Vers un nouveau design d'audio-vidéo-cours à l'Université : " l'encre numérique ": Description du dispositif et première analyse d'usages

7 pagesInternational audienceThis article presents a new audio-video lecture design for University teaching and reports its impact on the students' learning process. The system is composed of an original lecture presentation tool (the Tablet PC), associated with an online workbook. The lecture is first saved, sequenced, and then uploaded in small parts in the different directories of the workbook. The students may then use its contents as much as they wish. This system was tested on relatively weak students in order to support the "Succeed your Bachelor's degree" plan. The test essentially focused on correlations with results on exams, and on how often the video sequences were watched and tracked their activity and navigation in the different parts of the workbook.Cet article présente un nouveau design d'audio-vidéo-cours dans le cadre d'un enseignement universitaire et rend compte de son impact sur l'apprentissage des étudiants. Le dispositif se compose d'un outil original de présentation du cours magistral (Tablet PC) associé à un cahier de textes en ligne. Le cours est enregistré, séquencé et déposé dans l'arborescence du cahier de textes. Les étudiants peuvent alors consulter son contenu autant que de besoin. L'évaluation de ce dispositif entre dans le cadre du plan " Réussite en Licence ". Elle s'appuie sur les résultats aux examens et sur la fréquence de consultation des vidéos et un suivi (tracking) précis de la " navigation " dans les différents contenus du cahier de textes en ligne

Repulsion driven metallic phase in the ground state of the half-filled t−t′t-t^{\prime} ionic Hubbard chain

An unusual metallic phase is proven to develop in the one dimensional ionic Hubbard model, at half-filling and zero magnetization, at intermediate electron-electron repulsion $U$ when second neighbors hopping is allowed and tuned close to a topological Lifshitz transition (connected with a change of the Fermi surface in the non-interacting system). The metallic state lies between a band insulator phase at low repulsion and a correlated (Mott-like) insulator phase at high repulsion. In approaching the later, the metal supports spontaneous bond charge dimerization and antiferromagnetic correlations. The ground state of the system, attainable by cold atoms in optical lattices for a wide range of the parameter $U$, is extensively explored by numerically exact density-matrix renormalization-group (DMRG) calculations. A combination of mean field and effective field theory (bosonization) provides an analytical understanding of the physical processes underlying the observed phase transitions.Comment: 19 pages, 20 figure

Quantum Communication through Spin Chain Dynamics: an Introductory Overview

We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest (uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.Comment: Material covered till Dec 200

Cloud Service Brokerage-2014: Towards the Multi-cloud Ecosystem

In the future multi-cloud ecosystem, many cloud providers and consumers will interact to create, discover, negotiate and use software services. Cloud service brokers will play a central role in bringing providers and consumers together, assisting with software service creation (from abstract models to platform-specific deployments), multi-cloud translation (model-driven adaptation and deployment of services) quality assurance (governance; functional testing and monitoring), service continuity (failure prevention and recovery) and market competition (arbitrage; service optimization; service customization). The emerging ecosystem will be supported by common standards, service models, methods and mechanisms that will operate across a wide variety of platforms and infrastructure, and across disparate service protocols

Long-range spin chirality dimer order in the Heisenberg chain with modulated Dzyaloshinskii-Moriya interactions

