students and professor

Past Events

  • 4/10/2014

    Weekly Geology & Physics Departmental TEA

    The Geology, Physics & Astronomy Departments are hosting the regular weekly departmental TEA. Share some tea and snacks with your colleagues and catch up with each other in the first floor atrium OLRI.

  • 4/7/2014

    Physics Seminar-Testing Relativity: The Search for New Physics at the High-Sensitivity Frontier

    Dr. Jay Tasson, Visiting Assistant Professor, Carleton College, Departments of Physics and Astronomy:

    The principle of relativity states that the results of experiments are independent of their orientation and velocity. In spite of the fact that this idea dates back over 350 years, an explosion of new tests of relativity has occurred over the past several decades. Spurred by a categorization of large classes of ways in which relativity could be violated, the new generation of experiments has constrained some of these possibilities to less than parts in 10^30. In doing so, these table-top tests gather information about the highest relevant energies known to physics. Although such astounding sensitivities have been achieved, other possible relativity violations remain nearly untested, leaving room for comparatively large relativity violations in nature. Recently, methods of investigating the unexplored possibilities using gravitational experiments and observations have been developed and are being explored using systems ranging in size from atoms to binary-star orbits.  This presentation will provide a general introduction to relativity testing and a summary of recent experimental results and proposals.

    Refreshments at 3:00 PM

  • 4/3/2014

    Physics Seminar-Nano-Engineering at the Forefront of Rotating Disk Storage Technology

    David E. Fowler, Ph.D., Senior Director, Thermo-Mechanical Design, Magnetic Head Operations at Western Digital Technologies, Inc., is speaking.

    The demand for digital information storage continues to grow unabated. Rotating, hard disk drives are the cost-preferred solution for handling the bulk of this ocean of data. This will continue to be the case for the foreseeable future, provided hard drive technology continues to be pushed to its physical limits. To meet this challenge, we are pursuing engineering solutions that control critical dimensions and positioning accuracy to within a few nanometers. Success requires a highly skilled and diverse team of nano-engineers who aggressively pursue both conventional and unconventional technology paths.

    Refreshments at 4 PM, OLRI first floor atrium.

  • 4/2/2014

    Physics Seminar-Quark Gluon Plasma: The Hottest Liquid in the Universe

    Dr. Todd Springer, Visiting Assistant Professor, Colgate College, is speaking:

    Relativistic heavy ion collision experiments aim to study the behavior of nuclear matter at extreme temperatures and densities. Particle colliders near Brookhaven, NY (RHIC) and Geneva, Switzerland (LHC) are currently operating at unprecedented energies.  It is now well accepted that quark gluon plasma (a state of matter which existed only a few microseconds after the big bang) is created in such collisions.  Surprisingly, this matter appears to behave as a very strongly interacting liquid.  In this talk I will outline what we have learned from heavy ion collisions, how we know it, and what we are still hoping to learn.

    (Picture taken from CERN Press Release)

  • 3/28/2014

    Special Physics Seminar--Native Skywatchers: Lions & Fire in the Sky, Ojibwe & D(L)akota Star Knowledge

    Professor Annette S. Lee, Planetarium & Native Skywatchers Director at St. Cloud State University, Department of Astronomy & Physics, will speak about seeing the night sky through the lens of Ojibwe and Dakota Star Knowledge. This presentation will show some of the stars of winter setting and spring rising. Also discussed will be how to successfully combine the interdisciplinary work of art and science and native culture.

    Refreshments at 3 p.m.

  • 3/7/2014

    Physics & Astronomy Senior Capstone Presentation

    Aaron Laursen, “Liquid Filled Photonic Crystal Fiber Transmission Scaling via Refractive Index Scaling.”This talk presents original research performed with the Manolia research group during the summer of 2013. Transmission-band shifting via refractive index scaling using liquid-filled photonic crystal fibers is experimentally demonstrated. The results are consistent with work performed by Antonopoulos et al. illustrating and empirically supporting a simple theoretical scaling law for fibers with varied low-index materials.

  • 3/6/2014

    RESCHEDULED! Physics Seminar-Phase Shifts, Photons, & Feedback: Irradiance Detectors in the Eye

    Jay Demas, St. Olaf College. The light sensitive portion of the eye, the retina, signals the brain about the pattern, intensity, and wavelength of light striking the retina. However, this information is used for more than just seeing. A special class of retinal neurons called melanopsin retinal ganglion cells (mRGCs) mediate behaviors that depend on light, but not on vision. These behaviors include synchronizing behavior with the external environment by setting the phase of our brain's circadian oscillator. Melanopsin, for which these cells are named, is a light-sensing protein that makes mRGCs intrinsically photosensitive. We are interested in understanding how mRGCs regulate the gain and dynamics of their light response through feedback from a class of interacting proteins called arrestins.

