Band Theory and Beyond: Applications of Quantum Algorithms for Quantum Chemistry (open access)

Band Theory and Beyond: Applications of Quantum Algorithms for Quantum Chemistry

In the past two decades, myriad algorithms to elucidate the characteristics and dynamics of molecular systems have been developed for quantum computers. In this dissertation, we explore how these algorithms can be adapted to other fields, both to closely related subjects such as materials science, and more surprising subjects such as information theory. Special emphasis is placed on the Variational Quantum Eigensolver algorithm adapted to solve band structures of a periodic system; three distinct implementations are developed, each with its own advantages and disadvantages. We also see how unitary quantum circuits designed to model individual electron excitations within a molecule can be modified to prepare a quantum states strictly orthogonal to a space of known states, an important component to solve problems in thermodynamics and spectroscopy. Finally, we see how the core behavior in several quantum algorithms originally developed for quantum chemistry can be adapted to implement compressive sensing, a protocol in information theory for extrapolating large amounts of information from relatively few measurements. This body of work demonstrates that quantum algorithms developed to study molecules have immense interdisciplinary uses in fields as varied as materials science and information theory.
Date: May 2022
Creator: Sherbert, Kyle Matthew
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Classical Simulations of the Drift of Magnetobound States of Positronium (open access)

Classical Simulations of the Drift of Magnetobound States of Positronium

The production and control of antihydrogen at very low temperatures provided a key tool to test the validity for the antimaterial of the fundamental principles of the interactions of nature such as the weak principle of equivalence (WEP), and CPT symmetry (Charge, Parity, and Time reversal). The work presented in this dissertation studies the collisions of electrons and positrons in strong magnetic fields that generate magnetobound positronium (positron-electron system temporarily bound due to the presence of a magnetic field) and its possible role in the generation of antihydrogen.
Date: August 2021
Creator: Aguirre Farro, Franz
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Computational Techniques for Accelerated Materials Discovery (open access)

Computational Techniques for Accelerated Materials Discovery

Increasing ubiquity of computational resources has enabled simulation of complex electronic systems and modern materials. The PAOFLOW software package is a tool designed to construct and analyze tight binding Hamiltonians from the solutions of DFT calculations. PAOFLOW leverages localized basis sets to greatly reduce computational costs of post-processing QE simulation results, enabling efficient determination of properties such as electronic density, band structures in the presence of electric or magnetic fields, magnetic or spin circular dichroism, spin-texture, Fermi surfaces, spin or anomalous Hall conductivity (SHC or AHC), electronic transport, and more. PAOFLOW's broad functionality is detailed in this work, and several independent studies where PAOFLOW's capabilities directly enabled research on promising candidates for ferroelectric and spintronic based technologies are described. Today, Quantum computers are at the forefront of computational information science. Materials scientists and quantum chemists can use quantum computers to simulate interacting systems of fermions, without having to perform the iterative methods of classical computing. This dissertation also describes a study where the band structure for silicon is simulated for the first time on quantum hardware and broadens this concept for simulating band structures of generic crystalline structures on quantum machines.
Date: December 2021
Creator: Cerasoli, Franklin
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Deep Minima and Vortices for Positronium Formation in Positron-Hydrogen and Positron-Helium Collisions (open access)

Deep Minima and Vortices for Positronium Formation in Positron-Hydrogen and Positron-Helium Collisions

This dissertation work is a study of positronium formation for positron-hydrogen and positron-helium collisions in the Ore gap (the energy region between the threshold for ground-state positronium formation and the first excitation level of the target atom) using variational K-matrices. We have fitted the K-matrices using multichannel effective range theories and using polynomials. Using the variational K-matrices and their fits, we have located zeros in the positronium-formation scattering amplitude and corresponding deep minima in the positronium-formation differential cross section. The zeros are related to the vortices in the extended velocity field associated with the positronium-formation scattering amplitude. For positron-hydrogen collisions, we have found two zeros in the positronium-formation scattering amplitude, and corresponding deep minima in the positronium-formation differential cross section, while we have obtained a zero in the positronium-formation scattering amplitude for positron-helium collisions. We have connected the zeros in the positronium-formation scattering amplitude to vortices in the extended velocity fields. Our work shows that vortices can occur for charge exchange in atomic collisions.
Date: May 2021
Creator: Alrowaily, Albandari Wanes
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Defect Modulated Properties of Molybdenum Disulfide Monolayer Films (open access)

