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Cette thèse est constituée de trois parties. La première est consacrée à dégager les notions de "bonne mesure" et de "mesure réduite" pour deux problèmes paraboliques non linéaires. Pour chacun de ces problèmes et suite à un phénomène de relaxation, on construit une suite qui converge vers la plus "grande" sous-solution du problème donné. En plus, on cherche des "capacités universelles" et on établit des équivalences avec des mesures de Hausdorff. Dans la deuxième partie, on cherche des conditions d'existence et d'unicité de "grande solutions" pour des problèmes paraboliques dont le terme non linéaire est un terme d'absorption. Des conditions sur le bord du domaine permettent de prouver l'unicité de la solution. Dans la troisième partie, on étudie les "singularités" de deux problèmes paraboliques non linéaires. / The thesis at hand is composed of three parts. The first part is devoted to present the notions of "good measure" and "reduced measure" for two non-linear parabolic problems. For each of these problems we construct a sequence, after a relaxation phenomenon, which converges to the "greatest" sub-solution of the given problem. Moreover, we look for "universal capacities" and we establish equivalence with Hausdorff measure. In the second part, we establish existence and uniqueness conditions for "large solutions" of parabolic problems whose non-linear term is an absorption one. Some boundary conditions will permit to prove uniqueness of solutions. In the last part we study the "singularities" of two non-linear parabolic problems.

Summary: The possible involvement of an adrenergic-endorphin system in the mediation of the pressor response to isometric muscular contraction was studied in cats. Fatiguing contractions of the gastrocnemius and plantaris muscles caused an increase in the mean arterial blood pressure by 35 to 70 mmHg. Intravenous infusion (30 μg·kg-1) as well as intracisternal injection (2.5 μg) of clonidine-HCl eliminated the pressor response to muscular contraction. In both sets of experiments, the mean blood pressure remained at the resting level throughout the duration of the isometric contraction. Injection of naloxone (0.5 μmol·litre-1) into the cisterna magna did not alter the resting blood pressure and did not affect the rise in mean arterial pressure during muscle contractions. Intracisternal injection of naloxone (0.5 μmol·litre-1) prior to an intracisternal injection of clonidine (2.5 μg) did not alter the resting blood pressure but effectively antagonised the anti-pressor effects of clonidine during fatiguing isometric contractions. These data may indicate that activation of muscle "ergoreceptor" afferents (group III and IV fibres) during muscular contraction may cause an increase in the arterial blood pressure by interfering with an inhibitory adrenergic-endorphinergic pathway in the brainstem.

The purpose of this study was to examine the relationships between age, gender and fatigue resistance, and further, to determine the relative influence that estrogen status, membrane excitability, absolute force and muscle length have over the development of fatigue. A total of 48 subjects, classified by age and gender participated in this study; 12 young males (25.3 ± 2.1 yrs.), 12 young females (23.5 ± 2.1 yrs.), 12 elderly males (71.7 ± 5.6 yrs.) and 12 elderly females (69.5 ± 4.6 yrs.). The young females were all eumenorrheic, not taking oral contraceptives and tested in the mid-follicular phase of the menstral cycle. None of the elderly females were on hormone replacement therapy. A 3 minute paradigm of intermittent maximal voluntary contractions (MVC) was used to fatigue the adductor pollicis muscle, in which 5s MVC's were alternated with 2s rest periods. In addition, maximal twitches were evoked in each 2s rest period. No gender difference in fatigability was evident between young males and young females when considering the fatigue index of the evoked twitch (FI-PT) (young males: 39.8 ± 26.7%, young females: 36.6 ± 19.0%). There was also no gender difference in fatigability found between elderly males and elderly females when considering the FI-PT (elderly males: 24.9 ± 26.6%, elderly females: 16.4 ± 48.9%). However, potentiation of the evoked twitches during fatigue may have confounded these measures. When considering the changes in voluntary force during fatigue, there was a strong trend for a gender by time interaction between young males and young females.(p=0.06), which suggests that the former were more fatigable. The trend for this gender difference was also apparent in the voluntary fatigue index (FI-MVC) (young males: 44.7 ± 10.5%, young females: 37.8 ± 14.1 %; p=0.12). Similarly, young males had a significant decrease in M-wave amplitude during the fatigue protocol and a trend for a decrease in M-wave area (p=0.08), while young females showed no significant decreases in either M-wave measure during the fatigue protocol. There was no gender difference found between the elderly males and elderly females when considering the FI-MVC (elderly males: 24.2 ± 10.7%, elderly females: 26.3 ± 14.5%). Both groups also showed small but significant reductions in theM-wave amplitude during the fatigue protocol, although M-wave area was well maintained. The fact that a strong trend for a gender difference in fatigability was found in the young subjects but not the elderly subjects, suggests that estrogen may possess fatigue resisting properties, even during short duration exercise in which glycogen depletion is not a concern. With respect to the age-related differences in fatigue, elderly males were found to be significantly more fatigue resistant than young males as indicated by the FI-MVC (p<0.01), and the significant age by time interaction during the fatigue protocol (p<0.01). In contrast, only a trend was found for an age by time interaction between the young and elderly females during the fatigue protocol (p=0.06). This trend for an age-related difference in fatigue amongst women was also reflected in the FI- MVC (p=0.13). / Thesis / Master of Science (MSc)

