Phase stability and electronic structures of YbAl3−xMx (M = Mg, Cu, Zn, In and Sn) studied by first-principles calculations

YbAl₃ is a potential thermoelectric (TE) material to be used in TE power generator utilizing waste heat sources. This work systematically investigated the alloying behavior of M in YbAl_3−xM_x (M = Mg, Cu, Zn, In and Sn) and their electronic structures by first-principles calculations. The solubility of alloying elements M and phase stability of YbAl_3−xM_x were studied by analyzing the elastic constants, formation and cohesive energies. The results show that Mg, In and Sn are the effective alloying elements for preparing YbAl_3−xM_x solid solutions, which are helpful for improving TE properties of YbAl₃.     

The ductility and shape-memory properties of Ni–Mn–Co–Ga high-temperature shape-memory alloys

Ni–Mn–Co–Ga alloys with Ni/Mn or Ni and Mn substituted by Co were investigated as candidates for high-temperature shape-memory alloys. Ni_56?xCo_xMn₂₅Ga₁₉ alloys with x < 8 consist of single phase martensite, whereas Ni_56?xCo_xMn₂₅Ga₁₉ (x ? 8), Ni₅₆Mn_25?yCo_yGa₁₉ (y = 4, 8) and Ni_56?z/2Mn_25?z/2Co_zGa₁₉ (z = 4, 6) alloys consist of a two-phase mixture of martensite and γ phase. The mechanical and shape-memory properties of Ni₅₆Mn_25?yCo_yGa₁₉ and Ni_56?z/2Mn_25?z/2Co_zGa₁₉ alloys, which were hot-rolled into 0.5 mm thin plates by conventional hot rolling process, were investigated. The ductility and hot-workability of Ni–Mn–Co–Ga alloys were greatly improved by increasing the amount of ductile γ phase. Dynamic tensile tests and scanning electron microscopy observations of fracture surfaces confirm that the existence of γ phase plays a key role in improving the ductility of Ni–Mn–Co–Ga alloys.     

Parametric study on the combined thermal and hydraulic performance of single phase micro pin-fin heat sinks part I: Square and circle geometries

This paper is the first part of a three paper series studying the overall performance of a micro pin-fin heat sink with single phase liquid flow and different pin-fin geometries operating under and similar conditions. Two different heat sinks, one with square shaped pin-fins and the other with circular pin-fins are selected for study in this paper. The paper focuses on studying the effect of thermal resistance and pressure drop of micro heat sinks when subjected to various factors such as pitch distance in axial and transverse directions, aspect ratio of the pin-fin, hydraulic diameters of the pin-fin, and the liquid flow rate through the device. A figure of merit (FOM) involving both the thermal resistance and pressure drop across the heat sink is introduced in the paper and the performance is evaluated on the basis of this FOM. The heat sinks are subjected to uniform heat flux at the bottom of the heat sink and the characteristic study is based on constant Reynolds number of liquid flow at the entrance of the channel. Water is used as the fluid in this study. The study is conducted over the Reynolds number range of 50–500. The characteristic study is carried out with the help of simulations developed using commercially available computational fluid dynamics software CoventorWare?. The characteristic study carried out in this paper is divided into four cases. In the first case the axial pitch distance is varied between 350 μm and 650 μm by keeping the aspect ratio of the pin-fin structure constant at 0.5. For the second case the transverse pitch distance is varied between 150 μm and 300 μm and the aspect ratio is kept the same as in the first case. Third case studies the effect of varying the aspect ratio (between 0.33 and 1) of the pin-fin structures by keeping both pitches constant. Case four studies the variation in the performance of the heat sink with the change in the hydraulic diameter of the pin-fins. The study conducted in this paper reveals the importance of considering the pressure drop along with the thermal resistance in evaluating the overall performance of the micro pin-fin heat sink. At low Reynolds number (below 300) the heat sinks with circular pin-fins shows better performance compared with heat sinks with square pin-fins and vice versa at high Reynolds number (above 300). FOM varies considerably with the change in the parameters like axial pitch distance, transverse pitch distance, aspect ratio and hydraulic diameter of the pin-fins.     

