Modeling Active Microwave Remote Sensing of Snow Using Dense Media Radiative Transfer (DMRT) Theory With Multiple-Scattering Effects

Dense media radiative transfer (DMRT) theory is used to study the multiple-scattering effects in active microwave remote sensing. Simplified DMRT phase matrices are obtained in the 1-2 frame. The simplified expressions facilitate solutions of the DMRT equations and comparisons with other phase matrices. First-order, second-order, and full multiple-scattering solutions of the DMRT equations are obtained. To solve the DMRT equation, we decompose the diffuse intensities into Fourier series in the azimuthal direction. Each harmonic is solved by the eigen-quadrature approach. The model is applied to the active microwave remote sensing of terrestrial snow. Full multiple-scattering effects are important as the optical thickness for snow at frequencies above 10 GHz often exceed unity. The results are illustrated as a function of frequency, incidence angle, and snow depth. The results show that cross polarization for the case of densely packed spheres can be significant and can be merely 6 to 8 dB below copolarization. The magnitudes of the cross polarization are consistent with the experimental observations. The results show that the active 13.5-GHz backscattering coefficients still have significant sensitivity to snow thickness even for snow thickness exceeding 1 m     

Measurement of Layer Thickness and Permittivity Using a New Multilayer Model From GPR Data

The conventional method, i.e., the common middle point (CMP) method, has been used for many years for estimating the depth and permittivity of layered media from ground-penetrating radar (GPR) data. However, the CMP method results in noticeable errors in thickness and permittivity readings with the increase of antenna separation. To improve the measurement accuracy, a new mathematical model is presented, covering GPR measurement in one- and two-layer cases. In this model, we first check all the possible wave paths when the GPR signal propagates in the multilayer environment. We not only consider the effects from the air-ground interface but also introduce a ray-path-searching process in the GPR measurement using Fermat's shortest path law. The shortest path is then used in the process of GPR data inversion in order to calculate the depth and permittivity of each layer. Finally, we use the transmission-line matrix (TLM) method to simulate the propagation of a GPR signal in the multilayered formation. A time-sequence image that was produced by the finite-difference time-domain method has also been used to explain this presented model. By comparing the numerical simulation results with the measured results, it is found that the estimated layer thickness and permittivity by the new model agree well with the simulated results. It proves that the new model is more accurate and closer to the real measured situation.     

An In-Depth, Theoretical Investigation Into Modeling Metal-Insulator-Metal Capacitors Using Symmetric Coupled Lines in a Homogeneous Medium Model

In monolithic microwave integrated circuits (MMIC) design, a metal-insulator-metal (MIM) capacitor is one of the key passive components. Research on modeling MIM capacitors in an accurate yet efficient fashion has been around for years. Models for series capacitors of small electrical length have been well established. In the authors' previous work was pioneered the novel approach to modeling shunt capacitors of significant electrical length on multiple grounding vias with the effect of lossy media incorporated. With this in mind, this letter further expands on, and provides a significant supplement with, the previous works. At the core of this letter is to gain an in-depth, theoretical insight into the rationale that, under the condition of tight conductor coupling, asymmetric coupled lines in an inhomogeneous medium reduce to symmetric coupled lines in a homogeneous medium.     

Modeling the Electromagnetic Emission of a Microcontroller Using a Single Model

This paper presents a methodology for building an integrated circuit behavioral model that enables the prediction of its electromagnetic (EM) emissions up to several gigahertz. The model, built upon S-parameter characterization and conducted emission measurements, is used to predict the EM emissions of a commercial 16-bit microcontroller. The emission measurements are performed according to several EM compatibility standards, namely, 1 Omega /150 Omega , surface scan, and transverse EM/gigahertz transverse EM (GTEM) method, and their results show an excellent fit with model predictions.     

