The relationship between the surface EMG and force transients in muscle: Simulation and experimental studies

The surface electromyogrmn (EMG) is an easily measured signal which when quantified by present techniques is a reliable measure of whether a muscle is active, a fairly reliable measure of steady state force and a rather unreliable measure of force transients in muscle. There is a real need for a reliable indicator of dynamic changes in muscle activity for the control of prosthetics, in diagnosis of neuromuscular diseases, in studies of the motor control system and in fundamental studies of muscle mechanics. This paper outlines the principles underlying the development of force and the EMG in muscle. The EMG is a poor estimate of muscle force since it is the result of the linear superposition of biphasic action potentials which result in an interference pattern. This in turn is dependent on the details of the firing intervals for each motor unit, whereas the force is quite insensitive to these details. Experimental results for the human biceps brachii are described in which it was not possible to obtain a consistent estimate of muscle active state from the EMG. An extensive computer simulation was used to explore the relationship between EMG and force under a variety of assumptions. The conclusion is that it is technically impossible to obtain consistent estimates of muscle force (or active state) unless a filter with a time constant of 300 ms is applied to the rectified EMG. This is inconsistent with the estimation of active state for voluntary contractions with observed rise time constants of 30-70 ms. It is susgested that the only solution is to repeat an experiment many times and average the rectified EMG. Unfortunately, in practice it is difficult to repeat certain aspects of voluntary muscular contractions.     

Some effects of localized stress on silicon planar transistors

When local compressive stress is applied to the emitter surface of a silicon planar transistor, increases in collector and base currents are observed. From the relationship between these currents and the base-to-emitter junction potential, it is inferred that changes in minority-carrier current occur in the stressed material. It is well known that the energy gap of a semiconductor is affected by mechanical stress, and the effects described here are consistent with a decrease in energy gap of a few tenths of an electron volt at compressive stresses of the order of 10¹¹dynes cm^-2. It is shown that the influence of stress on the current gain of a transistor depends on the strain distribution in the material. When the stress is applied over a relatively large area using a blunt stressing element, the increased minority-carrier current causes a rise in common-emitter current gain at low currents. In the case of the stress pattern produced by a sharper stressing element, a decrease in current gain is observed over a wide current range. It is proposed that this decrease results from a degradation in emitter efficiency caused by the stress concentration in the emitter region.     

Optical pulse sequence transmission through single-mode fibers:interference signal analysis

The transmission of a pulse sequence through a single-mode fiber is considered under first- and second-order dispersion. An expression is given for the output power signal envelope in terms of the Fourier transform of a spectral function. The output envelope is composed of two terms: a linear one which is a distorted replica of the information sequence, and a nonlinear interference term. The latter is expressed in a more meaningful way and analyzed. The results allow a characterization and a classification of the interference pulses in terms of physically intuitive parameters     

GaAs dynamic memory design

Subthreshold leakage loss is a serious problem for GaAs dynamic memory. Since the leakage current in a MESFET is several orders of magnitude higher than that in a MOSFET, it is difficult to retain the charge at dynamic nodes resulting in data storage errors, In order to solve this problem, a novel DRAM architecture is proposed. The design is based on a cell consisting of a MESFET switch and a metal-insulator-metal (MIM) planar capacitor as the storage element. The leakage current is reduced by a level-shift technique and a self-biased transistor is used to maintain the dynamic charge during the sense period. A high performance sense amplifier is used to detect small bit line voltage changes and refresh the stored data. A 1 Kb prototype, fabricated in a 1 μm nonself-aligned GaAs MESFET technology, exhibited a total read/write access time of the order of 3 ns     

Robust detection of a known signal in nearly Gaussian noise

A detector that is not nonparametric, but that nevertheless performs well over a broad class of noise distributions is termed a robust detector. One possible way to obtain a certain degree of robustness or stability is to look for a min-max solution. For the problem of detecting a signal of known form in additive, nearly Gaussian noise, the solution to the min-max problem is obtained when the signal amplitude is known and the nearly Gaussian noise is specified by a mixture model. The solution takes the form of a correlator-limiter detector. For a constant signal, the correlator-limiter detector reduces to a limiter detector, which is shown to be robust in terms of power and false alarm. By adding a symmetry constraint to the nearly normal noise and formulating the problem as one of local detection, the limiter-correlator is obtained as the local min-max solution. The limiter-correlator is shown to be robust in terms of asymptotic relative efficiency (ARE). For a pulse train of unknown phase, a limiter-envelope sum detector is also shown to be robust in terms of ARE.     

