The University of Mississippi
Department of Physics and Astronomy

Seminars/Colloquia, Spring 2018

Unless noted otherwise, Tuesday Colloquia are at 4:00 PM
with refreshments served 15 minutes before each colloquium.

Scheduling for additional seminars will vary.

Date/Place Speaker Title (and link to abstract)
Tue, Jan 23
Lewis 101
Jake Bennett
Department of Physics
Carnegie Mellon University
Amplitude Analysis: A Powerful Tool for Hadron Spectroscopy
Tue, Jan 30
Lewis 101
Brian Anderson
Department of Physics and Astronomy
Brigham Young University
Listening For Cracks Using Resonance And Time Reversal Techniques To Prevent Radiation Leakage From Nuclear Storage Containers
Thurs, Feb 8
NCPA Auditorium
Aaron Zimmerman
Canadian Institute for Theoretical Astrophysics
University of Toronto
Black Holes, Alone and in Pairs
Thurs, Feb 15
Lewis 101
Jessica McIver
Division of Physics, Mathematics and Astronomy
California Institute of Technology
Gravitational Wave Astrophysics: A New Era of Discovery
Tue, Feb 20
Lewis 101
Dan Cherdack
Department of Physics
Colorado State University
Searching for CP-Violation with the DUNE Experiment
Tue, Feb 27
Lewis 101
Tony Jun Huang
Pratt School of Engineering
Duke University
Acoustofluidics: Merging Acoustics and Microfluidics for Biomedical Applications
Tue, Mar 6
Lewis 101
Harry Swinney
Center for Nonlinear Dynamics
University of Texas — Austin
Universality in Nature
Tue, Mar 13
Lewis 101
Spring Break
 
 
 
Tue, Mar 20
Lewis 101
Tyrone Porter
Department of Mechanical Engineering and Biomedical Engineering
Boston University
Tensionless Bubbles and Exploding Droplets
Tue, Mar 27
Lewis 101
David Meyer
Department of Mathematics
University of California — San Diego
Data Science and Quantum Gravity
Tue, Apr 3
Lewis 101
Mir Emad Aghili, Vishal Baibhav, and Shrobana Ghosh
Department of Physics and Astronomy
University of Mississippi

Presentations by Graduate Students

Manifoldlikeness of Causal Sets” by Mir Emad Aghili
Systematic Errors and Energy Estimates in Binary Black Hole Ringdown” by Vishal Baibhav
Detectability of Gravitational Radiation from Superradiant Instabilities” by Shrobana Ghosh

Tue, Apr 10
Lewis 101
Bruno Uchoa
Department of Physics and Astronomy
University of Oklahoma
Topology and Quantum Phenomena in Nodal Matter
Tue, Apr 17
Lewis 101
Mukunda Acharya, Khagendra Adhikari, and Xudong Fan
Department of Physics and Astronomy
University of Mississippi

Presentations by Graduate Students

Sound Speed Profiles of the Global Ocean calculated from Physical Oceanographic Data” by Mukunda Acharya
Deforming the Fredkin Spin Chain Away from its Frustration-free Point” by Khagendra Adhikari
Enhancing Sound Emission by Using Subwavelength Metacavities” by Xudong Fan

Tue, Apr 24
Lewis 101
Deidre Shoemaker
School of Physics
Georgia Institute of Technology
Numerical Relativity in the Age of Gravitational Wave Observations
Tue, May 1
Lewis 101
Emanuele Berti
Department of Physics and Astronomy
University of Mississippi
Strong Gravity and Astrophysics with Compact Binaries at the Dawn of Gravitational-wave Astronomy
Tue, May 8
Lewis 101
Final Exam Week  

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Abstracts of Talks


Jake Bennett
Department of Physics
Carnegie Mellon University

Amplitude Analysis: A Powerful Tool for Hadron Spectroscopy

Extracting useful information from experimental data is often far from straightforward. This is particularly true for studies in hadron spectroscopy that seek to determine the properties of constituent quark states. The presence of multiple, often broad, states leads to potentially intricate interference patterns that make the extraction of meaningful information challenging. Amplitude analysis is a powerful tool to disentangle the effects of interference and extract useful properties of hadronic states. This information is vital for a deeper understanding of the fundamental laws of nature. In this talk, I will review the experimental challenges that are associated with amplitude analysis, as well as its potential as a tool for hadron spectroscopy at Belle II.


