Events List for the Academic Year

Event Time: Tuesday, June 25, 2019 | 2:00 pm - 4:00 pm
Event Location:
Room 318, Hennings Bldg.
Add to Calendar 2019-06-25T14:00:00 2019-06-25T16:00:00 Departmental Oral Examination (Thesis Title: "Search for New High-Mass Phenomena in Events with Two Muons using the ATLAS Detector at the Large Hadron Collider") Event Information: Abstract: Although elementary particles and their interactions are extremely well modeled by the Standard Model of particle physics, some experimental measurements cannot be explained entirely by this theory. Many extensions of the Standard Model predict the existence of new phenomena at high energies. In particular, new resonance models and contact interaction models leading to dimuon final states are numerous. This dissertation presents a search for new high-mass phenomena in events with two muons using the ATLAS detector at the Large Hadron Collider. The search results are found to be consistent with the Standard Model background prediction. Interpretations both in the context of resonant and non-resonant new physics models are carried out. In particular, lower limits on the mass of hypothetical Z' bosons are set between 4.0 TeV for the Z'SSM model and 3.3 TeV for the Z'ψ model, and lower limits on the contact interaction energy scale Λ are set between 18 TeV and 30 TeV, depending on the chiral structure of the contact interaction. In addition to data analysis at the energy frontier, the performance of muon reconstruction and identification within the ATLAS experiment is detailed. More precisely, calculations of muon trigger scale factors for high-pΤ muons using events containing a leptonically decaying W boson and jets are presented. A new muon identification working point is also investigated. Finally, as the ATLAS experiment enters its second long shutdown, the first layer of the endcap regions of the muon spectrometer will be replaced with the New Small Wheels (NSWs) in order to improve both the triggering and tracking capabilities of the ATLAS detector. One of the two main technologies used in the NSW is small-strip Thin Gap Chambers (sTGCs). Work carried out with the sTGC collaboration, which aims to characterize and integrate the NSW into the ATLAS detector in the coming years, is described. Particularly, results of various test beam campaigns carried out at Fermilab and at CERN are presented. Position resolution measurements of less than 50μm are obtained. Measurements using the latest electronics readout chain of the sTGC detectors under realistic conditions are also presented. Event Location: Room 318, Hennings Bldg.
Event Time: Friday, June 21, 2019 | 2:00 pm - 4:00 pm
Event Location:
Room 318, Hennings Bldg.
Add to Calendar 2019-06-21T14:00:00 2019-06-21T16:00:00 Departmental Oral Examination (Thesis Title: "Search for the production of Higgs bosons in association with top quarks and decaying into bottom quark pairs with the ATLAS detector") Event Information: Abstract: The Standard Model of particle physics (SM) describes mass generation of fundamental particles via the Brout-Englert-Higgs mechanism. It predicts Yukawa interactions between the Higgs boson and fermions, with interaction strengths proportional to the fermion masses. The largest Yukawa coupling is that of the top quark, and its value has implications in particle physics and beyond. As the SM is not a complete theory of nature, detailed measurements of its predictions are a mandatory step towards improving the understanding of nature. This dissertation presents a search for Higgs boson production in association with a top quark pair, a process directly sensitive to the top quark Yukawa coupling. The search uses 36.1 fb−1 of data at √s = 13 TeV, collected with the ATLAS detector at the Large Hadron Collider (LHC) in 2015 and 2016. It is designed for Higgs boson decays to bottom quarks, and decays of the top quark pair resulting in one or two electrons or muons. The discrimination between the signal Higgs boson production process and background processes, dominated by the production of top quark pairs, is performed with multivariate analysis techniques. The matrix element method is used and optimized for this search. Possible machine learning extensions of the method are investigated to help overcome its large computational demand. The obtained ratio of the measured cross-section for the signal Higgs boson production process to the prediction of the SM is µ = 0.84 (+0.64, −0.61). The expected sensitivity of an extension of the search, using 139.0 fb−1 of data collected between 2015–2018, is 3.3σ. Data collected between 2016–2018 is also used in a measurement of the ATLAS muon trigger system efficiency. A statistical combination of searches for Higgs bosons produced in association with top quark pairs is performed, including the search for Higgs boson decays to bottom quarks and additional final states. The combination results in the observation of this Higgs boson production process with an observed significance of 5.4σ, compared to an expected sensitivity of 5.5σ. It experimentally establishes Yukawa interactions in the SM. Event Location: Room 318, Hennings Bldg.
