References of "Gilet, Tristan"
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See detailFluid fragmentation shapes rain-induced foliar disease transmission
Gilet, Tristan ULg; Bourouiba, Lydia

in Journal of the Royal Society, Interface (2015), 12

Plant diseases represent a growing threat to the global food supply. The factors contributing to pathogen transmission from plant to plant remain poorly understood. Statistical correlations between ... [more ▼]

Plant diseases represent a growing threat to the global food supply. The factors contributing to pathogen transmission from plant to plant remain poorly understood. Statistical correlations between rainfalls and plant disease out- breaks were reported; however, the detailed mechanisms linking the two were relegated to a black box. In this combined experimental and theoretical study, we focus on the impact dynamics of raindrops on infected leaves, one drop at a time. We find that the deposition range of most of the pathogen-bear- ing droplets is constrained by a hydrodynamical condition and we quantify the effect of leaf size and compliance on such constraint. Moreover, we identify and characterize two dominant fluid fragmentation scenarios as responsible for the dispersal of most pathogen-bearing droplets emitted from infected leaves: (i) the crescent-moon ejection is driven by the direct interaction between the impacting raindrop and the contaminated sessile drop and (ii) the inertial detachment is driven by the motion imparted to the leaf by the raindrop, lead- ing to catapult-like droplet ejections. We find that at first, decreasing leaf size or increasing compliance reduces the range of pathogen-bearing droplets and the subsequent epidemic onset efficiency. However, this conclusion only applies for the crescent moon ejection. Above a certain compliance threshold a more effective mechanism of contaminated fluid ejection, the inertial detachment, emerges. This compliance threshold is determined by the ratio between the leaf velocity and the characteristic velocity of fluid fragmentation. The inertial detachment mechanism enhances the range of deposition of the larger con- taminated droplets and suggests a change in epidemic onset pattern and a more efficient potential of infection of neighbouring plants. Dimensionless parameters and scaling laws are provided to rationalize our observations. Our results link for the first time the mechanical properties of foliage with the onset dynamics of foliar epidemics through the lens of fluid fragmentation. We discuss how the reported findings can inform the design of mitigation strategies acting at the early stage of a foliar disease outbreak. [less ▲]

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See detailDroplet synchronization in multiple interconnected parallel channels
Van Loo, Stéphanie ULg; Stoukatch, Serguei ULg; Gilet, Tristan ULg

Poster (2014, July)

In droplet microfluidics, the pairing of droplets in parallel channels is sometimes required, e.g. to control their encounter and to promote their coalescence. Prakash and Gershenfeld [1] showed that ... [more ▼]

In droplet microfluidics, the pairing of droplets in parallel channels is sometimes required, e.g. to control their encounter and to promote their coalescence. Prakash and Gershenfeld [1] showed that passive synchronization could be achieved with bubbles in a ladder-like channel network. Bubbles flow in the rails and induce recirculation in the interconnecting rungs, which supposedly provides the feedback and subsequent synchronization. Ahn et al. recently extended this study to trains of droplets in flow-rate-driven conditions [2]. We here present an extensive experimental and theoretical investigation of droplets synchonization in multiple parallel channels. Droplets are produced with independent flow-focusing structures. Several experimental conditions are tested, including several geometries (and subsequent flow resistance) and inlet conditions (pressure-driven vs. flow-rate-driven). An extension to three rails is also considered. The microfluidic chips are designed with the help of a lumped-element model in which droplets are driven by the flows. [1] M. Prakash and N. Gershenfeld, Science 2007, 315, 832-835 [2] Ahn et al., Lab-on-a-chip, 2011, 11, 3956-3962 [less ▲]

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See detailRain-operated Foliar Disease Transmission
Gilet, Tristan ULg; Bourouiba, Lydia

Conference (2014, January 07)

Plant diseases are a major cause of crop loss worldwide. They are known to be triggered by rainfalls. We here combine high-speed visualizations and physical modelling to elucidate the causal link between ... [more ▼]

Plant diseases are a major cause of crop loss worldwide. They are known to be triggered by rainfalls. We here combine high-speed visualizations and physical modelling to elucidate the causal link between rain impact on foliage and pathogen spreading. We identify two dominant scenarios by which the pathogens get ejected from leaves. The leaf compliance is shown to strongly affect these mechanisms. The laws of fluid dynamics set tight limits on this epidemiological problem. They suggest a revision of the current agricultural practices in order to contain the spread of foliar diseases. [less ▲]