    Refreshments at 4 PM, OLRI atrium

  • 2/28/2014

    Physics & Astronomy Senior Capstone Presentation

    Andrew Hansen, "Langmuir Probe Measurements of an Argon Plasma." In the semiconductor industry, many techniques are used to grow semiconductors as thin-films. One such method, Plasma Enhanced Chemical Vapor Deposition (PECVD) uses high energy electrons from an ionized gas to catalyze the deposition of the films. During my research, I worked with Professor Jim Doyle to develop techniques to measure a plasma's properties to better understand this film-growing process.

    Laura Avena, "Force Constants of Coordinated CO and β-amino Substituted Isocyanides Using Infrared Spectroscopy." Metal carbonyls and isocyanides have characteristic peaks in infrared spectra. While the energies are useful in a qualitative determination of relative bond strengths, a more quantitative approach is needed to cross-compare similar complexes. Using a harmonic oscillator approximation, it is possible to determine the effective force   constants of carbon-oxygen and carbon-nitrogen bonds. This allowed me to show that negatively charged bis(diphenylphosphinomethyl)diphenylborate used in our laboratory is a better donor than its neutral analogue 1,2-bis(diphenylphosphino)ethane.

  • 2/21/2014

    Physics & Astronomy Senior Capstone Presentation

    John Graham, Kinetics of Solid Phase Crystallization of a-Ge Thin Films: The study of semiconductors has never been more exciting. One semiconductor, called thin films, is an option for solar cell and infra-red detector construction. This new model explains the crystallization process of thin film Germanium, and develops a method to explore the physics behind solid state crystallization.

    Mike Darrow, Finesse Measurement in Fabry-Perot Interferometers: Space­time Asymmetry Research is an experimental satellite that measures anisotropy in the speed of light to unprecedented resolutions using two orthogonal Fabry­Perot interferometers. To achieve the desired level of precision, the optical cavities must have finesse values greater than 100,000.  Two methods for measurement of finesse were tested: full­width half max measurement and the ringdown technique. 

  • 2/14/2014

    Physics & Astronomy Senior Capstone Presentation

    Melissa Marshall–”Persistence and Reciprocity Failure in Near Infrared Detectors”

    HgCdTe infrared detectors, such as the one aboard the Hubble Space Telescope’s Wide Field Camera 3, suffer from unusual behavior known as image persistence and reciprocity failure. These two effects introduce serious error into otherwise precise astronomical research. We present initial findings of the characteristics of image persistence and reciprocity failure, and potential avenues of further study.

    Maggie Molter–”VHE Observation of Distant Blazars using VERITAS “

    Very High Energy (VHE) gamma-ray astronomy is an exciting subfield of astrophysics that has emerged in the past 25 years or so.  VERITAS and other ground-based telescopes have detected about 40 blazars, a specific type of Active Galactic Nucleus (AGN) with its relativistic jet pointing right at the Earth's line of sight.  By examining the variability of blazars on different timescales, we hope to confirm or rule out models of Ultra High Energy Cosmic Rays (UHECRs), which may be produced by blazars and later observed indirectly by our telescopes as secondary gamma rays.

  • 1/30/2014

    Physics Seminar-Phase Shifts, Photons, & Feedback: Irradiance Detectors in the Eye

    Dr. Jay Demas, St. Olaf College. The light sensitive portion of the eye, the retina, signals the brain about the pattern, intensity, and wavelength of light striking the retina. However, this information is used for more than just seeing. A special class of retinal neurons called melanopsin retinal ganglion cells (mRGCs) mediate behaviors that depend on light, but not on vision. These behaviors include synchronizing behavior with the external environment by setting the phase of our brain's circadian oscillator. Melanopsin, for which these cells are named, is a light-sensing protein that makes mRGCs intrinsically photosensitive. We are interested in understanding how mRGCs regulate the gain and dynamics of their light response through feedback from a class of interacting proteins called arrestins.

    Refreshments at 4 PM, OLRI Atrium.

  • 12/5/2013

    Physics Seminar - The Strong Nuclear Force in Table-Top Simulations

    Dr. Mohamed Anber, Dept. of Physics, Univ. of Toronto.

    The strong nuclear force is responsible for holding the quarks inside the nucleons. This is usually referred to as the confinement phenomenon. However, the quarks will be liberated (deconfined) at some critical temperature as we increase the temperature of the nuclei.  Surprisingly enough, after almost 50 years since the discovery of the strong force, it is safe to say that until today we do not have a thorough understanding of the details of the confinement/deconfinement mechanisms, thanks to the complexity of the mathematics of the strong force. However, there are very few examples where we can modify the mathematics of the strong force in a way that makes it possible to study the confinement/deconfinement phenomena by analytical means. In this talk, I will shed light on one of these modifications that enables us to map the strong force into simple two-dimensional condensed matter systems known as the XY models, which capture all the essential physics of the strong nuclear force near the deconfinement temperature. In a series of works with undergraduate students, we have just begun to reveal the rich physics of the deconfinement phenomenon by conducting Monte Carlo simulations of the XY models.

    Departmental TEA at 4 PM, OLRI first floor atrium.

