Events List for the Academic Year
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Thursday, June 24, 2021 | 4:00 pm - 5:00 pm
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2021-06-24T16:00:00
2021-06-24T17:00:00
Measuring the Largest Structures in the Universe with the Smallest Telescopes in Space
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Observational astrophysics is often driven by the desire for ever increasing angular resolution, which has resulted in larger and more expensive telescopes with time. However, telescopes with very small apertures can sometimes perform cosmological measurements as important as their larger siblings. In this talk, I will present several examples of small aperture, space-based experiments providing unique views of the large scale structure of the Universe as traced at optical and infrared wavelengths. I will discuss recent results from the Cosmic Infrared Background Experiment (CIBER) that has successfully measured the amplitude of the near-IR background fluctuations on arcminute scales, and our work using the Long Range Reconnaissance Imager (LORRI) on New Horizons to measure the cosmic optical background. Looking forward, missions like the CIBER-2 sounding rocket and SPHEREx, a mid-class NASA Explorer mission designed to probe the inflationary history of the Universe and the evolution of galaxies, are expected to generate important new results in the next 5 years.
Dr. Zemcov's primary research focus is experimental astrophysics and cosmology, particularly the development of instruments and data analysis methods for a variety of platforms, including ground-based, sub-orbital rockets, and orbital observatories. He is currently an Assistant Professor in the School of Physics & Astronomy and the Center for Detectors at the Rochester Institute of Technology and an Affiliate Scientist at Jet Propulsion Laboratory. Prior to coming to RIT in 2015, Dr. Zemcov was a Senior Postdoctoral Fellow at the California Institute of Technology and a NASA Postdoctoral Fellow. He received his PhD from Cardiff University, Wales in 2006 and his BSc from the University of British Columbia in 2003.
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Wednesday, June 23, 2021 | 10:00 am - 11:00 am
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2021-06-23T10:00:00
2021-06-23T11:00:00
The Search for Ionizing Radiation at High Redshift
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Determining the contribution of galaxies to the reionization of the universe is a fundamental goal for studies of the intergalactic medium (IGM), and galaxy formation and evolution. A direct measurement of ionizing Lyman-continuum radiation escaping from galaxies is not possible at the epoch of reionization, due to the high optical depth of the IGM, and therefore observations of this process at slightly lower redshift are crucial for understanding what happens at z>6. For the past several years, we have been attempting direct imaging and spectroscopic observations of escaping ionizing radiation at z~3, using both ground-based and HST data. These observations have uncovered many possible sources of Lyman continuum radiation, but also reveal the challenges associated with low-redshift contamination. We highlight the current state of the field and promising upcoming methods for determining f_esc, the escape fraction of ionizing radiation.
"2021 BC Galaxy Summer Seminars" is an online seminar series organized jointly by SFU, UBC and UVic. For the full series schedule, visit the series webpage. Subscribe to our e-mail list here to get reminders about these seminars.
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Friday, June 18, 2021 | 10:00 am - 11:00 am
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2021-06-18T10:00:00
2021-06-18T11:00:00
The hidden cold circumgalactic medium
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The circumgalactic medium (CGM) represents the boundary between the interstellar medium and the cosmic web, and its properties are directly shaped by the baryon cycle in galaxies. The CGM was traditionally believed to consist mostly of warm and hot gas, but recent breakthroughs have presented a new scenario according to which an important fraction of its mass may reside in an "hidden" cold atomic and molecular phase. This would have major implications for galaxy formation and evolution theories, because it would imply that the CGM entrains dense gas that is readily available for star formation.
"2021 BC Galaxy Summer Seminars" is an online seminar series organized jointly by SFU, UBC and UVic. For the full series schedule, visit the series webpage. Subscribe to our e-mail list here to get reminders about these seminars.
