Matching Items (33)
Description
An X class solar flare has the potential to remove our satellites from orbit, permanently deactivate our main forms of communication and bring humanity into a technology-free age. By using Geant4, it is possible to simulate several layers of the Earth's atmosphere and send a simulated solar flare and coronal mass ejection. This thesis will show the interaction of photons and protons of various energies with several kilometers of atmosphere.
ContributorsDolghier, Kristian Adrian (Author) / Shovkovy, Igor (Thesis director) / Steinkamp, Brian (Committee member) / Economics Program in CLAS (Contributor) / College of Integrative Sciences and Arts (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
The nucleon resonance spectrum consists of many overlapping excitations. Polarization observables are an important tool for understanding and clarifying these spectra. While there is a large data base of differential cross sections for the process, very few data exist for polarization observables. A program of double polarization experiments has been conducted at Jefferson Lab using a tagged polarized photon beam and a frozen spin polarized target (FROST). The results presented here were taken during the first running period of FROST using the CLAS detector at Jefferson Lab with photon energies ranging from 329 MeV to 2.35 GeV. Data are presented for the E polarization observable for eta meson photoproduction on the proton from threshold (W=1500 MeV) to W=1900 MeV. Comparisons to the partial wave analyses of SAID and Bonn-Gatchina along with the isobar analysis of eta-MAID are made. These results will help distinguish between current theoretical predictions and refine future theories.
ContributorsMorrison, Brian (Author) / Ritchie, Barry (Thesis advisor) / Dugger, Michael (Committee member) / Shovkovy, Igor (Committee member) / Davies, Paul (Committee member) / Alarcon, Ricardo (Committee member) / Arizona State University (Publisher)
Created2011
Description
Monte Carlo methods often used in nuclear physics, such as auxiliary field diffusion Monte Carlo and Green's function Monte Carlo, have typically relied on phenomenological local real-space potentials containing as few derivatives as possible, such as the Argonne-Urbana family of interactions, to make sampling simple and efficient. Basis set methods such as no-core shell model or coupled-cluster techniques typically use softer non-local potentials because of their more rapid convergence with basis set size. These non-local potentials are typically defined in momentum space and are often based on effective field theory. Comparisons of the results of the two types of methods are complicated by the use of different potentials. This thesis discusses progress made in using such non-local potentials in quantum Monte Carlo calculations of light nuclei. In particular, it shows methods for evaluating the real-space, imaginary-time propagators needed to perform quantum Monte Carlo calculations using non-local potentials and universality properties of these propagators, how to formulate a good trial wave function for non-local potentials, and how to perform a "one-step" Green's function Monte Carlo calculation for non-local potentials.
ContributorsLynn, Joel E (Author) / Schmidt, Kevin E (Thesis advisor) / Alarcon, Ricardo (Committee member) / Lebed, Richard (Committee member) / Shovkovy, Igor (Committee member) / Shumway, John (Committee member) / Arizona State University (Publisher)
Created2013
Description
In this thesis, we present the study of several physical properties of relativistic mat- ters under extreme conditions. We start by deriving the rate of the nonleptonic weak processes and the bulk viscosity in several spin-one color superconducting phases of quark matter. We also calculate the bulk viscosity in the nonlinear and anharmonic regime in the normal phase of strange quark matter. We point out several qualitative effects due to the anharmonicity, although quantitatively they appear to be relatively small. In the corresponding study, we take into account the interplay between the non- leptonic and semileptonic weak processes. The results can be important in order to relate accessible observables of compact stars to their internal composition. We also use quantum field theoretical methods to study the transport properties in monolayer graphene in a strong magnetic field. The corresponding quasi-relativistic system re- veals an anomalous quantum Hall effect, whose features are directly connected with the spontaneous flavor symmetry breaking. We study the microscopic origin of Fara- day rotation and magneto-optical transmission in graphene and show that their main features are in agreement with the experimental data.
