功率RF LDMOS的关键参数研究

在功率RF LDMOS器件中,击穿电压、截止频率fT和导通电阻Ron是器件性能的关键参数,为提高这几个器件性能参数可采取的各种措施又往往是互相矛盾和相互制约的.文中研究了几个关键参数之间的关系和优化方案,以及国际上在这方面所开展的研究和取得的进展,为进一步的研究和探索提供参考.     

Summary of the First Generation High Temperature Superconducting Wire： Processing, Characterization and Applications

Silver-clad （Bi,Pb）2Sr2Ca2Cu3O10＋x long wires produced by powder-in-tube techniques, which have been recognized as the first generation of the High Temperature Superconducting （HTS） wires, are expected to apply widely especially in strong current applications. In this work, the processing, characterization and application of the silver-clad （Bi,Pb）2Sr2Ca2Cu3Ol0＋x HTS wires are summarized. The HTS wires are fabricated using the combination of powder-in-tube technique, and the resulting wires are fully characterized by the means of chemical analyses, microstructural observation, electrical and magnetic measurements. The relationship among fabrication parameters, chemical and microstructural characteristics, and electrical and magnetic properties are analyzed. Applications of the HTS wires have also been introduced according to their strong current behaviors with various prototype devices made.     

Jamming sensor networks: attack and defense strategies

Wireless sensor networks are built upon a shared medium that makes it easy for adversaries to conduct radio interference, or jamming, attacks that effectively cause a denial of service of either transmission or reception functionalities. These attacks can easily be accomplished by an adversary by either bypassing MAC-layer protocols or emitting a radio signal targeted at jamming a particular channel. In this article we survey different jamming attacks that may be employed against a sensor network. In order to cope with the problem of jamming, we discuss a two-phase strategy involving the diagnosis of the attack, followed by a suitable defense strategy. We highlight the challenges associated with detecting jamming. To cope with jamming, we propose two different but complementary approaches. One approach is to simply retreat from the interferer which may be accomplished by either spectral evasion (channel surfing) or spatial evasion (spatial retreats). The second approach aims to compete more actively with the interferer by adjusting resources, such as power levels and communication coding, to achieve communication in the presence of the jammer.     

利用应用程序备份SQL Server数据策略的选择

SQL Server功能强大操作简便,日益为广大数据库用户所喜爱,许多的开发人员选择它作为后台数据库管理系统,而怎样利用应用程序来备份SQL Server数据库是很多程序员所面临的普遍性问题,文中探讨了用应用程序备份SQL Server数据库的策略和实现方法,并给出了应用实例.     

Effect of an arcjet plume on satellite reflector performance

The effect of an arcjet plume on the performance of satellite reflector antennas is studied. The arcjet plume is modeled as a weakly ionized plasma. The spatial permittivity distribution of the plume is approximated using the measured electron density profile and a cold plasma model. Geometrical optics is applied to determine the ray paths as well as the transmitted fields through the inhomogeneous plume. The ray optics results are compared against several exact solutions for scattering from inhomogeneous dielectrics, and good agreement is observed for sufficiently large scatterer size. The far-field antenna patterns of the reflector in the presence of the plume are calculated from the transmitted ray fields using a ray-tube integration scheme. For arcjet prototypes in the 1-kW class, the plume effect on the antenna performance is small. As the electron density increases, the main beam and sidelobe level gradually degrade. The main beam also tends to squint away from the plume region     

A New Method for the Synthesis of C/D Ring Synthon of Vitamin D

Inrecentyears,vitaminDresearchareahasbeenstimulatedbythediscoveriesthatIQ,25-dihydroxyvitaminD,,theactivemetaboliteofvitaminD,,inadditiontotheclassicalrolesofregulatingcalciumandphosphorusmetabolisms',hasamuchbroaderspectrumofactivitiesthanoriginallythought,suchaspromotingcelldifferelltiationandinhibitingcellproliferation"'.Thebiologicalsignificanceandmedicalneedshaveledeffortstowardthesearchforanaloguesofpotentcelldifferelltiationandantiproliferationactivitywithouttoxichypercalcemiaassociate…     

一种新型的双极功率器件—BST

针对常规双极功率晶体管（ＢＰＴ）中存在的高频、高电流增益和高ＣＥ击穿电压间的固有矛盾，基于一新工艺提出了一种新型的双极功率器件──ＢＳＴ（ＢａｓｅＳｈｉｅｌｄｉｎｇＴｒａｎｓｉｓｔｏｒ）结构。分析了ＢＳＴ夹断后的两维电场解析解，可知深Ｐ＋多晶硅基区的引入对有源Ｐ基区产生明显的电场屏蔽效应，该基区屏蔽效应随Ｐ＋基区深入Ｎ－区中的深度Ｌ的增加以及相邻Ｐ＋基区间距２Ｄ的减小而增强。正是这种基区屏蔽效应，使得ＢＳＴ的特征频率ｆＴ、电流增益ｈｆｅ和ＣＥ击穿电压ＢＶｃｅ０都较常规ＢＰＴ大为提高，较好地解决了常规ＢＰＴ中存在的主要矛盾。实验验证了理论分析的结果。     

磷化氢与烯烃反应的原位NMR谱研究

本文应用加压原位(in-situ)核磁共振技术,在反应温度70～75℃,压力1.0～2.0MPa,氘代苯为溶剂,偶氮二异丁腈(AIBN)为引发剂的条件下探索了磷化氢与丙烯腈,4-乙烯基吡啶,烯丙基胺,丙烯酰胺,氨基吡啉和N-乙烯基咔唑的自由基加成反应,结果表明除氨基吡啉之外的其它五种含氮化合物均能与磷化氢发生反应,从而找到合成含氮有机膦的良好路线。     

杨村煤与石油渣油共处理高温缩聚反应特性的研究

用ＧＪ－２型微型反应釜研究了兖州杨村煤与石油渣油在４７０℃时共处理反应的特性，结果表明，杨树煤和石油渣油在高温下进行共处理反应时，宏观表现是缩聚反应占主导地位，程序升温可提高煤的转化率，添加四氢萘到石油渣油中可抑制缩聚反应，而且添加量越大，抑制效果越明显，煤液化产物的重新加氢也会发生一定的缩聚反应，可产生微量结渣。     

高功率激光反射镜的几个关键技术

 分析了制作高功率连续激光反射镜材料的热性能、缺陷及其加工工艺, 提出了制作高功率激光反射镜应考虑的几个关键问题: 反射镜材料的综合热性能比值S, 材料的微观结构、缺陷的大小和晶向的选择, 以及加工工艺的设计。并介绍了实验结果。