No description available.

Bibliography : leaves i-xx / xi, 168, [99], xx leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1991

<p>High-energy neutrinos are capable of carrying information over vast distances, and neutrino telescopes such as AMANDA-II provide the means to probe deep inside the violent and energetic interior of the universe. AMANDA-II is located in the glacial ice at South Pole in Antarctica and is optimised to detect Cherenkov emission from neutrino-induced muon tracks with energies above 100 GeV. </p><p>Data acquired in 2003 with the AMANDA-II detector were searched for a non-localised flux of neutrinos with energies in excess of 1 PeV. Because of the energy dependence of the neutrino mean free path, the Earth is essentially opaque to neutrinos above PeV energies. Combined with the limited overburden of the AMANDA-II detector (about 1.5 km), this means that a potential ultra-high energy neutrino signal will be concentrated at the horizon. The background for the analysis consists of large bundles of muons produced in atmospheric air showers. Owing to their energy losses, muons cannot penetrate the Earth, and the background will be downwards moving. </p><p>After applying different selection criteria, one event was observed in the final data sample, while 0.16±0.04 background events are expected. The corresponding 90% confidence level upper limit is 4.3. The expected number of neutrino signal events for a 10^-6 <i>E</i>^-2 GeV/(s sr cm² ) flux assuming a Φ(ν_e) : Φ(ν_μ) : Φ(ν_τ) = 1:1:1 flavour ratio is 4.1±0.2, yielding an upper limit on the all-flavour neutrino flux of <i>E</i>² Φ₉₀ ≤ 1.1∙10^-6 GeV/(s sr cm² ), including systematics and with the central 90% of the signal found in the energy range 480 TeV - 1.6 EeV. </p>

<p>The main aims of this project were to contribute to the knowledge about tropical climate variations, and to investigate the possibilities of obtaining cosmic ray influx data from stalagmites.</p><p>Stalagmites from Tanzania and northern South Africa were palaeoclimatologically analysed.</p><p>U-series dating, combined with previously published 14C-data (Goslar et al. 2000), shows that one of the Tanzanian stalagmites was precipitated during the latter half of the latest glacial, between approximately 39 and 27 ka. Results from stable isotope analysis (δ13C and δ18O) were interpreted as indicating millennial-scale fluctuations in atmospheric CO2-level during that time. These fluctuations show a pattern which is similar to that of the δ18O records from the GRIP and Byrd ice-cores – suggesting that the stalagmite record captures a global climate signal.</p><p>U-series dating shows that the largest of the South African stalagmites covers most of the last 25 ka. The δ13C- and δ18O-data indicate millennial-scale variation in the South African climate throughout the time of the formation of this stalagmite. Because of similarities to Antarctic records (Steig et al. 2000), the driving force for these variations was suggested to be atmospheric circulation changes associated with change in the Southern Hemisphere circumpolar westerly wind vortex. Like the Tanzanian results, these South African data lend further support to the theory about global persistent millennial-scale climate-fluctuations.</p><p>A beryllium isotope study was then performed on the two stalagmites described above. This study assesses, for the first time, the potential of the cosmogenic isotope 10Be as a tool in stalagmite studies. As a control, 9Be-analysis was also made on each 10Be-sample.</p><p>The aim of the study was to test the idea that stalagmites could be a new source of well-dated and directly climate-proxy synchronized information about past variations in cosmic ray influx intensity – i.e., a source that would serve as a new tool for general improvement of the knowledge about past variations in cosmic ray influx, and that could possibly also provide further clues to whether such variations can affect Earth’s climate.</p><p>The main excursions/fluctuations in the 10Be-and 9Be-data from these stalagmites do not coincide. Hence, the excursions in 10Be-content may be interpreted as indicating excursions in cosmic ray influx. The 10Be-data show three pronounced peaks at around 38, 35 and 21 ka respectively; plausibly corresponding to the peaks previously observed at approximately 39, 32 and 23 ka in cosmogenic isotope data from sediments and ice.</p><p>In glacial parts of the stalagmite material, the 9Be-concentration fluctuates on a millennial-scale; inversely synchronized with fluctuations in δ13C-data from the same material. This indicates that 9Be could, apart from being a necessary control for 10Be-results, also function as a palaeoclimatological proxy in stalagmite studies.</p><p>In order to improve dating facilities for stalagmites, a procedure for high-precision measurements of U and Th isotope ratios was also developed, using an IsoProbe® Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS). The 230Th/232Th ratio for the thorium concentration-standard Alfa Th was determined to 7.96 (±0.012) × 10-7 (2σ), and the δ234U obtained for the uranium standard SRM950a was 18.4 ±0.6(2σ). The thorium results show, that even extremely biased isotope ratios, in low-concentration samples, can be measured with remarkably good precision. The quality of each sample measurement can also easily be evaluated. However, due to repeated technical problems with the instrument, it has not yet been possible to use the developed procedure for routine analysis and dating of samples.</p>

Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2008.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 90-94).

No description available.

