Matching Items (51)
Description
Type Ia supernovae are important, but mysterious cosmological tools. Their standard brightnesses have enabled cosmologists to measure extreme distances and to discover dark energy. However, the nature of their progenitor mechanisms remains elusive, with many competing models offering only partial clues to their origins. Here, type Ia supernova delay times are explored using analytical models. Combined with a new observation technique, this model places new constraints on the characteristic time delay between the formation of stars and the first type Ia supernovae. This derived delay time (500 million years) implies low-mass companions for single degenerate progenitor scenarios. In the latter portions of this dissertation, two progenitor mechanisms are simulated in detail; white dwarf collisions and mergers. From the first of these simulations, it is evident that white dwarf collisions offer a viable and unique pathway to producing type Ia supernovae. Many of the combinations of masses simulated produce sufficient quantities of 56Ni (up to 0.51 solar masses) to masquerade as normal type Ia supernovae. Other combinations of masses produce 56Ni yields that span the entire range of supernova brightnesses, from the very dim and underluminous, with 0.14 solar masses, to the over-bright and superluminous, with up to 1.71 solar masses. The 56Ni yield in the collision simulations depends non-linearly on total system mass, mass ratio, and impact parameter. Using the same numerical tools as in the collisions examination, white dwarf mergers are studied in detail. Nearly all of the simulations produce merger remnants consisting of a cold, degenerate core surrounded by a hot accretion disk. The properties of these disks have strong implications for various viscosity treatments that have attempted to pin down the accretion times. Some mass combinations produce super-Chandrasekhar cores on shorter time scales than viscosity driven accretion. A handful of simulations also exhibit helium detonations on the surface of the primary that bear a resemblance to helium novae. Finally, some of the preliminary groundwork that has been laid for constructing a new numerical tool is discussed. This new tool advances the merger simulations further than any research group has done before, and has the potential to answer some of the lingering questions that the merger study has uncovered. The results of thermal diffusion tests using this tool have a remarkable correspondence to analytical predictions.
ContributorsRaskin, Cody (Author) / Scannapieco, Evan (Thesis advisor) / Rhoads, James (Committee member) / Young, Patrick (Committee member) / Mcnamara, Allen (Committee member) / Timmes, Francis (Committee member) / Arizona State University (Publisher)
Created2011
Description
Chemical and mineralogical data from Mars shows that the surface has been chemically weathered on local to regional scales. Chemical trends and the types of chemical weathering products present on the surface and their abundances can elucidate information about past aqueous processes. Thermal-infrared (TIR) data and their respective models are essential for interpreting Martian mineralogy and geologic history. However, previous studies have shown that chemical weathering and the precipitation of fine-grained secondary silicates can adversely affect the accuracy of TIR spectral models. Furthermore, spectral libraries used to identify minerals on the Martian surface lack some important weathering products, including poorly-crystalline aluminosilicates like allophane, thus eliminating their identification in TIR spectral models. It is essential to accurately interpret TIR spectral data from chemically weathered surfaces to understand the evolution of aqueous processes on Mars. Laboratory experiments were performed to improve interpretations of TIR data from weathered surfaces. To test the accuracy of deriving chemistry of weathered rocks from TIR spectroscopy, chemistry was derived from TIR models of weathered basalts from Baynton, Australia and compared to actual weathering rind chemistry. To determine how specific secondary silicates affect the TIR spectroscopy of weathered basalts, mixtures of basaltic minerals and small amounts of secondary silicates were modeled. Poorly-crystalline aluminosilicates were synthesized and their TIR spectra were added to spectral libraries. Regional Thermal Emission Spectrometer (TES) data were modeled using libraries containing these poorly-crystalline aluminosilicates to test for their presence on the Mars. Chemistry derived from models of weathered Baynton basalts is not accurate, but broad chemical weathering trends can be interpreted from the data. TIR models of mineral mixtures show that small amounts of crystalline and amorphous silicate weathering products (2.5-5 wt.%) can be detected in TIR models and can adversely affect modeled plagioclase abundances. Poorly-crystalline aluminosilicates are identified in Northern Acidalia, Solis Planum, and Meridiani. Previous studies have suggested that acid sulfate weathering was the dominant surface alteration process for the past 3.5 billion years; however, the identification of allophane indicates that alteration at near-neutral pH occurred on regional scales and that acid sulfate weathering is not the only weathering process on Mars.
