Convergence of Adaptive Finite Element Methods

Adaptive finite element methods (FEMs) have been widely used in applications for over 20 years now. In practice, they converge starting from coarse grids, although no mathematical theory has been able to prove this assertion. Ensuring an error reduction rate based on a posteriori error estimators, together with a reduction rate of data oscillation (information missed by the underlying averaging process), we construct a simple and efficient adaptive FEM for elliptic partial differential equations. We prove that this algorithm converges with linear rate without any preliminary mesh adaptation nor explicit knowledge of constants. Any prescribed error tolerance is thus achieved in a finite number of steps. A number of numerical experiments in two and three dimensions yield quasi-optimal meshes along with a competitive performance. Extensions to higher order elements and applications to saddle point problems are discussed as well.Fil: Morin, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Matemática Aplicada del Litoral. Universidad Nacional del Litoral. Instituto de Matemática Aplicada del Litoral; ArgentinaFil: Nochetto, Ricardo Horacio. University of Maryland; Estados UnidosFil: Siebert, Kunibert G.. Universität Heidelberg

Accurate photonic temporal mode analysis with reduced resources

The knowledge and thus characterization of the temporal modes of quantum light fields is important in many areas of quantum physics ranging from experimental setup diagnosis to fundamental-physics investigations. Recent results showed how the auto-correlation function computed from continuous-wave homodyne measurements can be a powerful way to access the temporal mode structure. Here, we push forward this method by providing a deeper understanding and by showing how to extract the amplitude and phase of the temporal mode function with reduced experimental resources. Moreover, a quantitative analysis allows us to identify a regime of parameters where the method provides a trustworthy reconstruction, which we illustrate experimentally

Decoherence-protected memory for a single-photon qubit

The long-lived, efficient storage and retrieval of a qubit encoded on a photon is an important ingredient for future quantum networks. Although systems with intrinsically long coherence times have been demonstrated, the combination with an efficient light-matter interface remains an outstanding challenge. In fact, the coherence times of memories for photonic qubits are currently limited to a few milliseconds. Here we report on a qubit memory based on a single atom coupled to a high-finesse optical resonator. By mapping and remapping the qubit between a basis used for light-matter interfacing and a basis which is less susceptible to decoherence, a coherence time exceeding 100 ms has been measured with a time-independant storage-and-retrieval efficiency of 22%. This demonstrates the first photonic qubit memory with a coherence time that exceeds the lower bound needed for teleporting qubits in a global quantum internet.Comment: 3 pages, 4 figure

Impacts de changements climatiques sur le régime hydrologique : le cas de la riviere Moisie

