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We assess a variant of linear-response range-separated time-dependent density-functional theory (TDDFT), combining a long-range Hartree-Fock (HF) exchange kernel with a short-range adiabatic exchange-correlation kernel in the local-density approximation (LDA) for calculating isotropic C6 dispersion coefficients of homodimers of a number of closed-shell atoms and small molecules. This range-separated TDDFT tends to give underestimated C6 coefficients of small molecules with a mean absolute percentage error of about 5%, a slight improvement over standard TDDFT in the adiabatic LDA which tends to overestimate them with a mean absolute percentage error of 8%, but close to time-dependent Hartree-Fock which has a mean absolute percentage error of about 6%. These results thus show that introduction of long-range HF exchange in TDDFT has a small but beneficial impact on the values of C6 coefficients. It also confirms that the present variant of range-separated TDDFT is a reasonably accurate method even using only a LDA-type density functional and without adding an explicit treatment of long-range correlation.
A predictive model of the Falcon enhanced gravity separator has been derived from a physical analysis of its separation principle, and validated against experimental data. After summarizing the previous works that led to this model and the hypotheses on which they rely, the model is extended to cover a wide range of operating conditions and particle properties. The most significant development presented here is the extension of the analytical law to concentrated suspensions, which makes it applicable to actual plant operating conditions. Two examples of industrial use cases are described and studied by interrogation of the model: dredged sediment waste reduction and coal recovery from fine tailings. Comparisons with empirical studies available in the literature show a good agreement between model predictions and industrial data. The model is then used to identify separation efficiency limitations as well as possible solutions to overcome them. These two examples serve to show how this predictive model can be used to obtain valuable information to improve physical separation processes using a Falcon concentrator, or to evaluate Falcon separator's abilities for new applications.
A series of novel organically templated metal sulfates, [C(5)H(14)N(2)][M(II)(H(2)O)(6)](SO(4))(2) with (M(II) = Mn (1), Fe (2), Co (3) and Ni (4)), have been successfully synthesized by slow evaporation and characterized by single-crystal X-ray diffraction as well as with infrared spectroscopy, thermogravimetric analysis and magnetic measurements. All compounds were prepared using a racemic source of the 2-methylpiperazine and they crystallized in the monoclinic systems, P2(1)/n for (1, 3) and P2(1)/c for (2,4). Crystal data are as follows: [C(5)H(14)N(2)][Mn(H(2)O)(6)](SO(4))(2), a = 6.6385(10) Å, b = 11.0448(2) Å, c = 12.6418(2) Å, β = 101.903(10)°, V = 906.98(3) Å(3), Z = 2; [C(5)H(14)N(2)][Fe(H(2)O)(6)](SO(4))(2), a = 10.9273(2) Å, b = 7.8620(10) Å, c = 11.7845(3) Å, β = 116.733(10)°, V = 904.20(3) Å(3), Z = 2; [C(5)H(14)N(2)][Co(H(2)O)(6)](SO(4))(2), a = 6.5710(2) Å, b = 10.9078(3) Å, c = 12.5518(3) Å, β = 101.547(2)°, V = 881.44(4) Å(3), Z = 2; [C(5)H(14)N(2)][Ni(H(2)O)(6)](SO(4))(2), a = 10.8328(2) Å, b = 7.8443(10) Å, c = 11.6790(2) Å, β = 116.826(10)°, V = 885.63(2) Å(3), Z = 2. The three-dimensional structure networks for these compounds consist of isolated [M(II)(H(2)O)(6)](2+) and [C(5)H(14)N(2)](2+) cations and (SO(4))(2-) anions linked by hydrogen-bonds only. The use of racemic 2-methylpiperazine results in crystallographic disorder of the amines and creation of inversion centers. The magnetic measurements indicate that the Mn complex (1) is paramagnetic, while compounds 2, 3 and 4, (M(II) = Fe, Co, Ni respectively) exhibit single ion anisotropy.
We present a mathematical study of the order book as a multidimensional continuous- time Markov chain where the order ow is modeled by independent Poisson processes. Our aim is to bridge the gap between the microscopic description of price formation (agent- based modeling), and the Stochastic Di erential Equations approach used classically to describe price evolution at macroscopic time scales. To do this, we rely on the theory of in nitesimal generators and Foster-Lyapunov stability criteria for Markov chains. We motivate our approach using an elementary example where the spread is kept constant (\perfect market making"). Then we compute the in nitesimal generator associated with the order book in a general setting, and link the price dynamics to the instantaneous state of the order book. In the last section, we prove that the order book is ergodic| in particular it has a stationary distribution|that it converges to its stationary state exponentially fast, and that the large-scale limit of the price process is a Brownian motion.