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Thursday, June 17, 2021 | 4:00 pm - 5:00 pm
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2021-06-17T16:00:00
2021-06-17T17:00:00
The new SI and fundamental constants
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The International System of Units (SI) underwent a revolutionary change on May 20, 2019. In October 2017, the International Committee on Weights and Measures met at the International Bureau of Weights and Measures near Paris and recommended a new definition of the SI such that a particular set of constants would have certain values when expressed in the new SI units. In particular, the SI is now defined by the statement:
The International System of Units, the SI, is the system of units in which
the unperturbed ground state hyperfine splitting frequency of the caesium 133 atom nu_Cs is 9 192 631 770 Hz,
the speed of light in vacuum c is 299 792 458 m/s,
the Planck constant h is 6.626 070 15 x 10^-34 J/Hz,
the elementary charge e is 1.602 176 634 x 10^-19 C,
the Boltzmann constant k is 1.380 649 x 10^-23 J/K,
the Avogadro constant N_A is 6.022 140 76 x 10^23 mol^-1,
the luminous efficacy K_cd of monochromatic radiation of frequency 540 x 10^12 hertz is 683 lm/W.
The numerical values of the constants were determined by a special CODATA adjustment of the values of the constants using data in papers that were accepted for publication by July 1, 2017.
The Convention of the Meter (Convention du Metre), a treaty that species international agreement on how units are defined, was established in 1875 with 17 nations initially signing on, including the US. The SI, established within the treaty in 1960, is more recent and continues to evolve. Currently, the treaty is agreed to by fifty-eight Member States, including all the major industrialized countries. Even though a majority of people in the US still use units such as inches and pounds, the official standards for these units are based on the SI units.
The redefinition has had a signicant impact on the fundamental constants when expressed in SI units. Not only are the defining constants exact, but many others are now also exact, and still others have considerably reduced uncertainties. This reflects a shift from macroscopic measurement standards to quantum based standards.
This talk will describe the new SI, review reasons for the change, and show how units can be based on assigned values of certain physical constants.
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Monday, June 14, 2021 | 3:00 pm - 4:00 pm
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2021-06-14T15:00:00
2021-06-14T16:00:00
Constraining the Timescales of Galaxy Evolution using Observations and Simulations
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A diverse range of physical processes are responsible for regulating star formation across galaxies. Understanding their relative contributions to galaxy growth and quenching at different epochs is one of the key questions in galaxy evolution today. Since the processes driving galaxy growth, quenching and morphological transformations are thought to have characteristic timescales, studying the strength of stochastic star formation rate (SFR) fluctuations on these timescales allows us to disentangle their relative contributions for a population of galaxies. In this talk, I will give a brief summary of current work focusing on (i) establishing a formalism to study the stochasticity of star formation at a given time-scale and analyzing a variety of cosmological galaxy evolution simulations using this formalism, and (ii) observational methods of reconstructing star formation histories, which yield constraints on the time-scales of galaxy growth, morphological transformations, and quenching. Taken together, simulations and observations leverage predictive power against observational constraints, allowing us to develop a fuller picture of how galaxies evolve over time.
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Thursday, June 10, 2021 | 4:00 pm - 5:00 pm
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2021-06-10T16:00:00
2021-06-10T17:00:00
Modelling COVID-19 variants and vaccination
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COVID-19 spreads quickly, with different regions experiencing waves of infections at different times. While the initial waves reflected changes in social behaviour, the most recent waves in Canada and elsewhere were influenced by variants and vaccination. This talk introduces basic epidemic modelling and presents analyses of data from BC and around the world that show how variants and vaccination affected the past and will shape the future of the pandemic.
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Wednesday, June 9, 2021 | 10:00 am - 11:00 am
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2021-06-09T10:00:00
2021-06-09T11:00:00
AGN emission line diagnostic diagrams
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TBA
"2021 BC Galaxy Summer Seminars" is an online seminar series organized jointly by SFU, UBC and UVic. For the full series schedule, visit the series webpage. Subscribe to our e-mail list here to get reminders about these seminars.
