21,070 research outputs found
MIMAC : A micro-tpc matrix for directional detection of dark matter
Directional detection of non-baryonic Dark Matter is a promising search
strategy for discriminating WIMP events from background. However, this strategy
requires both a precise measurement of the energy down to a few keV and 3D
reconstruction of tracks down to a few mm. To achieve this goal, the MIMAC
project has been developed. It is based on a gaseous micro-TPC matrix, filled
with CF4 and CHF3. The first results on low energy nuclear recoils (H, F)
obtained with a low mono-energetic neutron field are presented. The discovery
potential of this search strategy is discussed and illustrated by a realistic
case accessible to MIMAC.Comment: 6 pages, Proc. of the fifth international symposium on large TPCs for
low energy rare event detection, Paris, France, Dec. 2010. To appear in
Journal of Physic
Localization and the effects of symmetries in the thermalization properties of one-dimensional quantum systems
We study how the proximity to an integrable point or to localization as one
approaches the atomic limit, as well as the mixing of symmetries in the chaotic
domain, may affect the onset of thermalization in finite one-dimensional
systems. We consider systems of hard-core bosons at half-filling with nearest
neighbor hopping and interaction, and next-nearest neighbor interaction. The
latter breaks integrability and induces a ground-state superfluid to insulator
transition. By full exact diagonalization, we study chaos indicators and
few-body observables. We show that when different symmetry sectors are mixed,
chaos indicators associated with the eigenvectors, contrary to those related to
the eigenvalues, capture the onset of chaos. The results for the complexity of
the eigenvectors and for the expectation values of few-body observables confirm
the validity of the eigenstate thermalization hypothesis in the chaotic regime,
and therefore the occurrence of thermalization. We also study the properties of
the off-diagonal matrix elements of few-body observables in relation to the
transition from integrability to chaos and from chaos to localization.Comment: 12 pages, 13 figures, as published (Fig.09 was corrected in this
final version
The Overlooked Potential of Generalized Linear Models in Astronomy-III: Bayesian Negative Binomial Regression and Globular Cluster Populations
In this paper, the third in a series illustrating the power of generalized
linear models (GLMs) for the astronomical community, we elucidate the potential
of the class of GLMs which handles count data. The size of a galaxy's globular
cluster population is a prolonged puzzle in the astronomical
literature. It falls in the category of count data analysis, yet it is usually
modelled as if it were a continuous response variable. We have developed a
Bayesian negative binomial regression model to study the connection between
and the following galaxy properties: central black hole mass,
dynamical bulge mass, bulge velocity dispersion, and absolute visual magnitude.
The methodology introduced herein naturally accounts for heteroscedasticity,
intrinsic scatter, errors in measurements in both axes (either discrete or
continuous), and allows modelling the population of globular clusters on their
natural scale as a non-negative integer variable. Prediction intervals of 99%
around the trend for expected comfortably envelope the data,
notably including the Milky Way, which has hitherto been considered a
problematic outlier. Finally, we demonstrate how random intercept models can
incorporate information of each particular galaxy morphological type. Bayesian
variable selection methodology allows for automatically identifying galaxy
types with different productions of GCs, suggesting that on average S0 galaxies
have a GC population 35% smaller than other types with similar brightness.Comment: 14 pages, 12 figures. Accepted for publication in MNRA
A Conserved Bach Current
The Bach tensor and a vector which generates conformal symmetries allow a
conserved four-current to be defined. The Bach four-current gives rise to a
quasilocal two-surface expression for power per luminosity distance in the
Vaidya exterior of collapsing fluid interiors. This is interpreted in terms of
entropy generation.Comment: to appear in Class. Quantum Gra
Bloch-Like Quantum Multiple Reflections of Atoms
We show that under certain circumstances an atom can follow an oscillatory
motion in a periodic laser profile with a Gaussian envelope. These oscillations
can be well explained by using a model of energetically forbidden spatial
regions. The similarities and differences with Bloch oscillations are
discussed. We demonstrate that the effect exists not only for repulsive but
also for attractive potentials, i.e. quantum multiple reflections are also
possible.Comment: LaTeX, 7 pages, 7 figure
Experiência brasileira sobre captação, armazenamento, gestão e qualidade da água de chuva para consumo humano em comunidades rurais do Haiti.
