Department of Physics & Astronomy Colloquia

Hilbun 150, 125 Hilbun Hall, Mississippi State University

Mondays at 3:30 PM

Feb. 20^th, 2020$☆$ Dr. Michael Mascagni, Florida State University

  Geometry Entrapment in Walk-on-Subdomains Monte Carlo

  Host: Dr. Mark Novotny

  Abstract:

       One method of computing the electrostatic energy of a biomolecule in a solution uses a continuum representation of the solution via the Poisson-Boltzmann equation. This can be solved in many ways, and we consider a Monte Carlo method of our design that combines the Walk-on-Spheres and Walk-on-Subdomains algorithms.
      In the course of examining the Monte Carlo implementation of this method, an issue was discovered in the Walk-on-Subdomains portion of the algorithm which caused the algorithm to sometimes take an abnormally long time to complete. As the problem occurs when a walker repeatedly oscillates between two subdomains, it is something that could cause a large increase in runtime for any method that used a similar algorithm. This issue is described in detail and a potential solution is examined. Our solutions uses the relatively new concept of first-passage under restart to propose a solution.
      This is joint work with John Thrasher, who is currently my graduate student.

Feb. 10^th, 2020 Dr. Jinwu Ye, Mississippi State university

  Quantum Chaos, Black holes and Sachdev-Ye-Kitaev (SYK) models

  Host: Dr. Gautam Rupak

  Abstract:

       There are recent extensive research activities on Sachdev-Ye-Kitaev (SYK) model and its possible quantum gravity dual. In this colloquium, we introduce the two basic, but different approaches to study quantum chaos and quantum information scramblings in SYK models and black holes: Out of time ordered correlation (OTOC) functions to extract the quantum Lyapunov exponent and Random Matrix Theory (RMT). Then using the two approaches, we review the recent progress in SYK models and their global impacts in various branches of physics such as quantum gravity, conformal field theory, condensed matter physics and quantum information science. We sketch my group's recent work on the periodic table of SYK and supersymmetric SYK models by RMT and its possible impacts on the bulk quantum gravity. We elucidate some intrinsic connections between the two complementary approaches and outline a few future perspectives. Possible experimental realizations of SYK models are also briefly discussed.

Feb. 7^th, 2020$☆$ Dr. Samarendra Mohanty, Nanoscope Instruments, Inc. (USA)

  Optical Coherence Tomography guided Laser Micro-irradiation, Molecular Delivery, Stimulation and Activity Detection in Cells

  Host: Dr. Prabhakar Pradhan

  Abstract:

       I will present use of Optical Coherence Tomography (OCT) based on low-coherence interferometry for determination of tissue structure and its applications in disease detection. Additionally, I will discuss OCT-guided laser micro-irradiation for creation of injury/disease-model. Further, OCT guided spatially targeted delivery of genes and other impermeable molecules into cells using continuous wave laser beam via surface plasmon resonance of nanoparticles or ultrafast laser beam (without requiring nanoparticles) will be presented with specific emphasis for therapy of visual disorders involving geographic atrophies. In addition, I will present label-free detection of functional dynamics of cells using phase-sensitive OCT and multifractal analysis. Such OCT guided targeted manipulation and stimulation of tissue and monitoring of structure and function is significant for disease diagnosis and therapy.

Feb. 3^rd, 2020 Dr. Laszlo Ujj, Department of Physics, University of West Florida

  Contribution to the Coherent Raman and Four-Wave Mixing Field: Past, Present, and the Future

  Host: Dr. Mark Novotny

  Abstract:

       This talk will start with a brief historical introduction to coherent Raman spectroscopy with special emphasis on the physical basis of the scattering and his former pioneering results of applications of the method on photoactive proteins. The tasks needed to get reliable measurements and the necessary data processing will be discussed. His recent recognition on the usefulness of 3-color two-beam coherent Raman scattering, to measure low-frequency vibrational spectra will be detailed. The lecture will be concluded with predictions for future applications and useful instrumentation on coherent Raman micro-spectroscopy and microscopy.

Jan. 20^th, 2020 Dr. Dipangkar Dutta, Department of Physics & Astronomy, Mississippi State University

  The incredible shrinking proton and the proton radius puzzle

  Host: Dr. Lamiaa El-Fassi

  Abstract:

       For nearly half a century the charge radius of the proton had been obtained from measurements of the energy levels of the hydrogen atom or by scattering electrons from hydrogen atoms. In 2010 the proton charge radius was obtained for the first time by precisely measuring the energy levels of an exotic kind of hydrogen atom called muonic hydrogen. The charge radius of the proton obtained from muonic hydrogen was found to be significantly smaller than those obtained from regular hydrogen atoms. This was called the ``proton charge radius puzzle'' and led to a rush of experimental as well as theoretical efforts to understand why the size of the proton appears to be different when measured in regular hydrogen vs. muonic hydrogen. Many physicists were excited by the possibility that the ``puzzle'' was an indication of a possible new force that acted differently on electrons and muons.
      The Proton Charge Radius (PRad) experiment at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) was one such major new effort which used electron scattering from a regular hydrogen atom, but with several innovations that made it the highest precision electron scattering measurement. I will discuss the PRad experiment, the new results from this experiment, the current status of the ``puzzle'' and future prospects.

Nov. 11^th, 2019 Mr. Troy Schaudt, Wolfram Research, Inc.