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Monday, June 7, 2021 | 3:00 pm - 4:00 pm
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2021-06-07T15:00:00
2021-06-07T16:00:00
Biogenic Worlds: From atmospheric HCN production to the building blocks of RNA in warm little ponds
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What is the origin of the building blocks of life on early Earth? Is it necessary that they were delivered by meteorites or interplanetary dust? Or was early Earth "biogenic," and could produce key biomolecules on its own? An atmosphere rich in HCN is a distinguishing feature of what we term biogenic worlds. HCN is a key species produced in Miller-Urey electric discharge experiments simulating lightning-based chemistry in the primordial atmosphere. HCN reacts in water to form nucleobases and ribose, the building blocks of RNA, and amino acids, the building blocks of proteins. To determine whether early Earth was biogenic, we develop a self-consistent chemical kinetic model for the production and rainout of HCN in the early atmosphere, and couple it to a comprehensive model of warm little ponds to compute the in situ production of the building blocks of RNA. We model two epochs of the Hadean eon, at 4.4 Gya (giga-years ago) and 4.0 Gya, which differ in composition, luminosity, UV intensity, and impact bombardment rate. At 4.4 Gya, UV intensity was high due to the active newly formed Sun, and asteroids and comets were bombarding the planet at an overwhelming rate of 1x1015 kg/yr. Impact degassing at this time produced a reducing, H2-dominant atmosphere. At 4.0 Gya, the atmosphere was depleted in hydrogen due to escape from the upper atmosphere, and volcanic outgassing led to an oxidizing CO2-dominant world. The reducing models at 4.4 Ga lead to RNA building block production in ponds that is comparable in concentration to what would result from meteoritic delivery (ppm-range). Unlike the RNA building blocks delivered to ponds by meteorites, which survive for less than a few years, the concentrations produced in situ are maintained indefinitely due to the steady influx of HCN from the troposphere. The oxidizing models at 4.0 Ga lead to substantially lower RNA building block concentrations (ppq-range). These results suggest that early Earth was biogenic at 4.4 Ga, and transitioned out of this phase sometime before 4.0 Ga.
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Thursday, June 3, 2021 | 4:00 pm - 5:00 pm
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2021-06-03T16:00:00
2021-06-03T17:00:00
Directed Aging: Using Memory and Nature's Greed as a New Principle for Materials Design
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It is a well-known and indisputable fact that materials age and deform over time, which often leads to detrimental degradation. In contrast to this view, I will seek to embrace aging and develop it as a methodology to create desired and novel functionality in matter. The central idea is that a material retains a memory of the external stimuli to which it was exposed during its preparation history and, in reaction to those applied cues, can be directed to evolve desired behaviors not easily found otherwise. “Directed aging” thus has the potential to become a general, new and unconventional methodology for creating material function; it stands in direct juxtaposition to the normal paradigm where materials are designed for specific functions. Just as stem cells evolve differently depending on the environment to which they are exposed, we envisage materials that develop new types of response upon exposure to different cues. We are left with the question: How far can this vision be pushed to generate broad classes of materials with desired functionality?
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Wednesday, June 2, 2021 | 10:00 am - 11:00 am
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2021-06-02T10:00:00
2021-06-02T11:00:00
Science of VLTI/GRAVITY near-infrared interferometer and the studies of luminous AGNs
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TBA
"2021 BC Galaxy Summer Seminars" is an online seminar series organized jointly by SFU, UBC and UVic. For the full series schedule, visit the series webpage. Subscribe to our e-mail list here to get reminders about these seminars.
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Monday, May 31, 2021 | 3:00 pm - 4:00 pm
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2021-05-31T15:00:00
2021-05-31T16:00:00
Spin state and moment of inertia of Venus
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Earth-based radar observations in 2006–2020 enabled the first measurement of the spin precession rate and moment of inertia of Venus. The observations also showed that the spin period of the solid planet changes by tens of minutes. The length-of-day variations are due to variations in atmospheric angular momentum transferred to the solid planet. Some of the variations appear to follow the diurnal cycle.
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Thursday, May 27, 2021 | 4:00 pm - 5:00 pm
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2021-05-27T16:00:00
2021-05-27T17:00:00
Adventures of a lapsed physicist: from solid state physics to Covid-19 vaccines
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I graduated from the UBC Physics Department with a PhD in solid state physics in 1972. In this talk I will relate an improbable journey from ESR studies of phosphorus-doped silicon at 4°K to enabling the Pfizer/BioNTech Covid-19 vaccine. The story begins with a move to the Biochemistry Department at Oxford University as a Postdoctoral Fellow to use NMR to study the functional roles of lipids in biological membranes. This required the use of simplified “model membrane” vesicular systems consisting of well-defined lipid species. I soon became interested in the potential of these model membranes as drug delivery vehicles and, on my return to UBC in 1978, focused most of my efforts in this area. Initial work led to three lipid nanoparticle (LNP) systems containing cancer drugs that were approved by the FDA and EMA. This success led to work beginning in the late 1990s to deliver nucleic acid-based drugs such as small interfering RNA (siRNA) for gene silencing and mRNA for gene expression. Some 20 years later, these efforts resulted in LNP systems that could deliver encapsulated mRNA to the interior of target cells in vivo. Through a series of rather serendipitous events these LNP systems now enable the mRNA coding for the SARS-CoV-2 spike protein in the Pfizer/BioNTech Covid-19 vaccine to be delivered into muscle and immune cells, enabling vaccine potency. The Pfizer/BioNTech vaccine is playing a major role in quelling the global pandemic.