Brian Anderson
Department of Physics and Astronomy
Brigham Young University

Listening For Cracks Using Resonance And Time Reversal Techniques To Prevent Radiation Leakage From Nuclear Storage Containers

Spent nuclear fuel is often stored in stainless steel canisters in the United States. Stainless steel is susceptible to Stress Corrosion Cracking (SCC). This presentation will discuss progress on the use of the Time Reversed Elastic Nonlinearity Diagnostic (TREND) and Nonlinear Resonant Ultrasound Spectroscopy (NRUS) to determine whether SCC is present and attempt to quantify the depth of the cracking. NRUS is the measurement of the amplitude dependence of a sample's resonance frequency, which occurs because of a softening of the elastic modulus in damaged media. NRUS provides a global indication of damage in a sample. TREND employs time reversal acoustics, which focuses wave energy at various points of interest to excite localized high amplitude. The amplitude dependence of this localized energy allows pointwise inspection of a sample.


Aaron Zimmerman
Canadian Institute for Theoretical Astrophysics
University of Toronto

Black Holes, Alone and in Pairs

The recent detections of gravitational waves have revealed an invisible side of the universe: black holes in binaries. These observations test our understanding of black holes, their violent mergers, and the theory of general relativity. A combination of analytic approximations and full numerical simulations is required to understand black hole binaries and predict the gravitational waves they emit. I will take us on a tour of these systems, discuss the “ringdown” of the final merged black hole, and present the most recent results from the Advanced LIGO and Virgo detectors.


Jessica McIver
Division of Physics, Mathematics and Astronomy
California Institute of Technology

Gravitational Wave Astrophysics: A New Era of Discovery

Large-scale interferometric detectors including LIGO and Virgo sense gravitational waves; minuscule fluctuations in space-time from the most extreme phenomena in the Universe. The recent detection of gravitational waves by LIGO and Virgo in concert with an associated electromagnetic counterpart was a breakthrough in multi-messenger astronomy that confirmed the association between neutron star collisions and short gamma-ray bursts (GRBs) and yielded new insight into the physical engine driving GRBs. Future gravitational wave observations have the potential to provide critical insight into key open questions in astrophysics, including the distribution of compact objects in the Universe, the evolution of compact binary systems, galaxy formation, and the explosion mechanism of core-collapse supernovae.

I will present the major outstanding challenges in gravitational wave astrophysics, including searching for transient signals in noisy data that contains a high rate of transient noise artifacts. I will discuss future prospects for how this quickly growing field will shape our understanding of the Universe.


Dan Cherdack
Department of Physics
Colorado State University

Searching for CP-Violation with the DUNE Experiment

Of the four known fundamental forces the weak force has many unique properties. It is the only standard model force that couples to all known fermions, that has massive exchange bosons, and that induces particle flavor changes. Even more surprising is that the weak force maximally violates parity symmetry, and has even been demonstrated to break charge-parity (CP) symmetry, meaning the weak force interacts differently with matter and anti-matter. This last property may hold the key to understanding several fundamental mysteries of the universe from the three-generation structure of matter, to the missing link between the big bang and the observed universe.

Neutrinos only interact via the weak force which means they are hard to detect, but provide a unique test bed for studying the weak interaction. Over the past few decades it was discovered that neutrinos have mass and change flavors. Studying the way neutrinos change flavors, termed neutrino oscillations, allows us to search for a new source of CP-violation. The next-generation Deep Underground Neutrino Experiment (DUNE) will usher in an era of high precision neutrino physics with the worlds most intense neutrino beam and high resolution Liquid Argon (LAr) Time Projection Chamber (TPCs) detectors. The Fermilab Short-Baseline Neutrino (SBN) Program will employ three LAr TPCs, which will provide and excellent test bed for LAr TPC R&D, and allow for many important measurements crucial to DUNE. I will discuss the theoretical framework we use to describe neutrino oscillations, and the exciting opportunities and new challenges afforded us by these experiments.