  Mathematica 12 in Education and Research

  Host: Dr. Lamiaa El-Fassi

  Abstract:

       This technical talk will show live calculations in Mathematica 12 and other Wolfram technologies relevant to courses and research. Specific topics include:

            * Enter calculations in everyday English, or using the flexible Wolfram Language,
            * Visualize data, functions, surfaces, and more in 2D or 3D,
            * Store and share documents locally or in the Wolfram Cloud,
            * Use the Predictive Interface to get suggestions for the next useful calculation or function options
            * Access trillions of bits of on-demand data,
            * Use semantic import to enrich your data using Wolfram curated data,
            * Easily turn static examples into mouse-driven, dynamic applications,
            * Access 10,000 free course-ready applications,
            * Utilize the Wolfram Language's wide scope of built-in functions, or create your own,
            * Get deep support for specialized areas including machine learning, time series, image processing, parallelization, and control systems, with no add-ons required.

      Current users will benefit from seeing the many improvements and new features of Mathematica 12 (https://www.wolfram.com/mathematica/new-in-12/), but prior knowledge of Mathematica is not required.

Nov. 4^th, 2019 Dr. Luca Guazzotto, Physics Department, Auburn University

  A physics-based goal in the quest for fusion energy

  Host: Dr. Dipangkar Dutta

  Abstract:

       Nuclear fusion energy production has been the ultimate goal of an active field of research for several decades. In addition to the technological and physics challenges that need to be overcome to achieve fusion energy production, some considerations at a macroscopic level are also necessary. In particular, a precise energy balance needs to be satisfied in order to achieve net energy production. The so-called "Lawson criterion", derived from the original work by Lawson in 1957, has been for decades the de-facto standard of our understanding of energy balance in nuclear fusion reactors and experiments. In this talk we will review the basis for energy balance and power production in fusion devices and discuss the details of the Lawson criterion. In the last part of the talk, we will highlight some of the recent improvement and extensions to the Lawson criterion that will allow us to gain better understanding of the requirements for fusion energy production.

Oct. 28^th, 2019 Dr. Andrew Lawton, Department of Biological Sciences, Mississippi State University

  Cerebellar folding is initiated by mechanical constraints on a fluid-like layer without a cellular pre-pattern

  Host: Dr. Dipangkar Dutta

  Abstract:

       During human brain development the cerebellum and cerebral cortex fold into robust patterns that increase and compartmentalize neural circuits. Models based in differential expansion of elastic materials, axonal constraints, directed growth, or multi-phasic combinations have been proposed to explain brain folding. We use the murine cerebellum with a simple alignment of 8-10 stereotypical folds as a genetically tractable model of brain folding to challenge folding models with in vivo data from the time of folding initiation. We show that at folding initiation differential expansion is created by the outer layer of proliferating progenitors expanding faster than the core. However, the tissue stiffness differential, compressive forces, and emergent thickness variations required by elastic material models are not present. We find that folding occurs without an obvious cellular pre-pattern, that the outer layer expansion is uniform and fluid-like, and that the cerebellum is under radial and circumferential constraints. We apply a multi-phase model incorporating differential expansion of a fluid outer layer and radial and circumferential constraints and approximate the in vivo shape evolution observed during initiation of cerebellar folding. This new framework creates predictions for setting the amount and pattern of brain folding.

Oct. 21^st, 2019 Dr. Mariama Rebello de Sousa Dias, Department of Physics, University of Richmond

  Mixing to match: how alloyed nanostructures can enhance the performance of optoelectronic devices

  Host: Dr. Benjamin Crider

  Abstract:

       The use of alloyed nanostructures in next-generation optoelectronic devices is a promising route to improve their performance. Mainly due to their potential of overcoming constraints imposed by pure materials, such as the pre-defined dielectric function. In order to fully characterize, understand, and predict the optical behavior of this new class of materials, we use a combination of experimental and computational technics. In this talk, I will highlight recent progress in using alloys with different chemical compositions as a pathway to control their optical response. I will focus on two classes of materials, bimetallic alloys (Ag, Au, Al, Pd, and Cu) and metal oxide alloys (CdO and ZnO). The former explores the role of thin films and nanostructures for energy harvesting, (photo)catalysis, photovoltaics, and superabsorber. The latter has the potential of enhancing light absorption in a photonic crystal organic solar cells.

Oct. 14^th, 2019 Dr. Lamiaa El Fassi, Mississippi State University

  QCD Signatures in Nuclei: Hadronization and Color Transparency Studies

  Host: Dr. Dipangkar Dutta

  Abstract:

       Over the last few decades several experiments have used atomic nuclei as unique laboratories to probe the internal structure of the strongly interacting particles, namely hadrons. Indeed, the nucleus can be used as a revealing medium of the time evolution of elementary configurations of the hadron wave function. One way to probe this picture is to study the transition from the colored partons (quarks and gluons, the underlying structure of nuclei) to colorless hadrons – the hadronization or fragmentation process – or to measure the effects of Color Transparency (CT) – the production and propagation of a small size hadron like configuration which, under specific conditions, stays intact in a transparent nuclear medium. These phenomena are a direct prediction of the strong interaction theory, Quantum ChromoDynamics (QCD), and still are challenging topics in lepton nucleus scattering at Jefferson Lab. In this talk, I will highlight the first ever study of the semi-inclusive deep inelastic production of $\Lambda$ hyperon in the current and target fragmentation regions, and give a brief overview of CT studies to motivate the planned experiment that aims to study CT in the exclusive diffractive $\rho$0 electro-production off nuclei, using the upgraded Jefferson Lab beam energy and the Hall-B CLAS12 spectrometer.

2019-2020 Committee