星载寄生式SAR系统干涉性能与空间分辨能力分析

以星载寄生式SAR系统成像信号模型为基础,详细分析了这一新系统的干涉性能和空间分辨能力,给出了 各自的限制条件。分析了两者限制的本质一致性,并统一以基线形式表示出来,同时提出了距离向有效基线和方位向有效 基线的新概念。最后以Cartwheel编队构形进行了实例分析,特别指出了基线耦合、多基线对性能的影响。     

In Situ Preparation and Thermoelectric Properties of B4C1−x –TiB2 Composites

B₄C_1?x –TiB₂ composites were prepared by in situ reactive spark plasma sintering of B₄C with addition of nano-TiO₂ powder. The effect of TiO₂ addition on the sinterability of boron carbide was studied. The composition and the microstructure of the dense composites are characterized by means of x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDX). The studies show that the composites contain boron carbide and TiB₂ phases with a homogeneous structure. In addition, the correlation between the composition and the thermoelectric properties was investigated. The electrical conductivity of the composite increased with increasing addition of TiO₂, and the Seebeck coefficient decreased with TiO₂ addition. The percolation threshold ø _c for TiB₂ in the B₄C_1?x –TiB₂ system was found to be in the range of 0.139 to 0.189. The thermal conductivity was reduced in the whole measuring temperature range from 50°C to 800°C below ø _c. Accordingly, a significant enhancement in the dimensionless figure of merit ZT of the composites was achieved compared with that of boron carbide without TiO₂ addition, with ZT achieving its maximum value at 10 wt.% TiO₂.     

SOA工作条件对全光异或输出性能的影响研究

理论分析了SOA动态模型和SOA-MZI全光异或原理,采用光通信系统设计软件OptiSystem搭建了基于SOA-MZI的全光异或实验模型,仿真研究了注入SOA的数据信号光功率、连续探测光功率、偏置电流等工作条件对异或输出消光比、Q值以及误码性能的影响,取得了一组最佳工作条件,即数据信号光功率为3dBm,连续探测光功率为0dBm,偏置电流为600mA,此时可以得到最佳的异或输出性能:消光比约11.5dB,Q值约22,误码率约10-108量级。研究方法和相关结论可以推广到基于SOA的其他全光信号处理应用中,为未来全光网络的全面建设做准备。     

软抛光垫条件下非晶态Ge2Sb2Te5的化学机械抛光

Chemical mechanical planarization（CMP） of amorphous Ge₂Sb₂Te₅（a-GST） is investigated using two typical soft pads（politex REG and AT） in acidic slurry.After CMP,it is found that the removal rate（RR） of a-GST increases with an increase of runs number for both pads.However,it achieves the higher RR and better surface quality of a-GST for an AT pad.The in-situ sheet resistance（R_s） measure shows the higher R_s of a-GST polishing can be gained after CMP using both pads and the high R_s is beneficial to lower the reset current for the PCM cells. In order to find the root cause of the different RR of a-GST polishing with different pads,the surface morphology and characteristics of both new and used pads are analyzed,it shows that the AT pad has smaller porosity size and more pore counts than that of the REG pad,and thus the AT pad can transport more fresh slurry to the reaction interface between the pad and a-GST,which results in the high RR of a-GST due to enhanced chemical reaction.     

SAFE: A Source Deduplication Framework for Efficient Cloud Backup Services

Due to the relatively low bandwidth of WAN that supports cloud backup services and the increasing amount of backed-up data stored at service providers, the deduplication scheme used in the cloud backup environment must remove the redundant data for backup operations to reduce backup times and storage costs and for restore operations to reduce restore times. In this paper, we propose SAFE, a source deduplication framework for efficient cloud backup and restore operations. SAFE consists of three salient features, (1) Hybrid Deduplication, combining the global file-level and local chunk-level deduplication to achieve an optimal tradeoff between the deduplication efficiency and overhead to achieve a short backup time; (2) Semantic-aware Elimination, exploiting file semantics to narrow the search space for the redundant data in hybrid deduplication process to reduce the deduplication overhead; and (3) Unmodified Data Removal, removing the files and data chunks that are kept intact from data transmission for some restore operations. Through extensive experiments driven by real-world datasets, the SAFE framework is shown to maintain a much higher deduplication efficiency/overhead ratio than existing solutions, shortening the backup time by an average of 38.7 %, and reduce the restore time by a ratio of up to 9.7 : 1.     

