The Physics and Astronomy Department at Pomona has extraordinary access to research equipment and facilities, and we encourage our students to undertake research. Below are recent projects that students completed via Pomona's Summer Undergraduate Research Program.
Fabrication and Characterization of Thin-Film OFET and OLED Devices
Ricardo Espinoza ’19; Advisor: Janice Hudgings
Currently, modern electronics is based on metal-oxide semiconductors, silicon most abundantly; however, organic semiconductors have tremendous benefits in both manufacturing time and costs. In addition, certain electronic devices made from organic semiconductors may be biocompatible, opening new avenues for biological sensor technologies. The shortcoming of these organic semiconductors is that they have yet to achieve the efficiency standards of their inorganic counterparts. In an effort to explore ways to improve devices made from these compounds, tests were conducted on field-effect transistors coated with a poly (3-hexylthiophene) (P3HT) active layer. IV curve measurements were obtained from several devices and charge-carrier mobility was determined. The second set of tests were conducted on LEDs made with one of two semiconducting organic active layers: poly (ethylene fluorene) and a newly synthesized carborane-based compound, poly (bisfluorenyl carborane-co-dihexyl fluorene). IV curves were generated to determine the functionality of the devices. Electrically, most of the devices showed signs of good conductivity. There was much variation in the data and some devices did not perform as expected. The next steps will be to construct devices for MARS imaging, which will allow us to map out the charge carrier distribution on the surface of the device and analyze where the densities of charge-carriers are on the device and how we can facilitate the mobility of charge through it.
Funding Provided By: Paul K. Richter and Evalyn E. Cook Richter Memorial Fund
Demystifying High Temperature Superconductivity: An ARPES Study of Cuprate Hg1201
Ben Gregory ’18; Advisor: Scott Medling
Since their discovery in 1986, high temperature superconductors (HTS) have been an active area of research as their underlying physics cannot be accounted for by our conventional theory of superconductivity. The cuprates comprise one of the major HTS families and have been studied extensively with many experimental techniques. Angle-resolved photoemission spectroscopy (ARPES) is an ideal tool for probing the electronic band structure of advanced materials since it can simultaneously measure the energy and momentum of photoemitted electrons. With the highest Tc in the cuprate family, HgBa2CuO4 (Hg1201) has been the subject of much research, yet it remains understudied with ARPES for lack of a charge-neutral cleavage plane. Here we have studied underdoped Hg1201 with ARPES to first and foremost place its properties in the greater context of the cuprate family and to ultimately elucidate the origin of its record Tc. We have accessed the antinodal region of the Fermi surface, allowing us to calculate the Luttinger volume and thus the doping of the material. Additionally, it has been suggested that Hg1201 shows a Fermi liquid-like behavior indicated by a quadratic resistivity. We explored the temperature dependence of the quasiparticle scattering rate and obtained early results that are consistent with this Fermi liquid hypothesis. Upcoming experiments will seek to characterize spectral broadening as well as probe the mysterious pseudogap.
Funding Provided By: The Elgin Fund for Summer Student Research
Characterizing the 300km/s Stream Near Segue-1 Using Survey Data
Wanying Fu ’19; Advisor: Philip Choi
The characterization of stellar streams in the Milky Way halo provides important observational constraints on the LCDM cosmological model, which posits that galaxies form via the accretion of smaller satellites. One such stream, the 300 km/s stellar stream near the dwarf galaxy Segue 1 (300S), was detected in narrow-field spectroscopic surveys, but has not been traced over a wider portion of the sky. In this study, we search for members of 300S in survey data to map out the stream's extent and further characterize its progenitor. We add to the existing catalog of 300S stars by finding new members of 300S in SEGUE-1, SEGUE-2, and APOGEE-2 survey data, and confirm the kinematic association of 300S with an elongated substructure found in both SDSS and PanSTARRS photometric data. From chemical abundance data and a measured stream velocity dispersion of 5.4 km/s, we infer that the progenitor of 300S is a dwarf galaxy. We analyze the chemical abundance data of 300S stars to characterize the stream progenitor’s star formation history, and compare 300S chemical abundances with that of other Milky Way components to infer satellite accretion scenarios.
Funding Provided By: Craddock-McVicar Summer Undergraduate Research Fund
Exploring Acoustic Metamaterials
Alexander Nguyen ’18; Advisor: Alma Zook; Collaborator: William Lamb ’18
This summer, we decided to investigate acoustic metamaterials, specially crafted materials with properties derived more from their engineered structure than from any unusual characteristics of their constituent materials. These materials are capable of exhibiting curious properties in specific frequency ranges, e.g. negative effective density or bulk modulus, and have led to progress in exciting applications like subwavelength imaging and cloaking. Beginning with a one-dimensional analogue, we successfully demonstrated negative effective mass using a system of masses and springs. Then, proceeding along a rather different tangent, we explored the process of designing a specific metamaterial, starting with an arbitrary coordinate transformation and turning it into a set of material parameters. Finite element analysis simulations were performed in an attempt to probe the necessary geometries for creating materials with said parameters. Finally, using additive manufacturing, we attempted to create a ground cloak. The creation and cleaning processes led to substantial flaws in the cloak’s geometry, but subsequent testing yielded results that appear to be mostly consistent with our predictions, with significant signal attenuation around 3000 Hz. However, more work needs to be done to resolve unexpected amplification effects at lower frequencies, and to refine our experimental setup and remove extraneous variables.
Funding Provided By: Sontag Endowment for Physics Fund
Construction and Implementation of a Combined MASS-DIMM System on Table Mountain Observatory
Gabrielle Mehta ’18; Advisor: Philip Choi
Over the past year, the Pomona College 1-meter telescope at Table Mountain Observatory has undergone significant system upgrades. Under the guidance of Professor Philip Choi, Kutay Nazli (PO ’19), Isaac Cui (PO ’20), and Rachel Mochama (SC ’19), along with a team at the Jet Propulsion Laboratory (JPL), including Adam Mitchell (PO ’18), have spent the summer characterizing and optimizing system performance. Specifically, as part of a Pomona College collaboration with JPL, the team focused on improving the telescope’s astrometric capabilities to meet JPL’s ultra-high precision requirements for tracking fast-moving satellites. To achieve this, the team devised and executed tests to characterize the proficiency of the system in terms of its pointing accuracy and tracking stability. Currently, the system has improved sufficiently to be able to track 18th magnitude high-speed near-earth objects reliably on time-scales of hours, however there is more mechanical work that is necessary to achieve even greater precision. Once the system is optimized, the telescope will have useful national security and environmental applications in monitoring space debris, searching for satellites, and discovering near-earth objects with the potential of colliding with the Earth.
This experiment describes the design and production of a combined multi-aperture scintillation sensor (MASS) and differential image motion monitor (DIMM) instrument on Table Mountain Observatory. The purpose of the MASS-DIMM is to provide a complete atmospheric turbulence profile, which allows observers to directly measure overhead seeing conditions. The term seeing describes the degree of optical turbulence within the atmosphere, and is one of the most important criteria for performing ground-based observations. While it is possible to obtain a seeing estimation using a DIMM alone, the MASS-DIMM is able to reconstruct a full atmospheric turbulence profile. A DIMM measures image fluctuations between two images of the same object usually created from two apertures cut into a mask covering the primary mirror. From these fluctuations, the Fried parameter can then be estimated which can then give way to a seeing estimate. However, this estimate does not tell where the distortion occurred, only how big the distortion is. The MASS is able to work simultaneously with the DIMM to restore the vertical turbulence profile. By opening a third aperture in the mask, this third path is then sectioned off into four beams behind the secondary by a series of four tilted annular mirrors whose radii are on the order of the Fresnel radius. From these apertures, four scintillation indices and six differential scintillation indices are used to then reconstruct a vertical turbulence profile.
