Interior Evolution of Mercury

The interior evolution of Mercury—the innermost planet in the solar system, with its exceptional high density—is poorly known. Our current knowledge of Mercury is based on observations from Mariner 10’s three flybys. That knowledge includes the important discoveries of a weak, active magnetic field and a system of lobate scarps that suggests limited radial contraction of the planet during the last 4 billion years. We review existing models of Mercury’s interior evolution and further present new 2D and 3D convection models that consider both a strongly temperature-dependent viscosity and core cooling. These studies provide a framework for understanding the basic characteristics of the planet’s internal evolution as well as the role of the amount and distribution of radiogenic heat production, mantle viscosity, and sulfur content of the core have had on the history of Mercury’s interior. The existence of a dynamo-generated magnetic field suggests a growing inner core, as model calculations show that a thermally driven dynamo for Mercury is unlikely. Thermal evolution models suggest a range of possible upper limits for the sulfur content in the core. For large sulfur contents the model cores would be entirely fluid. The observation of limited planetary contraction (∼1–2 km)—if confirmed by future missions—may provide a lower limit for the core sulfur content. For smaller sulfur contents, the planetary contraction obtained after the end of the heavy bombardment due to inner core growth is larger than the observed value. Due to the present poor knowledge of various parameters, for example, the mantle rheology, the thermal conductivity of mantle and crust, and the amount and distribution of radiogenic heat production, it is not possible to constrain the core sulfur content nor the present state of the mantle. Therefore, it is difficult to robustly predict whether or not the mantle is conductive or in the convective regime. For instance, in the case of very inefficient planetary cooling—for example, as a consequence of a strong thermal insulation by a low conductivity crust and a stiff Newtonian mantle rheology—the predicted sulfur content can be as low as 1 wt% to match current estimates of planetary contraction, making deep mantle convection likely. Efficient cooling—for example, caused by the growth of a crust strongly in enriched in radiogenic elements—requires more than 6.5 wt% S. These latter models also predict a transition from a convective to a conductive mantle during the planet’s history. Data from future missions to Mercury will aid considerably our understanding of the evolution of its interior.     

A superposed epoch study of the effects of solar wind stream interface events on the upper mesospheric and lower thermospheric temperature

The response of mesosphere and lower thermosphere (MLT) temperature to energetic particle precipitation over the Earth’s polar regions is not uniform due to complex phenomena within the MLT environment. Nevertheless, the modification of MLT temperatures may require an event-based study to be better observed. This work examines the influence of precipitation, triggered by solar wind stream interfaces (SI) event from 2002 to 2007, on polar MLT temperature. We first test the relationship between the ionospheric absorption measured by the SANAE IV (South African National Antarctic Expedition IV) riometer and the layer of energetic particle precipitation from POES (Polar Orbiting Environmental Satellites). The combined particle measurements from POES 15, 16, 17 and 18 were obtained close in time to the pass of the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature retrieval. Here, a superposed epoch technique is described and implemented to obtain average temperature profiles during SI-triggered particle precipitation. The superposed epoch average shows no significant temperature decrease below 100 km prior to the onset of SI-triggered precipitation, whereas a clear superposed average temperature decrease is observed at 95 km after the SI impact. A case study of SI event also yields similar observations. Results indicate that cooling effects due to the production of mesospheric odd hydrogen might be major contributors to temperature decrease under compressed solar wind stream.     

Dynamics of the convection in the inner magnetosphere by observations of the diffuse aurora,SAR arc and ionospheric drift

The first results of the comparison of subauroral luminosity dynamics in 557,7 and 630,0 nm emission with simultaneous measurements of the ionospheric drift in the F2 region with a digisonde DPS-4 at the Yakutsk meridian (CGMC: 55–60N, 200°E) at Kp = 2–6 are presented. It is shown from the analysis of individual events that during the magnetospheric convection intensification after the turn of the IMF B_z – component to the south the equatorward extension of diffuse aurora takes place. At the same time the westward ionospheric drift velocity increases both in the diffuse aurora region and much equatorward of it due to the occurrence of the northward polarization electric field. We suppose that the generation of polarization field can be associated with the development of the region 2 FAC during the intensification of magnetospheric convection. The comparison of ground-based observations with measurements of the plasma drift aboard the DMSP-F15 satellite has been carried out.     

