Time-delay systems : stability, sliding mode control and state estimation

University of Technology, Sydney. Faculty of Engineering and Information Technology.Time delays and external disturbances are unavoidable in many practical control systems such as robotic manipulators, aircraft, manufacturing and process control systems and it is often a source of instability or oscillation. This thesis is concerned with the stability, sliding mode control and state estimation problems of time-delay systems. Throughout the thesis, the Lyapunov-Krasovskii (L-K) method, in conjunction with the Linear Matrix Inequality (LMI) techniques is mainly used for analysis and design. Firstly, a brief survey on recent developments of the L-K method for stability analysis, discrete-time sliding mode control design and linear functional observer design of time-delay systems, is presented. Then, the problem of exponential stability is addressed for a class of linear discrete-time systems with interval time-varying delay. Some improved delay-dependent stability conditions of linear discrete-time systems with interval time-varying delay are derived in terms of linear matrix inequalities. Secondly, the problem of reachable set bounding, essential information for the control design, is tackled for linear systems with time-varying delay and bounded disturbances. Indeed, minimisation of the reachable set bound can generally result in a controller with a larger gain to achieve better performance for the uncertain dynamical system under control. Based on the L-K method, combined with the delay decomposition approach, sufficient conditions for the existence of ellipsoid-based bounds of reachable sets of a class of linear systems with interval time-varying delay and bounded disturbances, are derived in terms of matrix inequalities. To obtain a smaller bound, a new idea is proposed to minimise the projection distances of the ellipsoids on axes, with respect to various convergence rates, instead of minimising its radius with a single exponential rate. Therefore, the smallest possible bound can be obtained from the intersection of these ellipsoids. This study also addresses the problem of robust sliding mode control for a class of linear discrete-time systems with time-varying delay and unmatched external disturbances. By using the L-K method, in combination with the delay decomposition technique and the reciprocally convex approach, new LMI-based conditions for the existence of a stable sliding surface are derived. These conditions can deal with the effects of time-varying delay and unmatched external disturbances while guaranteeing that all the state trajectories of the reduced-order system are exponentially convergent to a ball with a minimised radius. Robust discrete-time quasi-sliding mode control scheme is then proposed to drive the state trajectories of the closed-loop system towards the prescribed sliding surface in a finite time and maintain it there after subsequent time. Finally, the state estimation problem is studied for the challenging case when both the system’s output and input are subject to time delays. By using the information of the multiple delayed output and delayed input, a new minimal order observer is first proposed to estimate a linear state functional of the system. The existence conditions for such an observer are given to guarantee that the estimated state converges exponentially within an Є-bound of the original state. Based on the L-K method, sufficient conditions for Є-convergence of the observer error, are derived in terms of matrix inequalities. Design algorithms are introduced to illustrate the merit of the proposed approach. From theoretical as well as practical perspectives, the obtained results in this thesis are beneficial to a broad range of applications in robotic manipulators, airport navigation, manufacturing, process control and in networked systems

Blood groups and evolutionary relationships among domestic Sheep (Ovis aries), domestic Goat (Capra hircus), Aoudad (Ammotragus lervia) and european Mouflon (Ovis musimon)

