Predicted flash x-ray environments using standard converter configurations

Using a sophisticated Monte Carlo model, we have obtained predictions of the forward radiation fields generated by a series of monoenergetic electron sources, with kinetic energies ranging from 0.5 to 15.0 MeV, normally incident on standard converter configurations. The tantalum converter foil thickness that maximizes the total forward-going x-ray energy ranges from 0.3 times the continuous-slowing-down-approximation electron range at 0.5 MeV to 0.6 times that range at 15.0 MeV. This result is not very sensitive to the presence or absence of typical electron absorbers or debris shields. The forward extraction efficiency exhibits a slightly superlinear dependence on source electron kinetic energy. Electron backscatter and photon absorption are shown to be the chief transport phenomena that limit x-ray extraction. Dependence of x-ray spectra on emission angle results from the complicated interplay of cross-section kinematics, slant-thickness absorption, and slant-thickness buildup. The response of common dosimetry materials to the radiation fields was also studied. The systematics of energy deposition in high-Z and low-Z dosimetry materials as a function of source energy, converter geometry, and emission angle are presented in terms of an effective absorption coefficient. The utility of this coefficient for predicting the energy deposition in one material from the measured dose in another material is demonstrated. It is shown that the converter thickness that optimizes dose is less than the thickness that optimizes the forward extraction efficiency. 11 refs., 32 figs

Tribute to Donald A. Winslow

This article is comprised of a series of tributes to Donald A. Winslow, who was a law professor at the University of Kentucky College of Law

Biomass production of herbaceous energy crops in the United States: field trial results and yield potential maps from the multiyear regional feedstock partnership

Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small-scale and short-term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy (US DOE)/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long-term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field-scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm-scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM-ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country

Tribute to Donald A. Winslow

This article is comprised of a series of tributes to Donald A. Winslow, who was a law professor at the University of Kentucky College of Law

Effect of P(II) and Its Homolog GlnK on Reversible ADP-Ribosylation of Dinitrogenase Reductase by Heterologous Expression of the Rhodospirillum rubrum Dinitrogenase Reductase ADP-Ribosyl Transferase–Dinitrogenase Reductase-Activating Glycohydrolase Regulatory System in Klebsiella pneumoniae

Reversible ADP-ribosylation of dinitrogenase reductase, catalyzed by the dinitrogenase reductase ADP-ribosyl transferase–dinitrogenase reductase-activating glycohydrolase (DRAT-DRAG) regulatory system, has been characterized in Rhodospirillum rubrum and other nitrogen-fixing bacteria. To investigate the mechanisms for the regulation of DRAT and DRAG activities, we studied the heterologous expression of R. rubrum draTG in Klebsiella pneumoniae glnB and glnK mutants. In K. pneumoniae wild type, the regulation of both DRAT and DRAG activity appears to be comparable to that seen in R. rubrum. However, the regulation of both DRAT and DRAG activities is altered in a glnB background. Some DRAT escapes regulation and becomes active under N-limiting conditions. The regulation of DRAG activity is also altered in a glnB mutant, with DRAG being inactivated more slowly in response to NH(4)(+) treatment than is seen in wild type, resulting in a high residual nitrogenase activity. In a glnK background, the regulation of DRAT activity is similar to that seen in wild type. However, the regulation of DRAG activity is completely abolished in the glnK mutant; DRAG remains active even after NH(4)(+) addition, so there is no loss of nitrogenase activity. The results with this heterologous expression system have implications for DRAT-DRAG regulation in R. rubrum

Biomass production of herbaceous energy crops in the United States: field trial results and yield potential maps from the multiyear regional feedstock partnership

Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small-scale and short-term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy (US DOE)/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long-term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field-scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm-scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM-ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country