16 research outputs found
Creation of prompt and thin-sheet splashing by varying surface roughness or increasing air pressure
A liquid drop impacting a solid surface may splash by emitting a thin liquid
sheet that subsequently breaks apart or by promptly ejecting droplets from the
advancing liquid-solid contact line. Using high-speed imaging, we show that air
pressure and surface roughness influence both splash mechanisms. Roughness
increases prompt splashing at the advancing contact line but inhibits the
formation of the thin sheet. If the air pressure is lowered, droplet ejection
is suppressed not only during thin-sheet formation but for prompt splashing as
well. The threshold pressure depends on impact velocity, liquid viscosity and
surface roughness
Flow in linearly sheared two dimensional foams: from bubble to bulk scale
We probe the flow of two dimensional foams, consisting of a monolayer of
bubbles sandwiched between a liquid bath and glass plate, as a function of
driving rate, packing fraction and degree of disorder. First, we find that
bidisperse, disordered foams exhibit strongly rate dependent and inhomogeneous
(shear banded) velocity profiles, while monodisperse, ordered foams are also
shear banded, but essentially rate independent. Second, we introduce a simple
model based on balancing the averaged drag forces between the bubbles and the
top plate and the averaged bubble-bubble drag forces. This model captures the
observed rate dependent flows, and the rate independent flows. Third, we
perform independent rheological measurements, both for ordered and disordered
systems, and find these to be fully consistent with the scaling forms of the
drag forces assumed in the simple model, and we see that disorder modifies the
scaling. Fourth, we vary the packing fraction of the foam over a
substantial range, and find that the flow profiles become increasingly shear
banded when the foam is made wetter. Surprisingly, our model describes flow
profiles and rate dependence over the whole range of packing fractions with the
same power law exponents -- only a dimensionless number which measures the
ratio of the pre-factors of the viscous drag laws is seen to vary with packing
fraction. We find that , where , corresponding to the 2d jamming density, and suggest that this scaling
follows from the geometry of the deformed facets between bubbles in contact.
Overall, our work suggests a route to rationalize aspects of the ubiquitous
Herschel-Bulkley (power law) rheology observed in a wide range of disordered
materials.Comment: 16 pages, 14 figures, submitted to Phys. Rev. E. High quality version
available at: http://www.physics.leidenuniv.nl/sections/cm/gr
Wavelet analysis of epileptic spikes
Interictal spikes and sharp waves in human EEG are characteristic signatures
of epilepsy. These potentials originate as a result of synchronous,
pathological discharge of many neurons. The reliable detection of such
potentials has been the long standing problem in EEG analysis, especially after
long-term monitoring became common in investigation of epileptic patients. The
traditional definition of a spike is based on its amplitude, duration,
sharpness, and emergence from its background. However, spike detection systems
built solely around this definition are not reliable due to the presence of
numerous transients and artifacts. We use wavelet transform to analyze the
properties of EEG manifestations of epilepsy. We demonstrate that the behavior
of wavelet transform of epileptic spikes across scales can constitute the
foundation of a relatively simple yet effective detection algorithm.Comment: 4 pages, 3 figure
Thin-Sheet Creation and Threshold Pressures in Drop Splashing
A liquid drop impacting a smooth solid substrate splashes by emitting a thin
liquid sheet from near the contact line of the spreading liquid. This sheet is
lifted from the substrate and ultimately breaks apart. Surprisingly, the splash
is caused by the ambient gas, whose properties dictate when and if the sheet is
created. Here I focus on two aspects of this process. Using high-speed imaging
I find that the time of thin-sheet creation displays a different quantitative
dependence on air pressure if the sheet is created during the early stages of
spreading, rather than when the liquid has already spread to a large radius.
This result sheds light on previously observed impact velocity regimes.
