3,383 research outputs found
Trayectorias: a new model for online task-based learning
This paper discusses a framework for designing online tasks that capitalizes on the possibilities that the Internet and the Web offer for language learning. To present such a framework, we draw from constructivist theories (Brooks and Brooks, 1993) and their application to educational technology (Newby, Stepich, Lehman and Russell, 1996; Jonassen, Mayes and McAleese, 1993); second language learning and learning autonomy (Benson and Voller, 1997); and distance education (Race, 1989; White, 1999). On the one hand our model balances the requirements of the need for control and learning autonomy by the independent language learner; and on the other, the possibilities that online task-based learning offer for new reading processes by taking into account new literacy models (Schetzer and Warschauer, 2000), and the effect that the new media have on studentsâ knowledge construction and understanding of texts. We explain how this model works in the design of reading tasks within the specific distance learning context of the Open University, UK. Trayectorias is a tool that consists of an open problem-solving Web-quest and provides students with âscaffoldingâ that guides their navigation around the Web whilst modelling learning approaches and new learning paradigms triggered by the medium. We then discuss a small-scale trial with a cohort of students (n = 23). This trial had a double purpose: (a) to evaluate to what extent the writing task fulfilled the investigatorsâ intentions; and (b) to obtain some information about the studentsâ perceptions of the task
Quantitative analysis of Clausius inequality
In the context of driven diffusive systems, for thermodynamic transformations
over a large but finite time window, we derive an expansion of the energy
balance. In particular, we characterize the transformations which minimize the
energy dissipation and describe the optimal correction to the quasi-static
limit. Surprisingly, in the case of transformations between homogeneous
equilibrium states of an ideal gas, the optimal transformation is a sequence of
inhomogeneous equilibrium states.Comment: arXiv admin note: text overlap with arXiv:1404.646
Minimum dissipation principle in stationary non equilibrium states
We generalize to non equilibrium states Onsager's minimum dissipation
principle. We also interpret this principle and some previous results in terms
of optimal control theory. Entropy production plays the role of the cost
necessary to drive the system to a prescribed macroscopic configuration
Hide and seek on complex networks
Signaling pathways and networks determine the ability to communicate in
systems ranging from living cells to human society. We investigate how the
network structure constrains communication in social-, man-made and biological
networks. We find that human networks of governance and collaboration are
predictable on teat-a-teat level, reflecting well defined pathways, but
globally inefficient. In contrast, the Internet tends to have better overall
communication abilities, more alternative pathways, and is therefore more
robust. Between these extremes the molecular network of Saccharomyces cerevisea
is more similar to the simpler social systems, whereas the pattern of
interactions in the more complex Drosophilia melanogaster, resembles the robust
Internet.Comment: 5 pages, 5 figure
On the long range correlations of thermodynamic systems out of equilibrium
Experiments show that macroscopic systems in a stationary nonequilibrium
state exhibit long range correlations of the local thermodynamic variables. In
previous papers we proposed a Hamilton-Jacobi equation for the nonequilibrium
free energy as a basic principle of nonequilibrium thermodynamics. We show here
how an equation for the two point correlations can be derived from the
Hamilton-Jacobi equation for arbitrary transport coefficients for dynamics with
both external fields and boundary reservoirs. In contrast with fluctuating
hydrodynamics, this approach can be used to derive equations for correlations
of any order. Generically, the solutions of the equation for the correlation
functions are non-trivial and show that long range correlations are indeed a
common feature of nonequilibrium systems. Finally, we establish a criterion to
determine whether the local thermodynamic variables are positively or
negatively correlated in terms of properties of the transport coefficients.Comment: 4 page
Large deviation approach to non equilibrium processes in stochastic lattice gases
We present a review of recent work on the statistical mechanics of non
equilibrium processes based on the analysis of large deviations properties of
microscopic systems. Stochastic lattice gases are non trivial models of such
phenomena and can be studied rigorously providing a source of challenging
mathematical problems. In this way, some principles of wide validity have been
obtained leading to interesting physical consequences.Comment: Extended version of the lectures given by G. Jona-Lasinio at the 9th
Brazilian school of Probability, August 200
Macroscopic current fluctuations in stochastic lattice gases
We study current fluctuations in lattice gases in the macroscopic limit
extending the dynamic approach to density fluctuations developed in previous
articles. More precisely, we derive large deviation estimates for the
space--time fluctuations of the empirical current which include the previous
results. Large time asymptotic estimates for the fluctuations of the time
average of the current, recently established by Bodineau and Derrida, can be
derived in a more general setting. There are models where we have to modify
their estimates and some explicit examples are introduced.Comment: 4 pages, LaTeX, Changed conten
Large deviations of the empirical current in interacting particle systems
We study current fluctuations in lattice gases in the hydrodynamic scaling
limit. More precisely, we prove a large deviation principle for the empirical
current in the symmetric simple exclusion process with rate functional I. We
then estimate the asymptotic probability of a fluctuation of the average
current over a large time interval and show that the corresponding rate
function can be obtained by solving a variational problem for the functional I.
For the symmetric simple exclusion process the minimizer is time independent so
that this variational problem can be reduced to a time independent one. On the
other hand, for other models the minimizer is time dependent. This phenomenon
is naturally interpreted as a dynamical phase transition.Comment: 26 page
Ab initio study of reflectance anisotropy spectra of a sub-monolayer oxidized Si(100) surface
The effects of oxygen adsorption on the reflectance anisotropy spectrum (RAS)
of reconstructed Si(100):O surfaces at sub-monolayer coverage (first stages of
oxidation) have been studied by an ab initio DFT-LDA scheme within a
plane-wave, norm-conserving pseudopotential approach. Dangling bonds and the
main features of the characteristic RAS of the clean Si(100) surface are mostly
preserved after oxidation of 50% of the surface dimers, with some visible
changes: a small red shift of the first peak, and the appearance of a distinct
spectral structure at about 1.5 eV. The electronic transitions involved in the
latter have been analyzed through state-by-state and layer-by-layer
decompositions of the RAS. We suggest that new interplay between present
theoretical results and reflectance anisotropy spectroscopy experiments could
lead to further clarification of structural and kinetic details of the Si(100)
oxidation process in the sub-monolayer range.Comment: 21 pages, 8 figures. To be published in Physical Rev.
Lagrangian phase transitions in nonequilibrium thermodynamic systems
In previous papers we have introduced a natural nonequilibrium free energy by
considering the functional describing the large fluctuations of stationary
nonequilibrium states. While in equilibrium this functional is always convex,
in nonequilibrium this is not necessarily the case. We show that in
nonequilibrium a new type of singularities can appear that are interpreted as
phase transitions. In particular, this phenomenon occurs for the
one-dimensional boundary driven weakly asymmetric exclusion process when the
drift due to the external field is opposite to the one due to the external
reservoirs, and strong enough.Comment: 10 pages, 2 figure
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