Renna Yi--Apr 22
The Origin of Life
How do we define and demonstrate the transition from non-life to life? The origin of life remains an unsolved scientific puzzle, despite numerous attempts from multiple disciplines. Here I will highlight approaches to the problem from chemistry and physics and whether we are anywhere near solving the problem.
Cheng-Li Chiu--Princeton Physics--Apr 15
2D Material Research Life
Electrons confine in 2D material can have distinct behaviors than in bulk crystal. The electron-electron interaction can easily be enhanced when the effective mass is reduced by lowering the charge density or the increase of the inter electron distance. Many quantum phenomena have been realized in such low dimensional platform such as graphene or TMD and making the 2D material a hot topic. In the talk I will give some introduction to 2D physics and telling the story of my life doing such research. I will also introduce my hometown Taiwan and compare my life there and here.
Xianghan Xu--Apr 08
How Material Synthesis Promotes Physics
Material synthesis is not just a "gray area" between chemistry and physics, but a crucial stepstone to practice exotic phenomena in textbooks experimentally. In this talk, I'll show examples that how new materials unravel physics puzzles, especially our recent work of the meta-stable ferroelectric phase in HfO2 bulk single crystals. The relevant experimental techniques will be introduced in detail. Hope my talk can give you a flavor of what we're doing and inspirations for future research.
Charlotte Olsen--Apr 01
Finding Evidence for Synchronized Star Formation in Local Volume Dwarf Galaxies
Star Formation Histories (SFHs) reveal physical processes that influence how galaxies form their stellar mass. We compare the SFHs of a sample of 36 nearby (D < 4 Mpc) dwarf galaxies from the ACS Nearby Galaxy Survey Treasury (ANGST), inferred from the Color Magnitude Diagrams (CMDs) of individually resolved stars in these galaxies, with those reconstructed by broad-band Spectral Energy Distribution (SED) fitting using the Dense Basis SED fitting code. Metrics for comparing individual SFHs from both methods show overall agreement. For both the CMD and SED methods, the median normalized SFH of galaxies in the sample shows surprising synchronous star formation beginning between 4 and 6 Gyrs ago and continuing to the present day.
Nicodemos Varnava--Feb 25
Everettian Quantum Mechanics
Quantum mechanics (QM) is the best description of reality we currently have. Yet, we don't really understand what is going on behind the scenes. In fact, we decided to hide our ignorance under the rug by postulating the collapse of the wavefunction after a measurement. In this talk, inspired by Sean Carroll's book "Something deeply hidden", I will argue that as physicists we should care more about the foundation of QM and I will present my personal favorite formulation, "Everettian QM" or "Many worlds interpretation of QM". We will see that by taking the wavefunction seriously our classical experience manifests as single worlds whose superposition constitutes the wavefunction of the universe. On a practical level the ongoing second quantum revolution, defined by coherent manipulation of quantum systems, demands a more careful examination of what measurement is. This is exemplified by the famous "Wigner's friend paradox" which I will discuss. I will end my talk with some philosophical speculation about the meta-issue at work. Namely, at the heart of the measurement problem (and the consciousness problem) lies the inability to distinguish the system from the observer, which is the crux of the scientific method. Understanding the philosophical implications should at least help us better define our questions and at best it could be an indicator that a new paradigm shift is needed.
Yi-Shiou Duh from Stanford Physics--Feb 18
Rock Climbing and My PhD Life
Rock climbing is a trendy sport but full of failure and falling. Similarly, PhD degree is the accomplishment of overcoming a series of challenges. It is rewarding to pursue both goals in my PhD life. In the talk, I will invite you to my climbing journeys and share with you some valuable lesson, which is hard to learn elsewhere. Moreover, I will talk about how I combine both my passion together to publish a paper about deep learning and climbing. In the end, I will talk about how rock climbing influences me as a person.
Danny Doucette from Pittsburgh Physics--Feb 4
How can Physics Education Research Improve Equity in Physics?
