277 research outputs found
Multifractality of wavefunctions at the quantum Hall transition revisited
We investigate numerically the statistics of wavefunction amplitudes
at the integer quantum Hall transition. It is demonstrated that
in the limit of a large system size the distribution function of is
log-normal, so that the multifractal spectrum 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 inclusĂŁo social atravĂ©s do ensino das ciĂȘncias: um estudo centrado nos currĂculos brasileiro e portuguĂȘs
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 , with 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
FORMAĂĂO DE VĂNCULOS 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 artículo es resultado de la investigación que tuvo como objetivo construir una estrategia de trabajo en equipo en enfermería para favorecer las relaciones interpersonales, o sea, los vínculos profesionales, para el alcance de un cuidado terapéutico comprometido con las personas usuarias de los servicios de salud. La metodología tiene respaldo en la corriente constructivista y contó con las siguientes fases: entrevista y observación. Después del análisis de los datos surgieron los temas: posición individual y grupal en el microespacio de actuación; movimiento de las relaciones grupales; proceso de comunicación; educación continuada; competencia profesional. Las estrategias para el trabajo en equipo en enfermería se basan en los fundamentos teóricos de la dinámica de las interrelaciones grupales, determinando una nueva mirada para la función gerencial del enfermero, a partir de la formación y afirmación de los vínculos profesionales que agreguen, en los cuales las relaciones interpersonales puedan favorecer una praxis crítica, reflexiva y participativa.Este artigo é resultado da investigação que teve como objetivo construir uma estratégia de trabalho em equipe na enfermagem, para favorecer as relações interpessoais, ou seja, os vínculos profissionais, para o alcançe de um cuidado terapéutico comprometido com os usuários dos serviços de saúde. A metodologia tem o respaldo na corrente construtivista e conto com as seguintes fases: entrevista e observação. Depois da análise dos dados surgiram os temas: posição individual e grupal no micro espaço de atuação; movimiento das relações grupais; proceso de comunicação; educação continuada; competencia profissional. As estratégias para o trabalho na equipe em enfermagem tem base nos fundamentos teóricos da dinâmica das interrelações grupais, determinando um novo olhar para a função gerencial do enfermeiro, a partir da formação e afirmação dos vínculos profissionais, nos quais as relações interpessoais podem favorecer uma praxis crítica, reflexiva e participativ
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
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/Îł-ray spectrometer (20 keVâ8 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 âsyntheticâ 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 sourcesâ 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
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