BCS theory for trapped ultracold fermions

We develop an extension of the well-known BCS-theory to systems with trapped fermionic atoms. The theory fully includes the quantized energy levels in the trap. The key ingredient is to model the attractive interaction between two atoms by a pseudo-potential which leads to a well defined scattering problem and consequently to a BCS-theory free of divergences. We present numerical results for the BCS critical temperature and the temperature dependence of the gap. They are used as a test of existing semi-classical approximations. Received 18 December 1998     

激光偏振方向和强度变化对分光光强的影响

在双光路补偿强度调制型光电检测系统中,采用分光镜后透射光强和反射光强会随着激光光源偏振方向和强度的变化而变化,这严重破坏了强度补偿机理。详细推导了激光光源偏振方向变化时分光比的变化公式,举例说明了分光比随偏振角的变化情况,并给出了反射光强和透射光强的变化规律。重点讨论了当激光光源偏振方向和强度同时变化时分光比的变化规律。提出了采用偏振光源或偏振片的两种解决办法。     

Realizing 20 Gbits OTDM Transmission over 50km Truewave Fiber with Dispersion Compensation

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TSC study of the dielectric relaxations of human‐bone collagen

Differential scanning calorimetry (DSC) and thermally stimulated current (TSC) were used to characterize human‐bone collagen. DSC glass‐transition and denaturation temperatures of the collagen in a dehydrated state were 90 and 215 °C, respectively. By TSC, the main relaxation mode, labeled α and located around 90 °C, could be attributed to the dielectric manifestation of the glass transition. The corresponding molecular movements are cooperative with a compensation temperature close to the denaturation temperature. At low temperatures and in a hydrated state, a second mode labeled β₂ was observed at −110 °C. Dehydration shifted this mode to higher temperatures, revealing a weak mode labeled γ at −150 °C. This γ mode was attributed to motions of aliphatic side chains. An analysis of low‐temperature elementary spectra allowed us to assign the β₂ mode to structural water movements and revealed an additional compensation phenomenon in the temperature range (−80 to −50 °C). Because the compensation temperature of this mode was close to the collagen glass‐transition temperature, the corresponding mode β₁ was attributed to polar side‐chain motions, precursors of a collagen glass transition. Finally, around ambient temperature, three sharp peaks were attributed to hydrogen bonds breaking. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 987–992, 2000     

啁啾脉冲放大激光系统中展宽器色散的解析算法

时域色散精密控制是超短激光产生及其应用中的关键技术之一,它通过控制各波长的光程产生相对延迟从而改变脉冲宽度.展宽器是啁啾脉冲放大激光系统中对激光脉冲展宽的装置,基于光线追迹法研究光线在展宽器中的传输路径,可计算飞秒脉冲中各波长的光程,进而计算脉冲展宽量并应用于系统设计.由于展宽器的光程表达式复杂,直接对其求导获得色散表达式较困难,目前只能采用数值导数获得近似解,这在计算过程中会引入误差,不利于激光系统精确设计和优化.本文介绍了一种易实现的求解展宽器色散的解析算法,通过归纳展宽器光程表达式特点,引入四个基元函数,将光程表达式分解和反复代换,可得到高阶色散的精确解析值.本文首先对Martinez型展宽器重新光线追迹,获得与Offner型展宽器一致的相位表达式,其次通过解析算法获得了两种展宽器的精确高阶色散值,最后将解析算法与数值算法的结果进行了比较.该解析算法对于啁啾脉冲放大系统的参数设计具有实用价值.     

Critical behaviors of a (2 + 1)-dimensional black hole with a nonlinear electrodynamics source

On the basis of a charged BTZ black hole, we add an extra term in the metric function to describe the contribution from nonlinear electrodynamics. In this way we artificially construct a (2 + 1)-dimensional black hole in general relativity coupled with a nonlinear electrodynamics source. The thermodynamic quantities and Smarr formula are derived. It is found that this black hole has T−S criticality like that of an RN-AdS black hole. Further modifying the metric function, we obtain a (2 + 1)-dimensional black hole possessing P−V critical behaviors similar to that of van der Waals fluid. To our knowledge, this is the first example of (2 + 1)-dimensional black holes having this kind of critical behavior.     

热声系统中振荡滞后特性的试验研究

针对热声热机中存在着强烈的非线性热声自激振荡现象,在自行研制的"驻波型热声发动机试验平台"上,对采用He/Ar混合工质的驻波热声发动机系统的起振与消振过程的动态特性进行了详细的试验研究.试验结果表明:对于混合工质热声发动机系统同样存在热声自激振荡的滞后现象和振荡滞后回路;并且在一定的氦氩配比下,发现了"二次起振"的现象,更进一步验证了热声自激振荡的复杂性.     

一种全帧型CCD航空相机像移补偿方法

提出一种全帧型CCD航空相机像移补偿的实现方法.应用全帧型CCD在机械快门不关闭的情况下连续曝光的特点,并根据不同的速高比控制暂停脉冲的个数和宽度,控制了CCD垂直转移的速度,使CCD在曝光的同时进行转移和读出,实现了全帧型CCD航空数码相机航向方向的像移补偿.实验数据表明：该方法能够实现全帧型CCD像移补偿的功能.     

基于偏振度椭球的PMD补偿的前馈信息提取方法

通过建立一个简单的模型推导了偏振模色散与偏振度椭球的关系式,可以直接从偏振度椭球的长轴和短轴得到偏振模色散的大小.将得到的一阶偏振模色散大小与理论上从琼斯矩阵中计算的结果进行比较,发现在差分群时延小于20 ps时,模拟结果与理论计算值较好相符.分析了如何从偏振度椭球的长轴判断偏振模色散矢量的方向.因此,从得到的偏振模色散矢量的大小和方向信息可以为一阶偏振模色散补偿提供前馈信息.