Graduate Theses & Dissertations

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Heavy Rydberg Photo-dissociation Cross-section Calculations and Experimental Progress Towards Cold Collisions in Lithium
This thesis is divided into two parts, each of which supports constructing and using a lithium magneto-optical trap for cold collision studies: Part I One outgoing channel of interest from cold collisions is the production of ion pairs. We describe an effective method for calculating bound-to-continuum cross-sections for charged binary systems by examining transitions to states above the binding energy that become bound when the system is placed within an infinite spherical well. This approach is verified for ionization of a hydrogen atom, and is then applied to the heavy Rydberg system Li+...I-. Part II A wavemeter previously built in the lab is redesigned for increased reliability and ease of use by replacing the optical hardware with a rocker system, which can be aligned in mere minutes rather than half a day as was previously the case. The new wavemeter has been tested through saturated absorption spectroscopy of lithium. Author Keywords: cross-section, dissociation, lithium, magneto-optical trap, Michelson, wavemeter
Model for the Differential Susceptibility of Strontium Titanate
The appearance of a two-dimensional electron gas (2DEG) in oxide interfaces between strontium titanate (STO) and other materials has become a major area of study. The behaviour of the 2DEG in STO is not well understood in part because the dielectric properties of STO are not well characterized. The differential susceptibility has a major impact on the electric fields within strontium titanate, and therefore to understand the 2DEG a better understanding of the susceptibility is needed. An expression for the soft mode phonon frequency of bulk strontium titanate is derived and used to model the susceptibility as a function of spatially homogeneous electric field, temperature and wavevector. This model is used to discuss the effect of spatially inhomogeneous electric fields and the local vs. nonlocal nature of the susceptibility. The critical exponents and the free energy are determined and discussed. Author Keywords: critical exponents, differential susceptibility, quantum paraelectric, strontium titanate
Frequency-time and polarization considerations in spectral-focusing-based CARS microscopy
Spectral-focusing-based coherent anti-Stokes Raman scattering (SF-CARS) microscopy is a powerful imaging technique that involves temporally and spectrally stretching ultrashort laser pulses and controlling their frequency-time characteristics. However, a broader and more detailed understanding of the frequency-time characteristics of the laser pulses and signals involved, how they are related, and how they influence important aspects such as the spectral resolution is needed to understand the full potential of SF-CARS systems. In this work, I elucidate these relationships and discuss how they can be exploited to optimize SF-CARS microscopy setups. I present a theoretical analysis of the relationships between the spectral resolution, the degree of chirp-matching, and pulse bandwidth in SF-CARS. I find that, despite allowing better ultimate spectral resolution when chirp-matching is attained, the use of the broadest bandwidth pulses can significantly worsen the spectral resolution if the pulses are not chirp-matched. I demonstrate that the bandwidth of the detected anti-Stokes signal is minimized when the pump is twice as chirped as the Stokes, meaning that (perhaps counter-intuitively) a narrow anti-Stokes bandwidth does not imply good spectral resolution. I present approximate expressions that relate the bandwidths of the pump, Stokes, and anti-Stokes pulses to the degree of chirp-matching and outline how these could be used to estimate the amount of glass needed to attain chirp-matching. I develop a spectral-focusing-based polarization-resolved (SFP-CARS) setup, by modifying our existing system, to explore the merits of integrating polarization-dependent detection as an add-on to existing SF-CARS setups. By using the system to study polarization-dependent features in the CARS spectrum of benzonitrile, I assess its capabilities and demonstrate its ability to accurately determine Raman depolarization ratios. Ultimately, the detected anti-Stokes signals are more elliptically polarized than desired, hindering a complete suppression of the non-resonant background. Nevertheless, I find that the SFP-CARS setup is a useful tool for studying polarization-dependent features in the CARS spectra of various samples and is worthy of further investigation. This work clarifies several technical aspects of SF-CARS microscopy and provides researchers with valuable information to consider when working with SF-CARS microscopy systems. Author Keywords: coherent anti-Stokes Raman scattering, nonlinear microscopy, polarization, spectral focusing, spectroscopy
