418 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
A decomposition technique for pursuit evasion games with many pursuers
Here we present a decomposition technique for a class of differential games.
The technique consists in a decomposition of the target set which produces, for
geometrical reasons, a decomposition in the dimensionality of the problem.
Using some elements of Hamilton-Jacobi equations theory, we find a relation
between the regularity of the solution and the possibility to decompose the
problem. We use this technique to solve a pursuit evasion game with multiple
agents
Regularity properties of optimal controls for problems with time-varying state and control constraints
Accepted versio
(NĂŁo) leituras de obras literárias em contexto escolar: um estudo de caso a partir de versĂŁo integral e adaptações de "O Cortiço", de AluĂsio Azevedo
O presente trabalho se insere nas discussões do grupo de pesquisa Literatura e Educação e investigou, no contexto de uma escola pĂşblica de Ensino Fundamental e MĂ©dio do municĂpio de Guarapari (ES), como sĂŁo as relações entre livros e leitores - por meio das contribuições teĂłricas e metodolĂłgicas da Nova HistĂłria Cultural - a partir de trĂŞs diferentes versões da obra O cortiço do autor AluĂsio Azevedo: versĂŁo adaptada por Fabio Pinto da coleção É sĂł o começo (2009); adaptação com roteiro de Ivan Jaf e arte de Rodrigo Rosa em histĂłria em quadrinhos (2010) distribuĂda pelo PNBE; e c) versĂŁo 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 dĂŁo as relações entre livro, leitor e leitura e pensar o modo como algumas adaptações literárias sĂŁo 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, constituĂdo por alunos de segundo e terceiro ano do Ensino MĂ©dio da escola campo, que, no âmbito do processo de educação literária, tentou responder Ă s 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 (nĂŁo) realizar as leituras propostas pelo currĂculo escolar?: A pesquisa justifica-se em face: a) do interesse, nos campos da HistĂłria e da Literatura, pelas práticas de leitores literários empĂricos e pelos usos que sĂŁo feitos de materiais impressos, em contextos institucionais, em tensĂŁo com orientações oficiais; b) da necessidade de se pensar as questões econĂ´mico-ideolĂłgicas que circundam a leitura em tensionamento com o mercado editorial; c) do nosso diagnĂłstico tomado aqui como pressuposto de que muitos alunos nĂŁo leem obras literárias sugeridas pelo currĂculo escolar; d) da necessidade de se pensar as nĂŁo leituras literárias para alĂ©m da culpabilização discente. Com a investigação, conhecemos as formas de aquisição dos livros, algumas preferĂŞncias, os principais mediadores de leitura, traçando assim um perfil de leitor de leitura literária da escola campo. Chegamos tambĂ©m Ă conclusĂŁo 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 JoĂŁo Wanderlei Geraldi (2010) (livro e leitura no contexto brasileiro); Annie Rouxel (2013), Maria AmĂ©lia 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
Towards two-dimensional metallic behavior at LaAlO3/SrTiO3 interfaces
Using a low-temperature conductive-tip atomic force microscope in
cross-section geometry we have characterized the local transport properties of
the metallic electron gas that forms at the interface between LaAlO3 and
SrTiO3. At low temperature, we find that the carriers do not spread away from
the interface but are confined within ~10 nm, just like at room temperature.
Simulations taking into account both the large temperature and electric-field
dependence of the permittivity of SrTiO3 predict a confinement over a few nm
for sheet carrier densities larger than ~6 10^13 cm-2. We discuss the
experimental and simulations results in terms of a multi-band carrier system.
Remarkably, the Fermi wavelength estimated from Hall measurements is ~16 nm,
indicating that the electron gas in on the verge of two-dimensionality.Comment: Accepted for publication in Physical Review Letter
Plasmon-pole approximation for semiconductor quantum wire electrons
We develop the plasmon-pole approximation for an interacting electron gas
confined in a semiconductor quantum wire. We argue that the plasmon-pole
approximation becomes a more accurate approach in quantum wire systems than in
higher dimensional systems because of severe phase-space restrictions on
particle-hole excitations in one dimension. As examples, we use the
plasmon-pole approximation to calculate the electron self-energy due to the
Coulomb interaction and the hot-electron energy relaxation rate due to
LO-phonon emission in GaAs quantum wires. We find that the plasmon-pole
approximation works extremely well as compared with more complete many-body
calculations.Comment: 16 pages, RevTex, figures included. Also available at
http://www-cmg.physics.umd.edu/~lzheng
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