The field of Physics Education Research (PER) brings methods and frameworks from the social sciences to bear on physics, with the goal of improving student learning. Although PER has traditionally focused on improving instruction, some recent work has focused on the lived experiences and biases that curtail diversity and inclusion in our field. In this talk, I will introduce some themes from equity-focused research in PER. I will highlight some important research results about the causes of inequities, and introduce some research-oriented approaches to improve equity in large public universities in the USA.
Steffie Thayil--Jan 28
Detecting particles with the Compact Muon Solenoid
The Compact Muon Solenoid (CMS) is a general purpose detector on the Large Hadron Collider (LHC) ring at CERN. CMS records the debris from particle collisions at the LHC, using a variety of detector technologies to measure the momentum and energy of different types of particles. This information is then used to reconstruct the physics processes that occurred in the collision. Millions of such collisions are recorded and processed at CMS to make measurements on the Standard Model of particle physics, as well as to search for new physics beyond the Standard Model.
In this talk, we'll discuss the hardware that makes these measurements possible-- the subdetector components, which use various physics phenomena to make energy/momentum measurements; the trigger system, which decides which events to record; and the way these come together to provide a realistic picture of the underlying particle interactions.
Lana Eid--Nov 19
Source Reconstruction of the Gravitationally Lensed Giant Arc in the Galaxy Cluster Abell 370
Gravitational lensing by galaxy clusters provides a unique way to study distant galaxies in higher magnifications than would normally be seen. However, the lensed images we see of high-redshift objects have been warped and distorted, so we need to de-lens the image(s) in order to study the morphology of the source. We aim to use giant arcs to study the effects of using an extended source on both the lens model and the reconstructed source.
Generally, lens models are constrained with lensed images by assuming a simple point source. Spectroscopy can be used to determine which images are from the same source, and the positions of different images are used as constraints in the lens model. A giant arc naturally provides more constraints than images from an unresolved point source, but with this higher level of complexity comes a larger number of parameters to fit, such as the structure of the source in addition to the point-spread function. Our goal is to determine whether any improvements to the lens model and reconstructed source merit the difficulty of handling the extra constraints.
As a specific example, we consider the giant arc in the Abell 370 galaxy cluster, which is at redshift z = 0.375. Raney et al. (2020) used the lensmodel code (Keeton, 2001 and 2011) to model the galaxy clusters in the Hubble Frontier Fields program, and they found from their lens model that the arc is comprised of five merging images of the same source, which is at a redshift of z = 0.725. We used the deflection maps, source position, and image positions from the analysis in Raney (2019) to test different ellipticities and orientations of an extended source and see how it compared to the shape of the observed arc. The next step is to use the pixsrc code from Tagore (2014) to perform a full reconstruction of the source.
Phillip Rechani--Nov 12
A Quest to Image Live Cells at the Single Molecule Level
Optical tweezers were created by Arthur Ashkin in 1970. He demonstrated the effect of light’s momentum on microscopic particles by using two counter propagating lasers horizontally on transparent beads in water. Since then, people have been using optical tweezers on particles of varying sizes (~50nm to 1μm) in various geometries for biological physics and nanophotonics. In Sang-Hyuk Lee’s lab, we use optical tweezers for biological physics. Optical tweezers can be used to measure forces of single molecules such as DNA, RNA or Proteins using various techniques, all of which involve attaching two ends of these molecules to beads and then trapping the beads with lasers. This can measure the spring constants of these molecules as well as folding and unfolding forces and the Gibbs Free Energies of these conformations all as a function of displacement. One of the ultimate goals in our lab is to do chemical sensing at the single molecule level. This would involve trapping a metal “nanostar," a metal nanoparticle with several sharp points on its surface, with a trapping laser, and a probing laser used to get the Raman spectrum unique to neighboring molecules. This concept of using nanostars as chemical sensors is called Surface Enhanced Raman Scattering or SERS. This will, theoretically, allow, chemical sensing inside cells in vivo (while the cell is alive). I will be speaking about the history of optical tweezers, a glance at the physics of trapping particles of different sizes and materials using light, the applications for measuring forces and the goal of using them for metal nanoparticles for chemical sensing.