Funding Provided By: Sontag Endowment for Physics Fund
An attempt to incorporate spin into a gravitational wave simulation program for LISA
Yijun Wang ’19; Advisor: Thomas Moore
The Laser Interferometer Space Antenna (LISA) is a gravitational wave detector consisting of three Sun-orbiting satellites. Similar to its ground-based counterpart, the Laser Interferometer Gravitational wave Observatory, LIGO, LISA is to detect space-time deformations from gravitational waves, but its space-based nature and orbit design improve how precisely we can know about the wave source and allow for detection on a different range of wave sources from LIGO. Ultimately, we extract information on properties of the wave source from the waveform and the phase of the signal. However, instrument noise introduces overall uncertainties, and our grand project objective is to calculate the associated uncertainties for each parameter based on how the parameters contribute to the waveform and the phase in theory. This summer, we attempted to expand an existing LISA simulation program by more realistically modeling the wave source, namely by adding spins to the binary star system. A Pomona graduate wrote a spin simulation code, and firstly we translated this code into the coding language of the master program, Xojo. We enhanced the accuracy of this code while retaining a reasonable computation efficiency. We renovated the master program by adding in spin-related terms and importing the spin code module. The program should replicate the results from the previous no-spin program when spin-related parameters are set to zero, but the debugging process is left as future work.
Funding Provided By: Sontag Endowment for Physics Fund
Microwave Spectroscopy of Exotic Diatomic Molecules PbF and BaF
Yongrak Kim ’18; Advisor: Richard Mawhorter; Collaborator: Jose Munoz-Lopez ’19
Our group set out to better understand four different diatomic molecules: PbF, BaF, YbF, and TaN. Our main interest is the electron’s electric dipole moment (eEDM). This is a predicted tiny charge asymmetry in the electron; the only problem is that the Standard Model eEDM is far too small to measure. However, newer theories predict it may be up to 1010 times larger and possibly attainable. Our task this summer was to develop a more detailed understanding of these molecules actively in use in this pursuit. In June we traveled to Hannover, Germany to use a Fourier Transform Microwave (FTMW) spectrometer. Its high precision is ideal for detailed analysis of the molecules we are working with. Currently PbF and BaF have highest priority. PbF is interesting because of opposite parity states that appear to converge towards zero at the high vibrational level v = 8. BaF, on the other hand, is a popular diatomic that is currently being evaluated for eEDM measurements by a Dutch team that we met with this summer. Our results this summer yielded higher vibrational data (up to v =7) for PbF. Work with the powder precursor BaF2 showed that it is necessary to use a highly reactive metallic Ba sample instead, requiring further efforts to use safely. However, we did create a model of BaF which encompasses all 59 lines of existing data from three isotopes of Ba and vibrational states v = 0-4. This study will be of use to a number of groups currently building experiments to study BaF.
Funding Provided By: Sontag Endowment for Physics Fund
Binary Star System Simulation
Nikolaos Angelos Papastavrou ’20; Advisor: Thomas Moore
Funding Provided By: Sontag Endowment for Physics Fund
A Preliminary DPIV Based Investigation of Ruellia ciliatiflora Seeds
Sophie Zagerman ’18; Mentors: Dwight Whitaker and John Dabiri (Caltech); Collaborator: David Vejar ‘18
The small disk-like seeds of Ruellia ciliatiflora pose an interesting fluid dynamics puzzle. High speed video analyses show that the flower ejects the seeds at speeds upwards of 10 m/s and with significant backspin while generating high lift and low drag. The rotation and irregular shape of the seed make it a poor candidate for mathematical modeling, so this project uses data collected using a technique called DPIV (Digital Particle Image Velocimetry) to analyze the flow of fluid around a 3D printed model, along with an exploration of literature concerning flow around objects of similar shapes, in order to better understand the seeds’ efficient flight . Preliminary data collected from wake profile integrations on the PIV vector fields suggests that the seeds may fly in the range just before the transition from skin friction to pressure dominant drag. That said, the calculations proved difficult due to deficits in the previously collected data sets, which led the team to agree that more data, especially at lower speeds, is necessary. The literature survey was challenging, as studies concerning similarly shaped objects proved sparse. Future work includes construction of a small towing tank to acquire more data, possible 3D flow surveys, and work with other species of exploding plants to explore the role of seed morphology in efficient flight.
Funding Provided By: Pomona Unrestricted (Vejar), Sontag (Zagerman)
Blind Detection of Near-Earth Asteroids Using Pomona College's 1-Meter Telescope
Adam Mitchell ’18; Mentor: Philip Choi; Collaborators: Kevin Hale (HMC '15), Thomas Werne (NASA Jet Propulsion Laboratory)
This summer marked the beginning of the Near-Earth Asteroid Observation Program, a collaboration between NASA’s Jet Propulsion Laboratory and Pomona College. A near-earth asteroid is a small, rocky object in the solar system whose orbit brings it within close proximity of the Earth. Using the Pomona College 1-meter telescope at JPL’s Table Mountain Observatory, our goal was to observe these near-earth asteroids in order to analyze and determine their specific orbits. Throughout many nights of observation, we observed nine faint asteroids, which are roughly one thousand trillion times (1E-15) fainter than a full moon, in addition to taking blind surveys of the sky in order to potentially discover new near-earth asteroids. Our results validated the Near-Earth Object Observation Program at Pomona College with successful direct observations. Finally, this summer provided opportunities to fine-tune observation skills and telescope operations that will be used in the Pomona/JPL Near-Earth Asteroid Observation Program and other research projects in the years to come.
Funding Provided By: Richter
Fabrication and Stability of Inverted P3HT:PCBM Solar Cells
Sabrina Li ’17; Mentor: David Tanenbaum
Organic solar cells provide a potential solution to growing energy demands. Organic photovoltaics (OPV) is based on an organic semiconductor, in this case a mixture of two organic chemicals P3HT, a polymer, and PCBM, a fullerene derivative. While organic semiconductors will theoretically be more cost effective in the long run compared to inorganic semiconductors (e.g. silicon, and GaAs), they are also more chemically reactive and therefore less stable when exposed to open air. Thus, stability is an important aspect of OPV research. Inverted P3HT:PCBM devices were fabricated with six solar cells each. The structure of glass/ITO/ZnO/P3HT:PCBM/HTL/Ag was created using a spin coater and thin-film thermal evaporator. The HTL (hole transport layer) was either nothing, evaporated MoO3, or solution processed MoO3 (sMoO3). The sMoO3 process still requires refinement as it has not been applied on inverted cells prior to this project. The solar cells fabricated between Dec. 2013 and this summer were studied over time. Some devices improved while others degraded. Cells that improved drastically compared to their initial power conversion efficiency (PCE) maintained their higher PCE, but degraded over time similarly to those cells that did not see a jump in PCE. A cell fabricated in summer of 2014 showed PCE improvement from 1.641% to 3.554%, over twice the original PCE. The cause of improvement is not yet understood and warrants further study.
Funding Provided By: Sontag
Fabrication of Plasmonics using Electron Beam Lithography
Hannah Bishop ’16; Mentor: David Tanenbaum
Plasmonics redirect light by propagating electron excitation along a conductor, and can be used to increase the efficiency of solar cells by focusing more energy into the electricity-generating layer of the cell. Being able to reliably fabricate these nanostructures is a crucial step towards testing the extent to which plasmonics can increase the efficiency of solar cells. To create these dot arrays, a silicon wafer is coated with a film of PMMA, and electron beam lithography is used to expose the array in the film. The wafer is then developed in an MIBK, removing film from the exposed areas. After examining the patterns, silver is evaporated into the patterns and adhered to the silicon. The wafer is then developed in MIBK overnight, which removes the remaining PMMA and excess silver. This leaves arrays of silver dots, which are then analyzed in the SEM. I have successfully created several dot arrays, but need to work on producing more consistent and uniform results. The remaining silver was not sufficiently even across the patterns, but successful adhesion to the silicon was an improvement upon previous research in this lab. The next step is to fine-tune the lithography and evaporation procedures to enable consistent dot fabrication.
Funding Provided By: Sontag
Hyperfine Spectra and the Search for New Physics
David Sharfi ’16; Mentors: Richard Mawhorter, Jens Uwe Grabow (Leibniz University), and Timothy Steimle (Arizona State University); Collaborators: Andreas Biekert '16, Alexander Hof '18, Carson Witte '16, Zachary Glassman '14
The majority of our work this summer consists of high resolution Fourier transform microwave spectroscopy (FTMW), which we use to probe very small energy scales with great precision. Our spectrometer excites heavy, polar diatomic molecules with a microwave pulse and sensitively captures their radiative decay signal. This process allows us to test detailed quantum mechanical models and gather important physical information about our molecules of study. Our primary motivation for studying diatomic molecules is that they have recently gained significant research attention in the hunt for physics beyond the standard model. In this search for new physics, it is important to have detailed spectroscopic information on potential candidates for study, as this allows one to devise experiments in which molecules are carefully controlled to increase sensitivity to certain effects. This summer we observed and analyzed many new transitions for rubidium chloride (RbCl), potassium iodide (KI), lead fluoride (PbF), ytterbium fluoride (YbF), and tantalum nitride (TaN). One of our main goals is to determine the ratios between nuclear quadrupole coupling constants of molecules containing different isotopes in order to determine if electron overlap in and near the nucleus is producing a measurable effect on our observations. This data is of use for the design of future experiments on diatomic molecules, and for informing theoretical predictions of these subtle effects.
