614 research outputs found
Moderate deviations for the determinant of Wigner matrices
We establish a moderate deviations principle (MDP) for the log-determinant
of a Wigner matrix matching four moments with
either the GUE or GOE ensemble. Further we establish Cram\'er--type moderate
deviations and Berry-Esseen bounds for the log-determinant for the GUE and GOE
ensembles as well as for non-symmetric and non-Hermitian Gaussian random
matrices (Ginibre ensembles), respectively.Comment: 20 pages, one missing reference added; Limit Theorems in Probability,
Statistics and Number Theory, Springer Proceedings in Mathematics and
Statistics, 201
A Model for High Temperature Superconductors using the Extended Hubbard Model
We derive a method to study the phase diagram for high temperature
superconductors (HTCS). Our starting point is the Hubbard Hamiltonian with a
weak attractive interaction to obtain the formation of bound pairs. We consider
this attractive potential at different positions for different compounds
accordingly to the experimental results of the coherence length. We then
construct a wave function of the BCS type by a variational method using the
Fourier transform of this extended Hubbard potential and then derive an energy
gap equation. This approach allows us to obtain the critical temperature as
function of the doping concentration which gives very good agreement with the
experimental phase diagrams of YBaCuO and La(Sr,Ba)CuO compounds.Comment: 9 pages, RevTex preprint style, 2 figs. packed with uufile
Gyroid cuticular structures in butterfly wing scales: biological photonic crystals
We present a systematic study of the cuticular structure in the butterfly wing scales of some papilionids (Parides sesostris and Teinopalpus imperialis) and lycaenids (Callophrys rubi, Cyanophrys remus, Mitoura gryneus and Callophrys dumetorum). Using published scanning and transmission electron microscopy (TEM) images, analytical modelling and computer-generated TEM micrographs, we find that the three-dimensional cuticular structures can be modelled by gyroid structures with various filling fractions and lattice parameters. We give a brief discussion of the formation of cubic gyroid membranes from the smooth endoplasmic reticulum in the scale's cell, which dry and harden to leave the cuticular structure behind when the cell dies. The scales of C. rubi are a potentially attractive biotemplate for producing three-dimensional optical photonic crystals since for these scales the cuticle-filling fraction is nearly optimal for obtaining the largest photonic band gap in a gyroid structure
Order of Two-Dimensional Isotropic Dipolar Antiferromagnets
The question of the existence of order in two-dimensional isotropic dipolar
Heisenberg antiferromagnets is studied. It is shown that the dipolar
interaction leads to a gap in the spin-wave energy and a nonvanishing order
parameter. The resulting finite N\'eel-temperature is calculated for a square
lattice by means of linear spin-wave theory.Comment: 10 pages, REVTEX, 1 figure available upon request, TUM-CP-93-0
Antiferromagnetic resonance in ferroborate NdFe(BO)$_4
The AFMR spectra of the NdFe(BO) crystal are measured in a wide
range of frequencies and temperatures. It is found that by the type of magnetic
anisotropy the compound is an "easy-plane" antiferromagnet with a weak
anisotropy in the basal plane. The effective magnetic parameters are
determined: anisotropy fields =1.14 kOe and =60 kOe and
magnetic excitation gaps =101.9 GHz and =23.8 GHz.
It is shown that commensurate-incommensurate phase transition causes a shift in
resonance field and a considerable change in absorption line width.
