The role of the myosin ATPase activity in adaptive thermogenesis by skeletal muscle

Resting skeletal muscle is a major contributor to adaptive thermogenesis, i.e., the thermogenesis that changes in response to exposure to cold or to overfeeding. The identification of the “furnace” that is responsible for increased heat generation in resting muscle has been the subject of a number of investigations. A new state of myosin, the super relaxed state (SRX), with a very slow ATP turnover rate has recently been observed in skeletal muscle (Stewart et al. in Proc Natl Acad Sci USA 107:430–435, 2010). Inhibition of the myosin ATPase activity in the SRX was suggested to be caused by binding of the myosin head to the core of the thick filament in a structural motif identified earlier by electron microscopy. To be compatible with the basal metabolic rate observed in vivo for resting muscle, most myosin heads would have to be in the SRX. Modulation of the population of this state, relative to the normal relaxed state, was proposed to be a major contributor to adaptive thermogenesis in resting muscle. Transfer of only 20% of myosin heads from the SRX into the normal relaxed state would cause muscle thermogenesis to double. Phosphorylation of the myosin regulatory light chain was shown to transfer myosin heads from the SRX into the relaxed state, which would increase thermogenesis. In particular, thermogenesis by myosin has been proposed to play a role in the dissipation of calories during overfeeding. Up-regulation of muscle thermogenesis by pharmaceuticals that target the SRX would provide new approaches to the treatment of obesity or high blood sugar levels

Thermal Flows

Flows of thermal origin and heat transfer problems are central in a variety of disciplines and industrial applications. The present book entitled Thermal Flows consists of a collection of studies by distinct investigators and research groups dealing with different types of flows relevant to both natural and technological contexts. Both reviews of the state-of-the-art and new theoretical, numerical and experimental investigations are presented, which illustrate the structure of these flows, their stability behavior, and the possible bifurcations to different patterns of symmetry and/or spatiotemporal regimes. Moreover, different categories of fluids are considered (liquid metals, gases, common fluids such as water and silicone oils, organic and inorganic transparent liquids, and nano-fluids). This information is presented under the hope that it will serve as a new important resource for physicists, engineers and advanced students interested in the physics of non-isothermal fluid systems; fluid mechanics; environmental phenomena; meteorology; geophysics; and thermal, mechanical and materials engineering

Finite-Dimensional Description of Non-Newtonian Vortex Flows

The application of finite-dimensional dynamical systems theory to non-Newtonian vortex flow indicates the presence of complex temporal dynamics that is attributed to shear thinning and normal stress (giving rise to the so-called Weissenberg rod climbing phenomenon). These aspects are examined for Rayleigh-Benard thermal convection and Taylor-Couette rotational flow, in an attempt to elucidate on the mechanisms behind the onset and destabilization of secondary vortex flow common to these and possibly other non-Newtonian flows in the transition regime. Three transition scenarios are particularly explored, namely, the transition to chaos via intermittency, quasiperiodicity and period doubling. 1 Introduction Like any flow in the transition or turbulent regime, the Rayleigh-Benard thermal convection and Taylor-Couette flow involve a continuous range of excited spatio-temporal scales. In order to assess the effect on the motion of the arbitrarily many smaller length scales, one would have ..

Finite-dimensional description of non-newtonian vortex flows

The application of finite-dimensional dynamical systems theory to non-Newtonian vortex flow indicates the presence of complex temporal dynamics that is attributed to shear thinning and normal stress (giving rise to the so-called Weissenberg rod climbing phenomenon). These aspects are examined for Rayleigh-Benard thermal convection and Taylor-Couette rotational flow, in an attempt to elucidate on the mechanisms behind the onset and destabilization of secondary vortex flow common to these and possibly other non-Newtonian flows in the transition regime. Three transition scenarios are particularly explored, namely, the transition to chaos via intermittency, quasiperiodicity and period doubling

