Astrophysical flows have an enormous dynamic range of relevant length scales. The physics occurring on the smallest scales often influences the physics of the largest scales, and vice versa. I present a detailed study of the multiscale and multidimensional behavior of three high-energy astrophysical flows: jet-driven supernovae, massive black hole accretion, and current-driven instabilities in gamma-ray burst external shocks. Both theory and observations of core-collapse supernovae indicate these events are not spherically-symmetric; however, the observations are often modeled assuming a spherically-symmetric explosion. I present an in-depth exploration of the effects of aspherical explosions on the observational characteristics of supernovae. This is accomplished in large part by high-resolution, multidimensional numerical simulations of jet-driven supernovae. The existence of supermassive black holes in the centers of most large galaxies is a well-established fact in observational astronomy. How such black holes came to be so massive, however, is not well established. In this work, I discuss the implications of radiative feedback and multidimensional behavior on black hole accretion. I show that the accretion rate is drastically reduced relative to the Eddington rate, making it unlikely that stellar mass black holes could grow to supermassive black holes in less than a Hubble time. Finally, I discuss a mechanism by which magnetic field strength could be enhanced behind a gamma-ray burst external shock. This mechanism relies on a current-driven instability that would cause reorganization of the pre-shock plasma into clumps. Once shocked, these clumps generate vorticity in the post-shock plasma and ultimately enhance the magnetic energy via a relativistic dynamo process. / text

This work presents two research efforts, one involving planetary science education research and a second involving the surface composition of Mars. In the former, student beliefs and reasoning difficulties associated with the greenhouse effect were elicited through student interviews and written survey responses from >900 US undergraduate non-science majors. This guided the development of the Greenhouse Effect Concept Inventory (GECI), an educational research tool designed to assess pre- and post-instruction conceptual understanding of the greenhouse effect. Three versions of this multiple-choice instrument were administered to >2,500 undergraduates as part of the development and validation process. In contrast to previous research efforts regarding causes, consequences, and solutions to the enhanced greenhouse effect, the GECI focuses primarily on the physics of energy flow through Earth's atmosphere. The GECI is offered to the science education community as a research tool for assessing instructional strategies on this topic.It was confirmed that the study population subscribes to several previously identified beliefs. These include correct understandings that carbon dioxide is an important greenhouse gas and the greenhouse effect increases planetary surface temperatures. Students also commonly associate the greenhouse effect with increased penetration of sunlight into and trapping of solar energy in the atmosphere. Students intermix concepts associated with the greenhouse effect, global warming, and ozone depletion. Reinforcing the latter concept, a majority believe that the Sun radiates most of its energy as ultraviolet light. Students also describe inaccurate and incomplete trapping models, which include permanent trapping, trapping through reflection, and trapping of gases and pollution. Another reasoning difficulty involves the idea that Earth's surface radiates energy primarily during the nighttime.The second research effort describes the distribution of chlorine on Mars measured by the Mars Odyssey Gamma Ray Spectrometer (GRS). The distribution of chlorine is heterogeneous across the surface, with a concentration of high chlorine centered over the Medusa Fossae Formation. The distribution of chlorine correlates positively with hydrogen and negatively with silicon and thermal inertia. Four mechanisms (aeolian, volcanic, aqueous, and hydrothermal) are discussed as possible factors influencing the distribution of chlorine measured within the upper few tens of centimeters of the surface.

Exploration for large zinc silicate deposits is more challenging than zinc sulfide deposits, as they do not exhibit similar geophysical anomalies. The Vazante deposit, which is the world’s largest zinc silicate deposit, occurs in brecciated dolomite and comprises mainly willemite with various proportions of hematite, and minor franklinite and sphalerite. In the Vazante region, the exploration challenge is enhanced as outcrops are rare, bedrock generally sits below 10s of metres of laterite cover and barren hematite-rich breccias have a similar geophysical signature to willemite ore bodies. In order to evaluate the applications of geophysical surveys in the exploration of this type of deposit, data from 475 samples were investigated from drill holes representative of the various types of ore, host rocks and zones of known geophysical anomalies in the Vazante District. Geochemical (ICP-MS and XRF) and mineralogical (optical, EMPA, SEM and MLA) data were integrated with physical rock properties (density, magnetic susceptibility and K-U-Th gamma ray spectrometry) to assist in finding new ore zones. The most distinct physical property of the ore is density (3.0-4.3 g/cm3), compared with the host rocks (2.7-3.0 g/cm3). This is due to high proportion of denser minerals (hematite and willemite) in the ore. However, barren hematite breccias also have high densities (3.0-4.5 g/cm3). The zinc ore and hematite breccias yielded higher magnetic susceptibilities (0.1-38 x10-3 SI) than the surrounding host rocks, with the highest values associated with greater proportions of franklinite and magnetite (7-38 x10-3 SI). The zinc ore has an elevated U concentration (up to 33ppm) relative to the various host rocks (up to 7 ppm), yielding higher gamma spectrometric values. The results of this investigation indicate that an integration of magnetic, gravimetric and radiometric surveys would be required to identify zinc silicate ore zones and potentially differentiate them from barren hematite breccias and host rocks. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2014-03-27 13:32:54.132

