Colloquia - Previous Semesters
August 28, 2023 - Hartwin Peelaers (University of Kansas)
First-principles modeling of the properties of Ga2O3
Abstract: β-Ga2O3 is a wide-band-gap semiconductor with promising applications in high-power electronics and photodetectors that are transparent to visible light. In this talk, I will show how first-principles calculations, based on density functional theory with hybrid functionals, can be used to predict and explain the properties of Ga2O3.
We first focus on modifying Ga2O3’s properties for electronic applications through doping. While n-type doping is straightforward, p-type doping is elusive, with only deep acceptors available. We explore the properties of possible acceptors, and discuss the viability of obtaining semi-insulating material . All dopants we considered lead to deep acceptor levels that are more than 1.3 eV above the valence-band maximum. N and Mg were identified as the most promising deep acceptors. We evaluated incorporation in different configurations, and considered the effect of native defects as well as complexes. We also predict diffusion activation energies, finding that Mg is significantly more mobile, explaining experimental observations.
Alloying allows to modify the lattice constants, band gaps, and conduction-band offsets. We will provide quantitative results for alloys with In2O3 and Al2O3 for the ground state [2,3] and for the orthorhombic kappa structure [4,5], which has attracted significant attention due to its large predicted spontaneous polarization.
When Ga2O3 is used as a transparent conducting oxides (TCO), two conflicting properties have to be balanced: transparency and conductivity. The requirement of transparency is typically tied to the band gap of the material being sufficiently large to prevent absorption of visible photons. This is a necessary but not sufficient condition: indeed, the high concentration of free carriers, required for conductivity, can also lead to optical absorption. This absorption can occur through direct absorption to higher-lying conduction band states, or by an indirect process, for example mediated by phonons or charged impurities. We will elucidate the fundamental limitations of optical absorption in Ga2O3 and shed light on experimental observations [6-9].
 H. Peelaers, J. L. Lyons, J. B. Varley, and C. G. Van de Walle, APL Mater. 7, 022519 (2019).
 H. Peelaers, D. Steiauf, J. B. Varley, A. Janotti, and C. G. Van de Walle, Phys. Rev. B 92, 085206 (2015).
 H. Peelaers, J. B. Varley, J. S. Speck, and C. G. Van de Walle, Appl. Phys. Lett. 112, 242101 (2018).
 S. Seacat, J. L. Lyons, and H. Peelaers, Appl. Phys. Lett. 116, 232102 (2020).
 S. Seacat, J. L. Lyons, and H. Peelaers, Appl. Phys. Lett. 119, 042104 (2021).
 H. Peelaers and C.G. Van de Walle, Appl. Phys. Lett. 111, 182104 (2017).
 H. Peelaers and C.G. Van de Walle, Phys. Rev. B 100, 081202(R) (2019).
 A. Singh, O. Koksal, N. Tanen, J. McCandless, D. Jena, H. Xing, H. Peelaers, and F. Rana, Appl. Phys. Lett. 117, 072103 (2020).
 O. Koksal, N. Tanen, J. McCandless, D. Jena, H. Xing, H. Peelaers, F. Rana, and A. Singh., Phys. Rev. Research 3, 023154 (2021).
September 7, 2023 - Juergen Reuter (DESY)
Particle Physics Monte Carlo Event Generators for Present and Future Colliders
Abstract: Monte Carlo event generators are the mighty workhorses of collider-based particle physics, for signal simulation and event reconstruction. The main goal of the talk is to elucidate the inner structures of these versatile "black boxes" of particle physics. After a short motivation of collider physics, the different components of MC event generators will be discussed: phase space and event sampling, perturbative evaluation of matrix elements at fixed order, parton showers and hadronization and new physics simulations. A special focus will be given to future lepton colliders (e+e- and muon colliders) regarding beam simulation, lepton parton distribution functions and photon radiation.
September 18, 2023 - Allison Kirkpatrick (University of Kansas)
Probing Black Holes from the Boring to the Breathtaking
Abstract: All galaxies host a supermassive black hole at their centers, at least a million times the mass of the Sun. Material falling onto these monsters can be as bright as the galaxy itself, or it may be lurking unseen behind thick blankets of dust. Some of these monsters go through growth spurts and feeding frenzies that can greatly impact their host galaxies, possibly even terminating all nearby star formation. Other supermassive black holes seem to have no impact on their hosts, passively growing and evolving while galaxies take no notice. In this talk, I will explore the breathtaking Cold Quasars, which are some of the most luminous accreting black holes in the universe, and yet, surprisingly, their host galaxies have star formation rates of 1000 Msun/yr, casting doubt on whether black hole feedback impacts star formation at all. I will discuss how Cold Quasars are an anomaly in the current understanding of quasar formation. On the other hand, I will examine the boring black holes, what kinds of galaxies they live in, and what JWST is revealing about their life cycle.
October 2, 2023 - Jeff Neaton (UC, Berkeley)
Nature and fate of photoexcitations in energy materials
Abstract: The ability to synthesize and probe new classes of photoactive materials with tunable structure and composition – such as halide perovskites, transition metal oxides and nitrides, van der Waals heterostructures of 2d materials, organic crystals, and more – has driven the development of new theory, computational methods, and intuition for predicting their photophysics. In these novel semiconductors, photoexcited correlated electron-hole pairs, or excitons, can be strongly bound and do not conform to simple models, and new understanding is needed to interpret and predict their behavior. Here, I will discuss recent advances of ab initio calculations – based on density functional theory and field-theoretic many-electron Green's function formalisms – of excitons in these complex crystals, focusing on how the properties of these quasiparticles are influenced by lattice structure and dynamics, temperature, dielectric screening, and carrier concentration. I will compare with experiments and discuss how new theoretical methods and intuition can lead to the discovery of new physical behavior and the development of optoelectronic devices for energy applications.
