<p> Laser pulses propagating through plasma undergo spectral broadening through local energy exchange with driven plasma waves. During propagation, a high power laser pulse drives large amplitude plasma waves, depleting the pulse energy. At the same time, the large amplitude plasma wave provides a dynamic dielectric response that leads to spectral shifting. The loss of laser pulse energy and the approximate conservation of laser pulse action imply that spectral red-shifts accompany the depletion. Here we examine the spectral shift and broadening, energy depletion, and action conservation of nonlinear laser pulses using the modified paraxial solver in WAKE. For pulses causing complete cavitation, large wavenumber shifts and action decay are observed at the distance where 40&ndash;50% of the pulse energy is depleted, consistent with theoretical prediction. </p><p> A tenuous plasma, enveloped, full wave solver was further implemented and compared to the modified paraxial solver through studying the University of Maryland laser-plasma system. The full wave solver has the advantage of better predicting the dispersion relation and eliminating the problematic divergence in the dispersion of the modified paraxial solver as wavenumber approaches zero, which is important especially when considering long wavelength generation. </p><p> Numerical analysis of the two propagation algorithms has been conducted via monitoring conservation laws. For large spectral shifts, numerical damping and convection of radiation out of the simulation domain result in action decay. Implementing a higher order evaluation of numerical derivatives and smaller spatial step have reduced numerical damping. </p><p> Spectral red-shifting of high power laser pulses propagating through underdensed plasma channel can be a source of ultrashort mid-infrared (MIR) radiation. Parametric dependence of MIR generation on laser pulse power, initial pulse duration, and plasma density is investigated through characteristic wavenubmer estimates and simulations.</p>

<p> As of 2013, the Carbon Dioxide Information Analysis Center (CDIAC) estimates that the world emits approximately 36 trillion metric tons of Carbon Dioxide (CO₂) into the atmosphere every year. These large emissions have been correlated to global warming trends that have many consequences across the globe, including glacial retraction, ocean acidification and increased severity of weather events. With green technologies still in the infancy stage, it can be expected that CO₂ emissions will stay this way for along time to come. Approximately 41% of the emissions are due to electricity production, which pump out condensed forms of CO₂. This danger to our world is why research towards new and innovative ways of controlling CO₂ emissions from these large sources is necessary. </p><p> As of now, research is focused on two primary methods of CO₂ reduction from condensed CO₂ emission sources (like fossil fuel power plants): Carbon Capture and Sequestration (CCS) and Carbon Capture and Utilization (CCU). CCS is the process of collecting CO₂ using absorbers or chemicals, extracting the gas from those absorbers and finally pumping the gas into reservoirs. CCU on the other hand, is the process of reacting CO₂ to form value added chemicals, which can then be recycled or stored chemically. </p><p> A Dielectric Barrier discharge (DBD) is a pulsed, low temperature, non-thermal, atmospheric pressure plasma which creates high energy electrons suitable for dissociating CO₂ into its components (CO and O) as one step in the CCU process. Here I discuss the viability of using a DBD for CO₂ dissociation on an industrial scale as well as the fundamental physics and chemistry of a DBD for CO₂ dissociation. This work involved modeling the DBD discharge and chemistry, which showed that there are specific chemical pathways and plasma parameters that can be adjusted to improve the CO₂ reaction efficiencies and rates. Experimental studies using the Versatile Atmospheric dielectric barrier Discharge ExpeRiment (VADER) demonstrated how different factors, like voltage, frequency and the addition of a photocatalyst, change the efficiency of CO₂ dissociation in VADER and the plasma chemistry involved.</p>

The most severe problem for the vacuum arc deposition (VAD) technique is the formation of micron-size particles on the films. These particles degrade the films' properties. The present work studied the generation mechanisms and characteristics of the droplets that are produced in the carbon films deposited by vacuum arc technique. To achieve a better control of the generation mechanism of these droplets, the effect of the arc current, arc duration time, cathode spot temperature and distance between cathode and substrate on the size and population of the micro-droplets are studied. / The micro-droplets are in the range of 0.3 $ mu$m to 2 $ mu$m in diameter, and have a graphite structure. The most probable origin for these particles are the cathode. The size and population of these particles are directly proportional to the cathode spot temperature (i.e., to the arc current and/or arc duration time), and inversely proportional to the distance between the cathode and the substrate. The droplet production is mainly due to the heating effect.

The self preserving free jet in streaming flow has been investigated by studying the equations of mean motion for two-dimensional turbulent flow. It is found that at high Reynolds nurnber the jet may be self preserving if the free stream velocity varies as the downstream co-ordinate to a power which in turn depends on the non-dimensional velocity of the jet. The growth of the jet is then linear. The effect of an upstream boundary-Iayer on the outside of the slot is also considered. This analysis is then applied to the outer part of a wall jet in a similar pressure gradient. The effect of the inner boundary layer on the outer part of the flow is considered and formulae for the growth of the inner boundary-Iayer and the variation of skin friction are given. Also a form for the non-dimensional mean velocity profile including the inner boundary-layer is suggested. The predictions of the theory are found to be in substantial agreement with measurements of the mean velocity, the static pressure and the skin friction in wall jets with an equilibrium pressure gradient. Experimental measurements have also been made for wall jets in streaming flow with zero pressure gradient and wall jets in still air. The results of these experiments compare weIl with those of previous investigators . The law-of-wall and the velocity defect law for wall jets are investigated and the former is found to be limited in application. A simple power law appears to be useful for representing the whole boundary-layer velocity profile and forms the basis for the analysis of the inner boundary-layer .

