推模式和拉模式下无线传感器节点的能耗研究

以规模相等单跳分簇无线传感器网络为背景,针对传感器节点在数据传输过程中的推和拉两种模式,分别提出了簇内普通节点和簇首节点在数据传输过程中的能耗计算公式,并计算出两种数据传输模式下簇内节点的能耗。利用实验验证了所提出的能耗计算公式的有效性,方便用户根据不同需求选择传感器节点传输机制,最大限度地延长无线传感器网络的生命周期。     

基于crtmpserver的手机直播系统

分析现有视频直播方案,提出一种基于开源视频库FFmpeg和流媒体服务器crtmpserver的手机视频直播系统解决方案.在手机端利用FFmpeg进行编码压缩和流传输;在服务器端利用crtmpserver和nginx进行转发、存储和管理;在PC端利用FFmpeg接收视频流并解码播放,通过HTTP方式实现视频回放.实验结果表明,该方案在现有联通和电信的3G网络上具有较高的实时性和稳定性,且丢包率低,视频具有较高的质量.     

基于拟连续高阶滑模的高超声速飞行器再入姿态控制

考虑模型参数不确定和外界干扰对再入制导控制性能的影响,基于拟连续高阶滑模控制策略对高超声速飞行器的再入制导控制问题进行了研究.首先,给出再入制导指令的设计过程.其次,基于再入飞行特性对模型进行简化,获得面向控制的姿态模型,在此基础上,通过引入新的控制变量,设计解耦滑模面,实现姿态间的解耦.再次,为了削弱控制抖振,通过引入虚拟控制,对系统进行增广,基于齐次性理论设计拟连续三阶滑模再入姿态控制器,确保系统在有限时间实现对制导指令的稳定跟踪.最后,六自由度再入飞行器的制导控制一体化仿真结果表明,本研究给出的控制策略在不影响系统鲁棒性的同时,能够实现对标称轨迹和再入姿态的综合控制.     

基于Radau伪谱法的非线性最优控制问题的收敛性

在过去的10年里,伪谱方法(如Legendre伪谱法、Gauss伪谱法、Radau伪谱法)逐步成为求解不同领域中非线性最优控制问题的一种高效、灵活的数值解法.本文从最优控制问题解的存在性、收敛性以及解的可行性3个方面对采用Radau伪谱法求解一般非线性最优控制问题解的收敛性进行研究.证明了原最优控制问题的离散解存在、存在收敛到原最优控制问题解上的离散解和离散形式的收敛解是原最优控制问题的最优解.在此基础上,证明了Radau伪谱法的收敛性.本文结论与现有文献相比,去掉了一些必要条件,更适合一般的非线性时不变系统.     

元胞自动机交通流模型中的车辆更新方式研究

基于TASEP(Totally Asymmetric Simple Exclusion Process)模型,使用蒙特卡洛方法模拟开放边界条件下不同车辆更新方式对稳态时车辆特性及相变行为的影响,得到不同注入概率α和输出概率β条件下的交通流基本图。结果表明,不同更新方式对系统的稳态特性及相变行为有较大影响,流量和密度随α和β的不同而变化,模拟结果与解析解吻合。随机更新方式下道路车流量的大小由输出概率决定,当输出概率达到一定值时,它的增大无法提高道路上的车流量;顺序更新方式的优点是仅当输入和输出概率都相等时,系统保持畅行相;而局部并行更新方式下得出的相图则与顺序和全局并行更新这两种方式下得到的相图类似且可以更好地反映交通流现实。     

Thermogenic Effect from Nutritionally Enriched Coffee Consumption

Background  

The purpose of this study was to examine the effect of nutritionally enriched JavaFit™ (JF) coffee (450 mg of caffeine, 1200 mg of garcinia cambogia, 360 mg of citrus aurantium extract, and 225 mcg of chromium polynicotinate) on resting oxygen uptake (VO₂), respiratory exchange ratio (RER), heart rate (HR), and blood pressure (BP) in healthy and physically active individuals.     

Braking Behavior of C/SiC Composites Prepared by Chemical Vapor Infiltration

Carbon fiber-reinforced silicon carbide matrix composites have the potential to overcome the shortcoming of the currently used carbon/carbon friction materials in aircraft brakes. In this article, the carbon/silicon carbide (C/SiC) composites were prepared by chemical vapor infiltration method, and the brake disks with different densities and component content were finally obtained. The friction coefficient and friction stability can be significantly improved by increasing both material density and carbon content. When the density of C/SiC composite is 2.3 g/cm³, the coefficient of friction measured is 0.23, the coefficient of friction stability remains about 0.43, the liner wear rate is less than 9.3 μm/cycle, and the weight wear rate is less than 9.1 μm/cycle. The rapid increase of friction coefficient approaching the end of braking is mainly related to the increasing of surface temperature in a short time and the enhanced adhesion and abrasion of contact conjunctions and asperities. The C/SiC composites exhibited a good stability of braking against fading versus the braking number and surface temperature. The surfaces of C/SiC brake disks were covered with wear debris including the fragment of carbon fibers after the braking tests. The wear on the surfaces is significantly determined by cyclic mechanical and thermal stresses, which result in the micro-cracks in the SiC matrix, the thin flakes of the surface materials as well as the grooves.     

熔融缩聚法制备聚乳酸

通过熔融缩聚法制备了聚乳酸。探讨了反应温度、催化剂类型及用量、反应时间对聚乳酸的影响，并用红外光谱和1↑H NMR对聚合物进行了表征。结果表明，最佳的反应条件为：聚合时间30h左右、聚合温度160℃、以O．2％的对甲苯磺酸作为酸催化剂、O．5％的氯化亚锡为催化剂、真空度为O—1333Pa；而提高乳酸纯度是制备高摩尔质量聚乳酸的关键条件之一。     

冲压式舵机动态特性测试系统的研制

为了在实验室条件下模拟冲压式舵机的舵面在空中所受的气动载荷,实现舵机系统动态性能指标的综合检测,设计了基于PXI总线的舵机动态测试系统,工作过程中对舵偏角信号、工作电流信号、扭矩信号进行实时采集、显示,并配合测试流程完成对舵机动态性能的测试。设计中重点考虑了定刚度加载系统的小扭矩加载精度、小转动惯量以及同轴度问题。实验结果表明,该测试系统测试精度高、使用维护方便,满足要求。     

Enhanced Photocatalytic Hydrogen Evolution Over CaTi1−x Zr x O3 Composites Synthesized by Polymerized Complex Method

The solid solution of CaTi_1−x Zr _x O₃ (x = 0–0.15) was successfully synthesized by the polymerized complex (PC) method. This study has exhibited the advantage of the PC method to prepare a highly active CaTiO₃ compared with the conventional solid-state reaction (SSR) method. More importantly, further improvement in phase purity and large surface area was achieved by the doping of Zr⁴⁺, leading to remarkable enhancement of photocatalytic activities compared to pure CaTiO₃. The quantum yield for H₂ evolution over the most active photocatalyst, Pt (1.0 wt%)/CaTi_0.93Zr_0.07O₃, was 1.91% and 13.3% in photoreactions from pure water and aqueous ethanol solution, respectively for 0.1 g photocatalyst, which was about 3.3 and 2.5 times compared to that of PC-derived CaTiO₃.