In this paper, we consider a discrete time economy where we assume that the short term interest rate follows a quadratic term structure of a regime switching asset process. The possible non-linear structure and the fact that the interest rate can have different economic or financial trends justify the interest of Regime Switching Quadratic Term Structure Model (RS-QTSM). Indeed, this regime switching process depends on the values of a Markov chain with a time dependent transition probability matrix which can well captures the different states (regimes) of the economy. We prove that under this modelling that the conditional zero coupon bond price admits also a quadratic term structure. Moreover, the stochastic coefficients which appear in this decomposition satisfy an explicit system of coupled stochastic backward recursions.
In this note, we cast a Hawkes process-based order book model into a markovian setting, and using techniques from the theory of Markov chains and stochastic stability [16], show that the order book is stable and leads to a di usive price limit at large time scales.
Several ways of assigning probabilities to runs of timed automata (TA) have been proposed recently. When only the TA is given, a relevant question is to design a probability distribution which represents in the best possible way the runs of the TA. This question does not seem to have been studied yet. We give an answer to it using a maximal entropy approach. We introduce our variant of stochastic model, the stochastic process over runs which permits to simulate random runs of any given length with a linear number of atomic operations. We adapt the notion of Shannon (continuous) entropy to such processes. Our main contribution is an explicit formula defining a process $Y^*$ which maximizes the entropy. This formula is an adaptation of the so-called Shannon-Parry measure to the timed automata setting. The process $Y^*$ has the nice property to be ergodic. As a consequence it has the asymptotic equipartition property and thus the random sampling wrt. $Y^*$ is quasi uniform.
We present two extended forms of Fisher information that fit well in the context of nonextensive thermostatistics. We show that there exists an interplay between these generalized Fisher information, the generalized $q$-Gaussian distributions and the $q$-entropies. The minimum of the generalized Fisher information among distributions with a fixed moment, or with a fixed $q$-entropy is attained, in both cases, by a generalized $q$-Gaussian distribution. This complements the fact that the $q$-Gaussians maximize the $q$-entropies subject to a moment constraint, and yields new variational characterizations of the generalized $q$-Gaussians. We show that the generalized Fisher information naturally pop up in the expression of the time derivative of the $q$-entropies, for distributions satisfying a certain nonlinear heat equation. This result includes as a particular case the classical de Bruijn identity. Then we study further properties of the generalized Fisher information and of their minimization. We show that, though non additive, the generalized Fisher information of a combined system is upper bounded. In the case of mixing, we show that the generalized Fisher information is convex for $q\geq1.$ Finally, we show that the minimization of the generalized Fisher information subject to moment constraints satisfies a Legendre structure analog to the Legendre structure of thermodynamics.
This paper develops a structural symbol recognition method with integrated statistical features. It applies spatial organization descriptors to the identified shape features within a fixed visual vocabulary that compose a symbol. It builds an attributed relational graph expressing the spatial relations between those visual vocabulary elements. In order to adapt the chosen vocabulary features to multiple and possible specialized contexts, we study the pertinence of unsupervised clustering to capture significant shape variations within a vocabulary class and thus refine the discriminative power of the method. This unsupervised clustering relies on cross-validation between several different cluster indices. The resulting approach is capable of determining part of the pertinent vocabulary and significantly increases recognition results with respect to the state-of-the-art. It is experimentally validated on complex electrical wiring diagram symbols.
We present two extended forms of Fisher information that fit well in the context of nonextensive thermostatistics. We show that there exists an interplay between these generalized Fisher information, the generalized $q$-Gaussian distributions and the $q$-entropies. The minimum of the generalized Fisher information among distributions with a fixed moment, or with a fixed $q$-entropy is attained, in both cases, by a generalized $q$-Gaussian distribution. This complements the fact that the $q$-Gaussians maximize the $q$-entropies subject to a moment constraint, and yields new variational characterizations of the generalized $q$-Gaussians. We show that the generalized Fisher information naturally pop up in the expression of the time derivative of the $q$-entropies, for distributions satisfying a certain nonlinear heat equation. This result includes as a particular case the classical de Bruijn identity. Then we study further properties of the generalized Fisher information and of their minimization. We show that, though non additive, the generalized Fisher information of a combined system is upper bounded. In the case of mixing, we show that the generalized Fisher information is convex for $q\geq1.$ Finally, we show that the minimization of the generalized Fisher information subject to moment constraints satisfies a Legendre structure analog to the Legendre structure of thermodynamics.