The sensitivity of threshold voltage of ion-implanted MOSFET's to substrate doping and oxide thickness fluctuations

When the gate region of a MOSFET is implanted in order to adjust, the threshold voltage, the sensitivity of the threshold voltage to fluctuations in substrate doping will be affected. It is shown here that when the implanted ion is of the Same impurity type as the substrate, this sensitivity is lower than for a similar, unimplanted structure. However, the converse is found to he true when the implanted ion is of opposite type and the device is operating in a deep-depletion mode. The latter result has obvious importance in view of substrate–doping fluctuations over the surface of a single silicon wafer, and more so between many different wafers. The effect on the threshold voltage of oxide thickness variations is also investigated, and it is found there is a range of implant energy and dose over which the sensitivity can be very small. This is associated, however, with a sharp rise in the sensitivity outside this range.     

语音通信中的噪声抵消技术

讨论了一种语音通信中的有源噪声抵消技术,该技术可以提高移动语音通信的私密性。将人头等效成刚性球体,并将人嘴等效成活塞辐射,计算了人头散射声场和人嘴辐射声场,同时通过在人头周围放置控制声源控制人嘴辐射声场,声场分析计算和实验结果表明,该技术能有效控制人嘴向外辐射的声场能量,一定程度上提升了语音通话的私密性。     

A decomposition technique for efficient generation of correlatedNakagami fading channels

Correlated Nakagami m-fading is commonly encountered in wireless communications. Its generation in a laboratory environment is therefore of theoretical and practical importance. However, no generic technique for this purpose is available in the literature. Correlated Rayleigh fading is easy to simulate since it has a simple relationship with a complex Gaussian process. Unfortunately, this is not the case for Nakagami fading. The difficulty lies in that the fading parameter can be a real number and there is no general theory linking a Nakagami vector to a finite set of correlated Gaussian vectors. In this paper, by introducing a direct-sum decomposition principle and determining the statistical mapping between the correlated Nakagami process and a set of Gaussian vectors for its generation, a simple general procedure is derived for the generation of correlated Nakagami channels with arbitrary parameters. A key parameter in the statistical mapping can be determined by using an iterative method. The validity of the new technique is examined through the generation of a correlated Nakagami sequence, as encountered in U.S. digital cellular, and a multibranch vector channel as encountered in diversity reception     

Analysis of a strip in a waveguide

An analysis and an experimental study of a strip in a transverse plane of a rectangular waveguide below cutoff are presented. This work is a preliminary step in analyzing a stripline-fed slot antenna array in which each stripline feed is enclosed in a rectangular waveguide below cutoff. A numerical method is developed to solve a “pseudo” mixed-potential integral equation for the current on the strip excited by a delta-gap source at some point along the strip. The Green's function for dipole sources in the rectangular waveguide is used in the spectral and spatial representations and Shanks' transform is employed to speed up the convergence of the doubly infinite series. Numerical and experimental results are presented for a monopole fed at one wall of a rectangular waveguide and for a bottom-fed and bottom-loaded strip in a rectangular waveguide     

Determination of Test Intervals in Certain Repairable Standby Protective Systems

A System has associated with it a Safeguard such that whenever a failure in the Safeguard is detected, the System is shut down. The System is restarted as soon as the Safeguard is repaired. An example is a standby protective system attached to a nuclear power plant; as soon as failure is detected in the protective system the nuclear plant will be shut down until repair is completed. In order to insure that the Safeguard remains in the utmost state of readiness, the components of the Safeguard are periodically tested, and repaired if the test reveals a failure. In this paper we define a measure of readiness appropriate for the above systems and consider the problem of determining the testing frequency of the components of the Safeguard in such a way that an adequate level of readiness is maintained. As an illustration, the method is applied to a typical reactor-trip system.     

