Ion beam sputter etching

An ion beam etching process which forms extremely high aspect ratio surface microstructures using thin sputter masks is utilized in the fabrication of integrated circuits. A carbon rich sputter mask together with unmasked portions of a substrate is bombarded with inert gas ions while simultaneous carbon deposition occurs. The arrival of the carbon deposit is adjusted to enable the sputter mask to have a near zero or even slightly positive increase in thickness with time while the unmasked portions have a high net sputter etch rate

The use of plasma ashers and Monte Carlo modeling for the projection of atomic oxygen durability of protected polymers in low Earth orbit

The results of ground laboratory and in-space exposure of polymeric materials to atomic oxygen has enabled the development of a Monte Carlo computational model which simulates the oxidation processes of both environments. The cost effective projection of long-term low-Earth-orbital durability of protected polymeric materials such as SiO(x)-coated polyimide Kapton photovoltaic array blankets will require ground-based testing to assure power system reliability. Although silicon dioxide thin film protective coatings can greatly extend the useful life of polymeric materials in ground-based testing, the projection of in-space durability based on these results can be made more reliable through the use of modeling which simulates the mechanistic properties of atomic oxygen interaction, and replicates test results in both environments. Techniques to project long-term performance of protected materials, such as the Space Station Freedom solar array blankets, are developed based on ground laboratory experiments, in-space experiments, and computational modeling

U.S. BIOMASS SUPPLY FOR ELECTRICITY GENERATION: CLIMATE POLICY IMPLICATIONS AND CARBON NEUTRALITY

This paper investigates three important energy and climate policy issues: (1) the availability of biomass for electricity generation (i.e., supply), (2) climate policy effects on this supply, and (3) the net greenhouse gas reduction when biomass is used for electricity generation. Using a detailed model of U.S. agriculture and forestry markets and land-use, that includes a broad and diverse set of biomass feedstocks, we evaluate competing potential sub-national and feedstock specific supplies of biomass for U.S. electricity generation. Our preliminary results suggest significant supply, with residues dominating at lower delivered energy prices, and dedicated crops significant at higher prices. Sub-national variation is dramatic and will affect generation siting and sustainability. We find displacement of food crops, but net forest land and cropland expansion. We also find that GHG policies could substantially increase the delivered cost of biomass; however, the implications for individual regions and feedstocks is non-uniform, with some supplies falling to zero and others increasing. Finally, we find that bioelectricity is not carbon neutral, but can be emissions reducing relative to coal generation, yield greater direct GHG benefits than biofuels, and even result in domestic indirect emissions reductions with incentives for forest based feedstocks.Agricultural and Food Policy, Environmental Economics and Policy, Land Economics/Use, Resource /Energy Economics and Policy,

Greenhouse Gas Emissions, Stabilization and the Inevitability of Adaptation: Challenges for U.S. Agriculture