ContributorsWang, Xinyang, Ph.D (Author) / Shovkovy, Igor (Thesis advisor) / Belitsky, Andrei (Committee member) / Easson, Damien (Committee member) / Peng, Xihong (Committee member) / Vachaspati, Tanmay (Committee member) / Arizona State University (Publisher)
Created2013
Description
For this project, the diffuse supernova neutrino background (DSNB) has been calculated based on the recent direct supernova rate measurements and neutrino spectrum from SN1987A. The estimated diffuse electron antineutrino flux is ∼ 0.10 – 0.59 /cm2/s at 99% confidence level, which is 5 times lower than the Super-Kamiokande 2012 upper limit of 3.0 /cm2/s, above energy threshold of 17.3 MeV. With a Megaton scale water detector, 40 events could be detected above the threshold per year. In addition, the detectability of neutrino bursts from direct black hole forming collapses (failed supernovae) at Megaton detectors is calculated. These neutrino bursts are energetic and with short time duration, ∼ 1s. They could be identified by the time coincidence of N ≥2 or N ≥3 events within 1s time window from nearby (4 – 5 Mpc) failed supernovae. The detection rate of these neutrino bursts could get up to one per decade. This is a realistic way to detect a failed supernova and gives a promising method for studying the physics of direct black hole formation mechanism. Finally, the absorption of ultra high energy (UHE) neutrinos by the cosmic neutrino background, with full inclusion of the effect of the thermal distribution of the background on the resonant annihilation channel, is discussed. Results are applied to serval models of UHE neutrino sources. Suppression effects are strong for sources that extend beyond z ∼ 10. This provides a fascinating probe of the physics of the relic neutrino background in the unexplored redshift interval z ∼ 10 – 100. Ultimately this research will examine the detectability of DSNB, neutrino bursts from failed supernovae and absorption effects in the neutrino spectrum.
ContributorsYang, Lili, 1970- (Author) / Lunardini, Cecilia (Thesis advisor) / Alarcon, Ricardo (Committee member) / Shovkovy, Igor (Committee member) / Timmes, Francis (Committee member) / Vachaspati, Tanmay (Committee member) / Arizona State University (Publisher)
Created2013
Description
Numerical simulations are very helpful in understanding the physics of the formation of structure and galaxies. However, it is sometimes difficult to interpret model data with respect to observations, partly due to the difficulties and background noise inherent to observation. The goal, here, is to attempt to bridge this gap between simulation and observation by rendering the model output in image format which is then processed by tools commonly used in observational astronomy. Images are synthesized in various filters by folding the output of cosmological simulations of gasdynamics with star-formation and dark matter with the Bruzual- Charlot stellar population synthesis models. A variation of the Virgo-Gadget numerical simulation code is used with the hybrid gas and stellar formation models of Springel and Hernquist (2003). Outputs taken at various redshifts are stacked to create a synthetic view of the simulated star clusters. Source Extractor (SExtractor) is used to find groupings of stellar populations which are considered as galaxies or galaxy building blocks and photometry used to estimate the rest frame luminosities and distribution functions. With further refinements, this is expected to provide support for missions such as JWST, as well as to probe what additional physics are needed to model the data. The results show good agreement in many respects with observed properties of the galaxy luminosity function (LF) over a wide range of high redshifts. In particular, the slope (alpha) when fitted to the standard Schechter function shows excellent agreement both in value and evolution with redshift, when compared with observation. Discrepancies of other properties with observation are seen to be a result of limitations of the simulation and additional feedback mechanisms which are needed.
ContributorsMorgan, Robert (Author) / Windhorst, Rogier A (Thesis advisor) / Scannapieco, Evan (Committee member) / Rhoads, James (Committee member) / Gardner, Carl (Committee member) / Belitsky, Andrei (Committee member) / Arizona State University (Publisher)
Created2012
Description
Understanding the temperature structure of protoplanetary disks (PPDs) is paramount to modeling disk evolution and future planet formation. PPDs around T Tauri stars have two primary heating sources, protostellar irradiation, which depends on the flaring of the disk, and accretional heating as viscous coupling between annuli dissipate energy. I have written a "1.5-D" radiative transfer code to calculate disk temperatures assuming hydrostatic and radiative equilibrium. The model solves for the temperature at all locations simultaneously using Rybicki's method, converges rapidly at high optical depth, and retains full frequency dependence. The likely cause of accretional heating in PPDs is the magnetorotational instability (MRI), which acts where gas ionization is sufficiently high for gas to couple to the magnetic field. This will occur in surface layers of the disk, leaving the interior portions of the disk inactive ("dead zone"). I calculate temperatures in PPDs undergoing such "layered accretion." Since the accretional heating is concentrated far from the midplane, temperatures in the disk's interior are lower than in PPDs modeled with vertically uniform accretion. The method is used to study for the first time disks evolving via the magnetorotational instability, which operates primarily in surface layers. I find that temperatures in layered accretion disks do not significantly differ from those of "passive disks," where no accretional heating exists. Emergent spectra are insensitive to active layer thickness, making it difficult to observationally identify disks undergoing layered vs. uniform accretion. I also calculate the ionization chemistry in PPDs, using an ionization network including multiple charge states of dust grains. Combined with a criterion for the onset of the MRI, I calculate where the MRI can be initiated and the extent of dead zones in PPDs. After accounting for feedback between temperature and active layer thickness, I find the surface density of the actively accreting layers falls rapidly with distance from the protostar, leading to a net outward flow of mass from ~0.1 to 3 AU. The clearing out of the innermost zones is possibly consistent with the observed behavior of recently discovered "transition disks."
