A novel double-recessed 4H-SiC MESFET with partly undoped space region

In this paper, a novel double-recessed 4H-SiC metal semiconductor field effect transistor (MESFET) with partly undoped space region (DRUS-MESFET) is introduced. The key idea in this work is to improve the DC and RF characteristics of the device by introducing an undoped space region. Using two-dimensional and two-carrier device simulation, we demonstrate that breakdown voltage (V_BR) increases from 109 V in conventional double recessed MESFET (DR-MESFET) structure to 144.5 V in the DRUS-MESFET structure due to the modified channel electric field distribution of the proposed structure. The maximum output power density of the DRUS-MESFET structure is about 25.4% larger than that of the DR-MESFET structure. Furthermore, lower gate-drain capacitance (C_GD), higher cut-off frequency (f_T), larger maximum available gain (MAG), and higher maximum oscillation frequency (f_max) are achieved for the DRUS-MESFET structure. The results show that the f_max and f_T of the proposed structure improve 95.6% and 13.07% respectively, compared with that of the DR-MESFET structure. Also, the MAG of the DRUS-MESET is 4.5 dB higher than that of the DR-MESFET structure at 40 GHz. The results show that the DRUS-MESFET structure has superior electrical characteristics and performances in comparison with the DR-MESFET structure.     

KAg4I5-AgI复合体系的电导率研究

采用固相反应法将市购的AgI和KI按4.1 ∶1的摩尔组分配比,在避光干燥的条件下混合加热,制备出了KAg₄I₅ (10%AgI )复合体系.用X射线衍射谱、扫描电子显微镜、复阻抗谱、差示扫描量热等分析手段,对复合体系的结构、形貌、离子导电特性及相变温度进行了研究.结果发现,两相均为快离子导体的材料复合后,其复合体系的离子电导率比各自为纯相时都高,并且升降温-电导率曲线为迟滞回线,AgI的升降温相变温度分别滞后5和10 ℃.用界面间相互作用、空间电荷模型及Gou 关键词： 离子电导率 电化学势 空间电荷区 相变温度     

SOI部分耗尽SiGe HBT集电结空间电荷区模型

SOI上的薄膜异质SiGe晶体管通过采用"折叠"集电极,已成功实现SOI上CMOS与HBT的兼容.本文结合SOI薄膜上的纵向SiGe HBT结构模型,提出了包含纵向、横向欧姆电阻和耗尽电容的"部分耗尽 (partially depleted) 晶体管"集电区简化电路模型.基于器件物理及实际考虑,系统建立了外延集电层电场、电势、耗尽宽度模型,并根据该模型对不同器件结构参数进行分析.结果表明,空间电荷区表现为本征集电结耗尽与MOS电容耗尽,空间电荷区宽度随集电结掺杂浓度减小而增大,随集电结反偏电压提高而增大, 关键词： SOI SiGe HBT 集电区 空间电荷区模型     

典型“高山-绿洲-荒漠”生态区植被净初级生产力时空变化特征分析

“高山-绿洲-荒漠”作为干旱区独特的自然景观,其内部迥异的生态系统极易在全球变化影响下产生不同波动,而植被净初级生产力（NPP）作为评价生态环境质量的重要指标,对整体认识区域变化有重要意义。遥感影像的产生为大尺度、长时间的区域NPP估算提供了可能,通过土地利用类型数据划分的不同植物覆被下的最大光能利用效率也提高了NPP估算的精度。因此选取具有典型“高山-绿洲-荒漠”生态系统的叶尔羌河流域作为研究区,使用多年遥感影像数据、气象数据,选用基于光能利用率的CASA模型对其进行模拟并对各生态区NPP状况进行分析,得出以下结论：(1) 叶尔羌河流域NPP年均值在2000年之后整体呈波动上升状态,约有85.9%的区域呈上升趋势,在绿洲区域的水域以及居住地处NPP出现下降状况。(2) 流域内NPP变化与降水量相关性较强,其空间分布特征与NPP和温度的相关性表现出相反状态。(3) 叶尔羌河流域NPP在各生态区上表现出“绿洲最高,荒漠绿洲过渡带次之,高山以及荒漠最低”的状况,生态环境相对绿洲、荒漠绿洲过渡带更为脆弱的区域（荒漠、高山）NPP波动性更强。研究结果将为区域生态环境保护修复、应对气候变化、实现人类与自然协调发展、促进多民族共同繁荣提供科学支撑。     

Quantum properties near the instability boundary in optomechanical system

The properties of the system near the instability boundary are very sensitive to external disturbances, which is important for amplifying some physical effects or improving the sensing accuracy. In this paper, the quantum properties near the instability boundary in a simple optomechanical system have been studied by numerical simulation. Calculations show that the transitional region connecting the Gaussian states and the ring states when crossing the boundary is sometimes different from the region centered on the boundary line, but it is more essential. The change of the mechanical Wigner function in the transitional region directly reflects its bifurcation behavior in classical dynamics. Besides, quantum properties, such as mechanical second-order coherence function and optomechanical entanglement, can be used to judge the corresponding bifurcation types and estimate the parameter width and position of the transitional region. The non-Gaussian transitional states exhibit strong entanglement robustness, and the transitional region as a boundary ribbon can be expected to replace the original classical instability boundary line in future applications.     

