Droplets displacement and oscillations induced by ultrasonic surface acoustic waves: a quantitative study

We present an experimental study of a droplet interacting with an ultrasonic surface acoustic wave (SAW). Depending on the amplitude of the wave, the drop can either experience an internal flow with its contact-line pinned, or (at higher amplitude) move along the direction of the wave also with internal flow. Both situations appear together with oscillations of the drop free-surface. The physical origins of the internal mixing flow as well as the drop displacement and surface waves are still not well understood. In order to give insights of the underlying physics involved in these phenomena, we carried out an experimental and numerical study. The results suggest that the surface deformation of the drop can be related as a combination between acoustic streaming effect and radiation pressure inside the drop.Comment: 9 pages, 14 figures. To appear in Physical Review

Three-dimensional linear instability in pressure-driven two-layer channel flow of a Newtonian and a Herschel-Bulkley fluid

The three-dimensional linear stability characteristics of pressure-driven two-layer channel flow are considered, wherein a Newtonian fluid layer overlies a layer of a Herschel-Bulkley fluid. We focus on the parameter ranges for which Squire's theorem for the two-layer Newtonian problem does not exist. The modified Orr-Sommerfeld and Squire equations in each layer are derived and solved using an efficient spectral collocation method. Our results demonstrate the presence of three-dimensional instabilities for situations where the square root of the viscosity ratio is larger than the thickness ratio of the two layers; these "interfacial" mode instabilities are also present when density stratification is destabilizing. These results may be of particular interest to researchers studying the transient growth and nonlinear stability of two-fluid non-Newtonian flows. We also show that the "shear" modes, which are present at sufficiently large Reynolds numbers, are most unstable to two-dimensional disturbances

Cryo-STEM-EDX spectroscopy for the characterisation of nanoparticles in cell culture media

We present a study of barium titanate nanoparticles dispersed in cell culture media. Scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy was undertaken on samples prepared using both conventional drop casting and also plunge freezing and examination under cryogenic conditions. This showed that drying artefacts occurred during conventional sample preparation, whereby some salt components of the cell culture media accumulated around the barium titanate nanoparticles; these were removed using the cryogenic route. Importantly, the formation of a calcium and phosphorus rich coating around the barium titanate nanoparticles was retained under cryo-conditions, highlighting that significant interactions do occur between nanomaterials and biological media

Integration of the ASTER thermal infra-red bands imageries with geological map of Jabal Al Hasir area, Asir Terrane, the Arabian Shield

AbstractThermal infra-red bands of Advanced Spaceborne Thermal Emission and Radiometer (ASTER) have been used to investigate rocks, including white quartz veins, of Jabal Al Hasir area of the Asir Terrane, southwestern part of the Arabian Shield. The obtained data were processed using radiometric and geometric corrections. The processed data were then enhanced into false color images by Thermal Infra Red band ratioing. These composite images clearly differentiate between the light color felsic granite rocks and the dark color mafic gabbroic rocks. These images also differentiate quartz veins from wadi deposits, although, both of them appear very similar in light color and light grayscale tone. Results of the band ratioing have also been compared with the geological map of the study area, and were found in agreement. Keeping in view the obtained resolution, the band ratioing images have been found more informative and useful than the regular color composite images. Based on these observations, it can be claimed that the ASTER sensor is more powerful in terms of geological applications. Due to its success in the study area, the use of this sensor could also be extended to other complicated areas in the Arabian Shield and beyond

Monomer diffusion into static and evolving polymer networks during frontal photopolymerisation