Dans cette thèse, deux problèmes complètement indépendants sont étudiés. Le premier sujet porte sur l'analyse mathématique d'un modèle simple de délamination de films minces et d'apparition de cloques. Le second sujet est une étude fine de l'équation des milieux poreux motivée par des problèmes d'intrusion saline. Dans le premier sujet de ce travail, nous considérons un modèle variationnel simple unidimensionnel décrivant la délamination de films minces sous l'effet d'un refroidissement. Nous caractérisons les minimiseurs globaux qui correspondent à trois types de films: non-délaminés, partiellement délaminés (appelés cloques) ou bien complètement délaminés. Deux paramètres jouent un rôle crucial dans un tel phénomène : la longueur du film et la température. Dans le plan de phase de ces deux derniers, nous classifions l'ensemble des minimiseurs. Comme conséquence de notre analyse, nous identifions explicitement les cloques les plus petites pour ce modèle. Dans le deuxième sujet, nous répondons d'abord à une question ouverte depuis longtemps concernant l'existence de nouvelles contractions pour l'équation de type milieux poreux. Pour m>0, nous nous sommes intéressés à des solutions positives de l'équation suivanteU_t=Delta U^m. Pour 0<m<2, nous présentons une nouvelle famille de contractions pour cette équation en toute dimension, ce qui induit une extension des propriétés de la contraction L^1. Notre contraction peut être considérée comme étant la quatrième contraction connue pour cette équation. Même pour le cas m=1, notre approche aboutit à des nouveaux résultats pour l'équation de la chaleur standard. Dans un second temps, nous avons traité le même problème mais en utilisant une approche différentielle différente basée sur les distances géodésiques. Cette approche originale et générale sert à fabriquer des familles de contractions pour des équations aux dérivées parielles non linéaires, d'évolutions ou stationnaires. Nous présentons dans ce cadre diverses applications. En particulier, nous traitons à nouveau l'équation des milieux poreux et l'équation doublement non linéaire / In this thesis, we study two completely independent problems. The first one focuses on a simple mathematical model of thin films delamination and blistering analysis. In the second one, we are interested in the study of the porous medium equation motivated by seawater intrusion problems. In the first part of this work, we consider a simple one-dimensional variational model, describing the delamination of thin films under cooling. We characterize the global minimizers, which correspond to films of three possible types : non delaminated, partially delaminated (called blisters), or fully delaminated. Two parameters play an important role : the length of the film and the cooling parameter. In the phase plane of those two parameters, we classify all the minimizers. As a consequence of our analysis, we identify explicitly the smallest possible blisters for this model. In the second part, we answer a long standing open question about the existence of new contractions for porous medium type equations. For m>0, we consider nonnegative solutions U(t,x) of the following equationU_t=Delta U^m.For 0<m<2, we present a new family of contractions for this equation in any dimension, which extends the L^1 contraction properties. Our contraction can be seen as the fourth known contraction for this equation. Even for the case m=1, our approach leads to new results for the standard heat equation. A second work focuses on the same problem but using a differential approach based on geodesic distances. This original and general method is used to produce families of contractions for nonlinear partial differential equations, of evolution or stationary type. We present in this part various applications of this original method. In particular, we are concerned with the porous medium and the doubly nonlinear equations

