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

in Physicalia Magazine (2008), 30(3), 161-168

When a low viscosity oil droplet is laid onto the surface ofa high viscosity oil liquid, it stays at rest for a moment before coalescence. The coalescence can be delayed and sometimes inlibited by ... [more ▼]

When a low viscosity oil droplet is laid onto the surface ofa high viscosity oil liquid, it stays at rest for a moment before coalescence. The coalescence can be delayed and sometimes inlibited by injecting fresh air under the droplet. This can happen when the surface ofthe bath oscillates vertically. In this case the droplet basically bounces on the interface. We obsewe that the conditions for bouncing depends on the frequency, more precisely we observe resonance when the eigenfrequency of the droplet is excited. In some conditions, a droplet presents a non axi- symmetric mode of deformation. That leads to a rotation of the droplet and to a horizontal displacement. [less ▲]

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

Poster (2008, May)

Detailed reference viewed: 13 (6 ULg)
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See detailA drop of spectroscopy
Terwagne, Denis ULg; Gilet, Tristan ULg; Vandewalle, Nicolas ULg et al

Poster (2008, May)

Detailed reference viewed: 10 (6 ULg)
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See detailDrop size distribution measurement of ISO nozzles by shadowgraphy method
De Cock, Nicolas ULg; Massinon, Mathieu ULg; Ouled Taleb Salah, Sofiene ULg et al

in Drop size distribution measurement of ISO nozzles by shadowgraphy method (2015, May 19)

Detailed reference viewed: 41 (11 ULg)
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See detailDroplet internal flow measurement using micro-PIV
Lebeau, Frédéric ULg; Vetrano, Maria-Rosaria; van Beeck, Jeroen et al

Poster (2009, September 25)

The micro-PIV technique represents a development of the general particle image velocimetry technique to applications in fluid mechanics phenomena at a micrometric scale. It takes advantage from the very ... [more ▼]

The micro-PIV technique represents a development of the general particle image velocimetry technique to applications in fluid mechanics phenomena at a micrometric scale. It takes advantage from the very small depth of field of long distance objectives with high magnification to carry out accurate measurements in the focusing plane. The typical configuration consists of a microscope coupled to a pulsated laser and a double exposure PIV camera. The flow is seeded using sub-micrometric fluorescent particles. The laser light is directed on the investigated flow through the epifluorescent microscope objective. The light re-emitted by the fluorescent particles is detected by the PIV camera equipped of an optical filter to select only the fluorescence wavelength. The micro-PIV technique presents a large interest in the validation of numerical codes developed in different micro-fluidic framework such as biological flows and in industrial application as the ink-jet print-head. To investigate the micro-PIV measurements capabilities for fast moving and deforming droplets, measurement of the flow inside a jet ejected by a piezo-driven capillary up to the droplet formation by Rayleigh instability are studied in combination with PTV in order to distinguish the main liquid movement from the bulk one. Liquids differing from each other for their viscosity and their surface tension as well as piezo-element frequency in the 1 to 8 KHz range are investigated. The flow rate of the jet is adjusted by means of a pushing syringe system. Low concentration of 0.86 microns fluorescent particles is employed as seeding in order to have good signal to noise ratios. The ensemble averaging method is used to increase the height of the correlation peaks. Stroboscopic method is used to achieve several couples of frames taken in the same conditions thanks to high repeatability of piezo-driven instabilities. Moreover changing the delay of stroboscopy all the droplet formation phases can be analyzed in detail. In the experimental configuration, optical aberrations play a role since they affect the position and shape of the particle images and as a consequence the velocity field. The two main optical aberration experienced are astigmatism and measurement plane deformation. Astigmatism cannot be avoided in the experimental configuration, as it is clearly observed on droplet images were particles above and bellow the focalisation plane appear as perpendicular lines (Fig 1a). Nevertheless cross correlation method is not sensitive on particle image shape. As the measurement plane defined by the focal plane of the microscope is located inside a curved transparent object, it deformed as it was passing through a lens. The deformation of the objective plane affects the measurements as a function of the optical configuration, droplet curvature and relative refractive index. However, in the studied configuration, deformed plane differs only from the straight one of about 8 µm. The micro-PIV method is therefore suited to measure the instantaneous vector field inside droplets through cross-correlation methods (Fig 1b). The internal flow recirculation is observed. Measurements can be also performed in different planes inside the droplet depending on focalisation plane. [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 droplet of spectroscopy
Terwagne, Denis ULg; Gilet, Tristan ULg; Vandewalle, Nicolas ULg et al