Additionally, by measuring impacts of drops on surfaces comprised of both rough
and smooth regions, I identify a new threshold velocity that limits the times
at which the thin sheet can be created. This velocity determines the threshold
pressure below which splashing is suppressed
Development of suspension plasma spraying of hydroxyapatite, titanium oxide and yttria stabilized zirconia coatings and their mechanical characterization
La projection par plasma de suspension d hydroxyapatite, d oxyde de titane et de zircone yttriĂ©e permettant d obtenir des revĂȘtements biocompatibles, des barriĂšres thermiques ou encore des surfaces photo-catalytiques est Ă©tudiĂ©e. Les revĂȘtements sont projetĂ©s Ă l aide d une torche plasma SG-100. La puissance Ă©lectrique se situe entre 27 et 40 kW et les distances de projection entre 40 et 70 mm, selon le type de matĂ©riau projetĂ©. La stabilitĂ© de la suspension est dĂ©terminĂ©e par des mesures de potentiels Zeta. Les propriĂ©tĂ©s mĂ©caniques des revĂȘtements d hydroxyapatite aprĂšs projection et aprĂšs immersion dans un fluide physiologique sont comparĂ©es. Il en rĂ©sulte que la duretĂ© augmente avec la durĂ©e d immersion. Pour les revĂȘtements de titane, l essai de rayure a confirmĂ© la bonne adhĂ©rence et la bonne cohĂ©sion de ce type de revĂȘtement. Nous avons Ă©galement observĂ© que les revĂȘtements testĂ©s montrent de meilleures propriĂ©tĂ©s photo-catalytiques que les revĂȘtements commerciaux Pilkington Active glass. L Ă©tude des revĂȘtements Ă base d oxydes de zircone s est focalisĂ©e sur les propriĂ©tĂ©s mĂ©caniques et le transport thermique. L indentation instrumentĂ©e confirme les trĂšs bonnes propriĂ©tĂ©s mĂ©caniques de ces revĂȘtements, jusque 3.5 GPa pour la duretĂ© et jusque 130 GPa pour le module d Ă©lasticitĂ©. Nous avons aussi observĂ© que les valeurs de conductivitĂ© thermique des revĂȘtements testĂ©s sont plus faibles que celles des revĂȘtements projetĂ©s avec des mĂ©thodes conventionnelles.En conclusion, les revĂȘtements obtenus par projection plasma prĂ©sentent des propriĂ©tĂ©s qui les rendent utilisables dans de nombreuses applications.The basics of thermal spraying were presented. Suspension plasma spraying method was described and also possible applications, as biocompatible coatings, thermal barrier or photo-catalytic surfaces were presented. Instrumented indentation test was characterized. In work hydroxyapatite, titanium dioxide, yttria stabilized zirconia and yttria with ceria stabilized zirconia were used. Set-up of plasma spray installation was presented. The stability of suspension was determined by zeta potential measurements. Coatings were sprayed with plasma torch SG-100. Electric power was in range from 27 to 40 kW and spray distance varying from 40 to 70 mm, depending on type of sprayed material.Mechanical properties of hydroxyapatite coatings as-sprayed, as well as soaked in simulated body fluid were tested. Influence of soaking time on coatings hardness was noted, which increases with increasing time of soaking. In case of titania coatings, mechanical and photo-catalytic properties were estimated. Scratch test confirmed high values of cohesion and adhesion. Tested coatings exhibit better photo-catalytic properties than commercial Pilkington Active glass. Investigation of coatings based on zirconium oxide concerned on mechanical and thermal transport properties. Instrumented indentation test confirmed very good mechanical properties, up to 3.5 GPa and up to 130 GPa for hardness and elastic modulus, respectively. Values of thermal conductivity of tested coatings were lower than coatings sprayed with conventional methods. Based on conducted studies was found that suspension plasma sprayed coatings exhibit properties, which made possible its application on different fields of technique.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF
A comparison of microstructure and of thermal transport properties of yttria and ceria stabilized zirconia coatings deposited by suspension plasma spraying
International audienceThe single cathode plasma torch SG-100 was used to spray suspension prepared with the use of two kinds of commercial powders ZrO2+8 wt. % Y2O3 (8YSZ) and ZrO2 + 24 wt.% CeO2 + 2.5 wt.% Y2O3 (24CeYSZ). The suspensions were formulated using finely milled solid phase, water and ethanol. The operational spray parameters being the same for each powder were modified by changing: (i) spray distance; and (ii) torch scan linear speed. The coatings microstructures were analyzed with the use of optical and scanning electron microscopes as well as by X-ray diffraction. Their porosities were found with help of the image analysis of metallographically prepared cross-sections. Thermal diffusivity was measured with the use of commercial system LFA 447 NanoFlashŸ working at the temperatures limited to 300°C. The measurements were made with the use of the coatings sprayed on the steel substrate and a 2-layers numerical model was applied to determine thermal diffusity of the coatings. The obtained data were used to calculate thermal conductivity of stabilized zirconia coatings
A Study on the Microstructural Characterization and Phase Compositions of Thermally Sprayed Al2O3-TiO2 Coatings Obtained from Powders and Water-Based Suspensions
In this work, the alumina (Al2O3) and alumina-titania coatings with different contents of TiO2, i.e., Al2O3 + 13 wt.% TiO2 and Al2O3 + 40 wt.% TiO2, were studied. The coatings were produced by means of powder and liquid feedstock thermal spray processes, namely atmospheric plasma spraying (APS), suspension plasma spraying (SPS) and suspension high-velocity oxygen fuel spraying (S-HVOF). The aim of the study was to investigate the influence of spray feedstocks characteristics and spray processes on the coating morphology, microstructure and phase composition. The results revealed that the microstructural features were clearly related both to the spray processes and chemical composition of feedstocks. In terms of phase composition, in Al2O3 (AT0) and Al2O3 + 13 wt.% TiO2 (AT13) coatings, the decrease in α-Al2O3, which partially transformed into γ-Al2O3, was the dominant change. The increased content of TiO2 to 40 wt.% (AT40) involved also an increase in phases related to the binary system Al2O3-TiO2 (Al2TiO5 and Al2−xTi1+xO5). The obtained results confirmed that desired α-Al2O3 or α-Al2O3, together with rutile-TiO2 phases, may be preserved more easily in alumina-titania coatings sprayed by liquid feedstocks