Topic
Transfer function
About: Transfer function is a research topic. Over the lifetime, 14362 publications have been published within this topic receiving 214983 citations. The topic is also known as: system function & network function.
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TL;DR: A recently proposed data-driven H2-optimal control approach is demonstrated and an analysis of the dominant error sources shows that optimal control may reduce the temporal error.
Abstract: A recently proposed data-driven H2-optimal control approach is demonstrated on a laboratory setup. Most adaptive optics (AO) systems are based on a control law that neglects the temporal evolution of the wavefront. The proposed control approach is able to exploit the spatiotemporal correlation in the wavefront without assuming any form of decoupling. By analyzing the dynamic behavior of the wavefront sensor (WFS), it is shown that if the wavefront correction device can be considered static, the transfer function from control input to WFS output reduces to a two-tap impulse response and an integer number of samples delay. Considering this model structure, a data-driven identification procedure is developed to estimate the relevant parameters from measurement data. The specific structure allows for an analytical expression of the optimal controller in terms of the system matrices of the minimum-phase spectral factor of the atmospheric disturbance model. The performance of the optimal controller is compared with that of the standard AO control law. An analysis of the dominant error sources shows that optimal control may reduce the temporal error.
71 citations
TL;DR: In this paper, a stability analysis procedure for single-degree-of-freedom structures is presented that includes both the actuator delay and an explicit integration algorithm, and the stability of the system is investigated by examining the poles of the closed-loop transfer function.
Abstract: Real-time hybrid testing is a method that combines experimental substructure(s) representing component(s) of a structure with a numerical model of the remaining part of the structure. These substructures are combined with the integration algorithm for the test and the servo-hydraulic actuator to form the real-time hybrid testing system. The inherent dynamics of the servo-hydraulic actuator used in real-time hybrid testing will give rise to a time delay, which may result in a degradation of accuracy of the test, and possibly render the system to become unstable. To acquire a better understanding of the stability of a real-time hybrid test with actuator delay, a stability analysis procedure for single-degree-of-freedom structures is presented that includes both the actuator delay and an explicit integration algorithm. The actuator delay is modeled by a discrete transfer function and combined with a discrete transfer function representing the integration algorithm to form a closed-loop transfer function for the real-time hybrid testing system. The stability of the system is investigated by examining the poles of the closed-loop transfer function. The effect of actuator delay on the stability of a real-time hybrid test is shown to be dependent on the structural parameters as well as the form of the integration algorithm. The stability analysis results can have a significant difference compared with the solution from the delay differential equation, thereby illustrating the need to include the integration algorithm in the stability analysis of a real-time hybrid testing system. Copyright © 2007 John Wiley & Sons, Ltd.
71 citations
TL;DR: The proposed approach allows efficient automation of transfer function generations, and exploration on the data to be carried out based on controlling of opacity residue flow rate instead of complex low-level transfer function parameter adjustments.
Abstract: Transfer functions facilitate the volumetric data visualization by assigning optical properties to various data features and scalar values. Automation of transfer function specifications still remains a challenge in volume rendering. This paper presents an approach for automating transfer function generations by utilizing topological attributes derived from the contour tree of a volume. The contour tree acts as a visual index to volume segments, and captures associated topological attributes involved in volumetric data. A residue flow model based on Darcy's law is employed to control distributions of opacity between branches of the contour tree. Topological attributes are also used to control color selection in a perceptual color space and create harmonic color transfer functions. The generated transfer functions can depict inclusion relationship between structures and maximize opacity and color differences between them. The proposed approach allows efficient automation of transfer function generations, and exploration on the data to be carried out based on controlling of opacity residue flow rate instead of complex low-level transfer function parameter adjustments. Experiments on various data sets demonstrate the practical use of our approach in transfer function generations.
71 citations
08 May 2009
TL;DR: In this paper, the authors follow a bottom-up approach for modeling the channel transfer function aiming at realizing a fast statistical channel simulator, derived from transmission line theory, which computes the transfer function via a fast procedure that calculates the voltage ratio between the receiver port and the transmitter port given a real or randomly generated network topology.
Abstract: We follow a bottom-up approach for modelling the channel transfer function aiming at realizing a fast statistical channel simulator. The simulator is derived from transmission line theory. It computes the transfer function via a fast procedure that calculates the voltage ratio between the receiver port and the transmitter port given a real or randomly generated network topology. The approach allows not only taking into account the cable characteristics, the number and length of branches, but also the effect of loads. In particular the effect of time-variant loads that cause the channel transfer function to be time-variant.
71 citations
TL;DR: Experimental results demonstrate that the proposed beamformer outperforms the transfer function GSC (TF-GSC) in reverberant environments and achieves both improved noise reduction and reduced speech distortion.
Abstract: In this paper, we propose a convolutive transfer function generalized sidelobe canceler (CTF-GSC), which is an adaptive beamformer designed for multichannel speech enhancement in reverberant environments. Using a complete system representation in the short-time Fourier transform (STFT) domain, we formulate a constrained minimization problem of total output noise power subject to the constraint that the signal component of the output is the desired signal, up to some prespecified filter. Then, we employ the general sidelobe canceler (GSC) structure to transform the problem into an equivalent unconstrained form by decoupling the constraint and the minimization. The CTF-GSC is obtained by applying a convolutive transfer function (CTF) approximation on the GSC scheme, which is a more accurate and a less restrictive than a multiplicative transfer function (MTF) approximation. Experimental results demonstrate that the proposed beamformer outperforms the transfer function GSC (TF-GSC) in reverberant environments and achieves both improved noise reduction and reduced speech distortion.
70 citations