Conference (2008, November)

Droplet coalescence in a liquid bath can be delayed by oscillating the surface of the bath vertically (frequency from 20 Hz to 400 Hz), the droplet bounces on the interface [1,2]. A low viscous oil ... [more ▼]

Droplet coalescence in a liquid bath can be delayed by oscillating the surface of the bath vertically (frequency from 20 Hz to 400 Hz), the droplet bounces on the interface [1,2]. A low viscous oil droplet is dropped on a high viscous oil bath. We observe that the conditions for bouncing depends on the frequency, more precisely we observe resonance when the eigenfrequency of the droplet is excited. In some conditions, droplet presents a non axi-symmetric mode of deformation. That leads to a rotation of the drop and to a horizontal displacement. [less ▲]

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Peer Reviewed
See detailDroplet Size Spectra And Drift Effect Of Two Phenmedipham Formulations And Four Adjuvants Mixtures
Stainier, C.; Destain, Marie-France ULg; Schiffers, Bruno ULg et al

in Crop Protection (2006), 25(12),

Relative drift potential was evaluated for three types of hydraulic nozzles (a flat-fan nozzle, a hollow cone nozzle and an air induction nozzle) spraying different liquids: water, emulsifiable ... [more ▼]

Relative drift potential was evaluated for three types of hydraulic nozzles (a flat-fan nozzle, a hollow cone nozzle and an air induction nozzle) spraying different liquids: water, emulsifiable concentrate (EC) and suspension concentrate (SC) formulations of phenmedipham dispersed in water, with or without addition of 4 different tank-mix adjuvants. The droplet size spectra were measured for these 15 spray mixtures using a Malvern Particle Sizer and characterised by the Volume Median Diameter (VMD) and the percentage of liquid contained in droplets less than 100 m (% < 100 m). Horizontal ground drift was measured in a wind tunnel, on glass fibre collectors using a fluorescent tracer dye technique. The relative drift of each spray mixture was characterised by the Drifted Part (DP) which is the part of the sprayed volume drifted between 2 and 6 metres. Although the nozzle type was the predominating parameter regarding to the droplet size spectra and the DP, differences were observed due to the liquids characteristics. The EC formulation produced a smaller droplet size and a greater DP than the SC formulation whatever the tank mix adjuvant used. For the different spray mixtures, the DP was poorly correlated to the VMD or the % < 100 m. However, correlations between the VMD, the % < 100 m and the DP of the flat-fan nozzle and of the hollow cone nozzle were significant. This suggests that a reference nozzle could be used to estimate the drift potential of other nozzle with a similar liquid sheet break-up mechanism. [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 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 detailDroplets climbing a rotating helical fiber
Darbois-Texier, Baptiste ULg; Dorbolo, Stéphane ULg

in European Physical Journal E -- Soft Matter (2015), 38

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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 detailLa drosophile, les récepteurs Toll-like et nous.
PIERARD, Gérald ULg; FRANCHIMONT, Claudine ULg; SZEPETIUK, Grégory ULg et al

in Dermatologie Actualité (2012), 132

Detailed reference viewed: 17 (1 ULg)
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See detailDrospirenone and interference with renin-antiotensin system
VROONEN, Laurent ULg; Cavalier, Etienne ULg; Vranken, Laura ULg et al

in Annales d'Endocrinologie - 28ème congrès de la société Française d'Endocrinologie (2011)

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See detailDrought risk assessment in pasture arid Morocco through remote sensing
Mahyou, Hamid; Karrou, Mohamed; Mimouni, Jamal et al

in African Journal of Environmental Science and Technology (2010), 4(12), 845-852

During the last three decades, Morocco has experienced several stern and extended episodes of drought that severely affected pasture production. To cope with this phenomenon, the policy makers have put ... [more ▼]