In this work, the dependence of the vacuum arc spot velocity on physical and electrical properties of different graphite cathode materials is investigated in the presence of a variable magnetic field. A pulsed arc system is used to perform preliminary experiments on the arc mobility for the different types of graphite for the selection of proper material morphology and the design of a continuous vacuum arc system. The characteristics of arc mobility, erosion rate, and carbon ion flux emitted from the continuous carbon source are then evaluated in view of particle-free diamond-like protective coatings. Results show that the arc spot velocity on graphite cathodes is larger on cathodes having larger grain size, lower electrical resistivity and higher apparent density. The spot velocity is also lower for cathodes having larger pore sizes and total porosity. The arc spot velocity is also found to be increased by increasing the magnetic field intensity over the surface of any graphite type. Reduced residence time of the spot on a given site of the cathode resulting from arc velocity increase should lead to a reduction in the heat load input in the cathode spot. This correlates with results on the number of emitted particles, the film thickness and roughness, and the erosion rate that are found to decrease, while the ion flux emission is increased. Diamond-like carbon (DLC) films free of particles are produced in a continuous arc ion plating (AIP) system. The ion energy in the continuous AIP system is found to vary with the graphite surface properties and the intensity of a plasma confining magnetic field in front of the cathode. The ion energies measured vary between 39.8 eV to 62.6 eV.

We develop a coarse grained methodology to study solvent mediated interactions between two or more hydrophobic spheres. The free energy of a configuration of two hydrophobic hard spheres is calculated as a function of their separation to understand the thermodynamic force between them mediated by water. The range of the hydrophobic interaction is found to be of the order of the equilibrium correlation length of water; beyond this range the hydrophobicity induced force is negligible. We also examine the free energy landscape corresponding to the two interacting hydrophobic spheres, and find a new intermediate state between the two states of separate and non-interacting spheres and a weakly bound cluster. The nature of this intermediate state changes depending on the size of the spherical particles, and even disappears beyond a minimum critical radius. Our results are relevant to the understanding of hydrophobic mediated interactions in coarse grained models of protein folding and protein protein interactions which, to date, have only accounted for hydrophobicity in an empirical way.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7403. Adviser: William RC Phillips. Includes bibliographical references (leaves 62-64) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Lehigh University, 2007. / Adviser: Yong W. Kim.

Thesis (Ph.D.)--Lehigh University, 2009. / Adviser: Arnold Kritz.

Many technological and biomedical applications ranging from water filtration and oil extraction to arteriosclerosis and vein thrombosis rely upon the transport of solids in liquids. Particulate matter suspended in liquid flowing through channels that are often microscopic or millimeters in size which leads to clogging. This dissertation examines the clogging behavior of microscopic channels by microscopic particles suspended in liquid. We physically model clogging in microchannels by flowing microparticles through microfluidic channels. Unlike previous studies, we choose non-uniform microchannels; specifically, we study clogging in microchannels whose width narrows over the length of the channel. Converging channels are inspired by the pore size variations in real porous media like membrane filters and sandstone. Initially we study the clogging behavior of microparticles in arrays of parallel microchannels as we vary the microchannel entrance (mouth) width and microchannel length. We measure the time until each channel clogs and we calculate the number of particles that pass prior to clogging. Contrary to expectation, we show that the number of particles passing through a pore increases exponentially with increasing mouth width but decreases linearly as the channel length increases. Changing the dimensions of the channels changes the particulate suspension’s flow rate which in turn changes the shear stresses that particles experience near the channel wall. When particles experience higher near-wall shear stress, the particles are less likely to adhere to channel walls and engender clogging. We confirm the effect of flow rate on channel clogging by demonstrating that the number of particles needed to clog a tapered channel increases as the pressure applied to the particulate suspension increases. The connection between flow rate and clogging highlights the interplay between hydrodynamic forces and intermolecular forces that govern particle attachment and ultimately clogging. We further explore this relationship by modulating the interaction between the particle and channel wall in a single tapered channel. While observing single channels clogging, we also resolve individual particles gradually building up on channel walls and forming clogs. Interestingly, particles also cluster on upstream channel walls only to later detach and clog at the downstream constriction. At low pressures, the channel clogs when particles accumulate individually near the constriction. At high pressures, the channel clogs when particle clusters detach from channel walls upstream and flow into the constriction. Finally, we compare the clogging behavior of particles with long, electrosteric stabilizing molecules on the surface to the clogging behavior of particles with shorter electrostatic stabilizing molecules on the surface. We also compare the clogging behavior of both particle types in the presence of varying concentrations of a monovalent salt. We show that clogging is mitigated when Debye length is comparable to the length of the stabilizing molecule on the particle’s surface. / Engineering and Applied Sciences - Applied Physics