4,702 research outputs found
Ecological intuition versus economic "reason"
This article discusses the discount rate to be used in projects that aimed at improving the environment. The model has two different goods, one is the usual consumption good whose production may increase exponentially, the other is an environmental good whose quality remains limited. The stylized world we describe is fully determined by four parameters, reflecting basic preferences "ecological" and intergenerational concerns and feasibility constraints. We define an ecological discount rate and examine its connections with the usual interest rate and the optimized growth rate. We discuss, in this simple world, a variety of forms of the precautionary principle.discount rate ; ecological discount rate ; environmental goods ; relative prices ; irreversible damage ; precautionnary principle
Les apprentissages informels au sein des associations dans une société de connaissances en mutation
Atelier 22 : Travail social et bénévolatDerrière une vision classique du savoir dans l'accumulation de connaissances de type académique, se joue une mutation importante dans nos sociétés éducatives. Dans nos recherches, nous nous sommes intéressés à l'observation de parcours où les expériences de la vie quotidienne peuvent être porteuses de connaissances. Pour identifier ces processus d'apprentissage informel, nous avons " interrogé " des bénévoles au sein des associations sur leur parcours identitaire. Les récits recueillis et retranscrits ont fait l'objet d'une analyse de contenu à l'aide du logiciel d'analyse statistique Alceste. Ces observations mettent en évidence la richesse des apprentissages souvent informels dans les tiers lieux de la vie quotidienne, et des modes de transmission originaux au sein de réseaux sociaux électifs
Linear diffusion with singular absorption potential and/or unbounded convective flow: the weighted space approach
In this paper we prove the existence and uniqueness of very weak solutions to
linear diffusion equations involving a singular absorption potential and/or an
unbounded convective flow on a bounded open set of . In most of
the paper we consider homogeneous Dirichlet boundary conditions but we prove
that when the potential function grows faster than the distance to the boundary
to the power -2 then no boundary condition is required to get the uniqueness of
very weak solutions. This result is new in the literature and must be
distinguished from other previous results in which such uniqueness of solutions
without any boundary condition was proved for degenerate diffusion operators
(which is not our case). Our approach, based on the treatment on some distance
to the boundary weighted spaces, uses a suitable regularity of the solution of
the associated dual problem which is here established. We also consider the
delicate question of the differentiability of the very weak solution and prove
that some suitable additional hypothesis on the data is required since
otherwise the gradient of the solution may not be integrable on the domain
Paper Session II-A - Operational Evolution in the Ariane Launch Process
Space transportation is entering into a strong development and evolution phase. Commercial business is moving in this area. The access to space is enlarging it’s capacities to cope with new missions. A lot of new launch systems are foreseen by the turning of the century. Defense, Science and commercial appliances are presenting new requirements, new performances with a common basis : how to render more flexible and less costly the access to space
Hyperspectral Imaging for Peach Ripening Assessment
The present research is focused on the application of artificial vision to peach ripening assessment, avoiding multiplicative and additive effect. Original images were acquired with a hyperspectral camera. Vision allows a spatially detailed determination of the ripening stage of the fruit. Optical indexes are proposed, based on the combination of wavelengths close to the chlorophyll absorption peak at 680 nm. Ind1 corresponds approximately to the depth of the absorption peak, and Ind2 corresponds to the relative absorption peak. An artificial image of each index was obtained by computing the corresponding reflectance images. Score images have been also computed from Principal Components and Partial Least Squares Analysis. In any case the best performances correspond to such images that correct multiplicative and additive effects. Ind2 is the preferred index; it showed the highest discriminating power between ripening stages and no influence of convexity. Ind2 also allowed the differentiation of ripening regions within the fruits, and it showed the evolution of those regions during ripening. This fact has been also observed in some of the score image
Lithium-6 : Evolution from Big Bang to Present
The primordial abundances of Deuterium, he4, and li7 are crucial to
determination of the baryon density of the Universe in the framework of
standard Big Bang nucleosynthesis (BBN). li6 which is only produced in tiny
quantities and it is generally not considered to be a cosmological probe.
