Dissipative quantum phase transition in a biased Tavis-Cummings model

We study the dissipative quantum phase transition(QPT)in a biased Tavis–Cummings model consisting of an ensemble of two-level systems(TLSs)interacting with a cavity mode,where the TLSs are pumped by a drive field.In our proposal,we use a dissipative TLS ensemble and an active cavity with effective gain.In the weak drive-field limit,the QPT can occur under the combined actions of the loss and gain of the system.Owing to the active cavity,the QPT behavior can be much differentiated even for a finite strength of the drive field on the TLS ensemble.Also,we propose to implement our scheme based on the dissipative nitrogen-vacancy(NV)centers coupled to an active optical cavity made from the gainmedium-doped silica.Furthermore,we show that the QPT can be measured by probing the transmission spectrum of the cavity embedding the ensemble of the NV centers.     

Measurements of aerosol distribution by an elastic-backscatter lidar in summer 2008 in Beijing

Elastic lidar observations of profiles of the aerosol extinction, backscattering coefficients, and the lidar ratio have been performed in Beijing. The elastic lidar transmitts wavelengths of 532 and 355 nm. The measurement altitude can reach up to 6 km. The similarity of the extinction and baekscattering profiles suggests a close relation between the mean transmission and reflection properties. The lidar ratio on July 22, 2008 varied from 10 to 30 sr with the mean value of 20 sr. The profiles of the aerosol properties indicate the cirrus at 6 km altitude and a well-mixed boundary layer from July 22 to 24, 2008. The detected boundary layer also agrees well with the high and stable ozone concentration obtained from the differential optical absorption spectroscopy （DOAS） system.     

SYNTHESIS OF POLYSILOXANE-SUPPORTED SELENAETHER PLATINUM COMPLEX AND ITS CATALYTIC PROPERTY FOR HYDROSILYLATION OF OLEFINS

A new type of selenious polymer, silica-bound polybispropoxyethyl-selenidesilsesquioxane,and its platinum complex were synthesized from bis-allyloxyethyl selenide via hydrosily-lation with triethoxysilane, followed by immobilized on fumed silica, and then reactingwith potassium chloroplatinite under nitrogen atmosphere in acetone. It was found thatthe platinum complex can catalyze the hydrosilylation of olefins with triethoxysilane effec-tively The effects of the nature of the substrate, the amount of complex used, and thereaction temperature on the catalytic activity were investigated.     

单晶与纳米多晶锡层裂的分子动力学研究

低熔点金属的层裂是目前延性金属动态断裂的基础科学问题之一。采用非平衡态分子动力学方法模拟了冲击压力在13.5～61.0 GPa下单晶和纳米多晶锡的经典层裂和微层裂过程。研究结果表明：在加载阶段,冲击速度不影响单晶模型中的波形演化规律,但影响纳米多晶模型中的波形演化规律,其中经典层裂中晶界滑移是影响应力波前沿宽度的重要因素;在单晶模型中,经典层裂和微层裂中孔洞成核位置位于高势能处;在纳米多晶模型中,经典层裂中的孔洞多在晶界（含三晶界交界处）处成核,并沿晶定向长大,产生沿晶断裂,而微层裂中孔洞在晶界和晶粒内部成核,导致沿晶断裂、晶内断裂和穿晶断裂;孔洞体积分数呈现指数增长,相同冲击速度下单晶和纳米多晶Sn孔洞体积分数变化规律一致;经典层裂中孔洞体积分数曲线的两个转折点分别表示孔洞成核与长大的过渡和材料从损伤到断裂的灾变性转变。     

Atomosphere boundary layer height determination and observation from ceilometer measurements over Hefei during the total solar on July 22,2009 eclipse

<正>Using an improved inflexion point method(IIPM),we investigate atmosphere boundary layer(ABL) height evolution over Hefei during the total solar eclipse on July 22,2009.A lidar ceilometer is used in ground-based observations.Estimations of ABL heights before,during,and after the solar eclipse are analyzed using the IIPM.Results indicate that the IIPM,which is less sensitive to background noise,is more suitable in detecting ABL height and temporal evolution.Data demonstrate that the total solar eclipse resultes in a decrease in ABL height,indicating a suppression of turbulence activity,similar to that observed during the sunset hours.Changes in ABL height are associated with a slow change in temperature,indicating a significant weakening of penetrative convection and a time lag between ABL response and the reduction in solar radiation.     

