Role of transverse temperature gradients in the generation of lamellar eutectic solidification patterns

In directional solidification, a sample is pulled in an externally imposed temperature gradient. When the pulling direction and the temperature gradient are not perfectly aligned, a transverse temperature gradient is generated in the sample. We investigate the dynamics of lamellar eutectic patterns, both by experimental observations and by numerical simulations, and find that it is dramatically affected by a transverse gradient. Whereas, in its absence, the labyrinth patterns that are formed in the initial stage of solidification persist over the entire duration of the experiments, a transverse temperature gradient induces a drift of the pattern which rapidly generates a regular array of lamellae. The drift speed is found to be consistently larger than expected from the normal growth hypothesis, both in simulations and experiments.     

Flow behaviour of carrot puree: modelling the influence of time,temperature and potato flakes addition

Rheological properties of carrot puree were investigated in the 1–1000 s^?1 shear rate range with the objective of modelling the influence of time, temperature and addition of potato flakes on the flow behaviour. Carrot puree exhibited a shear‐thinning behaviour that was well described by the Ostwald‐de Waele (Power Law) model with a flow behaviour index of 0.34 (±0.02) at 20 °C. The time‐dependent behaviour was characterised by a second‐order Structural Kinetic Model. The decay of the structural parameter with time was found to be independent of shear rate. The Arrhenius model was used to explain the effect of temperature in the range from 4 to 60 °C. The dry matter was increased by adding potato flakes (0–5%). A power law model (for the concentration) and the Arrhenius relationship (for the temperature) were combined to simultaneously describe the effects of temperature and concentration. This study provides essential data for equipment and process design.     

Quantitative coherent anti-Stokes Raman scattering microspectroscopy using a nanosecond supercontinuum light source

We describe and characterize a multiplex CARS microspectroscopic system that uses a nanosecond supercontinuum generated from a photonic crystal fiber and a sub-nanosecond pulse laser. This system has a high spectral resolution (<0.1 cm^?1) and an ultrabroadband spectral coverage (>2500 cm^?1). The estimated spatial resolutions are 0.45 μm (lateral) and 4.5 μm (axial), respectively. This system enables us to obtain CARS spectra and corresponding images in the fingerprint region as well in the CH stretch region. Using this system, we have successfully obtained label-free and multi-mode vibrational images of a yeast cell.     

Identification of equivalent topography in an open channel flow using Lagrangian data assimilation

We present a Lagrangian data assimilation experiment in an open channel flow above a broad-crested weir. The observations consist of trajectories of particles transported by the flow and extracted from a video film, in addition to classical water level measurements. However, the presence of vertical recirculations on both sides of the weir actually conducts to the identification of an equivalent topography corresponding to the lower limit of a surface jet. In addition, results on the identification of the Manning coefficient may allow to detect the presence of bottom recirculations.     

An efficient reduced simulation of residual stresses in composite forming processes

An efficient simulation of thermal and mechanical models involved in thermosetting composites forming needs to overcome some numerical difficulties related to: (i) the multi-scale behaviour; (ii) the complex geometries involved needing too many degrees of freedom; (iii) the large time intervals where the solution has to be computed; (iv) the non-linearity of the involved evolution equations; (v) the numerous couplings… In this work, an efficient strategy based on a separated representation is proposed. This method enables to avoid the use of an incremental strategy and can lead to impressive computing time savings especially when the model involves fine meshes and very small time steps. The local non-linear chemical kinetics and its coupling with the global heat balance equation are naturally introduced in the separated representation algorithm. Moreover, the dependence of the thermal conductivity and the specific heat on the temperature and on the reaction advancement degree are also taken into account. Knowing the history of the temperature field, the separated representation is again used to solve the thermo-mechanical problem in order to determine the residual stresses.     

évolution du trouble d’opposition et du trouble des conduites au cours de l’enfance.

This study aimed at describing the evolution of the symptoms of the oppositional disorder and conducts disorder on a 4-year period (3 times of measurement), depending on whether both disorders appear simultaneously or separately. The sample was composed of 336 children (6–13 years-old), separated in three groups according to the nature of the disorder they presented at the beginning of the study: oppositional disorder only, conducts disorder only, both oppositional and conducts disorders. Structured diagnostic interviews based on the diagnostic criterions of the Diagnostic and Statistical Manual of Mental Disorders (4 éd., texte rév.; American Psychiatric Association, 2000) were used in order to evaluate the average number of symptoms associated to each disorder at each time of measurement. Multilevel regression analysis suggest that the initial co-occurrence of the disorders is neither associated to the evolution of the symptoms of the conducts disorder nor to those of the oppositional disorder. However, this co-occurrence, that can also include the attention-deficit/hyperactivity disorder, can increase the number of symptoms in children, which likely contributes to maintain the diagnostics in some cases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The evolution of the corrosion of iron in hydraulic binders analysed from 46- and 260-year-old buildings

Corrosion patterns on samples taken on binder and rebars from two buildings, respectively, aged of 46 and 260 years old have been characterised by coupling different analytical methods at microscopic scale. Different corrosion patterns have been observed. The first one is constituted by the initial mill scale made of wustite, magnetite and hematite. The second one contains remains of this mill scale embedded in phases formed after aqueous corrosion: oxyhydroxides as goethite or lepidocrocite containing marblings of ferrihydrite, maghemite and magnetite. On the thicker and older layers, marblings were only constituted of magnetite and maghemite. It is proposed that the structural evolution of the pattern and their marbling is linked to wet/dry cycles and/or pH condition evolution during the corrosion processes.     

Method for Accurate Surface Temperature Measurements During Fast Induction Heating

A robust method is proposed for the measurement of surface temperature fields during induction heating. It is based on the original coupling of temperature-indicating lacquers and a high-speed camera system. Image analysis tools have been implemented to automatically extract the temporal evolution of isotherms. This method was applied to the fast induction treatment of a 4340 steel spur gear, allowing the full history of surface isotherms to be accurately documented for a sequential heating, i.e., a medium frequency preheating followed by a high frequency final heating. Three isotherms, i.e., 704, 816, and 927°C, were acquired every 0.3 ms with a spatial resolution of 0.04 mm per pixel. The information provided by the method is described and discussed. Finally, the transformation temperature Ac1 is linked to the temperature on specific locations of the gear tooth.     

Dynamics and control of solar thermochemical reactors

A general dynamic model for solar-driven thermochemical processes is formulated based on unsteady mass and energy conservation equations coupled to the reaction kinetics. It is applied to two pertinent high-temperature thermochemical reactors for fuel production that make use of concentrated solar energy as the source of process heat, namely: an indirectly irradiated batch-operated packed bed reactor for the carbothermic reduction of zinc oxide, and a directly irradiated continuously operated particle flow reactor for the steam-gasification of petcoke. Model parameter identification and validation is accomplished by comparing numerically simulated and experimentally measured temperatures and outlet product concentrations. A linear feedback controller was implemented using the LQG/LTR design method. Simulations of the controlled reactor system with real solar irradiation data indicates improved quality and steadiness of product composition throughout transient solar input phases and superior solar-to-chemical energy conversion efficiency.