students and professor

Past Events

  • 3/26/2015

    Physics & Astronomy Seminar--The Three LITTLE Dwarfs: Evolutionary tales uncovered by stars

    Dr. Megan Johnson, CSIRO, Australia.

    In popular cosmology models, dwarf galaxies are the “building blocks” of giant galaxies and are assumed to be disks. Yet, observationally, even the basic structure of dwarf irregular (dIrr) galaxies remains controversial. Studies of the projected minor-to-major axis ratios in dIrrs provide inconclusive evidence for their three dimensional shape.  Fortunately, the stellar velocity dispersion, together with rotational information, is a diagnostic of how kinematically hot a system is, and, therefore, of its structure.  Here, I present recent results from a kinematic study of three nearby dwarf irregular galaxies.  We use longslit optical spectroscopy to obtain intrinsic stellar velocities and velocity dispersions of NGC 1569, DDO 168, and DDO 46, which are part of the LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes; The HI Nearby Galaxy Survey) survey.  

  • 3/12/2015

    Physics & Astronomy Senior Capstone Presentations

    Brittany Ehmann will speak on "Ultrafast Photoconductivity Measurements of a Thermoelectric Nanocomposite: Tellurium Nanowire/PEDOT:PSS."

    Jaren Willard will also speak.

    Refreshments at 4 PM, OLRI first floor atrium.

  • 3/5/2015

    Physics & Astronomy Senior Capstone Presentation

    Senior Alex Boldin speaking on "Analysis of Spin Polarization in Half Metallic Heusler Alloys" and senior Dan Shi speaking on "Investigating Color Management Technologies."

  • 2/26/2015

    Physics Seminar--Lithium Ion Batteries: Where we are and where we need to go

    Kaitlin Tyler, from the Materials Science and Engineering Department at the University of Illinois Urbana-Champaign, will speak on the topic of lithium ion batteries: "Batteries are used in many different aspects of our lives. Lithium ion batteries have been highly talked about in recent years as a solution for the problems with battery technology. Despite these claims, there is still a ways to go as far as Li-ion battery research is concerned. This presentation will highlight the underlying motivations for using lithium ion based batteries and what research is currently happening to improve on this technology." 

    Refreshments at 4 PM in OLRI atrium.

  • 2/19/2015

    Physics & Astronomy Seminar-Kilonovae: The Glow from Merging Neutron Stars

    Jennifer Barnes, Mac '09, UC-Berkeley, Dept. of Physics will speak: In the final stages of a violent compact object merger, a small amount of matter is dynamically ejected from the system. This material, if sufficiently neutron rich, could produce heavy elements via rapid neutron capture (the r-process). The freshly synthesized heavy nuclei would then decay to stability, radioactively powering a dim electromagnetic transient called a kilonova. Kilonovae offer a clue to the as-yet undetermined site of r-process production. They are also a promising EM counterpart to the gravitational wave signals from merging neutron stars, which Advanced LIGO/Virgo expect to detect routinely in the near future. A major challenge to modeling kilonovae is calculating the opacities of the heavy elements present in the merger ejecta. Barnes will discuss new models of r-process opacities, present recent radiation transport simulations of kilonovae, and explain how these results are informing the search for r-process transients.

  • 2/12/2015

    Physics & Astronomy Seminar-From Researcher to Editor: Exoplanets and Magazines

    Mac alum and associate editor at Astronomy magazine, Dr. Korey Haynes '09 (PhD, George Mason University ‘14) will talk about her recent dissertation work characterizing hot Jupiter exoplanets. She used the Hubble Space Telescope to successfully search a half-dozen of these planets' atmospheres for signs of water. In one of these planets, she found the first spectral evidence for titanium oxide, the molecule suspected of causing temperature inversions in hot Jupiter atmospheres. She will also discuss her new position as an associate editor at Astronomy magazine, what an editing job entails, and how a PhD in astronomy led her to a job in magazine publishing.

    Refreshments at 4 PM in OLRI atrium.

  • 2/10/2015

    Physics & Astronomy Seminar: Magnetism at the Nanoscale

    E. Dan Dahlberg, School of Physics and Astronomy, Univ. of MN. Prof. Dahlberg is one of the pioneers and foremost authorities on magnetism at the nanoscale, which has profound implications for fundamental physics, applications in information technology, and biological physics.

    Major breakthroughs in micromagnetics have resulted from the development of new magnetic imaging techniques.  Through the powerful magnetic force microscope (MFM), a variant of the atomic force microscope, we can understand the domain structure and magnetization reversal in nanometer-sized particles.  I will present an introduction to micromagnetics research and description of MFM with a demonstration of the basic principle and discuss one of the magnetic materials we study, magnetite crystals. Lastly we will discuss the magnetic states and the magnetization reversal process in magnetosome chains.

