The first step on the way to understanding the complicated dynamics of spray is to study the behavior of isolated droplets. In many industrial and natural processes such as turbulent combustion, agricultural sprays, spray cooler, falling raindrops and cloud evolution the droplet is subjected to a chaotic unsteady external flow field. The interaction between the liquid and gaseous phases results in very intricate droplet dynamics like capillary instabilities, atomization, droplet collision and coalescence and vaporization, to name a few. In this dissertation, the focus is on shape oscillations, atomization and vaporization dynamics of pendant and sessile droplets. A droplet residing on a substrate which vibrates vertically at ultrasonic frequency will exhibit different modes of shape oscillation. The competition between capillary forces and inertia forces is basically responsible for these oscillations. However, when an acoustic force field is introduced asymmetrically around the droplet, we discover with the help of ultra high-speed imaging, a new droplet spreading phase. This new method of droplet manipulation could nd application in micro fluidics and lab-on-a-chip systems. By lading the droplet with nanoparticles, the spreading rate can be easily controlled. The spreading phase is followed by an atomization phase where surface ligaments grow to disintegrate into daughter droplets; the intensity of atomization is found to decrease with increase in fluid viscosity. The ability to control atomization characteristics of droplets by lading them with nanoparticles is a powerful technique that may be implemented in spray coolers and combustors to control the spray characteristics or combustion efficiency. Both the spreading and ligament dynamics have been theoretically simulated and the physics behind the observed trends is explained. The growth rate of the ligaments is found to be governed by Weber number modified to include the acoustic pressure level of the standing wave. The frequency of ligament breakup is found to decrease with fluid viscosity and this observation is adequately supported by a theory developed based on the evolution crater on the droplet surface. Turning now to the pendant droplets, by decomposing the droplet shape into Legendre modes, the shape oscillations exhibited by a droplet hanging from the junction of cross-wire placed at the center of an air jet is studied. Both high-speed imaging and hot-wire anemometry are employed. The driving force of oscillation of droplets subjected to the air jet is proved to be the inherent pressure fluctuations in the jet. The effect of surface tension, viscosity and Reynolds number on the shape oscillation level has been examined. The first experimental evidence of viscous attenuation of lower frequencies in a particular mode in glycerol/water mixture is reported. A theoretical model was developed to simulate the droplet shape oscillations induced by different ambient flow fields like pulsatile flow, vortical flow and flow with broadband energy spectrum. The time of interaction of the droplet with an eddy in the flow is found to be very crucial in determining the amplitude of oscillation of the droplet. The shorter the interaction time, the higher are the chances of the droplet oscillation being pushed into resonance. Finally, the heat transfer and droplet regression dynamics of pendant droplets in a hot air stream of various chemical compositions (like conventional fuels, alternative fuels and nanosuspensions) have been experimentally analyzed using high speed imaging. The droplet is deployed at the junction of cross-wire at the centre of a vertical air jet. A hybrid timescale has been proposed which incorporates the effects of latent heat of vaporization, saturation vapor pressure and thermal diffusivity. This timescale in essence encapsulates the different parameters that influence the droplet vaporization rate. The analysis further permitted the evaluation of the effect of various parameters such as surrounding temperature, Reynolds number, far-field vapor presence, impurity content and agglomeration dynamics (nanosuspensions) in the droplet.

No description available.

A millimetric droplet may bounce and self-propel on the surface of a vertically vibrating bath, where its horizontal `walking' motion is induced by repeated impacts with its accompanying Faraday wave field. This hydrodynamic pilot-wave system exhibits many features that were previously thought to be exclusive to the quantum realm, including quantized dynamics and emergent wavelike statistics. We develop a discrete-time iterative map to analyse the pilot-wave dynamics in a number of settings, employing a sophisticated fluid model to capture the intricacies of the Faraday wave evolution neglected by previous works. We first study the stability of bouncing and walking dynamics, and elucidate further features of the droplet's wave-induced added mass. We also explore the periodic and chaotic dynamics arising when the droplet is subjected to a harmonic potential, a Coriolis force, or the interaction with a seconddroplet. Finally, we modify our fluid model to account for interactions with submerged boundaries, allowing us to rationalise the pilot-wave dynamics in a circular corral.

