平板湍流边界层底层的不稳定波

湍流边界层底层的相干结构及猝发现象对决定边界层的特性有很重要的意义,但直至现在对相干结构的性质及起因仍不清楚。在本文中,对湍流边界层的底层进行了非线性稳定性分析,发现该处确可产生不稳定波,可能用以说明相干结构的起因。     

微乳液-水热结合法制备光色可调的α-NaYF4:Yb,Er,Tm纳米材料

采用微乳液-水热结合法制备了NaYF4:Yb3+,Er3+,Tm3+纳米粒子,利用X射线衍射(XRD)、扫描电镜(SEM)等手段对样品的物相、结构和形貌进行了分析与表征。产物的X射线衍射峰与标准卡片PDF#77-2042完全一致,属于立方相NaYF4;SEM图片显示所制备的纳米粒子形貌和粒径都比较均一,为120nm左右的棉花状小球,由纳米微粒聚集而成;在980nm光的激发下,纳米粒子能够同时发出蓝光(438和486nm)、绿光(523和539nm)和红光(650nm);通过调节Tm3+:Er3+的比例(0,0.5,0.8,1,2,3,5,7),由色度坐标图(CIE)可以看出当Tm3+和Er3+的比例从0增加到2时,样品的整体发光光色是向绿光方向移动;当Tm3+和Er3+的比例为1:1时,得到伪白光;Tm3+和Er3+的比例从2到7时,样品整体的发光向红光方向移动。     

回收LNG冷能的新型碳二烃两级膨胀朗肯循环

提出了一种新型的回收LNG冷能的两级膨胀朗肯动力循环,可以乙烯或乙烷作为工质。此工艺流程采用多股流低温板翅式换热器(MSCHE)作为主要设备,使工质两级膨胀并采用回热过程,可以使循环的冷能利用效率得到明显提高。针对此工艺分别以乙烯或乙烷为工质,与LNG直接膨胀结合和不结合,共四种方案采用HYSYS软件进行工艺模拟,并对模拟结果进行了比较和分析,可得出无LNG膨胀的乙烯两级膨胀工艺流程最为合理,其冷能和火用的利用率可以分别达到19.67%和21.75%。     

基于Stokes矢量的实时偏振差分水下成像研究

偏振差分水下成像能够有效地克服光散射效应造成的图像退化问题, 在水下物体探测与识别领域具有重要应用价值. 传统的偏振差分方法靠光学检偏器的无规则机械转动来实现对散射背景的共模抑制, 限制了其在水下成像过程中的实时探测性能. 本文通过分析偏振差分探测原理来建立偏振差分成像模型, 从理论上提出了基于Stokes矢量的计算偏振差分水下实时成像系统, 并进行了实验验证. 研究结果表明, 基于Stokes矢量的计算偏振差分成像不仅与传统的偏振差分方法具有相同的水下探测效果, 更重要的是可以实现快速成像过程. 该方法可以应用到目前的偏振成像仪器系统, 实现无需人-机互动的自动化实时偏振差分水下成像, 进一步提高水下物体探测与识别的效率.     

光致变色材料多阶光存储模型与实验

光致变色材料具有光子型反应的特点,控制光致变色材料吸收的光子数就可以控制材料的反应程度,从而实现多阶存储。根据光化学反应的原理,分析了光致变色材料的写入过程,建立了光致变色多阶存储写入过程的反射率模型。根据该模型的仿真计算结果,设定了一组合适的曝光量,在1,2_双(2_甲基_5_(4_(1,3_二氧戊环基)苯基)噻吩_3_基)全氟环戊烯材料上实现了8阶存储。     

基于生物视觉center-surround机制的光团目标检测与跟踪

基于生物视觉的center-surround机制,提出一种用改进的LoG(Laplacian of Gaussian)算子检测光团目标的方法。首先明确了光团目标的成像模型,分析了LoG算子的性质及其响应,接着提出了归一化的LoG算子。理论上指出该算子可用于检测光团目标。仿真和实验证明：该算子可以用于检测图像中已知大小和未知大小的光团目标,并且实用性优于其他常规方法。结合Kalman滤波和粒子滤波,该算子还可以用于序列图像中单目标和刚体的跟踪。理论推导和实验结果表明,该方法是稳健和高效的。     