Les résultats du modèle de circulation générale (MCG) à haute résolution du Centre climatologique canadien (CCC) sont utilisés pour estimer l'ampleur des impacts d'éventuels changements climatiques sur le régime hydrologique d'une rivière de la côte nord du Saint-Laurent.Pour le Québec, le MCG du CCC prévoit des augmentations annuelles de l'ordre de 0 à 15 % pour les précipitations et de 4 à 5° C pour les températures, tandis que les variations saisonnières seraient beaucoup plus importantes, les températures hivernales (décembre à février) augmentant de 6 à 9° C et les précipitations 15 à 20 %.Le modèle hydrologique CEQUEAU est appliqué au bassin versant de la rivière Moisie, pour simuler les débits dans le contexte climatique actuel et dans ce nouveau contexte climatique. Pour ce bassin versant, les précipitations annuelles seraient pratiquement inchangées alors que les températures annuelles augmenteraient de 4° C.En appliquant, aux 24 dernières années (1986-1989), les changements mensuels de précipitation et température découlant du MCG, le débit annuel moyen serait réduit d'environ 5 % et l'écart-type augmenterait de 15 %. La probabilité des années humides serait pratiquement inchangée alors que pour les années les plus sèches enregistrées au cours de ces 25 dernières années soit 600 mm, la probabilité de non dépassement dans ce nouveau contexte climatique passerait de 0,12 à 0,28 ; les débits annuels, d'occurence décennale, diminueraient d'environ 10 %.On assisterait à une modification plus importante dans la distribution mensuelle des écoulements. Les débits moyens des mois d'été (juillet à septembre) seraient réduits d'environ 35 % tandis que pour les mois d'hiver les écoulements moyens seraient plus soutenus.The output of the Canadian Climate Center (CCC) General Circulation Model (GCM), coupled with the hydrologic deterministic modes CEQUEAU is used to evaluate the possible impact of a doubling of atmospheric C02 on the hydrologic regime of the Moisie river on the North Shore of the St Lawrence.In regions where snow plays an important contribution to the annual runoff and the ground is covered with snow for periods from 4 to 6 months, the seasonal variations of climatic changes under a 2 x C02 scenario may have very different impact on hydrologic regimes; Figures 1 and 3 show the annual and winter distributions of temperature changes for Quebec under the CCC 2 x C02 scenarios, white figure 2 shows the possible changes in annual precipitation. The annual temperature will increase around 4 to 5° C, white winter temperatures may increase as much as 6 to 9° C ; annual precipitation will increase by 15 % to 20 %.The CEQUEAU hydrologic model (MORIN et al., 1981 ; MORIN et COUILLARD, 1990) is a deterministic model which takes into account number of physiographic characteristics of the drainage basin (such as elevation and percent of forest and lake area) as defined in number of square grids. The model uses for input daily minimum and maximum temperatures and daily solid and liquid precipitation (rainfall and snowfall). As such meteorological information is usually available for a limited number of stations, the values are interpolated to each grid element of the drainage basin.The CEQUEAU deterministic model uses the degree-days method (CORPS OF ENGINEERS, 1960) to estimate daily snowmelt under forest canopy and in the open and Thornthwaite equation to calculate daily evapotranspiration, for each square grid of the basin. Daily water budget, using linear reservoir storage for soil moisture and ground water storage is then used on each square grid element, to estimate daily runoff production ; this daily runoff production on each grid is then routed downstream to the basin outlet. The CEQUEAU model is applied to the drainage basin of the Moisie river on the North shore of the Saint-Lawrence river. The Moisie river drainage basin covers an area of 19 248 km2, and we have used square grids of 20 km by 20 km to model this basin which is oriented roughly north to south with a length of 320 km and a width of 70 km.Climatic Normals for the 1951-1980 period for the Sept îles and Wabush Lake climate stations are used to calculate the coefficients of the Thornthwaite formula for the present conditions.Daily temperatures and precipitation for the Sept îles and Wabush Lake climate stations are then used as input to the CEQUEAU model, la calculate the flows for the 1966-1989 period. Even if calculations of flows have been made on a daily scale monthly values are used for the analysis of results. Table 1 presents a comparison of monthly and annual observed and calculated runoff for this period and show that the model satisfactorily reproduces the observed flows ; the annual difference is only - 1.2 % white monthly differences vary tram - 7 % to + 6 %.Monthly flows (fig. 4) adequately represent the annual cycle and there is no important under or over estimation of mean monthly values. Frequency analysis of ail monthly flows (fig. 5) show that the observed sequence is adequately simulated even for extreme values. The coefficient of correlation between annual observed and calculated flows is 0.88 and the error of estimation of calculated values is only 48 mm.Monthly changes in temperature and precipitation as output by the Canadian GCM under a 2 x C02 scenario are then used to simulate daily flows under changed climate conditions. The values at the grid points of the GCM are interpolated to the Sept-Iles and Wabush Lake Stations.Climate normals for the two stations, table 2, are first modified by these monthly changes in precipitation and temperature to reflect new conditions for the application of the Thornthwaite formula under a 2 x C02 scenario. Then daily temperature and precipitation values for the 1966-1989 period are modified by these monthly changes and used as input to the CEQUEAU model.The hydrologic results of this 2 x C02 scenario are presented in table 3 and figures 7 to 10. White annual runoff is reduced by only about 5 %, monthly values show much larger variations.Figure 7 and table 3 present a comparison of average monthly flows under present and the 2 x C02 scenario. Winter flows are significantly increased (from 19 % to 210 %) due to much more frequent snow melts in the beginning and end of winter, and winter low flows are significantly higher. The monthly spring flow is about the same (fig. 7), but is concentrated in a shorter period. Summer fiows (June to October) decrease by 25 % to 40 % due to increase in temperature and therefore evapotranspiration but are still higher than winter flows.Figure 8 shows the coefficients of variation of monthly flows. Like mentioned previously one notices a significant increase for winter months (December to Match), due to more frequent snow melts, white for the month of April the coefficient of variation is significantly reduced. For the summer months (May to October) the variation does not change very much.Probability distribution of simulated annual flows (fig. 9) show that for wet years the probability of occurrence does not change significantly, white for dry years, i.e. runoff of about 600 mm, corresponding to the driest years in the 1966-1989 period, the probability of not exceedence goes from 0, 12 to 0,28; i.e. the years of low runoff will happen much more frequently.For summer months the situation will be different as it is the wet years that will be more affected by changes in temperature; as an example for the month of August (fig. 10) the probability of occurences of dry years will not change as drastically as the frequency of wet years; increases in temperature and therefore possible evapotranspiration, will have no effect if no sufficient soil moisture is available

