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Loop Gain (loop + gain)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

Three-dimensional nonlinear H, guidance law

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 2 2001
Ciann-Dong Yang
Abstract This paper proposes a novel three-dimensional missile guidance law design based on nonlinear H, control. The complete nonlinear kinematics of pursuit,evasion motion is considered in the three-dimensional spherical co-ordinates system; neither linearization nor small angle assumption is made here. The nonlinear H, guidance law is expressed in a simple form by solving the associated Hamilton,Jacobi partial differential inequality analytically. Unlike adaptive guidance laws, the implement of the proposed robust H, guidance law does not require the information of target acceleration, while ensuring acceptable interceptive performance for arbitrary target with finite acceleration. The resulting pursuit,evasion trajectories for both the H, -guided missile and the worst-case target are determined in closed form, and the performance robustness against variations in target acceleration, in engagement condition, and in control loop gain, is verified by numerical simulations. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Development of respiratory control instability in heart failure: a novel approach to dissect the pathophysiological mechanisms

THE JOURNAL OF PHYSIOLOGY, Issue 1 2006
Charlotte H. Manisty
Observational data suggest that periodic breathing is more common in subjects with low F, high apnoeic thresholds or high chemoreflex sensitivity. It is, however, difficult to determine the individual effect of each variable because they are intrinsically related. To distinguish the effect of isolated changes in chemoreflex sensitivity, mean F and apnoeic threshold, we employed a modelling approach to break their obligatory in vivo interrelationship. We found that a change in mean CO2 fraction from 0.035 to 0.045 increased loop gain by 70 ± 0.083% (P < 0.0001), irrespective of chemoreflex gain or apnoea threshold. A 100% increase in the chemoreflex gain (from 800 l min,1 (fraction CO2),1) resulted in an increase in loop gain of 275 ± 6% (P < 0.0001) across a wide range of values of steady state CO2 and apnoea thresholds. Increasing the apnoea threshold F from 0.02 to 0.03 had no effect on system stability. Therefore, of the three variables the only two destabilizing factors were high gain and high mean CO2; the apnoea threshold did not independently influence system stability. Although our results support the idea that high chemoreflex gain destabilizes ventilatory control, there are two additional potentially controversial findings. First, it is high (rather than low) mean CO2 that favours instability. Second, high apnoea threshold itself does not create instability. Clinically the apnoea threshold appears important only because of its associations with the true determinants of stability: chemoreflex gain and mean CO2. [source]

Mobile GPS carrier phase tracking using a novel intelligent dual-loop receiver

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2008
Wei-Lung Mao
Abstract Carrier phase information is necessary for accurate measurements in global positioning system (GPS) applications. This paper presents a novel intelligent GPS carrier tracking loop with variable-bandwidth characteristics for fast acquisition and better tracking capability in the presence of dynamic environments. Our dual-loop receiver is composed of a frequency-locked loop-assisted phase-locked loop structure, the fuzzy controllers (FCs), and the ATAN discriminator functions. The soft-computing FCs provide the time-varying loop gains to perform accurate and reliable control of the dual-loop paradigm. Once the phase dynamic errors become large under kinematic conditions, the fuzzy loop gains increase adaptively and achieve rapid acquisition. On the other hand, when the tracking errors approach zero in the steady state, the loop gains decrease and the corresponding dual-loop receiver returns to a narrowband system. Four types of carrier phase signals, i.e. phase offset, decaying sinusoidal phase jitter, frequency offset, and frequency ramp offset, are considered to emulate realistic mobile circumstances. Simulation results show that our proposed receiver does achieve a superior performance over conventional tracking loops in terms of faster settling time and wider acquisition range while preventing the occurrence of cycle slips. Copyright © 2008 John Wiley & Sons, Ltd. [source]