October 9, 2023 - Andrea Delgado (Oak Ridge National Lab)
Crafting Generative Models & Unraveling High Energy Physics with Parameterized Quantum Circuits
Abstract: The advent of Noisy Intermediate-Scale Quantum (NISQ) computing has spotlighted the significance of parameterized quantum circuits (PQCs) as essential tools in quantum technology. Particularly in the realm of quantum generative models, PQCs have shown promise in encapsulating complex data distributions, reproducing the statistics of the training data, and detecting anomalous instances.
This seminar will weave a narrative around the confluence of PQCs in both quantum machine learning and the intricate world of high energy physics. Through a fusion of case studies and in-depth discussions, I will highlight the promise and potential of PQCs, standing at the crossroads of data-driven innovation and fundamental scientific discovery.
October 23, 2023 - Roland Kawakami (Ohio State University)
Discovery of New Hall Effects
Abstract: The discovery of new Hall effects has spanned the decades of physics, starting from the discovery of the original Hall effect in 1879 to the orbital Hall effect this year. Part of the fascination in Hall effects are the connections to topology and Berry curvature, which are manifested in the spin Hall effect (2004), quantum spin Hall effect (2007), anomalous Hall effect (1881), and quantum anomalous Hall effect (2013). In this talk, I will describe the Berry phase and Berry curvature and their relation to the aforementioned Hall effects. In connection to these, I will discuss our group’s work on the magneto-optic detection the orbital Hall effect in chromium  and our development of prospective new materials for the quantum anomalous Hall effect. These have potential ramifications for spintronics and help establish the emerging field of “orbitronics.”
 Igor Lyalin et al., Phys. Rev. Lett. 131, 156702 (2023).
October 30, 2023 - Peisi Huang (UNL)
The First Picosecond and the Dark Secrets of the Universe
Abstract: The study of cosmic phase transitions (PTs) is of central interest in modern cosmology. Cosmic PTs could have a variety of essential roles in the evolution of the Universe, from creating matter-antimatter asymmetry to forming dark matter and primordial black holes, and generating a potentially observable background of gravitational radiation. The study of cosmic PTs offers compelling opportunities to advance our understanding of the origin of cosmic structure. The rapidly developing gravitational wave and collider experiments provide exciting possibilities for direct and indirect probes of cosmic PTs. In this talk, I will focus on the possible cosmic PT during the first picosecond after the big bang, and their roles in solving some of the fundamental mysteries of the Universe.
November 6, 2023 - Mila Kryjevskaia (North Dakota State)
Examining student thinking in physics: intuition, conceptual understanding, and reasoning
Abstract: Most physics instructors will probably agree that one major goal of our instruction is cultivating the ability to use formal knowledge to construct logically sound arguments. When students struggle to build such arguments, it can be easy to assume that they either do not possess the necessary content knowledge or their reasoning skills are weak. While these interpretations may be productive, dual-process theories of reasoning from cognitive psychology suggest that intuition is also a critical aspect of cognition. In fact, intuition is often powerful enough to significantly enhance or hinder explicit reasoning (even by those who hold correct formal knowledge). Indeed, many physicists and expert teachers believe that their intuition makes thinking and problem-solving more productive and enjoyable. However, this may not be the case for our students who are just starting their journey toward developing their expertise. In this talk, I will discuss how insights from cognitive psychology can help physics instructors gain a deeper understanding of the roles of intuition and formal knowledge in reasoning in physics. I will describe common reasoning pathways suggested by the dual-process theories of reasoning and discuss reasoning hazards present along the way. I will highlight promising instructional approaches to help physics students navigate the reasoning hazards more successfully.
November 13, 2023 - Karl R. Stapelfeldt (Jet Propulsion Laboratory, California Institute of Technology)
The Path to Direct Imaging Characterization of Habitable Exoplanets
Abstract: The most obvious method of studying extrasolar planets - directly imaging them alongside their parent star - is also the most difficult. Image contrasts exceeding a billion to one, at sub-arcsecond separations, are required to detect an analog of our solar system in reflected starlight. Following the the Astro2010 Decadal Survey, the NASA Exoplanet Exploration Program (ExEP) was tasked with developing the technology and precursor science needed to realize the goals of directly imaging Earth analogs and characterizing their atmospheres for habitability and the presence of life. In this talk I will review the history of efforts to image extrasolar planets; the methods that can be used, and technical challenges that must be met to image and characterize Earth analogs; the role of exoplanet imaging on NASA's JWST and upcoming Roman Space Telescope mission; and the early plans for the Habitable Worlds Observatory, the next large U.S. space telescope recommended by the Astro2020 Decadal Survey.
Dr. Karl Stapelfeldt is Chief Scientist in NASA's Exoplanet Exploration Program Office at the Jet Propulsion Laboratory in Pasadena CA. He is an observational astronomer specializing in studying circumstellar disks, exoplanets, and planet formation at optical, infrared, and millimeter wavelengths. He has a B.S.E. in Engineering Physics from Princeton University and a Ph.D. in Astrophysics from Caltech. From 1993-1998 he was a member of the HST/WFPC2 instrument science team that restored the vision of the Hubble Space Telescope, followed by more than a decade in Project Science Office for the Spitzer Space Telescope. He has extensive experience in studies of future space missions for exoplanet direct imaging. From 2011-2016 he was Chief of the Exoplanets and Stellar Astrophysics Laboratory at NASA Goddard Space Flight Center.
November 27, 2023 - Nicolle Zellner (Albion College)
Lunar Impact Glasses: Big Science from Small Samples
Abstract: The Moon continues to provide scientific answers – and pose new questions – over 50 years after the last Apollo mission. While the Moon provides the most clear and complete history of impact events in the inner Solar System since its formation ~4.5 billion years ago, the timing is not well understood and has been a topic of continued interest and persistent uncertainties. As our closest planetary neighbor, the Moon’s impact record, if properly interpreted, can be used to gain insights into how the Earth has been influenced by impacting events in its first billion years and for billions of years thereafter.
