Department of Physics & Astronomy "Colloquia and Seminars" Series

Virtual or R-150, Hilbun Hall, Mississippi State University

Fridays @ 2:00 PM

Apr. 29^th, 2022 Dr. Zahra Hazari, Department of Teaching and Learning and STEM Transformation Institute, Florida International University

   STEP UP: Supporting Teachers to Encourage the Pursuit of Undergraduate Physics for Women

  Host: Dr. Lamiaa El Fassi

  Abstract:

       In the US, nearly half of students taking physics in high school are women, but only a fifth of the students interested in physics majors in college are women. This issue has persisted over decades. As such, the STEP UP project () launched a nationwide initiative in the US to mobilize and help high school physics teachers better engage women in physics by disrupting narrow perceptions of physics and promoting supportive classroom cultures. This talk will present some of the research evidence used by STEP UP to develop, test, and promote strategies that facilitate the physics identity development and future physics intentions of young women. These evidence-based strategies are being used by physics educators as part of the national campaign, which has grown to include a network of more than three thousand physics teachers, faculty, students, and community members, to inspire a new generation of women physicists. (Supported by the National Science Foundation under Grant No. 1720810, 1720869, 1720917, and 1721021).

Apr. 22^nd, 2022 Dr. Mary Kidd, Department of Physics, Tennessee Technological University

   Investigation of neutron-induced backgrounds in isotopes of interest for 0νββ decay searches

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Neutrinoless double-beta (0νββ) decay is one of the slowest proposed nuclear decay rates. Detecting processes like 0νββ requires a detailed knowledge of potential background events. Even deep underground, neutron-induced reactions can occur in all components of detectors searching for rare events. The isotopes $76$Ge, $100$Mo, $130$Te, and $136$Xe are all in current or planned 0νββ-decay searches. Additionally, even enriched detectors made from these isotopes may include other nuclides, such as $95,\; 97$Mo or $134$Xe. For $136$Xe (Q$$_ββ= 2457.8 keV), a recently-discovered level in $134$Xe by Peters et al. decays with the emission of a 2485.7 keV gamma ray. For $130$Te, (Q$$_ββ= 2527.5 keV), a neutron-induced excitation of the 2527.1 keV state was investigated. In $100$Mo (Q$$_ββ= 3034.4 keV), a nuclear level with energy 3039.4 ± 1.0 keV cascades to the ground state. The isotopes $95$Mo and $97$Mo also have energy levels that lie within the region of interest: 3037 keV and 3035 keV respectively. Finally, $76$Ge (Q$$_ββ= 2039.1 keV) has a nuclear level at 3951.9 keV that has been reported to emit a 2040.7 keV gamma ray, but which was not observed in studies by Crider et al. At Triangle Universities Nuclear Laboratory (TUNL), we can study these potential backgrounds by exciting enriched targets with neutrons. Here, we will report our results from our cross-section measurements of neutron inelastic scattering (n,n'γ) on $134,136$Xe and $130$Te, and we will update our initial results from our investigation of gamma-ray cascades resulting from (n, n'γ) on $nat$Mo and $76$Ge.

Apr. 15^th, 2022 Easter Break: No Colloquium!

Apr. 8^th, 2022 Dr. Adriana Moreo, Department of Physics & Astronomy, University of Tennessee at Knoxville

   Iron Pnictides: A New Piece in the High Tc Superconductivity Puzzle.

  Host: Dr. Dipangkar Dutta

  Abstract:

       During most of the XX century superconductivity was observed in some metals at the very low temperatures achieved with liquid Helium. Below a critical temperature Tc electrons overcome their Coulomb repulsion thanks to an attraction created by the distortions of the ionic lattice and form Cooper pairs that can move without resistance. The efforts to raise Tc were unsuccessful until the discovery of the high Tc superconducting cuprates in 1986. This family of materials are magnetic ceramic insulators that become superconductors with Tc’s that in many cases can be achieved with liquid Nitrogen, when electrons or holes are doped into them. However, the mechanism that produces the electron pairing in the cuprates still remains a puzzle. The interaction between the electrons and the lattice does not seem to be sufficient and it is believed that magnetism plays a role. The discovery of a new family of high Tc superconductors, the iron pnictides, in 2006 provided a new trove of data. While many similarities with the cuprates were found, such as the need to introduce electrons or holes in a magnetic parent compound to develop superconductivity, there are important differences as well. The parent compounds are poor metals, rather than insulators, the magnetic order is not the same as the one in the cuprates, and, in addition to the magnetism, it appears that the orbital degrees of freedom are active. This poses extra challenges, but it also creates the need to develop novel experimental and theoretical approaches to deal with the added complexity. Novel approaches to the study of the iron pnictides based mostly on computational methods will be presented and comparison with experiments will be made. The focus will be on simplified geometries such as chains [1] and ladders [2]. Using numerical techniques such as DMRG a variety of novel magnetic phases characterized by the presence of ordered spin blocks [3, 4, 5, 6] indicate that the physics of Fe based superconductors could bring novel surprises.