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Wednesday, May 26, 2021 | 3:00 pm - 4:00 pm
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2021-05-26T15:00:00
2021-05-26T16:00:00
Special CM Seminar - Magic behavior of low-dimensional nanostructures
Event Information:
https://ubc.zoom.us/j/66400573212?pwd=U2txNjdnazcrMjJ4L2FZMWtXOFc2dz09
Meeting ID: 664 0057 3212
Passcode: 139139
Magic behavior of low-dimensional nanostructures
David Tománek - Physics and Astronomy Dept., Michigan State University, East Lansing, MI 48824, USA
Abstract: Like in a magic trick, atomically thin layers of specific materials can be mixed and stacked in a well-defined way. Due to the inter-layer interaction and charge transfer, the heterostructure may exhibit sometimes unexpected behavior. This occurs in the case of elemental boron, which is notorious for a large number of stable allotropes not only in 3D bulk, but also in 2D. We find that a previously unknown 2D ε–B allotrope converts stepwise to a stable honeycomb structure when doped with electrons, resembling a magic conversion of boron to carbon atoms that carry one more valence electron [1]. As seen in Fig. 1(b), sufficient extra charge to initiate this transition may be provided when 2D boron is brought into contact with the 2D electride Ca2N. A different apparent example of magic involves the previously overlooked twist degree of freedom in 2D structures like bilayer graphene, which changes the Moiré pattern, as shown in the left panel of Fig. 1(c). Recent theoretical and experimental evidence suggests that the electronic structure near the Fermi level of twisted bilayer graphene (TBLG) depends extremely sensitively on the twist angle θ. Near the magic angle value θm≈1.08°, a flat band emerges at EF, separated from
conduction and valence states by energy gaps. This unexpected behaviour likely provides valuable insight into electron correlation and superconductivity in 2D systems. Even though TBLG and related non-periodic structures can not be treated by standard band structure theory, their electronic structure can be interpreted quantitatively using a parameterized model [2] that can be simply extended to consider also other deformations including shear [3].
This study was partly supported by the NSF/AFOSR EFRI 2-DARE grant number #EFMA1433459.
References
[1] Dan Liu and David Tománek, Effect of Net Charge on the Relative Stability of 2D Boron Allotropes, Nano Lett. 19, 1359-1365 (2019).
[2] Xianqing Lin and David Tománek, Minimum model for the electronic structure of twisted bilayer graphene and related structures, Phys. Rev. B. 98, 081410(R) (2018).
[3] Xianqing Lin, Dan Liu and David Tománek, Shear instability in twisted bilayer graphene, Phys. Rev. B. 98, 195432 (2018).
Figure 1: (a) Card magic illustrating the van der Waals assembly of 2D materials to a functional nanostructure. (b) Conversion of a 2D boron monolayer to a honeycomb lattice due to electron doping provided by a 2D electride. (c) Unusual changes in the electronic structure of twisted bilayer graphene near the magic twist angle θm≈1.08°.
Bio: David Tománek studied Physics in Switzerland and received his Ph.D. from the Free University in Berlin. While holding a position as Assistant Professor of Physics in Berlin, he got engaged in theoretical research in Nanostructures at the AT&T Bell Laboratories and the University of California at Berkeley. He established the field of Computational Nanotechnology at Michigan State University, where he holds a position as Full Professor of Physics. His scientific expertise lies in the development and application of numerical techniques for structural, electronic and optical properties of surfaces, low dimensional systems and nanostructures. Since he was working on his PhD Thesis, he promoted the use of computer simulations to understand atomic-level processes at surfaces and in atomic clusters. Witnessed in several hundred publications and invited talks are his results on the electronic structure, mechanical, thermal, and optical properties, as well as quantum conductance of nanostructures. His contributions to Computational Nanotechnology, in particular in the field of fullerenes and nanotubes, have been rewarded by a Fellowship of the American Physical Society, the Alexander-von-Humboldt Foundation Distinguished Senior Scientist Award and the Japan Carbon Award for Life-Time Achievement.