Lunar impact glasses, pieces of melted lunar regolith created by energetic impacting events, can offer information about the Moon’s impact history. These samples possess the composition of the target material and can be dated by the 40Ar/39Ar (argon) method in order to determine their formation age. Understanding the ages of impact glasses, along with their compositions, allows us to begin to piece together information about the rate of impact events in the inner Solar System and their effects on Earth.
In this talk, I will present an overview of the bombardment scenarios that have been proposed to explain the size and distribution of impact craters observed on the Moon (and in the inner solar system) and how lunar impact glass data are being used to address outstanding issues related to bombardment. These include the form of the large-impact distribution with respect to time (e.g., smooth decline versus cataclysmic spike), whether there is periodicity in Earth-Moon cratering history, the rate of delivery of biomolecules, and the applicability of the lunar record to other planets (including Mars). Of great interest to astrobiology and the study of the origin of life is the impact flux prior to ~3.7 Ga ago, and specifically, whether or not early life, if it existed on Earth before 4.0 Ga ago, may have been destroyed during these early impact events. Applications to Mars’ history will be suggested.
December 4, 2023 - The Office of Civil Rights and Title IX (University of Kansas)
Abstract: The Office of Civil Rights and Title IX will present on KU’s civil rights grievance procedures, mandatory reporting requirements, and the parameters of KU civil rights policies. We will cover addressing microaggressions, University-wide and local resources, reporting trends, and options for reporting incidents to OCRTIX. We will also provide time for questions and answers from the group!
February 27, 2023 - Corey Maley (KU Philosophy)
The essence of computation
Computation is strange and interesting. Despite much work in the mathematical foundations of computability theory, we do not yet have a complete understanding of the nature of computation. This is due, in part, with mistaking these mathematical foundations—a model of one type of computation—for a foundation of computation in general. I will argue why this is a mistake, and sketch a way that we might fix this mistake. On the account I sketch, we can make sense of computation in digital and analog systems, and in artificial and natural systems. Moreover, we can provide empirical criteria for when some physical system is a genuine computer, versus when it can be merely described in computational terms.
March 6, 2023 - Haiyan Gao (Brookhaven National Laboratory and Duke University)
The Structure of the Nucleon
Nucleons (protons and neutrons) are the building blocks of atomic nuclei and are responsible for more than 99% of the visible matter in the universe. Despite decades of efforts in studying the structure of the proton, there are still interesting puzzles surrounding the proton such as its spin and the charge radius. The mass of the proton is another fascinating topic as most of the proton mass has little to do with the mass of its constituents. In this talk I will review some recent advances in the study of the nucleon structure, and then discuss future studies with an Electron-Ion Collider to be built at the Brookhaven National Laboratory in the coming decade.
March 20, 2023 - Dr. Rafael Luque (University of Chicago)
THE DEMOGRAPHICS OF SMALL EXOPLANETS
The diversity of the exoplanet population is beyond our imagination. The more than 5000 known exoplanets vastly differ in mass, size, orbital period, dynamics, and host type. Demographic studies, however, aim to find patterns in the population that inform us about their origin, composition, and evolution. Among these features, perhaps the most surprising is the abundance of planets with no analog in the solar system, also known as sub-Neptunes. In this talk, I will review the state-of-the-art regarding the detection and characterization of such planets and what we know today about their enigmatic nature. A definitive answer, however, seems within reach during this decade thanks to the game-changing observations that will be provided by JWST, PLATO, and ARIEL.
March 27, 2023 - Fang Liu (Stanford)
Top-down Production of Macroscopic Monolayers For Study of Static and Dynamical Properties
Two dimensional (2D) materials and their artificial structures hold great promises for electronic, optoelectronic, and electrochemical applications. The best quality monolayers for exploring the exotic quantum properties so far are mostly produced by scotch tape exfoliation, which is stochastic and often yields microscopic sized monolayers. On the other hand, bottom-up growth techniques such as chemical vapor deposition often produces monolayers lower in quality. Beyond the Scotch tape exfoliation, we developed a few new scalable and controllable top-down processes to exfoliate a variety of van der Waals (vdW) single crystals into monolayers and monolayer nanoribbons with high yield, high quality, and macroscopic dimensions. High-quality and large-area crystals will allow us to further assemble them into artificial heterostructures. The monolayers and other 2D artificial structures have been demonstrated to achieve enhanced nonlinear optical responses, and integrate into multiple pump probe techniques as electron diffractions to explore the key static and dynamic properties in these low dimensional systems. Obtaining high quality materials with enhanced yield will not only facilitate the basic research, but also take us one step closer to mass production and commercialization of the 2D devices in the future.
April 3, 2023 - Dr. Carol Scarlett (FAMU, Argonne)
New Search Methods for DM Particles
Abstract: It is well known that a light, pseudo-scalar particle called the Axion can solve several fundamental physics problems. Proposed to explain the lack of a neutron EDM, such a weakly interacting particle has the right characteristics to explain formation of galaxies, by providing the needed mass in the form of Cold Dark Matter. There have been a number of completed and proposed experiments to detect axionic particles taking approaches as varied as condensed matter energy band gap to superconducting magnetic cavities. This talk will review the theory behind axion particles, examples of early experimental searches and some new search techniques. One question this talk will broach is whether or not observations of nuclear behavior, a place where axionic matter is theorized to play a role in neutron spin, can provide appropriate experimental conditions to be used in axion searches.
