基于网络行为的强制访问技术在铁路客票系统中的应用

铁路客票系统属于国家关键信息基础设施,其运行安全关乎国家安全和人民安全.通过将主机上的访问行为映射到网络层面,提出对网络行为进行5×5要素界定的访问控制体系,以此解除对操作系统的依赖,实现对传输控制协议/网际协议(TCP/IP)5层模型全覆盖.将此思想应用于铁路客票系统,能在特定的网络服务点施行访问控制,并对不同的层次...     

AIGaAsSb Buffer/Barrier on GaAs substrate for InAs channel devices with high electron mobility and practical reliability

InAs/AlGaAsSb deep quantum well was successfully formed on GaAs substrate and examined for two electron devices, Hall elements (HEs), and field-effect transistors (FETs). With a thin buffer layer of 600 nm AIGaAsSb on GaAs substrate, we observed high electron mobility more than 23000 cm²/Vs and extrinsic effective electron velocity of 2.2 x 10⁷ cm/s for a 15 nm thick InAs channel at room temperature. AIGaAsSb lattice matched to InAs was discussed from the view points of insulating property, carrier confinement, and oxidization rate. Reliability data good enough for practical use were also obtained for HEs. We demonstrated AIGaAsSb as a promising buffer/barrier layers for InAs channel devices on GaAs substrate, and we discussed the possible advantages of AIGaAsSb also for InGaAs FETs.     

碳化硅加热元件的电性能和使用

本文介绍碳化硅加热元件的电特性、表面负荷以及工作气氛对它的影响，并对它设计和使用要点举例予以说明。     

ATM交换结构综述

本文从国内外ATM交换领域有关最新研究成果出发，全面综述了宽带综合业务数字网中ATM交换结构的实现方法，并对它们的重要特点和性能进行了讨论。提出了ATM交换结构研究中存在的主要问题和今后的发展方向。     

Chemical composition of melia volkensii gurke: An unrealised browse potential for semi-arid agroforestry systems

Results of chemical analyses of some nutritional characteristics of Melia volkensii browse, important for large wild and domestic herbivores in East Africa, are presented. Seeds, fruit pulp, leaves and twigs had high levels of crude protein, crude fat, minerals and fibre. Newly coppiced shoots (leaves and twigs), old shoots, fruit pulp and seed contained 230, 190, 130 and 320 g kg^-1 dry weight crude protein, respectively. The essential amino acid profile compared well with the FAO scoring pattern. Tyrosine was the first limiting amino acid in the coppice leaves and twigs, lysine in the cotyledons, and threonine and lysine in the endosperm. The concentrations of crude fat in the seed, fruit pulp, coppice shoots and old shoots were 480, 100, 80 and 50 g kg^-1, respectively. The fatty acids in the cotyledon and endosperm were mainly palmitic (110 and 109 g kg^-1, respectively), oleic (327 and 252 g kg^-1, respectively) and linoleic (487 and 573 g kg^-1, respectively). The levels of P, Na, K, Ca, Mg and the Ca/P ratio per kg dry weight were on average higher than the optimum recommended for ruminants. These results demonstrate that M volkensii browse, especially coppice leaves and twigs, have a high index for nutrient content, and the planting of this species should be promoted in the semi-arid areas to supplement senescent grasses and cereal crop residues.     

粤北石人嶂钨矿放射性矿化研究

粤北石人嶂石英脉型钨矿床的石英脉、花岗岩、云英岩均发育晶质铀矿、含钍晶质铀矿、钍石、方钍石等系列放射性矿物。为了探寻是否存在放射性矿化,笔者通过系统测试发现以下规律:1)矿区含钨石英脉的放射性元素(U、Th)含量相对较低,绝大多数样品比地壳克拉克值还低;2)花岗岩的平均含量均比华南产铀花岗岩高出2¹0倍;3)云英岩的U、Th含量更高,而富含硫化物的钨矿脉U、Th含量也很高,并发育放射性矿物;4)自55010倍;3)云英岩的U、Th含量更高,而富含硫化物的钨矿脉U、Th含量也很高,并发育放射性矿物;4)自550³40m中段,各类地质体或不同矿脉的放射性元素含量呈现由小→大的变化趋势;5)矿区深部及富含硫化物钨矿脉和云英岩是寻找放射性矿化的重要方向。研究成果可为矿山资源综合利用及放射性防护工作提供地质依据。     

飞行模拟训练保障建设影响因素分析

模拟训练已成为信息化条件下提高飞行训练质量的重要方法和手段,飞行模拟训练保障是一个由保障内容、机构和管理等要素构成的复杂系统,抓好飞行模拟训练保障建设,需要系统分析研究其影响因素;从经济环境、科学技术环境、训练任务环境和武器装备发展等方面分析了飞行模拟训练保障的外部影响因素,从器材、场地、人员、管理和配套等方面提出了其内部构成要素,并进一步探讨了外部因素与内部构成要素的作用关系。     

各向异性材料部分涂覆导体的散射特性研究

利用物理光学法(PO)与有限元法(FEM)混合方法,研究了有各向异性媒质局部涂覆的电大导体目标的电磁散射问题.在有复杂媒质涂覆的电小结构区域采用有限元法,在未涂覆媒质的电大导体区域采用物理光学法结合等效电磁流法.将两部分区域的边界进行消隐处理,考虑耦合效应,并利用共同的等相位面,将不同区域产生的散射场矢量叠加得到总散射场.文中的实例结果与传统的FEM很好的一致,说明了该方法的有效性和精确性.     

Helical‐Like 3D Ultrathin Piezoelectric Element for Complicated Ultrasonic Field

The developments of personalized medicine, ultrasound imaging, and contactless “microscopic handle” techniques are pushing ultrasonic transducers toward features of high frequency, device miniaturization, and even novel function. However, the conventional ultrasonic transducer has severely limited the development of novel ideas for applications due to its ordinary ultrasonic field. Although transducer arrays and monolithic acoustic holograms are capable of producing the complicated ultrasonic field, it is still difficult to achieve high frequency, device miniaturization, and novel function simultaneously. Here, a simple but effective approach is introduced that aims at reconstructing the complicated and high‐frequency ultrasonic field via a compact single‐element ultrasonic transducer. The 3D ultrathin piezoelectric element with a complex configuration is demonstrated theoretically and experimentally to produce the desired complicated ultrasonic field. With helical‐like configuration, the single‐element ultrasonic transducer offers efficient noncontact trapping and manipulation of suspended microparticles and biological cells. Moreover, its strong trapping capability leads to the 3D stacking of microparticles, which is a novel and interesting phenomenon achieved by a single‐element ultrasonic transducer. This work brings the possibility of a complicated ultrasonic field for achieving novel high‐frequency ultrasound applications through the design of smart structure ultrathin piezoelectric materials.     

绝热无比型动态触发器和同步时序电路综合

该文从电路三要素理论出发研究低功耗电路，定量描述绝热无比型动态记忆电路。绝热无比型动态触发器利用电容接收和保存信息，避免目前绝热电路中电容上的信息得而复失的现象，其中绝热D和T'触发器只用6管，带‘与或非’输入的绝热D触发器只用9管。在上述理论基础上该文提出绝热无比型动态同步时序电路综合方法，用此法设计出绝热5421BCD码十进制计数器，仅用32管，总功耗小于一个PAL－2N四位二进制计数器的功耗，计算机模拟验证该文方法正确。