Academic literature on the topic 'Contractional system'

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.<br>Includes bibliographical references (leaves 87-90).<br>This thesis derives new results in nonlinear system analysis using methods inspired from fluid mechanics and differential geometry. Based on a differential analysis of convergence, these results may be viewed as generalizing the classical Krasovskii the­orem, as well as linear eigenvalue analysis. A central feature is that convergence and limit behavior are in a sense treated separately, leading to significant conceptual simplifications. We establish new combination properties of nonlinear dynamic systems and use them to derive simple controller and observer designs for mechanical systems such as aircraft, underwater vehicles, and robots. The method is also applied to chemical chain reactions and mixture processes. The relative simplicity of these designs stems from their effective exploitation of the systems' structural specificities. Next, we analyze and quantify the global stability properties of physical partial differential equations such as the heat equation, or the Schroedinger equation. Lyapunov exponents are not coordinate-invariant, and thus their exact physical meaning is somewhat questionable. As an alternative, we suggest an extension of linear eigenvalue analysis to nonlinear dynamic systems. Finally, the thesis derives new controller and observer designs for general nonlinear dynamic systems. In particular, an extension of feedback linearization is proposed when the corresponding integrability conditions are violated.<br>by Winfried Stefan Lohmiller.<br>Ph.D.

Deux systèmes biologiques distincts, les muscles squelettiques et les sites d'adhésion de cellules kératocytes en mouvement, sont considérés dans un même cadre en raison de la similitude profonde de leur structure et de leur fonctionnalité. La réponse passive de l'un et de l'autre peut être modélisée à l'aide d'un grand nombre d'unités multi-stables couplées par des interactions à longue portée, et exposées à un désordre spatial fixé et un bruit thermique/mécanique. Les interactions à longue portée dans de tels systèmes conduisent à une synchronisation malgré les fluctuations temporelles et spatiales. Bien que les deux systèmes biologiques considérés présentent des différences structurelles importantes, nous montrons que l'on peut identifier une structure de verre de spin sous-jacente commune. À la lumière de cette analogie, ces systèmes vivants semblent être proches de points critiques et, à cet égard, le désordre gelé, reflétant l’incommensurabilité stérique des unités parallèles, peut être fonctionnel. Un autre paramètre important fixant la réponse est la rigidité interne du système qui couple les unités entre elles<br>Two biological systems, a half-sarcomere of a skeletal muscle and an adhesive cluster of a crawling keratocyte, are considered in parallel because of the deep similarity in their structure and functionality. Their passive response can be modeled by a large number of multi-stable units coupled through long-range interactions, frustrated by quenched disorder and exposed to thermal noise. In such systems, long-range interactions lead to synchronization, defying temporal and spatial fluctuations. We use a mean-field description to obtain analytic results and elucidate the remarkable ensemble-dependence of the mechanical behavior of such systems in the thermodynamic limit. Despite important structural differences between muscle cross-bridges and adhesive binders, one can identify a common underlying spin glass structure, which we fully exploit in this work. Our study suggests that the muscle machinery is fine-tuned to operate near criticality, and we argue that in this respect the quenched disorder, reflecting here steric incommensuration, may be functional. We use the analogy between cell detachment and thermal fracture of disordered solids to study the statistics of fluctuations during cellular adhesion. We relate the obtained results to recent observations of intermittent behavior involved in cell debonding, also suggesting near-criticality. In addition to the study of the equilibrium properties of adhesive clusters, we also present the first results on their kinetic behavior in the presence of time-dependent loading

The one which is considered the standard model of theory change was presented in [AGM85] and is known as the AGM model. In particular, that paper introduced the class of partial meet contractions. In subsequent works several alternative constructive models for that same class of functions were presented, e.g.: safe/kernel contractions ([AM85, Han94]), system of spheres-based contractions ([Gro88]) and epistemic entrenchment-based contractions ([G ar88, GM88]). Besides, several generalizations of such model were investigated. In that regard we emphasise the presentation of models which accounted for contractions by sets of sentences rather than only by a single sentence, i.e. multiple contractions. However, until now, only two of the above mentioned models have been generalized in the sense of addressing the case of contractions by sets of sentences: The partial meet multiple contractions were presented in [Han89, FH94], while the kernel multiple contractions were introduced in [FSS03]. In this thesis we propose two new constructive models of multiple contraction functions, namely the system of spheres-based and the epistemic entrenchment-based multiple contractions which generalize the models of system of spheres-based and of epistemic entrenchment-based contractions, respectively, to the case of contractions (of theories) by sets of sentences. Furthermore, analogously to what is the case in what concerns the corresponding classes of contraction functions by one single sentence, those two classes are identical and constitute a subclass of the class of partial meet multiple contractions. Additionally, and as the rst step of the procedure that is here followed to obtain an adequate de nition for the system of spheres-based multiple contractions, we present a possible worlds semantics for the partial meet multiple contractions analogous to the one proposed in [Gro88] for the partial meet contractions (by one single sentence). Finally, we present yet an axiomatic characterization for the new class(es) of multiple contraction functions that are here introduced.<br>Eduardo Fermé