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Wednesday, May 26, 2021 | 10:00 am - 11:00 am
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2021-05-26T10:00:00
2021-05-26T11:00:00
Islands no more: how do mergers affect galaxies and their satellites?
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Large, disk-dominated galaxies like the Milky Way live in the center of vast ecosystems - dark matter, circumgalactic gas, and satellite galaxies. This ecosystem and the large galaxies in them grow hierarchically through merging. Yet, in our pictures of the evolution of galaxies like the Milky Way and the study of their satellites as probes of dark matter and small-scale cosmology merging generally plays a peripheral role. What do the mergers of these ecosystems and the galaxies in them do to galaxies like our own? Using powerful resolved-star datasets from HST and Subaru in concert with hydrodynamical models of galaxy formation, I will show evidence that galaxies like the Milky Way have experienced a diverse range of most important mergers, from systems like the Milky Way with a quiet merger history (until soon, when it will merge with the Magellanic Clouds) to the Andromeda Galaxy that suffered a nearly major merger around 2Gyr ago. Surprisingly, the properties of the Milky Way-mass galaxies are poorly correlated with merger history, suggesting that galaxy merging is not the only way that black holes and galactic bulges grow. Furthermore, to luminosity limits similar to faint classical dwarf galaxies, there is now evidence for a nearly order-of-magnitude range in the number of satellite galaxies of Milky Way-like central galaxies. While some of this variation scales with the mass of the central galaxy, the driver of most of this variation remains unclear. Intriguingly, we find that the number of satellites correlates tightly with the mass of the largest satellite ever accreted by the central galaxy (either already merged or still interacting) — a behavior not seen in state-of-the-art hydrodynamical galaxy formation models. In order to probe this behavior with superior number statistics, sensitivity to ultra-diffuse satellites, and order-of-magnitude fainter luminosity limits, next-generation surveys need to adopt wide-field resolved star techniques. Using deep ground-based Subaru datasets, I present our search methodology and candidate ultra-faint satellites in the M81 group. With such techniques, existing or near-future datasets from Subaru or the Rubin Observatory should reach complete to M_V~-6.5 (similar to current limits for Andromeda satellites), roughly doubling the number of known satellites galaxies in nearby groups. Star-galaxy separation is the limiting factor of current searches, and I illustrate also the dramatic improvements (reaching completeness of roughly M_V~-4) that can be achieved if nearby galaxy groups are surveyed for resolved stars using the Nancy Grace Roman Space Telescope.
"2021 BC Galaxy Summer Seminars" is an online seminar series organized jointly by SFU, UBC and UVic. For the full series schedule, visit the series webpage. Subscribe to our e-mail list here to get reminders about these seminars.
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Tuesday, May 25, 2021 | 1:00 pm - 3:00 pm
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2021-05-25T13:00:00
2021-05-25T15:00:00
Departmental Doctoral Oral Examination (Thesis Title: “Timing Pulsars and Detecting Radio Transients with CHIME”)
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Abstract:
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit telescope located at the Dominion Radio Astrophysical Observatory in Kaleden, BC. Though initially designed to map redshifted neutral hydrogen and constrain dark energy, it also supports several commensal science projects. This thesis focuses on work conducted with the CHIME/FRB fast radio burst searching backend and the CHIME/Pulsar pulsar timing backend.
This thesis focuses on pulsars and fast radio bursts. Pulsars are rapidly rotating, highly magnetized neutron stars, the remnants of massive stars following their supernova explosions. Fast Radio bursts are mysterious millisecond duration radio transients, originating from outside the Milky Way Galaxy. Although their origin is still unknown, evidence is mounting that FRBs also originate from neutron stars or other compact objects, much like pulsars.
First, we discuss ongoing efforts to integrate CHIME/Pulsar daily cadence pulsar timing data into large-scale pulsar timing datasets maintained by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is engaged in a long-term effort to detect gravitational wave signals from supermassive black hole mergers via pulsar timing. The full NANOGrav array consists of approximately 70 sources; in this initial work, we present timing solutions from CHIME/Pulsar data for approximately 10 sources. Though CHIME/Pulsar is a less sensitive instrument than other NANOGrav telescopes like the Green Bank Telescope and the Arecibo Observatory, CHIME/Pulsar's lower frequency and daily observation cadence allow it to provide substantial statistical power to the NANOGrav dataset.
