20,168 research outputs found
Ratchet behavior in nonlinear Klein-Gordon systems with point-like inhomogeneities
We investigate the ratchet dynamics of nonlinear Klein-Gordon kinks in a
periodic, asymmetric lattice of point-like inhomogeneities. We explain the
underlying rectification mechanism within a collective coordinate framework,
which shows that such system behaves as a rocking ratchet for point particles.
Careful attention is given to the kink width dynamics and its role in the
transport. We also analyze the robustness of our kink rocking ratchet in the
presence of noise. We show that the noise activates unidirectional motion in a
parameter range where such motion is not observed in the noiseless case. This
is subsequently corroborated by the collective variable theory. An explanation
for this new phenomenom is given
Neutron background at the Canfranc Underground Laboratory and its contribution to the IGEX-DM dark matter experiment
A quantitative study of the neutron environment in the Canfranc Underground
Laboratory has been performed. The analysis is based on a complete set of
simulations and, particularly, it is focused on the IGEX-DM dark matter
experiment. The simulations are compared to the IGEX-DM low energy data
obtained with different shielding conditions. The results of the study allow us
to conclude, with respect to the IGEX-DM background, that the main neutron
population, coming from radioactivity from the surrounding rock, is practically
eliminated after the implementation of a suitable neutron shielding. The
remaining neutron background (muon-induced neutrons in the shielding and in the
rock) is substantially below the present background level thanks to the muon
veto system. In addition, the present analysis gives us a further insight on
the effect of neutrons in other current and future experiments at the Canfranc
Underground Laboratory. The comparison of simulations with the body of data
available has allowed to set the flux of neutrons from radioactivity of the
Canfranc rock, (3.82 +- 0.44) x 10^{-6} cm^{-2} s^{-1}, as well as the flux of
muon-induced neutrons in the rock, (1.73 +- 0.22(stat) \+- 0.69(syst)) x
10^{-9} cm^{-2} s^{-1}, or the rate of neutron production by muons in the lead
shielding, (4.8 +- 0.6 (stat) +- 1.9 (syst)) x 10^{-9} cm^{-3} s^{-1}.Comment: 17 pages, 8 figures, elsart document class; final version to appear
in Astroparticle Physic
Maximum power, ecological function and efficiency of an irreversible Carnot cycle. A cost and effectiveness optimization
In this work we include, for the Carnot cycle, irreversibilities of linear
finite rate of heat transferences between the heat engine and its reservoirs,
heat leak between the reservoirs and internal dissipations of the working
fluid. A first optimization of the power output, the efficiency and ecological
function of an irreversible Carnot cycle, with respect to: internal temperature
ratio, time ratio for the heat exchange and the allocation ratio of the heat
exchangers; is performed. For the second and third optimizations, the optimum
values for the time ratio and internal temperature ratio are substituted into
the equation of power and, then, the optimizations with respect to the cost and
effectiveness ratio of the heat exchangers are performed. Finally, a criterion
of partial optimization for the class of irreversible Carnot engines is herein
presented.Comment: 17 pages, 4 figures. Submitted to Energy Convers. Manag
A photometric search for active Main Belt asteroids
It is well known that some Main Belt asteroids show comet-like features. A
representative example is the first known Main Belt comet 133P/(7968)
Elst-Pizarro. If the mechanisms causing this activity are too weak to develop
visually evident comae or tails, the objects stay unnoticed. We are presenting
a novel way to search for active asteroids, based on looking for objects with
deviations from their expected brightnesses in a database. Just by using the
MPCAT-OBS Observation Archive we have found five new candidate objects that
possibly show a type of comet-like activity, and the already known Main Belt
comet 133P/(7968) Elst-Pizarro. Four of the new candidates, (315) Constantia,
(1026) Ingrid, (3646) Aduatiques, and (24684) 1990 EU4, show brightness
deviations independent of the object's heliocentric distance, while (35101)
1991 PL16 shows deviations dependent on its heliocentric distance, which could
be an indication of a thermal triggered mechanism. The method could be
implemented in future sky survey programmes to detect outbursts on Main Belt
objects almost simultaneously with their occurrence.Comment: 8 pages, 10 figures. Accepted for publication in A&A on December 20,
201
Thermoelectric power quantum oscillations in the ferromagnet UGe
We present thermoelectric power and resistivity measurements in the
ferromagnet UGe as a function of temperature and magnetic field. At low
temperature, huge quantum oscillations are observed in the thermoelectric power
as a function of the magnetic field applied along the axis. The frequencies
of the extreme orbits are determined and an analysis of the cyclotron masses is
performed following different theoretical approaches for quantum oscillations
detected in the thermoelectric power. They are compared to those obtained by
Shubnikov-de Haas experiments on the same crystal and previous de Haas-van
Alphen experiments. The agreement of the different probes confirms
thermoelectric power as an excellent probe to extract simultaneously both
microscopic and macroscopic information on the Fermi-surface properties.
Band-structure calculations of UGe in the ferromagnetic state are compared
to the experiment.Comment: 10 figures, 12 pages, accepted for publication in Phys. Rev.
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