[1] N. Patel et al., PRB 96, 024520 (2017).
[2] N. Patel et al., PRB 94, 075119 (2016).
[3] J. Herbrych et al., Nat. Comm. 9, 3736 (2018).
[4] J. Herbrych et al., PRL 123, 027203 (2019).
[5] J. Herbrych et al., PNAS 117, 16226 (2020).
[6] J. Herbrych et al., Phys. Rev. B 102, 115134 (2020).

Apr. 1^st, 2022 Dr. Manavi Jadhav, Department of Physics, University of Louisiana at Lafayette

   Laboratory investigations of stardust & other extraterrestrial materials

  Host: Dr. Dipangkar Dutta

  Abstract:

       The laboratory study of stardust is an important sub-field of astrophysics. It combines sophisticated chemical, structural, and isotopic laboratory measurements, on micron-sub-micron stardust particles, with the theoretical ideas of nucleosynthesis and stellar evolution that exist to understand astrophysical observations. Isotopic data for these grains reveal more precise information about their parent stars than do spectroscopic observations of circumstellar dust. The goal of laboratory measurements is to provide clues on the stellar environments in which the grains formed and on their subsequent histories. Additionally, investigations into the preservation of these grains in different meteorites provide information about early solar system conditions and chronology. These goals can be achieved by coordinated, multi-technique investigations of stardust grains in the laboratory.
      This talk will focus on some key results from coordinated, multi-technique measurements of stardust grains and what they tell us about the stars that contributed presolar materials to our nascent Solar System. I will also talk about other investigations of extraterrestrial samples that my research group is involved with.

Mar. 25^th, 2022 Ms. Udeshika Perera$*$ and Ms. Saja Teeti$**$ , Department of Physics & Astronomy, Mississippi State University

   $*$ Physical mechanism, Odd-even effects, and trends in Charge radii

   $**$ Extension of the nuclear landscape beyond spin-zero limits: rotation in extremely proton-rich nuclei

  Host: Dr. Lamiaa El Fassi

  Abstract:

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      $*$ A systematic global investigation of differential charge radii has been performed within the CDFT framework for the first time. Theoretical results obtained with conventional covariant energy density functionals and the separable pairing interaction are compared with experimental differential charge radii in the regions of the nuclear chart in which available experimental data crosses the neutron shell closures at N= 28, 50, 82, and 126. The analysis of absolute differential radii of different isotopic chains and their relative properties indicate clearly that such properties are reasonably well described in model calculations in the cases when the mean-field approximation is justified. The impact of the latter has been evaluated for spherical shapes and it was shown that the relative energies of the single-particle states and the patterns of their occupation with increasing neutron number have an appreciable impact on the evolution of the δ<𝑟$2$>$N,\; N\text{'}$ values. These factors also limit the predictive power of model calculations in the regions of high densities of the single-particle states of different origins. It is shown that the kinks in the charge radii at neutron shell closures are due to the underlying single-particle structure and due to the weakening or collapse of pairing at these closures. It is usually assumed that pairing is a dominant contributor to an odd-even staggering (OES) in charge radii. Our analysis paints a more complicated picture. It suggests a new mechanism in which the fragmentation of the single-particle content of the ground state in odd-mass nuclei due to particle-vibration coupling provides a significant contribution to OES in charge radii.​

      $**$ Recent investigations reveal a number of physical mechanisms by which it is possible to extend the nuclear landscape beyond the spin-zero limit. One of these is related to the so-called birth of particle-bound rotational bands in neutron-rich nuclei which have been first suggested in Ref. [1]. In this mechanism, strong Coriolis interaction acting on high-j orbitals transforms particle-unbound (resonance) nucleonic configurations into particle-bound ones with increasing angular momentum. A similar mechanism is active also in the nuclei in the vicinity of the proton drip line [2] but it is modified by the presence of the Coulomb barrier. As a result, the particle-unbound part of the band will have discrete rotational states which can decay by proton emission. A systematic investigation of this phenomenon has been performed in proton-rich even-even Z= 4-36 nuclei within the framework of cranked relativistic mean-field theory with the goals to find the general features of this phenomenon and the best candidates for experimental observation [3]. One of the interesting predictions is a new phenomenon of rotation-induced giant proton halos which is active in a substantial number of nucleonic configurations of light nuclei.