We study the asymptotic behavior of the maximum likelihood estimator corresponding to the observation of a trajectory of a Skew Brownian motion, through a uniform time discretization. We characterize the speed of convergence and the limiting distribution when the step size goes to zero, which in this case are non-classical, under the null hypothesis of the Skew Brownian motion being an usual Brownian motion. This allows to design a test on the skewness parameter. We show that numerical simulations that can be easily performed to estimate the skewness parameter, and provide an application in Biology.
Using an approach recently developed by Nourdin and Poly, we improve the rate in an inequality for the total variation distance between two double Wiener-Itô integrals originally due to Davydov and Martynova. An application to the rate of convergence of a functional of a correlated two-dimensional fractional Brownian motion towards the Rosenblatt random variable is then given, following a previous study by Maejima and Tudor.
Les techniques de mesure sans contact par scanning laser permettent d'acquérir un grand nombre de points, à une cadence très rapide. Elles sont de plus en plus utilisées pour des applications industrielles telles que la rétro-conception, le contrôle de forme,... Toutefois, les incertitudes de mesures sont plus importantes que celles obtenues par les techniques classiques de mesure par contact. Nous proposons une procédure de correction des erreurs systématiques basée sur démarche expérimentale et qui concerne la mesure de pièces présentant une surface mate (peu de présence de bruit spéculaire). Les paramètres retenus dans la procédure sont les paramètres de positionnement du capteur par rapport à la surface de l'objet mesuré: distance, angles d'incidence et ortho-incidence du plan laser. La procédure de correction est appliquée à plusieurs pièces " types " composées de plans ou présentant des surfaces gauches. Les résultats obtenus sont comparés à ceux obtenus avec une procédure classique de mesure avec capteur à contact considérée comme référence. Les erreurs par rapport à la mesure réputée vraie sont réduites et la méthode proposée améliore la performance du système.
We present two extended forms of Fisher information that fit well in the context of nonextensive thermostatistics. We show that there exists an interplay between these generalized Fisher information, the generalized $q$-Gaussian distributions and the $q$-entropies. The minimum of the generalized Fisher information among distributions with a fixed moment, or with a fixed $q$-entropy is attained, in both cases, by a generalized $q$-Gaussian distribution. This complements the fact that the $q$-Gaussians maximize the $q$-entropies subject to a moment constraint, and yields new variational characterizations of the generalized $q$-Gaussians. We show that the generalized Fisher information naturally pop up in the expression of the time derivative of the $q$-entropies, for distributions satisfying a certain nonlinear heat equation. This result includes as a particular case the classical de Bruijn identity. Then we study further properties of the generalized Fisher information and of their minimization. We show that, though non additive, the generalized Fisher information of a combined system is upper bounded. In the case of mixing, we show that the generalized Fisher information is convex for $q\geq1.$ Finally, we show that the minimization of the generalized Fisher information subject to moment constraints satisfies a Legendre structure analog to the Legendre structure of thermodynamics.
Self-potential (SP) data are of interest to vadose zone hydrology because of their direct sensitivity to water flow and ionic transport. There is unfortunately little consensus in the literature about how to best model SP data under partially saturated conditions and different approaches (often supported by one laboratory data set alone) have been proposed. We argue herein that this lack of agreement can largely be traced to electrode effects that have not been properly taken into account. A series of drainage and imbibition experiments are considered, in which we find that previously proposed approaches to remove electrode effects are unlikely to provide adequate corrections. Instead, we explicitly model the electrode effects together with classical SP contributions using a flow and transport model. The simulated data agree overall with the observed SP signals and allow decomposing the different signal contributions to analyze them separately. By reviewing other published experimental data, we suggest that most of them include electrode effects that have not been properly taken into account. Our results suggest that previously presented SP theory works well when considering the modeling uncertainties presently associated with electrode effects. Additional work is warranted to not only develop suitable electrodes for laboratory experiments, but also to assure that associated electrode effects that appear inevitable in longer-term experiments are predictable, such that they can be incorporated in the modeling framework.
