Browsing by Author "Yalin, Azer, committee member"
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Item Open Access A calcium aluminate electride hollow cathode(Colorado State University. Libraries, 2014) Rand, Lauren Paula, author; Williams, John, advisor; Reynolds, Melissa, committee member; Sampath, Walajabad, committee member; Yalin, Azer, committee memberThe development and testing of a hollow cathode utilizing C12A7 (12CaO.Al2O3) electride as an insert are presented. Hollow cathodes are an integral part of electric propulsion thrusters on satellites and ground-based plasma sources for materials engineering. The power efficiency and durability of these components are critical, especially when used in flight applications. A low work function material internal to the cathode supplies the electrons needed to create the cathode plasma. Current state-of-the- art insert materials are either susceptible to poisoning or need to be heated to temperatures that result in a shortened cathode lifetime. C12A7 electride is a ceramic in which electrons contained in sub-nanometer sized lattice cages act as a conductive medium. Due to its unique atomic structure and large size, C12A7 electride has a predicted work function much lower than traditional insert materials. A novel, one-step fabrication process was developed that produced an amorphous form of C12A7 electride that had a measured work function 0.76 eV. A single electride hollow cathode was operated on xenon for over 60 hours over a two-month period that included 20 restarts and 11 chamber vent pump-down sequences with no sign of degradation, and on iodine for over 20 hours with no apparent reactivity issues. The operations of cathodes with three different orifice sizes were compared, and their effects on the interior cathode plasma modeled in a zero- dimensional phenomenological model.Item Open Access A low-cost monitor for simultaneous measurement of fine particulate matter and aerosol optical depth(Colorado State University. Libraries, 2018) Wendt, Eric, author; Volckens, John, advisor; Jathar, Shantanu, committee member; Yalin, Azer, committee member; Pierce, Jeffrey, committee memberExposure to airborne particulate matter with diameters less than 2.5 µm (PM2.5) is a leading cause of death and disease globally. In addition to affecting health, PM2.5 affects climate and atmospheric visibility. NASA currently uses satellite imaging technology to measure particulate matter air pollution across the world. Satellite image data are used to derive aerosol optical depth (AOD), which is the extinction of light in the atmospheric column. Although AOD data are often used to estimate surface PM2.5 concentration, there is considerable uncertainty associated with the relationship between satellite-derived AOD and ground-level PM2.5. Instruments known as Sun photometers can measure AOD from the Earth's surface and are often used for validation and calibration of satellite data. Reference-grade Sun photometers generally do not have co-located PM2.5 measurements and are too expensive to deploy in large numbers. The objective of this work was to develop an inexpensive and compact integrated PM2.5 mass and AOD sampler known as the Solar-Powered Aerosol Reference Calibrator (SPARC). PM2.5 is sampled using an ultrasonic pumping system, a size-selective cyclone separator, and a filter. Filter measurements can be used to correct the output from a low-cost direct-reading PM2.5 sensor housed within the SPARC. AOD is measured using optically filtered photodiodes at four discrete wavelengths. A suite of integrated sensors enable time-resolved measurement of key metadata including location, altitude, temperature, barometric pressure, relative humidity, solar incidence angle and spatial orientation. The AOD sensors were calibrated relative to a reference monitor in the Aerosol Robotics Network (AERONET). Field validation studies revealed close agreement for AOD values measured between co-located SPARC and AERONET monitors and for PM2.5 mass measured between co-located SPARC and EPA Federal Reference Method (FRM) monitors. These field validation results for this novel monitor demonstrate that AOD and PM2.5 can be accurately measured for the evaluation of AOD:PM2.5 ratios.Item Open Access A non-invasive Hall current distribution measurement system for Hall effect thrusters(Colorado State University. Libraries, 2015) Mullins, Carl Raymond, author; Williams, John, advisor; Shipman, Patrick, committee member; Yalin, Azer, committee memberA direct, accurate method to measure thrust produced by a Hall Effect thruster on orbit does not currently exist. The ability to calculate produced thrust will enable timely and precise maneuvering of spacecraft—a capability