  • 12/4/2013

    Chemistry & Physics Seminar - Molecular Spectroscopy in Support of Fundamental Physics: Molecules as Venues for eEDM and Anapole Moment Determination

    Prof. Timothy Steimle, Department of Chemistry & Biochemistry, ASU

    Parity non-conservation (PNC) measurements, either via the interaction of electric dipole moment of the electronde, with the internal electric field or the interaction of the anapole moment of the nucleus,kA, with the electron spin has given added impetus for both experimental and theoretical determination of properties of heavy polar diatomic molecures. Most “small scale laboratory”PNCrelated studies focus on the determination of thede. Any non-zero value of de violates both parity (P) and time reversal (T) symmetry. The Standard Model of particle physics predicts |de|≈10-38e-cm, but various extensions to this model predict much larger, and experimentally measurable values. Critical to the design and interpretation of the current and proposed experimental attempts to determinedeandkAis the determination of electric dipole moments,μel, the magnetic dipole moments,μm, and magnetic hyperfine interactions. Here we describe our recent high-resolution spectroscopic studies of YbF, ThO, HfF and WC.

  • 11/21/2013

    Physics Seminar: Neutrino Oscillations and the NOvA Experiment

    Dr. Dan Cronin-Hennessy, Associate Professor of Physics, University of Minnesota, School of Physics & Astronomy will speak on the NOvA Experiment.

    The NOvA experiment, using the existing NuMI beamline, at Ash River, Minnesota is just beginning data acquisition. I will talk about the design and construction of this experiment as well as covering neutrino physics with an emphasis on neutrino mixing and oscillation.

    The NOvA experiment will provide a measurement of the neutrino mixing angle θ13,and may establish the hierarchy of the neutrino masses.

    Join us at the Departmental TEA at 4 p.m., first floor atrium, Olin-Rice.

  • 11/14/2013

    Physics Seminar: The Higgs Boson has Fleas

    Dr. John Hiller, University of Minnesota-Duluth, Department of Physics

    The recently discovered Higgs boson completes the picture of the Standard Model of particle physics. In this model, the masses of the other particles, such as electrons and quarks, arise from their interaction with the field of the Higgs boson. The inertia of such massive particles, as they move through the Higgs field, is roughly analogous to the resistance experienced by fleas moving through thick fur. The nonzero expectation value of the Higgs field in vacuum is determined by a self-interaction with a spontaneously broken symmetry. We consider a nonperturbative method for the calculation of this effect, after illustrating the distinction between perturbative and nonperturbative methods. Applications of our nonperturbative method to the calculation of the properties of the "fleas" will also be discussed.

    Join us for TEA at 4 PM, OLRI first floor atrium.

  • 10/31/2013

    Physics Seminar: The Discovery of the Higgs Boson

    Dr. Soeren Prell, Professor of Physics, Iowa State University, Department of Physics and Astronomy will talk about the discovery of the Higgs Boson.

    Ths 2013 Nobel Prize in Physics was awaraded for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the Higgs Boson by the ATLAS and CMS experiments at CERN's Large Hadron Collider (LHC). We will report on the discovery, the experimental effort that enabled it, and what else might be discovered at the LHC.

    Refreshments at 4 PM in the first floor atrium, OLRI.

  • 10/17/2013

    Weekly Geology & Physics Departmental TEA

    The Geology, Physics & Astronomy Departments are hosting the regular weekly departmental TEA. Share some tea and snacks with your colleagues and catch up with each other in the first floor atrium OLRI.

  • 10/11/2013

    Justin Johnson, PhD, Distinguished Alumni Research Seminar

    Justin Johnson, a 1999 graduate of Macalester with a double major in physics and chemistry, is a Senior Scientist at the National Renewable Energy Lab.  He will be giving a public seminar in Professor James Heyman's Modern Physics course (Phys331). 

  • 10/10/2013

    Physics Colloquium - The Search for Dark Matter

    Only about 5 percent of the known universe is composed of stars, planets, gas, and everything else we can see or detect. Well, what makes up the rest of it? It's called dark matter (and dark energy), but no one knows what it really is. This is one of the greatest mysteries of the century, but researchers like Prof. Vuc Mandic from the U of M are working to unravel the secret of dark matter. Join us for his talk about his work on the super-CDMS experiment, the goal of which is to directly detect the elusive dark matter,

    4:00 pm - Tea and snacks by prof offices.

    Photo: A computer simulation to depict dark matter.

  • 10/3/2013

    Macalester Observatory Public Night

    Public Nights is an ongoing event which allows the entire Macalester community to take advantage of the college's science-grade observatory. Come and see our telescope in action and learn about what you see in the sky. Please note that the public night observing session may be canceled on any given week due to cloudy skies or other inclement weather. 

  • 10/3/2013

    Physics Seminar: Systemic Surface Science Studies of Sapphire

    Mac Visiting Professor Tom Christensen from University of Colorado, Colorado Springs.

