一种北斗联合低轨星座的导航增强方法研究

单纯依靠北斗导航系统提供定位导航授时服务,存在卫星信号落地功率低、易受遮蔽和阻断的不足。针对此问题,研究了一种北斗联合低轨星座实现导航增强的系统架构;提出了一种新的适应严重遮蔽或干扰条件下,基于到达时间(TOA)和到达频率(FOA)联合观测的定位解算算法;对高中低轨混合星座条件下的覆盖特性和精度衰减因子进行了仿真分析。分析结果表明,用户可见星数平均增加了64.2%,位置精度衰减因子(PDOP)平均改善了28.7%。研究结果可为下一代北斗的论证设计与研制建设提供参考借鉴。     

Triangle strings: Structures for augmentation of vertex-disjoint triangle sets

Vertex-disjoint triangle sets (triangle sets for short) have been studied extensively. Many theoretical and computational results have been obtained. While the maximum triangle set problem can be viewed as the generalization of the maximum matching problem, there seems to be no parallel result to Berge's augmenting path characterization on maximum matching (C. Berge, 1957 [1]). In this paper, we describe a class of structures called triangle string, which turns out to be equivalent to the class of union of two triangle sets in a graph. Based on the concept of triangle string, a sufficient and necessary condition that a triangle set can be augmented is given. Furthermore, we provide an algorithm to determine whether a graph G with maximum degree 4 is a triangle string, and if G is a triangle string, we compute a maximum triangle set of it. Finally, we give a sufficient and necessary condition for a triangle string to have a triangle factor.     

Unpowered Knee Exoskeleton Reduces Quadriceps Activity during Cycling

Cycling is an eco-friendly method of transport and recreation. With the intent of reducing the energy cost of cycling without providing an additional energy source, we have proposed the use of a torsion spring for knee-extension support. We developed an exoskeleton prototype using a crossing four-bar mechanism as a knee joint with an embedded torsion spring. This study evaluates the passive knee exoskeleton using constant-power cycling tests performed by eight healthy male participants. We recorded the surface electromyography over the rectus femoris muscles of both legs, while the participants cycled at 200 and 225 W on a trainer with the developed wheel-accelerating system. We then analyzed these data in time–frequency via a continuous wavelet transform. At the same cycling speed and leg cadence, the median power spectral frequency of the electromyography increases with cycling load. At the same cycling load, the median power spectral frequency decreases when cycling with the exoskeleton. Quadriceps activity can be relieved despite the exoskeleton consuming no electrical energy and not delivering net-positive mechanical work. This fundamental can be applied to the further development of wearable devices for cycling assistance.     

Two augmentation preconditioners for nonsymmetric and indefinite saddle point linear systems with singular (1, 1) blocks

In this paper, two preconditioners based on augmentation are introduced for the solution of large saddle point-type systems with singular (1, 1) blocks. We study the spectral characteristics of the preconditioners, show that all eigenvalues of preconditioned matrices are strongly clustered. Finally, numerical experiments are also reported for illustrating the efficiency of the presented preconditioners.     

辐射换热器一次侧强化传热的研究之一

本文利用蒙特卡洛法对同心套筒式辐射换热器的一次侧强化侍热进行了数值研究,讨论了插入件强化一次侧传热的机理,并得到了插入件的最佳强化传热尺寸。     

CFD analysis of natural convection heat transfer augmentation from square conductive horizontal and inclined pin fin arrays

Numerical investigations on natural convection heat transfer from a vertical isothermal plate with pin fins have been made by solving the Navier–Stokes equation along with the energy equation. Average Nusselt number for the plate with different configurations of pin fins have been obtained. It was observed that the maximum increase of the average Nusselt number occurs at S_v/L?=?0.2 for θ?=?45° with fin height of 24?mm (H/t?=?8). The average Nusselt number increases with fin aspect ratio and decreases with angle of inclination. There is not much difference between the average Nusselt number for in-line and staggered arrangement of fins for the range of parameters studied in the present work. A correlation is developed to predict the average Nusselt number of the plate as a function of fin spacing in stream- and span-wise direction, aspect ratio of fins and its angle of inclination.     

增益指数检测在高血压健康管理中的应用

目的研究桡动脉反射波增益指数（Augmentation Index,AI）水平与高血压患者心脏舒张功能、肾脏功能之间关系,探讨AI水平变化在高血压健康管理评价中的作用。方法对符合入选条件的105例高血压患者进行桡AI、proBNP水平测定、肾脏功能测定及超声心动图检查,并进行相关分析,绘制AI的受试者特征曲线并评价其在心脏舒张功能不全中的作用。结果proBNP水平升高组患者AI水平明显增加,而肾功能减退组患者AI水平相应增加,proBNP与AI正向相关,相关系数0．3697（P=0．003）。肌酐清除率与AI水平之间存在负相关,相关系数为-0．348（P〈0．05）。受试者工作特征曲线提示以AI诊断舒张功能不全的最佳临界值为85．5,该点灵敏度0．909,特异度0．889。结论桡动脉AI水平变化反映高血压患者心脏舒张功能状态的变化,亦能体现高血压肾脏功能状态的改变,可作为高血压健康管理的动态随访无创性指标.     

Performance of the herringbone wavy fin under dehumidifying conditions

An experimental study reporting the airside performance of the herringbone wavy fin geometry in wet conditions is conducted. In the visualization of the condensate flow pattern, a very special “locally dry” spot of the corrugation wavy channel having a corrugation angle of 15° and a fin spacing of 8.4 mm is seen. This phenomenon is related to the recirculation of the airflow across the apex. Conversely, this phenomenon is not so clearly seen either for a fin pitch of 2.6 mm with a corrugation angle of 15° or a corrugation angle of 25°. Flow visualization of the non-uniform distribution of the condensation in the facets results in a dependence between axial length and friction factor. Based on the present test results, airside performance in terms of Nusselt number and Fanning friction factor for the present herringbone wavy fin geometry in wet conditions are developed. The mean deviations of the proposed correlations are 2.52% and 4.81%, respectively.     

美国星基增强系统发展现状和未来

本文介绍了星基增强系统产生的背景以及美国的星基增强系统WAAS（广域增强系统）的系统架构,回顾了WAAS（广域增强系统）的发展历史,分析了WAAS（广域增强系统）的发展现状和未来的发展方向。     

Afterburn Ignition Delay and Shock Augmentation in Fuel Rich Solid Explosives

We present experimental and computational results that explain some aspects of measured energy release in explosions of unconfined trinitrotoluene [TNT, C₆H₂(NO₂)₃CH₃], and an aluminum‐containing explosive formulation, and show how this energy release can influence shock wave velocities in air. In our interpretation, energy release is divided into early, middle, and late time regimes. An explanation is provided for the interdependence of the time regimes and their influence on the rate at which energy (detonation/explosion and afterburn) is released. We use a merging of the thermodynamic and chemical kinetic processes that predicts how chemical kinetics may determine the time delay of the afterburn of combustible gases produced by the initial detonation/explosion/fast reaction. The thermodynamic computer code CHEETAH is used to predict gaseous and solid products of early time energy release, and a chemical kinetic reaction mechanism (CHEMKIN format) is used to describe the subsequent afterburn of the gas phase products in air. Results of these calculations are compared with field measurements of unconfined explosions of 2 kg charge weights of TNT and an aluminum‐containing explosive formulation.