1,497 research outputs found
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 fotosĂntesis de dos profesores de educaciĂłn secundaria argentinos
En 1986 Lee Shulman pomueve un cambio de paradigma en la investigaciĂłn educativa y simultáneamente propone una aproximaciĂłn a la reforma educativa que permitiera inscribir a la enseñanza en una profesiĂłn, en ese contexto desarrolla un nuevo marco teĂłrico 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 currĂculo, de la evaluaciĂłn, entre otros. En este trabajo se analiza el CD de la fotosĂntesis 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 relaciĂłn sociedad-naturaleza. Los destinatarios son los alumnos de la carrera de profesorado en ciencia de la Universidad Nacional de Mar del Plata. A travĂ©s de ella los estudiantes podrán distinguir las diferencias presentes en los procesos tanto ecolĂłgicos como sociales, en base al concepto de articulaciĂłn sociedad-naturaleza en una realidad integral. Permite explicar los fenĂłmenos relativos a las acciones de los hombres organizados socialmente en relaciĂłn a un entorno determinado, en un tiempo y espacio especĂfico y con una tecnologĂa definida. La propuesta de enseñanza se basa en el modelo planteado por Gallopin (1986) el cual examina la relaciĂłn sociedad-naturaleza como resultado de la interacciĂłn de dos esferas la “Sociedad” y los "Sistemas EcolĂłgicos" 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
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