    Surface science brings together elements of physics, chemistry, and engineering to better understand properties of the top few atomic layers of materials. Experimental techniques frequently involve shooting beams of electrons and ions at surfaces which can change the surfaces even as we study them. Interesting effects resulted on sapphire surfaces of both bulk and thin film samples when exposed to electron beams as part of Auger Electron Spectroscopy and when exposed to AR ion beams as part of routine surface cleaning and then characterized with X-ray Photoelectron Spectroscopy. Further characterization allowed us to determine how to minimize the undesirable effects.

    Join us at the Physics & Geology TEA at 4, then attend the talk.

  • 9/26/2013

    Weekly Geology & Physics Departmental TEA

    The Geology, Physics & Astronomy Departments are hosting the regular weekly departmental TEA. Share some tea and snacks with your colleagues and catch up with each other in the first floor atrium OLRI.

  • 9/19/2013

    Weekly Geology & Physics Departmental TEA

    The Geology, Physics & Astronomy Departments are hosting the regular weekly departmental TEA. Share some tea and snacks with your colleagues and catch up with each other.

  • 9/5/2013

    Astronomy Seminar--ANGST X: Clustered Star Formation in Nearby Dwarf Galaxies

    David Cook, University of Wyoming

    In galaxies, the relationship between stars in bound clusters and those that populate the field is poorly understood. The formation of both populations is connected, whether stars form in clusters and dissolve to create field stars, or field stars form concurrently with clusters. Previous studies have found relationships between the field and cluster populations of mid to high star formation rate galaxies. I will present the behavior of field and clustered star formation in the low star formation rate regime of 52 dwarf galaxies by quantifying the fraction of stars that populate star clusters. The data show broad agreement with the previous relationships at higher star formation rates, but significant galaxy-to-galaxy scatter exists. In an attempt to account for this scatter, the effects of random sampling with low number statistics (stochasticity) and cluster disruption are explored.

    Refreshments at 4 PM.

  • 2/26/2013

    Astronomy Seminar--Giant Molecular Clouds in the Galactic Center: The Past, Current, and Future of Star Formation

    Dr. Cornelia Lang, University of Iowa, will discuss recent observations made with the Very Large Array (VLA) radio telescope in New Mexico aimed at studying the molecular clouds in the core of the Galaxy.

    This region of the Galaxy is opaque to optical light, so we use radio and infrared telescopes to make images of this exciting and  energetic region. In particular, we are interested in understanding their detailed properties of the molecular gas, which will be transformed into stars. This process may be quite different in the Galactic center, where the environment is densely packed and the physical conditions are more extreme than in the Solar neighborhood.  I will discuss very high resolution VLA observations of several molecular clouds in the central 1000 light years of the Galaxy that shed light on recent star formation in this region, ongoing star formation and the potential for new clouds to be forming the next generation of massive stars. In addition to studying the kinematic and morphology properties of the molecular gas with a number of spectral line tracers, we have discovered an unexpected abundance of Class I methanol maser emission. The widespread distribution of these masers suggests shocks play an important role in driving cloud evolution throughout this unique region of our Galaxy.

  • 2/12/2013

    Astronomy Seminar--From Ignition to Embers: Supermassive Black Hole Activity Across Cosmic Time and Space

    Dr. Brendan Miller, Astronomy Department, University of Michigan.

    I will discuss the formation, growth, and activity of supermassive black holes (SMBHs), from high redshift to the local Universe. As luminous but short-lived quasars, SMBHs accrete at several percent of the Eddington limit and can generate sufficient radiation and outflowing matter to impact the evolution of their host galaxy. We are currently investigating broad absorption line winds to better understand the geometry, covering factor, and kinetic energy of the outflowing gas. Even after exiting the quasar phase, weakly accreting SMBHs may provide ongoing mechanical feedback relevant to quenching star formation and reddening massive galaxies. Nearly quiescent SMBHs have been dynamically confirmed to inhabit the centers of many local galaxies, including our own Milky Way. We are carrying out volume-limited studies of optically-selected early-type galaxies to assess the relationship between low-level SMBH activity, as detected in X-ray emission, and gas supply, star formation, and the large-scale surrounding environment. Finally, I will describe our new assessment of the SMBH occupation fraction of nearby lower mass galaxies, and discuss prospects for using such measurements to differentiate between SMBH seed formation mechanisms

  • 2/7/2013

    Astronomy Seminar--High-Resolution Transmission Spectroscopy of Exoplanetary Atmospheres

    Dr. Adam Jensen, Astronomy Department, Wesleyan University.