Funding Provided By: Richter (Hof), Sontag (Sharfi), Pomona College Physics Department (Biekert), Pomona College Physics Department (Witte)
Immersive Visualization Analysis of Swift GRBs
Kate Hartman ’18; Mentors: Loredana Vetere and Ciro Donalek (Caltech)
Funding Provided By: Pomona Unrestricted
Improving the quality of growth and transfer of CVD graphene films
Hyunjin Hong ’18; Mentor: David Tanenbaum
Graphene is a single sheet of carbon atoms bonded in a 2D lattice. Graphene is being hailed as a promising nanomaterial in many fields due to its versatility and favorable characteristics which include outstanding electrical, optical, and mechanical properties. The production method considered to be the most effective for growing large-area graphene films today is chemical vapor deposition (CVD). In our research we sought to improve the quality of graphene grown in our lab using the chemical vapor deposition method. Research done during previous summers discovered the effect of the ratio of hydrogen to methane during growth. Building upon those results, we explored the effect of the cooling rate on graphene growth. By introducing new growth parameters, we hoped to compare the graphene grown under the new process with graphene grown under conditions suggested by our predecessors and reach a verdict on how to proceed forward. Results of graphene characterized under Raman spectroscopy suggest that the presence of methane during the cooling process with a faster cooling rate is more conducive to graphene growth, but the gas ratio proved to be the more influential factor for affecting growth quality.
Funding Provided By: Pomona Unrestricted
KAPAO: Capabilities, Future Goals, and an Overview of Pomona’s Facility Adaptive Optics System
Greta Zhong; Mentor: Philip Choi; Collaborators: Allison Ho '18, Adam Mitchell ‘18
KAPAO is Pomona College's adaptive optics system installed on the 1-meter telescope at Table Mountain Observatory. The system counteracts atmospheric distortions in real time to remove the twinkle from stars, producing space telescope quality images from the ground. This poster gives an overview of system improvements over time as well as future observation plans. After years of design, construction, alignment, and performance optimization, we now have an instrument with which we can readily observe. This summer, we’ve developed more streamlined observation and software analysis pipelines, so we can efficiently gather and analyze data for a wide range of targets. Future plans for observation include Washington Double Star Catalog surveys, bright star surveys, Robo-AO follow-ups, and Kepler follow-ups.
Funding Provided By: Pomona 1415 (Zhong), Richter (Ho), Richter (Mitchell)
KAPAO: Characterization of On-Sky System Performance
Allison Ho ’18; Mentor: Philip Choi; Collaborators: Greta Zhong '17, Scott Severson (Sonoma State University)
KAPAO is Pomona College's adaptive optics system installed on the 1-meter telescope at Table Mountain Observatory. The system counteracts atmospheric distortions in real time to remove the twinkle from stars, producing space telescope quality images from the ground. To measure the capabilities and performance quality of the system, we use a variety of tools that analyzes the corrected and uncorrected images. To quantify image quality, the energy intensity of aberrated images is compared to the maximum attainable intensity in a diffraction-limited ideal optical system - a metric called strehl ratio. Similarly, the contours of the incoming wavefront of light is compared to an ideal flat wavefront in a metric called RMS. Using these tools, this summer was spent evaluating the results of over two years of observations and building a refined data pipeline for the astronomical images obtained with KAPAO. Images are run using internally developed python/PYRAF strehl software in order to plot strehl ratio and growth curves of the enclosed energy for both the corrected and uncorrected images. By analyzing the strehl, we were able to confirm correlation between the magnitude of the object and the strehl of the corrected image, as well as the uncorrected strehl and the improvement in stehl, which demonstrates the quality of the system due to seeing conditions.
Funding Provided By: Richter (Ho), Pomona 1415 (Zhong)
Modeling Vortex Rings from Sphagnum Moss
Blair Subbaraman ’18; Mentor: Dwight Whitaker; Collaborator: Thomas Neumiller '17
Despite being a primitive plant, Sphagnum is a prolific plant genus covering an estimated 1% of Earth’s total land area. Part of the reason that Sphagnum is so successful—in spite of the fact that this moss grows extremely close to the ground, far out of the reach of air currents typically used for spore dispersal—is its capacity to launch spores high into the air, where the wind can catch them. Sphagnum achieves this using a neat trick of fluid dynamics: it propels and entrains the spores within vortex rings. Using computational fluid dynamics (CFD) software from ANSYS, this project presents a numerical analysis of this process. By testing an axisymmetric large eddy simulation (LES) on a digitally-rendered model of a Sphagnum spore capsule, different ambient air pressures are able to be tested inside of the plant’s capsule. Once the pressure is released, the trajectories of the resulting vortex rings are compared to high-speed video data showing the spore dispersal process. Thus, the pressure inside of the capsule can be inferred. Initial results show that this pressure does not create an optimal vortex ring, which is contrary to other biological systems.
Funding Provided By: Howard Hughes Medical Institute
Observing Blazars With gri Photometry and Polarimetry
Gabi Mehta ’18; Mentor: Alma Zook; Collaborator: Angela Twum ‘18
Blazars are a type of Active Galactic Nucles (AGN) whose jets emit are comprised of synchrotron radiation across all wavelengths. In this research project, blazars 3C279 and PKS 1510-089 were monitored using Pomona College’s 1-meter telescope located on Tabletop Mountain Observatory (TMO) to gather photometric and polarimetric data. The photometric results were gathered using the Sloan green, red, infrared (gri) filters to measure the intensity of the jet’s radiation, while the polarimetric results were taken using two Wollaston prisms to determine whether the emitted light from the synchrotron radiation is polarized, and if so, what the degree of polarization is. The data gathered from this project is meant to continue Pomona’s blazar monitoring program which contributes data to a worldwide blazar monitoring program. Due to telescope malfunctions and a wildfire, only one set of test photometric observations were taken and no polarimetric observations were taken in this project.
Funding Provided By: Sontag (Mehta), Pomona Unrestricted (Twum)
Teaching Problem Solving Skills: Development of an Educational Computer Program for Physics
Will Buchholtz ’16; Mentor: Thomas Moore; Collaborators: Malone Mischke '17, Kiran Siebel '17
Learning problem solving skills is one of the key elements of a physics undergraduate education. This summer, Professor Moore assembled our lab to begin creating an innovative computer program to aid this process. The ultimate goal for the program is that it would guide a student through homework problems, reinforcing good habits along the way. A student would be provided with essential tools such as a workspace to do algebra, a comprehensive drawing program, a menu of fundamental equations to use, and an editor with boxes to enter the known and unknown variables. Predictably, such a project requires an enormous amount of sophisticated coding, in part because one of the essential features is the ability to manipulate and interact with equations on the screen. The endeavor therefore represents a multi-year effort and our work was spent only on the foundational elements of the project. This meant designing and writing core modules of code for the program. By the end of the summer, we developed such features as a drawing program, an equation typesetting program and a library of methods allowing scalars to have units. Because of our work, the next major step in the project is to begin integrating the modules together into a single program.
Funding Provided By: Pomona Unrestricted (Buchholtz), Sontag (Mischke), Hahn Teaching With Technology Grant (Siebel)
Testing Out the New Polarimeter Design for Pomona College’s One Meter Telescope
Angela Twum ’18; Mentor: Alma Zook: Collaborator: Gabi Mehta ‘18
The majority of this summer was spent testing out the new polarimeter design to make sure it operates correctly once mounted on the camera up on Pomona College’s one-meter telescope on the Table Mountain Observatory for observations on blazar activity. The plan is to use this new design to record data in a more efficient way in order to determine the degree of polarization of the light from these active galactic nuclei in hopes of determining whether they do emit synchrotron radiation and from that learn more about their magnetic field strength , average electron energy and density.
