La rotation a un impact majeur sur la structure et l'évolution des étoiles. En particulier, elle est connue pour être responsable de processus de mélanges macroscopiques des éléments chimiques et de transport de moment cinétique au sein des zones radiatives des étoiles. Dans la première partie de cette thèse, nous montrons comment l'état actuel de la modélisation stellaire justifie une nouvelle approche bi-dimensionnelle qui ne repose pas sur les hypothèses usuelles de rotation faible ou de rotation différentielle sphérique. Nous développons, dans la deuxième partie, un modèle simplifié (approximation de Boussinesq) d'étoiles en rotation rapide, en deux dimensions, où la rotation différentielle qui s'instaure et la circulation méridienne associée sont calculées de manière cohérente. Nous y identifions les paramètres pertinents à la description de l'écoulement induit par une contraction gravitationnelle dans un environnement stratifié de manière stable. Dans la troisième partie, nous démontrons que cet écoulement de spin-up l'emporte sur l'écoulement barocline à l'issue d'un temps de Kelvin-Helmholtz. La rotation différentielle adopte un profil universel cylindrique et la circulation méridienne est celle d'un écoulement de spin-up. Une couche de Stewartson s'établit aussi sur le cylindre tangent au noyau du modèle et pourrait être la source d'un couplage efficace de la rotation du noyau et de celle de l'enveloppe d'une étoile en fin de Séquence Principale. Dans la dernière partie de cette thèse, nous étudions Achernar, étoile en rotation rapide de type Be à l'aide du code compressible ESTER. Les modèles obtenus tendent à montrer que l'étoile est en contraction gravitationnelle post-Séquence Principale. Pour en rendre compte, le code ESTER a été modifié afin de suivre l'évolution chimique de l'étoile sur une échelle de temps nucléaire. / Rotation greatly impacts stellar structure and evolution. Particularly, it is known to be responsible of macroscopic mixings of chemical elements and transport of angular momentum within the radia­tive zones of stars. In the first part of this thesis, we show how the actual state of stellar modeling calls for a bi-dimensional approach going beyond usual assumptions of slow rotation and spherical differential rotation. We develop, in the second part of this thesis, a simplified model (Boussinesq approximation) of rapidly rotating stars in two dimensions, where the establishing differential rotation and associated meridional circulation are solved self-consistently. We describe the relevant parameters of the flow induced by a gravitational contraction in a stably stratified environment. In the third part, we demonstrate that this spin-up flow outweighs the baroclinic flow on a Kelvin-Helmholtz timescale. The differential rotation adopts an universal cylindrical profile and the meridional circulation is typical of the spin-up flow. A Stewartson layer appears too upon the tangent cylinder to the core and could explain an efficient coupling between the rotation of the core and the one of the envelope for stars at the end of the Main Sequence. In the last part of this thesis, we study Achernar, a rapidly rotating Be star, with the full-compressible ESTER code. Models we obtain tend to show that the star is undergoing a post Main Sequence gravitational contraction. To account this, the ESTER code has been modified to follow the chemical evolution of stars on a nuclear timescale.

