This thesis contains discussions of a number of points which arose when the author was studying the "paramagnetic resonance line shape problem". The so-called moment method is discussed, and a new derivation of the moments of the line shape function is given. Single-spin operators are introduced which simplify the calculation of these moments. The Green's function technique, as applied to this problem, and the decoupling approximations associated with the technique, are looked at from the point of view of reliability and complexity. As a test of the reliability of any decoupling, a theorem concerning the moments of a line shape arising from such a decoupling is discussed and proved. The Green's function technique is applied to the case of the one-dimensional Ising model with spin ½, where no decoupling of the hierarchy of Green's function equations is necessary. A method of calculating thermal averages for this case, using difference equations, is given. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The proton resonance line in a single crystal of Na₂B₄O₇•4H₂O (kernite) placed in a magnetic field of 6300 gauss, was examined experimentally as the monoclinlc crystal was rotated about its twofold symmetry axis (cryetallographic b-axis) maintained perpendicular to the magnetic field. The observed variation with crystal position of the proton line shape was found to be consistent with that expected as a result of nuclear magnetic dipole-dipole interaction between protons in the molecules of water of crystallization. No evidence was found for any additional splitting of the proton line which might be correlated with the previously observed splitting of some of the components of the spectrum of B¹¹ in kernite. The expected spectrum of B¹⁰ in kernite was calculated theoretically for a Larmor frequency of 4Mc./sec., corresponding to an external magnetic field of 8741 gauss, and an unsuccessful experimental search for it was made. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Previous physiological work has established that factors such as power and status modulate the motor resonance system. Motor resonance is classified as motor activity that occurs during action observation in the absence of action execution. However, no previous work has explored whether these factors have downstream behavioural effects on automatic imitation using a community sample (as opposed to a university student sample). In addition, no prior work has examined whether online social hierarchies (as opposed to real-world social hierarchies) also modulate this system. As such, this dissertation aims to corroborate and extend on previous physiological work in the field and explore whether online status has similar downstream effects on motor resonance compared to previously documented effects of offline (real-world) status using behavioural and physiological methods. In chapters 2-3, I provide evidence from community-based behavioural studies that suggest high socioeconomic status (SES) and high power individuals are less susceptible to automatically imitating “other-oriented” social stimuli compared to their low SES and low power counterparts. In chapters 4-5, I show that Instagram followers exhibit significantly greater motor cortical output (via transcranial magnetic stimulation induced motor-evoked potentials) during action observation compared to Instagram leaders. I also show that this effect can be extended behaviourally using the automatic imitation task, whereby Instagram leaders are less susceptible to automatically imitating “other-oriented” social stimuli compared to Instagram followers. In chapter 6, I begin to explore the effect of online status on behavioural mimicry. I show that Instagram leaders exhibit reduced behavioural mimicry during an online interaction compared to Instagram followers. In the final chapter of this dissertation, I summarize the contributions and limitations of each chapter and recommend future avenues of research. Overall, this dissertation furthers our understanding on how online and offline social hierarchies modulate the motor resonance system using behavioural and physiological methods. / Dissertation / Doctor of Philosophy (PhD)

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Quadrupolar relaxation-based methods in Fast Field-Cycling MRI Nicholas R. Payne Aberdeen Biomedical Imaging Centre, University of Aberdeen, AB25 2ZD, Scotland, UK Fast Field-Cycling MRI (FFC-MRI) can access contrast based on the dependence of a sample's relaxation rate to the applied magnetic field strength. This technique can provide signal based on interactions with local quadrupolar nuclei through cross-relaxation, however, there are other so-called Nuclear Quadrupole Double Resonance (NQDR) techniques described in the literature. This work has been centred on efforts to apply these techniques to FFC-MRI and otherwise explore how interactions between protons and quadrupolar nuclei can be further exploited. Through this work two irradiation systems were designed and built for manual tuning, in the first instance, and automatic tuning. The latter was able to quickly retune to coil, however, it was limited in RF power handling capability. A second strand of work was concerned with the reduction in receiver deadtime required to detect signal from solid-state samples such as those previously used in NQDR experiments in the literature. However, circuitry designed to dampen coil ringing by temporarily reducing the resonator's Q-factor following a pulse, along with a novel method utilising field-cycling were not able to reduce the deadtime enough to detect signal from relevant samples. This, coupled with a lack of evidence of NQDR effects in gel-like samples, proved the ultimate stumbling block for NQDR in FFC-MRI. Success was seen in a third strand of work in which simulations were used to design custom experiments which could be used to provide large increases to the signal-to-noise ratio in some experiments. The simulated environment also allowed for fast testing and development of new post-process algorithms which could more accurately calculate relaxation rates. The work concluded that NQDR is unlikely to be useful in FFC-MRI due to the constraints on both the sample and the technique. However the information from quadrupolar nuclei can be improved with better post-processing and tailored pulse sequence parameters.

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: diffusion; tendon; NMR; fMRI. Includes bibliographical references (p. 172-179).

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