Improving TCP performance for vertical handover in heterogeneous wireless networks

The incorporation of wireless local area networks (WLANs) into existing cellular networks as supplementary access technologies has become an issue of great interest. However, vertical handover (VHO), which allows users to roam between a WLAN and a cellular network, causes an abrupt change in certain link characteristics such as the round trip time and data rate. Owing to such changes, reordering problem and premature timeout occur and trigger unnecessarily fast retransmission during VHO, causing throughput degradation. Thus, we propose a new transmission control protocol (TCP) mechanism, which resolves the reordering problem by suppressing unnecessary retransmission caused by spurious duplicate acknowledgments (dupacks) incurred because of the reordering problem, and prevents premature timeout by employing an adaptive retransmission timer. We analytically investigate the throughput of our proposed TCP scheme. The numerical and simulation results show that our proposed TCP performs better in terms of throughput than other schemes appearing in the literature. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance enhancement of mSCTP for vertical handover across heterogeneous wireless networks

In the mobile Stream Control Transmission Protocol (mSCTP) for vertical handover, a mobile user may suffer from performance degradation due to the problems of packet reordering and retransmission timeout and due to the packet loss during handover. To solve these problems, we propose a new scheme of handover retransmission for mSCTP handover, in which the correspondent node retransmits the outstanding data packets to the mobile node over the new primary path. From simulation results, it is shown that the proposed scheme can avoid the packet reordering and retransmission timeout problems during handover. Moreover, we can see that the proposed scheme can significantly improve throughput of mSCTP handover, compared with the existing schemes. Copyright © 2009 John Wiley & Sons, Ltd.     

膨胀机力学模拟试验装置

为了适应当前发展的需要,本试验装置可以研究G-M制冷机中的膨胀机在动态环境下能否可靠工作,为其提供了强有力的试验平台。本装置可以单独实现水平面的旋转或垂直面的翻转,还可以同时实现水平面的旋转和垂直面的翻转。对G-M制冷机扩大应用领域是不可或缺的试验装置。     

Experimental Study of Natural Convection from Electrically Heated Vertical Cylinders Immersed in Air

Abstract

An experimental study of laminar steady-state natural convection heat transfer from electrically heated vertical cylinders immersed in air has been undertaken. Three stainless steel (316 SS) test sections of different slenderness ratios were employed. Surface temperature profiles along the vertical cylinders were obtained using miniature thermocouples when the cylinders were heated with different power levels resulting in different total wall heat fluxes. After the mandatory corrections for the radiation heat fluxes were made, three correlation equations relating the local Nusselt number Nu_y with the local modified Rayleigh number Ra^* _y and the position-to-cylinder diameter y/d were developed. The correlation equations are valid for Ra^* _y ≤ 2 × 10¹².     

A theoretical and numerical evaluation of the steady-state burning rate of vertically oriented PMMA slabs

The steady state burning rate of vertically oriented slabs of poly-methyl-methacrylate (PMMA) is numerically investigated. Model predictions are compared with measurements and results of the laminar boundary layer (LBL) theory. The numerical model provides a solution of the Favre-averaged Navier–Stokes equations coupled with sub-models for turbulence, combustion, soot production and radiation. The modelling of condensed phase processes is based on the one-dimensional heat transfer equation and pyrolysis is treated as a phase change using the latent heat approach. Results show that the pyrolysing region can be divided into three regions. In the laminar part of the flow (Gr _x < 4.3 × 10⁷), the predicted normalised burning rate, [mdot]″ _p x/μ_∞, is a power-law function of Gr _x with an exponent close to that of the LBL theory, surface re-radiation being the primary source of discrepancies. From the LBL theory for free flow, it is demonstrated that the local burning rate is inversely proportional to the shear velocity gradient. This is globally confirmed by numerical model results. At Gr _x = 4.3 × 10⁷ the change in slope of the burning rate observed experimentally, which indicates the end of the laminar flow region, is reproduced numerically. From Gr _x = 2.5 × 10⁹ model results show that the surface mass flux of pyrolyzate increases with x, in agreement with experimental data in literature.     

