Shielding and scattering analysis of lossy cylindrical shells usingan extended multifilament current approach

An investigation of the multifilament current method's (MFCM) ability to solve electromagnetic scattering and/or absorption problems involving inhomogeneous cylindrical structures is presented. Dielectric cylinders of arbitrary cross section covered by multiple layers of lossy dielectrics are considered. Both cases of wave incidence, TM and TE, are treated. Like some other moment-method solutions, the MFCM experiences numerical difficulties when dealing with a medium characterized by a high loss tangent or large electrical conductivity. To overcome this problem, a new boundary condition based on an impedance matrix equivalent circuit approach that accounts for the curvature of the surfaces has been developed. This new impedance matrix boundary condition (IMBC) extends the MFCM capability to the analysis of two-dimensional (2-D) structures involving conducting layers with ohmic losses. The usefulness of this extended method is confirmed by the study of metallic shells for which a strong energy coupling with the incident electromagnetic (EM) field is demonstrated at their structural resonance frequencies     

Intercomparison of inversion algorithms to retrieve rain rate from SSM/I by using an extended validation set over the Mediterranean area

The capability of some inversion algorithms to estimate surface rain rate at the midlatitude basin scale from the Special Sensor Microwave Imager (SSM/I) data is analyzed. For this purpose, an extended database has been derived from coincident SSM/I images and half-hourly rain rate data obtained from a rain gauge network, placed along the Tiber River basin in Central Italy, during nine years (from 1992 to 2000). The database has been divided in a training set, to calibrate the empirical algorithms, and in a validation one, to compare the results of the considered techniques. The proposed retrieval methods are based on both empirical and physical approaches. Among the empirical methods, a regression, an artificial feedforward neural network, and a Bayesian maximum a posteriori (MAP) inversion have been considered. Three algorithms available in the literature are also included as benchmarks. As physical algorithms, the MAP method and the minimum mean square estimator have been used. Moreover, in order to test the behavior of the algorithms with different kinds of precipitation, a classification of rainy events, based on some statistical parameters derived from rain gauge measurements, has been performed. From this classification, an attempt to identify the type of event from radiometric data has been carried out. The purposes of this paper are to determine whether the use of an extended training set, referred to a limited geographical area, can improve the SSM/I skill in rain detection and estimation and, mainly, to confirm the validity of the physical approach adopted in previous works. It will be shown that, among all the estimators, the neural network presents the best performances and that the physical techniques provide results only slightly worse than those given by empirical methods, but with the well-known advantage of an easy application to different geographical zones and different sensors.     

Ocean surface wind speed and direction retrievals from the SSM/I

A semiempirical model is developed that retrieves ocean surface wind direction information in addition to improved wind speeds from Special Sensor Microwave/Imager (SSM/I) measurements. Radiative transfer and neural network techniques were combined in the authors' approach. The model was trained and tested using clear sky cases, but atmospheric transmittance is retrieved so that retrieval in other than clear sky conditions is possible. With two SSM/I instruments currently providing operational ocean surface wind speed retrievals, the addition of wind direction information and improved wind speed retrievals will enhance the impact of this data in weather prediction models and marine weather forecasting     

风力发电机转速控制系统的建模与仿真

针对风力发电机非线性、随机性、扰动大等特点,设计基于带动量项的粒子群优化的支持向量机的风力发电机转速控制建模的新方法。利用支持向量机对小样本、高维度、非线性特性的映射能力,将风电系统的采样数据映射到高维的特征空间进行建模。支持向量机惩罚因子C和核参数σ的选择对建模效果影响较大,经验试凑的方法难以获得较好的参数,引入粒子群算法进行参数寻优。为了克服传统粒子群算法易陷入局部最优且收敛速度慢的缺陷,提出带动量项的改进粒子群算法寻优。以采集的风速、风力发电机转矩、桨距角作为输入信号,发电机转速数据作为输出信号,在Matlab环境中进行建模。实验结果表明,与传统算法相比,采用该方法的模型在准确性和收敛速度方面得到较大改善。     

Ocean surface wind speed measurements of the Special SensorMicrowave/Imager (SSM/I)

An operational wind speed algorithm was developed. This algorithm is based on the D-matrix approach, which seeks a linear relationship between measured SSM/I brightness temperatures and environmental parameters. D-matrix performance in the low-to-medium wind speed range was validated by comparing algorithm-derived wind speeds with near-simultaneous and colocated measurements made by the anemometers of offshore ocean buoys. Results indicate that for approximately 85% of the time, the D-matrix-retrieved winds will have an accuracy better than the Defense Meteorological Space Program goal of ±2 m/s. For the remaining 15% of the time, the scene will be rain-flagged and retrieval accuracies will be worse than ±2 m/s     

目标航向航速解算及验证方法研究

主要论述了在雷达产品应用中对海空目标相对和绝对航向航速的解算方法,并对几种可以提高航向航速解算精度的方法进行了探讨,最后提供了一种验证相对和绝对航向航速解算精度的方法。     

