BPSK调制器发射时延的一种高精度标定方法

在高精度卫星测控、导航定位等领域,系统设备的绝对时延是影响精度的主要因素之一。示波器方案是目前能够测量BPSK调制器调制信号输入端到射频信号输出端的时延的唯一方法。文章提出采用宽带数字存储示波器结合包络检测信号处理技术,以提高调制器时延测量的精度,标准不确定度可优于50ps,避免了手工测试的主观不确定性。该方法也可推广用于变频器时延的精确测量。     

新型声表面波气体传感器

介绍了声表面波（SAW）气体传感器的工作原理及器件制作，提出了1种表面波SO2传感器，它采用三乙醇胺（TEA）覆盖薄膜，分辨率可达70×10－9。还讨论了SAW气体传感器的稳定性、可靠性、灵敏度及选择性等问题，并给出了有关的实验结果。     

仿真系统中CIG实时性问题研究

在本文中对计算机成像系统在成像制导仿真过程中的一些主要延迟因素作了分析。在假定系统带宽有限的条件下对延迟进行了补偿，并对补偿算法的工程实现问题进行了讨论。仿真结果表明该补偿算法在假定带宽范围内具有很好性能，提高了计算机成像系统的实时性。     

LEO卫星网络的切换策略及性能分析

采用Dijkstra算法,分析了低轨(LEO)卫星网络的距离最短、时延最小、跳数最小、持续时间最长等典型路由切换策略,并比较了性能。在综合考虑切换性能和时延等指标的基础上,提出了一种持续时间最长和时延最小组合,以及完全路由重构与部分路由重构结合的混合切换策略。各切换策略性能比较的结果表明,该混合切换策略的性能较优。     

论GPS与相对论时空观

在ＧＰＳ中，观测者对时钟所显时间值和物理事件所发光信号传播过程所作全面描述应包括“看到的情况”和“实际的情况”；作为具有特定物质性、运动性、结构性和开放性的动力学系统，时种所显时间值与其内部特定物质性、运动性和结构性等内因有关，与其所受引力和电磁力等外因有关；根据速度值定义，除特别约定，具体光子相对具体参照物的具体速度值应由观测者使用具体时种和量尺观测而定。以上述时空新认识弥补了相对论时空观有关观点的认识不足。     

频率变换器件群时延测量方法的探讨与分析

阐述与分析以混频器为代表的频率变换器件群时延特性的几种经典与最新的测量方法,基于矢量网络分析仪的静态法和基于载波调制的动态法的各自特点及国际上相关测量方法的最新进展。最后指出了现有方法中共同存在且亟待解决的问题。     

Group force mobility model and its obstacle avoidance capability

Many mobility models attempt to provide realistic simulation to many real world scenarios. However, existing mobility models, such as RPGM [X. Hong, M. Gerla, G. Pei, C. Chiang, A group mobility model for ad hoc wireless networks, in: Proceedings of ACM/IEEE MSWiM’99, Seattle, WA, August 1999, pp. 53–60] and others, fail to address many aspects. These limitations range from mobile node (MN) collision avoidance, obstacle avoidance, and the interaction of MNs within a group. Our research, the group force mobility model (GFMM) [S.A. Williams, D. Huang, A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006], proposes a novel idea which introduces the concept of attraction and repulsion forces to address many of these limitations. Williams and Huang [A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006] described some of the limitations and drawbacks that many models neglect. This model effectively simulates the interaction of MNs within a group, the interaction of groups to one another, the coherency of a group, and the avoidance of collision with groups, nodes, and obstacles. This paper provides an overview of GFMM and particularly illustrates the GFMM's ability to avoid collision with obstacles, which is a vital property to posses in order to provide a realistic simulaition. We compare our model with the commonly used RPGM model and provide statistical assessments based on connectivity metrics such as link changed, link duration, and relative speed. All will be detailed and explained in this paper.     

Characterizing parameters of Jatropha curcas cell cultures for microgravity studies

Jatropha (Jatropha curcas) is a tropical perennial species identified as a potential biofuel crop. The oil is of excellent quality and it has been successfully tested as biodiesel and in jet fuel mixes. However, studies on breeding and genetic improvement of jatropha are limited. Space offers a unique environment for experiments aiming at the assessment of mutations and differential gene expression of crops and in vitro cultures of plants are convenient for studies of genetic variation as affected by microgravity. However, before microgravity studies can be successfully performed, pre-flight experiments are necessary to characterize plant material and validate flight hardware environmental conditions. Such preliminary studies set the ground for subsequent spaceflight experiments. The objectives of this study were to compare the in vitro growth of cultures from three explant sources (cotyledon, leaf, and stem sections) of three jatropha accessions (Brazil, India, and Tanzania) outside and inside the petriGAP, a modified group activation pack (GAP) flight hardware to fit petri dishes. In vitro jatropha cell cultures were established in petri dishes containing a modified MS medium and maintained in a plant growth chamber at 25 ± 2 °C in the dark. Parameters evaluated were surface area of the explant tissue (A), fresh weight (FW), and dry weight (DW) for a period of 12 weeks. Growth was observed for cultures from all accessions at week 12, including subsequent plantlet regeneration. For all accessions differences in A, FW and DW were observed for inside vs. outside the PetriGAPs. Growth parameters were affected by accession (genotype), explant type, and environment. The type of explant influenced the type of cell growth and subsequent plantlet regeneration capacity. However, overall cell growth showed no abnormalities. The present study demonstrated that jatropha in vitro cell cultures are suitable for growth inside PetriGAPs for a period of 12 weeks. The parameters evaluated in this study provide the basic ground work and pre-flight assessment needed to justify a model for microgravity studies with jatropha in vitro cell cultures. Future studies should focus on results of experiments performed with jatropha in vitro cultures in microgravity.     

Validation of an active transponder for KOMPSAT-5 SAR image calibration

This paper describes the development and validation of a transportable active transponder designed for the image calibration of Korea Multi-Purpose Satellite-5 (KOMPSAT-5) with a synthetic aperture radar (SAR). Ground targets are essential in SAR image calibration. The environment for the deployment of ground targets for SAR image calibration should provide uniformity and minimum interference. The Amazon or deserts are regarded as desirable environments. However, such environments for SAR image calibration are difficult to find in Korea. Thus, it will be advantageous to have an active transponder whose performance will not be severely limited by the absence of such uniform environment. We have therefore developed an active transponder which has an adjustable internal delay and into which the orbit data of an arbitrary satellite can be loaded. The stored obit data with the aid of an internal global positioning system (GPS) receiver and gyroscope enables the active transponder to point to a selected satellite. In addition, a virtual deployment of the active transponder is possible due to its adjustable internal delay. Thus, the developed active transponder can be deployed at any place without environmental constraint. The performance of the developed active transponder is validated using the satellite TerraSAR-X, which is already in operation. The test results show that the active transponder is successfully compliant with the requirements for KOMPSAT-5 image calibration.     

基于数字化仿真技术的模块化装配单元应用

传统航空机电产品尤其是液压产品的装配工艺复杂,总装工艺流程长,生产过程控制困难,装配质量难以保证。利用数字化仿真技术实现模块化部件装配单元规划,有利于提升装配专业化水平,缩短总装周期,实现产品的快速产出。