6,898 research outputs found
Gradient discretization of Hybrid Dimensional Darcy Flows in Fractured Porous Media with discontinuous pressures at the matrix fracture interfaces
We investigate the discretization of Darcy flow through fractured porous
media on general meshes. We consider a hybrid dimensional model, invoking a
complex network of planar fractures. The model accounts for matrix-fracture
interactions and fractures acting either as drains or as barriers, i.e. we have
to deal with pressure discontinuities at matrix-fracture interfaces. The
numerical analysis is performed in the general framework of gradient
discretizations which is extended to the model under consideration. Two
families of schemes namely the Vertex Approximate Gradient scheme (VAG) and the
Hybrid Finite Volume scheme (HFV) are detailed and shown to satisfy the
gradient scheme framework, which yields, in particular, convergence. Numerical
tests confirm the theoretical results. Gradient Discretization; Darcy Flow,
Discrete Fracture Networks, Finite Volum
Mass predictions, partial difference equations and higherâorder isospin effects
The GarveyâKelson mass relation has been extended by introducing inhomogeneous source terms to improve problems with longârange extrapolations. Such mass relations are thirdâorder partial difference equations with solutions representing mass equations. It was found that inhomogeneous source terms based on shellâdependent Coulomb and symmetry energy terms are not sufficient to improve upon extrapolations. However, contributions from higherâorder perturbations in isospin (mostly cubic) have a significant effect. A manyâparameter mass equation was constructed as the solution of an inhomogeneous difference equation with properly adjusted shellâdependent source terms. The standard deviation for reproducing the experimental mass values is Ïm=194 keV. Nuclear contributions were subjected to the constraint of charge symmetry, and Coulomb displacement energies are reproduced with Ïc=41 keV. Mass predictions for over 4000 nuclei with Aâł16 and both Nâ„Z and N<Z (except N=Z=odd for A<40) are reported.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87305/2/62_1.pd
Amélioration des performances d'un modÚle stochastique de génération de hyétogrammes horaires: application au pourtour méditerranéen français
Depuis quelques annĂ©es, un modĂšle stochastique de gĂ©nĂ©ration de hyĂ©togrammes horaires est dĂ©veloppĂ© au groupement d'Aix-en-Provence du Cemagref, pour ĂȘtre couplĂ© Ă une modĂ©lisation de la pluie en dĂ©bit, fournissant ainsi une multitude de scĂ©narios de crues analysĂ©s statistiquement et utilisĂ©s en prĂ©dĂ©termination des dĂ©bits de crues. L'extension de la zone d'application du modĂšle de pluies horaires au-delĂ de sa zone de conception, a fait apparaĂźtre une hĂ©tĂ©rogĂ©nĂ©itĂ© dans les rĂ©sultats. Ce constat a entraĂźnĂ© certaines modifications du modĂšle comme : la recherche d'une loi de probabilitĂ© thĂ©orique peu sensible aux problĂšmes d'Ă©chantillonnage pour une variable du modĂšle (intensitĂ© d'une averse), la prise en compte originale de la dĂ©pendance observĂ©e entre deux variables du modĂšle (durĂ©e et intensitĂ© d'une averse), et la modĂ©lisation de la persistance des averses au sein d'une mĂȘme pĂ©riode pluvieuse. Ces diffĂ©rentes modifications apportĂ©es au modĂšle initial ont entraĂźnĂ© une trĂšs nette amĂ©lioration de ses performances sur la cinquantaine de postes pluviographiques du pourtour mĂ©diterranĂ©en français. On obtient ainsi un outil beaucoup plus robuste et validĂ© sur une zone Ă©tendue, capable de fournir de multiples formes de hyĂ©togrammes, couvrant toute la gamme des frĂ©quences, permettant ainsi de s'affranchir des pluies de projet uniques. On aborde aussi une nouvelle approche du comportement Ă l'infini des distributions de frĂ©quences des pluies qui semble parfois supĂ©rieur Ă une tendance strictement exponentielle. De plus, l'Ă©tude de plusieurs Ă©vĂ©nements par an dont chacun prĂ©sente plusieurs rĂ©alisations des diffĂ©rentes variables du modĂšle augmente la taille des Ă©chantillons analysĂ©s, semblant rendre la mĂ©thode plus rapidement fiable qu'une approche statistique classique basĂ©e par exemple sur l'ajustement de valeurs maximales annuelles.A stochastic model for generating hourly hyetographs has been recently developed, in the Cemagref of Aix-en-Provence, to be coupled with a rainfall runoff conversion modelling. Thus, by simulation of very long periods (1000 years for example), we obtain a large number of hourly hyetographs and flood scenarios that are statistically studied and used in flood predetermination problems. The rainfall model studied is based on the theory that rainfall can be linked to a random and intermittent process whose evolution is described by stochastic laws. It is also based on the hypothesis of independence between variables describing hyetographs and on the hypothesis of the stationary nature of the phenomenon studied. Generating a rainfall time series involves