Remarks on Finite W Algebras

The property of some finite W algebras to be the commutant of a particular subalgebra of a simple Lie algebra G is used to construct realizations of G. When G=so(4,2), unitary representations of the conformal and Poincare algebras are recognized in this approach, which can be compared to the usual induced representation technique. When G=sp(2,R) or sp(4,R), the anyonic parameter can be seen as the eigenvalue of a W generator in such W representations of G. The generalization of such properties to the affine case is also discussed in the conclusion, where an alternative of the Wakimoto construction for sl(2) level k is briefly presented. This mini review is based on invited talks presented by P. Sorba at the ``Vth International Colloquium on Quantum Groups and Integrable Systems'', Prague (Czech Republic), June 1996; ``Extended and Quantum Algebras and their Applications to Physics'', Tianjin (China), August 1996; ``Selected Topics of Theoretical and Modern Mathematical Physics'', Tbilisi (Georgia), September 1996; to be published in the Proceedings.Comment: LaTeX, 16 pages, references adde

Non-Polynomial Realizations of W-Algebras

Relaxing first-class constraint conditions in the usual Drinfeld-Sokolov Hamiltonian reduction leads, after symmetry fixing, to realizations of W algebras expressed in terms of all the J-current components. General results are given for G a non exceptional simple (finite and affine) algebra. Such calculations directly provide the commutant, in the (closure of) G enveloping algebra, of the nilpotent subalgebra $G_-$, where the subscript refers to the chosen gradation in G. In the affine case, explicit expressions are presented for the Virasoro, $W_3$, and Bershadsky algebras at the quantum level.Comment: 33 pages, LaTeX file, minor LaTex error correcte

W-realization of Lie algebras: application to so(4,2) and Poincare algebras

The property of some finite W-algebras to appear as the commutant of a particular subalgebra in a simple Lie algebra G is exploited for the obtention of new G-realizations from a "canonical" differential one. The method is applied to the conformal algebra so(4,2) and therefore yields also results for its Poincare subalgebra. Unitary irreducible representations of these algebras are recognized in this approach, which is naturally compared -or associated- to the induced representation technic.Comment: LaTeX, 18 page

