Physics Commons^™

Beta-Delayed Neutron Data And Models For Scale, Kemper Dyar Talley

Doctoral Dissertations

Recent advancements in experimental and theoretical nuclear physics have yielded new data and models that more accurately describe the decay of fission products compared to historical data currently used for many applications. This work examines the effect of the adopting the Effective Density Model theory for beta-delayed neutron emission probability on calculations of delayed-neutron production and fission product nuclide concentrations after fission bursts as well as the total delayed neutron fraction in comparison with the Keepin 6-group model. We use ORIGEN within the SCALE code package for these calculations. We show quantitative changes to the isotopic concentrations for fallout nuclides …

Large Scale Brownian Dynamics Simulation Of Dilute And Semidilute Polymeric Solutions, Amir Saadat

Doctoral Dissertations

Excluded Volume (EV) and Hydrodynamic Interactions (HI) play a central role in static and dynamic properties of macromolecules in solution under equilibrium and nonequilibrium settings. The computational cost of incorporating HI in mesoscale Brownian dynamics (BD) simulations, particularly in the semidilute regime has motivated significant research aimed at development of high-fidelity and efficient techniques.

In this study, I have developed several algorithms for the mesoscale bead-spring representation of a macromolecular solution in dilute and semidilute regimes. The Krylov subspace method enables fast calculation of single chain dynamics with simulation time scaling of O(N_b²) [order N …

Optical Spectroscopy And The Contruction Of An Optimal Wannier Basis With Application To The Development Of Ab Initio Models, Robert Gerard Van Wesep

Doctoral Dissertations

Understanding the role of local orbital degrees of freedom in the behavior of solid state systems has long been understood as a key to unraveling the mysteries presented by complex transition metal compounds. A general approach to the many-body problem is density functional theory (DFT) and its time-dependent extension (TDDFT), which provide a realistic representation of the material-dependent symmetry and chemistry of a compound. Calculation of quantities in (TD)DFT are most often performed using the basis of Bloch states, which is not natural for investigating local degrees of freedom. The Wannier basis provides localized orbitals that retain all of the …

Chasing New Physics: From Electroweak Baryogenesis To Dark Matter, Huaike Guo

Doctoral Dissertations

The origin of the baryon asymmetry in the universe and the nature of the dark matter remain mysteries and addressing these cosmological puzzles requires physics beyond the standard model. Electroweak baryogenesis remains a highly testable framework for explaining the baryon asymmetry and is employed in this work to study the capability of baryon generation for beyond standard model physics models and to explore new physics discovery potential in high energy and precision frontier. Weakly interacting massive particles as cold dark matter are also studied in this work featuring loop induced direct detection signals and novel nuclear responses within the recently …

Study Of Charge Transport Mechanism In Microbial Nanowires, Ramesh Adhikari

Doctoral Dissertations

Conductivity of an individual proteinaceous filaments, called pili or microbial nanowires, produced by wild type Geobacter sulfurreducens was measured using a low-noise electrical transport technique. It was shown that the conductivity is diminished if aromatic amino acid residues are removed from the pili. It was demonstrated that the conductivity of G. sulfurreducens pili is similar to that of synthetic organic polymers and is related to the respiration rate of the bacteria. Conductivity measurements were performed on microbial nanowires produced by other species of Geobacter with a different aromatic amino acid distribution along the wire. Also, measurements on a mutated pili …

A Period Examination Through Contemporary Energy Analysis Of Kevin Roche’S Fine Arts Center At University Of Massachusetts-Amherst, L Carl Fiocchi Jr

Doctoral Dissertations

Studies of buildings belonging to a subset of Modernist architecture, Brutalism, have included discussions pertaining to social and architectural history, critical reception, tectonic form and geometry inspirations, material property selections, period technology limitations, and migration of public perceptions. Evaluations of Brutalist buildings’ energy related performances have been restricted to anecdotal observations with particular focus on the building type’s poor thermal performance, a result of the preferred construction method, i.e. monolithic reinforced concrete used as structure, interior finish and exterior finish. A valid criticism, but one that served to dismiss discussion that the possibility of other positive design strategies limiting energy …

X-Ray Characterization Of Mesophases And Phase Transitions Of Dna Analogues In Solutions, Mustafa Selcuk Yasar

