Neuromuscular mechanisms and neural strategies in the control of time-varying muscle contractions

2013 ◽  
Vol 110 (6) ◽  
pp. 1404-1414 ◽  
Author(s):  
Sophia Erimaki ◽  
Orsalia M. Agapaki ◽  
Constantinos N. Christakos
Keyword(s):  
Feedforward Control ◽  
Low Frequency ◽  
Control Mechanisms ◽  
Time Varying ◽  
Population Activity ◽  
Force Oscillation ◽  
Neural Input ◽  
Force Tracking ◽  
Force Signal ◽  
Human Finger

The organization of the neural input to motoneurons that underlies time-varying muscle force is assumed to depend on muscle transfer characteristics and neural strategies or control modes utilizing sensory signals. We jointly addressed these interlinked, but previously studied individually and partially, issues for sinusoidal (range 0.5–5.0 Hz) force-tracking contractions of a human finger muscle. Using spectral and correlation analyses of target signal, force signal, and motor unit (MU) discharges, we studied 1) patterns of such discharges, allowing inferences on the motoneuronal input; 2) transformation of MU population activity (EMG) into quasi-sinusoidal force; and 3) relation of force oscillation to target, carrying information on the input's organization. A broad view of force control mechanisms and strategies emerged. Specifically, synchronized MU and EMG modulations, reflecting a frequency-modulated motoneuronal input, accompanied the force variations. Gain and delay drops between EMG modulation and force oscillation, critical for the appropriate organization of this input, occurred with increasing target frequency. According to our analyses, gain compensation was achieved primarily through rhythmical activation/deactivation of higher-threshold MUs and secondarily through the adaptation of the input's strength expected during tracking tasks. However, the input's timing was not adapted to delay behaviors and seemed to depend on the control modes employed. Thus, for low-frequency targets, the force oscillation was highly coherent with, but led, a target, this timing error being compatible with predictive feedforward control partly based on the target's derivatives. In contrast, the force oscillation was weakly coherent, but in phase, with high-frequency targets, suggesting control mainly based on a target's rhythm.

Effects of Local Nicotinic Activation of the Superior Colliculus on Saccades in Monkeys

2005 ◽  
Vol 93 (1) ◽  
pp. 519-534 ◽  
Author(s):  
Masayuki Watanabe ◽  
Yasushi Kobayashi ◽  
Yuka Inoue ◽  
Tadashi Isa
Keyword(s):  
Superior Colliculus ◽  
Reaction Times ◽  
Low Frequency ◽  
Visually Guided ◽  
Population Activity ◽  
Affected Area ◽  
Movement Field ◽  
Neural Interactions ◽  
Restricted Region

To examine the role of competitive and cooperative neural interactions within the intermediate layer of superior colliculus (SC), we elevated the basal SC neuronal activity by locally injecting a cholinergic agonist nicotine and analyzed its effects on saccade performance. After microinjection, spontaneous saccades were directed toward the movement field of neurons at the injection site (affected area). For visually guided saccades, reaction times were decreased when targets were presented close to the affected area. However, when visual targets were presented remote from the affected area, reaction times were not increased regardless of the rostrocaudal level of the injection sites. The endpoints of visually guided saccades were biased toward the affected area when targets were presented close to the affected area. After this endpoint effect diminished, the trajectories of visually guided saccades remained modestly curved toward the affected area. Compared with the effects on endpoints, the effects on reaction times were more localized to the targets close to the affected area. These results are consistent with a model that saccades are triggered by the activities of neurons within a restricted region, and the endpoints and trajectories of the saccades are determined by the widespread population activity in the SC. However, because increased reaction times were not observed for saccades toward targets remote from the affected area, inhibitory interactions in the SC may not be strong enough to shape the spatial distribution of the low-frequency preparatory activities in the SC.

Numerical Study on Hydrodynamic Responses of a Two-Body System in Side-by-Side Operation

2016 ◽  
Author(s):  
Shaowu Ou ◽  
Shixiao Fu ◽  
Wei Wei ◽  
Tao Peng ◽  
Xuefeng Wang
Keyword(s):  
Numerical Study ◽  
Low Frequency ◽  
Optimal Operation ◽  
Hydrodynamic Interactions ◽  
Irregular Waves ◽  
Mooring System ◽  
Time Varying ◽  
Body System ◽  
The Time Domain ◽  
Two Bodies

Typically, in some side-by-side offshore operations, the speed of vessels is very low or even 0 and the headings are manually maneuvered. In this paper, the hydrodynamic responses of a two-body system in such operations under irregular seas are investigated. The numerical model includes two identical PSVs (Platform Supply Vessel) as well as the fenders and connection lines between them. A horizontal mooring system constraining the low frequency motions is set on one of the ships to simulate maneuver system. Accounting for the hydrodynamic interactions between two bodies, 3D potential theory is applied for the analysis of their hydrodynamic coefficients. With wind and current effects included, these coefficients are further applied in the time domain simulations in irregular waves. The relevant coefficients are estimated by experiential formulas. Time-varying loads on fenders and connection lines are analyzed. Meanwhile, the relative motions as well as the effects of the hydrodynamic interactions between ships are further discussed, and finally an optimal operation scheme in which operation can be safely performed is summarized.

