Multifractality of wavefunctions at the quantum Hall transition revisited

We investigate numerically the statistics of wavefunction amplitudes $\psi({\bf r})$ at the integer quantum Hall transition. It is demonstrated that in the limit of a large system size the distribution function of $|\psi|^2$ is log-normal, so that the multifractal spectrum $f(\alpha)$ is exactly parabolic. Our findings lend strong support to a recent conjecture for a critical theory of the quantum Hall transition.Comment: 4 pages Late

Towards a new generation of multi-dimensional stellar evolution models: development of an implicit hydrodynamic code

This paper describes the first steps of development of a new multidimensional time implicit code devoted to the study of hydrodynamical processes in stellar interiors. The code solves the hydrodynamical equations in spherical geometry and is based on the finite volume method. Radiation transport is taken into account within the diffusion approximation. Realistic equation of state and opacities are implemented, allowing the study of a wide range of problems characteristic of stellar interiors. We describe in details the numerical method and various standard tests performed to validate the method. We present preliminary results devoted to the description of stellar convection. We first perform a local simulation of convection in the surface layers of a A-type star model. This simulation is used to test the ability of the code to address stellar conditions and to validate our results, since they can be compared to similar previous simulations based on explicit codes. We then present a global simulation of turbulent convective motions in a cold giant envelope, covering 80% in radius of the stellar structure. Although our implicit scheme is unconditionally stable, we show that in practice there is a limitation on the time step which prevent the flow to move over several cells during a time step. Nevertheless, in the cold giant model we reach a hydro CFL number of 100. We also show that we are able to address flows with a wide range of Mach numbers (10^-3 < Ms< 0.5), which is impossible with an anelastic approach. Our first developments are meant to demonstrate that the use of an implicit scheme applied to a stellar evolution context is perfectly thinkable and to provide useful guidelines to optimise the development of an implicit multi-D hydrodynamical code.Comment: 21 pages, 18 figures, accepted for publication in A&

A inclusão social através do ensino das ciências: um estudo centrado nos currículos brasileiro e português

info:eu-repo/semantics/publishedVersio

Theory of dynamic crack branching in brittle materials

The problem of dynamic symmetric branching of an initial single brittle crack propagating at a given speed under plane loading conditions is studied within a continuum mechanics approach. Griffith's energy criterion and the principle of local symmetry are used to determine the cracks paths. The bifurcation is predicted at a given critical speed and at a specific branching angle: both correlated very well with experiments. The curvature of the subsequent branches is also studied: the sign of $T$, with $T$ being the non singular stress at the initial crack tip, separates branches paths that diverge from or converge to the initial path, a feature that may be tested in future experiments. The model rests on a scenario of crack branching with some reasonable assumptions based on general considerations and in exact dynamic results for anti-plane branching. It is argued that it is possible to use a static analysis of the crack bifurcation for plane loading as a good approximation to the dynamical case. The results are interesting since they explain within a continuum mechanics approach the main features of the branching instabilities of fast cracks in brittle materials, i.e. critical speeds, branching angle and the geometry of subsequent branches paths.Comment: 41 pages, 15 figures. Accepted to International Journal of Fractur

Non-Equilibrium Electron Transport in Two-Dimensional Nano-Structures Modeled by Green's Functions and the Finite-Element Method

We use the effective-mass approximation and the density-functional theory with the local-density approximation for modeling two-dimensional nano-structures connected phase-coherently to two infinite leads. Using the non-equilibrium Green's function method the electron density and the current are calculated under a bias voltage. The problem of solving for the Green's functions numerically is formulated using the finite-element method (FEM). The Green's functions have non-reflecting open boundary conditions to take care of the infinite size of the system. We show how these boundary conditions are formulated in the FEM. The scheme is tested by calculating transmission probabilities for simple model potentials. The potential of the scheme is demonstrated by determining non-linear current-voltage behaviors of resonant tunneling structures.Comment: 13 pages,15 figure

