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5. Stripes instability of an oscillating non Brownian iso-dense suspension of spheres

Author

Roht, Y. L., Ippolito, I., Hulin, J. P., Salin, D., and Gauthier, G.

Subjects
Physics - Fluid Dynamics
Abstract

We analyze experimentally the behavior of a non-Brownian, iso-dense suspension of spheres submitted to periodic square wave oscillations of the flow in a Hele-Shaw cell of gap $H$. We do observe an instability of the initially homogeneous concentration in form of concentration variation stripes transverse to the flow. The wavelength of these regular spatial structures scales roughly as the gap of the cell and is independent of the particle concentration and of the period of oscillation. This instability requires large enough particle volume fractions $\phi\geq 0.25$, a gap large enough compared to the spheres diameter ($H/d \geq 8$) and is observed in a rather broad range of periods of the square waves and amplitudes of the fluid displacement. We map the domain of existence of this instability in the space of the control parameters. The analysis of the concentration distribution across the gap shows that the instability is likely to be associated to the migration of the particles from the center towards the cell walls. In order to account for the main features of this stripes instability, we use the theory of longitudinal instability due to normal stresses difference and recent measurements of the first normal stresses difference dependence with particles concentration.

Published
2017
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6. Frozen Fronts Selection in flow against self-sustained chemical waves

Author

Chevalier, T., Salin, D., and Talon, L.

Subjects
Nonlinear Sciences - Pattern Formation and Solitons
Abstract

Autocatalytic reaction fronts between two reacting species in the absence of fluid flow, propagate as solitary waves. The coupling between autocatalytic reaction front and forced hydrodynamic flow may lead to stationary front whose velocity and shape depend on the underlying flow field. We focus on the issue of the chemo-hydrodynamic coupling between forced advection opposed to self-sustained chemical waves which can lead to static stationary fronts, i.e Frozen Fronts, $FF$. Towards that purpose, we perform experiments, analytical computations and numerical simulations with the autocatalytic Iodate Arsenious Acid reaction ($IAA$) over a wide range of flow velocities around a solid disk. For the same set of control parameters, we observe two types of frozen fronts: an upstream $FF$ which avoid the solid disk and a downstream $FF$ with two symmetric branches emerging from the solid disk surface. We delineate the range over which we do observe these Frozen Fronts. We also address the relevance of the so-called eikonal, thin front limit to describe the observed fronts and select the frozen front shapes., Comment: draft

Published
2016

7. Autocatalytic reaction front in a pulsative periodic flow

Author

Leconte, M., Martin, J., Rakotomalala, N., and Salin, D.

Subjects
Physics - Fluid Dynamics, Physics - Chemical Physics
Abstract

Autocatalytic reaction fronts between reacted and unreacted species may propagate as solitary waves, namely at a constant front velocity and with a stationary concentration profile, resulting from a balance between molecular diffusion and chemical reaction. A velocity field in the supporting medium may affect the propagation of such fronts through different phenomena: convection, diffusion enhancement, front shape changes... We report here on an experimental study and lattice BGK numerical simulations of the effect of an oscillating flow on the autocatalytic reaction between iodate and arsenous acid in a Hele-Shaw cell. In the low frequency range covered by the experiments, the front behavior is controlled by the flow across the gap and can be reproduced with 2D numerical simulations. An analytical solution is also derived under the condition of a weak flow velocity, and is found to be in reasonable agreement with our data., Comment: 17 pages, 11 figures, to be submitted to Physics of Fluids

Published
2005

8. Pattern of Reaction Diffusion Front in Laminar Flows

Author

Leconte, M., Martin, J., Rakotomalala, N., and Salin, D.

Subjects
Physics - Fluid Dynamics
Abstract

Autocatalytic reaction between reacted and unreacted species may propagate as solitary waves, namely at a constant front velocity and with a stationary concentration profile, resulting from a balance between molecular diffusion and chemical reaction. The effect of advective flow on the autocatalytic reaction between iodate and arsenous acid in cylindrical tubes and Hele-Shaw cells is analyzed experimentally and numerically using lattice BGK simulations. We do observe the existence of solitary waves with concentration profiles exhibiting a cusp and we delineate the eikonal and mixing regimes recently predicted., Comment: 4 pages, 3 figures. This paper report on experiments and simulations in different geometries which test the theory of Boyd Edwards on flow advection of chemical reaction front which just appears in PRL (PRL Vol 89,104501, sept2002)

Published
2002
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11. Being the bigger person: Investigating the relationship between workplace bullying exposure and enactment and the role of coping in ending the bullying spiral

Author

Vranjes, I., Salin, D., Baillien, E., Vranjes, I., Salin, D., and Baillien, E.

