Crystalline Bi4Ge3O12 fibers fabricated by micro-pulling down technique for optical high voltage sensing

AbstractCommonly optical high voltage sensors employ the Pockels effect in a bulk electro-optic crystal such as Bi4Ge3O12 (BGO). Typically, the maximum crystal length is 100-200mm and determined by the limits of the conventional growth technique (Czochralski). In this paper we report on the growth by a micro-pulling down technique of long single crystalline BGO fibers as an alternative to bulk crystals and their characterization for voltage sensing. The fiber thickness may range from a few 100μm to a few mm. The parameters needed for stable growth over the entire length of the crystal were analyzed and optimized. Thin rods with a length of up to 850mm were grown. Samples were characterized with respect to homogeneity of growth, residual birefringence (BGO is free of natural birefringence), crystal orientation, and performance under voltage

Transport, optical and electronic properties of the half metal CrO2

The electronic structure of CrO_2 is critically discussed in terms of the relation of existing experimental data and well converged LSDA and GGA calculations of the electronic structure and transport properties of this half metal magnet, with a particular emphasis on optical properties. We find only moderate manifestations of many body effects. Renormalization of the density of states is not large and is in the typical for transition metals range. We find substantial deviations from Drude behavior in the far-infrared optical conductivity. These appear because of the unusually low energy of interband optical transitions. The calculated mass renormalization is found to be rather sensitive to the exchange-correlation functional used and varies from 10% (LSDA) to 90% (GGA), using the latest specific heat data. We also find that dressing of the electrons by spin fluctuations, because of their high energy, renormalizes the interband optical transition at as high as 4 eV by about 20%. Although we find no clear indications of strong correlations of the Hubbard type, strong electron-magnon scattering related to the half metallic band structure is present and this leads to a nontrivial temperature dependence of the resistivity and some renormalization of the electron spectra.Comment: 9 Revtex 2 column pages, including 8 postscript figures. Two more figures are included in the submission that are not embedded in the paper, representing DOS and bandstructure of the paramagnetic CrO

Five-Dimensional Moving Brane Solutions with Four-Dimensional Limiting Behaviour

Under certain conditions some solutions to five-dimensional heterotic M-theory can be accurately described by the four-dimensional action of the theory - they have a four-dimensional limit. We consider the connection between solutions of four and five-dimensional heterotic M-theory when moving five-branes are present in the bulk. We begin by describing how to raise the known four-dimensional moving brane solutions to obtain approximate solutions to the five-dimensional theory, presenting for the first time the metric template necessary for this procedure. We then present the first solutions to the five-dimensional theory containing moving five-branes. We can then discuss the connection between our new exact five-dimensional solution and the four-dimensional ones. It is shown that our new solution corresponds to a solution with a static brane in four-dimensions. In other words our new solution could not have been identified as containing a moving brane from a purely four-dimensional viewpoint.Comment: 18 pages, 6 figure

Stability Walls in Heterotic Theories

We study the sub-structure of the heterotic Kahler moduli space due to the presence of non-Abelian internal gauge fields from the perspective of the four-dimensional effective theory. Internal gauge fields can be supersymmetric in some regions of the Kahler moduli space but break supersymmetry in others. In the context of the four-dimensional theory, we investigate what happens when the Kahler moduli are changed from the supersymmetric to the non-supersymmetric region. Our results provide a low-energy description of supersymmetry breaking by internal gauge fields as well as a physical picture for the mathematical notion of bundle stability. Specifically, we find that at the transition between the two regions an additional anomalous U(1) symmetry appears under which some of the states in the low-energy theory acquire charges. We compute the associated D-term contribution to the four-dimensional potential which contains a Kahler-moduli dependent Fayet-Iliopoulos term and contributions from the charged states. We show that this D-term correctly reproduces the expected physics. Several mathematical conclusions concerning vector bundle stability are drawn from our arguments. We also discuss possible physical applications of our results to heterotic model building and moduli stabilization.Comment: 37 pages, 4 figure

On the asymptotic behaviour of solutions to the fractional porous medium equation with variable density

We are concerned with the long time behaviour of solutions to the fractional porous medium equation with a variable spatial density. We prove that if the density decays slowly at infinity, then the solution approaches the Barenblatt-type solution of a proper singular fractional problem. If, on the contrary, the density decays rapidly at infinity, we show that the minimal solution multiplied by a suitable power of the time variable converges to the minimal solution of a certain fractional sublinear elliptic equation.Comment: To appear in DCDS-

The view of young Spaniards towards online activism: advantages, scepticism and supported causes

© 2022 The authors. This document is made available under the CC-BY-NC-SA 4.0 license http://creativecommons.org/licenses/by-nc-sa/4.0/ This document is the Accepted version of a Published Work that appeared in final form in EMPIRIA. Revista de Metodología de Ciencias Sociales. To access the final edited and published work see DOI/ Empiria.56.2022.34440Los nuevos procesos de comunicación pública entre los jóvenes han facilitado una nueva forma de entender la participación ciudadana colectiva: la llamada e- participación. No se ha publicado e investigado lo suficiente sobre este fenómeno que supone una nueva perspectiva de entender estos procesos sociales. Este estudio muestra opiniones de los jóvenes sobre la participación online y aporta las posibles ventajas e inconvenientes de esta vía de participación, así como se señalan las principales causas apoyadas y las plataformas más conocidas y utilizadas. Se analiza hasta qué punto el activismo online de los jóvenes es un activismo proactivo o no. Se trata de un trabajo exploratorio que apunta nuevas vías de investigación sobre una tendencia comunicativa y participativa que en el actual contexto de comunicación global se verá potenciada y justificada en años venideros. Se utilizan datos primarios en metodología mixta. Se recogen datos mediante una encuesta original (N=463) y se emplean grupos de discusión, buscando una triangulación metodológica en jóvenes entre 18 y 22 años. Los resultados muestran cómo el activismo online está arraigado entre los jóvenes estudiados y que lo ven como una forma complementaria a las vías tradicionales, y no como una alternativa. Además, destacan sobre todo el seguimiento decausas sociopolíticas y medioambientales como los grandes ejes en este tipo de e-participación frente a causas de carácter más tradicional.New public communication processes among young people have facilitated a new way of understanding collective citizen participation: the so-called e-participation. Not much has been published and researched on this phenomenon, which represents a new perspective for understanding these social processes. This study aims to present the general opinion of this phenomenon among young Spaniards and to provide the possible advantages and disadvantages of this new form of participation, as well as to point out the main causes supported and the most widely known and used platforms. Finally, the aim is to analyse to what extent young people's online activism is a proactive activism or not. It is an exploratory study that opens up new avenues of research into a communicative and participatory trend that, in the current context of global communication, will be strengthened and justified in the years to come. Primary data are used in a mixed methodology, using an original survey (N=463) and qualitative methodology based on discussion groups, seeking a methodological triangulation in youth people (18 to 22 years). The results show how this phenomenon is deeply rooted among young Spaniards, who see it as a complementary form of traditional methods, and not as a substitute. Moreover, they highlight above all the monitoring of socio-political and environmental causes as the main axes in this type of e-participation as opposed to more traditiona