[1] A. V. Afanasjev, N. Itagaki and D. Ray, Phys. Lett. B 794, 7 (2019).
[2] A. V. Afanasjev, S.E. Agbemava and A. Taninah, Acta Phys. Polonica B 13, 347 (2020).
[3] S. Teeti, A. Taninah, and A.V. Afanasjev, submitted to Phys. Rev. C and in preparation.

Mar. 18^th, 2022 Spring Break: No Colloquium; Enjoy :) and be Safe!

Mar. 11^th, 2022 Dr. Jun Chen, Department of Bioengineering, University of California, Los Angeles

   Smart Textiles for Personalized Health Care

  Host: Dr. Kun Wang

  Abstract:

       There is nothing more personal than healthcare. Health care should move from its current reactive and disease- centric system to a personalized, predictive, preventative, and participatory model with a focus on disease prevention and health promotion. As the world marches into the era of the Internet of Things (IoT) and 5G wireless, technology renovation enables the industry to offer a more individually tailored approach to healthcare with better health outcomes, higher quality, and lower cost. However, empowering the utility of IoT-enabled technologies for personalized health care is still significantly challenged by the shortage of cost-effective wearable biomedical devices to continuously provide real-time, patient-generated health data. Textiles have been concomitant and playing a vital role in the long history of human civilization. The textile forms endow biomedical devices with biocompatible, biodegradable, even bioabsorbable features, allowing them to serve as on-body healthcare platforms with incomparable wearing comfort. Merging biomedical devices and textiles becomes increasingly important owing to the growing trend of IoT. In this talk, I will introduce our current research on smart textiles for biomedical monitoring, textile for therapy, and textile power generation as an energy solution for future wearable medical devices.

Mar. 4^th, 2022 Dr. Saikat Chakraborty Thakur, Department of Physics, Auburn University

   Helicon Core Formation in rf Plasmas

  Host: Dr. Chuji Wang

  Abstract:

       Most rf plasma devices can operate in the capacitively coupled mode (CCP), inductively coupled mode (ICP) or the helicon mode. The helicon mode is typically characterized by a narrow, elongated, bright plasma column at the center of the cylindrical device, commonly known as the helicon core. Even though the existence of the helicon core has been known for the last few decades, there is no consensus on the physics behind the formation of the helicon core. Controlled Shear Decorrelation eXperiment (CSDX) is a helicon device used to simulate the scrape off layer and divertor regions of fusion devices. Here we report that helicon core formation in CSDX is accompanied by the formation of a radial transport barrier and simultaneous axial plasma detachment; via a self-organized global transport bifurcation [1, 2]. Evidence from both Langmuir probes and fast imaging show that the radial extent of the transport barrier is similar to the width of the helicon core. Using spectroscopy and neutral pressure measurements, we simultaneously observe spontaneous axial plasma detachment, which follow the same hysteresis patterns associated with the radial transport bifurcation. We report dramatic changes in both mean and fluctuation profiles across this transition. This self-organized global transition is universal, but the transition-threshold depends on the helicon source parameters. 2-D bifurcation diagrams elucidate various regimes of operation of rf plasma sources (CCP, ICP, Helicon-detached, Helicon-attached), allowing access to study various plasma instabilities, turbulence and transport, as well as divertor-relevant plasma detachment. Spontaneous plasma detachment has serious implications on the relevance of similar rf devices [3, 4] designed to study plasma material interactions. In addition, this work also gives us the opportunity to study instabilities associated with divertor plasma detachment, similar to those observed in fusion devices such as ASDEX-Upgrade [5] and are currently an important field of investigation for plasma detachment studies [6, 7].

[1] S. C. Thakur, et. al., Plasma Sources Science and Technology, 23 044006 (2014).
[2] L. Cui, et. al., Physics of Plasmas, 23 055704 (2016).
[3] B. D. Blackwell, et. al., Plasma Sources Science and Technology, 21 055033 (2012).
[4] J. Rapp, et. al., Nuclear Fusion, 57 116001 (2017).
[5] P. Manz, et. al., Nuclear Materials and Energy, 12 1152-1156 (2017).
[6] N. Ohno, Plasma Physics and Controlled Fusion, 59 034007 (2017).
[7] N. Ohno, Plasma Physics and Controlled Fusion, 59 034007 (2017).