Identifying ILI Cases from Chief Complaints: Comparing the Accuracy of Keyword and Support Vector Machine Methods

We compared the accuracy of two methods of identifying ILI cases from chief complaints. We found that a support vector machine method was more accurate than a keyword method

Investigation of the relation between substance use and cognitive performance and its mediating effect on psychopathology symptoms

Le projet de thèse porte sur la consommation de substances psychoactives chez les adolescents et le lien séquentiel entre la consommation de drogues, la performance cognitive, et la santé mentale des jeunes. Les objectifs de la thèse sont : 1) de tester la relation entre la prise de cannabis, ou d’alcool, et la performance cognitive, et d’en observer la séquence, 2) de vérifier si la relation entre la consommation et la performance cognitive permet, en partie, de comprendre l’apparition de symptômes de psychopathologie chez les jeunes, et 3) de définir les pratiques les mieux fondées empiriquement pour prévenir la consommation de substances chez les adolescents. Le premier chapitre de la thèse évalue la relation et la séquence entre les habitudes de consommation d’environ 4000 jeunes de la région métropolitaine de Montréal (Qc, Canada) et la trajectoire de leur développement cognitif sur une période de quatre ans. Dans un deuxième chapitre, la thèse évalue comment la relation entre la consommation et la performance cognitive de ces mêmes jeunes peut expliquer, sur une période de cinq ans, une partie de la relation observée entre la consommation et l’apparition de symptômes de psychopathologie. Dans un dernier chapitre, la thèse fait la revue des données portant sur trois types d’interventions préventives afin d’identifier comment la recherche empirique peut bonifier les efforts de prévention de la toxicomanie chez les adolescents. Les données ont été extraites d’une cohorte d’adolescents issus de la population générale, suivis longitudinalement, dans le cadre de l’étude Co-Venture (n = 3826, âgés de 12 ans à l’admission dans l’étude, suivis annuellement pendant 5 ans). Les résultats ont démontré que, bien que certains facteurs semblent prédisposer un sous-groupe de jeunes à une consommation hâtive ainsi que des difficultés neuropsychologiques, la consommation de drogues, notamment de cannabis, semble liée, de façon à la fois ponctuelle et durable, à un délai du développement cognitif, plus particulièrement des fonctions exécutives. Cette association avec le cannabis semble, en faible partie, jouer un rôle médiateur dans la relation qui unit cette consommation et l’émergence de symptômes de psychopathologie chez les adolescents. Toutefois, des facteurs prédisposants semblent contribuer à l’association entre ces trois variables. Bien que la recherche identifie que plusieurs programmes de prévention peuvent être efficaces, la majorité d’entre eux présentent des effets modestes et ponctuels. Les programmes les plus probants semblent s’inscrire dans le registre des approches de prévention ciblées. Pour bonifier nos méthodes de prévention de la toxicomanie chez les adolescents, nous pourrions tenir compte de certains facteurs prédisposants et les utiliser comme cible d’intervention; par exemple, le fonctionnement cognitif basal pourrait constituer une piste intéressante. De plus, le tempérament ou la personnalité semblent mieux établis pour prévenir la consommation de façon durable et pour aborder les enjeux cognitifs et psychologiques associés à la consommation abusive de substances. Mots-clés : Alcool, cannabis, adolescence, fonctions cognitives, symptômes de psychopathologie, devis longitudinaux, médiation, préventionThis thesis project addresses adolescents’ substance misuse and the sequential link between drug use, cognitive performance, and mental health outcomes in youth. The objectives of this thesis are: 1) to test the relation and sequence between cannabis or alcohol use and cognitive outcomes, 2) to verify if the relation between substance use and cognitive outcomes could help understand, in part, why young substance users report psychopathology symptoms, and 3) to review evidence-based interventions to prevent adolescent substance misuse and to assess what contribution could stem from the collected empirical data. The first chapter of this thesis assesses the relation and sequence between substance use behaviour of nearly 4000 youth from the Montreal metropolitan area (QC, Canada) and their cognitive development over four years. In a second chapter, this thesis analyzes how the association between substance use and cognitive outcomes could partially explain, over five years, the link observed between substance use and the appearance of psychopathology symptoms. In a final chapter, this thesis reviews data surrounding three types of preventative interventions to identify how empirical research could improve addiction prevention strategies. The data was extracted from a group of adolescents issued from the general population followed longitudinally in the scope of the Co-Venture study (n = 3826, from 12 years of age upon admission to the study, followed up annually for a period of five years). The results demonstrated that, although certain factors seem to predispose a sub-group of young people to early consumption and neuropsychological difficulties, drug consumption, especially cannabis consumption, seem to reliably predict a delay in the development of cognitive faculties, particularly the executive functions of the brain. This association with cannabis appears, to a small extent, to partially mediate the link already observed between said consumption and the emergence of psychopathology symptoms in adolescents. Still, predisposing factors seem to contribute to the association between these three variables. Although research would appear to show that several prevention strategies could be effective, most of them present modest and punctual results. The best-substantiated programs appeared to be those that adhered to a targeted prevention approach. To improve our methods of substance use prevention, one could take predisposing factors into account and use them to inform specialized intervention. Baseline cognitive functioning could constitute a particularly promising avenue. All the same, certain predisposing factors such as temperament or personality seem better equipped to prevent early-onset substance misuse and to address the psychological and cognitive issues associated with adolescent substance intake. To improve addiction prevention methods in adolescents, one could factor into account predisposing factors and use them to inform specialized intervention; for example, baseline cognitive functioning could constitute a promising avenue. In addition, temperament or personality traits seem better established to prevent early-onset substance use and to address the psychological and cognitive issues associated with adolescents’ substance misuse. Key words: Alcohol, cannabis, adolescence, cognitive functions, psychopathology symptoms, longitudinal data, mediation, preventio

