Student Posters

Rotation

Katarzyna Bieniek

Helicobacter pylori(H.pylori),a helical shaped bacteria known to live in the mucus layer of stomachs of more than half of the world's population, can lead to ulcers and gastric cancer. The naturally occurring pH gradient present in the protective gastric mucus lining of the stomach, varying from 2-4 on the lumen to 7 on the epithelial cell surface, presents a gradient in viscoelasticity because mucin, the glycoprotein in mucus, transforms from a liquid to a gel below pH 4. In order to survive and colonize the host system, the acidophobic bacteria must travel across the gastric mucus, away from the low pH, to reach the epithelial cells. We investigate the correlation between mucin pH, its viscoelasticity, and the motility of the bacteria. For these studies we use a clinical isolate strain J99 and purified porcine gastric mucin (PGM) to determine how pH levels effect the shape, size, and rotation speeds of the bacteria.

Production and Characterization of Ultrafast Light Pulses

Iona Binnie, Emily Stump

We research the arrangement of the atoms in a crystal during structural transformations. To observe these processes, we use ultrafast electron diffraction to compile images of the atoms during a physical or chemical transition. These images will help us to learn about how the macroscopic properties of materials arise from their atomic-scale properties. Our poster discusses the production of ultrafast pulses as well as simulation, design, and construction of various components of our experiment.

3D piezoresponse force microscopy using contact resonances

Grace Cai

Piezoresponse force microscopy (PFM), a common method for characterization of ferroelectric materials at nanometer scales, is used to study multiferroic hexagonal manganites HoMnO₃ and YbMnO₃. For a material with unknown orientation, there could be both out-of-plane and in-plane piezoelectric responses. The out-of-plane deformation leads to vertical deflection of the cantilever, while the in-plane deformation leads to torsional and buckling deformation of the cantilever. The torsional mode of the atomic force microscopy (AFM) cantilever results in a “lateral” signal of the AFM position sensor, while both deflection and buckling result in a “deflection” signal, which complicates the analysis of ferroelectric domain pattern in PFM images. Herein, we propose a method to differentiate these two modes without rotating the sample utilizing the contact resonance of either deflection or buckling mode. If we succeed, this would allow 3D PFM imaging without sample rotation. We performed controlled PFM experiments on two different surfaces, (110) and (001), of hexagonal manganites with in-plane and out-of-plane polarization, respectively. The buckling contact resonance is approximately 400 kHz, and the deflection contact resonance is approximately 450 kHz. Preliminary results indicate that the ratio of the two contributions can be varied significantly by changing excitation frequency. Due to the close proximity of the buckling and deflection contact resonances, however, it is difficult to achieve complete separation of these two responses. This project is supported by funding from National Science Foundation grant PHY-1560077 and grant DMR-1506618.

Interactive Environment for Undergraduate Physics Learning

Devon Christman

Challenges in undergraduate physics learning include non-interactive textbooks, labs which are often incidental to cementing more complex concepts as well as simplified physical descriptions of phenomena which diverge with common experiences of them. These challenges often lead to difficult to surmount barriers to learning. We present a framework for an environment for learning undergraduate physics which utilizes a multi-pronged and multi-media approach focusing on core concepts. Content is made available in textual, visual and interactive ways through the use of touch-enabled and virtual reality simulation tools. This content will be iteratively developed through feedback from student use in formal and informal settings supporting physics learning. We plan to continue the project with the goal of eventually placing all content online accessible to all students and instructors through an interactive mind map.

Quenching and Tunable Recovery of Photoluminescence in van der Waals Heterostructures

Monika Eggenberger

Photoluminescence properties of monolayer materials present exciting frontiers in nanoscale optoelectronics. We observe crystrographically aligned growth of monolayer Bi2Se3 on grown single-crystal monolayer MoS2 via chemical vapor deposition. This results in quenching of the photoluminescence job monolayer MoS2. We show that that this photoluminescence is tunably recoverable with controlled exposure to a laser, and that repeated laser treatment also displays evidence of laser annealing of Bi2Se3, shifts in peak energy, discrete stable energy levels, and convergence of A and A- exciton intensities. This presents unique opportunities in materials engineering, nano device construction, and potential for bit writing systems.

Monte Carlo wave functions to model Doppler laser cooling

Derek Galvin

We use Monte Carlo wave functions to simulate the electronic and motional states of an atom interacting with laser fields in a reservoir made of electromagnetic vacuum modes. We hope to use this method to develop a quantum description of some novel laser cooling techniques.

Jet Mass Differential Cross Section

Lauren Hay

We present a measurement of the differential jet production cross section as a function of the jet mass and transverse momentum in events with a dijet topology, with and without a jet grooming algorithm applied. For ungroomed jets, leading-order and next-to-leading order QCD Monte Carlo programs are found to predict the jet mass spectrum in the data reasonably well, with some disagreement at very low and very high masses. For groomed jets, the agreement between the Monte Carlo programs and the data improves overall, and extends lower in jet mass due to the removal of soft and collinear portions of the jet. First-principles theoretical calculations of the groomed jet mass are also compared to the data for the first time ever at a hadron collider, and agree with the data in the range of validity of the calculations.

