81,154 research outputs found
Out of equilibrium quantum field dynamics in external fields
The quantum dynamics of the symmetry broken \lambda (\Phi^2)^2 scalar field
theory in the presence of an homogeneous external field is investigated in the
large N limit. We consider an initial thermal state of temperature T for a
constant external field J. A subsequent sign flip of the external field, J to
-J, gives rise to an out of equilibrium nonperturbative quantum field dynamics.
We review here the dynamics for the symmetry broken lambda(\Phi^2)^2 scalar N
component field theory in the large N limit, with particular stress in the
comparison between the results when the initial temperature is zero and when it
is finite. The presence of a finite temperature modifies the dynamical
effective potential for the expectation value, and also makes that the
transition between the two regimes of the early dynamics occurs for lower
values of the external field. The two regimes are characterized by the presence
or absence of a temporal trapping close to the metastable equilibrium position
of the potential. In the cases when the trapping occurs it is shorter for
larger initial temperatures.Comment: LaTeX, 3 pages, 2 figures. Presented at the IVth International
Conference on Quarks and Nuclear Physics (QNP06). Selected to appear in Eur.
Phys. J.
Interband impact ionization and nonlinear absorption of terahertz radiations in semiconductor heterostructures
We have theoretically investigated nonlinear free-carrier absorption of
terahertz radiation in InAs/AlSb heterojunctions. By considering multiple
photon process and conduction-valence interband impact ionization (II), we have
determined the field and frequency dependent absorption rate. It is shown that
(i) electron-disorder scatterings are important at low to intermediate field,
and (ii) most importantly, the high field absorption is dominated by II
processes. Our theory can satisfactorily explain a long standing experimental
result on the nonlinear absorption in THz regime.Comment: 4 pages including 3 EPS fig
SUSY Dark Matter In Light Of CDMS/XENON Limits
In this talk we briefly review the current CDMS/XENON constraints on the
neutralino dark matter in three popular supersymmetric models: the minimal
(MSSM), the next-to-minimal (NMSSM) and the nearly minimal (nMSSM). The
constraints from the dark matter relic density and various collider experiments
are also taken into account. The conclusion is that for each model the current
CDMS/XENON limits can readily exclude a large part of the parameter space
allowed by other constraints and the future SuperCDMS or XENON100 can cover
most of the allowed parameter space. The implication for the Higgs search at
the LHC is also discussed. It is found that in the currently allowed parameter
space the MSSM charged Higgs boson is quite unlikely to be discovered at the
LHC while the neutral Higgs bosons and may be accessible at the LHC in
the parameter space with a large parameter.Comment: talk given at 2nd International Workshop on Dark Matter, Dark Energy
and Matter-Antimatter Asymmetry, Nov 5-6, 2010, Hsinchu, Taiwan (to appear in
Int. J. Mod. Phys. D
Transport reversal in a delayed feedback ratchet
Feedback flashing ratchets are thermal rectifiers that use information on the
state of the system to operate the switching on and off of a periodic
potential. They can induce directed transport even with symmetric potentials
thanks to the asymmetry of the feedback protocol. We investigate here the
dynamics of a feedback flashing ratchet when the asymmetry of the ratchet
potential and of the feedback protocol favor transport in opposite directions.
The introduction of a time delay in the control strategy allows one to
nontrivially tune the relative relevance of the competing asymmetries leading
to an interesting dynamics. We show that the competition between the
asymmetries leads to a current reversal for large delays. For small ensembles
of particles current reversal appears as the consequence of the emergence of an
open-loop like dynamical regime, while for large ensembles of particles it can
be understood as a consequence of the stabilization of quasiperiodic solutions.
We also comment on the experimental feasibility of these feedback ratchets and
their potential applications.Comment: LaTeX, 7 pages, 6 figure
Detecting peroxiredoxin hyperoxidation by one-dimensional isoelectric focusing
The activity of typical 2-cys peroxiredoxin (Prxs) can be regulated by hyperoxidation with a consequent loss of redox activity. Here we developed a simple assay to monitor the level of hyperoxidation of different typical 2-cys prxs simultaneously. This assay only requires standard equipment and can compare different samples on the same gel. It requires much less time than conventional 2D gels and gives more information than Western blotting with an antibody specific for hyperoxidized peroxiredoxin. This method could also be used to monitor protein modification with a charge difference such as phosphorylation
Zonal Flow Magnetic Field Interaction in the Semi-Conducting Region of Giant Planets
All four giant planets in the Solar System feature zonal flows on the order
of 100 m/s in the cloud deck, and large-scale intrinsic magnetic fields on the
order of 1 Gauss near the surface. The vertical structure of the zonal flows
remains obscure. The end-member scenarios are shallow flows confined in the
radiative atmosphere and deep flows throughout the entire planet. The
electrical conductivity increases rapidly yet smoothly as a function of depth
inside Jupiter and Saturn. Deep zonal flows will inevitably interact with the
magnetic field, at depth with even modest electrical conductivity. Here we
investigate the interaction between zonal flows and magnetic fields in the
semi-conducting region of giant planets. Employing mean-field electrodynamics,
we show that the interaction will generate detectable poloidal magnetic field
perturbations spatially correlated with the deep zonal flows. Assuming the peak
amplitude of the dynamo alpha-effect to be 0.1 mm/s, deep zonal flows on the
order of 0.1 - 1 m/s in the semi-conducting region of Jupiter and Saturn would
generate poloidal magnetic perturbations on the order of 0.01% - 1% of the
background dipole field. These poloidal perturbations should be detectable with
the in-situ magnetic field measurements from the Juno mission and the Cassini
Grand Finale. This implies that magnetic field measurements can be employed to
constrain the properties of deep zonal flows in the semi-conducting region of
giant planets.Comment: 38 pages, 12 figures, revised submission to Icaru
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