Events List for the Academic Year
Event Time:
Thursday, November 29, 2018 | 2:00 pm - 3:00 pm
Event Location:
AMPL 311
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2018-11-29T14:00:00
2018-11-12T15:00:00
Moiré is Different: Wigner Solidification at Magic Angles in Doped Twisted bi-layer Graphene
Event Information:
In a recent paper, the MIT group led Pablo Jarillo-Herrero has found that doping twisted bi-layer graphene can generate strongly correlated insulating states and superconductivity at particular twist angles called magic angles.
This problem has excited the condensed matter community because it establishes that graphene, normally viewed as a weakly interacting system, is a new platform for strongly correlated physics.
The experimentalists as well as a host of theorists have attributed the insulating states to Mottness. However, this interpretation has been called into question because the simplest experimental set-up in which one charge resides in each unit cell exhibits metallic transport not Mott insulation. I will review the experiments and
1) explain why the one-electron/unit cell case is a metal,
2) show that the insulating behaviour is consistent with a series of Wigner crystalline states that are enhanced by hydrostatic pressure as observed in the newest experiments of Dean and Young, and
3) discuss how superconductivity arises from doping such crystalline states.
Event Location:
AMPL 311
Event Time:
Wednesday, November 28, 2018 | 3:30 pm - 4:30 pm
Event Location:
Hennings 301
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2018-11-28T15:30:00
2018-11-28T16:30:00
Leveraging Space to Promote Engagement in Intermediate Electricity & Magnetism
Event Information:
Physics 301 has been flagged as a challenging course in the department for a myraid of reasons. First, this is one of the first “advanced” physics courses. While the content is largely familiar, students must integrate ideas from previous physics and math courses and utilize a coordinated set of tools when solving problems. Secondly, the class is comprised of 160-180 students from a variety of programs, with variations in prerequisite courses and incoming abilities. This talk will cover how we’ve utilized the active learning theater (Henn200) to promote collaboration and engagement to teach this notoriously difficult course.
Event Location:
Hennings 301
Event Time:
Wednesday, November 28, 2018 | 1:00 pm - 2:00 pm
Event Location:
Henn 318. 6224 Agricultural Rd.
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2018-11-28T13:00:00
2018-11-28T14:00:00
Extreme fine-tuning of the cosmological constant is not needed
Event Information:
We show that when the bare cosmological constant in the Einstein field equations takes large negative values, the average distance between any two nearby geodesics moving in the spacetime sourced by quantum fields vacuum would gradually increase at a slow accelerating rate due to the weak parametric resonance effect caused by the fluctuations of the quantum vacuum energy density. In this scenario, the extreme fine-tuning of the cosmological constant is not needed. This resolves the cosmological constant problem and provides an explanation to the accelerating expansion of our universe.
Event Location:
Henn 318. 6224 Agricultural Rd.
Event Time:
Wednesday, November 28, 2018 | 12:30 pm - 2:30 pm
Event Location:
Room D207, Buchanan Block D Building
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2018-11-28T12:30:00
2018-11-28T14:30:00
Final Doctoral Oral Examination for ALAN PATRICK MANNING
Event Information:
Thesis Title: T1 Relaxation and Inhomogeneous Magnetization Transfer in Brain: Physics and Applications
Abstract:
A major goal of the Magnetic Resonance Imaging (MRI) community is myelin quantification in white matter. MRI contrast depends on tissue microstructure, so quantitative models require good understanding of Nuclear Magnetic Resonance (NMR) physics in white matter's complex, heterogeneous environment. In this thesis, we study the underlying physics behind two different 1H contrast mechanisms in white and grey matter tissue: T1 relaxation and the recently developed Inhomogeneous Magnetization Transfer (ihMT).
Using ex-vivo white and grey matter samples of bovine brain, we performed a comprehensive solid-state NMR study of T1 relaxation under six diverse initial conditions. For the first time, we used lineshape fitting to quantify the non-aqueous magnetization during relaxation. A four pool model describes our data well, matching with earlier studies. We also show examples of how the observed T1 relaxation behaviour depends upon the initial conditions.
ihMT's sensitivity to lipid bilayers, like those in myelin, was originally thought to rely upon hole-burning in the supposedly inhomogeneously-broadened lipid lineshape. Our work shows that this is incorrect and that ihMT only requires the presence of dipolar coupling, not a specific kind of line broadening. We developed a simple explanation of ihMT using a spin-1 system. We then performed ihMT and T1D measurements (dipolar order relaxation time) using solid-state NMR on four samples: a multilamellar lipid system (Prolipid-161), wood, hair, and bovine tendon. ihMT was observed in all samples, even those with homogeneous broadening (wood and hair). Moreover, we saw no evidence of hole-burning.
