The NASA planetary biology internship experience

By providing students from around the world with the opportunity to work with established scientists in the fields of biogeochemistry, remote sensing, and origins of life, among others, the NASA Planetary Biology Internship (PBI) Program has successfully launched many scientific careers. Each year approximately ten interns participate in research related to planetary biology at NASA Centers, NASA-sponsored research in university laboratories, and private institutions. The PBI program also sponsors three students every year in both the Microbiology and Marine Ecology summer courses at the Marine Biological Laboratory. Other information about the PBI Program is presented including application procedure

Dynamics of vegetation and soils of oak/saw palmetto scrub after fire: Observations from permanent transects

Ten permanent 15 m transects previously established in two oak/saw palmetto scrub stands burned in December 1986, while two transects remained unburned. Vegetation in the greater than 0.5 m and the less than 0.5 m layers on these transects was sampled at 6, 12, 18, 24, and 36 months postburn and determined structural features of the vegetation (height, percent bare ground, total cover). The vegetation data were analyzed from each sampling by height layer using detrended correspondence analysis ordination. Vegetation data for the greater than 0.5 m layer for the entire time sequence were combined and analyzed using detrended correspondence analysis ordination. Soils were sampled at 6, 12, 18, and 24 months postburn and analyzed for pH, conductivity, organic matter, exchangeable cations (Ca, Mg, K, Na), NO3-N, NH4-N, Al, available metals (Cu, Fe, Mn, Zn), and PO4-P. Shrub species recovered at different rates postfire with saw palmetto reestablishing cover greater than 0.5 m within one year, but the scrub oaks had not returned to preburn cover greater than 0.5 m in 3 years after the fire. These differences in growth rates resulted in dominance shifts after the fire with saw palmetto increasing relative to the scrub oaks. Overall changes in species richness were minor, although changes occurred in species richness by height layers due to different growth rates. Soils of well drained and poorly drained sites differed markedly. Soil responses to the fire appeared minor. Soil pH increased at 6 and 12 months postfire; calcium increased at 6 months postburn. Nitrate-nitrogen increased at 12 months postburn. Low values of conductivity, PO4-P, Mg, K, Na, and Fe at 12 months postburn may be related to heavy rainfall the preceding month. Seasonal variability in some soil parameters appeared to occur

Ion Interactions at the Mineral-Water Interface During Biogeochemical Iron and Manganese Cycling

