3,088 research outputs found
Pebble accretion at the origin of water in Europa
Despite the fact that the observed gradient in water content among the
Galilean satellites is globally consistent with a formation in a circum-Jovian
disk on both sides of the snowline, the mechanisms that led to a low water mass
fraction in Europa () are not yet understood. Here, we present new
modeling results of solids transport in the circum-Jovian disk accounting for
aerodynamic drag, turbulent diffusion, surface temperature evolution and
sublimation of water ice. We find that the water mass fraction of pebbles
(e.g., solids with sizes of 10 -- 1 m) as they drift inward is globally
consistent with the current water content of the Galilean system. This opens
the possibility that each satellite could have formed through pebble accretion
within a delimited region whose boundaries were defined by the position of the
snowline. This further implies that the migration of the forming satellites was
tied to the evolution of the snowline so that Europa fully accreted from
partially dehydrated material in the region just inside of the snowline.Comment: Accepted for publication in Ap
Combining Parametric and Non-parametric Algorithms for a Partially Unsupervised Classification of Multitemporal Remote-Sensing Images
In this paper, we propose a classification system based on a multiple-classifier architecture, which is aimed at updating land-cover maps by using multisensor and/or multisource remote-sensing images. The proposed system is composed of an ensemble of classifiers that, once trained in a supervised way on a specific image of a given area, can be retrained in an unsupervised way to classify a new image of the considered site. In this context, two techniques are presented for the unsupervised updating of the parameters of a maximum-likelihood (ML) classifier and a radial basis function (RBF) neural-network classifier, on the basis of the distribution of the new image to be classified. Experimental results carried out on a multitemporal and multisource remote-sensing data set confirm the effectiveness of the proposed system
First disk-resolved spectroscopy of (4) Vesta
Vesta, the second largest Main Belt asteroid, will be the first to be
explored in 2011 by NASA's Dawn mission. It is a dry, likely differentiated
body with spectrum suggesting that is has been resurfaced by basaltic lava
flows, not too different from the lunar maria.
Here we present the first disk-resolved spectroscopic observations of an
asteroid from the ground. We observed (4) Vesta with the ESO-VLT adaptive
optics equipped integral-field near-infrared spectrograph SINFONI, as part of
its science verification campaign. The highest spatial resolution of ~90 km on
Vesta's surface was obtained during excellent seeing conditions (0.5") in
October 2004.
We observe spectral variations across Vesta's surface that can be interpreted
as variations of either the pyroxene composition, or the effect of surface
aging. We compare Vesta's 2 micron absorption band to that of
howardite-eucrite-diogenite (HED) meteorites that are thought to originate from
Vesta, and establish particular links between specific regions and HED
subclasses. The overallcomposition is found to be mostly compatible with
howardite meteorites, although a small area around 180 deg. East longitude
could be attributed to a diogenite-rich spot. We finally focus our spectral
analysis on the characteristics of Vesta's bright and dark regions as seen from
Hubble Space Telescope's visible and Keck-II's near-infrared images.Comment: 13 pages, 11 figures, 3 table
Lo normal y lo polĂtico
Las obras de Montesquieu y Durkheim, separadas comĂșnmente por corrientes disciplinarias, muestran sin embargo importantes coincidencias tanto en los conceptos centrales que desarrollaron como en las aporĂas que debieron sortear al intentar responder al problema fundador del pensamiento moderno: la irreductible diversidad que caracteriza el mundo humano. Este artĂculo propone una visiĂłn conjunta de sus obras a partir de un anĂĄlisis paralelo de la nociĂłn de conveniencia (convenance) en la obra Montesquieu y de patologĂa social (pathologie sociale) en la obra de Durkheim. Se intenta mostrar asimismo los lĂmites a los que se enfrentĂł cada una asĂ como los legados que dejaron en la filosofĂa social contemporĂĄnea
Use of programme budgeting and marginal analysis to set priorities for local NHS dental services: learning from the north east of England
Background - Priority setting is necessary where competing demands exceed the finite resources available. The aim of the study was to develop and test a prioritization framework based upon programme budgeting and marginal analysis (PBMA) as a tool to assist National Health Service (NHS) commissioners in their management of resources for local NHS dental services.
Methods - Twenty-seven stakeholders (5 dentists, 8 commissioners and 14 patients) participated in a case-study based in a former NHS commissioning organization in the north of England. Stakeholders modified local decision-making criteria and applied them to a number of different scenarios.
Results - The majority of financial resources for NHS dental services in the commissioning organization studied were allocated to primary care dental practitionersâ contracts in perpetuity, potentially constraining commissionersâ abilities to shift resources. Compiling the programme budget was successful, but organizational flux and difficulties engaging local NHS commissioners significantly impacted upon the marginal analysis phase.
Conclusions - NHS dental practitionersâ contracts resemble budget-silos which do not facilitate local resource reallocation. âContext-specificâ factors significantly challenged the successful implementation and impact of PBMA. A local PBMA champion embedded within commissioning organizations should be considered. Participants found visual depiction of the cost-value ratio helpful during their initial priority setting deliberations
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