Extraction and Characterization of Hyaluronic Acid and Collagen from Eggshell Membrane Waste
Connecting academia to industry is one important way to advance towards meeting the United Nations (UN) Sustainability Goals (SDGs).1 Sustainability can be applied to all industrial sectors with the SDGs being implemented by 2030.2 This research contributes to the SDGs by investigating a way to remediate an industrial waste stream in the egg-breaking industry. If adopted, this would reduce the amount of eggshell membrane (ESM) waste placed in landfill where it does not decompose properly. The work described in this thesis specifically targets extraction of collagen and hyaluronic acid (HA), two components of the ESM that are of commercial value in the cosmetic, pharmaceutical, and biomedical industries3,4 . Deliverables from this research include economically viable extraction methods, developed based on green chemistry approaches, that can be transferred from lab bench to industrial scale. The extraction development process was guided by the 12 Principles of Green Chemistry5,6,7 and the 12 Principles of Green Engineering.8 HA was most successfully extracted using a sodium acetate solution on ground ESM. Filtrate was collected, exhaustively dialyzed and lyophilized. High molecular weight HA was recovered. Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy and proton nuclear magnetic resonance (NMR) spectroscopy compared extracted material to reference HA identifying successful extraction. Collagen was extracted using acetic acid or pepsin enzyme digestion. Hydrophilic interaction liquid chromatography (HILIC) coupled with mass spectrometry (MS) compared amino acid composition of extracted materials to reference collagen material. FTIR-ATR spectra also supported successful extraction of collagen. This work identifies that HA and collagen can be conveniently extracted from ESM using an economical approach that can be implemented into egg-breaking facilities. This work highlights the benefits of connecting academia to industry to advance green chemical approaches while implementing sustainable practices into existing industry. Author Keywords: collagen, eggshell membrane waste, extraction, green chemistry, hyaluronic acid, sustainability
Phosphoric Acid Chemically Activated Waste Wood
Activated Carbon (AC) is commonly produced by gasification, but there has been increasing interest in chemical activation due to its lower activation temperatures and higher yields. Phosphoric acid, in particular, succeeds in both these areas. Phosphoric acid activated carbon (PAC) can be environmentally sustainable, and economically favourable, when the phosphoric acid used in the activation is recycled. This thesis describes the digestion and activation of waste wood using phosphoric acid, as well as methods used to recover phosphoric acid, functionalize the produced activated carbon with iron salts and then test their efficacy on the adsorption of target analytes, selenite and selenate. In order to achieve an efficient phosphoric acid based chemical activation, further understanding of the activation process is needed. A two-step phosphoric acid activation process with waste wood feed stock was examined. The filtrate washes of the crude product and the surface composition of the produced PAC were characterized using X-ray Photoelectron Spectroscopy (XPS), Fourier Transform-Infrared spectroscopy (FT-IR), Ion Chromatography (IC), and 31P Nuclear Magnetic Resonance (NMR). XPS of the unwashed PAC contained 13.3 atomic percent phosphorous, as phosphoric acid, while the washed sample contained 1.4 atomic percent phosphorous as PO43-, and P2O74-. Using 31P NMR, phosphoric acid was identified as the primary phosphorous species in the acidic 0.1 M HCl washings, with pyrophosphates also appearing in the second 0.1 M NaOH neutralizing wash, and finally a weak signal from phosphates with an alkyl component also appearing in the DI wash. IC showed high concentrations of phosphoric acid in the 0.1 M HCl wash with progressively lower concentrations in both the NaOH and DI washes. Total phosphoric acid recovery was 96.7 % for waste wood activated with 25 % phosphoric acid, which is higher than previous literature findings for phosphoric acid activation. The surface areas of the PAC were in the 1500-1900 m2g-1 range. Both pre and post activation impregnation of iron salts resulted in iron uptake. Pre-activation resulted in only iron(III) speciation while post-activation impregnation of iron(II)chloride did result in iron(II) forming on the PAC surface. The pre-activated impregnated PAC showed little to no adsorption of selenite and selenate. The post-activation impregnated iron(II)chloride removed up to 12.45 ± 0.025 mg selenium per g Iron-PAC. Competitive ions such as sulfate and nitrate had little effect on selenium adsorption. Phosphate concentration did affect the uptake. At 250 ppm approximately 75 % of adsorption capacity of both the selenate and the selenite solutions was lost, although selenium was still preferentially adsorbed. Peak adsorption occurred between a pH of 4 and 11, with a complete loss of adsorption at a pH of 13. Author Keywords: Activated Carbon, doping, Iron, phosphoric acid, selenium
