Bulletin of the American Physical Society
10th Annual Meeting of the Northwest Section of APS
Volume 53, Number 6
Thursday–Saturday, May 15–17, 2008; Portland, Oregon
Session A1: Plenary Session I |
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Chair: Ernest Henley, University of Washington Room: Evans Auditorium |
Friday, May 16, 2008 8:30AM - 8:45AM |
A1.00001: Welcome and Introductory Remarks |
Friday, May 16, 2008 8:45AM - 9:21AM |
A1.00002: Magnetars Invited Speaker: Simply put magnetars are neutron stars whose magnetic fields dominate their emission, evolution and manifestations. In the late 1970s and early 1980s, a fleet of sensitive detectors of high-energy radiation uncovered two new phenomena, the soft-gamma repeater and the anomalous x-ray pulsar. Strongly magnetized neutron stars provide the most compelling model for both types of object, and observations over the past few years indicate that these phenomena are two manifestations of the same type of object. Soft-gamma repeaters exhibit quiescent emission similar to that of anomalous x-ray pulsars and anomalous x-ray pulsars sometimes burst. What makes magnetars a hot topic of research is the rich variety of physical phenomena that strong magnetic fields exhibit. [Preview Abstract] |
Friday, May 16, 2008 9:21AM - 9:57AM |
A1.00003: Semiconductor Nanowires: Defects Update Invited Speaker: Structural defects commonly observed in semiconducting nanowires by electron microscopy will be reviewed and their origins discussed. Their effects on electrical and optical properties will be illustrated with examples from GaSb, InAs, and ZnSe nanowires grown by MOCVD and MBE. [Preview Abstract] |
Friday, May 16, 2008 9:57AM - 10:33AM |
A1.00004: Radiation Detection for Homeland Security Applications Invited Speaker: In the past twenty years or so, there have been significant changes in the strategy and applications for homeland security. Recently there have been significant at deterring and interdicting terrorists and associated organizations. This is a shift in the normal paradigm of deterrence and surveillance of a nation and the `conventional' methods of warfare to the `unconventional' means that terrorist organizations resort to. With that shift comes the responsibility to monitor international borders for weapons of mass destruction, including radiological weapons. As a result, countries around the world are deploying radiation detection instrumentation to interdict the illegal shipment of radioactive material crossing international borders. These efforts include deployments at land, rail, air, and sea ports of entry in the US and in European and Asian countries. Radioactive signatures of concern include radiation dispersal devices (RDD), nuclear warheads, and special nuclear material (SNM). Radiation portal monitors (RPMs) are used as the main screening tool for vehicles and cargo at borders, supplemented by handheld detectors, personal radiation detectors, and x-ray imaging systems. This talk will present an overview of radiation detection equipment with emphasis on radiation portal monitors. In the US, the deployment of radiation detection equipment is being coordinated by the Domestic Nuclear Detection Office within the Department of Homeland Security, and a brief summary of the program will be covered. Challenges with current generation systems will be discussed as well as areas of investigation and opportunities for improvements. The next generation of radiation portal monitors is being produced under the Advanced Spectroscopic Portal program and will be available for deployment in the near future. Additional technologies, from commercially available to experimental, that provide additional information for radiation screening, such as density imaging equipment, will be reviewed. Opportunities for further research and development to improve the current equipment and methodologies for radiation detection for the important task of homeland security will be the final topic to be discussed. [Preview Abstract] |
Friday, May 16, 2008 10:33AM - 10:45AM |
A1.00005: BREAK
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Friday, May 16, 2008 10:45AM - 11:21AM |
