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.

Large deviations of extreme eigenvalues of random matrices

Abstract: We calculate analytically the probability of large deviations from its mean of the largest (smallest) eigenvalue of random matrices belonging to the Gaussian orthogonal, unitary, and symplectic ensembles. In particular, we show that the probability that all the eigenvalues of an (N x N) random matrix are positive (negative) decreases for large N as approximately exp[-betatheta(0)N2] where the parameter beta characterizes the ensemble and the exponent theta(0)=(ln3)/4=0.274 653... is universal. We also calculate exactly the average density of states in matrices whose eigenvalues are restricted to be larger than a fixed number zeta, thus generalizing the celebrated Wigner semicircle law. The density of states generically exhibits an inverse square-root singularity at zeta.

Betic-Rifian and Tyrrhenian Arcs : Distinctive Features, Genesis and Development Stages

Abstract: The Betic-Rifian and the Tyrrhenian Arcs bound both ends of the Maghrebide Chain.,Their external zones originated from the South-Iberian, African and Apulian margins while the internal zones, with large basement nappes, originated from the Alboran, Kabylian, Peloritan and Calabrian (“ALKAPECA”) South-European margins. During the Alpine convergence of the European and African plates, ALKAPECA was cut into blocks. The ejection along strike-slip faults of the blocks issued from the Western and Eastern extremities of ALKAPECA gave rise to the Arc of Gibraltar and to the Tyrrhenian Arc. The Western block (Alboran) was deformed as it was introduced into the area, reducing continuously throughout time, between Europe and Africa and as it collided with more and more external zones. The Eastern block (Aeolian) has bent the initially continuous African and Apulian margins. The Tyrrhenian Arc could be predeterminated during Jurassic distensional events : it corresponds to the paleogeographic angle made by the Ligurian basin (NE-SW trending) and the Mograbin basin (E-W trending).

Autoregressive Forecasting of Some Functional Climatic Variations

Abstract: Many variations such as the annual cycle in sea surface temperatures can be considered to be smooth functions and are appropriately described using methods from functional data analysis. This study defines a class of functional autoregressive (FAR) models which can be used as robust predictors for making forecasts of entire smooth functions in the future. The methods are illustrated and compared with pointwise predictors such as SARIMA by applying them to forecasting the entire annual cycle of climatological El Nino- Southern Oscillation (ENSO) time series one year ahead. Forecasts for the period 1987-1996 suggest that the FAR functional predictors show some promising skill, compared to traditional scalar SARIMA forecasts which perform poorly.

Mechanistic Aspects of Phenol Electrochemical Degradation by Oxidation on a Ta / PbO2 Anode

Abstract: The electrochemical oxidation of phenol in an aqueous solution is a complex transformation involving several transfer steps of oxygen atoms and electrons. Transfer of the oxygen atom occurs through the intermediary of hydroxyl radicals adsorbed on the active sites of the anode. Galvanostatic electrolyses of phenol (10.5 to 105 mmol/dm{sup 3}) in aqueous solution at pH 2 on a Ta/PbO{sub 2} anode were followed by high-pressure liquid chromatography and by analysis of the total organic carbon. Hydroquinone, catechol, 1,4-benzoquinone (1,4-BQ), maleic and fumaric acids, and carbon dioxide are the main products. The nonidentified products consist mainly of polymers. Study of the influence of temperature shows that the rate consumption of phenol initially at 21 mmol/dm{sup 3} is mass transport limited. CO{sub 2} is immediately formed following the 1,4-BQ-maleic acid pathway involving 20 faradays and forming 4 mol of CO{sub 2} and/or the 1,4-BQ-intermediary in C2 pathway at 16 faradays with formation of 2 mol of CO{sub 2}. The faradaic yield values show that a phenol molecule adsorbed on a catalytic site undergoes a succession of oxidation steps involving, on average, five electrons without desorption of the intermediate products. This number of electrons varies according to the operating conditions (temperature, anodicmore » current density, initial phenol concentration, hydrodynamic conditions, etc.). The mean faradaic yield decreases during electrolysis; it can reach 70% at the beginning of electrolysis of a 21 mmol/dm{sup 3} phenol solution for an anodic current density of 100 mA/cm{sup 2}. The phenol conversion into insoluble polymers increases as a function of its initial concentration and the anodic current density but it does not exceed 10%.« less