particularly important to satellite formation flying. The means to determine thrust directly is achievable by remotely measuring the magnetic field of the thruster and solving the inverse magnetostatic problem for the Hall current density distribution. For this thesis, the magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned outside the channel of a 1.5 kW Colorado State University Hall thruster equipped with a center-mounted electride cathode. In this location, the static magnetic field is approximately 30 Gauss, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is greater than tens of milligauss, which is within the sensitivity range of the TMR sensors. Due to the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field along with a non-negativity constraint and a zero boundary condition provides current density distributions. Our system measures the sensor outputs at 2 MHz allowing the determination of the Hall current density distribution as a function of time. These data are shown in contour plots in sequential frames. The measured ratios between the average Hall current and the discharge current ranged from 0.1 to 10 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 2.0 kW exhibited a breathing mode of 37 kHz, which was in agreement with temporal measurements of the discharge current.Item Open Access A study of the influence of process parameter variations on the material properties and laser damage performance of ion beam sputtered Sc2O3 and HfO2 thin films(Colorado State University. Libraries, 2016) Langston, Peter F., author; Menoni, Carmen, advisor; Rocca, Jorge, committee member; Marconi, Mario, committee member; Yalin, Azer, committee memberThis work is a study of the influence of process parameter variations on the material properties and laser damage performance of ion beam sputtered Sc2O3 and HfO2 thin films using a Vecco Spector ion deposition system. These parameters were explored for the purpose of identifying optically sensitive defects in these high index materials after the deposition process. Using a host of optical metrology and materials analysis techniques we report on the relationship between oxygen partial pressure in the deposition chamber during film growth and optical absorption in the grown material at 1 μm. These materials were found to be prone to excess oxygen incorporation. Positive identification of this excess oxygen is made and exactly how this oxygen is bound in the different materials is discussed. The influence of this defect type on the optical and mechanical properties of the material is also given and discussed. Laser damage results for these single layers are presented. The influence of higher and lower deposition energy was also studied to determine the potential for defect creation both at the surface and in the bulk of the material grown. Optimized thin films of HfO2, Sc2O3 and Ta2O5 were grown and tested for laser damage with a 1030 nm laser having a pulse width of ~375 ps and a nominal spot size of ~100 um FWHM. The laser damage threshold ranking of these materials followed fairly well with the band gap of the material when tested in air. When these same materials were tested in vacuum Sc2O3 was found to be very susceptible to vacuum mediated laser induced surface defect creation resulting in a greatly reduced LIDT performance. Ta2O5 showed much the same trend in that its in vacuum performance was significantly reduced from its in air performance but there was not as great of a difference between the in air and in vacuum performance as there was for Sc2O3. HfO2 also showed a large reduction in its in vacuum LIDT results compared with its in air LIDT values however, this material showed the smallest decrease of the three high index materials tested. A second contribution of this work is in the investigation of the impact of capping layers on the in air and in vacuum LIDT performance of single layer films. Ultra thin capping layers composed of different metal oxides were applied to 100 nm thick single layers of the same high index materials already tested, HfO2, Sc2O3 and Ta2O5. These capped samples were then LIDT tested in air and in vacuum. These ultra thin capping layers were shown to greatly influence the in air and in vacuum damage performance of the uncapped single layers. Damage probability curves were analyzed to retrieve surface and bulk defect densities as a function of local fluence. Methods for maximizing the LIDT performance of metal oxides based on our studied materials for use in air and in vacuum are discussed.Item Open Access Buck converter for on-chip reference generation(Colorado State University. Libraries, 2010) Rai, Abhay K., author; Collins, George, advisor; Yalin, Azer, committee member; Reising, Steven, committee