Defect Modulated Properties of Molybdenum Disulfide Monolayer Films

In this dissertation work, the study focuses on large areal growth of MoS2 monolayers and a study of the structural, optical and electrical properties of such monolayers before and after transfer using a polymer-lift off technique. This work will discuss the issue of contact resistance and the effect of defects (both intrinsic and extrinsic) on the overall quality of the monolayer films. The significance of this dissertation work is that a reproducible strategy for monolayer MoS2 film growth and quantification of areal coverage as well as the detrimental effects of processing on device performance is presented.
Date: May 2022
Creator: Jiang, Yan
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Degradation Mechanisms and Dynamics of Silicon Telluride: A Guide to the Effective Fabrication and Characterization of Silicon Telluride-Based Devices (open access)

Degradation Mechanisms and Dynamics of Silicon Telluride: A Guide to the Effective Fabrication and Characterization of Silicon Telluride-Based Devices

Silicon telluride (Si2Te3) and many other tellurium containing compounds show emergent Raman peaks located at ~120 cm-1 and ~140 cm-1 as they age. The origin of these two emergent peaks is controversial in the literature and has been attributed to myriad causes such as the intrinsic Raman modes of the telluride materials, surface oxidation, defects, double resonances, and tellurium precipitates. The controversial nature of these peaks has led to the misidentification of highly degraded materials as pristine and to the misinterpretation of changes in Raman spectra. For the first time, quality thin film and bulk crystals of Si2Te3 are grown using a chemical vapor deposition (CVD) process. We then present a comprehensive and multimodal study of various Si2Te3 samples and find that the two emergent Raman peaks originate from tellurium nano-crystallites formed in the degraded surface layers of Si2Te3. The formation of the tellurium nano-crystallites are shown to be a result of a hydrolysis process in which Si2Te3 reacts with atmospheric water vapor. The challenges involved in the fabrication of Si2Te3 based devices are also discussed and ways in which degradation can be either prevented or reversed are demonstrated. Finally, we present preliminary data which shows promising low voltage switching …
Date: December 2023
Creator: Hathaway, Evan Allen
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Developing Ultra-Fast Plasmonic Spiking Neuron via Integrated Photonics

This research provides a proof of concept and background theory for the physics behind the state-of-the-art ultra-fast plasmonic spiking neurons (PSN), which can serve as a primary synaptic device for developing a platform for fast neural computing. Such a plasmonic-powered computing system allows localized AI with ultra-fast operation speed. The designed architecture for a plasmonic spiking neuron (PSN) presented in this thesis is a photonic integrated nanodevice consisting of two electro-optic and optoelectronic active components and works based on their coupling. The electro-optic active structure incorporated a periodic array of seeded quantum nanorods sandwiched between two electrodes and positioned at a near-field distance from the topmost metal layer of a sub-wavelength metal-oxide multilayer metamaterial. Three of the metal layers of the metamaterials form the active optoelectronic component. The device operates based on the coupling of the two active components through optical complex modes supported by the multilayer and switching between two of them. Both action and resting potentials occur through subsequent quantum and extraordinary photonics phenomena. These phenomena include the generation of plasmonic high-k complex modes, switching between the modes by enhanced quantum-confined stark effect, decay of the plasmonic excitations in each metal layer into hot-electrons, and collecting hot-electrons by …
Date: August 2022
Creator: Goudarzi, Abbas, Sr.
Object Type: Thesis or Dissertation
System: The UNT Digital Library
The Electrochemical Etching Process of a Tungsten Wire (open access)

The Electrochemical Etching Process of a Tungsten Wire

This study produced and analyzed shaped tungsten wire tips formed through electrochemical etching. Specifically, the cone length and the radius of curvature of the tip were analyzed. Having the tips move dynamically through an electrolytic solution, such as potassium hydroxide, and tuning the initial starting depth of the tungsten wire along with the dynamic speed of the tungsten wire as it passed throughout the solution allowed various types of tip profiles to be produced. The tip's radius of curvature was able to be reproduced with an accuracy between 88 - 92 %. The method provided would be applicable for the production of various styles of liquid-metal ion source (LMIS) probes and scanning probe microscope (SPM) tips.
Date: August 2021
Creator: Richardson, Aaron Michael
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Extending the Capabilities of Continuum Embeddings in First-Principle Simulations of Materials

