Events

Ken Bader
Department of Internal Medicine
University of Cincinnati

Mechanical Ablation of Tissue with Focused Ultrasound

Histotripsy is a transcutaneous focused ultrasound therapy that ablates tissue through the mechanical oscillations of microbubbles, or cavitation. Preclinical studies have found histotripsy effective for the treatment of prostate pathologies, cancer, deep vein thrombosis, and congenital heart disease. In this talk, the forms of histotripsy and their ablative mechanisms will be modeled in silico, and image-guidance techniques for mechanical ablation will be discussed. An analytic model will be presented to predict the extent of the treatment zone. This analytic model can be used for treatment planning, and to aid the FDA in the development of regulatory standards for histotripsy. Image-guidance of histotripsy will be demonstrated with a new ultrasound imaging modality called passive cavitation imaging (PCI). Studies in a prostate phantom demonstrate that PCI correlates well with the width of the ablation zone, indicating PCI can be used as a predictive metricfor tissue ablation from histotripsy. Finally, PCI will be used to monitor cavitation when histotripsy is used in combination with a lytic agent to lyse clots in a model of deep vein thrombosis. A significant improvement was observed in the thrombolytic efficacy for the combination treatment over histotripsy alone, suggesting a synergistic effect between histotripsy and the lytic agent.

Thomas Sotiriou
School of Physics & Astronomy
University of Nottingham

Black Holes Without Relativity

Lorentz symmetry is central to the concept of a black hole, as it precludes superluminal motion. It is not obvious that one can even define what a black hole is if Lorentz symmetry is abandoned, so one might expect that any observational evidence supporting the existence of black holes will impose very stringent constraints on Lorentz violations. I will discuss some basic aspects of causality in theories that violate Lorentz symmetry and I will argue that, remarkably, the concept of a black hole survives in these theories. After defining the appropriate notion of black hole, I will explore their basic aspects and discuss how they differ from black holes in General Relativity.

Richard Brito
Gravitation in Técnico
Instituto Superior Técnico — CENTRA

Interaction Between Bosonic Fields and Compact Objects

Fundamental bosonic fields generically arise as possible dark matter candidates and in extensions of General Relativity, but are also a useful proxy for more complex interactions. In this talk I will discuss the rich phenomenology of fundamental bosonic fields around black holes and compact stars. In particular I will discuss: (i) the interaction of self-gravitating bosonic structures with compact stars; (ii) superradiant instabilities around black holes and how it can be used to constrain particle masses.

Pengfei Zhang
Department of Mathematics
University of Mississippi

Homoclinic Intersections for Geodesic Flows on Convex Spheres

Transverse homoclinic intersection was discovered by Poincare in the study of stability properties of periodic orbits of n-body problem. Poincare realized that this is a mechanism which not only destroys the stability of periodic orbits but also leads the existence of chaos in the phase space.

In this talk, we will study the geodesic flows on convex spheres. We show that, generically, every closed geodesic is either hyperbolic or irrationally elliptic. Moreover, every hyperbolic closed geodesic admits some transverse homoclinic intersection. Therefore, (everywhere) chaotic dynamics can happen generically on manifolds with simple/trivial topology.

Greg Dooley
Kavli Institute for Astrophysics and Space Research
Massachusetts Institute of Technology

Tidal Stripping with Self-Interacting Dark Matter

Self-interacting dark matter (SIDM) postulates that dark matter is not entirely collisionless, but self scatters at a low rate. By transforming dark matter halo cusps to cores, SIDM offers a solution to the “too big to fail” problem and cusp/core problem in the Milky Way and local field. Two classes of models exist, with velocity-independent and velocity-dependent cross sections. While tight constraints exist on velocity-independent models, constraining velocity-dependent models remain elusive. In this talk, I discuss the implications of both types of SIDM on the tidal disruption of satellite galaxies in a Milky Way-like host. While the total dark matter mass loss rate is not affected, stellar mass loss is enhanced due to lower binding energy in subhalo cores. I discuss the variables affecting the strength of the increased stellar mass loss rate, the effect on observables in the Milky Way, and where we need to look to further constrain or identify self-interacting dark matter.

