Cr^4＋：YAG调Q特性的理论和实验研究

从理论和实验两个方面研究Ｃｒ＾４＋：ＹＡＧ的调Ｑ特性，测量了Ｃｒ＾４＋：ＹＡＧ调ＱＮｄ＾３＋：ＹＡＧ激光器在不同条件下脉冲能量和脉冲宽度，并与理论结果进行比较，结果显示脉冲能量的理论结果与实验结果能较发地符合，脉冲工的理论结果与实验结果变化趋势大致相一致，文中还对Ｃｒ＾４＋：ＹＡＧ调ＱＮｄ＾３＋：ＹＡＧ激光器的其它实验现象给出定性解释。     

采用飞秒光纤激光同步泵浦的自启动锁模钛宝石激光研究

针对常规连续激光泵浦钛宝石激光振荡器不能自启动锁模的缺点,采用倍频飞秒光纤激光同步泵浦,通过调节振荡器腔长与泵浦腔长匹配,实现了飞秒钛宝石激光的自启动锁模。实验中采用3.4 W的倍频掺镱光纤激光同步泵浦钛宝石激光振荡器,获得了平均功率大于130 mW、重复频率75 MHz、光谱宽度大于47 nm、脉冲宽度17 fs的锁模脉冲输出,不仅能够稳定可靠地实现自启动锁模,解决了常规钛宝石激光振荡器锁模启动的困难,而且还具有同步输出1040,800,520 nm三束飞秒激光的特点,为进一步开展飞秒激光相干合成以及光参量放大等研究提供了优势基础。     

多复变Cauchy积分和被动算子与多重色散关系

本文阐述多重色散关系联系着矩阵z(p)的实部与虚部:,式中z(p)是阻抗z(ζ)的边值.     

用非简并泵浦探测方法研究C70/甲苯溶液的激发态吸收动力学

通过非简并的时间分辨泵浦探测技术对C70富勒烯/甲苯溶液的非线性光学性质进行了研究。在532 nm波长的皮秒激光脉冲泵浦下,用600 nm的皮秒激光脉冲测量了C70富勒烯的激发态非线性吸收动力学响应。利用五能级模型对实验结果进行了数值模拟,得到了非简并情况下C70富勒烯分子的光物理参数。实验结果表明:C70富勒烯在简并和非简并情况下的激发态寿命没有变化,但非简并情况下的单重态吸收截面要比简并情况下单重态吸收截面小。     

Investigation on Heat Transfer and Pressure Drop of Copper–Water Nanofluid Flow in Plain and Perforated Channels

This article reports an experimental study on copper–water nanofluid flow inside plain and perforated channels. The effects of flow rate and nanoparticle concentration on the heat transfer and pressure drop are studied. It is found that the perforated channel has a remarkable heat transfer enhancement of 24.6%. Furthermore, by using the copper–water nanofluid instead of the base fluid, the heat transfer coefficient as well as pressure drop are increased for both plain and perforated channels. A noticeable thermal performance factor of 1.34 is obtained for the simultaneous utilization of both the heat transfer enhancement techniques considered in this article.     

The effect of subgrid-scale models on the entrainment of a passive scalar in a turbulent planar jet

Classical large-eddy simulation (LES) modelling assumes that the passive subgrid-scale (SGS) models do not influence large-scale quantities, even though there is now ample evidence of this in many flows. In this work, direct numerical simulation (DNS) and large-eddy simulations of turbulent planar jets at Reynolds number Re_H = 6000 including a passive scalar with Schmidt number Sc = 0.7 are used to study the effect of several SGS models on the flow integral quantities e.g. velocity and scalar jet spreading rates. The models analysed are theSmagorinsky, dynamic Smagorinsky, shear-improved Smagorinsky and the Vreman. Detailed analysis of the thin layer bounding the turbulent and non-turbulent regions – the so-called turbulent/non-turbulent interface (TNTI) – shows that this region raises new challenges for classical SGS models. The small scales are far from equilibrium and contain a high fraction of the total kinetic energy and scalar variance, but the situation is worse for the scalar than for the velocity field. Both a-priori and a-posteriori (LES) tests show that the dynamic Smagorinsky and shear-improved models give the best results because they are able to accurately capture the correct statistics of the velocity and passive scalar fluctuations near the TNTI. The results also suggest the existence of a critical resolution Δ_x, of the order of the Taylor scale λ, which is needed for the scalar field. Coarser passive scalar LES i.e. Δ_x ≥ λ results in dramatic changes in the integral quantities. This fact is explained by the dynamics of the small scales near the jet interface.     

一种基于多普勒频移的被动合成孔径声纳探测方法*

由于自主小平台声纳孔径有限,对声纳探测的分辨率的提高有所限制。小平台的机动可以有效的与声纳探测方法相结合来提高声纳探测性能。针对这一特点,提出一种基于多普勒频移技术的被动合成孔径声纳探测方法。该方法根据自主小平台的机动所引起声纳的接收信号多普勒频移的变化,进行目标的频率与方位联合估计。本文将自主小平台的机动引入到波束形成技术当中形成一种新的被动合成孔径技术。数值仿真表明,该方法可以有效的进行目标方位估计,并且获得较高的方位分辨率,改善了自主小平台的探测性能。     

Thermal Bias on the Pumped Spin-Current in a Single Quantum Dot

Temperature effect on the spin pump in a single quantum dot(QD) connected to Normal(NM) and/or Ferromagnetic(FM) leads is investigated with the help of master equation method. Results show that the magnitude and the direction of the temperature difference between the source(L) and drain(R) leads have great impact on the spin current processes. In practical devices, the thermal bias is quite general and then our results may be useful in quantum information processing and spintronics.     

A Novel All-optical Wavelength ConverterBased on Self-pump Four-wave Mixing

A novel scheme of all-optical wavelength converter(AOWC) based on dual pump four-wave mixing(DP-FWM) was demonstrated. To suppress the ASE noise of the semiconductor optical amplifier (SOA), one of the two pumps was generated interiorly from a loop laser constructed mainly by tunable optical filter and SOA. The theoretical model and some experimental results were presented.     

昆虫翼拍动中受载变形的粘弹性本构模型

昆虫翼拍动受载时发生被动变形,被看作为有助于改善飞行性能的机制之一．决定这种被动变形大小的一个关键因素是昆虫翼的材料本构关系,至今缺乏研究．基于蜻蜓翼(离体)的应力松弛实验和模型翼拍动时受载变形的有限元数值分析,揭示了粘弹性本构关系是昆虫翼材料性能的合理描述,并研究了粘弹性参数对被动变形的影响．