Performance of gain-switched all-solid-state quasi-continuous-wave tunable Ti:sapphire laser system

We have made a gain-switched all-solid-state quasi-continuous-wave （QCW） tunable Ti：sapphire laser system, which is pumped by a 532 nm intracavity frequency-doubled Nd：YAG laser. Based on the theory of gain-switching and the study on the influencing factors of the output pulse width, an effective method for obtaining high power and narrow pulse width output is proposed. Through deliberately designing the pump source and the resonator of the Ti：sapphire laser, when the repetition rate is 6 kHz and the length of the cavity is 220 mm, at an incident pump power of 22 W, the tunable Ti：sapphire laser from 700 to 950nm can be achieved. It has a maximum average output power of 5.6W at 800nm and the pulse width of 13.2 ns, giving an optical conversion efficiency of 25.5% from the 532 mn pump laser to the Ti：sapphire laser.     

光谱法研究BLM解旋酶的稳定性

BLM解旋酶是RecQ家族DNA解旋酶中的一个重要成员,在维持染色体的稳定性中具有重要的作用,其突变会导致Bloom综合症.Bloom综合症是一种罕见隐性常染色体遗传疾病,患者易患各种类型癌症.本研究利用紫外吸收光谱法研究了pH、反应时间、NaCl浓度对BLM解旋酶的稳定性和ATP酶活性的影响.结果显示,pH会影响BL...     

Purification of the recombinant hepatitis B virus core antigen (rHBcAg) produced in the yeast Saccharomyces cerevisiae and comparative observation of its particles by transmission electron microscopy (TEM) and atomic force microscopy (AFM)

Hepatitis B virus core antigen (HBcAg) gene (C gene) was expressed in Saccharomyces cerevisiae and the products (rHBcAg or core particles) were purified from a crude lysate of the yeast by three steps: Sephrose CL-4B chromatography, Sucrose step-gradient ultracentrifugation and CsCl-isopycnic ultracentrifugation. It has been observed that HBcAg was synthesized in yeast cells as a particle consisting of polypeptides with a molecular weight of 21.5 kDa (p21.5). Results of ELISA test and density analysis of CsCl-isopycnic ultracentrifugation indicated that the purified products (rHBcAg particles) with HBcAg antigenicity mainly located at the densities of 1.27 and 1.40 g ml(-1), respectively. Observation and analysis of the purified rHBcAg products by TEM indicated that rHBcAg peptides could mainly self-assemble into two size classes of core particles. The larger particles were approximately 30.1 nm and the smaller were approximately 21.5 nm in mean diameter. Further observation and analysis of the same rHBcAg (core) particles by AFM also indicated that rHBcAg (core) particles were similar to the native HBcAg (core) particles from infected human hepatocytes and mainly composed of two size classes of partides core. The larger particles were approximately 31.3 nm and the smaller were approximately 22.5 nm in mean diameter which was similar to the results obtained by TEM. All results from both TEM and AFM suggested that core particles (capsids) produced in S. cerevisiae possessed dimorphism.     

(Nd_(1-x)Er_x)_2Co_(15.5)V_(1.5)的结构转变与磁性

利用电弧熔炼制备了 (Nd1 xErx) 2 Co1 5 5V1 5(x=0— 1 0 )化合物样品 .通过x射线衍射分析和磁性测量研究了Er替代Nd2 Co1 5 5V1 5中的Nd时对化合物结构和磁性的影响 .研究结果表明 ,低Er含量 (x <0 4 ) ,化合物为Th2 Zn1 7型结构 ;高Er含量时 (x >0 5 ) ,化合物转变为Th2 Ni1 7结构 ;Er含量为x =0 4和 0 5时 ,两种结构共存 .两种结构的晶胞参数a ,c和晶胞体积V随着Er含量的增加都呈现递减的趋势 .随着Er含量的增加 ,(Nd1 xErx) 2 Co1 5 5V1 5化合物的居里温度和饱和磁化强度都单调下降 .(Nd1 xErx) 2 Co1 5 5V1 5化合物的室温各向异性由低Er含量时的易锥型转变为高Er含量时的易轴型 .x =0— 0 5的化合物在温度升高时发生自旋重取向转变 ,自旋重取向温度Tsr随Er含量的增加而减小