Non-linear oscillatory rheological properties of a generic continuum foam model: comparison with experiments and shear-banding predictions

The occurence of shear bands in a complex fluid is generally understood as resulting from a structural evolution of the material under shear, which leads (from a theoretical perspective) to a non-monotonic stationnary flow curve related to the coexistence of different states of the material under shear. In this paper we present a scenario for shear-banding in a particular class of complex fluids, namely foams and concentrated emulsions, which differs from other scenarii in two important ways. First, the appearance of shear bands is shown to be possible both without any intrinsic physical evolution of the material (e.g. via a parameter coupled to the flow such as concentration or entanglements) and without any finite critical shear rate below which the flow does not remain stationary and homogeneous. Secondly, the appearance of shear bands depends on the initial conditions, i.e., the preparation of the material. In other words, it is history dependent. This behaviour relies on the tensorial character of the underlying model (2D or 3D) and is triggered by an initially inhomogeneous strain distribution in the material. The shear rate displays a discontinuity at the band boundary, whose amplitude is history dependent and thus depends on the sample preparation.Comment: 18 pages - 17 figure

Numerical coupling of Landau damping and Raman amplification

In this paper, we present a numerical model for laser-plasma interaction involving Raman instability and Landau damping. This model exhibits three main difficulties. The first one is the coupling of PDE's posed both in Fourier space and in physical space. The second one is a three wave resonance condition that has to be verified. The third one is the boundary conditions. We overcome these difficulties using respectively a splitting scheme, a numerical dispersion relation and absorbing boundary conditions. We present some comparison between several phenomena that are involved and the influence of the Raman amplification and the Landau damping

A multiscale mathematical model of cancer, and its use in analyzing irradiation therapies

Background: Radiotherapy outcomes are usually predicted using the Linear Quadratic model. However, this model does not integrate complex features of tumor growth, in particular cell cycle regulation. Methods: In this paper, we propose a multiscale model of cancer growth based on the genetic and molecular features of the evolution of colorectal cancer. The model includes key genes, cellular kinetics, tissue dynamics, macroscopic tumor evolution and radiosensitivity dependence on the cell cycle phase. We investigate the role of gene-dependent cell cycle regulation in the response of tumors to therapeutic irradiation protocols. Results: Simulation results emphasize the importance of tumor tissue features and the need to consider regulating factors such as hypoxia, as well as tumor geometry and tissue dynamics, in predicting and improving radiotherapeutic efficacy. Conclusion: This model provides insight into the coupling of complex biological processes, which leads to a better understanding of oncogenesis. This will hopefully lead to improved irradiation therapy.Comment: 19 pages, 14, figures. Article available at http://www.tbiomed.com/content/3/1/7 Copyright 2006 Ribba et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cite

A multi-D model for Raman amplification

In this paper, we continue the study of the Raman amplification in plasmas that we have initiated in \cite{colins1} and \cite{colins2}. We point out that the Raman instability gives rise to three components. The first one is colinear to the incident laser pulse and counter propagates. In 2-D, the two other ones make a non-zero angle with the initial pulse and propagates forward. Furthermore they are symmetric with respect to the direction of propagation of the incident pulse. We construct a nonlinear system taking into account all these components and perform some 2-D numerical simulations

Influence of mean circulation on large-scale decadal basin modes

The effect of large-scale mean circulation on the generic property of intrinsic basin modes of decadal variability is investigated through linear stability analysis of a two-layer shallow water model over a flat- and a variable-bottom topography. The mean circulation is forced through either surface wind stress or vertical velocities at the layers interface representing surface heat flux. Regardless of the type of forcing, the large-scale mean circulation reduces the damping of the decadal basin modes. The wind forcing mostly affects the mode damping, by up to 30% for a climatological amplitude, whereas the heat flux forcing mostly increases the oscillation period, by several years (up to 30%). The oscillation period, characteristic of the adjustment process to the steady mean flow, displays, however, different behavior depending on the meridional shift of the eastward barotropic advection in the region of maximum basin mode amplitude: The period gets shortened (lengthened) in the wind-forced (thermally forced) experiment with respect to the unforced one. The results are rationalized through the analysis of long Rossby waves propagation and underscore the key role of two processes in setting the oscillation period of the basin adjustment: (1) changes in Rossby wave speed due to changes in isopycnals depth and (2) changes in the mean barotropic zonal flow. These processes reinforce each other in the thermal-forcing case, resulting in large modifications of the mode period, but almost compensate in the wind-forced case, resulting in slight changes of the mode period, compared with the reference rest state

Oxidation modelling of a Si3N4–TiN ceramic: microstructure and kinetic laws

International audienceThe oxidation of a silicon nitride–titanium nitride ceramic has been studied. Based on microstructural observations, a phenomenological oxidation model is described, and an oxidation kinetic model has been proposed. For temperatures <1000 °C, only the TiN phase is oxidised. The oxidation process is then controlled by oxygen diffusion through TiO2, described by a parabolic oxidation kinetic law. The process is more complex above 1000 °C, because of the simultaneous oxidation of both Si3N4 and TiN phases. Three oxidation modes, controlled by distinct diffusion mechanisms, take place successively. In a first step, Si3N4 and TiN phases are independently oxidised, respectively into SiO2 and TiO2 phases. Si3N4 oxidation is controlled by oxygen diffusion through SiO2, while TiN oxidation is controlled by titanium diffusion through TiO2. In a second step, the TiN oxidation is controlled by oxygen diffusion through TiO2 and through SiO2 formed by Si3N4 oxidation. In the third step, oxidation of the TiN and Si3N4 phases is controlled by oxygen diffusion through the silica layer. Kinetic laws have been proposed for each of these three oxidation modes

Comparing monthly statistical distributions of wind speed measured at wind towers and estimated from ERA-Interim

International audienceThe energy sector is undergoing a major transformation with an increasing share of power supply from variable renewable energy sources and an increasing variability in energy demand in a variable and changing climate. The European Climatic Energy Mixes (ECEM) project will develop a demonstrator to assess how well different energy supply mixes in Europe will meet demand, over seasonal to long-term decadal time horizons, focusing on the role climate has on the mixes. ECEM is funded under the Copernicus Climate Change Service, operated by ECMWF on behalf of the European Union. Many surface climate variables needed to develop energy profiles are provided by the ERA-Interim Reanalysis. Among these profiles, are wind power supply with wind speed at different heights as main inputs to determine periods when the wind power plants are expected to produce more or less than expected. In this view, a preliminary assessment of the monthly statistical distribution of wind speed at the standard height for wind power plants (80 m) has been performed. Time series of wind speed were obtained for the towers at Cabauw in The Netherlands and offshore at Docking Shoal in the North Sea. Reference statistical distributions were built for each month. Similarly, estimated statistical distributions were built using ERA-Interim estimates of wind speed at different levels. One series was built with a power approach and a second with a log approach. The estimated statistical distributions are then compared to the reference for each month. The log approach produces stronger winds than the power approach for both sites. At Cabauw, both approaches do not produce enough large wind speed for all months. At Docking Shoal, the power approach exhibits statistical distributions very close to the reference ones. Those from the log approach are biased towards higher wind speeds