Seminar Tuesday August 25 – Paul Smith

Speaker: Paul Smith
Location: Physics 175
Time: August 25 2015

All dressed up and ready to go: a quick look at dressed fields.

Abstract: Exotic states not predicted by the conventional quark model, such as X(3872), have been discovered en masse over the past decade. Traditionally, exotic heavy-light diquark correlation functions formulated using Schwinger strings have been used to study these states. In this talk I explore the possibility of using a “dressed” field as an alternative means of gathering gauge-invariant information about diquark interactions.

Alternative Abstract: Join me on a magical journey through the realms of particle physics, quantum field theory, and locally gauge invariant fields! A brief gander through history will be taken as I look (very briefly) at the development of the standard model. The major players (gluons, pions, quarks, and more!) will be introduced in a casual, almost personal, fashion and their characteristics and interactions will be introduced. Of course, this will only be done after laying down a little bit of world-building through the establishment of some of the main components that drive the QCD life. Action and drama is the name of the game as the struggle for gauge invariant information is brought to a shocking conclusion.

Be there. Experience QCD, gauges, and Bohr bashing like never before (In all reality, it’ll probably just be a generic grad student seminar, but let’s keep that on the dl).

Seminar Tuesday August 18 – Masaru Nakajima

Speaker: Masaru Nakajima
Location: Physics 175
Time: 3:30 August 18, 2015

Geodesic acoustic mode in STOR-M

Abstract: Our study pertains to plasma physics in application for nuclear fusion energy. Numerous instabilities and turbulent transport have plagued fusion devices such as tokamak, and their cause and effect are topics of active research today. My topic, geodesic acoustic mode (GAM), falls under such a category of work. GAM was first predicted as a standing wave of density on flux surfaces in toroidal devices. The last two decades have seen observations of GAM in many toroidal devices and further development in its theory. The increasing interest in GAM is due to the roles that GAM can play in (in)stability, turbulent transport, and other oscillations.

Our focus is to detect GAM in SOTR-M device, the tokamak device at University of Saskatchewan, and study its behaviour under external effects such as electrode biasing. To date, we obtained a signature of GAM in our preliminary experiments. In my presentation I will discuss
basic plasma physics for GAM, our experiments and first findings.

Seminar Tuesday August 11 – Caelia Gardiner

Speaker: Caelia Gardiner
Location: Physics 175
Time: 3:30 August 11 2015

Forecasting Space Weather with SuperDARN

Abstract: Space weather can interfere with human activity in a variety of ways. Satellites and spacecraft can be damaged, human lives in orbit endangered, communications and GPS on the surface disrupted and power grids impaired. Due to the large effect space weather can have on our lives, research is conducted worldwide to help predict space weather patterns. Currently, the Canadian Space Weather Forecast Center of Natural Resources Canada is performing forecast services, collecting data on the magnetic field of the Earth at different points and issuing geomagnetic storm warnings. Because SuperDARN also provides international research stations with information on plasma motion in the ionosphere, it would be advantageous to have a similar forecast system based on radar readings. This system can be used to collaborate with existing magnetometer predictions to produce a more robust forecast process.

Convection patterns in the ionosphere arise due to the solar wind plasma and the interplanetary magnetic field orientation. These patterns are inferred from particle velocity readings taken by the SuperDARN. The combination of convection maps and particle velocity line graphs will help predict plasma motion in the atmosphere. The existing convection maps, created using IDL and the Go library, display a rudimentary outline of the polar coast. It would be more beneficial to the reader to have a more explicit image of the polar coast under the convection maps, with the added functionality of labeling specific locations. Existing equirectangular map projections are warped to provide a polar stereographic view, with a conversion from geographic latitude/longitude to geomagnetic coordinates. This warped image is placed under the convection map in place of the coastal outline to provide a more visually coherent image. While this projection functionality will make the convection maps less ambiguous, it will also be useful in future polar maps, for educational or outreach purposes.

Seminar Tuesday August 4 – Tristan de Boer

Speaker: Tristan de Boer
Location: Physics 175
Time: 3:30 August 04 2015

Abstract: Broadly speaking, an important factor behind our ever-improving standards of living is the continuous improvement of the basic materials used in the devices around us. Synthesizing new materials and characterizing them is an essential part of developing new and improved devices. To this end I’ll present recent work on two material systems, MSiN2 (M = Mg, Ca) and In2O3. Our approach utilizes spectroscopic X-ray measurements sensitive to the partial electronic density of states together with first principles density functional theory (DFT) calculations to gain insight into the electronic properties of material systems.

