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A thermodynamic approach to ferromagnetism and phase transitions.
No full textThe paper provides a modelling of the magnetization curve and of the ferromagnetic–paramagnetic transition within a continuum thermodynamic setting. The general model of the nonlinear, time dependent behaviour of ferromagnetic materials is accomplished by regarding the magnetization vector as an internal variable, namely as a vector field whose time evolution is a constitutive equation subject to the requirements of the second law of thermodynamics. The exchange interaction of the magnetization is modelled through a dependence of the free energy on the magnetization gradient. Consistent with the non-simple character of the material, the second law allows for a non-zero extra-entropy flux. A general three-dimensional scheme is elaborated which seems to be new in the literature. The three-dimensional setting is then established for stationary and homogeneous fields thus finding the collinearity and the corresponding form of the magnetic susceptibility. The whole evolution problem for the temperature and the magnetization is provided so that temperature-induced transition processes are allowed. The model accounts also for the dependence of the saturation magnetization on the temperature. Also for the sake of comparison with the existing literature, the evolution equations for the direction and the intensity of magnetization are derived. Known models, such as those of Landau–Lifshitz and Gilbert, are recovered as particular cases of saturated bodies. Next, the model is made more specific so as to account in detail for the saturation, the residual or spontaneous magnetization and the coercive field. First, the classical potential, which traces back to Ginzburg, and the Weiss model are revisited. The corresponding lack of the saturation effect or the description via implicit relations are emphasized. Hence, a new potential, with a logarithmic dependence on the magnetization, is investigated which provides the residual magnetization and the coercive field in an explicit way and satisfies expected properties of the residual magnetization as a function of the temperature
Equivalent histories, minimal state and initial value problem in viscoelasticity. Math. Methods Appl. Sci. 28 (2005), no. 2, 233--251.
No full textReferences: 10 [-] Reference Citations: 0 Review Citations: 0
In the standard theory of viscoelasticity the constitutive equation for the stress is where is the infinitesimal strain tensor, is the relaxation function, defined by and assumed to be such that is positive definite, and is the history. The main idea of this paper is to replace (1) by where denotes the contribution to by the stress at a previous time . It follows that and moreover has the operative meaning of the stress tensor at time once the solid is held at a constant strain since , i.e., , . Representation (2) involves the relation function , which is required only to have a limit value . Then, the authors consider the following initial-boundary value problem: Here , , and are known functions on the pertinent domain, and the body force and are known on , and Using the variational approach they prove that the functional associated with (3)--(6) has a stationary point if and only if is a solution to the mixed problem (3)--(4).
Next, the authors consider a virtual-work type formulation which provides a weak form of the initial-value problem for the system of the dynamics of viscoelastic solids.
Applying the Fourier transform to the initial-boundary value problem which represents the weak formulation of the problem where , under some assumption about they prove that there exists a unique virtual-work solution of problem (7)--(8) in a certain class of functions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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