The biogeochemical cycling of iron and manganese involves the reductive dissolution and oxidative precipitation of Fe(III) and Mn(IV/III) oxides. Biogenic Fe(III) and Mn(IV/III) oxides are often characterized by high surface areas and therefore high sorptive capacities. As a result, these minerals can substantially alter the chemistry of natural waters and the availability of micronutrients in soils and sediments by scavenging trace metals. Recent research indicates that the adsorption of aqueous Fe(II) onto Fe(III) oxides involves oxidative adsorption, electron transfer, and subsequent reductive dissolution at another surface site [a process collectively referred to as `electron transfer-atom exchange\u27 (ET-AE)]. Aqueous Mn(II) adsorption onto Mn(IV/III) oxides likely also involves oxidation, but because of the potential for Mn(II) Mn(IV) comproportionation reactions and the accessibility of nearly all atoms in Mn(IV/III) oxide sheets to reaction with aqueous solution, aqueous Mn(II)-solid Mn(IV/III) interactions are expected to differ substantially from the analogous Fe system. These complex interactions between reduced and oxidized forms of Fe (and Mn) occur at redox interfaces and can exert substantial effects on trace metal fate. These processes may, in turn, be affected by ions common in natural systems. The main objective of this dissertation is to determine how interactions between ions commonly present during biogeochemical Fe or Mn cycling in natural systems [e.g., phosphate, sulfate, Ni, Zn, Fe(II), or Mn(II)] alter one another\u27s interactions with Fe and Mn oxide surfaces. This research specifically seeks to (1) identify the mechanisms through which the oxoanions phosphate and sulfate alter Fe(II) adsorption onto Fe oxides; (2) determine how oxoanion-Fe(II) interactions alter trace metal partitioning between the mineral surface, bulk mineral structure, and aqueous phase; (3) characterize the effect of Mn(II) on phyllomanganate sheet structures; and (4) examine the effect of Mn(II) on trace metal sorption on phyllomanganates. Macroscopic adsorption edges show that Fe(II) cooperatively co-adsorbs with sulfate and phosphate on Fe(III) oxide surfaces. Both attenuated total reflectance Fourier transform infrared spectroscopy and surface complexation modeling indicate that this cooperative adsorption behavior arises from a combination of ternary complexation and electrostatic interactions. The formation Fe(II)-oxoanion ternary complexes suggests that processes associated with Fe(II) Fe(III) ET-AE reactions may be altered in the presence of oxoanions, depending on the stability and identity of the ternary complex that forms. The effect of these oxoanions on one such process, trace metal repartitioning, was investigated in detail. Sulfate and, to a larger degree, phosphate suppress Ni cycling through hematite during Fe(II)-catalyzed recrystallization by altering Ni adsorption, structural incorporation, and release back into solution. Conversely, Ni cycling through goethite is unaffected or enhanced by phosphate and sulfate. This dissertation also investigated Mn(II) effects on phyllomanganate structure and the fate of associated trace metals. Powder X-ray diffraction and X-ray absorption fine structure spectroscopic measurements indicate that Mn(II) causes distortion of the sheet structure of Mn(IV/III) oxides and alters sheet stacking at low pH, but has a minimal effect on phyllomanganate structures at circumneutral pH. As a result, Ni and Zn adsorption mechanisms on phyllomanganates are altered in the presence of aqueous Mn(II) at pH 4, but exhibit few changes at pH 7. The Ni and Zn adsorption behaviors with aqueous Mn(II) suggests that Mn(II) alters phyllomanganate reactivities by decreasing phyllomanganate vacancy content. These results emphasize the importance of understanding adsorbate interactions in systems with coexisting reduced and oxidized Fe or Mn, as under such conditions Fe and Mn oxide minerals undergo dynamic structural transformations. Trace metal uptake and partitioning between Fe oxide surfaces can be altered in systems with appreciable amounts of phosphate or sulfate (e.g., riparian zones, estuaries, or marine sediments). The complex interactions at iron oxide surfaces must be considered when evaluating trace metal fate at redox interfaces or interpreting trace metal proxies in the rock record to reconstruct ancient water compositions. The Mn(II)-induced phyllomanganate structural changes observed here suggest a relationship between water composition and the reactivity of Mn oxides as adsorbent materials. The identified phyllomanganate restructuring may also modify the capacity of Mn oxides to serve as oxidants of inorganic and organic compounds in aquatic systems. This dissertation highlights the complex structural and chemical processes that occur via cooperative and competitive interactions of ion at iron and manganese oxide surfaces

Fluorine in the solar neighborhood - is it all produced in AGB-stars?

The origin of 'cosmic' fluorine is uncertain, but there are three proposed production sites/mechanisms: AGB stars, $\nu$ nucleosynthesis in Type II supernovae, and/or the winds of Wolf-Rayet stars. The relative importance of these production sites has not been established even for the solar neighborhood, leading to uncertainties in stellar evolution models of these stars as well as uncertainties in the chemical evolution models of stellar populations. We determine the fluorine and oxygen abundances in seven bright, nearby giants with well-determined stellar parameters. We use the 2.3 $\mu$m vibrational-rotational HF line and explore a pure rotational HF line at 12.2 $\mu$m. The latter has never been used before for an abundance analysis. To be able to do this we have calculated a line list for pure rotational HF lines. We find that the abundances derived from the two diagnostics agree. Our derived abundances are well reproduced by chemical evolution models only including fluorine production in AGB-stars and therefore we draw the conclusion that this might be the main production site of fluorine in the solar neighborhood. Furthermore, we highlight the advantages of using the 12 $\mu$m HF lines to determine the possible contribution of the $\nu$-process to the fluorine budget at low metallicities where the difference between models including and excluding this process is dramatic

Studies on the electron transfer pathway, topography of iron-sulfur centers, and site of coupling in NADH-Q oxidoreductase.