Doctoral Dissertations

We think of DNA as double-stranded helices (duplex), but the polymer exists in many conformations. Several triplex and quadruplex DNA structures can be formed in laboratory settings and exist in nature. This thesis first provides a brief description of the nature of the order in arrays of duplex DNA under biologically relevant molecular crowding conditions. Then we compare the duplex DNA mesophases with the corresponding liquid crystalline phase behavior of the triplex and quadruplex DNA analogues. In particular, we focus on G-quadruplexes. Observed in the folds of guanine-rich oligonucleotides, G-quadruplex structures are based on G-quartets formed by hydrogen bonding and …

Evaporation Induced Self-Assembly And Characterization Of Nanoparticulate Films: A New Route To Bulk Heterojunctions, Yipeng Yang

Doctoral Dissertations

Polymer-based semiconducting materials are promising candidates for large-scale, low-cost photovoltaic devices. To date, the efficiency of these devices has been low in part because of the challenge of optimizing molecular packing while also obtaining a bicontinuous structure with a characteristic length comparable to the exciton diffusion length of 10 to 20 nm. In this dissertation we developed an innovative evaporation-induced nanoparticle self-assembly technique, which could be an effective approach to fabricate uniform, densely packed, smooth thin films with cm-scale area from home-made P3HT nanoparticles. Unlike the previous reports of nanoparticle-based film formation, we use a mixture of two solvents so …

A Quantitative Measurement Of Structural Changes Of Rna Kissing Complexes Using Fluorescence Resonance Energy Transfer, Sheema Rahmanseresht

Doctoral Dissertations

Many RNA interactions in cells occur in the form of loop-loop interactions, also known as a "kissing complex". In the bacterial and viral systems discussed here, there are transiently bound proteins involved that modulate the function of kissing complex. These proteins either stabilize the kissing complex or facilitate its conversion to extended duplex. I studied R1inv-R2inv kissing complex (KC), derivatived from RNAI-RNAII complex of E.Coli. Rop protein is known to stabilize the bent R1inv-R2inv KC against dissociation. The goal was to study structural change of this kissing complex after binding of the stabilizing Rop protein. In this work for …

Search For Long-Lived, Weakly Interacting Particles That Decay To Displaced Hadronic Jets In Proton-Proton Collisions At √S = 8 Tev With The Atlas Detector, Preema R. Pais

Doctoral Dissertations

Many new physics models predict the existence of neutral, weakly interacting, long-lived particles that can decay within the detector volume, producing a distinctive experimental signature. A search is performed for a pair of such particles, using proton-proton collision data at √s = 8 TeV collected by the ATLAS detector in 2012, corresponding to a total integrated luminosity of 20.3 fb^-1. Novel techniques are developed for the reconstruction of displaced decays to hadronic jets in the inner tracking detector and muon spectrometer. No significant deviation is found from the number of background events expected from Standard Model processes. The …

Prospects For Infrared Quantum Gravity: From Cosmology To Black Holes, Basem K. Mahmoud El-Menoufi

Doctoral Dissertations

Although perturbatively non-renormalizable, general relativity is a perfectly valid quantum theory at low energies. Treated as an effective field theory one is able to make genuine quantum predictions by applying the conventional rules of quantum field theory. The low energy degrees of freedom and couplings of quantum gravity are fully dictated by the symmetries of general relativity. To realize the full EFT treatment one has to supplement the theory with experimental input necessary to fix the Wilson coefficients of the most general Lagrangian. In spite of the fact that this is not feasible, one can still extract the leading quantum …

Kinetics And Dynamics Of Electrophoretic Translocation Of Polyelectrolytes Through Nanopores, Harshwardhan Katkar

Doctoral Dissertations

The idea of sequencing a DNA based on single-file translocation of the DNA through nanopores under the action of an electric field has received much attention over the past two decades due to the societal need for low cost and high-throughput sequencing. However, due to the high speed of translocation, interrogating individual bases with an acceptable signal to noise ratio as they traverse the pore has been a major problem. Experimental facts on this phenomenon are rich and the associated phenomenology is yet to be fully understood. This thesis focuses on understanding the underlying principles of polymer translocation, with an …