However, recent major observational advances have produced an estimate of the
li6/li7 ratio in a few very old stars in the galactic halo which impacts the
question whether or not the lithium isotopes are depleted in the outer layers
of halo stars, through proton induced reactions at the base of (or below) the
convective zone. li6 is a pure product of spallation through the major
production reactions, fast oxygen and alphas interacting on interstellar H, He
(especially in the early Galaxy). The rapid nuclei are both synthesized and
accelerated by SN II. In this context, the \li6 evolution should go in step
with that of beryllium and boron, recently observed by the Keck and HST
telescopes. Li6 adds a new constraint on the early spallation in the Galaxy. In
particular, if confirmed, the Li6/Be9 ratio observed in two halo stars (HD
84937, BD +263578) gives strong boundary conditions on the composition and the
spectrum of the rapid particles involved. We show that Li6 is essentially
intact in halo stars, and a fortiori \li7. We can define a range of the Li6
abundance in the very early Galaxy consistent with Big Bang nucleosynthesis
(5.6 10(-14) to 3. 10(-13) . Following the evolution at increasing metallicity,
we explain the abundance in the solar system within a factor of about 2.Comment: 16 pages, 4 figure
Hyperspectral images segmentation: a proposal
Hyper-Spectral Imaging (HIS) also known as chemical or spectroscopic imaging is an emerging technique that combines
imaging and spectroscopy to capture both spectral and spatial information from an object. Hyperspectral images are
made up of contiguous wavebands in a given spectral band. These images provide information on the chemical
make-up profile of objects, thus allowing the differentiation of objects of the same colour but which possess make-up
profile. Yet, whatever the application field, most of the methods devoted to HIS processing conduct data analysis without
taking into account spatial information.Pixels are processed individually, as an array of spectral data without any spatial
structure. Standard classification approaches are thus widely used (k-means, fuzzy-c-means hierarchical
classification...). Linear modelling methods such as Partial Least Square analysis (PLS) or non linear approaches like
support vector machine (SVM) are also used at different scales (remote sensing or laboratory applications). However,
with the development of high resolution sensors, coupled exploitation of spectral and spatial information to process
complex images, would appear to be a very relevant approach. However, few methods are proposed in the litterature.
The most recent approaches can be broadly classified in two main categories. The first ones are related to a direct
extension of individual pixel classification methods using just the spectral dimension (k-means, fuzzy-c-means or FCM,
Support Vector Machine or SVM). Spatial dimension is integrated as an additionnal classification parameter (Markov
fields with local homogeneity constrainst [5], Support Vector Machine or SVM with spectral and spatial kernels
combination [2], geometrically guided fuzzy C-means [3]...). The second ones combine the two fields related to each
dimension (spectral and spatial), namely chemometric and image analysis. Various strategies have been attempted. The
first one is to rely on chemometrics methods (Principal Component Analysis or PCA, Independant Component Analysis or
ICA, Curvilinear Component Analysis...) to reduce the spectral dimension and then to apply standard images processing technics on the resulting score images i.e. data projection on a subspace. Another approach is to extend the definition
of basic image processing operators to this new dimensionality (morphological operators for example [1, 4]).
However, the approaches mentioned above tend to favour only one description either directly or indirectly (spectral or
spatial). The purpose of this paper is to propose a hyperspectral processing approach that strikes a better balance in the
treatment of both kinds of information....Cet article présente une stratégie de segmentation d’images hyperspectrales liant de façon symétrique et
conjointe les aspects spectraux et spatiaux. Pour cela, nous proposons de construire des variables latentes
permettant de définir un sous-espace représentant au mieux la topologie de l’image. Dans cet article, nous
limiterons cette notion de topologie à la seule appartenance aux régions. Pour ce faire, nous utilisons d’une
part les notions de l’analyse discriminante (variance intra, inter) et les propriétés des algorithmes de
segmentation en région liées à celles-ci. Le principe générique théorique est exposé puis décliné sous la
forme d’un exemple d’implémentation optimisé utilisant un algorithme de segmentation en région type split
and merge. Les résultats obtenus sur une image de synthèse puis réelle sont exposés et commentés
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