Funding Provided By: Sontag (Mehta), Pomona Unrestricted (Twum)
A Semi-Analytic Model Study of the Metallicity Profiles of Disc Galaxies
Nathan Sandford ’17; Mentor: Yu Lu (Carnegie Observatories)
The metallicity gradients of disc galaxies contain valuable information about the physics governing their formation and evolution. The observed metallicity profiles have negative gradients that are steeper at high redshifts, indicating an inside-out formation of disc galaxies. We improve on our semi-analytic galaxy formation model (Lu, Mo & Wechsler 2015) by incorporating the radial distribution of metals into the model. With the improved model, we explore how feedback scenarios affect metallicity gradients. The model features 3 feedback scenarios: An Ejective (EJ) model, which includes ejective supernova (SN) feedback, a Pre-Heating (PR) model, which assumes that the intergalactic medium is preheated, preventing it from collapsing onto galaxies, and a Re-Incorporation (RI) model, which also includes SN feedback but allows ejected gas to re-accrete onto the galaxies. We compare the models with observations from Ho et al. (2015) and find that while all models struggle to match the observed metallicity gradient-stellar mass relationship, the PR model predicts similar strength metallicity gradients to observations. We also find that the RI model predicts a flat gradient because its outflow and re-accretion replenish the disc uniformly with newly accreted enriched gas, erasing the mark of inside-out formation. Our findings suggest feedback plays a key role in shaping the metallicity gradients of disc galaxies and require more detailed theoretical modeling to understand them.
Funding Provided By: Carnegie Institute for Science
Total Internal Reflection Raman Microspectroscopy of Lipid Bilayers
Fernando Ortega (2015); Student Collaborator(s): Kelly Nguyen (2015); Mentor(s): Alfred Kwok
Abstract: It has been hypothesized that lipid rafts are regions within membranes that are enriched with cholesterol and glycosphingolipids and serve as platforms for signaling proteins to aggregate. However, their composition has not yet been well- defined. In this study, we attempt to use Total Internal Reflection Raman (TIRR) microspectroscopy using both an infrared Ti:Sapphire and visible green Nd:Vanadate laser to determine the composition of raft-like domains in lipid bilayers. POPC lipid bilayers containing 1% dye-labelled DPPE are formed when the lipid molecules self-assemble onto a quartz microscope slide. The laser beams are redirected to the sample area using a quartz prism, producing an evanescent wave when they are totally internally reflected at the quartz slide- water interface inside the sample chamber. This evanescent wave produces a ‘fingerprint’ Raman spectrum unique to the lipids, enabling us to identify the individual concentrations of the various lipids in a bilayer. Although we have yet to obtain any such signal from the lipid bilayers, we were able to obtain a consistent, subtractable background Raman spectrum of the quartz slide. We were also able to test various chemical compounds for their viability as coupling fluids to interface between the quartz prism and slides, of which we found that methyl salicylate and to a lesser extent benzaldehyde performed the most effectively.
Funding Provided by: Pomona College SURP (FO); Howard Hughes Medical Institute (KN)
Altering the Polarimeter Box Design as a Part of the TMO Instrument Package
Leif Jerome Jahn (2017); Additional Collaborator(s): Glenn Flohr; Mentor(s): Alma Zook
Abstract: The one-meter telescope found at Pomona College's Table Mountain Observatory site can be run using an extraneous polarimeter box. In previous years, this box has had to house purely a CCD camera and two Apogee filter wheels, which enabled the astronomer to switch between Johnson BVRI and Sloan g'r'i' filters and a Savart-plate polarimeter. The majority of the summer was spent altering the design and rebuilding the frame of the box to allow for the addition of two Wollaston prisms and corrective lenses to the upper filter wheel as well as side panels to shield the inside from light. This required using the SolidWorks program to design parts which would facilitate the installation of the Wollaston prisms and lenses to the upper filter wheel. Depending on the necessary material, these parts were then fabricated using both Pomona College’s Physics Machine Shop as well as its 3D printer. This box is still being finished up and will hopefully be ready to install within the first few weeks of the 2014 Fall Semester.
Funding Provided by: Paul K. Richter and Evalyn E. Cook Richter Memorial Fund
Revealing The Night Sky: A Closer Look at Bright Objects
Elexis Witkin (2017); Mentor(s): Alma Zook
Abstract: Our ancestors made a habit of sticking their noses into the night-sky. Peering into the beauty of our universe, they would trace shapes out of the fascinating clouds of glitter. Today, we have the awesome power to look closely at individual stars and bright objects and create stunning photos that would have floored our ancestors. My research revolved around creating high quality images of bright objects using 5-meter telescope images and a process called data reduction. In addition, I edited a data reduction manual written by Dr. Alma Zook in attempt to help others learn how to more clearly see the ethereal points of light that have mystified our species for thousands of years.
Funding Provided by: Pomona Alumni SURP Fund
A Study of Cyclones and Anticylones in Jupiter's North Tropical Zone, 2003-2013
Franklin Marsh (2017); Additional Collaborator(s): Amy Simon (NASA Goddard Space Flight Center), John Rogers (Cambridge University); Mentor(s): Bryan Penprase
Abstract: In our study, the relationship between Jupiter's Northern Equatorial Belt and North Tropical Zone Storms is explored in detail. Positional data on the storms comes from the JUPOS database, maintained by an international team of observers. Over 2,000 observations of 80 storms in the 2003-2013 time period were used to characterize trends in both latitudinal and longitudinal position, and velocity over time. We found that after the year of 2009, the storms began forming at lower latitudes than in the pre-2009 time period. We hypothesize that small changes in the differential zonal wind caused this new, southerly zone to be more favorable for storm production. Because these storms form in an area of lower zonal wind speed, they also travel at lower velocities. Additionally, by comparing our analysis of JUPOS observations to Hubble and Cassini measurements of wind speed, we were able to characterize the relationship between storm size and storm velocity and a fraction of the zonal flow, and build an empirical model useful for predicting jovian storms in the future.
Funding Provided by: Pomona College SURP
Inverted P3HT:PCBM Organic Photovoltaic Cells
Sabrina Li (2017); Mentor(s): David Tanenbaum
Abstract: Solar cells are the most promising answer to the increasing energy demands of an exponentially growing human population. Organic photovoltaics convert the energy in photons to electrical energy at potentially lower costs to the environment than inorganic photovoltaics. However, due to the volatile nature of organic compounds, the stability and efficiency of OPVs need to improve before they can compete with the current technology. Inverted P3HT:PCBM solar cells were fabricated with different combinations of cleaning methods, P3HT:PCBM ratios, and hole- transport layers (HTL). Substrates, glass slides that would contain six solar cells each, underwent ZONE cleaning ,Plasma cleaning procedures, or UV-light exposures. Active layer solutions of P3HT:PCBM were made in ratios of 1:1 and 1:0.9. Cells were made with HTL of either evaporated MoO3 (eMoO3), solution processed MoO3 (sMoO3), PEDOT:PSS, or no HTL at all. The stability and initial power conversion efficiency (PCE) of solar cells were measured and characterized. The cells that underwent more intensive initial cleaning processes yielded better PCEs. The highest PCEs for the different types of cells made this summer are 1.705% (eMoO3 as HTL), 1.641% (PEDOT:PSS as HTL) and 1.115% (no HTL). Cells with eMoO3 were more stable under constant illumination than cells with PEDOT:PSS.
Funding Provided by: Sontag Summer Undergraduate Research Fund
Improving the System for Growth and Characterization of Graphene
Jerry Martinez (2016); Mentor(s): David Tanenbaum
Abstract: Graphene is a hexagonal array of carbon atoms extending over two dimensions that exhibits incredible optical, electrical, and mechanical properties. The purpose of our project was to improve both the quality and characterization of graphene grown in our lab. The process used for producing our graphene is a chemical vapor deposition process. In the CVD process, a heated metal foil is introduced to various gasses to deposit a layer of carbon on the surface. The thickness and uniformity of the graphene films can be controlled by carefully varying the gas flow rates, temperature, exposure time, and geometry of the foil. One way we hoped to improve our graphene production process was by implementing a standing foil method. With this technique, we observed Raman spectra consistent with 2-4 layered graphene. We also attempted an envelope enclosure method for producing graphene, but were only able to grow 20 layered sheets. Our best results were obtained by adjusting the gas flow rates of our system. We were able to consistently produce 1-2 layered graphene sheets by using flow rates of 2 sccm and 9.14 sccm for oxygen and methane respectively. Lastly, we implemented a new single mode fiber to our system which lowered the spot size of our Raman tool's laser beam from 48 to 26 micrometers; thereby improving our Raman spectroscopy collection process. The new modifications to our CVD system this summer have allowed for better growth and characterization of graphene and with further adjustments, production of consistent single layered graphene is probable.
