1,819 research outputs found
Microscopic theory of the coupling of intrinsic Josephson oscillations and phonons
A microscopic theory for the coupling of intrinsic Josephson oscillations and
dispersive phonon branches in layered superconductors is developed. Thereby the
effect of phonons on the electronic c-axis transport enters through an
effective longitudinal dielectric function. This coupling provides an
explanation of recently observed subgap resonances in the --
curve of anisotropic cuprate superconductors forming a stack of short Josephson
junctions. Due to the finite dispersion these resonances can appear at
van-Hove-singularities of both optical and acoustical phonon branches,
explaining low-voltage structures in the I-V-characteristic, which are not
understood in phonon models without dispersion. In long junctions the
dispersion of collective electron-phonon modes parallel to the layers is
investigated.Comment: 4 pages, 3 figures, 1 table, espcrc2.sty, invited contribution to
"Materials and Mechanisms of Superconductivity and High Temperature
Superconductors VI - M2S-HTSC-VI", Houston, Texas, 20-25 Feb 2000, to appear
in Physica
Theory for the coupling between longitudinal phonons and intrinsic Josephson oscillations in layered superconductors
In this publication a microscopic theory for the coupling of intrinsic
Josephson oscillations in layered superconductors with longitudinal
c-axis-phonons is developed. It is shown that the influence of lattice
vibrations on the c-axis transport can be fully described by introducing an
effective longitudinal dielectric function. Resonances in the
I-V-characteristic appear at van Hove singularities of both acoustical and
optical longitudinal phonon branches. This provides a natural explanation of
the recently discovered subgap structures in the I-V-characteristic of highly
anisotropic cuprate superconductors. The effect of the phonon dispersion on the
damping of these resonances and the coupling of Josephson oscillations in
different resistive junctions due to phonons are discussed in detail.Comment: submitted to Phys. Rev. B, corrections following referee repor
P53 and Beta-Catenin Activity during Estrogen treatment of Osteoblasts
BACKGROUND: This study was undertaken to examine the relationship between the tumor suppressor gene p53 and the nuclear signaling protein beta-catenin during bone differentiation. Cross talk between p53 and beta-catenin pathways has been demonstrated and is important during tumorigenesis and DNA damage, where deregulation of beta catenin activates p53. In this study, we used estrogen treatment of osteoblasts as a paradigm to study the relationship between the two proteins during osteoblast differentiation. RESULTS: We exposed osteoblast-like ROS17/2.8 cells to 17-beta estradiol (E2), in a short term assay, and studied the cellular distribution and expression of beta-catenin. We found beta-catenin to be up regulated several fold following E2 treatment. Levels of p53 and its functional activity mirrored the quantitative changes seen in beta-catenin. Alkaline phosphatase, an early marker of osteoblast differentiation, was increased in a manner similar to beta-catenin and p53. In order to determine if there was a direct relationship between alkaline phosphatase expression and beta-catenin, we used two different approaches. In the first approach, treatment with LiCl, which is known to activate beta-catenin, caused a several fold increase in alkaline phosphatase activity. In the second approach, transient transfection of wild type beta-catenin into osteoblasts increased alkaline phosphatase activity two fold over basal levels, showing that beta catenin expression can directly affect alkaline phosphatase expression. However increase in beta catenin activity was not associated with an increase in its signaling activity through TCF/LEF mediated transcription. Immunofluorescence analyses of p53 and beta-catenin localization showed that E2 first caused an increase in cytosolic beta-catenin followed by the accumulation of beta-catenin in the nucleus. Nuclear p53 localization was detected in several cells. Expression of p53 was accompanied by distribution of beta-catenin to the cytoplasm and cell borders. A sub population of cells staining strongly for both proteins appeared to be apoptotic. CONCLUSION: These results suggest that interactions between p53 and beta-catenin signaling pathways may play a key role in osteoblast differentiation and maintenance of tissue homeostasis
Orbital motion in T Tauri binary systems
Using speckle-interferometry we have carried out repeated measurements of
relative positions for the components of 34 T Tauri binary systems. The
projected separation of these components is low enough that orbital motion is
expected to be observable within a few years. In most cases orbital motion has
indeed been detected. The observational data is discussed in a manner similar
to Ghez et al. (1995). However, we extend their study to a larger number of
objects and a much longer timespan. The database presented in this paper is
valuable for future visible orbit determinations. It will yield empirical
masses for T Tauri stars that now are only poorly known. The available data is
however not sufficient to do this at the present time. Instead, we use short
series of orbital data and statistical distributions of orbital parameters to
derive an average system mass that is independent of theoretical assumptions
about the physics of PMS stars. For our sample this mass is 2.0 solar masses
and thus in the order of magnitude one expects for the mass sum of two T Tauri
stars. It is also comparable to mass estimates obtained for the same systems
using theoretical PMS evolutionary models.Comment: Accepted by Astronomy and Astrophysic
Nonequilibrium dynamics of fully frustrated Ising models at T=0
We consider two fully frustrated Ising models: the antiferromagnetic
triangular model in a field of strength, , as well as the Villain
model on the square lattice. After a quench from a disordered initial state to
T=0 we study the nonequilibrium dynamics of both models by Monte Carlo
simulations. In a finite system of linear size, , we define and measure
sample dependent "first passage time", , which is the number of Monte
Carlo steps until the energy is relaxed to the ground-state value. The
distribution of , in particular its mean value, , is shown to
obey the scaling relation, , for both models.
Scaling of the autocorrelation function of the antiferromagnetic triangular
model is shown to involve logarithmic corrections, both at H=0 and at the
field-induced Kosterlitz-Thouless transition, however the autocorrelation
exponent is found to be dependent.Comment: 7 pages, 8 figure
Zweckmäßigkeit und menschliches Glück : Bamberger Hegelwochen 1993
Zweckmäßigkeit und menschliches Glück : Bamberger Hegelwochen 199
Future of superheavy element research: Which nuclei could be synthesized within the next few years?
Low values of the fusion cross sections and very short half-lives of nuclei
with Z120 put obstacles in synthesis of new elements. Different nuclear
reactions (fusion of stable and radioactive nuclei, multi-nucleon transfers and
neutron capture), which could be used for the production of new isotopes of
superheavy (SH) elements, are discussed in the paper. The gap of unknown SH
nuclei, located between the isotopes which were produced earlier in the cold
and hot fusion reactions, can be filled in fusion reactions of Ca with
available lighter isotopes of Pu, Am, and Cm. Cross sections for the production
of these nuclei are predicted to be rather large, and the corresponding
experiments can be easily performed at existing facilities. For the first time,
a narrow pathway is found to the middle of the island of stability owing to
possible -decay of SH isotopes which can be formed in ordinary fusion
reactions of stable nuclei. Multi-nucleon transfer processes at near barrier
collisions of heavy (and very heavy, U-like) ions are shown to be quite
realistic reaction mechanism allowing us to produce new neutron enriched heavy
nuclei located in the unexplored upper part of the nuclear map. Neutron capture
reactions can be also used for the production of the long-living neutron rich
SH nuclei. Strong neutron fluxes might be provided by pulsed nuclear reactors
and by nuclear explosions in laboratory conditions and by supernova explosions
in nature. All these possibilities are discussed in the paper.Comment: An Invited Plenary Talk given by Valeriy I. Zagrebaev at the 11th
International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio,
Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in
Journal of Physics: Conference Series (JPCS
Mensch, Welt, Widerspruch : Bamberger Hegelwochen 96
Mensch, Welt, Widerspruch : Bamberger Hegelwochen 199
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