Autogenous shrinkage is of concern in high performance concrete mixtures, when specific properties like strength and durability are enhanced. Factors like low watercement ratio, low porosity and increased hydration kinetics which are associated with high performance concrete mixtures are also responsible for the development of autogenous shrinkage. With about two decades of research into autogenous shrinkage, uncertainties still exist with testing procedure, effect of supplementary cementitious materials, modelling and prediction of autogenous shrinkage. The primary focus of this study is to understand mechanisms which have been postulated to cause autogenous shrinkage like chemical shrinkage and self desiccation. In addition, this study has considered properties like porosity and internal empty voids in the analysis of the causes of bulk volume deformations of the cementitious paste systems with and without mineral admixtures. The study begins with an experimental investigation of chemical shrinkage in hydrating cementitious paste systems with the addition of fly ash, slag and silica fume using the test method recently accepted by the ASTM. This was followed by the experimental investigation of autogenous shrinkage in cementitious paste. The autogenous shrinkage in paste mixtures is studied from an early age (~1.5 hours after addition of water) for cementitious systems at a water-cementitious ratio of 0.32 (w/c 0.25 for limited mixture proportions). A non-contact measurement method using eddy current sensors were adopted. The hydration mechanism of the cementitious paste systems was then modelled using CEMHYD3D, which is a 3 dimensional numerical modelling method successfully used to study, simulate and present the hydration developments in cementitious systems. Properties like chemical shrinkage, degree of hydration, total porosity and free water content; all of which have been obtained from the CEMHYD3D simulation have been cross correlated with the experimental results in order to more comprehensively understand the mechanism contributing to bulk volume change under sealed conditions. The experimental investigations are extended to study the development in concrete with and without mineral admixtures (i.e., silica fume, fly ash and slag). Self desiccation driving the development of autogenous shrinkage has been used extensively across literature but as an alternative the author has proposed using internal drying factor in modelling autogenous shrinkage. The "internal drying factor" is described as the ratio of the empty voids (due to chemical shrinkage) to the total porosity at any point of time of hydration. Independent of the mixture proportions, a linear trend was observed between the autogenous shrinkage strain and increase in internal drying factor. Thus the internal drying factor could be incorporated into semiempirical models while attempting to predict autogenous shrinkage. An increase in the compressive strength of matured concrete at 1 year had a strong correlation to the observed autogenous shrinkage strains irrespective of the cementitious system. It is believed this could be because of the increase in gel-space ratio which is intern linked to the degree of hydration and porosity of the microstructure. The author has obtained strong evidence that the micro-structural changes associated with high strength and durable concrete have a direct impact on the autogenous shrinkage of concrete. Hence, the author suggests that autogenous shrinkage should be investigated and allowable values be stipulated as design criterion in structures that use high strength-high performance concrete.

Currently, the plastics industry has a wide range of applications due to the possibility of a fully automated process or through increased production efficiencies. The reason for this choice of the thesis was to understand the whole issue of plastic injection molding process. The specified component is used to atach the sail, which serves to protect workers in the welding sector. A specified number of the series is 350 000. The work includes a theoretical problem of injection molding process, selection of technology, material selection and design of mold. An integral part of every design mold is a simulation of injection, which is also included. In conclusion of thesis is the calculation of the various stages of production and operation of the injection mold.

A promising approach to treat patients with vocal fold paralysis using electrical stimulation is investigated throughout this research work. Functional Electrical Stimulation works by stimulating the atrophied muscle or group of muscles directly by current when the transmission lines between the central nervous system are disrupted. This technique helps maintain muscle mass and promote blood flow in the absence of a functioning nervous system. The goal of this work is two-fold: develop control techniques for muscle contraction to optimize muscle stimulation and develop a small-scale electromagnetic system to provide stimulation to the laryngeal muscles for patients with vocal fold paralysis. These studies; therefore, focus on assessing a linear Proportional-Integral (PI) controller and two nonlinear controllers: Model Reference Adaptive Controller (MRAC) and an Adaptive Augmented PI (ADP-PI) system to identify the most appropriate controller providing effective stimulation of the muscle. Direct stimulation is applied to mouse skeletal muscle in vitro to test the controllers along with numerical simulations for validation of these experimental tests. The experiments included muscle contractions following four distinct trajectories: a step, sine, ramp, and square wave. Overall, the closed-loop controllers followed the stimulation trajectories set for all the simulated and tested muscles. When comparing the experimental outcomes of each controller, we concluded that the ADP-PI algorithm provided the best closed-loop performance for speed of convergence and disturbance rejection. Next, the focus of the research work was on the implementation of an electromagnetic system to generate appropriate currents of stimulation using the aforementioned controllers. For this study, Nickel-Titanium shape memory alloys were used to assess activation (contraction) through a two-coil system guided by the controllers. The application of the two-coil system demonstrated the effectiveness of the approach and a main effect was observed between the PI, MRAC, and ADP-PI controllers when following the trajectories. Lastly, a small scale two-coil system is developed for animal testing in the muscle-mass-spring setup. Experiments were successful in generating the appropriate stimulation controlled by the output-based algorithms for muscle contraction. Trials conducted for this study were compared to the muscle contractions observed in the first study. The controllers were able to provide appropriate stimulation to the muscle system to follow the set trajectories: a step, ramp, and sinusoidal input. More trials are required to draw statistical conclusions about the performance of each controller. Regardless, the small-scale two-coil system along with the applied controllers can be reconfigured to be an implantable system and tested for appropriate stimulation of the laryngeal muscles.<br>Ph. D.

