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Schouten AC Vlugt ED van der Helm FC 《IEEE transactions on bio-medical engineering》2008,55(5):1612-1619
This study aimed to identify the functional contribution of reflexes to human motor control during posture maintenance. Continuous random force disturbances were applied at the hand while the subjects were instructed to minimize the deviation resulting from the force disturbances. The results were analyzed in the frequency domain with frequency response functions (FRFs). Two FRFs were evaluated: 1) the mechanical admittance and 2) the reflexive impedance, expressing the dynamic relation between position and muscle activation (assessed via electromyography, EMG). The reflexive impedance is a direct measure of the proprioceptive reflexes. To record all relevant dynamical characteristics of the arm, wide bandwidth signals were used as force disturbance. Distributing the power of the signal over fewer frequencies within the bandwidth improved the signal-to-noise-ratio SNR of the EMG recordings, facilitating reliable estimation of the reflexive impedance. The coherence indicated that the relation between force disturbance and EMG is linear under the given conditions and improved with the SNR. The method of designing disturbance signals and the estimation of the reflexive impedance are useful for studies aiming to quantify proprioceptive reflexes and to investigate its functionality. 相似文献
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El-Jaroudi A. Redfern M.S. Chaparro L.F. Furman J.M. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1996,84(9):1312-1318
We apply time-frequency (TF) spectral analysis techniques, namely evolutionary spectral estimators, to postural sway data gathered during quiet standing and in response to external visual stimuli. These techniques provide insight into the time-varying properties of the human balance control systems during standing. We demonstrate by means of individual and group examples that the results of the TF methods can be used to characterize the behavior of the balance system for groups of patients and controls. Specifically we show that, for healthy control subjects, sway at a visual stimulus frequency toward and away from the subject shows an amplitude which decays in time. On the other hand, patients display a response whose amplitude at the stimulus frequency increases with time. Thus TF analysis yields insights into the time-varying nature of the postural control system 相似文献
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脑信号跨频耦合现象与人的意识活动密切相关。本文将精细化的频带划分方法和多种跨频耦合的度量方法相结合,研究不同类型手腕运动的脑磁信号跨频耦合特征。首先对四类手运动脑磁信号进行精细化的频带分解,采用了三种具有主次关系的耦合度量方法(相干、虚部相干、调制指数),在高频耦合低频、低频耦合高频两种耦合形式下对某一运动方向类型信号显著区别于其它运动方向类型信号的频带数、通道对、频带对进行了统计分析,可以区分出不同方向手腕运动的MEG信号;进一步利用通道间的频带耦合关系以及源频带及其激励通道与响应通道等概念,采用相干耦合度量方法对上述两种耦合形式下的统计结果进行分析,获得相应的源频带、激励通道、响应通道,从而可以更加有效地区分不同方向手腕运动的MEG信号。 相似文献
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Schouten AC de Vlugt E van Hilten JJ van der Helm FC 《IEEE transactions on bio-medical engineering》2008,55(1):311-321
This study aimed to analyse the dynamic properties of the muscle spindle feedback system of shoulder muscles during a posture task. External continuous force disturbances were applied at the hand while subjects had to minimize their hand displacements. The results were analysed using two frequency response functions (FRFs) from which the model parameters were derived, being 1) the mechanical admittance and 2) the reflexive impedance. These FRFs were analysed by a neuromusculoskeletal model that implicitly separates the reflexive feedback properties (position, velocity and acceleration feedback gains) from intrinsic muscle visco-elasticity. The results show substantial changes in estimated reflex gains under conditions of variable bandwidth of the applied force disturbance or variable degrees of external damping. Position and velocity feedback gains were relatively larger when the force disturbance contained only low frequencies. With increasing damping of the environment, acceleration feedback gain decreased, velocity feedback gain remained almost constant and position feedback gain increased. It is concluded that under the aforementioned circumstances, the reflex system increases its gains to maximize the mechanical resistance to external force disturbances while preserving sufficient stability. 相似文献
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《Quantum Electronics, IEEE Journal of》2009,45(7):755-761
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《Mechatronics》2014,24(4):289-297
This paper considers the identification of structural dynamics by identifying its frequency response functions (FRFs) – a mathematical representation of the relationship between the vibration response at one location and excitation at the same or another location. The spatially-varying characteristics of the FRFs at various input and output locations are explored, and lead to a spatial linear parameter varying (LPV) representation. A local LPV identification technique for lumped systems is adapted here to spatially-interconnected systems. The identification of a spatial LPV model facilitates the experimental work, and also simplifies the controller synthesis. The proposed approach is applied to identify an actuated beam equipped with an array of collocated piezoelectric actuators and sensors for performance illustration. 相似文献