April 10, 2023 - Christophe Royon (KU)
Measuring intact protons at the LHC: From the odderon discovery to the search for axion-like particles
Abstract: In the first part of the talk, we will describe the odderon discovery by the TOTEM and D0 experiments. The analysis compares the p pbar elastic cross section as measured by the D0 Collaboration at Fermilab at a center-of-mass energy of 1.96 TeV to that in pp collisions as measured by the TOTEM Collaboration at CERN at 2.76, 7, 8, and 13 TeV. The two data sets disagree at the 3.4 sigma level and thus provide evidence for the odderon. Combining these results with previous TOTEM results leads to a combined significance larger than 5 sigma.
In a second part of the talk, we will describe the search for axion-like particles with intact protons in the final state, leading to sensitivities to beyond standard model physics that improve by 2 to 3 orders of magnitude on the coupling compared to LHC standrad methods.
We will finish by describing briefly the ultra fast silicon detectors for timing measurements as well as for medical and cosmic ray physics applications with KU medical and NASA.
April 17, 2023 - James Analytis (Berkeley)
Transitions without Symmetry: exploring exotic materials that challenge our conventions
Abstract: The collective behavior of electrons in solids is at the root of some of the most important questions in condensed matter physics, from solving the riddle of high temperature superconductivity to creating quantum technologies. Two concepts are critical foundations of our understanding of electrons in materials; the concept of the quasiparticle and the concept of broken symmetry phase transitions. In exotic metals, many of which are connected to unconventional superconductors, both these concepts break down. In this colloquium, I give a summary of the challenge that these systems present to the conventional picture of condensed phases of matter, some intriguing new developments in the field and possible ways forward.
April 24, 2023 - Jufri Setianegara, Harold Li
High Resolution Storage Phosphor Dosimetry
Abstract: Proton beams are increasingly utilized for radiotherapy as they can confer unique dosimetric advantages due to their highly targeted dose deposition within a narrow Bragg peak. Electromagnetic interactions stemming from their charged nature result in the bulk of their radiation dose being deposited under a narrow area under their Bragg peaks which spares distal organs-at-risk. Other than its inherent physics, recent advances in medical cyclotron designs have also allowed for the creation of smaller proton beams are magnetically scanned across a tumor volume. While such beam delivery techniques are more challenging than their predecessors, this technology is rapidly becoming a mainstay within modern proton centers due to their ability to create highly conformal proton plans which greatly expands its clinical usefulness. However, the potential clinical benefit of proton therapy is heavily contingent on the spatial and dosimetric accuracies of these proton beams; any slight systematic variations in the pencil beams’ nominal position or dose can lead to significant differences in the clinical outcome especially due to the reduced robustness of proton treatments. These differences may be even further accentuated due to protons being more biologically damaging than photons by virtue of its higher linear-energy-transfer (LET) value. Despite this, there is not a convenient commercial solution to the current clinical need of a high-resolution absolute proton dosimeter. In this work, we studied the use of near water-equivalent storage phosphor dosimeter materials for high-resolution proton dose and LET simultaneous measurements. Storage phosphors are a class of dosimetry materials that function using the mechanism of photostimulated luminescence (PSL). Irradiation of these dosimeters will result in the production of electron-hole pairs that will be stored in metastable charge storage centers. The spatial distribution of these charge carriers will form a latent image that can be read out by optically stimulating the charge carriers to recombine and release PSL photons that are proportional in intensity to the locally deposited dose. The latent charges remaining after readout can be erased completely with a bright, broadband light which will render the material reusable. Their clinical use can also be potentially expanded in the near future for the purposes of proton FLASH dosimetry, high-resolution patient-specific conformal filter dosimetry, and spatial fractionated proton dosimetry.
May 1, 2023 - Dr. Brian Moeckly (Commonwealth Fusion)
High-Temperature Superconductors for Fusion Energy
Abstract: Decades of worldwide, government-sponsored research in fusion science have established the tokamak-based configuration as the leading approach to confining fusion-grade plasmas with strong magnetic fields. Yet in the past even state-of-the art superconducting magnet technology required tokamaks to be enormous to produce net fusion energy. High-temperature superconductors have recently reached industrial maturity. Commonwealth Fusion Systems is using these high-temperature superconductors to build smaller and lower-cost tokamak fusion systems. Following our successful demonstration of a large-bore, 20-Tesla, all-HTS magnet in September 2021, we have begun construction of an energy-breakeven fusion device called SPARC that will be commissioned in 2025. A fusion pilot plant called ARC will follow, with the aim of putting fusion power on the grid in the early 2030s. In this talk I will explain why high-field HTS magnets are a game changer for fusion energy, and I will review progress on the design and construction of fusion machines that will provide limitless, clean, fusion energy to combat climate change.
August 29, 2022 - Stephanie Juneau (NOIR lab)
September 12, 2022 - Daniel Tapia Takaki (KU)
Using the LHC as a photon collider and synergies with the Electron-Ion Collider
In this talk, we will review the science of photon-induced interactions at the CERN Large Hadron Collider. Special emphasis will be put on recent research work and prospects of new experiments led by the PI. Finally, the synergies and new research projects in the context of the Electron-Ion Collider to be built at Brookhaven National Laboratory will also be discussed.
September 19, 2022 - Ian Crossfield (KU), The Final Frontier? The Composition of Rocky Exoplanets and Their Host Stars
The study of exoplanets and their atmospheric compositions is set to
dramatically expand in the coming years with the recent start of JWST
science observations. I will present "JWST precursor" results in two areas
from the KU ExoLab. First, I will report on our successful measurement of the infrared
thermal emission from a terrestrial planet, at 1.2 Earth radii the smallest
planet for which such measurements have been made. Our
measurement begins to constrain surface mineralogy and also reveals
that the planet has essentially no atmosphere for a wide range of
plausible atmospheric compositions, and sets the stage for JWST follow-up.