Nitridosilicates MSiN2 (M = Mg, Ca) are promising candidates for manifold industrial applications which require excellent thermal, mechanical and electronic properties, as well as for rare-earth doped LED-Phosphors. For MgSiN2 the band gap has been determined to be 5.6 ± 0.2 eV, in agreement with a theoretically predicted band gap of 5.72 eV. For CaSiN2 the band gap has been determined to be 3.8 ± 0.2 eV in contrast with a theoretically predicted value of 4.88 eV. Good agreement between the measured and calculated spectra is obtained, supporting the calculated electronic density of states of these materials.

Recent studies on In2O3  have revealed a rich phase diagram and led to the discovery of new polymorphs, including the synthesis and ambient recovery of Pbcn In2O3. The electronic properties of this new phase are studied together with other better known polymorphs (Ia-3 and R-3c) using soft X-ray absorption and emission spectroscopy. Together with complementary full-potential all electron DFT calculations, this allows important material parameters, such as the electronic band gap and partial density of states, to be elucidated. Excellent agreement between experiment and theory is obtained, with band gaps of  3.2±0.3, 3.1±0.3 and $2.9±0.3 eV determined for the  Ia-3, R-3c and Pbcn In2O3 polymorphs, respectively. The effective mass of carriers in Pbcn In2O3 is predicted to be 12% less than in the widely used Ia-3 polymorph while having a similar effective optical band gap.

Seminar Thursday July 28 – William Davis

Speaker: William Davis
Location: Physics 175
Time: 3:30, July 28, 2015

Characterization and Study of a Medical Linear Accelerator Mounted Mini-Beam Collimator

Abstract: Conventional external beam radiotherapy makes use of uniform beams to deliver a dose of radiation.  This method has proven effective in the treatment of many cancers, but unavoidably deposits dose in healthy tissue as well.  Spatial fractionation techniques seek to minimize the damage to healthy tissue caused by the radiation beam.  Mini-beam radiotherapy is a method of spatial fractionation which makes use of an array of parallel planar beams.  A group at the Saskatchewan Cancer Agency have developed a mini-beam collimator for use with a medical linear accelerator operated at a nominal energy of 6MV.
Various attributes of the mini-beam collimated beam are under study at the Saskatoon Cancer Centre.   The dose distribution and its consistency across a set of medical linear accelerators have been measured and simulated.  Variations in dose due to accelerator settings are being characterized.  The effect of mini-beam irradiation on cells is currently being examined.

Seminar Tuesday July 21 – Reza Behbahani

Speaker: Reza Behbahani
Location: Physics 175
Time: 14 July, 2015, 3:30

Energetic ion beam emission enhancement for short lived radio isotopes (SLRs) production by using a low energy dense plasma focus device.

Abstract: ​Short lived radioisotopes (SLR) such as 13N, 17F, 18F, 15O, and 11C have been produced through either external solid (exogenous method) or high atomic number gas (endogenous method) targets. These radioisotopes are positron emitter used for positron emission tomography (PET) imaging. Positron emission tomography is an imaging technique that shows the distribution of positron-emitting nuclides in a patient’s body. SLRs (10 min. to 100 min. half lifetime) must be produced in proximity of treatment or diagnostic facilities .Cyclotron is often used for this purpose. A new Dense Plasma Focus machine ( DPF) is being develop at University of Saskatchewan to produce Nitrogen-13 radioisotope. Nitrogen-13 is used to tag ammonia molecules for PET myocardial perfusion imaging. Dense Plasma Focus machine ( DPF) can generate high energetic ion with suitable flux to produce Nitrogen-13 through the 12C(d, n)13N nuclear reaction. In this presentation I am going to introduce DPF machine, progress of the project and the future approach.

