<p> Approximately eighty new neodymium model ages were determined on grey orthogneisses in the Mattawa region of Ontario and were used to develop a Grenvillian tectonic model in the region. A residual-magnetic field map developed from aeromagnetic data provides an additional constraint on the terranes mapped based on Nd-model ages. The field area was divided into three sections: the northern section, the Mattawa klippe, and the southern section. </p> <p> The objectives of mapping in the northern section were two-fold: 1) to map the location of erosional remnants of the allochthon boundary thrust (ABT) and 2) to test the hypothesis that northwestward thrusting of the ABT over the parautochthonous belt caused decollement of a magmatically reworked Archean terrane, creating a duplex thrust sheet and consequent northwestward thrusting of the magmatically reworked Archean parautochthon. </p> <p> Two allochthonous units previously mapped in this region are the Lac Watson nappe and the Lac Booth klippe. These allochthonous units, characterized by Nd-model ages <1.8 Ga are bound by a magmatically reworked Archean terrane (referred to as the reworked Archean parautochthon) with a Nd-model age range of 1.9-2.6 Ga. Likewise, the perimeter of the reworked Archean parautochthon is truncated by a pristine Archean terrane which exclusively hosts Nd-model ages> 2.6 Ga, indicating that there are three crustal stacking levels in the northern section. </p> <p> Nd-model age mapping was employed in the Mattawa klippe region with the same objectives as in the northern section and additionally to provide constraints on the methodology that is to be used when mapping first-order tectonic boundaries such as the ABT. Ketchum and Davidson (2000) suggested that the ABT trended northward in this region based on the presence of 1.16 Ga coronitic metagabbros which Ketchum (1994) concluded were exclusively confined to the allochthonous polycyclic belt (APB). It was detennined here that although the metagabbros are confined to allochthonous crust, based on Nd-model ages, they are contained within an allochthonous klippe (Mattawa klippe) overlying the reworked Archean parautochthon, that transported the coronitic metagabbros northwestward. Therefore, this klippe represents an erosional remnant ofthe APB but the main ABT is located further south. </p> Nd-model age mapping in the southern region identified three distinct crustal terranes. The Mattawa fault was detennined to be a brittle fault following approximately along a pre-Grenvillian suture. This separates the reworked Archean parautochthon from the Paleoproterozoic parautochthon, which had a Nd-model age range from 1.8-1.9 Ga The Paleoproterozoic parautochthon was found to be truncated by the main body of the APB, containing Nd-model ages < 1.8 Ga. The boundary between the Paleoproterozoic parautochthon and the APB was interpreted as the location of the main ABT. </p> <p> Based on the distnbution of Nd-model ages in the region, four distinct crustal terranes were identified representing two thrusting events. Initially the ABT was overthrust on the parautochthonous belt causing decollement of the reworked Archean parautochthon. The entrainment of the reworked Archean parautochthon under the APB generated a duplex thrust sheet, which resulted in the consequent northwestward thrusting of the reworked Archean parautochthon over the pristine Archean terrane. Finally, the ABT was offset by post-Grenvillian normal faulting associated with Ottawa-Bonnechere graben. </p> / Thesis / Master of Science (MSc)

This study examined the short term memory (STM) difference of magnetic resonance imaging (MRI) technologists versus non-MRI technologists. Human and animal studies have indicated that residual magnetic fields have caused changes within the cerebral structure. Research on residual magnetic fields and their effect on STM is still at its infancy. A quasi-experimental design was used to determine if any significant difference existed between the STM of MRI technologists (n = x) and a control population sample (n = x). The STM of both groups was assessed with the use of the Rivermead Behavioural Memory Test-Third Edition. Solicitation of the participants was from a national MRI organization, the American Society of Radiologic Technologists, and community workers within the profession. The control group of participants was solicited through community board postings. Only the New York/New Jersey metro area and the New Hampshire/Maine area participants were used for this study. These participants were of various age ranges, genders, and educational levels. ANOVA and regression analyses were used to analyze the data. The study showed mixed results, indicating no significant STM difference in the overall memory scores of both groups F (1, 80) =3.061, p =..084, but it did show a significant difference in STM when it came to prospective memory, memory of planned events. These findings illustrate a need for further research in this area. Expanding the geographical reach and sample size could clarify the role of MRI on STM. The results of this study suggest that procedures that limit the exposure of the MRI technologists to the residual magnetic fields surrounding MRI machines could yield a reduction in loss of prospective memory.

Small satellites are gaining popularity in a wide range of applications where attitude systems require high precision performance. One of the main sources of errors, in case of magnetic attitude control systems, is the residual magnetic moment (RMM) of the spacecraft. To keep the RMM low and stable, mitigation methods shall be applied based on the satellite’s magnetic dipole moment (MDM) characterization, which shall be measured accurately. For small satellites, the most common technique involves the generation of a field-free region for the magnetic measurements using a test bed. The test bed measurement setup is normally mechanical, where measurements from the device under test (DUT) are very tedious. Optical magnetic test beds (OMTB) are being developed for MDM characterization providing simpler set ups and faster measurements than mechanical test beds. In this work, accuracy of OMTB of Aalto University has been evaluated by measuring three permanent magnets in two configurations. The measurements show a relationship between the estimation accuracy and the DUT’s marker area seen by the camera. Moreover, it was observed that the field-free region generated by Helmholtz coil cage can generate false data points. Based on these observations, the detection of the marker’s positions have been evaluated using the view area (VA) and the pointing angle (PA). The analysis shows that there is a consistent pattern depending on the combination of the VA and PA. Hence, the method of data acquisition was improved in order to prioritize the markers which position allow better accuracy. The achieved improvement of MDM estimation results is 2 %, and the test bed’s overall error evaluated is a 13 % in MDM position estimation and 23 % in MDM magnitude estimation. The improved OMTB was used to characterize the MDM of four magnetic attitude coils of Foresail-1 satellite. The measurements results are consistent with design parameters, showing three dipole configuration in all coils with a MDM magnitude order of 10−2 A·m2. / Foresail-1

Conventional resistance spot welds are not visible from the outside. Therefore, it is not straightforward to evaluate the joint quality non-destructively. The pulse-echo method of manual ultrasonic is widely used for non-destructive testing. Another option is the passive magnetic flux density testing, which is being developed at Technische Universität Dresden, Germany. The spot weld is magnetized in the normal direction and the residual magnetic flux density is measured on top of the surface of the joint. This method is suitable for spot welds on typical car body steels. Previous investigations show that the magnetic properties of the materials influence the test result. In order to develop this new non-destructive testing method further, it is necessary to know the magnetic properties of the different microstructure regions of a spot weld. This article focuses on methods to measure and evaluate the magnetic properties of these regions, especially of the base material and the weld. Different measuring methods and approaches are presented and compared with each other. Based on the results, recommendations for future measurements for magnetic characterizations are given.