Ironman Training and Grad School: A personal account of goal setting, perseverance, and work-life balance.
In September 2020, I completed an Ironman Distance Triathlon, a single-day long-distance race consisting of a 2.4 mile swim, 112 mile bike, and 26.2 mile run. Preparing for this event involved balancing 30+ hour training weeks while maintaining progress on my courses and research. Additionally, the Coronavirus brought about race cancellations and other challenges to overcome. Along the way, I learned many lessons that have carried over to my success as a student, including the importance of overall health, structured routines, and sticking to a plan. They say grad school is a marathon, not a sprint, so come hear how literal marathon swim-run-bike training helped me become a better student!
Tsung-Chi Wu--Oct 29
*Recorded Video Link*
*Slides*
Promotion of Equity, Diversity, and Inclusion in STEM fields – Drawing Inspiration from Universities’ and Companies’ Inclusion Statements and Videos
The inequality of gender, sex orientation, and race in science, technology, engineering, and math (STEM) fields has remained constant for decades. For example, a recent study showed that women are 20% more likely than men to leave fulltime STEM employment after their first child [1]. Also, a multilevel regression model demonstrated sexual minority students were 7% less likely to be retained in STEM compared to switching into a non-STEM program [2-3]. Moreover, racial diversity in PhD-level Earth scientists has not improved over the past four decades, with faculty of colour holding only 3.8% of tenured or tenure track positions in the top 100 geoscience departments [4]. These studies suggest the importance of having a workplace that celebrates the diversity of faculty, students, and staff, and an environment that includes, values, and trusts each other. In the talk, I will first reveal several facts about the inequality in STEM fields. After that, together we will read statements and watch videos about equity, diversity, and inclusion from several universities and companies. Hopefully, we can draw inspiration from them and get motivated to promote equity, diversity, and inclusion at the levels of the research group, department, university, and whole academic community.
[1] E. A. Cech and M. Blair-Loy, PNAS 116, 4182-4187 (2019).
[2] J. Freeman, Nature 559, 27-28 (2018).
[3] B. E. Hughes, Science Adv. 4, eaao6373 (2018).
[4] K. Dutt, Nature Geoscience 13, 2–3 (2020).
Charlotte Olsen & Sabrina Appel--Oct 22
*Recorded Video Link*
Women in Physics: A Case Study of Equity Issues in Physics
Answering fundamental questions in physics requires the combined effort of the brightest minds the community has to offer, regardless of gender, race, ethnicity, religion, sexual identity, or any other demographic. Yet, in spite of an abundance of interest and ability, few individuals from underrepresented populations in physics and astronomy make it through to a PhD. We will investigate this “leaky pipeline” with the help of numerous recent studies regarding the challenges and obstacles faced by women in physics and astronomy as a case study of broader equity issues in physics. We will offer actionable solutions that can be implemented at a range of levels (ranging from individual to department solutions). We will also workshop a number of scenarios to develop strategies for handling different situations in order to work towards an environment where every physicist thrives.
Victor Drouin-Touchette--Oct 15
*Recorded Video Link*
*Slides Link*
ARPES: Uncovering the Superconducting Gap
In this presentation, I will survey the experimental technique of angular resolved photo-
emission spectroscopy (ARPES), and its use in the determination of the symmetry of
the superconducting gap in cuprates. ARPES is based on the property of matter that
when exposed to light of frequency ν, electrons will be expulsed from the material if
~ ν ≥ Φ, with Φ the energy needed to delocalize an electron from the surface. Further,
the energy of the collected electron will grow linearly with ν. This effect, explained by
Einstein, can be used to probe the electronic structure of matter.
The intensity of the collected electrons can be mapped out with respect to their mo-
mentum k and their energy ~ ω: I(k, ω). Using interacting electron theory, the intensity
of the electrons hence collected can be related to the spectral function for one-particle
excitation, i.e. the “easiness” to rip an electron out of the dispersion bands in the
material.