A field-deployable instrument has been developed that isolates from an ambient aerosol population only those particles that have critical supersaturations, Sc, within a narrow, user-specified, range. This Differential Critical Supersaturation Separator (DScS) is designed to supply one or more particle size and/or composition analyzers to permit the direct examination of the factors that influence the activation properties of ambient aerosols. The DScS consists of two coupled parallel plate continuous flow thermal gradient diffusion cloud chambers housed within a single enclosure. Descriptions of instrument operation, construction and calibration data collected, when pure ammonium sulfate aerosols were injected into the DScS for operation at 0.15%< Sc<0.175%, 0.30%< Sc<0.35%, and 0.60% < Sc<0.70%, are included. Following instrument development, the DScS was deployed during March 2006 for the Megacities Impact on Regional And Global Environment (MIRAGE) field campaign in Mexico City, Mexico. Throughout the MIRAGE field campaign a Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) system measured aerosol size distributions and size-resolved hygroscopicity of DScS separated aerosol. The dry diameter (Dp*) of particles sampled in the TDMA system as well as the known Sc prescribed in the DScS were combined in a modified version of Köhler Theory to make predictions of particle hygroscopicity. These predictions frequently overestimated the measurements. Further analysis of DScS separated aerosols compares the known particle Sc to a predicted particle Sc, providing insight into particle activation efficiency. Overall, the sampled aerosol exhibited properties that indicate they were more efficient at activation than Köhler Theory would predict.

Coral reefs ecosystems are some of the most productive and diverse in the world. The symbiotic association between cnidarians and their symbiotic microalgae is of great importance in coral reef ecosystems; however, its underlying molecular mechanism remains unclear even after decades of research. Rab small GTP binding proteins are critical regulators of vesicle trafficking. Here we present the experimental evidence supporting a possible association of ApRab37 with the surface of lipid droplets in the endosymbiosis between the sea anemone, Aiptasia pulchella and the symbiotic dinoflagellate (commonly known as zooxanthellae). ApRab37, a protein of 215 amino acids, displays strong homology with human Rab37. In transfected COS7 cells, EGFP-ApRab37 localized to lipid droplets and clustered in the peri-nuclear region, which stained positive for the ER (endoplasmic reticulum) marker. Immunostaining analysis found ApRab37 associated with symbiosomes and lipid droplets, which was also confirmed by Western blot analysis of in the enrich lipid droplet fraction. Phagocytosis assay showed that ApRab37 involved in late phase of phagocytosis. DCMU treatment indicates symbiosome association of ApRab37 is mediated by zooxanthellae. I propose that ApRab37 plays a pivotal role in the regulation of lipid trafficking from the symbiosomes to the host cell during the Aiptasia-zooxanthellal endosymbiosis.

A field-deployable instrument has been developed that isolates from an ambient aerosol population only those particles that have critical supersaturations, Sc, within a narrow, user-specified, range. This Differential Critical Supersaturation Separator (DScS) is designed to supply one or more particle size and/or composition analyzers to permit the direct examination of the factors that influence the activation properties of ambient aerosols. The DScS consists of two coupled parallel plate continuous flow thermal gradient diffusion cloud chambers housed within a single enclosure. Descriptions of instrument operation, construction and calibration data collected, when pure ammonium sulfate aerosols were injected into the DScS for operation at 0.15%< Sc<0.175%, 0.30%< Sc<0.35%, and 0.60% < Sc<0.70%, are included. Following instrument development, the DScS was deployed during March 2006 for the Megacities Impact on Regional And Global Environment (MIRAGE) field campaign in Mexico City, Mexico. Throughout the MIRAGE field campaign a Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) system measured aerosol size distributions and size-resolved hygroscopicity of DScS separated aerosol. The dry diameter (Dp*) of particles sampled in the TDMA system as well as the known Sc prescribed in the DScS were combined in a modified version of Köhler Theory to make predictions of particle hygroscopicity. These predictions frequently overestimated the measurements. Further analysis of DScS separated aerosols compares the known particle Sc to a predicted particle Sc, providing insight into particle activation efficiency. Overall, the sampled aerosol exhibited properties that indicate they were more efficient at activation than Köhler Theory would predict.

