4,840 research outputs found

    Preliminary studies of soil patterns observed in radar images, Bishop area, California

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    Soil patterns observed by aerial radar photograph

    Math modeling for helicopter simulation of low speed, low altitude and steeply descending flight

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    A math model was formulated to represent some of the aerodynamic effects of low speed, low altitude, and steeply descending flight. The formulation is intended to be consistent with the single rotor real time simulation model at NASA Ames Research Center. The effect of low speed, low altitude flight on main rotor downwash was obtained by assuming a uniform plus first harmonic inflow model and then by using wind tunnel data in the form of hub loads to solve for the inflow coefficients. The result was a set of tables for steady and first harmonic inflow coefficients as functions of ground proximity, angle of attack, and airspeed. The aerodynamics associated with steep descending flight in the vortex ring state were modeled by replacing the steady induced downwash derived from momentum theory with an experimentally derived value and by including a thrust fluctuations effect due to vortex shedding. Tables of the induced downwash and the magnitude of the thrust fluctuations were created as functions of angle of attack and airspeed

    Quantitative patterns in drone wars

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    Attacks by drones (i.e., unmanned combat air vehicles) continue to generate heated political and ethical debates. Here we examine the quantitative nature of drone attacks, focusing on how their intensity and frequency compare with that of other forms of human conflict. Instead of the power-law distribution found recently for insurgent and terrorist attacks, the severity of attacks is more akin to lognormal and exponential distributions, suggesting that the dynamics underlying drone attacks lie beyond these other forms of human conflict. We find that the pattern in the timing of attacks is consistent with one side having almost complete control, an important if expected result. We show that these novel features can be reproduced and understood using a generative mathematical model in which resource allocation to the dominant side is regulated through a feedback loop.Comment: 5 pages, 3 figure

    Three New Species of Melita (Crustacea: Amphipoda), with Notes on the Amphipod Fauna of the Apalachicola Estuary of Northwest Florida

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    Three undescribed species of Melita have been collected in the Apalachicola estuary of northwest Florida. These new species, Melita elongata, M. longisetosa, and M. intermedia, are similar to and co-occur with M. nitida Smith, 1873, along the U.S. Gulf Coast. The new species of the nitida complex are yet unknown on the Atlantic coast north of Florida, although M. nitida occurs north to the Gulf of St. Lawrence. A key to the males of the species in the M. nitida complex is given. Nineteen other amphipod species have been collected in the Apalachicola estuary, six of which are at present undescribed. The life history, abundance patterns and ecological attributes are given for each species to the limit of available information

    Trophic Resource Utilization by Three Species of Sciaenid Fishes in a Northwest Florida Estuary

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    Food habits of Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus), and sand seatrout (Cynoscion arenarius) were examined in 1976 collections from Apalachicola Bay, Florida. Ontogenetic, spatial, and temporal aspects of diet were considered. Polychaetes were the main food of croakers over all collections, followed in importance by detritus, fishes, insect larvae, mysids, and infaunal shrimp. Diet specialization occurred with growth of croakers, so that one or two food types dominated the diet. Intraspecific diet correlation using the Spearman Rank Correlation Coefficient, indicated three feeding groups: 10-39 mm fish, 40-39 mm fish, and 90-159 mm fish. Croaker feeding in shallow, low salinity sites in the estuary was distinct from feeding in deeper, more saline areas. Temporal analysis (January-September) of the croaker diet reflected four feeding patterns: (1) first entry into the estuary by small size fauna; (2) area-wide distribution of many size classes, (3) concentration of mid-sized individuals in the upper estuarine areas, and (4) emigration of large size classes. Polychaetes and harpacticoid copepods dominated the average spot diet, followed by detritus, bivalves and nematodes. Several distinctive patterns in feeding were noted on ontogenetic and spatial bases, but not on a temporal basis. Intraspecific diet correlation indicated similar feeding patterns in all but the smallest (20-29 mm) and largest (100-109 mm) size classes examined. Juvenile fishes (mainly Anchoa mitchilli) dominated the sand seatrout diet, while mysids ranked a distant second. There was a clear sequence of ontogenetic changes in sand seatrout feeding (also indicated by intraspecific correlation), wherein smaller size classes preyed heavily on mysids followed by a switch to piscivory by larger individuals. Spatial analysis indicated heavy consumption of fishes by sand seatrout near high salinity passes to the estuary, grading into heavy consumption of mysids in shallow, low salinity areas. Temporal analysis (May-November) revealed relatively lower predation on fishes in late summer when various crustaceans were important diet components. Interspecific diet comparisons indicated little overall trophic overlap among the three sciaenids, but diets of small croakers (10-59 mm) and spot (20-79 mm) were significantly correlated. Few correlations in diet were found between sand seatrout and either croaker or spot. A sieve fractionation technique used to analyze food habits yielded a clear distinction in prey size between the two benthic feeders. While diets were superficially similar, croakers consumed larger polychaetes and larger food items in general than did spot

    The Yorktown Pottery Industry, Yorktown, Virginia

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    No abstract is available at this time

    Topic-dependent sentiment analysis of financial blogs

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    While most work in sentiment analysis in the financial domain has focused on the use of content from traditional finance news, in this work we concentrate on more subjective sources of information, blogs. We aim to automatically determine the sentiment of financial bloggers towards companies and their stocks. To do this we develop a corpus of financial blogs, annotated with polarity of sentiment with respect to a number of companies. We conduct an analysis of the annotated corpus, from which we show there is a significant level of topic shift within this collection, and also illustrate the difficulty that human annotators have when annotating certain sentiment categories. To deal with the problem of topic shift within blog articles, we propose text extraction techniques to create topic-specific sub-documents, which we use to train a sentiment classifier. We show that such approaches provide a substantial improvement over full documentclassification and that word-based approaches perform better than sentence-based or paragraph-based approaches
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