12,191 research outputs found
GEM/POPs: a global 3-D dynamic model for semi-volatile persistent organic pollutants ? Part 1: Model description and evaluations of air concentrations
International audienceGEM/POPs was developed to simulate the transport, deposition and partitioning of semi-volatile persistent organic pollutants (POPs) in the atmosphere within the framework of Canadian weather forecasting model GEM. In addition to the general processes such as anthropogenic emissions, atmosphere/water and atmosphere/soil exchanges, GEM/POPs incorporates a dynamic aerosol module to provide the aerosol surface areas for the semi-volatile POPs to partition between gaseous and particle phases and a mechanism for particle-bound POPs to be removed. Simulation results of three PCBs (28, 153 and 180) for the year 2000 indicate that the model captured the main features of global atmospheric PCBs when compared with observations from EMEP, IADN and Alert stations. The annual averaged concentrations and the fractionation of the three PCBs as a function of latitudes agreed reasonably well with observations. The impacts of atmospheric aerosols on the transports and partitioning of the three PCBs are reasonably simulated. The ratio of particulate to gaseous PCBs in the atmospheric column ranges from less than 0.1 for PCB28 to as high as 100 for PCB180, increasing from the warm lower latitudes to the cold high latitudes. Application of GEM/POPs in a study of the global transports and budgets of various PCBs accompanies this paper
Non-existence of Extended Holographic Dark Energy with Hubble Horizon
The extended holographic dark energy model with the Hubble horizon as the
infrared cutoff avoids the problem of the circular reasoning of the holographic
dark energy model. We show that the infrared cutoff of the extended holographic
dark energy model cannot be the Hubble horizon provided that the Brans-Dicke
parameter satisfies the experimental constraint , and
this is proved as a no-go theorem. The no-go theorem also applies to the case
in which the dark matter interacts with the dark energy.Comment: 12 pages with revtex, 4 figures, v2: minor corrections to match the
version appeared in JCA
Hologrphy and holographic dark energy model
The holographic principle is used to discuss the holographic dark energy
model. We find that the Bekenstein-Hawking entropy bound is far from saturation
under certain conditions. A more general constraint on the parameter of the
holographic dark energy model is also derived.Comment: no figures, use revtex, v2: use iop style, some typos corrected and
references updated, will appear in CQ
Thermodynamical properties of the Universe with dark energy
We have investigated the thermodynamical properties of the Universe with dark
energy. Adopting the usual assumption in deriving the constant co-moving
entropy density that the physical volume and the temperature are independent,
we observed some strange thermodynamical behaviors. However, these strange
behaviors disappeared if we consider the realistic situation that the physical
volume and the temperature of the Universe are related. Based on the well known
correspondence between the Friedmann equation and the first law of
thermodynamics of the apparent horizon, we argued that the apparent horizon is
the physical horizon in dealing with thermodynamics problems. We have
concentrated on the volume of the Universe within the apparent horizon and
considered that the Universe is in thermal equilibrium with the Hawking
temperature on the apparent horizon. For dark energy with , the
holographic principle and the generalized second law are always respected.Comment: two figures; v2: minor corrections and updates, JCAP in pres
Rashbons: Properties and their significance
In presence of a synthetic non-Abelian gauge field that induces a Rashba like
spin-orbit interaction, a collection of weakly interacting fermions undergoes a
crossover from a BCS ground state to a BEC ground state when the strength of
the gauge field is increased [Phys. Rev. B {\bf 84}, 014512 (2011)]. The BEC
that is obtained at large gauge coupling strengths is a condensate of tightly
bound bosonic fermion-pairs whose properties are solely determined by the
Rashba gauge field -- hence called rashbons. In this paper, we conduct a
systematic study of the properties of rashbons and their dispersion. This study
reveals a new qualitative aspect of the problem of interacting fermions in
non-Abelian gauge fields, i.e., that the rashbon state induced by the gauge
field for small centre of mass momenta of the fermions ceases to exist when
this momentum exceeds a critical value which is of the order of the gauge
coupling strength. The study allows us to estimate the transition temperature
of the rashbon BEC, and suggests a route to enhance the exponentially small
transition temperature of the system with a fixed weak attraction to the order
of the Fermi temperature by tuning the strength of the non-Abelian gauge field.
The nature of the rashbon dispersion, and in particular the absence of the
rashbon states at large momenta, suggests a regime of parameter space where the
normal state of the system will be a dynamical mixture of uncondensed rashbons
and unpaired helical fermions. Such a state should show many novel features
including pseudogap physics.Comment: 8 pages, 6 figure
A Note on Temperature and Energy of 4-dimensional Black Holes from Entropic Force
We investigate the temperature and energy on holographic screens for
4-dimensional black holes with the entropic force idea proposed by Verlinde. We
find that the "Unruh-Verlinde temperature" is equal to the Hawking temperature
on the horizon and can be considered as a generalized Hawking temperature on
the holographic screen outside the horizons. The energy on the holographic
screen is not the black hole mass but the reduced mass , which is
related to the black hole parameters. With the replacement of the black hole
mass by the reduced mass , the entropic force can be written as
, which could be tested by experiments.Comment: V4: 13 pages, 4 figures, title changed, discussions for experiments
added, accepted by CQ
Decoherence and the rate of entropy production in chaotic quantum systems
We show that for an open quantum system which is classically chaotic (a
quartic double well with harmonic driving coupled to a sea of harmonic
oscillators) the rate of entropy production has, as a function of time, two
relevant regimes: For short times it is proportional to the diffusion
coefficient (fixed by the system--environment coupling strength). For longer
times (but before equilibration) there is a regime where the entropy production
rate is fixed by the Lyapunov exponent. The nature of the transition time
between both regimes is investigated.Comment: Revtex, 4 pages, 3 figures include
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