Environmental Economics and Policy, Q1, Q54, Q58,

PERSISTENT POVERTY ACROSS THE RURAL-URBAN CONTINUUM

Persistent poverty is overwhelmingly rural and is very geographically concentrated. We have redefined the USDA ERS persistent poverty classification to include metropolitan counties meeting the 20 percent or higher poor criterion and we extend the time period through the 2000 Census. With this updated definition, there are 382 counties that have had poverty rates of 20 percent or more in each decennial census between 1960 and 2000. These persistent poverty counties are overwhelmingly rural (95 percent) and disproportionately rural (16 percent of nonmetro counties versus 2 percent of metro). The local economic environment in persistent poverty counties is much less favorable than in the nation as a whole. Per capita income is lower and unemployment rates higher in persistent poverty counties. Employment is more concentrated in services, extractive, construction/maintenance, and production/transportation occupations. Residents of persistent poverty counties tend to have lower education levels, and persistent poverty counties generally have larger shares of minority populations. The number of persistent poverty counties reduced considerably during the 1990s, but the "leavers" were disproportionately metropolitan, making persistent poverty increasingly a rural problem. Persistent poverty is overwhelmingly rural and it is very concentrated geographically. In this paper, we examine these striking regularities in U.S. economic geography, seeking to understand the causes and dynamics of poverty across the rural urban continuum. We also consider how alternative characterizations of "persistent poverty" and "rural and urban" might deepen our understanding of poverty and place. The paper has four sections. In the first, we examine how poverty and persistent poverty vary across the Rural Urban Continuum Codes and Urban Influence Codes developed by the USDA Economic Research Service (ERS). We start with the very useful "persistent poverty" classification developed by ERS that defines nonmetropolitan counties as persistent poverty counties if the poverty rate is 20 percent or higher in each decennial census between 1960 and 1990.We redefine persistent poverty to include metropolitan counties meeting the 20 percent or more poor criterion and we extend the time period through the 2000 Census. We also examine where poverty is concentrated in the United States and how persistent poverty varies across the new Core Based Statistical Area definitions for counties, developed recently by the Office of Management and Budget. In the second section, we examine how the demographic characteristics of the population vary across the rural-urban spectrum, comparing persistent poverty county demographics with those of all counties. The third section examines the dynamics of poverty and place. We examine the location, rurality and demographics of counties that escaped persistent poverty statues between 1990 and 2000, and how those characteristics compare to counties that remained in persistent poverty. We then identify the new entrants into high poverty since 1960. In the fourth section, we consider implications of reconceptualizing both "persistent poverty" and "rural and urban diversity". First, we explore the "persistent poverty" county classification, and how alternative definitions of persistent poverty counties might alter the conclusions one reaches about the geography of persistent poverty. We do this by exploring how defining persistent poverty with a different base year such as 1970 or 1980 affects the number of "persistent poverty" counties. We then explore what happens to "persistent poverty" if we raise the poverty threshold to 30 and 40 percent in defining persistent poverty counties. We then examine how conclusions about rural and urban persistent poverty change if one looks at poverty persistence in individual households rather than counties. Using PSID data, this analysis examines rates of persistent household poverty by looking at how the percent of households who remain in poverty for all 5 years during the 1993-98 period varies across central metro county to remote rural county continuum (an aggregation of Beale codes). Finally, we briefly explore how conclusions about the geography of poverty change if one divides metropolitan areas into "central city" and "suburb", and nonmetropolitan areas into "adjacent" and "nonadjacent."Food Security and Poverty,

Mutations in \u3cem\u3eRhizobium phaseoli\u3c/em\u3e that Lead to Arrested Development of Infection Threads

Two Rhizobium phaseoli mutants, isolated previously by Tn5 mutagenesis, elicited infection threads which ceased development prematurely, usually within root hairs. These infection threads were wide, globular, and otherwise altered in morphology, compared with normal infection threads. Anatomy and division of the root cortical cells during initial stages of nodule morphogenesis appeared normal. However, later nodule differentiation deviated considerably from normal development, and release of bacteria from infection threads was not observed. In tryptone-yeast extract medium the mutants sedimented during growth in shaken cultures and formed rough colonies on agar. Electrophoresis of washed cultures solubilized in dodecyl sulfate revealed that the major carbohydrate band was absent from the mutants. The behavior of this carbohydrate in phenol-water extraction and gel chromatography, its apparent ketodeoxyoctonate content, and its susceptibility to mild acid hydrolysis suggested that it was a lipopolysaccharide. From the results of genetic crosses or reversion analysis, the defect in synthesizing this carbohydrate material and the defect in infection could be attributed to a single mutation in each mutant

Atomic oxygen interaction with solar array blankets at protective coating defect sites

Atomic oxygen in the low-Earth-orbital environment oxidizes SiOx protected polyimide Kapton solar array blankets at sites which are not protected such as pin windows or scratches in the protective coatings. The magnitude and shape of the atomic oxygen undercutting which occurs at these sites is dependent upon the exposure environment details such as arrival direction and reaction probability. The geometry of atomic oxygen undercutting at defect sites exposed to atomic oxygen in plasma asher was used to develop a Monte Carlo model to simulate atomic oxygen erosion processes at defect sites in protected Kapton. Comparisons of Monte Carlo predictions and experimental results are presented for plasma asher atomic oxygen exposures for large and small defects as well as for protective coatings on one or both sides of Kapton. The model is used to predict in-space exposure results at defect sites for both directed and sweeping atomic oxygen exposure. A comparison of surface textures predicted by the Monte Carlo model and those experimentally observed from both directed space ram and laboratory plasma asher atomic oxygen exposure indicate substantial agreement

The NASA atomic oxygen effects test program

The NASA Atomic Oxygen Effects Test Program was established to compare the low earth orbital simulation characteristics of existing atomic oxygen test facilities and utilize the collective data from a multitude of simulation facilities to promote understanding of mechanisms and erosion yield dependence upon energy, flux, metastables, charge, and environmental species. Four materials chosen for this evaluation include Kapton HN polyimide, FEP Teflon, polyethylene, and graphite single crystals. The conditions and results of atomic oxygen exposure of these materials is reported by the participating organizations and then assembled to identify degrees of dependency of erosion yields that may not be observable from any single atomic oxygen low earth orbital simulation facility. To date, the program includes 30 test facilities. Characteristics of the participating test facilities and results to date are reported