Electron beam compression with electric and magnetic fields

Electron beam compression with electrostatic and magnetostatic field

Research opportunities in loss of red blood cell mass in space flight

Decreases of red blood cell mass and plasma volume have been observed consistently following manned space flights. Losses of red cell mass by United States astronauts have averaged 10 to 15% (range: 2 to 21%). Based on postflight estimates of total hemoglobin, Soviet cosmonauts engaged in space missions lasting from 1 to 7 months have exhibited somewhat greater losses. Restoration of red cell mass requires from 4 to 6 weeks following return to Earth, regardless of the duration of space flight

Wetlands: A potentially significant source of atmospheric methyl bromide and methyl chloride

Tropospheric methyl bromide (CH3Br) and methyl chloride (CH3Cl) are significant sources of ozone (O3) destroying halogens to the stratosphere. Their O3 depletion potential (ODP) can be determined from atmospheric lifetimes and therefore their atmospheric budgets, both of which are out of balance with known sink terms larger than identified sources. We have discovered a new source of CH3Br and CH3Cl emissions to the atmosphere at two wetland sites in the Northeastern United States. We have reason to believe that these compounds are biologically produced in situ. Our measurements indicate that the global annual flux of CH3Br and CH3Cl from wetlands could be as high as 4.6 Gg yr−1 Of CH3Br and 48 Gg yr−1 of CH3Cl. These are preliminary estimates based on measurements made during the end of the 1998 growing season, a time period of decreased emissions of other trace gases such as methane (CH4)

A Photographic Journey along El Camino Real de los Tejas

This is a photographic traveling exhibit in conjunction with the National Park Service. The exhibit was made possible through the Challenge Cost Share Program in cooperation with Stephen F. Austin State University. This matching fund program allows the National Park Service and partners to work together to preserve and improve resources on national trails. To view selected images from the project visit El Camino Real de los Tejas National Historic Trail

An estimate of the uptake of atmospheric methyl bromide by agricultural soils

Published estimates of removal of atmospheric methyl bromide (CH3Br) by agricultural soils are 2.7 Gg yr−1 (Gg = 109 g) [Shorter et al., 1995] and 65.8 Gg yr−1 [Serça et al., 1998]. The Serça et al. estimate, if correct, would suggest that the current value for total removal of atmospheric CH3Br by all sinks of 206 Gg yr−1 (based on Shorter et al., 1995) would be 30% too low. We have calculated a new rate of global agricultural soil uptake of atmospheric CH3Br from a larger sampling of cultivated soils collected from 40 sites located in the United States, Costa Rica, and Germany. First order reaction rates were measured during static laboratory incubations. These data were combined with uptake measurements we reported earlier based on field and laboratory experiments [Shorter et al. 1995]. Tropical (10.2°–10.4°N) and northern (45°–61°N) soils averaged lower reaction rate constants than temperate soils probably due to differing physical and chemical characteristics as well as microbial populations. Our revised global estimate for the uptake of ambient CH3Br by cultivated soils is 7.47±0.63 Gg yr−1, almost three times the value that we reported in 1995

Deviations from ozone photostationary state during the International Consortium for Atmospheric Research on Transport and Transformation 2004 campaign: Use of measurements and photochemical modeling to assess potential causes

Nitric oxide (NO) and nitrogen dioxide (NO2) were monitored at the University of New Hampshire Atmospheric Observing Station at Thompson Farm (TF) during the ICARTT campaign of summer 2004. Simultaneous measurement of ozone (O3), temperature, and the photolysis rate of NO2 (jNO2) allow for assessment of the O3 photostationary state (Leighton ratio, Φ). Leighton ratios that are significantly greater than unity indicate that peroxy radicals (PO2), halogen monoxides, nitrate radicals, or some unidentified species convert NO to NO2 in excess of the reaction between NO and O3. Deviations from photostationary state occurred regularly at TF (1.0 ≤ Φ ≤ 5.9), particularly during times of low NOx (NOx = NO + NO2). Such deviations were not controlled by dynamics, as indicated by regressions between Φ and several meteorological parameters. Correlation with jNO2 was moderate, indicating that sunlight probably controls nonlinear processes that affect Φ values. Formation of PO2 likely is dominated by oxidation of biogenic hydrocarbons, particularly isoprene, the emission of which is driven by photosynthetically active radiation. Halogen atoms are believed to form via photolysis of halogenated methane compounds. Nitrate radicals are believed to be insignificant. Higher Φ values are associated with lower mixing ratios of isoprene and chloroiodomethane and lower ratios of NOx to total active nitrogen, indicating that photochemical aging may very well lead to increased Φ values. PO2 levels calculated using a zero‐dimensional model constrained by measurements from TF can account for 71% of the observed deviations on average. The remainder is assumed to be associated with halogen atoms, most likely iodine, with necessary mixing ratios up to 0.6 or 1.2 pptv, for chlorine and iodine, respectively

Nuclear density determination and the purification of wild type Neurospora nuclei using Percoll gradients.

Nuclear density determination and the purification of wild type Neurospora nuclei using Percoll gradients

Electron interferometry with nano-gratings

We present an electron interferometer based on near-field diffraction from two nanostructure gratings. Lau fringes are observed with an imaging detector, and revivals in the fringe visibility occur as the separation between gratings is increased from 0 to 3 mm. This verifies that electron beams diffracted by nanostructures remain coherent after propagating farther than the Talbot length $z_T = 2d^2/\lambda$ = 1.2 mm, and hence is a proof of principle for the function of a Talbot-Lau interferometer for electrons. Distorted fringes due to a phase object demonstrates an application for this new type of electron interferometer.Comment: 4 pgs, 6 figure

Interactions among lignin, cellulose, and nitrogen drive litter chemistry-decay relationships.

Litter decay rates often correlate with the initial ratios of lignin:nitrogen (N) or lignin:cellulose in litter. However, the chemical and microbial mechanisms that give rise to these patterns are still unclear. To identify these mechanisms, we studied the decomposition of a model plant system, Arabidopsis thaliana, in which plants were manipulated to have low levels of lignin, cellulose, or litter N. Nitrogen fertilizer often increases the loss of cellulose, but it suppresses the breakdown of lignin in plant litter. To understand the mechanisms driving these patterns, we decomposed plants in litterbags for one year in control and N-fertilized plots in an Alaskan boreal forest. We found that litter N had a positive effect on total mass loss because it increased the loss of lignin, N, and soluble C. Lignin had a negative effect on rates of total litter mass loss due to decreases in the loss of cellulose and hemicellulose. Cellulose had a positive effect on lignin loss, supporting the concept of a "priming effect" for lignin breakdown. However, the low-cellulose plants also lost more of their original cellulose compared to the other plant types, indicating that decomposers mined the litter for cellulose despite the presence of lignin. Low-lignin litter had higher fungal biomass and N-acetyl glucosaminidase (NAG, a chitinase) activity, suggesting that lignin restricted fungal growth and may have influenced competitive interactions between decomposers. Nitrogen fertilization increased NAG activity in the early stages of decay. In the later stages, N fertilization led to increased cellulase activity on the litters and tended to reduce lignin losses. The transition over time from competition among decomposers to high cellulase activity and suppressed lignin loss under N fertilization suggests that, in N-limited systems, N fertilization may alter decomposer community structure by favoring a shift toward cellulose- and mineral-N users