Lastly, we present results from ihMT experiments with CPMG acquisition on the same bovine brain samples. We show that myelin water has a higher ihMT signal than water outside the myelin. It was determined that this was due to the unique thermal motion in myelin lipid. In doing so, we developed a useful metric for determining magnetization transfer's and dipolar coupling's relative contributions to ihMT. Also, we applied a four pool model with dipolar reservoirs as a qualitative model. Together, our results are consistent with myelin lipids having a uniquely long T1D, despite recent measurements to the contrary.
Event Location:
Room D207, Buchanan Block D Building
Event Time:
Monday, November 26, 2018 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2018-11-26T15:00:00
2018-11-26T16:00:00
Hunting for Cool Brown Dwarfs with WISE
Event Information:
ABSTRACT: The study of brown dwarfs with effective temperatures less than 500 K can offer important insights into the complex physics of ultracool atmospheres, the shape of the initial mass function, and the low-mass limit of star formation. We have been using the Wide-field Infrared Survey Explorer (WISE) to search for just such a population of brown dwarfs and have identified roughly twenty cool browns dwarfs that populate a new spectral class, dubbed 'Y'. In this talk, I will present the discovery of the Y dwarfs, summarize our current understanding of their basic physical properties, discuss how HST photometry has improved our understanding of the coolest (Teff ~ 250 K) brown dwarf known, WISE 0855-0714, and discuss our initial attempts to understand condensate clouds in Y dwarf atmospheres using joint HST+Spitzer observations.
Please join us for coffee, tea and snacks before the Colloquium in Hennings 318 at 2:45 pm
Event Location:
Hennings 318
Event Time:
Thursday, November 22, 2018 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2018-11-22T16:00:00
2018-11-22T17:00:00
Biomechanics and neural control of maneuvering flight
Event Information:
My research program is motivated by fascination with bird flight. My laboratory group uses a multi- disciplinary approach that includes biomechanics, physiology, and neuroscience to examine flight ability. Our current research is organized around two topics: 1) how birds morph their wings and what benefits this provides; and 2) how optic flow signals are encoded in the avian brain and used to guide their flight. As we gain understanding of flight mechanisms, we further endeavor to apply comparative approaches that provide deeper insight into avian ecology and evolution.
Event Location:
Hennings 201
Event Time:
Thursday, November 22, 2018 | 2:00 pm - 3:00 pm
Event Location:
BRIM 311
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2018-11-22T14:00:00
2018-11-22T15:00:00
CM Seminar: TOPOLOGICAL CAVITY STATES IN TWO-DIMENSIONAL PHOTONIC/PHONONIC CHIPS
Event Information:
Topological insulators are electronic systems with an insulating bulk and topologically protected boundary states. Conventional 2D topological insulators induce 1D edge states. Recent studies indicate that lower-dimensional topological states are also possible in electronic systems through higher-order topology, which, however, has been confirmed only in Bismuth in experiments [1]. In this talk, I will show that lower-dimensional topological wave trapping can be achieved in photonic and acoustic systems through several different mechanisms. First, with concurrent real-space and wavevector-space topology, we show topological 0D light-trapping on a dislocation [2]. Second, with two different schemes of higher-order topological insulators, we demonstrate topological 0D corner states in photonic crystals and sonic crystals [3,4]. The underlying physics indicates the possibility of achieving frequency-stable topological cavity states in two-dimensional photonic/phononic chips that may enable scalable quantum photonic interface and other unprecedented functions in integrated photonics/acoustics.
[1] F. Schindler et al. Higher-order topology in bismuth. Nature Physics 14, 918-924 (2018).
