Steven M. Collins

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Deep Impact collided with comet Tempel 1, excavating a crater controlled by gravity. The comet's outer layer is composed of 1- to 100-micrometer fine particles with negligible strength (<65 pascals). Local gravitational field and average nucleus density (600 kilograms per cubic meter) are estimated from ejecta fallback. Initial ejecta were hot (>1000(More)
Analyses of 21 N stable isotope tracer experiments, designed to examine food web dynamics in streams around the world, indicated that the isotopic composition of food resources assimilated by primary consumers (mostly invertebrates) poorly reflected the presumed food sources. Modeling indicated that consumers assimilated only 33–50% of the N available in(More)
Understanding how comets work--what drives their activity--is crucial to the use of comets in studying the early solar system. EPOXI (Extrasolar Planet Observation and Deep Impact Extended Investigation) flew past comet 103P/Hartley 2, one with an unusually small but very active nucleus, taking both images and spectra. Unlike large, relatively inactive(More)
The Deep Impact Spacecraft flew past Comet 103P/Hartley 2 on November 4th, 2010. Images revealed the comet to be enveloped in a field of debris composed of fine grained dust, ice, and hundreds of discrete millimeter to decimeter sized particles. In this work, a selection of the brightest particles are identified and photogrammetrically located in 3D space(More)
1Dept. of Astronomy, University of Maryland, College Park, MD 20742-2421, USA 2BSEI, 430 S. Randolph Way, Tucson, AZ 85716, USA 3Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, CA 91109, USA 4JHU Applied Physics Laboratory, SD/SRE, ZMP-3, 7707 Montpelier Rd W-155, Laurel, MD 20723, USA 5Inst. for Astronomy, 2680 Woodlawn Dr., Honolulu, HI 96822,(More)
During fasting, a cyclical pattern of rhythmic peristaltic motor activity is known to occur in the small intestine. It is called the migrating motor complex (MMC), and periodically sweeps the small bowel of secretions. It is usually abolished by feeding. This report is the first description of an MMC observed during the fluoroscopic examination of a patient(More)
This paper sets the scene for future patterns of nursing and nursing education and traces the ways in which the nursing profession has reached the present position. It illustrates the development of nursing over the past 100 years, and examines the key influences which have affected, and are likely to continue to affect, nursing, namely: the Government, the(More)