In recent years, continuum models of solvation have had exceptional success in materials simulations as well as condensed matter physics. They can easily capture the effects of disordered systems, such as neutral liquids or electrolytes solutions, on material interfaces without the need for expensive statistical sampling. The Environ library (www.quantum-environ.org) implements different continuum models and correction schemes, which is the focus of this presentation. Recently refactored into a stand-alone library, many changes have been introduced in Environ, making it more flexible and computationally efficient. Introduction of a double-cell formalism allows for faster ab initio DFT calculations while reparameterization of soft-sphere continuum model allows for smaller density cutoffs. Furthermore, Environ's periodic boundary conditions correction schemes have been expanded by including the AFC90 library, which allows for faster DFT calculations of partially periodic systems, such as slabs, wires, and isolated molecules. Finally, stand-alone Environ can now provide atomic and molecular descriptors, which can be used to characterize solvated interfaces, e.g. in machine learning applications. The specific details of the implementations are reviewed as well as their efficiency and some choice applications for different calculation setups and systems.
Date: May 2023
Creator: Medrano, Gabriel
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Fabrication of Nano-Channel Templates and a Study of the Electrical and Magnetic Properties of Nanowires Grown in Template Pores

This thesis is a study of the structural, electrical and magnetic properties of indium antimonide (InSb) nanowires (NWs), that were synthesized by a template-assisted ordered growth technique via electrochemical deposition. InSb was chosen for this study because of its intrinsic properties that make it a material of choice for applications in high channel mobility, infrared (IR) sensing, thermoelectrics, and magnetoresistive sensing martials. This work has four main components: (i) Growth in commercially available anodic aluminum oxide (AAO) template, where hole-dominated conduction was observed, following NW growth in a low pH electrolyte. The challenge in using these AAO templates was in covering the back surface of the pores with a metal film. Uncovered pores resulted in electrolyte leakage and non-reproducible results. (ii) Growth in flexible polycarbonate membranes, where the flexibility of the membranes resulted in polycrystalline or high defect density NW growth. (iii) Fabrication of an AAO template, where the barrier layer thinning technique was found to be efficient in removal of the think aluminum oxide barrier that exists at the interface between the template and the aluminum metal. This allows for direct growth of NWs into the template pores without the need for metal evaporation. (iv) Fabrication of a heterostructure …
Date: May 2020
Creator: Singh, Abhay Pratap
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Information and Self-Organization in Complex Networks (open access)

Information and Self-Organization in Complex Networks

Networks that self-organize in response to information are one of the most central studies in complex systems theory. A new time series analysis tool for studying self-organizing systems is developed and demonstrated. This method is applied to interacting complex swarms to explore the connection between information transport and group size, providing evidence for Dunbar's numbers having a foundation in network dynamics. A complex network model of information spread is developed. This network infodemic model uses reinforcement learning to simulate connection and opinion adaptation resulting from interaction between units. The model is applied to study polarized populations and echo chamber formation, exploring strategies for network resilience and weakening. The model is straightforward to extend to multilayer networks and networks generated from real world data. By unifying explanation and prediction, the network infodemic model offers a timely step toward understanding global collective behavior.
Date: December 2021
Creator: Culbreth, Garland
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Investigating Accretion Mechanisms and Host Galaxy Environments of z~4 Quasars

Observations of quasars at the highest accessible redshifts have revealed supermassive black holes (SMBHs) with masses much too massive to be accounted for by the growth mechanisms observed in the local universe. Masses up to 10 10 M ⊙ up to z~7 seem to suggest some type of secular evolution or external influence to feed the earliest SMBHs at extremely high rates. Observations at such redshifts come at expensive technical cost and require significant dedicated space-telescope observing time. However, in the z~4 regime, SMBHs are still relatively young, exhibit extreme growth rates, and are economically accessible for both frequent shallow snapshots as well as deep observations. In this dissertation, the accretion mechanisms of z~4 quasars and the structure of their host galaxies and nearby companions are investigated to search for evolution over cosmic time as well as outside influence on star formation rates (SFRs) and SMBH growth. Building the longest available X-ray light curves of four representative radio-quiet quasars, X-ray variability is evaluated at timescales from days to years in the rest frame, and robust simulations allow both qualitative and quantitate measurements of variability to compare with samples at lower redshifts. At all timescales, X-ray variability is consistent with or …
Date: December 2022
Creator: Thomas, Marcus
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Investigation of Room Temperature Soft Ferromagnetism in Indium Phosphide Substrate Synthesized via Low Energy Nickel Ion Implantation