Data presented in this report are concerned with the results of blood typing of 7 aoudad (Ammotragus lervia), 20 european mouflons (Ovis musimon) and 260 domestic goats (Capra hircus). The blood samples were tested with 31 different sheep blood typing reagents to see if sheep-like blood-group antigens existed in the red cells of the three species. The polymorphism of serum transferrin and hemoglobin was analyzed by means of horizontal starch gel electrophoresis. Evidence is presented for the existence in european mouflon of blood-group antigens similar to or identical with those recognized in the eight blood group systems of deomstic sheep (i.e., the sheep blood-group systems A, B, C, D, M, R, F30 and F41 The electrophoretic pattern of the mouflon transferrin is also identical with that of domestic sheep homozygous for the transferrin D allele. Likewise, the two hemoglobin variants observed in mouflon are indistinguishable from the hemoglobins A and B of domestic sheep. On the basis of such extensive similarity in antigenic structures in the red cells and in the electrophoretic mobility of transferrins and hemoglobins, domestic sheep (Ovis aries) and european mouflon (Ovis musimon) may have close evolutionary affinity to each other. The present data also indicate that both aoudad (Ammotragus lervia) and domestic goat (Cap Hircus) have blood-group antigens related to those of the B, C, M, R, and F30 systems of sheep. With respect to serological reactions in the M and R systems, Ammotragus resembles Capra much more closely than Ovis. With respect to the A system, however, Ammotragus appears to be more closely related to Ovis than to Capra; the latter, unlike Ammotragus, apparently does not have blood-group antigens related to those recognized in the A system of sheep. On the other hand, the three genera seem to be quite distinct from each other on the basis of differences in the electrophoretic mobility of their major variants of transferrin and hemoglobin. These observations, in conjunction with those reported earlier and mentioned in the introductory remarks of this report, suggest that Ammotragus is intermediate between Capra and Ovis. But, on the basis of the data presently available, it is not possible to establish more precisely the evolutionary relationships among the three genera.Les antigènes érythrocytaires de mouflons à manchettes (Ammotragus Lervia), de 20 mouflons d’Europe (Ovis musimon) et de 260 chèvres (Capra Hircus) ont été examinés à l’aide de 31 réactifs préparés pour la détermination des groupes sanguins du mouton (Ovis aries). Le polymorphisme de la transferrine sérique et de l’hémoglobine de ces différentes espèces a été analysé par la technique d’électrophorèse en gel d’amidon. Les résultats de ces examens sérologiques ont montré que le mouflon d’Europe possède des antigènes de groupes sanguins similaires ou identiques à ceux qui font partie de 8 systèmes de groupes sanguins définis chez le mouton (systèmes A, B, C, D, M, R, F30 et F41. Ces 2 espèces du genre Ovis ne peuvent, d’ailleurs, être distinguées l’une à l’autre, sur la base de la mobilité électrophorétique de leur transferrine et de leur hémoglobine. Cette très grande ressemblance, tout au moins en ce qui concerne les caractères sanguins considérés, indique clairement que le mouflon d’Europe (Ovis musimon) et le mouton (Ovis aries) sont très proches l’un de l’autre sur l’échelle zoologique des espèces et que leur séparation doit donc être récente. Les résultats de cette comparaison ont révélé, en outre, que le mouflon à manchettes (Ammotragus) et la chèvre (Capra) possèdent également des antigènes de groupes sanguins similaires à ceux qui sont reconnus dans les systèmes B, C, M, R et F30 du mouton. Cependant, si les réactions sérologiques observées dans les systèmes M et R suggèrent que l’Ammotragus se rapproche plus du genre Capra que du genre Ovis, les données concernant le système A indiquent que l’Ammotragus paraît être plus proche du genre Ovis que du genre Capra. D’autre part, ces 3 genres semblent se différencier nettement entre eux, sur la base de la mobilité électrophorétique de leur transferrine et de leur hémoglobine. Ces observations, ainsi que celles rapportées dans la littérature et mentionnées dans ce rapport, permettent de penser que, sur l’échelle évolutive des espèces, l’Ammotragus occupe une position intermédiaire entre les genres Caprai et Ovis. Dans l’état actuel des connaissances, il n’est pas possible d’établir, avec plus de précision, les relations évolutives entre les 3 genres Capra, Ovis et Ammotragu

Combinative effects of Thanh Hao Miet Giap Thang (sweetwormwood and tortoise shell decoction) ingredients on antioxidative activity in vitro

Background: Traditional formulae usually exhibit therapeutic effects through the combinations of different ingredients. The purpose of this study was to investigate in vitro anti-oxidative activity of Thanh Hao Miet Giap Thang (THMGT) (Sweet Wormwood and Tortoise Shell Decoction) formula and the interactions of its ingredients leading to the overall anti-oxidative effect.Materials and Methods: We prepared 31 combinations containing two to four of the five ingredients including Herba Artemisia apiacea L (HbA),Carapax Trionycis (Tryonix sinensis) (CT), Rhizoma Anemarrhenae (Anemarrhena asphodeloides) (RzA), Radix Rehmanniae (Rehmannia glutinosaLibosch) (RdR), Moutan Cortex (Paeonia suffruticosa) (MC). These  combinations were tested for anti-oxidative activity using DCFH-DA and DPPH assays on Hep G2 cells. We also analyzed changes in expression of genes involved in antioxidant defense system including Nuclear Factor Erythroid-Derived 2-Like 2 (NFE2L2), catalase (CAT), heme oxygenase-1 (HO-1), glutathione peroxidase (GPx), cytoplasmic superoxide dismutase (SOD1), mitochondrial superoxide dismutase (SOD2).Results: The complete formula and all combinations containing Moutan Cortex showed high antioxidant activity in both radical solution-basedchemical assay and cellular-based assay. On the contrary, Carapax Trionycis displayed inhibitory effect on the overall antioxidant activity whenpresent in a combination, an effect clearly emphasized in cellular-based assay. Hep G2 cells treated with the formula showed increased geneexpression of HO-1 and SOD2 while expression of CAT, SOD1, GPx was unchanged.Conclusion: Our results suggested that THMGT had anti-oxidative activity essentially through intrinsic reducing capacities and the overall activity ofthe formula resulted from enhancing and inhibiting interactions of  ingredients.Key words: Thanh Hao Miet Giap Thang, Sweet Wormwood and Tortoise Shell Decoction, antioxidant, traditional formulaAbbreviations: THMGT, Thanh Hao Miet Giap Thang; HbA, Herba Artemisia apiacea; CT, Carapax Tryonicis; RzA, Rhizoma Anemarrhenae; MC,Moutan Cortex; RdR, Radix Rehmanniae; ROS, Reactive oxygen species; NFE2L2, Nuclear Factor Erythroid-Derived 2-Like 2; CAT, catalase; GPx,glutathione peroxidase; SOD1, cytoplasmic superoxide dismutase; SOD2, mitochondrial superoxide dismutase; HO-1, heme oxygenase-1

