281 research outputs found
Multifunctions of Bounded Variation, Preliminary Version I
Consider control systems described by a differential equation with a control
term or, more generally, by a differential inclusion with velocity set
. Certain properties of state trajectories can be derived when, in
addition to other hypotheses, it is assumed that is merely measurable
w.r.t. the time variable . But sometimes a refined analysis requires the
imposition of stronger hypotheses regarding the dependence of .
Stronger forms of necessary conditions for state trajectories that minimize a
cost can derived, for example, if it is hypothesized that is Lipschitz
continuous w.r.t. . It has recently become apparent that interesting
addition properties of state trajectories can still be derived, when the
Lipschitz continuity hypothesis is replaced by the weaker requirement that
has bounded variation w.r.t. . This paper introduces a new concept
of multifunctions that have bounded variation w.r.t. near a given
state trajectory, of special relevance to control system analysis. Properties
of such multifunctions are derived and their significance is illustrated by an
application to sensitivity analysis.Comment: Preliminary version of a article which will submitted to a journal
for publicatio
(Não) leituras de obras literárias em contexto escolar: um estudo de caso a partir de versão integral e adaptações de "O Cortiço", de Aluísio Azevedo
O presente trabalho se insere nas discussões do grupo de pesquisa Literatura e Educação e investigou, no contexto de uma escola pública de Ensino Fundamental e Médio do município de Guarapari (ES), como são as relações entre livros e leitores - por meio das contribuições teóricas e metodológicas da Nova História Cultural - a partir de três diferentes versões da obra O cortiço do autor Aluísio Azevedo: versão adaptada por Fabio Pinto da coleção É só o começo (2009); adaptação com roteiro de Ivan Jaf e arte de Rodrigo Rosa em história em quadrinhos (2010) distribuída pelo PNBE; e c) versão com texto integral (2014 [1890]); todas encontradas na biblioteca da escola campo. A pesquisa foi desenvolvida em dois momentos, sendo o primeiro de cunho bibliográfico-documental, que buscou perceber como se dão as relações entre livro, leitor e leitura e pensar o modo como algumas adaptações literárias são inseridas no mercado, inclusive as que integram programas de distribuição de livros como o PNBE. O segundo momento foi um estudo de caso com questionário e grupo focal, constituído por alunos de segundo e terceiro ano do Ensino Médio da escola campo, que, no âmbito do processo de educação literária, tentou responder às seguintes questões: a) como se dá a apropriação do texto integral e das diversas adaptações de uma obra pelos estudantes?; b) os textos adaptados despertam no leitor o desejo de conhecer o texto integral?; c) como os alunos agem para (não) realizar as leituras propostas pelo currículo escolar?: A pesquisa justifica-se em face: a) do interesse, nos campos da História e da Literatura, pelas práticas de leitores literários empíricos e pelos usos que são feitos de materiais impressos, em contextos institucionais, em tensão com orientações oficiais; b) da necessidade de se pensar as questões econômico-ideológicas que circundam a leitura em tensionamento com o mercado editorial; c) do nosso diagnóstico tomado aqui como pressuposto de que muitos alunos não leem obras literárias sugeridas pelo currículo escolar; d) da necessidade de se pensar as não leituras literárias para além da culpabilização discente. Com a investigação, conhecemos as formas de aquisição dos livros, algumas preferências, os principais mediadores de leitura, traçando assim um perfil de leitor de leitura literária da escola campo. Chegamos também à conclusão de que algumas adaptações podem ser instrumentos de mediação de leitura em sala de aula. Os autores que nortearam nosso estudo foram: Regina Zilberman (1999, 2013), Márcia Abreu (2001), Edmir Perrotti (1999) e João Wanderlei Geraldi (2010) (livro e leitura no contexto brasileiro); Annie Rouxel (2013), Maria Amélia Dalvi (2012, 2013, 2013a) e Neide Rezende (2013) (educação literária); Roger Chartier (1999, 2002, 2002a, 2010, 2013, 2013a) (práticas e representações, apropriação)
Optimal Control Problems with Mixed and Pure State Constraints
This paper provides necessary conditions of optimality for optimal control problems, in which the pathwise constraints comprise both “pure” constraints on the state variable and “mixed” constraints on control and state variables. The proofs are along the lines of earlier analysis for mixed constraint problems, according to which Clarke's theory of “stratified” necessary conditions is applied to a modified optimal control problem resulting from absorbing the mixed constraint into the dynamics; the difference here is that necessary conditions which now take into account the presence of pure state constraints are applied to the modified problem. Necessary conditions are given for a rather general formulation of the problem containing both forms of the constraints, and then these are specialized to problems having special structure. While combined pure state and mixed control/state problems have been previously treated in the literature, the necessary conditions in this paper are proved under less restrictive hypotheses and for novel formulations of the constraints
Just-In-Time Compilation of NumPy Vector Operations
In this paper, we introduce JIT compilation for thehigh-productivity framework Python/NumPy in order to boost theperformance significantly. The JIT compilation of Python/NumPyis completely transparent to the user – the runtime system willautomatically JIT compile and execute the NumPy instructionsencountered in a Python application. In other words, we introducea framework that provides the high-productivity from Pythonwhile maintaining the high-performance of a low-level, compiledlanguage.We transforms NumPy vector instruction into an AbstractSyntax Tree representation that creates the basis for furtheroptimizations. From the AST we auto-generate C code whichwe compile into computational kernels and execute. These incorporatetemporary array removal and loop-fusion which are mainbenefactors in the achieved speedups. In order to amortize theoverhead of creation, we also implement a cache for the compiledkernels.We evaluate the JIT compilation by executing several scientificcomputing benchmarks on an AMD. Compared to NumPy, weachieve speedups of a factor 4.72 for a N-Body application and7.51 for a Jacobi Stencil application executing on a single CPUcore
