Events List for the Academic Year
Event Time:
Monday, September 16, 2024 | 12:30 pm - 2:30 pm
Event Location:
Hybrid: in-person at TRIUMF ISAC-II Conference Room (4004 Wesbrook Mall) and Zoom: https://ubc.zoom.us/j/62516482273?pwd=5UBub9EbYj9lLJZevXYfa31Heo76OP.1
Meeting ID: 625 1648 2273 Password: 129025
Meeting ID: 625 1648 2273 Password: 129025
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2024-09-16T12:30:00
2024-09-16T14:30:00
Exotic Decay Measurements at the Experimental Storage Ring for Neutron Capture Processes
Event Information:
[Abstract]
The slow (s) and rapid (r) neutron capture processes are responsible for producing almost all elements heavier than iron. Both processes require a lot of nuclear data to make more reliable predictions, and heavy-ion storage rings provide unique methods for measuring nuclear masses and exotic decay modes that can play an important role in these processes. A prime example is bound-state β− decay, where the β-electron is produced in a bound state of the decaying nuclei. This decay mode for highly-charged ions can currently only be measured at the Experimental Storage Ring (ESR) at the GSI Helmholtz Centre in Darmstadt, Germany.
This thesis describes the analysis of the bound-state β− decay of
205Tl81+ at the ESR. 205Tl is a particularly interesting isotope due to
its applications in solar neutrino spectrometry and for dating the early Solar System. A bound β-decay half-life of 291(+33)(−27) days was measured, which was much longer than previously predicted. The experimental half-life determines the nuclear matrix element of this transition, which allows for the calculation of accurate astrophysical decay rates of 205Tl and 205Pb in the stellar plasma. This enables models of the s process in AGB stars to provide accurate 205Pb yields, which are essential for using 205Pb as a cosmochronometer to date processes in the early Solar System, like the isolation time of solar material from its parent molecular cloud. This thesis presents a preliminary determination of the isolation time of the Solar System using 205Pb.
In complement, a heavy-ion detector called PLEIADES was constructed and commissioned at the ESR, which will be used to detect decay products leaving the storage ring acceptance. PLEIADES is a δE–E telescope that uses silicon pads to measure energy loss and a scintillator stopper to measure the total ion energy. It was commissioned with a 208Pb beam at the ESR, and achieved a FWHM resolution of δZ = 0.66 and δA = 1.14.
PLEIADES and its predecessor CsISiPHOS will be used as multi-purpose detectors for future measurements in the ESR.
Event Location:
Hybrid: in-person at TRIUMF ISAC-II Conference Room (4004 Wesbrook Mall) and Zoom: https://ubc.zoom.us/j/62516482273?pwd=5UBub9EbYj9lLJZevXYfa31Heo76OP.1
Meeting ID: 625 1648 2273 Password: 129025
Event Time:
Thursday, September 12, 2024 | 4:00 pm - 5:00 pm
Event Location:
Mathematics Annex (MATX) 1100, 1986 Mathematics Road, UBC-V campus
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2024-09-12T16:00:00
2024-09-12T17:00:00
Exploring Exoplanet Demographics with Kepler, TESS, and Beyond
Event Information:
Abstract:
Searches for planets beyond the Solar System ("exoplanets") have been spectacularly successful in identifying thousands of diverse new worlds, placing the Solar System in context and informing our understanding of how planets form and evolve. Finding large numbers of planets also enables demographic studies, through which we can uncover which types of planets are more common than others and why. I will highlight contributions to exoplanet discovery and demographics, from planets of all sizes and implications for the existence of other Earths from Kepler, to the exciting potential of TESS to significantly expand our understanding of planets around nearby, bright stars amenable to follow-up and further characterization. Finally, I will identify a set of important open questions that remain to be answered and outline future goals to push exoplanet science to new frontiers, especially in the context of the search for habitable worlds.
Bio:
I am an Assistant Professor in the Department of Physics and Astronomy at the University of British Columbia.My research is primarily focused on exoplanet detection, characterization, and demographics. I approach these fields in data-driven ways, developing and improving techniques to extract as much as we can from exoplanet surveys while answering key science questions along the way.
I was previously a Torres postdoctoral fellow and TESS postdoctoral associate at MIT. I obtained my PhD in Astronomy from UBC in 2020.
