Spring 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, February 2nd - 12:05 p.m.
Melanie Lott, PhD Candidate in Physics, Bryn Mawr College
"The Physics of Balance During Rotations in Dance"

 

Abstract: Applying physical principles to human bodies in motion can provide insight into ways in which the body can move more efficiently and how injuries can be prevented.  This presentation will deal with one of the most common movements in dance - the pirouette, or a turn around a vertical axis with one supporting foot on the floor.  Dancers are often taught to perform pirouettes by beginning the movement as close to a balanced position as possible and holding the body rigidly, as opposed to trying to correct for an imbalance with small adjustments during the turn. Many, even advanced, dancers have significant difficulty performing more than a two- or three-turn pirouette before losing balance, despite continued trial and error efforts to improve.  How can dancers use physics to improve their pirouettes?  Insight gained from the analysis of a theoretical model of a dancer toppling from a pirouette is combined with data collected from real dancers performing pirouettes.  By comparing the strategies used by various dancers to regain balance during a pirouette, we can better understand how dancers can perform multiple rotations as an aesthetically pleasing, balanced movement.

 

Thursday, February 16th - 12:05 p.m.
Sabrina Savage, NASA Goddard
Title: "Re-interpretation of Supra-Arcade Downflows in Solar Flares"

 

Abstract: Following the eruption of a filament from a flaring active region, sunward-flowing voids are often seen above developing post-eruption arcades.  First discovered using the soft X-ray telescope aboard Yohkoh, these supra-arcade downflows (SADs) are now an expected observation of extreme ultra-violet (EUV) and soft X-ray coronal imagers and spectrographs (e.g., TRACE, SOHO/SUMER, Hinode/XRT, SDO/AIA).  Observations made prior to the operation of AIA suggested that these plasma voids (which are seen in contrast to bright, high-temperature plasma associated with current sheets) are the cross-sections of evacuated flux tubes retracting from reconnection sites high in the corona.  The high temperature imaging afforded by AIA's 131, 94, and 193 Angstrom channels coupled with the fast temporal cadence allows for unprecedented scrutiny of the voids.  For a flare occurring on 2011 October 22, we provide evidence suggesting that SADs, instead of being the cross sections of relatively large, evacuated flux tubes, are actually wakes (i.e., trailing regions of low density) created by the retraction of much thinner tubes.  This re-interpretation is a significant shift in the fundamental understanding of SADs, as the features once thought to be identifiable as the shrinking loops themselves now appear to be "side effects" of the passage of the loops throught the supra-arcade plasma.  In light of the fact that previous measurements have attributed to the shrinking loops characteristics that may instead belong to their wakes, she will discuss the implications of this new interpretation on previous parameter estimations, and on reconnection theory.

 

Thursday, February 23rd - 12:05 p.m.
Margaret Trippe, University of Maryland
Title: "Our Spin On Supermassive Black Holes"

 

Abstract: In active galaxies the central supermassive black hole is surrounded by an accretion disk, which can extend to the hole's innermost stable circular orbit.  X-ray emission lines (such as Fe K-alpha at 6.4 keV) from the inner part of the disk therefore have the potential to probe the spin of the hole.  She will discuss the results of her group's work to constrain the spin of the supermassive black holes in a couple local, bright active galaxies using deep exposures from the Suzaku X-ray observatory.

Thursday, March 29th - 12:05 p.m.

Chris Reynolds - University of Maryland
Title: "How Do Black Holes Grow?"

 

Abstract: Some of the most spectacular phenomena in the Universe are powered by gas falling (accreting) into black holes.  However, the most basic question of how gas manages to fall into a black hole (shedding its angular momentum in the process) has a remarkably subtle answer.  In short, we now know that gas orbiting a black hole in an accretion disk becomes turbulent, and that the turbulence is an essential ingredient in physics that drives accretion disks, and show the results of recent supercomputer simulations of this phenomenon.  He will proceed to show how, armed with supercomputer simulations; we can begin to understand some of the complex behavior displayed by accreting black holes.

 

Thursday, April 5th - 12:05 p.m.
Engineers without Borders - Benjamin Zaczek
Title: "Engineers Without Borders: A New Perspective on Small to Medium Scale Humanitarian Projects"

 

Abstract: Engineers Without Borders (EWB) USA is the home to over 12,000 members which over the past ten years of its existence have completed over 350 projects in over 45 countries.  Its innovative practices and impact are well known and respected throughout the engineering community.  We will discuss three different projects at different stages of development to exemplify the current standing and practices in EWB.