Frontal photopolymerisation (FPP) is a directional solidification process that converts monomer-rich liquid into crosslinked polymer solid by light exposure and finds applications ranging from lithography to 3D printing. Inherent to this process is the creation of an evolving polymer network that is exposed to a monomer bath. A combined theoretical and experimental investigation is performed to determine the conditions under which monomer from this bath can diffuse into the propagating polymer network and cause it to swell. First, the growth and swelling processes are decoupled by immersing pre-made polymer networks into monomer baths held at various temperatures. The experimental measurements of the network thickness are found to be in good agreement with theoretical predictions obtained from a nonlinear poroelastic model. FPP propagation experiments are then carried out under conditions that lead to swelling. Unexpectedly, for a fixed exposure time, swelling is found to increase with incident light intensity. The experimental data is well described by a novel FPP model accounting for mass transport and the mechanical response of the polymer network, providing key insights into how monomer diffusion affects the conversion profile of the polymer solid and the stresses that are generated during its growth. The predictive capability of the model will enable the fabrication of gradient materials with tuned mechanical properties and controlled stress development

Скринінг гіпоглікемічної активності екстрактів з листя Мучниці звичайної та вивчення гострої токсичності

Diabetes mellitus type 2 (DM2) is a global health problem. The plant origin medicinal preparations revealed different mechanisms of antidiabetic action. Despite a wide range of plants that have already been studied, other species are of interest. Particularly, Bearberry (Arctostaphylos uva-ursi) attracted our attention because its leaves are rich with biologically active compounds, but hypoglycemic activity has not been studied yet.The aim of our experiment was studding acute toxicity and hypoglycemic activity of Bearberry extracts on non-diabetic standard models.Materials and methods. It was conducted the screening of hypoglycemic effect in healthy rats, oral glucose tolerance test in healthy rats and study of acute toxicity. The object of study were water and alcohol polyphenol extracts of Bearberry leaves (extractor –alcohol 50 % and 90 %). Results and discussion. Screening and comparative study shows that the maximal hypoglycemic activity revealed Bearberry leaves alcohol extract (extractor – 50 % ethanol, PE50) in dose 100 mg/kg. The least pronounced effect was observed for the introduction of water extract administration.Conclusions. The results indicate the practicability of this Bearberry leaves extract further study for renewal the range of medicinal products that revealed hypoglycemic activity.Сахарный диабет 2 типа (СД2) является глобальной проблемой здравоохранения. Эффективность лекарственных препаратов растительного происхождения объясняется различными механизмами антидиабетического действия. Несмотря на широкий спектр изученных растений, интерес представляют и другие виды. В частности, Толокнянка обыкновенная (Arctostaphylos uva-ursi) представляет научный интерес, так как ее листья богаты биологически активными соединениями, однако их гипогликемическая активность еще не изучена.Целью нашего эксперимента было изучение острой токсичности и гипогликемической активности экстрактов Толокнянки обыкновенной на недиабетических стандартных моделях.Материалы и методы. Было проведено исследование гипогликемической активности на здоровых крысах, пероральный тест толерантности к глюкозе на здоровых крысах и исследование острой токсичности. Объектом исследования были водный и спиртовые полифенольные экстракты листьев Толокнянки обыкновенной (экстрагент – алкоголь 50 % и 90 %).Результаты и их обсуждение. Скрининг и сравнительное исследование показывают, что максимальную гипогликемическую активность проявил спиртовый экстракт из листьев Толокнянки обыкновенной (экстрагент – 50 % этанола, PE50) в дозе 100 мг/кг. Наименьший гипогликемический эффект наблюдался при введении водного экстракта.Выводы. Результаты показали целесообразность дальнейшего изучения экстракта листьев Толокнянки обыкновенной для пополнения ассортимента лекарственных препаратов с гипогликемической активностью.Цукровий діабет 2 типу (ЦД2) є глобальною проблемою охорони здоров’я. Ефективність лікарських препаратів рослинного походження пояснюється різними механізмами антидіабетичної дії. Незважаючи на широкий спектр рослин, які вже піддавалися вивченню, інтерес представляють і інші види. Зокрема, Мучниця звичайна (Arctostaphylos uva-ursi) привернула нашу увагу, так як її листя багате на біологічно активні сполуки, однак їх гіпоглікемічна активність ще не вивчена.Мета даного експерименту полягала у вивченні гострої токсичності та гіпоглікемічної активності екстрактів Мучниці звичайної на стандартних моделях у здорових щурів.Матеріали та методи. Було проведено дослідження гіпоглікемічної активності на здорових щурах, пероральний тест толерантності до глюкози на здорових щурах і дослідження гострої токсичності. Об’єктом дослідження були водний і спиртові поліфенольні екстракти листя мучниці звичайної (екстрагент – етанол 50 % і 90 %).Результати та їх обговорення. Скринінг і порівняльне дослідження показують, що максимальну гіпоглікемічну активність проявив спиртовий екстракт з листя Мучниці звичайної (екстрагент – 50 % етанолу, PE50) в дозі 100 мг/кг. Найменший гіпоглікемічний ефект спостерігався при введенні водного екстракту.Висновки. Результати показали доцільність подальшого вивчення екстракту листя Мучниці звичайної для оновлення асортименту лікарських препаратів з гіпоглікемічною активністю