memberMost modern day chips use an on chip voltage reference, also known as a bandgap voltage reference generator, to provide a stable reference, independent of power supply voltage (VDD) ripples and compensated for temperature variations. When power supply voltage decreases as the process feature size (gate length) decreases, it imposes challenges in terms of headroom and other factors to achieve a stable bandgap voltage reference. It also needs to be scaled down to VDD/2 for practical uses and provide a common mode voltage of VDD/2 of on-chip circuits. This thesis discusses a buck converter which uses an alternative to pulse width modulation (PWM) for stable reference generation and directly generates a VDD/2 reference using a novel inductor ripple current cancellation technique, which cancels inductor ripple current and therefore does not require a large capacitance for filtering of inductor ripple. An alternative to the pulse width modulation (PWM) technique is proposed, which uses common mode bias and transconductance (gm) tuning to keep the reference output constant for variable loads, and a temperature compensation techniques is used to minimize temperature sensitivity.Item Open Access Characterization of laser-produced plasmas as light sources for extreme ultraviolet lithography and beyond(Colorado State University. Libraries, 2019) Yin, Liang, author; Rocca, Jorge J., advisor; Menoni, Carmen S., committee member; Marconi, Mario C., committee member; Yalin, Azer, committee memberLithography is a critical process in the fabrication of integrated circuits. The continuous increase in computing power for more than half a century has depended in the ability to print smaller and smaller features, which has required the use of light sources operating at increasingly shorter wavelengths. There is keen interest in the development of high-power light sources for extreme ultraviolet (EUV) lithography at λ=13.5 nm and future beyond extreme ultraviolet (BEUV) lithography near λ=6.7 nm. The work conducted in this dissertation has characterized aspects of laser-produced plasmas (LPPs) that serve as light sources for EUV / BEUV lithography. The laser pulse shape dependence of the conversion efficiency of λ=1.03 μm laser into in-band 13.5 nm EUV emission in a Sn LPP was studied as a function of laser pulse shape and durations. Laser pulses of arbitrary temporal shape with variable energy and pulse widths were generated using a programmable pulse synthesizer based on a diode-pumped chirped pulse amplification Yb: YAG laser. The pulse synthesizer is based on wave front splitting and pulse stacking for the generation of arbitrary shape laser pulses of Joule-level energy. Pulses ranging from hundreds of ps to several ns were generated with a single laser. The measurements showed the CE favors the use of nearly square pulses of duration longer than 2 ns, in agreement with hydrodynamic/atomic physics simulations. A significant increase in CE was observed when Q-switched pulses were substituted by square pulses of similar duration. Conditions were observed at which the EUV pulse duration significantly outlasts the laser pulse in the direction normal to the target surface, in contrast at grazing angles the measured EUV pulse duration is shorter and similar to the laser pulse duration. The physics leading to this angular anisotropy is discussed, along with the spectroscopic characterization of EUV emission and at-wavelength images that characterize the source size. Another aspect of this dissertation includes a comprehensive study of the emission from Gd and Tb LPPs in the λ=6.5 - 6.7 nm region. BEUV emission spectra were measured as a function of laser pulse duration (120 ps - 4 ns), emission angle, and spatial location within the plasma. At-wavelength images of the BEUV emitting plasma region were obtained as a function of irradiation parameters. The peak of the emission spectrum was observed to broaden and to shift to longer wavelengths as the laser pulses are shortened from ns to hundreds of ps. Transient self-consistent hydrodynamic/atomic physics simulations show that the picosecond irradiation creates significantly hotter plasmas in which the dominant emission originates from more highly ionized species. Gd LPP emission driven by nanosecond laser pulses best matched the reflectivity band of our La/B4C mirrors. Spatially resolved spectra of the Gd LPP were acquired for different laser parameters and were compared to simulations. The CE into in-band BEUV emission was determined by integrating angularly resolved measurements obtained using an array of calibrated energy monitors. A maximum CE of 0.47% / 0.45% for the Gd / Tb LPPs was obtained within a 0.6% bandwidth. The results are of potential