Events List for the Academic Year
Event Time:
Wednesday, April 24, 2019 | 11:00 am - 12:30 pm
Event Location:
Hennings 318
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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
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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
Event Time:
Thursday, April 11, 2019 | 9:00 am - 11:00 am
Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road)
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2019-04-11T09:00:00
2019-04-11T11:00:00
Final PhD Oral Examination (Thesis Title: “Precise Measurement of Rare Pion Decay”)
Event Information:
Abstract: A precise measurement of the pion to positron or muon decay branching ratio provides a test of lepton universality incorporated in the Standard Model (SM) of particle physics. If a measurement is consistent with the SM, new constraints could be set on new physics. Most remarkably, a deviation could imply the presence of a new pseudo-scalar interaction whose energy scales up to O(1000 TeV) would enhance the branching ratio by O(0.1%). In some instances, these constraints can far exceed the reach of direct searches at colliders. This dissertation represents the latest experimental measurement effort by the PIENU collaboration. The current analysis presented in this thesis is blinded but includes the highest quality data portion available of around 3M π → e ν events. Furthermore, major experimental systematic problems have been solved, allowing for increased precision up to 0.12% in the branching ratio and up to 0.06% in test of lepton universality.
Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road)
Event Time:
Wednesday, April 10, 2019 | 7:30 pm - 9:00 pm
Event Location:
Centre for Interactive Research on Sustainability (CIRS) - Room 1250 / UBC
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2019-04-10T19:30:00
2019-04-10T21:00:00
Are We Seeing Hawking Points in the Microwave Sky?
Event Information:
A dedicated analysis of the cosmic microwave background (CMB), as revealed by both the WMAP and Planck satellites, has discovered numerous previously unobserved highly energetic anomalous 'spots' in the CMB. Such spots are implications of conformal cyclic cosmology (CCC), which proposes that our Big Bang was the (conformal) continuation of a previous cosmic "aeon", wherein these anomalous spots would be the result of the conformally compressed Hawking radiation from supermassive black holes in that previous aeon. It is very hard to see how such anomalous spots can be explained in terms of the conventional inflationary picture of our very early universe.
Event Location:
Centre for Interactive Research on Sustainability (CIRS) - Room 1250 / UBC
Event Time:
Tuesday, April 9, 2019 | 12:00 pm - 2:00 pm
Event Location:
Room 700, Research Pavilion, Vancouver General Hospital (828 West 10th Avenue)
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2019-04-09T12:00:00
2019-04-09T14:00:00
Departmental Oral Examination (Thesis Title: "Personalized dosimetry protocol for the optimization of Lutetium-177 DOTATATE radionuclide therapy")
Event Information:
Abstract: Targeted radionuclide therapy has been shown to be one of the most effective treatment options for metastatic neuroendocrine tumours (NETs).
In particular, peptide receptor radionuclide therapy (PRRT) with Lutetium-177 (177Lu) labeled DOTATATE results in significantly improved tumour control, while only low to moderate normal tissue toxicity. There is growing evidence that the efficacy of this treatment can be further improved by performing personalized administration of radiopharmaceutical. However, since dosimetry for PRRT is usually considered challenging, traditionally NET patients are treated with same or very similar amounts of 177Lu DOTATATE. The objective of this thesis was to propose a simple, yet accurate dosimetry protocol, which could be easily implemented in clinics for the optimization of 177Lu DOTATATE radionuclide therapy. To achieve this aim, the following physics questions, that are related to image-based dose calculation, were investigated:
The performance of camera calibration method using simple planar scans, was compared to that obtained from tomographic acquisitions. To assess the quantitative accuracy of commercial SPECT reconstruction software (Siemens Flash3D), a number of phantom experiments with different photon attenuation conditions were performed. The influence of camera dead-time correction on the estimated dose was investigated. The kidney doses obtained from four time-activity curve creation methods using three data points were compared. In order to simplify the dosimetry, the accuracy of dose estimated based on two data points, or even potentially one data point, was evaluated.
Our results show that gamma camera can be accurately calibrated with planar scan of a point-like source. The error of 177Lu activity quantification in large volume (>100mL) was about 5% when proper segmentation was applied to Siemens Flash3D reconstructions. Dead-time correction was found to have no impact on the estimated dose. Kidney dose estimated based on single data measured at 48-72 hours produced small error (<10%) for the majority of patients, thus could be recommended for clinical use. This single data point method can also be applied to other organ, as long as its bio-kinetics can be described by a monoexponential function and the statistical behavior of the population effective half-lives in that organ has been estimated.