The VLBA-BU-BLAZAR Project

Katya Leidig

An active galactic nucleus (AGN) is a compact, luminous region at the center of a galaxy. It consists of an accretion disk around an active supermassive black hole that produces twin relativistic jets. The VLBA-BU-Blazar program aims to determine the locations and origin of high energy photons in blazars, a category of AGN whose jet is pointing towards earth. By using the Very Large Baseline Array (VLBA), a system of ten radio telescopes located around the US, at 43 GHz, the program carries out monthly monitoring of a sample consisting of 34 blazar and 3 radio galaxy jets to obtain images including linear polarization measurements. After initial calibration, images are made through an iterative process using the software package Difmap. Events originating near the black hole propagate down the jet in the form of a shock wave or other disturbance, energizing electrons and emitting synchrotron radiation. These electrons can also scatter photons to X-ray and gamma-ray energies, which are observed by orbiting telescopes. The goal of<br>the VLBA-BU-BLAZAR observations is to determine where these electrons get energized and to test theories for how such high-speed, high-energy jets are created. I will present images of selected blazars that reveal changes in the jets over time that track the motions of bright "blobs" created by the disturbances, many of which are related to outbursts of visible light, X-rays, and gamma-rays.

Determining Light Decay Curves in a Plastic Scintillator using Cosmic Rays

Sarah Mandanas

Plastic scintillators are used in HEDP and ICF research to measure neutron energies using a time of flight method. The energy resolution and sensitivity of an nToF system has a direct correlation to scintillation decay time of the plastic. To decrease the decay time, xylene scintillators are quenched with oxygen and consequentially become less efficient at producing light. As time passes, the scintillator becomes oxygen deficient which increases light production and the decay time. Mono-energetic calibration neutrons are unavailable at most HEDP and ICF facilities to monitor these increases. As a result, it is difficult to determine if oxygen concentration has decreased within these systems. Here, a possible method of calibrating xylene detectors in situ is presented. If the detectors response to cosmic ray muons is studied, it can be used to determine the scintillation decay curve produced by a mono energetic neutron. As a result, the need for the removal of the xylene detectors is eliminated.

The Arecibo Pisces-Perseus Supercluster Survey: Declination Strip 35<br>

Chelsey McMichael

The Arecibo Pisces-Perseus Supercluster Survey (APPSS) will provide strong observational constraints on the mass-infall rate onto the main filament of the Pisces-Perseus Supercluster. The survey data consist of HI emission-line spectra of cluster galaxy candidates, obtained primarily at the Arecibo Observatory (with ALFA as part of the ALFALFA Survey and with the L-Band Wide receiver as part of APPSS observations). Here we present the details of the data reduction process and spectral-analysis techniques used to determine if a galaxy candidate is at a velocity consistent with the Supercluster, as well as the detected HI-flux and rotational velocity of the galaxy, which will be used to estimate the corresponding HI-mass. We discuss the results of a preliminary analysis on a subset of the APPSS sample, corresponding to 98 galaxies located within ~1.5° of DEC = +35.0°, with 65 possible detections. We also highlight several interesting emission-line features and galaxies discovered during the reduction and analysis process and layout the future of the APPSS project. This work has been supported by NSF grants AST-1211005 and AST-1637339.

Parameters That Effect Brine Shrimp Pattern Selection

Zoha Naqawe

Self-propelled particles are physically rich systems that are also relevant in biology such as microorganisms, schools of fish, flocks of birds, and even human crowds. In this poster, we will cover the preliminary experimental work of the collective motion of an active-matter system of Artemia franscicana: (brine shrimp). Large collections of these shrimp will aggregate in such a way that they will form three-dimensional patterns, which depend on environmental properties that play into the driving and dissipation of the system. These parameters include domain size, water salinity, and the shrimp's phototaxis response to different light exposure. These differences can cause a phase separation to occur where shrimp separate into slower and faster swarms and causes spatial patterns. We also look at the individual properties such as shrimp speed and how that is affected by age i.e. size, and temperature. We quantify these properties through looking at both group behavior and individual dynamics. Ultimately, we hope to use the experimental data to model how these environmental and individual parameters effect the pattern selection to gain a better understanding of swarming and flocking which may be able to be applied to other biological systems.

Exact Canonical Transformation to Study Quantum Impurities in Graphene

Christina Nguyen

We present numerical method to study quantum impurities in graphene and other materials. It consists of an exact canonical transformation that maps the lattice Hamiltonian onto a one dimensional chain. The many-body problem of a quantum magnetic impurity in graphene can then be efficiently solved with techniques such as quantum Monte Carlo or the density matrix renormalization group (DMRG). The real space resolution allows us to capture the spatial distribution of correlations around the atom or substitutional impurity. Furthermore, the method is scalable to include multiple impurity spins, to study systems with various boundary conditions, and to study very large systems.

