基于DRFM的SAR干扰技术研究

本文从DRFM的时钟分析出发,研究了DRFM的A/D、D/A时钟差异对输出信号的影响,并以此为基础研究了DRFM输出信号对SAR进行干扰所带来的影响,研究了A/D、D/A时钟的差异与干扰模式和干扰效果的关系,最后通过仿真对前文的分析进行了验证。     

Scheduling broadcasts in multihop radio networks

A comprehensive study of the problem of scheduling broadcast transmissions in a multihop, mobile packet radio network is provided that is based on throughput optimization subject to freedom from interference. It is shown that the problem is NP complete. A centralized algorithm that runs in polynomial time and results in efficient (maximal) schedules is proposed. A distributed algorithm that achieves the same schedules is then proposed. The algorithm results in a maximal broadcasting zone in every slot     

A new architecture for non-linear analogue-digital conversion

A modified architecture is proposed for the non-linear analogue-digital conversion of a transducer response. It is proved that by making use of a dual-slope A/D converter and by changing the clock frequency fed to the A/D converter during the deintegration period and blocking some of the pulses during this period, a nonlinear A/D conversion can be achieved. This method was used to linearize a Pt-PtRh thermocouple response and excellent results were obtained. Further, it is proved that the frequency change depends only on the maximum slope of the transducer response that is to be corrected.     

Reference refreshing cyclic analog-to-digital and digital-to-analog converters

A method of cyclic analog-to-digital (A/D) and digital-to-analog (D/A) conversion using switched-capacitor techniques is described. By periodically modifying the reference voltage to compensate for the nonideal signal-transfer-loop gain, it is possible in principle to build A/D and D/A converters whose linearity is independent of component ratios and that occupy only a small die area. These converters require two moderate-gain MOS operational amplifiers, one comparator, and a few capacitors. A test chip for A/D conversion was built and evaluated. The test data show that the A/D performs as a monotonic 13-bit converter with maximum 1-LSB differential and 2-LSB integral nonlinearity.     

An approach to high-performance, high-speed data networks

An approach that establishes a framework of design for high performance that scales well with increasing delay-bandwidth products is described. A basic conceptual model to explain the roles of window and access controls is presented. A static model of the system is then studied. The steady-state distribution of the buffer sizes, asymptotic expressions, and relationships between window size and delay that will be used to control windows are derived. A class of adaptive control schemes is proposed, and some results on simulation studies of one scheme are presented. A fluid model with dynamics is introduced to study fundamental questions of adaptive windows to adaptive rates. Bursty sources are considered. The proposals are then compared with other approaches     

Jacobian calculation using the multidimensional fast Fouriertransform in the harmonic balance analysis of nonlinear circuits

A technique which allows the gradient of frequency-domain simulation variables to be analytically determined using time-domain derivative information and the multidimensional fast Fourier transform is discussed. It is shown that this technique can be efficiently implemented when a circuit is driven by any number of incommensurate input frequencies. A harmonic balance simulator that uses this technique to determine the entries of the Jacobian matrix needed in a quasi-Newton iteration scheme is constructed. A significant reduction of simulation time is observed when compared with a harmonic balance simulator that uses transforms based on matrix multiplication     

Two-dimensional Bayesian estimate of images

A dynamic model for pictorial data that can be represented by a random field of an exponential autocorrelation function is developed. A partial difference equation describes the dynamic model and is used to realize a two-dimensional recursive filter that gives a Bayesian-estimate of the pictorial data from a noisy observation of the data. It is assumed that the noise is additive, white, and uncorrelated with the signal. Practical application of the estimation technique is illustrated by applying the results to enhance several pictures. A comparison of this technique and its one-dimensional counterpart (Kalman filter) is made, and generalization of the estimation technique to other autoregressive sources is considered.     

