Polarity Correlator for Conduction Velocity Measurement

Techniques for the estimation of skeletal muscle fiber conduction velocity are of considerable interest. These techniques use, in general, some form of cross correlation or zero-crossing analysis. Cross correlation is a straightforward method of conduction velocity estimation, however, it is difficult to realize low-cost real-time processors. Polarity correlation offers a method which preserves the advantages of cross correlation and satisfies the speed-cost constraint. This paper describes the algorithm for implementation of a polarity cofrelator instrument using a microprocessor. The instrument is tested with deterministic and stochastic signals and used to estimate the conduction velocity of biceps brachii fibers of ten normal subjects. The performance of the instrument is compared to the zero-crossing technique described by Lynn.     

Modeling of Mammalian Skeletal Muscle

A model of mammalian skeletal muscle is developed from experimental results from a rat gracilis anticus muscle at 17.5°C. The approach consists of factoring pertinent variables of muscle contraction (length, force, velocity, and duration of stimulation) into a series of physically realizable functions. The analysis indicates that for lengths less than 120 percent of rest length, mammalian skeletal muscle can be modeled as a nonlinear force generator, a function of length and time, bridged by a nonlinear viscous-like element, a function of time, length, and velocity, in series with a nonlinear elastic element, a function of length. A close correlation exists between the results obtained during an analog computer simulation of the model and those from a typical rat gracilis anticus muscle.     

The Measurement of Muscle Fiber Conduction Velocity Using a Gradient Threshold Zero-Crossing Method

The conduction velocity of myoelectric potential along muscle fiber is known to be an index of the degree of muscular fatigue or muscular disease. When detecting the myoelectric potential by means of surface electrodes, the conduction velocity must be extracted from an apparently random wave of a myoelectric signal. In this paper, a method for determining conduction velocity is proposed based upon a zero-crossing time delay measurement with reference to the derivative of a myoelectric signal. The slope value of the input signal provides an effective criterion for rejecting undesired zero crossing caused by noise. This method needs no spectral analysis nor correlation calculation. Compared to another previously reported zero-cossing approach using digital filter preprocessing, it shows a more accurate and rapid estimation of velocity.     

FES and spasticity

A model of hemiplegic spasticity based on electromyographical and biomechanical parameters measured during passive muscle stretching is presented. Two components of spasticity can be distinguished--phasic and tonic. This classification depends on the pattern of stretch reflex activity which can be either phasic or tonic as well as on the muscle stretch/tension characteristic. Stretch reflex, as a control loop, is in phasic spasticity characterized by increased sensitivity to velocity of stretching. In tonic spasticity, sensitivity to length of stretching is increased. After the injury, phasic spasticity appears first and invokes monosynaptic reflex pathways. The intensity of tonic spasticity increases with the duration of disability and hence causes changes in muscle fiber biomechanical properties. The model mentioned above has been used to evaluate the effects of FES on spasticity. Hemiplegic patients with implanted peroneal nerve stimulator for gait correction were followed up for one year starting a week before implantation. Long-term use of FES resulted in decrease of tonic spasticity in both ankle joint antagonistic muscle groups. In stimulated tibialis anterior muscle, the phasic type of spasticity increased. To obtain the correlation between changes in spasticity and functional abilities of patients, the maximal voluntary isometric contraction of both muscle groups was also measured. An improvement in voluntary strength was also observed. This can be taken as additional evidence that tonic spasticity is of greater physiological and clinical significance than phasic spasticity. It may be concluded that use of FES can decrease tonic spasticity and, if applied early after the injury, can prevent the appearance of tonic spasticity.     

