3,662 research outputs found
Evaluation of the thermal and hydraulic performances of a very thin sintered copper flat heat pipe for 3D microsystem packages
The reported research work presents numerical studies validated by
experimental results of a flat micro heat pipe with sintered copper wick
structure. The objectives of this project are to produce and demonstrate the
efficiency of the passive cooling technology (heat pipe) integrated in a very
thin electronic substrate that is a part of a multifunctional 3-D electronic
package. The enhanced technology is dedicated to the thermal management of high
dissipative microsystems having heat densities of more than 10W/cm2. Future
applications are envisaged in the avionics sector. In this research 2D
numerical hydraulic model has been developed to investigate the performance of
a very thin flat micro heat pipe with sintered copper wick structure, using
water as a refrigerant. Finite difference method has been used to develop the
model. The model has been used to determine the mass transfer and fluid flow in
order to evaluate the limits of heat transport capacity as functions of the
dimensions of the wick and the vapour space and for various copper spheres
radii. The results are presented in terms of liquid and vapour pressures within
the heat pipe. The simulated results are validated by experiments and proved
that the method can be further used to predict thermal performance of the heat
pipe and to optimise its design.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Income segregation and suburbanization in France: a discrete choice approach
National audienceThis paper focuses on residential sorting by social and ethnic status in large French urban areas. Three major determinants of segregation are stressed in the economic literature (i) Alonso sorting based on distance, due to the trade-off between land consumption and accessibility to the central city, (ii) sorting based on local householdsâ income, due to the taste for endogenous amenities produced by residentsâ income and (iii) Tiebout sorting over jurisdictions, due to the taste for local public goods. The last two mechanisms result in an interjurisdictional sorting according to jurisdictionâs average household income, while the first one leads to a radioconcentric sorting. Our objective is to assess the relative importance of these two types of sorting. Our methodology draws on Schmidheiny (2006). First, a conditional logit model is estimated for each urban area, in which moving households are assumed to sort based on jurisdictionsâ distance to the central city and jurisdictionsâ mean household income (as a proxy for the level of endogenous amenities and local public goods). Second, our estimation results are used to simulate the counterfactual residential patterns that would prevail if, alternatively, one or the other of these segregation channels were inactive. The contribution of the two types of sorting to the social and ethnic segregation is finally appreciated by comparing the values of dissimilarity indexes computed on the basis of the observed and counterfactual residential distributions of households. Interjurisdictional sorting based on income emerges as the primary cause of social segregation among wage-earning households. On the contrary, Alonso-type sorting appears to be the main driver of segregation between economically active and inactive households, as well as between French-citizen and Foreign-citizen households
Coûts environnementaux du développement périurbain : impact des configurations urbaines et des choix résidentiels
[Departement_IRSTEA]Territoires [TR1_IRSTEA]DTAM [Axe_IRSTEA]DTAM1-REPRO [Axe_IRSTEA]DTAM-QT1-INEGALITESCe projet de recherche part du constat que la littĂ©rature existante sur la durabilitĂ© des espaces pĂ©riurbains n'a pas apportĂ© de rĂ©ponse sur deux points particuliers. En premier lieu, la question du transport est gĂ©nĂ©ralement considĂ©rĂ©e du seul point de vue du transport de personnes, dans une optique d'Ă©quilibre partiel dans laquelle le transport des biens produits et consommĂ©s dans la ville n'est pas pris en compte. Or la thĂ©orie Ă©conomique rĂ©cente, dans le cadre des modĂšles d'Ă©conomie gĂ©ographique, montre que la localisation des mĂ©nages est Ă©troitement liĂ©e Ă celle des entreprises, et que les configurations existant Ă l'Ă©quilibre dĂ©pendent fortement des interrelations entre ces deux catĂ©gories d'agents Ă©conomiques. En d'autres termes, s'il est indispensable de considĂ©rer les choix rĂ©sidentiels des mĂ©nages pour analyser les flux de transport engendrĂ©s par ces derniers, il est tout aussi indispensable de tenir compte des consĂ©quences de ces localisations rĂ©sidentielles sur la localisation des