运载火箭多体系统动力学发展及应用

从工程实际角度,对运载火箭中的相关多体系统动力学问题进行分析与思考,提出运载火箭研制过程中多体系统动力学学科发展的重要性,并指出多体系统动力学在运载火箭研制方面后续需发展的若干方向,诸如贮箱晃动、分离装置、关节类机构等。建议结合运载火箭大过载、多相耦合的特点,开展针对模型高阶、强非线性相关动力学研究与工程软件研发。     

"OTO"76mm舰炮的螺旋扬弹机分析

介绍了“OTO”76mm舰炮供弹系统的重要部件螺旋扬弹机，给出了部分数据和结构示意图，对扬弹鼓、链式提升机及其提弹车的结构和工作原理进行了分析，推算出了螺旋扬弹机的转动速度及链条运动速度、链条节距及总长度、提升高度及其对应时间和提弹间距等结构及其运动状态参数。     

能实现多点攻击的巡航导弹指挥模型研究

在深入研究巡航导弹飞行过程的基础上,描述了支持多点攻击的巡航导弹有关作战概念,考虑战术巡逻因素,对移动目标实时搜索模型进行了改进;建立了指挥系统与巡航导弹信息铰链模型,定义了接口信息类型,并进行了软件仿真.该指挥模型可以克服以往巡航导弹发射后地面指挥操作员不能再对其实施控制的缺陷,实现地面指挥官控制飞行中的导弹进行多点攻击,以攻击移动目标和突然出现的时间敏感目标.     

Research on topology control based on Voronoi diagram algorithm in FSO networks

Telecommunication Systems - In a wireless sensor network (WSN) where positioning information is not assumed or is partially available, efficient data access is a very challenging issue especially...     

颗粒轨道模型中颗粒跟踪与定位算法研究

颗粒轨道模型的一个难点是跟踪颗粒在不同时刻所处的网格位置,才能确定颗粒与当地流体间的相互作用.最近发展的3种颗粒跟踪和定位算法,通过比较发现Chen-Pereira算法和R.Chorda算法搜索的网格数目一样,都比Zhou-Leschziner算法搜索的网格数目少,但R. Chorda算法所需要的时间更少.该文将R. Chorda算法应用于带有颗粒相喷流反作用系统的高超声速拦截器外流场数值模拟.     

一类非线性系统的模糊输出反馈控制

简单介绍了T-S模糊模型, 基于T-S模糊模型给出了一类非线性系统的模糊模型.论述了非线性系统模糊输出反馈控制, 在满足假设的一定条件下, 这些方法和模糊算法能有效处理某类定义不完善或难以精确建模的控制过程.     

Dual-polarised single-layer slotted patch antenna

A compact design of the single-layer slotted microstrip patch antenna is presented, which has two highly decoupled orthogonal input ports and is capable of generating dual-polarised radiation. The proposed antenna displays a desired characteristic for reducing polarisation loss between the transmitting and receiving antenna units at arbitrary angles. The measured results show that the proposed antenna with resonance frequency at 5.93 GHz has a bandwidth of about 300 MHz, an average gain of greater than 8 dBi, and an input isolation of exceeding 20 dB for the entire impedance bandwidths of the two polarisations.     

Precision fabrication techniques and analysis on high-Q evanescent-mode resonators and filters of different geometries

High-Q evanescent-mode resonators and filters are realized by both silicon micromachining and layer-by-layer polymer processing. Capacitively loaded cavities can be reduced to a size much smaller than a wavelength, but still have a much higher unloaded Q than lumped elements. The loaded resonators are utilized for reduced-size filters with a low insertion loss enabled by the relatively high-Q factor. The small fabrication tolerances of silicon micromachining and polymer stereolithography processing enable the realization of highly loaded evanescent-mode resonators and filters. A 14-GHz resonator micromachined in silicon has a volume of 5 mm /spl times/ 5 mm /spl times/ 0.45 mm, representing a resonant frequency reduction of 66.8% compared to an empty cavity of the same dimensions. The polymer-based fabrication is used to create resonators of different three-dimensional geometries with Q's up to 1940 and frequency reductions up to 49.9%. An insertion loss of 0.83 dB is measured in a 1.69% bandwidth filter created by polymer processing with a frequency reduction of 47% compared to an unloaded cavity. The frequency sensitivity to fabrication tolerances of these structures is also analyzed.     

A Framework for MPEG‐4 Contents Delivery over DMB

Digital Multimedia Broadcasting (DMB) is an upcoming standard in Korea used to provide mobile multimedia broadcasting service based on the Eureka‐147 Digital Audio Broadcasting (DAB) system. The current dominant multimedia coding standard, MPEG‐4, is foreseen to play an important role in forthcoming DMB services. However, the current approaches for transporting MPEG‐4 content over DMB networks are not optimized. To address this issue we propose a novel MPEG‐4 stream multiplexer, called M4SMux, which provides better stream multiplexing and delivery over DMB networks. M4SMux features an MPEG‐4 elementary‐stream interleaving mechanism that reduces the multiplexing overhead and a multiplex configuration mechanism that utilizes M4SLinkTable for easy content access. In addition, we propose an error correction method which enhances transport efficiency.     

Asymptotic Distortion Performance of Source-Channel Diversity over Multihop and Relay Channels

A key challenge in the design of real-time wireless multimedia systems is the presence of fading coupled with strict delay constraints. A very effective answer to this problem is the use of diversity achieving techniques to overcome the fading nature of the wireless channels caused by the mobility of the nodes. The mobility of the nodes gives rise to the need of cooperation among the nodes to enhance the system performance. This paper focuses on comparing systems that exhibit diversity of three forms: source coding diversity, channel coding diversity, and user cooperation diversity implemented through multihop or relay channels with amplify-and-forward or decode-and-forward protocols. Commonly used in multimedia communications, performance is measured in terms of the distortion exponent, which measures the rate of decay of the end-to-end distortion at asymptotically high signal-to-noise ratio (SNR). For the case of repetition coding at the relay nodes, we prove that having more relays is not always beneficial. For the general case of having a large number of relays that can help the source using repetition coding, the optimum number of relay nodes that maximizes the distortion exponent is determined in this paper. This optimum number of relay nodes will depend on the system bandwidth as well as the channel quality. The derived result shows a trade-off between the quality (resolution) of the source encoder and the amount of cooperation (number of relay nodes). Also, the performances of the channel coding diversity-based scheme and the source coding diversity-based scheme are compared. The results show that for both relay and multihop channels, channel coding diversity provides the best performance, followed by the source coding diversity.