1,720,961 research outputs found
Thermodynamical setting for gradient continuum theories with vectorial internal variables:Application to granular materials
No full textThe exploitation of the entropy principle in thermodynamics with Lagrange multipliers, the so–called
Liu procedure,is based on the celebrated Liu theorem. In some recent papers, the Liu procedure has
been generalized by considering the gradients of the governing equations as additional constraints.
Here, we apply this generalized procedure to the equations of a continuum with vectorial internal
variable and first-order non-loca lstate space. Then, owing to the obtained results, we develop a
thermodynamic model for continua with scalar microstructure
Thermo-electrodynamics of rigid superconductors
No full textThis paper deals with a continuum model of rigid superconductors. It is assumed
that their property of shifting to the superconductive state for suitable values of
temperature and magnetic field is due to a vectorial internal variable, related to the
superelectron current by a linear constitutive law. The compatibility of the model
with the second law of thermodynamics is investigated. The propagation of thermoelectromagnetic
waves through a one-dimensional conductor is analyzed as well. Comparison
is made with different continuum approaches which may be found in the
literature
Phase-field evolution in Cahn–Hilliard–Korteweg fluids
No full textIn this paper, the diffusion of different phases in a third-grade Korteweg fluid is modeled by introducing a phase-field as a new independent thermodynamic variable. The constitutive equations are supposed to depend on the mass density and its spatial derivatives up to the second order, as well as on specific internal energy, barycentric velocity and phase-field, together with their first-order spatial derivatives. The compatibility of the model with the second law of thermodynamics is exploited by applying a generalized Liu procedure. For isothermal and isochoric phases, a general evolution equation for the phase-field, which generalizes the classical Cahn–Hilliard equation, is derived. Specific entropy and free energy are proved to depend on the basic unknown fields as well as on their gradients. A general constitutive equation for the Cauchy stress, which encompasses the classical one postulated by Korteweg in 1901, is obtained
A nonlocal phase-field model of Ginzburg-Landau-Korteweg fluids
Full text linkA thermodynamic model of Korteweg fluids undergoing phase transition and/or phase separation
is developed within the framework of weakly nonlocal thermodynamics. Compatibility with second law of
thermodynamics is investigated by applying a generalized Liu procedure recently introduced in the literature.
Possible forms of the free energy and of the stress tensor, which generalize some earlier ones proposed by
several authors in the last decades, are carried out. Owing to the new procedure applied for exploiting the
entropy principle, the thermodynamic potentials are allowed to depend on the whole set of variables spanning
the state space, including the gradients of the unknown fields, without postulating neither the presence of an
energy or entropy extra-flux, nor an additional balance law for microforce
On the stability of the equilibrium states for hamiltonian dynamical systems arising in non-equilibrium thermodynamics
No full textIn this paper we consider a thermodynamic system with an internal state variable,
and study the stability of its equilibrium states by exploiting the reduced entropy inequality.
Remarkably, we derive a Hamiltonian dynamical system ruling the evolution of the system in a
suitable thermodynamic phase space. The use of the Hamiltonian formalism allows us to prove
the equivalence of the asymptotic stability at constant temperature, at constant entropy and at
constant energy, thus extending some classical results by Coleman and Gurtin (J. Chem. Phys.,
47, 597–613, 1967)
On the thermodynamics of Korteweg fluids with heat conduction and viscosity
No full textA model of third-grade Korteweg fluid with heat conduction and viscosity is developed.
The restrictions placed by the Dissipation Principle are investigated by applying
two different methods which generalize the classical Coleman-Noll and Liu procedures.
Compatibility with thermodynamics is achieved for arbitrary form of the energy and entropy
fluxes. In the one-dimensional case a particular solution of the system of thermodynamic restrictions
is provided
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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