entreprises, et aussi des effets en retour des localisations des entreprises sur la distribution spatiale des mĂ©nages. Cette question fait l'objet du premier axe de notre recherche. En second lieu, les travaux existants nĂ©gligent en gĂ©nĂ©ral le fait que les espaces pĂ©riurbains accueillent des mĂ©nages de catĂ©gories sociales variĂ©es qui ont des comportements diffĂ©rents en termes de dĂ©placement. Or, il semble important de proposer une analyse du dĂ©veloppement pĂ©riurbain intĂ©grant la question du choix rĂ©sidentiel des mĂ©nages en fonction de leur catĂ©gorie sociale, ceci afin de dresser des pistes d'Ă©volution possible des flux de transport engendrĂ©s par les espaces pĂ©riurbains. C'est ce qui est dĂ©veloppĂ© dans le second axe de notre recherche. Enfin, ces analyses portant sur la localisation rĂ©sidentielle des diffĂ©rentes catĂ©gories socio-professionnelles nous amĂšnent aussi Ă analyser la sĂ©grĂ©gation rĂ©sidentielle dans les zones pĂ©riurbaines, en lien avec les dĂ©terminants des choix de localisation rĂ©sidentielle des mĂ©nages. / This research starts from the premise that the existing literature on the sustainability of suburban areas has not provided answers to two specific points. Firstly, the issue of transport is generally considered from the point of view of the transport of persons, in a partial equilibrium framework in which the transport of goods produced and consumed in the city is not taken into account. But the recent economic theory, with the new economic geography models, shows that the location of households is closely linked to the location of firms, and that the existing equilibrium configurations depend strongly on the interrelationships between these two categories of agent. In other words, it is essential to consider the residential choices of households to analyze the traffic flows they generate, but it is also necessary to take into account the consequences of these residential locations on the location of firms and the feedback effects of corporate locations on the spatial distribution of households. This question is the subject of the first axis of our research. Second, existing studies generally neglect the fact that the suburban areas host various social groups of households that have different behaviors in terms of mobility. However, it seems important to provide an analysis of suburban development incorporating the issue of residential choices of households according to their social class, in order to establish avenues for possible evolution of transport flows generated by the suburban areas. This is what is developed in the second focus of our research. Finally, the residential location of the different socio-professional categories is also analyzed in terms of urban segregation, in relation with the determinants of householdsâ choices
The Cauchy problem for the 3-D Vlasov-Poisson system with point charges
In this paper we establish global existence and uniqueness of the solution to
the three-dimensional Vlasov-Poisson system in presence of point charges in
case of repulsive interaction. The present analysis extends an analogeous
two-dimensional result by Caprino and Marchioro [On the plasma-charge model, to
appear in Kinetic and Related Models (2010)].Comment: 28 page
Identifying Multiple Predictors of Physical Rehabilitation Outcomes
Previous studies have suggested that disability in activities of daily living (ADLs) is an outcome of cognitive impairment, physical limitations, psychosocial factors, and environmental constraints. We hypothesis that cognitive abilities and psychosocial factors measured at admission can be used to predict a patients physical therapy progression in a transitional care facility. Environmental conditions were held constant for all patients and physical limitations were not used as a predictor of therapy progression, as the test for therapy progression is based on physical ability. In a sample of adults (n=93) aged 38-98 receiving physical rehabilitation treatment, we collected Minimum Data Set (MDS) data, St. Louis University Mental Status (SLUMS) exam scores, and 6 Minute Walk Test (6MWT) scores for each participant from a local transitional care facility. Linear regression models indicated that cognitive ability (SLUMS score B=.420;
A non-variational approach to nonlinear stability in stellar dynamics applied to the King model
In previous work by Y. Guo and G. Rein, nonlinear stability of equilibria in
stellar dynamics, i.e., of steady states of the Vlasov-Poisson system, was
accessed by variational techniques. Here we propose a different,
non-variational technique and use it to prove nonlinear stability of the King
model against a class of spherically symmetric, dynamically accessible
