有耗媒质表面阻抗的计算及应用

给出了在不满足阻抗边界条件所需的几个条件下有耗媒质表面阻抗的分析和计算方法。文章采用传输线理论考虑了复折射角,给出了平面多层有耗媒质表面阻抗的具体计算表达式。对于圆柱多层材料表面阻抗的计算进行了讨论,提出了模式表面阻抗及平均表面阻抗的概念。文章还给出了应用实例。数值计算及实验表明,用本文的方法计算的表面阻抗而求出的具有开槽的表面阻抗加载的二维柱劈融合体的RCS与实验结果基本~致。     

氮化硅短纤维多孔材料制备与性能研究

以氮化硼为烧结助剂,采用抽滤成型方法制备氮化硅短纤维多孔材料。通过氮化硼和氮化硅纤维的氧化过程分析,确定了最佳烧结制度。对不同氮化硼含量材料的微观结构、压缩及介电性能进行了测试分析。结果表明:在1 200℃时,氮化硼氧化增重达20%,氮化硅纤维表面明显氧化;随着氮化硼含量的增加,氮化硅纤维粘结明显,粘结点主要成分为二氧化硅和硼硅酸盐,氮化硅短纤维多孔材料的ε随着密度的增加从1. 36增加到1. 62,tanδ从7. 8×10~(-4)增加到9. 5×10~(-4),材料10%压缩应变下的压缩强度从0. 58 MPa提升到2. 03 MPa。     

空间液体润滑多孔储油器特性研究

液体润滑普遍存在于大多数空间运动部件中.然而,由于空间环境恶劣(低重力、高真空)所造成的润滑剂严重损失,许多液体润滑运动部件都不能达到其使用寿命的要求.因此,有必要采取措施对空间运动部件进行补油,利用多孔储油器补油便是其中的方法之一.由于其体积小、结构简单而广泛应用于小型航天仪器中,并在维持轴承腔内油膜厚度和油分布方面也能取得令人满意的效果,因此备受关注.离心作用和加热效应是使储油器溢油的两种方法,本文针对这两种方法,对空间多孔储油器的液体润滑剂储运规律进行理论分析,同时设计了离心供油和加热供油两套实验装置.      

Equilibration Processes in the Warm-Hot Intergalactic Medium

The Warm-Hot Intergalactic Medium (WHIM) is thought to contribute about 40–50% to the baryonic budget at the present evolution stage of the universe. The observed large scale structure is likely to be due to gravitational growth of density fluctuations in the post-inflation era. The evolving cosmic web is governed by non-linear gravitational growth of the initially weak density fluctuations in the dark energy dominated cosmology. Non-linear structure formation, accretion and merging processes, star forming and AGN activity produce gas shocks in the WHIM. Shock waves are converting a fraction of the gravitation power to thermal and non-thermal emission of baryonic/leptonic matter. They provide the most likely way to power the luminous matter in the WHIM. The plasma shocks in the WHIM are expected to be collisionless. Collisionless shocks produce a highly non-equilibrium state with anisotropic temperatures and a large differences in ion and electron temperatures. We discuss the ion and electron heating by the collisionless shocks and then review the plasma processes responsible for the Coulomb equilibration and collisional ionisation equilibrium of oxygen ions in the WHIM. MHD-turbulence produced by the strong collisionless shocks could provide a sizeable non-thermal contribution to the observed Doppler parameter of the UV line spectra of the WHIM.     

考虑辐射效应的多孔材料传热有限元算法

应用有限元法求解一维半透明多孔介质辐射对流传热问题。通过对辐射传递方程与边界条件中积分项的离散 ,推导出有限元求解列式。对于多孔介质传热控制方程和气体传热控制方程的求解 ,采用时间积分技术对两相温度统一进行求解。而对于边界方程处理 ,则通过传热方程与边界方程的循环求解 ,求出任意时刻温度场的瞬态解。给出数值算例 ,得出了放置在通风口、同时受到伴随辐射作用的半透明多孔介质传热的瞬态解 ,讨论了部分参数对瞬态温度场以及换热效果的影响      

Structure of low-head two-phase flow in flat nozzles during outflow of the liquid into rarefied medium

Outcomes of experimental researches of the low-pressure adiabatic flow of the boiling liquid through two-dimensional Laval nozzles in a vacuum atmosphere were adduced. Requirements of critical conditions of flow were determined. Structural forms of a stream were investigated and their connection with crisis of flow was shown. It was established periodic non-stationary macrostructures of a stream which was stipulated by the rotational gear of origin of a vapor phase.      

Local Interstellar Medium Summary of Working Group VI

This report summarizes the issues discussed in Working Group VI concerning the accuracy of measurements of D/H and 3He/H in the local interstellar medium, possible systematic errors, and emerging trends in the results.     

Observations of Extended Radio Emission in Clusters

We review observations of extended regions of radio emission in clusters; these include diffuse emission in ‘relics’, and the large central regions commonly referred to as ‘halos’. The spectral observations, as well as Faraday rotation measurements of background and cluster radio sources, provide the main evidence for large-scale intracluster magnetic fields and significant densities of relativistic electrons. Implications from these observations on acceleration mechanisms of these electrons are reviewed, including turbulent and shock acceleration, and also the origin of some of the electrons in collisions of relativistic protons by ambient protons in the (thermal) gas. Improved knowledge of non-thermal phenomena in clusters requires more extensive and detailed radio measurements; we briefly review prospects for future observations.     

中介粗集及其在数据挖掘中的应用

粗集理论已成功应用于数据挖掘,如基于粗集方法的属性发现和决策规则的约简等。中介集合论是以中介逻辑为基础,也可以用于数据挖掘。文中将两者相结合,提出了中介粗集的概念。中介粗集是普通粗集的推广,为不完全信息系统的数据挖掘提供了新的工具,不仅可用于一般的信息系统,还适用于数据取空值的信息系统（允许结论取空值）。利用中介粗集进行数据挖掘不但可以得出粗集理论中的约简,还能得到更为简洁的中介约简。文中还给出了     

纳米复合相变材料熔化过程数值模拟

相变储能技术在航空航天等领域具有广泛的应用前景,但是相变材料导热性能差制约了其工程化应用。高导热的纳米材料能够有效提高相变材料的导热性能。为了对其相变现象进行更精细的模拟分析,基于Maxwell-Garnett等效介质理论（EMT）建立3种具有代表性结构的纳米复合相变材料详细物性参数,将流体体积（VOF）模型与焓-多孔介质模型相耦合,在考虑相变材料体积膨胀的情况下,数值模拟了纯石蜡、添加不同体积组分金刚石纳米粒子（ND）、单壁碳纳米管（SWCNT）和石墨烯纳米片（GnP）的纳米复合相变材料在定温边界条件下的固液相变过程。结果表明:相变材料熔化过程中对流效应主要分布在临近固液相界面、临近加热壁面及临近气液两相交界面这3个区域;3种纳米粒子中GnP的导热强化效果最佳,相比纯石蜡,添加体积分数为3%的GnP纳米复合相变材料固相导热系数提高了486%,相变材料的熔化时间缩短了69%;升高壁面温度能够有效缩短复合相变材料的熔化时间。