Feb. 25^th, 2022 Dr. Breese Quinn, Department of Physics & Astronomy, University of Mississippi

   First Results from the Fermilab Muon g-2 Experiment

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Almost 20 years ago, an experiment at Brookhaven National Laboratory measured the muon anomalous magnetic moment aμ=(g-2)/2 to a precision of 540 ppb. That result disagrees with the Standard Model prediction by 3.7 standard deviations (σ) and represents one of the strongest hints we have had of new physics for the past two decades. To investigate this longstanding tension, the Muon g-2 experiment was built at Fermilab using the BNL storage ring along with new muon beam and detector systems to achieve the goal of measuring aμ to a precision of ~100 ppb. I will present the first results from the ongoing FNAL Muon g-2 experiment, based on 6% of the expected final μ+ dataset. These first results confirm the earlier BNL measurement, and combined push the g-2 discrepancy to 4.2 σ giving us the strongest evidence to date of new physics beyond the Standard Model. I will also discuss what’s next for Muon g-2, including the current status of data-taking and analysis and a future μ- data collection run which has recently been approved.

Feb. 18^th, 2022$☆$ Dr. Laura McCullough, Department of Chemistry and Physics, Wisconsin's Polytechnic University (UW-Stout)

   Standards-based Grading in College Physics

  Host: Dr. Dipangkar Dutta

  Abstract:

       How often have you given a grade to a student where you weren’t sure they really had earned that grade? With a typical points model for grades, and especially with participation or attendance points, a final letter grade does not always reflect how much a student has really learned in a class. An alternative grading model is Standards-Based Grading (SBG) where students earn a grade based solely on how many objectives or standards they have passed. This model can be used for conceptual and numerical problems, as well as lab reports and writing assignments. In this talk, I will share how I use SBG to be confident my students leave my classes knowing physics.
      Standards-based grading (SBG) is an alternative to the standard points model of grading. Students earn a grade based solely on how many objectives or standards they have passed. This model can be used for conceptual and numerical problems, as well as lab reports and writing assignments. In this talk, I will share how I use SBG to be confident my students leave my classes knowing physics.

Feb. 11^th, 2022 Dr. Luisa Rebull, Science & Data Center for Astrophysics & Planetary Sciences (IPAC), California Institute of Technology

   Stellar Rotation in Young Clusters using K2 and TESS

  Host: Dr. Angelle Tanner

  Abstract:

       K2 has provided a phenomenal opportunity to study properties of stars in clusters, particularly young low-mass stars, far beyond the expectations of the original Kepler mission. The high-precision photometry provided by K2 allows us to probe stellar variability to lower masses and lower amplitudes than has ever been done before. Younger stars are generally more rapidly rotating and have larger star spots than older stars of similar masses, so spots rotating into and out of view reveal the (surface) rotation rate of these stars. K2 has monitored stars from several clusters, most notably Rho Oph (~1 Myr), Taurus (~5 Myr), USco (~20 Myr), the Pleiades (~125 Myr), and Praesepe (~700 Myr). The light curves have yielded thousands of rotation rates, and revealed far greater diversity in light curves than was anticipated. Now that we have TESS data as well, we can add the Upper Centaurus-Lupus (UCL) and Lower Centaurus-Crux (LCC) young moving groups (~15 Myr). In this talk, I will review the K2 results and present early results from UCL/LCC.

Feb. 4^th, 2022 Dr. Gombojav Ariunbold, Department of Physics & Astronomy, Mississippi State University

   Quantum Particles in A “Synchronized Dance”: A New Look at Old Problems and Emergent Behaviors in Complex Networks of Atoms, Molecules and Excitons

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Who could have thought that a simple model of weakly coupled oscillators would offer lucid interpretation to exotic, though naturally occurring, synchronized patterns such as bird flocking, fish schooling, and much more? A modern complexity theory (referred to as “A New Kind of Science” by Philip Anderson, the Nobel Laureate) has been applied to explore that synchronized dance. Self-organized synchronization has become the foundation of interpreting numerous classical processes in physics, chemistry, biology, and social sciences. Recently, the German and Indian research groups working independently have demonstrated for the first time that quantum particles can indeed dance in sync. Such studies of synch in the quantum world hold a promise for establishing a robust quantum mechanical entanglement.
      This talk will emphasize the comparison of the Kuramoto coupled oscillator model and the Dicke superfluorescence model in the search for synched ensembles of atoms. Discussions will be guided by my research interest in superfluorescence that stretches over the last two decades. In the light of our recent findings, I will also explain the sixty-year-old model commonly describing the coherent Raman scattering process of vibrating molecules from a new perspective. Further, I will discuss plans on how to experimentally demonstrate and theoretically interpret the complex network of synched vibrating molecules. I will conclude my talk by discussing the recent experimental demonstrations of superfluorescence of excitons in hybrid perovskites by the research group from the North Carolina State University.