Asthma is characterised by airway remodelling and an increase in airway resistance. A greater understanding of the mechanisms involved in airway inflammation and airway hyper-responsiveness (AHR) may highlight therapeutic opportunities for asthma. This study initially aimed to optimise the preparation of precision cut lung slices (PCLS) in mouse and pig to investigate the influence of calcium (Ca2+) homeostasis on airway smooth muscle (ASM) contraction as a prelude to human studies. The PCLS technique was then applied to a murine model of allergic airway disease to explore the inflammatory process and pathogenesis of airway hyper-reactivity in sensitised mice. Initial experiments using murine and porcine airways validated the PCLS model and demonstrated the significance of release and refilling of Ca2+ from internal stores to induce and maintain an airway contraction. Results also highlight interesting species differences in agonist sensitivity, with the porcine system sharing similar pharmacology to human airways. Using a murine model of allergic airway disease, agonist induced contractile responses in peripheral airways were measured in vitro using the PCLS technique. BALB/c mice underwent initial sensitisation by intraperitoneal administration of ovalbumin, receiving a 3 day challenge with aerosolised OVA l% (vlv), for varying periods of up to 3 weeks for acute, mid-chronic and chronic sensitisation protocols. To investigate the influence of the inflammatory environment, naive murine lung slices were incubated with selected inflammatory mediators. OVA sensitisation led to progressive structural remodelling and AHR to methacholine (MCh) challenge. However, this hyperresponsiveness was decreased 48 hours post lung removal. Of the inflammatory mediators selected for lung slice incubation, IL-33 significantly increased AHR to MCh. IL-33 is a proinflammatory cytokine with transcriptional repressor properties, playing a role in initiating the TH2 inflammatory response. In lung slices prepared from IL-33 receptor (ST2) KO mice IL-33 was unable to sensitise the contractile response. These data suggest the inflammatory environment promotes AHR and disassociates this airway sensitivity from structural remodelling. These data suggest a key role for IL-33 in mediating AHR in this murine model. Investigation of the mechanisms involved in airway hyper-reactivity revealed mRNA expression of IL-33 and the IL-33 receptor (ST2) in soluble and membrane bound forms were significantly increased in the mid-chronic and chronic ovalbumin sensitised murine lung tissue. Further quantitative analysis in human lung showed expression of IL-33 in epithelial and ASM cells. The human ST2 receptor (also known as IL-IRL-l) was expressed in mast cells. Together these results suggest IL-33 is a sensor of tissue damage; indirectly inducing AHR through further inflammatory cell activation to target ASM. This study demonstrates IL-33's role as an inflammatory marker of asthma and suggests a novel therapeutic intervention by targeting of the ST2 receptor.

Diagnosing cardiac patient problems contains many uncertainties, and to fully diagnose the patient's condition usually requires a lengthy drug regimen to see what works and what does not. Compounding this problem is that even after the correct drug regimen has been discovered, the underlying cause for the problem may remain a mystery. Thus, the uncertainty and the length of time required to provide an accurate and adequate solution makes it very difficult to provide quality care to the patient. Templeton and others have shown that lumped cardiac muscle parameters can be extracted from an isolated heart by injecting small volumes at high frequencies relative to the heart rate and measuring the pressure response to this volume change. Using the Hill muscle model of two springs and a dash pot to portray the different elements of the cardiac muscle, the pressure and volume relationship makes it possible to calculate these muscle parameters using frequency response analysis techniques. The hypothesis to be tested is "Is it possible to develop a method to test cardiac muscle for stiffness, resistance, and contractile force from measuring ventricular pressure and injected flow?" To test this hypothesis, an isovolumic heart model is developed and allowed to develop pressure, along with a small volume injected to create a pressure response. Analysis of the pressure and flow waveforms produces a measured value of the cardiac model parameter values to compare to the model values. Results from injecting small volume changes into a mathematical heart model show that it is possible to extract the muscle model parameters of non-linear resistance, inertia of the fluid and muscle, and stiffness of the muscle while filling and contracting. The injected frequency and volume were varied to find usable conditions, both with regard to the calculations and the practical limits. Analyzing the error between the measured and model values for a large number of different combinations of model parameters shows an average error of less than 1%.<br>Iron Range Engineering