二阶锁相环非线性捕获和非线性跟踪性能研究

采用MATLAB软件,编制了求解描述二阶PLL非线性捕获的二阶非线性微分方程的程序,计算机自动绘制了相轨迹和时间响应图;求出了二阶PLL的捕获带随初始相差的变化关系曲线.     

一种新的OFDM相位编码频率步进雷达信号及其特性

OFDM相位编码脉冲雷达体制具有很多良好的性质,但工程实现上存在着一些的技术挑战,其中之一就是瞬时带宽等于信号的总带宽,当信号带宽很大时对接收设备提出了很高的要求。针对这个问题,该文提出了一种OFDM相位编码频率步进的新雷达信号,其核心思想是通过载频的频率步进,利用多个带宽较小的OFDM相位编码脉冲组成一个脉冲串,合成大的带宽。在推导这种新雷达信号的模糊函数的基础上,着重分析了信号的距离高分辨特性和多普勒特性,通过比较得出结论：OFDM相位编码频率步进信号能有效实现距离高分辨,其多普勒敏感度介于OFDM相位编码和步进频信号之间。     

X射线二极管平响应滤片的制作

针对X射线二极管平响应滤片的设计要求,采用电子束蒸发生长薄金层、紫外光曝光光刻、微电镀厚金层、体硅腐蚀制作镂空结构和等离子体刻蚀去掉PI等技术,成功制备了阵列结构的圆孔直径为5μm,周期为10.854μm,金层厚度分别为50,400nm的薄、厚两种金层滤片。电镀过程中采用台阶仪多次测量图形四周电镀厚度后取均值的方法得到尽可能准确的电镀厚金层。滤片交付实验后,在X光能量0.1～4keV取得的平响应曲线标准偏差与均值之比在13%以内,可以满足相关单位的具体物理研究实验要求。     

移动互联网对电信运营商转型的要求

本文试图从转型的观点看电信运营商如何适应数据核心业务.电信运营商的转型至少包括企业战略转型、市场转型与技术转型.     

A Low Noise 100 GHz Sideband-Separating Receiver

We have built a 100 GHz sideband-separating receiver. The receiver, a breadboard for the band 3 cartridges for ALMA, achieves a SSB noise temperature of 6hf/k with a 4–8 GHz IF. We show that it is possible to meet the ALMA specifications. The design of the receiver is reviewed and the relationships between the receiver noise temperature and properties of the components used in the receiver are discussed.     

Enhanced solder joint bonding strength of electronic packaging with electrowetting effect

This paper reports a novel method to enhance solder ball or solder ring bonding strength by using electrowetting-on-dielectric (EWOD) effect. With a low melting point, the metal Sn has been widely used in electronic packaging technology. Since Sn will be molten into liquid when the temperature is increased above the melting point, the method for treating liquid can be herein employed. Contact angle of the molten Pb-free balls or ring structure on silicon substrate have been experimentally changed by applying electric field across the thin dielectric film between the molten solder and the conductive silicon substrate. The contact area between the solder and the substrate is enlarged due to the decrease of the contact angle. Our testing results on the EWOD enhanced packaging structures of solder balls, flip-chip and solder ring hermetic package generally show about 50% enhancement in bonding shear strength. The significantly enhanced solder link bonding strength is hopeful for improving packaging reliability and is promising to be used in high performance silicon based electronic or microelectromechanic SiP (system in package) technologies.     

Phototunable Underwater Oil Adhesion of Micro/Nanoscale Hierarchical‐Structured ZnO Mesh Films with Switchable Contact Mode

Controllable surface adhesion of solid substrates has aroused great interest both in air and underwater in solving many challenging interfacial science problems such as robust antifouling, oil‐repellent, and highly efficient oil/water separation materials. Recently, responsive surface adhesion, especially switchable adhesion, under external stimulus in air has been paid more and more attention in fundamental research and industrial applications. However, phototunable underwater oil adhesion is still a challenge. Here, an approach to realize phototunable underwater oil adhesion on aligned ZnO nanorod array‐coated films is reported, via a special switchable contact mode between an unstable liquid/gas/solid tri‐phase contact mode and stable liquid/liquid/solid tri‐phase contact mode. The photo‐induced wettability transition to water and air exists (or does not) in the micro/nanoscale hierarchical structure of the mesh films, playing important role in controlling the underwater oil adhesion behavior. This work is promising in the design of novel interfacial materials and functional devices for practical applications such as photo‐induced underwater oil manipulation and release, with loss‐free oil droplet transportation.     

Low-dimensional materials for photovoltaic application

The photovoltaic(PV)market is currently dominated by silicon based solar cells.However technological diversification is essential to promote competition,which is the driving force for technological growth.Historically,the choice of PV materials has been limited to the three-dimensional(3D)compounds with a high crystal symmetry and direct band gap.However,to meet the strict demands for sustainable PV applications,material space has been expanded beyond 3D compounds.In this perspective we discuss the potential of low-dimensional materials(2D,1D)for application in PVs.We present unique features of low-dimensional materials in context of their suitability in the solar cells.The band gap,absorption,carrier dynamics,mobility,defects,surface states and growth kinetics are discussed and compared to 3D counterparts,providing a comprehensive view of prospects of low-dimensional materials.Structural dimensionality leads to a highly anisotropic carrier transport,complex defect chemistry and peculiar growth dynamics.By providing fundamental insights into these challenges we aim to deepen the understanding of low-dimensional materials and expand the scope of their application.Finally,we discuss the current research status and development trend of solar cell devices made of low-dimensional materials.     

Efficient three-stage auction schemes for cloudlets deployment in wireless access network

Wireless Networks - Cloudlet deployment and resource allocation for mobile users (MUs) have been extensively studied in existing works for computation resource scarcity. However, most of them...