Jan. 28^th, 2022 Dr. Prabhakar Pradhan, Department of Physics & Astronomy, Mississippi State University

   Light Transport and Localization properties of Mesoscopic Optical Disordered Media: Applications in Biological and Soft Matter Systems

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Scientific interest in measuring and quantifying meso- to nanoscopic light transport properties of weakly optical disordered media ranges from dielectric soft condensed matter systems, such as colloids, to biological systems, including cells and tissues. However, conventional optical microscopy cannot probe the weak refractive index fluctuations found, for example, in biological cells, which possess weak scattering properties. Moreover, the diffraction limit cannot be exceeded by standard optical microscopy. Recently, however, we have developed experimental optical spectroscopic techniques that do, in fact, enable us to probe the transport properties of weakly disordered media, such as biological cells, with nanoscale sensitivity beyond the diffraction limit. In this talk, I will first describe the genesis and functions of these novel techniques. Next, I will discuss their practical applications in the study of biological and soft matter systems, including the early-stage detection of cancer and brain abnormalities by probing and quantifying the nanoscopic light transport properties of single biological cells.

Jan. 21^st, 2022 Dr. Ciprian Gal, Department of Physics & Astronomy, Mississippi State University

   Parity Violating Electron Scattering from E122 to the EIC

  Host: Dr. Lamiaa El Fassi

  Abstract:

       A new golden age for nuclear physics in the United States is coming. With the currently upgraded CEBAF accelerator at Jefferson Lab, the under construction Facility for Rare Isotope Beams, and the projected Electron Ion Collider (EIC) facility, we are on the cusp of new discoveries and deeper understanding of the universe. In this talk I will discuss how probing one of the fundamental symmetries of the Standard Model, namely parity, can expand the range of measurements we can do with electron scattering. Since the development of the technique for the E122 experiment a great deal of progress has been made and currently we are in an era of high precision measurements that can probe physics beyond the Standard Model on par with other high energy collider experiments. The versatility of the technique has been highlighted over the years through measurements of the strange contents of the proton and determinations of the neutron radius of heavy nuclei. Finally, at the EIC we expect to be able to use similar techniques to better understand protons and neutrons, which give about 90% of the mass in the visible universe.

Past Colloquia/Seminars

Nov. 19^th, 2022 Cancelled; Enjoy your Winter Break :)!

Nov. 12^th, 2021 Dr. Shengxi Huang, School of Electrical Engineering and Computer Science, Pennsylvania State University

   Designer 2D materials for new sensing paradigms

  Host: Dr. Kun Wang

  Abstract:

       Emerging 2D quantum materials have gained increasing attention due to their unique electronic and optical properties, and have shown promise in sensing applications. The realization of sensing devices using these materials still faces several challenges. For example, it is critical to gain clear understandings of (1) the fundamental light-matter interactions and their relations to the atomic structures, which govern many key material properties and device performances; and (2) the coupling with other nanostructures and molecules, which is a required structure for sensing devices and systems. This talk introduces new discoveries and pioneering works on these critical challenges, and novel applications of these materials in biochemical sensing. The first part of this talk presents multi-dimensional engineering techniques to augment material performance, including 2D Janus conversion, 1D nanoscrolling, and 0D atomic defect creation. The characterization techniques employed, including low-frequency Raman spectroscopy, polarization- and time-resolved spectroscopy, and ultrafast electron diffraction, can be widely used in other material systems. The second part of this talk focuses on the interaction of 2D materials with organic molecules and related sensing applications. In particular, a novel enhancement effect of molecular Raman signals on 2D surface was discovered, which offers a new paradigm of biochemical sensing with high specificity, high multiplexity, and low noise. The selection rule for the 2D material substrates has been revealed, which is critical for device design. Two sensing applications for Alzheimer’s disease and respiratory viruses will also be discussed. Overall, the works presented in this talk are significant in fundamental quantum science, and offer important guidelines for practical applications in sensing and quantum technologies. The methodologies used here also provide a framework for the future study of many emerging materials and sensing scenarios.