    Snacks at 3:00!

  • 12/4/2014

    Physics & Astronomy Alumni Roundtable for Majors

    PHYSICS & ASTRONOMY MAJORS: Have you ever wondered about how to get a satisfying job after graduation? Come to the first annual Physics and Astronomy Alumni Roundtable to find out. This is an opportunity for you to learn from the post-Mac experiences of four recent physics and astronomy graduates.
    Emily Gras '08 (Medtronic), Hans Harlane '10 (Mahtomedi High School), Maggie Clay-ton '06 (MTS Minnesota Connections Academy), and Matt Wegmann '08 (Tillges Or-thotic Laboratory) still live and work in the area and will return to our department to tell you about the paths they took to their jobs. They are looking forward to connecting with you, our current physics and astronomy majors. Each of the alumni will give a short introduction, followed by an opportunity for informal discussion. Please come prepared with questions!

    Light snacks following the roundtable discussion.

  • 11/20/2014

    Physics & Astronomy Seminar-CSI: Universe>Determining the Role of Collisions in Galaxy Evolution

    Dr. Elizabeth Wehner, Assistant Prof., St. Thomas, Physics Department is speaking:

    One of the principal theories in galaxy evolution suggests that galaxies are formed as the result of many mergers between smaller, building-block galaxies. I will discuss the physical processes of galaxy interactions and how collisions can drive galaxy evolution, highlighting specific examples of galaxies undergoing significant changes, such as NGC 3310 (Archer Galaxy). This galaxy is currently experiencing rapid star formation across its disk and is surrounded by large arcs of stellar debris.  Analysis of these stellar arcs suggest that NGC 3310 recently collided with a dwarf companion galaxy, destroying it in the process.  I will also show how remnants of previous collisions can be used to trace the star formation histories of more dormant galaxies, such as the giant elliptical, NGC 3311, which lies at the center of the massive Hydra galaxy cluster.

  • 11/18/2014

    Physics & Astronomy Seminar-The Cycle of Baryons: How Gas is Gained and Lost from Galaxies

    Dr. Charlotte Christensen, Assistant Professor, Grinnell College, Department of Physics will speak on "The cycle of baryons: how gas is gained and lost from galaxies."

    The stellar and gas disks of galaxies are the product of both gas accretion and gas expulsion.  While gas accretion fuels star formation, stars themselves produce feedback energy capable of blowing gas back out of galaxies. I use simulations of galaxy formation to track the cycling of gas for galaxies spanning over two orders of magnitude in mass.  These simulations show the degree to which stellar feedback determines the stellar and baryonic mass of galaxies and the structure of their disks.  Remarkably, stellar feedback-driven outflows are so ubiquitous that less than 20% of gas ever accreted onto galaxy disks is retained at present day.

  • 11/6/2014

    Physics & Astronomy Information Session

    Studying the Mysteries of the Universe: Summer Research Opportunities for Students

    Interested in doing physics and astronomy research in summer 2015? This session will be an informational meeting about both on-campus and off-campus summer research opportunities.

    We will discuss what options are available and the application procedures.

    Join us at noon for pizza and pop.

    Great Information, Plus Lunch!

  • 10/30/2014

    Physics Seminar-Experimental Observation of Contact-induced Spin Relaxation in Hanle Spin Precession Measurements

    Dr. Bruce Bolon, Associate Professor & Chair, Hamline University, Department of Physics

    This seminar is based on research performed during Dr. Bolon’s spring 2014 sabbatical working with Dr. Chris Leighton’s group in the Department of Chemical Engineering and Materials Science, University of Minnesota.

    Understanding spin injection and transport in metals is crucial for future all-metallic spintronic devices. By separating spin and charge currents, the non-local spin valve (NLSV, sample shown here) provides considerable insight into pure spin relaxation. In NLSV devices, the electrical Hanle effect—the dephasing of a spin accumulation due to its precession about a perpendicular magnetic field—is a useful tool for determining spin relaxation rates.

    In this work we experimentally verify contact-induced spin relaxation.Simulations of the Hanle effect in our devices reproduce the observed trends well with no need to invoke additional relaxation mechanisms.

    Refreshments at 4 PM, first floor OLRI atrium.