Tony Jun Huang
Pratt School of Engineering
Duke University

Acoustofluidics: Merging Acoustics and Microfluidics for Biomedical Applications

The past two decades have witnessed an explosion in lab-on-a-chip research with applications in biology, chemistry, and medicine. The continuous fusion of novel properties of physics into microfluidic environments has enabled the rapid development of this field. Recently, a new lab-on-a-chip frontier has emerged, joining acoustics with microfluidics, termed acoustofluidics. Here we summarize our recent progress in this exciting field and show the depth and breadth of acoustofluidic tools for biomedical applications through many unique examples, from exosome separation to cell-cell communications to 3D bioprinting, from circulating tumor cell isolation and detection to ultra-high-throughput blood cell separation for therapeutics, from high-precision micro-flow cytometry to portable yet powerful fluid manipulation systems. These acoustofluidic technologies are capable of delivering high-precision, high-throughput, and high-efficiency cell/particle/fluid manipulation in a simple, inexpensive, cell-phone-sized device. More importantly, the acoustic power intensity and frequency used in these acoustofluidic devices are in a similar range as those used in ultrasonic imaging, which has proven to be extremely safe for health monitoring during various stages of pregnancy. As a result, these methods are extremely biocompatible; i.e., cells and other biospecimen can maintain their natural states without any adverse effects from the acoustic manipulation process. With these unique advantages, acoustofluidic technologies meet a crucial need for highly accurate and amenable disease diagnosis (e.g., early cancer detection and prenatal health) as well as effective therapy (e.g., transfusion and immunotherapy).


Harry Swinney
Center for Nonlinear Dynamics
University of Texas — Austin

Universality in Nature

In the seventeenth century Newton thought about the gravitational force between the earth and an apple falling from a tree, and he said “I began to think of gravity extending to the orb of the Moon.” This led him to postulate that his gravitational force law is a universal law of nature, applying to any two masses in the universe. We now know that there are three other fundamental universal forces in nature, the electromagnetic and the strong and weak nuclear forces. Systems of many atoms or molecules can similarly exhibit universal behavior. For example, studies of phase transitions in the 20th century culminated with Kenneth Wilson's theory of universality in phase transitions of systems as different as fluids and magnets. The present talk examines spatial patterns that emerge in systems driven away from thermodynamic equilibrium by imposed gradients in pressure, temperature, or nutrient concentration. Experiments and mathematical models provide insights into the formation of patterns in physical, chemical, and biological systems, as will be illustrated through examples that reveal mathematical similarity in phenomena such as in the fractal wrinkling of flower petals and plastic sheets.


Tyrone Porter
Department of Mechanical Engineering and Biomedical Engineering
Boston University

Tensionless Bubbles and Exploding Droplets

Fluid-filled particles play a pivotal role in biomedical applications of ultrasound. This talk will cover two examples, lipid-coated microbubbles and vaporizable nanoemulsions, highlighting their interesting nonlinear dynamics and utility. Due to their compressibility, microbubbles are more echogenic than tissue, making them ideal ultrasound contrast agents. The microbubble surface must be coated with surface-active molecules such as lipids in order to reduce the interfacial tension and stabilize the microbubble against dissolution. The interfacial tension is a function of lipid surface density, which varies from zero upon deep compression to that of an uncoated bubble upon expansion. The forces acting on the microbubble wall vary as the interfacial tension changes, resulting in a nonlinear response to acoustic excitation. Using monodisperse lipid-coated microbubbles, we have studied this nonlinear behavior, including pressure-dependent resonance frequency and subharmonic emissions at ultralow excitation pressures. In contrast to microbubbles, liquid perfluorocarbon nanoemulsions are incompressible and thus poorly echogenic. The nanoemulsions can be vaporized with high pressure acoustic pulses. The phase conversion is immediate and highly energetic and thus resembles an explosion on a microscale. The resultant bubbles can be used to transiently permeabilize cell membranes, thus enabling drug delivery to intracellular targets, or can be used to enhance tissue absorption of ultrasound, making ultrasound-mediated ablation more efficient. These studies provide insight into the unique nonlinear behavior of these fluid-filled particles and how they may be leveraged for exciting biomedical applications.


