Spring 2013 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, January 31st
Dr. Michelle Selvans, National Air & Space Museum, Smithsonian Institution
"Sleuthing on the Smallest Planet: What is the Relationship Between Tectonics and Crustal Thickness on Mercury?"


Abstract:  Better understanding the tectonic history of the smallest terrestrial planet in our Solar System gives us insight into the full range of possibility for what solid planet surfaces are like, including 'Earth-like' exoplanets. Interior cooling and the resultant radial contraction of Mercury dominated the contribution to the contractional strain expressed by lobate scarps and high-relief ridges. The underlying large thrust faults should be randomly distributed over the surface if their formation was purely the result of global contraction, but instead these features appear to be concentrated in some regions and relatively deficient in others. I therefore ask the questions: What combination of stresses caused lobate scarps and high-relief ridges to form at the observed locations? Was mantle convection partly responsible for concentrating tectonic features? In this talk, I address the latter question in particular, using data from the MESSENGER mission.


Thursday, February 28th
Douglas Ratay, Decisive Analystics
"Exploiting High Dimensional Spaces to Identify Objects: A Non-Linear Path from Physics to Computer Vision"


Abstract: The explosion in both the number of data collection systems and the amount of data collected by any one system has created new
opportunities for the development of intelligent algorithms designed to make sense of complex data.  While in the recent past, the only way
in which data could be analyzed was through the use of scientists and engineers utilizing their expertise to identify features and patterns
in data, it is now becoming practical and cost effective to construct algorithms which can self-identify important data structures in
existing data and make decisions based on new data.  This talk will focus on the development of one sub-field of these types of algorithms, known generally as "Dimension Reduction" or "Manifold Learning".  I will discuss how these algorithms can be applied to scientific data, and how they can be used in larger systems that produce useful results such as object identification.  As a running sub-theme, I will also discuss a career path running from small liberal arts college physics/astronomy through academia to industry. I will attempt to provide relevant information on skill sets deemed useful by industry and a general outlook on the sector.


Thursday, March 21st
Harold "Sonny" White, Eagleworks Labs (NASA)
"Warp Field Mechanics 102 - How Hard is Interstellar Flight?"


Abstract: This talk identifies the colossal challenge of sending a robotic probe (let alone human mission) to our nearest stellar neighbor, and speculates on how, using a loophole in general relativity, we might bring the stars within our grasp. A short review of the Alcubierre warp drive metric is provided to describe how the idea of a space warp might work. The impractical energy requirements discussed in the literature are identified, and a warp bubble topology optimization approach is discussed. The idea of a warp drive in a higher dimensional space-time (manifold) is briefly considered by comparing the null-like geodesics of the Alcubierre metric to the Chung-Freese metric and another energy optimization technique is identified. The energy optimization results are presented and show that the idea of a space warp may have been moved from impractical to plausible. Finally, an overview of the warp field interferometer test bed being implemented in Eagleworks Laboratories at the Johnson Space Center will be detailed.


Thursday, April 11th
Dr. Tom Richard, Penn State
"Smart Energy"


Abstract: A little over a decade ago the National Academy of Engineering named the electricity grid the most significant engineering achievement of the 20th century. In the US this grid has been remarkably successful in providing reliable and affordable power to meet over 40% of our total energy demand. But the next few decades will see a dramatic transformation of this system, with distributed power generation from renewables and natural gas, distributed storage including the batteries in plug-in vehicles, and an interactive control system that generates power, charges batteries, heats and cools buildings, and runs appliances to minimize energy use and costs.  The first wave of this transformation is already occurring at colleges and universities, with combined heat and power systems, integrated building control systems, and most important: a population of engaged and committed students, faculty and staff.


Monday, April 22nd @ 4:15 p.m.
Physics Senior Research Presentation

Melia Bonomo, Casey Caslin and David Liftschitz


The purpose of this project is to investigate the singularity that forms at the tip of water droplets freezing on a flat surface, as described in a recent AJP article [1].  We designed and built an apparatus to observe 10μL drops of purified water freezing on a chilled aluminum plate. A video camera is used to obtain a movie of the solidifying drop and capture the singularity that forms in the final moments.  We performed video analysis to examine the changing dimensions of the liquid and solid portions of the drop during solidification.


By making several simplifications about the freezing process, we use a geometric model to derive a set of coupled differential equations that describe the volume, radius, and contact angle of the unfrozen liquid, and to describe the solidification rate.  We designed a computer-based simulation that predicts the frozen droplet shape, which is dependent on the density ratio of the solid to the liquid.  We then analyze our system of differential equations and determined the appearance of a pointy tip for liquids with a density ratio less than 0.75.   Finally, we use the simulation to generate intermediate shapes throughout the freezing process to produce a graphical animation of the shape transformation.


While the simplified model does predict the formation of singularities, it does not accurately predict the shape of frozen water droplets, which have an approximate density ratio of 0.9. We are currently working on a more detailed geometric model that accounts for the slightly curved solid-liquid contact line, which has been observed experimentally under certain initial conditions [2].


[1] Snoeijer, J, Brunet, P. Am. J. Phys. 80, 764-771 (2012).


[2] Nauenberg, M. Am. J. Phys. 81, 150-151 (2013).


