Dynamical and Steady State Properties of a Bose-Hubbard Chain with Bond-Dissipation: A Study based on Matrix Product Operators

We study a dissipative Bose-Hubbard chain subject to an engineered bath using a superoperator approach based on matrix product operators. The dissipation is engineered to stabilize a BEC condensate wave function in its steady state. We then characterize the steady state emerging from the interplay between incompatible Hamiltonian and dissipative dynamics. While it is expected that interactions lead to this competition, even the kinetic energy in an open boundary condition setup competes with the dissipation, leading to a non-trivial steady state. We also present results for the transient dynamics and probe the relaxation time revealing the closing of the dissipative gap in the thermodynamic limit.Comment: 9 pages, 13 figure

Quantum phase transitions in three-leg spin tubes

We investigate the properties of a three-leg quantum spin tube using several techniques such as the density matrix renormalization group method, strong coupling approaches and the non linear sigma model. For integer spins S, the model proves to exhibit a particularly rich phase diagram consisting of an ensemble of 2S phase transitions. They can be accurately identified by the behavior of a non local string order parameter associated to the breaking of a hidden symmetry in the Hamiltonian. The nature of these transitions are further elucidated within the different approaches. We carry a detailed DMRG analysis in the specific cases S = 1. The numerical data confirm the existence of two Haldane phases with broken hidden symmetry separated by a trivial singlet state. The study of the gap and of the von Neumann entropy suggest a first order phase transition but at the close proximity of a tricritical point separating a gapless and a first order transition line in the phase diagram of the quantum spin tube.Comment: 20 pages, 18 figure

El conocimiento didáctico del contenido sobre la fotosíntesis de dos profesores de educación secundaria argentinos

En 1986 Lee Shulman pomueve un cambio de paradigma en la investigación educativa y simultáneamente propone una aproximación a la reforma educativa que permitiera inscribir a la enseñanza en una profesión, en ese contexto desarrolla un nuevo marco teórico introduciendo el concepto de conocimiento didáctico del contenido (CDC). Este se construye a partir de varios tipos de conocimientos: conocimiento del contenido de la disciplina a enseñar, conocimiento didáctico, conocimiento de currículo, de la evaluación, entre otros. En este trabajo se analiza el CD de la fotosíntesis de dos profesores de secundaria a partir de tres instrumentos: una entrevista semiestructurada, un cuestionario y las observaciones de la práctica. Estos nos permitieron establecer las necesarias relaciones entre el conocimiento con el que se identifican, el que declaran y el que llevan a la práctica

Le mythe de Robinson Crusoé à l’épreuve du monde global: il n’y a pas d’ailleurs. Étude du motif de l’empreinte dans L’Empreinte à Crusoé de Patrick Chamoiseau

De quel ailleurs peut bien nous parler la réécriture contemporaine du mythe de Robinson Crusoé par Patrick Chamoiseau, en 2012, alors que la planète est à la fois menacée par les déséquilibres écologiques et engagée dans une mondialisation des échanges ? L’empreinte à Crusoé est le récit sans aventure d’un homme qui, incapable de se souvenir d’où il vient véritablement, comprend qu’il habite un lieu chargé d’ailleurs. Or, c’est à travers l’empreinte de pas découverte sur la plage que se révèle et se recompose l’identité d’Ogomtemêli et sa place dans le monde. Plus qu’une péripétie, l’empreinte est un motif à partir duquel le naufragé devient la conscience historique et écologique de l’humanité vivant sur une seule et même terre, un lieu-monde dans lequel la relation doit supplanter l’exploitation

The effect of multiple paternity on genetic diversity during and after colonisation