Information internalisation and internationalisation-Evidence from Vietnamese firms

Previous research on internationalisation has mainly focused on the collection and use of information. In this article we examine the role of information internalisation in international business activities of Vietnamese firms. A theoretical model incorporating key antecedents and outcomes of information internalisation is developed. The antecedents are market orientation and learning orientation, and the outcomes are international orientation and foreign sales intensity. A survey of 144 Vietnamese internationalising firms was conducted to test the model in conjunction with its two competing models by means of a two-step approach to structural equation modelling. We found that both information internalisation has direct and indirect effects (mediated by international orientation) on foreign sales intensity. Further, market orientation and learning orientation underlie information internalisation. Implications for managers and directions for future research are also addressed. © 2006 Elsevier Ltd. All rights reserved

Streaming sparse Gaussian process approximations

Sparse pseudo-point approximations for Gaussian process (GP) models provide a suite of methods that support deployment of GPs in the large data regime and enable analytic intractabilities to be sidestepped. However, the field lacks a principled method to handle streaming data in which both the posterior distribution over function values and the hyperparameter estimates are updated in an online fashion. The small number of existing approaches either use suboptimal hand-crafted heuristics for hyperparameter learning, or suffer from catastrophic forgetting or slow updating when new data arrive. This paper develops a new principled framework for deploying Gaussian process probabilistic models in the streaming setting, providing methods for learning hyperparameters and optimising pseudo-input locations. The proposed framework is assessed using synthetic and real-world datasets

ACQUIRING SYNTACTIC VARIATION: REGULARIZATION IN WH-QUESTION PRODUCTION

Children are often exposed to language-internal variation. Studying the acquisition of variation allows us to understand more about children’s ability to acquire probabilistic input, their preferences at choice points, and factors contributing to such preference. Using wh-variation as a case study, this dissertation explores the acquisition of syntactic variation through corpus analyses, behavioral experiments, and computational simulation. In English and some other languages (e.g., French, Brazilian Portuguese, etc.), information-seeking wh-questions allow for at least two variants: a wh-in-situ variant and a fronted-wh variant. How do English-speaking children acquire wh-variation, and what factors condition their course of acquisition? Experimental results show that 3-to-5 year-old children regularize to fronted wh-questions in their production even in contexts that allow for both variants to be used interchangeably. Based on the characteristics of the variants, two factors are identified to potentially contribute to the preference for fronted wh-questions: frequency and discourse restrictions. Two artificial language learning (ALL) experiments are then conducted so that the effect of discourse can be studied separately from frequency. The results show that learners prefer the variant with fewer or no discourse restrictions (i.e., the fronted-wh variant) when frequency is controlled. Thus, regularization in language acquisition is conditioned by both domain-general factors, such as frequency, and language-specific factors, such as discourse markedness. The dissertation also looks into the motivation for regularization. One prominent hypothesis is that regularization serves as a means to reduce the cognitive burden associated with learning multiple variants at once. Instead of mastering all the variants, learners can simplify the learning process and minimize their chance of violating a constraint by producing the dominant variant. This work provides additional evidence for the hypothesis in three ways. First, we replicate the findings that tasks that are more cognitively taxing induce more regularization. Second, we present new evidence that participants with a lower composite working memory score tend to have a higher regularization rate. Third, we provide a computational simulation showing that regularization behavior only happens when an intake limit (reflecting limited working memory capacity) and a parsimony bias to reduce the cognitive burden are incorporated in the model