Accurate position control of a pneumatic actuator using on/offsolenoid valves

The development of a fast, accurate, and inexpensive position-controlled pneumatic actuator that may be applied to a variety of practical positioning applications is described. A novel pulse width modulation (PWM) valve pulsing algorithm allows on/off solenoid valves to be used in place of costly servo valves. The open-loop characteristic is shown both theoretically and experimentally to be near symmetrical. A comparison of the open- and closed-loop responses of standard PWM techniques and that of the novel PWM technique shows that there has been a significant improvement in the control. A linear process model is obtained from experimental data using system identification. A proportional integral derivative controller with added friction compensation and position feedforward has been successfully implemented. A worst case steady-state accuracy of 0.21 mm was achieved with a rise time of 180 ms for step inputs from 0.11 to 64 mm. Following errors to 64-mm S-curve profiles were less than 2.0 mm. The controller is robust to a sixfold increase in the system mass. The actuator's overall performance is comparable to that achieved by other researchers using servo valves     

A single-chip CMOS analog/digital mixed NTSC decoder

A single-chip CMOS LSI that integrates all analog-to-digital (A/D), digital-to-analog (D/A), peripheral, and digital signal processing circuits necessary for a digital National Television System Committee (NTSC) signal decoder is described. The LSI chip accepts composite NTSC video signals in analog form, digitizes them using the on-chip A/D converter, converts them to component RGB signals, and then converts the signals to analog form by using the on-chip D/A converters. The development of circuits that maximize use of the input digital data is discussed. A 6-b A/D circuit is used to reduce the circuit size. Circuits that help maintain acceptable picture quality despite 6-b resolution were developed. Besides analog NTSC signal input and RGB signal output, the IC can also input and output digital NTSC signals, Y/C (luminance, chrominance) signals, and RGB signals. Applications of the LSI are presented     

双路对消抑制对合成孔径雷达的弹射式干扰

重点介绍了用双路对消抑制弹射式干扰的原理及结果。从理论上分析了双路对消的工作原理,并用模拟原始数据生成和成像处理技术对双路对消作了仿真实验。实验结果表明双路对消很好地抑制了弹射式干扰,同时也证实了双路对消技术的理论正确性。通过对干扰机定位误差和雷达飞行速度不满足对消条件时对抑制干扰的影响的分析,得出本技术对干扰机定位精度要求不高,对飞机飞行速度精度要求不高的结论。     

MBE growth of AlGaAs/GaAs double- heterostructure light emitting diodes on GaAs(111)A and (211)A substrates using all-silicon doping

Al_0.3Ga_0.7As/GaAs double-heterostructure (DH) light emitting diodes have been grown on GaAs (111)A and (211)A substrates by molecular beam epitaxy using only Si dopant. Scanning electron microscope observations and current-voltage characteristics for these samples show that the DH structures have been successfully formed. The peak wavelength of the emission spectra for both the (111)A and (211)A samples is 875 nm at 300 K, and this peak is attributed to the emission in the i-GaAs layer. The peak intensity of the (211)A sample is stronger than that of the (111)A sample owing to an improved AlGaAs/GaAs interface structure.     

Amplifier systems with quasifeed-forward control

The applicability of signal-error feedforward is usually restricted, owing to the output signal adder that is required. A quasifeedforward configuration is presented here which extends the improvement obtained by feedforward to this output adder. A practical example is given with the numerical results that were obtained.     

基于面积特征的城区航空影像匹配方法

基于特征的影像匹配是一类极为广泛和重要的方法。已有的研究体现出了特征对于实施最为匹配的影像之一－－城区航空影像有着极为明显的优越性。文中给出一种新的匹配目标函数的构建，并基于此提出一种城区航空影像匹配算法，给出了算法的实现过程，并以部分东京城区图进行了试验，结果表明文中的方法具有乘法明了，可靠易行和抗旋转性的优点。     

A new non-orthogonal space-time code with low decoding complexity

A full diversity block space-time code over two transmit antennas and two symbol periods is introduced. In this method, each code is equal to the addition of two matrices; A/sup m/ and DA/sup n/, where A and D are the two constant matrices and m and n are the two data symbols. A is selected such that the set A/sup m/, 0 /spl les/ m /spl les/ 2/sup b/ - 1 is closed under the matrix multiplication. This structure allows a simple maximum likelihood (ML) decoding method, and at the same time, simplifies the optimization of the coding advantage. Simulations show that the performance of the new code is very close to that of the Damen code (M. O. Damen et al., 2002) which is the best known block space-time code in terms of the coding advantage. Moreover, the decoding complexity of the proposed method is significantly lower than that of the Damen code.     

