## Spring 2019 Physics Colloquium

**Thursday, January 31st**

Tsampikos Kottos, Wesleyan University

"Time-Reversal Symmetry and its Applications to Waveform Shaping and System Protection"

Time-reversal symmetry and its violation is one of the most powerful concepts in physics. It has applications in many physics subfields ranging from condensed matter, optics and atomic physics to mathematical physics and quantum field theories. In this talk, we will focus on two specific implementations of time-reversal symmetry (and its violation) in the field of electrodynamics with relevance to: (a) the design of waveforms of incident electromagnetic radiation that efficiently direct energy at focal points, with applications varying from non-invasive medical therapies and wireless telecommunications to electromagnetic warfare; and (b) the design of reflective photonic limiters used for protection of sensitive sensors from high-power/fluence incoming radiation. We will highlight the connections between these two (at first glance diametrically different) applications while at the same time we will be placing the presented research effort within the framework of recently emerging sub-field of non-Hermitian wave transport.

Noon | Toome 115

Lunch provided

**Thursday, February 14th**

Carl Mungan, US Naval Academy

"Who Says Freshman Physics is Elementary? Investigations of Apparently Simple Phenomena"

He will discuss a variety of interesting topics in the three traditional fields of classical physics: mechanics, E&M, and thermodynamics. The dynamics of a yo-yo, falling U-shaped chain, and unrolling carpet will be analyzed. We will explore particles moving under the action of a 1D inverse-square force. He will introduce the notion of entropic dissipation of a piston in a gas-filled cylinder. We will consider how a Faraday isolator works. He will demonstrate the surprising behavior of a hand-cranked electrical generator. We will learn some elementary probability using a deck of cards. I will distinguish group and phase velocity by simulating wave motion.

Noon | Tome 115

Lunch provided

**Thursday, March 21st**

Zoe Boekelheide, Lafayette College

"Magnetic reversal in nanoparticles: Mechanisms, measurement, and biological applications"

Magnetic materials are used in a wide array of modern applications, from data storage to cancer treatment, and research into the magnetic properties of materials has been largely driven by these applications. The mechanisms by which magnetic materials reverse the direction of their magnetization are of interest for many of these applications. Nanoscale magnets in particular are intriguing because of their small size, and they exhibit rich and complex magnetic reversal behavior. In this talk, She will discuss a few different ways her group is studying magnetic reversal in nanoparticles: both experimental measurement and micromagnetic modeling, as well as exploring biomedical applications which take advantage of the magnetic reversal process, such as magnetic hyperthermia cancer treatment.

Noon | Tome 115

Lunch provided

**Thursday, April 11th**

Jon Custer, Sandia National Laboratories, Albuquerque NM

"A Brief History of Accelerators in Physics"

The discovery of the nucleus, using naturally occurring alpha particles, stimulated a desire to controllably generate high energy particles to probe this exciting new entity. Within a few years of each other, all the basic particle accelerator types were invented and applied to problems in nuclear physics. Beyond their impact on physics, these new technologies were rapidly applied to a range of other problems. By combining history and physics, the role of fundamental physics research in spawning new ideas is illustrated.

Noon | Tome 115

Lunch provided

**Tuesday, April 16th**

Senior Research Presentations

Houssem Mhiri & Moyi Tian - "Bifurcation, symmetry breaking, and synchronization in a coupled-logistic map circuit"

We built a circuit that closely mimics a coupled-logistic-map system and introduces automated manipulation of the initial conditions and of the coupling strength through a NI DAQ device and LabVIEW. This control allows for a close exploration of symmetric and symmetry-broken states that the coupled logistic maps can exhibit under specific initial conditions. We also sweep through initial conditions and thus generate experimental basins of attraction, and these basins nicely highlight the effects of the coupling strength on the symmetric and symmetry-broken regions. We then delve into the chaotic regime where we find regions in parameter space of synchronized, unsynchronized and symmetry-broken chaos, and we produce the corresponding bifurcation diagrams. Finally, we investigate a unidirectional coupled system, where one logistic map is the driver and the second follows. When the driven map would prefer chaos, but the driver wants to enforce period-1, we see a period-doubling cascade in reverse as the coupling is increased.

Hieu Le - "Numerical analysis of nonlinear localized modes in vibrational and magnetic lattices"

We numerically investigate the existence of nonlinear, spatially localized modes for various lattice Hamiltonians using Newton-Raphson method to obtain numerically exact solutions. We start by examining the well-known one-dimensional Fermi-Pasta-Ulam lattice with quadratic and quartic potentials and obtain solution branches in both frequency and nonlinear coefficient via continuation, then propagate the solution in time with Runge-Kutta degree 4 (RK4) method. We then turn to one- and two-dimensional ferromagnetic and antiferromagnetic lattices, and explore both the formation of nontrivial localized modes from small instabilities and their long term stability.

Noon | Tome 115

Lunch provided

**Thursday, April 18th**

Senior Research Presentations

Julia Huddy - "Design, construction, and performance testing of the RD-SAH"

A radically different design of a solar air heater (SAH) is presented that simultaneously optimizes the solar to thermal energy conversion efficiency and the SAH’s cost effectiveness. We compare several different design options, each of which considers the environmental impact of the construction materials used for the SAH. While traditional SAHs typically consist of a glazing and a rectangular, insulated wooden enclosure (or a foam board enclosure made of, e.g., Polyisocyanurite), our re-designed SAH consists of a Polygalâ double glazing and a fiber-reinforced Mylar radiation barrier foil. The air space between the glazing and the Mylar foil is maintained with a blackened wire-fencing, bent in the shape of a rectangular wire crate. A blackened and deliberately wrinkled aluminum foil serves as the SAH’s absorber. The wrinkles present an artificially roughened surface to increase the turbulence of the air as it passes the absorber, thereby increasing the thermal transfer efficiency. Exterior to the wire crate the SAH is insulated with a layer of foil-faced Fiberglass insulation. A second Mylar foil serves as a vapor barrier and IR reflector. Finally, a weathertight enclosure consisting of powder-coated aluminum roll stock, gives the SAH its exterior form. The mostly empty interior of our SAH ensures an enormously low pressure drop across the SAH. We present here our newly designed, environmentally friendly, and cost effective SAH, along with our theoretical calculations and experimental results of its solar to thermal energy conversion efficiency as a function of the mass flow rate.

Sophie Kirkman - "Active reduction of heat losses through the glazing of a solar air heater"

A solar air heater’s (SAH’s) efficiency is limited by heat loss through the glazing and the walls. As the walls are typically well insulated, the majority of a SAH’s losses are through the glazing. We present here a novel method to reduce the glazing losses, whereby ambient air is diverted into the channels of an 8mm Polygalâ double glazing. This decreases the temperature difference between the inside of a glazing channel and the outside air, thereby decreasing heat transfer from the interior of the glazing to the ambient air, and thus reducing the overall glazing loss. The extra heat that flows from the inside of the SAH into the glazing channels is regained by rejoining the channel air with the SAH’s output. The theory and simulations are presented, as well as laboratory experimental results, which show that the glazing heat losses can be reduced by up to 70%. This set-up is then tested on a gridded, single pass solar air heater. The efficiency of the SAH with active glazing loss reduction is compared to the previously determined efficiency of the same SAH having stagnant air inside the glazing.

Noon | Tome 115

Lunch provided

**Thursday, May 2nd**

New Majors' Induction Ceremony

Join us as we welcome & induct our newest members to the Physics & Astronomy Department. Wear your Dickinson Physics T-Shirts!

Noon | Tome 115

Lunch & Cake Provided