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Graduate Research at the Frontiers of Physics & Astronomy

Fri. Nov. 27 03:00 PM - Fri. Nov. 27 04:45 PM
Location: University of Manitoba, 330 Allen Building

3:00pm - Caffeine, confections and congeniality
3:30pm - Lectures commence
4:45pm - Quaff, peck and ponder


1.  Sheryl Herrera

Using oscillating gradient spin-echo sequences to infer micron-sized bead and pore radii

Sheryl will be explaining diffusion weighted magnetic resonance imaging (MRI), and discuss some of the progress she has made aimed at developing and optimizing a method for distinguishing the size of very small (~1 μm) tissue structures, such as small axon diameters.

This method relies on probing the shortest probable diffusion time scales so that the transition from restricted to hindered diffusion within the smallest structures can be detected. Current state-of-the-art methods cannot distinguish these small structures because these methods use pulse sequences which limit the ability to probe the shortest diffusion times. My method circumvents those limitations by using oscillating gradients in lieu of pulsed gradients. The new method will have important biological and neuroscience applications; one example is probing axon diameter distributions.

 

2.  Vinod Paidi

Magnetic Susceptibility as a Probe to Identify the Intrinsic Oxygen in Shape Selected CeO2 nanoparticles.

Oxygen vacancy defects are of special importance to the physics and chemistry of solids due to their impact on the structure and electronic properties of the material, especially its surface. The study of defects on CeO2 is of interest due to CeO2's nonreactive and nonmagnetic nature in the bulk, transforming to reactive and nanomagnetic at the nanoscale. Many of nanoceria's properties are due to the redox cyclability of Ce4+/Ce3+ transformations depending on the surrounding oxygen partial pressure. Quantifying these oxygen vacancies and understanding the mechanisms behind their formation is challenging due to their elusive and dilute nature. Results from traditional spectroscopic and temperature programmed probes are ambiguous due to the surface reduction of the system in ultra high vacuum and at high temperatures. I present a novel way to identify and quantify the oxygen vacancies by magnetic susceptibility. This technique is sensitive to the transformation of diamagnetic Ce4+ to paramagnetic Ce3+ (4f1 with S=1/2 and J=5/2), and is key to understanding the mechanisms behind oxygen vacancy formation and its implications on the resulting nanomagnetism. Three different shaped CeO2 nanoparticles (cubes, rods and spheres) are examined with different terminations of the surface, and thereby changing the Ce4+/Ce3+ and oxygen vacancies. I identified that the missing oxygen atoms in the crystal are adsorbed as molecular oxygen (O2), and their antiferromagnetic-to-paramagnetic transition is used to quantify and understand CeO2's unusual magnetism and reactivity in catalytic processes.

 

3.  Melissa Anholm

A Search for Right-Handed Currents in 37K Beta Decay

The TRINAT collaboration has performed precision measurements of the kinematics of the daughter particles in the decay of 37K. This isotope decays by β+ emission in a mixed Fermi/Gamow-Teller transition to its isobaric analog, 37Ar. Because the higher-order standard model corrections to this decay process are well understood, it is an ideal candidate for for improving constraints on interactions beyond the standard model. The experimental setup utilizes a magneto-optical trap to confine and cool samples of 37K, which are then spin-polarized by optical pumping. This allows measurements to be performed on both polarized and unpolarized nuclei, which is valuable for a complete understanding of systematic effects. Precision measurements of this decay are expected to be sensitive to the presence of right-handed vector currents, as well as a linear combination of scalar and tensor currents. Progress towards a final result is presented here.