Learn More:
See Michelle's website here: About | Michelle Kunimoto (mkunimoto.github.io)
See Michelle's PHAS faculty page here: mkuni | UBC Physics & Astronomy
Find out more about exoplanets: The exoplanet zoo | Canadian Space Agency (asc-csa.gc.ca)
Event Location:
Mathematics Annex (MATX) 1100, 1986 Mathematics Road, UBC-V campus
Event Time:
Thursday, September 12, 2024 | 10:00 am - 11:00 am
Event Location:
AMPEL 311
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2024-09-12T10:00:00
2024-09-12T11:00:00
Sliding Ferroelectricity in Rhombohedral MoS2: A New Approach to Nonvolatilely Switch the Interaction between Light and Matter
Event Information:
Abstract:
The tunability in the stacking of layered materials with van der Waals bonding provides a new and powerful approach to engineer their physical properties. Sliding ferroelectricity is one such example where an electric field drives one layer of materials to move relative to its neighbours due to an out-of-plane electric polarization arising from interlayer coupling. Sliding ferroelectricity can therefore occur in traditionally non-ferroelectric materials and has been observed in artificially stacked boron nitrides and transition metal dichalcogenides (TMDs). In this talk, I will show that such a hysteric phenomenon can occur in chemically synthesized rhombohedral molybdenum disulfide (3R-MoS2) crystals with pre-existing domain walls. I will first discuss our studies on domain characterization using photocurrent and scanning probe microscopy. I will then show that these polarization domains and their switching behavior can be probed by optical spectroscopy, revealing the existence of a variety of switching pathways. Due to their strong excitonic effects and sliding ferroelectricity, rhombohedral TMDs can be built into nonvolatile optical memories with high performances.
Bio:
We are an optical spectroscopy group studying light matter interaction in low-dimensional materials. We are currently focused on exploring how topology, correlation effects, and other emergent degrees of freedom interact with each other in two-dimensional van der Waals materials such as graphene, phosphorene, transition metal dichalcogenide, hexagonal boron nitride, high-Tc cuprates and their heterostructures. Our expertise includes ultrafast optical spectroscopy with diffraction-limited resolution at low temperatures and strong magnetic fields as well as nearfield optical microscopy. In the past, we have utilized ultrafast nonlinear optical spectroscopies to reveal the crystal and electronic structure of TMDCs. We are currently interested in developing novel optical microscopy techniques to interrogate the 2D material’s intrinsic response and to control them with the strong optical field provided by coherent laser light. In the meantime, novel devices based on bulk photovoltaic effect and topological superconductivity are being actively explored in the group for classical and quantum applications.
Learn More:
Ziliang's Investigator biography page at the Stewart Blusson Quantum Matter Institute: Ziliang Ye - Stewart Blusson Quantum Matter Institute (ubc.ca)
Ziliang's faculty page for the Department of Physics & Astronomy: zlye | UBC Physics & Astronomy
Event Location:
AMPEL 311
Event Time:
Thursday, September 12, 2024 | 9:00 am - 11:00 am
Event Location:
Room 200, Graduate Student Centre (6371 Crescent Road)
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2024-09-12T09:00:00
2024-09-12T11:00:00
Scaling theories and simulation of ductile yielding in amorphous solids
Event Information:
Amorphous solids are a diverse class of materials that have significant interest owing to their ubiquity in industry, yet a unifying theory to describe their mechanical response to load under temperature is lacking. Using a combination of highly parallelized numerical routines to simulate an elastoplastic model (EPM) of amorphous solids, as well the corresponding mean-field theory, I develop a scaling theory for the yielding of amorphous solids for non-zero temperature and driving rates.
First, I simulate very large systems at zero temperature. Here, ductile yielding proceeds through localized rearrangements that, under sufficient load, self-organize into extended avalanches. I study the appearance of the recently described stability plateau, which violates the existing athermal scaling theories for amorphous yielding. Using finite-size scaling, I show that this deviation originates in the spatial extent of the largest avalanches, and that this plateau in turn affects the energy available to avalanches. Consequently, this changes the scaling description for amorphous yielding at zero temperature.
Second, I introduce a temperature-dependent failure to the EPM. With extensive numerical simulations, as well as scaling arguments from mean-field theory, I map out a phase-diagram for different regimes of behaviour, depending on both temperature and the rate at which energy is loaded into the system. I verify the boundaries of the phase-diagram by showing changes in behaviour across each of the phase lines, test predictions for avalanche size and flow stress in each flow regime. Contrary to recently proposed theories based on mean-field modelling alone, I show that the competition between driving rate and temperature differs between the continuously flow regime (in which avalanches merge) and the intermittent flow regime.