    Observations over the last two decades have revolutionized our understanding of planetary systems in the Milky Way.  There are now hundreds of known, confirmed exoplanets and thousands of additional candidates likely to be exoplanets, statistically implying perhaps billions of planets in our galaxy alone.  As the detection of exoplanets continues to progress, characterizing these planets and their atmospheres becomes extremely important.  An exoplanetary atmosphere was not detected until 2002 (Charbonneau et al. 2002), and in 2013 we remain at only tens of unambiguous detections.  I will provide a brief overview of exoplanetary detection methods, highlighting transits in particular.  Within that context, I will discuss using transmission spectroscopy to study exoplanetary atmospheres and highlight our program at Wesleyan University, which uses high-resolution (R~60k) spectroscopy from the 9.2m Hobby-Eberly Telescope at McDonald Observatory in Texas.  Our work has led to the first ground-based detection of an exoplanetary atmosphere (Na I by Redfield et al. 2008) and the first detection of exoplanetary H-alpha (Jensen et al. 2012).  I will review the challenges inherent to our ground-based observing methods, and discuss the interpretation of our results with respect to atmospheric temperature inversions and the potential processes for creating and sustaining n=2 hydrogen that result in H-alpha absorption.  I will also outline the present and future of our program, including new targets for the HET and upcoming observations with the 10m Keck I and 3.5m WIYN Telescopes.

  • 2/5/2013

    Astronomy Seminar--Leo P: An Extremely Metal Deficient Galaxy & Other Strange Stories

    Danielle Berg, Department of Astronomy, University of Minnesota.

    Leo P is a strange dwarf irregular galaxy. A rare gem discovered recently in the Arecibo ALFALFA survey with a single bright star-forming (H II) region. KPNO 4-m and LBT/MODS spectroscopic observations were obtained of this H II region. We are able to accurately measure the temperature sensitive [O III] λ4363 line and determine a “direct” oxygen abundance that shows Leo P is an extremely metal deficient (XMD) galaxy. A surprise to all, Leo P turns out to be one of the most metal deficient galaxies of all! For its estimated luminosity, Leo P is consistent with the relationship between luminosity and oxygen abundance seen in nearby dwarf galaxies. 

    The oxygen abundance is exciting enough, but the other elements do not disappoint. A helium mass fraction was derived which compares well with the WMAP + BBN prediction for the primordial helium abundance; an independent observed confirmation of theoretical predictions. Leo P also shows normal α element abundances (Ne/O, S/O, and Ar/O) when compared to other XMD galaxies, but elevated N/O, consistent with the “delayed release” hypothesis for N/O abundances. 

    What could this mean? I will tell you of KPNO nitrogen, LBT nitrogen, primary nitrogen, secondary nitrogen. 

    “From there to here, from here to there, funny things are everywhere.” (Dr. Seuss)

  • 12/6/2012

    Physics & Astronomy Seminar Presentations by Post-Bac Researchers

    Two Macalester post-bac reserachers' presentations:

    Elise Larson--"Making Headway in SHIELD: The Scientific Method's Influence on Data Reduction." Figuring out how to best go about research is a challenge faced by scientists throughout their careers. I look at these issues as I work through the calibration and imaging of data from 12 galaxies studied during the Survey of HI in Extremely Low-mass Dwarfs (SHIELD). After discussing the data reduction process, I summarize current results and directions for research in the future.

    Zofia Kaminski--"Terahertz Spectroscopy of Graphene." This presentation covers the fascinating properties of graphene and the methodology of terahertz spectroscopy used in the Heyman Research Lab. Graphene is a new material and its properties and applications are still being explored. Terahertz spectroscopy is a unique measurement method allowing for highly interesting results: it can be used indirectly to measure the conductivity of graphene, an important factor in developing future technologies.

  • 11/29/2012

    Physics Seminar - Higgs Discovery: Implications for the Standard Model and Beyond

    Dr. Brian Batell, Research Associate at Enrico Fermi Institute & Department of Physics, University of Chicago.

    Experiments at the Large Hadron Collider (LHC) have discovered a new particle with properties consistent with the long-sought Higgs boson. In this talk I will review the discovery and discuss what it means for the Standard Model, our current theory of fundamental matter and forces, as well as theories that go beyond the Standard Model. I will focus especially on how precise measurements of the properties of the new Higgs-like particle, such as its couplings to other known particles, can guide us in searches for new physics at the LHC.

    Join us for refreshments at 4 PM.


  • 11/15/2012

    Studying the Mysteries of the Universe: Physics & Astronomy Summer Research Opportunities

    Physics & Astronomy Students:

    Professors Tonnis ter Veldhuis, John Cannon, Jim Doyle, and James Heyman, faculty members of the Physics and Astronomy Department present their research interests and staffing needs for their summer research projects. If you are interested in working with one of these scholars during the summer of 2013, please attend with your curiosity and questions. You will find out what topics each professor will be studying, how many research assistants they will need, and how previous students have spun these summer opportunities into valuable research and job possibilities of their own.

    Great information, plus pizza.

