Physical Sciences and Mathematics Commons^™

Analysis Of Spin Polarization In Half-Metallic Heusler Alloys, Alexandra Mcnichol Boldin

Macalester Journal of Physics and Astronomy

Half-metals have recently gained great interest in the field of spintronics because their 100% spin polarization may make them an ideal current source for spintronic devices. This project examines four Heusler Alloys of the form Co₂Fe_xMn_1−xSi that are expected to be half-metallic. Two magnetic properties of these alloys were examined, the Anisotropic Magnetoresistance (AMR) and the Anomalous Hall Effect (AHE). These properties have the potential to be used as simple and fast ways to identify materials as half-metallic or non-half-metallic. The results of these measurements were also used to examine the spin …

Modelling Transient Terahertz Magneto-Spectroscopy Measurements Of P-Type Cvd Graphene Leading To A Negative Photoconductivity., Rhyan Foo Kune

Macalester Journal of Physics and Astronomy

Ultrafast Terahertz (THz) Magneto-Spectroscopy (UTMS) measurements were performed on p-type CVD graphene sample to investigate the intrinsic carrier dynamics of the material. We investigated static and time-resolved THz transmission measurements, in which the sample was photo-excited by a near infrared (NIR) pump pulse, in order to study its behavior in a magnetic field. In these measurements the free carriers were probed to independently measure the carrier density and scattering rate in this film. We observed, in our graphene sample, an increase in transmission related to a negative photoconductivity (decrease in conductivity after photoexcitation) consistent with previous research. This decrease is …

Ultrafast Photoconductivity Measurements Of A Thermoelectric Nanocomposite: Tellurium Nanowire/Pedot:Pss, Brittany A. Ehmann

Macalester Journal of Physics and Astronomy

This project explores the conductivity properties of a novel thermoelectric hybrid material (Tellurium nanowires in a conducting polymer PEDOT:PSS) using both static and time-resolved conductivity measurements. We find that the effect of the conducting polymer PEDOT is weak and that the observed differences in conductivity measurements between the hybrid and non-hybrid material are most likely caused by the different sizes of the nanowires.

Mid-Ir Excitation Of Graphene, Andrew R. Banman, James Heyman

Macalester Journal of Physics and Astronomy

In this research we investigate how the conductivity of graphene changes in response to mid-infrared photoexcitation. Our p-type sample was formed through chemical vapor deposition. Pump/probe methodology produced the time-resolved Terahertz transmission, from which the photoconductivity was calculated. We probed the sample with energies above and below the Fermi energy, which was determined by Fourier transform infrared spectroscopy. Our results support a model in which heating of the electron gas, leading to high carrier scattering rates, is responsible for a decrease in conductivity. We observe this negative photoconductivity at all pump energies, allowing us to rule out the possibility of …

The Role Of Cold Gas In Low-Level Supermassive Black Hole Activity, Erik D. Alfvin

Macalester Journal of Physics and Astronomy

The nature of the relationship between low-level supermassive black hole activity and galactic cold gas, if any, is currently unclear. It has been hypothesized that feedback may heat or expel gas and quench star formation; alternatively, central black holes may feed at higher rates (either directly or as a secondary effect from stellar winds) in gas-rich galaxies. We use a combination of radio data from the on-going ALFALFA survey and from the literature, along with archival X-ray flux measurements from the Chandra X-ray observatory, to investigate this potential relationship. We construct a sample of 136 late-type galaxies, with MB < −18 out to 50 Mpc, that have both HI masses and sensitive X-ray coverage. Of these, 76 host a nuclear X-ray source, a 56% detection fraction. There is a highly significant correlation between LX and Mstar with a slope of 1.5±0.2, and a tentative correlation (significant at the 2.5σ level) between LX and MHI. However, a joint fit to LX as a function of both Mstar and MHI finds no significant dependence on MHI, and similarly the residuals of LX − LX(Mstar) show no trend with MHI. We conclude that the galaxy-wide cold gas content in these spirals does not strongly influence their low-level supermassive black hole activity.