Funding Provided by: Sontag Summer Undergraduate Research Fund
Probing the Aerodynamics of High Speed Seed Dispersal in Acanthaceae Seeds
Peter Yuanxi Chen (2017); Student Collaborator(s): David Vejar (2018); Mentor(s): Dwight Whitaker
Abstract: The goal of this research is the study the aerodynamics of the seed dispersion within the Acanthaceae family of plants. These seeds travel about 10 m/s in translational speed and spin at about 1 kilohertz. When the seed pods explode, either hygrocastically or xerocasically, the seeds are flung from the mother plant by hooks called retiniculae, located on the inside of the fruit. The seeds are too small to observe their aerodynamics in a wind tunnel. Because of this, we have been working on a method to accurately scale up the seeds to a model that is of a workable size. We have been able to take high quality photos, and by using software called Photosynth, generate a point cloud of the seed. This point cloud captures the curves and shape of the seed from the pictures that we took. We then clean it up using Blender, deleting any extraneous points, and mesh the point cloud in Meshlab, using a Poisson surface reconstruction filter. After creating this watertight mesh, we export it as an .stl file and print it on 3-d printer. We have been working on making this process as accurate and consistent as we can, and after finalizing this, we plan on starting wind tunnel testing these models.
Funding Provided by: Howard Hughes Medical Institute (PC); Howard Hughes Medical Institute HAP (DV)
Swift Observations of X-Ray Naked GRBs
Ferrel Atkins (2016); Student Collaborator(s): Tatsu Monkman (2016); Mentor(s): Loredana Vetere
Abstract: Ten years after its launch Swift has successfully localized and observed almost nine hundred Gamma Ray Bursts. Thanks to its great rapidity to repoint in the direction of the source Swift succeeds detecting an afterglow more than 93% of the time BAT triggers a new event. Never before the afterglow emission have been followed so quickly and in so much detail starting as early as 70 sec after the BAT trigger. In a few cases XRT actually detected a fast decaying emission (α~3) that fell below the detection threshold after ~1000s. These events are called “naked” GRBs. “Naked” Gamma Ray Bursts, first predicted by models of burst-progenitors in low-density environments, are extremely rare and difficult to detect to their fast decaying emission. Currently a widely accepted progenitor model has not yet been established, although in a recent paper R. Hasoet et. al. (2011) obtains constraints on the density of the environment and the microphysics parameters which are imposed by the absence of a detected afterglow. An even more unconventional class of GRBs is the one that show no x-ray emission at all. For at least seven Long GRBs, XRT could not measure any X-afterglow, even as early as 100s after the BAT trigger. Are these extreme naked GRB? Is this a completely new class of objects with an uncommon emission release? In this work we analyze all the fast-decaying GRBs detected by Swift and the seven Long GRBs without any X-ray emission and discuss their singular origin.
Funding Provided by: Pomona College SURP
Astronomical Adaptive Optics with KAPAO: I Telescope Integration and Performance Characterization
Kelli Rockwell (2017); Student Collaborator(s): Greta Zhong (2017), Franklin Marsh (2017), Stephanie Church (2015 Sonoma State University); Additional Collaborator(s): Scott Severson (Sonoma State University); Mentor(s): Philip Choi
Abstract: KAPAO is Pomona's adaptive optics system installed on the 1-meter telescope at Table Mountain Observatory. The system counteracts atmospheric distortions in real time to remove the twinkle from stars and so produce space telescope quality images from the ground. A four-year NSF funded instrumentation project that achieved first light in August 2013, KAPAO uses the same software as the Robo-AO system at Palomar Observatory and operates in the optical and near infrared. The system uses a deformable mirror with a wavefront sensor to correct for atmospheric distortions of light from targets and take sharp imaging data for analysis. This summer, our team worked on hardware alignment as well as software and data analysis improvement, resulting in significant advances in running the system and acquiring data. At the end of the summer, a seven night observing run at the telescope produced a wealth of AO data that demonstrated a clear improvement over the instrument's Beta versions. There are several system diagnostic tools we use to measure the quality of image correction, each assessing a different characteristic of the light output. In this poster, we will present tools that measure image quality both directly, using the Strehl ratio, and indirectly, using the RMS wavefront error as measured by our wavefront sensor. This way, we are able to see in which areas our AO system performed best and most consistently, as well as gaining other insights about future improvements to be made.
Funding Provided by: Sontag Summer Undergraduate Research Fund (KR); Kenneth T. and Eileen L. Norris Foundation (GZ); Pomona College SURP (FM)
Astronomical Adaptive Optics with KAPAO: II On- Sky Calibration and Optimization
Greta Zhong (2017); Student Collaborator(s): Kelli Rockwell (2017), Franklin Marsh (2017), Stephanie Church (2016 Sonoma State University), Emily Yang (2014), Henry Steiner (2018 Sonoma State University); Additional Collaborator(s): Scott Severson (Sonoma State University); Mentor(s): Philip Choi
Abstract: KAPAO is Pomona's adaptive optics system installed on the 1-meter telescope at Table Mountain Observatory. The system counteracts atmospheric distortions in real time to remove the twinkle from stars and so produce space telescope quality images from the ground. A four-year NSF funded instrumentation project that achieved first light in August 2013, KAPAO uses the same software as the Robo-AO system at Palomar Observatory and operates in the optical and near infrared. The system uses a deformable mirror with a wavefront sensor to correct for atmospheric distortions of light from targets and take sharp imaging data for analysis. This summer, our team worked on hardware alignment as well as software and data analysis improvement, resulting in significant advances in running the system and acquiring data. At the end of the summer, a seven night observing run at the telescope produced a wealth of AO data that demonstrated a clear improvement over the instrument’s Beta versions. By exploring our parameter space and examining the resulting system performance, we were able to determine the ideal parameters for a target of a given brightness, improving performance and increasing the number of targets we could observe with KAPAO. In fact, by the end of the summer, we were able to observe targets that were 40-100 times fainter than previous ones, increasing the number of potential target from several hundred to hundreds of thousands.
Funding Provided by: Kenneth T. and Eileen L. Norris Foundation (GZ); Sontag Summer Undergraduate Research Fund (KR); Pomona College SURP (FM)
Observing Spectral Lines of RbI, KI, PbF, and 171YbF
Will Buchholtz (2016); Student Collaborator(s): Carson Witte (2015); Mentor(s): Richard Mawhorter
Abstract: Quantum mechanics tells us that molecular energies can only occur in discrete, quantized values. The study of spectroscopy is to observe transitions between these energy states caused by the absorption and emission of electromagnetic waves. In our research we used the JPL programs SPFIT and SPCAT to analyze all available data (RF, microwave, IR, & optical) for the four molecules KI, RbI, PbF, and YbF. We first predicted spectra for these molecules, and then traveled to Germany in order to use a high resolution Coaxial Oriented Beam-Resonator- Arrangement (COBRA) spectrometer at the Leibniz University in Hannover. We were able to measure almost 250 transitions, most of them new, ranging in frequency from 3-26 GHz with a typical uncertainty of only 500 Hz, i.e. .0000005 GHz. This knowledge is useful to the scientific community in several ways. Precise measurements of molecular spectra can help researchers identify the composition of unknown substances. Furthermore, from a molecule’s spectrum a number of parameters can be determined which characterize the energy contribution of each of the physical interactions occurring in a given molecule. Changing isotopes in a molecule can enable further interactions, and this more detailed knowledge can inform fundamental physics studies of the electron’s penetration of the nucleus and the nuclear anapole moment as well as the shape (electric dipole moment) of the electron and the possible variation of fundamental constants over the eons.
Funding Provided by: Sherman Fairchild Foundation (CW); Professor Mawhorter's Sontag Fellowship (WB)
Building a Surface Plasmon Resonance Device on the Tip of an Optical Fiber for Protein Detection
Andreas Biekert (2016); Mentor(s): Qimin Quan (Harvard University, The Rowland Institute), Richard Mawhorter
Abstract: Surface plasamon resonance (SPR) devices are useful for sensitive, label-free, real-time protein detection but require a certain amount of sample removed from its native environment. In this project we look to improve upon existing SPR techniques utilizing optical fibers coated in silver or gold so that measurement can be accomplished with smaller sample size. We explore device fabrication using a variety of fiber types (single mode, multimode, double-cladding, multi-core) and metal coating techniques (gold nanorod deposition and sputter coating) and discuss preliminary results for refinement. We also examine the theoretical conditions, including material choice and incident light angle, for observing surface plasmon modes in thin-film metals and discuss drawbacks in our initial approaches. Based on this theoretical work, we suggest a new design with simplified geometry and promising computational results. The new design revolves around a glass capillary that is heat-pulled to 45 degree conical shape. We coat a thin layer of silver (~10 nm) on the outer layer of the capillary tube to achieve an SPR mode. We use one fiber to provide the incident light for the mode and use another fiber to recollect it, thus providing a compact unit for point-of-care diagnostics applications. Finally, we explore initial efforts in developing repeatable fabrication methods towards our new design.