Generalized Hydrodynamics for Cylindrical Couette Flow of a Lennard-Jones Fluid

Note:In the present thesis numerical calculations of flow properties are carried out on the cylindrical Couette flow of a Lennard-Jones gas by using the generalized hydrodynamic equations. Thermoviscous coupling and normal stress effects are taken into account. These generalized hydrodynamic equations are based on the modified moment method for the solution of the Boltzmann equation. Calculations are first conducted in the absence of normal stresses with the view of investigating the dissipative terms in the constitutive equations. The range of Knudsen numbers covers the normal, transition and free molecular regimes. There is good agreement with experiment and results based on the Monte Carlo simulation method. Agreement with experiment is improved when normal stress effects are included. In this case, a phase-transition-like behaviour emerges in the flow properties and a slip in the gas velocity appears at the inner cylinder, as the Knudsen number exceeds a critical value. This behaviour results in the singularity in the entropy production which is reminiscent of a second-order phase transition in thermodynamic systems. For a fluid subject to a high shear rate, the flow is shown to approach the Eulerian behaviour in the limit of infinite Reynolds number. At the critical Reynolds number one observes the onset of a phase-transition-like behaviour with a decrease in slope in the drag coefficient vs. Reynolds number curve. Linear stability analysis shows the existence of two critical Reynolds numbers and three marginal stability curves in the case of axisymmetric stationary oscillations.La présente thèse traite numériquement le calcul des propriétés de courant cylindrique de Couette d’un gaz de Lennard-Jones en utilisant les équations hydrodynamiques généralisées. Le couplage thermovisqueux et les effets de contraintes normales sont tenus en compte. Ces équations hydrodynamiques généralisées sont basées sur la méthode de moments modifiée pour la résolution de l’équation de Boltzmann. En premier lieu, les calculs sont performés en l’absence de contraintes normales en vue d’examiner les termes de nature dissipative dans les relations de comportement. Les trois régimes de densité normale, de transition et moléculaire libre sont couverts dans les calculs. Il en résulte un bon accord avec les résultats expérimentaux et ceux bases sur la méthode de simulation de Monte Carlo. L'accord avec les résultats expérimentaux est amélioré quand les effets de contraintes normales sont inclus. Dans ce cas, un comportement similaire a une transition de phase dans les propriétés du courant et un glissement dans la vitesse du gaz au cylindre intérieur apparaissent, une fois que le nombre de Knudsen excède une valeur critique. Ce comportement résulte en la singularité dans la production d'entropie qui rappelle une transition de phase de second degré dans les systèmes thermodynamiques. Pour un fluide sujet à un haut gradient de vitesse, le courant s’approche du comportement Eulérien dans la limite infinie du nombre de Reynolds. A la valeur critique du nombre de Reynolds on observe l'émergence de la transition de phase avec une diminution de la tangente a la courbe du coefficient de trainée en fonction du nombre de Reynolds. L’analyse de stabilité linéaire révèle l’existence de deux nombres de Reynolds critiques et trois courbes de stabilité marginale dans le cas d’oscillations axisymétriques stationnaires

A spectral approach to inertial confined thin-film flow

International audienceA spectral approach is proposed to determine the flow field of a thin film inside narrow channels of arbitrary shape. Although the method is easily extended to transient flow, only steady flow is considered here. The flow field is represented spectrally in the depthwise direction in terms of orthonormal shape functions, which together with the Galerkin projection lead to a system of ordinary differential equations that can be solved using standard methods. The method is particularly effective for nonlinear flow, including nonlinearities of geometrical or material origins. The validity of the proposed method is demonstrated for a flow with inertia, and, unlike the depth-averaging method, is not limited to a flow at small Reynolds number. The problem is closely related to high-speed lubrication flow. The validity of the spectral representation is assessed by examining the convergence of the method, and comparing it with the fully two-dimensional finite-element solution, and the widely used depth-averaging method from shallow-water theory. It is found that a low number of modes are usually sufficient to secure convergence and accuracy. The influence of inertia is examined on the velocity and pressure fields. The pressure distributions reflect excellent agreement between the low-order spectral method and the finite-element solution, even at moderately high Reynolds number. The depth-averaging solution is unable to predict accurately (qualitatively and quantitatively) the high-inertia flow. Comparison of the velocity field reflects the expected discrepancy in a boundary layer formulatio