 

Indian Solar: Solar panel implementation project that is underway in India to help a school have access to electricity to advance the education of the local populous.

 

Fish farm in Mali: A completed project with a tremulous future, a fish farm built in central-west Africa (Mali) serves to show how sometimes even the best practices and sufficient budget may not be enough to handle what is beyond your control.

 

The birth of a project in Fiji: how EWB helps guide the process of not only helping communities, but establishing partnerships and ownership for the project to help ensure its success.

 

These projects, once explored, will give oversight on the best-practices of EWB on a national, regional, and local level.  We will also touch on how individuals with any background and time commitment can become involved at the different levels.

Thursday, April 12th - 12:05 p.m.

Larry Marschall, Gettysburg College
Title: "The Transit of Venus: The Space Race of the 19th Century"

 

On June 5, 2012, the planet Venus will be silhouetted against the face of the Sun for about 6 hours. This happened 8 years ago, on June 8, 2004, but before that no one alive had ever seen this rare event, since the last times it occurred were December 9, 1874 and December 6, 1882.   Though few professional astronomers have scientific interest in the 2004 and 2012 transits, that was not the case in the past; in the 1700's and 1800's, the observation of these rare Transits of Venus was considered a matter of national importance. England sent Mason and Dixon to the island of Sumatra to observe one in 1761, even while the wars with France were raging. Captain Cook was sent around the world to observe the 1769 transit from a remote island in the South Pacific. And in the 19th Century, the superpowers, including the U.S., sent over 50 expeditions at a cost of billions of dollars, just to put observers under the shadow of Venus for a few hours. What was so important about the Transit of Venus?  Dr. Marschall will answer this question and present pictures, movies, and stories that touch not just on astronomy, but also on Emily Dickinson, the U.S. Marine Band and, - of course - the Da Vinci Code, to both entertain and to explain the significance of this once-or-twice-in-several-lifetimes event. He'll also demonstrate a program developed by Project CLEA and the National Solar Observatory that uses modern images of the 2004 transit, taken with the GONG telescopes, to reproduce the measurements of the 19th Century astronomers - in the comfort of a laptop pc. Come join us for what promises to be an entertaining, enlightening tour of the history, philosophy, and politics of 19th Century science!   

 

Thursday, April 19th - 12:00 p.m. (Stafford Lecture Room)
David Jackson, Dickinson College - RUSH HOUR TALK
Title: "Sustainability at Home: (Near) Net-Zero-Energy Living"

 

Abstract: Dickinson College just finished a month-long energy challenge where the goal was to reduce the college's energy use by 10% over the entire month compared to the previous year.  Come and see how some common-sense planning and modern construction techniques helped a local family reduce their energy consumption by approximately 90% annually.

Tuesday, April 24th - 12:05 p.m.
Senior Presentations

Morgan Cheatham and Abra Fein - "A Hohlraum Receiver for a Sun-Tracking Concentrating Solar Collector"

 

Abstract: A Hohlraum receiver is a blackbody cavity. When outfitted with a heat exchanger and mounted on a sun-tracking concentrating solar collector as a receiver, it converts solar energy into thermal energy.  The goal of this project is to design, build, and test such a Hohlraum receiver for the concentrating solar collector built by Hans Pfister and Rick Lindsey.  By placing the aperture of the receiver at the smallest focal area of the collector and by shielding the sides of the receiver with a reflective Mylar foil, the conversion efficiency of the solar collector is increased.

 

Marc Koehler and Greg Lawrence  - "An Active Thermal Storage Device Utilizing PCMs"

 

Abstract: Global climate change is by now an accepted fact.  We urgently need to find ways to reduce our CO2 emissions.  This can be done in two ways:  (i) by resorting to Renewable Energy Sources, and (ii) by increasing efficiencies in the use of energy (using less and wasting less).  One opportunity to improve energy efficiency presents itself in the climate control of our houses and buildings. For example, when a room has to be cooled, we propose to not dispose of the excess thermal energy to the outside by means of an air conditioning unit, but instead, to save the excess thermal energy in a ‘box’.  This thermal energy can then be released from the box in the evening and at night as needed.  We present here such a thermal energy ‘box,’ a device that not only reduces our carbon footprint, but also a homeowner’s heating and cooling cost. and Greg Lawrence will present "An Active Thermal Storage Device Utilizing PCMs""

