The marine viromes of four oceanic regions.

Viruses are the most common biological entities in the marine environment. There has not been a global survey of these viruses, and consequently, it is not known what types of viruses are in Earth's oceans or how they are distributed. Metagenomic analyses of 184 viral assemblages collected over a decade and representing 68 sites in four major oceanic regions showed that most of the viral sequences were not similar to those in the current databases. There was a distinct "marine-ness" quality to the viral assemblages. Global diversity was very high, presumably several hundred thousand of species, and regional richness varied on a North-South latitudinal gradient. The marine regions had different assemblages of viruses. Cyanophages and a newly discovered clade of single-stranded DNA phages dominated the Sargasso Sea sample, whereas prophage-like sequences were most common in the Arctic. However most viral species were found to be widespread. With a majority of shared species between oceanic regions, most of the differences between viral assemblages seemed to be explained by variation in the occurrence of the most common viral species and not by exclusion of different viral genomes. These results support the idea that viruses are widely dispersed and that local environmental conditions enrich for certain viral types through selective pressure.

Effects of interaction volume on X-ray line-scans across an ultrasonically consolidated aluminum/copper interface.

Diffusion as a bonding mechanism for ultrasonic consolidation of metals is widely debated due to the short weld times and low processing temperatures. To quantify interdiffusion coefficients, X-ray energy dispersive spectroscopy (XEDS) line-scans were performed across an Al-Cu interface using the Scanning Electron Microscope (SEM) with accelerating voltages ranging from 6 to 22 KeV in increments of 2 KeV and a step size of 0.05 microns. Higher accelerating voltages resulted in broader concentration profiles, indicating higher apparent interdiffusion coefficients when scanned at the same location of the same sample. This error due to the interaction volume interference was quantified using Monte Carlo simulations. It was found that an accelerating voltage of 22 KeV and diffusion distance less than 5 microns resulted in at least 50% error. Even at a smaller accelerating voltage of 6 KeV, the percent error in calculation of the interdiffusion coefficient for a diffusion distance of 0.5 microns is expected to be 15-20%. An approximate diffusion distance and apparent interdiffusion coefficient for ultrasonically consolidated Al-Cu were 0.503 microns and 0.013 um(2) /s, respectively. In this study, a methodology is presented that allows one to estimate the error in the calculation of an interdiffusion coefficient from the accelerating voltage used and the diffusion distance measured by the SEM XEDS at that accelerating voltage.