1,510 research outputs found
Galactic positrons and electrons from astrophysical sources and dark matter
A very interesting puzzle about the origin of electron and positron cosmic
rays is deduced from the latests experimental results. We model the propagation
of such cosmic rays in terms of a successfully tested two--zone propagation
model. Several theoretical uncertainties -- like ones related to propagation --
are considered to study different types of electron and positron sources: dark
matter annihilation, secondary production, and supernova remnants.Comment: 3 pages, 1 figure. Proceedings for conference "Topics in
Astroparticle and Underground Physics" (TAUP2009). Rome, July 1-5, 200
Determination of characteristic relaxation times and their significance in glassy disordered insulators
We revisit the field effect procedure used to characterise the slow dynamics
of glassy Anderson insulators. It is shown that in the slowest systems the
procedure fails and the "characteristic" time values extracted are not
intrinsic but determined by the experimental procedure itself. In other cases
(like lightly doped indium oxide) qualitative indications about the dynamics
might be obtained, however the times extracted cannot be seen as characteristic
relaxation times of the system in any simple manner, and more complete
experiments are necessary. Implications regarding the effect of carrier
concentration on the emergence of glassiness are briefly outlined.Comment: published with minor proof correction
Screening and conductance relaxations in insulating granular aluminium thin films
We have recently found in insulating granular Al thin film a new experimental
feature (Delahaye et al., Phys. Rev. Lett. 106, 186602, 2011), namely the
existence of a conductance relaxation that is not sensitive to gate voltage
changes. This conductance relaxation is related to the existence of a
metallic-like screening in the film and can be used to estimate its
characteristic length scale. In the present paper, we give some experimental
details on how this feature was measured and present our first results on the
screening length temperature dependence.Comment: 14th Transport in interacting disordered systems (TIDS14) conference,
September 5-8 2011, Acre (Israel
Observation of thermally activated glassiness and memory dip in a-NbSi insulating thin films
We present electrical conductance measurements on amorphous NbSi insulating
thin films. These films display out-of equilibrium electronic features that are
markedly different from what has been reported so far in disordered insulators.
Like in the most studied systems (indium oxide and granular Al films), a slow
relaxation of the conductance is observed after a quench to liquid helium
temperature which gives rise to the growth of a memory dip in MOSFET devices.
But unlike in these systems, this memory dip and the related conductance
relaxations are still visible up to room temperature, with clear signatures of
a temperature dependent dynamics
Dark Matter detection via lepton cosmic rays
Recent observations of lepton cosmic rays, coming from the PAMELA and FERMI
experiments, have pushed our understanding of the interstellar medium and
cosmic rays sources to unprecedented levels. The imprint of dark matter on
lepton cosmic rays is the most exciting explanation of both PAMELA's positron
excess and FERMI's total flux of electrons. Alternatively, supernovae are
astrophysical objects with the same potential to explain these observations. In
this work, we present an updated study of the astrophysical sources of lepton
cosmic rays and the possible trace of a dark matter signal on the positron
excess and total flux of electrons.Comment: 6 pages and 3 figures. Proceedings for PASCOS 2010, Valencia, Spai
Measurement of the sign of the spectroscopic quadrupole moment for the 2 state in Se: no evidence for oblate shape
Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of 70Se ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation γ rays in the highly segmented MINIBALL γ-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2+ state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2+ state in 70Se, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes
A comparative study for merging and sequencing flows in TMA