多层防御反坦克阵地效能建模与仿真

现代反坦克防御作战中,陆军多采用武装直升机、车载式反坦克导弹与便携式反坦克导弹相结合的立体、多层部署的方法对重点区域进行防御。敌方常通过施放红外热源、烟幕等电子干扰方式来提高其生存能力和突防效率。基于排队论和反坦克作战理论,建立了电光干扰对抗环境下的多层防御反坦克阵地的排队服务模型,并对作战想定进行了仿真应用。仿真结果表明了模型的可信性和实用性。     

Retrieval of Atmospheric Water Vapor Density With Fine Spatial Resolution Using Three-Dimensional Tomographic Inversion of Microwave Brightness Temperatures Measured by a Network of Scanning Compact Radiometers

Quantitative precipitation forecasting is currently limited by the paucity of observations on sufficiently fine temporal and spatial scales. Three-dimensional water vapor fields can be retrieved with improved spatial coverage from measurements obtained using a network of scanning microwave radiometers. To investigate this potential, an observation system simulation experiment was performed in which synthetic examples of retrievals using a network of radiometers were compared with results from the Weather Research and Forecasting model at a grid scale of 500 m. These comparisons show that the 3-D water vapor field can be retrieved with an accuracy of better than 15%-20%. A ground-based demonstration network of three compact microwave radiometers was deployed at the Atmospheric Radiation Measurement Southern Great Plains site in Oklahoma. Results using these network measurements demonstrated the first retrieval of the 3-D water vapor field in the troposphere at fine spatial and temporal resolutions.     

Analysis of Melting Particle Model and Microwave and MM-Wave Scatterings Due to a Melting Layer of Precipitation

In this paper, the water-coated snow sphere model of melting particles has been given. Based on this model, the scattering properties and albedo w₀ of melting particles have been calculated by use of the coated sphere BHCOAT method. It is shown that the albedo of melting particles may be more than the raindrops and snow spheres at 5 (C-band) and 14GHz (Ku-band). The albedo of melting particles are nearly less than the equivalent mass raindrops albedo at the Ka and mm-band of f > 20GHz. These results are in agreement with the conclusion radar observed and literature given^[1,2]. It demonstrates that the water-coated snow sphere model of melting particles is appropriate and practicable. The study is significant for the utilization of the low fade margin system in satellite communication.     

中高温熔点金属材料固–液相变点导热系数测量

设计了一种中、高温熔点金属材料固-液相变点温度附近热物性动态测算方法,并与计算机实时数据采集和测控技术结合起来,研制了相应的动态测试仪。通过实验测定相界面的移动速率与相变导热反问题的数值计算相结合的办法来确定被测材料的热物性。分别对相变室、炉体、相界面探测器、温度在线检测与控制系统、测试过程进行了设计,对测试系统的测量误差进行了定量分析,发现采用此方法测试的系统误差不超过3%。用已知热物性的锌、铝金属对此方法进行了检定,得到了较为满意的测试结果。     

中高温熔点金属材料固–液相变点导热系数测量

设计了一种中、高温熔点金属材料固-液相变点温度附近热物性动态测算方法,并与计算机实时数据采集和测控技术结合起来,研制了相应的动态测试仪。通过实验测定相界面的移动速率与相变导热反问题的数值计算相结合的办法来确定被测材料的热物性。分别对相变室、炉体、相界面探测器、温度在线检测与控制系统、测试过程进行了设计,对测试系统的测量误差进行了定量分析,发现采用此方法测试的系统误差不超过3%。用已知热物性的锌、铝金属对此方法进行了检定,得到了较为满意的测试结果。     

利用新型经验函数模拟云底亮温及误差分析

Stephen在2008年提出了一种新型亮温经验函数,为反演云底高提供了一种无需计算大气中实时水汽含量的新方法.利用SBDART模式和Stephen亮温函数比较系统地研究了不同天顶角、水汽、云、气溶胶、能见度等气象要素条件下,云底红外亮温Tb随天顶角的变化情况,并对其进行误差分析.模拟结果显示,水汽、云、天顶角及能见度小于5 km时对Tb影响较大,不同气象要素条件下,Stephen亮温函数模拟的云底亮温与SBDART模拟结果相近,所以,采用Stephen亮温函数模拟云底亮温具有可行性.     