  • 10/16/2014

    Physics & Astronomy Seminar-The WISP Survey: overview of recent results for galaxies

    Professor Claudia Scarlata, Minnesota Institute of Astrophysics, University of Minnesota will speak. "The WFC3 Infrared Spectroscopic Parallel Survey (WISP) is a large ( ~1000 orbits) HST program that uses WFC3 slitless spectroscopy to detect thousands of galaxies across a wide redshift range 0.3 < z < 2.3. I will discuss the properties of passive galaxies at z∼1.5 derived from the combination of the WISP spectra with broad-band photometry from HST-UVIS and Spitzer images. I will also present an overview of recent results on emission line galaxies, including a statistical determination of their dust extinction properties, the discovery of a new population of extremely strong emission-line dwarf galaxies, and the implication of the observed number counts for the EUCLID mission."

    Refreshments at 4 PM, OLRI atrium

  • 10/10/2014

    Julie Pullen, distinguished science alum, lecture

    Julie Pullen, PhD, ’91, double majored in physics and mathematics and is the Director of the Maritime Security Laboratory at the Stevens Institute of Technology. She will speak in Jim Doyle's Science of Renewable Energy class as part of the Student Research Poster Session.

  • 10/8/2014

    Physics & Chemistry Seminar-Making Molecular Movies: Watching molecules react on ultrafast time scales and at nanometer length scales

    Dr. Renee Frontiera, Assistant Professor, University of Minnesota, Department of Chemistry.

    This talk will focus on following chemical reactions as they occur through the use of an innovative technique called Femtosecond Stimulated Raman Spectroscopy (FSRS). FSRS takes “molecular snapshots” on the time scale of nuclear motion, allowing us to watch bonds form and break in real time. I will discuss using the FSRS technique to follow excited state proton transfer in the Green Fluorescent Protein. Surprisingly, it is a vibrational motion which drives the reaction and makes this protein so fluorescent. I will then show recent efforts to extend FSRS to the single molecule regime by increasing the signal through the use of plasmonic nanoparticles. This new ultrafast surface-enhanced Raman technique can now be used to follow light-driven chemistry on nanoparticle surfaces. Finally, I’ll discuss current research in my group, specifically on developing a new microscopy technique to look at structure in living cells on the 1-10 nm length scale, approximately the size of a single transmembrane protein.

  • 10/2/2014

    Physics & Astronomy Seminar-Presentations by Post-bac Researchers

    SHIELD Research Assistant Andrew McNichols will speak about "Modeling Star Formation: Simulating the Magnetic Field Structure of Collapsing Molecular Clouds." Astronomers are still trying to build a model that demonstrates complete understanding of the processes by which protostars and their subsequent evolution occur from the gaseous interstellar medium (ISM). I will present the results of a series of simulation programs that plot the most recent mathematical models of hourglass magnetic fields and their expected Stokes parameters.

    Research Assistant Roni Teich will speak about "Astrophysics on the Liberal Arts Front." Research in the field of astronomy and astrophysics is often done at large observatories or universities, but the projects that are undertaken at small liberal arts schools are less well-known. My current position at Mac is conducting low-mass galaxy research with Prof. John Cannon.

    Refreshments at 4 PM, OLRI first floor atrium

  • 9/25/2014

    Physics & Astronomy Seminar-Quarks in the 5th Dimension: A Holographic Model of the Strong Nuclear Force

    Dr. Sean Bartz, Visiting Assistant Professor, Macalester College, Department of Physics & Astronomy is speaking: "The strong nuclear force binds together particles called quarks into the particles that make up nuclear matter. At the rest energies of these particles, the force is too strong to use traditional techniques quantum chromodynamics (QCD). It is difficult, for example, to calculate the excited energy states of particles made of quarks. Holographic models allow us to make these calculations at the cost of adding a fifth dimension to our models.

    "I present a holographic model of QCD that accurately captures an important feature known as chiral symmetry breaking. I describe the background fields of the model, and the calculation of the excited states of mesons, particles made up of one quark and one anti-quark."

    Refreshments at 4:00 PM

  • 9/18/2014

    Physics & Astronomy Seminar-Pulsars: Rapidly Spinning Neutron Stars as Ideal Probes of Relativistic Gravitation & the Interstellar Medium

    Dr. Joel M. Weisberg, Stark Professor of Physics & Astronomy and the Natural Sciences, Carlton College, presents "Pulsars: Rapidly Spinning Neutron Stars as Ideal Probes of Relativistic Gravitation & the Interstellar Medium." 

