111,380 research outputs found
Manifold Parzen Windows
The similarity between objects is a fundamental element of many learning algorithms. Most non-parametric methods take this similarity to be fixed, but much recent work has shown the advantages of learning it, in particular to exploit the local invariances in the data or to capture the possibly non-linear manifold on which most of the data lies. We propose a new non-parametric kernel density estimation method which captures the local structure of an underlying manifold through the leading eigenvectors of regularized local covariance matrices. Experiments in density estimation show significant improvements with respect to Parzen density estimators. The density estimators can also be used within Bayes classifiers, yielding classification rates similar to SVMs and much superior to the Parzen classifier. La similaritĂ© entre objets est un Ă©lĂ©ment fondamental de plusieurs algorithmes d'apprentissage. La plupart des mĂ©thodes non paramĂ©triques supposent cette similaritĂ© constante, mais des travaux rĂ©cents ont montrĂ© les avantages de les apprendre, en particulier pour exploiter les invariances locales dans les donnĂ©es ou pour capturer la variĂ©tĂ© possiblement non linĂ©aire sur laquelle reposent la plupart des donnĂ©es. Nous proposons une nouvelle mĂ©thode d'estimation de densitĂ© Ă noyau non paramĂ©trique qui capture la structure locale d'une variĂ©tĂ© sous-jacente en utilisant les vecteurs propres principaux de matrices de covariance locales rĂ©gularisĂ©es. Les expĂ©riences d'estimation de densitĂ© montrent une amĂ©lioration significative sur les estimateurs de densitĂ© de Parzen. Les estimateurs de densitĂ© peuvent aussi ĂȘtre utilisĂ©s Ă l'intĂ©rieur de classificateurs de Bayes, menant Ă des taux de classification similaires Ă ceux des SVMs, et trĂšs supĂ©rieurs au classificateur de Parzen.density estimation, non-parametric models, manifold models, probabilistic classifiers, estimation de densitĂ©, modĂšles non paramĂ©triques, modĂšles de variĂ©tĂ©s, classification probabiliste
Génératrice à aimants permanents à flux axial à grand diamÚtre avec entrefer immergé
Cette Ă©tude propose une mĂ©thode de modĂ©lisation et de conception adaptĂ©e aux machines Ă flux axial et Ă Double Stator (poly-entrefer) destinĂ©e Ă ĂȘtre intĂ©grĂ©e comme gĂ©nĂ©ratrice pour une hydrolienne RIM-DRIVEN de grande puissance. La particularitĂ© du concept RIM-DRIVEN ou Ă entrainement circonfĂ©rentiel rĂ©side dans le fait que la machine Ă©lectrique se situe sur la pĂ©riphĂ©rie de lâhĂ©lice. De plus, dans cette Ă©tude, lâentrefer de la machine est considĂ©rĂ© immergĂ© dans lâeau de mer. Les particularitĂ©s du systĂšme imposent de mettre au point des modĂšles de dimensionnement adaptĂ©s. Ainsi, un modĂšle Ă©lectromagnĂ©tique analytique 2D inversĂ© permettant le calcul des dimensions gĂ©omĂ©triques principales est prĂ©sentĂ©. De mĂȘme, un modĂšle thermique spĂ©cifique aux machines Ă entrefer immergĂ© est dĂ©crit. Ces modĂšles permettent dâestimer la masse et le coĂ»t des parties actives. Cette machine Ă flux axial est comparĂ©e en termes de coĂ»ts matiĂšres, masses et comportement thermique avec une machine Ă flux radial Ă aimants permanents dimensionnĂ©e pour un mĂȘme cahier des charges. Il en ressort clairement que la machine Ă flux axial double stator est thermiquement moins contrainte que les machines Ă simple stator
Large deviations of a velocity jump process with a Hamilton-Jacobi approach
We study a random process on R n moving in straight lines and changing
randomly its velocity at random exponential times. We focus more precisely on
the Kolmogorov equation in the hyperbolic scale (t, x, v) t , x
, v, with \textgreater{} 0, before proceeding to a
Hopf-Cole transform, which gives a kinetic equation on a potential. We show
convergence as 0 of the potential towards the viscosity
solution of a Hamilton-Jacobi equation t\"I + H (x\"I) = 0
where the hamiltonian may lack C 1 regularity, which is quite unseen in this
type of studies. R{\'e}sum{\'e
The determinants of urban public transport: an international comparison and econometric analysis
The analysis presented in this paper is based on the database created by the UITP (International Association of Public Transport), "The Millennium Cities Database", which covers the public transport systems in 100 of the world's cities. It contains data on demography, urban structure, transport networks, daily mobility, environmental impacts, etc. Our analysis demonstrates the contrasts between European and American travel practices. It explores possible links between public transport market share and geographical and economic conditions on the one hand and the characteristics and performances of public transport systems on the other. Our research has generated an explanatory econometric model for public transport market share. To end with, a consideration of the levers that can be used to influence the public transport system leads into a discussion about the future of cities with ''European urban mobility'' and the danger of a slide towards ''American urban mobility'' taking place.Transport systems ; Urban mobility ; Transport policy ; Public transport
Les conflits d'usage des espaces périurbains et le contentieux administratif. Le cas de la région Ile-de-France..
