EDDINGTON'S “Internal Constitution of the Stars” was published in 1926 and gives what now ranks as a classical account of his own researches and of the general state of the theory at that time. Since then, a tremendous amount of work has appeared. Much of it has to do with the construction of stellar models with different equations of state applying in different zones. Other parts deal with the effects of varying chemical composition, with pulsation and tidal and rotational distortion of stars, and with the precise relations between the interior and the atmosphere of a star. The striking feature of all this work is that so much can be done without assuming any particular mechanism of stellar energy-generation. Only such very comprehensive assumptions are made about the distribution and behaviour of the energy sources that we may expect future knowledge of their mechanism to lead mainly to more detailed results within the framework of the existing general theory. An Introduction to the Study of Stellar Structure By S. Chandrasekhar. (Astrophysical Monographs sponsored by The Astrophysical Journal.) Pp. ix+509. (Chicago: University of Chicago Press; London: Cambridge University Press, 1939.) 50s. net.

An Introduction to the Study of Stellar Structure

頚椎部 instability の計測法

These notes are devoted to the analysis of reacting flows in systems where the reactants are initially unpremixed. We shall deal here with the combustion reactions, encountered very often in applications, which take place in the gas phase, between a fuel and an oxidizer, (typically the oxygen of the air). The combustion reactions are exothermic, so that we shall see large temperature differences in the flow field, and the reaction rates are very sensitively dependent on temperature. Then in regions of the flow field where the temperature is low the reactants will mix without chemical reactions, while in regions of high temperature the flow will be in chemical equilibrium. When the reaction can be modelled by an overall irreversible reaction between the fuel and the oxygen, the chemical equilibrium condition implies that one of the reactants has locally zero concentration, because it has been previously completely consumed by the chemical reaction. The chemical reaction has taken place in thin reaction layers in the form of rich or lean premixed flames, when they separate regions of frozen flow from regions of equilibrium flow, or diffusion flames, when they separate a region without fuel from a region without oxidizer.

The structure of diffusion flames

In this study, the cardiovascular system and heart hemodynamic performance are modeled using lumped method electrical analogy to evaluate the effects of abnormal heartbeats on the cardiovascular system performance. Lumped method voltage-current relations of an electrical circuit is able to simulate the cardiovascular CV system behavior in various physiological conditions. CV system consists of 42 compartments, including artery, vein, capillary set, and heart chambers. Each blood circulatory subsystem compartment is modeled using electrical elements, such as resistor, capacitor, and inductor. In this study, by utilizing lumped model, CV system is simulated in matlab software SIMULINK environment. There are two major types of irregular heart rates. In tachycardia, the heartbeats are too quick: over 100 beats per minute. In bradycardia, the heart beat is too slow: less than 60 beats per minute. Healthy blood circulation and heart performance are modeled heartbeat: 75 beat/minute, and the results such as left atrium outflow-time graph and pressure-time diagram of aorta artery and pulmonary circulation are obtained. The present results are found to be in agreement with numerical and experimental studies. Then, by increasing and decreasing the heartbeat, the abnormality 150 and 50 beat/minute representing tachycardia and bradycardia, respectively is simulated. The results show that the tachycardia leads to a significant reduction of capillary blood flow into less than 100ml/s, while it exceeds 100ml/s when heart has normal function. The results of the present study have clinical implications for detailed diagnosis of CV diseases when experimental studies have limitation. Copyright © 2014 John Wiley & Sons, Ltd.

A lumped parameter mathematical model to analyze the effects of tachycardia and bradycardia on the cardiovascular system

The global stability of laminar axisymmetric low-density jets is investigated in the low Mach number approximation. The linear modal dynamics is found to be characterised by two features: a stable arc branch of eigenmodes and an isolated eigenmode. Both features are studied in detail, revealing that, whereas the former is highly sensitive to numerical domain size and its existence can be linked to spurious feedback from the outflow boundary, the latter is the physical eigenmode that is responsible for the appearance of self-sustained oscillations in low-density jets observed in experiments at low Mach numbers. In contrast to previous local spatio-temporal stability analyses, the present global analysis permits, for the first time, the determination of the critical conditions for the onset of global instability, as well the frequency of the associated oscillations, without additional hypotheses, yielding predictions in fair agreement with previous experimental observations. It is shown that under the conditions of those experiments, viscosity variation with composition, as well as buoyancy, only have a small effect on the onset of instability.

Global instability of low-density jets

Object-oriented modeling and simulation of the closed loop cardiovascular system by using SIMSCAPE

On the critical conditions for pool-fire puffing

The present study employs a linear global stability analysis to investigate buoyancy-induced flickering of axisymmetric laminar jet diffusion flames as a hydrodynamic global mode. The instability-driving interactions of the buoyancy force with the density differences induced by the chemical heat release are described in the infinitely fast reaction limit for unity Lewis numbers of the reactants. The analysis determines the critical conditions at the onset of the linear global instability as well as the Strouhal number of the associated oscillations in terms of the governing parameters of the problem. Marginal instability boundaries are delineated in the Froude-number/Reynolds-number plane for different fuel-jet dilutions. The results of the global stability analysis are compared with direct numerical simulations of time-dependent axisymmetric jet flames and also with results of a local spatio-temporal stability analysis.

Diffusion-flame flickering as a hydrodynamic global mode

A theoretical and numerical analysis of the rupture of a nonwetting, ultrathin liquid film placed on a solid substrate reveals that the lubrication description experiences a crossover to a universal self-similar solution of the Stokes equations prior to the singularity.

Stokes theory of thin-film rupture

The present study employs a linear global stability analysis to investigate buoyancy-induced flickering of axisymmetric laminar jet diffusion flames as a hydrodynamic global mode. The instability-driving interactions of the buoyancy force with the density differences induced by the chemical heat release are described in the infinitely fast reaction limit for unity Lewis numbers of the reactants. The analysis determines the critical conditions at the onset of the linear global instability as well as the Strouhal number of the associated oscillations in terms of the governing parameters of the problem. Marginal instability boundaries are delineated in the Froude number/Reynolds number plane for different fuel jet dilutions. The results of the global stability analysis are compared with direct numerical simulations of time-dependent axisymmetric jet flames and also with results of a local spatio-temporal stability analysis.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002211201600358X

D. Moreno-Boza

Papers

Object-oriented modeling and simulation of the closed loop cardiovascular system by using SIMSCAPE

On the critical conditions for pool-fire puffing

Diffusion-flame flickering as a hydrodynamic global mode

Stokes theory of thin-film rupture

Diffusion-flame flickering as a hydrodynamic global mode