Fall 2012 Physics Colloquium

Unless otherwise noted, lunch is served 15 minutes before each colloquium. Colloquium schedules from other semesters can be found at the *Colloquium Archive*.

Thursday, August 30th - 12:05 p.m.
Professor Faustino Palmero from Nonlinear Physics Group of the University of Seville, Spain
"Nonlinear Localized Excitations in Discrete Systems"

Abstract:  Nonlinear physics of discrete systems has witnessed enormous development in the past years.  In particular, a great deal of attention has been paid to the existence and properties of intrinsic localized modes, or discrete breathers, which result from the combination of nonlinearity and spatial discreteness.  Their existence and persistence under general conditions has been proved mathematically, observed in a wide variety of different systems, and recently, in some cases, the direct control and manipulation of such states has been enabled experimentally.  We will review some contributions in the field of discrete breathers, and focus on a particular set of systems, a family of closely related macroscopic electrical lattices, where dynamics can be measured fully in space and time, and also characterized theoretically by means of simple models.  These systems are, arguably, ideal to make quantitative contact between theoretical and experimental results.  Also, we have achieved a substantial spatial control of these excitations.

Thursday, September 6th - 12:05 p.m.
Melia Bonomo '13 - "Creating Bessel Beams with a 4-f Spatial Filter"

Abstract: A Bessel beam is a non-diffracting solution to the Helmholtz wave equation; unlike typical Gaussian laser beams it consists of a narrow core surrounded by concentric rings. The purpose of this project was to create zero-order Bessel-like beams by a recently described 4-f spatial filtering method (Kowalczyk, Smith, and Szarmes, AJP 2009) and study their formation and evolution with a CCD camera and ImageJ software. Observed beams maintain a core diameter under 45 microns over a distance of 47 mm. This work was supported by the Stony Brook Physics and Astronomy REU program and the Laser Teaching Center.

Olivia Lanes '14 - "Driving Sodium/Potassium Pumps with an Oscillating Electric Field: Effects on Muscle Fatigue"

Abstract:  A new technique called Synchronization Modulation has recently been shown to be effective in synchronizing and speeding up the sodium/potassium pumps in cell membranes. When synchronized, it is thought that these pumps are more efficient because they require less ATP. My colleagues and I hypothesized that if this was correct, this technique may be used to reduce muscle fatigue. To test our hypothesis, we had multiple test subjects hold a 15 lb weight for as long as they could while isolating the bicep muscle and applying an oscillating electric field. Our preliminary results that were analyzed with EMG and Fast Fourier Transform suggest that the Fatigue Index decreased at a slower rate in the trials where the subject held the weight with Synchronization Modulation.

Thursday, September 20th - 12:05 p.m.
Sophia Acevedo '14 - "Interning at the Jet Propulsion Laboratory"

Abstract: For the past three summers, I have worked as an Engineering Undergraduate intern at the Jet Propulsion Laboratory in La Cañada, CA. In this time, I have been part of many different kinds of projects, such as creating specification sheets of every lab in my division, drop test building design, and inspections on the  Mars Science Laboratory (MSL): Curiosity. I will be talking about these projects and my experiences interning at JPL.

Sung Woo Kim '13 - "Desalination"

Abstract: Water is an essential source for our life. Yet, its availability is becoming scarce throughout the world rapidly. Many scientists and engineers study different methods of turning sea water into potable water, process which is referred as 'desalination.' In the talk, different modes of desalination - forward osmosis, reverse osmosis, and membrane distillation - will be discussed.

Thursday, September 27th - Noon - RUSH HOUR - (Rector Hall - Stafford Lecture Room)

Professor Catrina Hamilton-Drager
"KH 15D: A Proto-Tatooine and Rosetta Stone for Planet Formation"

KH 15D is a young binary system composed of similar, but not identical, low-mass pre-main sequence stars in an orbit of eccentricity of ~ 0.6 with a period of 48.37 days.  The binary orbit is viewed nearly edge-on and is embedded in an accretion disk from which a well-collimated outflow emerges.  A thin circumbinary ring of evolved solids has precipitated from the gas disk within the terrestrial zone (1-4 AU) of this system.  The ring reveals itself as an opaque screen with a razor-sharp edge at optical and near-infrared wavelengths.  For decades, the leading edge of this structure has been slowly moving across the binary orbit, apparently resulting from the slightly inclined ring.  At a time when NASA's Kepler Mission is discovering multiple-planet systems around evolved binary systems, KH 15D presents us with an opportunity to explore the process of planet formation in such binary systems.  This talk will discuss the search for exo-solar planets and focus on the particular opportunities that a system such as KH 15D can provide for the advancement of pre-main sequence stellar evolution and planet formation theories.