Surfaces containing a family of plane curves not forming a fibration

We complete the classification of smooth surfaces swept out by a 1-dimensional family of plane curves that do not form a fibration. As a consequence, we characterize manifolds swept out by a 1-dimensional family of hypersurfaces that do not form a fibration.Comment: Author's post-print, final version published online in Collect. Mat

О влиянии свойств инструментального материала на усадку стружки при резании сталей

The exploitation of solar power for energy supply is of increasing importance. While technical development mainly takes place in the engineering disciplines, computer science offers adequate techniques for simulation, optimisation and controller synthesis. In this paper we describe a work from this interdisciplinary area. We introduce our tool for the optimisation of parameterised solar thermal power plants, and report on the employment of genetic algorithms and neural networks for parameter synthesis. Experimental results show the applicability of our approach

Numerical Simulations of Dynamos Generated in Spherical Couette Flows

We numerically investigate the efficiency of a spherical Couette flow at generating a self-sustained magnetic field. No dynamo action occurs for axisymmetric flow while we always found a dynamo when non-axisymmetric hydrodynamical instabilities are excited. Without rotation of the outer sphere, typical critical magnetic Reynolds numbers $Rm_c$ are of the order of a few thousands. They increase as the mechanical forcing imposed by the inner core on the flow increases (Reynolds number $Re$). Namely, no dynamo is found if the magnetic Prandtl number $Pm=Rm/Re$ is less than a critical value $Pm_c\sim 1$. Oscillating quadrupolar dynamos are present in the vicinity of the dynamo onset. Saturated magnetic fields obtained in supercritical regimes (either $Re>2 Re_c$ or $Pm>2Pm_c$) correspond to the equipartition between magnetic and kinetic energies. A global rotation of the system (Ekman numbers $E=10^{-3}, 10^{-4}$) yields to a slight decrease (factor 2) of the critical magnetic Prandtl number, but we find a peculiar regime where dynamo action may be obtained for relatively low magnetic Reynolds numbers ($Rm_c\sim 300$). In this dynamical regime (Rossby number $Ro\sim -1$, spheres in opposite direction) at a moderate Ekman number ($E=10^{-3}$), a enhanced shear layer around the inner core might explain the decrease of the dynamo threshold. For lower $E$ ($E=10^{-4}$) this internal shear layer becomes unstable, leading to small scales fluctuations, and the favorable dynamo regime is lost. We also model the effect of ferromagnetic boundary conditions. Their presence have only a small impact on the dynamo onset but clearly enhance the saturated magnetic field in the ferromagnetic parts. Implications for experimental studies are discussed