We then discuss new pulsars and rotating radio transients (RRATs) discovered via detection of single pulses by CHIME/FRB. Discovering new pulsars with single pulses is a new technique with the potential to revolutionize our understanding of previously difficult to detect sources. Conventional pulsar searches look at small patches of sky for short periods of time; in contrast, CHIME/FRB views the entire Northern sky each day. CHIME/FRB is thus ideally situated to detect sources with substantial periods of intermittency or high levels of transience. CHIME/Pulsar's ability to track sources digitally allows us to follow-up initial detections with more conventional search mode observations. The combined effect has allowed us to discover and characterize seven new sources so far.
Finally, we discuss observations conducted with the Arecibo Observatory's 300-m single dish radio telescope, following-up low declination FRBs discovered with CHIME/FRB. This work focused on better understanding repeating FRBs by observing a small number of known repeaters in depth, as well as a moderate number of observations of non-repeating FRBs with a downward-drifting time-frequency structure commonly associated with repeating FRBs. This work did not result in the detection of new bursts from these sources, but it allows us to put tighter constraints on the repetition rate of these sources and the possibility of a low-luminosity population of repeat bursts from known repeating FRBs.
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Thursday, May 20, 2021 | 4:00 pm - 5:00 pm
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2021-05-20T16:00:00
2021-05-20T17:00:00
Reading the Invisible Library: Virtual Unwrapping and the Scroll from En-Gedi
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Abstract
Progress over the past decade in the digitization and analysis of text found in cultural objects (inscriptions, manuscripts, scrolls) has led to new methods for reading the "invisible library". This talk explains the development of non-invasive methods, showing results from restoration projects on Homeric manuscripts, Herculaneum material, and Dead Sea scrolls. Premised on "virtual unwrapping" as an engine for discovery, the presentation culminates in a new approach that may indeed be the pathway for rescuing still-readable text from some of the most stubbornly damaged materials, like the enigmatic Herculaneum scrolls.
Short Bio
W. Brent Seales is Professor and Chairman of the Department of Computer Science at the University of Kentucky and a Getty Conservation Institute Scholar (2019-20). Seales' research applies data science and computer vision to challenges in the digital restoration and visualization of antiquities. In the 2012-13 academic year he was a Google Visiting Scientist in Paris, where he continued work on the "virtual unwrapping" of the Herculaneum scrolls. In 2015, Seales and his research team identified the oldest known Hebrew copy of the book of Leviticus (other than the Dead Sea Scrolls), carbon dated to the third century C.E. The reading of the text from within the damaged scroll has been hailed as one of the most significant discoveries in biblical archaeology of the past decade.
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Wednesday, May 19, 2021 | 12:30 pm - 2:30 pm
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2021-05-19T12:30:00
2021-05-19T14:30:00
Departmental Doctoral Oral Examination (Thesis Title: “A study of the quantum-to-classical transition in gravity, and a study of the consequences of constraints in gauge theory path-integrals”)
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Abstract:
In this thesis we discuss various aspects of low energy quantum gravity from a number of different angles. The ultimate goal we have in mind is to prepare ourselves for the upcoming wave of low-energy experiments which may test quantum gravity. In the first part of this thesis we remain within “conventional” quantum theory. We start with a study of quantum decoherence via the emission of low energy gravitational radiation. We find that after sufficiently long times this radiation can completely decohere a matter system. In studying decoherence we needed a better understanding of gauge invariance and physical states in path-integrals with prescribed boundary data. We generalize the standard Faddeev-Popov procedure to fit this purpose, and in doing so we better understand the nature of electric fields around quantum charges. The analogous work is also done in linearized quantum gravity. This language is useful for analyzing the debate around a recently proposed gravitational-entanglement experiment. We do such an analysis, and ultimately agree that these experiments indeed test conventional quantum gravity. As a tangential project we study the interactions of quarks in background gluon condensate, and show how this can cause confinement. In the second part of the thesis we study an “alternative” quantum gravity theory, the Correlated WorldLine (CWL) theory. We study the theory perturbatively, and also make use of a large-N expansion to study it non-perturbatively. We apply our results to physical systems: verifying that two-path systems experience “path-bunching” which suppresses superpositions of massive objects. We also predict a frequency band in the microhertz range where tests of CWL involving massive objects are expected to see a signature.
