Robust Backstepping Control of Robotic Systems Using Neural Networks

Neural network (NN) controllers for the robust back stepping control of robotic systems in both continuous and discrete-time are presented. Control action is employed to achieve tracking performance for unknown nonlinear system. Tuning methods are derived for the NN based on delta rule. Novel weight tuning algorithms for the NN are obtained that are similar to -modification in the case of continuous-time adaptive control. Uniform ultimate boundedness of the tracking error and the weight estimates are presented without using the persistency of excitation (PE) condition. Certainty equivalence is not used and regression matrix is not computed. No learning phase is needed for the NN and initialization of the network weights is straightforward. Simulation results justify the theoretical conclusions.     

A TSP-GA multi-objective algorithm for flow-shop scheduling

A multi-objective evolutionary search algorithm using a travelling salesman algorithm and genetic algorithm for flow-shop scheduling is proposed in this paper. The initial sequence is obtained by solving the TSP. The initial population of the genetic algorithm is created with the help of a neighbourhood creation scheme known as a random insertion perturbation scheme, which uses the sequence obtained from TSP. The proposed algorithm uses a weighted sum of multiple objectives as a fitness function. The weights are randomly generated for each generation to enable a multi-directional search. The performance measures considered include minimising makespan, mean flow time and machine idle time. The performance of the proposed algorithm is demonstrated by applying it to benchmark problems available in the OR-Library.     

A portable fault-tolerant parallel software MPEG-1 encoder

MPEG video compression is quite difficult to achieve in real time, and hardware solutions for this problem are expensive. We present a portable, fault-tolerant, parallel, MPEG-1 encoder implemented in software. We detail the implementation strategy for the encoder and give performance results on a network of workstations and a massively parallel processor. We also show that our encoder can efficiently adapt to fluctuating processing power typical in workstation networks.     

Lie algebraic treatment of dioptric power and optical aberrations

The dioptric power of an optical system can be expressed as a four-component dioptric power matrix. We generalize and reformulate the standard matrix approach by utilizing the methods of Lie algebra. This generalization helps one deal with nonlinear problems (such as aberrations) and further extends the standard matrix formulation. Explicit formulas giving the relationship between the incident and the emergent rays are presented. Examples include the general case of thick and thin lenses. The treatment of a graded-index medium is outlined.     

TS/Scheme: Distributed data structures in Lisp

We describe a parallel object-oriented dialect of Scheme called TS/SCHEME that provides a simple and expressive interface for building asynchronous parallel programs. The main component in TS/SCHEME's coordination framework is an abstraction that serves the role of a distributed data structure. Distributed data structures are an extension of conventional data structures insofar as many tasks may simultaneously access and update their contents according to a well-defined serialization protocol. The semantics of these structures also specifies that consumers which attempt to access an as-of-yet undefined element are to block until a producer provides a value.TS/SCHEME permits the construction of two basic kinds of distributed data structures, those accessed by content, and those accessed by name. These structures can be further specialized and composed to yield a number of other synchronization abstractions. Our intention is to provide an efficient medium for expressing concurrency and synchronization that is amenable to modular programming, and which can be used to succinctly and efficiently describe a variety of diverse concurrency paradigms useful for parallel symbolic computing.     

Pharmacokinetics and CNS pharmacodynamics of the 5-HT1A agonist buspirone in humans following acute L-tryptophan depletion challenge