Nov. 5^th, 2021 Dr. Gabriela González, Department of Physics & Astronomy, Louisiana State University

   Gravitational Waves Astronomy

  Host: Dr. Dipangkar Dutta

  Abstract:

       The first detection of gravitational waves in 2015 by the LIGO detectors, created by the merger of black holes more than a billion years ago, was followed by several other signals from black holes. In 2017, the merger of neutron stars was detected by LIGO and Virgo detectors and by gamma-ray telescopes, and was found by many electromagnetic observations too: a new era of gravitational wave astrophysics has started with very bright prospects for the future. LIGO and Virgo took data again for a year in 2019-2020, and many more merging black holes and neutron stars have been discovered. We will describe the technology involved in the LIGO gravitational wave detectors, details of the latest discoveries and the exciting prospects for more detections in the next years.

Oct. 29^th, 2021 Dr. Edward (Denny) Dahl, Quantum Applications Director, ColdQuanta

   Building a quantum computer from Cesium atoms

  Host: Dr. Mark Novotny

  Abstract:

       Over the past few years, people have begun building quantum computers using superconducting qubits, trapped ion qubits, photonic qubits and spin qubits. The newest technology is the cold atom approach. This technology shares much with trapped ions, but since cold atoms are neutral, there are significant differences in the scalability and performance characteristics of a cold atom system. During this talk, I will describe the approach taken by ColdQuanta to build a complete digital gate-based cold atom quantum computer.
       I will present an overview of the cesium atom approach and mention the connection to its clock states, which have formed the basis of the definition for the second since 1967. I will describe the mechanism used to stabilize the two-dimensional array of qubits. I will also describe the Rydberg excited states of the cesium atoms and the unique features of these states that make them ideal for implementing entangling gates.
       A cold atom system possesses unique features that promise to make it an effective quantum platform. High qubit count, long coherence time and scalable connectivity differentiate this platform from other modalities. The challenge is to understand how these features interact with different quantum circuits. Simulation at scale is not possible for these systems and so we will need to gather empirical data to help guide our development of quantum circuits and algorithms to make effective use of this hardware.

Oct. 22^nd, 2021 Dr. Roman Liera, Department of Educational Leadership, Montclair State University

  Learning legitimacy: Exploring the transition to doctoral candidacy in the physical sciences

  Host: Dr. Dipangkar Dutta

  Abstract:

       The transition to candidacy is a common attrition point within the doctoral journey; however, it is both undertheorized and underexamined. We examined how students and faculty in highly ranked and lower ranked physical sciences PhD programs construct the transition to candidacy, how the candidacy process mediates learning, and how students are socialized into disciplinary norms that maintain inequalities. Through comparative case study, we find the transition to candidacy is a process of learning disciplinary legitimacy—students demonstrate or perform it, and faculty evaluate it. We find disciplinary language use is a critical practice for students’ sense of belonging, and program status shapes the design of the transition and what candidacy means. We explore implications for student learning and wellbeing.

Oct. 15^th, 2021 Dr. Anne Staples, Department of Biomedical Engineering and Mechanics, Virginia Tech

   Between the branches: Large eddy simulations of local coral colony hydrodynamics

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Local hydrodynamics play a central role in physiological processes like respiration and nutrient uptake in coral reefs. Despite the importance of reefs as hosts to a quarter of all marine life, and the pervasive threats facing corals, characterizing the hydrodynamics between the branches of scleractinian corals has remained a significant challenge. Here, we present results from large eddy immersed boundary simulations of the flow through and around Pocillopora meandrina, Pocillopora eydouxi, and Montipora capitata coral colonies. The studies suggest that colonies with higher branch densities have more complex mean velocity profiles with three different characteristic regions, while more loosely branched colonies have approximately constant mean velocity profiles along the flow direction; that surface roughness can counterintuitively increase the Reynolds stresses above the colony and hence enhance vertical transport; that passive geometric features of branching colonies produce highly vortical internal flows that enhance mass transfer at the interior of the colony, compensating almost exactly for flows speed reductions there of up to 64% so that the advection time scale remains roughly constant throughout the colony; and that the mean vortex diameter, rather than the mean branch diameter, may be the correct length scale to use to calculate the mass transfer Stanton number for intercolonial coral flows.

Oct. 8^th, 2021 Fall Break: No Colloquium; Enjoy :) and be Safe!