In this work, we have utilized an ion beam process known as gettering to migrate implanted Ni ions much deeper into the bulk substrate than their initial projected end of the range. The projected mean depth is known as Rp. The gettering effect is the most crucial part of the fabrication and we have found that for an H fluence of 3x 1016 cm-2 there is a threshold fluence of approximately 7.5 x 1015 cm-2 that cannot be surpassed if the gettering process is to be completed along with the substrate recovered to the high crystalline quality. This hard threshold is due to the gettering process relaxation induced mechanism that is responsible for migrating the Ni to the Rp/2 location while the H is vacating during the thermal annealing process. If the total number of vacancies produced by the H dissociation is not substantially larger than the total number of implanted Ni atoms the Ni will migrate to the Rp location of the Ni implantation at the amorphous and crystalline interface and toward the surface. When the gettering condition is not met the resulting magnetic responses vary from an exceptionally weak ferromagnetic response to not exhibiting a magnetic response. Additionally, …
Date: May 2021
Creator: Jones, Daniel C.
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Investigation of Specialized Laser and Optical Techniques to Improve Precision Atomic Spectroscopy of Helium (open access)

Investigation of Specialized Laser and Optical Techniques to Improve Precision Atomic Spectroscopy of Helium

The aim of this thesis is to develop both Yb and Tm fiber laser sources with all fiber cavities. Both wavelength ranges provide useful laser sources for optical pumping of helium. The goal is to develop Tm laser sources operating at 2058 nm to optically quench 3He (2058.63 nm) and 4He (2058.69 nm) singlets (21S0). We also have developed Yb laser sources at 1083 nm to optical pump the triplet states of helium and laser cool an atomic beam of helium.
Date: May 2020
Creator: Currey, Ronnie
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Ionized Molecular Hydrogen Confinement Using Electron Space-Charge: A Plasma Trap (open access)

Ionized Molecular Hydrogen Confinement Using Electron Space-Charge: A Plasma Trap

An ion trap has been constructed that creates a potential well suitable for confining ions with the space charge of an electron cloud. The trap uses the concept of artificially structured boundaries, regions of overlapping electric and magnetic fields, to confine particles in a relatively field free volume. Measurements are presented from the build-up of ionized molecular hydrogen over time. Molecular hydrogen is introduced into the confinement volume by direct electron bombardment ionization of neutral background H2 leaked into the trap. Detailed analysis of the data is conducted using particle-in-cell simulations of trap operation and rate mechanics analysis. Pressure dependent estimates of ion lifetimes in the trap are on the order of milliseconds. Along with discussion of the trap a full introduction to the particle-in-cell technique is conducted through an original code implementation.
Date: May 2022
Creator: Kiester, Allen Scott
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Low-Energy Electron Irradiation of 2D Graphene and Stability Investigations of 2D MoS2

In this work, we demonstrate the mechanism for etching exfoliated graphene on SiO2 and other technological important substrates (Si, SiC and ITO), using low-energy electron sources. Our mechanism is based on helium ion sputtering and vacancy formation. Helium ions instead of incident electrons cause the defects that oxygen reacts with and etches graphene. We found that etching does not occur on low-resistivity Si and ITO. Etching occurs on higher resistivity Si and SiC, although much less than on SiO2. In addition, we studied the degradation mechanism of MoS2 under ambient conditions using as-grown and preheated mono- and thicker-layered MoS2 films. Thicker-layered MoS2 do not exhibit the growth of dendrites that is characteristic of monolayer degradation. Dendrites are observed to stop at the monolayer-bilayer boundary. Raman and photoluminescence spectra of the aged bilayer and thicker-layered films are comparable to those of as-grown films. We found that greater stability of bilayers and thicker layers supports a previously reported mechanism for monolayer degradation involving Förster resonance energy transfer. As a result, straightforward and scalable 2D materials integration, or air stable heterostructure device fabrication may be easily achieved. Our proposed mechanisms for etching graphene and ambient degradation of MoS2 could catalyze research on realizing …
Date: August 2021
Creator: Femi Oyetoro, John Dideoluwa
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Modeling, Characterization, and Magnetic Behavior of Transition Metal Nanosystems Synthesized in Silicon Using Low Energy Ion Implantation

