The evolution of the cluster size distribution in a coagulation system

The coagulation equation with kernelK _ij =A+B(i+j)+C _ij and arbitrary initial conditions is studied analytically and a simple expression for the solution is found. For monodisperse initial conditions, we recover the known size distribution expressed in terms of a degeneracy factorN _k, which is determined by a recursion relation. For polydisperse initial conditions, a similar solution form is found, which includes a degeneracy factorN _kl, also determined by a recursion relation. The physical meaning ofN _kl and the recursion relation is given. A method to get explicit expressions forN _k andN _kl is illustrated. Finally, the pre-gel solution is given explicitly and a general method to get the post-gel solution is proposed.     

Coercivity analysis in R17Fe83−χBχ magnets

We studied the coercivity in magnets of composition R₁₇Fe_83−χB_χ (R = Nd, Pr and χ = 8, 30), using measurements of the coercive field H_c, its angular dependence, and the magnetic viscosity coefficient S_v, for temperatures between 4.2 and 500 K. The results are discussed in relation to a model which does not specifically consider the detailed mechanisms involved in magnetization reversal, but which provides information about the magnetic properties in the activation volume v where magnetization reversal is initiated. It is concluded that the ordering temperature in v tends to be slightly smaller than in the bulk and that the room temperature anisotropy in v is not strongly reduced with respect to the bulk value. Finally, a direct evaluation of the dipolar interactions is in good agreement with results obtained from H_c(T).     

Angular momentum effect in prescission particle multiplicities for a light system by diffusion model

The effect of angular momentum on the competition between fission and particle emission during light system fission process was studied via fission diffusion model. The prescission particle multiplicities were found to increase with decreasing angular momentum. The experimental prescission proton and α particle multiplicities can be fitted for 10.6 MeV/nucleon ⁸⁴Kr(²⁷Al,binary fission) reaction with this model. Entrance channel effect found in [1] is proved to be angular momentum effect.     

A DIRECT METHOD FOR THE UNIT CIRCLE PROBLEM

The unit circle problem is the problem of finding the number of eigenvalues of a non-Hermitian matrix inside and outside the unit circle . To reduce the cost of computing eigenvalues for the problem, a direct method, which is analogous to that given in [5], is proposed in this paper.     

X-ray evidence for the absence of 90°-domains in polycrystalline PbTiO3 thin films with grains below a critical size

3 thin films is systematically studied by using X-ray diffraction (XRD). The PbTiO₃ thin films with different average grain sizes were prepared on various substrates by a sol-gel process. The films on NaCl and fused glass are randomly grain-oriented, while those on (111)Pt/Ti/SiO₂/Si are highly {100} cubic index grain-oriented . It is found from the XRD patterns of the films on NaCl that with decreasing average grain size from 230 to 80 nm, the intensities of high h index (h>l) peaks (hkl), such as (100), (110), (200), (201), (210), (211), etc., decrease rapidly and ultimately disappear, whereas another set of peaks (lkh), including (001), (002), (102), (112), etc., are still intense. This interesting result suggests that at grain size below a certain critical size an increasing number of grains no longer show 90°-domains, which is confirmed by TEM observations. Meanwhile, X-ray evidence of such a grain-size-related absence of 90°-domains is also found for PbTiO₃ films on Pt(111) and fused-glass substrates. The volume fractions of single-domain grains (without 90°-domains) in the films are estimated from their XRD patterns. By combining SEM and TEM investigations, the critical grain size for the formation of 90°-domains is further determined to be near 200 nm. Received: 19 December 1996/Accepted: 24 March 1997     

非线性物理简介:8.光学孤子及其在光纤通讯中的应用

本文介绍了光学孤子的形成、特性及其在光纤通讯中的应用．     

采用级联原子滤光器的新型卫星激光链路系统研究

提出级联佛克脱型原子滤光器(Linked VADOF)的新构想。从理论上分析并计算了级联佛克脱型原子滤光器的透射谱。结果表明，级联佛克脱型原子滤光器将佛克脱型原子滤光器的多峰改造为单峰结构，具有比佛克脱型原子滤光器更窄的线宽和更高的噪声抑制比。将这种新型结构应用于激光信标锁频。该锁频方案提高了信标光频率的稳定性。在此基础上，给出了发射端采用级联佛克脱型原子滤光器锁频，接收端采用法拉第型原子滤光器(FADOF)滤光的新型卫星激光链路系统。外场初步联调实验表明了该系统的可行性。     

Regular simple geodesic loops on a tetrahedron

A regular simple geodesic loop on a tetrahedron is a simple geodesic loop which does not pass through any vertex of the tetrahedron. It is evident that such loops meet each face of the tetrahedron. Among these loops, the minimal loops are those which meet each face exactly once. Necessary and sufficient conditions for the existence of minimal loops are obtained. These conditions fall naturally into two categories, conditions in the first category being called coherence conditions and conditions in the second category being called separation conditions. It is shown that for the existence of three distinct minimal loops through any point on the face of a tetrahedron it is necessary and sufficient that the tetrahedron be isosceles, which, in turn, amounts to the tetrahedron satisfying three coherence conditions. All other regular simple geodesic loops on an isosceles tetrahedron are then classified. Finally, coherence conditions for the existence of similar loops on an arbitrary tetrahedron are found.     

Direct imaging of a high-power diode laser cavity using a transparent indium-tin-oxide (ITO) contact

We describe a novel "see-through" indium-tin-oxide contact on the n-side of a high power unstable resonator semiconductor laser (URSL) that allows direct observation of the cavity during high power operation. Under optimized annealing conditions this transparent ITO contact has a low enough specific contact resistivity to permit normal high power CW operation of the URSL and allows the observation of filamentation. This contact scheme is applicable to a wide range of semiconductor lasers and is especially appropriate for high power devices. The same structure can also be used to obtain a 2-D thermal map of the laser cavity.