Parallel Fully-Implicit Computation of MHD Acceleration Experiments

A three-dimensional MHD solver is described in the paper. The solver simulates reacting flows with nonequilibrium between translational-rotational, vibrational and electron translational modes. The conservation equations are discretized with implicit time marching and the second-order modified Steger-Warming scheme, and the resulted linear system is solved iteratively with Newton-Krylov-Schwarz method that is implemented by PETSc package. The results of convergence tests are plotted, which show good scalability and convergence around twice faster when compared with the DPLR method. Then five test runs are conducted simulating the experiments done at the NASA Ames MHD channel, and the calculated pressures, temperatures, electrical conductivity, back EMF, load factors and flow accelerations are shown to agree with the experimental data. Our computation shows that the electrical conductivity distribution is not uniform in the powered section of the MHD channel, and that it is important to include Joule heating in order to calculate the correct conductivity and the MHD acceleration.

Thermodynamic analysis of GaSb-GaCl3 vapor phase epitaxy

A thermodynamic model for the GaSb-GaCl3 system in a closed quartz ampoule was proposed. The species in the gas phase are GaCl, GaCl3, Sb-4, Sb-2. The partial pressures of these species and total pressure in the ampoule have been calculated. The calculated results indicate that the equilibrium partial pressures of GaCl, GaCl3, Sb4, Sb2 and the total pressure in the ampoule have strong dependence on temperature, free volume inside the closed ampoule and amount of transport agent GaCl3. The total pressure will give strong influence not only on the flow pattern in the ampoule, but also on the uniformity of the epilayer.

Effect of rapid thermal annealing on the Raman spectrum of Si0.33Ge0.67/Si (100) alloy

The effect of thermal annealing on the Raman spectrum of Si0.33Ge0.67 alloy grown on Si (100) by molecular beam epitaxy is investigated in the temperature range of 550-800 degrees C. For annealing below 700 degrees C, interdiffusion at the interface is negligible and the residual strain plays the dominant role in the Raman shift. The strain-shift coefficients for Si-Ge and Ge-Ge phonon modes are determined to be 915 +/- 215 cm(-1) and 732 +/- 117 cm(-1), respectively. For higher temperature annealing, interdiffusion is significant and strongly affects the Raman shift and the spectral shape.

Stoichiometry in GaAs grown in outer space measured nondestructively

A semi-insulating (SI) GaAs single crystal ingot was successfully grown in a recoverable satellite. The two-dimensional distribution of stoichiometry in space-grown SI-GaAs single crystal wafer was studied nondestructively based upon x-ray Band diffraction. The avenge stoichiometry in the space-grown crystal is 0.50007 with mean square deviation of 6 x 10(-6), and shows a better stoichiametric property than the ground-grown SI-GaAs. The average etch pit density (EPD) of dislocations in the crystal revealed by molten KOH is 2.0 x 10(4) cm(-2), and the highest EPD is 3.1 x 10(4) cm(-2). This result indicates that the structural properly of the crystal is quite good.

Parallel Fully-Implicit Computation of Magnetohydrodynamics Acceleration Experiments

A three-dimensional MHD solver is described in the paper. The solver simulates reacting flows with nonequilibrium between translational-rotational, vibrational and electron translational modes. The conservation equations are discretized with implicit time marching and the second-order modified Steger-Warming scheme, and the resulted linear system is solved iteratively with Newton-Krylov-Schwarz method that is implemented by PETS,: package. The results of convergence tests arc plotted, which show good scalability and convergence around twice faster when compared with the DPLR method. Then five test runs are conducted simulating the experiments done at the NASA Ames MHD channel, and the calculated pressures, temperatures, electrical conductivity, back EMF, load factors and flow accelerations are shown to agree with the experimental data. Our computation shows that the electrical conductivity distribution is not uniform in the powered section of the MHD channel, and that it is important to include Joule heating in order to calculate the correct conductivity and the MHD acceleration.

