Fall 2013 Physics Colloquium
Colloquium Fall 2013
Thursday, September 5th
Welcome to the Department by Physics & Astronomy faculty
Professors Pfister, Smith, Pearson, Boyle & Jackson
Tuesday, September 17th
Dr. Tom Greenslade
One day in my early teens my father sat me down and gave me the talk – about electronics! Under his guidance I was soon developing a technique for transmitting music on a light beam, building my first crystal sets, and beginning to understand how vacuum diodes and triodes worked. Later, when I took the electronics course in my junior year of college, I was introduced to more sophisticated vacuum tube electronics, which culminated in my senior honors project: a secondary frequency standard that weighed 100 pounds. Today you might wear this device on your wrist, – if you are old-fashioned. Let me introduce you to my early world of crystals, diodes and triodes.
Thursday, September 26th
Dr. Dave Crandall, Department of Energy (retired)
"Why Should You Care about Nuclear Fusion?"
Three quick answers to the title’s question: fusion energy will be a topic of discussion for your entire life; the science and engineering challenges in obtaining sustained fusion on earth are interesting; fusion connects to nearly all science in part because it is the fuel for the universe, powering all stars. The talk will define fusion and how it works in stars. The current efforts to sustain inertial and magnetic fusion in the laboratory will be summarized. The talk will describe in some detail the most interesting endeavor right now, the attempt to reach inertial fusion ignition at the National Ignition Facility in Livermore, California using the world’s largest laser to drive explosion of a tiny fusion fuel target. The world’s largest fusion endeavor, the International Thermonuclear Experimental Reactor (ITER) under construction in Cadarache, France, will be outlined along with the magnetic confinement of plasma that it will rely on. Connections of these fusion concepts to astrophysics and materials science will be described. Why fusion energy is so attractive and so elusive will be discussed. This is a general talk on fusion science and energy.
Thursday, October 10th
Dr. Clint Sprott, University of Wisconsin
"Self-Organization - Nature's Intelligent Design"
Complex patterns are common throughout nature, from the distribution of the galaxies in the Universe to the organization of neurons in the human brain. It is generally assumed that such complex structure must have a complex cause, but it may be that the patterns spontaneously arise through the repeated application of simple rules. This talk will provide examples of self-organization in nature and will describe six simple computer models that can replicate the features of these patterns. The models typically produce fractal spatial structure and chaotic temporal dynamics characterized by power laws and unpredictability, even when the models are simple and purely deterministic. The work has application to fields as diverse as physics, ecology, political science, economics, sociology, and art.
Thursday, October 17th
Memorial Service for Rick Lindsey
Tuesday, November 12th
Dr. Christopher Kerestes '04
"Photovoltaic Solar Cells: From Single Junction Silicon to Quantum Dot Triple Junction"
Technological advances and applications of solar cells have increased dramatically over the past 60 years. Early development focused on single junction solar cells whose initial implementation was to provide low levels of power for cell phone repeaters. More recent developments aimed at high efficiency have focused on multiple junction solar cells that provide hundreds of kilowatts to satellites and over 100 MW for a single terrestrial photovoltaic energy farm. This talk will review the basic operation and fabrication of single junction silicon solar cells. From the basic operating principles of photovoltaic devices reasoning behind high efficiency designs will be examined. Focus in high efficiency is given to recent work performed with quantum dot solar cells and their enhancements for space and terrestrial photovoltaic systems.
Meal to follow in the HUB Social Hall - for those who signed up in advance
Thursday, November 14th
Eleanor Sayre, Kansas State University
"Thinking like a Physicist: What is it, and How Can We Tell?"
A major goal of undergraduate education in physics is fostering "thinking like a physicist" among physics majors. This is an elusive goal, and one that is hard to assess in our physics classes. In this talk, I'll discuss what we mean when we say "thinking like a physicist" and present some discourse markers for identifying when students are more likely to be physicist-like. I suggest instructional strategies to promote students thinking like physicists, and ways we can assess this in our upper-division physics classes.