interest BEUV lithography.Item Open Access Demonstration of a compact 100 Hz, 0.1 J, diode-pumped picosecond laser(Colorado State University. Libraries, 2011) Curtis, Alden, author; Rocca, Jorge, advisor; Krapf, Diego, committee member; Yalin, Azer, committee memberIn this work I present an all laser diode pumped chirped pulse amplification laser system that is capable of producing 100 mJ laser pulses at 100 Hz repetition rate with durations of under 5 ps. The primary focus of this work consists of the development of two amplification stages that boost the temporally stretched pulses from a few hundred picoJoules to more than 100 mJ. The first amplifier is a Yb:YAG based regenerative amplifier operated at room temperature, which amplifies the pulses by a factor of about 106. The second stage is a multi-pass, Yb:YAG based amplifier, which is operated at cryogenic temperatures, and further amplifies the pulses by a factor of about 100. This is the first time a combination of room temperature and cryogenically cooled Yb:YAG amplifiers has been demonstrated. The room temperature pre-amplifier maintains more bandwidth than in the cryogenic case for increased compressibility. The cryogenic cooling of the power amplifier allows for increased heat dissipation and decreased saturation intensity for efficient operation. The optical efficiency of this amplifier is higher than that of other diode-pumped systems of comparable energy.Item Open Access Diagnostics and characterization of direct injection of liquified petroleum gas for development of spray models at engine-like conditions(Colorado State University. Libraries, 2023) Sharma, Manav, author; Windom, Bret, advisor; Yalin, Azer, committee member; Yost, Dylan, committee memberResearch within the realm of internal combustion (IC) engines is concentrated on enhancing fuel efficiency and curbing tailpipe emissions, particularly CO2 and regulated pollutants. Promising solutions encompass the utilization of direct injection (DI) and alternative fuels, with liquefied petroleum gas (LPG) standing out as a notable candidate. LPG presents a pragmatic and economical option for fueling the heavy-duty transportation sector in the United States. However, widespread adoption hinges on achieving energy conversion efficiencies in LPG engines comparable to those in diesel engine platforms. The overarching goal of this research is to address fundamental limitations to achieving or surpassing near-diesel efficiencies in heavy-duty on-road liquefied petroleum gas engines. Owing to substantial differences in physical properties compared to traditional fuels, an enhanced understanding and modeling of LPG sprays become imperative. This work conducts an experimental and numerical analysis of direct-injected propane and iso-octane, serving as surrogates for LPG and gasoline, respectively, under diverse engine-like conditions. The overall objective is to establish a baseline for the fuel delivery system required in future high-efficiency DI-LPG heavy-duty engines. Propane, emulating LPG, undergoes injection across various engine-like conditions, encompassing early and late injections, as well as boosted engines, using a range of direct injectors available in both research and commercial domains. Optical diagnostics, including high-speed schlieren and planar Mie scattering imaging, were performed to study the spray penetration, liquid and vapor phase regions, and mixing of propane and to characterize bulk and the plume-specific spray behavior of propane. The study also investigates the influence of injector geometry on spray performance. Iso-octane was used as a surrogate for gasoline, and propane was used to compare LPG's behavior with more conventional DI fuel. The experimental results and high-fidelity internal nozzle-flow simulations were then used to define best practices in computational fluid dynamics (CFD) Lagrangian spray models. Optical imaging revealed that, unlike iso-octane, propane's spray propagation was fed by its flash boiling, spray collapse, and a high degree of vaporization, resulting in a direct proportionality of propane's penetration length to temperature. These unique attributes categorize propane as an unconventional spray, necessitating corrections to injection and breakup models to replicate under-expanded jet dynamics and emulate flash boiling-driven spray development across various research and commercial injectors.Item Open Access Dynamics of low-density ultracold plasmas in externally applied electric and magnetic fields(Colorado State University. Libraries, 2013) Wilson, Truman M., author; Roberts, Jacob, advisor; Krueger, David, committee member; Lundeen, Stephen, committee member; Yalin, Azer, committee memberThe experiments described