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See detailDynamics and statistics of wave-particle interactions in a confined geometry
Gilet, Tristan ULg

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2014), 90

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See detailRain-induced Ejection of Pathogens from Leaves: Revisiting the Hypothesis of Splash-on-Film using High-speed Visualization
Gilet, Tristan ULg; Bourouiba, Lydia

in Integrative & Comparative Biology (2014), 54

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See detailDroplets bouncing on a wet, inclined substrate
Gilet, Tristan ULg; Bush, John W.M.

in Physics of Fluids (2012), 24

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See detailManipulation of Droplets onto a Planar Interface
Gilet, Tristan ULg; Terwagne, Denis ULg; Vandewalle, Nicolas ULg et al

in miller, reinhard; liggieri, libero (Eds.) Progress in Colloid and Interface Science, 2 (2011)

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See detailOptimal concentrations in nectar feeding
Kim, Wonjung; Gilet, Tristan ULg; Bush, John W.M.

in Proceedings of the National Academy of Sciences of the United States of America (2011), 108(40), 16618

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest ener- getic rewards, the sharp increase of viscosity with sugar concentra ... [more ▼]

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest ener- getic rewards, the sharp increase of viscosity with sugar concentra- tion makes it the most difficult to transport. We here demonstrate that the sugar concentration that optimizes energy transport depends exclusively on the drinking technique employed. We iden- tify three nectar drinking techniques: active suction, capillary suction, and viscous dipping. For each, we deduce the dependence of the volume intake rate on the nectar viscosity and thus infer an optimal sugar concentration consistent with laboratory mea- surements. Our results provide the first rationale for why suction feeders typically pollinate flowers with lower sugar concentration nectar than their counterparts that use viscous dipping. [less ▲]

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See detailDouble émulsion rebondissante
Terwagne, Denis ULg; Gilet, Tristan ULg; Vandewalle, Nicolas ULg et al

Conference (2010, January 28)

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See detailFrom a bouncing compound drop to a double emulsion
Terwagne, Denis ULg; Gilet, Tristan ULg; Vandewalle, Nicolas ULg et al

in Langmuir (2010), 26(14), 11680

We show that a double emulsion (oil in water in oil) can be created starting from a compound droplet (surfactant solution in oil). The compound drop bounces on a vertically vibrated liquid surface. When ... [more ▼]

We show that a double emulsion (oil in water in oil) can be created starting from a compound droplet (surfactant solution in oil). The compound drop bounces on a vertically vibrated liquid surface. When the amplitude of the vibration exceeds a threshold value, the oil layer penetrates the water content and leaves a tiny oil droplet within. As this phenomenon occurs at each vigorous impact, the compound drop progressively transforms into a double emulsion. The emulsification threshold, which is observed to depend on the forcing frequency but not on the drop size, is rationalized by investigating the impact of compound drops onto a static liquid surface. The droplet creation occurs when the kinetic energy released at impact is larger than the energy required to deform the compound drop, namely when the Weber number is higher than a given threshold value. [less ▲]

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See detailDroplets sliding on fibres
Gilet, Tristan ULg; Terwagne, Denis ULg; Vandewalle, Nicolas ULg

in European Physical Journal E -- Soft Matter (2010), 31(3), 253

We present the results of a combined experimental and theoretical investigation of oil droplets sliding on fibres. First, both the axisymmetric shape and the motion of a droplet on a vertical fibre are ... [more ▼]

We present the results of a combined experimental and theoretical investigation of oil droplets sliding on fibres. First, both the axisymmetric shape and the motion of a droplet on a vertical fibre are described. The motion is shown to result from a balance between the droplet weight and the viscous stresses. On a long-term range, the droplet loses some mass through coating the fibre, which decreases its velocity. In a second time, we rationalize the behaviour of a droplet that encounters a junction between vertical and horizontal fibres. Depending on its size, the droplet may cross the junction or remain blocked. The transition is well described by an ordinary differential equation equivalent to a damped harmonic oscillator truncated to the neighbourhood of the horizontal fibre. This simple system is the basic element for more complex fiber networks that would be useful in microfluidic applications involving droplets. [less ▲]

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See detailThe mayonnaise droplet
Terwagne, Denis ULg; Gilet, Tristan ULg; Vandewalle, Nicolas ULg et al

Conference (2009, November 23)

A compound drop is made of a millimetric water drop encapsulated by an oil shell. They are obtained by merging one drop of each component (water and oil). Afterwards, they are laid on a high viscosity oil ... [more ▼]

