Testing of 30-GHz low noise receivers

NASA-sponsored studies of the growth in communications traffic have indicated that the frequency spectrum allocated to fix-service satellites at the C and Ku bands will reach saturation by the early 1990's. The next higher frequency bands allocated for communications satellties are 27.5 to 30 GHz for the uplink and 17.7 to 20.2 GHz for the downlink. Current plans for developing satellite systems that use these bands include a NASA demonstration satellite (ACTS). One of the components identified as critical to the success of that mission is a 27.5 to 30 GHz satellite receiver. In response to that identification, NASA has sponsored the development of such a receiver to the proof-of-concept (POC) level. Design and fabrication of such POC model receivers was carried out under parallel contracts awarded to LNR Communications, Inc. of Hauppauge, New York and to ITT Defense Communications Division of Nutley, New Jersey. The most significant of the performance goals were a 5 db maximum noise figure, a 2.5 GHz passband, and e0 dB Rf to If gain. Following delivery of hardware from each of the contractors, an in-house test program was undertaken at NASA's Lewis Research Center in order to verify the contractor-reported performance and to provide a comparison of the two receivers under identical test conditions. The present paper reports the results of those tests

Path, theme and narrative in open plan exhibition settings

Three arguments are made based on the analysis of science exhibitions. First,sufficiently refined techniques of spatial analysis allow us to model the impact oflayout upon visitors' paths, even in moderately sized open plans which allow almostrandom patterns of movement and relatively unobstructed visibility. Second, newlydeveloped or adapted techniques of analysis allow us to make a transition frommodeling the mechanics of spatial movement (the way in which movement is affectedby the distribution of obstacles and boundaries), to modeling the manner in whichmovement might register additional aspects of visual information. Third, theadvantages of such purely spatial modes of analysis extend into providing us with asharper understanding of some of the pragmatic constrains within which exhibitioncontent is conceived and designed

Range imager performance comparison in homodyne and heterodyne operating modes

Range imaging cameras measure depth simultaneously for every pixel in a given field of view. In most implementations the basic operating principles are the same. A scene is illuminated with an intensity modulated light source and the reflected signal is sampled using a gain-modulated imager. Previously we presented a unique heterodyne range imaging system that employed a bulky and power hungry image intensifier as the high speed gain-modulation mechanism. In this paper we present a new range imager using an internally modulated image sensor that is designed to operate in heterodyne mode, but can also operate in homodyne mode. We discuss homodyne and heterodyne range imaging, and the merits of the various types of hardware used to implement these systems. Following this we describe in detail the hardware and firmware components of our new ranger. We experimentally compare the two operating modes and demonstrate that heterodyne operation is less sensitive to some of the limitations suffered in homodyne mode, resulting in better linearity and ranging precision characteristics. We conclude by showing various qualitative examples that demonstrate the system’s three-dimensional measurement performance

Zooplankton Community Composition and Grazing in the Amazon River Plume and Western Tropical North Atlantic Ocean

Large river plumes and frontal zones are important physical features influencing plankton distribution in the marine environment. In the western tropical North Atlantic Ocean (WTNA) the Amazon River plume may extend over an area reaching 1.5 x 106 km2. The freshwater plume creates a low-density lens in the surface 25m and supplies silicon and phosphorus to the WTNA. These physical and chemical gradients create an ideal environment for large-scale blooms of diatom diazotroph associations (DDAs), a symbiotic relationship between nitrogen-fixing cyanobacteria and chain-forming diatoms. While the physical and chemical properties of the plume with regard to influences on phytoplankton have been reported, zooplankton distributions and the fate of enhanced primary production in the plume are largely unknown. I investigated mesozooplankton (\u3e200 μm) composition and grazing in the Amazon River plume-influenced WTNA in spring (May-June 2010) and fall (Sept.-Oct. 2011). Changes in zooplankton distribution and grazing occurred over the sea surface salinity (SSS) gradient from low salinity and mesohaline plume waters to high salinity oceanic waters. Distinct communities were identified in each season along the salinity gradient with several taxa primarily constrained in the surface plume waters (e.g., Lucifer faxoni). The plume appears to function as an “extended estuary”, with a number of taxa (e.g., decapods, euphausiids, and fish larvae) utilizing the plume as a nursery habitat or dispersal mechanism for larval stages. Mesozooplankton grazing was elevated in plume waters compared to oceanic waters and was 2-3 times higher in the fall vs. spring. These patterns suggest a lag in the peak mesozooplankton abundance and grazing in response the observed spring DDA bloom, at least in low salinity plume waters. Comparison of micro- and mesozooplankton grazing along the SSS gradient supported a transition from an “export” food web in waters with SSS \u3c 33 where mesozooplankton grazing dominated and potential for export via fecal pellet production is higher, to a “retention” food web at SSS above 33 where microzooplankton grazing was highest and recycling of nutrients in surface waters is predicted. Using molecular techniques to investigate feeding on DDAs and other N- fixers, I found that copepods consumed DDAs (Hemialus-Richelia and Rhizosolenia- Richelia, diatom-diazotroph respectively) as well as the colonial cyanobacterium Trichodesmium. Investigation of mesozooplankton grazing more broadly on other cyanobacteria with 16S rRNA sequencing revealed consumption of Synechococcus, Prochlorococcus, and the unicellular diazotroph UCYN-A Candidatus Atelocyanobacterium thalassa. Together, these results have important implications for our understanding of biogeochemical cycling in the WTNA, and other regions with abundant DDAs (e.g., the Mekong and Congo River plumes)