Spring 2017 Physics Colloquium
Thursday, March 23rd
Douglas J. Jerolmack, University of Pennsylvania
"Creepy landscapes and critical points: how rivers and hillslopes behave like glass"
Soil on hillslopes slowly and imperceptibly creeps downhill, but suddenly liquefies to produce landslides. The transition between creeping and flowing is a critical point, often defined in terms of the shear stress, that depends on the characteristics of the soil and the geologic environment. We show that the nature of this transition, however, is general. Creep is the localized and erratic motion of soil grains below the critical point; because this kind of fragility is a generic consequence of disorder (no minimum energy state can be achieved because there is no crystal), soil creep should be similar to amorphous glass. Indeed, we find that the transition from creeping to landsliding is a continuous phase transition that follows predictions from glass transition models. The generality of this transition suggests that the onset of sediment transport in rivers should behave in a similar manner, and we demonstrate that this is the case using laboratory experiments and simulations. Because the sediment transport rate rapidly increases for stresses above critical, many landscapes such as rivers organize to be close to the critical point. In essence, landscapes flicker back and forth across the glass transition. We show that this critical behavior has consequences for how landscapes respond to external forcings such as climate. In particular, self-organization of near-critical river channels filters the climate signal evident in discharge, blunting the impact of extreme rainfall events on landscape evolution
Thursday, March 30th
Tom Solomon, Bucknell University
"One-way barriers that block reaction fronts and swimming organisms in laminar fluid flows"
We present experiments on the effects of vortex-dominated flows on the spreading of the excitable Belousov-Zhabotinsky chemical reaction and on the motion of bacteria. The results of these experiments have applications for a wide range of systems including microfluidic chemical reactors, cellular-scale processes in biological systems, and blooms of phytoplankton in the oceans. To predict the behavior of reaction fronts, we adapt tools used to describe chaotic fluid mixing in laminar flows. In particular, we propose "burning invariant manifolds" (BIMs) that act as one-way barriers that locally block the motion of reaction fronts and "smooth swimming" bacillus subtilus. These ideas are tested and illustrated experimentally in a chain of alternating vortices, a spatially-random flow, vortex flows with imposed winds, a three-dimensional, nested vortex flow, and a hyperbolic microfluidic flow.
Wednesday, April 12th
(poster titles & abstracts due by April 5th - email firstname.lastname@example.org)
HUB Social Hall
Monday, April 24th
Physics Research Presentations
Michelle Orden ‘17 - “Modeling the Cooling of Pillow Lavas and their Fracture Patterns”
Pillow lavas are lava morphologies that form when molten lava comes in contact with ice or water, causing it to cool as a bulbous structure. Looking at the cross-sections of pillow lavas found in Southwest Iceland, we have investigated fracture patterns formed during this cooling process. Among the fracture patterns, we have identified seven end-member characteristics: fractures propagating radially from the pillow edge to the core (5-10cm), fractures on the outer edge (2-4cm), fractures between the edge and core, horizontal fractures, fractures inside the core, fractures propagating from the outer edge through the core, and ‘web-like’ fractures. We have also recorded data on pillow size and fracture spacing at various points on the pillow lavas. Using the discretized Heat Equation we have created an Excel based computer simulation that predicts the change in temperature at thousands of locations across the cross section of a pillow lava as it cools in time. Using this model in tandem with Young’s Modulus and known properties of basalt and ice, we have produced a mathematical model that predicts when and where fractures originate as well as where the fractures will propagate in time. This model can be easily manipulated to fit many different sets of emplacement conditions. More recently, we have created a new thermal model based on the solution to the Heat Equation in cylindrical coordinates. This model allows us to determine analytical solutions for temperature as a function of radius and time, allowing us analyze the fractures in a more accurate manner. Both thermal models have the potential to be manipulated and used in fields such as engineering or other geosciences in order to better understand when and why
certain materials fracture.
Tyler Richey-Yowell ‘17 - “Characterizing Short Period Eclipsing Binaries in the Field of NGC 2362”
We present light curves of seven previously unknown and two scarcely-covered eclipsing systems in the field of the young (t ~ 5 Myr) cluster NGC 2362. These light curves represent binaries of the Algol, Beta Lyrae, and W Ursa Majoris types. Some of these stars show signs of the O’Connell effect, caused by either hot spots or circumstellar material. The light curves have been modeled in Binary Maker 3.0 and have been used to determine the characteristics of these binary systems (i.e. mass ratio, temperature, fillout, disk and spot parameters) for stars of each type. The results of the models support current evolutionary theories regarding eclipsing binary star systems and shed light onto sources of the O’Connell effect and why it is seen most in certain evolutionary stages.