Tuesday, April 23rd
Physics Senior Research Presentation Talks

Joseph F. Stormes - "Parity-Time Symmetry Breaking in a Non-Linear Gain/Lost Circuit"


Parity-Time (PT) symmetry is the quality of being symmetric with respect to both spatial inversion and time inversion. We studied this kind of symmetry by observing the behavior of modes that arose within a gain/loss resonance circuit, an amplifying resonator magnetically coupled to a dampening resonator. To do this we first reproduced the behavior in the standard linear version of this circuit [1]. We then added non-linearity into the circuit in the form voltage variable capacitances. These voltage variable capacitances cause the amplitude of the oscillations within the circuit to change the resonant qualities of the circuit, thus producing non-linear behavior. We studied the effects this had on the PT-symmetric modes that arose in the circuit and found that at low amplitudes it approximates the linear modes and at larger amplitudes non-linear symmetric modes are also attainable. The behavior that these modes exhibit is observed in the numeric and theoretical models created by our collaborators at other universities.


[1] J. Schindler, A. Li, M.C. Zheng, F.M. Ellis, T. Kottos, Phys. Rev. A 84, 040101 (2011).


Liam Timms - "Synchronization in a Network of Phase-Coupled Oscillators: The Role of Learning and Time Delay"


Abstract: Emergent phenomena are those that cannot be fully understood by examining the mechanisms of single components in a system. Synchronization, the process where by oscillators come into phase and move with the same frequency, is a mathematically tractable way to study these general phenomena. A popular model of sync is the Kuramoto Model which has been applied neural networks .  We combine two extensions to the Kuramoto model that are very important neurologically: the inclusion of finite action potential propagation speed through time-delays and the inclusion of variable synaptic strength through dynamically changing coupling [6]. One of the simplest models for variable synaptic strength is the Hebbian Learning Rule. This rule says that, “neurons that fire together, wire together." In this study we formulated the model and numerically solve the governing equations. We used general one and two dimensional array structure before attempting to narrow our investigations to more readily applicable results.


Thursday, April 25th
Physics Senior Research Presentation

Joshua Margolis - "Manipulating Spatial Frequencies through LabView"


Abstract: We shine light through an aperture in order to produce its far-field diffraction pattern, which represents the two-dimensional Fourier transformation of the aperture.  We specifically consider shining light through a spatial square wave, which consists of alternating transparent and opaque regions.  The light incident upon the object will diffract and separate into its spatial frequencies, which contain the information about the aperture's shape.  When permitted to propagate, these spatial frequencies recombine to form an image of the aperture.  If some of these frequencies are masked, then we produce an image different from that of the aperture.  Moreover, we use LabView to predict the shape of the reconstructed image, depending upon the frequencies masked, and compare it to the experimental results.  We wish to verify the relationship between an object and it's corresponding diffraction pattern.  Thus, we can identify objects using their diffraction patterns, which has numerous applications in crystallography and holography.  We find that higher spatial frequencies correspond to the fine details of an image, while the low frequencies determine the outline, or rough shape.  Additionally, we designed a LabView program to mask an image digitally.


Sung Woo Kim - "A Highly Efficient, Low-Cost Solar Air Heater Using a Gridded Absorber"


Abstract: We present an efficient, low-cost, 4'x8' solar air heater (SAH) that uses a multi-layer blackened aluminum grid as the absorber of the solar radiation. We analyzed the rate of heat flow between the sun, the absorbing material, the air going through the box, and the ambient and the heat loss through conduction and radiation. This analysis guided us to choose aluminum grids as absorbing material and a simple design that minimizes conduction heat loss and keeps the cost minimal. Rather that aiming at a record conversion efficiency, which would result in a very expensive solar air heater, we designed our SAH such that it would have a high efficiency and minimal ROI (return on investment). Following this guideline, we were able to construct our SAH  for about $200, corresponding to an ROI of approximately two years, while still featuring a very large energy conversion efficiency of over 60%. Experimental results are compared with theoretical analysis. Our SAH is also equipped with realtime insolation and mass air flow sensors that give us valuable data for SAH research.


Thursday, May 2nd
Crystal Bailey, American Physical Society
"Breaking The Myth of the "Non-Traditional" Physicist: The Real Story About Employment for Physics PhDs"


Abstract: Physics PhDs are among the most employable in the world, often doing everything from managing a research lab at a multi-million dollar corporation, to developing solutions to global problems in their own small startups.  Employers know that with a physics training, a potential hire has acquired a broad problem-solving skill set that translates to almost any environment, as well as an ability to be self-guided and -motivated so that they can teach themselves whatever is needed to be successful at achieving their goals.  Therefore it's no surprise that the majority of PhD graduates find employment in private-sector, industrial settings. At the same time, less than 10%of graduating PhDs will take a permanent faculty position--yet academic careers are usually the only track to which students are exposed while earning their degrees. This talk will explore less-familiar (but more common!) career paths for physics and PhDs, and will provide information on resources to boost your career planning and job hunting skills.  


Thursday, May 2nd
Physics New Majors Induction Ceremony and BBQ

Join us as we welcome and induct our newest members into the department.  The seniors will introduce each student and learn something interesting and funny about each one. We will BBQ first followed by introductions and finally...CAKE!


4:15 p.m. in Tome Hall Back Lawn Area (Rain Location: Rector Atrium/Lecture Room)