Self-potential (SP) data are of interest to vadose zone hydrology because of their direct sensitivity to water flow and ionic transport. There is unfortunately little consensus in the literature about how to best model SP data under partially saturated conditions and different approaches (often supported by one laboratory data set alone) have been proposed. We argue herein that this lack of agreement can largely be traced to electrode effects that have not been properly taken into account. A series of drainage and imbibition experiments are considered, in which we find that previously proposed approaches to remove electrode effects are unlikely to provide adequate corrections. Instead, we explicitly model the electrode effects together with classical SP contributions using a flow and transport model. The simulated data agree overall with the observed SP signals and allow decomposing the different signal contributions to analyze them separately. By reviewing other published experimental data, we suggest that most of them include electrode effects that have not been properly taken into account. Our results suggest that previously presented SP theory works well when considering the modeling uncertainties presently associated with electrode effects. Additional work is warranted to not only develop suitable electrodes for laboratory experiments, but also to assure that associated electrode effects that appear inevitable in longer-term experiments are predictable, such that they can be incorporated in the modeling framework.
Bioturbation is known to stimulate microbial communities, especially in macrofaunal burrows where the abundance and activities of bacteria are increased. Until now, these microbial communities have been poorly characterized and an important ecological question remains: do burrow walls harbor similar or specific communities compared with anoxic and surface sediments? The bacterial community structure of coastal sediments inhabited by the polychaete worm Hediste diversicolor was investigated. Surface, burrow wall and anoxic sediments were collected at the Carteau beach (Gulf of Fos, Mediterranean Sea). Bacterial diversity was determined by analyzing small subunit ribosomal RNA (16S rRNA) sequences from three clone libraries (168, 179 and 129 sequences for the surface, burrow wall and anoxic sediments, respectively). Libraries revealed 306 different operational taxonomic units (OTUs) belonging to at least 15 bacterial phyla. Bioinformatic analyses and comparisons between the three clone libraries showed that the burrow walls harbored a specific bacterial community structure which differed from the surface and anoxic environments. More similarities were nevertheless found with the surface assemblage. Inside the burrow walls, the bacterial community was characterized by high biodiversity, which probably results from the biogeochemical heterogeneity of the burrow system. (C) 2011 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.
The fate of ingested eukaryotic photoautotrophic fatty acids during gut transit in the lugwormArenicolamarina (L.) and the influence of A. marina's faeces on the evolution of fatty acid distribution and bacterial community structure in superficial sediments were studied under laboratory conditions. Dead phytoplanktonic cells (food portions) were fed to individual A. marina and subsequently incubated, or allowed to directly incubate in the presence of fresh egesta or non-ingested sediment. Changes in fatty acid composition and genetic structure of bacterial communities during gut transit and/or incubation were monitored using gas-chromatography/mass-spectrometry and a DNA fingerprint approach (RISA), respectively. Results, supported by principal component analyses, suggest that A. marina's feeding activity can directly and indirectly affect the lipid biomarker composition and the bacterial community structure of inhabited sediments. Faecal casts produced fromfood portions appeared qualitatively enriched in saturated fatty acids relative to (poly)unsaturated ones due, partly, to an increase of some bacterial fatty acids and to the preferential removal of some polyunsaturated fatty acids (PUFAs). The incubation of food portions in the presence of fresh A. marina's egesta (designed to study the indirect impact of feeding by A. marina) induced a significant increase in the concentrations of C20 and C22 polyunsaturated fatty acids (PUFAs), whereas these compounds almost disappeared following direct feeding and subsequent incubation, indicating that some dietary fatty acidsmay be more accessible to biodegradation following passage through the gut of A. marina. The aforementioned increase in PUFAs was attributed to a bacterial production during incubation, suggesting the presence of PUFA-producing bacteria in the fresh egesta of A. marina. Those bacteria were either enteric bacteria thatwere releasedwith the egesta or ingested bacteria that have survived gut passage, as suggested by the variations of the bacterial community structure (i.e. RISA profiles) during incubation. The results suggest that aged faeces from A. marina might be, in some circumstances, of relatively high nutritional value to trophic levels which are unable to synthesize essential PUFAs de novo. The presence of PUFA-producing bacteria in guts of marine lugworms deserves further attention.
