422 research outputs found
Strength Reduction in Electrical and Elastic Networks
Particular aspects of problems ranging from dielectric breakdown to metal
insu- lator transition can be studied using electrical o elastic networks. We
present an expression for the mean breakdown strength of such networks.First,
we intro- duce a method to evaluate the redistribution of current due to the
removal of a finite number of elements from a hyper-cubic network of
conducatances.It is used to determine the reduction of breakdown strength due
to a fracture of size .Numerical analysis is used to show that the
analogous reduction due to random removal of elements from electrical and
elastic networks follow a similar form.One possible application, namely the use
of bone density as a diagnostic tools for osteorosporosis,is discussed.Comment: one compressed file includes: 9 PostScrpt figures and a text fil
Systematic thermal reduction of neutronization in core-collapse supernovae
We investigate to what extent the temperature dependence of the nuclear
symmetry energy can affect the neutronization of the stellar core prior to
neutrino trapping during gravitational collapse. To this end, we implement a
one-zone simulation to follow the collapse until beta equilibrium is reached
and the lepton fraction remains constant. Since the strength of electron
capture on the neutron-rich nuclei associated to the supernova scenario is
still an open issue, we keep it as a free parameter. We find that the
temperature dependence of the symmetry energy consistently yields a small
reduction of deleptonization, which corresponds to a systematic effect on the
shock wave energetics: the gain in dissociation energy of the shock has a small
yet non-negligible value of about 0.4 foe (1 foe = 10^51 erg) and this result
is almost independent from the strength of nuclear electron capture. The
presence of such a systematic effect and its robustness under changes of the
parameters of the one-zone model are significative enough to justify further
investigations with detailed numerical simulations of supernova explosions.Comment: 15 pages, 2 tables, 3 figure
Effect of band-filling and structural distortions on the Curie temperature of Fe-Mo double perovkites
By means of high resolution neutron powder diffraction at low temperature we
have characterized the structural details of
() and () series of compounds. This study reveals a similar variation of the mean
bond-angle \FeOMo in both series. In contrast, the mean bond-distance \FeMoO\
increases with La but not with Ca substitution. Both series also present a
different evolution of the Curie temperature (), which raises in the La
series and slightly decreases in the Ca one. We thus conclude that the
enhancement of in the La series is due to the electron filling of the
conduction band and a concomitant rising of the density of states at the Fermi
level.Comment: Revtex, 4 Journal pages, 2 figures, 1 tabl
Using Nonlinear Response to Estimate the Strength of an Elastic Network
Disordered networks of fragile elastic elements have been proposed as a model
of inner porous regions of large bones [Gunaratne et.al., cond-mat/0009221,
http://xyz.lanl.gov]. It is shown that the ratio of responses of such
a network to static and periodic strain can be used to estimate its ultimate
(or breaking) stress. Since bone fracture in older adults results from the
weakening of porous bone, we discuss the possibility of using as a
non-invasive diagnostic of osteoporotic bone.Comment: 4 pages, 4 figure
Spin-Orbit Splitting in Non-Relativistic and Relativistic Self-Consistent Models
The splitting of single-particle energies between spin-orbit partners in
nuclei is examined in the framework of different self-consistent approachs,
non-relativistic as well as relativistic. Analytical expressions of spin-orbit
potentials are given for various cases. Proton spin-orbit splittings are
calculated along some isotopic chains (O, Ca, Sn) and they are compared with
existing data. It is found that the isotopic dependence of the relativistic
mean field predictions is similar to that of some Skyrme forces while the
relativistic Hartree-Fock approach leads to a very different dependence due to
the strong non-locality.Comment: 12 pages, RevTeX, 4 new figs.in .zip format, unchanged conclusions,
Phys. ReV.