Computed Tomography (CT) - Methods of Tube Current Modulation (Simulation with VirtualDose)

Isabelle Peck

Modern CT scanning machines utilize a technique called tube current modulation (TCM) to maximize the benefit of medical imaging while minimizing the radiation dose that a patient receives. VirtualDose is a software that allows medical professionals and health physicists to estimate the amount of radiation delivered to a patient based on simulations. This project aims to determine a methodology and develop a program (currently in Python, later to potentially be translated into C#) that will ultimately add a TCM option to the simulation for more accurate estimates. By determining and analyzing the densities of various organs and materials in the body, we can deduce how the current must be changing in the machines such that each projection obtained has the same average resulting intensity. With better assessment of the benefits versus the risks of CT scans and the information able to be learned from the scan itself, healthcare providers can work with patients to prescribe better treatment plans.

Dynamics and chaotic properties of a spatially extended oil-candle array

Hannah Phillips

Extensive research has been devoted to the discovery of simple media that display chaotic properties. One such simple system is a candle wick that draws flammable oil from a reservoir. By varying oil viscosity and wick material, the system exhibits refractoriness and nonlinear restitution dynamics under constant periodic re-ignition. When arranged in a grid these candles can ignite their neighbors, creating propagating fire waves that can display complex spatial dynamics. In this talk, I will discuss our experimental results of the oil-candle system in multiple geometries. Furthermore, I will discuss a simple return map we have derived based on these experimental data, from which we characterize families of system parameters associated with dynamical phenomena such as period-doubling and chaos.

Measuring Transit Detection Efficiency in Ultracool Dwarfs Observed by K2

Sheila Sagear

An effective method of detecting exoplanets, planets outside our solar system, is the transit method: detecting a periodic dip in the host star's brightness as a planet passes in front of it. It is particularly interesting to study exoplanet detection around ultracool dwarfs, or small, cool stars, as these objects are expected to host earth-sized terrestrial planets. We focus on a sample of 39 ultracool dwarfs and obtain a function of their brightness over time, a light curve, from K2, the repurposed mission of NASA's Kepler telescope. We are interested in our ability to recover various types of transits around these objects. To investigate this, we inject transits that simulate planets of various orbital periods and sizes. First, we fit a box shape to these transits to estimate an orbital period and planet size. Next, we fit a more refined transit shape using these estimates as a guess. We perform this analysis on 780 distinct combinations of period and planet size injected into these 39 light curves, and study the period and radius combinations we are more likely to recover, especially related to signal to noise ratio. We find that while it is likely that planets of shorter period, larger size, and higher signal to noise ratio are more likely to be recovered, more light curves with a wider range of signal to noise ratios are needed to confirm this conclusion. We plan to use our findings in our search for exoplanets around other ultracool dwarfs in the future.

Improving power conversion efficiencies in organic solar cell bulk-heterojunctions

Juliane Scholtz

Organic solar cells typically have smaller power conversion efficiencies than their inorganic counterparts. Research suggests a link between power conversion efficiency and the morphology of the organic solar cell's bulk-heterojunction. Bulk-heterojunction are modeled here by a complex three dimensional network of diodes and resistors, with the diodes representing transport between p- and n-type materials and the resistors representing transport within p and n-type materials. Using the Jacobi iterative method in MATLAB, the currents, voltages, and power are computed for networks with over 10,000 nodes. Three different computer-generated morphologies were considered. The first sample type had the percentages of p-type and n-type materials uniform throughout the sample. The second used a linearly varying percentage pair. The third sample type consisted of a large middle region with its percentage pair, capped at the ends by regions subject to a second p-n ratio. Favorable power densities were found in the samples with 60% p-type/40% n-type throughout, as well as in the capped samples with percentages 50%-50%--60%-40%--50%-50%. In contrast, the second sample type displayed poor net power densities. This work was supported through NSF grant DMR-1461019.

High Latitude Pulsating and Flickering Auroral Morphology

Michelle Tebolt

This project investigated the physical behavior of aurora in Greenland over varying spatial and temporal scales by analyzing ground-based imager data. The aurora is crucial in fully understanding the magnetosphere, as the dynamic processes that occur within the magnetotail are mapped through the aurora at the polar caps. This set of auroral data was analyzed in order to identify flickering and pulsating auroral features and compare them to each other, as well as examine the behavior of the aurora at high latitudes. Images of the entire sky were taken at 30 frames per second over multiple hours every night in January 2011. The images that showed a clear night with visible aurora were then selected to be inspected even further through use of a narrow field camera over smaller temporal scales. Keograms were made of these specific images, and some were found to have features indicating the presence of flickering aurora. Overall, about 7 instances of flickering aurora and 2 hours worth of pulsating aurora were identified from the data. Future research using this data analysis will include calculating the velocity of the flickering aurora as it moves across the night sky, as well as comparing the flickering and pulsating aurora from this location in Greenland to auroral features present at lower latitudes such as Alaska and Montana.

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