[2] Fei-Fei Li, Hai-Xiao Wang, Zhan Xiong, Qun Lou, Ping Chen, Rui-Xin Wu, Yin Poo, Jian-Hua Jiang, and Sajeev John. Topological light-trapping on a dislocation. Nature Communications 9, 2462 (2018)
[3] Bi Ye Xie, Hong Fei Wang, Hai-Xiao Wang, Xue Yi Zhu, Jian-Hua Jiang, Ming Hui Lu, and Yan Feng Chen. Second-order photonic topological insulator with corner states. arXiv:1805.07555. Physical Review Letters under review.
[4] Xiujuan Zhang, Hai-Xiao Wang, Zhi-Kang Lin, Yuan Tian, Biye Xie, Ming-Hui Lu, Yan-Feng Chen, and Jian-Hua Jiang. Observation of second-order topological insulators in sonic crystals. arXiv:1806.10028. Nature Physics under review.
Event Location:
BRIM 311
Event Time:
Monday, November 19, 2018 | 3:00 pm - 4:15 pm
Event Location:
Hennings 318
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2018-11-19T15:00:00
2018-11-19T16:15:00
To be announced: speaker Megan Ansdell (Berkeley)
Event Information:
Please join us before the Colloquium in Hennings 318 for coffee, tea and snacks at 2:45 pm
Event Location:
Hennings 318
Event Time:
Monday, November 19, 2018 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2018-11-19T15:00:00
2018-11-19T16:00:00
Things that go "dip" in the night: from disintegrating planets to alien megastructures
Event Information:
The advent of space-based telescopes that provide high-precision time-series photometry, such as CoRoT and Kepler/K2, have revealed a zoo of stellar variability on timescales from minutes to months. In this talk, I will focus on classes of objects whose light curves show distinctive "dips" that can tell us a surprising amount about planet formation, evolution, and death. These include disintegrating planets, young dipper systems, likely exocomets, and unlikely alien megastructures.
Event Location:
Hennings 318
Event Time:
Monday, November 19, 2018 | 1:00 pm - 2:00 pm
Event Location:
TRIUMF Conference Room
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2018-11-19T13:00:00
2018-11-19T14:00:00
Cosmology with Massive Neutrinos
Event Information:
The non-zero mass of neutrinos suppresses the growth of cosmic structure on small scales. Since the level of suppression depends on the sum of the masses of the three active neutrino species, the evolution of large-scale structure is a promising tool to constrain the total mass of neutrinos and possibly shed light on the mass hierarchy. I will discuss recent progress and future prospects to constrain the neutrino mass sum with cosmology.
Event Location:
TRIUMF Conference Room
Event Time:
Friday, November 16, 2018 | 12:30 pm - 2:30 pm
Event Location:
Room 488, The Brimacombe Building, 2355 East Mall
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2018-11-16T12:30:00
2018-11-16T14:30:00
Final PhD Oral Examination (Thesis Title: “Peierls Bipolarons and Localization in Solid-State and Molecular Systems")
Event Information:
Thesis Abstract:
In this thesis, I investigate the behavior of particles dressed by quantum field excitations and random interactions.
First I consider two-carrier states in the Peierls model describing the modulation of the particle hopping due to lattice distortions. I compute the spectral response using the Momentum Average approximation. Combining accurate numerical techniques and analytical arguments, I provide a complete picture of the Peierls bipolarons. It is found that polarons bind into strongly bound yet light bipolarons in the singlet sector, even at large values of the electron-phonon coupling strength. At finite electron fillings, these bipolarons may condense into a high-Tc superconductor. On the other hand, phonons mediate a repulsive interaction in the triplet sector, or equivalently (in one dimension), between two hard-core particles. In this case, the ground-state dimers bound by sufficiently attractive bare interactions exhibit two sharp transitions, one of which is the first known example of a self-trapping transition at the two-carrier level. In both cases, phonons mediate unusual pair-hopping effective interactions between the carriers. I further study some aspects of the excited spectrum for the two hard-core particles, a situation relevant to ultracold quantum simulators. It is found that the repulsive phonon-mediated interaction binds a repulsive bipolaron embedded in the excited spectrum.