Jacob Grant ‘17 - “The Unexpected Behavior of Variable Stars: GM Ori & V723 Cas”
The star systems GM Ori and V723 Cas are officially classified as a RRc Lyrae and a cataclysmic variable, respectively. However, recent studies have shown odd behaviours in both systems, causing them to behave in ways not normally seen in stars of such classification. GM Ori, a pulsating variable, is supposed to behaving via the k-mechanism and continue a very strict routine, keeping the same average amplitude and magnitude throughout its lifetime. However, our recent findings seem to suggest that it is instead getting brighter over time. Meanwhile, V723 Cas, a binary variable, is supposed to be in the stage in its life known as pre-maximum meaning it will soon become a novae. Instead our findings reveal a significant change in amplitude in B, V, and R filters and a dramatic decrease in magnitude in the R filter suggests a near to complete halt in mass transfer.
Cameron Ruhl ‘17 - “Complexity from Simplicity: Observations of the Nonlinear Dynamics of Driven, Vertically Hanging Chains”
While the usual study of oscillating strings involves that of a transversely oscillating, horizontal string fixed at both ends, the situation explored in this project is of a string fixed at a single point of suspension hanging freely under gravity when it is driven horizontally or vertically. These relatively simple mechanical scenarios, result in behaviors of varied complexities, from rod-like/planar pendulum-like motions to types of rotational and chaotic motions, with several regions of stability/instability and many different transition boundaries. The motions of these chains are experimentally determined at several positions along their length, using high speed photography and video analysis, and then compared to numerically calculated results from different theoretical models in various regimes of the parameters: chain length, driver amplitude, and driver Frequency. Extending these characterizations, regions previously found to have complex behavioral states were sampled again for the vertically driven case. This sampling identified evidence of both self-knotting and stellate behavior. Moreover, a characterization of the parameter space for the vertically driven scenario with an additional fixed boundary condition imposed on the chain was performed. This characterization revealed even more complex and interesting behavioral dynamics than the simpler “free” scenario. Another aspect of the project was to gather, design, or make the apparatuses, information, and tools needed to describe and characterize the various behaviors of driven freely hanging vertical chains. The goal being to create a new senior research capstone project for future students that focuses on the resonance and chaotic behavior of driven mechanical systems, with different imposed constraints.
Tuesday, April 25th
Physics Senior Presentations
Eli Laue & Troy Thornton - “A Comprehensive Solar Air Heater Research Station for the New Senior Capstone Experience”
In accordance with the new direction of the senior seminar, we aim to create a comprehensive capstone project that involves state-of-the art research on a solar air heater. Solar air heaters (SAHs) have a very high potential for use as sustainable, efficient, and affordable sources of heat. They consist of an insulated box, possibly filled with materials of high thermal conductivity, covered with a clear glazing, through which air is pushed and heated. At an entry level SAH research does not require extensive background knowledge, allowing any professor to advise such a project and permitting students to engage with the material expeditiously. Furthermore, a SAH leaves room for endless possibilities of modification, increased complexity, and extensive research of various aspects of the device. The SAH's versatility allows for it to be studied with foci in multiple different concentrations, such as fluid dynamics, thermodynamics, materials physics, and even interdisciplinary fields such as environmental science. Finally, research may be done not only experimentally, but also theoretically and through computer simulations. Our goal is to create a cohesive research station, instructor’s manual, and student manual that addresses all these criteria to allow the whole research team to start promptly and maximize their time for research in senior seminar.
Harry Swanson - “Simulating the Orbital Dynamics of Accretion”
Accretion is a prominent aspect of many astrophysical bodies, from stellar nurseries to quasars. Utilizing the programming Language Python 2.7, various codes were created to model satellites orbiting stellar bodies. As an elementary programmer, the codes began with intense simplicity with gradual increase in complexity. Each of these codes is a step on the journey of creating a final simulation that accurately depicts inelastic collisions and the formation of an accretion disk surrounding a supermassive object.