Pulsars, as rotating magnetised neutron stars got much attention during the last 40 years since their discovery. Observations revealed them to be gamma-ray emitters with energies continuing up to the sub 100 GeV region. Better observation of this upper energy cut-off region will serve to enhance our theoretical understanding of pulsars and neutron stars. The H-test has been used the most extensively in the latest periodicity searches, whereas other tests have limited applications and are unsuited for pulsar searches. If the probability distribution of a test statistic is not accurately known, it is possible that, after searching through many trials, a probability for uniformity can be given, which is much smaller than the real value, possibly leading to false detections. The problem with the H-test is that one must obtain the distribution by simulation and cannot do so analytically. For such simulations, random numbers are needed and are usually obtained by utilising so-called pseudo-random number generators, which are not truly random. This immediately renders such generators as useless for the simulation of the distribution of the H-test. Alternatively there exists hardware random number generators, but such devices, apart from always being slow, are also expensive, large and most still don't exhibit the true random nature required. This was the motivation behind the development of a hardware random number generator which provides truly random U(0,l) numbers at very high speed and at low cost The development of and results obtained by such a generator are discussed. The device delivered statistically truly random numbers and was already used in a small simulation of the H-test distribution. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2005.

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<p>Two separate experimental searches for second-order weak nuclear decays to excited final states were conducted. Both experiments were carried out at the Kimballton Underground Research Facility to provide shielding from cosmic rays. The first search is for the two-neutrino double-beta decay of 96Zr to excited final states of the daughter nucleus, 96Mo. As a by product of this experiment, the beta decay of 96Zr was also investigated. Two coaxial high-purity germanium detectors were used in coincidence to detect gamma rays produced by the daughter nucleus as it de-excited to the ground state. After collecting 1.92 years of data with 17.91 g of enriched 96Zr, half-life limits at the level of 10^20 yr were produced. Measurements of this decay are important to test neutrinoless double-beta decay nuclear matrix element calculations, which are necessary to extract the neutrino mass from a measurement of the neutrinoless double-beta decay half-life. </p><p>The second experiment is a search for the resonantly-enhanced neutrinoless double-electron capture decay of 156Dy to excited states in 156Gd. Double-electron capture is a possible experimental alternative to neutrinoless-double beta decay, which could distinguish the Dirac or Majorana nature of the neutrino. Two clover high-purity germanium detectors were used in coincidence to investigate the decay. A 213.5 mg enriched 156Dy sample was observed for 0.635 year, producing half-life limits of 10^17 yr. The limits produced by both of these experiments are currently the most stringent limits available for these decays.</p> / Dissertation

名古屋大学年代測定総合研究センターシンポジウム報告

Pulsars, as rotating magnetised neutron stars got much attention during the last 40 years since their discovery. Observations revealed them to be gamma-ray emitters with energies continuing up to the sub 100 GeV region. Better observation of this upper energy cut-off region will serve to enhance our theoretical understanding of pulsars and neutron stars. The H-test has been used the most extensively in the latest periodicity searches, whereas other tests have limited applications and are unsuited for pulsar searches. If the probability distribution of a test statistic is not accurately known, it is possible that, after searching through many trials, a probability for uniformity can be given, which is much smaller than the real value, possibly leading to false detections. The problem with the H-test is that one must obtain the distribution by simulation and cannot do so analytically. For such simulations, random numbers are needed and are usually obtained by utilising so-called pseudo-random number generators, which are not truly random. This immediately renders such generators as useless for the simulation of the distribution of the H-test. Alternatively there exists hardware random number generators, but such devices, apart from always being slow, are also expensive, large and most still don't exhibit the true random nature required. This was the motivation behind the development of a hardware random number generator which provides truly random U(0,l) numbers at very high speed and at low cost The development of and results obtained by such a generator are discussed. The device delivered statistically truly random numbers and was already used in a small simulation of the H-test distribution. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2005.