1,721,083 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
Classical limit of relativistic moments associated with Boltzmann–Chernikov equation: Optimal choice of moments in classical theory
No full textThe moment system associated with the Boltzmann equation is largely used in many applications
and is the main ingredient of Rational Extended Thermodynamics (RET). The choice of
truncation ofmoments is arbitrary and many possibilities are present in the literature depending
in particular on many contracted indexes in each moment tensor considered.Moreover, in
a polyatomic gas, we have two hierarchies of moments with different indexes of truncation.
As any classical theory can be considered as a limiting case of a relativistic one, we study in
this paper the moments associated with the relativistic Boltzmann–Chernikov equation until
the index of truncation N. We take the classical limit for both polyatomic and monatomic
rarefied gases and prove that there exists only unique possible choice of the moments in the
classical case for a given N
Shock structure in extended thermodynamics with second-order maximum entropy principle closure
Full text linkAn investigation on the features of the shock structure solution of the 13-moment system of extended thermodynamics with a second-order closure based on the maximum entropy principle is presented. The results are compared to those obtained by means of the traditional first-order closure and to those obtained in the framework of kinetic theory by solving the Boltzmann equation with a BGK model for the collision term. It is seen that when adopting a second-order closure, the strength of the subshock that appears in the shock structure profile for large enough Mach numbers is remarkably reduced with respect to what is found with the first-order closure, and the overall profile of the shock structure solution is in better agreement with the results obtained with the kinetic theory approach. The analysis is extended to the case of the 14-moment system of a polyatomic gas, and some preliminary results are presented also for this case
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
Relativistic extended thermodynamics of rarefied polyatomic gas
No full textThe goal of the present paper is to construct a relativistic extended thermodynamics (ET) theory of rarefied polyatomic gases. This is achieved by adopting the closure procedure for the 14 generalized moments of a distribution function that, as in the classical case, depends on an additional continuous variable representing the energy of the internal modes of a molecule. This permits the theory to take into account the energy exchange between translational modes and internal modes of a molecule in binary collisions. The theory includes the ET theory of monatomic gases as a singular limit and converges to the corresponding ET theory of polyatomic gases in the classical limit. In contrast to a monatomic gas in which the order of magnitude of the dynamical pressure is O(1/c2), the dynamical pressure in a polyatomic gas is not small due to the internal motion of molecules as is the case in the classical limit. Therefore the present theory might result particularly useful in cosmology to describe some aspects of the post-recombination era
The Bénard problem for quasi-thermal-incompressible materials: A linear analysis
No full textIn this paper we apply the ideas introduced with the so-called extended-quasi-thermal-incompressible (EQTI) model, recently proposed by Gouin and Ruggeri (Int. J. Non-Linear Mech. 47 (2012) 688–693) [12]. In particular, in the Oberbeck–Boussinesq approximation we consider the more realistic constitutive equation compatible with the thermodynamical stability by putting in the buoyancy term a density which depends not only by the temperature but also on the pressure. The equation for the pressure is then modified by an extra dimensionless parameter β^ which is proportional to the positive compres- sibility factor β. The 2-D linear instability of the thermal conduction solution in horizontal layers heated from below (Bénard problem) is investigated. It is shown that for any β^ : (i) the rest state pressure profile is different from the parabolic one; (ii) if convection arises, then it first arises via a stationary state and the strong principle of exchange of stability holds; for small β^ : (iii) convection certainly arises provided Ra is sufficiently large; (iv) the related critical Rayleigh number coincides -in the limit of vanishing β^ – with the classical one, and decreases as β^ increases
Ultra-relativistic limit of extended thermodynamics of rarefied polyatomic gas
Full text linkThe aim of this paper is to evaluate the ultra-relativistic limit of a recent causal theory proposed for polyatomic dissipative relativistic gas. The explicitly expression of characteristic velocities of the hyperbolic system is found in term of the degree of freedom of the gas and compared with the one of monatomic gas
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