Field-linked States of Ultracold Polar Molecules
We explore the character of a novel set of ``field-linked'' states that were
predicted in [A. V. Avdeenkov and J. L. Bohn, Phys. Rev. Lett. 90, 043006
(2003)]. These states exist at ultralow temperatures in the presence of an
electrostatic field, and their properties are strongly dependent on the field's
strength. We clarify the nature of these quasi-bound states by constructing
their wave functions and determining their approximate quantum numbers. As the
properties of field-linked states are strongly defined by anisotropic dipolar
and Stark interactions, we construct adiabatic surfaces as functions of both
the intermolecular distance and the angle that the intermolecular axis makes
with the electric field. Within an adiabatic approximation we solve the 2-D
Schrodinger equation to find bound states, whose energies correlate well with
resonance features found in fully-converged multichannel scattering
calculations
On The Mobile Behavior of Solid He at High Temperatures
We report studies of solid helium contained inside a torsional oscillator, at
temperatures between 1.07K and 1.87K. We grew single crystals inside the
oscillator using commercially pure He and He-He mixtures containing
100 ppm He. Crystals were grown at constant temperature and pressure on the
melting curve. At the end of the growth, the crystals were disordered,
following which they partially decoupled from the oscillator. The fraction of
the decoupled He mass was temperature and velocity dependent. Around 1K, the
decoupled mass fraction for crystals grown from the mixture reached a limiting
value of around 35%. In the case of crystals grown using commercially pure
He at temperatures below 1.3K, this fraction was much smaller. This
difference could possibly be associated with the roughening transition at the
solid-liquid interface.Comment: 15 pages, 6 figure
Nonequilibrium Evolution of Correlation Functions: A Canonical Approach
We study nonequilibrium evolution in a self-interacting quantum field theory
invariant under space translation only by using a canonical approach based on
the recently developed Liouville-von Neumann formalism. The method is first
used to obtain the correlation functions both in and beyond the Hartree
approximation, for the quantum mechanical analog of the model. The
technique involves representing the Hamiltonian in a Fock basis of annihilation
and creation operators. By separating it into a solvable Gaussian part
involving quadratic terms and a perturbation of quartic terms, it is possible
to find the improved vacuum state to any desired order. The correlation
functions for the field theory are then investigated in the Hartree
approximation and those beyond the Hartree approximation are obtained by
finding the improved vacuum state corrected up to . These
correlation functions take into account next-to-leading and
next-to-next-to-leading order effects in the coupling constant. We also use the
Heisenberg formalism to obtain the time evolution equations for the equal-time,
connected correlation functions beyond the leading order. These equations are
derived by including the connected 4-point functions in the hierarchy. The
resulting coupled set of equations form a part of infinite hierarchy of coupled
equations relating the various connected n-point functions. The connection with
other approaches based on the path integral formalism is established and the
physical implications of the set of equations are discussed with particular
emphasis on thermalization.Comment: Revtex, 32 pages; substantial new material dealing with
non-equilibrium evolution beyond Hartree approx. based on the LvN formalism,
has been adde
Racial Differences in the Effects of Hormone Therapy on Incident Open-Angle Glaucoma in a Randomized Trial
Purpose: We conducted a secondary analysis of a randomized, placebo-controlled trial to test if hormone therapy (HT) altered the risk of open-angle glaucoma (OAG), and if the risk reduction varied by race. Design: Secondary analysis of randomized controlled trial data. Methods: We linked Medicare claims data to 25 535 women in the Women's Health Initiative. Women without a uterus were randomized to receive either oral conjugated equine estrogens (CEE 0.625 mg/day) or placebo, and women with a uterus received oral CEE and medroxyprogesterone acetate (CEE 0.625 mg/day + MPA 2.5 mg/day) or placebo. We used Cox proportional hazards models to calculate hazard ratios (HR) and 95% confidence interval. Results: After exclusion of women with prevalent glaucoma or without claims for eye care provider visits, the final analysis included 8102 women (mean age = 68.5 ± 4.8 years). The OAG incidence was 7.6% (mean follow-up = 11.5 ± 5.2 years; mean HT duration = 4.4 ± 2.3 years). Increased age (P trend =.01) and African-American race (HR = 2.69, 95% CI = 2.13–3.42; white as a reference) were significant risk factors for incident OAG. We found no overall benefit of HT in reducing incident OAG (HR = 1.01, 95% CI = 0.79–1.29 in the CEE trial, and HR = 1.05, 95% CI = 0.85–1.29 in the CEE + MPA trial). However, race modified the relationship between CEE use and OAG risk (P interaction =.01), and risk was reduced in African-American women treated with CEE (HR = 0.49, 95% CI = 0.27–0.88), compared to placebo. Race did not modify the relation between CEE + MPA use and OAG risk (P interaction =.68). Conclusions: Analysis suggests that HT containing estrogen, but not a combination of estrogen and progesterone, reduces the risk of incident OAG among African-American women. Further investigation is needed
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