Thursday, November 21st
Olivia Wilkins, NRAO Internship
"Life in the Quiet Zone: Living in Green Bank and the Research Experience"
“Life in the Quiet Zone” discusses the experiences associated with living in the National Radio Quiet Zone (NRQZ), home to the National Radio Astronomy Observatory (NRAO). It also describes the bridges among science disciplines in a research field that is comprised primarily of physics, astronomy, and engineering students from large research universities. It delves into the specifics of a research assistant project at NRAO—HI absorption against pulsars—which focused on calculating the distance between our solar system and neutral hydrogen gas in the Milky Way. The goal of this research was to determine the source of turbulence within the galaxy by exploring various factors, including star formation and the rotation of the galaxy, which was done using the Robert C. Byrd Green Bank Telescope (GBT)—the largest fully-steerable radio telescope in the world.
Monday, December 2nd @ 4:30 p.m.
Senior Research Talks
Justin Brown - "Photometry of the Under-Observed RR Lyrae Star: GM Orionis"
GM Orionis, a star located in the Orion Constellation, is an RR Lyrae variable star meaning it should be a star with a regularly changing magnitude. Previous photometric observations show that this is not the case. In the last hundred years, observations have shown an inconsistency in the star's observed brightness, while the amplitude of variability has remained constant. Research this semester was aimed at determining if this trend is accurate partially by figuring out if it is still occurring.
Byron Tannous and Michael Vecchio -"Design of a Heliostat for Active Lighting"
Heliostats are typically used in large concentrating solar power plants, known as heliostat power plants, or central tower power plants. Here hundreds of large, flat mirrors are moved in synchrony to reflect sunrays to a predetermined area on a receiving tower where the solar energy is used to melt a salt, such as sodium nitrate and potassium nitrate, or to heat liquid sodium. The thermal energy in this working medium is then used to operate a turbine and electric generator. In our application we use a heliostat to redirect sunlight not toward a tower but toward the northern side of a house or building. By aiming the heliostat at one or more windows of the building the rooms associated with the windows are being illuminated with natural sunlight.
We present here a design for a heliostat, which accurately tracks the sun's diurnal and seasonal motion by creating sharp shadow lines. Four light-dependent resistors (LDRs) are located adjacent to the foot of a small, square prism. If the prism is directed toward the sun, no shadow is being cast, all four LDRs receive the same amount of light, and no motion is necessary. As the sun moves west, for example, a shadow is cast on the eastern LDR, and the motor connected to the tracking unit receives a signal to move the tracking unit until both the eastern and western LDR are again illuminated equally. As the tracking unit moves through an angle , the mirror of the heliostat moves through an angle of /2. While most heliostats use three gea-rs to obtain the angle division, we have achieved the angle division using merely two gears. To obtain the most cost-effective tracking unit we have explored two principally different electronic approaches: (i) using an Arduino Uno single-board microcontroller receiving its input signal from the four LDRs and transmitting its output signal via solid state relays and an H-bridge to the azimuth and altitude motors, and (ii) discrete electronic components such as comparators, potential dividers, and solid state relays to activate the alt-az. motors. Our 2nd approach saves electric power by turning itself on only when the sun shines, i.e., only when tracking is required.
Yike Li - "Characterization of Ultrashort Laser Pulses using Two-Photon Absorption in a Photodiode"
Ultrafast (or ultrashort) lasers generate electromagnetic pulses with time durations on the order of femtoseconds (10-15s). Such short pulses with high intensities produce nonlinear interactions with a variety of materials, which allows time-resolved study of ultrafast processes. Because ultrafast lasers are widely used in spectroscopy and biological microscopy, the characterization of ultrashort laser pulses has great significance in improving these techniques. In this senior research project we experimentally characterize the two-photon response of a Gallium Phosphide (GaP) photodiode by using a femtosecond laser. The two-photon-induced photocurrent in the GaP photodiode is measured as a function of the incident light power. The linear and nonlinear dependences of the photocurrent on the incident light power are investigated. Further analyses will provide clearer information on the nonlinear components of the signal.
Tuesday, December 3rd @ 4:30 p.m.