A compound drop is made of a millimetric water drop encapsulated by an oil shell. They are obtained by merging one drop of each component (water and oil). Afterwards, they are laid on a high viscosity oil bath which is vertically vibrated. When the forcing acceleration is higher than a given threshold, compound drops can bounce on the surface. We show that above a second threshold some oil contained in the shell enters in the inner water droplet. In a second experiment, we drop the compound droplet on the oil bath at rest. We can determine the range of impact speed in which capillary waves developed on the surface are able to generate an oil drop (coming from the shell) in the water drop. When the bouncing trajectories of the droplets are analyzed a correlation between the emulsion threshold and the static analysis can be made. [less ▲]

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See detailMicrofluidic on a wire
Terwagne, Denis ULg; Vandewalle, Nicolas ULg; Gilet, Tristan ULg

Poster (2009, November)

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See detailThe mayonnaise droplet
Terwagne, Denis ULg; Gilet, Tristan ULg; Vandewalle, Nicolas ULg et al

Poster (2009, September)

Compound drops are made of a millimetric water drop encapsulated by an oil shell. They are laid on a high viscosity oil bath which is vertically vibrated. When the forcing acceleration is higher than a ... [more ▼]

Compound drops are made of a millimetric water drop encapsulated by an oil shell. They are laid on a high viscosity oil bath which is vertically vibrated. When the forcing acceleration is higher than a given threshold, compound drops can bounce on the surface. We show that above an another threshold a double emulsion occurs in the drop. We measured this emulsion threshold for various size and water/oil volume ratio of the compound drop. [less ▲]

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See detailDroplet manipulations
Gilet, Tristan ULg

Doctoral thesis (2009)

In this thesis, we discuss some physical phenomena related to the manipulation of droplets, and their possible use as alternatives for digital microfluidics. In a first part, the behavior of droplets in ... [more ▼]

In this thesis, we discuss some physical phenomena related to the manipulation of droplets, and their possible use as alternatives for digital microfluidics. In a first part, the behavior of droplets in the vicinity of another liquid interface is explored. We have shown that droplets can be kept bouncing onto a liquid interface, provided this latter is vertically vibrated. The bouncing mechanisms are investigated in several configurations. Bouncing droplets may also experience self-propulsion and partial coalescence. The second part of this thesis is dedicated to the study of droplets sliding down fibers. The basic microfluidic operations are advantageously implemented with simple fiber networks. [less ▲]

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See detailA drop of spectroscopy
Terwagne, Denis ULg; Gilet, Tristan ULg; Vandewalle, Nicolas ULg et al

Conference (2009, May)

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See detailThe mayonnaise droplet
Terwagne, Denis ULg; Mack, Nicolas; Dorbolo, Stéphane ULg et al

Poster (2009, March)

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See detailCompletely inelastic ball
Gilet, Tristan ULg; Vandewalle, Nicolas ULg; Dorbolo, Stéphane ULg

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2009)

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See detailThe fluid trampoline: droplets bouncing on a soap film
Gilet, Tristan ULg; Bush, John W.M.

in Journal of Fluid Mechanics (2009), 625

We present the results of a combined experimental and theoretical investigation of droplets falling onto a horizontal soap film. Both static and vertically vibrated soap films are considered. In the ... [more ▼]

We present the results of a combined experimental and theoretical investigation of droplets falling onto a horizontal soap film. Both static and vertically vibrated soap films are considered. In the static case, a variety of behaviours were observed, including bouncing, crossing and partial coalescence. A quasi-static description of the soap film shape yields a force–displacement relation that provides excellent agreement with experiment, and allows us to model the film as a nonlinear spring. This approach yields an accurate criterion for the transition between droplet bouncing and crossing. Moreover, it allows us to rationalize the observed constancy of the contact time and scaling for the coefficient of restitution in the bouncing states. On the vibrating film, a variety of bouncing behaviours were observed, including simple and complex periodic states, multi-periodicity and chaos. A simple theoretical model is developed that captures the essential physics of the bouncing process, reproducing all observed bouncing states. The model enables us to rationalize the observed coexistence of multiple periodic bouncing states by considering the dependence of the energy transferred to the droplet on the phase of impact. Quantitative agreement between model and experiment is deduced for simple periodic modes, and qualitative agreement for more complex periodic and chaotic bouncing states. Analytical solutions are deduced in the limit of weak forcing and dissipation, yielding insight into the contact time and periodicity of the bouncing states. [less ▲]

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