7,736 research outputs found
Strong Correlations in Actinide Redox Reactions
Reduction-oxidation (redox) reactions of the redox couples An(VI)/An(V),
An(V)/An(IV), and An(IV)/An(III), where An is an element in the family of early
actinides (U, Np, and Pu), as well as Am(VI)/Am(V) and Am(V)/Am(III), are
modeled by combining density functional theory with a generalized Anderson
impurity model that accounts for the strong correlations between the 5f
electrons. Diagonalization of the Anderson impurity model yields improved
estimates for the redox potentials and the propensity of the actinide complexes
to disproportionate.Comment: 17 pages, 10 figure, 3 tables. Corrections and clarifications; this
version has been accepted for publication in The Journal of Chemical Physic
Black Hole Entropy and Superconformal Field Theories on Brane-Antibrane Systems
We obtain the enropy of Schwarzschild and charged black holes in D>4 from
superconformal gases that live on p=10-D dimensional brane-antibrane systems
wrapped on T^p. The preperties of the strongly coupled superconformal theories
such as the appearance of hidden dimensions (for p=1,4) and fractional strings
(for p=5) are crucial for our results. In all cases, the Schwarzschild radius
is given by the transverse fluctuations of the branes and antibranes due to the
finite temperature. We show that our results can be generalized to multicharged
black holes.Comment: 24 pages in phyzzx.te
Dynamics of First Order Transitions with Gravity Duals
A first order phase transition usually proceeds by nucleating bubbles of the
new phase which then rapidly expand. In confining gauge theories with a gravity
dual, the deconfined phase is often described by a black hole. If one starts in
this phase and lowers the temperature, the usual description of how the phase
transition proceeds violates the area theorem. We study the dynamics of this
phase transition using the insights from the dual gravitational description,
and resolve this apparent contradiction.Comment: 11 pages, 1 figure. v2: minor clarifications, reference adde
Unitarity, quasi-normal modes and the AdS_3/CFT_2 correspondence
In general, black-hole perturbations are governed by a discrete spectrum of
complex eigen-frequencies (quasi-normal modes). This signals the breakdown of
unitarity. In asymptotically AdS spaces, this is puzzling because the
corresponding CFT is unitary. To address this issue in three dimensions, we
replace the BTZ black hole by a wormhole, following a suggestion by Solodukhin
[hep-th/0406130]. We solve the wave equation for a massive scalar field and
find an equation for the poles of the propagator. This equation yields a rich
spectrum of {\em real} eigen-frequencies. We show that the throat of the
wormhole is , where is Newton's constant. Thus, the quantum
effects which might produce the wormhole are non-perturbative.Comment: 9 page
Neutrino Trapping in a Supernova and Ion Screening
Neutrino-nucleus elastic scattering is reduced in dense matter because of
correlations between ions. The static structure factor for a plasma of
electrons and ions is calculated from Monte Carlo simulations and parameterized
with a least squares fit. Our results imply a large increase in the neutrino
mean free path. This strongly limits the trapping of neutrinos in a supernova
by coherent neutral current interactions.Comment: 9 pages, 1 postscript figure using epsf.st
Designing optimal discrete-feedback thermodynamic engines
Feedback can be utilized to convert information into useful work, making it
an effective tool for increasing the performance of thermodynamic engines.
Using feedback reversibility as a guiding principle, we devise a method for
designing optimal feedback protocols for thermodynamic engines that extract all
the information gained during feedback as work. Our method is based on the
observation that in a feedback-reversible process the measurement and the
time-reversal of the ensuing protocol both prepare the system in the same
probabilistic state. We illustrate the utility of our method with two examples
of the multi-particle Szilard engine.Comment: 15 pages, 5 figures, submitted to New J. Phy
Phase separation in the crust of accreting neutron stars
Nucleosynthesis, on the surface of accreting neutron stars, produces a range
of chemical elements. We perform molecular dynamics simulations of
crystallization to see how this complex composition forms new neutron star
crust. We find chemical separation, with the liquid ocean phase greatly
enriched in low atomic number elements compared to the solid crust. This phase
separation should change many crust properties such as the thermal conductivity
and shear modulus. The concentration of carbon, if present, is enriched in the
ocean. This may allow unstable thermonuclear burning of the carbon and help
explain the ignition of the very energetic explosions known as superbursts.Comment: 8 pages, 6 figures, minor changes, Physical Review E in pres
String Form Factors
We compute the cross section for scattering of light string probes by
randomly excited closed strings. For high energy probes, the cross section
factorizes and can be used to define effective form factors for the excited
targets. These form factors are well defined without the need for infinite
subtractions and contain information about the shape and size of typical
strings. For highly excited strings the elastic form factor can be written in
terms of the `plasma dispersion function', which describes charge screening in
high temperature plasmas.Comment: 18 pages, 3 figures. Typos corrected, 1 footnote (in Section 4) and 1
reference adde
Delta Excitations in Neutrino-Nucleus Scattering
We derive the contribution of -h excitations to quasielastic
charged-current neutrino-nucleus scattering in the framework of relativistic
mean-field theory. We discuss the effect of production on the
determination of the axial mass in neutrino scattering experiments.Comment: 14 pages, revtex, 3 postscript figures (available upon request
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