Event Time: Thursday, June 20, 2019 | 12:30 pm - 2:30 pm
Event Location:
Room 301, Hennings Building
Add to Calendar 2019-06-20T12:30:00 2019-06-20T14:30:00 Final PhD Oral Examination (Thesis Title: “Dirac Materials and the Response to Elastic Lattice Deformation”) Event Information: Abstract: Dirac materials have formed a thriving and prosperous direction in modern condensed matter physics. Their bulk bands can linearly attach at discrete points or along curves, leading to arc or drumhead surface states. The candidate Dirac materials are exemplified by Dirac/Weyl semimetals, Dirac/Weyl superconductors, and Dirac/Weyl magnets. Owing to the relativistic band structure, these materials have unique responses to the applied elastic crystalline lattice deformation, which can induce pseudo-magnetic and pseudo-electric fields near the band crossings and produce transport distinguished from that caused by ordinary magnetic and electric fields. In this dissertation, I will demonstrate exotic transport due to the strain-induced gauge field in Weyl semimetals, Weyl superconductors, and Weyl ferromagnets. I will first elucidate that a simple bend deformation can induce a pseudo-magnetic field that can give rise to the Shubnikov-de Haas oscillation in Weyl semimetals. Then I will elaborate that strain can Landau quantize charge neutral Bogoliubov quasiparticles as well and result in thermal conductivity quantum oscillation in Weyl superconductors. Lastly, I will consider the strain-induced gauge field beyond the fermionic paradigm and explain various quantum anomalies of magnons in Weyl ferromagnets. Event Location: Room 301, Hennings Building
Event Time: Wednesday, June 19, 2019 | 1:00 pm - 3:00 pm
Event Location:
Room 309, Hennings Bldg.
Add to Calendar 2019-06-19T13:00:00 2019-06-19T15:00:00 Departmental Oral Examination (Thesis Title: "Studies of atmospheric properties for optical ground-based Astronomy and methods for laser guide star adaptive optics performance increase") Event Information: Abstract: Ground-based Astronomy suffers from wavefront distortion by the turbulent atmosphere, preventing telescopes to reach diffraction-limited resolution. Modern large telescopes and next generation extremely-large telescopes use or will use adaptive optics systems with laser guide stars to correct for atmospheric wavefront distortion. The first part of the thesis deals with astronomical site testing and the second part with methods for adaptive optics system improvement. Meteorological data for 15 observatory sites have been studied. Monthly averages of cloud cover, wind speed at 200 hPa, precipitable water vapour, vertical wind velocity and aerosol index have been compared for the sites. The longterm evolution over 45 years of these five atmopsheric quantities was investigated. Site testing campaigns aim at the characterization of potential telescope sites in terms of optical turbulence. Using scintillometers, ground layer turbulence profiles can be measured. For an assessment of sites long-term statistics are needed. Two campaigns for daytime and nighttime turbulence profiling have been started and preliminary results will be shown. Methods for increasing adaptive optics system performance are being studied. Polarization modulation of the adaptive optics laser might be a method for laser guide star return flux enhancement. An experiment has been carried out at the Roque de la Muchachos Observatory on La Palma. As a byproduct of the experiment the Larmor frequency of mesospheric sodium was measured and the magnetic field strength in the mesosphere was determined. Adaptive optics system could benefit from an estimate of the mesospheric sodium density profile. Sodium density profiles can be retrieved by partial amplitude modulation with pseudo-random binary sequences of continuous-wave lasers. Results for an experiment at the Large Zenith Telescope in Maple Ridge and a feasibility study of this method for extremely-large telescopes will be presented. Event Location: Room 309, Hennings Bldg.
