Effective thermal conductivity of porous solder layers

Microscopic voids in the die attachment solder layers of power semiconductor devices degrade their overall thermal transfer performance. This paper presents analytical results of the effect of spherical and spheroidal void geometries on the thermal conductivity of bulk media. Analytical results are compared with axially symmetric and three-dimensional thermal simulations of single and multiple cavity defects in planar structures. The effective thermal conductivity of the die to the case attachment solder layer of two commercial metal oxide semiconductor field effect transistor (MOSFET) devices is estimated using these results, with cavity dimensions and distributions obtained by electron microscopy.     

Effective conductivity of a polycrystalline medium with weak macroscopic anisotropy

In the effective medium approximation, an analytical solution is obtained for calculating the tensor of the effective conductivity of a polycrystalline medium with weak uniaxial texture. The medium is assumed to consist of a single type of biaxial spherical crystallites. The orientation of the crystallites is taken into account by means of the theory of rotation group representations. A solution generalized to triaxial textures is obtained.     

Effective conductivity of a polycrystalline medium. Uniaxial texture and biaxial crystallites

The effective conductivity tensor of a polycrystalline medium with a texture has been calculated based on the method of self-consistent solution and the theory of rotation group representations. The medium consists of a single-type of biaxial spherical crystallites, oriented in space according to some probabilistic law, which implies the existence of uniaxial texture. An analytical solution is obtained for two cases: (i) weakly anisotropic crystallites and (ii) a small spread in the orientations of one of the crystallite axes with respect to the texture axis.     

Fuzzy control for active suspensions

A methodology for the design of active car suspension systems is presented. The goal is to minimize vertical car body acceleration, for passenger comfort, and to avoid hitting suspension limits, for component lifetime preservation. A controller consisting of two control loops is proposed to attain this goal. The inner loop controls a nonlinear hydraulic actuator to achieve tracking of a desired actuation force. The outer loop implements a fuzzy logic controller which interpolates linear locally optimal controllers to provide the desired actuation force. Final controller parameters are computed via genetic algorithm-based optimization. A numerical example illustrates the design methodology.     

高导热电封装复合材料界面热传导的扫描热显微镜分析

本文利用扫描热显微镜（SThM),以微米级的空间分辨率,测量了SiC/Cu和SiC/Al电封装复合材料增强相－基体的界面特征和界面导热性能,SThM热图显示出材料界面导热性能的差异,对形貌数据和热数据进行统计分析和转换,确定了复合材料的界面宽度和界面导热率。     

胚胎及成人心脏心肌细胞的立体构筑与心电传导相关的研究

具有泵样作用的心脏是人体血循环的中枢器官 ,心脏血液动力学及心肌细胞立体构筑的变化均与心肌细胞的电传导和代谢相关 ,本研究应用扫描电镜及透射电镜对人胚胎及成人心脏的心肌一般作业、心肌细胞及心传导系心肌细胞的立体构筑及相关的心电传导功能进行了比较性研究。材料和方法　本研究选用医院水囊引产正常胎儿及非心脏病死亡成人心脏各 6例 ,主动脉生理盐水灌流后 1 2Ｋａｒｎｏｖｓｋｙ’ｓ固定液灌流 ,取左心室游离壁 ,ＮａＯＨ 超声波消化法处理后 ,一般扫描电镜方法脱水、干燥、镀膜、扫描电镜观察。结果　正常人心脏的心肌细胞呈…     

基于解析电导率模型的相变存储器SPICE模型

在相变存储器的外围电路设计中,相变存储单元的电路模型是连接器件与电路的桥梁。在本文中,提出了一种基于解析电导率模型的相变存储器电路模型,与前面的工作相比,该模型利用解析电导率模型代替了使用传统模型中需要利用测试结果建模的缺点,可以通过材料的参数计算相变存储单元的电阻,能够反映相变材料中的载流子传输特性。同时,基于等温假设,提出了解析温度模型,并基于JMA方程建立的相变动力学模型,结果表明,该模型能够进行相变存储单元瞬态与稳态电路仿真,并与测试结果符合较好。     

Android手机访问服务器的一种数据交互方法

通过时Android手机访问Web服务器的API的分析和实践,提出了一种解决手机终端和Web服务器交互提取各种类型数据的清晰有效的方法,扩展了Android平台在访问Web服务器进行交互时的解析数据能力,给移动商务软件开发人员在开发数据交互实践过程提供了参考.     

Visualization of surface conductivity distributions of tomography cross-section using conductivity zones method

Conductivity zones method is suggested that allows reconstructing the image of electrical impedance tomography with essentially lower computation expenses. Results of reconstruction performed by regularizing the matrix of contour-edge voltage derivatives with respect to zones’ surface conductivities.     

Analogue conductivity switch

The current/voltage characteristics of Au-CaF2-n GaAs diodes have been found to exhibit a continuum of memory states, switchable with forward or reverse voltage pulses. The phenomenon is described and a possible charge-trapping mechanism indicated as being responsible.     

