Physics Commons^™

Physics And Applications Of Exceptional Points, Qi Zhong

Dissertations, Master's Theses and Master's Reports

Exceptional points (EPs) are singularities that arise in non-Hermitian physics. Crossing EPs is believed to be related with phase transitions between parity-time-(PT-)symmetric phase and broken PT phase. Owing to their peculiar topology, EPs can remotely induce observable effects when encircled by closed trajectories in the parameter space. In this dissertation, first of all, we investigate the extreme dynamics of non-Hermitian systems near higher order EPs constructed using the bosonic algebra method. The strong power oscillations for certain initial conditions can occur as a result of the peculiar eigenspace geometry and its dimensionality collapse near these singularities. And in the PT …

Aerosol-Cloud Interactions In Turbulent Clouds: A Combined Cloud Chamber And Theoretical Study, Kamal Kant Chandrakar

Dissertations, Master's Theses and Master's Reports

The influence of aerosol concentration on the cloud droplet size distribution is investigated in a laboratory chamber that enables turbulent cloud formation through moist convection. In chapter 2, moist Rayleigh-Bénard convection with water saturated boundaries is explored using a one-dimensional-turbulence model. This study provides some background about supersaturation statistics in moist convection. Chapters 3 - 7 discuss the experimental and theoretical investigation of aerosol-cloud interactions and cloud droplet size-distributions in turbulent conditions. The experiments are performed in a way so that steady-state microphysics are achieved, with aerosol input balanced by cloud droplet growth and fallout. As aerosol concentration is increased …

Light Propagation Through A Turbulent Cloud: Comparison Of Measured And Computed Extinction, Eduardo Rodriguez-Feo Bermudez

Dissertations, Master's Theses and Master's Reports

Remote sensing techniques used for measurement of atmospheric cloud properties operate under the notion that light extinction caused by scattering and absorption is exponential due to Beer-Lambert law. This is expected to be valid for a uni-form medium with no spatial correlations between particle position. The aim of this research was to show that under turbulent conditions, cloud droplets cannot be interpreted as non-correlated, and in turn will exhibit a lower than exponential light decay from scattering. The research took place at the MTU π-Chamber laboratory. A temperature difference between the floor and ceiling of the chamber was applied to …

Evaporation Of A Sessile Droplet On A Slope, Mitch Timm

Dissertations, Master's Theses and Master's Reports

We theoretically examine the drying of a stationary liquid droplet on an inclined surface. Both analytical and numerical approaches are considered, while assuming that the evaporation results from a purely diffusive transport of the liquid vapor and that the contact line is a pinned circle. For the purposes of our analytical calculations, we suppose that the effect of gravity relative to the surface tension is weak, i.e. the Bond number (Bo) is small. Then, we express the shape of the drop and the vapor concentration field as perturbation expansions in terms of Bo. When the Bond number is zero, the …

Evaluating The Effectiveness Of Current Atmospheric Refraction Models In Predicting Sunrise And Sunset Times, Teresa Wilson

Dissertations, Master's Theses and Master's Reports

The standard value for atmospheric refraction on the horizon of 34', used in all publicly available sunrise and sunset calculators, is found to be inadequate. The assumptions behind atmospheric models that predict this value fail to account for real meteorological conditions. The result is an uncertainty of one to five minutes in sunrise and sunset predictions at mid-latitudes (0° - 55° N/S). A sunrise/set calculator that interchanges the refraction component by varying the refraction model was developed. Two atmospheric refraction models of increasing complexity were tested along with the standard value. The predictions were compared with data sets of observed …

Novel Faraday Rotation Effects Observed In Ultra-Thin Iron Garnet Films, Brandon Blasiola

Dissertations, Master's Theses and Master's Reports

Recent work performed by A. Chakravarty and M. Levy showed experimentally a dramatic increase in the specific Faraday Rotation (FR) of the iron garnet Bi_0.8Lu_0.2Gd₂Fe₅O₁₂. A theoretical model, based purely on classical electrodynamics, attempting to explain this behavior was developed by colleagues in Russia that not only confirmed the asymptotic increase in the specific FR at sub-50nm film thicknesses but also suggested that the specific FR should exhibit significant fluctuations at sub-500 nm film thicknesses. The original data points were widespread with steps of 50 nm or more between data …

Generalizable Modeling Of Charge Transport In Single Electron Transistor Devices: Application To Thermal Sensitivity In Semiconducting Island Systems, Paniz Khanmohammadi Hazaveh