two steps : descriptive study of the phenomenon (nine independent variables are chosen to describe the phenomenon and these variables are defined by a theoretical law of probability fitted to the observations) and creation of a rainfall time series using descriptive variables generated randomly from their law of probability. Initially developed on the RĂ©al Collobrier watershed data, the model has been applied to fifty raingauges located on the Mediterranean French seaboard. The extension of the model applying area has shown heterogeneousness in the results. Therefore, modifications have been made to the model to improve its performances. Among these modifications, three of them have presented notable improvements. A study of the sensitivity of the parameters has been made. Parameters of shape variables and of some other variables had only a slight influence on depth of generated rainfalls. But, the law of mean rainfall intensities clearly differentiates the stations. Then, a theoretical probability distribution for the storm intensity variable, less sensitive to the sampling problems, has been searched. An exponential distribution is fitted to the value smaller than four times the mean of the variable. A slope breakage was then introduced to generate all the values beyond this limit. The breakage at the value four times the mean of the variable and modelling this breakage were based on a study of so-called "regional" distributions of the storm intensity variable. These distributions were designed by clustering the variable's homogenized values for all 50 studied stations. A second modification has been made to develop new model for the observed dependence between two variables (duration and intensity of the storm). The study of this dependence has been considered directly based on the cumulative frequency of the two variables. Then, an additional parameter was defined to model the dependence between the probabilities of the two variables. This parameter characterises the cumulative frequency curve of the sum of the probabilities of the two variables. This point, neglected during a long time, has been very important in the improvement of the model. Finally, the modelling of storm persistence in a same rainfall episode has been studied to generate some high 24 hours maximum rainfalls. Persistence modelling is entirely justified by the fact that "ordinary storms" cluster together around the "main storm" (the "main storm" is the greatest storm of an episode and the "ordinary storms" are the other storms of the episode). When the study of this phenomenon is extended, it can be observed that there is a certain positive dependency between occurrence probability of the "main storm" and occurrence probability of storms which come before or after it. Two combined effects occur : within one rainy episode, the strongest "ordinary storms" are preferentially clustered together around the "main storm", and considering the number of "ordinary storms" throughout all the episodes, the strongest storms close to the "main storm" are preferentially associated with the strongest "main storms" and vice versa. This modification improves the performances of the altitude raingauges, which are characterised by high daily rainfall accumulations. The different modifications added to the initial model, give very important improvements on the calibration of the fifty raingauges studied on the French Mediterranean seaboard. Its aptitude to generate rains observed in Mediterranean climate, strongly variables, consolidates us in the idea of its application on a zone much larger. The generation of hyetographs makes it possible to use the maximum the temporal information of the rain. Thus, we obtain a reliable tool, validated on a large area, for simulating hyetographs and hourly flood scenarios at all frequencies, and used instead of a unique design storm and design flood. The approach allows a new cumulative probability curve extrapolation, which seems sometimes greater than an exponential behaviour. Moreover, the study of many events per year, with many occurrences of the different variables of the model, increase the analysed sample size and seems to make the method more reliable than a statistical approach simply based, for example, on the fitting of annual maximum values
Belief Hierarchical Clustering
In the data mining field many clustering methods have been proposed, yet
standard versions do not take into account uncertain databases. This paper
deals with a new approach to cluster uncertain data by using a hierarchical
clustering defined within the belief function framework. The main objective of
the belief hierarchical clustering is to allow an object to belong to one or
several clusters. To each belonging, a degree of belief is associated, and
clusters are combined based on the pignistic properties. Experiments with real
uncertain data show that our proposed method can be considered as a propitious
tool
Anyonic Excitations in Fast Rotating Bose Gases Revisited
