1,720,975 research outputs found
Shock structure in the 14 moment system of extended thermodynamics with high order closure based on the maximum entropy principle
Full text linkAn analysis of the shock structure in the 14 moment system of extended thermodynamics with first, second and third order closure based on the maximum entropy principle (MEP) is presented, as a follow up of a recent investigation of the shock structure in the 13 moment system with first and second MEP-based closure. It is seen that when adopting higher order closures, 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 experimental results
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
Investigation on bistabelity in inductively-coupled plasma torches with non-conventional coil
No full textIn previous works on ICPTs with split coil [1, 2], the Authors pointed out that for a particular choice of the geometric parameters two equilibrium states for the plasma exist for the same induction coil current. In the present study, a deep investigation of the transition between the two states is performed with a time-dependent simulation code, evidencing a sort of hysteresis phenomenon. A parametric study is carried out in order to find threshold parameters for the bistability in different geometries. For some cases, time oscillating behaviour of plasma is found
Energy dissipation in viscoelastic Bessel media
Full text linkWe investigate the specific attenuation factor for the Bessel models of viscoelasticity. We find that the quality factor for this class can be expressed in terms of Kelvin functions and that its asymptotic behaviours confirm the analytical results found in previous studies for the rheological properties of these models
New approach to the thermodynamics of scalar-tensor gravity
Full text linkWe discuss and expand a new approach to the thermodynamics of scalar-tensor gravity and its diffusion toward general relativity (seen as an equilibrium state) proposed in a previous paper [Phys. Rev. D 103, L121501 (2021)PRVDAQ2470-001010.1103/PhysRevD.103.L121501, upon which we build. We describe scalar-tensor gravity as an effective dissipative fluid and apply Eckart's first order thermodynamics to it, obtaining explicitly effective quantities such as heat flux, "temperature of gravity,"viscosities, entropy density, plus an equation describing the "diffusion"to Einstein gravity. These quantities, still missing in the usual thermodynamics of spacetime, are obtained with minimal assumptions. Furthermore, we examine certain exact solutions of scalar-tensor gravity to test the proposed formalism and gain some physical insight on the "approach to equilibrium"for this class of theories
On variable-order fractional linear viscoelasticity
No full textA generalization of fractional linear viscoelasticity based on Scarpi’s approach to variable-order fractional calculus is presented. After reviewing the general mathematical framework, a variable-order fractional Maxwell model is analysed as a prototypical example for the theory. Some physical considerations are then provided concerning the fractionalisation procedure and the choice of the transition functions. Lastly, the material functions for the considered model are derived and numerically evaluated for exponential-type and Mittag-Leffler-type order functions
Mass (re)distribution for quantum dust cores of black holes
No full textThe collective ground state for a spherical symmetric dust ball has been investigated recently in R. Casadio [Phys. Lett. B 843 (2023) 138055]. In this study, we refine that model by obtaining a mass distribution that accounts for the superposition of wave functions across different layers. The refined mass distribution shows significant deviations from the approximation without quantum superpositions. Specifically, the new nearly parabolic distribution replaces the linear mass profile of the original work, featuring an overall downward concavity, which leads to a nonvanishing tension. Notably, the regularity of the metric and causal structure are preserved in the refined analysis
Navier–Stokes–Fourier equations as a parabolic limit of a general hyperbolic system of rational extended thermodynamics
No full textThis paper aims to prove that a general system of 14 balance laws for a compressible, possibly dense, gas that satisfies the universal principles of Rational Extended Thermodynamics (RET) converges to the Navier–Stokes–Fourier equations in the first step of the Maxwellian iteration. Moreover, in a theory not far from equilibrium, we show that the production terms of the hyperbolic system are uniquely determined as soon as the heat conductivity, the shear viscosity, and the bulk viscosity are assigned. The obtained results are tested on the RET theories for rarefied monatomic and polyatomic gases
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
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