Effects Of Time-varying Parameters Research Articles

Study of dynamic performance and adaptive control of the variable stiffness actuator with time-varying parameters

The study of dynamic performance and adaptive control of variable stiffness actuators with time-varying parameters is significant for the realization of stable and efficient human-computer interaction. In this paper, for the previously proposed variable stiffness actuator, the dynamics model of the variable stiffness actuator system is established according to the two-inertia-system theory, and the effects of time-varying parameters on the dynamic performance of the variable stiffness actuator system are analyzed. Then the adaptive control strategy of the variable stiffness actuator system with time-varying parameters is studied, and the correctness and effectiveness of the control strategy are verified experimentally. The results show that the time-varying parameters have a more obvious effect on the dynamic performance of the variable stiffness actuator system, and the difficulty in designing the system control strategy, which is caused by the complex dynamics modeling of variable stiffness actuator systems with time-varying parameters, can be effectively solved by using the proposed adaptive control strategy. Moreover, the control strategy has good stability and generalization ability.

Availability and Reliability of Service Function Chain: A Quantitative Evaluation View

Service function chain (SFC) based on network function virtualization (NFV) technology can handle network traffic flexibly and efficiently. The virtual network function (VNF), as the core function unit of SFC, can experience software aging, which reduces the availability and reliability of SFC and even leads to service interruption, after it runs continuously for a long time. Software rejuvenation technique can effectively combat software aging. However, its effectiveness in improving the availability and reliability of SFC needs to be evaluated. Compared with existing models, this paper proposes a semi-Markov model to capture the behaviors of each VNF in a SFC from the occurrence of software aging to recovery by software rejuvenation technique under the condition that the failure times and recovery times follow general distribution, while considering trigger intervals of software rejuvenation technique. We then derive the calculation formulas of the steady-state availability, transient availability, and reliability, which are applied to evaluate the effectiveness of software rejuvenation technique. Finally, we conduct sensitivity analysis and numerical experiments to analyze the effects of system parameters, the number of VNFs and trigger interval of software rejuvenation technique on availability and reliability of SFC, and the effects of time-varying parameters on transient availability of SFC.

Tracking Respiratory Mechanics With Oscillometry: Introduction of Time-Varying Error

Oscillometry is a useful measure of lung function and recently has been used to estimate temporal variation in physiological mechanical properties of the lung, but to date, analysis methods assume stationarity or short-time stationarity despite substantial temporal variation, particularly in disease. The effect of time-varying parameters on the accuracy of estimates of impedance has not been previously analyzed. In this paper we analytically, computationally, and with added experimental data from seven children with asthma, assess the time-frequency transfer function of the time-varying respiratory system. We then evaluate the accuracy in determining the time-varying parameters of respiratory impedance. We introduce, for the first time, the error arising from respiratory time variation, termed the time-varying error (TVE) and demonstrate how TVE unexpectedly increases with increasing breathing rate independent of breathing noise amplitude. For breathing rates less than 0.4 Hz, we found that common analysis methods could be moderately accurate with less than 5% error. Since tracking time-varying impedance shows strong potential for assessing the severity of respiratory disease, it is import to recognize that errors should be avoided, or compensation circuits and systems developed based on the TVE, particularly important in patients with high variation or breathing rate such as children and infants.

Event Study Analysis with Time-Varying Alphas, Betas and Variances: The Case of M&As

This paper proposes a new approach to control the effects of time-varying parameters on the estimates of abnormal returns. Event studies usually assume that the parameters of the market model are s ...

Currency Hedge Design: Accounting for Uncertain Correlation and Volatility

In previous Peregrine Securities work, it was shown that currency hedge selection can be approached in an optimization framework and that the particular choice of hedge is strongly dependent on the correlation between the exchange rate and the foreign asset. Unfortunately, correlations between assets are generally unstable and it can be difficult to forecast an appropriate value to use as input to the optimizer. In this work we outline an approach to the determination of an optimal currency hedge in the presence of non-constant volatility and correlation. It is shown that implementation of the dynamic conditional correlation (DCC) model in a simulation framework allows one to incorporate the effects of time-varying parameters into the hedge selection process in a systematic and quantitative manner. An important finding is that the particular choice of short-term hedge depends to a large extent on the current value of correlation, emphasising the need for a modelling framework that provides accurate estimates of time-varying correlation.

Distributed Adaptive Synchronization for Complex Dynamical Networks with Uncertain Nonlinear Neutral-Type Coupling

Distributed adaptive synchronization control for complex dynamical networks with nonlinear derivative coupling is proposed. The distributed adaptive strategies are constituted by directed connections among nodes. By means of the parameters separation, the nonlinear functions can be transformed into the linearly form. Then effective distributed adaptive techniques are designed to eliminate the effect of time-varying parameters and made the considered network synchronize a given trajectory in the sense of square error norm. Furthermore, the coupling matrix is not assumed to be symmetric or irreducible. An example shows the applicability and feasibility of the approach.