Nerve-bundle conduction velocity distribution measurement and transfer function analysis

Human peripheral nerves are composed of thousands of individual nerve fibers whose signal conduction velocities vary from 0.2 to 100 m/s. Though good correlation exist between fiber velocity and the physiological function subserved by these fibers, considerable variation is found for specific end organs (20 to 40 m/s for a single muscle). Though clinical neurophysiologists have routinely measured the maximum conduction velocity of peripheral motor nerves for 30 years, it has not been possible to determine the velocity distributions. This report details a model and noninvasive methodology for motor axon conduction latency distribution mesurement. This distribution, proportional to velocity dispersion, possesses a low-pass filter characteristic which agrees with theoretical predictions and may be significant in some sensory and motor functions.     

Effect of group velocity mismatch on the measurement of ultrashort optical pulses via second harmonic generation

The use of second harmonic generation as a technique for optical pulse width measurements is analyzed to determine the effects of both phase velocity and group velocity mismatch between fundamental and second harmonic fields. An expression for the time average second harmonic energy, which except for special cases differs from the intensity autocorrelation function, is derived. For Type I phase matching, the measurement yields an apparent correlation width which can be either shorter or longer than the actual intensity correlation width, depending on the specific pulse shape. When the group velocity mismatch is nonzero, the measurement becomes sensitive to the phase matching condition. Two special pulse shapes for which the measurement is independent of group and phase velocity mismatch are the Gaussian and the single-sided exponential.     

A technique to track individual motor unit action potentials in surface EMG by monitoring their conduction velocities and amplitudes

The speed of propagation of an action potential along a muscle fiber, its conduction velocity (CV), can be used as an indication of the physiological or pathological state of the muscle fiber membrane. The motor unit action potential (MUAP), the waveform resulting from the spatial and temporal summation of the individual muscle fiber action potentials of that motor unit (MU), propagates with a speed referred to as the motor unit conduction velocity (MUCV). This paper introduces a new algorithm, the MU tracking algorithm, which estimates MUCVs and MUAP amplitudes for individual MUs in a localized MU population using SEMG signals. By tracking these values across time, the electrical activity of the localized MU pool can be monitored. An assessment of the performance of the algorithm has been achieved using simulated SEMG signals. It is concluded that this analysis technique enhances the suitability of SEMG for clinical applications and points toward a future of noninvasive diagnosis and assessment of neuromuscular disorders.     

Muscle-like contraction control of tendon-sheath artificial muscle

The development of artificial muscles has focused on a high energy–weight ratio and soft structures, however, little work has been done towards muscle-like contraction behaviors. This unfortunately leads to a lack of comfort and safety, which is especially important for robotic applications like orthotics and exoskeletons. In this paper, we propose a contraction control method for a tendon-sheath artificial muscle to contract and relax like biological muscles. In view of the nonlinear transmission characteristics of the tendon-sheath artificial muscle, a transmission model is established and its accuracy is verified through experiments. A muscle-like contraction control method is then proposed based on the transmission model and the Hill-type muscle model. Through this method, the contraction force of the tendon-sheath artificial muscle can be adjusted according to the output displacement and velocity of the tendon-sheath mechanism estimated by the transmission model. Isometric contraction and quick-release experiments are then conducted. The experimental results demonstrate that this control method allows the tendon-sheath artificial muscle to contract with specific muscle-like force–length and force–velocity properties.     

Deconvolution estimation of motor unit conduction velocity distribution

A conduction velocity distribution (CVD) estimator that incorporates volume conductor modeling of the muscle voluntary response is introduced in this paper. The CVD estimates are obtained from two correlation functions, an autocorrelation and a cross, computed from myoelectric signal recorded at the skin surface. The performance of the proposed estimator is evaluated for simulated and experimental data. The study includes assessment of the estimator bias and standard deviation, as well as its sensitivity to errors in the model parameters. Simulations show its good performance in terms of estimator bias. A filtering technique also helps reduce its variance. However, the inaccuracy introduced in the estimation of model parameters considerably deteriorates the estimator performance.     