热损失型风速传感器流体动力学分析与实验研究

为解决传统机械式风速计难以准确测量低风速的难题,设计一种热损失型风速传感器。该传感器主要由Cortex-M3 ARM处理器、高精度低噪声测量电路及恒功率加热电路等组成。通过计算流体动力学(CFD)方法确定探头加热功率,并得到双探头温度差值与风速的曲线关系。搭建一套基于高低温试验箱的实验平台,对-10～50℃范围内的传感器温度特性进行测试,结合L-M算法对温漂进行修正。实验结果表明,在0～5 m/s范围内,该风速传感器的均方根误差(RMSE)为0.09 m/s,在低风速测量领域具有一定的应用潜力。     

高速安全微控制器发展与前景

本文主要介绍全新高速安全微控制器的结构特征与优势,并从中指出它的发展与应用前景     

定制化的专业通信将加速发展——访SELEX公司亚太区经理Attilio BASILE

集群通信数字化在中国已经推广多年,多种数字集群通信制式在中国市场均取得较大进展,其中,TETRA制式数字集群在网络、终端等相关厂商的推动     

Development and laboratory validation of in-line multiplexed low-coherence interferometric sensors

In this paper, we present the development and laboratory validation of in-line multiplexing for a low-coherence interferometric strain sensor suitable for industrial deployment and application to civil structures. The sensor is the multiplexed version of the standard SOFO, developed, produced and commercialized by Smartec SA. While the standard SOFO employs total reflectors at the end of the measurement and reference fibers, allowing measurement of the strain only over a single field, in the solution presented in-line multiplexing is obtained separating each measurement field by partial reflectors, consisting of broadband Fiber Bragg Gratings (FBGs) with a 5% reflectivity. Laboratory tests have been carried out on a prototype 3-field sensor, to investigate effectiveness, resolution and temperature sensitivity. Outcomes show a linear response of the sensor with RMS resolution lower than 3 μm, independent of the measurement base, of the same order as the single field sensor. Consistently with the theoretical prediction, the system exhibits an apparent thermal expansion coefficient of 2 με °C⁻¹, relatively low if compared with the thermal expansion coefficient of steel or concrete structures. This temperature dependency can even be eliminated by appropriate selection of the length of the reference fiber. Theoretical analysis indicates that the maximum number of fields that can be arranged in series is in the order of 10; however this limit can be overcome by appropriately selecting the power of the light source of the interrogation unit.     

基于离散预约速率与分组长度组结构的高速路由器公平队列调度算法实现

本文提出一种基于离散预约速率与分组长度组单元的公平隐列调度器实现结构,该结构可根据不同预约速率需求,为其方便灵活的提供不同的预约带宽实现精度。组单元的模块化设计结构与流水线设计技术使得硬件逻辑资源得到更有效的利用。文中同时提了一种适用于结构的定点时标重构技术,利用该技术可有效节约存储流时标的所需的外部存储空间,算法仿真与FPGA综合结果表明,该结构可支持1．2Gbit/s 的输出链路,通过有效的集成方式,该设计可进一步应用到端口速率为OC－48（2．4Gbps)的高速路由器中。l     

Overview and performance of CCITT/ANSI embedded ADPCM algorithms

Embedded adaptive differential pulse coded modulation (ADPCM) algorithms quantize the differences between the input signal and the estimated signal into core bits and enhancement bits. CCITT Recommendation G.727, which describes embedded ADPCM encoding algorithms with 5, 4, 3, and 2 core bits, is virtually identical to the corresponding ANSI standard T1.310. The main features of G.727 and T1.310 and performance results are presented. A formal subjective evaluation of the speech performance of embedded ADPCM algorithms indicates that a midrise quantizer provides better voice transmission performance than its midtread counterpart when two core bits are used. The subjective data also show that the performance of the 40-kb/s midrise ADPCM algorithm with two feedback bits is indistinguishable from that of 64-kb/s pulse code modulation (PCM) for up to four tandem encodings. Embedded algorithms are therefore recommended for flexible congestion control of integrated traffic in multinode networks     

基于LabVIEW的电机转速测控系统研制

电机转速的测量与控制是现代工业生产和试验过程中经常遇到的问题。针对传统电机测控系统的一些不足,研制了一种基于Lab VIEW的电机转速测控系统。基于虚拟仪器的设计思想,采用NI开发的Lab VIEW图形化设计软件,结合数据采集技术和PID控制技术,设计完成了一套电机转速测控系统。系统综合运用了数据采集技术、虚拟仪器技术、测控技术,实现了转速信号采集、处理、显示以及反馈控制等功能。最后进行了实验测试,结果表明所研制的系统操作简单,人机界面友好,测量精度高,控制效率好,性能稳定,便于广泛应用。     