This thesis is mainly concerned with the study of the role of cGMP in regulating contractility in the heart and blood vessels. A novel cGMP lowering agent, LY83583 (6-anilino-5,8-quinolinedione), was employed as a tool to determine the involvement of cGMP in mediating pharmacological and biological responses in the tissues being examined. In the first study, the role of cGMP in atriopeptin II-induced vascular relaxation was investigated. Atriopeptin II is believed to produce its vasorelaxant effect by virtue of its ability to elevate cGMP. However, the ability of the guanylate cyclase inhibitor, methylene blue, to inhibit the atriopeptin II-induced vasorelaxation has not been conclusively demonstrated. In the present study, LY83583 was found to partially prevent the rise in cGMP level caused by atriopeptin II but was without effect on the extent of the relaxation. This lack of correlation between cGMP elevation and relaxation may indicate either functional compartmentalization of the cyclic nucleotide or the existence of a cGMP-independent pathway for relaxation. Alternatively, the attenuated cGMP level may still be sufficient to elicit full relaxation. The inability of atriopeptin II to relax KC1-contracted bovine coronary arteries agrees with other reports in the literature and may indicate that the drug is less effective in antagonizing vascular responses associated with a marked degree of cell membrane depolarization. In the second study, the role of cGMP in mediating the endothelium-dependent inhibition of contractile responses of vascular tissue to alpha adrenoceptor stimulation was examined. There are reports in the literature that EDRF released from the endothelium elevates cGMP and depresses the response of the vessels to vasoconstrictors such as clonidine and norepinephrine. In the present study, LY83583 was used to examine the role of cGMP in mediating this effect. The treatment with LY83583 significantly lowered basal levels of cGMP and markedly enhanced the contractile response of endothelium-containing rat arteries to clonidine and norepinephrine. cGMP measurements indicate that clonidine did not elevate cGMP levels; hence the drug is unlikely to stimulate EDRF release. On the other hand, the depressant action of LY83583 on basal cGMP levels supports the hypothesis that inhibition of contractile responses may be a result of spontaneous release of EDRF, which results in tonic elevation of cGMP. The ability of 8-bromo-cGMP to reverse LY83583-induced enhancement of contractile responses to clonidine and norepinephrine further supports the involvement of cGMP in EDRF-induced vascular relaxation. In the final study, the role of cGMP in regulating cardiac contractility of amphibian ventricles was examined. The importance of cGMP in controlling mammalian cardiac function is controversial. However, a remarkable correlation between cGMP and contractile force has been reported in hypodynamic frog ventricles, and cAMP and cGMP were reported to act in a reciprocal fashion to regulate contractility. The present investigation attempted to verify whether such a relationship actually exists in the frog ventricles. Carbachol elicited a dose-dependent reduction in contractility without altering cGMP levels. On the contrary, sodium nitroprusside (100µM) did not reduce cardiac contractility despite a significant elevation of cGMP. At 1mM sodium nitroprusside, a huge elevation of cGMP and a small reduction in contractile tension were observed. Qualitatively similar results were obtained with a degraded sample of sodium nitroprusside. cAMP/cGMP ratios were not correlated with contractility. Hence, these findings were inconsistent with those found in earlier studies on hypodynamic frog hearts and do not support the proposed role of cGMP as a second messenger. The disparate findings may be caused by differences in experimental design. Alternatively, functional compartmentalization of cGMP (in the case of sodium nitroprusside) and the involvement of other cGMP-independent pathways (in the case of carbachol) cannot be ruled out. All these findings suggest that cGMP may play a more crucial role in regulating vascular than cardiac contractility. / Pharmaceutical Sciences, Faculty of / Graduate

In this experiment, fluorescent N- (1-pyrenyl) iodoacetamide modified the two reactive thiols, SH1 (Cys 707) and SH2 (Cys 697) on myosin to detect SH1-SH2 a -helix melting. The excimer forming property of pyrene is well suited to monitor the dynamics of the SH1 and SH2 helix melting, since the excimer should only form during the melted state. Decreased anisotropy of the excimer relative to the monomeric pyrene fluorescence is consistent with the disordering of the melted SH1-SH2 region in the atomic model. Furthermore, nucleotide analogs induced changes in the anisotropy of the excimer, suggesting that the nucleotide site modulates the flexibility of SH1-SH2 region.

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%. / Iron Range Engineering

published_or_final_version / Physiology / Master / Master of Philosophy

No description available.

No description available.

Although the neural mechanisms responsible for the orderly recruitment of motor units have been investigated extensively, the flexibility of the underlying neural circuitry remains unclear. For example, the effects of electrical stimulation on the recruitment order of motor units is not well understood. This project was designed to study the recruitment order of motor units in man during different stimulation protocols. Examination of the compound-twitch characteristics of electrically evoked responses allowed an indirect determination of motor-unit recruitment order. The results demonstrate that the recruitment order of quadriceps femoris and triceps surae motor units differs according to the stimulation protocols used. Analysis of the compound-twitch characteristics indicated that the recruitment order of motor units during Hoffmann reflexes is similar to that of volitional muscle contractions but effectively the reverse of that during direct-motor responses. Moreover, the results suggest that cutaneous-afferent stimulation alters the recruitment thresholds of different motor unit types during the Hoffman reflex.

This thesis evaluates the use of fibrous reinforced concrete as a viable structural repair alternative. An independent laboratory investigation was conducted to substantiate the validity of the marketed claims of Polypropylene Fiber Reinforced Concrete (PFRC) and of Steel Fiber Reinforced Concrete (SFRC) to improve the long-term performance of conventional portland cement concrete. The study found that SFRC significantly increases the compression strength, flexural behavior, and material toughness of PCC, whereas the test response for PFRC yielded minimal contributory strengths. The work examines the function of fibers; FRC's historical background, prevalent economic considerations, and modern repair applicational developments; remedies to overcome the negative aspects of SFRC; current research programs; and future trends. The author recommends trial field demonstration of Steel Fiber Reinforced Micro-Silica Dense Concrete (SFR-MSDC) as a cost-competitive material alternate in lieu of non-fibrous Latex-Modified Concrete (LMC) to more proficiently rehabilitate fatigue-distressed bridge decks.

No description available.