1,721,525 research outputs found
On the layering transition of an SOS surface interacting with a wall. II. The Glauber dynamics
No full textWe continue our study of the statistical mechanics of a 2D surface above a fixed wall and attracted towards it by means of a very weak positive magnetic field h in the solid on solid (SOS) approximation, when the inverse temperature beta is very large. In particular we consider a Glauber dynamics for the above model and study the rate of approach to equilibrium in a large cube with arbitrary boundary conditions. Using the results proved in the first paper of this series we show that for all h is an element of (h(k+1)*, h(k)*) ({h(k)*} being the critical values of the magnetic field found in the previous paper) the gap in the spectrum of the generator of the dynamics is bounded away from zero uniformly in the size of the box and in the boundary conditions. On the contrary, for h = h(k)* and free boundary conditions, we show that the gap in a cube of side L is bounded from above and from below by a negative exponential of L. Our results provide a strong indication that, contrary to what happens in two dimensions, for the three dimensional dynamical Ising model in a finite cube al low temperature and very small positive external field, with boundary conditions that are opposite to the field on one face of the cube and are absent (free) on the remaining faces, the rate of exponential convergence to equilibrium, which is positive in infinite volume, may go to zero exponentially fast in the side of the cube
Control of a logistic node via Neuro-Dynamic Programming
No full textIn this paper we consider the dynamic model of a logistic node of a transportation network. A necessary and sufficient condition for the existence of a stable feedback policy is given. Optimal dispatching rules can be derived in the case of small instances either by solving an integer programming problem or by considering a dynamic programming approach. Both methods present a combinatorial complexity which makes them not viable in realistic scenarios. For this reason, a neuro-dynamic programming (NDP) approach is introduced and used to refine a heuristic solution of the problem. The solution computed through the NDP approach aligns with the decisions given by a sub-optimal control policy inspired by the literature available for manufacturing systems
A scheduling problem for a finite buffer capacity pull manufacturing systems
No full textStudies a scheduling problem for a pull manufacturing system, with finite inventory/backlog space and constant demand rate. The system is a single machine, multi part-type one, and the control objective is that of minimizing an infinite horizon undiscounted cost in the inventory and backlog level, and demand losses. No set-up times and costs are considered. The analysis is made in the framework of continuous flow approximation. The optimal policy is derived analytically and compared with the solution of an infinite buffer capacity proble
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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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