This work describes the development of a microfluidic platform that can be used to study suspension stability and crystallization with in droplets as a function of time and concentration. Techniques for monodisperse droplet formation, droplet trapping and storage, and droplet dehydration are developed and used to design a microfluidic platform that can be adapted for the applications of interest. A geometric model is developed to predict the droplet shape and emulsion structure generated by microfluidic nozzles. However, droplet volume and structure spacing cannot be independently controlled using microfluidic nozzles, and a design consisting of an array of traps is considered to achieve the desired structure for stable, extended droplet observation. The dehydration of aqueous droplets stored in the array is characterized as a function of relative humidity, and is shown to be reasonably estimated as a species diffusing from a sphere into an infinite medium. The microfluidic platform for droplet dehydration is combined with particle tracking to show that the stability of particle suspensions can be probed as a function of salt concentration. The flocculation behavior observed in the trapped droplets agrees well with corresponding macroscale measurements as well as with previously published studies. The platform is also used to generate substantial sample sizes to measure nucleation statistics and crystal growth rates of glycine as a function of initial concentration, environmental conditions, and the presence of additives. These applications show proof of concept that the microfluidic platform is a useful tool for the analysis of the behavior observed during particle aggregation and crystallization.

No description available.

Thesis (M.S.) -- Worcester Polytechnic Institute. / Keywords: emissive probes; electrospray; colloid thrusters; plasma potential. Includes bibliographical references (p. 111-113 ).

Indiana University-Purdue University Indianapolis (IUPUI) / Coxiella burnetii is an intracellular bacterium that causes the human disease Q fever. C. burnetii is transmitted from infected animals to humans through inhalation of infectious droplets. Acute Q fever is a flu-like illness lasting 10-14 days. Patients often have respiratory symptoms and present with pneumonia. Patients with suppressed immune systems or valvular heart disease can develop chronic Q fever, which causes endocarditis and vasculitis long after initial infection. Chronic Q fever is difficult to treat, and if untreated, is typically fatal. Currently, the United States lacks any vaccine for Q fever. In order to better prevent and treat this disease, it is important to understand how C. burnetii interacts with mammalian cells. Within the host cell, C. burnetii forms a large, acidic Coxiella-containing vacuole (CCV) and uses a Type 4B secretion system (T4SS) to secrete effector proteins into the host cell cytoplasm. While the CCV membrane is rich in sterols, cholesterol accumulation in the CCV is bacteriolytic, suggesting that C. burnetii regulation of lipid transport is critical for infection. The mammalian lipid transport protein ORP1L localizes to the CCV membrane and mediates CCV-ER membrane contact sites. ORP1L functions in lipid transport, including cholesterol efflux from late endosomes/lysosomes. Its sister isoform ORP1S binds cholesterol but localizes to the cytoplasm and nucleus. In ORP1- null cells, we found that CCVs were smaller than in wildtype cells, highlighting the importance of ORP1 in CCV development. CCVs in ORP1-null cells had higher cholesterol content than CCVs in wildtype cells, suggesting ORP1 functions in cholesterol efflux from the CCV. ORP1-null MH-S cells do not accumulate lipid droplets upon C. burnetii infection, supporting our hypothesis that ORP1 promotes cholesterol transfer from the CCV to the ER, as lipid droplets form from neutral lipids in the ER. While the absence of ORP1 led to a C. burnetii growth defect in MH-S cells, there was no growth defect in HeLa cells. Together, our data demonstrate that C. burnetii uses the host sterol transport protein ORP1 to promote CCV development, potentially by using ORP1 to facilitate cholesterol efflux from the CCV to diminish the bacteriolytic effects of cholesterol.