891 research outputs found
Transition Spectra for a BCS Superconductor with Multiple Gaps: Model Calculations for MgB_2
We analyze the qualitative features in the transition spectra of a model
superconductor with multiple energy gaps, using a simple extension of the
Mattis-Bardeen expression for probes with case I and case II coherence factors.
At temperature T = 0, the far infrared absorption edge is, as expected,
determined by the smallest gap. However, the large thermal background may mask
this edge at finite temperatures and instead the secondary absorption edges
found at Delta_i+Delta_j may become most prominent. At finite T, if certain
interband matrix elements are large, there may also be absorption peaks at the
gap difference frequencies | Delta_i-Delta_j | . We discuss the effect of
sample quality on the measured spectra and the possible relation of these
predictions to the recent infrared absorption measurement on MgB_2
Factorization of Seiberg-Witten Curves with Fundamental Matter
We present an explicit construction of the factorization of Seiberg-Witten
curves for N=2 theory with fundamental flavors. We first rederive the exact
results for the case of complete factorization, and subsequently derive new
results for the case with breaking of gauge symmetry U(Nc) to U(N1)xU(N2). We
also show that integrality of periods is necessary and sufficient for
factorization in the case of general gauge symmetry breaking. Finally, we
briefly comment on the relevance of these results for the structure of N=1
vacua.Comment: 24 pages, 2 figure
Vibrational properties of amorphous silicon from tight-binding O(N) calculation
We present an O(N) algorithm to study the vibrational properties of amorphous
silicon within the framework of tight-binding approach. The dynamical matrix
elements have been evaluated numerically in the harmonic approximation
exploiting the short-range nature of the density matrix to calculate the
vibrational density of states which is then compared with the same obtained
from a standard O() algorithm. For the purpose of illustration, an
1000-atom model is studied to calculate the localization properties of the
vibrational eigenstates using the participation numbers calculation.Comment: 5 pages including 5 ps figures; added a figure and a few references;
accepted in Phys. Rev.
Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRuRhO
The solid-solution SrRuRhO () is a
variable-electron-configuration system forming in the nearly-cubic-perovskite
basis, ranging from the ferromagnetic 4 to the enhanced paramagnetic
4. Polycrystalline single-phase samples were obtained over the whole
composition range by a high-pressure-heating technique, followed by
measurements of magnetic susceptibility, magnetization, specific heat,
thermopower, and electrical resistivity. The ferromagnetic order in long range
is gradually suppressed by the Rh substitution and vanishes at .
The electronic term of specific-heat shows unusual behavior near the critical
Rh concentration; the feature does not match even qualitatively with what was
reported for the related perovskites (Sr,Ca)RuO. Furthermore, another
anomaly in the specific heat was observed at .Comment: Accepted for publication in PR
Non-Fermi liquid behavior and scaling of low frequency suppression in optical conductivity spectra of CaRuO
Optical conductivity spectra of paramagnetic CaRuO are
investigated at various temperatures. At T=10 K, it shows a non-Fermi liquid
behavior of , similar to the case
of a ferromagnet SrRuO. As the temperature () is increased, on the other
hand, in the low frequency region is progressively
suppressed, deviating from the 1/{\omega}^{\frac 12%}-dependence.