A New Melting Particle Model and its Application to Scattering of Radiowaves by a Melting Layer of Precipitation

A melting layer of precipitation is composed of melting snow particles, and we modeled them by three-layered spherical particles, in which the innermost layer is air, the middle ice and the outermost water. Based on this model, the radar reflectivity, together with the specific phase shift and the specific attenuation of a melting layer of precipitation, were computed at 1–100 GHZ by using the Mie theory. The radar bright band is explained by this model. We compared our numerical results with that in the literature Zhang (IEEE Transactions on Antennas and Propagation 42(3):347–356, 1994), Zhang (IEEE Transactions on Antennas and Propagation 42(3):492–500, 1994). It demonstrates that the three-layered snow sphere model is appropriate and practicable, so the computed results are more accurate. This study can be used in radar remote sensing and satellite-earth communications.     

变温C-V和传输线模型测量研究AlGaN/GaN HEMT温度特性

通过对异质结材料上制作的肖特基结构变温C-V测量和传输线模型变温测量,研究了蓝宝石衬底AlGaN/GaN异质结高电子迁移率晶体管的直流特性在25～200℃之间的变化,分析了载流子浓度分布、沟道方块电阻、欧姆比接触电阻和缓冲层泄漏电流随温度的变化规律.得出了器件饱和电流随温度升高而下降主要由输运特性退化造成,沟道泄漏电流随温度的变化主要由栅泄漏电流引起的结论.同时,证明了GaN缓冲层漏电不是导致器件退化的主要原因.     

Thermoelectric Performance of ZnO:Al/ZnO:(Al,In) Quantum Well Multilayer Structures as a Function of Indium Composition and Band-Gap Offset at High Operating Temperatures

This study investigates the thermoelectric (TE) power factor for radiofrequency (RF)-sputtered n-type ZnO:Al/ZnO:(Al,In) multilayer quantum wells (QW) and the dependence on band-gap offset at high operating temperatures. The structures are 50 periods of 10-nm-thick barrier and well layers. The TE power factors for all films are promising (>20?×?10^?4?W/m²?K); however, a decline in electronic transport is evident for each of the doped wells over a specific range of operating temperatures. This supports the need for optimum doping levels for a specific operating temperature range; e.g., 2?at.%, 5?at.%, and 8?at.% indium are optimum at 300?K to 600?K, 600?K to 725?K, and >725?K, respectively. A model has also been developed to calculate the QW electronic transport as a function of temperature and band-gap offset, which is subsequently related to doping concentration. This model confirms a loss in electrical conductivity due to charge carriers gaining enough kinetic energy to overcome the QW barrier, which results in multilayer hopping across well?Cbarrier interfaces. In addition, film microstructure and interface roughness have been determined by x-ray and spectroscopy techniques.     

变温C-V和传输线模型测量研究AlGaN/GaN HEMT温度特性

通过对异质结材料上制作的肖特基结构变温C-V测量和传输线模型变温测量,研究了蓝宝石衬底AlGaN/GaN异质结高电子迁移率晶体管的直流特性在25～200℃之间的变化,分析了载流子浓度分布、沟道方块电阻、欧姆比接触电阻和缓冲层泄漏电流随温度的变化规律.得出了器件饱和电流随温度升高而下降主要由输运特性退化造成,沟道泄漏电流随温度的变化主要由栅泄漏电流引起的结论.同时,证明了GaN缓冲层漏电不是导致器件退化的主要原因.     

采用 Al2O3/ITO 阳极的有机电致发光器件

在采用α-naphtylphenyliphenyl diamine (NPB)和 tris-8-hydroxyquinoline almninura (Alq3 材料的双层有机电致发光器件(OLED)中,在阳极与有机层间插入纳米级厚度的氧化铝作为缓冲层来提高器件的效率.研究了氧化铝的厚度对器件性能的影响,并提出一种模型解释该现象.实验发现,当氧化铝的厚度为 0.3 nm 时,器件的亮度提高 30%,同时在相同电压下,提高了器件电流、量子效率与能量效率,同时降低了器件的阈值电压.相信由于简单与高效,该工艺会对 OLED 技术有很好的影响.     