Abstract

Item does not contain fulltext, While most of the workplace bullying research has focused on targets and the devastating consequences they face from being exposed to such negative behaviour, bullying does not occur in a social vacuum. Previous research has suggested that people who are exposed to bullying sometimes engage in such behaviour themselves. In this paper, we wanted to test the reciprocal nature of bullying behaviour over time and potential moderators of this relationship in two studies. In Study 1, using two-wave full panel data, we test whether bullying exposure predicts bullying enactment and vice versa. In Study 2, using another two-wave dataset, we test whether individual coping styles moderate the relationship between bullying exposure and enactment. The results of the two studies provide support for the reciprocal nature of bullying behaviour and show that employees who tend to cope actively and instrumentally with being exposed to bullying have a higher chance of engaging in bullying. The reverse holds for people who tend to cope by disengaging and talking to others. This study has important implications for both the bullying literature and for practitioners working on bullying prevention and resolution.

Published
2022

12. Putting workplace bullying in context: The role of high-involvement work practices in the relationship between job demands, job resources, and bullying exposure

Author

Vranjes, I., Notelaers, G., Salin, D., Vranjes, I., Notelaers, G., and Salin, D.

Abstract

Item does not contain fulltext, Previous research has demonstrated the crucial association between employee stressors and workplace bullying. In this article, we argue that a nurturing organizational context will protect employees from exposure to workplace bullying and will interact with individual demands and resources known to have effect on exposure to bullying in the workplace. In specific, we look at high-involvement work practices (HIWPs) - which include participation, information-sharing, competence development, and rewards. Multilevel analyses on the data from 28,923 Belgian employees from 144 organizations show that organization-level HIWPs are negatively associated with bullying exposure. Moreover, HIWPs interact with individually experienced job demands and resources, by decreasing the association between employee work pressure and bullying and by somewhat compensating for the lack of experienced social support from colleagues at work. HIWPs did not moderate the relationship between employee job insecurity and bullying and social support from the supervisor and bullying. These findings highlight the important role HIWPs can play in protecting employees from workplace bullying, while also suggesting the difficulty of compensating for certain individual risk factors.

Published
2022

14. Heterogeneous porous media: Fronts and noise

Author

Chaouchel, M., Rakotomalala, N., Salin, D., Xu, B., Yortsos, Y. C., Araki, H., editor, Brézin, E., editor, Ehlers, J., editor, Frisch, U., editor, Hepp, K., editor, Jaffe, R. L., editor, Kippenhahn, R., editor, Weidenmüller, H. A., editor, Wess, J., editor, Zittartz, J., editor, Beiglböck, W., editor, Bardhan, Kamal K., editor, Chakrabarti, Bikas K., editor, and Hansen, Alex, editor

Published
1994
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16. Magnetic wetting transition

Author

Bacri, J. C., Perzynski, R., Salin, D., Araki, H., editor, Ehlers, J., editor, Hepp, K., editor, Kippenhahn, R., editor, Ruelle, D., editor, Weidenmüller, H. A., editor, Wess, J., editor, Zittartz, J., editor, Beiglböck, W., editor, De Coninck, Joël, editor, and Dunlop, François, editor

Published
1990
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17. Volume fraction instability in an oscillating non-Brownian iso-dense suspension.

Author

Roht Y.L., Gauthier G., Hulin J.P., Salin D., Chertcoff R., Auradou H., and Ippolito I.