基于室温脉冲工作量子级联激光器的脉间光谱技术研究

量子级联(QC)激光器是唯一能在室温产生中红外辐射的半导体激光器。它的宽调谐范围、高输出功率和单模工作的特性,使得它非常适用于高分辨率光谱分析。结合中红外光谱区是气体分子的基频强吸收特性,基于室温脉冲工作的量子级联激光器的吸收光谱检测技术以其灵敏度高、选择性强及响应快速等特点,成为痕量气体探测的有效方法。介绍了基于分布式量子级联激光器的脉间光谱技术,通过分析比较不同工作参数下的激光光谱信号,寻求最佳的激光器工作参数,并且在选定的工作参数下对目标气体的吸收谱线进行测量,得到了中心在2178.2cm-1附近的N2O的吸收谱线。     

基于希尔伯特-黄变换的激光云高仪后向散射信号去噪方法

基于希尔伯特-黄变换(HHT)和Savitzky-Golay滤波,提出了一种结合HHT时频分析的半导体激光云高仪后向散射信号去噪方法.该方法在对云高仪后向散射信号的噪声特性及传统去噪方法的缺陷进行研究的基础上,选择截止分量阶一定的自适应时变时空滤波器组(TFB)结构并辅助Savitzky-Golay滤波抑制噪声,最后利...     

基于室温量子级联激光器的脉内光谱技术测量N_2O

中红外激光光源覆盖了大鼍气体的基频吸收带,尤其适合于痕量气体的高灵敏检测.其中具有高输出功率、宽调谐范围、能够在室温工作的量子级联激光器为高灵敏痕量气体检测技术的研究提供了理想的光源.基于脉冲量子级联激光器的脉内光谱技术提供了一种简单而又有效的测量痕量气体的方法.当一个长激发脉冲作用在激光器上时,激光器的频率随着脉冲持续时间的增加而线性减小,从而在单个脉冲上扫描出被测气体分子的特征吸收谱线,实现对目标气体的定性或者定量分析.介绍了基于分布式量子级联激光器的脉内光谱技术,并采用该技术对N_2O进行了光谱测量.一个500 ns的长激发脉冲应用在脉冲量子级联激光器上用于快速波长扫描,达到接近1 cm~(-1)的线性调谐范围,得到了中心在1 274 cm~(-1)附近的N_2O的吸收谱线,与HITRAN数据库相应的N_2O吸收谱线有着良好的一致性.     

63Sn-37Pb钎料合金在非比例循环加载下的非弹性流动特性研究

基于63Sn-37Pb钎料舍金在多种非比例应变循环加载下的实验结果,通过考察材料的非弹性应变率与偏应力之间的夹角随累积非弹性应变的变化规律,对63Sn-37Pb钎料合金的非弹性流动特性进行了定量分析。分析结果显示：在相同的非比例加载路径下,当加载等效应变幅值相同时,等效应变率越高,非弹性应变率与偏应力之间夹角平均水平越低,当等效应变率相同时,等效应变幅值越大,相应的夹角平均水平越低;在保持时间范围内,非弹性应变率方向与偏应力方向趋于一致;当非比例路径形状不同时,其非弹性应变率与偏应力之间的夹角随累积非弹性应变的变化趋势明显不同。研究表明,材料的非弹性流动特性强烈依赖于等效应变幅值、等效应变率、保持时间、非比例路径形状。     

测云技术研究进展

云的形成和变化是非常复杂的,是气象预测和航空航海等领域中非常重要的因素之一,云对大气辐射平衡影响也很大,直接影响气候和水文学变化,因此,对云进行观测具有重要的现实意义。通常对云的气象观测主要有:云状、云量和云高三项。简要介绍了关于云的一些基本概念和观测标准。目前,对于云量和云状的观测主要还是靠目测,但云高测量的各项技术业已成熟,出现了许多用于测量云高的仪器。激光雷达是用来测量云高最实用的方法,世界各国都投入大量费用和精力进行研究。