnetic properties of one-dimensional spin-1 ferromagnetic Heisenberg model in a magnetic field within Callen approximation

The effect of magnetic field h on the magnetic properties of the one-dimensional spin-1 ferromagnetic Heisenberg model is studied by the double-time Green’s function method. The magnetization and susceptibility are obtained within the Callen approximation. The zero-field susceptibility is as a decreasing function of the temperature T. The magnetization m increases in the whole field region, but the susceptibility maximum χ(T_m) decreases. The position T_m of the susceptibility maximum is both solved analytically and fits well to be a power law T_m∼h^γ at low fields and to be linear increasing at high fields. The height χ(T_m) decreases as a power law χ(T_m)∼h^−β with h increasing. The exponents (γ,β) obtained in our results agree with the other theoretical results. Our results are roughly in agreement with the results obtained in the experiment of Ni(OH)(NO₃)H₂O.     

变形谐振子势的能谱方程

讨论了3种变形谐振子势:左右两边不同参数的谐振子势、左边方形势加右边谐振子势和谐振子势中间加δ势中的能量本征态函数.这些函数都可以由厄米函数表示.由波函数及其一次导数在原点的衔接条件,得到了能谱方程.     

Bosonic enhancement of spontaneous emission near an interface

We show how the spontaneous emission rate of an excited two-level atom placed in a trapped Bose-Einstein condensate of ground-state atoms is enhanced by bosonic stimulation. This stimulation depends on the overlap of the excited matter-wave packet with the macroscopically occupied condensate wave function, and provides a probe of the spatial coherence of the Bose gas. The effect can be used to amplify the distance-dependent decay rate of an excited atom near an interface.     

Anisotropy of sound velocity for a new PbB4O7 crystal as determined by the laser ultrasonic technique

4 O₇ crystal is a new nonlinear optical crystal. For the first time the anisotropy of the velocities of its longitudinal and surface acoustic waves (SAWs) are determined by laser ultrasonic technique. The velocities of surface waves for X-, Y-, and Z-cut crystals are also calculated. The theoretical calculations of slowness curves are in good agreement with experimental results. The SAW slowness curve is elliptical for Y- or Z-cut crystal wafers, and circular for an X-cut wafer. Received: 27 January 1997/Accepted: 30 July 1997     

Effect of Finite Rise Time on the Strength of the Magnetic Field Generated in a Switched Plasma

The effect of a magnetized transient plasma on a circularly polarized source wave, when the rise time of the electron density profile is comparable to the source wave period, is considered. The H-formulation Green's function is developed to study the effect of a finite rise time on the generation of a wiggler magnetic field.     

多碱阴极光电发射机理研究

通过比较有Cs-Sb表面层多碱阴极和未有Cs-Sb表面层多碱阴极的荧光谱,发现有Cs-Sb表面层多碱阴极的荧光谱峰值波长向短波方向“蓝移”以及荧光峰增强的现象.这一现象表明在多碱阴极Na2KSb基层上制作Cs-Sb表面层之后,不仅多碱阴极的逸出功降低,而且 Na2KSb基层的结构也发生了变化.这意味着在相同功率和相同频率入射光照射下,经过表面Cs-Sb处理的Na2KSb基层能够产生更多的跃迁电子并且跃迁能级更高,逸出表面的机率更大,获得的阴极灵敏度更高.这表明Cs-Sb表面层既具有表面效应,又具有体效应.要进一步提高多碱阴极的灵敏度,除进一步降低多碱阴极的逸出功外,还需进一步提高Na2KSb基层的性能,使相同功率和频率的入射光能产生更多的跃迁电子,并且跃迁的能级更高,这就需要进一步改进工艺,提高Na2KSb材料的性能.     

Spherical particle Brownian motion in viscous medium as non-Markovian random process

The Brownian motion of a spherical particle in an infinite medium is described by the conventional methods and integral transforms considering the entrainment of surrounding particles of the medium by the Brownian particle. It is demonstrated that fluctuations of the Brownian particle velocity represent a non-Markovian random process. The features of Brownian motion in short time intervals and in small displacements are considered.