An evolutionary algorithm (ES) for automated deconvolution of γ-ray spectra is described that fits peak shape
morphologies typical of spectra acquired from variably radiation damaged γ-ray detectors. Space radiation effects
significantly impair semi-conductor γ-ray detector efficiency and induce variable degrees of nuclide peak broadening,
distortion in spectra. Mars Odyssey Gamma-ray spectrometer data are used to demonstrate applicability of described
algorithms for three degrees of radiation damage. ES methods accurately identify and quantify the discrete set of
nuclide peaks in an arbitrary spectrum using a nuclide library. A novel method of constraining peak low energy tails,
broadened by detector radiation damage, reduces the peak shape model from six parameters to four yielding a
significant minimization of model complexity. Benefits of this approach include the simple implementation of highly
specific parameter constraints that appropriately define feasible solution spaces. Methods describe peak low energy
tailing descriptors as a continuum of low energy peak tailing curves representing increasing degrees of radiation
damage. Curves are addressable by a single real valued parameter. Results illustrate the use of methods to simply
describe relative radiation dosimetry using this parameter. Analysis of degraded spectra indicates method sensitivity
to low and high levels of space radiation damage prior to and post MO-GRS detector annealings.
Increased blood glucose stimulates pancreatic β-cells and induces an exocytotic release of insulin. The β-cell, which contains ~10^4 insulin-containing granules, releases only a few percent of the granules during a given stimulus such as a meal. The temporal response function to a square wave increase in the concentration of glucose is characteristically biphasic. It is not known whether the granules exhibit random or directed migration patterns as a function of phase. Directed migration would suggest the development of an intracellular gradient directing the path and velocity of insulin granule movement. Our ongoing research investigates this process using manual morphometric analysis of electron micrographs of rat pancreatic β-cells. This is a tedious and time-consuming stereological process. Consequently, we have developed an automated algorithm for accurately segmenting and deriving granule counts, areas, and measuring distance to the plasma membrane. The method is a data-driven image processing approach that implements Mahalanobis classifiers to hierarchically classify pixel candidates and subsequently pixel aggregates as insulin granules. Granule cores and halos are classified independently and fused by intersecting the convex difference of granule halos with core candidates. Once fused, total and individual granule areas and distance metrics to the β-cell plasma membrane are obtained. This algorithm provides a rapid and accurate method for the determination of granule numbers, location, and potential gradients in the pancreatic β-cell under different experimental conditions.
The on-board flight software for the Near Earth Asteroid Rendezvous (NEAR) spacecraft was modified to produce continuous 1-sec sampled rate information from the shield of the x-ray and gamma ray spectrometer (XGRS) instrument. Since the XGRS shield can also detect gamma ray bursts (GRB), this rate information can be used in combination with the GRB detections by the Ulysses and near-Earth GRB instruments as part of the interplanetary network (IPN) to triangulate the source direction of GRBs. It is the long baseline of NEAR combined with the Ulysses baseline that makes small error box locations possible. We have developed an automated system to analyze the periodic telemetry dumps from the NEAR spacecraft. It extracts this new data type, scans the ate information for increases which are plausibly of GRB origin, and combines these with the GRB detections from the others spacecraft. Because the processing is automated, the time delay to produce the triangulated positions is kept to a minimum, up to 48 hours. This automated processing and distribution of the GRB locations is done within the GRB Coordinates Network system. About 60 locations per year with errors ranging from a few to tens of arcminutes are expected. These rapid precise localizations may provide about 10 times the rate currently provided by the WFC and NFI instruments on BeppoSAX.
Timothy McClanahan, Irina Mikheeva, Jacob Trombka, Samuel Floyd, William Boynton, H. Bailey, Jasbir Bhangoo, Richard Starr, Pamela Clark, Larry Evans, Steven Squyres, Elaina McCartney, E. Noe, Ralph McNutt, Johannes Brueckner
An x-ray and gamma-ray spectrometer (XGRS) is onboard the Near Earth Asteroid Rendezvous (NEAR) spacecraft to determine the elemental composition of the surface of the asteroid 433 Eros. The Eros asteroid is highly non-spherical in physical shape and the development of data management and analysis methodologies are in several areas a divergence from traditional remotely sensed geographical information systems techniques. Field of view and asteroid divergence from traditional remotely sensed geographical information system techniques. Field of view and asteroid surface geometry must be derived virtually and then combined with real measurements of solar, spectral and instrument calibration information to derive meaningful scientific results. Spatial resolution of planned geochemical maps will be improved from the initial conditions of low statistical significance per integration by repeated surface flyovers and regional spectral accumulation. This paper describes the results of a collaborative effort of design and development of the NEAR XGRS instrument ground system undertaken by participants at the Goddard Space Flight Center, University of Arizona, Cornell University, Applied Physics Laboratory, and Max Planck Institute.
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