3,674 research outputs found
Extraction of the atmospheric neutrino fluxes from experimental event rate data
The precise knowledge of the atmospheric neutrino fluxes is a key ingredient
in the interpretation of the results from any atmospheric neutrino experiment.
In the standard atmospheric neutrino data analysis, these fluxes are
theoretical inputs obtained from sophisticated numerical calculations. In this
contribution we present an alternative approach to the determination of the
atmospheric neutrino fluxes based on the direct extraction from the
experimental data on neutrino event rates. The extraction is achieved by means
of a combination of artificial neural networks as interpolants and Monte Carlo
methods.Comment: 6 pages, 2 figs, to appear in the proceedings of the 2nd
International Conference on Quantum Theories and Renormalization Group in
Gravity and Cosmology, Barcelona, July 200
Microscopic origin of granular ratcheting
Numerical simulations of assemblies of grains under cyclic loading exhibit
``granular ratcheting'': a small net deformation occurs with each cycle,
leading to a linear accumulation of deformation with cycle number. We show that
this is due to a curious property of the most frequently used models of the
particle-particle interaction: namely, that the potential energy stored in
contacts is path-dependent. There exist closed paths that change the stored
energy, even if the particles remain in contact and do not slide. An
alternative method for calculating the tangential force removes granular
ratcheting.Comment: 13 pages, 18 figure
Symmetry breaking and clustering in a vibrated granular gas with several macroscopically connected compartments
The spontaneous symmetry breaking in a vibro-fluidized low-density granular
gas in three connected compartments is investigated. When the total number of
particles in the system becomes large enough, particles distribute themselves
unequally among the three compartments. Particles tend to concentrate in one of
the compartments, the other two having the (relatively small) same average
number of particles. A hydrodynamical model that accurately predicts the
bifurcation diagram of the system is presented. The theory can be easily
extended to the case of an arbitrary number of connected compartments
Constraints on hidden gravitons from fifth-force experiments and stellar energy loss
We study different phenomenological signatures associated with new spin-2
particles. These new degrees of freedom, that we call hidden gravitons, arise
in different high-energy theories such as extra-dimensional models or
extensions of General Relativity. At low energies, hidden gravitons can be
generally described by the Fierz-Pauli Lagrangian. Their phenomenology is
parameterized by two dimensionful constants: their mass and their coupling
strength. In this work, we analyze two different sets of constraints. On the
one hand, we study potential deviations from the inverse-square law on
solar-system and laboratory scales. To extend the constraints to scales where
the laboratory probes are not competitive, we also study consequences on
astrophysical objects. We analyze in detail the processes that may take place
in stellar interiors and lead to emission of hidden gravitons, acting like an
additional source of energy loss.Comment: 15 pages, 7 figure
Mechanical Unfolding of a Simple Model Protein Goes Beyond the Reach of One-Dimensional Descriptions
We study the mechanical unfolding of a simple model protein. The Langevin
dynamics results are analyzed using Markov-model methods which allow to
describe completely the configurational space of the system. Using transition
path theory we also provide a quantitative description of the unfolding
pathways followed by the system. Our study shows a complex dynamical scenario.
In particular, we see that the usual one-dimensional picture: free-energy vs
end-to-end distance representation, gives a misleading description of the
process. Unfolding can occur following different pathways and configurations
which seem to play a central role in one-dimensional pictures are not the
intermediate states of the unfolding dynamics.Comment: 10 pages, 6 figure
An eccentric companion at the edge of the brown dwarf desert orbiting the 2.4 Msun giant star HIP67537
We report the discovery of a substellar companion around the giant star
HIP67537. Based on precision radial velocity measurements from CHIRON and FEROS
high-resolution spectroscopic data, we derived the following orbital elements
for HIP67537: msin = 11.1 M,
= 4.9 AU and = 0.59. Considering
random inclination angles, this object has 65% probability to be
above the theoretical deuterium-burning limit, thus it is one of the few known
objects in the planet to brown-dwarf transition region. In addition, we
analyzed the Hipparcos astrometric data of this star, from which we derived a
minimum inclination angle for the companion of 2 deg. This value
corresponds to an upper mass limit of 0.3 M, therefore the
probability that HIP67537 is stellar in nature is 7%. The large
mass of the host star and the high orbital eccentricity makes HIP67537 a
very interesting and rare substellar object. This is the second candidate
companion in the brown dwarf desert detected in the sample of intermediate-mass
stars targeted by the EXPRESS radial velocity program, which corresponds to a
detection fraction of = 1.6%. This value is larger than the
fraction observed in solar-type stars, providing new observational evidence of
an enhanced formation efficiency of massive substellar companions in massive
disks. Finally, we speculate about different formation channels for this
object.Comment: Accepted for publication to A&
Indeterminacy, Memory, and Motion in a Simple Granular Packing
We apply two theoretical and two numerical methods to the problem of a disk
placed in a groove and subjected to gravity and a torque. Methods assuming
rigid particles are indeterminate -- certain combinations of forces cannot be
calculated, but only constrained by inequalities. In methods assuming
deformable particles, these combinations of forces are determined by the
history of the packing. Thus indeterminacy in rigid particles becomes memory in
deformable ones. Furthermore, the torque needed to rotate the particle was
calculated. Two different paths to motion were identified. In the first,
contact forces change slowly, and the indeterminacy decreases continuously to
zero, and vanishes precisely at the onset of motion, and the torque needed to
rotate the disk is independent of method and packing history. In the second
way, this torque depends on method and on the history of the packing, and the
forces jump discontinuously at the onset of motion.Comment: 11 pages, 7 figures, submitted to Phys Rev
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