Event Location:
Room 700, Research Pavilion, Vancouver General Hospital (828 West 10th Avenue)
Event Time:
Tuesday, April 9, 2019 | 11:00 am - 12:30 pm
Event Location:
Hennings 318
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2019-04-09T11:00:00
2019-04-09T12:30:00
Tunable correlated phases in ultra-high mobility oxides
Event Information:
Clean two-dimensional electron systems have been intensively studied due to the astounding array of correlated electronic phases they elicit. In this presentation, I will introduce ZnO-based heterostructures as a new strongly interacting oxide platform for studying the transport of ultra-high mobility carriers. In a magnetic field, we observe a delicate competition between gapped incompressible, compressible and anisotropic nematic phases which may be tuned between by modifying the spin polarization of carriers. In the absence of a magnetic field, dilute samples display a metal-insulator transition as the strength of interactions is increased. Concomitantly, the signatures of a divergent spin susceptibility and spontaneous spin polarization are resolved, suggesting the realization of the elusive Stoner ferromagnet transition in a two-dimensional metal.
Event Location:
Hennings 318
Event Time:
Monday, April 8, 2019 | 3:00 pm - 5:30 pm
Event Location:
Fred Kaiser Building, Room 2020/2030.
2332 Main Mall
2332 Main Mall
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2019-04-08T15:00:00
2019-04-08T17:30:00
Creating and controlling quantum resources on photonic chips
Event Information:
As the various quantum photonic platforms mature, we rapidly approach the advent of viable quantum devices. The different ways in which we can manipulate and create quantum states, and how efficiently we can do so, will determine the types of devices that we can realistically construct. In this talk, I will cover our recent progress on the control of the properties of epitaxially grown InAs quantum dots embedded in GaAs nanophotonic waveguides, and over their interaction with photons. I will touch on the high quality of these interactions, and their nonlinear and directional nature, showing that this combination can be used to create a viable photon sorter, and even a bell-state analyzer. I will also cover the manner in which these interactions can be actively and optically controlled by exploiting the inherent nonlinearity of a two-level quantum emitter. In total, these results demonstrate a route towards future quantum technologies, ranging from the creation of single-photon sources to the realization of large-scale quantum networks.
Event Location:
Fred Kaiser Building, Room 2020/2030.
2332 Main Mall
Event Time:
Friday, April 5, 2019 | 11:00 am - 1:00 pm
Event Location:
Room 488, QMI
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2019-04-05T11:00:00
2019-04-05T13:00:00
Departmental 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:
Room 488, QMI
Event Time:
Thursday, April 4, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2019-04-04T16:00:00
2019-04-04T17:00:00
Searching for Axion Dark Matter: Quantum Sensors and the Dark Matter Radio
Event Information:
One of the most enduring mysteries in particle physics is the nature of the non-baryonic dark matter that makes up 85% of the matter in the universe. For several decades, most searches for this mysterious substance have focused on Weakly Interacting Massive Particles (WIMPs). Recently, there has been a surge in theoretical interest in ultra-light, wave-like dark matter candidates, including the strongly motivated QCD axion. I will describe a suite of experiments (including both NMR and electromagnetic coupling) that will be used to probe the QCD axion over more than six orders of magnitude of mass (~100 Hz to ~300 MHz), and the development of quantum sensors to enhance these searches. I will focus in particular on the Dark Matter Radio (DM Radio), an experiment searching for axions by their coupling to a lumped-element electromagnetic resonators. Quantum measurement techniques can be used to evade the standard quantum limit by the exploitation of quantum correlations in the electromagnetic signals in a resonator. In fact, the use of quantum sensors is required to be able to fully probe the QCD axion over the mass range below 300 MHz. I will describe the RF Photon Upconverter (RPU), which can be used to implement techniques including backaction evasion to outperform the Standard Quantum Limit at the RF frequencies probed by DM Radio.