in this thesis were focused on the influence of external electric and magnetic fields and electron evaporation on the evolution of ultracold plasmas (UCPs). The UCPs were created from the photoionization of 85Rb which was first captured in a magneto-optical trap (MOT) and then magnetically trapped and transferred by a set of magnetic coils attached to a motorized translation stage to a region of the vacuum chamber with a set of electrodes. The first experiment studied the response of the UCP to sharp electric field pulses, which included 2 cycles of a sine wave pulse. These experiments showed a resonant response to the 2 cycles of rf that was density dependent, but was not a collision based mechanism. Instead, the response was caused by a rapid energy transfer to individual electrons through the collective motion of the electron cloud in the UCP. This density-dependent response allowed us to develop a technique for measuring the expansion rate of the UCPs in our system. It was also observed in second set of experiments that electron evaporation from the UCP had a significant effect on the amount of energy that was transferred to the ions to drive the UCP expansion. Model calculations show that we should expect electron evaporation to have a more significant influence on the UCP expansion rate at the relatively low densities of the UCPs that we create compared to other experiments. By modeling electron evaporation during expansion, our data are consistent with evaporation reducing the electron temperature significantly, which lowers the overall UCP expansion rate. In addition to these studies, we also performed an experiment in which it was observed that in the presence of a magnetic field there was a significant increase in the initial UCP expansion rate coupled with a deceleration of the ion expansion at later times in the UCP evolution. Our observations to date are consistent with the magnetic field influencing electron screening and UCP formation. By restricting the electrons motion in the direction transverse to the magnetic field lines to circular orbits around the magnetic field lines, the electrons cannot move appropriately to screen the internal radial electric fields produced by the excess of ions. Studies of this effect are currently under way. Future studies include direct measurements of the electron temperature and collision rates between the components of the UCP as we move towards trapping the UCP in a Penning trap.Item Open Access Instrumentation for ultra-intense laser matter interaction studies at high repetition rates(Colorado State University. Libraries, 2022) Nedbailo, Ryan, author; Rocca, Jorge, advisor; Marconi, Mario, committee member; Yalin, Azer, committee memberA new class of high-repetition rate (HRR) Peta-Watt-class (PW) laser systems make it possible to study laser matter interaction processes, like laser ion acceleration (LIA) and laser plasma instabilities (LPI), at unprecedented rates. These systems have the potential to generate immense amounts of data through rapid multivariable parameters scans of laser energy, pulse shape, spot size and others, in order to better diagnose and characterize the conditions underlying LPI and LIA. However, detection media, typically image plates, film, CR-39, presently limits the repetition rate at which data can be collected from these systems. Rep-rated diagnostics are being redesigned to match the capabilities of current multi-Hz present and near future, PW-class laser systems. Here we present the development of a compact Thomson Parabola Ion Spectrometer capable of characterizing various ion species of multi-MeV ion beams from >10^20 W/cm^2 laser produced plasmas at rates commensurate with the laser operation rates. This diagnostic makes use of a Polyvinyltoluene (PVT) based fast plastic scintillator (EJ-260), where the emitted light is collected by an optical imaging system coupled to a thermoelectrically cooled scientific complementary metal–oxide–semiconductor (sCMOS) camera. This offers a robust solution for data acquisition at HRR while avoiding the added complications and non-linearities of microchannel plate (MCP) based systems. Different ion energy ranges can be probed using the modular magnet setup, variable electric field, and a varying drift-distance. We have demonstrated operation and data collection with this system at up to 0.2 Hz from plasmas created by irradiating a solid target, limited only by the motorized target motion system. With the appropriate software and the use of machine learning techniques, on-the-fly ion spectral analysis will be possible, enabling real-time experimental control. The diagnostic design, calibration, and results from experiments at the ALEPH laser facility at Colorado