1,762 research outputs found
Geographic space, assets, livelihoods and well-being in rural Central America
"This paper uses an asset-base framework to analyze the determinants of rural growth and sustainable poverty reduction for the three poorest countries in Central America: Guatemala, Honduras and Nicaragua...Using a combination of GIS mapping techniques, quantitative household analysis, and qualitative analyses of assets and livelihoods, the authors generate a description of rural territories that recognizes the differential effects of policies and asset bundles across space and households. They identify the combinations of human, natural and physical, social and location-specific assets that matter most to raise household well-being and take advantage of prospects for poverty-reducing growth." from Authors' AbstractPoverty reduction ,rural livelihoods ,Households Economic aspects ,
Density waves in the shearing sheet I. Swing amplification
The shearing sheet model of a galactic disk is studied anew. The theoretical
description of its dynamics is based on three building blocks: Stellar orbits,
which are described here in epicyclic approximation, the collisionless
Boltzmann equation determining the distribution function of stars in phase
space, and the Poisson equation in order to take account of the self-gravity of
the disk. Using these tools I develop a new formalism to describe perturbations
of the shearing sheet. Applying this to the unbounded shearing sheet model I
demonstrate again how the disturbances of the disk evolve always into `swing
amplified' density waves, i.e. spiral-arm like, shearing density enhancements,
which grow and decay while the wave crests swing by from leading to trailing
orientation. Several examples are given how such `swing amplification' events
are incited in the shearing sheet.Comment: small corrections, uses new A&A style fil
Evidence for a meteoritic origin of the September 15, 2007, Carancas crater
On September 15th, 2007, around 11:45 local time in Peru, near the Bolivian border, the
atmospheric entry of a meteoroid produced bright lights in the sky and intense detonations. Soon after,
a crater was discovered south of Lake Titicaca. These events have been detected by the Bolivian
seismic network and two infrasound arrays operating for the Comprehensive Nuclear-Test-Ban Treaty
Organization, situated at about 80 and 1620 km from the crater. The localization and origin time
computed with the seismic records are consistent with the reported impact. The entry elevation and
azimuthal angles of the trajectory are estimated from the observed signal time sequences and backazimuths.
From the crater diameter and the airwave amplitudes, the kinetic energy, mass and
explosive energy are calculated. Using the estimated velocity of the meteoroid and similarity criteria
between orbital elements, an association with possible parent asteroids is attempted. The favorable
setting of this event provides a unique opportunity to evaluate physical and kinematic parameters of
the object that generated the first actual terrestrial meteorite impact seismically recorded
Propagators in Lagrangian space
It has been found recently that propagators, e.g. the cross-correlation
spectra of the cosmic fields with the initial density field, decay
exponentially at large-k in an Eulerian description of the dynamics. We explore
here similar quantities defined for a Lagrangian space description. We find
that propagators in Lagrangian space do not exhibit the same properties: they
are found not to be monotonic functions of time, and to track back the linear
growth rate at late time (but with a renormalized amplitude). These results
have been obtained with a novel method which we describe alongside. It allows
the formal resummation of the same set of diagrams as those that led to the
known results in Eulerian space. We provide a tentative explanation for the
marked differences seen between the Eulerian and the Lagrangian cases, and we
point out the role played by the vorticity degrees of freedom that are specific
to the Lagrangian formalism. This provides us with new insights into the
late-time behavior of the propagators.Comment: 14 pages, 5 figure
Class of invariants for the 2D time-dependent Landau problem and harmonic oscillator in a magnetic field
We consider an isotropic two dimensional harmonic oscillator with arbitrarily
time-dependent mass and frequency in an arbitrarily
time-dependent magnetic field . We determine two commuting invariant
observables (in the sense of Lewis and Riesenfeld) in terms of some
solution of an auxiliary ordinary differential equation and an orthonormal
basis of the Hilbert space consisting of joint eigenvectors of
. We then determine time-dependent phases such that
the are solutions of the
time-dependent Schr\"odinger equation and make up an orthonormal basis of the
Hilbert space. These results apply, in particular to a two dimensional Landau
problem with time-dependent , which is obtained from the above just by
setting . By a mere redefinition of the parameters, these
results can be applied also to the analogous models on the canonical
non-commutative plane.Comment: 13 pages, 3 references adde
Approche semi-quantitative de la minéralisation des aquifères schisteux en zone équatoriale de transition : Cas de la région Sikensi-Agboville (Côte d’Ivoire)
L’aquifère des schistes (Sikensi-Agboville) compte d’importants ouvrages permettant l’approvisionnement en eau potable des populations locales. Toute fois, la couleur et le goût inhabituels, par endroit, des eaux prélevées sont quelques peu inquiétants, bien qu’aucun risque sanitaire grave n’est jusqu’à présent décelé. Pour tenter d’apporter un élément de compréhension à cette question, nous utilisons la géochimie des roches, laminéralogie et l’hydrochimie pour étudier les interactions entre l’eau et son aquifère. Les résultats montrent que les schistes en question sont constitués d’albite, de chlorites, de micas noirs, d’épidotes, du sphène et de l’apatite, susceptibles de fournir leurs cations majeurs à la nappe. La dissolution incongruente de ces minéraux au contact de l’eau à pH 6 et à ~26 °C, montre que le Na+ provient majoritairement de l’albite et le Mg2+ des chlorites, qui sont en proportion considérable dans les schistes, avec des concentrations respectives de ~0,463 mmol.L-1 et de ~0,171 mmol.L-1. Un faible taux de 0,025 mmol.L-1 de Mg2+ est fourni par la biotite tandis que le K+, avec une concentration de ~0,018 mmol.L-1, provient à la fois de la biotite et de l’annite. La principale source du Ca2+ concerne les épidotes, avec un taux de ~0,188 mmol.L-1 puis viennent l’apatite et le sphène, avec des taux moyens respectifs de 0,251 mmol.L-1 et de ~0,090 mmol.L-1.Mots clés: Nappe, silicates, hydrolyse, interaction, concentration, cations majeurs
Simultaneous infection of Ixodes ricinus nymphs by two Borrelia burgdorferi sensu lato species: possible implications for clinical manifestations.
info:eu-repo/semantics/publishe
Reduced Gutzwiller formula with symmetry: case of a finite group
We consider a classical Hamiltonian on , invariant by a
finite group of symmetry , whose Weyl quantization is a
selfadjoint operator on . If is an irreducible
character of , we investigate the spectrum of its restriction
to the symmetry subspace of
coming from the decomposition of Peter-Weyl. We give
reduced semi-classical asymptotics of a regularised spectral density describing
the spectrum of near a non critical energy . If
is compact, assuming that periodic orbits are
non-degenerate in , we get a reduced Gutzwiller trace formula
which makes periodic orbits of the reduced space appear. The
method is based upon the use of coherent states, whose propagation was given in
the work of M. Combescure and D. Robert.Comment: 20 page
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