Colloquia - Spring Semester - 2013
Series Intro
Colloquia are held in DeMeritt Hall Rm 240 at 4:00pm on Fridays, refreshments are served in DeMeritt Hall Rm 239, unless otherwise noted
The Interaction of the Solar (and Stellar) Winds with the Interstellar Medium
Gary Zank
Center for Space Plasma and Aeronomic Research, The University of Alabama in Huntsville
Friday, February 1, 2013
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 pm (refreshments at 3:30 PM)
Abstract
The interaction of the solar wind with the interstellar medium is complicated by the presence of a substantial neutral component, interstellar hydrogen. The self-consistent inclusion of neutral hydrogen (and other heavier atoms) requires that models include the effects of charge exchange and scattering properly. With the crossing of the heliospheric termination shock by the Voyager 1 and 2 spacecraft, understanding the outer heliosphere and the heliospheric boundaries has assumed increasing interest. IBEX is now returning observations of Energetic Neutral Atoms (ENAs) created in the solar wind – interstellar medium boundary regions, and these are providing both new insights and new challenges to our understanding of the physics in this complex region. We will describe the status of modeling the solar wind-local interstellar medium interaction, its relationship to Voyager 1 and 2 and IBEX and other remote observations, and the implications for the interaction of stellar winds with their local interstellar environments. The discovery of the hydrogen wall around our heliosphere and other “astrospheres” will be described.
How the nuclear medium affects nucleon structure
Patricia Solvignon
The Thomas Jefferson National Accelerator Laboratory, Newport News, VA
Friday, February 8, 2013
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 pm (refreshments at 3:30 PM)
Abstract
One of the great unanswered questions in nuclear physics is why the proton structure appears significantly different when observed in or out of the nuclear medium. Since the discovery of this so called EMC effect (by the European Muon Collaboration), theorists and experimentalists have been trying to find an explanation. An overview of the EMC effect will be provided, with an emphasis on a new round of experiments from Jefferson Lab which aims to explain the in-medium behavior in terms of the local overlaps between protons and neutrons. We will also discuss a select set of related experiments scheduled to run at Jefferson Lab after the ongoing 12 GeV upgrade is completed.
Molecular Spintronics: Creating Externally-Tunable Spin in Solids with Chemistry
Dan Dougherty
Physics Department, North Carolina State University
Friday, February 15, 2013
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 pm
Abstract
Traditional electronic devices operate via the transport and storage of charge in the form of electrons. The intrinsic spin of the electrons represents a degree-of-freedom in addition to their charge that could be used to control information transport and storage. In fact, spin-based electronics or "spintronics" has been used for years to create very sensitive computer hard-drive read head sensors out of thin films of magnetic metals. New spintronics applications require the identification of materials with novel spin-dependent properties. One material class of interest from this perspective is that of coordination compounds containing iron whose spin state can be controlled by external stimuli such as heat or light. I’ll describe recent collaborative efforts between chemists, physicists and materials scientists that are aimed at integrating these molecular materials into thin film spintronic device environments.
Dan Dougherty earned a a PhD in Physics from the University of Maryland in 2004. His thesis work involved using Scanning Tunneling Microscopy to observe the real time dynamics of defects on solid surfaces. He went on to do post-doctoral research in molecular electronics at the University of Pittsburgh and organic electronics materials at NIST in Gaithersburg. In 2008 he joined the Physics Department at NC State University where his group characterizes interfaces in carbon-based materials for electronic and spintronic applications.
Applications of Lasers to Cancer Detection and Treatment
Steven J. Davis
Physical Sciences, Inc., Andover, MA
Friday, February 22, 2013
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 pm
Abstract
Over the last decade there has been a dramatic increase in the use of lasers and light for new detection and treatment modalities for cancer and other diseases. These include optical biopsy, image guided treatments, and photodynamic therapy (PDT). I will provide a short introduction of some of these methods and will focus on PDT. This emerging treatment for number of cancers involves the interaction of light, a photosensitizer (similar to a laser dye), and oxygen in living tissue. The photosensitizer (PS) is either injected systemically or applied topically and is preferentially retained by tumors. The PS absorbs light via a radiatively allowed transition to an excited singlet state. A rapid intramolecular energy transfer populates a metastable triplet state that subsequently collisionally excites an extremely metastable state of molecular oxygen known as singlet oxygen. This species kills cancer cells via several mechanisms that will be discussed. Because the PS is preferentially retained in tumors, the PDT is a selective, targeted treatment. It is now being applied to a number of cancers as we will discuss.
Our work has focused on in-vivo, optical detection of singlet oxygen, the key cytotoxic species in PDT. We have developed and tested both point and spatially imaging devices and will present data that shows the first direct correlation of tumor regression with singlet oxygen produced during PDT.
During the talk, I will stress how physicists are now working in partnership with physicians to develop new treatments and diagnostics. It is a growing collaboration.