U.S. Drought Monitor, May 12, 2015, Brian Fuchs

United States Agricultural Commodities in Drought Archive

Drought map of U.S. for May 12, 2015 (5/12/15) plus: U.S. crop areas experiencing drought (map), Approximate percentage of crop located in drought, by state (bar graph), Percent of crop area located in drought, past 52 weeks (line graph) for: Corn, Soybeans, Hay, Cattle, Winter wheat.

Estimating Stormwater Runoff For Community Gardens In New York City, Mara Gittleman

Theses and Dissertations

While much of the literature cites community gardens as providing urban ecosystem services, there is very little research quantifying these benefits. This thesis compares the stormwater runoff rates of urban vacant lots, community gardens, and residential developments in New York City and evaluates community gardens as green infrastructure.

Early Rayleigh-Scatter Lidar Temperature Measurements From The Lower Thermosphere, Leda Sox, Vincent B. Wickwar

Leda Sox

Rayleigh-scatter lidar observations were made on many clear nights at the Atmospheric Lidar Observatory (ALO) at Utah State University (USU) from 1993 to 2004 in the altitude range 45–90 km. An upgraded facility, 66 times more sensitive, has been brought on line. It has resulted in temperature measurements with maximum altitudes that extend into new territory—the lower thermosphere. All-night temperature averages have been recorded up to an altitude of 114 km. Temperatures from each month, starting in June 2014, are presented and discussed. They are compared to each other, to the ALO-USU climatology from the original lidar, and to temperatures …

Double Robust Estimation Of Encouragement-Design Intervention Effects Transported Across Sites, Kara E. Rudolph, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

We develop double robust targeted maximum likelihood estimators (TMLE) for transporting intervention effects from one population to another. Specifically, we develop TMLE estimators for three transported estimands: intent-to-treat average treatment effect (ATE) and complier ATE, which are relevant for encouragement-design interventions and instrumental variable analyses, and the ATE of the exposure on the outcome, which is applicable to any randomized or observational study. We demonstrate finite sample performance of these TMLE estimators using simulation, including in the presence of practical violations of the positivity assumption. We then apply these methods to the Moving to Opportunity trial, a multi-site, encouragement-design intervention …

Analysis And Dynamics Of Laser Models, Kassaundra Przelomski

Honors Program Theses and Projects

Lasers produce a strong focused ray of light that is useful in many industries, including medicine and technology. For example, they can be used for guiding surgical instruments or playing compact discs. In this thesis I characterize the dynamics of a fundamental laser model. A mathematical goal is to determine the number of photons in the laser cavity as time evolves. Different choices of parameter values produce qualitatively different behaviors of the system. I perform a bifurcation analysis in order to capture the different physical situations, identifying equilibrium solutions and their stability properties. I sketch representative solutions using the bifurcation …

Exploring Residents’ Attitudes Toward Solar Photovoltaic System Adoption In China, Yaqin Sun

Honors Program Theses and Projects

As the largest energy consuming country, China is facing environmental deterioration, which results from the overuse of non-renewable conventional energy such as coal. Solar photovoltaic (PV) energy, an unlimited and clean energy with minimal impacts on the environment, is considered to be a good alternative to alleviate this severe issue. A survey was designed and conducted among residents in some major cities. Based on the first hand data, basic statistical methods were utilized to examine Chinese residents’ knowledge of, concerns, and attitudes towards PV adoption. The research aims to identify the drivers and dynamics that most encourage customers to install …

Topological Data Analysis Of Biological Aggregation Models, Chad M. Topaz, Lori B. Ziegelmeir, Tom Halverson

Faculty Publications

No abstract provided.

An Analysis Of Numerical Methods On Traffic Flow Models, Terry Mullen

Honors Program Theses and Projects

In this thesis, we implement Euler's method and the Runge-Kutta method to solve initial value problems. A goal of the project is to compare the two methods on preliminary problems illustrating limitations and advantages. We also apply the Runge-Kutta method to a mathematical model of traffic flow. This thesis sheds light on how the fourth-order Runge-Kutta method is implemented to solve the Optimal Velocity Model (Kurata & Nagatani, 2003). We identify initial conditions and base cases to run simulations of the model. We consider one-car and two-car systems to validate the application of the fourth-order Runge-Kutta method and the Optimal …

