Slow quench dynamics of a trapped one-dimensional Bose gas confined to an optical lattice

We analyze the effect of a linear time-variation of the interaction strength on a trapped one-dimensional Bose gas confined to an optical lattice. The evolution of different observables such as the experimentally accessible onsite particle distribution are studied as a function of the ramp time using time-dependent exact diagonalization and density-matrix renormalization group techniques. We find that the dynamics of a trapped system typically display two regimes: for long ramp times, the dynamics are governed by density redistribution, while at short ramp times, local dynamics dominate as the evolution is identical to that of an homogeneous system. In the homogeneous limit, we also discuss the non-trivial scaling of the energy absorbed with the ramp time.Comment: 4 pages, 4 figures, version published in PR

Colliding wind binaries and gamma-ray binaries : relativistic version of the RAMSES code

Gamma-ray binaries are colliding wind binaries (CWB) composed of a massive star a non-accreting pulsar with a highly relativistic wind. Particle acceleration at the shocks results in emission going from extended radio emission to the gamma-ray band. The interaction region is expected to show common features with stellar CWB. Performing numerical simulations with the hydrodynamical code RAMSES, we focus on their structure and stability and find that the Kelvin-Helmholtz instability (KHI) can lead to important mixing between the winds and destroy the large scale spiral structure. To investigate the impact of the relativistic nature of the pulsar wind, we extend RAMSES to relativistic hydrodynamics (RHD). Preliminary simulations of the interaction between a pulsar wind and a stellar wind show important similarities with stellar colliding winds with small relativistic corrections.Comment: Proceeding of the 5th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2012). arXiv admin note: text overlap with arXiv:1212.404

Invisible waveguides on metal plates for plasmonic analogues of electromagnetic wormholes

We introduce two types of toroidal metamaterials which are invisible to surface plasmon polaritons (SPPs) propagating on a metal surface. The former is a toroidal handlebody bridging remote holes on the metal surface: It works as a kind of plasmonic counterpart of electromagnetic wormholes. The latter is a toroidal ring lying on the metal surface: This bridges two disconnected metal surfaces i.e. It connects a thin metal cylinder to a flat metal surface with a hole. Full-wave numerical simulations demonstrate that an electromagnetic field propagating inside these metamaterials does not disturb the propagation of SPPs at the metal surface. A multilayered design of these devices is proposed, based on effective medium theory for a set of reduced parameters: The former plasmonic analogue of electromagnetic wormhole requires homogeneous isotropic magnetic layers, while the latter merely requires dielectric layers.Comment: 17 figure

Acoustic cloaking and mirages with flying carpets

Carpets under consideration here, in the context of pressure acoustic waves propagating in a compressible fluid, do not touch the ground: they levitate in mid-air (or float in mid-water), which leads to approximate cloaking for an object hidden underneath, or touching either sides of a square cylinder on, or over, the ground. The tentlike carpets attached to the sides of a square cylinder illustrate how the notion of a carpet on a wall naturally generalizes to sides of other small compact objects. We then extend the concept of flying carpets to circular cylinders. However, instead of reducing its scattering cross-section like in acoustic cloaks, we rather mimic that of another obstacle, say a square rigid cylinder. For instance, show that one can hide any type of defects under such circular carpets, and yet they still scatter waves just like a smaller cylinder on its own. Interestingly, all these carpets are described by non-singular acoustic parameters. To exemplify this important aspect, we propose a multi-layered carpet consisting of isotropic homogeneous fluids with constant bulk modulus and varying density which works over a finite range of wavelengths. We have discussed some applications, with the sonar boats or radars cases as typical examples. For instance, we would like to render a pipeline lying on the bottom of the sea or floating in mid-water undetectable for a boat with a sonar at rest just above it on the surface of the sea. Another possible application would be protecting parabolic antennas.Comment: 26 pages, 9 figures. Key words: Mathematical methods in physics; Mathematical Physics, electromagnetic theory; Metamaterials;Anisotropic optical materials; invisibility; cloa

Blind frame synchronisation for Block code

Publication in the conference proceedings of EUSIPCO, Florence, Italy, 200

Launching of a New Currency in a Simple Random Matching Model

No abstract.

CCCP: A CCD Controller for Counting Photons

CCCP, a CCD Controller for Counting Photons, is presented. This new controller uses a totally new clocking architecture and allows to drive the CCD in a novel way. Its design is optimized for the driving of EMCCDs at up to 20MHz of pixel rate and fast vertical transfer. Using this controller, the dominant source of noise of EMCCDs at low flux level and high frame rate, the Clock Induced Charges, were reduced to 0.001 - 0.0018 electron/pixel/frame (depending of the electron multiplying gain), making efficient photon counting possible. CCCP will be deployed in 2009 on the ESO NTT through the 3D-NTT1 project and on the SOAR through the BTFI project.Comment: 10 pages, 10 figures, to appear in "Ground-based and Airborne Instrumentation for Astronomy II" SPIE conference, Marseille, 23-28 June 200

Learning ‘rules’ of practice within the context of the practicum triad: A case study of learning to teach

This case study sought to determine the professional development circumstances in which a preservice teacher learned rules of practice (Wittgenstein, 1996) on practicum while interacting with a cooperating teacher and university supervisor. Borrowing from a theoretical conceptualization of teacher professional development based on the postulates of a general theory of learning (Berducci, 2004; Nelson, 2008) and collective action (Wittgenstein, 1996), this study showed that teaching rules of practice is (i) effective when it makes use of contexts and exemplars anchored in the preservice teacher’s experience and, (ii) before the preservice teacher is able to follow the rules in the classroom, he needs to be monitored by the cooperating teacher and university supervisor within a community of practice. These share with the preservice teacher the cognitive background and associated intentions that they bring to the setting and that he does not (yet) have and that he will construct through discourse and actual teaching.Keywords: Teacher training; pre-service teacher; training collective; work rules; learning circumstances.Cette étude de cas a cherché à déterminer dans quelles circonstances de perfectionnement professionnel un enseignant en formation a appris les règles de pratique (Wittgenstein, 1996) pendant son stage, tout en interagissant avec un enseignant coopératif et le superviseur académique. S'appuyant sur une conceptualisation théorique de perfectionnement professionnel des enseignants basée sur les postulats d'une théorie générale de l'apprentissage (Berducci, 2004; Nelson, 2008) et de l'action collective (Wittgenstein, 1996), cette étude amontré que l'enseignement des règles de la pratique est efficace quand il fait usage des contextes et des modèles ancrés dans l'expérience de l'enseignant en formation et, avant que l'enseignant en formation soit en mesure de suivre les règles dans la classe, il doit être suivi par l'enseignant coopératif et le superviseur académique au sein d'une communauté de pratique. Et ce, afin de transmettre et de partager avec l'enseignant en formation les compétences cognitives et les intentions associées qu'il n'a pas (encore) et qu'il va construire àtravers le discours et l'enseignement proprement dit.Mots clés: Formation des enseignants; enseignant en formation; formation collective, règles de travail, circonstances d'apprentissage