Second, I will present initial results from our ongoing efforts to measure
precise chemical abundances of exoplanet host stars. Such measurements
are needed because historically measurements of exoplanetary atmospheric
composition have compared only to *solar* abundances (overlooking intrinsic
*stellar* abundances), and are essential in order to permit accurate
interpretation of JWST measurements of exoplanets' atmospheres, surfaces,
October 17, 2022 - Jeyhan Kartaltepe (RIT), The Growth of Galaxy Structure, as Told by Early JWST Imaging
The first images taken with the James Webb Space Telescope (JWST) are unveiling galaxies in the distant universe and enabling detailed studies of their properties. In this talk, I will present some of the first results on how our understanding of the growth of galaxy structure in the universe has changed based on these first images. We have conducted a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z=3-9 using the NIRCam images at 1-5 microns taken as part of the Cosmic Evolution Early Release Science (CEERS) Survey in June 2022. This sample consists of 850 galaxies at z>3 detected in both CANDELS Hubble WFC3 imaging as well as JWST CEERS NIRCam images to enable a comparison of HST and JWST morphologies. Our team conducted a set of visual classifications, with each galaxy in the sample classified by three different individuals. We also measure quantitative parametric and non-parametric morphologies using the publicly available codes Galfit, Galapagos-2/GalfitM, and statmorph across all seven NIRCam filters. Using these measurements, I will present the fraction of galaxies of each morphological types as a function of redshift, compare their morphologies to what we knew based on Hubble imaging, and discuss the implication of these results for galaxy evolution. I will also highlight what we expect to learn from future JWST observations in CEERS, COSMOS-Web, and other Cycle 1 surveys.
October 24, 2022 - Rebecca Levy (U. Arizona), Feeding and Feedback: “Super” Star Clusters in the Center of NGC253
The cycle of star formation governs the evolution of galaxies. At earlier cosmic times, the amount of cold gas and the star formation rate were higher than in the present day. A major open question is whether the process of star formation has also changed over cosmic time. To investigate this question, I present observational results from an archetypal nearby starburst galaxy, NGC253. The star formation rate in the center of this galaxy is much higher than normally star-forming galaxies today and may be more similar to galaxies at earlier cosmic times. First, I will discuss how gas flows to the center of this galaxy along its bar to fuel the extreme burst of star formation. Using very high spatial resolution data from ALMA tracing emission from dust and dense molecular gas, we find that the massive, compact, very young “super” star clusters (SSCs) found in the center of this galaxy are arranged in a ring. Moreover, we find that the SSCs and dense molecular gas are found at the innermost orbit predicted by the barred potential of this galaxy, as expected. Next, I will discuss the detection of massive outflows of molecular gas detected from three of the SSCs. These outflows carry a substantial fraction of the gas mass away from the clusters and may stop these clusters from growing even larger. The precise physical mechanism powering these outflows is uncertain, but winds from massive stars and dust-reprocessed radiation pressure are the best candidates - different from lower mass, less extreme star clusters. Finally, I will discuss the result of this extreme burst of star formation on the galaxy as a whole: the central starburst is driving a galaxy-scale, multiphase superwind. I will show a new detection of the thermal emission from warm dust located on the outermost edge of the superwind. Together, these new observations of NGC253 paint a more complete picture of gas feeding and feedback in an extreme star-forming environment and set the stage for JWST observations coming in Cycle 1.
October 31, 2022 - Neda Hejazi (KU), Cool Dwarfs: Clues on the Chemical History of the Milky Way
Similar to many other galaxies in the Universe, the Milky Way is a highly evolved spiral galaxy. However, despite the advent of large observing programs in the last decade, we are still far from a full understanding of our galaxy’s formation and evolution. Although accounting for large-scale kinematic and dynamic properties of stellar populations is essential in constructing Galactic evolutionary models, the chemical composition of stars holds fundamental clues on how the Galaxy formed and how it has evolved over time. Among different stellar types, low-mass dwarfs, in particular K and M dwarfs, can be used as tools to probe the structure and chemodynamical evolution of the Milky Way. These dwarfs are the most abundant stars in our Galaxy, which constitute a significant part of the Galaxy’s mass in the form of baryonic matter. In addition, due to the slow fusion process in their interiors, the main-sequence lifetime of these cool dwarfs is much longer than the current age of the Universe. As a result, their atmospheric abundances are pristine indicators of the chemical properties of the progenitor molecular clouds where they were born. Moreover, cool dwarfs have increasingly become attractive targets as planet host candidates, because widely used methods in detecting exoplanets such as radial velocity and transit techniques are more sensitive to planets orbiting low-mass stars. The chemical evolution of protoplanetary disks and subsequent planetary formation can be determined by comparing the composition of host stars and their planets. I will underline recent studies of Galactic chemical properties, highlighting approaches to utilize cool dwarfs as tracers of the chemical enrichment history of the Milky Way.
November 7, 2022 - Moiya McTier, The Milky Way: Our Galaxy, a Book, and a Shift in Perspective
Every single human who has ever lived could have called our Milky Way Galaxy "home," but it was only 100 years ago that we learned we live in a galaxy at all. In this talk, Dr. Moiya McTier will highlight the different ways humans have connected to the night sky throughout our history, from myths to telescopes. She will tell you about her process for writing an "autobiography" for the Milky Way, and share how the experience changed the way she interacts with the world. No knowledge of space will be assumed.
November 14, 2022 - David E. Meltzer, Arizona State University, Investigating and addressing physics students’ mathematical difficulties
Throughout the history of physics education, physics students’ mathematical preparation and skills have been a concern both for instructors and educational researchers. The impact of that preparation on students’ success in physics courses has been studied, and many specific mathematical difficulties faced by physics students have been identified. A variety of instructional approaches have been suggested to address these difficulties. I will survey some of the key research findings, and discuss a number of pedagogical strategies that have been employed or are under development.