Polymer And Small Molecule Designs For Anion Conducting Membranes: Connected Ion-Channel Morphologies And Highly Alkaline Stable Ammonium Cations, Sedef P. Ertem

Doctoral Dissertations

Fuel cells are one of the oldest sustainable energy generation devices, converting chemical energy into electrical energy via reverse-electrolysis reactions. With the rapid development of polymer science, solid polymer electrolyte (SPE) membranes replaced the conventional liquid ion transport media, rendering low-temperature fuel cells more accessible for applications in portable electronics and transportation. However, SPE fuel cells are still far from commercialization due to high operation cost, and insufficient lifetime and performance limitations. Anion exchange membrane fuel cells (AEMFCs) are inexpensive alternatives to current proton exchange membrane fuel cell (PEMFC) technology, which relies on utilizing expensive noble-metal catalysts and perfluorinated SPE …

The Effect Of Attractive Polymer-Nanoparticle Interactions On The Local Segmental Dynamics Of Polymer Nanocomposites, Adam Prillaman Holt

Doctoral Dissertations

Considerable progress has been made in understanding the miscibility and morphology of polymer nanocomposites (PNCs). However, to date, there is little understood concerning the modification of segmental mobility at the polymer-nanoparticle interface, which due to prevalence of interfaces in PNCs, will predominately control the viscoelastic and mechanical properties of these materials.

In this dissertation, static and dynamic experimental techniques are combined to identify the specific parameters controlling the modification of segmental dynamics at the polymer-nanoparticle interface in the model system of poly(2-vinyl pyridine)/silica nanocomposites. In general, the experimental results clearly demonstrate that the segmental dynamics at the polymer-nanoparticle interface are …

A Generalized Method For Fissile Material Characterization Using Short-Lived Fission Product Gamma Spectroscopy, Justin Richard Knowles

Doctoral Dissertations

Characterizing the fissile content of nuclear materials is of particular interest to the safeguards and nuclear forensics communities. Short-lived fission product gamma spectroscopy offers a significant reduction in analysis time and detection limits when compared to traditional non-destructive assay measurements. Through this work, a fully generalizable method that can be applied to variations in fissile compositions and neutron spectra was developed for the modeling and measurement of short-lived fission product gamma-rays. This method uses a 238-group neutron flux that was characterized for two pneumatic tube positions in the High Flux Isotope Reactor using flux monitor irradiations. This flux spectrum was …

Characterizing Local Order And Physical Properties Of Rare Earth Complex Oxides, Thomas Jacob Shamblin

Doctoral Dissertations

With more than 500 compositions, materials possessing the pyrochlore structure have a myriad of technological applications and physical phenomena. Three of the most noteworthy properties are the structure’s ability to resist amorphization making it a possible host matrix for spent nuclear fuel, its exotic magnetic properties arising from geometric frustration, and fast ionic conductivity for solid-oxide fuel cell applications. This work focuses on these three aspects of the pyrochlore’s many potential uses. Structural characterization revealed that pyrochlore-type oxides have a tendency to disorder from a high symmetry cubic structure to a lower symmetry orthorhombic arrangement in response to a variety …

Spectroscopic Imaging Of Aluminum Containing Plasma, David Michael Surmick

Doctoral Dissertations

This dissertation aims to characterize laser-induced plasma from a physics point of view as warm, dense matter. Use of nominal nanosecond pulsed laser radiation initiates a plasma with electron temperatures of the order of 10 electron volts and electron densities of the order of air species densities at standard ambient temperature and pressure. For laser ablation and/or optical breakdown at or near a solid surface, the electron density can amount to be 1000 times greater. Spectroscopic investigations of the plasma emissions provide a method by which the electron density, temperature, and shockwave expansion may be determined. Of particular interest are …

Actinium-225 Production Via Proton Irradiation Of Thorium-232, Justin Reed Griswold

Doctoral Dissertations

High energy proton spallation reactions on natural thorium metal targets have been utilized to produce multi mCi [milliCurie] quantities of Actinium-225. Theoretical cross sections for actinium and thorium isotopes as well as for a select number of the fission products produced in these reactions were generated by the Monte Carlo radiation transport code PHITS to simulate the experimental data obtained from sixteen irradiations of thorium metal targets with 25-210 µA [microampere] proton beams ranging in energies from 77 to 192 MeV. Irradiations were conducted at Brookhaven National Laboratory (BNL) and Los Alamos National Laboratory (LANL), while target dissolution and processing …

