ELECTRONIC STATES IN GRADED-GAP JUNCTIONS WITH BAND INVERSION

We theoretically study electronic states in graded-gap junctions of IV-VI compounds with band inversion. Using a two-band model within the ${\bf k}\cdot{\bf p}$ approximation and assuming that the gap and the gap centre present linear profiles, we demonstrate the existence of a set of localized states along the growth direction with a discrete energy spectrum. The envelope functions are found to be combination of harmonic oscillator eigenfunctions, and the corresponding energy levels are proportional to the square root of the quantum number. The level spacing can be directly controlled by varying the structure thickness.Comment: REVTEX 3.0, 7 pages, no figures, to appear in Phys. Lett.

Vortex dynamics in disordered Josephson junction arrays: from plastic flow to flux flow

We study the dynamics of Josephson junction arrays with positional disorder and driven by an external current. We consider weak magnetic fields, corresponding to a frustration $f=n+1/25$ with $n$ integer. We find that above the critical current $i_c$ there is a plastic flow of vortices, where most of the vortices are pinned and only a few vortices flow through channels. This dynamical regime is characterized by strong fluctuations of the total vorticity. The number of the flow channels grow with increasing bias current. At larger currents there is a dynamical regime characterized by the homogeneous motion of all the vortices, i.e. a flux flow regime. We find a dynamical phase transition between the plastic flow and the flux flow regimes when analyzing voltage-voltage correlation functions.Comment: 9 pages. 3 Figures available upon request. Presented in the Workshop on Josephson Junction Arrays, ICTP (August 1995). To appear in Physica B (1996

Exact Solutions of Two-Band Models of Graded-Gap Superlattices

We have theoretically investigated two-band models of graded-gap superlattices within the envelope-function approximation. Assuming that the gap varies linearly with spatial coordinate, we are able to find exact solutions of the corresponding Dirac-like equation describing the conduction- and valence-band envelope-functions. The dispersion relation inside allowed miniband of the superlattice may be expressed in terms of confluent hypergeometric functions in a closed form.Comment: 7 pages in REVTeX 3.0. 1 Figure on request to F. D-A ([email protected]). FM-UCM-3

A Genetic Algorithm for solving the Discrete Ordered Median Problem with Induced Order

The Discrete Ordered Median Problem with Induced Ordered (DOMP+IO) is a multi-facility version of the classical discrete ordered median problem (DOMP), which has been widely studied. Several exact methods have been proposed to solve the DOMP, however these methods could only solve small-scale problems, which are far of real-life problems. In this work, a DOMP+IO with two kinds of facilities is considered and a heuristic method is proposed for its solving. The proposed procedure is based on a genetic algorithm and the preliminary results show the efficiency and capability to obtain good solutions for large-scale problems.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Theory of anomalous collective diffusion in colloidal monolayers on a spherical interface

A planar colloidal monolayer exhibits anomalous collective diffusion due to the hydrodynamic interactions. We investigate how this behavior is affected by the curvature of the monolayer when it resides on the interface of a spherical droplet. It is found that the characteristic times of the dynamics still exhibit the same anomalous scaling as in the planar case. The spatial distribution, however, shows a difference due to the relevance of the radius of the droplet. Since for the droplet this is both a global magnitude, i.e., pertaining the spatial extent of the spherical surface, and a local one, i.e., the radius of curvature, the question remains open as to which of these two features actually dominates in the case of a generically curved interface.Comment: 7 pages, 2 figure

Foreground detection enhancement using Pearson correlation filtering

Foreground detection algorithms are commonly employed as an initial module in video processing pipelines for automated surveillance. The resulting masks produced by these algorithms are usually postprocessed in order to improve their quality. In this work, a postprocessing filter based on the Pearson correlation among the pixels in a neighborhood of the pixel at hand is proposed. The flow of information among pixels is controlled by the correlation that exists among them. This way, the filtering performance is enhanced with respect to some state of the art proposals, as demonstrated with a selection of benchmark videos.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The External Relations of the European Union towards the United States: How Relevant is the European Union in Constraining or Replacing U.S. Hegemony?, Jean Monnet/Robert Schuman Paper Series, Vol. 1 No. 3, September 2002

(From the introduction). The study object of this paper is the external relations of the European Union towards the United States. The core question of this essay is not the U.S. hegemony by itself; in fact, both parties agree on a myriad of issues, share common values, and keep intensive and active economic and political exchanges. The 1950s and 1960s were witness to the shining power of the United States and Europe was willing to receive U.S. aid through the Marshall Plan. The problem arises when U.S. policies affect Europe and the EU is not able to provide concrete actions to reverse them. At this point, one inquiry is the focus of the analysis: How relevant is the EU in constraining or replacing U.S. hegemony? A simple answer is insufficient to shed light on this question. Most scholars underline the shortcomings of the EU and the influence of the United States in determining EU external relations. However, the EU in 2002 is quite different from the European Community at the beginning of the 1990s. Although reactive to international and regional, political and economic stimuli, the EU has forged informal and formal practices to provide coordinated positions. Depending on the specific area, the EU’s performance is more or less successful. Whereas in economic issues the EU has been able to respond to the U.S. in trade disputes, in political and security affairs the panorama is mostly discouraging. Accordingly, the hypothesis of this paper is: The more the EU is able to encapsulate the interests of the fifteen member states in a common front, the greater are the opportunities for more beneficial agreements with the United States, and to constrain or replace the actions or inactions of U.S. hegemony. In order to support this proposition, four areas of the transatlantic relationship are examined in this paper. The first part focuses on the current theoretical debate on the transatlantic relationship. Secondly, the paper analyzes the different natures of both foreign policies, emphasizing the problems associated with the European (intergovernmental and supranational) model to design its external relations. The third section describes the relative balance between the US and the EU on economic terms, and considers the benefits of having international institutions to regulate trade practices. Finally, the imbalance in security affairs is depicted, highlighting the new institutional developments in Europe to participate in regional crises with or without (but not against) the United States

Dwork families and D\mathcal{D}-modules

A Dwork family is a one-parameter monomial deformation of a Fermat hypersurface. In this paper we compute algebraically the invariant part of its Gauss-Manin cohomology under the action of certain subgroup of automorphisms. To achieve that goal we use the algebraic theory of $\mathcal{D}$-modules, especially one-dimensional hypergeometric ones.Comment: 24 pages, final versio