Modeling study on the flow, heat transfer and energy conversion characteristics of low-power arc-heated hydrogen/nitrogen thrusters

A modeling study is conducted to investigate the effect of hydrogen content in propellants on the plasma flow, heat transfer and energy conversion characteristics of low-power (kW class) arc-heated hydrogen/nitrogen thrusters (arcjets). 1:0 (pure hydrogen), 3:1 (to simulate decomposed ammonia), 2:1 (to simulate decomposed hydrazine) and 0:1 (pure nitrogen) hydrogen/nitrogen mixtures are chosen as the propellants. Both the gas flow region inside the thruster nozzle and the anode-nozzle wall are included in the computational domain in order to better treat the conjugate heat transfer between the gas flow region and the solid wall region. The axial variations of the enthalpy flux, kinetic energy flux, directed kinetic-energy flux, and momentum flux, all normalized to the mass flow rate of the propellant, are used to investigate the energy conversion process inside the thruster nozzle. The modeling results show that the values of the arc voltage, the gas axial-velocity at the thruster exit, and the specific impulse of the arcjet thruster all increase with increasing hydrogen content in the propellant, but the gas temperature at the nitrogen thruster exit is significantly higher than that for other three propellants. The flow, heat transfer, and energy conversion processes taking place in the thruster nozzle have some common features for all the four propellants. The propellant is heated mainly in the near-cathode and constrictor region, accompanied with a rapid increase of the enthalpy flux, and after achieving its maximum value, the enthalpy flux decreases appreciably due to the conversion of gas internal energy into its kinetic energy in the divergent segment of the thruster nozzle. The kinetic energy flux, directed kinetic energy flux and momentum flux also increase at first due to the arc heating and the thermodynamic expansion, assume their maximum inside the nozzle and then decrease gradually as the propellant flows toward the thruster exit. It is found that a large energy loss (31-52%) occurs in the thruster nozzle due to the heat transfer to the nozzle wall and too long nozzle is not necessary. Modeling results for the NASA 1-kW class arcjet thruster with hydrogen or decomposed hydrazine as the propellant are found to compare favorably with available experimental data.

Numerical Simulation of a Low-power Hydrazine Arcjet Thruster

A modeling study is conducted to investigate the plasma flow and heat transfer characteristics of low-power (kW class) arc-heated thrusters (arcjets) with 2:1 hydrogen/nitrogen to simulate decomposed hydrazine as the propellant. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, the Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. Typical computed results about the temperature, velocity and Mach number distributions within arcjet thruster are presented for the case with arc current of 9 A and inlet stagnant pressure of 3.3×105 Pa to show the flow and heat transfer characteristics. It is found that the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip, and the flow transition from the subsonic to supersonic regime occurs within the constrictor region. The effect of gas viscosity on the plasma flow within arcjet thruster is examined by an additional numerical test using artificially reduced values of gas viscosity. The test results show that the gas viscosity appreciably affects the plasma flow and the performance of the arcjet thruster for the cases with the hydrazine or hydrogen as the propellant. The integrated axial Lorentz force in the thruster nozzle is also calculated and compared with the thrust force of the arcjet thruster. It is found that the integrated axial Lorentz force is much smaller than the thrust force for the low-power arcjet thruster. Modeling results for the NASA 1-kW class arcjet thruster with simulated hydrazine as the propellant are found to be reasonably consistent with available experimental data.

基于LandsatTM/ETM数据的锡林河流域土地覆盖变化

根据1987年、1991年、1997年和2000年4期LandsatTM/ETM影像的土地利用/土地覆盖分类结果,运用地理信息系统空间分析方法,分析了内蒙古锡林河流域1987~2000年间各土地利用类型及草甸草原、典型草原、荒漠草原的数量变化和空间变化特征。分析结果显示,锡林河流域土地利用/土地覆盖变化的主要特征为草甸草原、典型草原面积的大幅减少和荒漠草原、农田和沙漠化土地面积的大幅增加及城镇的扩张。其中面积增加最大的是荒漠草原,增加了2328km2;相当于1987年荒漠草原面积的56%。农田和城镇面积逐年增大,分别从1987年的114.3km2和25.2km2增加到2000年的332.1km2和43.6km2。面积减少最多的是羊草+丛生禾草、羊草+杂类草等优良高产温带典型草原类型,共减少2040km2。草甸草原面积亦呈逐年减少的趋势,从1987年的1103km2减少到2000年375km2,面积减少了65.9%。农田、沙化地及城镇等非草原土地利用类型面积增加了62.5%。