Influence of tissue inhomogeneities on noninvasive muscle fiberconduction velocity measurements-investigated by physical and numericalmodeling

The determination of conduction velocity in the muscle fibers of single motor units from noninvasive recordings of single motor unit action potentials can be improved by the method of spatially filtering multielectrode EMG. The use of this conduction velocity as a diagnostic tool requires a high reliability of the detected values. However, experiments did reveal that the measured conduction velocity values showed remarkably high fluctuations depending on the recording site along the muscle fibers which could not be attributed to the influence of the endplate and tendon region. The present work examines the hypothesis that the observed fluctuations in propagation velocity were caused by electrically inhomogeneous tissue, regions of different electrical conductivity which are located between the excited muscle fibers and the recording electrodes and which cause a deformation of the extracellular electric current field. The investigation was performed by means of a physical model as well as by finite element model calculations. In both models single, simple shaped (cylindrical) inhomogeneity regions with a conductivity of 0.1 to 10 times that of the surrounding medium and diameters ranging between 1.6 and 2.7 mm were placed between excitation sources and recording site. The results indicate that the observed conduction velocity fluctuations of up to some 10% can be well attributed to inhomogeneity effects of the tissue conductivity. Based on these results, one may look for signal processing methods to cut down such fluctuations in conduction velocity measurements.     

基于多普勒耦合估计的弹道目标测距方法

反导预警与空间监视雷达通常采用高频段、大脉宽探测远距离目标,此时距离多普勒耦合对于雷达精确测距有较大影响。同时,距离多普勒耦合的准确修正是稳定跟踪目标的必要条件,然而传统的处理方法不能适用于弹道目标等高机动目标的准确处理。本文提出了基于多普勒耦合估计的弹道目标高精度测距方法：首先采用旁路速度-加速度估计方法求解目标的径向速度,对目标测量距离进行距离多普勒耦合修正,再进行IMM-UKF滤波完成目标距离估计。该方法具有以下优势：利用当前帧的测量数据,同时考虑了目标径向加速度对于耦合的影响,提高了距离和速度的估计精度;相比跟踪时增加测速波形的方法,节约了雷达的资源,同时避免了速度测量与航迹误关联的问题;距离和速度的精确估计能够提升航迹关联成功率。仿真实验中与传统的距离多普勒耦合处理方法进行了比较,实验结果显示该方法大幅提高了雷达测距的精度。     

The DEMATRON—A new crossed-field amplifier

A nonreentrant beam, distributed-emission, crossed-field, forward-wave amplifier, the DEMATRON, is described. The difficulties encountered by early experimenters in achieving gain in excess of 6 db in nonreentrant, crossed-field amplifiers are overcome in the DEMATRON by use of either an electron velocity taper or circuit velocity taper. A crossed-field amplifier design theory is given which is based on the use of equivalent magnetrons, and which takes into account the need for velocity compensation. In practice, electron velocity compensation is accomplished by either changing the sole-anode spacing, or by varying the dc magnetic field or a combination of both. Experiments with the DEMATRON have yielded gains in excess of 10 db over a 15 per cent bandwidth. Power levels between 300 and 500 kw have been achieved at an operating voltage of 25 kv. The design theory has been experimentally shown to be quite satisfactory in the large-signal, saturated gain region of operation, However, the lack of adequate small-signal theory has thus far prevented full optimization of the velocity compensation.     

Estimation of elbow-induced wrist force with EMG signals using fast orthogonal search

In many studies and applications that include direct human involvement-such as human-robot interaction, control of prosthetic arms, and human factor studies-hand force is needed for monitoring or control purposes. The use of inexpensive and easily portable active electromyogram (EMG) electrodes and position sensors would be advantageous in these applications compared to the use of force sensors, which are often very expensive and require bulky frames. Multilayer perceptron artificial neural networks (MLPANN) have been used commonly in the literature to model the relationship between surface EMG signals and muscle or limb forces for different anatomies. This paper investigates the use of fast orthogonal search (FOS), a time-domain method for rapid nonlinear system identification, for elbow-induced wrist force estimation. It further compares the forces estimated using FOS with the forces estimated by MLPANN for the same human anatomy under an ensemble of operational conditions. In this paper, the EMG signal readings from upper arm muscles involved in elbow joint movement and sensed elbow angular position and velocity are utilized as inputs. A single degree-of-freedom robotic experimental testbed has been constructed and used for data collection, training and validation.     