This study was designed to evaluate the relationship between the pharmacokinetic(s) (PK) and CNS pharmacodynamic(s) (PD) of buspirone, an antidepressant/anxiolytic, in 6 healthy male volunteers placed on an acute L-tryptophan deficient (ATD) diet. The study was a randomized, double-blind, placebo-controlled, four-period, three-way crossover study. The first study period was a single-blind familiarization period in which all subjects received placebo. During the remaining three study periods, subjects received either placebo, 10 mg or 30 mg oral buspirone. Subjects were administered the ATD diets 5 h prior to buspirone/placebo administration during each study period. All subjects underwent serial measurements of resting electroencephalography (REEG) and vigilance electroence-phalography (VEEG), cognitive tests, subjective rating scales, and blood was sampled for determination of unbound plasma L-tryptophan, serum prolactin, serum cortisol and plasma buspirone and its active metabolite, 1-pyrimdylpiperazine (1-PP). The ATD diet reduced the unbound plasma L-tryptophan concentrations to 20% of their baseline values. The intraindividual and interindividual variability in the unbound L-tryptophan concentration drop was less than 10% and 15%, respectively. Peak L-tryptophan depletion occurred 5 h after ATD diet was administered; L-tryptophan depletion lasted for approximately 11 h, and L-tryptophan concentrations recovered to baseline values approximately 13 h after administration of the ATD diet. PK-PD analysis for buspirone showed that: 1) peak plasma concentration (Cmax) and total area under the plasma concentration-time curve (AUC infinity) for buspirone following the 10 mg dose in this study were higher than those reported previously in the literature; 2) there was a transient response in the neuroendocrine measures, subjective rating scales and the EEG, but no changes in the cognitive tests with increasing doses of buspirone; 3) the PD measures were correlated with the doses of buspirone, but not with plasma concentrations of buspirone and 1-PP; and 4) the subjective rating scales were the most sensitive indicators of buspirone's CNS effects. This study provides evidence that ATD diet is a simple, specific and non-toxic experimental method to lower plasma L-tryptophan concentrations and thereby (indirectly) deplete brain tryptophan and serotonin (5-HT) concentrations. The ATD challenge may serve as a model of depression in healthy volunteers because of its ability to induce transient symptoms of the disease. Comparison of the results from this study to those reported in the literature suggests that the use of the ATD diet decreases the buspirone-induced neuroendocrine response, increases the buspirone-induced changes in subjective rating scales and, at the same time, increases the systemic exposure to buspirone and 1-PP.     

General Expressions for Reliability of Redundant Systems

General expressions for reliability and mean time-to-failure of parallel and standby redundant systems are shown. Each unit in the system has a constant failure rate and need not be good at the beginning.     

A concurrent abstract interpreter

Abstract interpretation [6] has been long regarded as a promising optimization and analysis technique for high-level languages. In this article, we describe an implementation of aconcurrent abstract interpreter. The interpreter evaluates programs written in an expressive parallel language that supports dynamic process creation, first-class locations, list data structures and higher-order procedures. Synchronization in the input language is mediated via first-class shared locations. The analysis computes intra- and inter-threadcontrol anddataflow information. The interpreter is implemented on top of Sting [12], a multi-threaded dialect of Scheme that serves as a high-level operating system for modern programming languages.     

Modular Checkpointing for Atomicity

Transient faults that arise in large-scale software systems can often be repaired by re-executing the code in which they occur. Ascribing a meaningful semantics for safe re-execution in multi-threaded code is not obvious, however. For a thread to correctly re-execute a region of code, it must ensure that all other threads which have witnessed its unwanted effects within that region are also reverted to a meaningful earlier state. If not done properly, data inconsistencies and other undesirable behavior may result. However, automatically determining what constitutes a consistent global checkpoint is not straightforward since thread interactions are a dynamic property of the program.In this paper, we present a safe and efficient checkpointing mechanism for Concurrent ML (CML) that can be used to recover from transient faults. We introduce a new linguistic abstraction called stabilizers that permits the specification of per-thread monitors and the restoration of globally consistent checkpoints. Global states are computed through lightweight monitoring of communication events among threads (e.g. message-passing operations or updates to shared variables). Our checkpointing abstraction provides atomicity and isolation guarantees during state restoration ensuring restored global states are safe.Our experimental results on several realistic, multithreaded, server-style CML applications, including a web server and a windowing toolkit, show that the overheads to use stabilizers are small, and lead us to conclude that they are a viable mechanism for defining safe checkpoints in concurrent functional programs. Our experiments conclude with a case study illustrating how to build open nested transactions from our checkpointing mechanism.