I then turn to the study of quenched randomness in an ultracold molecular plasma. I argue that the quenched ultracold plasma presents an experimental platform for studying quantum many-body physics of disordered systems in the long-time and finite energy-density limits. I analyze an experiment that quenches a plasma of nitric oxide to an ultracold system of Rydberg molecules, ions and electrons that exhibits a long-lived state of arrested relaxation. The qualitative features of this state fail to conform with classical models. I develop a microscopic quantum description for the arrested phase based on an effective many-body spin Hamiltonian that includes both dipole-dipole and van der Waals interactions. This effective model appears to offer a way to envision the essential quantum disordered non-equilibrium physics of this system.
This thesis thus examines the quantum many-body response in interacting systems coupled to bosonic fields or in disordered environments.
Event Location:
Room 488, The Brimacombe Building, 2355 East Mall
Event Time:
Friday, November 16, 2018 | 10:00 am - 11:00 am
Event Location:
BRIM 311
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2018-11-16T10:00:00
2018-11-16T11:00:00
CM Seminar: Theoretical Description of superconductivity in 2018: a personal assessment
Event Information:
Superconductivity is more than 100 years old, and the established theory of conventional superconductors is more than half as old. But how established is it, and how conventional are the 'old' superconductors? This talk will provide a brief summary of the “state-of-the-art” of superconductivity, and discuss one aspect of pairing that has received some attention lately — “kinetic-energy-induced” pairing. A parable that describes the chemistry of the Helium atom will be used to explain this idea, and how this concept ties in to possible experimental signatures.
Event Location:
BRIM 311
Event Time:
Thursday, November 15, 2018 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2018-11-15T16:00:00
2018-11-15T17:00:00
Feeling the strain: fields for electronic nematic order
Event Information:
It is common to think of strains in solids in a somewhat passive sense, simply as the response of a material to external forces. However, for certain types of electronic order, strains of a specific symmetry can have much more important roles to play, acting as longitudinal, and even transverse, fields for the order parameter. In this talk, I will first describe how antisymmetric strain can act as a longitudinal field for electronic nematic order. I'll then go on to describe appropriate transverse fields for nematic order, including orthogonal antisymmetric
strain, illustrating these points with various materials. Using such effects it becomes possible to tune materials that exhibit electronic nematic order towards a quantum phase transition. I'll explain why this is such an exciting prospect.
Event Location:
Hennings 201
Event Time:
Wednesday, November 14, 2018 | 7:30 pm - 9:00 pm
Event Location:
Earth Sciences Building - RM 1013 (2207 Main Mall) UBC
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2018-11-14T19:30:00
2018-11-14T21:00:00
Are We Quantum Brains, or Merely Clever Robots?
Event Information:
The effort to design and build quantum computers in the laboratory is now a billion dollar enterprise. But might we, ourselves, be quantum computers? Most scientists think that in the warm wet brain, this is highly unlikely; and certainly it would be at variance with what the medical profession believes. My strategy is one of reverse engineering, seeking to identify the biochemical substrate and mechanisms that could host such putative quantum processing. Remarkably, a specific neural qubit and a unique collection of ions, molecules and enzymes can be identified, illuminating an apparently single path towards nuclear spin quantum processing in the brain. If this is true, the implications for medicine and psychiatry would be very large.
Event Location:
Earth Sciences Building - RM 1013 (2207 Main Mall) UBC
Event Time:
Wednesday, November 14, 2018 | 1:00 pm - 2:00 pm
Event Location:
Henn room 318, 6224 Agricultural Road
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2018-11-14T13:00:00
2018-11-14T14:00:00
Renormalization of gauge theories and asymptotic freedom of Horava-Lifshitz gravity
Event Information:
Using the background-field method we demonstrate the Becchi-Rouet-Stora-Tyutin (BRST) structure of counterterms in a broad class of gauge theories. Put simply, we show that gauge invariance is preserved by renormalization in local gauge field theories whenever they admit a sensible background-field formulation and anomaly-free path integral measure. This class encompasses Yang--Mills theories and relativistic gravity, including both renormalizable and non-renormalizable (effective) theories. Our results also hold for non-relativistic models such as Yang--Mills theories with anisotropic scaling or Horava gravity. They strengthen and generalize the existing results in the literature concerning the renormalization of gauge systems. We illustrate our general approach with several explicit examples and show asymptotic freedom of the (2+1)-dimensional Horava-Lifshitz gravity.
