Sudden changes occur where the mean values associated with two adjacent non-overlapping windows of data are anomalously different, and the transition between the window means occurs over a scale that is small relative to the scale of the windows. Positions of sudden changes can be economically retrieved. The sudden change positions demarcate the data in a manner that can be physically interpreted. Associated with this thesis, are data analyses in terms of the scales, positions, and magnitudes of sudden changes in local (window) mean data values. A sudden change ideally includes an anomalously steep small scale gradient that is associated with change on a much larger scale. Preserving this structure when filtering small scale variance requires an adaptive cutoff scale, as constructed in the third study. The filter adapts a local cutoff scale to the scales, locations and relative magnitudes of the local extremes in the Haar transform, which ideally responds to sudden changes. In the fourth study a filter using a variable cutoff scale is applied in order to partition a nine hour time series of wind velocity. The variable cutoff scale filter separated a transport mode from an isotropic small scale mode more cleanly, in terms of traditional statistics, than did a constant cutoff scale filter. Generally, the positions of sudden changes distinguish windows of data. Windows can be centered on the sudden changes or between them. In the fifth study the sudden changes define boundaries of data windows. The within-window data then contains less variance associated with sudden changes, which deterministically occur between adjacent windows. A sampling procedure based on the locations of the sudden changes is applied in the sixth study in an analysis of surface layer measurements. The "non-random" sampling helps to clarify spatial and temporal patterns in samples of the mean wind and the turbulence stress; the "mesoscale effect" is less ambiguous. / Graduation date: 1996

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"July 2003." / Bibliography: p. 203-211. / xxii, 211 p. : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates properties of magnetic fields in galaxy clusters via both statistical Faraday rotation measures and diffuse source polarimetry, and investigates the nature and generation mechanisms for diffuse radio emission in the ACO cluster A3667. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 2003

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A computerised 8-channel data acquisition unit constructed by the Durham University Microprocessor Unit is described and the calibration of this unit is given in chapter 2. A test for the data acquisition unit using a Geiger-Mul1er cosmic ray telescope is described in Chapter 3. In Chapter 4 the main experiment is described. Two plastic scintillation counters each of 0.4 area and 5cm thick in coincidence were used in this experiment to measure the density spectrum of electrons at sea level in the range 20 - 600 electrons per m(^2). The microcomputer data acquisition system is employed to record the scintillator pulse heights. The measured integral density spectrum has been used to calculate the integral size spectrum at sea level. A brief description of the theory of electron-photon cascades and the formation of extensive are showers is give in Chapter 5.A FORTRAN program which uses Monte Carlo method to simulate extensive air showers generated by high energy protons with a given energy is described in Chapter 6. Using the relation between primary energy and average number of electrons arriving at sea level found by Monte Carlo calculation in Chapter 6 an estimate has been made of the integral primary energy spectrum in the range lO(^14)-lQ(^16)eV, and the result is given in Chapter 7.

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Current understanding of small-scale physical processes, such as mixing, in tropical water bodies is lacking and observations are scarce at best. This study sheds more light on these processes through a combined observational-modeling approach. For this purpose, observations were made in Valle de Bravo's freshwater reservoir, about 100 km west of Mexico City and at an elevation of 1830 m above sea surface. Turbulence kinetic energy dissipation (TKED) rates were estimated by fitting a theoretical Batchelor spectrum to the temperature gradient spectrum. From similarity scaling of dissipation rates, it was found that in the surface layer, winds were the main driving force in generating turbulence during the day, while convective forces were responsible during the night. Bottom boundary layer (BBL) mixing was mainly driven by internal wave (first vertical and first horizontal mode) breaking at the bottom. Lognormality of turbulence dissipation rates is also discussed for surface, intermediate and bottom boundary layers. For our modeling efforts, a state-of-the-art one-dimensional turbulence model was used and forced with the observed surface meteorology to obtain simulated temperature and dissipation rate profiles. The model results were found to be in good agreement with the observations, though minor differences in dissipation rates were found in the vicinity of the thermocline and the BBL.