Subjects
Physics, QC1-999
Abstract

The instability of an iso-dense non-Brownian suspension of polystyrene beads of diameter 40 μm dispersed in a water-glycerol mixture submitted to a periodic square wave oscillating flow in a Hele-Shaw cell is studied experimentally. The instability gives rise to stationary bead concentration waves transverse to the flow. It has been observed for average particle volume fractions between 0.25 and 0.4, for periods of the square wave flow variation between 0.4 and 10 s and in finite intervals of the amplitude of the fluid displacement. The study shows that the wavelength λ increases roughly linearly with the amplitude of the oscillatory flow; on the other hand, λ is independent of the particle concentration and of the period of oscillation of the flow although the minimum threshold amplitude for observing the instability increases with the period.

Published
2017
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18. Being the bigger person: Investigating the relationship between workplace bullying exposure and enactment and the role of coping in ending the bullying spiral

Author

Vranjes, I., Salin, D., Baillien, E., Vranjes, I., Salin, D., and Baillien, E.

Abstract

24 augustus 2021, Item does not contain fulltext, While most of the workplace bullying research has focused on targets and the devastating consequences they face from being exposed to such negative behaviour, bullying does not occur in a social vacuum. Previous research has suggested that people who are exposed to bullying sometimes engage in such behaviour themselves. In this paper, we wanted to test the reciprocal nature of bullying behaviour over time and potential moderators of this relationship in two studies. In Study 1, using two-wave full panel data, we test whether bullying exposure predicts bullying enactment and vice versa. In Study 2, using another two-wave dataset, we test whether individual coping styles moderate the relationship between bullying exposure and enactment. The results of the two studies provide support for the reciprocal nature of bullying behaviour and show that employees who tend to cope actively and instrumentally with being exposed to bullying have a higher chance of engaging in bullying. The reverse holds for people who tend to cope by disengaging and talking to others. This study has important implications for both the bullying literature and for practitioners working on bullying prevention and resolution.

Published
2021

26. Lock-exchange experiments with an autocatalytic reaction front.

Author

Malham, I. Bou, Jarrige, N., Martin, J., Rakotomalala, N., Talon, L., and Salin, D.

Subjects
AUTOCATALYSIS, FLUID dynamics, DIFFUSION, CHEMICAL reactions, SIMULATION methods & models, VISCOSITY, LATTICE theory, MOLECULAR dynamics
Abstract

A viscous lock-exchange gravity current corresponds to the reciprocal exchange of two fluids of different densities in a horizontal channel. The resulting front between the two fluids spreads as the square root of time, with a diffusion coefficient reflecting the buoyancy, viscosity, and geometrical configuration of the current. On the other hand, an autocatalytic reaction front between a reactant and a product may propagate as a solitary wave, namely, at a constant velocity and with a stationary concentration profile, resulting from the balance between molecular diffusion and chemical reaction. In most systems, the fluid left behind the front has a different density leading to a lock-exchange configuration. We revisit, with a chemical reaction, the classical situation of lock-exchange. We present an experimental analysis of buoyancy effects on the shape and the velocity of the iodate arsenous acid autocatalytic reaction fronts, propagating in horizontal rectangular channels and for a wide range of aspect ratios (1/3 to 20) and cylindrical tubes. We do observe stationary-shaped fronts, spanning the height of the cell and propagating along the cell axis. Our data support the contention that the front velocity and its extension are linked to each other and that their variations scale with a single variable involving the diffusion coefficient of the lock-exchange in the absence of chemical reaction. This analysis is supported by results obtained with lattice Bathnagar-Gross-Krook (BGK) simulations Jarrige et al. [Phys. Rev. E 81, 06631 (2010)], in other geometries (like in 2D simulations by Rongy et al. [J. Chem. Phys. 127, 114710 (2007)] and experiments in cylindrical tubes by Pojman et al. [J. Phys. Chem. 95, 1299 (1991)]), and for another chemical reaction Schuszter et al. [Phys. Rev. E 79, 016216 (2009)]. [ABSTRACT FROM AUTHOR]

Published
2010
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27. Mixing and reaction fronts in laminar flows.

Author

Leconte, M., Martin, J., Rakotomalala, N., Salin, D., and Yortsos, Y. C.

