Geodesic network method for flows between two rough surfaces in contact

A discrete network method based on previous asymptotic analysis for computing fluid flows between confined rough surfaces is proposed. This random heterogeneous geodesic network method could be either applied to surfaces described by a continuous random field or finely discretized on a regular grid. This method tackles the difficult problem of fluid transport between rough surfaces in close contact. We describe the principle of the method as well as detail its numerical implementation and performances. Macroscopic conductances are computed and analyzed far from the geometrical percolation threshold. Numerical results are successfully compared with the effective medium approximation, the application of which is also studied analytically

Barragem de enrocamento com face de concreto: simulação e parametrização por elementos finitos

To evaluate how the movements of the face slab of concrete face rockfill dam are influenced by having soft materials on the downstream portion of the dam, the construction and impoundment of Foz do Areia Dam is reproduced and a parametric analysis of the characteristics of rockfill stiffness is carried on. This study is done using the finite elements computer program CONSAT (MAHLER and PEREIRA, 1988) developed at COPPE/UFRJ. A wide review of the state of the art of design and construction of concrete face rockfill dams is also presented.Com o objetivo de observar de que maneira a deformação da laje da barragem de enrocamento com face de concreto é afetada pela colocação de materiais menos rígidos na sua porção de jusante, realiza-se a simulação da construção e enchimento da barragem de Foz do Areia e uma parametrização das características de rigidez do enrocamento. Esse estudo é feito com o auxílio de um programa de computador de elementos finitos, o CONSAT (MAHLER e PEREIRA, 1988), desenvolvido na COPPE/UFRJ. Apresenta-se também uma ampla revisão da técnica atual do projeto e construção das barragens de enrocamento com face de concreto

An Asymptotic Preserving Scheme for the Euler equations in a strong magnetic field

This paper is concerned with the numerical approximation of the isothermal Euler equations for charged particles subject to the Lorentz force. When the magnetic field is large, the so-called drift-fluid approximation is obtained. In this limit, the parallel motion relative to the magnetic field direction splits from perpendicular motion and is given implicitly by the constraint of zero total force along the magnetic field lines. In this paper, we provide a well-posed elliptic equation for the parallel velocity which in turn allows us to construct an Asymptotic-Preserving (AP) scheme for the Euler-Lorentz system. This scheme gives rise to both a consistent approximation of the Euler-Lorentz model when epsilon is finite and a consistent approximation of the drift limit when epsilon tends to 0. Above all, it does not require any constraint on the space and time steps related to the small value of epsilon. Numerical results are presented, which confirm the AP character of the scheme and its Asymptotic Stability

Effects of breastfeeding on body composition and maturational tempo in the rat

BACKGROUND: Features of life history are subject to environmental regulation in the service of reproductive fitness goals. We have previously shown that the infant-to-childhood transition reflects the adaptive adjustment of an individual's size to the prevailing and anticipated environment. METHODS: To evaluate effects of weaning age on life-history traits in rats, we repeatedly measured length and body mass index (BMI), as well as physiological development and sexual maturation in pups weaned early (d16), normally (d21) or late (d26). Males were bred to females of the same weaning age group for four generations. RESULTS: Here, we show that the age at weaning from lactation regulates a rat's life history, growth, body composition and maturational tempo. We show that early-weaned rats developed faster than normal- or late-weaned rats; they are leaner and longer than late-weaned ones who are heavier and shorter. Early-weaned progeny develop more rapidly (that is, fur budding, pinnae detachment, eye opening); females show earlier vaginal opening and estrous and males show earlier onset of testicular growth. In generations 3 and 4, early-weaned rats bear larger litter sizes and heavier newborn pups. The entire traits complex is transmitted to subsequent generations from the paternal side. CONCLUSIONS: The findings presented here lend support to the proposition that the duration of infancy, as indexed by weaning age, predicts and perhaps programs growth, body composition, and the tempo of physiological development and maturation, as well as litter size and parity and, thereby, reproductive strategy

Numerical approximation of the Euler-Maxwell model in the quasineutral limit

International audienceWe derive and analyze an Asymptotic-Preserving scheme for the Euler-Maxwell system in the quasi-neutral limit. We prove that the linear stability condition on the time-step is independent of the scaled Debye length $\lambda$ when $\lambda \to 0$. Numerical validation performed on Riemann initial data and for a model Plasma Opening Switch device show that the AP-scheme is convergent to the Euler-Maxwell solution when $\Delta x/ \lambda \to 0$ where $\Delta x$ is the spatial discretization. But, when $\lambda /\Delta x \to 0$, the AP-scheme is consistent with the quasi-neutral Euler-Maxwell system. The scheme is also perfectly consistent with the Gauss equation. The possibility of using large time and space steps leads to several orders of magnitude reductions in computer time and storage

Numerical approximation of the Euler-Poisson-Boltzmann model in the quasineutral limit

This paper analyzes various schemes for the Euler-Poisson-Boltzmann (EPB) model of plasma physics. This model consists of the pressureless gas dynamics equations coupled with the Poisson equation and where the Boltzmann relation relates the potential to the electron density. If the quasi-neutral assumption is made, the Poisson equation is replaced by the constraint of zero local charge and the model reduces to the Isothermal Compressible Euler (ICE) model. We compare a numerical strategy based on the EPB model to a strategy using a reformulation (called REPB formulation). The REPB scheme captures the quasi-neutral limit more accurately

Predictive policing ontcijferd:Een etnografie van het 'Criminaliteits Anticipatie Systeem' in de praktijk

Dit artikel beschrijft een etnografische studie naar het gebruik van statistische voorspellingen voor politiewerk (i.e., ‘predictive policing’). In dit onderzoek ‘ontcijferen’ wij zowel de input als de output van deze voorspellingen door in te gaan op hoe het gebruik van deze technologie in de praktijk tot stand komt. Dit begint bij de data scientist, die met het ontwerp van het algoritme de input en output beïnvloedt, en eindigt bij agenten op straat, die de voorspellingen wel of niet serieus nemen. Ons onderzoek gaat in tegen de algemene aanname dat een predictive policing algoritme als objectief en onafhankelijk instrument kan worden ingezet voor het verhogen van efficiëntie en effectiviteit. In plaats daarvan stellen wij dat het soms maanden werk vraagt en afhankelijk is van de handelingen en contextuele kennis van verschillende actoren (bijvoorbeeld, politieagenten, intelligence specialisten, politiemanagement, gemeente) die daarbij hun inzet en oordelen met de technologie verweven

A class of asymptotic preserving schemes for kinetic equations and related problems with stiff sources

In this paper, we propose a general framework to design asymptotic preserving schemes for the Boltzmann kinetic kinetic and related equations. Numerically solving these equations are challenging due to the nonlinear stiff collision (source) terms induced by small mean free or relaxation time. We propose to penalize the nonlinear collision term by a BGK-type relaxation term, which can be solved explicitly even if discretized implicitly in time. Moreover, the BGK-type relaxation operator helps to drive the density distribution toward the local Maxwellian, thus natually imposes an asymptotic-preserving scheme in the Euler limit. The scheme so designed does not need any nonlinear iterative solver or the use of Wild Sum. It is uniformly stable in terms of the (possibly small) Knudsen number, and can capture the macroscopic fluid dynamic (Euler) limit even if the small scale determined by the Knudsen number is not numerically resolved. It is also consistent to the compressible Navier-Stokes equations if the viscosity and heat conductivity are numerically resolved. The method is applicable to many other related problems, such as hyperbolic systems with stiff relaxation, and high order parabilic equations