Robust Control of Set-Valued Discrete Time Dynamical Systems

This thesis deals with the robust control of nonlinear systems subject to persistent bounded non-additive disturbances. Such disturbances could be due to exogenous signals, or internal to the system as in the case of parametric uncertainty. The problem solved could be viewed as an extension of l1- optimal control to nonlinear systems, however, now under very general non-additive disturbance assumptions. We model such systems as inclusions, and set up an equivalent robust control problem for the now set- valued dynamical system. Due to the fact that inclusions could arise from other considerations as well, we solve the control problem for this generation class of systems. The state feedback problem is solved via a game theoretic approach, wherein the controller plays against the plant. For the output feedback case, the concept of an information state is employed. The information state dynamics define a new infinite dimensional system, and enable us to achieve a separation between estimation and control. This concept is extended to the case of delayed measurements as well. For motivational purposes, we formally derive the information state from a risk-sensitive stochastic control problem via small noise limits. In general, the solution to the output feedback case involves solving an infinite dimensional dynamic programming equation. One way of avoiding this computation in practice is to consider certainty equivalence like controllers. This issue is considered, where we generalize the certainty equivalence controller to obtain other non-optimal, but dissipative output feedback policies. The approach followed yields both necessary and sufficient conditions for the solvability of the problem. We also present some applications of the theory developed

Alzheimer’s and Seizures: Interleukin-18, Indoleamine 2,3-Dioxygenase and Quinolinic Acid

Emergent seizures are common in Alzheimer’s disease (AD), although the mechanisms mediating this are unknown. It is proposed that stress induced interleukin-18 (IL-18), via interferon-gamma (IFNy) and independently, increases indoleamine 2,3-dioxygenase (IDO) and subsequent quinolinic acid (QA) in microglia. QA increases seizures and concurrently contributes to neuronal loss via excitotoxicity. The ApoE4 allele interacts with IL-18 polymorphisms to increase the risk of AD, and seems likely to potentiate the emergence of seizures. Concurrent changes in IDO and the kynurenine pathways at the blood-brain-barrier (BBB) have implications for treatment, including in the efficacy of different anti-hypertensives. Melatonin is proposed to inhibit these overlapping excitotoxic and neurodegenerative processes, and would be a useful adjunctive treatment

Cell division in apicomplexan parasites is organized by a homolog of the striated rootlet fiber of algal flagella

Apicomplexa are intracellular parasites that cause important human diseases including malaria and toxoplasmosis. During host cell infection new parasites are formed through a budding process that parcels out nuclei and organelles into multiple daughters. Budding is remarkably flexible in output and can produce two to thousands of progeny cells. How genomes and daughters are counted and coordinated is unknown. Apicomplexa evolved from single celled flagellated algae, but with the exception of the gametes, lack flagella. Here we demonstrate that a structure that in the algal ancestor served as the rootlet of the flagellar basal bodies is required for parasite cell division. Parasite striated fiber assemblins (SFA) polymerize into a dynamic fiber that emerges from the centrosomes immediately after their duplication. The fiber grows in a polarized fashion and daughter cells form at its distal tip. As the daughter cell is further elaborated it remains physically tethered at its apical end, the conoid and polar ring. Genetic experiments in Toxoplasma gondii demonstrate two essential components of the fiber, TgSFA2 and 3. In the absence of either of these proteins cytokinesis is blocked at its earliest point, the initiation of the daughter microtubule organizing center (MTOC). Mitosis remains unimpeded and mutant cells accumulate numerous nuclei but fail to form daughter cells. The SFA fiber provides a robust spatial and temporal organizer of parasite cell division, a process that appears hard-wired to the centrosome by multiple tethers. Our findings have broader evolutionary implications. We propose that Apicomplexa abandoned flagella for most stages yet retained the organizing principle of the flagellar MTOC. Instead of ensuring appropriate numbers of flagella, the system now positions the apical invasion complexes. This suggests that elements of the invasion apparatus may be derived from flagella or flagellum associated structures

Nonlinear HControl with Delayed Measurements

This paper considers the nonlinear Hcontrol problem for systems subject to delayed measurements. Necessary and sufficient conditions for the solvability of the problem are presented. We employ the concept of an information state to achieve separation between estimation and control. In particular, the information state derived is no longer the ﲷorst case cost to come function. We also briefly discuss certainty equivalence for systems with delayed measurements

Information State for Robust Control of Set-Valued Discrete Time Systems

In this paper, we construct the information state for robust output feedback control of set-valued discrete time dynamical systems. The information state is obtained as the small noise limit of an appropriate risk-sensitive stochastic control problem. It is possible to obtain this limit by an extension of the Vardgan-Laplace lemma. Finally, the relationship between the information state, and the indicator function of feasible sets is examined