Event Location:
Hennings 201
Event Time:
Thursday, April 4, 2019 | 2:00 pm - 3:30 pm
Event Location:
BRIM 311
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2019-04-04T14:00:00
2019-04-04T15:30:00
CM Seminar: Quantum materials: insights from near field nano-optics
Event Information:
In 1944 Hans Bethe reported on “the diffraction of electromagnetic radiation by a hole small compared with the wave-length” [Physical Review 66, 163 (1944)]. This seminal paper was among the early precursors to a new and vibrant area of research: near field nano-optics. I will discuss recent nano-optical experiments on quantum materials including graphene and other atomically layered crystals. Central to the nano-optical exploration of quantum materials is the notion of polaritons: hybrid light-matter modes that are omnipresent in polarizable media [Nature Materials 16, 1077 (2017)]. Infrared nano-optics allows one to directly image polaritonic standing waves yielding rich insights into the electronic phenomena of the host material supporting polaritons [Science 354, 195 (2016)]. We utilized this novel general approach to investigate the physics of ballistic electronic transport in graphene [Nature 557, 530 (2018)] and of topological conducting channels also in graphene [Science 362, 1153 (2018)].
Event Location:
BRIM 311
Event Time:
Monday, April 1, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2019-04-01T15:00:00
2019-04-01T16:00:00
The close flyby of the most distant solar system body yet explored: New Horizons at 2014 MU69, exploring a planetesimal
Event Information:
On the 1st of January 2019 NASA's New Horizons spacecraft made the most distant encounter with a solar system body yet achieved by humankind. Using targeting and navigational information acquired through the Canada-France Ecliptic Plane Survey and a dedicated CFHT observing program that enable an HST search and then Gaia based navigation, New Horizons flew a mere 3500km over the surface of this tiny world. I will document the processes that made this encounter possible and detail the rich dataset that has now (mostly) arrived back at Earth. These data are exposing the end state of the process of planetesimal formation in our distant solar system.
Event Location:
Hennings 318
Event Time:
Thursday, March 28, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2019-03-28T16:00:00
2019-03-28T17:00:00
Making cosmological measurements with standard rulers and standard shapes
Event Information:
Analyses of galaxy clustering in redshift surveys such as the Baryon Oscillation Spectroscopic Survey (BOSS), have provided robust cosmological measurements and are now considered as one of the pillars of modern observational cosmology. The key technique uses Baryon Acoustic Oscillations as a standard ruler with which to measure the expansion of the Universe: finding the BAO scale within the galaxy survey fixes the distance-redshift relation. Complementary measurements can be made on smaller scales using voids as standard shapes - on average voids have no preferred orientation with respect to us, and this can be used to make cosmological measurements. I will introduce both BAO and void-based methods, and present recent results using both, confirming and refining the standard LCDM cosmological model. Future surveys including the Dark Energy Spectroscopic Instrument (DESI), the Euclid satellite mission and the MaunaKea Spectroscopic Explorer (as well as the related CHIME project, based at UBC), will provide an order of magnitude more information than BOSS and I will introduce these surveys and discuss predictions for the expected measurements.
Event Location:
Hennings 201
Event Time:
Thursday, March 28, 2019 | 9:00 am - 11:00 am
Event Location:
Room 2710, BC Cancer Center, Vancouver
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2019-03-28T09:00:00
2019-03-28T11:00:00
Departmental Oral Examination
Event Information:
Thesis Title: “Monte Carlo Modelling of Peripheral Dose and Risk of Secondary Malignancy in Flattening-Filter-Free and 10 MV Photon Beams for Paediatric Radiotherapy”
Abstract:
One of the most serious late side effects of cancer treatments is the development of a second malignant neoplasm (SMN). While the risk of SMN is influenced by many factors, radiation therapy (RT) during childhood and adolescence has been shown to be one of the most significant factors associated with the development of a second cancer. The work presented in this thesis aims at determining how to minimize the risk of RT-induced SMN without affecting the quality and efficacy of RT treatments. To properly assess dose to the entire body in patients, a Monte Carlo and measurements based model was developed. This model was used to determine the dose delivered to a cohort of pediatric patients by three different photon radiotherapy treatment modes: 6MV flattened, 6MV flattening-filter-free (FFF) and 10MV FFF. To establish the clinical significance of the dose difference between the three modes, the risk of SMN as calculated by four different risk models were assessed for whole lung irradiation (WLI), a treatment used to treat lung metastases in pediatric patients. The mixed Monte Carlo and measurements model was found to be accurate. The uncertainty on the dose was found to be below
9.4 % of the local dose. A comparison of the out-of-field dose delivered by the 6MV FFF and 10MV FFF beams relative to the 6MV flattened beam was presented. The data demonstrated dose reductions of 3.9% (95% CI[2.1, 5.7]) and 9.8% (95% CI[8.0, 11.6]) at 5 cm from the planning treatment volume (PTV) and 21.9% (95% CI[13.7, 30.1]) and 25.6% ( 95% CI[17.6, 33.6]) at 30 cm for 6MV FFF and 10 MV FFF beams respectively compared to the 6MV flattened beam. In pediatric patients who were treated with WLI, this dose reduction lead to a risk ratio of <0.90 and <0.95 for 10 MV FFF and 6MV FFF respectively compared to the 6MV flattened beam. In conclusion, the work presented in this thesis provides evidence that FFF beams, specifically 10MV FFF beams, deliver lower out-of-field dose than 6MV flattened beams. For WLI treatments, this dose reduction reduces the estimated risk of RT-induced thyroid cancers.