State University (CSU) are presented. In addition, we describe the results of the development of a novel scheme for the generation of spike trains of uneven delay (STUD) laser pulses using an array of hexagonal mirrors. By individually driving the offset of each mirror segment, we can divide the wavefront of the laser creating a pulse train of arbitrary delay. This pulse-train forming device can be used to conduct experiments related to a proposed method of mitigating the effects of LPI for inertial confinement fusion (ICF). By periodically turning on and off the laser drive of the ICF process, it has been postulated that the growth of parametric instabilities can be mitigated by allowing damping during the off-cycle of the STUD pulses. The use of the pulse-train forming scheme demonstrated here will allow us to study the effects of pulse train delay and duration best suited to LPI mitigation.Item Open Access Investigating plasma modifications and gas-surface reactions of TiO2-based materials for photoconversion(Colorado State University. Libraries, 2012) Pulsipher, Daniel J. V., author; Fisher, Ellen R., advisor; Elliott, C. Michael, committee member; Van Orden, Alan, committee member; Strauss, Steven H., committee member; Yalin, Azer, committee memberPlasmas offer added flexibility for chemists in creating materials with ideal properties. Normally unreactive precursors can be used to etch, deposit and modify surfaces. Plasma treatments of porous and compact TiO2 substrates were explored as a function of plasma precursor, substrate location in the plasma, applied rf power, and plasma pulsing parameters. Continuous wave O2 plasma treatments were found to reduce carbon content and increase oxygen content in the films. Experiments also reveal that Si was deposited throughout the mesoporous network and by pulsing the plasma, Si content and film damage could be eliminated. Nitrogen doping of TiO2 films (N:TiO2) was accomplished by pulsed plasmas containing a range of nitrogen precursors. N:TiO2 films were anatase-phased with up to 34% nitrogen content. Four different nitrogen binding environments were controlled and characterized. The produced N:TiO2 films displayed various colors and three possible mechanisms to explain the color changes are presented. Both O2 treated and N:TiO2 materials were tested in photocatalytic devices. Preliminary results from photocatalytic activities of plasma treated P25 TiO2 powders showed that nitrogen doping treatments hinder photocatalytic activity under UV light irradiation, but silicon deposition can improve it. N:TiO2 materials were tested in photovoltaic devices to reveal improved short-circuit current densities for some plasma-modified films. To understand the gas-phase and surface chemistry involved in producing the N:TiO2 films, NH and NH2 species in pulsed NH3 plasmas were explored by systematically varying peak plasma power and pulsing duty cycle. Results from these studies using gas phase spectroscopy techniques reveal interconnected trends of gas-phase densities and surface reactions. Gas-phase data from pulsed plasmas with two different types of plasma pulsing reveal diminished or increased densities at short pulses that are explained by plasma pulse initiation and afterglow effects. Overall this work reveals characteristics of the plasma systems explored, knowledge of the resulting materials, and control over plasma etching, deposition, and modification of TiO2 surfaces.Item Open Access Large-eddy simulation of compressible flows using the stretched-vortex model and a fourth-order finite volume scheme on adaptive grids(Colorado State University. Libraries, 2022) Walters, Sean, author; Guzik, Stephen, advisor; Gao, Xinfeng, advisor; Randall, David, committee member; Yalin, Azer, committee memberState-of-the-art engineering workflows are becoming increasingly dependent on accurate large-eddy simulations (LES) of compressible, turbulent flows for off-design conditions. Traditional CFD algorithms for compressible flows rely on numerical stabilization to handle unresolved physics and/or steep gradient flow features such as shockwaves. To reach higher levels of physical-fidelity than previously attainable, more accurate turbulence models must be properly incorporated into existing, high-order CFD codes in a manner that preserves the stability of the underlying algorithm while fully realizing the benefits of the turbulence model. As it stands, casually combining turbulence models and numerical stabilization degrades LES solutions below the level achievable by using numerical stabilization alone. To effectively use high-quality turbulence models and numerical stabilization simultaneously in a fourth-order-accurate finite volume LES algorithm, a new method