Funding Provided by: Harvard School of Engineering and Applied Sciences REU
Scrambling in Matrix Black Holes
Alexander Cole (2015); Mentor(s): Vatche Sahakian (HMC)
Abstract: In recent years, there has been much controversy regarding the relationship between information and black holes. In order to avoid information loss, an acceptably general unitary model requires that infalling information be scrambled and then emitted as Hawking radiation. Sekino and Susskind conjectured that black holes are fast scramblers, generating entanglement at an efficiency that saturates the bound given by the no- cloning theorem. We set up a scheme to test this conjecture for black holes in Matrix theory – M- theory in the light-cone frame – using highly- parallelizable Runge-Kutta evolution. Previous examination of this system considered only fermionic degrees of freedom and did not find fast scrambling. We include the coupling between fermionic and bosonic degrees of freedom. In this case, one must consider the black hole’s spatial configuration. Our simulation is in the final stages of setup.
Funding Provided by: Kenneth T. and Eileen L. Norris Foundation
TWILIGHT: A 3D Polychromatic Ray-Tracing Radiative Transfer Simulation I. Scattering Properties of the Interstellar Medium
David Khatami (2016); Mentor(s): Barry Madore (California Institute of Technology)
Abstract: We present TWILIGHT, a fully 3D polychromatic ray-tracing radiative transfer simulation of astrophysical dust in arbitrary scales and geometries. TWILIGHT deterministically models the scattering and absorption/reemission of light through a dusty medium with orders-of-magnitude improvements in efficiency over similar codes relying on Monte Carlo methods. We use TWILIGHT to derive analytic expressions for the interstellar medium by assembling large-scale structures from up to millions of spatially-resolved dust grain cells. We test TWILIGHT against published radiative transfer benchmarks, in addition to providing proof- of-concept renderings of both symmetric and asymmetric astrophysical objects. Finally, we describe the polychromatic capabilities of TWILIGHT by performing preliminary UBVRIJHK synthetic photometry.
Funding Provided by: Caltech Summer Undergraduate Research Fellowships (EB); Carnegie Isntitution of Washington
Tunnel Diode Oscillators for Sensitive Magnetic Resonance
Vicente Robles (2016); Student Collaborator(s): Shangjie Guo (2015 University of Illinois at Urbana-Champaign), Aya (2016 University of Illinois at Urbana-Champaign), Mary Vollink (2015 University of Illinois at Urbana- Champaign); Mentor(s): Russell Giannetta (University of Illinois at Urbana-Champaign)
Abstract: Nuclear magnetic resonance is a radio frequency spectroscopic technique that has been used to identify chemical substances, determine molecular structures, study properties such as phase changes and more. The purpose of this project is to evaluate tiny changes in the magnetic susceptibility (x) of a material when nuclear magnetic transitions are excited. The magnetic susceptibility of a substance describes the magnetic response caused by an applied magnetic field, thus measuring this quantity will help explain how electrons behave in a variety of conducting materials. In order to make these measurements, a tunnel diode device will be incorporated into a radio a frequency oscillator circuit. Cryogenic temperatures, achieved by liquid helium (4.2 Kelvin), are required for stable oscillations.
Funding Provided by: Summer Research Opportunity Program at University of Illinois at Urbana-Champaign
Public good dispersal in Pseudomonas aeruginosa colonies
Jonathan Wong (2015); Mentor(s): Yilin Wu (The Chinese University of Hong Kong)
Abstract: The distribution of public goods amongst a population has been a primary question in the field of ecology. Because these public goods can be taken up by any individual in a population, non- producers of a public good gain an evolutionary advantage. The dispersal dynamics of public goods therefore can play an important role in the population dynamics by shaping the competitive landscape between public good producers and non- producers. In Pseudomonas aeruginosa, a siderophore called pyoverdine (pvd) is a public good for fetching soluble iron. Pvd has been shown to have limited dispersal in non-motile microcolonies on solid substrate, providing an avenue to maintain stable cooperation of pvd production in the population. However, it is unclear whether the limited dispersal still holds in the presence of flagellar motility. Here we investigated this question by looking at the dispersal of pyoverdine in co-cultures of a non-flagellated, pvd producing colony and a motile, non-pvd producing colony. Surprisingly, when the colonies have made contact, pvd does not appear to disperse into the non- producing colony. In many cases the motile, non- pvd producing colony was able to take up individual pvd producing cells yet pvd from these pvd producing cells did not exhibit any noticeable dispersion into the surrounding motile cells. These findings support the notion that public goods producers mitigate their evolutionary disadvantage by limiting the spread of those public goods.
Funding Provided by: Sontag Summer Undergraduate Research Fund
Opto-electronic Characterization of Narrow Band Gap Semiconductors at Cryogenic Temperatures
Chanud Yasanayake (2016); Additional Collaborator(s): Chris Palmstrøm (University of California, Santa Barbara); Mentor(s): Mihir Pendharkar (University of California, Santa Barbara)
Abstract: Semiconductors are fundamental to modern technology, with uses ranging from scientific research to commercial applications in computing and telecommunications. There is a great deal of interest in studying these materials, both to improve their use in current technologies and to discover potential future applications in novel devices. In this project we work with a characterization apparatus used for studying semiconductors. This apparatus, consisting of a solid state 532 nm Nd:YAG laser, optical filters, fiber optic cables, a 10 K cryostat, and a monochromator, provides a photoluminescence spectrum of the studied material. The spectrum can then be used to determine the material's band gap, an important physical property. This work focuses on modifying the characterization setup to add the functionality of detecting semiconductors with narrow band gaps and measuring their electrical properties. These modifications include optimizing the arrangement of the setup's optical components, incorporating new components into the setup, and redesigning parts for the cryostat and monochromator using CAD software. The upgraded setup can both optically detect a wider range of semiconductors and electronically measure the semiconductors' properties. Preliminary photoluminescence studies were conducted on InGaAs samples with a peak emission wavelength of 1588 nm at room temperature.
Funding Provided by: National Science Foundation (University of California Santa Barbara)
KAPAO PRIME: III Telescope Integration and First Light Imaging
Dalton Bolger (2014); Student Collaborator(s): Jonathan Wong (2015); Fernando Ortega (2015); Christian Guerrero (2016 HMC); Katie Badham (2013 Sonoma State University); Additional Collaborator(s): Scott Severson (Sonoma State College); Mentor(s): Phil Choi
Abstract: We present preliminary on-sky results from the first-light observations of the Pomona College Adaptive Optics (AO) instrument, KAPAO Prime. KAPAO Prime underwent assembly and lab calibration throughout the majority of the summer. The summer concluded with installation onto the Table Mountain Observatory (TMO) 1-meter telescope during a three-night engineering run which began on July 30, 2013. We present details of the instrument mounting and alignment; characterization of atmospheric observing conditions; initial low-order, tip-tilt, corrections; and the final high-order, on-sky loop closure using reference stars, Beta Pegasi and Alpha Lyrae. On-sky results are compared to in-lab performance tests as well as discussion of further hardware development as part of an upcoming senior thesis.