Event Location:
Room 2710, BC Cancer Center, Vancouver
Event Time:
Tuesday, March 26, 2019 | 12:30 pm - 2:30 pm
Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road).
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2019-03-26T12:30:00
2019-03-26T14:30:00
Final PhD Oral Examination (Thesis Title: “Scale Symmetry and the Non-Equilibrium Quantum Dynamics of Ultra-Cold Atomic Gases”)
Event Information:
Thesis Abstract:
The study of the quantum dynamics of ultra-cold atomic gases has become a forefront of atomic research. Experiments studying dynamics have become routine in laboratories, and a plethora of phenomena have been studied.
Theoretically, however, the situation is often intractable unless one resorts to numerical or semiclassical calculations. In this thesis we apply the symmetry associated with scale invariance to study the dynamics of atomic gases, and discuss the implications of this symmetry on the full quantum dynamics. In particular we study the time evolution of an expanding two-dimensional Bose gas with attractive contact interactions, and the three-dimensional Fermi gas at unitarity. To do this we employ a quantum variational approach and exact symmetry arguments. It is shown that the time evolution due to a scale invariant Hamiltonian produces an emergent conformal symmetry. This emergent conformal symmetry has implications on the time evolution of an expanding quantum gas. In addition, we examine the effects of broken scale symmetry on the expansion dynamics. To do this, we develop a non-perturbative formalism that classifies the possible dynamics that can occur. This formalism is then applied to two systems, an ensemble of two-body systems, and for the compressional and elliptic flow of a unitary Fermi gas, both in three spatial dimensions.
Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road).
Event Time:
Thursday, March 21, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2019-03-21T16:00:00
2019-03-21T17:00:00
Engineering Correlated Physics in Two-Dimensional Moire Superlattices
Event Information:
Van der Waals heterostructures of atomically thin crystals offer an exciting new platform to design novel electronic and optical properties. In this talk, I will describe a general approach to engineer correlated physics using moire superlattice in two dimensional heterostructures. One example is the tunable Mott insulator realized in the ABC trilayer graphene (TLG) and hexagonal boron nitride (hBN) heterostructure with a moiré superlattice, where the moiré leads to narrow electronic minibands and allows for the observation of gate-tunable Mott insulator states at 1/4 and 1/2 fillings. In addition, signatures of superconductivity are observed at low temperature near the 1/4-filling Mott insulator state in the TLG/hBN heterostructures. Another example is the WS2/WSe2 heterostructure, where the moire superlattice leads to flat exciton subbands and emerging excitonic transitions.