The standard deviation of surface EMG (EMGσ) is often related to muscle force; the accuracy of EMGσ estimation is valuable for many application areas such as clinical biomechanics, prostheses control and sports medicine. Numerous researchers have developed methods to optimize EMGσ estimation. Whitening the EMG signal has been proved to improve the statistical efficiency of EMGσ estimation, but conventional linear whitening filters fail at low contraction level. An adaptive whitening filter was proposed by Clancy and Farry[14]. This technique has a better performance than prior whitening methods, however, the adaptive whitening filter needs to be calibrated each time electrodes are applied, which increase the complexity of the implementation. We designed a universal whitening filter which can omit most calibration steps for the adaptive whitening filter in future use. We used the ensemble mean of the power spectrum of 512 EMG recordings to form a general shape of a fixed whitening filter that can applied on any EMG signal. The test error on an EMG-torque task based on universal whitening over 512 subjects had a mean error of 4.80% maximum voluntary contraction (MVC) and standard deviation (std) of 2.03% MVC, compared with an original adaptive whitening filter error of 4.84±1.98% MVC. Additionally, the rest contraction modeling hasn’t received enough attention. Existing RMS estimates of EMGσ subtract noise in either the amplitude or power domain. These procedures have never been modeled analytically. We show that power domain noise subtraction is optimal. But rest contractions which are processed using power domain noise subtraction only estimate a zero-valued EMGσ approximately 50% of the time, which is undesirable in prosthesis-control. The prosthesis has a 50% possibility to slowly drift based on the current RMS estimator. We propose a new estimator to improve the zero-amplitude estimation probability during rest. We used 512 rest contraction recordings to validate the probability distribution of rest EMG signal showing that it only has 1.6% difference compared with Gaussian distribution. We also evaluated the percent of zero-valued EMGσ estimates using power domain noise subtraction and our new estimator, matching experimental findings to the theoretic predictions.

Belief Revision addresses the problem of how to change epistemic states, usually represented in the literature by sets of logical sentences. Solid theoretical results were consolidated with the AGM paradigm, which deals with theories (logically closed sets of sentences). After that, the theory was extended to belief bases, that is, arbitrary sets of sentences. Besides all this theoretical framework, AI researchers face serious difficulties when trying to implement belief revision systems. One of the major complications is the closure required by AGM theory, which cannot be easily computed. Even belief bases, which do not require closure, seem to be improper for practical purposes, since their changes are usually very rigid (syntax dependent). Some operations, known as pseudo-contractions, are in the middle ground between belief set change and belief base change. In the present work we have proposed a new pseudo-contraction operation, studied its properties and characterized it. We have also found connections between this operator and some other pseudo-contractions. / Revisão de Crenças aborda o problema de como alterar estados epistêmicos, normalmente representados na literatura como conjuntos de sentenças lógicas. Resultados teóricos sólidos foram consolidados com o paradigma AGM, que lida com teorias (conjuntos de sentenças logicamente fechados). Depois disso, a teoria foi estendida para bases de crenças, isto é, conjuntos arbitrários de sentenças. Apesar de todo esse arcabouço teórico, pesquisadores de IA enfrentam sérias dificuldades ao tentar implementar sistemas de revisão de crenças. Uma das maiores complicações é o fecho exigido pela teoria AGM, que não pode ser facilmente computado. Mesmo bases de crenças, que não exigem fechamento, parecem ser impróprias para fins práticos, pois suas alterações são geralmente muito rígidas (dependentes de sintaxe). Algumas operações, conhecidas como pseudo-contrações, estão no meio do caminho entre mudanças para conjuntos de crenças e mudanças para bases de crenças. Nesse trabalho, propomos uma nova operação de pseudo-contração, estudamos suas propriedades e a caracterizamos. Também encontramos conexões entre esse operador e algumas outras pseudo-contrações.

Made available in DSpace on 2014-06-11T19:23:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-07-30Bitstream added on 2014-06-13T20:50:44Z : No. of bitstreams: 1 souza_lhg_me_ilha.pdf: 1993240 bytes, checksum: b09e517d41877144e2a7b2634fd5fd55 (MD5) / Realiza-se a formulação matemática do escoamento potencial no interior de contrações bidimensionais usando sistemas de coordenadas cartesianas e cilíndricas. Para tal considera-se que as geometrias das contrações sejam bidimensionais no sistema de coordenadas cartesianas e bidimensionais com simetria axial no sistema de coordenadas cilíndricas. A formulação é adaptada a partir das equações tridimensionais de Euler em coordenadas cartesianas e cilíndricas, fazendo-se as hipóteses de bidimensionalidade, regime permanente, fluido invíscido e escoamento irrotacional. O formalismo diferencial do escoamento potencial no interior de contrações bidimensionais é formalmente resolvido utilizando-se a Técnica da Transformada Integral Generalizada – TTIG – cuja fundamentação está na expansão de funções-quadrado-integráveis em séries de funções ortogonais. Desenvolveu-se algoritmos computacionais, em linguagem computacional Fortran 95, para simular as soluções formais obtidas e produzir resultados numéricos que possibilitassem a análise do escoamento potencial nas referidas contrações. Realizou-se extensivos testes numéricos para quatro famílias de geometrias das contrações, sendo que cada família ainda possuía diferentes funções modeladoras do formato de suas paredes, bem como os parâmetros razão e esbeltez e razão de contração. Analisou-se os resultados visando sintetizar aspectos e características de como as contrações operam e que formatos são mais adequados ou não / It was done the mathematical formulation for potential flow inside two-dimensional contractions using both Cartesian and cylindrical coordinate systems. To achieve such aim it was considered that contraction geometries are two-dimensional in the Cartesian coordinate system and two-dimensional with axial symmetry in cylindrical system. Formulation is adapted from tri-dimensional Euler equations in Cartesian and cylindrical coordinate systems, doing hypothesis such as: two-dimensionality, steady flow regime, inviscid fluid and irrotational flow. Differential formulae that models potential flow inside two-dimensional contraction is formally solved using Generalized Integral Transform Technique – GITT – which is based upon orthogonal series expansion of square-integrable functions. It was developed some computational algorithms, using Fortran 95 computational language, to simulate the obtained formal solutions and to produce numerical results that allows potential flow analysis for referred contractions. It was done comprehensive numerical tests for four families of contraction geometries, being that each family yet has different contraction wall modeling functions, as well length and contraction ratios. Results were analyzed aiming to synthesize aspects and characteristics of how contractions operate and which forms are more adequate or not

