Stochastic generation of meteorological variables and effects on global models of water and carbon cycles in vegetation and soils

in Journal of Hydrology (1998), 213(1-4), 318-334

Global models of water and carbon cycles in continental vegetation and soils are usually forced with monthly mean climatic data-sets and thus neglect day to day variations of the weather. This treatment ... [more ▼]

Global models of water and carbon cycles in continental vegetation and soils are usually forced with monthly mean climatic data-sets and thus neglect day to day variations of the weather. This treatment may be justified for empirical models based on parametrizations validated at a monthly timescale. Mechanistic models handling hydrological and biological processes at much shorter timescales might, however, be largely affected by such an approximation, since the various processes described are highly nonlinear. A random generator of daily precipitations and temperatures applicable at the global scale has thus been developed from worldwide meteorological data covering 6 years of observations. The probability of a wet day is correlated to the weather encountered the previous day. The amount of precipitation, the daily mean temperature and the diurnal. range of temperature are described from the statistical point of view by the cumulative distribution functions (CDF) of three random variables. The CDF's a relative to temperatures are different for rainy and dry days. This stochastically generated weather field is used as input to IBM (Improved Bucket Model) and CARAIB (CARbon Assimilation In the Biosphere), two global models of respectively soil hydrology and vegetation productivity. Large differences in both the geographical distribution and the global value of soil water, vegetation productivity and carbon stocks are obtained between the model runs using monthly uniform weather on one side and randomly generated weather on the other. The main contribution to this difference at the global scale arises from the precipitation generation occurring as a result of high degree of nonlinearity of the interception scheme used in IBM. (C) 1998 Elsevier Science B.V. All rights reserved. [less ▲]

Stochastic gravito-inertial modes discovered by CoRoT in the hot Be star HD 51452

in Astronomy and Astrophysics (2012), 546

Context. Be stars are rapidly rotating stars with a circumstellar decretion disk. They usually undergo pressure and/or gravity pulsation modes excited by the κ-mechanism, i.e. an effect of the opacity of ... [more ▼]

Context. Be stars are rapidly rotating stars with a circumstellar decretion disk. They usually undergo pressure and/or gravity pulsation modes excited by the κ-mechanism, i.e. an effect of the opacity of iron-peak elements in the envelope of the star. In the Milky Way, p-modes are observed in stars that are hotter than or equal to the B3 spectral type, while g-modes are observed at the B2 spectral type and cooler. <BR /> Aims: We observed a B0IVe star, HD 51452, with the high-precision, high-cadence photometric CoRoT satellite and high-resolution, ground-based HARPS and SOPHIE spectrographs to study its pulsations in great detail. We also used the lower resolution spectra available in the BeSS database. <BR /> Methods: We analyzed the CoRoT and spectroscopic data with several methods: Clean-NG, FreqFind, and a sliding window method. We also analyzed spectral quantities, such as the violet over red (V/R) emission variations, to obtain information about the variation in the circumstellar environment. We calculated a stellar structure model with the ESTER code to test the various interpretation of the results. <BR /> Results: We detect 189 frequencies of variations in the CoRoT light curve in the range between 0 and 4.5 c d[SUP]-1[/SUP]. The main frequencies are also recovered in the spectroscopic data. In particular we find that HD 51452 undergoes gravito-inertial modes that are not in the domain of those excited by the κ-mechanism. We propose that these are stochastic modes excited in the convective zones and that at least some of them are a multiplet of r-modes (i.e. subinertial modes mainly driven by the Coriolis acceleration). Stochastically excited gravito-inertial modes had never been observed in any star, and theory predicted that their very low amplitudes would be undetectable even with CoRoT. We suggest that the amplitudes are enhanced in HD 51452 because of the very rapid stellar rotation. In addition, we find that the amplitude variations of these modes are related to the occurrence of minor outbursts. <BR /> Conclusions: Thanks to CoRoT data, we have detected a new kind of pulsations in HD 51452, which are stochastically excited gravito-inertial modes, probably due to its very rapid rotation. These modes are probably also present in other rapidly rotating hot Be stars. The CoRoT space mission, launched on December 27, 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD, and Science Programs), Germany, and Spain. This work uses observations partly made with the HARPS instrument at the 3.6-m ESO telescope (La Silla, Chile) in the framework of the LP182.D-0356, as well as data obtained with Sophie at OHP and from the BeSS database.Table 3 is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

Stochastic modeling in mechanics: course material

Learning material (2013)

