1,720,982 research outputs found
Hyperbolicity Region of a Rational Extended Thermodynamics Model with 14 Moments for a Non-polytropic Gas
No full textRational extended thermodynamics models are composed by a set of balance laws capable of describing far-from-equilibrium thermodynamic phenomena for rarefied gases. Such equations are usually approximated in the neighbourhood of an equilibrium state with respect to non-equilibrium variables and, for this reason, their hyperbolicity is confined in a domain of the phase space called hyperbolicity region. The present work aims to determine such a domain for a nonpolytropic rarefied gas described by a one-dimensional 14 moment theory with a firstorder approximation. The dependence of the heat capacity on the temperature influences significantly the shape of the hyperbolcity region. The para-H2 example is presented as a case study
New extended thermodynamics balance equations for an electron gas confined in a metallic body
Full text linkSommerfeld’s theory of metal electrons suggests that the electrons in a metal can be described as a gas of free fermion particles confined inside the metallic body. In this paper a new extended thermodynamics model is proposed starting from this idea. The model includes both the stress tensor and a quadratic expansion of the distribution function in the neighborhhod of an equilibrium state. Such contributions were neglected in the original model proposed by Müller in 1976; so this new set of balance laws represents an improvement aimed at the description of non-equilibrium phenomena. The application to a simple case is briefly analysed
Second-order approximation of extended thermodynamics of a monatomic gas and hyperbolicity region
Full text linkThe rational extended thermodynamics theory describes non-equilibrium phenomena for rarefied gases, and it is usually approximated in the neighborhood of an equilibrium state. Consequently, the hyperbolicity of its differential system holds only in some domain of the state variables (called hyperbolicity region). In this paper, we present a second-order approximation with respect to non-equilibrium variables, in the case of a monatomic gas theory with 13 fields. We verify that, in the case of one-dimensional space, the radius of the hyperbolicity region is larger than the corresponding radius of the first-order approximation. Moreover, when the model involves three-dimensional field variables, we prove that the equilibrium state for differential systems with quadratic approximation is inside the hyperbolicity region. This fact is in contrast with the first-order models that, in some cases of three-dimensional field variables, present the equilibrium point at the boundary of the hyperbolicity region
The role of the dynamic pressure in the behavior of an oscillating gas bubble
Full text linkThe paper contains a preliminary study on the role that dynamic pressure might play in the dynamics of a gas bubble oscillating in a liquid. To this aim, we introduce a mathematical model, proposed under the homobaricity hypothesis and deduced from the 14-moment theory of rational extended thermodynamics through significant simplifications, that makes the equations easily integrable over long time intervals. In the presence of a gas with high bulk viscosity, relevant effects can be observed in different physical conditions: isothermal or adiabatic regimes, small amplitude oscillations, non-linear oscillations, resonances, and sonoluminescence. To make the study more realistic, we always refer to carbon dioxide gas, which on the one hand could present high values of bulk viscosity and on the other hand is known for its peculiar behaviors in the framework of cavitation and gas bubbles
Acceleration waves in a spherical oscillating gas bubble containing a gas mixture
Full text linkThe non-equilibrium phenomena that characterize the dynamics of an oscillating bubble in a liquid are generally very complex. In this work we study the effects produced by the presence of a gas mixture in which the temperatures of each species are taken into account. Acceleration waves are used to test the stabilizing effects of the model and verify the possibility of shock formation within the bubble. It is shown that the diffusion associated with the presence of multiple temperatures cannot be neglected when describing what happens inside the bubble, even in the sonoluminescence regime
Acceleration Waves in Cylindrical Shrinking Gas Bubbles
Full text linkThe paper studies the case of shrinking cylindrical gas bubbles acting as a radial piston and generating acceleration waves. The behavior of such waves and their improbable transformation into shocks are illustrated theoretically, as well as through some examples inspired by experimental data. The use of rational extended thermodynamics enables us to highlight the relevance of the dissipation and the possible role played by dynamic pressure and stress tensor in bubble evolution or shock formation. These results constitute an extension and a completion of a previous work dedicated to the analysis of acceleration waves generated in oscillating spherical bubbles
Stationary heat transfer in helicoidal flows of a rarefied gas
No full textThe paper focuses on a stationary problem in a rarefied gas confined between two
coaxial cylinders kept at different constant temperatures. It is assumed that the external cylinder
is at rest, while the internal one rotates around its axis and contemporaneously moves upwards
with a constant axial velocity, so that a helicoidal motion of the fluid is generated. The equations
of Rational Extended Thermodynamics are introduced to study the physical effects due to the
combination of both helicoidal flow and heat transfer. It turns out that, although only a radial
temperature gradient is prescribed, both the tangential and the axial components of the heat
flux do not vanish. Moreover, all the components of the stress tensor are not null, even though
the radial and the axial velocity of the gas depend only on the radial coordinate. The results
are compared with the prediction of the corresponding Classical Thermodynamics model and
significative differences are observed. The role of the helicoidal motion is also analyzed through a
comparison with the cases of only rotation or only axial flows
Acceleration waves in rational extended thermodynamics of rarefied monatomic gases
Full text linkRational Extended Thermodynamics theories with different number of moments are usually introduced to study non-equilibrium phenomena in rarefied gases. Here, we use them to describe one-dimensional acceleration waves in a rarefied monatomic gas. In particular, we focus on the degeneracy of the acceleration wave to a shock wave, in order to test the validity of the models and the role played by an increasing number of moments. As a byproduct, some peculiarities of the characteristic velocities at equilibrium are analyzed as well
Role of jasmonic acid in plants: the molecular point of view
No full textKey message: Recent updates in JA biosynthesis, signaling pathways and the crosstalk between JA and others phytohormones in relation with plant responses to different stresses. Abstract: In plants, the roles of phytohormone jasmonic acid (JA), amino acid conjugate (e.g., JA-Ile) and their derivative emerged in last decades as crucial signaling compounds implicated in stress defense and development in plants. JA has raised a great interest, and the number of researches on JA has increased rapidly highlighting the importance of this phytohormone in plant life. First, JA was considered as a stress hormone implicated in plant response to biotic stress (pathogens and herbivores) which confers resistance to biotrophic and hemibiotrophic pathogens contrarily to salicylic acid (SA) which is implicated in plant response to necrotrophic pathogens. JA is also implicated in plant responses to abiotic stress (such as soil salinity, wounding and UV). Moreover, some researchers have recently revealed that JA controls several physiological processes like root growth, growth of reproductive organs and, finally, plant senescence. JA is also involved in the biosynthesis of various metabolites (e.g., phytoalexins and terpenoids). In plants, JA signaling pathways are well studied in few plants essentially Arabidopsis thaliana, Nicotiana benthamiana, and Oryza sativa L. confirming the crucial role of this hormone in plants. In this review, we highlight the last foundlings about JA biosynthesis, JA signaling pathways and its implication in plant maturation and response to environmental constraints
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