An improved Lozi function with alternate coefficients has been proposed. The modifications in the model allow to remove the holes in the attractor which are not desirable, but appeared in the previous Lozi function; in this way, an everywhere dense attractor can be obtained. Moreover, the strong sensitivity to the type of binarisation (conversion of real values to 0 and 1) has been demonstrated; this conversion to binary numbers is instrumental to apply the NIST tests for randomness. The results have been validated and compared via NIST tests, for the different methods of quantization. Finally, is has been verfied that the multi-random properties of the output signal have been improved thanks to the following strategies : under-sampling of the output signal, and the system order increasing. Keywords. Nonlinear dynamical system, ring-coupled map, Lozi function, NIST tests, discrete-time map, dense chaotic attractor, pseudo random number generator 1 I
The extreme characteristics of long wave run-up are studied in this paper. First we give a brief overview of the existing theory which is mainly based on the hodograph transformation (Carrier & Greenspan, 1958). Then, using numerical simulations, we build on the work of Stefanakis et al. (2011) for an infinite sloping beach and we find that resonant run-up amplification of monochromatic waves is robust to spectral perturbations of the incoming wave and resonant regimes do exist for certain values of the frequency. In the setting of a finite beach attached to a constant depth region, resonance can only be observed when the incoming wavelength is larger than the distance from the undisturbed shoreline to the seaward boundary. Wavefront steepness is also found to play a role in wave run-up, with steeper waves reaching higher run-up values.
The water wave theory traditionally assumes the fluid to be perfect, thus neglecting all effects of the viscosity. However, the explanation of several experimental data sets requires the explicit inclusion of dissipative effects. In order to meet these practical problems, the theory of visco-potential flows has been developed (see P.-F. Liu & A. Orfila (2004) and D. Dutykh & F. Dias (2007)). Then, usually this formulation is further simplified by developing the potential in an entire series in the vertical coordinate and by introducing thus, the long wave approximation. In the present study we propose a derivation of dissipative Boussinesq equations which is based on asymptotic expansions of the Dirichlet-to-Neumann (D2N) operator. Both employed methods yield the same system by different ways.
Les tâches d'empan de mémoire de travail sont des tâches dans lesquelles des items doivent être maintenus en mémoire à court terme pendant qu'un traitement concurrent est effectué. Le but de la présente étude était de déterminer si, comme le soutient le modèle de partage temporel des ressources (Barrouillet, Bernardin, & Camos, 2004), les traitements gênent le maintien parce que les deux composantes entrent en compétition pour des processus communs ou plus simplement parce que les stratégies de maintien des items à rappeler sont perturbées par l'intrusion de l'information à traiter simultanément. Quatre-vingt sujets adultes étaient soumis à une tâche d'empan où ils devaient maintenir des lettres en même temps qu'ils devaient juger soit de la parité soit de la position spatiale de nombre présentés successivement à l'écran. Par ailleurs, ces nombres apparaissaient à un rythme régulier et donc prévisible ou bien aléatoire. Conformément à nos attentes, et contrairement à l'hypothèse d'une perturbation des stratégies de maintien, les jugements de parité qui nécessitent des récupérations en mémoire entraînaient de plus faibles empans que la tâche spatiale qui ne requiert qu'une sélection de réponse alors que le rythme de réalisation de la tâche secondaire n'avait pas d'effet sur les empans.
The functional organization of the PFC from anterior to posterior regions reflects a hierarchy of cognitive control whereby progressively anterior sub-regions are associated with higher-order control. The present study aimed at providing behavioral evidence for two predictions issuing from this cascade model. First, even the lower-most sub-part of the cognitive control hierarchy, i.e. motor programming, should interfere with higher controlled processes such as maintenance in working memory. Second, this effect should be commensurate with the time during which control is required. In a computer-paced complex span task, adults had to maintain letters while they performed a secondary task. The demand imposed by this task was manipulated either at the selection or at the motor programming stage of response preparation. Results revealed that both manipulations have a disruptive effect on verbal memory, and that this effect is commensurate with the extra-time during which response selection and motor programming require cognitive control.
Memorizing is crucial for human beings because it constitutes the fundamental step in acquiring knowledge. Among the different memory systems, the one called "working memory" works continuously to simultaneously memorize and process information. It is particularly important in children who are continually confronted to learning situations. It has long been considered that memorizing required verbalizing and repeating. The present paper offers an alternative conception: working memory relies on attentional mechanisms constrained by time and do not depend on verbal characteristics. The empirical analyses we present here do not only conduct to important theoretical conclusions, they also give a glimpse of practical applications for preventing school failure.
Self-potential (SP) data are of interest to vadose zone hydrology because of their direct sensitivity to water flow and ionic transport. There is unfortunately little consensus in the literature about how to best model SP data under partially saturated conditions and different approaches (often supported by one laboratory data set alone) have been proposed. We argue herein that this lack of agreement can largely be traced to electrode effects that have not been properly taken into account. A series of drainage and imbibition experiments are considered, in which we find that previously proposed approaches to remove electrode effects are unlikely to provide adequate corrections. Instead, we explicitly model the electrode effects together with classical SP contributions using a flow and transport model. The simulated data agree overall with the observed SP signals and allow decomposing the different signal contributions to analyze them separately. By reviewing other published experimental data, we suggest that most of them include electrode effects that have not been properly taken into account. Our results suggest that previously presented SP theory works well when considering the modeling uncertainties presently associated with electrode effects. Additional work is warranted to not only develop suitable electrodes for laboratory experiments, but also to assure that associated electrode effects that appear inevitable in longer-term experiments are predictable, such that they can be incorporated in the modeling framework.
