Paul Sabatier University

About: Paul Sabatier University is a education organization based out in Toulouse, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 15431 authors who have published 23386 publications receiving 858364 citations.

WIND observations of coherent electrostatic waves in the solar wind

Abstract: . The time domain sampler (TDS) experiment on WIND measures electric and magnetic wave forms with a sampling rate which reaches 120 000 points per second. We analyse here observations made in the solar wind near the Lagrange point L1. In the range of frequencies above the proton plasma frequency fpi and smaller than or of the order of the electron plasma frequency fpe, TDS observed three kinds of electrostatic (e.s.) waves: coherent wave packets of Langmuir waves with frequencies f ~ fpe, coherent wave packets with frequencies in the ion acoustic range fpi f ~ 25λD, there is a small but finite electric potential drop, implying an average electric field generally directed away from the Sun. The IES wave forms, which have not been previously reported in the solar wind, are similar, although with a smaller amplitude, to the weak double layers observed in the auroral regions, and to the electrostatic solitary waves observed in other regions in the magnetosphere. We have also studied the solar wind conditions which favour the occurrence of the three kinds of waves: all these e.s. waves are observed more or less continuously in the whole solar wind (except in the densest regions where a parasite prevents the TDS observations). The type (wave packet or IES) of the observed LF waves is mainly determined by the proton temperature and by the direction of the magnetic field, which themselves depend on the latitude of WIND with respect to the heliospheric current sheet. Key words. Interplanetary physics (plasma waves and turbulence; solar wind plasma). Space plasma physics (electrostatic structures).

Virtual Atomic and Molecular Data Centre

Abstract: The Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu) is a European Union funded collaboration between groups involved in the generation, evaluation, and use of atomic and molecular data. VAMDC aims to build a secure, documented, flexible and interoperable e-science environment-based interface to existing atomic and molecular data. The project will cover establishing the core consortium, the development and deployment of the infrastructure and the development of interfaces to the existing atomic and molecular databases. It will also provide a forum for training potential users and dissemination of expertise worldwide. This review describes the scope of the VAMDC project; it provides a survey of the atomic and molecular data sets that will be included plus a discussion of how they will be integrated. Some applications of these data are also discussed.

Persistence exponents for fluctuating interfaces

Abstract: Numerical and analytic results for the exponent $\ensuremath{\theta}$ describing the decay of the first return probability of an interface to its initial height are obtained for a large class of linear Langevin equations. The models are parametrized by the dynamic roughness exponent $\ensuremath{\beta}$, with $0l\ensuremath{\beta}l1$; for $\ensuremath{\beta}=\frac{1}{2}$ the time evolution is Markovian. Using simulations of solid-on-solid models, of the discretized continuum equations as well as of the associated zero-dimensional stationary Gaussian process, we address two problems: The return of an initially flat interface, and the return to an initial state with fully developed steady-state roughness. The two problems are shown to be governed by different exponents. For the steady-state case we point out the equivalence to fractional Brownian motion, which has a return exponent ${\ensuremath{\theta}}_{S}=1\ensuremath{-}\ensuremath{\beta}$. The exponent ${\ensuremath{\theta}}_{0}$ for the flat initial condition appears to be nontrivial. We prove that ${\ensuremath{\theta}}_{0}\ensuremath{\rightarrow}\ensuremath{\infty}$ for $\ensuremath{\beta}\ensuremath{\rightarrow}0$, ${\ensuremath{\theta}}_{0}g~{\ensuremath{\theta}}_{S}$ for $\ensuremath{\beta}l$$\frac{1}{2}$ and ${\ensuremath{\theta}}_{0}l~{\ensuremath{\theta}}_{S}$ for $\ensuremath{\beta}g$$\frac{1}{2}$, and calculate ${\ensuremath{\theta}}_{0,S}$ perturbatively to first order in an expansion around the Markovian case $\ensuremath{\beta}=$$\frac{1}{2}$. Using the exact result ${\ensuremath{\theta}}_{S}=1\ensuremath{-}\ensuremath{\beta}$, accurate upper and lower bounds on ${\ensuremath{\theta}}_{0}$ can be derived which show, in particular, that ${\ensuremath{\theta}}_{0}g~(1\ensuremath{-}\ensuremath{\beta}{)}^{2}/\ensuremath{\beta}$ for small $\ensuremath{\beta}$.

Functional trait variation and sampling strategies in species-rich plant communities

Abstract: 1. Despite considerable interest in the application of plant functional traits to questions of community assembly and ecosystem structure and function, there is no consensus on the appropriateness of sampling designs to obtain plot-level estimates in diverse plant communities. 2. We measured 10 plant functional traits describing leaf and stem morphology and ecophysiology for all trees in nine 1-ha plots in terra firme lowland tropical rain forests of French Guiana (N = 4709). 3. We calculated, by simulation, the mean and variance in trait values for each plot and each trait expected under seven sampling methods and a range of sampling intensities. Simulated sampling methods included a variety of spatial designs, as well as the application of existing data base values to all individuals of a given species. 4. For each trait in each plot, we defined a performance index for each sampling design as the proportion of resampling events that resulted in observed means within 5% of the true plot mean, and observed variance within 20% of the true plot variance. 5. The relative performance of sampling designs was consistent for estimations of means and variances. Data base use had consistently poor performance for most traits across all plots, whereas sampling one individual per species per plot resulted in relatively high performance. We found few differences among different spatial sampling strategies; however, for a given strategy, increased intensity of sampling resulted in markedly improved accuracy in estimates of trait mean and variance. 6. We also calculated the financial cost of each sampling design based on data from our 'every individual per plot' strategy and estimated the sampling and botanical effort required. The relative performance of designs was strongly positively correlated with relative financial cost, suggesting that sampling investment returns are relatively constant. 7. Our results suggest that trait sampling for many objectives in species-rich plant communities may require the considerable effort of sampling at least one individual of each species in each plot, and that investment in complete sampling, though great, may be worthwhile for at least some traits.