A flip-flop sensor array with on-spot A/D conversion

A two-dimensional optical flip-flop sensor array, consisting of an 8×8 matrix of flip-flop sensors integrated in one chip together with sense amplifiers and access selection circuitry, is discussed. A flip-flop sensor contains two phototransistors, one of which is covered over the aluminum while the other is exposed to light. Each flip-flop senses the light intensity and converts it to a series of ones and zeros. It is operated by turning the supply current on and off with a high frequency. During the absence of light the flip-flop is totally symmetrical and the number of ones and zeros is equal. Light causes an asymmetry in the flip-flop that changes the ratio of ones and zeros. A fully digital output is obtained by counting the number of ones. A triangle-wave voltage is applied to the flip-flop to vary its threshold. The device showed that a large array of sensors with on-spot A/D (analog-to-digital) conversion can be realized using the flip-flop sensor technique     

Rayleigh hypothesis, the extended-boundary condition and point matching

A recent suggestion, that the Rayleigh hypothesis for electromagnetic scattering is exact, is shown, by counterexample, to be questionable. A point-matching solution for the surface current density (not the scattered field) is shown to be rigorously based. The solution is similar to that for the scattered field derived from the Rayleigh hypothesis.     

A High-Dynamic-Range Integrating Pixel With an Adaptive Logarithmic Response

A majority of charge-coupled device and complementary metal-oxide-semiconductor imaging sensors obtain a linear response by integrating the photocurrent in the pixel. This is a simple transduction method; however, the dynamic range of the resulting pixels is smaller than that of many scenes. A biologically inspired approach to solving this problem is to create a pixel with a logarithmic response. A new design for an integrating pixel with a logarithmic response is presented in this letter. The theory of operation of the pixel is described before results are reported that show that the pixel has an adaptive response and a dynamic range of more than 120 dB.     

Preferential Image Segmentation Using Trees of Shapes

A novel preferential image segmentation method is proposed that performs image segmentation and object recognition using mathematical morphologies. The method preferentially segments objects that have intensities and boundaries similar to those of objects in a database of prior images. A tree of shapes is utilized to represent the content distributions in images, and curve matching is applied to compare the boundaries. The algorithm is invariant to contrast change and similarity transformations of translation, rotation and scale. A performance evaluation of the proposed method using a large image dataset is provided. Experimental results show that the proposed approach is promising for applications such as object segmentation and video tracking with cluttered backgrounds.      

Improving the Specifications for Power-Line Filters

The most important requirement of a power-line filter is its insertion loss under load. This paper discusses methods of extending and improving the technique of measuring insertion loss as specified in MIL-STD-220A. It discusses present equipment limitations in MIL-STD-220A that restricts full-load tests to frequencies above 100 kHz and limits maximum current to 100 amperes. However, it is realized that MIL-STD-220A is the only available specification at present. Therefore, the paper discusses methods of extending the MIL-STD-220A technique for measuring the insertion loss of filters for frequencies as low as 14 kHz and under loads as high as 200 amperes. A new buffer network that allows such measurements is described. In addition, a method is discussed for improving voltage regulation and reducing distortion of the power-line waveshape caused by power filters. These are two parameters which have been totally ignored when specifying power filters and which have been found to cause considerable electrical problems after installation.     

Silica Nanodepletors: Targeting and Clearing Alzheimer's β‐Amyloid Plaques

Abnormal accumulation of β‐amyloid (Aβ) peptide aggregates in the brain is a major hallmark of Alzheimer's disease (AD). Aβ aggregates interfere with neuronal communications, ultimately causing neuronal damage and brain atrophy. Much effort has been made to develop AD treatments that suppress Aβ aggregate formation, thereby attenuating Aβ‐induced neurotoxicity. Here, the design of Aβ nanodepletors consisting of ultralarge mesoporous silica nanostructures and anti‐Aβ single‐chain variable fragments, with the goal of targeting and eliminating aggregative Aβ monomers, is reported. The Aβ nanodepletors impart a notable decline in Aβ aggregate formation, resulting in significant mitigation of Aβ‐induced neurotoxicity in vitro. Furthermore, stereotaxic injections of Aβ nanodepletors into the brain of an AD mouse model system successfully suppress Aβ plaque formation in vivo up to ≈30%, suggesting that Aβ nanodepletors can serve as a promising antiamylodoisis material.