Veros v0.1 – a fast and versatile ocean simulator in pure Python
A
general circulation ocean model is translated from Fortran to Python. Its
code structure is optimized to exploit available Python utilities, remove
simulation bottlenecks, and comply with modern best practices. Furthermore, support for
Bohrium is added, a framework that provides a just-in-time compiler for array
operations and that supports parallel execution on both CPU and GPU targets.For applications containing more than a million grid elements, such as a
typical 1° × 1° horizontal resolution global ocean model,
Veros is approximately half as fast as the MPI-parallelized Fortran base code
on 24 CPUs and as fast as the Fortran reference when running on a high-end
GPU. By replacing the original conjugate gradient stream function solver with
a solver from the pyAMG Python package, this particular subroutine
outperforms the corresponding Fortran version by up to 1 order of magnitude.The study is concluded with a simple application in which the North Atlantic
wave response to a Southern Ocean wind perturbation is investigated. It is
found that even in a realistic setting the phase speeds of boundary waves
matched the expectations based on theory and idealized models.</p
An effective mass theorem for the bidimensional electron gas in a strong magnetic field
We study the limiting behavior of a singularly perturbed
Schr\"odinger-Poisson system describing a 3-dimensional electron gas strongly
confined in the vicinity of a plane and subject to a strong uniform
magnetic field in the plane of the gas. The coupled effects of the confinement
and of the magnetic field induce fast oscillations in time that need to be
averaged out. We obtain at the limit a system of 2-dimensional Schr\"odinger
equations in the plane , coupled through an effective selfconsistent
electrical potential. In the direction perpendicular to the magnetic field, the
electron mass is modified by the field, as the result of an averaging of the
cyclotron motion. The main tools of the analysis are the adaptation of the
second order long-time averaging theory of ODEs to our PDEs context, and the
use of a Sobolev scale adapted to the confinement operator
Inelastic Coulomb scattering rates due to acoustic and optical plasmon modes in coupled quantum wires
We report a theoretical study on the inelastic Coulomb scattering rate of an
injected electron in two coupled quantum wires in quasi-one-dimensional doped
semiconductors. Two peaks appear in the scattering spectrum due to the optical
and the acoustic plasmon scattering in the system. We find that the scattering
rate due to the optical plasmon mode is similar to that in a single wire but
the acoustic plasmon scattering depends crucially on its dispersion relation at
small . Furthermore, the effects of tunneling between the two wires are
studied on the inelastic Coulomb scattering rate. We show that a weak tunneling
can strongly affect the acoustic plasmon scattering.Comment: 6 Postscript figure
Intrasubband and Intersubband Electron Relaxation in Semiconductor Quantum Wire Structures
We calculate the intersubband and intrasubband many-body inelastic Coulomb
scattering rates due to electron-electron interaction in two-subband
semiconductor quantum wire structures. We analyze our relaxation rates in terms
of contributions from inter- and intrasubband charge-density excitations
separately. We show that the intersubband (intrasubband) charge-density
excitations are primarily responsible for intersubband (intrasubband) inelastic
scattering. We identify the contributions to the inelastic scattering rate
coming from the emission of the single-particle and the collective excitations
individually. We obtain the lifetime of hot electrons injected in each subband
as a function of the total charge density in the wire.Comment: Submitted to PRB. 20 pages, Latex file, and 7 postscript files with
Figure
Towards A Census of Earth-mass Exo-planets with Gravitational Microlensing
Thirteen exo-planets have been discovered using the gravitational
microlensing technique (out of which 7 have been published). These planets
already demonstrate that super-Earths (with mass up to ~10 Earth masses) beyond
the snow line are common and multiple planet systems are not rare. In this
White Paper we introduce the basic concepts of the gravitational microlensing
technique, summarise the current mode of discovery and outline future steps
towards a complete census of planets including Earth-mass planets. In the
near-term (over the next 5 years) we advocate a strategy of automated follow-up
with existing and upgraded telescopes which will significantly increase the
current planet detection efficiency. In the medium 5-10 year term, we envision
an international network of wide-field 2m class telescopes to discover
Earth-mass and free-floating exo-planets. In the long (10-15 year) term, we
strongly advocate a space microlensing telescope which, when combined with
Kepler, will provide a complete census of planets down to Earth mass at almost
all separations. Such a survey could be undertaken as a science programme on
Euclid, a dark energy probe with a wide-field imager which has been proposed to
ESA's Cosmic Vision Programme.Comment: 10 pages. White Paper submission to the ESA Exo-Planet Roadmap
Advisory Team. See also "Inferring statistics of planet populations by means
of automated microlensing searches" by M. Dominik et al. (arXiv:0808.0004
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