249 research outputs found
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
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