Magnetic nano-clusters in silicon involving iron and cobalt were synthesized using low energy (50 keV) ion implantation technique and post-implantation thermal annealing. Before the irradiation, multiple ion-solid interaction simulations were carried out to estimate optimal ion energy and fluence for each experiment. For high-fluence low-energy irradiation of heavy ions in a relatively lighter substrate, modeling the ion irradiation process using dynamic code SDTrimSP showed better agreement with the experimental results compared to the widely used static simulation code TRIM. A saturation in concentration (~ 48%) profile of the 50 keV Fe or Co implants in Si was seen at a fluence of ~ 2 × 1017 ions/cm2. Further study showed that for structures with a curved surface, particularly for nanowires, better simulation results could be extracted using a code "Iradina" as the curve geometry of the target surface can be directly defined in the input file. The compositional, structural, and magnetic properties were studied using Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction, atom probe tomography, and vibrating sample magnetometry. Irradiation of high-current (~ 2 μA/cm2) 50 keV Fe ions into Si at a fluence of 2 × 1017 ions/cm2 showed the formation of Fe5Si3 nano structures in the near-surface …
Date: May 2021
Creator: Singh, Satyabrata
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Near-Infrared Spectroscopy of High Redshift Quasars: Bringing Distant Quasars into View (open access)

Near-Infrared Spectroscopy of High Redshift Quasars: Bringing Distant Quasars into View

The Gemini Near Infrared Spectrograph - Distant Quasar Survey (GNIRS-DQS) is the largest uniform, homogeneous survey of its kind, covering 260 quasars at 1.5 ≤ z ≤ 3.5. This unique survey, coupled with data from the Sloan Digital Sky Survey (SDSS), enables new investigations into redshifts, supermassive black hole masses (MBH), and accretion rates at high redshift through spectroscopic coverage of important rest-frame UV-optical emission lines. The importance of this survey is highlighted in the fact that the optical emission lines provide more reliable measurements of these quasar parameters than their UV counterpart. With such a unique sample compiled here, I construct prescriptions to calibrate these quasar parameters derived from rest-frame UV emission lines to those derived from rest-frame optical emission lines. These prescriptions provide important insight into how these parameters depend on redshift and are potentially biased as we look out further into the universe. Additionally, all the work completed with this sample will help shape our understanding of how these quasars and their host galaxies co-evolve over cosmic time.
Date: May 2023
Creator: Dix, Cooper Wilhelm
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Nonreciprocal and Non-Spreading Transmission of Acoustic Beams through Periodic Dissipative Structures (open access)

Nonreciprocal and Non-Spreading Transmission of Acoustic Beams through Periodic Dissipative Structures

Propagation of a Gaussian beam in a layered periodic structure is studied analytically, numerically, and experimentally. It is demonstrated that for a special set of parameters the acoustic beam propagates without diffraction spreading. This propagation is also accompanied by negative refraction of the direction of phase velocity of the Bloch wave. In the study of two-dimensional viscous phononic crystals with asymmetrical solid inclusions, it was discovered that acoustic transmission is nonreciprocal. The effect of nonreciprocity in a static viscous environment is due to broken PT symmetry of the system as a whole. The difference in transmission is caused by the asymmetrical transmission and dissipation. The asymmetrical transmission is caused solely by broken mirror symmetry and could appear even in a lossless system. Asymmetrical dissipation of sound is a time-irreversible phenomenon that arises only if both energy dissipation and broken parity symmetry are present in the system. The numerical results for both types of phononic crystals were verified experimentally. Proposed devices could be exploited as collimation, rectification, and isolation acoustic devices.
Date: May 2022
Creator: Zubov, Yurii
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Ongoing Developments on Continuum Solvation Models