Senior Research Talks
Eli Blumenthal and Kylie Logan - "Investigation of the Effect of Mass Flow Rates on the Efficiency of a Cost-Efficient Solar Air Heater"
Climate scientists have long recognized the reality of global climate change and pointed out the catastrophic effects that our fossil fuel consumption may have on our planet in the near future. Affordable, practical, renewable, and efficient modes of energy production offer an alternative to the perilous energy habits that we currently maintain. A Solar Air Heater (SAH) is one such device that converts solar energy into thermal energy, which can then be used, e.g., for supplemental space heating, drying applications, or desalination. Our investigation aims to improve the efficiency of the SAH developed at Dickinson College while maintaining a short Return on Investment (ROI) period. The energy conversion efficiency of a SAH depends, among other things, on the mass flow rate through the device. Our focus this semester centers on finding the optimal mass flow rate. We achieve this by using an in-line fan and varying the airflow speed from 0.7 m/s to 2.4 m/s. We present here the data and our findings obtained in daylong measurements with our SAH over the course of this past semester.
Ryan Lane - "Modeling the Evolution of the Classical Nova V723 Cassiopeia"
A long time ago in our galaxy far far away…the classical nova V723 Cassiopeia (V723 Cas) experienced a sudden thermonuclear outburst, a process by which hydrogen-rich material is accreted onto the surface of a white dwarf and ignited. Observations of the binary system from the last decade suggest that V723 Cas is still emitting in the X-rays as a Super-Soft-Source (SSS). Consequently, it has been hypothesized that V723 Cas has evolved into a permanent SSS and thus has begun its approach to the Chandrasekhar limit. For this reason V723 Cas has been closely followed since its original eruption. Here we present photometric data over a span of seven years (2006 through 2013) taken with the 31" telescope at the National Undergraduate Research Observatory (NURO) in Flagstaff, Arizona. A photometric analysis of the data produced light curves in the optical bands. Modeling of the binary system was also performed using the eclipsing binary star simulator Nightfall for comparison with observations.
Justin Kiehne and Shane Mitchell - "Experimental and Theoretical Characterization of a Latent Heat Storage Device"
Phase change materials (PCMs) are sometimes used in residential construction to increase energy efficiency of buildings and reduce heating and cooling costs. By providing a passive means of latent heat storage, PCMs enable low cost and low maintenance thermal regulation. A portable, self-contained latent heat storage device was constructed utilizing commercially available microencapsulated PCMs for use in residential thermal regulation. The performance of the device was tested experimentally and theoretically during PCM charging and discharging to characterize heat storage capability and efficiency of the device. A variable speed inline fan served to control the mass flow rate and heat was supplied by a portable ceramic infrared heater. Rate of energy transfer and total latent heat storage capacity were determined for several flow rates.
Thursday, December 5th @ 4:30 p.m.
Senior Research Talks
Ellie Was - "An Experimental and Mathematical Thermal Cooling Model for Subaqueous Pillow Lavas"
Subaqueous, or underwater, lava forms by unique processes that distinguish its cooling history from that of subaerial (land) lava, including the formation of an insulating glassy rim and a steam envelope around the lava. A thorough understanding of these processes is required to effectively infer lava flow dynamics, including eruption rates and diffusion of heat through a molten, non-steady state body. In this study, small pillow lavas-subaqueous lava tubes-are created at Syracuse University by pouring basalt melt along a moderately sloped ramp into a tub of water. High-temperature thermocouples are used to take temperature data at the center, rim, and directly between the center and rim of the flow. A beaker of sand and a solid glass cylinder have been heated and tested in a similar manner to serve as analogues to the Syracuse experiments and to infer the applicability of relevant mathematical models including finite element techniques and variations of the heat equation. By employing the proper parameters associated with the experimental materials, including diffusivity, the experimental data appears to correlate well with the established mathematical models. A quantitative understanding of the physics of heat transfer through subaqueous lava promotes a deeper understanding of lava flow dynamics than what currently exists, and will be useful in interpreting conditions of ancient lava flows and properties of basaltic materials used commercially for insulation.
Sophia Acevedo and Olivia Lanes - "Double Photon Ghost-Interference"
This semester we investigated the fundamentals of quantum optics leading towards our final goal of experimentally observing “ghost” interference. Ghost interference is an interference pattern created by a double slit, but astonishingly, appearing in the path of an entangled photon beam that does not contain a double slit. The only way this phenomenon can be explained is through entanglement and superposition. In the beginning of the semester, we had to add a new line for the laser to follow into a detector that we mounted on a translation stage. Once this was in place, we conducted multiple trials and tests with both the red, visible laser, and the invisible down-converted light. All of these steps are crucial in reaching our end goal. After successfully measuring patterns from both lasers, and calculating the exact measurements we need for path length and slit width, we are ready to conduct our final experiment.