Spring 2014 Physics Colloquium
Thursday, March 27th
Dr. Jeff Groff, Shepard University
"The Stochastic Physics of Cells"
In the macroscopic word, convection and advection are more significant than diffusion when it comes to the transport of matter from one place to another. On the other hand, diffusion and random, uncoordinated molecular motion are very consequential phenomena to cellular machinery. Cells have evolved to exist in the context of this randomness and even use it to their benefit. This talk will discuss the physical importance of diffusion in the microscopic world and the role of random, uncoordinated molecular motion in cellular processes drawing on examples from his research including computational studies of intracellular calcium signaling and neuronal communication.
Thursday, April 4th
Dr. JiaJia Dong, Bucknell University
"Applications of Nonequilibrium Statistical Mechanics "
Statistical mechanics (SM) for systems in thermal equilibrium, founded over a century ago, forms part of the current physics core curriculum. However, like most homework problems do not directly apply to real situations, textbook equilibrium SM falls short of characterization of systems in non-equilibrium (NE), such as biological systems. An overarching theoretical framework of NESM remains elusive and has been attracting increasing interest from physicists.
In this talk, I first contrast the key features of NESM with the familiar ESM. To illustrate how tools developed in NESM help untangle the complex biological process, I then zoom in on modeling protein synthesis in bacteria through a particle transport model (the totally asymmetric simple exclusion process, or TASEP). Quantitative effects of different elongation rates, associated with different codons, on the overall protein production rate are to be discussed. I conclude with some ongoing projects and open questions that nestle on the interface of physics and biology to set the stage for further investigation in this field.
Monday, April 21st
Senior Physics Research Talks
Justin Brown - "Observations of Under-Observed RR Lyrae Star: GM Orionis"
We report photometric observations of the under-observed RR Lyrae
variable star GM Orionis. Earlier observations show an inconsistency in the
star’s observed brightness, while the amplitude of variability has remained
constant. We show and discuss standardization of photometry that has
been collected over a three-year period demonstrating a continued increase
Ellie Was - "How Cool is Your Pillow? Geology and Physics to Investigate the Formation of Subglacial Pillow Lava"
Subaqueous, or underwater, lava forms by unique processes that
distinguish its cooling history from that of subaerial (land) lava, including
the formation of a pillow-shaped lava tube surrounded by an insulating
glassy rim and steam envelope. A thorough understanding of these
processes is required to infer lava flow dynamics, including eruption
rates and diffusion of heat through a molten, non-steady state body.
In this study, a cylindrical glass container of moderately well-sorted
quartz sand is heated in an oven and measured with thermocouples to
serve as an experimentally well-controlled analogue to natural pillow
lava. Data is also used to test a variation of the heat equation in
cylindrical coordinates that has been discretized in a new MATLAB
numerical model program. By employing the proper thermal diffusivity
and boundary conditions, MATLAB output correlates closely with the
experimental data. Such a quantitative understanding of the physics
of heat transfer through subaqueous lava promotes deeper
understanding of lava flow dynamics than what currently exists,
which is useful in interpreting conditions of ancient eruptions
and properties of basaltic materials used commercially for insulation.
Yike "Echo" Li - "Characterization of Ultrashort Laser Pulses Using Two-Photon Absorption Photodiodes"
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
commercial Gallium phosphide (GaP) photodiode and a handmade
photodiode by using a mode-locked ultrafast laser. The second-order
nonlinear responses of the photodiodes are investigated and compared
to each other. The handmade photodiode has shown a better second-order
response and can be further used for autocorrelation of the ultrashort laser pulses.
Tuesday, April 22nd
Senior Physics Research Talks
Olivia Lanes & Sophia Acevedo - "An Attempt to Observe Twin Photon Ghost Interference"
For the 2013-2014 academic year, we searched for experimental
evidence of Ghost Interference. Ghost Interference is double-slit diffraction
seen in a beam of entangled, down-converted light that does not pass through
a double-slit apparatus. This is possible through the quantum phenomenon
of entanglement. When a high energy photon beam is split and down-
converted through a nonlinear crystal, the resulting beams become entangled.
Creating an interference pattern in one beam by having it pass through a
double-slit apparatus will make it seem like its partner passed through the
slits as well. In order to validate our claims, we ensured that we were dealing
with single, entangled photons from a BBO crystal through correlation
measurements. We then created two paths for the entangled photons
–one path allows a photon beam to pass through a custom double-slit
aperture andthe other path does not manipulate the photon beam in any
way. We studied the patterns created from the double-slit in both paths and
examined our data theoretically in order to understand how and why
these non-classical descriptions of nature are possible.
Ryan Lane - "The Evolution of the Cataclysmic Variable V723 Cassiopeia"
On August 24th 1995, 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. The data analyzed here reveal an asymmetric light curve, the
overall structure of which exhibits a decrease in magnitude from year
Eli Blumenthal & Kylie Logan - "Dependence of the Conversion Efficiency of a Gridded Solar Air Heater on Mass Flow Rate and Grid Number"
Solar Air Heaters (SAHs) convert solar energy directly into
thermal energy. Sunlight enters the SAH through a double-layered
glazing and is then absorbed by a series of blackened aluminum
grids. Cold ambient air is then blown through the now hot grids,
becomes heated, and emerges from the other end of the SAH.
This hot air can be used, for example, to heat the room of a
house, a garage or a shop, to dry food, or to desalinate water.
Each joule of thermal energy produced by the SAH is one joule
of energy that we do not have to obtain by burning a fossil fuel.
The energy conversion efficiency of a SAH depends, among
other things, on the mass flow rate through the device and
the number of absorbing grids inside it. The research
presented focuses on finding the optimal mass flow rate
along with the optimal number of grids. Using an
in-line fan and varying the airflow speed from 0.7 m/s to
4.2 m/s we find an optimal airflow speed of 1.6 m/s. Using
this optimal airflow speed, we vary the number of grids
inside the heater to find the peak efficiency for n grids,
giving our SAH a solar to thermal conversion efficiency of
about 80% and a return on investment time of less than
Rector - Stafford Lecture Room
Thursday, April 24th
Senior Physics Research Talks
Byron Tannous & Michael Vecchio - "Autonomous Heliostat Design for Natural Room Lighting"
Heliostats are typically used in large concentrating solar
power plants (known as heliostat power plants), or central tower
power plants. We have designed and constructed an autonomous
heliostat, which redirects sunlight toward windows of a house or
building, illumination their respective rooms with natural sunlight.
Our heliostat accurately tracks the sun’s diurnal and seasonal motion
by creating sharp shadow lines onto four light-dependent resistors
(LDRs). These LDRs are located adjacent to the foot of a small,
rectangular prism attached to the body of the heliostat. If the
prism is directed toward the sun, no shadow will be cast, and
all four LDRs receive the same light intensity. This equality of
light intensity on each LDR indicates proper heliostat alignment.
Our circuit design will only actuate the heliostat’s tracking motor
if the sun shines and the heliostat is misaligned, i.e., if there is
an inequality of light on opposing LDRs. Our design explores
two principally different electronic approaches: (i) an Arduino
Uno single-board microcontroller, and (ii) an in-house
constructed circuit incorporating discrete electronic components
such as comparators, potential dividers, and solid-state relays.
Although the Arduino is a powerful and particularly elegant
environmental interfacing platform, we strive to create a
comparably advantageous circuit.
Shane Mitchell & Justin Kiehne - "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, May 1st
Physics New Majors Induction Ceremony & BBQ
Tome Hall Back Yard (Rain Location: Tome 115 & 1st floor)
BBQ food provided