Interestingly, the suppression of is found to scale with
at all temperatures. The origin of the scaling
behavior coupled with the non-Fermi liquid behavior is discussed.Comment: 4 pages, 3 figure
Quantized bulk fermions in the Randall-Sundrum brane model
The lowest order quantum corrections to the effective action arising from
quantized massive fermion fields in the Randall-Sundrum background spacetime
are computed. The boundary conditions and their relation with gauge invariance
are examined in detail. The possibility of Wilson loop symmetry breaking in
brane models is also analysed. The self-consistency requirements, previously
considered in the case of a quantized bulk scalar field, are extended to
include the contribution from massive fermions. It is shown that in this case
it is possible to stabilize the radius of the extra dimensions but it is not
possible to simultaneously solve the hierarchy problem, unless the brane
tensions are dramatically fine tuned, supporting previous claims.Comment: 25 pages, 1 figure, RevTe
Characterization of neutrino signals with radiopulses in dense media through the LPM effect
We discuss the possibilities of detecting radio pulses from high energy
showers in ice, such as those produced by PeV and EeV neutrino interactions. It
is shown that the rich radiation pattern structure in the 100 MHz to few GHz
allows the separation of electromagnetic showers induced by photons or
electrons above 100 PeV from those induced by hadrons. This opens up the
possibility of measuring the energy fraction transmitted to the electron in a
charged current electron neutrino interaction with adequate sampling of the
angular distribution of the signal. The radio technique has the potential to
complement conventional high energy neutrino detectors with flavor information.Comment: 5 pages, 4 ps figures. Submitted to Phys. Rev. Let
Super-Hubbard models and applications
We construct XX- and Hubbard- like models based on unitary superalgebras
gl(N|M) generalising Shastry's and Maassarani's approach of the algebraic case.
We introduce the R-matrix of the gl(N|M) XX model and that of the Hubbard model
defined by coupling two independent XX models. In both cases, we show that the
R-matrices satisfy the Yang--Baxter equation, we derive the corresponding local
Hamiltonian in the transfer matrix formalism and we determine the symmetry of
the Hamiltonian. Explicit examples are worked out. In the cases of the gl(1|2)
and gl(2|2) Hubbard models, a perturbative calculation at two loops a la Klein
and Seitz is performed.Comment: 26 page
Orbital Wave and its Observation in Orbital Ordered Titanates and Vanadates
We present a theory of the collective orbital excitation termed orbital wave
in perovskite titanates and vanadates with the triply degenerate
orbitals. The dispersion relations of the orbital waves for the orbital ordered
LaVO, YVO and YTiO are examined in the effective spin-orbital
coupled Hamiltonians associated with the Jahn-Teller type couplings. We propose
possible scattering processes for the Raman and inelastic neutron scatterings
from the orbital wave and calculate the scattering spectra for titanates and
vanadates. It is found that both the excitation spectra and the observation
methods of the orbital wave are distinct qualitatively from those for the
orbital ordered systems.Comment: 9 pages, 7 figure
Determinants and predictors for the long-term disease burden of intracranial meningioma patients
Introduction Meningioma is a heterogeneous disease and patients may suffer from long-term tumor- and treatment-related sequelae. To help identify patients at risk for these late effects, we first assessed variables associated with impaired long-term health-related quality of life (HRQoL) and impaired neurocognitive function on group level (i.e. determinants). Next, prediction models were developed to predict the risk for long-term neurocognitive or HRQoL impairment on individual patient-level. Methods Secondary data analysis of a cross-sectional multicenter study with intracranial WHO grade I/II meningioma patients, in which HRQoL (Short-Form 36) and neurocognitive functioning (standardized test battery) were assessed. Multivariable regression models were used to assess determinants for these outcomes corrected for confounders, and to build prediction models, evaluated with C-statistics. Results Data from 190 patients were analyzed (median 9 years after intervention). Main determinants for poor HRQoL or impaired neurocognitive function were patients' sociodemographic characteristics, surgical complications, reoperation, radiotherapy, presence of edema, and a larger tumor diameter on last MRI. Prediction models with a moderate/good ability to discriminate between individual patients with and without impaired HRQoL (C-statistic 0.73, 95% CI 0.65 to 0.81) and neurocognitive function (C-statistic 0.78, 95%CI 0.70 to 0.85) were built. Not all predictors (e.g. tumor location) within these models were also determinants. Conclusions The identified determinants help clinicians to better understand long-term meningioma disease burden. Prediction models can help early identification of individual patients at risk for long-term neurocognitive or HRQoL impairment, facilitating tailored provision of information and allocation of scarce supportive care services to those most likely to benefit.Neurolog
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