Funding Provided by: National Science Foundation #AST-0960343; Sherman Fairchild Foundation (JW, FO)
The World of Extragalactic 33GHz radio emission: Star Formation, Active Galactic Nuclei, Anomalous Dust and more
Dillon Dong (2015); Additional Collaborator(s): Eric Murphy (Caltech -IPAC); Mentor(s): Phil Choi
Abstract: One of the central questions of astronomy involves explaining how the universe became the diverse space we observe around us today. Charting the history of star formation by observing star forming regions in other galaxies at varying distances (and therefore varying times in the universe's life) helps fill in that puzzle. Our project, the Star Formation in Radio Survey uses the Jansky Very Large Array to target 118 galaxy nuclei and extranuclear star-forming regions in 56 nearby (d < 30Mpc) galaxies, each of which have infrared spectral mappings from the SINGS and KINGFISH surveys. These new 33GHz data probe free-free emission, providing a sensitive, extinction-unbiased measure of the current star formation activity in each complex. Thus, these data can accurately calibrate other empirical star formation rate diagnostics that are easier to measure for high redshift studies. Our initial investigation includes an extranuclear region in NGC 6946 that has shown a large excess of radiation at 33GHz relative to what is expected given lower frequency radio data. This has been identified as the first extragalactic detection of “anomalous dust" emission, likely from electric dipole radiation from rapidly rotating ultrasmall (a < 10^-6 cm) dust grains. This resolved ~2'' source is detected at >70σ at 33GHz, but has no detected counterpart at 8μm. We are also preparing a radio spectral index map of the massive (~13 Msun/yr) molecular outflow from an AGN with no apparent partner: NGC1266. This map will help model the gas's diffusion and probe its underlying physics.
Funding Provided by: Paul K. Richter and Evelyn E. Cook Richter Memorial Fund
High-Mass Star Formation in NGC6822: The Ultraviolet as a Tool for Identification
Anne Hedlund (2014); Additional Collaborator(s): Barry Madore (Carnegie Institute for Science); Mentor(s): Phil Choi
Abstract: One of the challenges involved in studying star formation rates is the inability to distinguish young, hot blue stars from generally older, cooler red stars based only on observations from the red part of their optical spectra. Since the blue part of the spectrum is difficult to obtain from ground, we will use the Galaxy Evolution Explorer (GALEX) space telescope to obtain UV data. We gathered photometric data from a GALEX mosaic of NGC6822 and matched around 1000 of theses sources with a ground-based, optical catalog, Massey. By matching GALEX data with Massey, we were able to create spectral energy distributions (SEDs) for the matched stars from the far ultraviolet to the near-infrared. We have begun examining the numerous ways to characterize the SED of an O and B star such as modeling O and B stars as blackbody sources and creating SEDs for stars of known spectral types from literature. In the future, we will be able to use the varying luminosities in the UV part of the spectrum of my cataloged SED’s to identify O and B stars and hence explore topics related to star formation by comparing H-alpha maps from TYPHOON and gas distributions with the spatial distributions of O and B stars that we find.
Funding Provided by: Kenneth T. and Eileen L. Norris Foundation; National Science Foundation #AST-0960343
Constraining the Low-Mass Luminosity Function
Claire Dickey (2014); Mentor(s): Philip Choi
Abstract: We present a novel technique for self-consistently constraining the full luminosity function of globular clusters by measuring the cumulative fraction of light from resolved stars as a function of the total integrated cluster light. Using HST WFPC2 observations of a sample of six metal-poor clusters in the Large Magellanic Clouds (NGC 1754, 1835, 1898, 1916, 2006, and 2019), we have resolved stars down to the main sequence turn-off. Color-magnitude diagrams for each cluster show well-developed horizontal branches, and the luminosity functions fit the expected power law slope of 0.3 along the red giant branch. Using the ratio of resolved to unresolved light, we then smoothly extrapolate the luminosity function below the (currently unresolved) main sequence turn-off. This technique allows for new and independent constraints on the initial mass function for globular clusters.
Funding Provided by: Paul K. Richter and Evelyn E. Cook Richter Memorial Fund; National Science Foundation #AST-0960343
KAPAO Prime: II Wavefront Sensing and Loop Performance Optimization
Fernando Ortega (2015); Student Collaborator(s): Jonathan Wong (2015); Dalton Bolger (2014); Christian Guerrero (2016 HMC); Katherine Badham (2013 Sonoma State University); Additional Collaborator(s): Scott Severson (Sonoma State University); Mentor(s): Philip Choi
Abstract: Adaptive Optics (AO) systems allow astronomers to counteract the light-distorting effects of the atmosphere, providing for a superior telescope image quality. A Wavefront Sensor (WFS) is essentially the eyes of an AO system, allowing the system to measure and correct the aberration of an incoming light beam in real time. KAPAO Prime, the AO system for use on Pomona College’s 1-meter telescope at the Table Mountain Observatory, uses a Shack-Hartmann style WFS. This type of WFS divides the wavefront into compartments and measures the compartments’ individual tilt in order to determine the total wavefront error. The system then corrects for the wavefront error using a deformable mirror. Careful alignment of the system’s WFS leg is essential for understanding and optimizing the performance of the AO feedback loop. Furthermore, with the use of various programs written in Interactive Data Language (IDL), we were better able to align KAPAO Prime’s WFS camera and visualize the telemetry of a working AO loop.
Funding Provided by: Sherman Fairchild Foundation (JW, FO); Paul K. Richter and Evelyn E. Cook Richter Memorial Fund (DB); National Science Foundation #AST¬0960343
KAPAO Prime I: Design and Assembly of an Adaptive Optics instrument
Jonathan Wong (2015); Student Collaborator(s): Dalton Bolger (2014); Fernando Ortega (2015); Christian Guerrero (2016 HMC); Katie Badham (2013 Sonoma State University); Additional Collaborator(s): Scott Severson (Sonoma State University); Mentor(s): Philip Choi
Abstract: KAPAO Prime is Pomona's permanent natural guide star Adaptive Optics instrument for the college's 1-meter telescope at Table Mountain Observatory (TMO). KAPAO Prime includes significant upgrades to improve the performance and robustness of the system compared to the prototype. Such upgrades include custom optics to improve image quality, dichroic optics instead of beam splitters for significantly better throughput, and a larger pickoff mirror to significantly widen the field of view. One of many processes this summer included aligning the static system up to the wavefront sensor (WFS) leg. The tolerances of specific optics while mounted to the telescope were also examined. KAPAO Prime was assembled and successfully operated both in a laboratory setting and on a live star during this summer. The system will be optimized and fully automated in the future.
Funding Provided by: Sherman Fairchild Foundation (JW, FO); Paul K. Richter and Evelyn E. Cook Richter Memorial Fund (DB); National Science Foundation #AST¬0960343
An Automated Photodiode Frequency Response Measurement System for LIGO
Alexander Cole (2015); Mentor(s): Eric Gustafson (Caltech)
Abstract: LIGO will detect gravitational waves using laser interferometers that will be quantum noise limited over most of the apparatus's operating frequency range. To build an interferometric gravitational wave detector that works at the limits set by quantum mechanics, one must ensure that the detector can be controlled and read out optically. In the LIGO interferometers, several photodiodes are used to sense various degrees of freedom and provide feedback signals so that the cavities are in optical resonance. In addition, the main interferometric gravitational wave signal is read out with a photodiode. It is thus necessary to treat the photodiode and its readout electronics as systems whose performances, including frequency response, can change over time and with changing operating conditions. This project’s purpose was to build an automatic frequency response measurement system for the interferometer’s photodiodes. We use a modulated diode laser coupled through a fiber optic distribution system to illuminate the photodiodes, and then automatically and quickly measure the frequency response of each photoreceiver using a network analyzer and an RF switch to select the photodiodes one after another. The experiment was carried out at Caltech on the LIGO 40m prototype interferometer and designed with Advanced LIGO scalability in mind.
Funding Provided by: National Science Foundation (Caltech)
Total Internal Reflection Microscopy of Lipid Bilayers on a Fused Silica Substrate
John Horne (2014); Mentor(s): Alfred Kwok
Abstract: Unavailable at press time.
Funding Provided by: Pomona College SURP
BOB YbF & RbF: Isotope Invariant Data Analysis
Zachary Glassman (2014); Additional Collaborator(s): Jens-Uwe Grabow (Leibnitz University, Hannover); Timothy Steimle (Arizona State University); Mentor(s): Richard Mawhorter
Abstract: Determining the electric dipole moment (eEDM, or “shape”) of the electron could unlock a path to physics beyond the standard model, which predicts a value less than 10-40 e•cm, while most other theories predict a much larger value. The current limiting measurement is ~10-27 e•cm, made by an Imperial College team on open shell molecule YbF. Observing the nuclear electric hyperfine structure (eQq) for YbF will help constrain the wave functions used to quantify the eEDM. There is also a very small but nonzero probability for electrons to be near and even inside the nucleus, resulting in a slight perturbation of the nuclear quadrupole moment Q for closed shell molecules like RbF, as well as in parity-violating (PV) shifts due to the relativistic electron-nucleus interaction in molecules like YbF and PbF. These include the larger spin-dependent anapole moment as well as the tiny spin-independent eEDM. We use Fourier transform microwave spectroscopy with sub-kHz resolution to explore these senistivities, and have also utilized isotope invariant data analysis techniques. This allows us to couple together data from different isotopes to determine more robust fit parameters and to predict spectra for unobserved molecules, as well as to see effects of the breakdown of the Born-Oppenheimer approximation, i.e. the complete separation of the nuclear and electronic wave functions. We have determined BOB values for several different diatomic molecules including KF, RbF and YbF.