Dissertations, Master's Theses and Master's Reports

Electronic devices, especially MOSFETs, have been dimensionally scaled down to enhance operation of integrated circuits, addressing challenges such as current leakage, fluctuation of intrinsic semiconductor properties, and power dissipation. Reaching dimensions below 20 nm, there are fundamental limitations that are difficult to overcome, driving alternative device paradigms to be sought utilizing the quantum mechanical behavior of electrons. Single electron transistor (SET) devices are examples of a new generation of low-power transistors designed to transport information via single electron tunneling through one or more islands separated by tunnel junctions. Experimentally explored SET devices have shown that there are advantages to using …

High Accuracy Methods And Regularization Techniques For Fluid Flows And Fluid-Fluid Interaction, Mustafa Aggul

Dissertations, Master's Theses and Master's Reports

This dissertation contains several approaches to resolve irregularity issues of CFD problems, including a decoupling of non-linearly coupled fluid-fluid interaction, due to high Reynolds number. New models present not only regularize the linear systems but also produce high accurate solutions both in space and time. To achieve this goal, methods solve a computationally attractive artificial viscosity approximation of the target problem, and then utilize a correction approach to make it high order accurate. This way, they all allow the usage of legacy code | a frequent requirement in the simulation of fluid flows in complex geometries. In addition, they all …

Probing Quantum Transport In Three-Terminal Nanojunctions, Meghnath Jaishi

Dissertations, Master's Theses and Master's Reports

One-dimensional (1D) nanoscale systems—structures with the lateral dimensions ranging from 1 nm to 100 nm — have received significant research interest due to their unique structure-guided properties that promise functionalities far more superior than their bulk counterparts. The quantum confinement effect in 1D nanostructures provides us with a very powerful tool to tune their electrical, magnetic, optical and thermal properties and opens the gateway for their multifunctional usages in next-generation electronics. In particular, carbon nanotubes and semiconductor nanowires are found to offer tremendous opportunities to form the junction devices with controlled electronic and optoelectronic properties crucial to predictable device functions. …

Magnetless And Topological Edge Mode-Based On-Chip Isolators And Spin-Orbit Coupling In Magneto-Optic Media, Dolendra Karki

Dissertations, Master's Theses and Master's Reports

The rapid growth of optical communication networks requires monolithic integration of various optical components such as lasers, modulators, detectors, amplifiers. Optical feedback due to reflected light at the interfaces of several components in a photonic circuit has detrimental effects to the normal operation of laser by increasing noise, forcing laser to oscillate into different lasing modes etc. So optical isolators are crucial components to make complex optical circuits possible by preventing the feedback signal from coupling back to the lasers sources. For this purpose, an optical isolator that can reduce the feedback signal by > 30 dB and at the same …

First-Principles Investigation Of The Interfacial Properties Of Boron Nitride, Kevin Waters

Dissertations, Master's Theses and Master's Reports

The interactions of nanomaterial surfaces with biological compounds, e.g. proteins, DNA, etc., unites the biological regime and nanomaterial world. Hybrid systems of boron-nitride nanotubes (BNNTs) and biological compounds are well-suited for a broad range of applications. First-principles methods are used to characterize the interface of these hybrid systems. Previous work has shown that the sensing capabilities of pristine BNNT are limited by long-ranged interactions. In this study the surfaces of pristine and functionalized BNNTs are investigated. The surfaces of the functionalized BNNTs give new properties to the tubes, which may enhance their sensing capabilities, while retaining their stability and chemical …

The Intrinsic Variability Of The Water Vapor Saturation Ratio Due To Mixing, Jesse Anderson

Dissertations, Master's Theses and Master's Reports

The water vapor concentration plays an important role for many atmospheric processes. The mean concentration is key to understand water vapor's effect on the climate as a greenhouse gas. The fluctuations about the mean are important to understand heat fluxes between Earth's surface and the boundary layer. These fluctuations are linked to turbulence that is present in the boundary layer. Turbulent conditions are simulated in Michigan Tech’s multiphase, turbulent reaction chamber, the π chamber. Measurements for temperature and water vapor concentration were recorded under forced Rayleigh- Bénard convection at several turbulent intensities. These were used to calculate the saturation ratio, …

Gamma/Hadron Separation For The Hawc Observatory, Michael J. Gerhardt

Dissertations, Master's Theses and Master's Reports

The High-Altitude Water Cherenkov (HAWC) Observatory is a gamma-ray observatory sensitive to gamma rays from 100 GeV to 100 TeV with an instantaneous field of view of ~2 sr. It is located on the Sierra Negra plateau in Mexico at an elevation of 4,100 m and began full operation in March 2015. The purpose of the detector is to study relativistic particles that are produced by interstellar and intergalactic objects such as: pulsars, supernova remnants, molecular clouds, black holes and more. To achieve optimal angular resolution, energy reconstruction and cosmic ray background suppression for the extensive air showers detected by …

Quantum Inspired Symmetries In Laser Engineering, Mohammad Hosain Teimourpour

Dissertations, Master's Theses and Master's Reports

In this thesis, quantum inspired symmetries including Parity-Time (PT) symmetry and Supersymmetry (SUSY) have been studied in the context of non-Hermitian engineered laser systems. This thesis starts with a short review of semiconductor lasers theory in second chapter, followed by an introduction to quantum inspired symmetries: PT symmetry and SUSY in optics and photonics in chapter three.