Se ha previsto diversos escenarios para explorar el futuro Sistema de Transporte Aéreo. De acuerdo con EUROCONTROL, el escenario más probable de los movimientos de vuelo IFR en Europa hasta 2035, prevé 14,4 millones de vuelos, lo cual es 50% más que en 2012. [10] El aumento en el tráfico aéreo se está traduciendo en diversos problemas tanto en el lado aire como en tierra. En el lado aire, se hace más evidente en el espacio aéreo circundante a los aeropuertos, donde las llegadas y salidas sirven a un gran número de aviones que están sometidos a diversos problemas logísticos que continuamente hay que resolver para asegurarse de que cada vuelo y pasajero viaje con seguridad y eficiencia hasta su destino final. La presente investigación propone una metodología basada en algoritmos evolutivos para resolver el problema de fusión y secuenciación de un conjunto de aeronaves. Para dicho fin, se realiza un análisis del diseño de la topología de las rutas de aterrizaje. Este enfoque propone para cada aeronave una nueva ruta y perfil de velocidad con el fin de evitar posibles conflictos en los puntos de fusión, mientras que se mantienen las normas de separación de la OACI. La función objetivo se basa en adquirir la desviación mínima de cada aeronave con respecto a su plan de vuelo original. El algoritmo se ha aplicado con éxito en el aeropuerto de Gran Canaria en España con muestras de la demanda de tráfico reales para lo que se ha encontrado una configuración óptima para la alimentación óptima pista.The imminent growing in the Air transport System has forecast diverse scenarios to explore the future of the aviation. According to EUROCONTROL forecast of IFR flight movements in Europe up to 2035, the most likely scenario predicts 14.4 million flights, which is 50% more than in 2012. [10] This increase in the air traffic is translating into diverse problems in the airside and landside. In the airside, it becomes more evident in the airspace surrounding airports, where the arrivals and departures serve a large number of aircraft which are subjected to many logistical problems that must continuously be solved to make sure each flight and passenger travels safely and efficiently. The present research proposes a methodology based on evolutionary algorithms to tackle the merging and sequencing problem of a set of aircraft by analyzing the topology design of the landing routes. It is proposed to merge the arrivals from different routes by changing the topology design of the STARs (Standard Terminal Arrival Route). The approach proposes to each aircraft a new route and speed profile in order to avoid potential conflicts at merging points while maintaining ICAO separation standards. The objective function is based on achieving the minimum deviation of each aircraft from it original flight plan. This algorithm has been successfully applied to Gran Canaria airport in Spain with real traffic demand samples for which conflict free flow merging is produced smoothly with optimal runway feeding.Grupo de Transporte Aéreo - Grupo de Ingeniería Aplicada a la Industri
OPserver: interactive online-computations of opacities and radiative accelerations
Codes to compute mean opacities and radiative accelerations for arbitrary
chemical mixtures using the Opacity Project recently revised data have been
restructured in a client--server architecture and transcribed as a subroutine
library. This implementation increases efficiency in stellar modelling where
element stratification due to diffusion processes is depth dependent, and thus
requires repeated fast opacity reestimates. Three user modes are provided to
fit different computing environments, namely a web browser, a local workstation
and a distributed grid.Comment: 5 pages, 1 figur
Des cultures temporaires face à la forêt classée. Exemples des paysages à l'ouest du Burkina Faso
Cette étude se propose d\u27analyser le rôle récent des espaces protégés sur l\u27évolution des paysages à l\u27ouest du Burkina Faso. L\u27analyse porte à la fois sur le changement du paysage-objet, mais aussi sur les représentations que ces espaces nouvellement protégés cristallisent. À partir d\u27une cartographie multidate et d\u27enquêtes menées sur une dizaine de terroirs villageois, situés à la périphérie d\u27une forêt classée (province du Tuy), nous tentons de comprendre comment ce découpage étatique est actuellement lu par les agriculteurs. Dans les champs, à travers l\u27observation de la terre, des jachères et des changements agricoles, nous mettons en évidence différentes pratiques et perceptions du paysage par les agriculteurs. Les modalités d\u27accès au foncier fortement liées au contexte local (position sociale de l\u27individu, saturation spatiale du terroir) semblent fortement influencer les pratiques et les représentations du paysage. Malgré les importantes mutations relevées, nous remarquons la permanence de formes et de comportements (habitat, culture temporaire, bois sacrés...) attestant de la forte dynamique locale de ces campagnes du pays Bwa
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