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To delineate the relative roles of each of the feedback sensors in the posture control system such as the visual, vestibular, and proprioceptive sensors, an identification technique was applied to measurements of antero-posterior sway angles of the body and ankle moments under the following conditions: standing on a fixed support with eyes open (ox), standing on a fixed support with eyes closed (cx), standing on a sway-referenced support with eyes open (os), and standing on a sway-referenced support with eyes closed (cs). Frequency response functions from the sway angle to the ankle moment were calculated. Gain and phase characteristics for conditions (os) and (cs) were similar to those of Nashner's (1972) vestibular model in the high-frequency range, which shows that the vestibular system may be dominant. The gain was higher under condition (cx) than under (ox). Judging from the phase characteristics, this was probably due to increased weighting of the proprioceptive sensor over the vestibular sensor. There was a tendency for gain to increase as balance tasks became more demanding 相似文献
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A Mathematical Model of the Vagus-Heart Period System in the Cat 总被引:1,自引:0,他引:1
The dynamic relation between changes in heart period and changes in the frequency of stimulation applied to the nerves involved in slowing the heart (vagus nerves) in chloralosed vagotomized cats pretreated with propranolol was investigated in ten cats using time-domain techniques. The strength of the stimuli was such that a sinus rhythm was always maintained. The typical response of heart period to step changes in the frequency of stimulation (range 4-50 Hz) was found to be an increase in heart period to a steady value preceded by an overshoot, and followed, after the stimulus was removed, by an undershoot (postvagal tachycardia). The observed response was accurately described by a dynamic model consisting of a third-order nonlinear system with time delay. The postvagal tachycardia was accounted for by including in the model a negative feedback loop; a portion of the overshoot was accounted for by the feedback loop and the remainder by including in the model a negative coefficient that varied as a negative exponential function of frequency. For small variations in the frequency of stimulation, it was shown in agreement with previous results, that the model could be approximated by a first-order system with time delay. In addition, it was found that provided a sinus rhythm was maintained, the steady-state value of heart period during vagal stimulation was neither a hyperbolic nor a logarithmic function of frequency of stimulation as suggested by previous investigators, but rather exhibited a maximum in the neighborhood of the middle of the frequency range studied. 相似文献
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In seismic reflection prospecting for oil and gas a key step is the ability to estimate the seismic wavelet (impulse response) traveling through the Earth. Such estimation enables filters to be designed to deblur the recorded seismic time series and allows the integration of “downhole” and surface seismic data for seismic interpretation purposes. An appropriate model for the seismic time series is a noisy-input/noisy-output linear model. The authors tackle the estimation of the impulse response in the frequency domain by estimating its frequency response function. They use a novel approach where multiple coherence analysis is applied to the replicated observed output series to estimate the output signal-to-noise ratio (SNR) at each frequency. This, combined with an estimate of the ordinary coherence between observed input and observed output, and with the spectrum of the observed input and cross-spectrum of the observed input and output, enables estimation of the frequency response function. The methodology is seen to work well on real and synthetic data 相似文献
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为解决无线基站宽带工作频带内电压驻波比(Voltage Standing Wave Ratio,VSWR)的实时测量,提出了一种采用信道估计法的测量方案。该方案实现简单,在基带处理单元高速率位置发送数据,依次抓取射频通道反馈和反射数据,分别求取信道响应序列,结合工厂装备测试数据,计算驻波反射系数和反射点位置。发送信号采用宽带正交频分复用信号,能检测到工作频段内任何频点处的驻波异常。有用信号前加循环前缀,并引入峰值抵消核,能正确检测到多个反射点驻波。仿真结果表明,该方案驻波测量精度和单回波点位置精度达到预期,多回波点测量能抓准外部主要故障点,在基站VSWR实时测量中具有良好的应用前景。 相似文献
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Chang‐Jun Ahn 《Wireless Communications and Mobile Computing》2006,6(8):1037-1045