Event Time: Wednesday, June 19, 2019 | 12:30 pm - 2:30 pm
Event Location:
188 - Brimacombe 2355 E Mall, Vancouver, BC V6T 1Z4
Add to Calendar 2019-06-19T12:30:00 2019-06-19T14:30:00 Final PhD Oral Examination (Thesis Title: “Realizing High-Energy Physics in Topological Semimetals”) Event Information: Abstract: The discovery of topological phases of matter has brought high-energy and condensed matter communities together by giving us shared interests and challenges. One fruitful outcome is the broadened range of possibilities to realize high-energy physics in table-top experiments. My collaborators and I have found scenarios in which influential high-energy ideas emerge in solid-state systems built from topological semimetals – gapless topological phases which have drawn intense research efforts in recent years. This Thesis details our proposals for realizing Majorana fermions, Adler-Bell-Jackiw anomaly, and holographic black holes in superconductor-Weyl-semimetal heterostructures, mechanically strained Weyl semimetal nanowires/films, and graphene flakes subject to strong magnetic fields, respectively. By analyzing the effects of realistic experimental conditions, we will demonstrate that our proposals are experimentally tangible with existing technologies. Event Location: 188 - Brimacombe 2355 E Mall, Vancouver, BC V6T 1Z4
Event Time: Friday, June 7, 2019 | 12:00 pm - 2:00 pm
Event Location:
Room 309, Hennings Bldg
Add to Calendar 2019-06-07T12:00:00 2019-06-07T14:00:00 Departmental Oral Examination (Thesis Title: "Energy, Entropy and Spacetime: Lessons from Semiclassical Black Holes") Event Information: Thesis Abstract: This doctoral thesis explores semiclassical effects on black hole physics. Semiclassical theory refers as the application of quantum field theory in curved, classical background geometries, which respond to the expectation value of the regularised stress-energy tensor of the quantum matter. Among the original findings, I develop a few useful techniques to help regularising the stress-energy tensor in two dimensions; and their application to a model of stellar collapse to analyse the importance of quantum mechanical effects in the collapse itself. I found an explicit example showing that the behaviour of the late-times Hawking radiation does not depend on the details of the collapse and argued that any quantum mechanical effect is negligible for the collapse of an astrophysical object (whose mass is comparable to the solar mass). In the realm of black hole thermodynamics, I proved its first law for stationary black holes, proposed a definition for the entropy in piecewise stationary black holes which I showed to obey the generalised second law of thermodynamics. After also discussing its zeroth law, it becomes clear that this set of laws are originated in the semiclassical approach and it is made clear which hypothesis are necessary for these laws to hold. The derivation of these laws also point towards the long-standing question of the interpretation of the Bekenstein-Hawking entropy as accounting from the information perspective. Event Location: Room 309, Hennings Bldg
Event Time: Thursday, June 6, 2019 | 2:00 pm - 3:30 pm
Event Location:
BRIM 311
Add to Calendar 2019-06-06T14:00:00 2019-06-06T15:30:00 CM Seminar: Kondo Blockade and Generative Hamiltonian Learning for molecular electronics Event Information: Abstract:  When nanoscale components are incorporated into external circuits, electronic transport can exhibit striking quantum phenomena with no classical analogue. Molecular junctions, in which a single molecule bridges the gap in a nanowire, constitute a particularly rich set of systems, demonstrating both strong correlation effects such as Coulomb blockade and Kondo, as well as quantum interference arising from orbital complexity. In this seminar, I discuss a general strategy for understanding the fundamental physics of such systems, which involves mapping complex microscopic models for the junction onto simpler generalized impurity problems that can be treated exactly. I highlight the limitations of the standard perturbative approaches, and introduce a new method for deriving effective models via machine learning techniques. The consequences for experimentally measurable quantum transport in molecular junctions are explored, including so-called "Kondo blockade". [1] Nature Communications, 8, 15210 (2017) Bio: Prof. Andrew Mitchell is a condensed matter theorist working on strongly correlated electron systems in the context of nanoelectronics, including quantum dot devices and molecular electronics. He obtained his PhD from Oxford University in 2010, and had postdoctoral fellowships at Cologne, Oxford, and Utrecht, before taking up a permanent position in theoretical physics at University College in Dublin, Ireland.   Event Location: BRIM 311
Event Time: Wednesday, June 5, 2019 | 3:00 pm - 4:30 pm
Event Location:
BRIM 311