SVPWM在Simulink下的一种实现方法及其验证

为简化、加速电机控制系统的设计过程。首先介绍空间矢量算法的基本原理,及在Matlab/Simlink环境下的一种实现方法,然后搭建永磁同步电机的离散控制仿真模型对其进行验证。通过此模型可以对多种波形进行仿真和分析。仿真结果验证了该实现方法的有效性,进而为电机控制系统的分析、设计和调试提供了一种有效的电脑辅助设计工具。     

A cross validation study of deep brain stimulation targeting: from experts to atlas-based, segmentation-based and automatic registration algorithms

Validation of image registration algorithms is a difficult task and open-ended problem, usually application-dependent. In this paper, we focus on deep brain stimulation (DBS) targeting for the treatment of movement disorders like Parkinson's disease and essential tremor. DBS involves implantation of an electrode deep inside the brain to electrically stimulate specific areas shutting down the disease's symptoms. The subthalamic nucleus (STN) has turned out to be the optimal target for this kind of surgery. Unfortunately, the STN is in general not clearly distinguishable in common medical imaging modalities. Usual techniques to infer its location are the use of anatomical atlases and visible surrounding landmarks. Surgeons have to adjust the electrode intraoperatively using electrophysiological recordings and macrostimulation tests. We constructed a ground truth derived from specific patients whose STNs are clearly visible on magnetic resonance (MR) T2-weighted images. A patient is chosen as atlas both for the right and left sides. Then, by registering each patient with the atlas using different methods, several estimations of the STN location are obtained. Two studies are driven using our proposed validation scheme. First, a comparison between different atlas-based and nonrigid registration algorithms with a evaluation of their performance and usability to locate the STN automatically. Second, a study of which visible surrounding structures influence the STN location. The two studies are cross validated between them and against expert's variability. Using this scheme, we evaluated the expert's ability against the estimation error provided by the tested algorithms and we demonstrated that automatic STN targeting is possible and as accurate as the expert-driven techniques currently used. We also show which structures have to be taken into account to accurately estimate the STN location.     

Design and analysis of joint data detection and frequency/phase estimation algorithms

The problem of joint data detection and frequency/phase estimation is considered in this paper. The traditional belief regarding exact generalized-likelihood-based joint detection and estimation is that its complexity is exponential in the sequence length N. This belief is justified due to the memory imposed on the transmitted sequence by the lack of knowledge of the auxiliary channel parameters. In this paper, we show that the exact solution can be performed with O(N/sup 4/) worst case complexity regardless of the operating signal-to-noise ratio. The concepts used in the proof of the polynomial complexity result are also utilized to evaluate tight performance bounds on the exact and a family of approximate algorithms.     

MAX12557型高速A/D转换器的特点及应用

MAX12557是Maxim公司新推出的一种低功耗、小尺寸和高动态特性的14位高速模/数转换器(ADC),成本低、使用方便,可广泛应用在要求低功耗的数据采集、数字接收机、便携式仪表等领域.介绍MAX12557的主要特点、内部结构及工作原理,给出其在宽带中频数字接收机中的应用.     

The operational speed and power dissipation of scaled one-transistor RTD/HFET memories

The scaling behaviour of a memory that uses resonant tunnelling diodes (RTDs), namely the one-transistor tunnelling SRAM (TSRAM), is compared with the dominant memory technology, silicon CMOS. The minimum feature size (MOSFET or HFET gate length λ) is scaled in the range from 500 nm to 50 nm. Appropriate scaling laws are used for the RTD and wiring elements. We set up a benchmark architecture that we have modelled in RTD/HFET and in silicon CMOS, and simulated with HSPICE, in order to determine the limits on operational frequency. The RTD-based memories show speeds about an order of magnitude higher than the equivalent CMOS memory, even for very large memories. The performance improves with smaller values of λ and smaller memory sizes. However, for larger memories, the power dissipation outside TSRAM memory cells is still very high for enhancement/depletion (E/D) HFET circuitry.     

Changes in the luminescent and electrical properties of InGaN/AlGaN/GaN light-emitting diodes during extended operation

Changes in the luminescence spectra and current-voltage and capacitance-voltage characteristics of light-emitting diodes based on InGaN/AlGaN/GaN heterostructures were investigated as functions of operating time during extended use. Sample blue and green light-emitting diodes with InGaN single quantum-well active layers were examined during operating times of 10²−2×10³ h at currents up to 80 mA. An increase in the efficiency at the working currents (15 mA) was observed in the first stage of aging (100–800 h) followed by a decrease in the second stage. The greatest changes in the spectra were observed at low currents (<0.15 mA). Studies of the distribution of charged acceptors in the space-charge region showed that their concentration grows in the first stage and falls in the second. Models explaining the two stages of aging are proposed: 1) activation of Mg acceptors as a result of destruction of residual Mg-H complexes, and 2) formation of N donor vacancies. A model of subthreshold defect formation by hot electrons injected into the quantum wells is discussed. Fiz. Tekh. Poluprovodn. 33, 224–232 (February 1999)