基于MODIS数据的中国陆面制图:方法软件和数据产品(英文)

本文介绍一个自动处理MODIS1B数据并生产覆盖全中国陆面产品的软件系统。该算法改进了LAI(MOD15),土地覆被分类(MOD12),云检测(MOD35),陆面反射率(MOD09)和气溶胶(MOD04)产品。这些算法的输入数据都是本地获取的参数,能够有效降低其带来的不确定性。产生的部分新产品是NASA标准产品中没有的,包括森林火烧迹地和PAR。数据处理系统运行于中国科学院资源与环境数据中心。

The statistic inversion algorithms of water constituents for the Huanghai Sea and the East China Sea

A group of statistical algorithms are proposed for the inversion of the three major components of Case-H waters in the coastal area of the Huanghai Sea and the East China Sea. The algorithms are based on the in situ data collected in the spring of 2003 with strict quality assurance according to NASA ocean bio-optic protocols. These algorithms are the first ones with quantitative confidence that can be applied for the area. The average relative error of the inversed and in situ measured components' concentrations are: Chl-a about 37%, total suspended matter (TSM) about 25%, respectively. This preliminary result is quite satisfactory for Case-H waters, although some aspects in the model need further study. The sensitivity of the input error of 5% to remote sensing reflectance (Rrs) is also analyzed and it shows the algorithms are quite stable. The algorithms show a large difference with Tassan's local SeaWiFS algorithms for different waters, except for the Chl-a algorithm.

Remote sensing of ocean waves by polarimetric SAR

A new method to measure ocean wave slope spectra using fully polarimetric synthetic aperture radar (POLSAR) data was developed without the need for a complex hydrodynamic modulation transform function. There is no explicit use of a hydrodynamic modulation transfer function. This function is not clearly known and is based on hydrodynamic assumptions. The method is different from those developed by Schuler and colleagues or Pottier but complements their methods. The results estimated from NASA Jet Propulsion Laboratory (JPL) Airborne Synthetic Aperture Radar (AIRSAR) C-band polarimetric SAR data show that the ocean wavelength, wave direction, and significant wave height are in agreement with buoy measurements. The proposed method can be employed by future satellite missions such as RADARSAT-2.

不同类型生态系统水热碳通量的监测与研究

亚太地区环境革新战略项目(APEIS)在中国5种主要生态系统类型区(草地:海北、耕地:禹城、稻田:桃源、林地:千烟洲、荒漠:阜康)建立了一个以连续观测能量、水分和碳素通量为中心,包括气象、水文、土壤、植被等各项生态要素的监测网络系统,被称之为APEIS-FLUX系统.作者首先对APEIS-FLUX系统的观测数据进行了初步分析,表明该系统稳定可靠,它可以实时地提供高质量、高精度、长期而连续的通量及生态要素的观测数据.对数据的比较清楚地反映出了不同生态系统类型区的水热碳通量的差异性.其次,利用APEIS-FLUX数据对美国航空航天局(NASA)的MODIS数据产品进行比较验证后发现,除部分产品如地表面温度(MOD11)等与观测数据较吻合以外,大部分数据产品如土地覆盖(MOD12),叶面积指数(MOD15)和光合速率与净第一性生产力(MOD17)等都与观测数据相差深远,有必要对其处理程序和模式进行修正.为此,我们利用APEIS-FLUX的数据作为MOD15和MOD17的生成模型(BIOME-BGC)的输入数据,并对该模型的有关参数进行了修订.结果表明,该模式在通过修正后,可以很好地模拟植被的生长过程及其相应的水热碳循环过程.