A dual planar reflectarray with synthesized phase and amplitude distribution

A quasi-planar reflector arrangement for generating an arbitrary phase and amplitude distribution in the antenna aperture and thus a wide range of far field patterns is presented. A parallel pair of reflectarrays is used. One is implemented as a standard reflectarray using rectangular patches on a microwave substrate with metallized backside. The other reflectarray is provided with a polarizing grid, which acts as a ground plane for one polarization and is transparent for the orthogonal polarization. An offset rectangular feed horn is embedded in the lower reflectarray to illuminate the upper reflector. A design procedure for a linear polarized antenna with a sector beam in the azimuth and a narrow beam width in the elevation is presented and is verified with measurement results.     

Nonlinear background-to-signal coupling in lateral photoeffects

An analysis of the effect of a large spatially uniform time-independent background illumination on the lateral electric fields produced by a small space- and time-varying illumination of ap-njunction is presented. It is shown that a nonlinear coupling between background and signal results in a decrease in the signal electric fields. A general solution is obtained, and a solution in terms of well-known functions for a physically interesting case is exhibited. The parameter dependences are discussed and the effect of finite conductivities in both regions is analyzed.     

Reflection and transmission operators for strips or disks embeddedin homogenous and layered media

A notation is proposed to simplify the solution of scattering by strips and disks. Vector Fourier transforms are used and a double dot product for inner products in an uncountably infinite dimensional linear vector space is introduced. Scattering by a strip or a disk is characterized using a reflection operator and a transmission operator that relate the continuum of scattered waves to a continuum of incident waves. After the reflection operator for a single strip or disk is derived, it is shown how the reflection operator for a strip or disk in the presence of another reflecting medium, e.g. a layered medium, can be derived. The scattering by N strips or disks in a homogeneous medium is also discussed. The reflection operator for an embedded strip or disk in a layered medium is then derived. The method can be generalized to N strips or disks embedded in a layered medium and to a slot or aperture     

Reliability evaluation for tree-structured systems with multistate components

A tree-structured system with multistate components consists of a certain number of components which are arranged in a tree structure and are capable of receiving and sending a signal. The signal source is located in the root node, the components located in the leaf nodes can only receive a signal. Each component located in neither a root nor a leaf node is capable of transmitting the received signal directly to a number of components located below it, where this transmission is possible only along arcs linking the nodes, in the direction from upper to lower nodes. A component x is considered to be failed if it cannot transmit a signal to any other component, otherwise it is in the working condition and its state is determined by a set of components receiving a signal directly from x. The whole system is in working condition if each leaf node (which is assumed to be always in working condition) receives the signal from the root node.     

Predictive modeling of board level shock-impact reliability of the HVQFN-family

A semi-empirical model is derived to predict the board level drop-impact lifetime of HVQFN-packages soldered on a printed circuit board. The strain that evolves in the soldered interconnections is evaluated by a finite element model and related to the experimentally determined lifetime. The result is a power law and it is compared to literature data. In addition, a measure for the strain on the board is obtained analytically and compared with the experimental data. Here, too, dependence in the form of a power law is found. The combination of both results strongly suggests a near-linear relationship between the strain in the solder and the strain in the board.     

Wave Propagation in Sinusoidally Stratified Dielectric Media

The dispersion properties and the fields of electromagnetic waves are investigated for propagation in a stratified infinite medium. The stratification is characterized by a dielectric constant which, along one coordinate, is modulated sinusoidally about an average value. A systematic and comprehensive study is presented for the case of H modes for which the pertinent wave equation is in the form of a Mathieu differential equation. The modes and dispersion characteristics are analyzed in terms of a "stability" chart, which is customary in the study of the Mathieu equation. Results are obtained for an unbounded medium and for a waveguide filled with the modulated medium. Also, the reflection occurring at an interface between free space and a semi-infinite medium of this type is examined. In addition to these rigorous results for arbitrary values of modulation, simple analytical expressions are given for all of these cases where the modulation in the dielectric is small. It is shown that the fields are then expressible in terms of the fundamental and the two nearest space harmonics. The fields within a unit cell in the stratified medium are calculated for both small and large modulation and for frequencies up through the second pass band. It is of interest that the variation of the fields is not, in general, simply related to the variation of the dielectric constant within a cell.     

