Kristine I. Spangard, Department Coordinator
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.
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
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.
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)
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
Physics Seminar--Electrodeposition of Copper Indium Disulfide for Photovoltaic Applications
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
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.
Physics Seminar--Phenomenological Studies of the Singlet Scalar Standard Model(SSM) using micrOMEGAS_2.4.1
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
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.
Physics Seminar--Search For Fourth Generation Quarks in the Lepton plus Jets decay Channel
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 identiï¬ed 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.
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.
Physics Seminar--Biophysical Characterization and Stablization of a Marketed Multivalent Vaccine
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.
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.
Physics Seminar--Fiber Laser Preamplifier
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
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.