Add to Calendar 2019-06-05T15:00:00 2019-06-05T16:30:00 CM Seminar: From MEMS to Gravitational Wave Detectors: modeling energy dissipation in oxyde glasses at the atomic scale Event Information: Abstract: How are sound waves attenuated when they travel in a medium? How to damp most efficiently the vibrations due to an earthquake? Inversely, how to build a stable resonator? or avoid loosing energy when a laser beam rebounds on a mirror in a gravitational wave detector, the process which currently limits the precision of these very large interferometers. In order to answer these questions, we need to understand how mechanical energy is dissipated in materials. This process is complex and originates from distinct sources depending on the frequency of the deformation and the ratio between its wavelength and the characteristic length scales of the medium. The situation is particularly complex in disordered solids, which show a hierarchy of length scales. In this talk, we will discuss energy dissipation in oxide glasses and in particular silica, which is both a model glass and a technological glass used in many applications, including MEMS and optical coatings.  We will show how atomistic modeling can address both the very low (~ MHz) and very high (~ THz) frequency regimes, using different approaches. At low frequencies, dissipation is controlled by the thermally activated relaxation of local bi-stable regions, two-level systems, whose properties can be measured by sampling the potential energy landscape of the glass. By way of contrast, at high frequencies, the glass dynamics becomes harmonic and can be described using a normal mode analysis. We will see that in silica, which forms a tetrahedral network without coordination defects, dissipation and viscoelastic effects at both low and high frequencies are due to the vibration and reorientation of the Si-O-Si bonds between tetrahedra. Biography: David Rodney graduated from Ecole Paris Mines and University of Orsay. After a PhD at the Polytechnic Institute of Grenoble, he became a lecturer at SIMaP lab at INP Grenoble. From 2008 to 2009 he was a visiting professor at MIT in the department of "Material Science and Engineering". IUF junior in 2009, he joined the UCB Lyon 1 and ILM in teams Model ization of Condensed Matter and Interfaces and SOPRANO. Currently David works on the simulation of the mechanical properties of solids.   Event Location: BRIM 311
Event Time: Friday, May 17, 2019 | 2:00 pm - 3:30 pm
Event Location:
MACLEOD 418, 2335 Engineering Lane
Add to Calendar 2019-05-17T14:00:00 2019-05-17T15:30:00 CM Seminar: Vector beams, high harmonic generation and THz solenoidal magnetic fields Event Information: Abstract:  We use intense vector beams to generate high harmonics or to create solenoidal currents in solids or gases.  We create circularly polarized harmonics and we predict THz magnetic fields reaching the scale that is only available at user facilities. Event Location: MACLEOD 418, 2335 Engineering Lane
Event Time: Thursday, May 16, 2019 | 10:00 am - 11:30 am
Event Location:
Hennings 318
Add to Calendar 2019-05-16T10:00:00 2019-05-16T11:30:00 The Physics Course Laboratory Report as a Rhetorical Act Event Information: The field of science education has paid considerable attention to what students should write in their lab reports, but comparatively little attention has been given the laboratory report writing as a rhetorical activity—one in which writers attempt to communicate with a particular audience for a specific purpose. This is unfortunate, since labs remain students’ primary experience with scientific writing in the undergraduate science curriculum—especially in mathematically-heavy fields such as physics. In many undergraduate courses, lab report writing assignments tend to reinforce misunderstandings about scientific communication students often bring from high school, rather than helping students develop a more sophisticated and effective understanding of effective scientific communication. This talk invites us to reconsider the experience of the undergraduate physics lab report—both for students as writers and instructors as readers. Relevant Publication: Inquiry-based writing in the laboratory course   Other talks by Cary while he is here   Public Talk: Text Recycling in Scientific Writing Cary Moskovitz, Director, Writing in the Disciplines, Thompson Writing Program, Duke University May 15, 10:00 - 11:30 am MSL 102 Text recycling (often called “self-plagiarism”) is the reuse of textual material from existing documents in a new text without the use of quotation marks or other means of identifying the reused material as such. While text recycling has long been common practice in some STEM fields, the recent adoption of digital plagiarism detection tools by scientific journals has made text recycling the subject of increasing controversy and ethical debate. Some researchers and editors argue that text recycling is inherently unethical or otherwise problematic. Others, including organizations such as the American Psychological Association and the Committee on Publication Ethics (COPE), state that some uses of text recycling are acceptable and, in limited circumstances, desirable—particularly in Introduction and Methods sections. Although