    Photo Courtesy of CERN

  • 11/8/2012

    Physics & Philosophy Seminar: Pascual Jordan and the Conundrum of the Wave-Particle Duality of Light

    Dr. Michel Janssen from the History of Science, Technology, and Medicine Program, University of Minnesota presenting: In 1909, Albert Einstein derived a formula for the energy fluctuations in a small subvolume of a box filled with so-called black-body radiation. This formula is the sum of a term one would expect if this radiation consisted of waves and a term one would expect if this radiation consisted of particles. Einstein thus concluded that radiation somehow had to be both a wave and a particle. In a famous joint paper with Max Born and Werner Heisenberg submitted in late 1925, Pascual Jordan used the new matrix mechanics to show that one recovers both these terms in a simple model of quantized waves. This result not only solved Einstein's puzzle about the wave-particle duality of light, it also provided striking evidence for matrix mechanics, and a strong argument for field quantization. After reviewing Einstein's early work on fluctuations in black-body radiation, I present Jordan’s result and the curious story of its reception. Rather than being hailed as a major contribution to quantum theory, Jordan’s result met mostly with skepticism, even from his co-authors. I will argue that the skeptics were wrong.

  • 10/18/2012

    Physics & Astronomy Seminar--Cosmic train wrecks: when galaxies collide

    Jillian Scudder, Macalester ‘09, presents new results that shed light on what really happens when galaxies collide:

    Galaxy interactions create some of the most dramatic and photogenic objects in the Universe.  These galaxies are going through a very tumultuous period in their lives, but how lasting are the changes these galaxies go through?  I will provide a review of the basic structure of an undisturbed galaxy and some of its key observable properties.  We can then investigate how these properties change in a galaxy with a nearby companion, and what these changes can tell us about the internal workings of the galaxy.  We are then presented with a series of new questions.  How complex is the evolution of these properties as an interaction progresses?  Is the current simple physical model sufficient, or do we need to nuance our model in order to understand recent observations?  More fundamentally, are these extragalactic train wrecks fleeting moments in a galaxy's lifetime, or do the changes have long-lasting effects upon a galaxy? New results help to answer these questions.

  • 10/12/2012

    Physics Seminar--Microprocessor: A History of Big Ideas

    Fitih M. Cinnor, Ph.D.  (’03). Staff Engineer PTD Lithography

    Intel Corporation, Logic Tehnology Development

    The microprocessor lies at the heart of the electronic revolution. Advances in computing, communications, and consumer electronics have been made possible by the advent of microprocessors that deliver high performance, more energy-efficient, and secure products, in increasingly connected, smarter devices. This talk introduces big ideas that have been crucial to making this revolutionary progress possible.

  • 10/11/2012

    Observatory Public Night

    Didn't know Macalester had a telescope? Well now you do! The Physics and Astronomy club is hosting a public observing night at the Macalester College Observatory (Olin Rice 404 - accessible from the South East staircase) tonight from 7pm-12am. Everyone is encouraged to come and look through the telescope, see how astronomical data is taken, and talk science with Physics and Astronomy majors. 

  • 10/11/2012

    Physics Seminar--Modeling of Electron Devices Fabricated from Novel Materials

    P. Paul Ruden, College of Science and Engineering, University of Minnesota

    The range of semiconductor materials under consideration for application in electron devices has increased dramatically over the last couple of decades. Much of this growth has been in the area of organic semiconductors, i.e. certain polymers and crystals of small hydrocarbon molecules. These materials have intriguing physical properties that are complementary to those of conventional inorganic semiconductors, such as silicon. Useful characterization data obtained for organic semiconductors is derived from relatively simple electronic device structures, and these devices often show features not encountered in their inorganic analogues. Device modeling is a key element in the exploration of the physics of organic semiconductors, as will be shown through several examples.

    Although the focus of this talk is specific to a particular research activity, its aim is to illustrate that there are many opportunities for physicists and chemists to pursue graduate studies in highly interdisciplinary fields such as the development of new materials for electronics.

  • 9/6/2012

    Physics and Astronomy Department Luncheon

    Interested in majoring in Physics? Want to learn about the new Physics and Astronomy Club?

    Please join us for the Department Luncheon! Hear students and professors discuss the curriculum and goals for the club. Both interested underclassmen and majors/minors should join us for pizza and discussion. 

    Where: Olin Rice 150

    When: Thursday, September 6th; 12 - 1 PM

    Incentive: FREE PIZZA and awesome people. 

  • 4/20/2012

    Physics Seminar

    Physics Seminar Transient Conductivity Measurement in CVD-Graphene

    Yilikal Zeleke Ayino

    We studied the response of CVD-Graphene to optical excitation. In the experiment we excited a graphene sample by a femtosecond laser pulse and measured the resulting change in conductivity with a delayed Terahertz (THz) pulse. By sending the THz pulse through the sample at different time delays before and after the excitation we found the concentration of carries as a function of time. The decay of the carries has a non-exponential part followed by an exponential component. To further understand this decay process we did experiments at different pump power.