Joint Opportunistic Spectrum Sharing and Dynamic Full Frequency Reuse in OFDMA Cellular Relay Networks

This paper considers the problem of spectrum sharing in orthogonal frequency division multiple access cellular relay networks. Firstly, a novel dynamic full frequency reuse scheme is proposed to improve the spectral efficiency. Different from the conventional full frequency reuse scheme which only allows the base station (BS) reusing the subcarriers in the specific regions, an improved full frequency reuse scheme is proposed to allow the BS reusing all the subcarriers in the whole BS coverage region to exploit additional multiuser diversity gain. In order to dynamically reuse the frequency resource among the BS and relay stations (RSs) to further improve the spectral efficiency, the adaptive subcarrier scheduling is introduced into the improved full frequency reuse scheme to obtain more multi-user diversity gain, which forms the proposed novel dynamic full frequency reuse scheme. Secondly, in order to further increase the system throughput, the opportunistic spectrum sharing scheme is introduced to allow the RSs selectively reusing the subcarriers among each other, which joint with the proposed dynamic full frequency reuse scheme to intelligently allocates the subcarriers originally reused by the BS and a RS to another suitable RS which can best improve the system performance after considering the additional interference. Thirdly, in order to select The optimal reusing combination scheme of BS and RSs to exploit more potential system performance, a heuristic approach based on genetic algorithm is proposed to search the optimal BS and RSs combination to opportunistically share the frequency resource. Simulation results show that the proposed dynamic full frequency reuse scheme can obtain high spectral efficiency, fine fairness and low outage probability compared to the conventional full frequency reuse scheme. Furthermore, the system performance can be improved when considering the opportunistic spectrum sharing among RSs. Finally, after adopting the genetic algorithm, the system performance can be greatly improved by the frequency reusing among the optimal BS and RSs combination.     

二维几种常见阵型阵列的阻塞矩阵构建

针对二维不同阵型,研究其二维阻塞矩阵的建立方法。阻塞矩阵因其常用于抑制干扰以及在GSC阵列中阻塞期望信号,因而在阵列信号处理中得到广泛应用。常用的是二项式对消方法,该方法简单有效且具有运算量小的特点。目前,通过二项式对消来构造阻塞矩阵的方法主要集中在一维线阵,涉及二维以及其它阵型的较少。为此,文中将基于二维具有代表性的阵型做了研究,并推导出具有凡导向矢量首项为1的阵型阻塞矩阵构造方法--一字阶梯累积法。仿真验证了该方法的简单有效。     

Prediction-based dynamic routing intelligent algorithm in power optical communication network

New energy power generation equipment has the characteristics of diurnal, perturbative, seasonal, and periodic power generation, which makes new power optical communication network(POCN) more dynamic and changeable. This is directly reflected in the dynamics of the link risk and service importance of the POCN. In this paper, aiming at the problem of the dynamic importance of service in POCN, and the resulting power optical communication network reliability decline problem, a new energy POCN dyna...     

表面处理对HfO_2栅介质MOS电容界面特性的影响

在溅射淀积HfO2栅介质之前,采用NO、N2O、O2+CHCCl3(TCE)进行表面预处理。结果表明,预处理能改善界面和近界面特性,减小界面层厚度,尤其是新颖的TCE+少量O2的表面处理工艺,能有效抑制界面层的生长,大大降低界面态密度,减小栅极漏电流。其机理在于TCE分解产生的Cl2和HCl能有效地钝化界面附近Si悬挂键和其它结构缺陷,并能去除离子污染。     

RTD/HEMT串联型RTT的设计与研制

依据RTD/HEMT串联型RTT的概念,设计了RTD/HEMT单片集成材料结构,该结构采用分子束外延技术生长.采用湿法化学腐蚀、金属剥离、台面隔离和空气桥互连技术,研制了RTD/HEMT串联型RTT,并对RTT及RTT中RTD和HEMT的直流特性进行了测试.测试结果表明:在室温下,器件具有明显的栅控负阻特性,正接型RTT的最大峰谷电流之比在2.2左右,反接型RTT的最大峰谷电流之比在4.6左右.实验为RTD/HEMT串联型RTT性能的优化和RTD/HEMT单片集成电路的研制奠定了基础.