November 21, 2022 - Noel Bartlow, University of Kansas Department of Geology, The mechanics of megathrust earthquake producing faults illuminated by GPS geodesy
Subduction zones are convergent plate tectonic boundaries which produce the largest earthquakes and tsunamis in the world. These destructive events can cause 10s to 100s of thousands of deaths and billions of dollars in damages. However, in any individual subduction zone these mega disasters occur every 500 to 1000 years, making it difficult to prepare for them. In between the times of large earthquakes subduction zones are not completely quiet, instead they exhibit small motions that can be measured by high precision GPS geodesy. By measuring and modeling these small motions we learn about the behavior of subduction zones, including where future earthquakes might strike and how big they might be. GPS geodesy has also enabled the discovery of so-called slow earthquakes, also called slow slip events, which occur over periods of weeks to years. While not dangerous, these slow slip events have the potential to trigger huge earthquakes and tsunamis and also illuminate the mechanics of friction on subduction zone faults. This talk will introduce GPS geodesy, Prof. Bartlow’s work on slow slip events, and new initiatives in seafloor geodesy with particular focus on a subduction zone in the Pacific Northwest region of the US.
November 28, 2022 - Prof. Tarun Sabarwal (Economics, KU), Control and spread of contagion in networks with global effects
We study proliferation of an action in binary action network coordination games that are generalized to include global effects. This captures important aspects of proliferation of a particular action or narrative in online social networks, providing a basis to understand their impact on societal outcomes. Our model naturally captures complementarities among starting sets, network resilience, and global effects, and highlights interdependence in channels through which contagion spreads. We present new, natural, computationally tractable, and efficient algorithms to define and compute equilibrium objects that facilitate the general study of contagion in networks and prove their theoretical properties. Our algorithms are easy to implement quantifying relationships previously inaccessible due to computational intractability. We conduct millions of Monte Carlo simulations in scale-free networks with 1,000 players, providing quantitative and qualitative insights. The scope of application is enlarged given the many other situations across different fields that may be modeled using this framework.
December 5, 2022 - Prof. Sebastien Lepine (Georgia State University), Dancing with the stars: tracking stellar motions in the vicinity of the Sun to decipher the structure and history of the Milky Way
Thanks to massive astrometric and spectroscopic surveys
we now know the distances, full spatial motions, and chemical abundances
for millions of stars in the vicinity of the Sun. How a star moves
locally depends on its specific orbit around the Galaxy which is
primarily determined by the star's age and point of origin. Stars can
notably be grouped into broad "populations" (disk, old disk, halo)
but a detailed analysis reveals a much more complex dynamical structure,
with stars swarming into "streams" or "moving groups" each with its
own specific origin and history. The kinematics of nearby stars can
thus be used to infer the and evolution of the Milky Way, by using
the stars as "fossils" to retrace the story of its formation and/or
assembly. In this presentation I will first explain how the distances
and motions of so many stars are being and how massive spectroscopic
programs like the Sloan Digital Sky Survey provide critical radial
velocity and abundance measurements, notably for the countless
low-mass stars (K and M dwarfs) which are ubiquitous and long-lived,
but dim and challenging to observe. I will then present results that
showcase the surprising dynamical complexity of our Galaxy, including
evidence for accretion and merger events, spiral arms and orbital
resonances, young moving groups, radial migration, and more.
January 24, 2022 - Alan Robock - Rutgers University
"Climatic and Humanitarian Impacts of Nuclear War"
A nuclear war between any two nations, such as India and Pakistan, with each country using 50 Hiroshima-sized atom bombs as airbursts on urban areas, could inject 5 Tg of soot from the resulting fires into the stratosphere, so much smoke that the resulting climate change would be unprecedented in recorded human history. Our climate model simulations find that the smoke would absorb sunlight, making it dark, cold, and dry at Earth’s surface and produce global-scale ozone depletion, with enhanced ultraviolet radiation reaching the surface. The changes in temperature, precipitation, and sunlight from the climate model simulations, applied to crop models show that these perturbations would reduce global agricultural production of the major food crops for a decade. Since India and Pakistan now have more nuclear weapons with larger yields, and their cities are larger, even a war between them could produce emissions of 27 or even 47 Tg of soot.
My current research project, being conducted jointly with scientists from the University of Colorado, Columbia University, and the National Center for Atmospheric Research, is examining in detail, with city firestorm and global climate models, various possible scenarios of nuclear war and their impacts on agriculture and the world food supply. Using six crop models we have simulated the global impacts on the major cereals for the 5 Tg case. The impact of the nuclear war simulated here, using much less than 1% of the global nuclear arsenal, could sentence a billion people now living marginal existences to starvation. By year 5, maize and wheat availability would decrease by 13% globally and by more than 20% in 71 countries with a cumulative population of 1.3 billion people. In view of increasing instability in South Asia, this study shows that a regional conflict using <1% of the worldwide nuclear arsenal could have adverse consequences for global food security unmatched in modern history. The greatest nuclear threat still comes from the United States and Russia. Even the reduced arsenals that remain in 2020 due to the New START Treaty threaten the world with nuclear winter. The world as we know it could end any day as a result of an accidental nuclear war between the United States and Russia. With temperatures plunging below freezing, crops would die and massive starvation could kill most of humanity.
As a result of international negotiations pushed by civil society led by the International Campaign to Abolish Nuclear Weapons (ICAN), and referencing our work, the United Nations passed a Treaty to Ban Nuclear Weapons on July 7, 2017. On December 10, 2017, ICAN accepted the Nobel Peace Prize “for its work to draw attention to the catastrophic humanitarian consequences of any use of nuclear weapons and for its ground-breaking efforts to achieve a treaty-based prohibition of such weapons.” Will humanity now pressure the United States and the other eight nuclear nations to sign this treaty? The Physicists Coalition for Nuclear Threat Reduction is working to make that happen.