    Properties of Hydrogenated Amorphous Silicon-Germanium Alloys Deposited by Dual Target Reactive Magnetron Sputtering

    Sam Levang (Honors Defense)

    Hydrogenated amorphous silicon-germanium alloy thin films (a-Si1-xGex:H) were deposited using reactive magnetron sputtering. Dual targets of silicon and germanium were sputtered in an argon + hydrogen atmosphere using rf excitation. Films with x = 0.4 were deposited as a function of substrate temperature and hydrogen partial pressure, and were evaluated by dark and photoconductivity, infrared absorption, and optical transmission. Photosensitivity reached a maximum value of about 5000 between 150 and 200 °C. Using the stretching modes in the region of 2000 cm-1, the hydrogen bonding was characterized in terms of the preferential attachment ratio (PA), which represents the ratio of H bonded to silicon to that bonded to germanium. The PA shows a systematic increase with increasing temperature, independent of hydrogen partial pressure. The interplay between thermodynamic and kinetics effects in determining PA and film quality will be discussed.

  • 4/6/2012

    Physics Seminar--Electrodeposition of Copper Indium Disulfide for Photovoltaic Applications

    Kate Zimmerman

    Copper Indium Disulfide (CuInS2) has potential as an inexpensive and efficient solar cell absorber layer. Although it is not as widely studied as the more conventional copper indium diselenide, it avoids the high toxicity of selenium. In this work I explored the use of sulfur annealing of electrodeposited copper and indium layers as an inexpensive and efficient method of CuInS2 deposition. Copper and indium were deposited as successive layers from acidic baths of CuSO4 and In2(SO4)3 respectively on stainless steel substrates. The amount of deposition was quantified using atomic absorption spectroscopy. The samples were annealed in a tube furnace at 500 C for 10 minutes in the presence of sulfur in an argon atmosphere. The films were characterized by scanning electron microscopy and x-ray diffraction. The resulting film appears to be primarily CuInS2 with some CuS. However, adhesion to the substrate was a problem during annealing.

    Quantum Mechanics on the Android Platform

    Andrew Rich

    Quantum mechanics is a weird field. As physicists, we interpret the strange results of quantum mechanics through rigorous mathematical analysis. With the help of computers, we can simulate these results in a comprehensible manner such that people with little physics background can understand them. Specifically, our goal was to put quantum mechanics in their hands by creating an Android app to graphically describe quantum tunnelling. Our app allows the user to pick a potential, manipulate potential width, and change an incoming particle's energy. Transmission and reflection coefficients are displayed on the screen alongside the particle wavefunction as it tunnels through the potential. A beta version was produced, and we hope to continue development. With this app, we hope to erase some of the mystery shrouding quantum tunnelling.

  • 3/30/2012

    Physics Seminar--Phenomenological Studies of the Singlet Scalar Standard Model(SSM) using micrOMEGAS_2.4.1

    Ishiaka Mansaray

    The Singlet Scalar Standard Model(SSM) is the simplest extension of the Standard model which allows a Cold Dark Matter(CDM) candidate and there is compelling evidence that dark matter exists. The SSM was implemented as a new model in micrOMEGAS 2.4.1 and the phenomenological properties of this model were calculated. The viable parameter space of the model was calculated, i.e the combinations of λH (the cross section of the scalar) and MSc(the mass of the scalar) that gave a relic density of 0.22. With these values, the annihilation cross section at low velocities which is relevant for the indirect detection of the dark matter candidate was calculated for Higgs masses 115 GeV, 120 GeV, 130 GeV and 145 GeV which is the current mass range the Higgs is thought to exist. The direct detection spin-independent cross section was also calculated as a function of the scalar mass in the viable parameter space of the model for the different Higgs masses stated above.

    Energy Dispersive X-ray Spectroscopy as a Method to Measure Film Thickness

    David Suchý

    The thickness of uneven and thin films deposited on non-flat substrates are difficult to measure using conventional methods such as stylus profilometry. In this work we explore an alternative method of film thickness measurement using the energy dispersive x-ray (EDAX) option on a scanning electron microscope (SEM). The EDAX signals from both the thin film and the substrate are monotonic functions of the film thickness. By growing a series of films of known thickness, we can calibrate detected EDAX photon counts as a function of the film thickness. Monte Carlo simulations using the CASINO program confirm our experimental results. The simulations allow in principle a calibration using a single standard.

  • 3/2/2012

    Physics Seminar--Search For Fourth Generation Quarks in the Lepton plus Jets decay Channel

    Natalee Raymond

    Our present understanding of fundamental physics denotes the existence of three generations of matter particles that are considered as structureless and elementary. What if there exists more than 3 generations of these particles? I will report the search for pair production of the down-type fourth generation quark, b’, in a data set of 1.04 f b−1integrated luminosity from proton-proton collisions, collected by the ATLAS detector at the LHC. Each b’ decays promptly to a top quark and W boson (tW) in the lepton + jets channel as b’ → Wt → WWb. The heavy down-type fourth generation quark decays produce high transverse momentum (pT) W bosons which can be identified by reconstructing the di-jet mass. Detectors for Nuclear Safeguards Paolo Venneri Nuclear safeguards employs a variety of detector systems to verify levels of enrichment and composition of radioactive material. This presentation will discuss work conducted at Los Alamos National Laboratory in improving and developing new detector systems revolving around the use of NaI crystal scintillators. The systems discussed include the use of silicon diodes for detector calibration, the temperature dependence of scintillators, and the use of Li6 + n reaction in measuring neutron radiation as an alternative to He3 neutron counting systems.