Subjects
LAMINAR flow, TAYLOR vortices, INTERFACES (Physical sciences), FLUIDS, HYDRODYNAMICS, REACTION mechanisms (Chemistry), MIXING
Abstract

Autocatalytic reaction fronts between unreacted and reacted mixtures in the absence of fluid flow propagate as solitary waves. In the presence of imposed flow, the interplay between diffusion and advection enhances the mixing, leading to Taylor hydrodynamic dispersion. We present asymptotic theories in the two limits of small and large Thiele modulus (slow and fast reaction kinetics, respectively) that incorporate flow, diffusion, and reaction. For the first case, we show that the problem can be handled to leading order by the introduction of the Taylor dispersion replacing the molecular diffusion coefficient by its Taylor counterpart. In the second case, the leading-order behavior satisfies the eikonal equation. Numerical simulations using a lattice gas model show good agreement with the theory. The Taylor model is relevant to microfluidics applications, whereas the eikonal model applies at larger length scales. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2004
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35. Experimental and numerical investigations of flow structure and momentum transport in a turbulent buoyancy-driven flow inside a tilted tube

Author

Znaien, J.G., Hallez, Y., Moisy, F., Magnaudet, J., Hulin, J.P., Salin, D., Hinch, E.J., Znaien, J.G., Hallez, Y., Moisy, F., Magnaudet, J., Hulin, J.P., Salin, D., and Hinch, E.J.

Abstract

BBuoyancy-driven turbulent mixing of fluids of slightly different densities [At = ¿¿/(2 ) = 1.15×10-2] in a long circular tube tilted at an angle ¿ = 15° from the vertical is studied at the local scale, both experimentally from particle image velocimetry and laser induced fluorescence measurements in the vertical diametrical plane and numerically throughout the tube using direct numerical simulation. In a given cross section of the tube, the axial mean velocity and the mean concentration both vary linearly with the crosswise distance z from the tube axis in the central 70% of the diameter. A small crosswise velocity component is detected in the measurement plane and is found to result from a four-cell mean secondary flow associated with a nonzero streamwise component of the vorticity. In the central region of the tube cross section, the intensities of the three turbulent velocity fluctuations are found to be strongly different, that of the streamwise fluctuation being more than twice larger than that of the spanwise fluctuation which itself is about 50% larger than that of the crosswise fluctuation. This marked anisotropy indicates that the turbulent structure is close to that observed in homogeneous turbulent shear flows. Still in the central region, the turbulent shear stress dominates over the viscous stress and reaches a maximum on the tube axis. Its crosswise variation is approximately accounted for by a mixing length whose value is about one-tenth of the tube diameter. The momentum exchange in the core of the cross section takes place between its lower and higher density parts and there is no net momentum exchange between the core and the near-wall regions. A sizable part of this transfer is due both to the mean secondary flow and to the spanwise turbulent shear stress. Near-wall regions located beyond the location of the extrema of the axial velocity (|z|¿0.36 d) are dominated by viscous stresses which transfer momentum toward (from) the wall near the top (bo

Published
2009

50. La toxicité de l'ammoniaque chez l'esturgeon sibérien, Acipenser baeri : effets morphologiques, physiologiques et métaboliques d'une exposition à des doses sublétales et létales

Author

Salin, D. and Irstea Publications, Migration

Subjects
[SDE] Environmental Sciences, CEMAGREF, thesis, thèse
Abstract

The exposure of Siberian sturgeons to sublethal and lethal doses of ammonia has shown: a degradation of the branchial tepithetrum; a modification of the acid-alkaline and ionic blood parameters, with a more or less good regulation; an introduction of ammoniac into the fish by mere NH3 diffusion if real PH computations take into account the trinit layer near the gills; no action on the intraerythrocyte oxygen-hemoglobin link but an increase of the blood volume; finally an important role of glutamate, glutamine, aspartate and of ATP in the ammonia toxicity., L'exposition d'esturgeons sibériens à des bases sublétales et totales d'ammoniaque a montré : une dégradation de tépithétrum branchial, une modification des paramètres acido-basique et ioniques du sang avec une régulation plus ou moins bonne ; une entrée de l'ammoniaque dans le poisson par simple diffusion de NH3 à condition de tenir compte pour les calculs du PH réel de la couche trinit aux abords des branchives ; aucune action sur la liaison oxygène-hémoglobine intraérythrocytène mais une augmentation du volume globulaire ; enfin un rôle important du glutamate, de la glutamine, de l'aspartate et de l'ATP dans la toxicité de l'ammoniaque.

Published
1992

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