Effects of process parameters on electrical properties of n-type Bi2Te3 prepared by mechanical alloying and spark plasma sintering

n-Type Bi₂Te₃ thermoelectric materials were prepared by spark plasma sintering (SPS) using mechanically alloyed powders. Seebeck coefficient and electrical conductivity of the resultant materials were measured, with emphasis on the effects of sintering process parameters on the electrical properties. The power factor was improved from 1.5 to 1.6 mW/mK² when the SPS pressure was increased from 20 to 50 MPa at 623 K, and was further increased to 2.1 mW/mK² under 50 MPa by raising the SPS temperature from 623 to 673 K. The maximum power factor was obtained for the sample sintered under optimized SPS process parameters, in which the sintering temperature and the sintering pressure are 673 K and 50 MPa, respectively.     

Radiation output of a spherical homogeneous plasma: Analytical models of computing the spectral brightness of plasma objects with various configurations

Analytical relationships between the photon-emission probability from a surface and the optical thickness along with analytical relationships between the spectral brightness of a homogeneous plasma of spherical geometry are derived with taking into account the radiation absorption. The photon-emission probability and the spectral brightness are also obtained for a plasma of cylindrical geometry and a plasma consisting of spherical layers. The relationships are given in the integral form, while attempts to find them analytically, i.e., to calculate the integrals, failed. However, they can be computed numerically. The formula for spectral brightness is derived for the case of radiation of two flat layers, which differ by the structure, thickness, and thermodynamic and spectral characteristics. The expressions for the spherical and flat layers are compared. The ratio of the dimensions permitted to approximate the flat case by the spherical case is found. The criteria of applicability and accuracy of such approximation have been elaborated. As examples of the application of the expressions derived, the radiation spectra of the aluminum, carbon, copper, and oxygen plasmas were calculated and plotted. __________ Translated from Preprint No. 33 of the P. N. Lebedev Physical Institute, Moscow (2006).     

变系数广义KdV方程新的类孤波解和精确解

用普通KdV方程作变换，构造变系数广义KdV方程的解，获得了变系数广义KdV方程新的Jacobi椭圆函数精确解、类孤波解、三角函数解和Weierstrass椭圆函数解. 关键词： KdV方程 变系数广义KdV方程 类孤波解 精确解     

超薄LiTaO3晶片的键合减薄技术

在制造红外热释电探测器阵列过程中，需要利用超薄钽酸锂(LiTaO₃)晶片作为红外热释电探测器件的敏感层。通常LiTaO₃晶片的厚度远厚于红外热释电探测器件要求的厚度，所以需要采用键合减薄技术对LiTaO₃晶片进行加工处理。键合减薄技术主要包括：苯并环丁烯（BCB）键合、铣磨、抛光、加热剥离、刻蚀BCB。加工后得到面积为10mm×10mm、厚度为25μm的超薄单晶LiTaO₃薄膜，晶片厚度、表面粗糙度和面形精度比较理想。测得了LT晶片减薄后的热释电系数为1.6×10^-4Cm^-2K^-1。得到的单晶LiTaO₃薄膜满足红外热释电探测器敏感层的要求。     

A highly clustered scale-free network evolved by random walking

In present paper, we propose a highly clustered weighted network model that incorporates the addition of a new node with some links, new links between existing nodes and the edge's weight dynamical evolution based on weight-dependent walks at each time step. The analytical approach and numerical simulation show that the system grows into a weighted network with the power-law distributions of strength, weight and degree. The weight-dependent walk length l will not influence the strength distribution, but the clustering coefficient of the network is sensitive to l. Particularly, the clustering coefficient is especially high and almost independent of the network size when l=2.     

Limit theorems in financial market models

Invariance principle states that a scaled simple random walk converges to the standard Brownian motion.In this article, we present a discrete time stochastic process, which reflects a microstructure of market dynamics, and prove a convergence to a scaling limit process with a drift term and a jump term. These terms are derived from a macroscopic condition on volumes traded in some time intervals. The mathematical tools for obtaining our results are Dobrushin-Hryniv theory and the method of cluster expansion developed in mathematical studies of statistical mechanics.     

Study of molecular surface coating on the stability of maghemite nanoparticles

In this study γ-Fe₂O₃ nanoparticle, surface-coated with increasing amount of oleic acid, have been prepared while the stability against particle degradation under laser excitation intensity was investigated. Maghemite nanoparticle was obtained via oxidation of magnetite nanoparticle, the latter synthesized by co-precipitation of Fe (II) and Fe (III) ions in alkaline medium. By varying the experimental conditions of surface-coating maghemite nanoparticles with oleic acid, samples with different grafting coefficient were obtained and investigated using X-ray diffraction and different spectroscopic techniques, namely Raman, Mössbauer, and infrared. The amount of oleic acid adsorbed on the maghemite surface was estimated via the carbon content obtained from elemental analysis.     

三能级光纤激光器速率方程组的阈值解析解

 在考虑了泵浦损耗及激光损耗的情况下，解析求解了阈值泵浦下的三能级光纤激光器速率方程组，获得了泵浦功率阈值的显函数解析表达式，泵浦功率沿光纤变化的隐函数表达式，以及用功率变化表示的各个能级的粒子数密度随位置变化的显函数表达式。并利用这些表达式对光纤激光器的阈值特性进行了研究，研究表明：泵浦功率阈值随泵浦损耗系数增大而增大；激光上能级粒子数密度随归一化位置呈下降趋势，而下能级粒子数密度的变化与此相反；泵浦功率阈值越大(光纤长度越长),净增益系数随归一位置下降就越快。所获得的结果适用于单包层和双包层光纤激光器。     

偏轴双腔互比型腔式束流位置监测器

 提出一种利用偏轴双腔来监测电子束位置的新方法，根据谐振腔归一化分流阻抗参数分析了其工作原理和主要特性。偏心束流在偏轴谐振腔中激发出较强的偶极模TM₁₁₀信号，根据两腔输出的偶极模信号幅度比可直接测量束流的中心偏移量。偶极模信号幅度变化反映了束流的偏移方向，省去了鉴相工作，简化了前端接收电路的的设计，基模抑制问题已被解决。利用MAFIA和HFSS软件对本征模进行仿真，并分析了模式耦合特性，仿真结果验证了新结构的可行性。     

近化学计量比Ce∶Mn∶LiNbO3晶体光折变性能研究

在LiNbO3中掺进0.015mass%MnCO3和 0.1mass%CeO2,以Czchralski法生长Li/Nb比为1.38的近化学计量比Ce∶Mn∶LiNbO3(Ce∶Mn∶SLN)晶体和Li/Nb比为0.946的同成分Ce∶Mn∶LiNbO3(Ce∶Mn∶CLN)晶体.测试了晶体的红外光谱和紫外可见吸收光谱,讨论了Ce∶Mn∶SLN晶体OH－吸收峰和吸收边移动机理.利用二波耦合光路测试了晶体的指数增益系数,Ce∶Mn∶SLN晶体指数增益系数Γ达到27 cm2－.同时,研究了Ce∶Mn∶SLN指数增益系数提高的机理.