based on scale separation is developed using adaptive grid technology for the stretched-vortex subgrid-scale (SGS) LES model. This method successfully demonstrates scheme-independent and grid-independent LES results at very-high-Reynolds numbers for the inviscid Taylor-Green vortex, the temporally-evolving double-shear-flow, and decaying, homogeneous turbulence. Furthermore, the method clearly demonstrates quantifiable advantages of high-order accurate numerical methods. Additionally, the stretched-vortex LES wall-model is extended to curvilinear mapped meshes for compressible flow simulations using adaptive mesh refinement. The capabilities of the wall-model combined with the stretched-vortex SGS LES model are demonstrated using the canonical zero-pressure-gradient flat-plate turbulent boundary layer. Finally, the complete algorithm is applied to simulate flow-separation and reattachment over a smooth-ramp, showing high-quality solutions on extremely coarse meshes.Item Embargo Molecular dynamics simulation studies and experimental measurements of radiofrequency heating for strongly coupled and extremely magnetized ultracold neutral plasmas(Colorado State University. Libraries, 2023) Jiang, Puchang, author; Roberts, Jacob L., advisor; Yost, Dylan, committee member; Lee, Siu Au, committee member; Yalin, Azer, committee memberUltracold neutral plasmas(UNPs) are good experimental platforms for fundamental plasma physics studies because of their experimentally adjustable parameters, accessible timescales, ability to enter the strong coupling parameter regime, and easy access to large degrees of electron magnetization. The work in this thesis contains both simulation and experimental studies of UNPs. One simulation project describes a new UNP heating mechanism discovered using Molecular Dynamics simulations: DC electric field heating. This DC electric field heating mechanism occurs when a DC electric field is present when the plasma is formed. sets a lower limit of how cold UNP electron temperatures can be reached experimentally. A second simulation project investigates a many-body physics effect on collisional damping in UNPs and a breakdown in standard plasma theory treatments when the plasma is approaching the strongly coupled regime. This breakdown arises due to the increasing significance of three- or many-body electron-ion interactions influencing the plasma transport properties and particle collisions. My simulations find evidence for this being the case. Experimental studies of UNP electron-ion collision physics during the application of high-frequency RF electric fields to the UNP were conducted, and measurements of the RF-induced electron heating rate from the weak magnetized regime to extremely magnetized regime were performed. The results obtained are in qualitative agreement with the theory prediction but there's quantitative disagreement. Possibilities for resolving this disagreement are presented.Item Open Access Probing folding/unfolding kinetics, reaction mechanism and thermodynamic stability of nucleic acid hairpins(Colorado State University. Libraries, 2013) Nayak, Rajesh Kumar, author; Van Orden, Alan, advisor; Barisas, George B., committee member; Chen, Eugene, committee member; McNaughton, Brian, committee member; Yalin, Azer, committee memberNucleic acid hairpins play pivotal roles in biological and cellular processes. The functions of the DNA and RNA hairpins depend upon the conformational changes they adopt during the biological process. Therefore, a clear understanding of their conformational dynamics such as folding and unfolding kinetics, reaction mechanism as well as thermodynamic stability is essential to understand their biological functions. This dissertation describes folding kinetics, reaction mechanism and thermodynamic stability of stem-loop nucleic acid hairpins by using rapid-mixing stopped-flow kinetics and other spectroscopic techniques. Firstly, the folding kinetics and reaction mechanism of a five base-paired stem and twenty one polythymidine loop DNA hairpin as a function of varying monovalent counter ion concentrations have been discussed. The important observation of this investigation is that the DNA hairpin folding is not simply a two-state process, and based on our experiments and kinetic modeling, we proposed a three-state reaction mechanism, wherein, the intermediate formation occurs on microsecond time scale and the complete hairpin formation occurs on millisecond time scale. Secondly, the loop length and counter ion dependent thermodynamic stability and folding of DNA hairpins have been described. This investigation provides a detailed understanding of how the stability and folding changes as a function of loop length and counter ion