162 research outputs found

    Remediation of potentially acidified Hanford wastes using tri-n-octyl phosphine oxide extraction chromatographic materials

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    As the Hanford site undergoes remediation, significant economies could be realized if aluminum and chromium are kept from High Level Waste glass produced at the Hanford Waste Treatment Plant (WTP). An acidic scrub of the Hanford sludge could enhance Al removal, although such treatment could lead to the mobilization of transuranic elements. If mobilization were minor, a chromatographic secondary cleanup of the acidic waste stream may be preferred to allow preconcentration of radionuclides prior to processing through the Hanford WTP. This study examines tri-n-octyl phosphine oxide coated resins as a chromatographic means for the removal of transuranics from a secondary waste stream. Metal uptake kinetics and mechanisms for transuranics and a simulant transuranic (europium) with the developed resin are characterized in both batch and column operation modes. Results indicate up to 99% of the radioactive material present from an acidic sludge leach may be recovered using extraction chromatography providing an effective avenue for high aluminum content tank pre-treatment

    Borrelioses, agentes e vetores

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    The Influence of Light on the Twilight Migrations of Grunts

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    Behaviors that precede the daily migrations of mixed-species schools of juvenile grunts (Pomadasyidae), from patch reefs to grass beds at dusk and vice versa at dawn, are defined and utilized to ascertain the precision of the migrations. Although premigratory behaviors differ at dusk and dawn, the migrations are precise twilight events which occur at the same light intensities during dawn and dusk. Histological sections of the retina reveal that both cones and rods are fully exposed to ambient light during the migrations. Under the difficult photic conditions that prevail during migration, the retina is structured photomechanically to maximize the absorption of ambient light. Body colorations of the grunts, which consist mostly of intense colored stripes during the day, are replaced at night by cryptic melanic patterns. The precision of migration, the photomechanical movements in the retina, and the changes in body coloration are considered adaptive because they reduce predation on grunts when they migrate and are most vulnerable to attack. In support of this conclusion, the migrations take place just before the evening and just after the morning \u27quiet period\u27 - thus they avoid that period during twilight when predation is highest in tropical fish communities
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