After surveying, the experimental challenges of ARPES relating to the condition of
the experimental setup, I will show how its application to Cu gives a purely parabolic
dispersion, as well as showing more minute details. This first example shows the great
resolution of ARPES.
Finally, experimental data of ARPES on lead allows us to directly observe the su-
perconducting gap due to the formation of bound Cooper pairs in the superconductor.
Using that as a stepping point, I will present the data on Bi-2212, a 96K cuprate super-
conductor, and how the analysis of the dispersion reveals the unusual gap symmetry.
Chad Ummel--Oct 8
*Recorded Video Link*
Watch your Back(ground)!—Measuring the Beam-Induced 13C(d,n)14N Background in Underground Nuclear Astrophysics Experiments
The 13C(α,n)16O reaction is the primary source of neutrons for the slow neutron capture process (s-process) of stellar nucleosynthesis, which is responsible for the creation of roughly half of all elements heavier than iron. Due to low yields, the reaction rate is poorly constrained in the astrophysically relevant energy range. As such, measurement of the 13C(α,n)16O cross section is being pursued heavily at high-intensity, low-background accelerator laboratories, primarily in facilities located deep underground. Preliminary neutron energy spectra from a measurement at Oak Ridge National Laboratory’s Multicharged Ion Research Facility (MIRF) showed high-energy background events corresponding to neutrons from the 13C(d,n)14N reaction, resulting from very low, but nonzero deuterium contamination in the alpha-particle beam. The 13C(d,n)14N cross section is many orders of magnitude greater than that of 13C(α,n)16O in the relevant energy range, and its contribution cannot be quantified via blank target runs. Thus, a direct measurement of the 13C(d,n)14N cross section in the energy range of interest is needed. Accordingly, an experimental effort was undertaken to measure the 13C(d,n)14N cross section at laboratory energies between 140 and 250 keV at MIRF. Preliminary results and the implications of this work will be discussed.
Anna Hallin--Oct 1
*Recorded Video Link*
A Taste of High Energy Physics
Welcome to a flavorful talk on high energy physics! The current model for the known elementary particles and their interactions, the Standard Model, is extraordinarily successful. However, we know that there is more to Nature than the particles we have found so far. How can we look for New Physics, using the physics we already know? In this talk we will get to know the flavor sector of the Standard Model, and learn how precision measurements can give us new insights into the nature of potential New Physics.
Wen-Sen Lu--Sept 24
*Recorded Video Link*
*Slides Link*
Marching Toward Quantum Readiness
Having seen recent national funding surges in quantum computing including US, Canada, UK, China, and more, did you ever wonder if quantum industry is going to be just another huge bubble? As one of the major public providers for quantum computing cloud services, IBMQ hosted a 11-days Qiskit free online summer school at the end of August to educate general publics (>4000 participants) from quantum circuit assembly to simple molecular simulations in quantum chemistry. What is its motivation behind all these efforts promoting quantum information education? Have you ever felt frustrated by the extremely unequal number of employees in terms of races and gender in high tech-industry? And if we can travel back in time to correct it, what could be done to prevent this?
In this talk I will try to address above questions by looking back the development of contemporary classical computer, comparing it with the progress of newly born quantum industry, and present what can cloud-based quantum computing services provide to fight against the injustices we are seeing in today's high-tech industries.
Charlotte Olsen--Sept 17
*Recorded Video Link*
Mental Health and Mental Hygiene: Developing Tools to Thrive while earning a Physics PhD
Graduate students report symptoms of anxiety and depression at six times the rate of the rest of the population (Evans el Al., 2018). When dealing with the stresses of graduate school, students frequently experience anxiety or depression even without underlying prior mental health issues. In this talk, we will discuss resources available both through the University and off campus. We will discuss various techniques to help to address both the symptoms and the source of the stress. This talk aims to propose a preventative framework to help de-stigmatize mental health hygiene and create a dialogue around and an environment of community support within the department.