During the last three decades, Morocco has experienced several stern and extended episodes of drought that severely affected pasture production. To cope with this phenomenon, the policy makers have put emphasis on a reactive short term management approach rather than on pro-active risk-based management measures. The purpose of this study is the assessment of drought by remote sensing, which is an important step in the design and implementation of drought management plan. To reach this objective we used bi-weekly TERRA Moderate Resolution Imaging Spectroradiometer (MODIS 250 m) data in arid pasture of Morocco. A preliminary mapping using Landsat TM5 of major land cover types was carried out to extract the pasture area. A comparison of annual and seasonal Normalised Difference Vegetation Indices (NDVI), Vegetation Condition Index (VCI) and rainfall during the time period of 2000 - 2008 were carried out. Results showed that stronger relationship of NDVI with previous seasonal rainfall as compared to VCI indicating that NDVI variation is a good indicator of vegetation changes and consequently can give a better idea on drought conditions in the study area. [less ▲]

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See detailDrought-related vulnerability and risk assessment of groundwater in Belgium: estimation of the groundwater recharge and crop yield vulnerability with the B-CGMS
Jacquemin, Ingrid ULg; Verbeiren, Boud; Vanderhaegen, Sven et al

Poster (2016, April 19)

Due to common belief that regions under temperate climate are not affected by (meteorological and groundwater) drought, these events and their impacts remain poorly studied: in the GroWaDRISK, we propose ... [more ▼]

Due to common belief that regions under temperate climate are not affected by (meteorological and groundwater) drought, these events and their impacts remain poorly studied: in the GroWaDRISK, we propose to take stock of this question. We aim at providing a better understanding of the influencing factors (land use and land cover changes, water demand and climate) and the drought-related impacts on the environment, water supply and agriculture. The study area is located in the North-East of Belgium, corresponding approximatively to the Dijle and Demer catchments. To establish an overview of the groundwater situation, we assess the system input: the recharge. To achieve this goal, two models, B-CGMS and WetSpass are used to evaluate the recharge, respectively, over agricultural land and over the remaining areas, as a function of climate and for various land uses and land covers. B-CGMS, which is an adapted version for Belgium of the European Crop Growth Monitoring System, is used for assessing water recharge at a daily timestep and under different agricultural lands: arable land (winter wheat, maize...), orchards, horticulture and floriculture and for grassland. B-CGMS is designed to foresee crop yield and obviously it studies the impact of drought on crop yield and raises issues for the potential need of irrigation. For both yields and water requirements, the model proposes a potential mode, driven by temperature and solar radiation, and a water-limited mode for which water availability can limit crop growth. By this way, we can identify where and when water consumption and yield are not optimal, in addition to the Crop Water Stress Index. This index is calculated for a given crop, as the number of days affected by water stress during the growth sensitive period. Both recharge and crop yield are assessed for the current situation (1980 – 2012), taking into account the changing land use/land cover, in terms of areas and localization of the agricultural land and where the proportion of the different crops had considerably evolved through time (e.g., increase of grain maize and potatoes while winter cereals decrease). The preliminary results of the recharge lead to an average value in the area showing a significant negative trend, in both simulations with fixed (base = 1980) and changing land cover. In the same time, we could observe an increasing number of water stress periods, especially for maize, one of the main crops in the area. Finally, a preliminary test will be presented for the horizon 2040, for which we use meteorological time series (for high and low hydrologic impacts) given by the CCI-HYDR Perturbation Tool (Ntegeka V. and Willems P., 2009). This preliminary test aims to (1) evaluate the amplitude of the potential recharge deficit and, (2) especially, to define vulnerability zones, affected by frequent water stress, in connection with irrigation needs which could possibly increase the groundwater extraction. [less ▲]

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See detailDrought-related vulnerability and risk assessment of groundwater resources under temperate conditions
Verbeiren, Boud; Huysmans, Marijke; Tychon, Bernard ULg et al

Conference (2013, September)

Drought hazards are usually associated with (semi-)arid regions. Due to the assumed insignificance of drought hazards under temperate conditions this field remains poorly studied. This study aims at ... [more ▼]