Electron transfer activities and steady state reduction levels of Fe-S centers of NADH-Q oxidoreductase were measured in mitochondria, submitochondrial particles (ETPH), and complex I after treatment with various reagents. p-Chloromercuribenzenesulfonate destroyed the signal from center N-4 (gx = 1.88) in ETPH but not in mitochondria, showing that N-4 is accessible only from the matrix side of the inner membrane. N-Bromosuccinimide also destroyed the signal from N-4 but without inhibiting rotenone-sensitive electron transfer to quinone, suggesting a branched pathway for electron transfer. Diethylpyrocarbonate caused oxidation of N-3 and N-4 in the steady state without changing N-1, suggesting N-1 is before N-3 and N-4. Difluorodinitrobenzene and dicyclohexylcarbodiimide inhibited oxidation of all Fe-S centers and tetranitromethane inhibited reduction of all Fe-S centers. Titrations of the rate of superoxide (O2-) generation in rotenone-treated submitochondrial particles were similar with the ratio [NADH]/[NAD] and that of 3-acetyl pyridine adenine nucleotide in spite of different midpoint potentials of the two couples. On reaction with inhibitors the inhibition of O2- formation was similar to that of ferricyanide reductase rather than quinone reductase. The rate of O2- formation during ATP-driven reverse electron transfer was 16% of the rate observed with NADH. The presence of NAD increased the rate to 83%. The results suggest that bound, reduced nucleotide, probably E-NAD., is the main source of O2- in NADH dehydrogenase. The effect of ATP on the reduction levels of Fe-S centers in well-coupled ETPH was measured by equilibrating with either NADH/NAD or succinate/fumarate redox couples. With NADH/NAD none of the Fe-S centers showed ATP induced changes, but with succinate/fumarate all centers showed ATP-driven reduction with or without NAD present. The effect on N-2 was smaller than that on N-1, N-3, and N-4. These observations indicate that the major coupling interaction is between N-2 and the low potential centers, N-1, N-3, and N-4. Possible schemes of coupling in this segment are discussed

A Case History of Chemical Attack of a Clay Shale

This paper describes the results of an extensive investigation made to determine the cause of excessive settlements of two 800 MN steam turbine units located at the Four Corners Steam Electric Station near Farmington, New Mexico. The units are located on a clay-shale formation with numerous gypsum seams. The settlement was originally attributed to the solutioning of these gypsum seams. It was found that the construction of a large unlined cooling pond raised the ground water table in the vicinity of the power plant. In this saturated environment, a chemical attack of the existing clay shales began. It is believed that the chemical reaction causing the degradation of the clay-shale has been identified and that a chemical solution to the problem has been found. The reaction involves the removal of the exchangeable cation from the clay lattice, which goes into solution. As the cations are leached out, the clays tend to weather toward the montmorillonite end of the transformation series

A computer program for hydrostatic bearings including the effects of non-uniform film thickness and relative velocity for various methods of lubricant supply final technical report

Computer program for hydrostatic bearing - effects of nonuniform film thickness and lubricant suppl

A New Approach to Swine Shade Construction

A project was initiated by the Agricultural Engineering Department at the South Dakota Agricultural Experiment Station to design a type of swine shade which would not require all the heavy timber under-framing of the current swine shade plans, and which would be actually portable. The need for such swine shelters has been established; research results from other stations have shown that some shading device, either natural or artificial, is necessary to protect swine, especially the heavier ones, from the direct heat of the sun. Extensive work conducted at California shows the effects of different types of surfaces and shade materials on the radiant heat load beneath the shade. Another report, one from Purdue University on the effectiveness of various types of shade on the growth of swine in a normal summer environment, concluded that there were no differences between materials used and no measurable effects of roof color on rate of gain of swine. While these studies may not agree on the effectiveness of different types of shading materials, their findings support the need for some type of shade for swine to maintain or improve rate of gain

Nonequilibrium plastic roughening of metallic glasses yields self-affine topographies with strain-rate and temperature-dependent scaling exponents

We study nonequilibrium roughening during compressive plastic flow of initially flat Cu$_{50}$ Zr$_{50}$ metallic glass using large-scale molecular dynamics simulations. Roughness emerges at atomically flat interfaces beyond the yield point of the glass. A self-affine rough topography is imprinted at yield and is reinforced during subsequent deformation. The imprinted topographies have Hurst exponents that decrease with increasing strain rate and temperature. After yield, the root-mean-square roughness amplitude grows as the square root of the applied strain with a prefactor that also drops with increasing strain rate and temperature. Our calculations reveal the emergence of spatial power-law correlations from homogeneous samples during plastic flow with exponents that depend on the rate of deformation and the temperature. The results have implications for interpreting and engineering roughness profiles

Gas damping force noise on a macroscopic test body in an infinite gas reservoir

We present a simple analysis of the force noise associated with the mechanical damping of the motion of a test body surrounded by a large volume of rarefied gas. The calculation is performed considering the momentum imparted by inelastic collisions against the sides of a cubic test mass, and for other geometries for which the force noise could be an experimental limitation. In addition to arriving at an accurated estimate, by two alternative methods, we discuss the limits of the applicability of this analysis to realistic experimental configurations in which a test body is surrounded by residual gas inside an enclosure that is only slightly larger than the test body itself.Comment: 8 pages. updated with correct translational damping coefficient for cylinder on axis. added cylinder orthogonal to symmetry axis, force and torque. slightly edited throughou