ContributorsLesniak, Michael V., III (Author) / Desch, Steven J. (Thesis advisor) / Scannapieco, Evan (Committee member) / Timmes, Francis (Committee member) / Starrfield, Sumner (Committee member) / Belitsky, Andrei (Committee member) / Arizona State University (Publisher)
Created2012
Description
This thesis deals with the first measurements done with a cold neutron beam at the Spallation Neutron Source at Oak Ridge National Laboratory. The experimental technique consisted of capturing polarized cold neutrons by nuclei to measure parity-violation in the angular distribution of the gamma rays following neutron capture. The measurements presented here for the nuclei Chlorine ( 35Cl) and Aluminum ( 27Al ) are part of a program with the ultimate goal of measuring the asymmetry in the angular distribution of gamma rays emitted in the capture of neutrons on protons, with a precision better than 10-8, in order to extract the weak hadronic coupling constant due to pion exchange interaction with isospin change equal with one ( hπ 1). Based on theoretical calculations asymmetry in the angular distribution of the gamma rays from neutron capture on protons has an estimated size of 5·10-8. This implies that the Al parity violation asymmetry and its uncertainty have to be known with a precision smaller than 4·10-8. The proton target is liquid Hydrogen (H2) contained in an Aluminum vessel. Results are presented for parity violation and parity-conserving asymmetries in Chlorine and Aluminum. The systematic and statistical uncertainties in the calculation of the parity-violating and parity-conserving asymmetries are discussed.
ContributorsBalascuta, Septimiu (Author) / Alarcon, Ricardo (Thesis advisor) / Belitsky, Andrei (Committee member) / Doak, Bruce (Committee member) / Comfort, Joseph (Committee member) / Schmidt, Kevin (Committee member) / Arizona State University (Publisher)
Created2012
Description
As the world energy demand increases, semiconductor devices with high energy conversion efficiency become more and more desirable. The energy conversion consists of two distinct processes, namely energy generation and usage. In this dissertation, novel multi-junction solar cells and light emitting diodes (LEDs) are proposed and studied for high energy conversion efficiency in both processes, respectively. The first half of this dissertation discusses the practically achievable energy conversion efficiency limit of solar cells. Since the demonstration of the Si solar cell in 1954, the performance of solar cells has been improved tremendously and recently reached 41.6% energy conversion efficiency. However, it seems rather challenging to further increase the solar cell efficiency. The state-of-the-art triple junction solar cells are analyzed to help understand the limiting factors. To address these issues, the monolithically integrated II-VI and III-V material system is proposed for solar cell applications. This material system covers the entire solar spectrum with a continuous selection of energy bandgaps and can be grown lattice matched on a GaSb substrate. Moreover, six four-junction solar cells are designed for AM0 and AM1.5D solar spectra based on this material system, and new design rules are proposed. The achievable conversion efficiencies for these designs are calculated using the commercial software package Silvaco with real material parameters. The second half of this dissertation studies the semiconductor luminescence refrigeration, which corresponds to over 100% energy usage efficiency. Although cooling has been realized in rare-earth doped glass by laser pumping, semiconductor based cooling is yet to be realized. In this work, a device structure that monolithically integrates a GaAs hemisphere with an InGaAs/GaAs quantum-well thin slab LED is proposed to realize cooling in semiconductor. The device electrical and optical performance is calculated. The proposed device then is fabricated using nine times photolithography and eight masks. The critical process steps, such as photoresist reflow and dry etch, are simulated to insure successful processing. Optical testing is done with the devices at various laser injection levels and the internal quantum efficiency, external quantum efficiency and extraction efficiency are measured.
ContributorsWu, Songnan (Author) / Zhang, Yong-Hang (Thesis advisor) / Menéndez, Jose (Committee member) / Ponce, Fernando (Committee member) / Belitsky, Andrei (Committee member) / Schroder, Dieter (Committee member) / Arizona State University (Publisher)
Created2010
Description
The first numerical predictions of the dynamical diquark model of multiquark exotic hadrons are presented. Using Born-Oppenheimer potentials calculated from lattice QCD and phenomenological diquark(triquark) masses, mass eigenvalues that are degenerate in spin and isospin are computed from numerical solutions to both coupled and uncoupled Schroedinger equations. Assuming reasonable estimates of the fine-structure splittings, we find that the band structure of our mass spectra agrees well with the experimentally observed spectrum of charmonium-like states. Using our best fits, we predict a number of unobserved states, such as pentaquark states that lie below the charmonium-plus-nucleon threshold.
ContributorsPeterson, Curtis Taylor Taylor (Author) / Lebed, Richard (Thesis director) / Belitsky, Andrei (Committee member) / Department of Physics (Contributor, Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05