Event Location:
Henn room 318, 6224 Agricultural Road
Event Time:
Monday, November 12, 2018 | 3:00 pm - 4:15 pm
Event Location:
Where you choose to observe
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2018-11-12T15:00:00
2018-11-12T16:15:00
REMEMBRANCE DAY OBSERVANCE - No Astronomy Colloquium today
Event Location:
Where you choose to observe
Event Time:
Thursday, November 8, 2018 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2018-11-08T16:00:00
2018-11-08T17:00:00
Soft Materials at surfaces and interfaces: Elastocapillarity
Event Information:
The physics of soft materials is distinct from hard matter, as the weaker intermolecular bonds can result in a large response to external stresses. In recent years, there has been a significant interest in understanding the interaction between a liquid’s surface tension and a solid’s elasticity: elastocapillarity. In particular, liquids can generate significant deformations of highly compliant materials. These elastocapillary interactions are highly relevant in a wide variety of systems including capillary origami, kirigami, and folding, soft tissues, wetting of fibers and hair, and micro-patterning of soft surfaces. In this talk I will summarize our recent work on the capillary interactions of liquid droplets with elastic surfaces.
Event Location:
Hennings 201
Event Time:
Thursday, November 8, 2018 | 2:00 pm - 3:00 pm
Event Location:
TRIUMF Auditorium
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2018-11-08T14:00:00
2018-11-08T15:00:00
Unification from Scattering Amplitudes
Event Information:
Scattering amplitudes are fundamental observables that encode the dynamics of interacting particles. In this talk, I describe how to systematically construct these objects without reference to a Lagrangian or an underlying spacetime. The physics of real-world particles like gravitons, gluons, and pions are thus derived from the properties of amplitudes rather than vice versa. Remarkably, the expressions gleaned from this line of attack are marvelously simple, revealing new structures long hidden in plain sight. As an example, I describe how gravitons are in a very precise way equivalent to products of gluons - a fact with far-reaching theoretical and phenomenological applications. Lastly, I show how gravity serves as the "mother of all theories" whose amplitudes secretly unify, among others, all gluon and pion amplitudes.
Event Location:
TRIUMF Auditorium
Event Time:
Monday, November 5, 2018 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2018-11-05T15:00:00
2018-11-05T16:00:00
A machine-learning view of our Milky Way
Event Information:
Every night, telescopes around the world obtain a flood of new data as parts of deep and wide surveys. This amount of data will steeply rise once upcoming sureys such as the Large Synoptic Survey Telescope (LSST), which will image the entire visible sky every few nights, start their operation. To investigate this huge amount of data, machine-learning algorithms are absolutely necessary for image analysis, classification of sources, time-series analysis and also structure finding.
Using the example of the Pan-STARRS1 3pi survey as a deep panoptic high-latitude survey in the time domain, in this talk it will be shown how to explore the capabilities of such surveys for carrying out time-domain science in a variety of applications. We use structure-function fitting, period fitting and subsequent machine-learning classification to search for and classify high-latitude as well as low-latitude variable sources, in particular RR Lyraes, Cepheids and QSOs. Our further analysis reveals the extent of the Sagittarius stream as well as other overdensities in the Milky Way's outer halo. In addition, it will be shown how carefully chosen follow-up observations can support large surveys, such as Pan-STARRS1 3pi, and our goal of investigating the structure of the Milky Way's halo.
Please join us before the Colloquium in Hennings 318 for coffee, tea and snacks at 2:45 pm
Event Location:
Hennings 318
Event Time:
Monday, November 5, 2018 | 2:00 pm - 3:00 pm
Event Location:
TRIUMF Auditorium
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2018-11-05T14:00:00
2018-11-05T15:00:00
Neutrino Interferometry at DUNE: Preparing for the Deep Underground Neutrino Experiment
Event Information:
The fact that neutrinos have mass and change flavors means that we can learn a great deal about them by studying what are effectively interference patterns that arise after neutrinos propagate over hundreds of kilometers. The DUNE experiment will measure these interference patterns over a broad neutrino energy range after neutrinos have propagated 1300km. In addition, DUNE will use a detector technology that provides exquisite detail about the interactions that make up the interference pattern. This talk will present the current state of neutrino interference measurements and the various ways the field is preparing to jump to a new level of understanding.
Event Location:
TRIUMF Auditorium