Robust Task Research Articles

TWO-STAGE IDENTIFICATION AND ITS APPLICATION TO ROBUST LQG CONTROLLER DESIGN

Consider an unknown, possibly unstable and linear time-invariant LTI system with output disturbance. Based on the concept of learning identification introduced in Teo et al. 1995 and the iterative scheme proposed in Zang et al. 1992, a new scheme for mutually enhanced data-based least squares identification and model-based LQG robust control design is presented. One of the novel features of this scheme is that both the identification and the robust control design tasks can be performed by minimizing a single cost function. To illustrate the effectiveness of the proposed scheme, a numerical example is presented.

Robust speech recognition based on joint model and feature space optimization of hidden Markov models

The hidden Markov model (HMM) inversion algorithm, based on either the gradient search or the Baum-Welch reestimation of input speech features, is proposed and applied to the robust speech recognition tasks under general types of mismatch conditions. This algorithm stems from the gradient-based inversion algorithm of an artificial neural network (ANN) by viewing an HMM as a special type of ANN. Given input speech features s, the forward training of an HMM finds the model parameters lambda subject to an optimization criterion. On the other hand, the inversion of an HMM finds speech features, s, subject to an optimization criterion with given model parameters lambda. The gradient-based HMM inversion and the Baum-Welch HMM inversion algorithms can be successfully integrated with the model space optimization techniques, such as the robust MINIMAX technique, to compensate the mismatch in the joint model and feature space. The joint space mismatch compensation technique achieves better performance than the single space, i.e. either the model space or the feature space alone, mismatch compensation techniques. It is also demonstrated that approximately 10-dB signal-to-noise ratio (SNR) gain is obtained in the low SNR environments when the joint model and feature space mismatch compensation technique is used.

Automatic task modelling for sewer studies

Research into the development of robotic modules is discussed in the context of cost-effective, small bore, non-man entry (NME) sewer renovation. Following an introduction to the engineering problem or task and the respective task-associated sensing system, interest is centred upon suitably robust task kinematics and control, where predictive modelling is implemented employing the GRASP robotic simulation software package. The physical prototype and its accompanying environment are discussed and general conclusions drawn.

Contrast dependence of colour and luminance motion mechanisms in human vision.

Conventional views of visual perception propose a colour-blind pathway conveying motion information and a motion-blind pathway carrying colour information. Recent studies show that motion perception is not always colour blind, is partially dependent on attention, can show considerable perceptual slowing around isoluminance and is contrast-dependent. If there is a single motion pathway, receiving luminance and chromatic input, then the dependence of relative perceived velocity on relative stimulus contrast should be the same for both luminance and chromatic targets. Here we provide a distinctive characterization of the motion mechanisms using a robust velocity-matching task. A relative contrast scale allows direct comparison of the performance with luminance and chromatic targets. The results show that the perceived speed of slowly moving coloured targets at isoluminance has a steep contrast dependence. The perceived speed of slowly moving luminance targets shows a much lower contrast dependence. At high speeds the contrast dependence is low for both luminance and isoluminant stimuli, although the behaviour is unlike either of the slow mechanisms. The results suggest two independent pathways that perceive slowly moving targets: one is luminance-sensitive and the other is colour-sensitive. Fast movement is signalled via a single motion pathway that is contrast-invariant and not colour blind.

Lazy task creation: a technique for increasing the granularity of parallel programs

When a parallel algorithm is written naturally, the resulting program often produces tasks of a finer grain than an implementation can exploit efficiently. Two solutions to the granularity problem that combine parallel tasks dynamically at runtime are discussed. The simpler load-based inlining method, in which tasks are combined based on dynamic bad level, is rejected in favor of the safer and more robust lazy task creation method, in which tasks are created only retroactively as processing results become available. The strategies grew out of work on Mul-T, an efficient parallel implementation of Scheme, but could be used with other languages as well. Mul-T implementations of lazy task creation are described for two contrasting machines, and performance statistics that show the method's effectiveness are presented. Lazy task creation is shown to allow efficient execution of naturally expressed algorithms of a substantially finer grain than possible with previous parallel Lisp systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Conduction velocity in ischemic muscle: effect on EMG frequency spectrum.

Conduction velocity in ischemic muscle: effect on EMG frequency spectrum.