Background: Arterial cannulation and intra-arterial (IA) fluid and blood resuscitation in the patients with severe shock is an easier approach compared with the intravenous (IV) access if concerns regarding the efficiency and safety of this approach are addressed. Objectives: We hypothesized that IA fluid resuscitation is more effective than IV resuscitation in restoring cardiac contractions (CC) of cardiac-arrested mice following severe hemorrhagic shock. Methods: Mice (N = 22) were anesthetized using ketamine/xylazine. Arterial and venous systems accessed through cannulation of the carotid artery and the Jugular vein, respectively. As much blood as possible was aspirated from the carotid artery access. Mice were observed until the complete cessation of chest wall motions. Following 30 seconds delay, IV (N = 5) and IA access (N = 6) were used for fluid resuscitation using Ringer Lactate (RL) in a similar volume to the aspirated blood. Mice were observed for restoration of chest wall motions. In phase-II of the study, after cessation of chest motions, mice (N = 11) underwent a thoracotomy and CCs were observed. In three mice, IV RL Infusion after cardiac arrest failed to restore CCs and was followed by IA RL infusion. In eight mice, following cardiac arrest intermittent IA RL infusion was performed. Results: While IV RL Infusion failed to restore chest motion in mice (N = 5), IA RL infusion restored chest motion in all mice examined (N = 6) (P = 0.0067). In three mice, IV RL infusion after cardiac arrest showed no effect on CC. After failure of venous infusion, IA RL infusion was performed which resulted in restoration of CC for 13.33 +/- 1.76 minutes. In eight mice, intermittent IA infusion of RL after cardiac arrest, sustained CC for 31.43 +/- 10.9 minutes (P = 0.017). Conclusions: IA fluid resuscitation is superior to IV resuscitation in hemorrhagic shock induced cardiac arrest.

Belief Revision addresses the problem of how to change epistemic states, usually represented in the literature by sets of logical sentences. Solid theoretical results were consolidated with the AGM paradigm, which deals with theories (logically closed sets of sentences). After that, the theory was extended to belief bases, that is, arbitrary sets of sentences. Besides all this theoretical framework, AI researchers face serious difficulties when trying to implement belief revision systems. One of the major complications is the closure required by AGM theory, which cannot be easily computed. Even belief bases, which do not require closure, seem to be improper for practical purposes, since their changes are usually very rigid (syntax dependent). Some operations, known as pseudo-contractions, are in the middle ground between belief set change and belief base change. In the present work we have proposed a new pseudo-contraction operation, studied its properties and characterized it. We have also found connections between this operator and some other pseudo-contractions. / Revisão de Crenças aborda o problema de como alterar estados epistêmicos, normalmente representados na literatura como conjuntos de sentenças lógicas. Resultados teóricos sólidos foram consolidados com o paradigma AGM, que lida com teorias (conjuntos de sentenças logicamente fechados). Depois disso, a teoria foi estendida para bases de crenças, isto é, conjuntos arbitrários de sentenças. Apesar de todo esse arcabouço teórico, pesquisadores de IA enfrentam sérias dificuldades ao tentar implementar sistemas de revisão de crenças. Uma das maiores complicações é o fecho exigido pela teoria AGM, que não pode ser facilmente computado. Mesmo bases de crenças, que não exigem fechamento, parecem ser impróprias para fins práticos, pois suas alterações são geralmente muito rígidas (dependentes de sintaxe). Algumas operações, conhecidas como pseudo-contrações, estão no meio do caminho entre mudanças para conjuntos de crenças e mudanças para bases de crenças. Nesse trabalho, propomos uma nova operação de pseudo-contração, estudamos suas propriedades e a caracterizamos. Também encontramos conexões entre esse operador e algumas outras pseudo-contrações.