1,721,009 research outputs found
A nonisothermal phase-field model for the ferromagnetic transition
No full textWe propose a model for nonisothermal ferromagnetic phase transition based on a phase field approach, in which the
phase parameter is related but not identified with the magnetization. The magnetization is split in a paramagnetic and in
a ferromagnetic contribution, dependent on a scalar phase parameter and identically null above the Curie temperature.
The dynamics of the magnetization below the Curie temperature is governed by the order parameter evolution equation
and by a Landau–Lifshitz type equation for the magnetization vector. In the simple situation of a uniaxial magnet,
it is shown how the order parameter dynamics reproduces the hysteresis effect of the magnetization
Well-posedness of an isothermal diffusive model for binary mixtures of incompressible fluids
No full textWe consider a model describing the behaviour of a mixture of two
incompressible fluids with the same density under isothermal conditions. The
model consists of three balance equations: a continuity equation, a Navier–
Stokes equation for the mean velocity of the mixture and a diffusion equation
(Cahn–Hilliard equation). We assume that the chemical potential depends
on the velocity of the mixture in such a way that an increase in the velocity
improves the miscibility of the mixture. We examine the thermodynamic
consistence of the model which leads to the introduction of an additional
constitutive force in the motion equation. Then, we prove the existence and
uniqueness of the solution of the resulting differential problem
Phase transitions in shape memory alloys: A non-isothermal Ginzburg-Landau mode
No full textWe propose a model to describe non-isothermal transitions from the austenite to the martensite phase
occurring in shape memory materials. The phenomenon is set in the context of the Ginzburg-Landau
theory of phase transitions, postulating a free energy depending on the temperature, the stress and the
order parameter. In the one-dimensional case, when only two martensitic variants are involved and stress
and deformation have a fixed direction, our choice of free energy allows us to deduce a phase diagram
describing the main features of a typical SMA. The Ginzburg-Landau equation ruling the evolution
of the order parameter is coupled with the equations of thermoelasticity by assuming a constitutive
equation relating stress, strain and order parameter. The consistency of the model with the second law of
Thermodynamics in the form of the Clausius-Duhem inequality is proved. Finally a possible generalization
to a three-dimensional model is proposed, by introducing a tensor-valued order parameter
A thermodynamic approach to isotropic- nematic phase transitions in liquid crystals.
No full textWe propose a dynamical model for (non-isothermal) phase transitions in liquid crystals. Macroscopic motions of the liquid crystal (LC) are neglected, while the coupling with the electromagnetic field is considered. The LC is described in terms of the classical order tensor Q, which is split as Q=sN, where N is a normalized tensor. Two independent evolution laws are given for s and N. The model includes an evolutive equation for the temperature field obtained from an appropriate form of the energy balance, in which the internal powers associated to the equations for s and N are accounted for. The thermodynamic restrictions in the constitutive relations which ensure the Clausius–Duhem inequality have been pointed out
A phase field model for brine channels in sea ice
No full textIn this paper, we present a phenomenological mathematical model for describing the features of the brine channels in sea ice. The differential system is composed of the Ginzburg–Landau and Cahn–Hilliard equations, in addition to the heat equation, that controls the ice–liquid phase transition by the temperature and hence the establishment of brine channels. The compatibility of this system with the thermodynamic laws and a maximum theorem is prove
A phase field model for liquid-vapour phase transition
No full textWe propose a model describing the liquid-vapour phase transition
according to a phase-field method. A phase variable φ is introduced whose
equilibrium values φ = 0 and φ = 1 are associated with the liquid and vapour
phases. The phase field obeys Ginzburg-Landau equation and enters the consti-
tutive relation of the density, accounting for the sudden density jump occurring
at the phase transition. In this paper we concern ourselves especially with the
problems arising in the phase field approach due to the existence of the critical
point in the coexistence line, which entails the merging of the phases described
by φ
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
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