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

Neonatal tolerance to Mls-1a determinants: deletion or anergy of Vβ6 + T lymphocytes depending upon MHC compatibility of neonatally injected cells

Recent investigations in mice revealed that natural immunologlcal tolerance to endogenous minor lymphocyte-stimulating locus 1a (MIs-1a antigen correlates primarily with deletion of Mls-1aspeciflc Vβ6+ T lymphocytes In the thymus. Similar mechanisms account for acquired tolerance in some Instancessince the neonatal injection of Mls-1 a-expressing MHC compatible cells in neonatal mice within the first 24 hof life causes clonal deletion of Vβ6+ T cells. Here we demonstrate that Vβ6+ T cells are not deleted In mice neonatally treated with Mls-1a spleen cells expressing allogenelc H-2 molecules. However, when such non-deleted Vβ6+ T cells were tested In vitro, no interleukin 2 (IL-2) secretion or proliferation was observed after Mls-1a stimulation. This non-responsive state could be overcome by addition of exogenous IL-2, consistent with the fact that Vβ6+ cells enlarged and expressed IL-2 receptors upon Mls-1a stimulation. Furthermore, the same neonatally treated mice showed In vitro functional unresponsiveness of cytotoxic T cells but not of IL-2-secreting cells specific for the tolerated allogeneic MHC antigens. Taken together, our data Indicate that neonatal tolerance to Mls-1a can be accomplished by either clonal deletion or clonal anergy, and that it does not necessarily correlate with tolerance to MHC determinant

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

Heterotic M-Theory Cosmology in Four and Five Dimensions

We study rolling radii solutions in the context of the four- and five-dimensional effective actions of heterotic M-theory. For the standard four-dimensional solutions with varying dilaton and T-modulus, we find approximate five-dimensional counterparts. These are new, generically non-separating solutions corresponding to a pair of five-dimensional domain walls evolving in time. Loop corrections in the four-dimensional theory are described by certain excitations of fields in the fifth dimension. We point out that the two exact separable solutions previously discovered are precisely the special cases for which the loop corrections are time-independent. Generically, loop corrections vary with time. Moreover, for a subset of solutions they increase in time, evolving into complicated, non-separating solutions. In this paper we compute these solutions to leading, non-trivial order. Using the equations for the induced brane metric, we present a general argument showing that the accelerating backgrounds of this type cannot evolve smoothly into decelerating backgrounds.Comment: 15 pages, Latex, 1 eps figur

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-

OJS Software Workshop Report

This report summarizes the achievements of the OJS community members from Germany and Switzerland in the OJS Workshop in Heidelberg University Library, Germany from February 20 and 21, 2020. Main goal of the workshop was to share knowledge and challenges, conceptualize and document problem solving suggestions and collectively develop software in and around OJS. Participants worked on a variety of subjects including data import/export plugins, search functionality, containerization, long-time archiving and XML workflows in and around OJS and OMP. The workshop is a continuation of fruitful meetings within the German OJS user and developer community under auspices of OJS-de.net networ

Resource description framework technologies in chemistry

ISSN:1758-294