Alexander B. Yakovlev
Department of Electrical Engineering
University of Mississippi

Non-local Susceptibility of the Wire Medium in the Spatial Domain Considering Material Boundaries

The interaction of electromagnetic waves and wire media has been of interest for many years, driven by applications utilizing artificial plasma, epsilon-near-zero materials, negative refraction, wave canalization and other uses. When the period of the wires is small compared to wavelength, the structure can be considered as a homogeneous (homogenized) medium. Early models of wire media neglected spatial dispersion of the homogenized material, but it has more recently been shown that non-local effects are verystrong for wire media and often cannot be ignored.

In this work, we show that the non-local susceptibility for a nontranslationally invariant homogenized wire medium is, modulo a constant, given by a simple Green's function related to the material geometry. We also show that two previous methods for solving wave interaction problems for bounded wire media (wave expansion method and transport equation) are equivalent to each other, and to a third method involving particle reflection at the boundary. We discuss the importance of the dead layer or virtual interface, and find it to be analogous to the excitonic semiconductor case. Several examples are provided to clarify the material.

Ahmed Rashed
Department of Physics and Astronomy
University of Mississippi

Non-standard Tau Neutrino Interactions

We now know that neutrinos have masses and that there is a leptonic mixing matrix just as there is a quark mixing matrix. The existence of neutrino masses and mixing requires physics beyond the standard model (SM). Hence, it is not unexpected that neutrinos could have new interactions beyond the standard model, or non-standard interactions (NSI). The effects of NSI have been widely considered in neutrino phenomenology. Bounds have been set on the NSI parameters. I will discuss the impact of the NSI on the measurement of neutrino mixing parameters such as the atmospheric and reactor mixing angles, mass hierarchy, and CP violation. We include form factor effects in our calculations and find the deviation of the actual mixing angle from the measured one, assuming the standard model cross section, can be significant and can depend on the energy of the neutrino.

A key property of the SM gauge interactions is that they are lepton flavor universal. Evidence for violation of this property would be a clear sign of new physics (NP) beyond the SM. Recently, hints of lepton flavor non-universality emerged from B-meson decay channels observed in the BaBar and LHCb experiments. We proposed tests of lepton flavor non-universality in tau-neutrino scattering. Different models have been introduced in this study of which charged Higgs, W', and Leptoquark.

Ice Cream Social

Michael S Turner
Kavli Institute for Cosmological Physics
University of Chicago

The Big Picture:  What We Know About How the Universe Began and What We Are Trying to Find Out

Today the Universe is made out of dark matter, dark energy and a small amount of ordinary matter (the atoms we are made of).  We can trace the history of the Universe back to when it was a microsecond and was a formless quark soup.  We now have good evidence for an early burst of tremendous expansion (inflation) that stretched sub-atomic quantum fluctuations to astrophysical size and created the seeds for galaxies.  But there is much to figure out, including what dark matter is made of, what the nature of the mysterious dark energy is, and when inflation took place.

Don Summers et al.
Department of Physics and Astronomy
University of Mississippi

Fascinating Physics Demonstrations

Fifty minutes of fascinating physics demonstrations, including milk jug rockets, will be presented.

Don Summers Presenting
Department of Physics and Astronomy
University of Mississippi

Powers of Ten

Powers of Ten illustrates the universe as an arena of both continuity and change, of everyday picnics and cosmic mystery. It begins with a close-up shot of a man sleeping near the lakeside in Chicago, viewed from one meter away. The landscape steadily moves out until it reveals the edge of the known universe. Then, at a rate of 10-to-the-tenth meters per second, the film takes us towards Earth again, continuing back to the sleeping man's hand and eventually down to the level of a carbon atom.