Seminar Tuesday July 14 – Niloofar Zarifi

Speaker: Niloofar Zarifi
Location: Physics 175
Time: 14 July, 2015, 3:30

Computational approaches and structural prediction of high pressure molecular solids

Abstract: ​My talk is divided into two main sections. The first part is to examine the performance and reliability of several current density functionals in the description of the electronic structures of small band gap materials and strongly correlated systems. To accomplish the first goal, we employed density functional theory (DFT) and several correlation corrected functionals to investigate the properties of solid AlH3 and EuO at high pressure. The second objective of this investigation is to predict energetically stable crystalline structures at high pressure. The reliability and relative efficiency of two recently proposed structure prediction methods, viz, Particle Swarm Optimization (PSO) and the Genetic Algorithm (GA) were critically examined. We applied the techniques to two separate systems. The first system is solid CS2 which was recently found to be a superconductor with a critical temperature of 6 K from 60 – 120 GPa and second system is prediction of plausible crystalline structures of Xe-halides at high pressure.

Seminar Tuesday July 7 – Greg Tomney

Speaker: Greg Tomney
Location: Physics 175
Time: 7 July, 2015, 3:30

Magnetic Saturation of the Iron Core in the STOR-M Tokamak

Abstract: In the field of controlled nuclear fusion, the tokamak (a toroidal vacuum chamber which uses magnets to confine and heat plasma to fusion temperatures/ pressures) is one of the most promising candidates for a fusion reactor. The spherical tokamak (ST) has been a good candidate for tokamak reactor designs since its inception in the 1980s. The design boasts economic benefits that are especially important for labs looking to build tokamaks for research as the ST cuts down on the cost of the large magnets needed to establish the strong magnetic fields in a tokamak. One of the problems with the ST design is less space for a centre solenoid which can be used to induce plasma current. Using the iron-core tokamak STOR-M we are able to study plasma performance as the core becomes increasingly magnetized. This effect is of some concern to the tokamak community as it becomes more pronounced as the size of the tokamak core region (the hole in the tokamak torus) decreases.

Seminar Tuesday June 30 – Thomas Tolhurst

Speaker: Thomas Tolhurst
Location: Physics 175
Time: 3:30 June 30 2015

Next-generation phosphors for solid-state lighting studied with X-ray spectroscopy and density functional theory

Abstract: The recently reported nitridolithoaluminate Sr[LiAl3N4]:Eu2+ and nitridomagnesosilicate Sr[Mg3SiN4]:Eu2+ are leading candidates for use in the next generation of phosphor-converted light-emitting diodes (pc-LEDs). They have garnered special interest due the their uniquely narrow bandwidths for Eu2+doped phosphors and high emission intensities in the critical, red region of the electromagnetic spectrum. A presentation of key features of their electronic structures, determined through density functional theory calculations and experimental soft X-ray spectroscopy measurements, will be given. This study builds on previously reported results observed through X-ray diffraction, visible light excitation and electron energy loss spectroscopy. Both materials are found to have large, indirect band gaps and an overall similar electronic structure. Both are narrow emitters, but Sr[Mg3SiN4]:Eu2+ shows the narrowest emissions to date of any red-emitting, Eu-doped phosphor. Further, they emit at noticeably different wavelengths in the red spectral region and have vastly different thermal quenching properties. These key differences in their emission properties in the visible region can be tied to subtle differences in their respective electronic structures. This talk will outline these structural differences and how they lead to the observed differences in the visible emissions of these phosphors.

Seminar Tuesday June 23 – Ashton Reimer

Speaker: Ashton Reimer
Location: Physics 175
Time: 23 June 2015 , 3:30

Measurement Techniques and Signal Processing with SuperDARN Radars

Abstract: Studying and understanding Geospace (Near-Earth Space) Weather is increasingly important as we consistently rely on more satellite based technologies like GPS. Magnetospheric and Ionospheric processes, like patches, or F-region irregularities can disrupt services like GPS. The Super Dual Aurora Radar Network (SuperDARN) radars are used to measure the magnetospheric plasma circulation via ionospheric F-region irregularities. Often these irregularities are overspread (long range: > 1000 km and high velocity: ~1 km/s), therefore SuperDARN radars employ a multi-pulse technique to overcome these range-doppler ambiguities. The accuracy and quality of the radar measurements primarily depends on the transmitted waveform and the signal processing techniques used on the received signal. In this talk I will briefly describe some different measurement techniques and fitting processes and present some of my work attempting to improve current operations.