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Search Results: 1 - 10 of 117692 matches for " T. Mathevet "
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Application of time-series analyses to the hydrological functioning of an Alpine karstic system: the case of Bange-L’Eau-Morte
T. Mathevet,M. l. Lepiller,A. Mangin
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2004,
Abstract: This paper analyses the hydrological functioning of the Bange-L’Eau-Morte karstic system using classical and original techniques, recession curves, correlation and spectral analyses, noise analysis and wavelet analyses. The main characteristics that can be deduced are the recession coefficients, the dynamic volume of storage, the response time of the system, the quickflow and baseflow components and the snowmelt characteristics. The non-stationary and timescale-dependent behaviour of the system is studied and particular features of the runoff are shown. The step-by-step use of these different techniques provides a general methodology applicable to different karstic systems to provide quantifiable and objective criteria for differentiation and comparison of karstic systems. Keywords: karstic hydrology, Bauges mountains, recession curves, correlation and spectral analysis, wavelet analysis, snowmelt
Statistical processing of forecasts for hydrological ensemble prediction: a comparative study of different bias correction strategies
I. Zalachori, M.-H. Ramos, R. Gar on, T. Mathevet,J. Gailhard
Advances in Science and Research (ASR) , 2012, DOI: 10.5194/asr-8-135-2012
Abstract: The aim of this paper is to investigate the use of statistical correction techniques in hydrological ensemble prediction. Ensemble weather forecasts (precipitation and temperature) are used as forcing variables to a hydrologic forecasting model for the production of ensemble streamflow forecasts. The impact of different bias correction strategies on the quality of the forecasts is examined. The performance of the system is evaluated when statistical processing is applied: to precipitation and temperature forecasts only (pre-processing from the hydrological model point of view), to flow forecasts (post-processing) and to both. The pre-processing technique combines precipitation ensemble predictions with an analog forecasting approach, while the post-processing is based on past errors of the hydrological model when simulating streamflows. Forecasts from 11 catchments in France are evaluated. Results illustrate the importance of taking into account hydrological uncertainties to improve the quality of operational streamflow forecasts.
A quasi-monomode guided atom-laser from an all-optical Bose-Einstein condensate
A. Couvert,M. Jeppesen,T. Kawalec,G. Reinaudi,R. Mathevet,David Guery-Odelin
Physics , 2008, DOI: 10.1209/0295-5075/83/50001
Abstract: We report the achievement of an optically guided and quasi-monomode atom laser, in all spin projection states ($m_F =$ -1, 0 and $+1$) of F=1 in Rubidium 87. The atom laser source is a Bose-Einstein condensate (BEC) in a crossed dipole trap, purified to any one spin projection state by a spin-distillation process applied during the evaporation to BEC. The atom laser is outcoupled by an inhomogenous magnetic field, applied along the waveguide axis. The mean excitation number in the transverse modes is $ = 0.65 \pm 0.05$ for $m_F = 0 $ and $ = 0.8 \pm 0.3$ for the low field seeker $m_F = -1$.
Faut-il en finir avec le développement durable ? Regard sur les zones humides méditerranéennes
Rapha?l Mathevet
Les Ateliers de l’éthique , 2006,
Abstract: Based on biodiversity conservation projects or integrated management projects of the Mediterranean wetlands, this paper shows that their sustainable development mainly depends on a political thinking about misdevelopment. The biodiversity conservation projects try with various successes to conciliate conservation and development. Amongst the problems, the decrease of the fresh water resource is added to the social disparity and the poverty. Promoting and managing institutional changes, increasing the stakeholders’social capital, learning and collectively deciding are the main keys of sustainable development. Many disparities still exist in the democratic processes atthe local,regional and national levels but a participative developmentis suggested.More centered on the needs of local communities than on economic growth, being more reflexive, and setting the science’s critic and the co-construction of projects at the heart of the process, this participative development may offer an alternative to the prevalent approaches that were used until now. The sustainable development of the Mediterranean wetlands is still promising if it increases the adaptive capacity of both social and ecological systems in order to reject any irreversibility.
HESS Opinions "Crash tests for a standardized evaluation of hydrological models"
V. Andréassian, C. Perrin, L. Berthet, N. Le Moine, J. Lerat, C. Loumagne, L. Oudin, T. Mathevet, M.-H. Ramos,A. Valéry
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2009,
Abstract: As all hydrological models are intrinsically limited hypotheses on the behaviour of catchments, models – which attempt to represent real-world behaviour – will always remain imperfect. To make progress on the long road towards improved models, we need demanding tests, i.e. true crash tests. Efficient testing requires large and varied data sets to develop and assess hydrological models, to ensure their generality, to diagnose their failures, and ultimately, help improving them.