FORMAÇÃO DE VÍNCULOS PROFISSIONAIS PARA O TRABALHO EM EQUIPE NA ENFERMAGEM

This article resulted from research that aimed to build a strategy of team work in nursing, to promote interpersonal relationships (Professional ties), to reach a therapeutic care committed to users of health services. The methodology is supported by the constructivist current and included the following phases: Interview and observation. After the data analysis these themes emerged: Individual and group position in the micro area of activity; movement of group relationships; communication process; continuing education; professional competence. Strategies for team work in nursing are based on the theoretical foundations of the dynamics of group interplay, providing a new look at the management role of the nurse in the creation and establishment of professional links, in which interpersonal relationships can promote critical, reflective, and participatory praxis.Este art&iacute;culo es resultado de la investigaci&oacute;n que tuvo como objetivo construir una estrategia de trabajo en equipo en enfermer&iacute;a para favorecer las relaciones interpersonales, o sea, los v&iacute;nculos profesionales, para el alcance de un cuidado terap&eacute;utico comprometido con las personas usuarias de los servicios de salud. La metodolog&iacute;a tiene respaldo en la corriente constructivista y cont&oacute; con las siguientes fases: entrevista y observaci&oacute;n. Despu&eacute;s del an&aacute;lisis de los datos surgieron los temas: posici&oacute;n individual y grupal en el microespacio de actuaci&oacute;n; movimiento de las relaciones grupales; proceso de comunicaci&oacute;n; educaci&oacute;n continuada; competencia profesional. Las estrategias para el trabajo en equipo en enfermer&iacute;a se basan en los fundamentos te&oacute;ricos de la din&aacute;mica de las interrelaciones grupales, determinando una nueva mirada para la funci&oacute;n gerencial del enfermero, a partir de la formaci&oacute;n y afirmaci&oacute;n de los v&iacute;nculos profesionales que agreguen, en los cuales las relaciones interpersonales puedan favorecer una praxis cr&iacute;tica, reflexiva y participativa.Este artigo &eacute; resultado da investiga&ccedil;&atilde;o que teve como objetivo construir uma estrat&eacute;gia de trabalho em equipe na enfermagem, para favorecer as rela&ccedil;&otilde;es interpessoais, ou seja, os v&iacute;nculos profissionais, para o alcan&ccedil;e de um cuidado terap&eacute;utico comprometido com os usu&aacute;rios dos servi&ccedil;os de sa&uacute;de. A metodologia tem o respaldo na corrente construtivista e conto com as seguintes fases: entrevista e observa&ccedil;&atilde;o. Depois da an&aacute;lise dos dados surgiram os temas: posi&ccedil;&atilde;o individual e grupal no micro espa&ccedil;o de atua&ccedil;&atilde;o; movimiento das rela&ccedil;&otilde;es grupais; proceso de comunica&ccedil;&atilde;o; educa&ccedil;&atilde;o continuada; competencia profissional. As estrat&eacute;gias para o trabalho na equipe em enfermagem tem base nos fundamentos te&oacute;ricos da din&acirc;mica das interrela&ccedil;&otilde;es grupais, determinando um novo olhar para a fun&ccedil;&atilde;o gerencial do enfermeiro, a partir da forma&ccedil;&atilde;o e afirma&ccedil;&atilde;o dos v&iacute;nculos profissionais, nos quais as rela&ccedil;&otilde;es interpessoais podem favorecer uma praxis cr&iacute;tica, reflexiva e participativ

On the Path of a Quasi-static Crack in Mode III

A method for finding the path of a quasi-static crack growing in a brittle body is presented. The propagation process is modelled by a sequence of discrete steps optimizing the elastic energy released. An explicit relationship between the optimal growing direction and the parameters defining the local elastic field around the tip is obtained for an anti-plane field. This allows to describe a simple algorithm to compute the crack path

Recent advances in sparse direct solvers

International audienceDirect methods for the solution of sparse systems of linear equations of the form A x = b are used in a wide range of numerical simulation applications. Such methods are based on the decomposition of the matrix into a product of triangular factors (e.g., A = L U ), followed by triangular solves. They are known for their numerical accuracy and robustness but are also characterized by a high memory consumption and a large amount of computations. Here we survey some research directions that are being investigated by the sparse direct solver community to alleviate these issues: memory-aware scheduling techniques, low-rank approximations, and distributed/shared memory hybrid programming

INTEGRAL/SPI data segmentation to retrieve sources intensity variations

International audienceContext. The INTEGRAL/SPI, X/γ-ray spectrometer (20 keV–8 MeV) is an instrument for which recovering source intensity variations is not straightforward and can constitute a difficulty for data analysis. In most cases, determining the source intensity changes between exposures is largely based on a priori information.Aims. We propose techniques that help to overcome the difficulty related to source intensity variations, which make this step more rational. In addition, the constructed “synthetic” light curves should permit us to obtain a sky model that describes the data better and optimizes the source signal-to-noise ratios.Methods. For this purpose, the time intensity variation of each source was modeled as a combination of piecewise segments of time during which a given source exhibits a constant intensity. To optimize the signal-to-noise ratios, the number of segments was minimized. We present a first method that takes advantage of previous time series that can be obtained from another instrument on-board the INTEGRAL observatory. A data segmentation algorithm was then used to synthesize the time series into segments. The second method no longer needs external light curves, but solely SPI raw data. For this, we developed a specific algorithm that involves the SPI transfer function.Results. The time segmentation algorithms that were developed solve a difficulty inherent to the SPI instrument, which is the intensity variations of sources between exposures, and it allows us to obtain more information about the sources’ behavior

The value of continuity: Refined isogeometric analysis and fast direct solvers

We propose the use of highly continuous finite element spaces interconnected with low continuity hyperplanes to maximize the performance of direct solvers. Starting from a highly continuous Isogeometric Analysis (IGA) discretization, we introduce . C0-separators to reduce the interconnection between degrees of freedom in the mesh. By doing so, both the solution time and best approximation errors are simultaneously improved. We call the resulting method "refined Isogeometric Analysis (rIGA)". To illustrate the impact of the continuity reduction, we analyze the number of Floating Point Operations (FLOPs), computational times, and memory required to solve the linear system obtained by discretizing the Laplace problem with structured meshes and uniform polynomial orders. Theoretical estimates demonstrate that an optimal continuity reduction may decrease the total computational time by a factor between . p2 and . p3, with . p being the polynomial order of the discretization. Numerical results indicate that our proposed refined isogeometric analysis delivers a speed-up factor proportional to . p2. In a . 2D mesh with four million elements and . p=5, the linear system resulting from rIGA is solved 22 times faster than the one from highly continuous IGA. In a . 3D mesh with one million elements and . p=3, the linear system is solved 15 times faster for the refined than the maximum continuity isogeometric analysis