    Discovered in 1967, pulsars are regularly pulsing radio sources. They are rapidly spinning (up to 40,000 rpm) neutron stars, born in supernova explosions. The observer sees a radio "pulse" each time its radio beam points at the Earth, hence the name. The extreme regularity of their pulses mimics the ticks of an ultraprecise clock. Some of them are orbiting in the strong gravitational field of another compact star, leaving us with the orbiting pulsar as a clock probing strongly curved spacetime - an ideal laboratory for the study of relativistic gravitation. Their highly polarized, pulsed emissions are also excellent probes of the interstellar medium of our Galaxy.

    Refreshments at 4:00 PM in OLRI first floor atrium.

  • 9/11/2014

    Physics Seminar-Gravitational Waves: A New Window on the Universe

    Dr. Tom Giblin, Associate Professor at Kenyon College, Department of Physics will speak: "For millennia we have harnessed information from observations of electromagnetic radiation from the cosmos. While these discoveries have taught us about physics from the microscopic to the astronomical, we are about to enter an age in which gravitational radiation will now complement our current observations. This will undoubtedly open new avenues for the verification (or falsification) of many areas of physics. I will remark on how we are using high-performance computing to predict gravitational wave signals from particle physics and what the observations of these signals might mean."

    Join us before the seminar at 4 PM for the Physics & Geology Departments' TEA in the OLRI atrium.

  • 9/4/2014

    Keep Calm and Study Physics

    First and second year students are invited to join the Department of Physics & Astronomy to learn about the physics major.

    Starts at 4:15 PM. Free pizza and soda!

    (Right after the Physics/Astronomy & Geology Departments' TEA at 4 PM)

    Hope to see you there.

  • 5/15/2014

    Physics Seminar-Dynamical Three-Field Model of Holographic Quantum Chromodynamics

    Sean  Bartz, University of Minnesota, Department of Physics

    The strong nuclear force binds together particles called quarks into the particles that make up nuclear matter. At the rest energies of these particles, the strength of the interaction is too great to use the techniques of quantum chromodynamics (QCD). Holographic models relate strongly-coupled field theories to weakly-coupled gravitational theories with an extra dimension, which allows for calculations that were previously intractable, including the spectrum of the excited states of mesons.

    I present a holographic model of QCD that accurately captures an important feature known as chiral symmetry breaking. I describe the construction of the potential for the background fields of the model, and the calculation of the excited states of the mesons, which match experimental data well.

  • 5/1/2014

    Last Geology & Physics Departmental TEA of the semester

    Last chance to talk shop and snack with your geology and physics/astronomy colleagues this semester. Congratulate seniors, thank faculty, talk, eat, amaze.

    Have a great summer!

  • 4/30/2014

    Physics Seminar-Simple Metallic Liquids: Theory and Simulation

    Dr. James A. Porter, Visiting Assistant Professor, Colby & Bates Colleges, Department of Physics & Astronomy

    How can information about the properties of simple metallic liquids be obtained through a combination of computer simulation and theoretical analysis? Details of the practical implementation of the Monte Carlo simulation method will be presented. Since the concept of the total energy of a physical system (particularly the total potential energy of the system) is critical to the success of this or any other simulation method, the different functional approximations used for the total potential energy of a liquid (both the advantages and drawbacks) will be examined. I will close by discussing how the usual choices for potential energy function are inadequate for investigating metallic systems, as well as a general method for constructing a more realistic potential energy function for these systems.

    Refreshments at 3 PM

  • 4/28/2014

    Ruby Byrne -- Physics & Astronomy Senior Honors Presentation

    "Modeling Non-Gaussianity from Scalar Field Inflation"

    The Cosmic Microwave Background (CMB) radiation encodes invaluable information about types of space-time distortions the universe experienced during its early inflationary epoch. This research draws upon data from the Planck Satellite to characterize the non-Gaussianity of the CMB fluctuations—in other words, the extent to which the fluctuations are independent at different angular scales. It then proposes a model of cosmological inflation based on coupled scalar fields that complies with the measured non-Gaussianity.

  • 4/25/2014

    Minh Nguyen -- Physics & Astronomy Senior Honors Presentation

    "Meson Spectrum by Holography"

    From Holographic Technicolor theory we can represent the Meson mass spectrum by the fluctuation spectrum of an 8D membrane in 10D space. This model has a corresponding quantum potential, which solution, however, is non-perturbative. The purpose of my project is to analytically explain the non-perturbative behavior obtained in the numerical solution of the quantum model, then generalize the method to a family of potential.

  • 4/24/2014

    Crunch Time! Geology & Physics Departmental TEA

    It's crunch time! Eat some crunchy foods during the weekly Geology, Physics & Astronomy Departmental TEA in the first floor atrium OLRI.

  • 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.