In chapter four, we have studied the robustness and mode selectivity in PT symmetric lasers. We investigate two important aspects of PT symmetric photonic molecule lasers, namely the robustness of their single longitudinal mode operation against instabilities triggered by spectral hole burning effects, …

An Assessment Of The Validity Of The Kinetic Model For Liquid-Vapor Phase Change By Examining Cryogenic Propellants, Kishan Bellur

Dissertations, Master's Theses and Master's Reports

Evaporation is ubiquitous in nature and occurs even in a microgravity space envi- ronment. Long term space missions require storage of cryogenic propellents and an accurate prediction of phase change rates. Kinetic theory has been used to model and predict evaporation rates for over a century but the reported values of accommodation coefficients are highly inconsistent and no accurate data is available for cryogens. The proposed study involves a combined experimental and computational approach to ex- tract the accommodation coefficients. Neutron imaging is used as the visualization technique due to the difference in attenuation between the cryogen and the metallic …

First-Principles Studies Of Group Iv And Group V Related Two Dimensional Materials, Gaoxue Wang

Dissertations, Master's Theses and Master's Reports

Two dimensional (2D) materials have been extensively studied due to their novel properties and technologically important applications. Especially, the discovery of graphene has stimulated an avalanche of investigations to exploit its novel properties for applications at nanoscale. In the post-silicon era, graphene has been widely regarded as the most promising building blocks for the electronic devices. However, its metallic nature together with sensitivity to the environment leads to somewhat limited scope of applications. A finite band gap in a material is known to be essential for the fabrication of devices such as transistors. Such a limitation associated with graphene has …

Investigation Of The Resistance To Demagnetization In Bulk Rare-Earth Magnets Comprised Of Crystallographically-Aligned, Single-Domain Crystallites With Modified Intergranular Phase, Jie Li

Dissertations, Master's Theses and Master's Reports

The research presented in this dissertation investigates whether an increased coercivity of Neodymium-Iron-Boron (Nd2Fe14B) based bulk magnets at elevated temperature (160°C), which is now only obtainable by substituting ~7wt% dysprosium (Dy) for a portion of neodymium (Nd), can be achieved through specific microstructural modifications with decreased Dy concentrations. The approach is to reduce the size of individual crystallographically-aligned grains in the magnet so that each grain can only support a single magnetic domain and to simultaneously dilute the Nd-Fe inter-granular phase present in conventional magnets with a non-Fe-containing, Nd-rich phase (Nd-Cu alloy) in an attempt to partially magnetically isolate the …

Search For Tev Gamma-Ray Sources In The Galactic Plane With The Hawc Observatory, Hao Zhou

Dissertations, Master's Theses and Master's Reports

Cosmic rays, with an energy density of $\sim1\,\text{eV}\,\text{cm}^{-3}$, play an important role in the evolution of our Galaxy. Very high energy (TeV) gamma rays provide unique information about the acceleration sites of Galactic cosmic rays. The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory is an all-sky surveying instrument sensitive to gamma rays from 100\:GeV to 100\:TeV with a 2\,steradian instantaneous field of view and a duty cycle of $>95\%$. The array is located in Sierra Negra, Mexico at an elevation of 4,100\,m and was inaugurated in March 2015. Thanks to its modular design, science operation began in Summer 2013 …

Relativistic Configuration Interaction Calculations Of The Atomic Properties Of Selected Transition Metal Positive Ions; Ni Ii, V Ii And W Ii, Marwa Hefny Abdalmoneam

Dissertations, Master's Theses and Master's Reports

Relativistic Configuration Interaction (RCI) method has been used to investigate atomic properties of the singly ionized transition metals including Nickel (Ni II), Vanadium (V II), and Tungsten (W II). The methodology of RCI computations was also improved. Specifically, the method to shift the energy diagonal matrix of the reference configurations was modified which facilitated including the effects of many electronic configurations that used to be difficult to be included in the energy matrix and speeded-up the final calculations of the bound and continuum energy spectrum. RCI results were obtained for three different cases:

1. Atomic moments and polarizabilities of Ni II; …