17 research outputs found
Flight Avionics Hardware Roadmap
As part of NASA's Avionics Steering Committee's stated goal to advance the avionics discipline ahead of program and project needs, the committee initiated a multi-Center technology roadmapping activity to create a comprehensive avionics roadmap. The roadmap is intended to strategically guide avionics technology development to effectively meet future NASA missions needs. The scope of the roadmap aligns with the twelve avionics elements defined in the ASC charter, but is subdivided into the following five areas: Foundational Technology (including devices and components), Command and Data Handling, Spaceflight Instrumentation, Communication and Tracking, and Human Interfaces
Rare earth element abundances in hydrothermal fluids from the Manus Basin, Papua New Guinea : indicators of sub-seafloor hydrothermal processes in back-arc basins
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 74 (2010): 5494-5513, doi:10.1016/j.gca.2010.07.003.Rare earth element (REE) concentrations are reported for a large suite of seafloor vent fluids
from four hydrothermal systems in the Manus back–arc basin (Vienna Woods, PACMANUS,
DESMOS and SuSu Knolls vent areas). Sampled vent fluids show a wide range of absolute REE
concentrations and chondrite–normalized (REEN) distribution patterns (LaN/SmN ~ 0.6 – 11;
LaN/YbN ~ 0.6 – 71; EuN/Eu*N ~ 1 – 55). REEN distribution patterns in different vent fluids range
from light–REE enriched, to mid– and heavy–REE enriched, to flat, and have a range of positive
Eu–anomalies. This heterogeneity contrasts markedly with relatively uniform REEN distribution
patterns of mid–ocean ridge hydrothermal fluids. In Manus Basin fluids, aqueous REE
compositions do not inherit directly or show a clear relationship with the REE compositions of
primary crustal rocks with which hydrothermal fluids interact. These results suggest that the
REEs are less sensitive indicators of primary crustal rock composition despite crustal rocks being
the dominant source of REEs in submarine hydrothermal fluids. In contrast, differences in
aqueous REE compositions are consistently correlated with differences in fluid pH and ligand
(chloride, fluoride and sulfate) concentrations. Our results suggest that the REEs can be used as
an indicator of the type of magmatic acid volatile (i.e., presence of HF, SO2) degassing in
submarine hydrothermal systems. Additional fluid data suggest that near seafloor mixing
between high–temperature hydrothermal fluid and locally entrained seawater at many vent areas
in the Manus Basin causes anhydrite precipitation. Anhydrite effectively incorporates REE and
likely affects measured fluid REE concentrations, but does not affect their relative distributions.This study received financial support from the Ocean
Drilling Program Schlanger Fellowship (to P.R. Craddock), the WHOI Deep Ocean Exploration
Institute Graduate Fellowship (to E. Reeves) and NSF grant OCE–0327448
Roles of Two Shewanella oneidensis MR-1 Extracellular Endonucleases â–ż â€
The dissimilatory iron-reducing bacterium Shewanella oneidensis MR-1 is capable of using extracellular DNA (eDNA) as the sole source of carbon, phosphorus, and nitrogen. In addition, we recently demonstrated that S. oneidensis MR-1 requires eDNA as a structural component during all stages of biofilm formation. In this study, we characterize the roles of two Shewanella extracellular endonucleases, ExeS and ExeM. While ExeS is likely secreted into the medium, ExeM is predicted to remain associated with the cell envelope. Both exeM and exeS are highly expressed under phosphate-limited conditions. Mutants lacking exeS and/or exeM exhibit decreased eDNA degradation; however, the capability of S. oneidensis MR-1 to use DNA as the sole source of phosphorus is only affected in mutants lacking exeM. Neither of the two endonucleases alleviates toxic effects of increased eDNA concentrations. The deletion of exeM and/or exeS significantly affects biofilm formation of S. oneidensis MR-1 under static conditions, and expression of exeM and exeS drastically increases during static biofilm formation. Under hydrodynamic conditions, a deletion of exeM leads to altered biofilms that consist of densely packed structures which are covered by a thick layer of eDNA. Based on these results, we hypothesize that a major role of ExeS and, in particular, ExeM of S. oneidensis MR-1, is to degrade eDNA as a matrix component during biofilm formation to improve nutrient supply and to enable detachment