Zeeman slowers made simple with permanent magnets in a Halbach configuration
P. Cheiney,O. Carraz,D. Bartoszek-Bober,S. Faure,F. Vermersch,C. M. Fabre,G. L. Gattobigio,T. Lahaye,D. Guéry-Odelin,R. Mathevet
Physics , 2011, DOI: 10.1063/1.3600897
Abstract: We describe a simple Zeeman slower design using permanent magnets. Contrary to common wire-wound setups no electric power and water cooling are required. In addition, the whole system can be assembled and disassembled at will. The magnetic field is however transverse to the atomic motion and an extra repumper laser is necessary. A Halbach configuration of the magnets produces a high quality magnetic field and no further adjustment is needed. After optimization of the laser parameters, the apparatus produces an intense beam of slow and cold 87Rb atoms. With a typical flux of 1 - 5 \times 10^10 atoms/s at 30 ms^-1, our apparatus efficiently loads a large magneto-optical trap with more than 10^10 atoms in one second, which is an ideal starting point for degenerate quantum gases experiments.
All-optical atom surface traps implemented with one-dimensional planar diffractive microstructures
O. Alloschery,R. Mathevet,J. Weiner
Physics , 2006, DOI: 10.1364/OE.14.012568
Abstract: We characterize the loading, containment and optical properties of all-optical atom traps implemented by diffractive focusing with one-dimensional (1D) microstructures milled on gold films. These on-chip Fresnel lenses with focal lengths of the order of a few hundred microns produce optical-gradient-dipole traps. Cold atoms are loaded from a mirror magneto-optical trap (MMOT) centered a few hundred microns above the gold mirror surface. Details of loading optimization are reported and perspectives for future development of these structures are discussed.
Fizeau's "aether-drag" experiment in the undergraduate laboratory
Thierry Lahaye,Pierre Labastie,Renaud Mathevet
Physics , 2012, DOI: 10.1119/1.3690117
Abstract: We describe a simple realization of Fizeau's "aether-drag" experiment. Using an inexpensive setup, we measure the phase shift induced by moving water in a laser interferometer and find good agreement with the relativistic prediction or, in the terms of nineteenth century physics, with Fresnel's partial-drag theory. This appealing experiment, particularly suited for an undergraduate laboratory project, not only allows a quantitative measurement of a relativistic effect on a macroscopic system, but also constitutes a practical application of important concepts of optics, data acquisition and processing, and fluid mechanics.
Computation of the phase induced by non-newtonian gravitational potentials in atom interferometry
R. Mathevet,R. Delhuille,C. Rizzo
Physics , 2002, DOI: 10.1088/0264-9381/19/8/101
Abstract: In this letter we present a computation of the phase induced by test masses of different geometry, in the framework of non-newtonian gravitation, on an ideal separated arms atom interferometer. We deduce the related limits on the non-newtonian gravitational strength in the sub-millimeter region for the potential range. These limits would be comparable with the best existing experimental limits but with the advantage of using a microscopic probe.
Waypoints on a Journey of Discovery: Mental Models in Human-Environment Interactions
Timothy Lynam,Raphael Mathevet,Michel Etienne,Samantha Stone-Jovicich
Ecology and Society , 2012, DOI: 10.5751/es-05118-170323
Abstract: Although the broad concept of mental models is gaining currency as a way to explore the link between how people think and interact with their world, this concept is limited by a theoretical and practical understanding of how it can be applied in the study of human-environment relationships. Tools and processes are needed to be able to elicit and analyze mental models. Because mental models are not directly observable, it is also important to understand how the application of any tools and processes affects what is measured. Equally important are the needs to be clear on the intent of the elicitation and to design the methods and choose the settings accordingly. Through this special edition, we explore how mental models are elicited using two approaches applied in two case-study regions. We analyze two approaches used in the Crocodile River catchment of South Africa: a graphically based approach, i.e., actors, resources, dynamics, and interactions (ARDI); and an interview- or text-based approach, i.e., consensus analysis (CA). A further experiment in the Rhone Delta (Camargue), France, enabled us to test a cross-over between these two methods using ARDI methodology to collect data and CA to analyse it. Here, we compare and explore the limitations and challenges in applying these two methods in context and conclude that they have much to offer when used singly or in combination. We first develop a conceptual framework as a synthesis of key social and cognitive psychology literature. We then use this framework to guide the enquiry into the key lessons emerging from the comparative application of these approaches to eliciting mental models in the two case regions. We identify key gaps in our knowledge and suggest important research questions that remain to be addressed.
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