Drought hazards are usually associated with (semi-)arid regions. Due to the assumed insignificance of drought hazards under temperate conditions this field remains poorly studied. This study aims at filling this gap by: (1) Increasing understanding of influencing factors determining drought in a temperate context; (2) Developing a methodology and quantitative tools aimed at planning and decision support with respect to groundwater management. In the first place drought is a phenomenon caused by deficient precipitation for a large area and significant duration and as such it is mainly a meteorological-related hazard. In case the temporary water deficiency affects groundwater bodies, the term groundwater drought is used. Groundwater droughts develop slowly but can have considerable socio-economic and environmental consequences. Groundwater drought is a complex phenomenon. Three main variables are important: groundwater recharge, groundwater level and groundwater discharge. Groundwater recharge is important as it is the source (inflow) of all groundwater. The groundwater table gives an indication of the storage, while groundwater discharge represents the outflow from the groundwater system. Next to natural meteorological variations also human induced factors play a role. In the Belgian context the main influencing factors determining the inflow and potentially resulting in a recharge deficit and an overall deterioration of groundwater resources are climate and land use/land cover. Groundwater demand for human activities has a direct effect on groundwater storage (level). The combined effect of these factors makes that some groundwater bodies are under pressure. In these groundwater bodies the outflow exceeds the inflow generating a reduction in storage and hence an unsustainable situation. A thorough knowledge of all three influencing factors and their interaction or combined effect is essential for a reliable estimate of the groundwater budget and a sustainable management. Hence, there is a need for an improved understanding of groundwater drought and the human-induced factors influencing the groundwater balance. This should form the basis for an integrated approach which allows tackling these negative effects and safeguarding sustainability of groundwater resources. [less ▲]

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Peer Reviewed
See detailDrought-stress and plant resistance affect herbivore performance and proteome: the case of the green peach aphid Myzus persicae (Hemiptera: Aphididae)
Verdugo, Jaime; Sauge, Marie-Helene; Laccroze, Jean-Philippe et al

in Pysiological Entomology (2015), 40

Abstract. Little is known about the simultaneous effects of drought stress and plant resistance on herbivorous insects. By subjecting the green peach aphid Myzus persicae Sulzer to well-watered and ... [more ▼]

Abstract. Little is known about the simultaneous effects of drought stress and plant resistance on herbivorous insects. By subjecting the green peach aphid Myzus persicae Sulzer to well-watered and drought-stressed plants of both susceptible and resistant peach (Prunus persica), the effects of both stressors on aphid performance and proteomics are tested. Overall, the influence of thewater treatment on aphid performance is less pronounced than the effect of host plant genetic resistance. On the susceptible cultivar, aphid survival, host acceptance and ability to colonize the plant do not depend on water treatment. On the resistant cultivar, aphid survival and ability to colonize are higher on drought-stressed than on well-watered plants. A study examining the pattern of protein expression aiming to explain the variation in aphid performance finds higher protein expression in aphids on the drought-stressed susceptible cultivars compared with the well-watered ones. In the susceptible cultivar, the regulated proteins are related to energy metabolism and exoskeleton functionality, whereas, in the resistant cultivar, the proteins are involved with the cytoskeleton. Comparison of the protein expression ratios for resistant versus susceptible plants reveals that four proteins are down-regulated in well-watered plants and 15 proteins are down-regulated in drought-stressed plants. Drought stress applied to the susceptible cultivar induces the regulation of proteins in M. persicae that enable physiological adaptation to maintain an almost unaltered aphid performance. By contrast, for aphids on the resistant cultivar subjected to drought stress, the down-regulation of proteins responds to an induced host susceptibility effect. [less ▲]

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See detailDrowsiness monitoring for road safety
Wertz, Jérôme ULg; François, Clémentine ULg; Verly, Jacques ULg

Conference (2013, December 13)

Detailed reference viewed: 20 (3 ULg)
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See detailDrowsiness monitoring: a matter of life and death !
Wertz, Jérôme ULg; François, Clémentine ULg; Verly, Jacques ULg

Conference (2012, March 19)

Detailed reference viewed: 45 (23 ULg)