Physics Colloquium, Spring 2021

Thursdays 4:00 p.m. Via Zoom.

Contact colloquium organizer Dr. Shun Saito at for the Zoom link.

(Link to main colloquium page)

Title: Unearthing the formation histories of the inner planets in extrasolar systems
Planets form in a disk around their parent star, and their orbits can change over time due to exchanging angular momentum with this disk and through gravitational interactions with other planets. This likely occurred to some extent in our Solar System, but the degree to which these processes shaped the inner planets of our Solar system and in exoplanet systems to become the systems we observe today is still an ongoing area of research. In this talk, I will discuss the plausible formation scenarios that produce the observed characteristics of the most common types of inner planets, super-Earths and mini-Neptunes, including the subset of these planet populations that are in chains of resonances with their planetary neighbors. From numerical simulations of planetary embryos colliding and merging in their residual protoplanetary disks, I will show what conditions during that phase of planet formation are conducive to forming planet populations with observationally consistent orbit and mass/size distributions. I will also discuss computational techniques used in modelling planet formation and how we can compare results from dynamical models to observed exoplanet populations.
Title: Ab Initio thermal transport: Boltzmann Transport Equation and beyond.
Abstract: In the colloquium, we will discuss the current state-of-the-art simulation techniques for the thermal transport properties based on first-principles calculations. The presentation will focus on the Boltzmann Transport Equation (BTE), as it makes possible a unified description of the transport with multiple carriers in the system. Applications to the lattice thermal conductivity will be presented.  In the case of GaAs we will compare the simulation’s results with the experiment for the individual phonons lifetimes, an important benchmark for the quality of the simulations. In the Ruddlesden-Popper phases of the Sr-Ti-O system we will illustrate a transition from the interfacial system to coherent bulk transport. Finally, we will discuss the high-entropy compounds, an example of material where BTE is not a feasible technique, and will describe the proposed approach to the thermal conductivity prediction in these systems.

Title: You can be a woman physicist.

Abstract: According to a study by the American Physical Society, only 22% of the Doctoral Degrees in Physics in the US were awarded to women in 2018. Recent Missouri S&T demographic data show a male-to-female student ratio of 4:1 in STEM, ranking our university 2001th nationwide in male-to-female diversity. In this talk, we will discuss the gender gap in physics and what the new S&T Women in Physics (WiP@MST) group is planning to do to address it at Missouri S&T. We will highlight a few effective measures that all of us can take individually and collectively as a department to help with the recruitment and retention of female students/faculty in physics. Through funding by APS we will develop a series of initiatives to encourage more women to pursue a career in physics at S&T. Some of WiP@MST’s planned activities include graduate students’ talk, journal clubs, seminars/talks on communication and negotiation skills, mental health awareness and some fun events like group dinners, ice cream socials, movie-nights, star-gazing nights, etc. We hope everyone will join WiP@MST to help make this initiative a success.

Title: Searching for Nanohertz Gravitational Waves with a Galactic-Scale Detector

Pulsar timing arrays open a new band of the gravitational wave spectrum by building a galactic-scale GW detector. They will detect a stochastic background of gravitational waves in the next few years. The strongest signal is expected to be the unresolvable background from supermassive black hole binaries at the centers of merged galaxies. While SMBBHs are expected to be the strongest source of GWs we are sensitive to any GW signal in the nanohertz regime. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is an NSF funded Physics Frontiers Center monitoring over 70 millisecond pulsars for the signature of these gravitational waves. In the NANOGrav 12.5-year dataset we are seeing significant evidence for a signal in our data that is common among many of the pulsars. We currently find no definitive evidence for the correlated pattern that is indicative of gravitational waves, however, if we are seeing the first signs of the GW background our models show that continued observations will lead to a detection within the next few years.


Progress in probing molecular structures with ultrafast intense laser pulses

Abstract: Recent progress in laser technology has led to new coherent light sources that can be used to investigate ultrafast processes in matter. To take advantage of these new light sources, different experimental techniques have been developed to reveal the inner-workings of coupled electron-nuclear dynamics in molecules. Concurrently, theoretical and computational tools have also been developed to understand and decode hidden information from the experimental measurements. In this talk, I will first review some of those experimental advancements. I will then present our group’s recent progress in understanding intense laser-matter interactions through the use of some of the most promising techniques such as laser-induced electron diffraction, high-harmonic generation spectroscopy, and attosecond transient absorption spectroscopy. Throughout the talk, I will also address the challenges and opportunities in this field.

Title: A New Measure:  The Revolutionary Quantum Reform of the Metric System

On 20 May 2019, World Metrology Day, the international metrology community adopted revolutionary changes to the International System of Units (the SI, or Metric System) wherein all of the base units of measure are defined by fixing the values of constants of nature. The SI is now firmly based on quantum methods of measurement. The Speaker will discuss why we needed such a reform and how we achieved it.


Title: A New Force from the ATOMKI Anomalies
Abstract: In science, theory and experiment work together to create accurate models of the Universe and its dynamics. Sometimes big questions drive the experimental efforts and sometimes unexpected experimental results drive theoretical modeling. Over the past few years experimental results in precision nuclear physics from ATOMKI have become examples of experiment leading theory. I provide a simple description of these results, and explain how they suggest the existence of a new fundamental force. I outline the theoretical models that are being examined and the future experimental tests that could confirm a new force in nature.

Title: Interpretable Machine Learning of Quantum Emergence

Abstract: Decades of efforts in improving computing power and experimental instrumentation were driven by our desire to better understand the complex problem of quantum emergence. However, the increasing volume and variety of data made available to us today present new challenges. I will discuss how these challenges can be embraced and turned into opportunities by employing machine learning. The rigorous framework for scientific understanding physicists enjoy through our celebrated tradition requires the interpretability of any machine learning essential. I will discuss our recent results using machine learning approaches designed to be interpretable from the outset. Specifically, I will present discovering order parameters and its fluctuations in voluminous X-ray diffraction data and discovering signature correlations in quantum gas microscopy data.

Title: Cosmology with MeerKAT and the SKA

The next generation of radio telescopes will open a new observational window for cosmology. In particular, SKA1-MID, to be set in South Africa, has the potential to measure the equation of state of dark energy out to z~3, constrain possible deviations from General Relativity or provide transformational measurements of the structure of the Universe on the largest accessible scales, thus constraining fundamental properties such as isotropy, homogeneity, and non-Gaussianity. Moreover, MeerKAT, already in operation, will already be able to provide cosmological constraints, in particular the detection of Baryon Acoustic Oscillations using the HI intensity mapping technique. I will describe the cosmological surveys planned for SKA1-MID as well as what can be achieved with a large survey using MeerKAT.