基于Alloy的发布/订阅系统的形式化模型及其检测

从软件形式化和模型检测着手,提出了一种利用Alloy语言对发布/订阅系统进行形式化描述,并利用Alloy分析器进行模型检测的方法.具体实例表明,利用Alloy可以方便的对发布/订阅系统进行建模,并进行自动模型检测,可应用于发布/订阅系统开发的分析和设计阶段.     

激光熔化沉积TiC/CaF2/Inconel 718复合材料的组织及高温摩擦磨损性能

采用激光熔化沉积技术制备了TiC/CaF2/Inconel 718高温合金基高温耐磨自润滑复合材料,对其显微组织、显微硬度及高温干滑动摩擦磨损性能进行了研究,探讨了其高温磨损机理。结果表明:复合材料的显微组织由TiC、CaF2、Cr7C3、γ″-Ni3Nb和γ-(Ni,Fe)构成,原位自生TiC初生相和细小CaF2/TiC共晶弥散分布在被Cr7C3和γ″-Ni3Nb等超细高温相强化的γ-(Ni,Fe)固溶体基体上;复合材料的平均显微硬度为820 HV;与激光熔化沉积Inconel 718对比样相比,复合材料具有良好的高温耐磨性及低且稳定的摩擦因数,复合材料优异的高温摩擦磨损性能源自于其合理的显微组织结构。     

Design and Modeling of a Nanomechanical Sensor Using Silicon Photonic Crystals

Conventionally a line defect in the photonic crystal (PhC) is used to create a waveguide for light propagation through the PhC. A PhC based filter is designed by introducing micro-cavities within the line defect so as to form the resonant bandgap structure for PhC. Such a PhC waveguide (PhCWG) filter shows sharp resonant peak in output wavelength spectrum. We proposed a suspended silicon bridge structure comprising this PhCWG filter structure. Since the output resonant wavelength is sensitive to the shape of air holes and defect length of the micro-cavity. Shift of the output resonant wavelength is observed for suspended PhCWG beam structure under particular force loading. In other words, the induced strain modifies the shape of air holes and the spacing among them. Such an effect leads to shift of resonant wavelength. Under optical detection limitation of 0.1 nm for resonant wavelength shift, the sensing capability of this nanomechanical sensor is derived as that vertical deformation is 20-25 nm at the center and the smallest strain is 0.005% for defect length. This innovative design conceptualizes a new application area for PhCs, i.e., the nanometer-scale physical sensors for strains and forces.     

Computation of the Electromagnetic Fields and Induced Temperatures Within a Model of the Microwave-Irradiated Human Eye

The electromagnetic fields within a detailed model of the human eye and its surrounding bony orbit are calculated for two different frequencies of plane-wave irradiation: 750 MHz and 1.5 GHz. The computation is performed with a finite-difference algorithm for the time-dependent Maxwell's equations, carried out to the sinusoidal steady state. The heating potential, derived from the square of the electric field, is used to calculate the temperatures induced within the eyeball of the model. This computation is performed with the implicit alternating-direction (IAD) algorithm for the heat conduction equation. Using an order-of-magnitude estimate of the heat-sinking capacity of the retinal blood supply, it is determined that a hot spot exceeding 40.4/spl deg/C occurs at the center of the model eyeball at an incident power level of 100 mW/cm/sup 2/ at 1.5 GHz.     

WSCP/R-net:一种新的服务动态聚合流程建模与分析模型

服务聚合流程建模和分析是流程驱动的服务聚合研究中两个关键问题.针对现有基于基本Petri网和WF-net的服务动态聚合流程建模与分析方法的不足,从服务聚合的过程维和资源维出发定义了服务聚合流程定义元模型;与流程定义元模型相一致,基于着色Petri网提出了一种新的服务聚合流程/资源描述模型WSCP/R-net,有效解决了服务聚合流程模型中不确定活动选择和服务的动态变化性问题;从流程结构正确性、数据依赖有效性和资源有效性三个方面提出了WSCP/R-net模型健壮性的概念,并对模型健壮性成立的充要条件及其组合特性进行了分析.