January 31, 2022 - Natasha Holmes - Cornell University
"The trouble with traditional physics labs"
When you ask physicists to reflect on their intro labs, responses include “boring”, “forgettable”, or “cookbook.” What is so wrong with the traditional lab? An instinctive answer is the structure: students follow procedures without having to think about what’s going on. In this talk, I’ll present work that challenges this instinct and I’ll suggest an alternative answer: namely, that the fundamental goal to use labs to demonstrate phenomena is problematic. I’ll describe several studies that have used quantitative assessments of student learning, analysis of student work, and videos of students conducting lab experiments to shed light on this issue. I’ll also briefly describe how we’ve restructured our introductory lab courses in response to these results.
March 7, 2022 - Tova Holmes (University of Tennessee)
Going the Distance: Searching for Overlooked Physics at the LHC
The LHC has reached a new era: nearly a decade without any large jumps in energy or luminosity. For those interested in finding Beyond the Standard Model (BSM) physics, a paradigm shift is required. In my talk I’ll discuss a search program looking for long-lived particles, which often escape detection from standard BSM searches, due to the difficulty of identifying their unconventional signatures. This results in a long-lived particle landscape full of unexcluded territory, opening up opportunities to find TeV-scale Supersymmetry, hidden sectors, right-handed neutrinos, and more. My talk will explore how and why we should search for these new signatures.
April 4, 2022 - Bjoern Penning (University of Michigan)
Searching for Dark Matter from the Lowest to the Highest Energies
Dark Matter (DM) is a long standing puzzle in fundamental physics and the goal of a diverse research program. In underground experiments such as LZ we search for DM directly using lowest possible energy thresholds, at the LHC we seek to produce dark matter at the very highest energies, and using telescopes we look for telltale signatures in the cosmos. I will present an overview of the status of DM searches using these different approaches and their connection before focusing on the status of the LZ direct Dark Matter experiment. LZ is the world's most sensitive DM experiment and is currently taking data.
April 11, 2022 - Ashley Chontos (University of Hawaii / MIT/ Princeton)
Precise Stellar and Planet Properties in the Kepler, K2 & TESS Era
The Kepler Mission has revolutionized exoplanet science, with over 2000 confirmed planets to date. However, most exoplanet host stars observed by Kepler are too faint to perform extensive radial-velocity follow-up to precisely measure Doppler semi-amplitudes and thus, planet masses. The recent successful launch of the NASA TESS Mission has now opened the door to precisely characterize transiting exoplanets orbiting bright stars in the solar neighborhood. The most promising planets will be those orbiting subgiants, whose rapid phase in stellar evolution provides a unique tool to infer precise stellar ages, masses, radii and densities. Subgiants also provide the opportunity to apply asteroseismology, which is currently the best tool for accurate and precise stellar characterization. In this talk, I will present benchmark Kepler and TESS asteroseismic discoveries, including Kepler’s first new planet host (or KOI-4) and the detection of oscillations in the naked-eye solar-analogue 𝛼 Men A. I will introduce the TESS-Keck Survey (TKS), which is a very large Keck radial velocity survey to confirm and characterize transiting exoplanets discovered by TESS. Finally, I will conclude with early results from an ensemble analysis of TESS planets orbiting subgiant stars as well as its implications for post main-sequence planet evolution.
May 2, 2022 - Kevin Hainline (University of Arizona)
The First Years of JWST: Discovering and Understanding Distant Galaxies
With the successful launch and deployment of JWST, we are only months away from a suite of deep extragalactic surveys that will uncover hundreds of thousands of galaxies well outside of the realm of current observational capabilities. In this talk, I will discuss where we stand in our understanding of the early extragalactic universe and describe how JWST will help us answer longstanding questions about reionization, the evolution of the metal content in the universe, and the role of active galaxies. As a member of the science team for the primary imager on board JWST, JWST/NIRCam, I will discuss the work that we’ve been doing to prepare for the GTO program JADES, the most comprehensive Cycle 1 deep survey which encompasses over 800 hours of combined NIRCam, NIRSpec, and MIRI observations of the well-studied GOODS-S and GOODS-N regions. I will place JADES in context with other planned extragalactic surveys and share the complexities of finding the farthest and faintest galaxies.
May 9, 2022 - Casey De Roo (University of Iowa)
Making and Using X-ray Grating to Study the Local Hot Universe
Exquisite cosmological measurements performed in the last decade provide tight constraints on the amount of baryons – “normal matter” – in the Universe. Yet surveys of our local Universe today come up far short: as much of 50% percent(!) of this normal matter is unaccounted for. Predictions from cosmological simulations suggest a significant fraction of the baryons are at X-ray temperatures and lie undetected in the extended halos of galaxies and clusters. Is there enough material in these reservoirs to get the “right” answer in our local Universe? And what can that material tell us about how it got there?
In my talk, I will discuss prospects for detecting and characterizing this hot gas with future X-ray grating spectrometers. I’ll divide my time between astronomy and instrumentation, giving a brief “state of the field” overview for astronomical X-ray instrumentation, touch on how we are leveraging advances in the semiconductor industry to develop and deploy next-generation X-ray optics, and discuss the advances in the past decade that put this science within reach.
September 20, 2021 - Dawn Williams - Alabama
"The IceCube Neutrino Observatory and the Beginning of Neutrino Astrophysics"
The IceCube Neutrino Observatory is the world’s largest neutrino detector, instrumenting a cubic kilometer of ice at the geographic South Pole. IceCube was designed to detect high-energy astrophysical neutrinos from potential cosmic ray acceleration sites such as active galactic nuclei, gamma ray bursts and supernova remnants. IceCube announced the detection of a diffuse flux of astrophysical neutrinos in 2013, including the highest energy neutrinos ever detected. In September 2018, IceCube observed a neutrino in coincidence with a flaring blazar. I will discuss the latest results from IceCube and discuss prospects for future upgrades and expansions of the detector.