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Wednesday, May 19, 2021 | 11:00 am - 12:00 pm
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2021-05-19T11:00:00
2021-05-19T12:00:00
Looking Back in Time with Gravitational Waves from Cosmic Strings
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Cosmic strings are macroscopic, approximately one-dimensional objects that arise in many theories of new fundamental physics. If they are created in the early universe after inflation, they form a network of horizon-length long strings and smaller closed loops. Oscillations of the closed loops shed energy in the form of gravitational waves and thereby produce a background of stochastic gravitational radiation with a characteristic frequency spectrum. In this talk I will show how measurements of such a gravitational wave spectrum can be used to deduce the energy content of the universe at very early times and probe non-standard cosmological histories such as early matter domination or kination. I will also discuss string network formation prior to inflation, and describe how remnants of such an early network can regrow and generate a distinctive burst signal of gravitational waves.
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Wednesday, May 19, 2021 | 10:00 am - 11:00 am
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2021-05-19T10:00:00
2021-05-19T11:00:00
Supersymmetry On a Strongly-Interacting Majorana Zero Mode Chain
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Majorana fermions have been an important subject of research for the past few years in the field of condensed matter physics. After the realization of Majorana zero mode (MZM) in a Kitaev-chain, studies on the systems of many-body MZMs have been increased. Throughout the previous research, it was found that a few of the Majorana zero mode 1-dimensional chain models possess a Tricritical Ising model conformal field theory as a critical point in their phase diagram. These critical points are supersymmetric and the supersymmetric behaviour remains at a near vicinity of them in their neighbouring gapped phase. This particular behaviour of these 1D strongly-interacting MZMs is believed to be interesting since the system possesses a supersymmetric phase whilst having a finite correlation length in the gapped phase. In this talk, I am going to explain the supersymmetric realization of these models in their gapped phase, try to understand their excitation levels with the concept of soliton/antisoliton states and try to find traces of supersymmetry in this system of a condensed matter.
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Friday, May 14, 2021 | 10:00 am - 12:00 pm
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2021-05-14T10:00:00
2021-05-14T12:00:00
Departmental Doctoral Oral Examination (Thesis Title: “New Raman Scattering Enhancement Methods with Potential for Improving the Detection of Breath VOCs”)
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Abstract:
Raman spectroscopy is a fingerprint type analysis tool useful for gas analysis. However, Raman spectroscopy of gases is challenging due to their low number density, in addition to the intrinsically weak probabilities of Raman scattering. Incorporating of enhancement techniques is essential for Raman analysis of gases. An effective enhancement technique commonly used for gas samples, is fiber enhanced Raman spectroscopy (FERS), where the intensity of spontaneous Raman scattering is enhanced by confining gas molecules and a CW laser pump light inside the core of a hollow core photonic crystal fiber. The first objective of this thesis was to investigate whether single beam pulsed laser excited stimulated Raman scattering (SRS) based FERS can function as an enhancement technique for gas analysis. Therefore, a FERS system was developed where Raman excitation was done using a nanosecond pulsed laser. Initial studies were performed with simple gases such as H2 and CO2 and the results confirmed that single beam SRS- FERS results in orders of magnitude enhancement of Raman intensities from the gases. Raman intensities grow exponentially with pulse energy and gas pressure. In the next step, single beam SRS-FERS was applied to propene, a VOC of metabolic association and measurements showed an exponential growth of Raman intensities as a function of pulse energy and gas pressure. This confirmed the potential of SRS+FERS for breath component analysis for cancer diagnosis through analysis of VOC biomarkers of breath. The second objective of this thesis was evaluating the collisional energy transfer between two different gas particles as an enhancement of Raman scattering intensities of analyte gas molecules. Exploratory experiments were performed with H2, and CO2 mixed with He/N2 in a single beam pulsed excited FERS system. The results were surprising as upon mixing the gases with He/N2, the intensity of Raman scattering grew exponentially with pressure of He/N2. Raman studies were performed with propene at a very low pressure mixed with He, and the results confirmed that indeed collision enhanced Raman scattering (CERS) functions as an ultra-efficient enhancement mechanism for analysis of trace amount gases. This novel technique can be used to improve the detection limit of Raman system significant for breath VOC analysis.
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via Zoom