Stochastic modelling of micro-organisms displacements in a stirred-tank bioreactor

Poster (2010)

Stochastic models to study the impact of mixing on a fed-batch culture of Saccharomyces cerevisiae.

in Biotechnology Progress (2006), 22(1), 259-69

The mechanisms of interaction between microorganisms and their environment in a stirred bioreactor can be modeled by a stochastic approach. The procedure comprises two submodels: a classical stochastic ... [more ▼]

The mechanisms of interaction between microorganisms and their environment in a stirred bioreactor can be modeled by a stochastic approach. The procedure comprises two submodels: a classical stochastic model for the microbial cell circulation and a Markov chain model for the concentration gradient calculus. The advantage lies in the fact that the core of each submodel, i.e., the transition matrix (which contains the probabilities to shift from a perfectly mixed compartment to another in the bioreactor representation), is identical for the two cases. That means that both the particle circulation and fluid mixing process can be analyzed by use of the same modeling basis. This assumption has been validated by performing inert tracer (NaCl) and stained yeast cells dispersion experiments that have shown good agreement with simulation results. The stochastic model has been used to define a characteristic concentration profile experienced by the microorganisms during a fermentation test performed in a scale-down reactor. The concentration profiles obtained in this way can explain the scale-down effect in the case of a Saccharomyces cerevisiae fed-batch process. The simulation results are analyzed in order to give some explanations about the effect of the substrate fluctuation dynamics on S. cerevisiae. [less ▲]

Stochastic Uncertainty Quantification of Eddy Currents in the Human Body by Polynomial Chaos Decomposition

Scientific conference (2011, July 07)

Stochastic Uncertainty Quantification of Eddy Currents in the Human Body by Polynomial Chaos Decomposition

(2011)

The finite element method can be used to compute the electromagnetic fields induced into the human body by envi- ronmental extremely low frequency fields. However, the electric properties of tissues are ... [more ▼]

The finite element method can be used to compute the electromagnetic fields induced into the human body by envi- ronmental extremely low frequency fields. However, the electric properties of tissues are not precisely known and may vary depending on the individual, his/her age and other physiological parameters. We propose to account for some uncertainties on the conductivities of the brain tissues and to spread them out to the induced fields by means of a non-intrusive approach based on the chaos Hermite polynomial with the finite element method as a black box [3], [4]. [less ▲]

Stock markets,banks and long run economic growth: a panel cointegration-based analysis

E-print/Working paper (2011)

The aim of this paper is to investigate the long run relationship between the development of banks and stock markets and economic growth. We make use of the Groen and Kleibergen (2003) panel cointegration ... [more ▼]

The aim of this paper is to investigate the long run relationship between the development of banks and stock markets and economic growth. We make use of the Groen and Kleibergen (2003) panel cointegration methodology to test the number of cointegrating vectors among these three variables for 5 developing countries. In addition, we test the direction of potential causality between nancial and economic development. Our results conclude to the existence of a single cointegrating vector between nancial development and growth and of causality going from nancial development to economic growth. We nd little evidence of reverse causation as well as bi-directional causality. [less ▲]

Stockage de bois sous bâches hermétiques

Conference given outside the academic context (2008)

Stockage géologique du CO2: l'étanchéité des puits

Master's dissertation (2011)

Carbon capture and storage is an innovator approach to fight climate changes through the reduction of greenhouse gas emissions. Abandoned coal mines are currently less studied than other reservoirs but ... [more ▼]

Carbon capture and storage is an innovator approach to fight climate changes through the reduction of greenhouse gas emissions. Abandoned coal mines are currently less studied than other reservoirs but could also be used for the storage of carbon dioxide. However the problem of shaft sealing appears to be central as far as the safety, economic, ecologic and health stakes of geological storage are concerned. The purpose of the present work is the study of shaft sealing in the framework of CO2 storage projects. More precisely the problem consists in the numerical study, with the LAGAMINE finite elements code, of gas transfers around a shaft seal system. A coupled hydro-mechanical model of unsaturated geomaterials is presented. The response of the flow model is first studied through a simple synthetic problem simulating the injection of gas in a concrete-made column. It stands out of this first modeling that the advection of the gas phase represents the main transfer mechanism of CO2 in highly unsaturated materials. Furthermore the setting of a bentonite barrier seal allows limiting considerably gas influx to the biosphere. A 2D axisymetric hydromechanical modeling of the Anderlues natural gas storage site is then performed. The design of the shaft seal system appears to be a determinant element to evaluate the risks of CO2 leakage. [less ▲]