Life On The Floodplain: An Analysis Of Falmouth, Massachusetts And Osaka, Japan, Shellie Johnson

Honors Program Theses and Projects

After Hurricane Katrina in 2005, the awareness of flooding threats to coastal areas increased. For Massachusetts in particular, Cape Cod is still at high risk of flooding with any storm that comes and goes. However, all of these recent devastating floods and natural disasters have caused insurance prices to skyrocket. With my research, I specifically looked at Falmouth, Massachusetts and the possibilities to lessen the risks and which of these options would be the most financially sound for a homeowner. The possibilities include elevating a house in a high flood risk zone, selling a current house to move in to …

Dual Species Magneto-Optical Trap, Daniel Woodbury, Scott Bergeson

Journal of Undergraduate Research

In the last several decades, laser cooling has become the primary tool for atomic research and, in our lab, has facilitated the study of ultracold plasma. Using a novel laser cooling setup, we created a vacuum chamber and related hardware for a dual species magneto-optical trap (MOT). The design of the MOT will allow us to improve trapping efficiency and atom density in our plasma, better understand laser cooling and trapping of calcium and ytterbium, and probe their interactions in ultracold hetero-nuclear plasma.

Benchmark Structures And Harmonic Vibrational Frequencies Near The Ccsd(T) Complete Basis Set Limit For Small Water Clusters: (H2o)N = 2, 3, 4, 5, 6, J. Coleman Howard, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

A series of (H₂O)_n clusters ranging from the dimer to the hexamer have been characterized with the CCSD(T) and the 2-body: Many-body CCSD(T):MP2 methods near the complete basis set (CBS) limit to generate benchmark-quality optimized structures and harmonic vibrational frequencies for these important systems. Quadruple-ζ correlation-consistent basis sets that augment the O atoms with diffuse functions have been employed in the analytic computation of harmonic vibrational frequencies for the global minima of the dimer, trimer, tetramer, and pentamer as well as the ring, book, cage, and prism isomers of the hexamer. Prior calibration [J. Chem. Phys. 2013, …

Stress Relieving Video Games: Creating A Game For The Purpose Of Stress Relief And Analyzing Its Effectiveness, Nicole Mercer

Honors Program Theses and Projects

Stress is an inevitable part of human life that can have both physical and mental repercussions if left to simmer. The purpose of this project was to make a simple game-like application that will be at least as effective at relieving stress as other games referenced in my research below. To accomplish this, I took common ideas known to relieve stress and designed a game that incorporates them, programming the game in Java. Then, to test the effectiveness of the created game, I had several subjects fill out a questionnaire about their stress levels and took their blood pressure. One …

Exploring The Calkin-Wilf Tree: Subtrees And The Births Of Numbers, Kayla Javier

Honors Program Theses and Projects

No abstract provided.

How Does Tutoring To Develop Conceptual Understanding Impact Student Understanding?, Kelsey Cummings

Honors Program Theses and Projects

No abstract provided.

The 2d Distribution Of Iron-Rich Ejecta In The Remnant Of Sn 1885 In M31, Robert A. Fesen, Peter A. Höflich, Andrew J. S. Hamilton

Dartmouth Scholarship

We present Hubble Space Telescope (HST) ultraviolet Fe i and Fe ii images of the remnant of Supernova 1885 (S And) which is observed in absorption against the bulge of the Andromeda galaxy, M31. We compare these Fe i and Fe ii absorption line images to previous HST absorption images of S And, of which the highest quality and theoretically cleanest is Ca ii H and K. Because the remnant is still in free expansion, these images provide a 2D look at the distribution of iron synthesized in this probable Type Ia explosion, thus providing insights and constraints …

Developing Key Sustainability Competencies Through Real-World Learning Experiences: Evaluating Community Environmental Services, Erin Lorene Anderson

Dissertations and Theses

This study focuses on sustainability in higher education and the competencies essential to address sustainability issues. Because sustainability issues are complex, "wicked", and dynamic, sustainability education programs need to reflect the interdisciplinary and collaborative nature of the field. Graduates who are competent in sustainability research and problem solving will have the knowledge, skills, and attitude necessary to analyze a sustainability problem systemically and comprehensively, then will construct and implement interventions to reach optimal sustainability solutions. To prepare graduates, sustainability education programs should facilitate the development of key sustainability competencies (Wiek, Withycombe, & Redman, 2011). Such programs provide an interdisciplinary approach …