Morphological And Material Effects In Van Der Waals Interactions, Jaime C. Hopkins

Doctoral Dissertations

Van der Waals (vdW) interactions influence a variety of mesoscale phenomena, such as surface adhesion, friction, and colloid stability, and play increasingly important roles as science seeks to design systems on increasingly smaller length scales. Using the full Lifshitz continuum formulation, this thesis investigates the effects of system materials, shapes, and configurations and presents open-source software to accurately calculate vdW interactions. In the Lifshitz formulation, the microscopic composition of a material is represented by its bulk dielectric response. Small changes in a dielectric response can result in substantial variations in the strength of vdW interactions. However, the relationship between these …

Hadron Physics In Tests Of Fundamental Symmetries, Chien Yeah Seng

Doctoral Dissertations

Low energy precision tests of fundamental symmetries provide excellent probes for the Beyond Standard Model Physics. Theoretical interpretations of these experiments often involve the application of non-perturbative Quantum Chromodynamics in the study of hadronic matrix elements that may either serve as signals of new physics or Standard Model backgrounds. In this work I present a series of studies on different hadronic matrix elements using various low-energy effective approaches to Quantum Chromodynamics, and discuss the impact of these studies on our knowledge of Standard Model and Beyond Standard Model physics.

Synthesis And Characterization Of Polymeric Anion Exchange Membranes, Wenxu Zhang

Doctoral Dissertations

As alkaline anion exchange membrane fuel cells (AAEMFC) are regarded as promising and important energy devices, the development of high performance anion exchange membranes are in urgent need, as well as fundamental investigation on the structure-property relationship, which are the motivation of this dissertation. Three different polymer systems are presented and focused on polymer synthesis, material morphology, and ion transport phenomena. Crosslinked membranes are promising as practical materials, however, the understanding and further improvement of its performance is hindered by the lack of an ordered morphology or well-defined chemical structure. In Chapter 2, a series of crosslinked membranes were design …

Experimental Investigation And Numerical Simulation Of A Copper Micro-Channel Heat Exchanger With Hfe-7200 Working Fluid, Eric Borquist

Doctoral Dissertations

Ever increasing cost and consumption of global energy resources has inspired the development of energy harvesting techniques which increase system efficiency, sustainability, and environmental impact by using waste energy otherwise lost to the surroundings. As part of a larger effort to produce a multi-energy source prototype, this study focused on the fabrication and testing of a waste heat recovery micro-channel heat exchanger. Reducing cost and facility requirements were a priority for potential industry and commercial adoption of such energy harvesting devices. During development of the micro-channel heat exchanger, a new fabrication process using mature technologies was created that reduced cost, …

Toward A Precision Measurement Of The Theta_13 Mixing Angle With The Double Chooz Detectors, Ben Thomas Rybolt

Doctoral Dissertations

Neutrinos are the most numerous and least understood particle in the universe. In the last few decades numerous experiments have been devoted to discovering their properties. The Double Chooz experiment was designed to make a precise measurement of θ₁₃ [theta 13], the neutrino mixing parameter which describes flavor oscillations governing short baselines. To accomplish this measurement, two identical neutrino detectors have been deployed at a near and far baseline outside two commercial nuclear reactors. The neutrino flux and spectrum at the near and far detector sites will determine the disappearance of anti-neutrinos created inside the reactors.

I have contributed …

Symbiotic Plasmonic Nanomaterials: Synthesis And Properties, Abhinav Malasi

Doctoral Dissertations

Metal particles of the dimensions of the order of 1 to 100's of nanometers show unique properties that are not clearly evident in their bulk state. These nanoparticles are highly reactive and sensitive to the changes in the vicinity of the particle surface and hence find applications in the field of sensing of chemical and biological agents, catalysis, energy harvesting, data storage and many more. By synthesizing bimetallic nanoparticles, a single nanoparticle can show multifunctional characteristics. The focus of this thesis is to detail the synthesis and understand the properties of bimetallic nanomaterial systems that show interesting optical, chemical, and …