David Meyer
Department of Mathematics
University of California — San Diego

Data Science and Quantum Gravity

Data, even “big data”, is finite, and thus discrete. A common goal is to describe them as the outcome of a random process specified by a small number of parameters; doing so at least compresses the data, and at best explicates the process by which they were generated. Some important approaches include low-rank matrix factorization and multi-dimensional scaling, both of which reveal a geometry behind the data. Such interplay between the discrete and the continuous is familiar in theoretical and computational physics, from the definition and regularization of path integrals to numerical methods for fluid dynamics. In this talk I'll explain how recent data science results in non-metric multidimensional scaling provide a new perspective on the Hawking-Malament theorem that is the foundation of the causal set program for quantum gravity. I'll describe a new algorithm for embedding causal sets in Lorentzian manifolds motivated by this perspective. And I'll end with some speculations about possible quantum dynamics for causal sets. Familiarity with the causal set program for quantum gravity will not be assumed.


Mir Emad Aghili
Department of Physics and Astronomy
University of Mississippi

Manifoldlikeness of Causal Sets

We study the distribution of maximal-chain lengths between two elements of a causal set, and its relationship with the embeddability of the causal set in a region of flat spacetime. We start with causal sets obtained from uniformly distributed points in Minkowski space. After some general considerations we focus on the 2-dimensional case and derive expressions for the expected number nk of maximal chains as a function of their length k, the most probable maximal-chain length k0, and the width Δ of the length distribution, as functions of the number N of causal set elements in the interval between the two points. These results, together with the results of numerical simulations of causal sets embedded in Minkowski space of various dimensionalities, show that for a given N the values of k0 and Δ can be used to estimate the dimensionality of a causal set embeddable in Minkowski space. Other dimension estimators are known for manifoldlike causal sets, but the length distribution also gives us a way to evaluate the embeddability of a causal set. We provide a first test of manifoldlikeness based on k0 and Δ, and end with a few simple examples of nk distributions for non-manifoldlike causal sets.


Vishal Baibhav
Department of Physics and Astronomy
University of Mississippi

Systematic Errors and Energy Estimates in Binary Black Hole Ringdown

High signal-to-noise ratio gravitational wave observations will enable us to measure the quasinormal frequencies of binary black hole merger remnants. In general relativity, these frequencies depend only on the remnant's mass and spin, so they can be used to test general relativity and the Kerr nature of the remnant. To carry out these tests, systematic errors must be subdominant with respect to statistical errors. I'll talk about how accurately ringdown frequencies can be extracted from state-of-the-art numerical simulations from the Simulating eXtreme Spacetimes (SXS) catalog. I'll also present some results on the relative excitation of different quasinormal modes. To quantify these excitations, one must define a suitable “starting time”, e.g. by maximizing the energy content “parallel” to a quasinormal mode (as suggested by Nollert). We used Nollert's method to quantify the energy radiated in quasinormal modes for aligned-spin binaries, and we produced post-Newtonian inspired fits of the resulting energy estimates.


Shrobana Ghosh
Department of Physics and Astronomy
University of Mississippi

Detectability of Gravitational Radiation from Superradiant Instabilities

An incident wave, when scattered off a black hole may get amplified, at the expense of the rotational energy of the black hole. This process is known as superradiance and due to this rotating black holes can serve as particle detectors. For a massive field, the mass of the field helps in confining the field. Therefore, even an ultralight bosonic field can form a non-axisymmetric cloud around the black hole due to repeated amplification from the black hole. This leads to emission of gravitational radiation that can be detected by ground-based or space-based gravitational wave detectors, depending on the mass of the boson. Based on astrophysical models we show that adLIGO should see 104 events in a 4 year mission for a scalar field mass of 3×10-12 eV, while LISA will see about 103 events in a 4 year mission for a scalar field mass of 10-17 eV. In the absence of detection at a particular detector, we can rule out the corresponding mass range of the scalar field. We also look at the detectability of such events from the remnants of the merger events already seen by adLIGO at the present and future ground-based detectors.


Bruno Uchoa
Department of Physics and Astronomy
University of Oklahoma

Topology and Quantum Phenomena in Nodal Matter

Nodal matter describes a new metallic form where the Fermi surface collapses into sets of points or lines, and is not stabilized by Fermi pressure but by symmetries. The non-trivial quantum phenomena of those systems are described by topology, a field of mathematics that studies properties that remain invariant under continuous deformations of shapes and surfaces. In the first part of the talk I will give a general overview of the field. In the second one, I will describe a particular class of nodal materials where the Fermi surface has the shape of closed lines. I will show that interactions can drive this system into an exotic topological phase in three dimensions (3D) known as the 3D anomalous quantum Hall effect, where the system has spontaneous and topologically protected surface currents.


