Experiments on binary drop collisions within an index-matched liquid were conducted for Weber numbers We) of 1-50 and collision angles of 15-80&deg； below the horizontal. Drop pairs of water/glycerin mixture were injected into silicone oil and, due to gravitational effects, traveled on downward trajectories before colliding. A dual-field high-speed PIV measurement system was employed to quantify drop trajectories and overall collision conditions while simultaneously examining detailed velocity fields near the collision interface. In the We range examined, for equal size drops, both rebounding and coalescing behavior occurred. The drops coalesced for We ＞ 10 and rebounded for We &lt； 10, and this boundary was found to be insensitive to collision angle. Coalescence was found to result from a combination of vortical flow within drops and strong drop deformation characteristic of higher We. Flow through the centers of opposing ring vortices, strengthened by drop deformation, enhanced drainage of the thin film in the impact region, leading to film rupture and coalescence. The collision angle affected the eventual location of film rupture, with the rupture location moving higher in the thin film region as the collision angle increased. The film rupture location correlated closely with the location of maximum downward velocity in the thin film. The time between collision and rupture increases with We until We ＝ 30. For We ＞ 30, the time decreases as We increases. Unequal size drop collisions with drop size ratios Ds/D L) of 0.7 and 0.5 were also examined. Coalescence occurs above We* ＝ 11 similar to equal size drops. As drop size ratio decreases, the intervening film deforms more. If the velocity ratio uL/u s &lt； 1, the deformed interface becomes flat before coalescence. The rupture location varies due to the asymmetry of the drops. As collision offset increases B ＞ 0), the film rupture time is shortened and mixing of the fluid from both drops is enhanced after coalescence. The presence of tracer particles in the intervening film does not affect the minimum Weber number for coalescence, but the film ruptures earlier compared with cases lacking tracer particles.

Terrestrial substorms have been studied for over four decades and our understanding about this phenomenon has improved through those studies. However, many issues regarding substorms are still controversial, especially the initiation mechanism of substorm onset. To understand the initiation mechanism, we have to first answer some important questions. What is the substorm expansion onset? What is the physics behind its phenomenological definition? Where does the initiation start? What is the relation of tail reconnection with near-Earth onsets? Where does tail reconnection occur? While one way to understand better the physics of substorms is to increase the number of spacecraft and the resolution of ground observations, another way is to compare substorm phenomena between different planets. In this study, we investigate the different phases of substorms both on the Earth and Jupiter. For Jovian dynamic event, we need to know if they are substorms? How are they driven? How can we better understand terrestrial substorms through studying Jovian substorms? We used Polar, GOES, Cluster and ground-station observations to study terrestrial substorms and used the Galileo observations to study Jovian dynamic events. A 3-day growth phase of Jovian substorm is discovered, which is also found driven by the internal processes including mass-loading at Io instead of the solar wind. This discovery establishes the substorm nature of those dynamics events which have counterparts of key elements of terrestrial substorms, including the connection of those events with the Jupiter’s polar auroral activity. Near-planet dipolarization caused by the mid-tail reconnection is also investigated. In the near-Earth tail region, dipolarizations appear to be associated with mid-tail reconnections, near-tail flow braking and formation of substorm current wedge. In both magnetospheres, major onsets of substorms are found to be due to the major tail reconnection which can globally release the loaded energy and return the accumulated magnetic flux in magnetotails. This major change of magnetotail energy and flux status should be used to define the expansion onset of terrestrial substorms. Through comparison of dipolarizations on the geosynchronous orbit (GOES) and 9 R E near-tail region (Polar), it is found that dipolarization region starts within a narrow region and then expands both in the radial and azimuthal directions. The near-Jupiter dipolarizations and plasmoids are used to infer the Jovian tail reconnection site and the most possible location of Jovian tail neutral point is found at the post-midnight sector and 80 RJ from the planet. It is also very found that the Jovian tail reconnection starts within a confined region and expands afterwards, which is consistent with the narrow width of initial near-Earth dipolarization region and suggests tail reconnection associated with substorms mostly starts from a neutral point instead of a neutral line.