Chandrima Chatterjee
Department of Physics and Astronomy
University of Mississippi

Experimental Investigation of Impurities and Their Effect on Acousto-Electric Properties of Lithium Niobate

The functional parameters of Lithium niobate that is used in various acousto-opto-electronic applications are questionable. The nonclassical nonlinear effect such as “acoustical memory” is not explained at full. Despite there being publications on crystal defects in Lithium niobate, the relationship between the defects and Acoustical Memory has not yet been established. Previous publications analyzed the Acoustical Memory effect without going into the microstructural detail of the level of point defects. The purpose of this research is to establish a connection between the microscopic point defects and the macroscopic nonlinear phenomena. The present research aims at finding new crystal characteristics including the identification of impurities and point defects, the distribution of the defects along the optical crystallographic z axis, and in a direction normal to the z axis. Bulk crystals and wafers are studied. The impurities are identified by their characteristic lines in the photoluminescence spectra, which are taken at room temperature in a range of 350 to 900 nm. The spectra reveal the following point defects: Ar, Ba, Cs, F-color center, Rb, Ru, Sn, Fe, K, Li, O, Nb, Kr, NbLi⁴⁺, Xe, etc. The peak corresponding to the F-center is found at 400.429 nm and has the highest number of photon counts. Further, the samples are shifted with a step of tens of microns along the z-axes or normal to it. This optical scanning allows to find a distribution of the impurities in the samples. The photon counts changes with crystal position for some impurities. The distribution of these defects is observed as peaks and valleys. The results may be used to discover the physical mechanisms behind nonclassical nonlinear phenomena in Lithium niobate.

Matteo Rini
Deputy Editor
American Physical Society

Science Communication: Take Charge of It!

Scientists have a responsibility to share the meaning and implications of their work, but receive little training in communication, and often feel unprepared to communicate with the public, the media, public officers and others outside their own field. In this talk, I will discuss how our journal Physics (htttp://physics.aps.org) strives to communicate research to a broad audience and share some thoughts and tips on science communication from my experience as a writer, editor, press officer and scientific consultant to policy makers.

Mairi Sakellariadou
Department of Physics
King's College — London

Unweaving the Fabric of the Universe

Our conventional understanding of space-time, as well as our notion of geometry, break down once we attempt to describe the very early stages of the evolution of our universe. The extreme physical conditions near the Big Bang necessitate an intimate interplay between physics and mathematics. The main challenge is the construction of a theory of quantum gravity, the long-sought unification of Einstein's general relativity with quantum mechanics. There are several attempts to formulate such a theory; they can be tested against experimental and observational results coming from high energy physics and astrophysics, leading to a remarkable interplay between gravity, particle physics and cosmology.

Karelle Siellez
Center for Relativistic Astrophysics
Georgia Institute of Technology

The Coincidence Between Gamma-Ray Bursts and Gravitational Waves: the Dawn of the Multi-Messenger Era!

Last year, while we celebrated the 100th anniversary of the Theory of the General Relativity of Einstein, we also detected the first direct observation of Gravitational Waves. LIGO opened the new area of Gravitational Wave Astrophysics with the detection of the coalescence of two black holes. Neutron star mergers (either double neutron star or neutron star - black hole systems) and collapsing massive stars are the next candidates for the detection of Gravitational Waves. They are though to be also the progenitor of respectively short and long Gamma-Ray Bursts. A detection in coincidence of both the Gravitational Waves and the electromagnetic emission would open the era of multimessenger astrophysics.

To detect those coincidences between GRB and GW, LIGO uses a different analysis that searches for a GW triggers coincident within some time window and sky position of a GRB in nearly real time thanks to the GCN sent by the satellite. We estimated the rate of coincident events that could be detected during the next run of O2 using observations in one hand and Monte Carlo simulations on the other. The small number of coincidence could be improved by using the untriggered GRBs missed by the Fermi GBM satellite. Thanks to a new code developed by the GBM team, we will discuss about the new kind of coincident detection that we could obtain.

This talk will describe the search of Gravitational Waves associated to GRBs. We will show the motivations and analysis made for the untriggered searches as well as the implication of those untriggered GRB on the expected rate of coincident event, the classification of long and short GRBs, and the possible new kind of progenitor for short GRBs at low redshift.