text recycling is an increasingly important ethical issue in scientific communication (even listed as a priority for RCR training in an ORS-funded study), it is rarely addressed in the ethical training of researchers or in scientific writing textbooks or websites. ***For full details and to register for the text recycling talk: https://events.ctlt.ubc.ca/events/text-recycling-in-scientific-writing/   Lunch Chat: Volunteer Expert Readers: The Duke Reader Project Cary Moskovitz, Director, Writing in the Disciplines, Thompson Writing Program, Duke University May 15, ~11:45 am - 1:30 pm CHEM D213 Volunteer Expert Readers (VER) is a novel approach to providing undergraduates with feedback on writing assignments via an otherwise untapped educational resource: university alumni and employees who normally play no role in the institution's educational mission. In the VER approach, students are paired with volunteers whose backgrounds make them suitable readers for specific writing assignments. Having the opportunity to discuss their work in progress with experts in the field increases students’ engagement in class writing assignments. The feedback also helps students learn to anticipate the needs and expectations of readers, and to revise their writing to make it more effective for the intended audience.  By participating as readers, members of the broader college community can play a direct role in helping students develop the communication and reasoning skills that are so important for their success in both professional and civic life. ***To register for the lunch chat, please email jandciu@science.ubc.ca Relevant Publications: Reader Experts Help Students Bring the Write Stuff Volunteer Expert Readers for STEM Student Writers  The Duke Reader Project: Engaging the University Community in Undergraduate Writing Instruction   Event Location: Hennings 318
Event Time: Saturday, May 11, 2019 | 10:00 am - 2:00 pm
Event Location:
Beaty Biodiversity Museum and various locations on campus
Add to Calendar 2019-05-11T10:00:00 2019-05-11T14:00:00 UBC Science Rendezvous Festival Event Information: Join us for The University of British Columbia’s 2019 Science Rendezvous festival. Science Rendezvous is an annual festival held across Canada showcasing the Art in Science. Science Rendezvous theme this year is “STEAM big” encouraging new exciting collaborations between scientists and artists, science and art. On Saturday May 11 (10 AM – 2 PM) race across the University to complete our Science Chase! From the Old Barn Community Centre to the Department of Chemistry, intrepid visitors will race across campus and experience the power of STEAM! Check out art-science performances (poetry and 3D-printed violin), take a ride on a hovercraft, discover micro-organisms in the pond, and learn about the tectonic forces that shape and alter our world. Make it through all the explosions, workshops, and hands-on experiments to emerge a science victor! Cool prizes awaits – including coupons for free summer camp spots, circuit kits, dinosaur bone samples, and Science Rendezvous T-shirts! For more information, including participating partners and activity descriptions, visit the event website: https://www.sciencerendezvous.ca/event_sites/ubc/ Event Location: Beaty Biodiversity Museum and various locations on campus
Event Time: Friday, May 10, 2019 | 11:00 am - 12:30 pm
Event Location:
Orchard 1001
Add to Calendar 2019-05-10T11:00:00 2019-05-10T12:30:00 How do you teach students to evaluate their answers to physics problems? Event Information: This is a public talk as part of the annual UBC Physics and Astronomy Education Research Group's Open Retreat. Abstract: Physicists need ways to evaluate our solutions to the problems we consider – the universe has no solution manual! This “solution evaluation” is just one aspect of physics sensemaking. To help students become more powerful physics sensemakers and build a habit of evaluating their solutions, my research team has developed an intermediate mechanics course for sophomore-level physics majors that has an explicit focus on physics sensemaking, particularly solution evaluation. The strategies we emphasize include: thinking about mathematical and physical “beasts,” considering special cases, and thinking about the covariational behavior of functions. I will describe how we’ve been thinking about evaluative sensemaking, some of the instructional strategies we’ve used the course, and some of our research about the ways students evaluate algebraic solutions to physics problems. We find that the variety of ways students make sense of algebraic answers to physics problems is dizzying, even when we suggest specific strategies to try. Event Location: Orchard 1001
Event Time: Friday, May 10, 2019 | 9:15 am - 10:45 am
Event Location:
Orchard 1001