Investigation of Using Phase Change Materials for Thermal Energy Storage in Adiabatic Compressed Air Energy Storage
There is an increasing global need for grid scale electrical energy storage to handle the implementation of intermittent renewable energy sources. Adiabatic compressed air energy storage is an emerging technology with similar performance to pumped hydro except it has the issue of heat loss during the compression stage. Previously, it has been considered to use sensible heat storage materials to store the heat created by compression in a thermal energy storage unit until energy is required, and then transfer the heat back to the air. This research proposes to instead use phase change materials to store the heat of compression, as this will reduce entropy generation and maximize roundtrip exergy efficiency. Different configurations and placements of the phase change materials are considered and exergy analyses are presented. The thermodynamic equations are derived and optimal setup conditions including amount of latent heat and melting temperatures are calculated. Author Keywords: Compressed Air Energy Storage, Energy Storage, Exergy, Phase Change Materials
Correlating density of states features with localization strength in disordered interacting systems
Johri and Bhatt found singular behavior near the band edge in the density of states as well as in the inverse participation ratio of the Anderson model. These singularities mark a transition to an energy range dominated by resonant states. We study the interacting case using an ensemble of two-site Anderson-Hubbard systems. We find the ensemble-averaged density of states and generalized inverse participation ratio have more structure than in the non-interacting case because there are more transitions and in particular the transitions depend on the ground state. Nonetheless, there are regions of sharp decline in the generalized inverse participation ratio associated with specific density of state features. Moreover these features move closer to the Fermi level with the addition of interactions making them more experimentally accessible. Unfortunately resonances unique to interacting systems cannot be specifically identified. Author Keywords: Correlated electrons, Disorder, Localization
silicon sol-gel approach to the development of forensic blood substitutes
The research and development of synthetic blood substitutes is a reported need within the forensic community. This work contributes to the growing body of knowledge in bloodstain pattern analysis by offering a materials science approach to designing, producing and testing synthetic forensic blood substitutes. A key deliverable from this research is the creation of a robust silicon-based material using the solution-gelation technique that has been validated for controlled passive drip and spatter simulation. The work investigates the physical properties (viscosity, surface tension and density) of forensic blood substitute formulations and describes the similarity in the spreading dynamics of the optimized material to whole human blood. It then explores how blood and other fluids behave in impact simulation using high-speed video analysis and supports the use of the optimized material for spatter simulation. Finally, the work highlights the practical value of the material as an educational tool for both basic and advanced bloodstain experimentation and training. Author Keywords: bloodstain pattern analysis, forensic blood substitutes, high-speed video analysis, silicon solution-gelation chemistry, thin-film deposition, training and education
Real-space renormalization group approach to the Anderson model
Many of the most interesting electronic behaviours currently being studied are associated with strong correlations. In addition, many of these materials are disordered either intrinsically or due to doping. Solving interacting systems exactly is extremely computationally expensive, and approximate techniques developed for strongly correlated systems are not easily adapted to include disorder. As a non-interacting disordered model, it makes sense to consider the Anderson model as a first step in developing an approximate method of solution to the interacting and disordered Anderson-Hubbard model. Our renormalization group (RG) approach is modeled on that proposed by Johri and Bhatt [23]. We found an error in their work which we have corrected in our procedure. After testing the execution of the RG, we benchmarked the density of states and inverse participation ratio results against exact diagonalization. Our approach is significantly faster than exact diagonalization and is most accurate in the limit of strong disorder. Author Keywords: disorder, localization, real-space renormalization, strong correlations