Investigation Of Asymmetric Impacts On Protective Headgear, Kristina Medero

Mahurin Honors College Capstone Experience/Thesis Projects

This project explores helmet-to-helmet impacts and their detriments with a unique perspective. The propagation of dangerous waves into the brain can result in a concussion. Considering 60% of NFL players have had at least one concussion (Epstein 2011), it is imperative to understand the materials that construct helmets and observe how these materials behave in regards to impact location while recording wave propagations from the impacts. This study interrogates the effect of asymmetric impacts on gridiron football helmets using the Large Chamber Scanning Electron Microscope (LC-SEM). Utilizing two standard issued football helmets made of polycarbonates, a hard plastic, vibrations from …

Synthesis And Application Of Pdib Nanostructures In Solar Cells, John T. Ferguson

Mahurin Honors College Capstone Experience/Thesis Projects

Perylenediimide bridged silsesquioxane (PDIB) nanoparticles were synthesized by sol-gel processes as described by the Stöber method. These particles were synthesized homogeneously from solution and with the use of silica nanoparticles and bipyridine iodide bridged silsesquioxane (BPIB) nanoparticles as nucleation sites. The morphology of the resulting particles was confirmed by TEM and the presence of PDI confirmed by UV spectroscopy. Although further research will test all of the particles across a range of concentrations and sizes, the silica nucleated PDIB nanoparticles were analyzed in the active layer of bulk heterojunction organic photovoltaic devices in conjunction with P3HT polymer. Devices with the …

Paleoenvironmental Reconstruction Of An Upper Ordovician Rocky Shoreline: The Lindsay Formation Of Heywood And Partridge Islands, Ontario, Hiba-Tul Naseer Maheen

Electronic Thesis and Dissertation Repository

The islands of Heywood and Partridge, located northeast of Manitoulin Island in Georgian Bay, Ontario, preserve a major unconformity between the Paleoproterozoic Bar River and Lorrain Formation quartz arenite and Upper Ordovician Lindsay Formation carbonate and mudrock. The Lindsay Formation strata record two transgressive pulses of an epeiric sea that flooded the North American continent during the Late Ordovician. During this time, mountain building processes associated with the Taconic Orogeny were taking place to the present east, and the tectonic effects of this orogeny resulted in subsidence of the Michigan Basin. The Lindsay Formation of the Trenton Group was deposited …

Optical Control Of Electron Phase Space In Plasma Accelerators With Incoherently Stacked Laser Pulses, Serge Y. Kalmykov, Xavier Davoine, Remi Lehe, Agustin F. Lifschitz, Bradley A. Shadwick

Serge Youri Kalmykov

Research In Mathematics Educational Technology: Current Trends And Future Demands, Shannon O. Driskell, Robert N. Ronau, Christopher R. Rakes, Sarah B. Bush, Margaret L. Niess, David K. Pugalee

Shannon O.S. Driskell

This systematic review of mathematics educational technology literature identified 1356 manuscripts addressing the integration of educational technology into mathematics instruction. The manuscripts were analyzed using three frameworks (Research Design, Teacher Knowledge, and TPACK) and three supplementary lenses (Data Sources, Outcomes, and NCTM Principles) to produce a database to support future research syntheses and meta-analyses. Preliminary analyses of student and teacher outcomes (e.g., knowledge, cognition, affect, and performance) suggest that the effects of incorporating graphing calculator and dynamic geometry technologies have been abundantly studied; however, the usefulness of the results was often limited by missing information regarding measures of validity, reliability, …

Prospective Teachers' Use Of Representations In Solving Statistical Tasks With Dynamic Statistical Software, Hollylynne Lee, Shannon O. Driskell, Suzanne R. Harper, Keith R. Leatham, Gladis Kersaint, Robin L. Angotti

Shannon O.S. Driskell

This study examined a random stratified sample (n=62) of prospective teachers' work across eight institutions on three tasks that utilized dynamic statistical software. Our work was guided by considering how teachers may utilize their statistical knowledge and technological statistical knowledge to engage in cycles of investigation. Although teachers did not tend to take full advantage of dynamic linking capabilities, they utilized a large variety of graphical representations and often added statistical measures or other augmentations to graphs as part of their analysis.