At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low
microwave power levels are observed
Cluster of Dipolar Coupled Spins as a Quantum Memory Storage
Spin dynamics of a cluster of coupled spins 1/2 can be manipulated to store
and process a large amount of information. A new type of dynamic response makes
it possible to excite coherent long-living signals, which can be used for
exchanging information with a mesoscopic quantum system. An experimental
demonstration is given for a system of 19 proton spins of a liquid crystal
molecule.Comment: 5 pages, 1 figur
Specific Heat Discontinuity in Impure Two-Band Superconductors
The Ginzburg-Landau coefficients, and the jump of the specific heat are
calculated for a disordered two-band superconductor. We start with the analysis
of a more general case arbitrary anisotropy. While the specific heat
discontinuity at the critical temperature T_c decreases with increasing
disorder, its ratio to the normal state specific heat at T_c increases and
slowly converges to the isotropic value. For a strong disorder the deviation
from the isotropic value is proportional to the elastic electron scattering
time. In the case of a two-band superconductor we apply a simplified model of
the interaction independent on momentum within a band. In the framework of this
model all thermodynamic values can be found explicitly at any value of the
scattering rate. This solution explains the sample dependence of the specific
heat discontinuity in MgB_2 and the influence of the disorder on the critical
temperature.Comment: New results relate to two-band superconductors, 9 pages, 2 figure
Properties of spin-triplet, even-parity superconductors
The physical consequences of the spin-triplet, even-parity pairing that has
been predicted to exist in disordered two-dimensional electron systems are
considered in detail. We show that the presence of an attractive interaction in
the particle-particle spin-triplet channel leads to an instability of the
normal metal that competes with the localizing effects of the disorder. The
instability is characterized by a diverging length scale, and has all of the
characteristics of a continuous phase transition. The transition and the
properties of the ordered phase are studied in mean-field theory, and by taking
into account Gaussian fluctuations. We find that the ordered phase is indeed a
superconductor with an ordinary Meissner effect and a free energy that is lower
than that of the normal metal. Various technical points that have given rise to
confusion in connection with this and other manifestations of odd-gap
superconductivity are also discussed.Comment: 15 pp., REVTeX, psfig, 2 ps figs, final version as publishe
Oscillatory wave fronts in chains of coupled nonlinear oscillators
Wave front pinning and propagation in damped chains of coupled oscillators
are studied. There are two important thresholds for an applied constant stress
: for (dynamic Peierls stress), wave fronts fail to propagate,
for stable static and moving wave fronts coexist, and
for (static Peierls stress) there are only stable moving wave
fronts. For piecewise linear models, extending an exact method of Atkinson and
Cabrera's to chains with damped dynamics corroborates this description. For
smooth nonlinearities, an approximate analytical description is found by means
of the active point theory. Generically for small or zero damping, stable wave
front profiles are non-monotone and become wavy (oscillatory) in one of their
tails.Comment: 18 pages, 21 figures, 2 column revtex. To appear in Phys. Rev.
Long-term patterns of excess mortality among endometrial cancer survivors
Background: We investigated excess mortality after endometrial cancer using conditional relative survival estimates and standardized mortality ratios (SMR). Methods: Women diagnosed with endometrial cancer during 2000-2017 (N ¼ 183,153) were identified in the Surveillance Epidemiology and End Results database. SMRs were calculated as observed deaths among endometrial cancer survivors over expected deaths among demographically similar women in the general U.S. population. Five-year relative survival was estimated at diagnosis and each additional year survived up to 12 years post-diagnosis, conditional on survival up to that year. Results: For the full cohort, 5-year relative survival was 87.7%, 96.2%, and 97.1% at 1, 5, and 10 years post-diagnosis, respectively. Conditional 5-year relative survival first exceeded 95%, reflecting minimal excess mortality compared with the general population, at 4 years post-diagnosis overall. However, in subgroup analyses, conditional relative survival remained lower for Black women (vs. White) and for those with regional/distant stage disease (vs. localized) throughout the study period. The overall SMR for all-cause mortality decreased from 5.90 [95% confidence interval (CI), 5.81-5.99] in the first year after diagnosis to 1.16 (95% CI, 1.13-1.19) at 10þ years; SMRs were consistently higher for non-White women and for those with higher stage or grade disease. Conclusions: Overall, endometrial cancer survivors had only a small survival deficit beyond 4 years post-diagnosis. However, excess mortality was greater in magnitude and persisted longer into survivorship for Black women and for those with more advanced disease. Impact: Strategies to mitigate disparities in mortality after endometrial cancer will be needed as the number of survivors continues to increase
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