Finally, motivated by experimental data on the creep of disordered mylar sheets, I study creep-flow in amorphous solids by considering an EPM at fixed stress and non-zero temperature. Here, we show that creep proceeds through cascades of correlated activity that occur over extremely long timescales. These ``thermal avalanches'' have long periods of quiescence, yet I argue they obey the same scaling laws and underlying physics as the mechanical avalanches of the ductile yielding transition.
Event Location:
Room 200, Graduate Student Centre (6371 Crescent Road)
Event Time:
Monday, September 9, 2024 | 4:00 pm - 5:00 pm
Event Location:
HENN 318
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2024-09-09T16:00:00
2024-09-09T17:00:00
Probing Quasar Outflows Through Absorption Line Spectroscopy
Event Information:
Abstract:
Quasars, among the most luminous astrophysical systems, are powered by supermassive black holes (SMBHs) accreting gas at the centers of their host galaxies. A critical aspect of quasar physics is the presence of powerful outflows, often identified through broad absorption lines (BALs) in quasar spectra. These outflows are key to understanding the interaction between SMBHs and their host galaxies, which is crucial for unraveling the processes that drive their co-evolution. In this talk, I will focus on the time variability of these outflows through long-term spectral monitoring of BAL quasars, a powerful tool for studying their origins and evolution. I will present a comprehensive analysis of time variability in C IV BALs over a span of seven years, based on a sample of 64 BAL quasars observed with the Southern African Large Telescope. The discussion will highlight both short- and long-term variations in absorption strength and examine how various quasar and BAL properties influence these changes. Additionally, I will talk about two unusual sources from our sample in detail, presenting insights from their extreme variability events and what they reveal about the nature of quasar outflows.
Bio:
I am an observational astrophysicist with a PhD from the Inter University Centre for Astronomy and Astrophysics (IUCAA), India, now pursuing a postdoctoral fellowship at Western University, Canada. My research focuses on extragalactic astronomy, specializing in quasar formation and evolution. I have extensive experience in data analysis techniques, programming and scientific writing.
Learn More:
See Amoral's LinkedIn profile here: (39) Aromal Pathayappura | LinkedIn
NASA information about Quasars :NASA’s Webb Will Use Quasars to Unlock the Secrets of the Early Universe - NASA
Event Location:
HENN 318
Event Time:
Monday, September 9, 2024 | 2:30 pm - 3:30 pm
Event Location:
HENN 318
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2024-09-09T14:30:00
2024-09-09T15:30:00
PHAS EDI Committee Monday Tea Event Launch
Event Information:
Welcome everyone to the launch of the PHAS EDI Monday Tea!
This is a weekly event for students, staff and faculty to meet new-to-you colleagues, catch up with your community and to learn about what's happening in the PHAS Department.
Meet your hosts in the EDI Community Building Working Group:
Jess McIver
Adele Ruosi
Megan Bingham
Evan Goetz
Mona Berciu
Howard Li
Mandana Amiri
Pedro Villalba Gonzalez
See you there!
Event Location:
HENN 318
Event Time:
Thursday, September 5, 2024 | 10:00 am - 11:00 am
Event Location:
AMPEL 311
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2024-09-05T10:00:00
2024-09-05T11:00:00
Quantum skyrmion Hall effect
Event Information:
Abstract:
A great variety of topological phases have been classified as a consequence of discovery of the quantum Hall effect, but this work has recently led to discovery of some topologically non-trivial phases of matter, which contradict key assumptions of established classification schemes. These phases, which are the topological skyrmion phases of matter, multiplicative topological phases of matter, and finite-size topological phases of matter, necessitate a paradigm shift from the quantum Hall effect framework to that of the quantum skyrmion Hall effect, in which the point charges of the quantum Hall effect are generalised to compactified p-branes. For compactification via fuzzification, these compactified p-branes carrying charge are necessarily expressed in terms of angular momentum as quantum skyrmions. Ostensibly (d+1)-dimensional systems, based on the number of Cartesian coordinates they possess, can then in fact have D additional dimensions encoded in (pseudo)spin degrees of freedom, and realize intrinsically (D+d+1)-dimensional topological states, a finding supported by results in lattice tight-binding models.
Bio:
Ashley Cook is a junior group leader at Max Planck Dresden.
Event Location:
AMPEL 311