亚太地区环境综合监测的研究方法--APEIS项目研究综述

为了对亚太地区的环境灾害、环境破坏和环境退化及其影响进行监测和评估,由日本环境省发起的亚太地区环境革新战略项目(APEIS)环境综合监测子项目(IEM)自2001年开始,建立了一个以MODIS卫星数据和地面观测资料为基础的综合环境监视网络系统.该网络系统起初是由日本国立环境研究所(NIES)和中国科学院地理科学与资源研究所(IGSNRR)共同合作建成的.之后,新加坡国立大学和澳大利亚联邦科学产业研究组织(CSIRO)地球观测中心也正式宣布加入,该系统覆盖整个亚太地区.美国宇航局(NASA)提供了一套MODIS的高级数据产品,然而,这些产品没能在亚洲地区利用当地的实测资料进行充分地比较和验证.APEIS项目旨在提供利用该地区精确地面观测数据进行了比较验证的高质量数据集.利用该数据集可以推导出水分亏缺指数、沙尘暴指数、地表面温度、土地覆盖变化,以及净第一性生产量等一系列生态环境指标,从而对环境破坏、环境退化和生态脆弱区进行长期有效的监测.为了评价水资源、食物生产等生态系所提供的产品与服务的现状和变化特征,本研究还开发了一个可利用MODIS数据的流域环境综合管理模型.该模型已经被用于对流域规模的水、热、碳循环、泥沙转移以及农业生产等生态要素的模拟和评估,并利用高精度的观测资料对其进行了验证.利用该模式可以对流域生态系统所提供的产品与服务的有效利用,以及流域的可持续发展提供一系列战略性的政策选项.

六轮摇臂式月球车环境交互动力学建模研究

目前，移动机器人被广泛应用于危险的非结构环境中，在诸如行星探测、灾难搜救、军事侦察、矿山开采等作业中， 机器人将起着越来越重要的作用。机器人在非结构环境中的运动能力和环境适应能力决定了机器人的作业性能。具备稳定性、机动性、越障能力、通过能力与可靠性的移动机器人将具有更好的环境适应能力，进而更好地完成作业任务。 本文针对中国科学院知识创新工程方向性项目“月球车月面探测作业支撑技术研究” 的实际需求， 在对国内外的同类研究深入分析综合的基础上， 对月球车移动系统与环境交互动力学的几个关键问题进行了研究与探讨。(1)研究月球车的运动稳定性和机动性问题。基于车体固定坐标系和地面固定坐标系， 分别建立了四轮转向的六轮摇臂转向架式月球车的转向动力学模型， 证明在两种坐标系下的模型转向动力学方程的一致性；分析了月球车运动的稳态特性和瞬态特性，采用机动性因子来定量地描述月球车运动的稳定性和机动性及其相互关系， 并用机动性因子来设计月球车的稳定性和机动性。(2)研究如何保持理想运动姿态的问题。建立了保持月球车运动姿态的理想模型， 模拟人驾驶汽车的过程建立月球车跟踪规划路径行驶的视觉预瞄模型，设计了保持月球车理想姿态行驶的模型参考自适应控制方案。(3)研究月球车的运动在环境扰动的干扰下会偏离规划路径的问题。利用Laplace 变换考察月球车运动动力学系统对几种典型的环境干扰力形式 的响应，研究环境干扰力对月球车运动的影响。(4)根据车辆地面力学的理论，设计月球车车轮的结构参数，使其充分利 用土壤推力，考虑纵列式月球车多轮通过土壤参数的修正，在NASA 建议的五种土壤上对月球车的支承通过性指标进行了计算； 研究刚性驱动轮在松软路面上行驶车轮滑转率和车轮结构参数对车轮挂钩牵引力、驱动力矩、车轮驱动效率等车轮驱动动力学特性的影响。(5)针对月球车在松软路面上不能正常行驶的主要原因是车轮过度下陷这个问题， 结合月球车行驶动力学模型， 设计以车轮滑转率为状态变量的滑模驱动控制器。仿真结果表明， 采用该控制器可以避免车轮的过度 滑转下陷，保证月球车能够在软质路面上正常行驶。(6)评价六轮摇臂转向架式月球车的越障能力，给出了车轮牵引系数与垂直越障高度的定量函数关系式； 针对月球车越障能力的评价以及越障时各车轮驱动力矩的协调分配的问题， 建立一种基于运动轨迹角的月球车越障能力判断准则， 引入了越障指数，用于定量地评价月球车的越障能力。(7)利用闭链坐标变换和瞬时重合坐标法，结合Kane 方程，同时考虑三维不平地形、松软路面和车轮的滑移，建立了六轮摇臂转向架式月球车的三维姿态动力学模型。