The role of anyonic excitations in fast rotating harmonically trapped Bose
gases in a fractional Quantum Hall state is examined. Standard Chern-Simons
anyons as well as "non standard" anyons obtained from a statistical interaction
having Maxwell-Chern-Simons dynamics and suitable non minimal coupling to
matter are considered. Their respective ability to stabilize attractive Bose
gases under fast rotation in the thermodynamical limit is studied. Stability
can be obtained for standard anyons while for non standard anyons, stability
requires that the range of the corresponding statistical interaction does not
exceed the typical wavelenght of the atoms.Comment: 5 pages. Improved version to be published in Phys. Rev. A, including
a physical discussion on relevant interactions and scattering regime together
with implication on the nature of statistical interactio
Neutral carbon in the Egg Nebula (AFGL 2688)
A search for sub-mm C I emission from seven stars that are surrounded by dense molecular gas shells led to the detection, in the case of the "Egg Nebula' (AFGL 2688), of an 0.9 K line implying a C I/CO value greater than 5. The material surrounding this star must be extremely carbon-rich, and it is suggested that the apparently greater extent of the C I emission region may be due to the effects of the galactic UV field on the shell's chemistry, as suggested by Huggins and Glassgold (1982)
Chemical solver to compute molecule and grain abundances and non-ideal MHD resistivities in prestellar core collapse calculations
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.We develop a detailed chemical network relevant to the conditions characteristic of prestellar core collapse. We solve the system of time-dependent differential equations to calculate the equilibrium abundances of molecules and dust grains, with a size distribution given by size-bins for these latter. These abundances are used to compute the different non-ideal magneto-hydrodynamics resistivities (ambipolar, Ohmic and Hall), needed to carry out simulations of protostellar collapse. For the first time in this context, we take into account the evaporation of the grains, the thermal ionisation of Potassium, Sodium and Hydrogen at high temperature, and the thermionic emission of grains in the chemical network, and we explore the impact of various cosmic ray ionisation rates. All these processes significantly affect the non-ideal magneto-hydrodynamics resistivities, which will modify the dynamics of the collapse. Ambipolar diffusion and Hall effect dominate at low densities, up to n_H = 10^12 cm^-3, after which Ohmic diffusion takes over. We find that the time-scale needed to reach chemical equilibrium is always shorter than the typical dynamical (free fall) one. This allows us to build a large, multi-dimensional multi-species equilibrium abundance table over a large temperature, density and ionisation rate ranges. This table, which we make accessible to the community, is used during first and second prestellar core collapse calculations to compute the non-ideal magneto-hydrodynamics resistivities, yielding a consistent dynamical-chemical description of this process
How Different Are Threshold and Other Specified Feeding and Eating Disorders? Comparing Severity and Treatment Outcome
Background: Other Specified Feeding and Eating Disorders (OSFED) are characterized by less frequent symptoms or symptoms that do not meet full criteria for another eating disorder. Despite its high prevalence, limited research has examined differences in severity and treatment outcome among patients with OSFED compared to threshold EDs [Anorexia Nervosa (AN), Bulimia Nervosa (BN), and Binge Eating Disorder (BED)]. The purpose of the current study was to examine differences in clinical presentation and treatment outcome between a heterogenous group of patients with OSFED or threshold EDs. Method: Patients with threshold EDs (AN = 42, BN = 50, BED = 14) or OSFED (n = 66) presenting for eating disorder treatment completed self-report questionnaires at intake and discharge to assess eating disorder symptoms, depression symptoms, impairment, and self-esteem. Results: At intake, OSFED patients showed lower eating concerns compared to patients with BN, but similar levels compared to AN and BED. The OSFED group showed higher restraint symptoms compared to BED, and similar restraint to AN and BN. Global symptoms as well as shape and weight concerns were similar between OSFED and threshold ED groups. There were no differences between diagnostic groups in self-esteem, depression scores, or symptom change from intake to discharge. Discussion: Our findings suggest that individuals with OSFED showed largely similar ED psychopathology and similar decreases in symptoms across treatment as individuals diagnosed with threshold EDs. Taken together, findings challenge the idea that OSFED is less severe and more resistant to treatment than threshold EDs
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