Growth compensations following a disturbance have been found in different species communities through experimentation, but there are few results obtained in natural conditions, in particular for forest ecosystems. The objective of this study was to determine whether there was growth compensation in a mixed oak-pine forest following a biotic disturbance: an outbreak of pine sawfly (Diprion pini) that caused massive defoliation of pines in Europe in the early 1980s. The data were collected in mixed oak-pine stands located in the plains of north-central France. We measured the ring widths of 223 oaks and 271 pines in nine mixed stands over a period ranging from 1972 to 2005. We established a model which incorporated climatic effects in order to predict the ring width under undisturbed conditions and to quantify the response of each species to the disturbance. We found that the growth of both species varied synchronously with a positive covariation outside of the disturbance. During the disturbance, the growth of both species covaried negatively especially in the plots where pine had been the most severely affected. For the year following the peak of the defoliations, the reduction in growth for pine was strong and ranged from -27% to -92% depending on the plot. In addition, the more significant the reduction in growth for pine, the more significant the increase in growth for oak. We found that a 100% reduction in pine growth was accompanied by a 61% increase in oak growth for the three years following the most severe defoliation. These results demonstrate that compensation between the two tree species following the insect outbreak did occur. We suggest that growth compensations would especially occur in the case of severe biotic disturbances but probably not in the case of climatic fluctuations.
Bioturbation is known to stimulate microbial communities, especially in macrofaunal burrows where the abundance and activities of bacteria are increased. Until now, these microbial communities have been poorly characterized and an important ecological question remains: do burrow walls harbor similar or specific communities compared with anoxic and surface sediments? The bacterial community structure of coastal sediments inhabited by the polychaete worm Hediste diversicolor was investigated. Surface, burrow wall and anoxic sediments were collected at the Carteau beach (Gulf of Fos, Mediterranean Sea). Bacterial diversity was determined by analyzing small subunit ribosomal RNA (16S rRNA) sequences from three clone libraries (168, 179 and 129 sequences for the surface, burrow wall and anoxic sediments, respectively). Libraries revealed 306 different operational taxonomic units (OTUs) belonging to at least 15 bacterial phyla. Bioinformatic analyses and comparisons between the three clone libraries showed that the burrow walls harbored a specific bacterial community structure which differed from the surface and anoxic environments. More similarities were nevertheless found with the surface assemblage. Inside the burrow walls, the bacterial community was characterized by high biodiversity, which probably results from the biogeochemical heterogeneity of the burrow system. (C) 2011 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.
Ces dernières années, l'enseignement adopte des formes variées et s'oriente vers l'enseignement massif (Massive Open Online Courses, premières années de médecine, ...) et l'évaluation diagnos- tique. De la masse de productions résultante naît un besoin de système d'évaluation assistée par ordinateur. Le besoin d'évaluation diagnostique détaillée popularise l'utilisation des grilles critériées. Nous envisageons dans cet article les apports de l'apprentissage automatique aﰂn de réaliser un système d'évaluation assistée par ordinateur par grille critériée. Le système ainsi conçu serait indépendant du domaine d'application et per- mettrait l'explicitation des connaissances tacites. Nous commencerons par proposer une représentation générique des productions et des évalu- ations de l'apprenant, puis la modélisation de la fonction d'évaluation qui lie une évaluation à chaque production. Nous proposerons et évaluerons alors un algorithme d'apprentissage original permettant d'apprendre cette fonction à partir d'un ensemble d'apprentissage réduit.
