Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies

The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19  MeV/c, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

The genome of black cottonwood, Populus trichocarpa (Torr. & Gray)

We report the draft genome of the black cottonwood tree, Populus trichocarpa. Integration of shotgun sequence assembly with genetic mapping enabled chromosome-scale reconstruction of the genome. More than 45,000 putative protein-coding genes were identified. Analysis of the assembled genome revealed a whole-genome duplication event; about 8000 pairs of duplicated genes from that event survived in the Populus genome. A second, older duplication event is indistinguishably coincident with the divergence of the Populus and Arabidopsis lineages. Nucleotide substitution, tandem gene duplication, and gross chromosomal rearrangement appear to proceed substantially more slowly in Populus than in Arabidopsis. Populus has more protein-coding genes than Arabidopsis, ranging on average from 1.4 to 1.6 putative Populus homologs for each Arabidopsis gene. However, the relative frequency of protein domains in the two genomes is similar. Overrepresented exceptions in Populus include genes associated with lignocellulosic wall biosynthesis, meristem development, disease resistance, and metabolite transport.

Radon measurements and mitigation at a fish hatchery

Groundwater radon concentration of 83 Bq L(-1) generated indoor radon levels exceeding 3,300 Bq m(-3) at a commercial fish hatchery. Passive and active mitigation strategies to reduce the waterborne radon levels included a packed column, a waterfall through perforated grates, surface aeration, and bottom bubblers. Waterborne concentrations were reduced up to 83% using a combination of mitigation procedures, but a comparable reduction in indoor radon concentrations was not observed. A diurnal cycle showed that indoor radon levels peaked in early afternoon, probably as a result of warmer air being dissolved in the water during mitigation. Reduction of indoor radon levels below 148 Bq m(-3) was seldom achievable with both water mitigation and direct air ventilation at 23 room air changes hourly.

Identification of the gene encoding the major cellobiohydrolase of the white rot fungus Phanerochaete chrysosporium

Previous studies have shown that the cellobiohydrolases of the white rot basidiomycete Phanerochaete chrysosporium are encoded by a family of structurally related genes. In this investigation, we identified and sequenced the most highly transcribed gene, cbh1-4. Evidence suggests that in this fungus the dominant isozyme, CBH1, is encoded by chb1-4.