ContributorsRampe, Elizabeth Barger (Author) / Sharp, Thomas G (Thesis advisor) / Christensen, Phillip (Committee member) / Hervig, Richard (Committee member) / Shock, Everett (Committee member) / Williams, Lynda (Committee member) / Arizona State University (Publisher)
Created2011
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
Historically, uranium has received intense study of its chemical and isotopic properties for use in the nuclear industry, but has been largely ignored by geoscientists despite properties that make it an intriguing target for geochemists and cosmochemists alike. Uranium was long thought to have an invariant 238U/235U ratio in natural samples, making it uninteresting for isotopic work. However, recent advances in mass spectrometry have made it possible to detect slight differences in the 238U/235U ratio, creating many exciting new opportunities for U isotopic research. Using uranium ore samples from diverse depositional settings from around the world, it is shown that the low-temperature redox transition of uranium (U6+ to U4+) causes measurable fractionation of the 238U/235U ratio. Moreover, it is shown experimentally that a coordination change of U can also cause measurable fractionation in the 238U/235U ratio. This improved understanding of the fractionation mechanisms of U allows for the use of the 238U/235U ratio as a paleoredox proxy. The 238U/235U ratios of carbonates deposited spanning the end-Permian extinction horizon provide evidence of pronounced and persistent widespread ocean anoxia at, or immediately preceding, the extinction boundary. Variable 238U/235U ratios correlated with proxies for initial Cm/U in the Solar System's earliest objects demonstrates the existence of 247Cm in the early Solar System. Proof of variable 238U/235U ratios in meteoritic material forces a substantive change in the previously established procedures of Pb-Pb dating, which assumed an invariant 238U/235U ratio. This advancement improves the accuracy of not only the Pb-Pb chronometer that directly utilizes the 238U/235U ratio, but also for short-lived radiometric dating techniques that indirectly use the 238U/235U ratio to calculate ages of Solar System material.
ContributorsBrennecka, Gregory A (Author) / Anbar, Ariel D (Thesis advisor) / Wadhwa, Meenakshi (Thesis advisor) / Herrmann, Achim D (Committee member) / Hervig, Richard (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2011
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
There are many lines of evidence for anisotropy at all scales in the explosions of core collapse supernovae, e.g. visual inspection of the images of resolved supernova remnants, polarization measurements, velocity profiles, "natal kicks" of neutron stars, or spectroscopic observations of different regions of remnants. Theoretical stability considerations and detailed numerical simulations have shown that Rayleigh-Taylor (RT) instabilities arise in the star after the explosion, which leads to the early fragmentation of parts of the ejecta. The clumps thus created are of interest to a variety of topics, one of them being the formation environment of the solar system. There is a high probability that the solar system formed in the vicinity of a massive star that, shortly after its formation, exploded as a core collapse supernova. As argued in this thesis as well as other works, a core collapse supernova generally is a good candidate for chemically enriching the forming solar system with material. As forming proto--planetary systems in general have a high probability of being contaminated with supernova material, a method was developed for detecting tracer elements indicative supernova contamination in proto--planetary systems.The degree of the anisotropy of the supernova explosion can have dramatic effects on the mode of delivery of that material to the solar system, or proto--planetary systems in general. Thus it is of particular interest to be able to predict the structure of the supernova ejecta. Numerical simulations of the explosions of core collapse supernovae were done in 3 dimensions in order to study the formation of structure. It is found that RT instabilities result in clumps in the He- and C+O rich regions in the exploding star that are overdense by 1-2 orders of magnitude. These clumps are potential candidates for enriching the solar system with material. In the course of the further evolution of the supernova remnant, these RT clumps are likely to evolve into ejecta knots of the type observed in the Cassiopeia A supernova remnant.
ContributorsEllinger, Carola I (Author) / Young, Patrick A (Thesis advisor) / Desch, Steven J (Committee member) / Timmes, Francis (Committee member) / Scannapieco, Evan (Committee member) / Lunardini, Cecilia (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
Harsh environments have conditions that make collecting scientific data difficult with existing commercial-off-the-shelf technology. Micro Electro Mechanical Systems (MEMS) technology is ideally suited for harsh environment characterization and operation due to the wide range of materials available and an incredible array of different sensing techniques while providing small device size, low power consumption, and robustness. There were two main objectives of the research conducted. The first objective was to design, fabricate, and test novel sensors that measure the amount of exposure to ionizing radiation for a wide range of applications including characterization of harsh environments. Two types of MEMS ionizing radiation dosimeters were developed. The first sensor was a passive radiation-sensitive capacitor-antenna design. The antenna's emitted frequency of peak-intensity changed as exposure time to radiation increased. The second sensor was a film bulk acoustic-wave resonator, whose resonant frequency decreased with increasing ionizing radiation exposure time. The second objective was to develop MEMS sensor systems that could be deployed to gather scientific data and to use that data to address the following research question: do temperature and/or conductivity predict the appearance of photosynthetic organisms in hot springs. To this end, temperature and electrical conductivity sensor arrays were designed and fabricated based on mature MEMS technology. Electronic circuits and the software interface to the electronics were developed for field data collection. The sensor arrays utilized in the hot springs yielded results that support the hypothesis that temperature plays a key role in determining where the photosynthetic organisms occur. Additionally, a cold-film fluidic flow sensor was developed, which is suitable for near-boiling temperature measurement. Future research should focus on (1) developing a MEMS pH sensor array with integrated temperature, conductivity, and flow sensors to provide multi-dimensional data for scientific study and (2) finding solutions to biofouling and self-calibration, which affects sensor performance over long-term deployment.