The main aims of this project were to contribute to the knowledge about tropical climate variations, and to investigate the possibilities of obtaining cosmic ray influx data from stalagmites. Stalagmites from Tanzania and northern South Africa were palaeoclimatologically analysed. U-series dating, combined with previously published 14C-data (Goslar et al. 2000), shows that one of the Tanzanian stalagmites was precipitated during the latter half of the latest glacial, between approximately 39 and 27 ka. Results from stable isotope analysis (δ13C and δ18O) were interpreted as indicating millennial-scale fluctuations in atmospheric CO2-level during that time. These fluctuations show a pattern which is similar to that of the δ18O records from the GRIP and Byrd ice-cores – suggesting that the stalagmite record captures a global climate signal. U-series dating shows that the largest of the South African stalagmites covers most of the last 25 ka. The δ13C- and δ18O-data indicate millennial-scale variation in the South African climate throughout the time of the formation of this stalagmite. Because of similarities to Antarctic records (Steig et al. 2000), the driving force for these variations was suggested to be atmospheric circulation changes associated with change in the Southern Hemisphere circumpolar westerly wind vortex. Like the Tanzanian results, these South African data lend further support to the theory about global persistent millennial-scale climate-fluctuations. A beryllium isotope study was then performed on the two stalagmites described above. This study assesses, for the first time, the potential of the cosmogenic isotope 10Be as a tool in stalagmite studies. As a control, 9Be-analysis was also made on each 10Be-sample. The aim of the study was to test the idea that stalagmites could be a new source of well-dated and directly climate-proxy synchronized information about past variations in cosmic ray influx intensity – i.e., a source that would serve as a new tool for general improvement of the knowledge about past variations in cosmic ray influx, and that could possibly also provide further clues to whether such variations can affect Earth’s climate. The main excursions/fluctuations in the 10Be-and 9Be-data from these stalagmites do not coincide. Hence, the excursions in 10Be-content may be interpreted as indicating excursions in cosmic ray influx. The 10Be-data show three pronounced peaks at around 38, 35 and 21 ka respectively; plausibly corresponding to the peaks previously observed at approximately 39, 32 and 23 ka in cosmogenic isotope data from sediments and ice. In glacial parts of the stalagmite material, the 9Be-concentration fluctuates on a millennial-scale; inversely synchronized with fluctuations in δ13C-data from the same material. This indicates that 9Be could, apart from being a necessary control for 10Be-results, also function as a palaeoclimatological proxy in stalagmite studies. In order to improve dating facilities for stalagmites, a procedure for high-precision measurements of U and Th isotope ratios was also developed, using an IsoProbe® Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS). The 230Th/232Th ratio for the thorium concentration-standard Alfa Th was determined to 7.96 (±0.012) × 10-7 (2σ), and the δ234U obtained for the uranium standard SRM950a was 18.4 ±0.6(2σ). The thorium results show, that even extremely biased isotope ratios, in low-concentration samples, can be measured with remarkably good precision. The quality of each sample measurement can also easily be evaluated. However, due to repeated technical problems with the instrument, it has not yet been possible to use the developed procedure for routine analysis and dating of samples.

New measurements of the antiproton flux and the antiproton-to-proton flux ratio at the top of the atmosphere between 80 MeV and 2.0 GeV are presented. The measurement was conducted from July 2006 to March 2008 with the PAMELA satellite experiment. This is a period of minimum solar activity and negative solar polarity and the PAMELA measurement is the first observation of antiprotons during this particular solar state. The PAMELA instrument comprises a permanent magnet spectrometer, a scintillator based time-of-flight system, an electromagnetic calorimeter and an anticoincidence shield. These detectors can identify antiprotons from a background of cosmic-ray electrons and locally produced pions. The PAMELA instrument is mounted on the Resurs DK1 satellite that was launched from the Baikonur Cosmodrome on June the 15th into a semi-polar orbit with an inclination of 70o. During approximately 500 days of data collection 170 antiprotons were identified. The derived antiproton spectrum shows a steep increase up to 2 GeV as expected for pure secondary production of galactic antiprotons. The antiproton flux is over-estimated by most current models of secondary production compared to PAMELA results. There are no indications of the excess of antiprotons at low energy predicted by theories of primordial black hole evaporation. The antiproton-to-proton flux ratio is in agreement with drift models of solar modulation, which are also favoured by recent PAMELA measurements of the positron fraction. / QC 20100811

No fault found (NFF) errors, i.e. errors which origin has not been established, irregularly occur in electronic devices. The actual cause of such errors varies but one, possibly more prominent, source for these soft errors is atmospheric radiation. The overarching aim of this thesis is to demonstrate: 1) the importance of keeping the atmospheric radiation environment in mind when designing robust airborne systems, 2) how to take this environment into consideration when applying mitigation techniques which may drastically reduce the risk of SEEs (Single Event Effects) which can cause NFF errors. To achieve these goals, Part 1 of this thesis describes how cosmic rays affect electronics (i.e. what kind of errors may be induced), which types of devices are susceptible to radiation, and why this subject is of extra importance for airborne systems. In addition, soft error mitigation techniques, which may be applied at different design levels to reduce the soft error rate (SER) or the impact of soft errors, are also presented. The aim is further corroborated by Part 2. Five subsystems of a modern aircraft are studied and real examples of failures potentially induced by atmospheric radiation are presented. For each of the five systems, all errors that have been reported for these (in the past few years) have been studied, and the number of errors found to be potentially induced by cosmic radiation has been listed and compared to number of expected soft errors based on calculations and previous experimental tests.