Add to Calendar 2019-05-10T09:15:00 2019-05-10T10:45:00 Teaching and learning how to troubleshoot in upper-division labs Event Information: This is a public talk as part of the annual UBC Physics and Astronomy Education Research Group's Open Retreat. Abstract: Troubleshooting systems is an integral part of experimental physics in both research and educational settings. Accordingly, developing students’ ability to troubleshoot is an important goal for undergraduate physics lab courses. My colleagues and I have investigated student approaches to troubleshooting using think-aloud interviews in which pairs of students from two institutions were asked to diagnose and repair a malfunctioning circuit. We have also conducted national-scale studies in which we interviewed over 50 lab instructors about their teaching strategies, with one study focused specifically on efforts to improve students’ troubleshooting abilities. In this presentation, I will draw on findings from these studies and the literature more broadly to paint a picture of teaching and learning how to troubleshoot. I will focus on the roles of model-based reasoning, peer-to-peer metacognitive interactions, and the cognitive apprenticeship style of instruction. Finally, I will discuss practical implications for upper-division lab courses. Electronics lab instructors’ approaches to troubleshooting instruction: https://journals.aps.org/prper/abstract/10.1103/PhysRevPhysEducRes.13.010102 Event Location: Orchard 1001
Event Time: Tuesday, May 7, 2019 | 10:00 am - 12:00 pm
Event Location:
Room 318, Hennings Bldg
Add to Calendar 2019-05-07T10:00:00 2019-05-07T12:00:00 Departmental Oral Examination (Thesis Title: "Aspects of quantum information theory in guantum field theory and gravity") Event Information: Abstract: We discuss applications of quantum information theoretic concepts to quantum gravity and the low-energy regime of quantum field theories. The first part of this thesis is concerned with how quantum information spreads in four-dimensional scattering experiments for theories coupled to quantum electro- dynamics or perturbative quantum gravity. In these cases, every scattering process is accompanied by the emission of an infinite number of soft photons or gravi-tons, which cause infrared divergences in the calculation of scattering probabilities. There are two methods to deal with IR divergences: the inclusive and dressed formalisms. We demonstrate that in the late-time limit, independent of the method, the hard outgoing particles are entangled with soft particles in such a way that the reduced density matrix of the hard particles is essentially completely decohered. Furthermore, we show that the inclusive formalism is ill-suited to describe scattering of wavepackets, requiring the use of the dressed formalism. We construct the Hilbert space for QED in the dressed formalism as a representation of the canonical commutation relations of the photon creation/annihilation algebra, and argue that it splits into superselection sectors which correspond to eigenspaces of the generators of large gauge transformations. In the second part of this thesis, we turn to applications of quantum information theoretic concepts in the AdS/CFT correspondence. In pure AdS, we find an explicit formula for the Ryu-Takayanagi (RT) surface for special subregions in the dual conformal field theory, whose entangling surface lie on a light cone. The explicit form of the RT surface is used to give a holographic proof of Markovicity of the CFT vacuum on a light cone. Relative entropy of a state on such special subregions is dual to a novel measure of energy associated with a timelike vector iiiflow between the causal and entanglement wedge. Positivity and monotonicity of relative entropy imply positivity and monotonicity of this energy, which yields a consistency conditions for solutions to quantum gravity. Event Location: Room 318, Hennings Bldg
Event Time: Monday, May 6, 2019 | 12:40 pm - 3:00 pm
Event Location:
Room 309, Hennings Bldg
Add to Calendar 2019-05-06T12:40:00 2019-05-06T15:00:00 Departmental Oral Examination (Thesis Title: "Investigating the Dark Sector of the Universe Using Cosmological Observables") Event Information: Abstract: Although the Standard Model of particle physics has been a phenomenal success in modelling known particles and predicting new, theoretically founded particles, it is known to be incomplete. Although the Standard Model of cosmology has been a phenomenal success in modelling the evolution of the Universe, it too has open questions that remain unresolved. In this thesis, we aim to address properties of new physics models that are being developed that aim to answer these open questions. In particular, we wish to focus on and examine in detail the connection between the dark sector of the Universe and the visible sector. In examining this connection, we may use cosmological observables to place strict limits on new theories that go beyond the Standard Model. In the first part of this thesis we will address the flow of energy from the visible sector to the hidden via a phenomenon known as freeze-in. Here, we explore the effects that early-time, ultraviolet energy transfer may have on the infrared, late-time evolution of a dark matter candidate. We use a simplified hidden-sector model to highlight the notion that operators that are