拉曼光谱表征无氢类金刚石薄膜的新方法

DLC薄膜的拉曼光谱表征主要依靠D峰和G峰的强度比值(ID/IG)来定性判断sp3含量,但当sp3所占百分比高于20%时,ID/IG值对sp3含量的变化不敏感,判断的误差很大.采用直流磁控溅射和多弧离子镀制备了一系列无氢DLC薄膜样品,并测量了样品的拉曼光谱和维氏硬度.通过数据分析,发现薄膜硬度和拉曼光谱中的G峰半峰宽具有很好的相关性,因而提出通过G峰半峰宽来定量判断DLC薄膜中sp3含量的拉曼光谱表征新方法.     

FM-DCSK混沌通信系统的原型设计与研究

文中设计了一个基于调频差分混沌键控通信系统的原型,并实现了部分关键电路。系统发射部分由Lorenz混沌电路和调频电路产生混沌调频载波信号,经采样后在FPGA中实现差分延时和调制;接收部分基于非相干相关法,位同步模块采用相关值与能量比值作为定时测度,通过设置门限和滑动搜索窗口寻找初始同步,而后引入数字锁相环进行相关峰值跟踪和位同步调整。建模验证结果表明,系统非相干解调的误码率指标接近理论分析值,仅相差0.2 dB。     

聚乙烯醇/聚乙烯吡咯烷酮共混膜的制备和性能

制备了聚乙烯醇(PVA)、PVA/聚乙烯吡咯烷酮(PVP)与戊二醛交联的PVA/PVP膜用于渗透蒸发对乙酸乙酯/乙醇/水三元共沸体系脱水。采用傅立叶变换红外光谱(FT-IR),X射线散射(XRD)和扫描电镜(SEM)等对膜的物理化学结构及形貌进行了表征。考察了PVP含量、交联度对共混膜结构和亲水性的影响。考察了PVP含量、交联度和温度对PVA均质膜的分离性能和溶胀行为的影响。结果表明,交联的PVA/PVP共混膜对乙酸乙酯/乙醇/水有着优异的分离性能。     

TiO_2/竹炭复合材料研究(Ⅰ)制备与表征

以60目竹炭为载体、钛酸四正丁酯为钛源,采用溶胶-凝胶法制备了TiO2/竹炭复合材料。用XRD、SEM、EDX等分析技术对其进行了表征,并就其对罗丹明B的光降解的催化作用进行了研究。结果表明,所制备的TiO2/竹炭复合材料经过500℃绝氧烧结后,其负载的TiO2主要呈锐钛矿型结构,具有较好的紫外光催化活性。     

Promoting effect of noble metals to Co/SiO2 catalysts for hydroformylation of 1-hexene

Small amount of Pt, Pd and Ru promoters in Co/SiO₂ led to great improvement of catalyst activity for hydroformylation of 1-hexene. The 1-hexene conversion as high as 89.7% and oxygenate products selectivity of 88.9% were obtained after 2 h reaction over Pd promoted Co/SiO₂ catalyst. The increasing of reduction degree, the minimizing of cobalt particle size and the enhancement of carbonyl and linear CO adsorption were responsible for the improved performance of the catalyst.     

数字签名技术在办公自动化系统中的实现

开发了一种基于密钥集中式管理的数字签名方法,并在开发的办公自动化系统中予以实现。该方法利用MD5算法来抽取公文信息指纹,利用RSA公开密钥算法在公文信息指纹上实施签名,从而保证了公文信息的完整性,并通过一种密钥生产管理系统来生产并管理办公自动化系统中所有合法用户的公/私密钥对,从而保证签名的真实性与安全性,并为用户使用密钥提供方便。通过测试表明,该文实现的数字签名具有良好的运行性能,完全可以满足在办公自动化系统下运行的要求。     

非接触式压力微传感器的设计

就如何利用MEMS技术,实现压力微传感器的设计进行详细论述。该传感器利用特殊的机械结构,大大改善了传统接触式压力传感器,工作区域狭小,线性度较差等问题,使压力传感器在高载荷条件下,由小扰度向大扰度过渡时,不产生非线性跳变,从而大大提高了器件的稳定性与动态特性。