Event Location:
Hennings 201
Event Time:
Tuesday, March 19, 2019 | 11:00 am - 12:30 pm
Event Location:
Hennings 318
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2019-03-19T11:00:00
2019-03-19T12:30:00
Probing quiescent black holes with tidal disruption events
Event Information:
Supermassive black holes (SMBHs) reside at the heart of most galaxies, with the most direct evidence of these massive objects arising from the detection of an Active Galactic Nuclei (AGN). However, for quiescent BHs in which accretion occurs at a much lower rate, it is more difficult to probe the nature of these sources using similar techniques as those used for AGN. However, tidal disruption events (TDEs), which are luminous accretion powered flares that occur when a star wanders too close and is ripped apart by the tidal forces of a BH, can be used to probe the nature of these objects and provide new ways to test our understanding of various aspects of accretion physics. Due to their multi-wavelength properties, wide-field optical transient surveys such as ASAS-SN and ZTF as well as UV and X-ray satellites have allowed us to identify a number of TDE candidates. Here I will present recent work in which we study the demographics of these sources in multiple wavelengths to better understand the diversity in their observational properties. In addition, I will highlight ways in which these events are observationally similar and different from those of AGN, which can aid us in classifying transients as TDEs in future surveys.
Event Location:
Hennings 318
Event Time:
Monday, March 18, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2019-03-18T15:00:00
2019-03-18T16:00:00
Revolutionizing our View of Disk and Multiple Star Formation: New Frontiers Explored by ALMA and the VLA
Event Information:
Protostellar disks are thought to form early in the star-formation process due to conservation of angular momentum. These disks are the future sites of planet formation, but may also be the sites of binary/multiple star formation if the disk is massive enough to be gravitationally unstable. There is now growing evidence that a substantial amount of disk evolution takes place during the protostellar phase and that these embedded, protostellar disks may be the true initial conditions of planet formation. Using ALMA and the VLA, we are conducting large continuum surveys (with a few molecular lines) of protostars in the nearby Perseus and Orion star-forming regions (with 15-40 AU resolution) to characterize the size, masses, and physical density structure of disks throughout the protostellar phase. The multi-wavelength data enable us to assess their planet-forming potential in terms of disk mass, grain growth, and radial distribution of grain sizes. At the same time, we are using these survey data to conduct the broadest characterization of protostellar multiplicity to date.
Event Location:
Hennings 318
Event Time:
Monday, March 18, 2019 | 11:00 am - 12:30 pm
Event Location:
Hennings 318
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2019-03-18T11:00:00
2019-03-18T12:30:00
Milky Way, machine learning, big data
Event Information:
Understanding physical processes responsible for the formation and evolution of galaxies like the Milky Way is a fundamental but unsolved problem in astrophysics. Fortunately, most stars are long-lived. As such, using the stars as "fossil records" (what is known as Galactic archaeology) can offer unparalleled insight into the assembly of galaxies. In recent years, the landscape of Galactic archaeology is rapidly changing thanks to on-going large-scale surveys (astrometry, photometry, spectroscopy, asteroseismology) which provide a few orders of magnitude more stars than before. In this talk, I will discuss new "phenomenological" opportunities enabled by large surveys. I will also discuss how machine-learning tools could leverage the big data about the Milky Way by maximally harnessing information from low-resolution stellar spectra as well as the time-series photometric fluxes of stars. I will also present the new opportunities in Galactic archaeology in the era of deep photometry and spectroscopy, such as TMT, CFHT/MSE, LSST, and JWST.
Event Location:
Hennings 318
Event Time:
Friday, March 15, 2019 | 2:00 pm - 4:00 pm
Event Location:
Room 309B, Hennings Building
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2019-03-15T14:00:00
2019-03-15T16:00:00
Final PhD Oral Examination (Thesis Title: “Aspects of Decoherence in Qubit Systems”)
Event Location:
Room 309B, Hennings Building
Event Time:
Thursday, March 14, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2019-03-14T16:00:00
2019-03-14T17:00:00
Disentabgling nature from nurture: tracing the origin of the first black holes
Event Information:
Black holes appear be ubiquitous in the universe – most galaxies, if not all, seem to host a supermassive one in their nucleus. The origin of the first, seed black holes, however, remains an open question. Observationally detected bright quasars powered by accreting black holes are found to be in place when the Universe was a fraction of its current age, and accounting for their existence necessitates rapid growth from a new class of initial seeds. I will present work on an alternate channel to form massive black hole seeds in the early Universe – direct collapse black holes – that form in pristine pre-galactic gas disks. I will also present the mounting evidence from multi-wavelength data that supports this picture, as well as the prospects for testing this seeding model and disentangling the confounding effects of accretion physics with data from future space observatories like the James Webb Space Telescope, WFIRST, eROSITA, ATHENA and the LISA mission.
Event Location:
Hennings 201