The equation of state (EOS) of materials at extreme temperatures and pressures is of interest to astrophysics, high-energy-density physics, and inertial confinement fusion (ICF). The behavior of hydrocarbon materials at high-pressures (＞1 Mbar) is essential to the understanding of ablator materials for ICF ignition targets. The EOS measurements on CHX presented here provide benchmark behavior of hydrocarbons under extreme conditions and the effect of stoichiometry (i.e. C:H ratio) on that behavior. Advances in diagnostics and analysis have made it possible to perform highly accurate measurements of shock velocity to &sim；1% precision in transparent materials. This refines the impedance-match (IM) technique for laser-driven shock experiments producing precise EOS data at extreme pressures using a transparent standard such as alpha-quartz. The OMEGA laser was used to produce principal (single-shock) Hugoniot EOS measurements on polystyrene (CH), polypropylene (CH2), Glow-Discharge-Polymer (GDP) (C43H56O), and Germanium-doped GDP at shock pressures of 1–10 Mbar, with an alpha-quartz standard. This precision data tightly constrains the Hugoniot behavior of these hydrocarbons, even with the inclusion of systematic uncertainties inherent in the IM technique. A novel target design providing double-shock (re-shock) measurements along with principal Hugoniot data is presented. Results of the single-and double-shock experiments on these hydrocarbons are presented and compared to various EOS models. Temperature measurements are presented for CH and CH2； measuring both the thermal and kinematic behavior of these materials provides their complete shock EOS. Reflectance measurements on CH and CH2 show that both hydrocarbons transition from transparent insulators to reflecting conductors at pressures of 1 to 2 Mbar.

Hall-effect thruster HET) cathodes are responsible for the generation of the free electrons necessary to initiate and sustain the main plasma discharge and to neutralize the ion beam. The position of the cathode relative to the thruster strongly affects the efficiency of thrust generation. However, the mechanisms by which the position affects the efficiency are not well understood. This dissertation explores the effect of cathode position on HET efficiency. Magnetic field topology is shown to play an important role in the coupling between the cathode plasma and the main discharge plasma. The position of the cathode within the magnetic field affects the ion beam and the plasma properties of the near-field plume, which explains the changes in efficiency of the thruster. Several experiments were conducted which explored the changes of efficiency arising from changes in cathode coupling. In each experiment, the thrust, discharge current, and cathode coupling voltage were monitored while changes in the independent variables of cathode position, cathode mass flow and magnetic field topology were made. From the telemetry data, the efficiency of the HET thrust generation was calculated. Furthermore, several ion beam and plasma properties were measured including ion energy distribution, beam current density profile, near-field plasma potential, electron temperature, and electron density. The ion beam data show how the independent variables affected the quality of ion beam and therefore the efficiency of thrust generation. The measurements of near-field plasma properties partially explain how the changes in ion beam quality arise. The results of the experiments show that cathode position, mass flow, and field topology affect several aspects of the HET operation, especially beam divergence and voltage utilization efficiencies. Furthermore, the experiments show that magnetic field topology is important in the cathode coupling process. In particular, the magnetic field separatrix plays a critical role in impeding the coupling between cathode and HET. Suggested changes to HET thruster designs are provided including ways to improve the position of the separatrix to accommodate the cathode.

Study of primary breakup of liquid jets is important because it is motivated by the application to gas turbine fuel injectors, diesel fuel injectors, industrial cleaning and washing machine, medical spray, and inkjet printers, among others. When it comes to good injectors, a liquid jet has to be disintegrated into a fine spray near injector region during primary breakup. However the dense spray region near the injectors is optically obscure for Phase Doppler Interferometer like Phase Doppler Particle Analyzers (PDPA). Holography can provide three dimensional image of the dense spray and eliminate the problem of the small depth of focus associated with shadowgraphs. Traditional film-based holographic technique has long been used for three dimensional measurements in particle fields, but it is time consuming, expensive, chemically hazardous. With the development of the CCD sensor, holograms were recorded and reconstructed digitally. Digital microscopic holography (DMH) is similar to digital inline holography (DIH) except that no lens is used to collimate the object beam. The laser beams are expanded with an objective lens and a spatial filter. This eliminates two lenses from the typical optical path used for in-line holography, which results in a much cleaner hologram recording. The DMH was used for drop size and velocity measurements of the breakup of aerated liquid jets because it is unaffected by the non-spherical droplets that are encountered very close to the injector exit, which would cause problems for techniques such as Phase Doppler Particle Analyzer, otherwise. Large field of view was obtained by patching several high resolution holograms. Droplet velocities in three dimensions were measured by tracking their displacements in the streamwise and cross-stream direction and by tracking the change in the plane of focus in the spanwise direction. The uncertainty in spanwise droplet location and velocity measurements using single view DMH was large at least 33%. This large uncertainty in the spanwise direction, however, can be reduced to 2% by employing double view DMH. Double view DMH successfully tracked the three dimensional bending trajectories of polymer jets during electrospinning. The uncertainty in the spatial growth measurements of the bending instability was reduced using orthogonal double view DMH. Moreover, a commercial grade CCD was successfully used for single- and double-pulsed DMH of micro liquid jet breakup. Using a commercial grade CCD for the DMH, the cost of CCD sensor needed for recording holograms can be reduced.