O Haiti está entre os países considerados prioritários para a cooperação externa do governo brasileiro. É um dos mais pobres do mundo, enfrenta graves problemas com a falta de água potável, alto índice de contaminação tanto nas áreas urbanas como rurais, falta de coleta de lixo e de serviços elementares, como saúde e educação, inclusive sua capital Porto Príncipe. Por isso o governo e instituições brasileiras firmaram parcerias com instituições haitianas com o intuito de desenvolver juntos programas de captação e armazenamento de água de chuva, para tentar minimizar a intensa problemática que o país enfrenta neste setor. A partir de intercâmbios de técnicos Argentinos ao Brasil e posteriormente técnicos brasileiros no Haiti, foi idealizada a realização de uma Missão Tripartite (Argentina/Brasil/Haiti), com o objetivo de cooperar com o desenvolvimento de comunidades rurais do Haiti, na área de produção de alimentos e abastecimento de água potável. Desse modo, foi constituído um grupo de técnicos brasileiros, da Embrapa Hortaliças (Brasília-DF), Embrapa Semi-árido (Petrolina-PE) e o Instituto Regional da Pequena Agropecuária Apropriada, IRPAA (Juazeiro-BA) que assumiram a responsabilidade de capacitar uma equipe de técnicos Haitianos no Brasil, capacitar uma equipe de multiplicadores de organizações das comunidades rurais de Porto Príncipe, fazer avaliação da qualidade das águas de fontes principais e implantar um programa de construção de cisternas armazenamento e gestão de água de chuva para consumo humano e produção de alimentos em algumas comunidades rurais de Porto Príncipe
PARTICLE SIZE DISTRIBUTION CORRECTION METHOD USING A SIMULATED ANNEALING TECHNIQUE
The procedure for obtaining the particle size distribution by visual inspection of a sample involves stereological errors, given the cut of the sample. A cut particle, supposedly spherical, with radius R, will be counted as a circular particle with radius r, r≤R. The difference between r and R depends on how far from the center of the sphere the cut was performed. This introduces errors when the extrapolation of the properties from two to three dimensions during the analysis of a sample. The usual method is to correct the distribution by probabilistic functions, which have large errors. This paper presents a method to reduce the error inherent to this problem. The method is to compute a simulation of the preparation process in a sample whose structure can be described by non-penetrating spheres of various diameters which meet a known probability distribution function, for example, a log-logistic function, or even a constant function. For each distribution radius, a number of spheres is generated and virtually cut, generating a bi-dimensional (2D) distribution. The 2D curves of the spheres distribution obtained in this simulation are compared with that obtained by the experimental procedure and then the parameters of the threedimensional distribution function are adjusted until the 2D curves are similar to the experimental one using the optimization method Simulated Annealing for the curve-fitting. In future this method will be applied to the analysis of the oil reservoir rocks
Medium Modifications of Charm and Charmonium in High-Energy Heavy-Ion Collisions
The production of charmonia in heavy-ion collisions is investigated within a
kinetic theory framework simultaneously accounting for dissociation and
regeneration processes in both quark-gluon plasma (QGP) and hadron-gas phases
of the reaction. In-medium modifications of open-charm states (c-quarks,
D-mesons) and the survival of J/psi mesons in the QGP are included as inferred
from lattice QCD. Pertinent consequences on equilibrium charmonium abundances
are evaluated and found to be especially relevant to explain the measured
centrality dependence of the psi'/psi ratio at SPS. Predictions for recent
In-In experiments, as well as comparisons to current Au-Au data from RHIC, are
provided.Comment: 4 Latex pages including 4 eps figures and IOP style files. Talk given
at the 17th International Conference on Ultra-Relativistic Nucleus-Nucleus
Collisions, Quark Matter 2004, Oakland, CA USA, 11-17 Jan 2004. To appear in
J. Phys.
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