Accurate Determination Of The Free–Free Gaunt Factor – Ii. Relativistic Gaunt Factors, P. A. M. Van Hoof, Gary J. Ferland, R. J. R. Williams, K. Volk, Marios Chatzikos, M. Lykins, R. L. Porter

Physics and Astronomy Faculty Publications

When modelling an ionized plasma, all spectral synthesis codes need the thermally averaged free–free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum. Until now no data set exists that would meet these needs completely. We have therefore produced a table of relativistic Gaunt factors over a much wider range of parameter space than has ever been produced before. We present tables of the thermally averaged Gaunt factor covering the range ¹⁰log γ² = −6 to 10 and ¹⁰log u = −16 to 13 for …

Precision Measurements Of AN1 In The Deep Inelastic Regime, K. Allada, C. Dutta, A. Kolarkar, Wolfgang Korsch, D. S. Parno, D. Flay, M. Posik, W. Armstrong, T. Averett, F. Benmokhtar, W. Bertozzi, A. Camsonne, M. Canan, G. D. Cates

Physics and Astronomy Faculty Publications

We have performed precision measurements of the double-spin virtual-photon asymmetry A₁ on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized ³He target. Our data cover a wide kinematic range 0.277 ≤ x ≤ 0.548 at an average Q² value of 3.078 (GeV/c)², doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in …

Precision Measurements Of A1n In The Deep Inelastic Regime, Diana S. Parno, David Flay, Matthew Posik, Kalyan C. Allada, Whitney Armstrong, Todd Averett, Fatiha Benmokhtar, William Bertozzi, Alexandre Camsonne, Mustafa Canan, Gordon D. Cates, Chunhua Chen, Jian-Ping Chen, Sunghyun Choi, Eugene Chudakov, Francesco Cusanno, Mark M. Dalton, Wouter Deconick, Kees W. De Jager, Xiaochao Deng, Alexandre Deur, Chiranjib Dutta, Lamiaa El Fassi, Gregg B. Franklin, Megan Friend, Haiyan Gao, Franco Garibaldi, Shalev Gilad, Ronald Gilman, Oleksandr Glamazdin, Serkan Golge, Javier Gomez, Lei Guo, Ole Hansen, Douglas W. Higenbotham, Timothy Holmstrom, Jacob Huang, Charles Hyde, Hassan F. Ibrahim, Xiaodong Jiang, Ge Jin, Joseph Katich, Aidan Kelleher, Ameya Kolarkar, Wolfgang Korsch, Gerfried Kumbartzki, John J. Lerose, Richard Lindgren, Nilanga Liyanage, Elena Long, Alex Lukhanin, Vahe Mamyan, Dustin Mcnulty, Zein-Eddine Meziani, Robert Michaels, Miha Mihovilovic, Bryan Moffit, Navaphon Muangma, Sirish Nanda, Amrendra Narayan, Vladimir Nelyubin, Blaine Norum, Nuruzzaman Nuruzzaman, Yoomin Oh, Jen-Chieh Peng, Xin Qian, Yi Qiang, Abdurahim Rakhman, Seamus Riordan, Arun Saha, Bradley Sawatzky, Mitra H. Shabestari, Albert Shahinyan, Simon Širca, Patricia Solvignon, Ramesh Subedi, Vincent Sulkosky, William A. Tobias, Wolfgang Troth, Diancheng Wang, Youcai Wang, Bogdan Wojtsekhowski, Xinhu Yan, Huan Yao, Yunxiu Ye, Zhihong Ye, Lulin Yuan, Xiaohui Zhan, Li Zhang, Yawei Zhang, Bo Zhao, Xiaochao Zheng

Articles

We have performed precision measurements of the double-spin virtual-photon asymmetry A₁A1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized ³He target. Our data cover a wide kinematic range 0.277≤x≤0.5480.277≤x≤0.548 at an average Q²Q2 value of 3.078 (GeV/c)², doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same …