Les jeux sérieux sont de plus en plus utilisés pour la formation, et en particulier dans le domaine de la gestion de crise. Afin d'améliorer la formation, l'évaluation des apprenants peut fournir des indications sur ce qui a été bien ou mal appris au cours d'une session de formation. Cette appréciation se complexifie lorsqu'elle doit prendre en compte non seulement les actions individuelles des acteurs mais également le résultat de leurs interactions (actions collectives). De plus, selon la nature des phénomènes à émuler (incendie, pollution...) et le nombre d'acteurs impliqués, des besoins de simulations s'ajoutent (propagation incendie, simulation de comportement d'acteurs absents...). L'évaluation des apprenants implique ainsi l'acquisition d'un ensemble hétérogène d'informations à la fois par leur nature (données brutes, connaissances, procédures) et par leur source (niveau logiciel). Cet article propose une approche multi-agents répondant à deux objectifs: i) permettre la production et l'exploitation de ces informations hétérogènes en vue de produire des indicateurs qui alimenteront une évaluation multi-critères; et ii) mettre en œuvre le processus d'évaluation par un système multi-agents accompagnant la production d'évaluations individuelles et collectives. Cette approche est développée et illustrée sur le jeu sérieux SIMFOR dédié à la gestion de crise pour le faire évoluer vers un Système tutoriel.
Le générateur semi-automatique d'exercices interactifs d'auto- évaluation du projet CLAIRE permet à un auteur de créer un modèle d'exercices dont il maîtrise totalement le contenu. Ce modèle est ensuite instancié de manière automatique pour donner lieu à diﰁérentes versions de l'exercice correspondant toutes aux attentes de l'auteur. Chaque exer- cice dispose de connaissances permettant le diagnostic automatique de la réponse de l'apprenant. Les types d'exercices proposés (textes à trous, appariement, etc.) sont indépendants du domaine. Si l'auteur souhaite que ses exercices comportent des connaissances du domaine, il lui revient donc de les décrire dans le modèle d'exercices. Cet article discute de l'en- semble des connaissances manipulées dans le générateur d'exercices : les connaissances du domaine mais également les connaissances sur les types d'exercices et les connaissances liées au diagnostic de la réponse de l'ap- prenant. Pour chacune de ces familles de connaissances, nous étudions leur rôle, leur utilisation, s'il est intéressant de les expliciter, comment les représenter et comment faciliter leur création et leur usage par un auteur non-informaticien. Chacun de ces points amène à un ensemble de questions ouvertes.
Les techniques de mesure sans contact par scanning laser permettent d'acquérir un grand nombre de points, à une cadence très rapide. Elles sont de plus en plus utilisées pour des applications industrielles telles que la rétro-conception, le contrôle de forme,... Toutefois, les incertitudes de mesures sont plus importantes que celles obtenues par les techniques classiques de mesure par contact. Nous proposons une procédure de correction des erreurs systématiques basée sur démarche expérimentale et qui concerne la mesure de pièces présentant une surface mate (peu de présence de bruit spéculaire). Les paramètres retenus dans la procédure sont les paramètres de positionnement du capteur par rapport à la surface de l'objet mesuré: distance, angles d'incidence et ortho-incidence du plan laser. La procédure de correction est appliquée à plusieurs pièces " types " composées de plans ou présentant des surfaces gauches. Les résultats obtenus sont comparés à ceux obtenus avec une procédure classique de mesure avec capteur à contact considérée comme référence. Les erreurs par rapport à la mesure réputée vraie sont réduites et la méthode proposée améliore la performance du système.
Ce papier décrit la conception et l'implémentation d'un réseau d'oscillateurs couplés totalement intégré en technologie BiCMOS SiGe 0,25 μm. Ce réseau est constitué de quatre VCOs NMOS différentiels couplés au moyen d'une résistance. Pour une tension d'alimentation de 2.5V, une puissance consommée de 125 mW à une fréquence d'oscillation de 6 GHz, le réseau présente un bruit de phase de -127dBc/Hz à 1MHz de la porteuse et un déphasage qui varie de façon continue entre -64° et +64 ° et entre -116° et +116°.
