Department of Physics (Fredericton)

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Single point measurement of magnetic field gradient time profile
Single point measurement of magnetic field gradient time profile
by Maurice Shea, Magnetic field gradients are used in Magnetic Resonance Imaging (MRI) to encode the spatial information of an object under study. The gradient should vary spatially but not vary with time. In reality, the gradient takes a finite amount of time to stabilize at its maximum and minimum amplitudes when switched on and off. I am proposing a new method of obtaining a time profile (or waveform) of the magnetic field gradient as it changes during the rise and fall times. Simulations and experiments show the recovered waveform is an accurate reproduction of the actual gradient., Appendix numbered 9.1-9.3
Some behaviors of thermoluminescent lithium fluoride
Some behaviors of thermoluminescent lithium fluoride
by Michael Finnamore, It is known that certain crystals exhibit luminescence after being irradiated and heated. Further there is a relation between the dose of radiation received and the luminescence observed. A series of experiments were performed to determine the effect of radiation dose, annealing time, beam quality and beam energy on the sensitivity of thermoluminescent dosimetry chips (TLDs). The chips in question were LiF doped with Magnesium and Titanium., 3 unnumbered pages before first numbered page
Some physical properties of sandstones lithified under the influence of differential stresses
Some physical properties of sandstones lithified under the influence of differential stresses
by Jamie Richard Alison, The result of two experiments is discussed in this thesis. The first experimental project involved the testing of concrete cubes solidified under the stress conditions of σ1 > σz=σ3 where σ1 was the experimental variable. Pulse velocity anisotropy occurred with the slower velocity in the 01 direction and the two faster (and equal) velocities corresponding to the σ z and σ3 directions. It was found that this effect became more marked as σ1 (pre stress) was increased. The effect of the test load on the velocities became less anomalous under higher load. Preferred fracture orientations perpendicular σ2 and σ3 were found in specimens that underwent induced tensile fracture testing. The second project involved the testing of sandstone core obtained from the Carboniferous sediments of New Brunswick. Preferred fracture orientation occurred in the core that underwent induce tensile fracture testing and the overall fracture orientation trends had a spatial and possibly a chronological nature. Pulse velocity testing of three sandstone cubes showed anisotropy with the slow velocity corresponding to the vertical stress.
Study of acoustic cavitation using NMR and MRI
Study of acoustic cavitation using NMR and MRI
by Samuel Kristoffersen, A very strong transducer was used to generate acoustic cavitation in a cuvette filled with water bubbled through with Freon-22. NMR and MRI were used to measure the cavitation and the diffusion of the gas, as well as the liquid. MRI is being used because it has advantages over other methods, such as optical and acoustic methods, due to the opacity of the media caused by the cavitation. It was found that the region of enhanced diffusion for the gas was away from the tip of the transducer, and the region of enhanced diffusion for the water was next to the tip. There were also T2 measurements, 2 and it was shown that there is some dependence of T2 on the acoustic cavitation., 2 unnumbered pages before the first numbered page
Study of the Au(110) surface lattice structure by Rutherford backscattering
Study of the Au(110) surface lattice structure by Rutherford backscattering
by Johan L.E. Stevens, The ion backscattering surface peak yield at 180° has been measured for 0.6 MeV, 1.0 MeV and 2.0 MeV He+ incident upon the <110> and <112> directions of a (110)Au single crystal at temperatures ranging between 40 K and 800 K. Based on the experimental results, a modified (1x2) surface structure for (110)Au has been calculated in this range of temperatures and incident ion energies, by a single string Monte Carlo simulation that includes the effects of enhanced vibrations in the surface layers and vibration correlations. A theoretical description of the backscatter yield at 180° is given. The calculated modified (1x2) surface structure is in agreement with observations in the 40 K to 500 K range.
Survey of magnetic pulsations at the geosynchronous orbit
Survey of magnetic pulsations at the geosynchronous orbit
by Chris Watson, Magnetic pulsations are Ultra Low Frequency (ULF) electromagnetic waves and are considered to be one of the modes for transfer of energy and momentum from the solar wind to the magnetosphere and different plasma regimes within the magnetosphere. Magnetic pulsations are usually identified using ground based magnetometer measurements and are classified into different categories. In this study, we have used ten years of GOES satellite geo-synchronous magnetic field measurements to identify and characterize magnetic pulsations. Our analysis resulted in 962 clear pulsation events in Pc5, Pi2 and Pc4 bands. Two satellite locations were used in the study, giving a comparison of pulsation events at two different local times. Upon finding a pulsation, a time-frequency spectral analysis was employed to determine the pulsation frequency. Pulsations were found to occur most frequently in the late morning to evening sector, with their time duration following a power law distribution. Frequencies in the 5 to 8 mHz band were the most common, however a broad range of frequencies were found. A possible frequency dependence on magnetic field inclination was found, although more study is needed to be conclusive.
Synchronized chaotic systems: theory and applications to nonlinear oscillator networks
Synchronized chaotic systems: theory and applications to nonlinear oscillator networks
by Santosh Gupta, Synchronized chaotic systems have received much attention in recent years as an example of systems that exhibit regularity at the "global" level while existing in seeming disorder "locally". The synchronization of chaotic oscillators forming a network is a topic of special interest, with a wide range of applicability. Here we review the basic theory and then apply it to a network of Lorenz systems. We also propose a method of improving the synchronizability of a network by choosing a form of coupling that makes the associated network tensor possess hyperbolicity for weak coupling.
The Bay of Fundy temperature inversion phenomenon
The Bay of Fundy temperature inversion phenomenon
by Gordon M. Miller, The structure of the atmosphere over Southern New Brunswick is dependent to a great extent on the conditions present in the atmosphere over the Bay of Fundy. The cold waters of the Bay of Fundy, fed by the Labrador Current, provide a steep temperature gradient at the interface between the water and the air above. This gradient is enhanced even more in the summer months when southerly winds blow warm air up the eastern coast of North America. Such situations often result in a temperature inversion (an increase in temperature with height). Through the studies presented in this paper, the required conditions for such situations are explained.

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