10,639 research outputs found
Asymptotics for hitting times
In this paper we characterize possible asymptotics for hitting times in
aperiodic ergodic dynamical systems: asymptotics are proved to be the
distribution functions of subprobability measures on the line belonging to the
functional class {6pt} {-3mm}(A){6mm}F={F:R\to [0,1]:\left\lbrack \matrixF is
increasing, null on ]-\infty, 0]; \noalignF is continuous and concave;
\noalignF(t)\le t for t\ge 0.\right.}. {6pt} Note that all possible asymptotics
are absolutely continuous.Comment: Published at http://dx.doi.org/10.1214/009117904000000883 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
About the barotropic compressible quantum Navier-Stokes equations
In this paper we consider the barotropic compressible quantum Navier-Stokes
equations with a linear density dependent viscosity and its limit when the
scaled Planck constant vanish. Following recent works on degenerate
compressible Navier-Stokes equations, we prove the global existence of weak
solutions by the use of a singular pressure close to vacuum. With such singular
pressure, we can use the standard definition of global weak solutions which
also allows to justify the limit when the scaled Planck constant denoted by
tends to 0
Configuration mixing within the energy density functional formalism: pathologies and cures
Configuration mixing calculations performed in terms of the Skyrme/Gogny
Energy Density Functional (EDF) rely on extending the Single-Reference energy
functional into non-diagonal EDF kernels. The standard way to do so, based on
an analogy with the pure Hamiltonian case and the use of the generalized Wick
theorem, is responsible for the recently observed divergences and steps in
Multi-Reference calculations. We summarize here the minimal solution to this
problem recently proposed [Lacroix et al, arXiv:0809.2041] and applied with
success to particle number restoration[Bender et al, arXiv:0809.2045]. Such a
regularization method provides suitable corrections of pathologies for EDF
depending on integer powers of the density. The specific case of fractional
powers of the density[Duguet et al, arXiv:0809.2049] is also discussed.Comment: 5 pages, Proceedings of the French-Japanese Symposium, September
2008. To be published in Int. J. of Mod. Phys.
A Lee-Yang--inspired functional with a density--dependent neutron-neutron scattering length
Inspired by the low--density Lee-Yang expansion for the energy of a dilute
Fermi gas of density and momentum , we introduce here a
Skyrme--type functional that contains only -wave terms and provides, at the
mean--field level, (i) a satisfactory equation of state for neutron matter from
extremely low densities up to densities close to the equilibrium point, and
(ii) a good--quality equation of state for symmetric matter at density scales
around the saturation point. This is achieved by using a density--dependent
neutron-neutron scattering length ) which satisfies the low--density
limit (for Fermi momenta going to zero) and has a density dependence tuned in
such a way that the low--density constraint is satisfied
at all density scales.Comment: 5 figure
Ultrafast dynamics of finite Hubbard clusters - a stochastic mean-field approach
Finite lattice models are a prototype for strongly correlated quantum systems
and capture essential properties of condensed matter systems. With the dramatic
progress in ultracold atoms in optical lattices, finite fermionic Hubbard
systems have become directly accessible in experiments, including their
ultrafast dynamics far from equilibrium. Here, we present a theoretical
approach that is able to treat these dynamics in any dimension and fully
includes inhomogeneity effects. The method consists in stochastic sampling of
mean-field trajectories and is found to be more accurate and efficient than
current nonequilibrium Green functions approaches. This is demonstrated for
Hubbard clusters with up to 512 particles in one, two and three dimensions
From dilute matter to the equilibrium point in the energy--density--functional theory
Due to the large value of the scattering length in nuclear systems, standard
density--functional theories based on effective interactions usually fail to
reproduce the nuclear Fermi liquid behavior both at very low densities and
close to equilibrium. Guided on one side by the success of the Skyrme density
functional and, on the other side, by resummation techniques used in Effective
Field Theories for systems with large scattering lengths, a new energy--density
functional is proposed. This functional, adjusted on microscopic calculations,
reproduces the nuclear equations of state of neutron and symmetric matter at
various densities. Furthermore, it provides reasonable saturation properties as
well as an appropriate density dependence for the symmetry energy.Comment: 4 figures, 2 table
Voltage induced control and magnetoresistance of noncollinear frustrated magnets
Noncollinear frustrated magnets are proposed as a new class of spintronic
materials with high magnetoresistance which can be controlled with relatively
small applied voltages. It is demonstrated that their magnetic configuration
strongly depends on position of the Fermi energy and applied voltage. The
voltage induced control of noncollinear frustrated materials (VCFM) can be seen
as a way to intrinsic control of colossal magnetoresistance (CMR) and is the
bulk material counterpart of spin transfer torque concept used to control giant
magnetoresistance in layered spin-valve structures.Comment: 4 pages, 4 figure
A frequency-adjustable electromagnet for hyperthermia measurements on magnetic nanoparticles
We describe a low-cost and simple setup for hyperthermia measurements on
colloidal solutions of magnetic nanoparticles (ferrofluids) with a
frequency-adjustable magnetic field in the range 5-500 kHz produced by an
electromagnet. By optimizing the general conception and each component (nature
of the wires, design of the electromagnet), a highly efficient setup is
obtained. For instance, in a useful gap of 1.1 cm, a magnetic field of 4.8 mT
is generated at 100 kHz and 500 kHz with an output power of 3.4 W and 75 W,
respectively. A maximum magnetic field of 30 mT is obtained at 100 kHz. The
temperature of the colloidal solution is measured using optical fiber sensors.
To remove contributions due to heating of the electromagnet, a differential
measurement is used. In this configuration the sensitivity is better than 1.5
mW at 100 kHz and 19.3 mT. This setup allows one to measure weak heating powers
on highly diluted colloidal solutions. The hyperthermia characteristics of a
solution of Fe nanoparticles are described, where both the magnetic field and
the frequency dependence of heating power have been measured
Using datasets from the Internet for hydrological modeling: an example from the Kntnk Menderes Basin, Turkey
River basin development / Water resources / Data collection / Models / Hydrology / Land classification / Water management / Water scarcity / Water allocation / Stream flow / Water demand / Turkey / Kntnk Menderes Basin
Pair-transfer probability in open- and closed-shell Sn isotopes
Approximations made to estimate two-nucleon transfer probabilities in
ground-state to ground-state transitions and physical interpretation of these
probabilities are discussed. Probabilities are often calculated by
approximating both ground states, of the initial nucleus A and of the final
nucleus A\pm 2 by the same quasiparticle vacuum. We analyze two improvements of
this approach. First, the effect of using two different ground states with
average numbers of particles A and A\pm2 is quantified. Second, by using
projection techniques, the role of particle number restoration is analyzed. Our
analysis shows that the improved treatment plays a role close to magicity,
leading to an enhancement of the pair-transfer probability. In mid-shell
regions, part of the error made by approximating the initial and final ground
states by a single vacuum is compensated by projecting onto good particle
number. Surface effects are analyzed by using pairing interactions with a
different volume-to-surface mixing. Finally, a simple expression of the
pair-transfer probability is given in terms of occupation probabilities in the
canonical basis. We show that, in the canonical basis formulation, surface
effects which are visible in the transfer probability are related to the
fragmentation of single-particle occupancies close to the Fermi energy. This
provides a complementary interpretation with respect to the standard
quasiparticle representation where surface effects are generated by the
integrated radial profiles of the contributing wave functions.Comment: 12 pages, 7 figure
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