Questioning non-completion in higher education : a study within the Argentine system

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Real Forms of Complex Higher Spin Field Equations and New Exact Solutions

We formulate four dimensional higher spin gauge theories in spacetimes with signature (4-p,p) and nonvanishing cosmological constant. Among them are chiral models in Euclidean (4,0) and Kleinian (2,2) signature involving half-flat gauge fields. Apart from the maximally symmetric solutions, including de Sitter spacetime, we find: (a) SO(4-p,p) invariant deformations, depending on a continuous and infinitely many discrete parameters, including a degenerate metric of rank one; (b) non-maximally symmetric solutions with vanishing Weyl tensors and higher spin gauge fields, that differ from the maximally symmetric solutions in the auxiliary field sector; and (c) solutions of the chiral models furnishing higher spin generalizations of Type D gravitational instantons, with an infinite tower of Weyl tensors proportional to totally symmetric products of two principal spinors. These are apparently the first exact 4D solutions with non-vanishing massless higher spin fields.Comment: 40 pages, late

D-branes in N=2 Strings

We study various aspects of D-branes in the two families of closed N=2 strings denoted by \alpha and \beta in hep-th/0211147. We consider two types of N=2 boundary conditions, A-type and B-type. We analyse the D-branes geometry. We compute open and closed string scattering amplitudes in the presence of the D-branes and discuss the results. We find that, except the space filling D-branes, the B-type D-branes decouple from the bulk. The A-type D-branes exhibit inconsistency. We construct the D-branes effective worldvolume theories. They are given by a dimensional reduction of self-dual Yang-Mills theory in four dimensions. We construct the D-branes gravity backgrounds. Finally, we discuss possible N=2 open/closed string dualities.Comment: 25 pages, Latex2

Introduction: diverging or converging dynamics? EU and US policies in North Africa - an introduction

According to a number of scholars of international relations, the transatlantic relationship is going through a very significant and possibly irreversible crisis. It is claimed that the different reactions of the United States and the European Union to both September 11th and the war in Iraq were the catalyst for a rift that had been deepening for some time, leading to competition between the two actors. The literature on the foreign policy of the US and the EU in the Middle East and North Africa also points to this rift in order to explain the seemingly contradictory policies that the two actors implement in the region, with the US being more forceful in its attempts to export democracy and in supporting Israel while the EU adopts a less confrontational attitude and is perceived to be more friendly to the Palestinians. This article, which introduces a special issue on the nature of US and EU foreign policies in North Africa, argues on the contrary that the transatlantic rift does not really exist. While there are certainly differences in discourse and policies, both the EU and the US share the same concerns and have similar strategic objectives in the region, leading the two actors towards cooperation and division of labour rather than confrontation

Homocysteine influences the human keratocytes cell cycle

BACKGROUND: Homocysteine (Hcy), a metabolic intermediate, is a sulfur-containing amino acid not present in the structure of proteins. It has been shown that high Hcy levels via oxidative stress, induced inflammation, and vessel dysfunction may affect the functioning of tissues, including the structures that form the eye, among others keratocytes. The visual disturbance caused by high levels of Hcy may also be associated with disturbed cell proliferation resulting from the effect of this amino acid on the cell cycle. The goal was to analyse the influence of Hcy on the keratocytes and to find out in which phase of the cell cycle its course is disturbed by this amino acid. MATERIALS AND METHODS: A normal human keratocytes (HK) cell line was used in the study. May-Grünwald-Giemsa (MGG) staining for morphology visualization and cytometric cell cycle analysis were performed. RESULTS: Hcy does not affect the G1 phase of the cycle, while it regulates the S and G2 phases. Changes in the amount of the sub-G1 population  indicative of a pro-apoptotic effect of Hcy on keratocytes were detected. The form of the Hcy administered (L stereoisomer or DL racemic mixture) and the amino acid concentration were also important. CONCLUSIONS: Homocysteine influences the keratocyte cell cycle. The change occurs at the stage of the G1-S transition, which suggests a decreasing level of cells in the S phase and an increasing level in the G2 phase. The long-term influence of Hcy on keratocytes may affect keratocytes proliferation and possible cornea regeneration