Lâarticle porte sur une analyse des conflits dâusages dâespace, traduits par les requĂȘtes devant la justice administrative française de 1981 Ă 2005. Le terrain dâĂ©tude est le pĂ©riurbain francilien, territoire qui connaĂźt une forte urbanisation et oĂč la diversitĂ© des modes dâoccupation du sol nĂ©cessite une meilleure comprĂ©hension de la dynamique spatiale et temporelle de la conflictualitĂ©. LâĂ©tude empirique montre une corrĂ©lation entre lâaugmentation des conflits dâusage en Ăle-de-France et la dynamique de pĂ©riurbanisation. Elle met en Ă©vidence un couplage entre certains types de conflits et certaines caractĂ©ristiques du territoire : les problĂšmes dâurbanisme font souvent lâobjet conflictuel dominant dans les communes plutĂŽt aisĂ©es, tandis que lâopposition aux infrastructures publiques se situe frĂ©quemment dans les communes Ă forte urbanisation. Les nuisances des installations classĂ©es sont souvent localisĂ©es dans des communes plutĂŽt peu aisĂ©es.The article provides an analysis of land-use conflicts extract from the rulings of French Administrative Courts from 1981 to 2005. It focuses on Parisâs suburb, where the urbanisation process and the diversity of land-use require a deeper comprehension of the problem. Our results show that the land-use conflictâs evolution is correlated with the urbanisation process. They also detect a coupling phenomenon between conflictâs type and territoryâs parameters : urbanism disputes often arise in wealthy municipalities, whereas oppositions to public infrastructure have particularly risen in strongly urbanising towns. Classified industrial facilityâs nuisances have been found in unfortunate municipalities.Ăle-de-France; contentieux; pĂ©riurbanisation; conflit dâusage; Paris region; periurbanisation; land-use conflict; litigation;
Accelerated Expansion as Predicted by an Ether Theory of Gravitation
Cosmology is investigated within a new, scalar theory of gravitation, which
is a preferred-frame bimetric theory with flat background metric. Before coming
to cosmology, the motivation for an " ether theory " is exposed at length; the
investigated concept of ether is presented: it is a compressible fluid, and
gravity is seen as Archimedes' thrust due to the pressure gradient in that
fluid. The construction of the theory is explained and the current status of
the experimental confrontation is analysed, both in some detail. An analytical
cosmological solution is obtained for a general form of the energy-momentum
tensor. According to that theory, expansion is necessarily accelerated, both by
vacuum and even by matter. In one case, the theory predicts expansion, the
density increasing without limit as time goes back to infinity. High density is
thus obtained in the past, without a big-bang singularity. In the other case,
the Universe follows a sequence of (non-identical) contraction-expansion
cycles, each with finite maximum energy density; the current expansion phase
will end by infinite dilution in some six billions of years. The density ratio
of the present cycle (ratio of the maximum to current densities) is not
determined by the current density and the current Hubble constant H0, unless a
special assumption is made. Since cosmological redshifts approaching z = 4 are
observed, the density ratio should be at least 100. From this and the estimate
of H0, the time spent since the maximum density is constrained to be larger
than several hundreds of billions of years. Yet if a high density ratio,
compatible with the standard explanation for the light elements and the 2.7 K
radiation, is assumed, then the age of the Universe is much larger still.Comment: 32 pages, Post-Script. v4 : Section 2 (general presentation of the
theory and its motivation) still reinforced, Subsection 5.3 added (Comments
on accelerated expansion and infinite dilution). To appear in "Physics
Essays", Vol. 14, No. 1, 200
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