Une ethnographie de l'intégration professionnelle du gardien de la paix et du policier constable

International audienc

Propriétés de superprisme des cristaux photoniques sur substrats SOI pour le démultiplexage en longueur d'onde

Ce travail de thèse constitue une contribution théorique et expérimentale aux études portant sur les cristaux photoniques (CPs) et leur utilisation pour le démultiplexage en longueur d'onde. Nous avons étudié la propagation de la lumière dans des CP bidimensionnels planaires sans défauts fabriqués à partir de substrats de silicium sur isolant. Pour cela, nous avons résolu le problème de réfraction entre un guide plan et un CP en utilisant le calcul 3D de leurs surfaces de dispersion. Des opérations supplémentaires sur celles-ci nous ont permis de caractériser la propagation des faisceaux dans le cristal et ainsi rechercher des structures permettant la réalisation de démultiplexeurs. Nos avons développé un procédé de fabrication de dispositifs à CPs sur SOI qui utilise les techniques de lithographie électronique et de gravure par plasma réactif. Nous avons étudié expérimentalement les effets de superprisme dans les CPs pour une large gamme de périodes et de facteurs de remplissage. Les phénomènes de dispersion observés ont pu être interprétés grâce aux modélisations développées, ce qui nous a permis de valider la méthode de calcul choisie. La compréhension des mécanismes de dispersion et la mise au point des étapes technologiques nous ont finalement permis de concevoir, réaliser, et caractériser un démultiplexeur CWDM à quatre canaux utilisant l'effet superprisme dans un cristal photonique. La structure présente une diaphonie de -16 dB pour un espacement en longueur d'onde de 25 nm, avec des pertes de 2 dB et une surface de cristal photonique de 2800 m .This PhD thesis brings a theoretical and experimental contribution to studies on photonic crystals (PCs) for wavelength demultiplexing. We have investigated light propagation within two dimensional planar PCs without defects, based on silicon on insulator (SOI) substrates. The modeling of light refraction at the interface between a planar waveguide and a PC has been achieved using 3D computations of the dispersion surfaces. Further calculations on band diagrams allowed characterizing the beam propagation inside the PC. Thanks to those calculations, PC structures have been explored for the realization of demultiplexers. A fabrication process of PCs on SOI substrates has been developed, using electron beam lithography and reactive ion etching technology. The superprism phenomena in PCs for a large panel of lattice size and filling factors have been experimentally studied. The observed dispersive effects correspond with modeling results. This agreement validated the calculation approach chosen for the problem. The understanding of dispersion effects and the development of the fabrication process has allowed designing, fabricating and characterizing a CWDM optical demultiplexer with four channels based on the superprism phenomena in PCs. The device presents a spectral spacing of 25 nm and a cross-talk level better than -16 dB using a 2800 m PhC region, with insertion losses of 2 dB.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Computation of light refraction at the surface of a photonic crystal using DtN approach

International audienceWhat we believe to be a new rigorous theoretical approach to the refraction of light at the interface of twodimensional photonic crystals is developed. The proposed method is based on the Dirichlet-to-Neumann (DtN) approach which consists of computing exactly the DtN operators associated with each half-space on both sides of the interface. It fully uses the properties of periodic optical media and takes naturally into account both the evanescent and propagative Bloch modes. Contrary to other proposed approaches, the new method is not based on modal expansions and their complicated electromagnetic field matching at the interfaces, but uses an operator vision. Intrinsically, each operator represents the effect along the interface of a particular medium independently of any medium and/or material that is placed in the other half-space. At the end, the whole computational effort to estimate DtN operators is restricted to the computation of a finite element problem in the periodicity cell of the photonic crystal. Field computations in arbitrary large part of the optical media can be then performed with a negligible computational effort. The method has been applied to the case of incoming plane waves as well as Gaussian beam profiles. It has successfully been compared with the standard plane wave expansion method and finite difference time domain (FDTD) simulations in the case of negative refraction, strongly dispersive, and lensing configurations. The proposed approach is amenable to the generalized study of dispersive phenomena in planar photonic crystals by a rigorous modeling approach avoiding the main drawbacks of FDTD. It is amenable to the study of arbitrary cascaded periodic optical media and photonic crystal heterostructures. © 2010 Optical Society of America

Establishing Evacuee Reception Centres by Czech Red Cross Humanitarian Crews

Import 26/06/2013Diplomová práce se zabývá zřizováním přijímacích středisek pro evakuované osoby Humanitárními jednotkami Českého červeného kříže. V práci je provedena analýza stávajícího systému fungování přijímacích středisek. Jsou zde vymezeny nedostatky v činnosti těchto jednotek, které zohledňují zejména výsledky cvičení Humanitární jednotky Českého červeného kříže Blansko. V závěru práce jsou navržena opatření pro zkvalitnění činnosti Humanitárních jednotek Českého červeného kříže při zřizování přijímacích středisek pro evakuované osoby.The thesis deals with establishing of receiving centres for evacuees by Humanitarian teams of Czech Red Cross. The thesis opens with an analysis presenting a current system of running the receiving centres. The main focus is on defining failings in functioning of these units which are based on results obtained from trainings of the Humanitarian Czech Red Cross in Blansko. Finally, in the conclusion there is an attempt to suggest actions for improving work of Humanitarian teams of the Czech Red Cross in the process of establishing the receiving centres.Prezenční050 - Katedra ochrany obyvatelstvavelmi dobř

An Earth-mass planet orbiting alpha Centauri B

International audienceExoplanets down to the size of Earth have been found, but not in the habitable zone--that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water-carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth-Sun distance)