Zero bias anomaly in the density of states of low-dimensional metals

We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln²-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e ⁴ appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω ₂ which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω ₁)^1/2exp(- Ω ₁/|ω|) at T = 0, where Ω ₁ is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance that can be compared with experiments. Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002     

Physics possibilities at India-based Neutrino Observatory

In this talk I review the physics possible at India-based Neutrino Observatory (INO). I discuss the improvement in the precision of currently known quantities and the possibility measuring the presently unknown quantities.     

磁场对四端量子波导中电子输运性质的影响

采用模匹配方法，研究了非均匀磁场下开放的四端量子波导中的电子输运性质. 结果表明，从一端入射的电子可以透射到两个与之垂直的输出端和一个与之平行的输出端. 在没有外加磁场的情况下，两个垂直输出端的输运概率是相同的，但垂直端与水平端的输运概率不同；在外加磁场下，由于磁边缘态效应，两个垂直输出端的输运概率也有着相当大的差别. 通过施加不同的磁场，我们能获得丰富的电子输运结构，如台阶，宽谷，尖峰等；通过调节磁场的大小和比例以及结构参数可控制该量子结构在各输出端的输运概率. 关键词： 电子输运 介观体系 磁效应     

Many-body effects in diffusion-limited kinetics

We review a novel approach to treating many-body effects in diffusion-limited kinetics. The derivation of the general expression for the survival probability of a Brownian particle in the presence of randomly distributed traps is given. The reduction of this expression to both the Smoluchowski solultion and the wellknown asymptotic behavior is demonstrated. It is shown that the Smoluchowski solution gives a lower bound for the particle survival probability. The correction to the Smoluchowski solution which takes into account the particle death slowdown in the initial process stage is described. The steady-state rate-constant concentration dependence and the reflection of many-body effects in it are discussed in detail.     

T-C模型中虚光子过程对光场压缩效应的影响

利用全量子理论,研究非旋波近似下TC模型中受激场的压缩效应.结果表明:非旋波近似下,由于虚光场的影响,Q的演化曲线出现了“小锯齿状”,表现为系统的量子噪声,随着ω和n的增大,量子噪声分别减小和增大,虚光子过程使光场的压缩程度明显加深;研究结果还揭示了原子场耦合系数λ及原子间耦合系数g与光场压缩效应的关系. 关键词： T-C模型 非旋波近似 压缩效应 量子噪声     

Design and Cold Tests of Asymmetric Quasioptical Resonators

This paper presents the design and test of asymmetric quasioptical resonators for gyrotron applications, where most of the diffraction output coupling comes from the smaller of two mirrors. A computer code based on scalar diffraction theory is used to calculate the resonator losses and the electric field near the mirrors. Resonators with mirror separations approaching confocal have reduced side lobes in the diffraction patterns, which should allow for better power transmission and focusing. Cold tests have been performed at 94 and 141 GHz to measure the quality factor of the asymmetric resonators as a function of mirror separation and mirror misalignment. Typical resonator parameters include 65 cm mirror separation, 1-3% output coupling and 85% of the losses from the small mirror. A half-symmetric resonator with one flat and one curved mirror has also been investigated. The calculated values of Q are in reasonably good agreement with the cold test measurements.     

市场竞争与国有企业所有权安排

改进了张维迎对地区间竞争与国有企业民营化的分析,给出了经营者的剩余索取份额对竞争性的连续依赖关系:国有企业若要降低成本,就必须参与市场竞争,随着市场竞争的加强,国有企业经营者的剩余索取份额应该逐渐增大,而当市场竞争水平超过某一阈值,国有企业经营者拥有全部剩余索取权是最优的.