perturbations. This model is very important in astrophysics and was out of
reach of the previous techniques
MACOC: a medoid-based ACO clustering algorithm
The application of ACO-based algorithms in data mining is growing over the last few years and several supervised and unsupervised learning algorithms have been developed using this bio-inspired approach. Most recent works concerning unsupervised learning have been focused on clustering, showing great potential of ACO-based techniques. This work presents an ACO-based clustering algorithm inspired by the ACO Clustering (ACOC) algorithm. The proposed approach restructures ACOC from a centroid-based technique to a medoid-based technique, where the properties of the search space are not necessarily known. Instead, it only relies on the information about the distances amongst data. The new algorithm, called MACOC, has been compared against well-known algorithms (K-means and Partition Around Medoids) and with ACOC. The experiments measure the accuracy of the algorithm for both synthetic datasets and real-world datasets extracted from the UCI Machine Learning Repository
Flat galaxies with dark matter halos - existence and stability
We consider a model for a flat, disk-like galaxy surrounded by a halo of dark
matter, namely a Vlasov-Poisson type system with two particle species, the
stars which are restricted to the galactic plane and the dark matter particles.
These constituents interact only through the gravitational potential which
stars and dark matter create collectively. Using a variational approach we
prove the existence of steady state solutions and their nonlinear stability
under suitably restricted perturbations.Comment: 39 page
Full sphere hydrodynamic and dynamo benchmarks
Convection in planetary cores can generate fluid flow and magnetic fields, and a number of sophisticated codes exist to simulate the dynamic behaviour of such systems. We report on the first community activity to compare numerical results of computer codes designed to calculate fluid flow within a whole sphere. The flows are incompressible and rapidly rotating and the forcing of the flow is either due to thermal convection or due to moving boundaries. All problems defined have solutions that allow easy comparison, since they are either steady, slowly drifting or perfectly periodic. The first two benchmarks are defined based on uniform internal heating within the sphere under the Boussinesq approximation with boundary conditions that are uniform in temperature and stress-free for the flow. Benchmark 1 is purely hydrodynamic, and has a drifting solution. Benchmark 2 is a magnetohydrodynamic benchmark that can generate oscillatory, purely periodic, flows and magnetic fields. In contrast, Benchmark 3 is a hydrodynamic rotating bubble benchmark using no slip boundary conditions that has a stationary solution. Results from a variety of types of code are reported, including codes that are fully spectral (based on spherical harmonic expansions in angular coordinates and polynomial expansions in radius), mixed spectral and finite difference, finite volume, finite element and also a mixed Fourierâfinite element code. There is good agreement between codes. It is found that in Benchmarks 1 and 2, the approximation of a whole sphere problem by a domain that is a spherical shell (a sphere possessing an inner core) does not represent an adequate approximation to the system, since the results differ from whole sphere results
A new variational approach to the stability of gravitational systems
We consider the three dimensional gravitational Vlasov Poisson system which
describes the mechanical state of a stellar system subject to its own gravity.
A well-known conjecture in astrophysics is that the steady state solutions
which are nonincreasing functions of their microscopic energy are nonlinearly
stable by the flow. This was proved at the linear level by several authors
based on the pioneering work by Antonov in 1961. Since then, standard
variational techniques based on concentration compactness methods as introduced
by P.-L. Lions in 1983 have led to the nonlinear stability of subclasses of
stationary solutions of ground state type.
In this paper, inspired by pioneering works from the physics litterature
(Lynden-Bell 94, Wiechen-Ziegler-Schindler MNRAS 88, Aly MNRAS 89), we use the
monotonicity of the Hamiltonian under generalized symmetric rearrangement
transformations to prove that non increasing steady solutions are local
minimizer of the Hamiltonian under equimeasurable constraints, and extract
compactness from suitable minimizing sequences. This implies the nonlinear
stability of nonincreasing anisotropic steady states under radially symmetric
perturbations
- âŠ