Ka波段Si基微机械宽带垂直过渡

介绍了一种适用于三维毫米波集成电路的Si基微机械垂直过渡,该垂直过渡是两层0.1mm厚的共面波导传输线通过0.3mm厚中间层,在中间层采用了同轴结构,该同轴结构通过金属化通孔来实现。这一设计原理简单,结构简洁,便于优化设计,具有很宽的带宽和平坦的幅度响应。运用三维电磁场仿真软件对该垂直过渡结构进行了建模,并作了优化设计与仿真计算,运用微机械金属化通孔工艺和多层键合工艺研制了样品。在片测试结果表明该样品性能良好,在26.5～34.0GHz该过渡插入损耗小于3.5dB,带内起伏小于2dB。     

用于纳米操作的硅基集成式微型 xy 定位平台

针对纳米级定位平台小型化和高定位精度的要求,基于体硅工艺研制出一种集结构、驱动和位移检测一体化的集成式微型纳米级xy定位平台. 采用体硅双面深度反应离子刻蚀（DRIE）技术释放出高深宽比的静电梳齿驱动器、检测梁及定位平台结构. 由于定位平台属于面内运动,为了提高面内运动位移检测的灵敏度提出了一种利用离子注入工艺和DRIE技术相结合制作检测梁侧壁压阻的方法,并利用该侧壁压阻工艺成功地把基于侧壁压阻式的位移传感器集成到微型xy定位平台上. 实验测试表明,位移传感器的灵敏度优于1.17mV/μm,线形度优于0.814%,当驱动电压取30V时,定位平台的单轴输出位移可达±10μm,并且定位平台x方向和y方向上的位移耦合量非常小;在空气条件下测得定位平台的一阶固有频率为983Hz.     

TFT-LCD中耦合电容Cpd影响因素的研究

LCD显示效果依赖于液晶分子在电场作用下的旋转,液晶分子具有各向异性的介电常数,不同旋转角度的液晶分子,在相同电容器中,表现出不同的电容值。像素电极和数据线构成耦合电容器Cpd,过大的耦合电容Cpd值会导致数据线信号传输的延迟,影响像素电极周边液晶分子分布,使显示器的画面品质出现垂向块状云纹等不良。针对如何降低耦合电容Cpd值,本文对影响耦合电容Cpd的因素进行了一系列模拟,研究了耦合电容Cpd变化机理,得出了一系列降低耦合电容Cpd的结论。     

亚微米BiCMOS电路纵向NPN管的ESD保护研究

文章以0.6μmN外延BiCMOS工艺为基础,研究了纵向NPN管的ESD保护行为,并对不同版图结构的纵向NPN管进行了ESD行为研究。实验表明,由于基区的内在电阻不一样,在该工艺条件下,CEB、CEBE结构比CBE、CBEB结构SNAPBACK效应明显,机器模式下ESD保护能力强。此外,还研究了兼容低压Vz工艺,单级保护NMOS输出管的纵向NPN器件的ESD行为,流片显示采用EB结齐纳击穿的纵向NPN能有效单级保护CMOS的输出级。     

Revisiting the structural and electronic properties of neutral,mono- and di-anionic titanium-doped silicon clusters TiSin0/−/2− (n = 6-16)

The systematic structures search for neutral and Zintl anionic Ti-doped silicon clusters TiSi_n^0/−/2− (n = 6-16) have been carried out using the ABCluster global search technique combined with a double-hybrid density functional method. Based on the predicted energies, adiabatic electron affinities, vertical detachment energies and the consistency between simulated and experimental photoelectron spectroscopy, the true global minimum structures are confirmed. The results show that structural growth pattern of neutral TiSi_n clusters is from linked structures (n = 10-12) to encapsulated configurations (n = 13-16). In contrast, the evolution pattern of Zintl anionic TiSi_n^−/2− clusters begins with the pentagonal bipyramid structure (n = 6). As the Si atoms increase, these Si atoms attach to the surface adjacent to Ti atom, and gradually surround Ti atom. Eventually, the encapsulated structure is formed when n = 12. Moreover, two extra electrons not only perfect the structure of TiSi₁₂ but also improve its chemical and thermodynamic stability.