typically considered early may have relevant late-time effects. Following this, we consider the reverse energy flow, and consider how dark-sector energy injection via decays of electromagnetic radiation may affect the products of Big Bang Nucleosynthesis. In this section, we focus on arbitrary light particle (< 100 MeV) decays, and identify how direct and indirect alteration of the light element abundances can be constrained using the measured values today. Direct alteration is caused by photodissociation, while indirect effects are felt through changes in the radiation energy density. Finally, we consider a full and rich dark sector, consisting of a non-Abelian SU(3) gauge force. This new gauge field presents itself as glueballs after a confining transition. We study the effects of this confining transition, as well as the subsequent dynamic evolution of the spectrum of glueballs produced. In the final chapter, we examine how decays to Standard Model particles via higher-dimensional, non-renormalizable operators can place stringent limits on the parameter space of this gauge force. Event Location: Room 309, Hennings Bldg
Event Time: Friday, April 26, 2019 | 7:00 pm - 8:30 pm
Event Location:
Hennings 202 (6224 Agricultural Road, Vancouver, BC V6T 1Z1)
Add to Calendar 2019-04-26T19:00:00 2019-04-26T20:30:00 Space & Storytelling: How discoveries of new worlds help tell stories of family Event Information: Ria and Elizabeth seem to be authors of a very different type: Ria is a YA (Young Adult) novelist, while Elizabeth is an astrophysicist who writes popular science. The first part of this talk will tackle a crucial question: why are they presenting together? The two authors will discuss how they came to work together unexpectedly through Ria’s novel. Ria will then explain the process and research for her novel, The Centre of the Universe, and how the use of space metaphors help explain relationships between the characters. Elizabeth will then cast a scientific eye over these same metaphors, before moving on to talk in more depth about her own research and book, The Planet Factory. Book signing to follow after the event. This event is presented by UBC Department of Physics & Astronomy and Curiosity Collider Art-Science Foundation. Bios Elizabeth Tasker is an astrophysicist at Japan’s national space agency, JAXA. Her research uses computer models to explore how stars and planets form. She is a keen science communicator, writing principally about planets and space missions for publications that have included Scientific American, Astronomy Magazine and Room, and she is a regular feature writer for the NASA NExSS ‘Many Worlds’ online column. Her popular science book, The Planet Factory, comes out in paperback in Canada this April.   Ria Voros is a YA author whose latest novel, The Centre of the Universe, explores the relationship between mothers and daughters and also explores a teen's passion for astronomy. Ria has an MFA in creative writing from UBC and her books have been nominated for several awards across the country. She writes, teaches and lives in Victoria. Event Location: Hennings 202 (6224 Agricultural Road, Vancouver, BC V6T 1Z1)
Event Time: Friday, April 26, 2019 | 2:00 pm - 5:00 pm
Event Location:
Room 318, Hennings Bldg.
Add to Calendar 2019-04-26T14:00:00 2019-04-26T17:00:00 Departmental Oral Examination (Thesis Title: "Measurement of the Arterial Input Function from Radial MR Projections") Event Information: Abstract: DCE-MRI provides a non-invasive method to probe the health status of tissue and help identify diseases, such as cancer.  Biologically relevant information is extracted by fitting the data to a pharmacokinetic model.  The accuracy of the fit parameters is highly sensitive to the quality of the input curves: the contrast-time curve in the tissue of interest, and the arterial input function, which characterizes the contrast kinetics of a blood vessel feeding the tissue.  The AIF is difficult to measure in pre-clinical studies in mice due to their small body size and limited number of vessels of sufficient size. As a result, several groups use a population averaged AIF from the literature.  This curve does not account for inter or intra individual differences, and is specific to a particular injection protocol. This thesis presents a projection-based measurement that measures the AIF from a single trajectory in k-space, which provides a temporal resolution equal to the repetition time (TR).  The projection-based AIF allows for acquisition of DCE-MRI data between successive measurements, while maintaining a high temporal resolution of both data sets.  A dual-coil experimental platform is set up to acquire a projection-based AIF in the mouse tail, concurrently with DCE-MRI data at a tumour implanted on the hind flank.  The results show that an AIF, with a temporal resolution of 100 ms, may be acquired in the mouse tail.  Using this curve in the model fit provided K_trans = 0.145 min^-1, and v_e = 0.269.  These values are consistent with other studies involving tumours. Event Location: Room 318, Hennings Bldg.