Distributed power allocation algorithm in wireless networks under SNR constraints

In this work, the distributed power allocation problem in wireless networks is studied under signal-to-noise ratio (SNR) constraints. The sources of uncertainty are assumed to come from the quantization process and measurement noise in the feedback system. The power allocation is formulated as a reference tracking problem of a pre-defined signal to noise-interference ratio. First, the synthesis problem with SNR constraints is studied as a 2-norm minimization process, which is equivalent to a linear-quadratic-regulator (LQR) problem. The solution of the associated Riccati equation in the LQR formulation is completely characterized, resulting in a feedback law with a recurrent structure. This control law is re-written in a transfer function format, where a simple control strategy is obtained which is dependant on the round-trip delay in the feedback system. In addition, the corresponding 2-norm closed-loop performance is also studied. Thus, the selection of the weight in the LQR problem establishes a compromise between robustness to quantization errors and measurement noise, and tracking performance. A comprehensive simulation evaluation validates the analytical derivations described in the paper.     

基于ZEMAX的半导体激光准直镜设计方法研究

针对目前采用单个球面镜压缩激光时存在发散角效果差或者球面镜片数过多的问题,通过ABCD矩阵法从理论上对高斯光束经过单透镜时的传输特性进行了分析,得出了单透镜无法实现半导体激光光束理想准直的结论。提出了一种基于ZEMAX的半导体光源准直镜的设计方案,并给出了设计与优化方法。结合工程中常用的808nm半导体激光器,设计了双片型808nm半导体激光准直镜,并在ZEMAX中使用合适的优化函数和权重对像差进行了校正。通过采用非球面镜获得了较好的准直效果,发散角达到了0．032mrad。该设计使用的镜片数较少,结构简单。     

Lee distance,Gray codes,and the torus

The torus is a topology that is the basis for the communication network of several multicomputers in use today. This paper briefly explores several topological characteristics of a generalized torus network using concepts from Coding theory and Graph theory. From Coding theory, the Lee distance metric and Gray codes are extended to mixed radix numbers. Lee distance is used to state the number and length of disjoint paths between two nodes in a torus. In addition, a function mapping a sequence of mixed radix numbers to a mixed radix Gray code sequence is described; and, provided at least one radix is even, this sequence is used to embed in the torus a cycle of any even length, including a Hamiltonian cycle. The torus is defined both as a cross product of cycles and using Lee distance. The graph-theoretic definition of a torus leads to a simple single node broadcasting algorithm, which is described in the last section. This revised version was published online in June 2006 with corrections to the Cover Date.     

Likelihood ratios for sequential hypothesis testing on Markov sequences

A variety of likelihood ratios are derived for detecting Gauss-Markov and finite-state Markov sequences in additive Gaussian noise. The Bayesian recursions appropriate to related filtering problems are exploited, together with "known-form" likelihood ratios, to obtain the desired results. In the derivation of a discrete-time Gauss-Markov likelihood ratio, a "pure" causal estimator-correlator structure is sought and a "locally stable" state estimator is encountered that is of some interest in its own right. The likelihood ratio is "pure" in the sense that the locally stable estimator is used in precisely the same manner as the stored replica is used in known-form signal detection problems to form the likelihood ratio. Consequently, the likelihood ratio is devoid of the extra data-dependent term that arises whenever one uses least squares state estimators to form the likelihood ratio statistic. The locally stable estimator equalizes, within a constant related to the {em a priori} and {em a posteriori} filtering error covariances, the {em a priori} and {em a posteriori} filtering densities. Heuristically, the estimator is a compromise between the one-step predictor and the filtered estimator of a discrete-time Kalman filter. When the observation noise covariance is unknown, a generalization of the so-called unknown level problem, then a Wishart prior is assigned to the innovations covariance and an integral representation is obtained for the desired likelihood ratio. The representation suggests a parallel structure for approximating the likelihood ratio when the observation noise covariance is unknown. Finally, the likelihood ratio for detecting finite-state Markov sequences is derived to illustrate that in general no "pure" estimator-correlator structure can exist when the state-space is finite.