Biophysical Studies Of Cell Division Protein Localization Mechanisms In Escherichia Coli, Matthew Wayne Bailey

Doctoral Dissertations

How nanometer-scale proteins position accurately within micron-scale bacteria has intrigued both biologists and physicists alike. A critical process requiring precise protein localization is cell division. In most bacteria, cell division starts with the self-assembly of the FtsZ proteins into filaments that form a ring-like structure encircling the cell at its middle, the Z-ring. The Z-ring is a scaffold for additional proteins that synthesize the lateral cell wall which separates the two daughter cells. If division planes are misplaced relative to bacterial chromosomes, also called nucleoids, daughter cells with incomplete genetic material can be produced. In Escherichia coli, research carried out …

Pulsed-Laser Induced Dewetting Of Metallic Nanostructures, Christopher Aidan Hartnett

Doctoral Dissertations

This dissertation explores the fluid dynamics of nano and microscale liquid metal filaments, with an emphasis on experimentally investigating the influences and causes of filament breakup and metallic nanostructure formation. Understanding and manipulating the liquid state properties of materials, especially metals, have the potential to advance the development of future technology, particularly nanoscale technology. The combination of top-down nanofabrication techniques with bottom-up, intrinsic self-assembly mechanisms are a powerful fusion, because it permits new and unusual nanostructures to be created, whilst revealing interesting nanoscale physics.

In fluid dynamics, wetting and dewetting is the spontaneous natural process that occurs when a liquid …

Fundamental Physics With Cold Neutron Beams, Kyle Brandon Grammer

Doctoral Dissertations

The neutron exhibits rich physics both as a tool for studying materials, particle and nuclear physics, as well as the object of experimental study. The neutron lifetime is an important input to Big Bang Nucleosynthesis models and is currently known only to approximately 0.3\% with the most precise measurements from two different experimental techniques in disagreement by more than 3$\sigma$ [sigma]. Parity violation has been the subject of study since its discovery in 1957. Parity violation experiments provide access to studying the hadronic weak interaction, which is otherwise suppressed by several orders of magnitude below that of the strong interaction. …

Spin Flipper, Neutron Polarimetry, And Simulation, For The N3he Experiment, Christopher Bradshaw Hayes

Doctoral Dissertations

The n3He experiment constructed on FnPB [Fundamental neutron Physics Beamline-13] probes the PV [parity violating] nuclear force by measuring the statistical distribution of decay protons which result from the interaction of helium-3 nuclei with a beam of cold neutrons. Pulses of neutrons at 60 Hz are generated by the SNS [Spallation Neutron Source] from a 1 GeV proton beam colliding with a liquid Mercury target. Spalled neutrons are then focused into an intense cold neutron beam thru the use of a liquid hydrogen moderator and a neutron guide making the beam an effective tool as a low energy probe of …

Investigation Of Langmuir Probes In Non-Maxwellian Plasma Using Particle-In-Cell (Pic) Modeling, Densu Aktas Lister

Doctoral Dissertations

This dissertation explores the development of a capability for simulating the plasma dynamics of Langmuir probes (LP) in complex plasmas where the velocity distributions are non-equilibrium and the electron energy spectrum is non-Maxwellian with respect to laboratory and space experiments. The results of this investigation are interpreted to give recommendations for design and use of LPs. This work is conducted using computational techniques to create the exact plasma conditions of the experimental testing environments. The investigations address the following topics:

• development of a technique to model non-Maxwellian physics,
• modification of a baseline-technique and optimization of it for this application,
• creation …

Electromagnetic Properties Of Metal-Dielectric Media And Their Applications, Shravan Rakesh Animilli

Doctoral Dissertations

The main objective of this dissertation is to investigate nano-structured random composite materials, which exhibit anomalous phenomena, such as the extraordinary enhancements of linear and non-linear optical processes due to excitation of collective electronic states, surface plasmons (SP). The main goal is to develop a time and memory efficient novel numerical method to study the properties of these random media in three dimensions (3D) by utilization of multi core processing and packages such as MPI for parallel execution. The developed numerical studies are then utilized to provide a comprehensive characterization and optimization of a surface plasmon enhanced solar cell (SPESC) …