986 resultados para Communicable Disease Center (U.S.)


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The development of sand ripples in an oscillatory-flow water tunnel was observed in 104 laboratory experiments approximating conditions at the seabed under steady progressive surface waves. The period, T, and amplitude, a, of the water motion were varied over wide ranges. Three quartz sands were used, with mean grain diameters, D = 0.55, 0.21, and 0.18 millimeter. In 24 experiments, with the bed initially leveled, T was reduced until ripples appeared, and their development to final equilibrium form was observed without further change in T. The remaining 80 experiments investigated the response of previously established bed forms to changes in T or a or both. The ripple length, lambda, and height, eta, were measured from photos, except when bed forms were three dimensional.

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As presently used, the immersed weight rate, I sub l, is the volume rate, Q, of longshore transport, multiplied by a constant. For use in engineering problems, I sub l must be converted back to the equivalent Q. The I sub l formulation may be important where the unit weight of sand differs significantly from the unit weight of sand at the open-coast sites contributing data to the design curve. Increase in void ratio may result in a 10- to 20-percent increase in actual (as compared to predicted) shoaling volumes where sand accumulates in protected water. Void ratio should be measured in field studies of longshore transport.

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"June 1980."

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Presents children in grade 1 through 3 with information about environmental dangers and ecology.

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Title from cover.

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Mode of access: Internet.

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"Approved for public release, distribution unlimited."

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Description based on: Feb. 1984; title from cover.

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Mode of access: Internet.

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"Contract no. N61339-1089."

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"Status report no. 12, Contract N6 onr-264, Task 15, Cornell University, December 1951"-leaf [1].