Observatoires de la vie étudiante des universités contre Portail étudiant du Ministère : conflit statistique, territorial ou organisationnel?

En France, l’université a fait longtemps l’objet d’un désintérêt sociologique, et ce, contrairement à celle des pays anglo-saxons. Cet article participe donc à l’ouverture de la boîte noire universitaire par une réflexion au coeur de l’actualité politique relative à l’autonomie et à l’adaptabilité de l’université au monde du travail. Afin de répondre à cette problématique contemporaine, le Ministère de l’enseignement supérieur et de la recherche a proposé la création d’un nouveau site Web, le Portail étudiant, auquel s’opposent les observatoires de la vie étudiante (OVE). L’analyse de ce conflit d’ordre méthodologique soulève un questionnement plus large sur la prégnance de la dimension territoriale dans la construction des indicateurs statistiques réalisés par les OVE.In France, unlike in Anglo-Saxon countries, university has been for a long time the object of a sociological indifference. This article contributes to the opening of the university black box and reflects on university autonomy and adaptability to the work field. In view of this problem, the French ministry of higher education and research has created a new Web site, the Portail étudiant, to which the observatories of student life (OVE) are opposed. The analysis of the methodological conflict raises a broader questioning on the importance of territorial dimension in the construction of statistical indicators realized by the OVE

El desarrollo de un pensamiento pluridimensional. The development of a thought pluridimensional

Este texto realiza una breve caracterización del contexto actual: un mundo que exige formas de comprensión más globales, más integradoras, para poder enfrentar los nuevos retos. Se considera que las ciencias naturales, por su parte, contribuyeron a marcar una ruptura con el ideal moderno de una ciencia cartesiano-positivista y permitieron introducir por primera vez las nociones complejas de desorden y auto-organización, la cuales dieron pie para hablar del método complejo de investigación que permite comprender el conocimiento del conocimiento.También se reflexiona acerca de la posibilidad de considerar un anti/multi/a/contra-método para calificar la búsqueda de una estrategia de investigación pluridimensional. Cuestiona la noción de método a la luz de las distintas orientaciones que se pueden evidenciar entre una perspectiva cartesiana (definición rígida y unilateral de un planteamiento discriminatorio) y un enfoque complejo (implica la idea de modelo flexible y adaptativo, de un horizonte cambiante que se puede alcanzar desde diferentes caminos).Asimismo, se explica que la complejidad no es en ninguna forma abandono de la ambición científica ni una invitación a la procrastinación intelectual, pues el pensamiento complejo no supone planteamientos confusos ni propone el abandono de la búsqueda misma de este método

Domain-wall motion induced by spin transfer torque delivered by helicity-dependent femtosecond laser

In magnetic wires with perpendicular anisotropy, moving domain with only current or only circularly polarized light requires a high power. Here, we propose to reduce it by using both short current pulses and femtosecond laser pulses simultaneously. The wires were made out of perpendicularly magnetized film of Pt/Co/Ni/Co/Pt. The displacement of the domain wall is found to be dependent on the laser helicity. Based on a quantitative analysis of the current-induced domain wall motion, the spin orbit torque contribution can be neglected when compared to the spin transfer torque contribution. The effective field of the spin transfer torque is extracted from the pulsed field domain wall measurements. Finally, our result can be described using the Fatuzzo-Labrune model and considering the effective field due to the polarized laser beam, the effective field due to spin transfer torque, and the Gaussian temperature distribution of the laser spot.Comment: 14 pages, 4 figure

Bayesian separation of spectral sources under non-negativity and full additivity constraints

This paper addresses the problem of separating spectral sources which are linearly mixed with unknown proportions. The main difficulty of the problem is to ensure the full additivity (sum-to-one) of the mixing coefficients and non-negativity of sources and mixing coefficients. A Bayesian estimation approach based on Gamma priors was recently proposed to handle the non-negativity constraints in a linear mixture model. However, incorporating the full additivity constraint requires further developments. This paper studies a new hierarchical Bayesian model appropriate to the non-negativity and sum-to-one constraints associated to the regressors and regression coefficients of linear mixtures. The estimation of the unknown parameters of this model is performed using samples generated using an appropriate Gibbs sampler. The performance of the proposed algorithm is evaluated through simulation results conducted on synthetic mixture models. The proposed approach is also applied to the processing of multicomponent chemical mixtures resulting from Raman spectroscopy.Comment: v4: minor grammatical changes; Signal Processing, 200

Potentiality of Pr3+- and Pr3+ + Ce3+ -doped crystals for tunable UV upconversion lasers

Gain experiments based on the interconfigurational 4f5d to 4f2 optical transitions in praseodymium-doped fluoride crystals were achieved. The measurements were performed under upconversion pumping of the 4f5d excited configuration via the 3PJ, 1I6 intermediate levels of the 4f2 configuration, using a pump-probe set-up with three synchronized Q-switched nanosecond pulsed lasers. In spite of this two-step excitation, optical losses, due excited state absorption (4f5d→conduction band transition) leading to Pr3+ ion photoionisation and color center formation, were too high to observe any amplification. However, these losses were found definitely weaker in fluoride crystals (Pr:LiYF4, Pr:LiLuF4) than in oxides (Pr:YAlO3) and, probing the 5d→4f emission of Ce3+ under two-step excitation pumping of the Pr3+ 4f5d states in co-doped Pr,Ce:LiLuF4 crystals, no losses were detected at all. © 2002 Elsevier Science B.V. All rights reserved

Single shot time-resolved magnetic x-ray absorption at a Free Electron Laser

Ultrafast dynamics are generally investigated using stroboscopic pump-probe measurements, which characterize the sample properties for a single, specific time delay. These measurements are then repeated for a series of discrete time delays to reconstruct the overall time trace of the process. As a consequence, this approach is limited to the investigation of fully reversible phenomena. We recently introduced an off-axis zone plate based X-ray streaking technique, which overcomes this limitation by sampling the relaxation dynamics with a single femtosecond X-ray pulse streaked over a picosecond long time window. In this article we show that the X-ray absorption cross section can be employed as the contrast mechanism in this novel technique. We show that changes of the absorption cross section on the percent level can be resolved with this method. To this end we measure the ultrafast magnetization dynamics in CoDy alloy films. Investigating different chemical compositions and infrared pump fluences, we demonstrate the routine applicability of this technique. Probing in transmission the average magnetization dynamics of the entire film, our experimental findings indicate that the demagnetization time is independent of the specific infrared laser pump fluence. These results pave the way for the investigation of irreversible phenomena in a wide variety of scientific areas.Comment: 9 pages, 5 figure

Indirect excitation of ultrafast demagnetization

Does the excitation of ultrafast magnetization require direct interaction between the photons of the optical pump pulse and the magnetic layer? Here, we demonstrate unambiguously that this is not the case. For this we have studied the magnetization dynamics of a ferromagnetic cobalt/palladium multilayer capped by an IR-opaque aluminum layer. Upon excitation with an intense femtosecond-short IR laser pulse, the film exhibits the classical ultrafast demagnetization phenomenon although only a negligible number of IR photons penetrate the aluminum layer. In comparison with an uncapped cobalt/palladium reference film, the initial demagnetization of the capped film occurs with a delayed onset and at a slower rate. Both observations are qualitatively in line with energy transport from the aluminum layer into the underlying magnetic film by the excited, hot electrons of the aluminum film. Our data thus confirm recent theoretical predictions