Thursday, October 11th - 12:05 p.m.
Vashti Sawtelle, University of Maryland
"Progress Through Paradox: Reconciling Interdisciplinary Perspectives"

Abstract: Recent national reports reflect an emerging consensus among scientists and educators that undergraduate science education needs to better prepare students to reason and communicate across disciplines. Enacting this change requires creating courses for students that attempt to bridge disciplinary barriers rather than reinforce them. At the University of Maryland, our interdisciplinary team of scientists and education researchers has begun the daunting task of thoughtfully redesigning and researching the transformation of an introductory physics course for biologists. In doing so, we are constantly faced with making decisions about how the disciplines of physics, chemistry, and biology interact and differ from one another. In this talk I will present several apparent paradoxes between physics and biology that we have examined in the context of redesigning this course, and discuss how we have taken up the challenge of helping students in reconciling perspectives from both physics and biology. We will discuss how taking up this challenge has led to a changing perspective on what we think is important for biology students to know from physics, and how that has informed development of this physics for biologists course.

Thursday, October 18th - 12:05 p.m.

Professor Brett Pearson, Dickinson College
"Laser Pulse Shaping for Biomolecular Control"

Abstract: Ultrafast lasers are powerful tools for observing and controlling molecular systems relevant in biochemistry.  Advances in both laser development and cellular imaging have revolutionized our ability to study complex biological and chemical processes.  In particular, "shaping" the laser pulses can enhance certain molecular responses, allowing one to discriminate between target molecular states.  In this talk I will discuss our development of an ultrafast laser pulse shaper and its application in biochemical control experiments.

Thursday, November 15th - 4:30 p.m.
Sigma Pi Sigma Induction Ceremony @ 4:30 pm in Tome 115 and a majors dinner to immediately follow in HUB Siderooms.

Narelle Hillier '06
"Novel Effects on High Pressure on Superconductivity"

Abstract: Following Kamerlingh Onnes' discovery of superconductivity in mercury in 1911, the superconducting state has been widely studied.  High pressure studies help to further our understanding of this exotic state and can lead to the discovery of new superconductors.  Following an introduction to superconductivity, I will give a brief overview of high pressure techniques utilized to study materials at extreme pressures.  In particular, I will focus on studies of two types of materials.  Under extreme pressure, Li shows a marked deviation from free-electron behavior, leading to a superconducting transition temperature that is among the highest of all elemental superconductors. Mg, however, has not been found to be superconducting. By substituting divalent Mg for monovalent Li to create Li(Mg) alloys, it is possible to explore the effect of increasing electron concentration on the phase diagram Tc(P).  Finally, the recent discovery of iron-based superconductors has attracted considerable attention. Among these, the LnFePO (Ln=La-Gd) compounds have not been studied as extensively due to their lower transition temperatures.  However, various high pressure measurements indicate a startling array of pressure dependences. For various pressure media, the transition temperature may either increase or decrease with increasing pressure. These findings, along with other high-pressure studies on iron-based compounds, show that superconductivity in these materials is extremely sensitive to strains and stresses within the sample. Hydrostatic and uniaxial studies are therefore vital for understanding the nature of superconductivity in these materials and determining how to enhance Tc.