This work explores a continuum representation for diffuse layer models, thereby endowing continuum embedding models the ability to capture electrostatic phenomena in the environment such as the existence of electrolyte ions, and the nature of ionic liquids. It introduces a new field-aware continuum model that adjusts the size of the quantum regime per atom based on the distribution of charge in a system. The model accounts for the asymmetric nature of solvent distribution when applied to cations versus anions; it also overcomes the need to parameterize continuum interface models for different charged systems. The continuum representation of cavitation in water does not account for the tendency for water to form a hydrogen bonding network that is broken due to the formation of cavities. This effect is a major contributor to hydrophobic solvation and is an important precondition to the investigation of solvated proteins with continuum embedding. A new model inspired by machine learning advances is trained on molecular dynamics simulations due to the difficulty of isolating the cavitation energy term in experiment. Thermodynamic integration is used to calculate the energy from a step-like repulsive potential from cavities in TIP4P water, cavities ranging from small organic molecules, to small proteins. Predictions …
Date: May 2022
Creator: Truscott, Matthew Anthony Si Ren
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Optical Control of Coherent Quantum Systems (open access)

Optical Control of Coherent Quantum Systems

Optical control of coherent quantum systems has many methods and applications. In this defense we will discuss the effects of an electric field interacting with molecules with dipole moments. The theoretical study of such molecules will consist of two-level atom and a three-level atom in the λ configuration. The methods that will be discussed are population trapping using both bright and dark starts obtained by both STIRAP and CHIRAP pulses. The application to be discussed is how to create a room temperature maser.
Date: December 2022
Creator: Roy, Colin Dean
Object Type: Thesis or Dissertation
System: The UNT Digital Library

Optical Property Study of 2D Graded Photonic Super-Crystals for Photon Management

In this dissertation, we study the optical property of 2D graded photonic super-crystals (GPSCs) for photon management. We focused primarily on manipulation and control of light by using the newly discovered GPSCs which present great opportunity for electromagnetic wave control in photonic devices. The GPSC has been used to explore the superior capability of improving the light extraction efficiency of OLEDs. The enhancement of extraction efficiency has been explained in term of destructive interference of surface plasmon resonance and out-coupling of surface plasmon through phase matching provided by GPSC and verified by e-field intensity distributions. A large light extraction efficiency up to 75% into glass substrate has been predicted through simulation. We also study the light trapping enhancement in GPSCs. Broadband, wide incident angle, and polarization independent light trapping enhancement is achieved in silicon solar cells patterned with the GPSCs. In addition, novel 2D GPSCs were fabricated using holographic lithography through the interference lithography by two sets of multiple beams arranged in a cone geometry using a spatial light modulator (SLM). Finally, we also report a fabrication of GPSCs with a super-cell size of 12a×12a by using e-beam lithography. Diffraction pattern from GPSCs reveals unique diffraction properties. In an application …
Date: May 2020
Creator: Hassan, Safaa
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Placing High-Redshift Quasars in Perspective: Unifying Distant Quasars with Their Lower Redshift Counterparts through Near-Infrared Spectroscopy (open access)

Placing High-Redshift Quasars in Perspective: Unifying Distant Quasars with Their Lower Redshift Counterparts through Near-Infrared Spectroscopy

I present spectroscopic measurements for 260 sources from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS). Being the largest uniform, homogeneous survey of its kind, it represents a flux-limited sample of Sloan Digital Sky Survey (SDSS) quasars at 1.5 < z < 3.5. A combination of the GNIRS and SDSS spectra covers principal quasar diagnostic features, chiefly the C IV λ1549, Mg II λλ2798, 2803, Hβ λ4861, and [O III] λλ4959, 5007 emission lines, in each source. The spectral inventory is utilized primarily to develop prescriptions for obtaining more accurate and precise redshifts, black hole masses, and accretion rates for all quasars. Additionally, the measurements facilitate an understanding of the dependence of rest-frame ultraviolet–optical spectral properties of quasars on redshift, luminosity, and Eddington ratio, and test whether the physical properties of the quasar central engine evolve over cosmic time.
Date: May 2023
Creator: Matthews, Brandon M.
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Relaxation Time Approximations in PAOFLOW 2.0 (open access)

Relaxation Time Approximations in PAOFLOW 2.0

Electronic transport properties have been used to classify and characterize materials and describe their functionality. Recent surge in computational power has enabled computational modelling and accelerated theoretical studies to complement and accelerate experimental discovery of novel materials. This work looks at methods for theoretical calculations of electronic transport properties and addresses the limitations of a common approximation in the calculation of these properties, namely, the constant relaxation time approximation (CRTA). This work takes a look at the limitations of this approximation and introduces energy and temperature dependent relaxation times. This study is carried out on models and real systems and compared with experiments.
Date: May 2022
Creator: Jayaraj, Anooja
Object Type: Thesis or Dissertation
System: The UNT Digital Library