Oct. 1^st, 2021 Dr. Quinton L. Williams, Department of Physics & Astronomy, Howard University

   Application of Carbon Nanomaterials to Li-Ion Batteries

  Host: Dr. Dipangkar Dutta

  Abstract:

       As the adoption of various forms of renewable energy continues to grow worldwide, interest has grown significantly in lithium-ion battery technology as, both, a mobile source of energy and as a stationary energy-storage solution. Additionally, explosive growth in the electric vehicle market has driven a significant increase in research on lithium-ion batteries. For mobile energy sources, the LiFePO4 (LFP) battery is a promising alternative to the successfully commercialized LiCoO2 battery due to its high theoretical capacity (170 mAh g$-1$), long cycling life, excellent thermal stability, inexpensive source materials, and nontoxicity. However, a significant drawback is that LFP suffers from poor intrinsic electronic conductivity (~ 10$-9$ S cm$-1$) and low lithium-ion diffusivity (~ 10$-14$ cm$2$ s$-1$) which results in poor rate capability; thus, practical applications with LFP have been limited.
      In this talk, an introductory overview of rechargeable batteries and a brief history of the rechargeable lithium-ion battery will be provided. Then, the presentation of several investigations taken by our research group for improving the electrochemical performance of LiFePO4 and Nickel-Cobalt-Manganese (NCM) batteries in terms of charging rates and specific energy capacity will be given. Finally, a key finding from our studies of the addition of various types of nanomaterials (i.e., metallic nanoparticles, carbon nanofibers, carbon nanotubes, graphene, etc.) will show that the electrical conductivity is a superposition of short-range- and long-range-contributions to an overall effective electrical conductivity. This result provides insight into improving the performance of fast-charging lithium-ion batteries.

Sep. 24^th, 2021 Dr. Preethi Nair, Department of Physics & Astronomy, the University of Alabama

   Constraining the Demographics of Accreting Supermassive Black Holes and their Role in Galaxy Quenching in the nearby Universe

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Understanding the mechanisms which trigger an Active Galactic Nuclei (AGN or accreting supermassive black hole) and the role of these AGN in galaxy evolution, specifically in regulating or quenching star formation in galaxies, is a highly debated area of study. Theoretically, it is expected that mergers of galaxies should lead to the triggering of an AGN. In fact, this triggering is required by simulations to reproduce the observed properties of galaxies. Unfortunately, confirming that mergers trigger AGN is observationally challenging. The large observed variation in the frequency of AGN in different merger stages (wide/close pairs, merger remnants) are due to a number of factors including obscuration, time delays, AGN luminosities and AGN lifetimes. The overall interdependence of AGN luminosities and lifetimes impacts any correlation that should be seen between merger signatures and AGN frequency. Here I present a volume limited catalog of visually identified close pairs and merger remnants from the Sloan Digital Sky Survey (SDSS). Using this sample, I will present results based on an ongoing NASA Chandra and related NSF project to constrain the AGN frequency and multi-wavelength properties of systems whose merger signature lifetimes are theoretically expected to be similar to low luminosity AGN lifetimes. I will describe the role of the SDSS MaNGA survey, as well as other observational follow-up surveys, in characterizing the galaxy properties of these low luminosity AGN and the cold gas outflows from these systems.

Sep. 17^th, 2021 Dr. Edward Thomas Jr., Department of Physics, Auburn University

   Using magnetic fields and microgravity to explore the physics of dusty plasmas

  Host: Dr. Chuji Wang

  Abstract:

       Over the last three decades, plasma scientists have learned how to control a new type of plasma system known as a “complex” or “dusty” plasma. These are four-component plasma systems that consist of electrons, ions, neutral atoms, and charged, solid, nanometer- to micrometer-sized particles. The presence of these microparticles allow us to “tune” the plasma to have solid-like, fluid-like, or gas-like properties. This means that dusty plasmas are not just a fourth state of matter – they can take on the properties of all four states of matter.

       From star-forming regions to planetary rings to fusion experiments, charged microparticles can be found in many naturally occurring and man-made plasma systems. Therefore, understanding the physics of dusty plasmas can provide new insights into a broad range of astrophysical and technological problems. This presentation introduces the physical properties of dusty plasmas – focusing on how the small charge-to-mass ratio of the charged microparticles gives rise to many of the characteristics of the system. In particular, dusty plasmas can be used to study a variety of processes in non-equilibrium or dissipative systems such as self-organization and energy cascade as well as a variety of transport and instability mechanisms. This presentation will discuss results from our studies of dusty plasmas in high (B ≥ 1 T) magnetic fields using the Magnetized Dusty Plasma Experiment (MDPX) device at Auburn University and in microgravity experiments using the Plasmakristall-4 (PK-4) laboratory on the International Space Station.