Funding Provided by: Pomona College SURP; Sontag Faculty Fellowship
Efficiency and Durability of P3HT:PCBM Inverted Organic Photovoltaics
Madeline McGaughey (2016); Mentor(s): David Tanenbaum
Abstract: Organic photovoltaics (OPVs) have been an area of increasing interest in the scientific community due primarily to their ability to be manufactured under ambient conditions and significantly lower production cost (compared with conventional silicon-based photovoltaics). To become a commercially viable alternative, however, their stability and efficiency must be improved. Further, a replacement must be found for indium tin oxide (ITO), which serves as a transparent electrode, but which is both brittle and expensive. Inverted poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) photovoltaic cells were fabricated and characterized for efficiency and decay/stability. Two different variants of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were added in some cells as an electron hole conducting layer. It was observed that cells with the less conductive PEDOT:PSS layer yielded a lower initial power conversion efficiency (PCE) than cells with no PEDOT:PSS layer (average 0.28% versus 0.75%s), while cells with the more conductive PEDOT:PSS layer yielded a higher average initial PCE (0.85%). Several samples with the more conductive PEDOT:PSS layer were encapsulated under ambient conditions using a piece of indented glass sealed with a UV-cure epoxy. Though the short-circuit current, a key factor in overall PCE degradation, was stabilized, the average initial PCE was lower than in the unencapsulated cells (0.47%). Further, the overall PCE stability was not noticeably improved due to a more rapid decay in open-circuit voltage.
Funding Provided by: Pomona College SURP; National Science Foundation #DMR-1126080
An Assessment of Organic Solar Cell Performance
Charles Owens (2014); Mentor(s): David Tanenbaum
Abstract: The maximum power output and degradation of 20 organic solar cells were measured over five months in both an inside and outside environment. These organic cells are state of the art, and came from eight different international collaborators. The degradation of each cell was measured by observing the power conversion efficiency (PCE) and normalized conversion efficiency (NPCE) of each cell. Multiple programs were written using Microsoft Excel 2010 VBA in order to locate each cell’s daily maximum power value along with graphing the maximum power’s corresponding current vs. voltage (I-V) curve. Since 12 cells were used in both the indoor and outdoor setups, the performances of these cells were able to be compared and evaluated with one another. For the outdoor setup, IAPP cells experienced complete degradation within the first ten days of measurement; one Heliatek cell and two IMEC cells experienced a sudden drop in performance after the first thirty-five and fifty-five days of measurement, respectively; all other cells are currently still active and producing positive PCE values.
Funding Provided by: Rose Hills Foundation
Deposition of Ultra-Thin Semiconductor Nanocrystal Films for use in Novel Photovoltaics
Eric Puma (2014); Additional Collaborator(s): Nanditha Dissanayake (Brookhaven National Laboratory); Matthew Eisaman (Brookhaven National Laboratory); Mentor(s): David Tanenbaum
Abstract: Due to the effects of quantum confinement, semiconductor nanocrystals (SNC) exhibit interesting optoelectronic properties which make them a candidate for use in novel photovoltaic (PV) devices. We believe ultra-thin (i.e. few monolayer) SNC layers can uncover improved optoelectronic properties leading to higher PV efficiencies. We explore dip and drop coating methods to deposit ultra-thin layers of SNCs and characterize these films with atomic force microscopy (AFM) and optical microscopy. Drop coating produces densely packed multilayer films, but offers little thickness control. Alternatively, a custom-built dip coater produces sub-monolayer films with ~30% coverage in one dip, while multiple dips can be used to assemble films of controlled thickness. To understand SNC film performance within a photovoltaic device, we fabricate graphene/SNC/metal-oxide/metal prototype PVs with SNC films and test the optoelectronic behavior. The devices demonstrate photocurrent together with doping-induced charge transport properties in the graphene layer. In future research, these ultra-thin SNC films will be applied in more complex PVs, which we predict can demonstrate hot-carrier based charge extraction leading to higher efficiency PVs from the SNC for the first time.
Funding Provided by: U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists under the Summer Undergraduate Laboratory Internships Program; U.S. Department of Energy, Sustainable Energy Technologies Department
High-resolution spatial mapping of thin-film photovoltaic cells
Emily Yang (2014); Additional Collaborator(s): Ahsan Ashraf (Sustainable Energy Technologies Department, Brookhaven National Laboratory; Department of Physics and Astronomy, Stony Brook University); Matthew Eisaman (Sustainable Energy Technologies Department, Brookhaven National Laboratory; Department of Physics and Astronomy, Stony Brook University); Mentor(s): David Tanenbaum
Abstract: We have developed a high-resolution spatial mapping capability for thin-film photovoltaics (PV) that will lead to improved device performance and lower cost. While PV characteristics such as power conversion efficiency (η) and fill factor are generally extracted by illuminating an entire cell and measuring the current-voltage response, some parameters are often overlooked without further analysis. Using Python, we implemented a lumped circuit model to extract these parameters such as shunt conductance (G) and temperature-dependent performance metrics. Next, in a new approach to the Light-Beam-Induced Current (LBIC) technique, we used a supercontinuum laser to measure the spatial variation in current-voltage response and associated parameters like η and G with a spatial resolution of less than 10 μm. We applied our model to U.S. Photovoltaic Manufacturing Consortium thin-film CIGS (Cu(In1-x,Gax)Se2) solar cells to identify spatial nonuniformities that reduce cell performance, and to connect these to possible improvements in the manufacturing process.
Funding Provided by: U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships Program (SULI); U.S. Department of Energy, Sustainable Energy Technologies Department under contract DE-AC02¬98CH10886
No Longer Retro: A Six Independent Beam MOT
Benjamin Girodias (2015); Student Collaborator(s): Erika Carlson (2015); Mentor(s): Dwight Whitaker
Abstract: Although theoretically predicted almost 90 years ago, Bose-Einstein Condensates (BECs), a state of matter in which macroscopic clouds of ultra-cold atoms display quantum mechanical characteristics, have only been created in the lab since 1995. To produce these BECs, rubidium atoms are initially collected and cooled in a Magneto-Optical Trap (MOT) and then further compressed before being transferred into a shallower magnetic or electric dipole trap where evaporative cooling allows the atoms to form a BEC. This compression process is not well understood, and different groups have had success with wildly different methods. In order to study this compression process as well as improve our existing experimental set-up, we replaced our MOT's three collimated retro-reflected laser beams with six independent diverging beams. By using this diverging beam design, we achieved a larger trapping volume than that was possible with collimated beams, yielding larger numbers of captured atoms despite the loss in beam intensity. Furthermore, this design will give us more degrees of freedom, such as adjustable intensity of each individual beam, to investigate the different compression methods used to form BECs. Initial efforts suggest that this six diverging-beam method would produce larger MOTs and has more parameters to examine, but the set-up has yet to be optimized.
Funding Provided by: Sherman Fairchild Foundation (BG); Paul K. Richter and Evelyn E. Cook Richter Memorial Fund (EC)
A More Efficient Polarimeter Design for the TMO Instrument Package
Chanud Yasanayake (2016); Student Collaborator(s): Vicente Robles (2016); Mentor(s): Alma Zook
Abstract: Pomona College's one-meter telescope is equipped with a CCD camera, Johnson BVRI and Sloan g'r'l' filters, and a Savart-plate polarimeter with a total instrument-package weight of about 100 pounds. A majority of the summer was spent designing and constructing a replacement for this box to provide a more efficient polarimeter as well as to reduce weight to allow adding a newly introduced adaptive optics setup. This replacement is still being built and will hopefully be permanently mounted on the telescope before the 2014 spring semester. In addition, a filter mounting platform and new filter wheel cover were designed to accommodate two Wollaston prisms added to the upper filter wheel. Both the filter mounting platform and the new cover were made on Pomona's 3D printer.
Funding Provided by: Pomona College SURP