  • 2/24/2012

    Joint Philosophy and Physics Seminar

    Of Cats, Mice, and Measurement The Role of the Observer in the Many-Worlds Interpretation of Quantum Mechanics

    Prof. Arthur Cunningham Department of Philosophy St. Olaf College

    One of the most puzzling aspects of quantum mechanics is the central role of observation in the theory. The postulate that an observation results in a discontinuous collapse of the quantum state of the observed system raises serious worries about the status of the quantum state and the adequacy of the theory as a description of reality. The famous thought experiment of Schrödinger’s cat was devised to highlight such worries; Einstein once expressed a related concern by asking, “When a person such as a mouse observes the universe, does that change the state of the universe?” One of the best-known—and most controversial—interpretations of quantum mechanics, the so-called “many-worlds interpretation,” was offered by its founder, Hugh Everett, as a way to reformulate the theory in such a way that its basic principles would make no reference to observation. The notion of an observer must eventually be introduced, on Everett’s view, but only in order to evaluate the correspondence between the theory and experience. A family of influential criticisms of the many-worlds interpretation charge that Everett’s discussion of observers is not theoretically innocuous. Physicist John Bell argues that Everett’s appeal to the notion of an observer actually saddles his interpretation with conceptual problems similar to those facing textbook quantum mechanics. Other critics charge that Everett’s interpretation can be made sense of only by making substantive, suspect assumptions about the relationship between sentient minds and physics.

    This talk will examine the role that the notion of the observer plays in Everett’s interpretation. I aim to provide some clarification about what Everett himself intended, and I will argue that some influential criticisms of his interpretation are misplaced. I will close with some remarks relating Everett’s account of collapse, and the appearance of classically definite properties in a quantum universe, to current ideas drawn from decoherence theory.

  • 2/17/2012

    Physics Seminar--Biophysical Characterization and Stablization of a Marketed Multivalent Vaccine

    Martin Blanchard

    Vaccinology is a vital pillar of modern medicine. Utilizing natural immunity, vaccines protect people, and even entire societies, from a constantly increasing number of bacterial and viral infections. However, there exist several obstacles to the creation and administration of many vaccines, most notably keeping target antigen proteins in a folded state so that they can be properly recognized by the human immune system. In this presentation, I will describe in detail some of the biophysical techniques I used at the University of Kansas Macromolecule and Vaccine Stabilization Center to characterize target antigens, and then discuss the process of identifying optimal buffer environments for storing those antigens.

  • 2/10/2012

    Physics Seminar--Understanding the Higgs Results from the LHC

     Jeremiah Mans University of Minnesota

     The LHC experiments (ATLAS and CMS) recently generated a stir with their presentation of results on the search for the Standard Model Higgs boson. These results greatly restrict the possible masses which a Standard Model Higgs could have and might possibly provide the first hint of where the Higgs may be. I will explain why this Higgs particle is quite so interesting, discuss the current results, and provide some hints of what may lie ahead from the results expected in 2012. The talk will also include some "primers" to help understand the relevance of some of the plots which are shown in such presentations.

  • 2/3/2012

    Physics Seminar--Fiber Laser Preamplifier

    Ryan Marshall

    My immediate goal was to build a fiber laser preamplifier to increase the power of a frequency combed laser. The overall goal of my group was to do direct frequency comb spectroscopy of acetylene in photonic crystal fibers. The frequency combs used in our lab are homemade and portable; it is necessary for the combs to be amplified in order to have enough power to do spectroscopy successfully. In the preamplifier, I used two, 0.5W backward pumping laser diodes at 1480nm to pump the gain fiber. I seeded the amplifier with a frequency-combed laser, centered at 1560nm. The three main steps in building a doped-fiber amplifier are: optimizing the gain fiber length to maximize average power output, optimize the single mode fiber length to maximize the peak power, and broaden the spectrum to achieve enough gain at the target wavelength. My target wavelength is 1532.8nm, which corresponds to the P13 absorbance peak of acetylene. After the first two steps, the preamplifier was a factor of five short on power at my target wavelength. In the future, adding highly non-linear fiber could shift the spectrum to attain my power goal at 1532.8nm, and the preamplifier could be used for spectroscopy.

    Collider Phenomenology of the Singlet Scalar

    Ben Alterman

    The simplest renormalizable extension of the Standard Model that can account for dark matter contains one additional particle: the Singlet Scalar (SC). This model also includes the Higgs boson, which couples directly to the SC. Using both the MadGraph 5 and MadAnalysis packages and assuming the Higgs has been discovered, we present a Monte Carlo analysis of a potential discovery method for the SC at future electron-positron colliders like the ILC. We assume Higgs mass mHiggs = 120 GeV/c2 and found that, using this method, it would require 1.875 fb−1 of data to discover the Singlet Scalar at the ILC.