In metapopulations, genetic variation of local populations is influenced by the genetic content of the founders, and of migrants following establishment. We analyse the effect of multiple paternity on genetic diversity using a model in which the highly promiscuous marine snail Littorina saxatilis expands from a mainland to colonise initially empty islands of an archipelago. Migrant females carry a large number of eggs fertilised by 1 - 10 mates. We quantify the genetic diversity of the population in terms of its heterozygosity: initially during the transient colonisation process, and at long times when the population has reached an equilibrium state with migration. During colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in comparison with the case of single paternity. The equilibrium state, by contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 % higher heterozygosity compared with single paternity. Further we find that far from the mainland, new mutations spreading from the mainland cause bursts of high genetic diversity separated by long periods of low diversity. This effect is boosted by multiple paternity. We conclude that multiple paternity facilitates colonisation and maintenance of small populations, whether or not this is the main cause for the evolution of extreme promiscuity in Littorina saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia

Analytical and numerical stability analysis of Soret-driven convection in a horizontal porous layer

We present an analytical and numerical stability analysis of Soret-driven convection in a porous cavity saturated by a binary fluid. Both the mechanical equilibrium solution and the monocellular flow obtained for particular ranges of the physical parameters of the problem are considered. The porous cavity, bounded by horizontal infinite or finite boundaries, is heated from below or from above. The two horizontal plates are maintained at different constant temperatures while no mass flux is imposed. The influence of the governing parameters and more particularly the role of the separation ratio, characterizing the Soret effect and the normalized porosity, are investigated theoretically and numerically. From the linear stability analysis, we find that the equilibrium solution loses its stability via a stationary bifurcation or a Hopf bifurcation depending on the separation ratio and the normalized porosity of the medium. The role of the porosity is important, when it decreases, the stability of the equilibrium solution is reinforced. For a cell heated from below, the equilibrium solution loses its stability via a stationary bifurcation when the separation ratio >0(Le,), while for 0, while a stationary or an oscillatory bifurcation occurs if mono the monocellular flow loses stability via a Hopf bifurcation. As the Rayleigh number increases, the resulting oscillatory solution evolves to a stationary multicellular flow. For a cell heated from above and <0, the monocellular flow remains linearly stable. We verified numerically that this problem admits other stable multicellular stationary solutions for this range of parameters

Propuesta para la enseñanza y el aprendizaje de la relación sociedad naturaleza en el nivel universitario. un ejemplo concreto en una cuenca hidrográfica en el sudeste de la provincia de Buenos Aires

La presente propuesta es para la enseñaza y el aprendizaje de la relación sociedad-naturaleza. Los destinatarios son los alumnos de la carrera de profesorado en ciencia de la Universidad Nacional de Mar del Plata. A través de ella los estudiantes podrán distinguir las diferencias presentes en los procesos tanto ecológicos como sociales, en base al concepto de articulación sociedad-naturaleza en una realidad integral. Permite explicar los fenómenos relativos a las acciones de los hombres organizados socialmente en relación a un entorno determinado, en un tiempo y espacio específico y con una tecnología definida. La propuesta de enseñanza se basa en el modelo planteado por Gallopin (1986) el cual examina la relación sociedad-naturaleza como resultado de la interacción de dos esferas la “Sociedad” y los "Sistemas Ecológicos" y se lleva a cabo en una cuenca hidrográfica

A hierarchy of models related to nanoflows and surface diffusion

In last years a great interest was brought to molecular transport problems at nanoscales, such as surface diffusion or molecular flows in nano or sub-nano-channels. In a series of papers V. D. Borman, S. Y. Krylov, A. V. Prosyanov and J. J. M. Beenakker proposed to use kinetic theory in order to analyze the mechanisms that determine mobility of molecules in nanoscale channels. This approach proved to be remarkably useful to give new insight on these issues, such as density dependence of the diffusion coefficient. In this paper we revisit these works to derive the kinetic and diffusion models introduced by V. D. Borman, S. Y. Krylov, A. V. Prosyanov and J. J. M. Beenakker by using classical tools of kinetic theory such as scaling and systematic asymptotic analysis. Some results are extended to less restrictive hypothesis