A1.00006: Fizzlers Invited Speaker: Type II Supernovae are produced by the collapse of the cores of massive stars at the ends of their nuclear lifetimes. The basic picture for the outburst mechanism of Type II Supernova explosions is rather secure with only the details of the shock generation and the outburst uncertain. {\it However, broad issues remain concerning our understanding of Type II Supernovae when the less studied, but more general case of rotating and/or magnetic progenitor stars is considered}. That rotation and magnetic fields may play large roles in core collapse has been suggested for almost 40 years dating from the discovery that pulsars, the remnants of Type II Supernovae, are strongly magnetic, rapidly rotating neutron stars. This fact has been further reinforced by the discovery of the class of neutron stars with ultra-strong magnetic fields known as {\it Magnetars}. The role that rotation plays in core collapse can be appreciated by noting that stable, stationary, degenerate equilibrium configurations are possible only for stars with central density $\rho_c$ $\approx$ 10$^4$-10$^9$ g cm$^{-3}$ (white dwarf densities) and $\rho_c$ $\approx$ 10$^{14}-10^{15}$ g cm$^{-3}$ (neutron star densities). Nonrotating objects with $\rho_c$ between that of white dwarfs (typical of the densities of the precollapse cores of Type II Supernovae) and neutron stars are unstable to radial collapse because of the low effective $\Gamma$ of their equations-of-state (EOS) (see Shapiro \& \& Teukolsky 1983). Stars at intermediate $\rho_c$ may be stabilized against collapse by rapid rotation. This possibility gives rise to what were coined {\it fizzlers} by Gold (1974) to describe {\it fizzled} core collapses of massive rotating stars through formation of rotation-supported stars with densities intermediate between those of the white dwarf-like precollapse core and a neutron star. Interest in fizzlers waned in the 1980s when it was showed that, although fizzlers could exist, they only occupied a small part of the precollapse core parameter space for cold equations-of-state (EOS). Interest in fizzlers was revived in the late 1990s when it was found that {\it fizzlers} could form under a wider range of conditions than had been suggested if hot dense EOSs were considered. Observationally, interest in fizzlers was also driven by the recognition that {\it fizzlers} could lead to the generation of gravitational wave emission in Type II Supernovae, emission potentially observable by LIGO, the Laser Interferometer Gravitational Wave Observatory), and other gravitational wave observatories, and that fizzlers could perhaps play roles in the $\gamma$-ray burster phenomenon and the formation of {\it strange} stars. We review the properties of {\it fizzlers} and consider their applications to LIGO, strange stars, and {\it Magnetars}. [Preview Abstract] |
Friday, May 16, 2008 11:21AM - 11:57AM |
A1.00007: Astroparticle Physics and the SNOLAB Underground Laboratory Invited Speaker: Astroparticle physics explores the intersections between particle physics and astrophysics. Major questions include the direct detection of dark matter and the determination of the mass, character, and influence of neutrinos. SNOLAB, a deep underground clean laboratory in Sudbury, Ontario has been built to enable such measurements. The SNOLAB laboratory will be described, as well as two experimental projects that will be sited there: The SNO+ double beta decay neutrino experiment and the DEAP/Clean Liquid Argon dark matter detector. [Preview Abstract] |
Friday, May 16, 2008 11:57AM - 12:33PM |
A1.00008: Climate Change and Aerosol Feedbacks Invited Speaker: Climate instability is expected as mixing ratios of greenhouse gases in the Earth's atmosphere increase. The current trend in rising temperature can be related to anthropogenic greenhouse gas emissions. However, this trend may change as feedback mechanisms amplify; one of the least-understood aspects of climate change. Formation of cloud condensation nuclei from rising sulfate concentrations in the atmosphere may counteract the current warming trend. A key point is where the sulfate, and cloud condensation nuclei are formed. Is cloud formation widespread or localized near sulfate emission sources? A major source of atmospheric sulfate is dimethylsulfide, a compound related to biotic turnover in the surface ocean that constitutes a widespread natural source of aerosols over the remote ocean. A second major source contributing a significant proportion of atmospheric sulfate in the northern hemisphere is produced over continents from industrial activities and fossil fuel combustion. Distinguishing the source of sulfate in well-mixed air is important so that relationships with cloud formation, sea-ice in polar regions, and albedo can be explored. This distinction in sulfate sources can be achieved using isotope apportionment techniques. Recent measurements show an increase in biogenic sulfate coincident with rising temperatures in the Arctic and large amounts sulfur from DMS oxidation over the Atlantic, potentially indicating a widespread biotic feedback to warming over northern oceans. [Preview Abstract] |
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