1.55 μm integrated modelocked semiconductor lasers

This thesis presents research on, and the realization of compact InP/InGaAsP integrated passively modelocked lasers (MLL) operating in the 1.55 µm wavelength range. The goal of this work was to obtain modelocked laser designs at a repetition rate of several tens of GHz that can be integrated with other devices on a single semiconductor wafer. These modelocked lasers should be usable as optical pulse sources in an all-optical clock recovery application in optical time domain multiplexing (OTDM) systems. The integration of the modelocked laser on a single chip is achieved using the active-passive integration technique. This technique allows one to integrate active components such as optical amplifiers and saturable absorbers, with passive components such as waveguides and optical power splitters. The modelocking mechanism of the integrated lasers is passive modelocking using a slow saturable absorber. The saturable absorber is a short optical amplifier section that is reversely biased. The work was largely concentrated on ring laser type cavities. Such a configuration has many advantages. Firstly it allows one to fix the repetition rate of the laser by photolithography. It also provides better performance thanks to the two counter-propagating pulses which collide in the saturable absorber. Finally the output of the laser can be directly interconnected on the same wafer with other devices such as an all-optical switch or a pulse compressor. From the first realization of integrated ring modelocked lasers (RMLLs) using active-passive integration and a demonstration of a device at 27 GHz, many issues came up and have been addressed in this thesis. First, the understanding of the modelocking mechanism and other dynamics needed to be better understood. To address this issue, a simulation tool of RMLL was developed. Simulation results showed that symmetrical cavities show a much wider operating range for stable modelocking. The transitions from a modelocked state of the laser to another operating regime have been explored with the model. The simulation tool requires parameters describing the gain properties of the material. These have been accurately measured using a new type of high resolution spectrum analyzer. Another important issue which came out from the first RMLL realization was the necessity to reduce all the reflections inside the modelocked laser cavity and in particular the reflections at the active-passive interfaces. Special efforts have therefore been made to characterize the optical losses and reflections at those interfaces and to minimize them to a sufficiently low value of less than -50 dB. To validate techniques of fabrication and materials required to achieve high repetition rate RMLL designs, the realization of more compact devices through the use of deep etching has been investigated in this thesis. Results are presented on, at that time, the world’s most compact AWG using a double-etch technique, and the world’s first InAs/InP quantum dot (QD) lasers employing narrow deeply etched ridge active waveguides in the 1.55 µm wavelength region. Before realizing a final RMLL design on an active-passive wafer, a series of allactive devices has been designed, fabricated and characterized. These all-active chips provided material for the gain measurements and allowed to look further into short pulse laser characterization techniques and to test designs for reducing reflections from other intra-cavity components. The results of the all-active MLLs have been obtained in different configurations. Firstly, 20 GHz and 40 GHz linear all active Fabry-Pérot MLL (FPMLL) lasers have been successfully fabricated. Modelocking has been achieved with these lasers in the colliding pulse modelocked (CPM) and self CPM configurations. Pulse lengths down to 1.6 ps (at 20 GHz) have been observed. A 40 GHz repetition rate was demonstrated in a CPM laser with a Saturable Absorber (SA) positioned in the center of the FP cavity. All-active 15 GHz RMLLs have also been successfully fabricated. These lasers show a relatively good timing stability due to the ring configuration. Measured output pulses are highly chirped and an FWHM bandwidth of up to 4.5 nm was obtained. Such lasers with high bandwidth pulses and compatible with active-passive integration are of great interest for optical code division multiple access applications, where information is coded in the spectrum. Finally, first results from MLLs realized on an active-passive wafer are presented. Passive modelocking has been demonstrated in these integrated Extended Cavity FPMLLs with minimized intra-cavity reflections. Pulses of 2.1 ps duration and with a small pedestal have been observed. The pulses are close to transform-limited. The longer timescale dynamics of the EC-FPMLLs are reduced compared to the all-active FPMLLs, which is understood to be due to the short amplifier section. The use of a MLL at 20 GHz for the all optical clock recovery (AOCR) application and a special RMLL design for AOCR at 40 GHz are presented in the last chapter of this thesis. Many characteristics of the AOCR at 20 GHz could be quantified. The design of the 40 GHz RMLL laser is for an active-passive wafer. The design utilizes all the minimizations of small intra-cavity reflections. For the AOCR application a novel way to couple the optical input signal into the MLL via a separate waveguide is presented. Based on the accumulated results presented in this thesis the timing jitter of the clock recovered from this laser is expected to be sufficiently low to comply with the telecom requirements at 40 GHz

Development of Boys and Young Men of Color: Implications of Developmental Science for My Brother's Keeper Initiative

This report describes the My Brother's Keeper Initiative. The report summarizes ideas gleaned from developmental science that may be useful in efforts to reach five of the six initiative's goals: school readiness; third-grade literacy; high school and college graduation; and reduction of violence. The authors discuss features of the initiative designed to promote more positive outcomes and highlight the contributions that developmental science may make to each. Policy recommendations are provided and a discussion about how developmental science may contribute to national dialogue and policy formation

Adversity and child development in South Africa: effects of socio-economic status and violence on functioning at age 4

African Studies Seminar series. Paper presented 19 February, 1996The social and political transformations currently under way in South Africa provide reasonable grounds for optimism about the future of this country and of most of its people. However the seeds of violence, social upheaval, and economic injustice planted and nurtured during the apartheid era continue to yield a bitter and abundant harvest. This enduring legacy of violence and poverty is endemic to the daily experiences of many African families(Ramphele) 1993). A purpose of this report is to review empirical data from an investigation of the development of South African children in order to determine whether socioeconomic status (marital status, educational status and access to material resources) and their concomitants (exposure to community and family violence) predict behavioral and emotional functioning. The central question to be addressed here can be stated as follows: By age 4 are the offspring of parents with limited access to material resources and who live in dangerous areas more likely to exhibit decrements or acquire competencies in behavioral and emotional domains than the offspring of their more advantaged counterparts