The ground-state phase diagram of a spin S = 1 2 XXZ Heisenberg chain with spatially modulated Dzyaloshinskii-Moriya interaction H= n{J(Sx nSx n+1 +Sy nSy n+1 )+JzSz nSz n+1 +[D0 +(−1)nD1](Sx nSy n+1 −S y nSx n+1 )}is studied using the continuum-limit bosonization approach and extensive density-matrix renormalizationgroupcomputations.Itisshownthattheeffectivecontinuum-limitbosonizedtheoryofthemodelisgivenby the double-frequency sine-Gordon model (DSG) where the frequencies, i.e., the scaling dimensions of the two competing cosine perturbation terms, depend on the effective anisotropy parameter γ∗ =Jz/ J2 +D2 0 +D2 1. Exploring the ground-state properties of the DSG model we show that the zero-temperature phase diagram contains the following four phases: (i) the ferromagnetic phase at γ∗ −1; (ii) the gapless Luttinger-liquid (LL) phase at−1 γ∗ C2 > 1 the gapped composite (C2) phase characterized in addition to the coexisting spin dimerization and alternating chirality patterns, by the presence of LRO antiferromagnetic order. The transition from the LL to the C1 phase at γ∗ C1 belongs to the Berezinskii-Kosterlitz-Thouless universality class, while the transition at γ∗ = γ∗ C2 from C1 to C2 phase is of the Ising type.Fil: Avalishvili, N.. Ilia State University; Georgia. Andronikashvili Institute of Physics; GeorgiaFil: Japaridze, G. I.. Ilia State University; Georgia. Andronikashvili Institute of Physics; GeorgiaFil: Rossini, Gerardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Josephson current through a molecular transistor in a dissipative environment

We study the Josephson coupling between two superconductors through a single correlated molecular level, including Coulomb interaction on the level and coupling to a bosonic environment. All calculations are done to the lowest, i.e., the fourth, order in the tunneling coupling and we find a suppression of the supercurrent due to the combined effect of the Coulomb interaction and the coupling to environmental degrees of freedom. Both analytic and numerical results are presented.Comment: 11 pages, 6 figures, to appear in Phys. Rev. B; v3: several misprints corrected - in particular, sign inconsistencies throughout the paper should be fixe

Decoherence induced by interacting quantum spin baths

We study decoherence induced on a two-level system coupled to a one-dimensional quantum spin chain. We consider the cases where the dynamics of the chain is determined by the Ising, XY, or Heisenberg exchange Hamiltonian. This model of quantum baths can be of fundamental importance for the understanding of decoherence in open quantum systems, since it can be experimentally engineered by using atoms in optical lattices. As an example, here we show how to implement a pure dephasing model for a qubit system coupled to an interacting spin bath. We provide results that go beyond the case of a central spin coupled uniformly to all the spins of the bath, in particular showing what happens when the bath enters different phases, or becomes critical; we also study the dependence of the coherence loss on the number of bath spins to which the system is coupled and we describe a coupling-independent regime in which decoherence exhibits universal features, irrespective of the system-environment coupling strength. Finally, we establish a relation between decoherence and entanglement inside the bath. For the Ising and the XY models we are able to give an exact expression for the decay of coherences, while for the Heisenberg bath we resort to the numerical time-dependent Density Matrix Renormalization Group.Comment: 18 pages, 20 figure

Feeding ecology of the seagrass-grazing nerite Smaragdia souverbiana (Montrouzier, 1863) in subtropical seagrass beds of eastern Australia

By amalgamating all seagrass-associated grazing invertebrates into an epiphyte-feeding guild, the currently accepted model of seagrass trophic dynamics ignores the diverse range of invertebrates that feed directly on, and do considerable damage to, seagrasses. Of the wide range of invertebrates documented to damage seagrass directly, the gastropod genus Smaragdia has adaptations and ecology that suggests it could be a specialized seagrass-feeding group, of which at least two species are known preferentially to consume seagrass. This paper investigated the dietary associations of Smaragdia souverbiana, one of the most widely distributed but least studied species of the genus, in the subtropical eastern Australian part of its range. Using field-based assessments of grazing damage and targeted laboratory feeding trials, we assessed the dietary associations, digestive ability and feeding preferences of S. souverbiana with local seagrasses (Halophila ovalis, Zostera capricorni and Cymodocea serrulata). We found that this species consumed and damaged all available species, but showed a strong preference for the most abundant and moderately digestible Z. capricorni. Although it avoided seagrass bearing a high epiphyte load in a laboratory context, considerable amounts of epiphytic material were found in the faeces of field-caught individuals. Grazing and digestibility of seagrass cells was higher in Z. capricorni and H. ovalis, and the former was preferred when both were available. This study adds to the growing body of literature demonstrating that S. souverbiana—and potentially many other grazing invertebrates—cause considerable damage to seagrasses directly, rather than targeting epiphytes.Versión del editor1,358