连续波雷达加速度和速度估计方法研究

针对连续波雷达测速过程中目标径向加速度对速度测量精度的影响,采用基于自相关函数与先验知识相结合的方法进行加速度估计和补偿。仿真试验结果表明,该方法能够有效地估计出目标的径向加速度,先验知识的引入进一步降低了正确估计对输入信噪比的要求,提高了估计精度,减小了计算量。     

传递函数快速相关法的激光测速技术研究

激光技术测量是实现传送带、热轧钢板等运动物体测速的主要手段，为了改善测量精度和响应速度，提出系统传递相关分析测速技术。采用计算发射端和接收端之间两路信号的系统传递函数进行相关性分析的方法，进行了理论验证和实验分析，得到了相对误差小于0.1%的实验结果。结果表明，利用系统传递函数相关分析构建激光测速系统，代替解调电路，简化信号调理电路，可降低电路部分引起的不确定度；互功率谱函数法实现快速相关分析和频域求得系统传递函数，可提高系统响应速度；合理设置发射端间距，取样积分提高测量信噪比，降低环境引起的不确定度，测量不确定度小于0.2%。该研究对传送带速率的实时测量有一定指导意义。     

一种多目标ISAR成像方法

在逆合成孔径雷达(ISAR)多目标成像中,当各目标相互靠近且目标相对雷达的径向速度又相差较大时,存在使用已有的多目标成像方法无法对其成像的问题,文中提出了一种结合Radon变换、包络相关和DCFT的多目标成像方法。该方法采用Radon变换估计目标个数并对目标包络进行粗对齐;用传统的包络相关法结合目标隔离和曲线拟合法对目标进行精确的包络对齐;通过DCFT算法完成相位补偿,最后获得多个目标清晰的ISAR像。仿真实验结果验证了该方法的有效性。     

Effect of mobile velocity on communications in fading channels

In a fading channel, it is well known that the rate of channel variation is dependent on the velocity of the mobile. Consequently, depending on the channel correlation, successive symbols transmitted over the channel can suffer from very similar or possibly very different fading conditions. In this paper, we present an analytical model to evaluate the effect of mobile velocity on the performance of a communication system operating in a multipath fading channel. To incorporate the effect of velocity, a Markov process is used which captures the correlated nature of the channel. An error recursion is then developed which considers the effect of closed-loop power control, channel coding, and finite interleaving. In the numerical analysis, we use the analytical model to investigate the tradeoffs when these various schemes are used. We demonstrate how the performance of these different schemes is sensitive to mobile velocity     

测定浓密悬浮颗粒流速的光学互相关系统

本文提出测定浓密悬浮颗粒平均流速的光学互相关系统。使用微型电子计算机采集和处理数据。通过确定两支激光束衰减扰动互相关函数的峰值位置，可以实现运动粒子速度的无接触测量。实验结果证实光强扰动的互相关技术可以有效地运用于双组份流量计量领域。     

Avalanche-induced 1/f noise in bipolar transistors

It has been proposed that degradation of low current hFE, as a result of avalanching the emitter-base junction of a bipolar transistor, can be attributed to an increase in surface recombination velocity within the emitter-base space-charge region. This work shows that 1/fnoise is also increased during avalanche and that this increase is consistent with a previously reported correlation between surface recombination velocity and 1/fnoise.     

LFMCW雷达高速目标速度解模糊新方法

线性调频连续波（LFMCW）雷达中高速的直升机目标将产生速度模糊。为了解决高速目标的速度模糊,提出了航迹关联的解模糊方法,通过对目标运动建模,计算目标平均速度,并用平均速度估算最大不模糊速度的系数,实现高速目标的解模糊。实例应用表明：该方法估算性能好、简单、可操作性强。