4,009 research outputs found

    The Submarine and The Washington Conference of 1921

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    Following the First World War, the tide of public opinion was overwhelmingly against the submarine as a weapon of war. The excesses of the German U-boat had stunned the sensibilities of the world but had, nonetheless, presented new ideas and possibilities of this weapon to the various naval powers of the time, The momentum of these new ideas proved so strong that by the opening of the first major international disarmament conference of the 20th century, practical uses of the submarine had all but smothered the moral indignation of 1918

    THE SUBMARINE AND THE WASHINGTON CONFERENCE OF 1921

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    Bequests as a Means of Payment

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    Although recent research suggests that intergenerational transfers play an important role in aggregate capital accumulation, our understanding of bequest motives remains incomplete. We develop a simple model of"exchange-motivated" bequests, in which a testator influences the decisions ofhis beneficiaries by holding wealth in bequeathable forms and by conditioning the division of bequests on the beneficiaries' actions. The model generates falsifiable empirical predictions which are inconsistent with other theories of intergenerational transfers. We present econometric and other evidence which strongly suggests that bequests are often used as a means of payment for services rendered by beneficiaries.

    The dynamic effects of internal robots on Space Station Freedom

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    Many of the planned experiments of the Space Station Freedom (SSF) will require acceleration levels to be no greater than microgravity (10 exp -6 g) levels for long periods of time. Studies have demonstrated that without adequate control, routine operations may cause disturbances which are large enough to affect on-board experiments. One way to both minimize disturbances and make the SSF more autonomous is to utilize robots instead of astronauts for some operations. The present study addresses the feasibility of using robots for microgravity manipulation. Two methods for minimizing the dynamic disturbances resulting from the robot motions are evaluated. The first method is to use a robot with kinematic redundancy (redundant links). The second method involves the use of a vibration isolation device between the robot and the SSF laboratory module. The results from these methods are presented along with simulations of robots without disturbance control

    Reaction-compensation technology for microgravity laboratory robots

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    Robots operating in the microgravity environment of an orbiting laboratory should be capable of manipulating payloads such that the motion of the robot does not disturb adjacent experiments. The current results of a NASA Lewis Research Center technology program to develop smooth, reaction-compensated manipulation based on both mechanism technology and trajectory planning strategies are present. Experimental validation of methods to reduce robot base reactions through the use of redundant degrees of freedom is discussed. Merits of smooth operation roller-driven robot joints for microgravity manipulators are also reviewed

    Contributions of the Conservation Reserve Program to Populations of Breeding Birds in North Dakota

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    Previous studies have shown that habitat provided by the Conservation Reserve Program (CRP), a feature of the 1985 farm bill, is used by many birds. The present study quantitatively assesses the importance of the CRP by estimating changes in breeding bird populations of North Dakota projected if CRP land would revert to cultivation. Of 18 species that were common in CRP or crop fields or both, 12 were more abundant in CRP habitats. Six of these species had suffered significant population declines during 1967-1990, according to the North American Breeding Bird Survey. In contrast, none of the six species that were more common in cropland than in CRP fields had declined significantly. Termination of the Conservation Reserve Program and a return of enrolled land to cultivation is projected to cause population declines in North Dakota exceeding 17% for Sedge Wren (Cistothorus platensis), Grasshopper Sparrow (Ammodramus savannarum), Savannah Sparrow (Passerculus sandwichensis), Dickcissel (Spiza americana), and Lark Bunting (Calamospiza melanocorys)

    AREA REQUIREMENTS OF GRASSLAND BIRDS: A REGIONAL PERSPECTIVE

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    Dramatic Increase of Le Conte\u27s Sparrow in Conservation Reserve Program Fields in the Northern Great Plains

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    During a continuing investigation in the northern Great Plains, we documented substantial increases of the Le Conte\u27s Sparrow (Ammodramus Leconteii) in Conservation Reserve Program (CRP) fields in 1994 compared with 1990-93. The most dramatic increases occurred in Eddy County, North Dakota, and Sheridan County, Montana. The changes in habitat associated with the drought from 1989 to early 1993 and above-normal precipitation from mid-1993 through mid-1994 likely produced favorable breeding conditions for this species in CRP fields in 1994

    Brown-headed Cowbird, Molothrus ater, Parasitism and Abundance in the Northern Great Plains

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    The Brown-headed Cowbird (Molothrus ater) reaches its highest abundance in the northern Great Plains, but much of our understanding of cowbird ecology and host-parasite interactions comes from areas outside of this region. We examine cowbird brood parasitism and densities during two studies of breeding birds in the northern Great Plains during 1990–2006. We found 2649 active nests of 75 species, including 746 nonpasserine nests and 1902 passerine nests. Overall, <1% of nonpasserine nests and 25% of passerine nests were parasitized by Brown-headed Cowbirds. Although the overall frequency of cowbird parasitism in passerine nests in these two studies is considered moderate, the frequency of multiple parasitism among parasitized nests was heavy (nearly 50%). The mean number of cowbird eggs per parasitized passerine nest was 1.9 ± 1.2 (SD; range = 1–8 cowbird eggs). The parasitism rates were 9.5% for passerines that typically nest in habitats characterized by woody vegetation, 16.4% for grassland-nesting passerines, 4.7% for passerines known to consistently eject cowbird eggs, and 28.2% for passerines that usually accept cowbird eggs. The Red-winged Blackbird (Agelaius phoeniceus) was the most commonly parasitized species (43.1% parasitism, 49.6% multiple parasitism, 71.2% of all cases of parasitism). Passerine nests found within areas of higher female cowbird abundance experienced higher frequencies of cowbird parasitism than those found in areas of lower female cowbird abundance. Densities of female cowbirds were positively related to densities and richness of other birds in the breeding bird community
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