NiSi is an attractive material in the production of CMOS devices. The problem with the utilization of NiSi, is that there is no proper method of cleaning the oxide on the surface. Sputtering is the most common method used for the cleaning, but it has its own complications. Dry cleaning methods include the reactions with radicals and these processes are not well understood and are the focus of the project. Dissociated NF3 and NH3 were used as an alternative and XPS is the technique to analyze the reactions of atomic fluorine and nitrogen with the oxide on the surface. A thermal cracker was used to dissociate the NF3 and NH3 into NF x＋F and NHx＋H. There was a formation of a NiF2 layer on top of the oxide and there was no evidence of nitrogen on the surface indicating that the fluorine and hydrogen are the reacting species. XPS spectra, however, indicate that the substrate SiO2 layer is not removed by the dissociated NF 3 and NiF2 growth process. The NiF2 over layer can be reduced to metallic Ni by reacting with dissociated NH3 at room temperature. The atomic hydrogen from dissociated ammonia reduces the NiF2 but it was determined that the atomic hydrogen from the ammonia does not react with SiO2.

A class of flux ropes has been discovered in the solar wind with durations on the order of tens of minutes which differ from the well-known magnetic clouds that share the unique magnetic topology. This discovery motivated the questions (1) are they a distinct population of structures, (2) what are their properties and evolution through the heliosphere, (3) where are they created and (4) what is the geomagnetic impact. In this dissertation, we develop and employ two methods of flux rope identification. We used both methods to identify a distinct, large population of small-scale flux ropes at 1 AU which have an anti-dependence on solar cycle consistent over solar cycles 21 to 23. We investigate their heliospheric evolution from 0.3 to 5.5 AU. We found that small-scale flux ropes have a large, rapid expansion within 1 AU, implying they are created within and nearly complete their evolution at 1 AU. They are likely to be found near sector crossings rather than be associated with ICMEs, constraining their possible origins to near the heliospheric current sheet. We found that small-scale flux ropes that impact the magnetosphere drive moderate substorm activity depending on their orientation.

This thesis is concerned with the application of silicon nanocrystals Si NCs) in photovoltaic devices. Two types of novel solar cells, hybrid solar cells and Si NCs-only thin-film photovoltaic devices, have been developed. Hybrid solar cells are made from polymers and Si NCs. The first hybrid solar cells were fabricated by using poly-3hexylthiophene) P3HT) which has a good hole mobility and matches the energy band alignment of Si NCs. The solar cell performance of Si NCs/P3HT devices was studied as a function of the weight ratio of Si NCs/P3HT and Si NC size. Three groups of Si NCs were used in this study: Si NCs 3-5 nm in diameter, 5-9 nm in diameter, and 10-20 nm in diameter. The open-circuit voltage and short-circuit current increased by using the smallest size NCs due to the high surface-area-to-volume ratio and quantum confinement effect. Those results indicate that Si NCs are a good candidate as an electron acceptor in hybrid solar cell application. To improve the efficiency of Si NCs/P3HT hybrid solar cells, we started to optimize the fabrication conditions by modification of the polymer concentration, usage of post-production heat treatment, and application of different metal electrodes. After optimization, a hybrid solar cell from 50wt% weight ratio) Si NCs/P3HT annealed at 150&deg；C for 2 hours with aluminum Al) electrodes had a power conversion efficiency of 1.47% with a fill factor of 0.47, short-circuit current of 3.8 mA/cm2, and open-circuit voltage of 0.8 V under air mass 1.5 direct AM 1.5D) one sun illumination. To understand the hole mobility of P3HT before and after post-production heat treatment, a hole-only device was fabricated by depositing gold Au) electrodes, which block electron injection from the electrodes to Si NCs. The results suggest that the hole mobility of 50wt% Si NCs/P3HT film increases one order of magnitude after heat treatment, due to improved crystallinity in the P3HT, which can enhance hybrid solar cell efficiency. Literature has reported that the compatibility of polymers and nanocrystals plays an important role in hybrid solar cell efficiency. Although P3HT is a good hole conductor and light absorber in solar cell applications, other polymers should be tested to find the best compatibility for Si NCs. Knowing this, P3HT was replaced by poly [2-methoxy-5-3,7-dimethyloctyloxy)-1,4-phenylenevinylene] MDMO-PPV) in 3-5 nm Si NCs/MDMO-PPV hybrid solar cells. Although Si NCs/MDMO-PPV devices have a higher open-circuit voltage than Si NCs/P3HT devices, the power conversion efficiency of Si NCs/MDMO-PPV devices is not as high as that of Si NCs/P3HT devices. To understand the reasons for the low efficiency from Si NCs/MDMO-PPV devices, the hole mobility of MDMO-PPV, energy band alignment between MDMO-PPV and Si NCs, and absorption spectrum of MDMO-PPV were studied and compared to those of P3HT. To measure the hole mobility of MDMO-PPV, Au electrodes were again utilized to block electron injection into the Si NCs. The results show that the hole mobility of MDMO-PPV is lower than that of P3HT. The absorption spectrum of MDMO-PPV 400-600 nm) is narrower than that of P3HT 400-650 nm) so that exciton generation in P3HT is more efficient than in MDMO-PPV under AM 1.5 conditions. Additionally, MDMO-PPV has a lower highest occupied molecular orbital level than P3HT so the efficiency of hole injection from Si NCs into MDMO-PPV may not be as efficient as for P3HT. These reasons explain why the efficiency of Si NCs/MDMO-PPV devices is not as good as Si NCs/P3HT devices. From Si NC solution processing, we found that 10-20 nm bare Si NCs without any surface modification can form a stable cloudy colloid with 1,2-dichlorobenzene. This colloid can be spin-cast onto an ITO substrate to form a continuous and dense thin film. A Schottky photovoltaic device consisting of a single layer of intrinsic Si NCs was fabricated in a glove box to verify that films can be cast from colloid Si NCs. This photovoltaic device has a sandwich structure with a 250 nm Si NC layer between ITO and Al electrodes. Under AM 1.5D one sun illumination, the Si NC Schottky device showed a significant photovoltaic response with a power conversion efficiency of 0.02%, a fill factor of 0.26, short circuit-current density of 0.148 mA/cm2, and open-circuit voltage of 0.51 V. This result suggests that the solution processing of bare Si NCs can be a new way to manufacture low-cost and high-quality silicon-based thin films.

