多通道GPS共视法时频传递接收机的研制

GPS共视法是国际上流行的远距离时间频率传递技术,核心是共视法接收机。我们成功研制了多通道GPS共视法时频传递接收机系统,硬件部分主要由自主研制的高精度时间间隔计数器和Motorola生产的VPONCORE GPS引擎组成,软件符合时间频率咨询委员会(CCTF)发布的GPS共视法数据处理软件标准化指南的要求,与单通道GPS定时接收机相比,界面更友好,操作更方便,具有很强的分析处理数据功能。经测试证明多通道GPS接收机零基线共钟共视时间比对的不确定度小于4 ns(仰角40°),与国外报道基本相同。     

生物智能型算法在信道分配策略中的应用

由于同步轨道卫星通信的传输时延较长,因此该类卫星对动态信道分配算法的延时性能非常敏感。针对宽带多媒体通信卫星的动态信道分配问题建立数学模型,并且使用生物智能型算法进行求解。仿真结果表明,与传统的分支定界法相比,采用生物智能型算法求解动态信道分配问题,其延时性能提高47%,并能得到更为高效的信道分配方案。     

GLONASS-based precise point positioning and performance analysis

Current precise point positioning (PPP) techniques are mainly based on GPS which has been extensively investigated. With the increase of available GLONASS satellites during its revitalization, GLONASS observations were increasingly integrated into GPS-based PPP. Now that GLONASS has reached its full constellation, there will be a wide interest in PPP systems based on only GLONASS since it provides a PPP implementation independent of GPS. An investigation of GLONASS-based PPP will also help the development of GPS and GLONASS combined PPP techniques for improved precision and reliability. This paper presents an observation model for GLONASS-based PPP in which the GLONASS hardware delay biases are addressed. In view of frequently changed frequency channel number (FCN) for GLONASS satellites, an algorithm has been developed to compute the FCN for GLONASS satellites using code and phase observations, which avoids the need to provide the GLONASS frequency channel information during data processing. The observation residuals from GLONASS-based PPP are analyzed and compared to those from GPS-based PPP. The performance of GLONASS-based PPP is assessed using data from 15 globally distributed stations.     

Calcium influx through stretch-activated channels mediates microfilament reorganization in osteoblasts under simulated weightlessness

We have explored the role of Ca²⁺ signaling in microfilament reorganization of osteoblasts induced by simulated weightlessness using a random positioning machine (RPM). The RPM-induced alterations of cell morphology, microfilament distribution, cell proliferation, cell migration, cytosol free calcium concentration ([Ca²⁺]_i), and protein expression in MG63 osteoblasts were investigated. Simulated weightlessness reduced cell size, disrupted microfilament, inhibited cellular proliferation and migration, and induced an increase in [Ca²⁺]_i in MG63 human osteosarcoma cells. Gadolinium chloride (Gd), an inhibitor for stretch-activated channels, attenuated the increase in [Ca²⁺]_i and microfilament disruption. Further, the expression of calmodulin was significantly increased by simulated weightlessness, and an inhibitor of calmodulin, W-7, aggravated microfilament disruption. Our findings demonstrate that simulated weightlessness induces Ca²⁺ influx through stretch-activated channels, then results in microfilament disruption.     

旋转叶片尾缘通道的换热特性

用实验的方法研究了旋转和静止状态下带交错肋和柱肋的涡轮叶片尾缘通道的换热特性.通道截面为楔形,交错肋段上下表面肋错开布置,节距比约为7,柱肋段包含大小两排扰流柱.在实验雷诺数为6 100~33 000,旋转数0~0.6的工况下对比分析了尾缘通道交错肋段和柱肋段的旋转静止换热特性.研究结果表明:静态下,交错肋段前后缘面存在换热差异,且该差异沿程减小;在交错肋充分发展段,旋转增强了后缘面的换热,削弱了前缘面的换热;交错肋段前后缘面叶间处换热旋转下均得到增强;旋转下柱肋段的过渡段尺度减小,换热最强点向低半径处偏移.     

ArcGIS中基于 DEM提取沟道特征

以陕西省延安市大南沟小流域5 m分辨率DEM数据为基础,利用ArcGIS9.3的grid模块平台提取研究区的沟道特征。在对原始地形数据进行填洼预处理后,生成河道沟系走向栅格数据、流域汇水面积栅格数据;然后,设定合适的临界汇水面积值提取出河道沟系;最后,对河道沟系进行分级。结果显示,提取出的沟道系统与实际基本吻合。     

八面体桁架结构在内冷通道中的流动传热特性研究

为探究八面体桁架结构在航空发动机热端部件内冷通道中的可应用性,掌握八面体桁架结构的流动传热特性,本文采用理论推导和三维数值模拟的方法,对八面体桁架单体的有效导热系数以及八面体桁架阵列结构的流动结构和传热性能开展了研究。首先,针对八面体桁架单体结构,推导出了考虑节点效应的有效导热系数关系式,并通过与数值计算结果对比,验证了其有效性。其次,针对八面体桁架阵列结构,开展了整体结构的三维数值计算,分析了其内部通道的流动结构和温度分布,获得了不同结构的流动阻力和对流传热系数随雷诺数的变化规律。最后,考虑到结构的综合传热性能,本文针对不同孔隙率的八面体桁架阵列结构,进行了基于相同泵功率下努塞尔数的对比。根据计算结果,本文给出了获得最佳传热性能的无量纲直径范围0.07~0.08,相应的孔隙率变化范围 0.872~0.841。分析其原因,由于随着结构孔隙率的减小,即固体率的增加,对流传热强度不断提高,然而,当孔隙率减小到84.1%以下时,由于内通道中流动阻力骤然增大,导致传热效率降低。将八面体桁架结构应用于航空发动机热端部件内冷通道中,是同时出于高效冷却和力学性能的考虑,本文掌握八面体桁架阵列结构的流动传热特性,为其在实际工程中的应用提供了理论支撑。     

主动冷却薄壁结构的通道布局与形状优化

针对基于传统分析方法的超然冲压发动机燃烧室主动冷却设计存在通用性差、周期长问题,采取子结构法建立主动冷却通道体胞的流固热多场耦合有限元模型,在与实验对比验证有限元模型有效性基础上,分析了结构质量和质量流率不变时通道数目对换热性能的影响;采用超椭圆方程描述通道截面形状,结合Kriging响应面和多目标遗传算法,开展了最小...     

排焰道流动损失对地下井引射性能的影响

针对地下井引射器设计问题,基于引射器函数理论和可压缩流体管道流动理论,提出了一种考虑排焰道流动损失的地下井引射器描述方法,并结合理想引射器数学模型,分别建立了考虑排焰道流动损失的基本引射器数学模型和极限引射器数学模型.基于这两个数学模型,引入考虑排焰道流动损失的引射器函数和静压协调函数,分析了发动机总压、混合室直径、总...