Justin Gardner - “Upgrading the Britton Observatory at Dickinson College: Installation of a New CCD and Filter Wheel Assembly and the Automation of Observatory Routines”
A new CCD camera, filter set, and filter wheel assembly have been installed on the 24-inch telescope in the Britton Observatory. To accommodate the new CCD, novel telescope mounts needed to be designed and machined. Once mounted, the CCD was calibrated, connected to the data acquisition computer, and proper communication between the two was validated. The new filter wheel has auto-guiding capabilities, which enables high-precision tracking during long exposures. High-precision tracking allows for accurate timing of events such as the ingress or egress of a planetary transit, or the determination of an orbital period of a binary system. In an attempt to make observing runs using the Britton Observatory more efficient and streamlined, steps have been taken to automate some of the tasks currently necessary to acquire accurate astronomical data for research. These steps include auto-guiding, data reduction, and airmass calculations. The data reduction program processes the raw data and removes systematic noise. Aside from initial parameter setup usually a simple GUI this process is fully automated. Airmass values, which represent the amount of Earth’s atmosphere an object is seen through, are necessary for accurate transformations from instrumental to standard magnitudes. The airmass is calculated based on the coordinates of the observed object and the time of exposure. It is shown that near the zenith the airmass can be approximated, simplifying calculations. Far from the zenith, however, a different approach is used to account for the nature of a spherical shell. The object name, coordinates, and airmass are all appended to the image header.
Stafford Lecture Room
Thursday, April 27th
Physics Senior Presentations
Kevin Skowronski, Sean Jones & Jacky Han- “Exotic Chaos: Exploring the Correlated Dynamics of Coupled Logistic Map Circuits”
Chaos has by now been examined in many physical systems. However, it is difficult to find suitable experiments that mimic time-discrete iterative maps, commonly used to introduce the study of chaos to undergraduate students. Our research is based heavily on work previously done by L'Her et al. (2016) involving a circuit that reproduces the logistic map function. This circuit operates discretely and can demonstrate behaviors such as period doubling, a type of bifurcation, and the onset of chaos. We proceed to build a larger system, which couples two logistic map circuits, representing a pair of coupled logistic map equations. We test for aspects of chaos in this system and observe exotic phenomena we call "almost synchronized" and "antisynchronized" chaos. These experimental results are supplemented by numerical simulations, which demonstrate good agreement. Providing undergraduate students with the ability to experience a tangible representation of the behaviors of chaos can allow for an accelerated learning process of the subject matter.
Megan Hansen - “Experimental Analysis and Theoretical Projection of Greenhouse Thermal Performance Following Installation of a Solar Air Heater and Phase-Change Material-Based Heat Storage Device”
Much of the scientific research exploring solutions to the global warming crisis, while imperative to our future, is unlikely to yield feasible and affordable technology within the near future. In the meantime, relatively cost-effective renewable energy sources should be popularized and utilized as much as possible. The objective of this project is to determine the energy savings to Dickinson’s Kaufman Greenhouse (KGH) if it were to incorporate inexpensive thermal energy-capturing devices - namely, a solar air heater (SAH) and a phase-change material (PCM). A SAH collects additional solar energy, increasing the overall thermal gain of the KGH. But more importantly, this additional thermal energy obtained with the SAH can be stored in a PCM (high latent heat of fusion and specific heat capacity) diurnally, and later released over the course of the night. Preliminary theoretical simulations predict changes in thermal energy gains and retention resulting from the integration of a SAH and/or PCM storage device into the KGH. Calculations take into account fluctuations in solar intensity, altitude, and azimuthal angles, as well as conductive, radiative, and convective heat losses. The experimental aspect involves constructing four greenhouse models cross-sectionally proportional to the KGH, each equipped with either a SAH, a PCM, both, or neither. Internal greenhouse temperatures, ambient air temperature, and light intensity are recorded and used to calculate thermal energy losses and gains for the models. Results are compared with the theoretical predictions and extrapolated to reveal how these devices could improve thermal performance of the KGH, and ultimately further contribute to Dickinson’s sustainability efforts.
Emily Whitaker & Amanda Ratajczak - “Where do Particles of Different Sizes Accumulate on Gravity-Capillary Waves?”
Previous works have found that micro-scale surfactant molecules tend to accumulate in the troughs of standing Faraday waves, and that macro-scale polystyrene particles tend to accumulate on the nodes or antinodes of these same waves. These varying accumulation behaviors suggest the existence of some size-based threshold—which we are aiming to identify—at which the particles’ accumulation location along the Faraday waves shifts. We used vertical sinusoidal oscillations to induce standing Faraday waves in water, and observed the system’s response using a high-speed camera and data that was taken by accelerometers attached to our shaker and processed in LabVIEW.
Thursday, May 4th
Physics Majors BBQ
Tome Backyard (outdoor classroom area)
Rain Location: Tome 115 & Tome 1st Floor Lobby