Event Time: Thursday, April 25, 2019 | 1:30 pm - 3:30 pm
Event Location:
Hennings 318
Add to Calendar 2019-04-25T13:30:00 2019-04-25T15:30:00 Departmental Oral Examination (Thesis Title: "Dirac materials and the response to elastic lattice deformation") Event Information: Abstract: Dirac materials have formed a thriving and prosperous direction in modern condensed matter physics. Their bulk bands can linearly attach at discrete points or along curves, leading to arc or drumhead surface states. The candidate Dirac materials are exemplified by Dirac/Weyl semimetals, Dirac/Weyl superconductors, and Dirac/Weyl magnets. Owing to the relativistic band structure, these materials have unique responses to the applied elastic crystalline lattice deformation, which can induce pseudo-magnetic and pseudo-electric fields near the band crossings and produce transport distinguished from that caused by ordinary magnetic and electric fields. In this dissertation, I will demonstrate exotic transport due to the strain-induced gauge field in Weyl semimetals, Weyl superconductors, and Weyl ferromagnets. I will first elucidate that a simple bend deformation can induce a pseudo-magnetic field that can give rise to the Shubnikov-de Haas oscillation in Weyl semimetals. Then I will elaborate that strain can Landau quantize charge neutral Bogoliubov quasiparticles as well and result in thermal conductivity quantum oscillation in Weyl superconductors. Lastly, I will consider the strain-induced gauge field beyond the fermionic paradigm and explain various quantum anomalies of magnons in Weyl ferromagnets. Event Location: Hennings 318
Event Time: Wednesday, April 24, 2019 | 11:00 am - 12:30 pm
Event Location:
Hennings 318
Add to Calendar 2019-04-24T11:00:00 2019-04-24T12:30:00 Spintronics with two-dimensional materials Event Information: Exploitation of the intrinsic spin of an electron, spintronics, could facilitate the development of multifunctional and novel devices. With respect to the material selection, two-dimensional (2D) crystals and their van der Waals heterostructures could enable new spintronics functionalities that are not accessible in bulk materials [1]. Towards building such van der Waals-bonded spin devices, spin transport and magnetic properties of novel 2D materials have been individually studied. In this talk, I will first introduce ultra-thin, semiconducting black phosphorus as a promising material for possible spintronics applications requiring rectification and amplification actions [2]. It exhibits remarkable spin transport properties even at room temperature after an in-situ h-BN encapsulation process. Then, I will demonstrate inducing magnetism into an otherwise non-magnetic 2D material with the creation of some specific types of defects [3]. Because of RKKY exchange couplings across ultra-thin films of this air-stable material, we also observe layer-dependent magnetism.  Finally, I will provide an outlook about the tremendous potential of 2D materials for fundamental spintronics research and the future applications in information storage and logic devices. Event Location: Hennings 318
Event Time: Tuesday, April 16, 2019 | 12:00 pm - 1:00 pm
Event Location:
Room 309
Add to Calendar 2019-04-16T12:00:00 2019-04-16T13:00:00 Magnetotransport in topological metals Event Information: Topological metals continue to attract attention as novel gapless states of matter.  While there by now exists an exhaustive classification of possible topologically nontrivial metallic states,  their observable properties, that follow from the electronic structure topology, are less well understood.  In this talk I will present my recent work on magnetotransport phenomena in topological metals, which may be related to the  chiral anomaly. I will demonstrate that the chiral anomaly leads to strong anisotropic magnetoresistance in such materials,  which manifests in very unusual negative longitudinal magnetoresistance and planar Hall effect. I will also argue that a  smoking-gun feature of the chiral anomaly in topological metals is the existence of propagating chiral density modes even  in the regime of weak magnetic fields. Finally, I will show that the optical conductivity of such metals exhibits an extra peak, which exists on top of the standard metallic Drude peak. The spectral weight of this peak is  transferred from high frequencies and its width is proportional to the chiral charge relaxation rate. Event Location: Room 309