Small drops and the thin-films of bubbles are similar in that the surface to volume ratio is large. Consequently, capillary forces, which result from changes in the surface energy, tend to dominate the drop and bubble dynamics. For example, capillarity is responsible for breaking up a liquid jet from a faucet in a sink into a stream of individual droplets, and for coalescing these droplets into a puddle at the bottom of the sink. This dissertation identifies four situations in which a drop or a bubble exhibits unusual and perhaps counter-intuitive dynamics. The first example Chapter 2) occurs when a drop impacts either an angled or moving dry, solid surface. Existing physical models attempt to predict the resulting dynamics, spreading or splashing, based on a variety of parameters. Yet it is unclear how these models would extend to include tangential velocity. Our high-speed experiments highlight a distinct third regime in which a fraction of the drop spreads while the other part splashes. The second example Chapter 3) occurs when a drop contacts a wettable surface with a finite contact angle. Our high-speed experiments challenge the existing models by both showing that the spreading is inertially dominated and that the distance spread follows a power-law scaling in time where the exponent depends on the equilibrium contact angle. The third example Chapter 4) occurs when two drops are drawn together in an electric field. When the voltage between the drops is low, the drops contact and coalesce. However, when the voltage is sufficiently high, the drops contact and then recoil. The fourth example Chapter 5) occurs when a bubble on a liquid or solid surface ruptures. Foam coarsening theory would predict that the bubble vanishes when it pops, yet our experiments show that a ring of smaller bubbles is created from the retracting film. This inverse coarsening phenomena is a source of aerosols, and therefore may have implications for health and climate. This dissertation sets out to describe each of these four phenomena and develop plausible physical mechanisms and includes a novel computational approach Chapter 6) to model retracting thin films.

WINDMI is a low dimensional plasma physics-based model of the coupled magnetosphere-ionosphere system. The nonlinear system of ordinary differential equations describes the energy balance between the basic nightside components of the system using the solar wind driving voltage as input. Of the eight dynamical variables determined by the model, the region 1 field aligned current and ring current energy is compared to the westward auroral electrojet AL index and equatorial geomagnetic disturbance storm time Dst index. The WINDMI model is used to analyze the magnetosphere-ionosphere system during major geomagnetic storms and substorms which are community campaign events. Numerical experiments using the WINDMI model are also used to assess the question of how much interplanetary shock events contribute to the geoeffectiveness of solar wind drivers. For two major geomagnetic storm intervals, it is found that the magnetic field compressional jump is important to producing the changes in the AL index. Further, the WINDMI model is implemented to compute model AL and Dst predictions every ten minutes using real-time solar wind data from the ACE satellite as input. Real-Time WINDMI has been capturing substorm and storm activity, as characterized by the AL and Dst indices, reliably since February 2006 and is validated by comparison with ground-based measurements of the indices. Model results are compared for three different candidate input solar wind driving voltage formulas. Modeling of the Dst index is further developed to include the additional physical processes of tail current increases and sudden commencement. A new model, based on WINDMI, is developed using the dayside magnetopause and magnetosphere current systems to model the magnetopause boundary motion and the dayside region 1 field aligned current which is comparable to the auroral upper AU index.