19,808 research outputs found
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
Darboux points and integrability of homogeneous Hamiltonian systems with three and more degrees of freedom
We consider natural complex Hamiltonian systems with degrees of freedom
given by a Hamiltonian function which is a sum of the standard kinetic energy
and a homogeneous polynomial potential of degree . The well known
Morales-Ramis theorem gives the strongest known necessary conditions for the
Liouville integrability of such systems. It states that for each there
exists an explicitly known infinite set \scM_k\subset\Q such that if the
system is integrable, then all eigenvalues of the Hessian matrix V''(\vd)
calculated at a non-zero \vd\in\C^n satisfying V'(\vd)=\vd, belong to
\scM_k. The aim of this paper is, among others, to sharpen this result. Under
certain genericity assumption concerning we prove the following fact. For
each and there exists a finite set \scI_{n,k}\subset\scM_k such that
if the system is integrable, then all eigenvalues of the Hessian matrix
V''(\vd) belong to \scI_{n,k}. We give an algorithm which allows to find
sets \scI_{n,k}. We applied this results for the case and we found
all integrable potentials satisfying the genericity assumption. Among them
several are new and they are integrable in a highly non-trivial way. We found
three potentials for which the additional first integrals are of degree 4 and 6
with respect to the momenta.Comment: 54 pages, 1 figur
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
Using Wavelets to reject background in Dark Matter experiments
A method based on wavelet techniques has been developed and applied to
background rejection in the data of the IGEX dark matter experiment. The method
is presented and described in some detail to show how it efficiently rejects
events coming from noise and microphonism through a mathematical inspection of
their recorded pulse shape. The result of the application of the method to the
last data of IGEX is presented.Comment: 14 pages, 8 figures. Submitted to Astrop. Phy
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
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.
Formal deduction of the Saint-Venant-Exner model including arbitrarily sloping sediment beds and associated energy
In this work we present a deduction of the Saint-Venant-Exner model through
an asymptotic analysis of the Navier-Stokes equations. A multi-scale analysis
is performed in order to take into account that the velocity of the sediment
layer is smaller than the one of the fluid layer. This leads us to consider a
shallow water type system for the fluid layer and a lubrication Reynolds
equation for the sediment one. This deduction provides some improvements with
respect to the classical Saint-Venant-Exner model: (i) the deduced model has an
associated energy. Moreover, it allows us to explain why classical models do
not have an associated energy and how to modify them in order to recover a
model with this property. (ii) The model incorporates naturally a necessary
modification that must be taken into account in order to be applied to
arbitrarily sloping beds. Furthermore, we show that this modification is
different of the ones considered classically, and that it coincides with a
classical one only if the solution has a constant free surface. (iii) The
deduced solid transport discharge naturally depends on the thickness of the
moving sediment layer, what allows to ensure sediment mass conservation.
Moreover, we include a simplified version of the model for the case of
quasi-stationary regimes. Some of these simplified models correspond to the
generalization of classical ones such as Meyer-PeterM\"uller and
Ashida-Michiue models. Three numerical tests are presented to study the
evolution of a dune for several definition of the repose angle, to see the
influence of the proposed definition of the effective shear stress in
comparison with the classical one, and by comparing with experimental data.Comment: 44 pages, sumbitted to Advances in Water Resources 17 july 201
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