Numerical simulations of miscible channel flow with chemical reactions

We study the pressure-driven miscible displacement of one fluid by another in a horizontal channel in the presence of an exothermic chemical reaction. We solve the continuity, Navier-Stokes, and energy conservation equations coupled to convective-discussion equations of the reactant and product. The viscosity is assumed to depend on the volume fraction of the reactant and product as well as the temperature. The effects of relevant parameters such as the Reynolds number, Schmidt number, Damköhler number and viscosity ratio of the reactant and product are studied. Our results indicate that increasing the intensity of the chemical reaction by increasing the Damköhler number and decreasing the dimensionless activation energy increases the displacement rate. We have also found that increasing Reynolds number leads to more pronounced instabilities and roll-up phenomena, which in turn promote rapid displacement of the resident fluid inside the channel. Variation of the relative significance of the heat of reaction and the Schmidt numbers of the reactants and products, however, has a negligible influence on the displacement rates for the parameter ranges considered in the present work

Data-driven modeling for drop size distributions

The prediction of the drop size distribution (DSD) resulting from liquid atomization is key to the optimization of multiphase flows from gas-turbine propulsion through agriculture to healthcare. Obtaining high-fidelity data of liquid atomization, either experimentally or numerically, is expensive, which makes the exploration of the design space difficult. First, to tackle these challenges, we propose a framework to predict the DSD of a liquid spray based on data as a function of the spray angle, the Reynolds number, and the Weber number. Second, to guide the design of liquid atomizers, the model accurately predicts the volume of fluid contained in drops of specific sizes while providing uncertainty estimation. To do so, we propose a Gaussian process regression (GPR) model, which infers the DSD and its uncertainty form the knowledge of its integrals and of its first moment, i.e., the mean drop diameter. Third, we deploy multiple GPR models to estimate these quantities at arbitrary points of the design space from data obtained from a large number of numerical simulations of a flat fan spray. The kernel used for reconstructing the DSD incorporates prior physical knowledge, which enables the prediction of sharply peaked and heavy-tailed distributions. Fourth, we compare our method with a benchmark approach, which estimates the DSD by interpolating the frequency polygon of the binned drops with a GPR. We show that our integral approach is significantly more accurate, especially in the tail of the distribution (i.e., large, rare drops), and it reduces the bias of the density estimator by up to 10 times. Finally, we discuss physical aspects of the model's predictions and interpret them against experimental results from the literature. This work opens opportunities for modeling drop size distribution in multiphase flows from data

Dynamics of surfactant-laden evaporating droplets

We consider the flow dynamics of a thin evaporating droplet in\ud the presence of an insoluble surfactant and small particles in the bulk. Evolution\ud equations for the film height, the interfacial surfactant and bulk particle concentra-\ud tion are derived using a lubrication model coupled by a constitutive relation for the\ud dependence of the viscosity on local particle concentration. An important ingredient\ud of our model is that it takes into account the fact that the surfactant adsorbed at\ud the surface hinders the evaporation. Time-dependent simulations are performed to\ud determine how the presence of surfactants affects the evaporation and flow dynamics\ud with and without the presence of particles in the bulk. We discuss the various mech-\ud anisms that affect the shape of the droplet as it evaporates as well as the resulting\ud pattern of particle deposition