ContributorsOiler, Jonathon (Author) / Yu, Hongyu (Thesis advisor) / Anbar, Ariel (Committee member) / Hartnett, Hilairy (Committee member) / Scannapieco, Evan (Committee member) / Timmes, Francis (Committee member) / Arizona State University (Publisher)
Created2013
Description
The temperature of a planet's surface depends on numerous physical factors, including thermal inertia, albedo and the degree of insolation. Mars is a good target for thermal measurements because the low atmospheric pressure combined with the extreme dryness results in a surface dominated by large differences in thermal inertia, minimizing the effect of other physical properties. Since heat is propagated into the surface during the day and re-radiated at night, surface temperatures are affected by sub-surface properties down to several thermal skin depths. Because of this, orbital surface temperature measurements combined with a computational thermal model can be used to determine sub-surface structure. This technique has previously been applied to estimate the thickness and thermal inertia of soil layers on Mars on a regional scale, but the Mars Odyssey Thermal Emission Imaging System "THEMIS" instrument allows much higher-resolution thermal imagery to be obtained. Using archived THEMIS data and the KRC thermal model, a process has been developed for creating high-resolution maps of Martian soil layer thickness and thermal inertia, allowing investigation of the distribution of dust and sand at a scale of 100 m/pixel.
ContributorsHeath, Simon (Author) / Christensen, Philip R. (Philip Russel) (Thesis advisor) / Bel, James (Thesis advisor) / Hervig, Richard (Committee member) / Arizona State University (Publisher)
Created2013
Description
The present understanding of the formation and evolution of the earliest bodies in the Solar System is based in large part on geochemical and isotopic evidences contained within meteorites. The differentiated meteorites (meteorites originating from bodies that have experienced partial to complete melting) are particularly useful for deciphering magmatic processes occurring in the early Solar System. A rare group of differentiated meteorites, the angrites, are uniquely suited for such work. The angrites have ancient crystallization ages, lack secondary processing, and have been minimally affected by shock metamorphism, thus allowing them to retain their initial geochemical and isotopic characteristics at the time of formation. The scarcity of angrite samples made it difficult to conduct comprehensive investigations into the formation history of this unique meteorite group. However, a dramatic increase in the number of angrites recovered in recent years presents the opportunity to expand our understanding of their petrogenesis, as well as further refine our knowledge of the initial isotopic abundances in the early Solar System as recorded by their isotopic systematics. Using a combination of geochemical tools (radiogenic isotope chronometers and trace element chemistry), I have investigated the petrogenetic history of a group of four angrites that sample a range of formation conditions (cooling histories) and crystallization ages. Through isotope ratio measurements, I have examined a comprehensive set of long- and short-lived radiogenic isotope systems (26Al-26Mg, 87Rb-87Sr, 146Sm-142Nd, 147Sm-143Nd, and 176Lu-176Hf) within these four angrites. The results of these measurements provide information regarding crystallization ages, as well as revised estimates for the initial isotopic abundances of several key elements in the early Solar System. The determination of trace element concentrations in individual mineral phases, as well as bulk rock samples, provides important constraints on magmatic processes occurring on the angrite parent body. The measured trace element abundances are used to estimate the composition of the parent melts of individual angrites, examine crystallization conditions, and investigate possible geochemical affinities between various angrites. The new geochemical and isotopic measurements presented here significantly expand our understanding of the geochemical conditions found on the angrite parent body and the environment in which these meteorites formed.
ContributorsSanborn, Matthew E (Author) / Wadhwa, Meenakshi (Thesis advisor) / Hervig, Richard (Committee member) / Sharp, Thomas (Committee member) / Clarke, Amanda (Committee member) / Williams, Lynda (Committee member) / Carlson, Richard (Committee member) / Arizona State University (Publisher)
Created2012