concentrations. The most important conclusion of this part of the investigation is that the thermodynamic stability of tetraloop hairpins depend upon counter ion concentration regimes and we explained the exceptional stability of a tetraloop hairpin in the higher concentration regime, compared to longer loop length hairpins on the basis of base-stacking effect. Finally, the folding and unfolding kinetics of RNA hairpins with identical four base-paired stem but different nucleotide loop sequence is discussed. Here we observed that the RNA hairpin folding and unfolding can be much more complex than previously thought and also RNA hairpin folding process can be different than DNA hairpin folding process.Item Open Access Scatter loss and surface roughness of hafnium oxide thin films(Colorado State University. Libraries, 2011) Tollerud, Jonathan, author; Menoni, Carmen, advisor; Yalin, Azer, committee member; Marconi, Mario, committee memberThe work presented in the thesis aims to characterize and improve the surface quality and scatter loss of HfO2 single layer thin films. Dual ion beam sputtered coatings of HfO2 produced at CSU have been shown to have a high damage threshold and low absorption. They have not been optimized for reduced surface roughness. Both surface quality and scattering of dual ion beam sputtered thin films depend on the growth conditions and substrate quality, so a study of growth parameters and substrate choice is conducted. The growth parameters selected in this work are beam voltage of the main ion source and sample thickness. Samples grown on standard optically polished substrates are compared to samples grown on two types of super-polished substrates. A multilayer coating is also examined to characterize how scatter loss scales with the number of layers. A device is built to measure scatter loss at 1064nm, 633nm and 405nm and an in depth analysis is conducted of the surfaces using atomic force microscopy and white light interferometry. The films scatter loss at 1064nm are shown to be sensitive to substrate choice, film thickness and main beam voltage. Scatter loss at 1064nm generally decreases when beam voltage is reduced. Scatter loss at lower wavelengths decreases much more significantly. Smoother substrates show improved scatter performance, but it is again much more noticeable at lower wavelengths. Thicker samples show increased scatter, especially at shorter wavelength. Surface scans are benchmarked using a variety of techniques, but power spectral density analysis is shown to be the best predictor of scatter loss for most samples. The best growth conditions and a super polished substrate yield a scatter loss of 6.7ppm for a single layer and 12.3ppm for an output coupler which is comparable to commercially available output couplers.Item Open Access Towards understanding the processes that govern variability in the Southern Hemisphere(Colorado State University. Libraries, 2013) Woodworth, Jonathan D., author; Thompson, David, advisor; Birner, Thomas, committee member; Yalin, Azer, committee memberThe climate at extratropical latitudes is strongly a result of the behavior of the zonal mean zonal wind and its inherent variability. This variability is dominated largely by the north-south fluctuation of the midlatitude jet and is identified in the Southern Hemisphere as the Southern Annular Mode (SAM). Recent observations have shown a tendency of the jet to move poleward due to, in part, the forcing associated with stratospheric cooling due to ozone loss and the tropical tropospheric warming from increasing greenhouse gases. Two dominant processes drive variability in the midlatitude jet: anomalies in the eddy momentum flux (EMF) and the eddy heat flux (EHF). In an attempt to link these processes, this study aims to diagnose a relationship in the observational data via two aspects: 1) To assess the extent to which feedbacks between the EMF and EHF give rise to the annular modes; and 2) To understand, in the context of the atmospheric energy cycle, the dominant patterns of variability of the EMF and EHF fields. Preliminary results reveal that the variability observed in the extratropical flow may exhibit a slight feedback between these processes. Additionally, it has been found that this variability may be viewed in the context of two distinct structures: (i) those that owe their existence to conversions between zonal-mean and eddy kinetic energy and (ii) those that owe their existence to conversions between zonal-mean and eddy potential energy. Past studies have largely focused on the former's impact on the extratropical circulation. However, not much emphasis has been placed on the latter, despite arguably playing an equally important role in driving the variability.