基于集对理论的空间战场态势定量分析

以集对分析的同异反联系度为基础,结合武器与人员因素分析战场态势。从全局的角度,对空间战场整体态势进行研究,引入指标权重,构建空间战场态势分析模型,通过实例计算分析空间战场态势优劣。     

Dynamic particle accumulation structure (PAS) in half-zone liquid bridge – Reconstruction of particle motion by 3-D PTV

Three-dimensional (3-D) velocity field reconstruction of oscillatory thermocapillary convections in a half-zone liquid bridge with a radius of O (1 mm) was carried out by applying 3-D particle tracking velocimetry (PTV). Simultaneous observation of the particles suspended in the bridge by two CCD cameras was carried out by placing a small cubic beam splitter above a transparent top rod. The reconstruction of the 3-D trajectories and the velocity fields of the particles in the several types of oscillatory-flow regimes were conducted successfully for sufficiently long period without losing particle tracking. With this application the present authors conducted a series of experiments focusing upon the collapse and re-formation process of the PAS by mechanically disturbing fully developed PAS.     

垂直平板层流自然对流的群论分析

本文对由热、质最扩散和化学反应引起的垂直平板定常层流自然对流问题用Ｍｏｒｇａｎ变换群理论进行了分析，得到了壁面温度和浓度分布均按变化时的相似性方程组，并用Ｒｕｎｇｅ－Ｋｕｔｔａ方法和Ｎａｃｈｔｓｈｅｉｎ－Ｓｗｉｇｅｒｔ迭代法，在Ｐｒ＝０．７２和不同的施密特数Ｓ＿ｃ、反应阶ｎ和参数Ｐ、Ｑ下进行了数值求解。给出了相应的速度分布、温度分布和浓度分布曲线。     

层间叉排微针肋液体冷却3D-IC流动及换热特性

用数值模拟的方法,研究了散热面积为1cm2带有层间微散热结构双面均热发热3D-IC内部流体层流流动与换热,对体积流量在36~290mL/min范围内,通道高度为200μm,通道间距为200μm的带有矩形微通道和叉排微针肋液体冷却3D-IC(three-dimensional integration circuit)的流动与换热进行了分析.结果表明:带有层间叉排微针肋液体冷却3D-IC具有良好的换热效果,在热流密度为1.25MW/m2,体积流量为290mL/min时,其发热面平均温度、最大温度只有318.31,323.16K,分别最大减小了12.31,20.14K,此时的功率为250W、体积热源为8.3kW/cm3.      

控制翼缝隙流传热实验研究

在Μ_∞=6.5—10,Re_∞=(0.35—3.5)×10~7m~(-1)的来流条件下测量了平板-控制翼上及其展向缝隙内的热流分布,以考察缝隙宽、翼偏转角、缝入口唇缘形状、来流参数对缝内外气动热的影响。     

冲击加发散双层壁冷却方式压降分配对斜孔内对流换热影响的研究

 以高推重比发动机燃烧室单位压力单位面积冷却气量为基准,研究了孔数比为1∶1 的冲击/ 发散冷却方式在不同冲击壁和发散孔壁压降分配情况下的发散斜孔内的局部换热系数和平均换热系数。研究发现,压降分配比例的变化对孔进口区( x/ d < 4) 的换热增强有较大的影响。通过CFD 计算孔内的流动,分析了孔进口区换热系数增强的原因。并给出了周向平均换热增强系数的拟合公式,为进一步的换热优化打下了基础。     

利用PIV方法测量半浮区液桥热毛细对流的速度场

利用PIV法对硅油液桥热毛细对流的定常速度场进行了实时测量。为了便于测量,液桥上桥端面采取了铜环中嵌透明材料的方法,从液桥的顶部进行观测。当液桥上下桥有温差时,热毛细对流出现;本实验对于不同上下桥的温差,对液桥横剖面内的速度场分别进行了测量,研究外加温差对于流场速度分布的影响;并且在液桥中取了几个典型横截面进行测量,以期对大Pr数液桥的定常速度场有比较全面的定量测量。此外,实验结果也可作为数值模拟计算结果的验证。