September 27, 2021- Cancelled
October 4, 2021- Pengpeng Zhang - Michigan State
"Phase Transformation and Interfacial Coupling in Heterostructures of Low-Dimensional Materials"
The rapid advances in low-dimensional materials of various crystalline symmetries and elemental compositions have generated rich functionalities. Artificially stacking or stitching dissimilar materials via construction of heterostructures further offers unprecedent potential for tailoring the properties of individual constituents and giving rise to exotic quantum phenomena. In this talk, I will first discuss how we utilize lateral heterostructures to induce phase transition in an inorganic transition metal dichalcogenide core-shell architecture and to unravel the microscopic process of insulator-to-metal transition in a correlated organic charge transfer complex system. I will then discuss the formation of new two-dimensional Sn phases enabled by interfacial coupling on hexagonal boron nitride monolayer on metal (h-BN/metal), which potentially provides a new avenue for engineering electronic and topological properties of 2D Sn.
October 18, 2021- Juliette Becker - Caltech
"Explaining the Orbits of Ultra-Short-Period Planets Through Disk-Planet and Star-Planet Interactions"
Ultra-short-period planets (USPs) reside interior to the expected truncation radius for a typical T Tauri disk, requiring extra explanations for their current orbital locations beyond simple disk migration. In particular, once a planet migrates close to the disk truncation radius, Type I torques will go to zero or switch direction depending on the stellar and disk conditions, and the result is that the planet is expected to stop migration and become trapped. In this presentation, we explain how for suitable disk parameters, magnetically-driven sub-Keplerian gas flow in the inner disk can naturally counteract these effects and subsequently produce USPs at their observed orbital radii. The sub-Keplerian gas flow provides a headwind to small planets, providing a strong torque which can overcome the effects of outwards Type I migration in the inner disk. We also discuss how post-disk dispersal, stellar evolution can lead to a particularly intriguing geometry of system containing ultra-short period planets in high multiplicity systems where the ultra-short period planet and the outer planets exist in two different dynamical states. This has manifested in the observational data as a small number of stars hosting systems of tightly packed coplanar inner planets as well as an ultra-short period planet, where the orbit of the latter is misaligned relative to the mutual plane of the former.
October 25, 2021- Janet Biggs
I am a visual artist whose practice incorporates science and technology. I have collaborated with experts ranging from aerospace engineers to astrophysicists. I will present a number of projects that open innovative ways of seeing and thinking, from the creation of a neurodiverse AI entity to my current collaboration with KU professors Agnieszka Miedlar and Daniel Tapia Takaki (part of the Spencer Museum of Art’s Integrated Arts Research Initiative). Moving between locations, situations, perspectives and disciplines can disrupt existing understandings and open new paths for knowledge building, insight, and communication. Questions are generated by a shift in perspective, a step sideways into an unexpected conversation. Cross-disciplinary collaborations can operate as innovative structures, integrated and substantive to all participant’s respective fields. This talk will introduce methods and models of generative thinking. What new questions can be asked? What new discoveries will be made?
November 1, 2021 - Phil Baringer - KU
"40 Years of the Standard Model"
We'll discuss how the Standard Model of particle physics grew from its uncertain infancy to its formidable adulthood. After some nostalgia about the successes of the theory we'll attempt to take a clear-eyed look at its present status.
November 8, 2021- Feng Wang - Berkeley
“Engineering Correlation and Topology in Two-Dimensional Moire Superlattices”
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 and topological physics using moire superlattice in two dimensional heterostructures. One example is the transition metal dichalcogenide moire superlattices, where a rich set of correlated insulator and generalized Wigner crystal states can be observed. The other example is the ABC trilayer graphene (TLG) and hexagonal boron nitride (hBN) moire superlattice, in which both the bandwidth and the topology of the electronic band can be controlled electrically. It allows us to realize many quantum phases, ranging from Mott insulator and superconductivity to orbital ferromagnetism and Chern insulator, all in a single device through electrostatic gating.
December 6, 2021 - Jorge A. Lopez - Texas El Paso
“Italian delicacies served up in a neutron star crust”
The matter in the outermost layer, or “crust,” of a neutron star (the remnant of a supernova) is believed to host a variety of phases in which dense regions of nucleons are filled with voids of lower density. The presence of the phases, euphemistically referred to as “nuclear pasta” because of their resemblance to the shapes of lasagna, gnocchi, and spaghetti, may affect the emission of neutrinos, the primary mechanism by which the neutron star cools. In this talk, molecular dynamics and a set of topological and geometric descriptors (volume, area, mean curvature, and its Euler characteristic—a number that represents the phase’s topology) are used to accurately identify the pasta phases predicted by dynamical simulations, a labeling scheme that could be used to directly map the shape of a pasta phase to its effect on neutrino emission and neutron star cooling. Ref. https://link.springer.com/article/10.1007%2Fs11467-020-1004-2.
3/2/2020 Professor Timothy Tait, University of California, Irvine - Searching for Particle Dark Matter
3/16/20204 Professor Daniel Tapia Takaki, University of Kansas - Unprecedented photons from the periphery and beyond
3/30/2020 Professor Corey Maley, University of Kansas Department of Philosophy - Analog Computation and Representation
11/4/2019 Professor Anne Medling, University of Toledo - Tracing Black Hole Fueling and Feedback with Adaptive Optics and ALMA
11/11/2019 Professor Javier Duarte (University of California, San Diego) - Deep learning for Higgs and new physics searches at the
11/18/2019 Professor Siyuan Han (University of Kansas) - Superconducting Circuits for Quantum Information Processing
11/25/2019 C.A. Bertulani (Texas A&M University-Commerce) - Neutron Skins, Symmetry Energy, and Neutron Stars
12/2/2019 Anthony R. Timmins (University of Houston) - The structure of the nucleus and proton at the LHC