Event reconstruction in high resolution Compton telescopes

The development of germanium Compton telescopes for nuclear gamma-ray astrophysics (~0.2-20 MeV) requires new event reconstruction techniques to accurately determine the initial direction and energy of photon events, as well as to consistently reject background events. This paper describes techniques for event reconstruction, accounting for realistic instrument/detector performance and uncertainties. An especially important technique is Compton Kinematic Discrimination, which allows proper interaction ordering and background rejection with high probabilities. The use of these techniques are crucial for the realistic evaluation of the performance and sensitivity of any germanium Compton telescope configuration.Comment: Accepted for publication in A&AS

Searching for annihilation radiation from SN 1006 with SPI on INTEGRAL

Historical Type Ia supernovae are a leading candidate for the source of positrons observed through their diffuse annihilation emission in the Galaxy. However, search for annihilation emission from individual Type Ia supernovae has not been possible before the improved sensitivity of \integral. The total 511 keV annihilation flux from individual SNe Ia, as well as their contribution to the overall diffuse emission, depends critically on the escape fraction of positrons produced in $^{56}$Co decays. Late optical light curves suggest that this fraction may be as high as 5%. We searched for positron annihilation radiation from the historical Type Ia supernova SN 1006 using the SPI instrument on \integral. We did not detect significant 511 keV line emission, with a 3$\sigma$ flux upper limit of 0.59 x 10$^{-4}$ ergs cm^-2 s^-1 for \wsim 1 Msec exposure time, assuming a FWHM of 2.5 keV. This upper limit corresponds to a 7.5% escape fraction, 50% higher than the expected 5% escape scenario, and rules out the possibility that Type Ia supernovae produce all of the positrons in the Galaxy (~ 12% escape fraction), if the mean positron lifetime is less than 10$^{5}$ years. Future observations with \integral will provide stronger limits on the escape fraction of positrons, the mean positron lifetime, and the contribution of Type Ia supernovae to the overall positron content of the Galaxy.Comment: 3 pages, 2 figures, accepted for publication in ApJ

First global analysis of SEASAT scatterometer winds and potential for meteorological research

The first global wind fields from SEASAT-A scatterometer (SASS) data were produced. Fifteen days of record are available on tape, with unique wind directions indicated for each observation. The methodology of the production of this data set is described, as well as the testing of its validity. A number of displays of the data, on large and small scales, analyzed and gridded, are provided

A new parameterization of an empirical model for wind/ocean scatterometry

The power law form of the SEASAT A Scatterometer System (SASS) empirical backscatter-to-wind model function does not uniformly meet the instrument performance over the range 4 to 24 /ms. Analysis indicates that the horizontal polarization (H-Pol) and vertical polarization (V-Pol) components of the benchmark SASS1 model function yield self-consistent results only for a small mid-range of speeds at larger incidence angles, and for a somewhat larger range of speeds at smaller incidence angles. Comparison of SASS1 to in situ data over the Gulf of Alaska region further underscores the shortcomings of the power law form. Finally, a physically based empirical SASS model is proposed which corrects some of the deficiencies of power law models like SASS1. The new model allows the mutual determination of sea surface wind stress and wind speed in a consistent manner from SASS backscatter measurements

Smart Mobile Devices and Competitive Strategy: A Resource-Based Perspective

This research examines the implications of smart mobile devices (SMDs), or smartphones, for organizational competitiveness. It employs a resource-based framework to analyze the relationship among smart mobile devices, strategy, and firm performance. Building on existing strategic management research which suggests that leveraging IT to build business strategies can be a source of sustainable competitive advantage, six propositions relating smart mobile devices to sustainable competitive advantage are presented. Drawing also from scholarly work in the information technology and information systems domains, strategic implications of mobile- device technology for firms are provided. It is suggested that SMDs impact firm communications, decision-making, innovation, and performance

Correspondence to General William Robertson Boggs, 1870s: January 21, 1875 - November 6, 1878

Boggs Papers, Box 1, Folder 2 Correspondence to General William Robertson Boggs, 1870s: January 21, 1875 - November 6, 1878https://digitalcommons.wofford.edu/littlejohnboggs/1001/thumbnail.jp

Analysing the sustainability of the physical rehabilitation sector in seven fragile countries through multi-stakeholder involvement using a participatory consensus tool

Background: Sustainability is identified by nearly all organisations working in global health as one of the key indicators for project evaluation. Though typically recognised as an essential component for good project management to ensure positive impact, it is rarely applied effectively in practical terms and there are very few practical methods or tools to support implementation and monitoring of sustainable interventions. Further, despite efforts of stakeholders at all levels, the rehabilitation sector is not usually at the top of policy-makers’ agendas, which often results in limited to no funding and makes the task of building sustainability even more challenging at field level

The Giant Flare of December 27, 2004 from SGR 1806-20

The giant flare of December 27, 2004 from SGR 1806-20 represents one of the most extraordinary events captured in over three decades of monitoring the gamma-ray sky. One measure of the intensity of the main peak is its effect on X- and gamma-ray instruments. RHESSI, an instrument designed to study the brightest solar flares, was completely saturated for ~0.5 s following the start of the main peak. A fortuitous alignment of SGR 1806-20 near the Sun at the time of the giant flare, however, allowed RHESSI a unique view of the giant flare event, including the precursor, the main peak decay, and the pulsed tail. Since RHESSI was saturated during the main peak, we augment these observations with Wind and RHESSI particle detector data in order to reconstruct the main peak as well. Here we present detailed spectral analysis and evolution of the giant flare. We report the novel detection of a relatively soft fast peak just milliseconds before the main peak, whose timescale and sizescale indicate a magnetospheric origin. We present the novel detection of emission extending up to 17 MeV immediately following the main peak, perhaps revealing a highly-extended corona driven by the hyper-Eddington luminosities. The spectral evolution and pulse evolution during the tail are presented, demonstrating significant magnetospheric twist and evolution during this phase. Blackbody radii are derived for every stage of the flare, which show remarkable agreement despite the range of luminosities and temperatures covered. Finally, we place significant upper limits on afterglow emission in the hundreds of seconds following the giant flare.Comment: 32 pages, 14 figures, submitted to Ap

Correspondence to Elizabeth ( Bessie ) McCaw Boggs Taylor, August 31, 1888 - December 10, 1901

Correspondence to Elizabeth ( Bessie ) McCaw Boggs Taylor, August 31, 1888 - December 10, 1901. Box 2, folder 5.https://digitalcommons.wofford.edu/littlejohnboggs/1015/thumbnail.jp