Thursday, April 26th - 12:05 p.m.
Senior Presentations

Stuart Flury - "Black Holes Dining: New Insights into the Messy Eaters of the Universe"

 

Abstract: Super massive black holes that live in the centers of other galaxies are sometimes surrounded by enormous disks of gas. When this happens, black holes feed on the gas, but as they suck it in, they release huge amounts of energy. This makes these objects, which we call active galactic nuclei (AGN), some of the brightest objects known. While we thought we understood AGN fairly well, new evidence not only tells us we know far less than we thought, but that we might have to rethink the way we understand these objects as a whole.

 

Christine Welling - "Photometry of Under-Observed RR Lyrae Variable Stars"

 

Abstract: RR Lyrae stars are pulsating variables that have been used in determining the cosmic distance scale.  We have defined under-observed RR Lyrae variable stars to be those RR Lyrae stars that are missing some information in the literature, such as the period, or that have incompatible data in the literature, such as two different light curves.  GM Orionus is an RR Lyrae variable star with two inconsistent light curves existent in the literature.  I have performed CCD photometry on my own observations of GM Orionus, and have put the photometric measurements on a standard scale in order to compare my measurements to those in the literature.

 

Monday, April 30th - 4:15 p.m.
Senior Presentations

Charlie Alcorn and Ilia Papa - "An Improved TEC Receiver for a Sun-Tracking Solar Concentrator"

 

Abstract: Supported by an Innovation Transfer Network grant, during the summer of 2009, Pfister and Lindsey designed and built a model sun-tracking solar concentrator with the purpose of converting sunlight directly into electricity. The direct conversion is achieved with a Thermoelectric Converter (TEC). Unfortunately, TECs have a very small conversion efficiency of only about 10%. Therefore, while their sun-tracking solar concentrator works extremely well, the conversion of solar power to electric power is severely limited by the intrinsic inefficiency of the TEC.  –  In this research project we are trying to compensate for the inefficiency of the TEC, by placing not one, but an assembly of four TECs into the focal area of the solar concentrator. The following questions arise: (i) How can the four TECs be placed suitably into the focal area without increasing the obstruction that the receiver generates for the insolation, (ii) What is the best way to supply the heat to the hot side of each of the TECs, and (iii) How can the heat rejected by the TEC be carried away? We present here solutions to all three of these questions.

 

Derek Frymark - "V723 Cas: Light Curves of a Cataclysmic Variable"

 

Abstract: V723 Cas was discovered on August 23, 1995 by M. Yamamoto when it flared up as a classical nova. The star was determined to be part of a binary system known as a cataclysmic variable and the nova was the result of the burning-off of excess hydrogen that had accreted onto V723 Cas from its sub-giant companion star.  Data taken on V723 Cas at Lowell observatory showed an asymmetric light curve in the B, V, and R filters, which was suggested by previous research to be the result of a hot spot on V723 Cas’ accretion disk. Further, the shape of the light curve has been evolving, indicating that the hot spot may be cooling or is being partially covered by warping of the accretion disk. This data has been supplemented with additional data taken at Lowell observatory as well as at the Britton observatory.

 

Michael Ryan - "Misbehaving Photon Measurements"

 

Abstract: The quantum optics lab provides equipment to measure single photon coincidences, which occur when pairs of single photons enter the detectors at the same time.  Previous work by Professors Brett Pearson and David Jackson showed an unexpected tail on measurements of the correlation coefficient, which describes how many coincidences actually come from twin photons, and which is expected to fall off very steeply.  This paper describes an investigation into the existence and causes of this tail.  We were able to verify the presence of the tail to several standard deviations with a reproduction of the same setup originally used.  In addition, we have been able to isolate the phenomenon to either the single-photon counting module or an unexpected quantum effect.  We suspect the module is to blame but are unable to verify.

 

Thursday, May 3rd - 12:05 p.m.
Physics New Majors Induction Ceremony

Come meet the newest members of the Physics & Astronomy Department!  Listen to the seniors as they introduce each student and learn something interesting and funny about each one.  Pizza will be served first, followed by the introductions, and finally CAKE!