Tuesday, November 27th - 12:05 p.m.
Physics Senior Presentations

Joseph Stormes - "Parity-Time Symmetry Breaking in a Non-Linear Gain/Loss Circuit"

Abstract: Parity-Time (PT) Symmetry is the quality of having symmetry with respect to spatial inversion and time reversal.  One such system that displays qualities of PT-symmetry is that of a gain/loss circuit, an amplifier resonance circuit magnetically coupled to a dampening resonance circuit. I explore the PT-symmetric qualities of a gain/loss circuit and the breaking of the PT-symmetry that is present after a transition point in the observable solutions of this circuit. Further, I explore the introduction of non-linearity into this circuit through the use of non-linear circuit components, such as diodes, and the effects this non-linearity has on PT-symmetry breaking.

Sung Woo Kim and Ilia Papa - "Low-Cost Solar Air Heater"

Abstract: Our need for producing energy from renewable sources is urgent. Using solar power has been one of the major practices. A solar air heater, a box which allows air to flow through it and collect sun's power, has been under-appreciated under the wide-spread popularity of PV panels. We investigated theoretical aspects, worked on the design and construction of our version of solar air heater, which is designed to provide supplemental space heating.  Our main goals were low-cost, simplicity, and high efficiency. In our talk, we will present analytical models we examined, different designs we studied, and the measurements of our current final design.

Thursday, November 29th - 12:05 p.m.
Physics Senior Presentations

Melia Bonomo, Casey Caslin and David Lifschitz -  "Analyzing the Singularities of Freezing Sessile Water Droplets"

Abstract:  The purpose of this project was to experimentally, mathematically, and computationally investigate the singularity that forms at the tip of water droplets freezing on a flat surface, as described in a recent AJP article (Snoeijer et al. 2012).  We designed and built our own apparatus in which a micropipet dropped 10μL purified water droplets onto an aluminum plate cooled by liquid nitrogen.  A ProScope was then used to record a close-up of the solidifying drop.  By making a number of simplifications about the freezing process, we derived a geometric model with differential equations to describe the rate of change of the radius, contact angle, and volume of the unfrozen liquid.  We then created a computer simulation using Easy Java Simulations to graphically predict the appearance of the pointy tip using these differential equations.  Our results suggest that the ratio of the density of the solid to the density of the liquid determines the shape of the frozen drop.

Liam Timms - "Time-Delayed Dynamically-Coupled Oscillators: A Model for Biological Systems"

Abstract: We investigate numerically the interplay of network "learning'' and finite  signal speed in one-dimensional arrays of coupled Kuramoto oscillators. The finite signal speed is introduced into the dynamical system via a time-delay in the coupling. The network structures we examine include various 1D arrays with both long and short-range connectivity; the structure of these arrays was imposed via a time delay and a connection matrix. The learning was governed by the Hebbian learning rule which allows the coupling strengths between pairs of oscillators to vary dynamically. It corresponds to a neurological type of learning in which the synapses between neural oscillators increase in strength when they fire action potentials together. We explore the coherent spatio-temporal patterns that can emerge as a function of model parameters such as learning rate and signal speed.

Friday, November 30th - 4:00 p.m.

Joseph P. Hornak, Ph.D., Professor of Chemistry and Imaging Science at Rochester Institute of Technology
"Keeping a Magnetic Resonance Imager Knocking"

Abstract: A magnetic resonance imager is perhaps one of the more complex pieces of diagnostic equipment found in a hospital.  Keeping it operating properly (knocking) can be a challenge because of its complexity and the pressure of every hour down, equates to the loss of one thousand dollars of revenue.  The recent development of quantitative magnetic resonance imaging (MRI) techniques have made the task more challenging as the operating specs are more demanding than routine anatomical MRI.  This talk discusses some of the challenges of keeping a whole body magnetic resonance imager performing at a level suitable for quantitative MRI applications.

Monday, December 3rd - 4:30 p.m.
Physics Senior Presentations

Josh Margolis - "Spatial Frequencies and Image Reconstruction"

Abstract: When light is incident upon an object, it diffracts, causing it to spread out over space.  As it does, it forms a diffraction pattern, called its Fouriertransformation, dependent upon the spatial frequencies it possesses.  When these frequencies are permitted to propagate and recombine, they form an image identical to the shape of the object.  However, if certain frequencies are blocked, and hence unable to propagate further, the resulting image is an alteration of the object.  Using Labview, we aim to study the effect each frequency has with respect to reconstructing an image of the object.