37 research outputs found
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Survival of Coho Salmon Fingerlings Passing Through a Perforated Bulkhead in an Empty Turbine Bay and Through Flow Deflectors (With and Without Dentates) on Spillway at Lower Monumental Dam, Snake River, April - May 1973
To reduce high levels of dissolved nitrogen and other gases in the Snake River, the U.S. Army Corps of Engineers has designed and tested the mechanical and hydraulic performance of perforated bulkheads in the intakes of skeleton turbine units and of experimental flow deflectors on spillways at dams in lower Snake River. At Lower Monumental Dam, a flow detector with dentates was installed in spillway bay No. 2 and a plain deflector in spillway bay No. 4. Although these hydraulic structures allow the passage of significant volumes of water through the dam with little, if any, increase in dissolved atmospheric gases, they may cause death or injury to young fish that pass through the structures on their migration to the sea. The National Marine Fisheries Service, under contract to the Corps of Engineers, is evaluating fingerling passage and survival through the bulkhead and flow deflector. Studies in 1972 showed that perforated bulkheads caused high mortality to young fall chinook salmon, but flow deflectors with dentates were less harmful. Similar tests were run in 1973 to compare the effects of flow deflectors (with and without dentates) and to examine the effects of the perforated bulkhead on passage and survival of yearling coho salmon. This report summarizes the results of the latter tests
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Evaluation of Fish Passage in the Vertical Slot Regulating Section of the South Shore Ladder at John Day Dam
None supplied. From introduction: The reluctance of shad to pass through the orifice-type regulating sections of the fish ladders has been a serious problem at John Day Dam. During the shad run the pools of the regulating sections have become extremely crowded with fish and many shad have died in the ladders before spawning. The coordinated effort of Engineers and Biologists resulted in the development of a vertical slot fish ladder that effectively passed shad in the laboratory and provided adequate flow regulation in the Corps\u27 model of the John Day fish ladder. The objective of the evaluation study was to ensure that the new vertical slot regulating section would satisfactorily pass shad and all other species of fish that ascend the John Day fish ladders
Ultrafast charge and spin dynamics in ferromagnets
With our experiment we demonstrate all-optical control of magnetization in a ferromagnet with an unprecedented sub-femtosecond time resolution. The reported results open the doors to a new generation of spintronic devices with petahertz clock-rates. (C) 2020 The Author(s
Light-wave dynamic control of magnetism
The enigmatic interplay between electronic and magnetic phenomena observed in many early experiments and outlined in Maxwell’s equations propelled the development of modern electromagnetism1. Today, the fully controlled evolution of the electric field of ultrashort laser pulses enables the direct and ultrafast tuning of the electronic properties of matter, which is the cornerstone of light-wave electronics2,3,4,5,6,7. By contrast, owing to the lack of first-order interaction between light and spin, the magnetic properties of matter can only be affected indirectly and on much longer timescales, through a sequence of optical excitations and subsequent rearrangement of the spin structure8,9,10,11,12,13,14,15,16. Here we introduce the regime of ultrafast coherent magnetism and show how the magnetic properties of a ferromagnetic layer stack can be manipulated directly by the electric-field oscillations of light, reducing the magnetic response time to an external stimulus by two orders of magnitude. To track the unfolding dynamics in real time, we develop an attosecond time-resolved magnetic circular dichroism detection scheme, revealing optically induced spin and orbital momentum transfer in synchrony with light-field-driven coherent charge relocation17. In tandem with ab initio quantum dynamical modelling, we show how this mechanism enables the simultaneous control of electronic and magnetic properties that are essential for spintronic functionality. Our study unveils light-field coherent control of spin dynamics and macroscopic magnetic moments in the initial non-dissipative temporal regime and establishes optical frequencies as the speed limit of future coherent spintronic applications, spin transistors and data storage media