This work was supported by the National Cancer Institute
Challenges in Space Radiation Dosimetry
Eric Benton
Physics Department, Oklahoma State University
Friday, March 1, 2013
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 pm
Abstract
Space radiation dosimetry presents one of the greatest challenges in the discipline of radiation protection. This is a result of both the highly complex nature of the radiation fields encountered in low-Earth orbit and interplanetary space, and on the constraints imposed by spaceflight on instrument design. In this presentation, I will review the sources and composition of the space radiation environment in low-Earth orbit (LEO) as well as beyond the Earth’s magnetosphere. Measurements made aboard the NASA Space Shuttles, the International Space Station and other spacecraft have highlighted the importance of secondary particle production within the structure of spacecraft and the effect of shielding on both crew dose and dose equivalent. Aboard the ISS, roughly half the dose on ISS is due to trapped protons and half from galactic cosmic rays (GCR). The dearth of neutron measurements aboard LEO spacecraft and the difficulty inherent in making such measurements has led to large uncertainties in estimates of the neutron contribution to total dose equivalent. Except for a limited number of measurements made aboard the Apollo lunar missions, no crew dosimetry has been conducted beyond the Earth’s magnetosphere. This data has now been supplemented by measurements on various space probes including MARIE on Mars Odyssey, CRaTER on LRO, and RAD on the Curiosity Lander. Nevertheless we are forced to rely on model-based estimates of crew dose and dose equivalent when planning for interplanetary missions. While space crews in LEO are unlikely to exceed the exposure limits recommended by such groups as the NCRP, dose equivalents of the same order as the recommended limits are likely over the course of a human mission to Mars. I will also review a number of new instruments useful in space dosimetry including a low-cost tissue equivalent proportional counter developed by the OSU Radiation Physics Laboratory.
Investigating what students do well in physics
Michael Wittmann
Department of Physics and Astronomy, University of Maine
Friday, March 22, 2013
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 pm
Abstract
Historically in physics education research, we have focused on the errors our students are making. Those might just be the easiest problems to solve - we recognize the errors quickly, driven by our teachers' instinct to see (and wish to correct) them. An often much harder task is to understand the subtleties and correct pieces of the answers that students are giving and use that understanding to build a model of how students construct their understanding of the physics. From this perspective, instruction that builds off of student strengths allows for more constructive learning. In this talk, I will present several examples of research in which we describe the strengths of student work (even when they make meaningful errors). Examples come from students creating solutions to a damped harmonic motion problem, students using their hands to convey more information than their words give when talking about projectile motion, and students' discussion of the nature of energy.
New Horizons: The First Mission to Pluto and the Kuiper Belt
Chris Hersman
Applied Physics Laboratory, Johns Hopkins University
Friday, April 12, 2013
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 pm
Abstract
New Horizons, which launched in 2006, is the first mission to Pluto and the Kuiper Belt. The spacecraft carries seven scientific instruments including imagers, spectrometers, particle and plasma sensors, a radio science experiment, and a dust counter. In 2007, New Horizons conducted scientific observations of Jupiter during a gravity-assist flyby. Currently, the team is preparing for a rehearsal of the Pluto observation sequence, in advance of the encounter in 2015. Other preparations relate to recent discoveries of additional moons in the Pluto system, which provide tantalizing opportunities for additional science, but also may pose additional risk to the spacecraft.
The NASA EV-2 Cyclone Global Navigation Satellite System (CYGNSS) Mission
Christopher S. Ruf
University of Michigan
Friday, May 3, 2013
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 pm
Abstract
The NASA EV-2 Cyclone Global Navigation Satellite System (CYGNSS) is a spaceborne mission focused on tropical cyclone (TC) inner core process studies. CYGNSS attempts to resolve the principle deficiencies with current TC intensity forecasts, which lie in inadequate observations and modeling of the inner core. The inadequacy in observations results from two causes: 1) Much of the inner core ocean surface is obscured from conventional remote sensing instruments by intense precipitation in the eye wall and inner rain bands. 2) The rapidly evolving (genesis and intensification) stages of the TC life cycle are poorly sampled in time by conventional polar-orbiting, wide-swath surface wind imagers. CYGNSS is specifically designed to address these two limitations by combining the all-weather performance of GNSS bistatic ocean surface scatterometry with the sampling properties of a constellation of eight satellites. The use of a dense constellation of microsatellites results in spatial and temporal sampling properties that are markedly different from conventional imagers. An overall mission design summary will be presented. Simulation studies examine the expected spatial and temporal sampling as functions of various orbit parameters of the constellation. Historical records of TC storm tracks are overlaid onto a simulated time series of the surface wind sampling enabled by the constellation. For comparison purposes, a similar analysis is conducted using the sampling properties of several past and present conventional spaceborne ocean wind scatterometers. Differences in the ability of the sensors to resolve the evolution of the TC inner core are examined.