Coarse graining spectral analysis of HR and BP variability in patients with autonomic failure

1996 ◽  
Vol 271 (4) ◽  
pp. H1555-H1564 ◽  
Author(s):  
A. P. Blaber ◽  
R. L. Bondar ◽  
R. Freeman
Keyword(s):  
Heart Rate ◽  
Autonomic Failure ◽  
Spectral Power ◽  
Low Frequency ◽  
Coarse Graining ◽  
Low Complexity ◽  
System Response ◽  
High Signal ◽  
Neural Input ◽  
Signal Complexity

We examined heart rate and blood pressure variability (HRV and BPV) during graded tilt (5 min in each position: supine, -10 degrees, 10 degrees, 30 degrees, 60 degrees, -10 degrees, supine) in autonomic failure patients and age-matched controls. Heart rate was not different between patients and controls and increased with tilt (P < 0.001). Total HRV was reduced in patients (P < 0.03). Patients had reduced low-frequency (0-0.15 Hz) HRV and BPV (P < 0.005). With tilt, low-frequency BPV increased in controls, whereas high-frequency (> 0.15 Hz) BPV increased in patients. The slope of the fractal component (beta) for HRV and BPV was not different between patients and controls. HRV-beta increased (1.5-1.9, P < 0.01) with tilt, but BPV-beta (approximately 1.8) was unaffected. Values of beta close to 1 indicate high signal regulatory complexity, and values of beta close to 2 indicate low complexity. HRV and BPV provide clear evidence of impaired sympathetic and parasympathetic autonomic nervous system response to tilt with autonomic failure. The similarity in signal complexity with reduced fractal and harmonic spectral power, in patients compared with controls, suggests unchanged cardiovascular neural input and integration with reduced output in autonomic failure.

Real-time feedforward control of low-frequency interior noise using shallow spherical shell piezoceramic actuators

1999 ◽  
Vol 8 (5) ◽  
pp. 579-584 ◽  
Author(s):  
V Jayachandran ◽  
Patrick King ◽  
Nancy E Meyer ◽  
Florence J Li ◽  
Maria Petrova ◽  
...  
Keyword(s):  
Spherical Shell ◽  
Real Time ◽  
Feedforward Control ◽  
Low Frequency ◽  
Interior Noise ◽  
Shallow Spherical Shell

scholarly journals Analysis of nonstationarity in renal autoregulation mechanisms using time-varying transfer and coherence functions

2008 ◽  
Vol 295 (3) ◽  
pp. R821-R828 ◽  
Author(s):  
Ki H. Chon ◽  
Yuru Zhong ◽  
Leon C. Moore ◽  
Niels H. Holstein-Rathlou ◽  
William A. Cupples
Keyword(s):  
Transfer Functions ◽  
Low Frequency ◽  
Time Varying ◽  
Frequency Range ◽  
Sprague Dawley ◽  
Dynamic Complexity ◽  
Spontaneously Hypertensive ◽  
Renal Autoregulation ◽  
Blood Flow Dynamics ◽  
Frequency Coherence

The extent to which renal blood flow dynamics vary in time and whether such variation contributes substantively to dynamic complexity have emerged as important questions. Data from Sprague-Dawley rats (SDR) and spontaneously hypertensive rats (SHR) were analyzed by time-varying transfer functions (TVTF) and time-varying coherence functions (TVCF). Both TVTF and TVCF allow quantification of nonstationarity in the frequency ranges associated with the autoregulatory mechanisms. TVTF analysis shows that autoregulatory gain in SDR and SHR varies in time and that SHR exhibit significantly more nonstationarity than SDR. TVTF gain in the frequency range associated with the myogenic mechanism was significantly higher in SDR than in SHR, but no statistical difference was found with tubuloglomerular (TGF) gain. Furthermore, TVCF analysis revealed that the coherence in both strains is significantly nonstationary and that low-frequency coherence was negatively correlated with autoregulatory gain. TVCF in the frequency range from 0.1 to 0.3 Hz was significantly higher in SDR (7 out of 7, >0.5) than in SHR (5 out of 6, <0.5), and consistent for all time points. For TGF frequency range (0.03–0.05 Hz), coherence exhibited substantial nonstationarity in both strains. Five of six SHR had mean coherence (<0.5), while four of seven SDR exhibited coherence (<0.5). Together, these results demonstrate substantial nonstationarity in autoregulatory dynamics in both SHR and SDR. Furthermore, they indicate that the nonstationarity accounts for most of the dynamic complexity in SDR, but that it accounts for only a part of the dynamic complexity in SHR.

scholarly journals Feedforward Control Based on Error and Disturbance Observation for the CCD and Fiber-Optic Gyroscope-Based Mobile Optoelectronic Tracking System