一种基于兴趣点分布的匿名框KNN查询方法

针对利用匿名框实现的兴趣点K近邻（KNN）查询带来的通信开销大、时延长等问题,提出了基于单一兴趣点Voronoi图划分和四叉树层次化组织的KNN查询方法。该方法根据兴趣点层次信息有针对性的构造查询匿名框用来获取详细查询信息,在保护位置隐私的同时,降低了查询通信开销,同时注入虚假查询保护了用户的真实查询内容隐私。最后分别采用模拟地理数据和真实地理数据进行理论分析和有效性验证。     

基于重加权?1范数惩罚的远近场混合源定位算法

现有信源定位方法大多假定信源是远场源或近场源,而实际定位系统中往往存在远场源和近场源共存的情况。为实现远、近场源分离及高精度信源定位,本文在稀疏信号重构理论框架下提出了一种新的远近场混合源定位算法。该算法利用阵列协方差矩阵反对角线元素和重加权l1范数惩罚获得所有信源的到达角（Direction Of Arrival, DOA）估计。在DOA估计的基础上,根据远场与近场源距离参数位于不同区间的特点利用一维搜索实现远、近场源分离以及近场源距离参数的估计。从理论角度分析了重加权l1范数惩罚算法的重构性能。本文所提算法不仅同时适用于高斯和非高斯信号,而且无需多维搜索和参数配对,也无需信源数的先验信息,同时还可以获得较好的定位精度。计算机仿真结果验证了所提算法的有效性。     

基于有限元法的高频开关电源PCB电磁兼容设计与仿真

在高频开关电源的设计中,功率开关器件在高频下的通断会产生强大的EMI,所以不可避免的会出现电磁兼容问题。这篇文章应用有限元法分别对自动布线后的高频开关电源PCB与按照电磁兼容设计规则布线后的PCB进行仿真,得到其在200 MHz、600 MHz、1 GHz频率处的近场辐射参数。仿真结果表明:自动布线生成的高频开关电源PCB近场辐射的范围和数值均较大,电磁干扰较强。根据电磁兼容的相关规则对PCB进行优化后,近场辐射的范围和数值均有所减小,提高了PCB板的电磁兼容性。     

硅基微通道板微孔结构形貌的实验研究

硅基微通道板(MCP)的重要技术挑战之一就是如何在硅基上制作高深宽比的微孔阵列结构。采用光助电化学刻蚀方法研究硅基高深宽比微孔阵列制作技术。考虑到实际反应条件下的物质输送、刻蚀液浓度、光照条件、温度等因素的影响都体现在刻蚀电流与电压上,重点研究了电流、电压与微结构形貌之间的关系。通过空间电荷区的大小以及刻蚀电流与溶液浓度之间的关系,得到合理的刻蚀参数。在5inch(1inch=2.54cm)硅基上制作出深度达200μm以上的均匀深孔,得到大面积、高深宽比的均匀微孔阵列,满足微通道板对结构形貌的要求。     

Differentiation of Cultivars of Flos Chrysanthemum with the Use of High-Performance Liquid Chromatography Fingerprints and Chemometrics

Flos Chrysanthemum is a generic name for a particular group of edible plants, which also have medicinal properties. There are, in fact, twenty to thirty different cultivars, which are commonly used in beverages and for medicinal purposes. In this work, four Flos Chrysanthemum cultivars, Hangju, Taiju, Gongju, and Boju, were collected and chromatographic fingerprints were used to distinguish and assess these cultivars for quality control purposes. Chromatography fingerprints contain chemical information but also often have baseline drifts and peak shifts, which complicate data processing, and adaptive iteratively reweighted, penalized least squares, and correlation optimized warping were applied to correct the fingerprint peaks. The adjusted data were submitted to unsupervised and supervised pattern recognition methods. Principal component analysis was used to qualitatively differentiate the Flos Chrysanthemum cultivars. Partial least squares, continuum power regression, and K-nearest neighbors were used to predict the unknown samples. Finally, the elliptic joint confidence region method was used to evaluate the prediction ability of these models. The partial least squares and continuum power regression methods were shown to best represent the experimental results.