To take account of the uncertainties introduced on the soft magnetic materials properties (magnetic behavior law, iron losses) during the manufacturing process, the present work deals with the stochastic modeling of the magnetic behavior law B-H and iron losses of claw pole stator generator. Twenty eight (28) samples of slinky stator (SS) coming from the same production chain have been investigated. The used approaches are similar to those used in mechanics. The accuracy of existing anhysteretic models has been tested first using cross validation techniques. The well known iron loss separation model has been implemented to take into account the variability of the losses. Then, the Multivariate Gaussian distribution is chosen to model the variability and dependencies between identified parameters, for both behavior law and iron loss models. The developed stochastic models allow predicting a 98% confidence interval for the considered samples
Background
The fate of ingested eukaryotic photoautotrophic fatty acids during gut transit in the lugwormArenicolamarina (L.) and the influence of A. marina's faeces on the evolution of fatty acid distribution and bacterial community structure in superficial sediments were studied under laboratory conditions. Dead phytoplanktonic cells (food portions) were fed to individual A. marina and subsequently incubated, or allowed to directly incubate in the presence of fresh egesta or non-ingested sediment. Changes in fatty acid composition and genetic structure of bacterial communities during gut transit and/or incubation were monitored using gas-chromatography/mass-spectrometry and a DNA fingerprint approach (RISA), respectively. Results, supported by principal component analyses, suggest that A. marina's feeding activity can directly and indirectly affect the lipid biomarker composition and the bacterial community structure of inhabited sediments. Faecal casts produced fromfood portions appeared qualitatively enriched in saturated fatty acids relative to (poly)unsaturated ones due, partly, to an increase of some bacterial fatty acids and to the preferential removal of some polyunsaturated fatty acids (PUFAs). The incubation of food portions in the presence of fresh A. marina's egesta (designed to study the indirect impact of feeding by A. marina) induced a significant increase in the concentrations of C20 and C22 polyunsaturated fatty acids (PUFAs), whereas these compounds almost disappeared following direct feeding and subsequent incubation, indicating that some dietary fatty acidsmay be more accessible to biodegradation following passage through the gut of A. marina. The aforementioned increase in PUFAs was attributed to a bacterial production during incubation, suggesting the presence of PUFA-producing bacteria in the fresh egesta of A. marina. Those bacteria were either enteric bacteria thatwere releasedwith the egesta or ingested bacteria that have survived gut passage, as suggested by the variations of the bacterial community structure (i.e. RISA profiles) during incubation. The results suggest that aged faeces from A. marina might be, in some circumstances, of relatively high nutritional value to trophic levels which are unable to synthesize essential PUFAs de novo. The presence of PUFA-producing bacteria in guts of marine lugworms deserves further attention.
It has been previously established that the Leopard Whipray, Himantura leoparda, consists of two genetically isolated, cryptic species, provisionally designated as 'Cluster 1' and 'Cluster 4' (Arlyza et al., Mol. Phylogenet. Evol. 65 (2013) [1]). Here, we show that the two cryptic species differ by the spotting patterns on the dorsal surface of adults: Cluster-4 individuals tend to have larger ocellated spots which also more often have a continuous contour than Cluster-1 individuals. We show that H. leoparda's holotype has the typical larger-ocellated spot pattern, designating Cluster 4 as the actual H. leoparda. The other species (Cluster 1) is described as Himantura tutul sp. nov. on the basis of the nucleotide sequence of a 655-base pair fragment of its cytochrome-oxidase I gene (GENBANK accession no. JX263335). Nucleotide synapomorphies at this locus clearly distinguish Himantura tutul sp. nov. from all three other valid species in the H. uarnak species complex, namely H. leoparda, H. uarnak, and H. undulata. Himantura tutul sp. nov. has a wide distribution in the Indo-West Pacific, from the shores of eastern Africa to the Indo-Malay archipelago. H. leoparda under its new definition has a similarly wide Indo-West Pacific distribution.
To take account of the uncertainties introduced on the soft magnetic materials properties (magnetic behavior law, iron losses) during the manufacturing process, the present work deals with the stochastic modeling of the magnetic behavior law B-H and iron losses of claw pole stator generator. Twenty eight (28) samples of slinky stator (SS) coming from the same production chain have been investigated. The used approaches are similar to those used in mechanics. The accuracy of existing anhysteretic models has been tested first using cross validation techniques. The well known iron loss separation model has been implemented to take into account the variability of the losses. Then, the Multivariate Gaussian distribution is chosen to model the variability and dependencies between identified parameters, for both behavior law and iron loss models. The developed stochastic models allow predicting a 98% confidence interval for the considered samples
Using an approach recently developed by Nourdin and Poly, we improve the rate in an inequality for the total variation distance between two double Wiener-Itô integrals originally due to Davydov and Martynova. An application to the rate of convergence of a functional of a correlated two-dimensional fractional Brownian motion towards the Rosenblatt random variable is then given, following a previous study by Maejima and Tudor.
We propose a family of multivariate heavy-tailed distributions that allow variable marginal amounts of tailweight. The originality comes from introducing multidimensional instead of univariate scale variables for the mixture of scaled Gaussian family of distributions. In contrast to most existing approaches, the derived distributions can account for a variety of shapes and have a simple tractable form with a closed-form probability density function whatever the dimension. We examine a number of properties of these distributions and illustrate them in the particular case of Pearson type VII and ttails. For these latter cases, we provide maximum likelihood estimation of the parameters and illustrate their modelling flexibility on simulated and real data clustering example.
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