Mukunda Acharya
Department of Physics and Astronomy
University of Mississippi

Sound Speed Profiles of the Global Ocean calculated from Physical Oceanographic Data

Sound speed profiles in the global ocean are useful for modeling of sound propagation over the global oceans. This talk presents the sound speed profiles calculated from physical oceanographic data that were collected in the world ocean circulation experiment. They are data of conductivity, temperature, and pressure, taken from multiple cruises with a typical spacing of 60 km along the route of each cruise and consisting of an elaborate series of zonal (east-west) and meridional (north-south) coast-to-coast cruises across the global oceans. Nearly 8000 sound speed profiles were mapped out that were then used to determine the dependence of sound speed minimum and depth for those minima on the longitude and latitude. Based on the characterization, practical formulas of the dependence were given.


Khagendra Adhikari
Department of Physics and Astronomy
University of Mississippi

Deforming the Fredkin Spin Chain Away from its Frustration-free Point

The Fredkin model describes a spin-half chain segment subject to three-body, correlated-exchange interactions and twisted boundary conditions. The model is frustration-free, and its ground state wave function is known exactly. Its low-energy physics is that of a strong xy ferromagnet with gapless excitations and an unusually large dynamical exponent. We study a generalized spin chain model that includes the Fredkin model as a special tuning point and otherwise interpolates between the conventional ferromagnetic and antiferromagnetic quantum Heisenberg models. We solve for the low-lying states, using exact diagonalization and density-matrix renormalization group calculations, in order to track the properties of the system as it is tuned away from the Fredkin point. We identify a zero-temperature phase diagram with multiple transitions and unexpected ordered phases. The Fredkin ground state turns out to be particularly brittle, unstable to even infinitesimal antiferromagnetic frustration. We remark on the existence of an “anti-Fredkin” point at which all the contributing spin configurations have a spin structure exactly opposite to those in the Fredkin ground state.


Xudong Fan
Department of Physics and Astronomy
University of Mississippi

Enhancing Sound Emission by Using Subwavelength Metacavities

Efficient directional emission of sound waves is critical in imaging and communication, yet is held back by the inefficient emission of a small source. A change in the surrounding environment of an acoustic source can lead to enhanced emission and mode conversion. This talk will present frames of enclosing small sound sources in subwavelength meta-cavities to achieve sound enhancement and conversion with high efficiency. The enhancement is an analog of modifying spontaneous emission rate of a quantum source in a resonant cavity. The enhancement by a subwavelength meta-cavity offers a practical path toward miniaturization in applications that demand efficient emission, such as sonar, loudspeakers, or ultrasound transducers.


Deidre Shoemaker
School of Physics
Georgia Institute of Technology

Numerical Relativity in the Age of Gravitational Wave Observations

The advent of gravitational wave astronomy has created opportunities to probe strong-field gravity as we measure the merger of black holes. Numerical relativity provides the means to confront the measurements with theoretical prediction. In this talk, I'll discuss the role numerical relativity played in the observed black hole binaries by LIGO and Virgo and the future potential for unveiling strong-field gravity in both future ground and space based detectors.


Emanuele Berti
Department of Physics and Astronomy
University of Mississippi

Strong Gravity and Astrophysics with Compact Binaries at the Dawn of Gravitational-wave Astronomy

Einstein's general relativity has passed all experimental verifications with flying colors, but cosmological observations and difficulties in quantizing gravity suggest that general relativity should be modified at some level. Strong-field modifications of general relativity (if they occur in nature) will in general affect the dynamics of black holes and neutron stars, with potentially observable signatures. Therefore compact objects - whether in isolation or in binary systems - are excellent astrophysical laboratories for high-energy physics and strong-field gravity. Furthermore, the gravitational radiation emitted during the inspiral and merger of compact binaries encodes important information on their astrophysical formation mechanism. I will discuss potential smoking guns of modified gravity in gravitational-wave detectors, and the theoretical and observational challenges associated with their search. I will also discuss the potential of Earth- and space-based detectors to further our understanding of the formation and evolution of compact binaries.