Nonlinear microwave optics in liquid suspensions of shapedmicroparticles

The use of shaped microparticle suspension for such active processes as phase conjugate via degenerate four-wave mixing at microwave and millimeter wavelengths is addressed. The theoretical method used to describe the interaction of shaped microparticles with coherent radiation is outlined. The generation of up to 250 mW phase conjugate radiation in a medium composed of rod-shaped carbon fibers suspended in a passive fluid dielectric that is maintained in a waveguide is reported. The theory for the nonlinear optical behavior of shaped particle suspensions is shown to be in excellent agreement with the available experimental data     

Rotary regenerative shock absorbers for automotive suspensions

The increasingly strict limits on pollutant emissions are pushing the car industry towards the electrification of the powertrain and chassis. This scenario has driven the automotive field to the use of energy harvesters. Among these, regenerative shock absorbers are mechatronic devices that enable the energy recovery from road irregularities, thus yielding benefits in terms of fuel saving and ride quality. The state of the art proposes different technologies for regenerative dampers. In this context, rotary dampers represent an unexplored field from the scientific point of view. These devices feature a linkage and a gearbox to convert the suspension linear motion into rotation of an electric machine. This work proposes a novel system-level design methodology for rotary regenerative shock absorbers and explores their performance from an experimental perspective. The design is focused in yielding a compact solution able to fulfill a given damping specification. Hence, the integrated definition of electric machine, gearbox and linkage is addressed by the proposed method. To support the methodology, a case study is presented. A fully functional prototype is produced and successfully validated in terms of damping capability, total conversion efficiency and acoustic behavior. The obtained results demonstrate the validity of the proposed methodology and the advantageous features of rotary dampers with respect to other regenerative suspension solutions.     

The Hall conductivity of graphene

Sensitivity of the Hall conductivity of graphene plane to gas molecule adsorption is investigated within the coherent potential approximation for the tight-binding model Hamiltonian. The results show that the Hall conductivity of system have a limit change when finite triatomic and tetratomic gas molecules adsorb and act as acceptors or donors.     

Microwave conductivity of thick-film conductors

The letter presents the results of an investigation aimed at minimising losses in thick-film screen-printed microstrip circuits. The Q factor of closed resonators of 30 ? and 50 ? impedances has been measured over the 1?10 GHz range. It is found that the effective r.f. conductivity is about one half that of bulk material over the major portion of the band considered.     

Low-temperature conductivity of gadolinium sulfides

In samples of GdS_x (x = 1.475–2) of various compositions, the conductivity temperature dependences are investigated for the case of direct current in the low-temperature region (4.2–225 K). The presence of the activation and activationless hopping mechanisms of charge transport over the band gap of the samples of GdS_x phases is established. The parameters of localized states in GdS_x are determined.     

光网络导通性能计算

对光波长交换网络中，存在连接源和目的节点的波长通道的概率，做了定量研究。文章首先计算单条路径、无波长交换节点的连通概率，接着计算无波长交换节点的小型网络的连通概率，然后计算掺入波长交换节点的光网络连通概率，最后对波长交换中的一些问题进行了讨论。     

Effective protection of sequential solution-processed polymer/fullerene bilayer solar cell against charge recombination and degradation

Both charge recombination and degradation in sequential solution processed polymer/fullerene bilayer organic photovoltaics (OPV) are effectively reduced by the insertion of a TiO₂ inter-layer between the bilayer and Al electrode. The polymer/fullerene bilayer composed of a poly(3-hexylthiophene) (P3HT) bottom-layer and a [6,6] phenyl C61-butyric acid methyl ester (PCBM) top-layer shows significant change in morphology due to the substantial inter-penetration of P3HT and PCBM during the thermal annealing process. Consequently, the bilayer surface becomes P3HT rich resulting in significant charge recombination at the bilayer/Al interface of the bilayer OPV. The charge recombination rate of the bilayer OPV is reduced by one order of magnitude upon the insertion of a TiO₂ nanoparticle inter-layer between the bilayer and the Al electrode after the thermal annealing process. In contrast, when the thermal annealing process is conducted after insertion of the inter-layer, the effect of the TiO₂ inter-layer becomes insignificant. The V_OC and efficiency of the bilayer OPV is greatly enhanced from 0.37 to 0.66 V and 1.2% to 3.7%, respectively by utilizing the properly constructed TiO₂ inter-layer in the bilayer OPV. Additionally, insertion of the TiO₂ inter-layer significantly improves the stability of the bilayer OPV. The bilayer OPV with a TiO₂ inter-layer maintains 51% of its initial PCE after storage under dark ambient conditions for 700 h without encapsulation, whereas the bilayer OPV without a TiO₂ inter-layer did not show any solar cell performance after 200 h under the same conditions.     

Determination of the electric conductivity of the seabed in shallow waters with varying conductivity profile

Assuming a natural electromagnetic field as signal source, various measuring techniques are discussed. It is shown that the measurement of horizontal magnetic-field components has some advantages, and a simple relationship between the conductivity of the seabed and the ratio of the magnetic component at the surface to that at the seabed is found.     

Permanent-magnets linear actuators applicability in automobile active suspensions

Significant improvements in automobile suspension performance are achieved by active systems. However, current active suspension systems are too expensive and complex. Developments occurring in power electronics, permanent magnet materials, and microelectronic systems justifies analysis of the possibility of implementing electromagnetic actuators in order to improve the performance of automobile suspension systems without excessively increasing complexity and cost. In this paper, the layouts of hydraulic and electromagnetic active suspensions are compared. The actuator requirements are calculated, and some experimental results proving that electromagnetic suspension could become a reality in the future are shown.