40,606 research outputs found
Collective Motion of Polarized Dipolar Fermi Gases in the Hydrodynamic Regime
Recently, a seminal STIRAP experiment allowed the creation of 40K-87Rb
molecules in the rovibrational ground state [K.-K. Ni et al., Science 322, 231
(2008)]. In order to describe such a polarized dipolar Fermi gas in the
hydrodynamic regime, we work out a variational time-dependent Hartree-Fock
approach. With this we calculate dynamical properties of such a system as, for
instance, the frequencies of the low-lying excitations and the time-of-flight
expansion. We find that the dipole-dipole interaction induces anisotropic
breathing oscillations in momentum space. In addition, after release from the
trap, the momentum distribution becomes asymptotically isotropic, while the
particle density becomes anisotropic
Revisiting the confrontation of the energy conditions with supernovae data
In the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) approach to model
the Universe the violation of the so-called energy conditions is related to
some important properties of the Universe as, for example, the current and the
inflationary accelerating expansion phases. The energy conditions are also
necessary in the formulation and proofs of Hawking-Penrose singularity
theorems. In two recent articles we have derived bounds from energy conditions
and made confrontations of these bounds with supernovae data. Here, we extend
these results in following way: first, by using our most recent statistical
procedure for calculating new q(z) estimates from the \emph{gold} and
\emph{combined} type Ia supernovae samples; second, we use these estimates to
obtain a new picture of the energy conditions fulfillment and violation for the
recent past () in the context of the standard cosmology.Comment: 5 pages. To appear in Int. J. Mod. Phys. D. Talk presented at the 3rd
International Workshop on Astronomy and Relativistic Astrophysics. V2: typos
correcte
Charge migration mechanisms in the DNA at finite temperature revisited; from quasi-ballistic to subdiffusive transport
Various charge migration mechanisms in the DNA are studied within the
framework of the Peyrard-Bishop-Holstein model which has been widely used to
address charge dynamics in this macromolecule. To analyze these mechanisms we
consider characteristic size and time scales of the fluctuations of the
electronic and vibrational subsystems. It is shown, in particular, that due to
substantial differences in these timescales polaron formation is unlikely
within a broad range of temperatures. We demonstrate that at low temperatures
electronic transport can be quasi-ballistic. For high temperatures, we propose
an alternative to polaronic charge migration mechanism: the
fluctuation-assisted one, in which the electron dynamics is governed by
relatively slow fluctuations of the vibrational subsystem. We argue also that
the discussed methods and mechanisms can be relevant for other organic
macromolecular systems, such as conjugated polymers and molecular aggregates
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