Variations fiscales autour du véhicule professionnel

International audienceCet article est le premier que Maurice m’ai demandé de rédiger dans le cadre d’un projet d’ouvrage intitulé « la fiscalité racontée au médecin libéral », effectué en collaboration avec Jean-Claude Chocque. L’ouvrage est à présent paru, mais Maurice n’est plus. Il reste ses généreux conseils, ses bienveillantes recommandations et son enthousiasme communicatif qui ont accompagné l’écriture de ce premier article et de tous ceux qui l’on suivi. Il m’a semblé pour cette raison que ce texte, malgré son orientation pratique, pouvait trouver sa place au sein de cet ouvrage. Que le lecteur m’excuse donc par avance si la valeur symbolique de l’article prend ici le pas sur la portée théorique du propos

Les finances publiques suisses

International audiencePrésentation des finances publiques en Suisse

3D Porous Graphene-Polymer Materials for CO2 capture

299 p.The era of energy demand will continue increasing in the next decades, and as a consequence, the emissions of pollutant greenhouse gases, especially CO2. Thus, there is a great interest in the development of efficient and cost effective CO2 adsorbent materials to be applied in post-combustion capture technology. One of the most promising strategy to take advantages of the unique properties of those individual graphene sheets in application perspective is the assembly of 2D graphene nanolayers into a macroscopic 3D monolithic structure. Furthermore, it has more advantages, including the improved textural properties such as hierarchical structure, surface area and porosity. On the other hand, the development of graphene-polymer composites modifies the surface chemistry of the 3D structures, and in this way, it could enhance the adsorption capacity and selectivity towards CO2. Emulsion polymers give the opportunity to produce structures with tuneable characteristics and specific properties during reaction. The objective of this PhD Thesis is to make a detail study of the synthesis and characterization of 3D graphene-polymer composite monolithic materials for selective CO2 capture. GO nanosheets and polymer nanoparticles were used as building blocks and the self-assembly was induced by chemical reduction reaction. Variables such as reduction conditions, mass ratios, and polymer microstructure are used to study their influence in textural properties, adsorption capacities, and selectivity towards CO2 gas over N2. An environmentally friendly procedure is exclusively followed in water, low energy and quite versatile method, where scale-up procedures are viable

Libres propos sur la notion de charges somptuaires

International audienceIl en va parfois de certaines notions juridiques comme de certaines évidences : à force de les avoir toujours connues, nul ne songe plus à en critiquer la pertinence, le bien-fondé ou tout simplement l'obsolescence. La notion de dépenses et de charges somptuaires fait ainsi partie de notre paysage fiscal et semble prospérer depuis plus de 50 ans sans véritable remise en cause ou adaptation propre à la faire évoluer au regard des nouvelles pratiques des entreprises du 21 ème siècle. Codifiée à l'article 39-4 du CGI, cette règle, rappelons-le, interdit la déductibilité du bénéfice de l'entreprise des frais qualifiés de somptuaires 1 : « Qu'elles soient supportées directement par l'entreprise ou sous forme d'allocations forfaitaires ou de remboursements de frais, sont exclues des charges déductibles pour l'établissement de l'impôt, d'une part, les dépenses et charges de toute nature ayant trait à l'exercice de la chasse ainsi qu'à l'exercice non professionnel de la pêche et, d'autre part, les charges, à l'exception de celles ayant un caractère social, résultant de l'achat, de la location ou de toute autre opération faite en vue d'obtenir la disposition de résidences de plaisance ou d'agrément, ainsi que de l'entretien de ces résidences ; les dépenses et charges ainsi définies comprennent notamment les amortissements »