Recently, unitary matrix modulation (UMM) has been investigated in multiple antenna systems which is called unitary space‐time modulation (USTM). In an OFDM, different channel delay profiles and path strengths bring different frequency selective patterns. Therefore, OFDM system can potentially provide a diversity at the frequency selective fading due to the different channel delay profiles. When we consider only the diagonal components of UMM with splitting over the coherence bandwidth, the system can obtain a frequency diversity in a single antenna, since the channel response of the diagonal components of UMM that split over the coherence bandwidth shows to be totally different. In this paper, we propose the diagonal components of UMM/OFDM with splitting over the coherence bandwidth (UMM‐S/OFDM) in a single antenna. The proposed system can obtain the frequency diversity with splitting the diagonal components of UMM/OFDM over the coherence bandwidth. Therefore, the proposed system with a single antenna can obtain good BER performance like the USTM/OFDM with two antennas. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Fransson PA Hafström A Karlberg M Magnusson M Tjäder A Johansson R 《IEEE transactions on bio-medical engineering》2003,50(12):1310-1319
The objective for this study was to investigate whether the adaptation of postural control was similar during galvanic vestibular stimulation and during vibratory proprioceptive stimulation of the calf muscles. Healthy subjects were tested during erect stance with eyes open or closed. An analysis method designed to consider the adaptive adjustments was used to evaluate the motion dynamics and the evoked changes of posture and stimulation response. Galvanic vestibular stimulation induced primarily lateral body movements and vibratory proprioceptive stimulation induced anteroposterior movements. The lateral body sway generated by the galvanic stimulation was proportionally smaller and contained more high-frequency movements (> 0.1 Hz) than the anteroposterior body sway induced by the vibratory stimulation. The adaptive adjustments of the body sway to the stimulation had similar time course and magnitude during galvanic and vibratory stimulation. The perturbations induced by stimulation were gradually reduced within the same time range (15-20 s) and both kinds of stimulation induced a body leaning whose direction was dependent on stimulus. The similarities in the adjustment patterns suggest that postural control operates in the same way independent of the receptor systems affected by the disturbance and irrespective of whether the motion responses were induced in a lateral or anteroposterior direction. 相似文献
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Pseudorandom noise (PRN) of various bandwidths was used in testing both normal and hearing impaired subjects by means of auditory-evoked potentials (AEP's). The AEP's were studied in the frequency domain via spectral analysis rather than in the time domain as is often done. Spectral analysis provides such system features as power spectral densities (PSD's) and transfer and coherence functions. The results show that these AEP's are similar to the frequency following responses obtained with pure tones. The PSD's of the evoked responses tend to correlate slightly with those of the PRN simuli, as verified by the presence of coherence between the stimulus and the response. The average coherence over the bandwidth of the stimulus decreases with increased sensory-neural hearing loss and also as the stimulus bandwidth is increased. No unique transfer functions, with respect to the subjects or the intensities of stimuli, could be obtained. However, an attempt has been made to correlate subjects' audiograms with the spectral analysis results. 相似文献
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The temporal coherence properties of picosecond pulses from GaAlAs semiconductor lasers have been studied by measuring first- and second-order autocorrelation functions with a Michelson interferometer. The time-bandwidth product and chirp have been evaluated for several different laser structures and frequency stabilization schemes. Time-bandwidth products from 1.2 for a CSP laser to 3.6 for a TJS laser were obtained with operating conditions representative of high-speed communication systems. Computer simulations based on the rate equations have been used to model the temporal coherence during the pulse and they show good agreement with our measurements. The results show that it is important to select the appropriate laser structure and stabilization scheme in applications where the temporal coherence is significant for system performance. 相似文献
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A. I. Efimov L. A. Lukanina A. I. Rogashkova L. N. Samoznaev I. V. Chashei M. K. Bird M. Pátzold 《Journal of Communications Technology and Electronics》2013,58(9):901-910
The statistical characteristics of Faraday-rotation fluctuations (FRFs) of a radio-wave polarization plane are analyzed when the circumsolar plasma is sounded by the signals of a Helios 1 space probe. The time spectra and auto- and crosscorrelation functions of FRFs, which are measured simultaneously at two ground stations separated by large distances, have been determined. The wavelet spectra of FRFs are presented, and the opportunities of the wavelet transform and other techniques used to reveal quasi-periodic FRFs with different periods are investigated. It is demonstrated that the quasi-periodic magnetic field oscillations, which are excited by the trains of Alfvén waves propagating through the solar supercorona (their period varies between 2 and 160 min), are observed at the heliocentric distances of 3–12 solar radii. 相似文献