Sep. 10^th, 2021 Dr. Chanda Prescod-Weinstein , Department of Physics & Astronomy, University of New Hampshire

   Large Scale Structure from Microphysics

  Host: Dr. Dipangkar Dutta

  Abstract:

       In this talk, I will describe my efforts to understand the nature of the mysterious dark matter. I provide an overview of the general problem and then describe my current approach to it, which is to characterize the behavior of a proposed dark matter particle, the axion. I will give some insight into how I am using a range of tools -- model building, computation, and high energy astrophysics -- to get at the basic question of “what is the statistical mechanics of axion dark matter?” I will discuss work that shows that the self-interaction should not be ignored and that the sign of the interaction makes a significant difference in the evolution of the system, both for QCD axions and fuzzy dark matter.

Sep. 3^rd, 2021 Dr. Benjamin Crider, Department of Physics & Astronomy, Mississippi State University

   Principles and Applications of a Gamma-ray Imaging Detector

  Host: Dr. Lamiaa El Fassi

  Abstract:

       The ability to create images of sources of radioisotopes has a long list of applications across a broad range of fields. While the equipment and detectors required to create such images of radioisotopes differs from those required for standard photographs utilizing visible light, many of the same techniques still apply. This general overview talk will explore some of the techniques used to create images of radioactive materials via detection of emitted gamma rays and draw parallels to standard photography that has, in many ways, been performed for over thousands of years. Several applications for images of radioisotopes will be explored, including applications involving sources of environmental radiation being pursued at the Institute for Clean Energy Technology here at Mississippi State University.

Aug. 27^th, 2021 Dr. Torsten Clay, Department of Physics & Astronomy, Mississippi State University

   The spin ladder to nowhere

  Host: Dr. Lamiaa El Fassi

  Abstract:

       High temperature correlated electron superconductivity is one of the most exciting areas of condensed-matter physics, but more than 30 years after its discovery it is yet to be understood. Many relatively simple (although still very difficult to solve) models have been proposed for the high T_c cuprates since then. One common assumption has been that the oxygen atoms in the copper-oxygen planes may be ignored and a simpler Cu-only single-band model can explain superconductivity. This model is well understood in the limit of a ladder, where spin singlets on each rung of the ladder take the place of Cooper pairs, and calculations on ladders find quasi-long-ranged superconducting correlations. In this talk I present results of large scale numerical calculations of pairing correlations on cuprate ladders, including both copper and oxygen orbitals. We find that in realistic cuprate ladder models the long-range superconducting order is suppressed. This shows that ladder physics, now more than 25 years old, is not relevant to superconductivity in the cuprates. Our results strongly suggest that any minimal model must include the oxygen orbitals of the copper-oxygen planes.

Aug. 20^th, 2021 Dr. Angelle Tanner, Department of Physics & Astronomy, Mississippi State University

   From Orbits to Einstein: 25 years of Galactic Center Research

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Over the past few decades, our knowledge of what lurks within the core of our Milky Way galaxy has evolved along with the instruments used to study it. The confirmation of the existence of the super-massive black hole, Sgr A*, was only the beginning. In addition to tracking the orbits of over a hundred S0 stars to estimate the mass of the black hole at 4.154x106 solar masses, we have noticed that they fall into different populations, interact with their environment and are influenced by the presence of the black hole when forming. In 2011, we discovered a cloud of gas, named G2, would pass a little too close to the black hole. It did just that and survived. Over the past few years, advances in telescope instrumentation have paved the way for extremely precise measurements of the orbits of the stars in the inner-most regions near the black hole at a few hundred astronomical units (AU). This includes the star, S0-2, which completes its orbit around the black hole every 17 years and has a closest approach of about 120 AU. During its latest closest passage in 2018, investigations with the biggest infrared telescopes in the world allowed us to study the effects of General Relativity on the star via gravitational redshift and orbital precession. It was this culmination of the direct confirmation of the predictions of GR that helped Drs. Andrea Ghez and Reinhard Genzel be awarded the 2020 Nobel Prize in Physics. As a member of Dr. Ghez’s research team during my time at UCLA, I was witness to some of the first revelations about the nature of the black hole. I’ll discuss the exciting history of the study of this unique location within our galaxy and point the way to what kinds of new discoveries we hope to make about it in the next few decades.

          

2021-2022 Committee