Robust Control of Set-Valued Discrete Time Dynamical Systems

This paper presents results obtained for the robust control of discrete time dynamical systems. The problem is formulated and solved using dynamic programming. Both necessary and sufficient conditions in terms of (stationary ) dynamic programming equalities are presented. The output feedback problem is solved using the concept of an information state, where a decoupling between estimation and control is obtained

Reduced Complexity Output Feedback Nonlinear HControllers and Relation to Certainty Equivalence

In this paper, we consider the problem of constructing reduced complexity controllers for output feedback nonlinear Hcontrol. We give sufficient conditions, under which the controllers so obtained, guarantee asymptotic stability of the closed-loop system when there are no exogenous inputs. The controllers obtained are non-optimal in general. However, in case optimality holds, we show that these controllers are in fact the certainty equivalence controllers

A toxicological review of Bhallataka

Bhallataka (Semecarpus anacardium Linn.) is mentioned in the group of Sthavar vanaspatika Visha in different Ayurvedic text book’s also it is irritant organic vegetable poison. All the parts are poisonous mostly seeds are hazadous to human, due to its irritant property. The Bhallataka nut contain bhilwanol and semecarpal as toxic ingredient show some medicinal properties. By its hot potency it has some local action like Sphotjananam (Ushna-Virya). An number of Ayurvedic formulation includes this drug after the proper Shodhana (purification) as in judicious use of Asuddha (impure) Bhallataka may results in toxic effect like burning sensation of skin blister formation, ulcer and so on. Treatment of toxic effect of Bhallataka is described various texts of Ayurveda. Modern toxicology also describes manifestation, treatment, autopsy finding and medico legal aspect of semecarpus anacardium linn

A structured record to implement the national Guidelines for diabetes and hypertension care

Background. Guidelines to improve standards of care for hypertension and diabetes were disseminated by the National Department of Health in 1996 but have generally not been implemented by health professionals in localprimary care. A strategy for the adoption and implementation of the Guidelines was developed in collaboration with health professionals in primary care.Objectives. The development of a structured record, with prompts for the management of diabetes and hypertension according to the Guidelines.Setting. Three community health centres (CHCs) in the Western Cape.Participants. Doctors and nurses managing patients with diabetes and hypertension.Methods. A draft of the structured record was developed at a single-pilot CHC in the Western Cape. Focus group discussions established the core requirements for a structured record. Process, result and structural indicators in line with the national Guidelines were considered for inclusion in the draft record. This draft record was then piloted at two other CHCs. Comments from semi-structured interviews and pre-and post-test evaluation questionnaires were used to compile the final instrument.Results. Eleven doctors and 8 nurses participated in the development of the final instrument. Important considerations in the design were a single-page, user-friendly format, tick-boxes to reduce writing, prompts, provision for sequential recording, target setting, and compatibility with the Guidelines. The final instrument was piloted and elicited a favourable overall response.Conclusion. The structured record simplifies the application of the Guidelines and the systematic recording of processes of care. The effectiveness of the Guidelines will be evaluated further in a randomised control qial using the structured record

Effect of melt conditioning on heat treatment and mechanical properties of AZ31 alloy strips produced by twin roll casting

In the present investigation, magnesium strips were produced by twin roll casting (TRC) and melt conditioned twin roll casting (MC-TRC) processes. Detailed optical microscopy studies were carried out on as-cast and homogenized TRC and MC-TRC strips. The results showed uniform, fine and equiaxed grain structure was observed for MC-TRC samples in as-cast condition. Whereas, coarse columnar grains with centreline segregation were observed in the case of as-cast TRC samples. The solidification mechanisms for TRC and MC-TRC have been found completely divergent. The homogenized TRC and MC-TRC samples were subjected to tensile test at elevated temperature (250-400 °C). At 250 °C, MC-TRC sample showed significant improvement in strength and ductility. However, at higher temperatures the tensile properties were almost comparable, despite of TRC samples having larger grains compared to MC-TRC samples. The mechanism of deformation has been explained by detailed fractures surface and sub-surface analysis carried out by scanning electron and optical microscopy. Homogenized MC-TRC samples were formed (hot stamping) into engineering component without any trace of crack on its surface. Whereas, TRC samples cracked in several places during hot stamping process.EPSRC – LiME, UK and Towards Affordable, Closed-Loop Recyclable Future Low Carbon Vehicle Structures – TARF-LCV(EP/I038616/1), Department of Mechanical Engineering, Imperial College London, UK, Mr. Steve Cook, Mr. Peter Lloyd, Mr. Graham Mitchell and Mr. Carmelo and BCAST, Brunel University London