Electronics ◽  
2018 ◽  
Vol 7 (10) ◽  
pp. 223 ◽  
Author(s):  
Yong Luo ◽  
Wei Ren ◽  
Yongmei Huang ◽  
Qiunong He ◽  
Qiongyan Wu ◽  
...  
Keyword(s):  
Fiber Optic ◽  
Control Method ◽  
Feedforward Control ◽  
Tracking System ◽  
Sampling Rate ◽  
Low Frequency ◽  
Integration Time ◽  
Fiber Optic Gyroscope ◽  
Loop Control ◽  
Boresight Error

In the mobile optoelectronic tracking system (MOTS) based on charge-coupled device (CCD) and fiber-optic gyroscope (FOG), the tracking performance (TP) and anti-disturbance ability (ADA) characterized by boresight error are of equal importance. Generally, the position tracking loop, limited by the image integration time of CCD, would be subject to a non-negligible delay and low-sampling rate, which could not minimize the boresight error. Although the FOG-based velocity loop could enhance the ADA of the system, it is still insufficient in the case of some uncertain disturbances. In this paper, a feedforward control method based on the results of error and disturbance observation was proposed. The error observer (EOB) based on the CCD data and model output essentially combined the low-frequency tracking feedforward and closed-loop disturbance observer (DOB), which could simultaneously enhance the low-frequency TP and ADA. In addition, in view of the poor low-frequency performance of the FOG due to drift and noise that may result in the inaccuracy of the observed low-frequency disturbance, the FOG-based DOB was used to improve the relatively high-frequency ADA. The proposed method could make EOB and DOB complementary and help to obtain a high-precision MOTS, for in practical engineering, we give more attention to the low-frequency TP and full-band ADA. Simulations and experiments demonstrated that the proposed method was valid and had a much better performance than the traditional velocity and position double-loop control (VPDC).

Vibration exercise for treatment of osteoporosis: A theoretical model

2008 ◽  
Vol 222 (7) ◽  
pp. 1161-1166 ◽  
Author(s):  
M Aleyaasin ◽  
J J Harrigan
Keyword(s):  
Theoretical Model ◽  
Low Frequency ◽  
Bed Rest ◽  
Finite Amplitude ◽  
Time Varying ◽  
Vibration Exercise ◽  
Varying Coefficients ◽  
Low Frequency Vibration ◽  
Analytical Result ◽  
Stiffness And Damping

Orthopaedic rehabilitation of osteoporosis by muscle vibration exercise is investigated theoretically using Wolff's theory of strain-induced bone ‘remodelling’. The remodelling equation for finite amplitude vibration to be transmitted to the bone via muscle corresponds to a slowly time-varying non-linear dynamic system. This slowly time-varying system is governed by a Riccatti equation with rapidly varying coefficients that oscillate with the frequency of the applied vibration. An averaging technique is used to determine the effective force transmitted to the bone. This force is expressed in terms of the stiffness and damping parameters of the connected muscle. The analytical result predicts that, in order to obtain bone reinforcement, the frequency and amplitude of vibration should not exceed specified levels. Furthermore, low-frequency vibration does not stimulate the bone sufficiently to cause significant remodelling. The theoretical model herein confirms the clinical recommendations regarding vibration exercise and its effects on rehabilitation. In a numerical example, the model predicts that a femur with reduced bone mass as a result of bed rest will be healed completely by vibration consisting of an acceleration of 2 g applied at a frequency of 30 Hz over a period of 250 days.

Disturbance Observer-Based Pitch Control of Wind Turbines for Enhanced Speed Regulation

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Yuan Yuan ◽  
X. Chen ◽  
J. Tang
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Disturbance Observer ◽  
Low Frequency ◽  
Time Varying ◽  
Control Loop ◽  
Wind Speeds ◽  
Speed Regulation ◽  
Guaranteed Stability ◽  
Linearized Model

Time-varying unknown wind disturbances influence significantly the dynamics of wind turbines. In this research, we formulate a disturbance observer (DOB) structure that is added to a proportional-integral-derivative (PID) feedback controller, aiming at asymptotically rejecting disturbances to wind turbines at above-rated wind speeds. Specifically, our objective is to maintain a constant output power and achieve better generator speed regulation when a wind turbine is operated under time-varying and turbulent wind conditions. The fundamental idea of DOB control is to conduct internal model-based observation and cancelation of disturbances directly using an inner feedback control loop. While the outer-loop PID controller provides the basic capability of suppressing disturbance effects with guaranteed stability, the inner-loop disturbance observer is designed to yield further disturbance rejection in the low frequency region. The DOB controller can be built as an on–off loop, that is, independent of the original control loop, which makes it easy to be implemented and validated in existing wind turbines. The proposed algorithm is applied to both linearized and nonlinear National Renewable Energy Laboratory (NREL) offshore 5-MW baseline wind turbine models. In order to deal with the mismatch between the linearized model and the nonlinear turbine, an extra compensator is proposed to enhance the robustness of augmented controller. The application of the augmented DOB pitch controller demonstrates enhanced power and speed regulations in the above-rated region for both linearized and nonlinear plant models.

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