Supercritical Water Chemistry
Supercritical water (SCW) exhibits unique properties that differentiates it from its low temperature behaviour. Hydrogen bonding is dramatically reduced, there is no phase boundary between liquid and gaseous states, heat capacity increases, and there is a drastic reduction of the dielectric constant. Efforts are underway for researchers to harness these properties in the applications of power generation and hazardous waste destruction. However, the extreme environment created by the high temperatures, pressures and oxidizing capabilities pose unique challenges in terms of corrosion not present in subcritical water systems. Molecular Dynamics (MD) simulations have been used to obtain mass transport, hydration numbers and the influence on water structure of molecular oxygen, chloride, ammonia and iron (II) cations in corrosion crevices in an iron (II) hydroxide passivation layer. Solvation regimes marking the transitions of solvation based versus charge meditated processes were explored by locating the percolation thresholds of both physically and hydrogen bonded water clusters. A SCW flow through reactor was used to study hydrogen evolution rates over metal oxide surfaces, metal release rates and the kinetics for the oxidation of hydrogen gas by oxygen in SCW. Insights into corrosion phenomena are provided from the MD results as well as the experimental determination of flow reactor water and hydrogen chemistry. Author Keywords: Flow Studies, Molecular Dynamics, Supercritical Water
Role of Dielectric Screening in SrTiO3-Based Interfaces
We build a theoretical model for exploring the electronic properties of the two-dimensional (2D) electron gas that forms at the interface between insulating SrTiO3 (STO) and a number of perovskite materials including LaTiO3, LaAlO3, and GdTiO3. The model treats conduction electrons within a tight-binding approximation, and the dielectric polarization via a Landau-Devonshire free energy that incorporates STO's strongly nonlinear, nonlocal, field-, and temperature-dependent dielectric response. We consider three models for the dielectric polarization at the interface: an ideal-interface model in which the interface has the same permittivity as the bulk, a dielectric dead-layer model in which the interface has permittivity lower that the bulk, and an interfacial-strain model in which the strain effects are included. The ideal-interface model band structure comprises a mix of quantum 2D states that are tightly bound to the interface, and quasi-three-dimensional (3D) states that extend hundreds of unit cells into the STO substrate. We find that there is a substantial shift of electrons away from the interface into the 3D tails as temperature is lowered from 300 K to 10 K. We speculate that the quasi-3D tails form the low- density high-mobility component of the interfacial electron gas that is widely inferred from magnetoresistance measurements. Multiple experiments have observed a sharp Lifshitz transition in the band structure of STO interfaces as a function of applied gate voltage. To understand this transition, we first propose a dielectric dead-layer model. It successfully predicts the Lifshitz transition at a critical charge density close to the measured one, but does not give a complete description for the transition. Second, we use an interfacial-strain model in which we consider the electrostrictive and flexoelectric coupling between the strain and polarization. This coupling generates a thin polarized layer whose direction reverses at a critical density. The transition occurs concomitantly with the polarization reversal. In addition, we find that the model captures the two main features of the transition: the transition from one occupied band to multiple occupied bands, and the abrupt change in the slope of lowest energy band with doping. Author Keywords:
Adoption of a Finite Element Model of Material Deformation Relevant to Studying Corneal Biomechanics
The human cornea is required to exhibit specific material properties to maintain its regular shape under typical intraocular pressures which then allow for its correct optical functionality. In this thesis, the basis of continuum solid mechanics and the finite element method are introduced. We use finite element modelling to simulate the extension of an effective-1d, linear-elastic bar, a cornea-like body governed by Poisson’s equation, and the deformation of a loaded, linear-elastic, cube. Preliminary results for the deformation of a simulated, linear-elastic, cornea have also been achieved using the finite element approach. Author Keywords: continuum solid mechanics, corneal biomechanics, finite element method, intraocular pressure

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Format: 2024/03/28