Search

Your search keyword '"Reeder, R. J."' showing total 38 results
Start Over Author "Reeder, R. J."
38 results on '"Reeder, R. J."'

4. Quantification of regional aerosol deposition patterns as a function of aerodynamic particle size in rhesus macaques using PET/CT imaging

Author

Dabisch, P. A., primary, Xu, Z., additional, Boydston, J. A., additional, Solomon, J., additional, Bohannon, J. K., additional, Yeager, J. J., additional, Taylor, J. R., additional, Reeder, R. J., additional, Sayre, P., additional, Seidel, J., additional, Mollura, D. J., additional, Hevey, M. C., additional, Jahrling, P. B., additional, and Lackemeyer, M. G., additional

Published
2017
Full Text
View/download PDF

9. Seawater pH control on the boron isotopic composition of calcite: Evidence from inorganic precipitation experiments

Author

Sanyal, A., Nugent, M., Reeder, R. J., Bijma, Jelle, Sanyal, A., Nugent, M., Reeder, R. J., and Bijma, Jelle

Abstract

Experiments involving boron co-precipitation with calcite have been carried out inorganically under controlled pH conditions (7.9+0.05, 8.3+0.05 and 8.6+0.05) to determine the dependence of boron isotopic composition (d11B) of calcite on the pH of seawater. Another purpose of these experiments was to estimate the magnitude of the biogenic influence on the d11B value of foraminifera by comparing their boron isotopic composition with that of the inorganic calcite over a common pH range. The results show a clear relationship between d11B of inorganic calcite and the pH of artificial seawater. The variation of boron isotopic fractionation between seawater and calcite with pH, estimated from these experiments, is similar to that estimated for cultured O. universa and the predicted trend. The results also support the hypothesis that B(OH)4- is the dominant species incorporated into the calcite structure. However, the boron isotopic fractionation between seawater and inorganic calcite is lower than that estimated for O. universa indicating the presence of a biogenic effect on the boron isotopic composition at least of this species of foraminifera. Most importantly, the results imply that in spite of a small biogenic influence on the boron isotopic composition of foraminifera, the variation in d11B of foraminiferal shells with pH (at least for O. universa) is consistent with that for inorganic calcite, demonstrating the potential of this isotopic signature in foraminifera as a reliable paleo pH proxy.

Published
2000

18. Structural relaxation in the MnCO3–CaCO3 solid solution: a Mn K-edge EXAFS study.

Author

Lee, Y. J., Reeder, R. J., Wenskus, R. W., and Elzinga, E. J.

Abstract

Mn K-edge EXAFS spectroscopy of solid-solution samples encompassing the complete MnCO3–CaCO3 series shows that first-shell Mn–O distances deviate little from the 2.19-Å distance observed in pure MnCO3. Very slight lengthening is observed only in the limiting case of dilute Mn(II) calcite solid solutions, where the Mn–O distance is 2.21 Å. The observed nearly complete structural relaxation and the composition independence of the Mn–O distance are consistent with the Pauling model behavior of solid solutions, and agree with previous studies showing a high degree of relaxation around hetero-sized substituents in the calcite structure. Strain occurs through bond bending, which is facilitated by the exclusively corner-sharing topology of calcite. Observed distances from Mn to more distant neighbors show significant variation across the solid-solution series that resembles Vegard's law-type behavior but reflects averaging. The high degree of relaxation suggests modest enthalpies of mixing in the solution, consistent with calorimetric studies. [ABSTRACT FROM AUTHOR]

Published
2002
Full Text
View/download PDF

20. Broad distribution of crystal-field environments for Nd 3+ in calcite

Author

Withers, S. H., Peale, R. E., Schulte, A. F., Braunstein, G., Beck, K. M., Hess, W. P., and Reeder, R. J.

Abstract

Calcite crystals were grown from solution with single-crystal dimensions up to 3 mm and doped up to ~0.1 at% with Nd 3+ ions. Phase purity was verified by powder X-ray diffraction. The concentration of Nd 3+ was measured by energy-dispersive spectrometry and Rutherford backscattering spectrometry. Micro X-ray fluorescence mapping of the calcite grains indicates uniform Nd distribution in as-grown crystal grains. X-ray absorption fine structure suggests that Nd 3+ is substituted for Ca 2+ with local lattice distortion. Temperature-dependent near-infrared spectroscopy of Nd 3+ impurities in calcite reveals large inhomogeneous linewidths and smooth line profiles that are characteristic of glassy hosts, though the samples are well crystallized.

Published
2003
Full Text
View/download PDF

23. Synthesis, Structure, and Dielectric Properties of (Bi<INF>1/2</INF>Ag<INF>1/2</INF>)TiO<INF>3</INF>

Author

Park, J.-H., Woodward, P. M., Parise, J. B., Reeder, R. J., Lubomirsky, I., and Stafsudd, O.

Abstract

The compound Bi1/2Ag1/2TiO3 has been synthesized, for the first time, at 14−14.5 GPa and 1000 °C using the uniaxial split sphere anvil type press (USSA-2000). The structure of the quenched powder sample was refined from synchrotron X-ray diffraction data using the Rietveld method. At room temperature, Bi1/2Ag1/2TiO3 exhibits an orthorhombic distortion of the cubic perovskite structure and was assigned to a space group of Ibam and lattice parameters of a = 5.48970(4) Å, b = 5.51954(5) Å, and c = 7.77585(7) Å. The refinements are consistent with a random distribution of Bi3+ and Ag+ on the A-sites. Diffraction results at various temperatures show two phase transitions as the temperature is increased. At 573 K, tetragonal symmetry is observed and was assigned to a space group of I4/mcm with lattice parameters of a = 5.51664(8) Å and c = 7.8134(2) Å, while at 673 K, the cubic perovskite structure, with space group Pm&thremacr;m and a = 3.90607(8) Å, was determined. Plane capacitor dielectric contact measurements at 100 kHz gave a dielectric constant of 354 at ambient temperature for the sample. The dielectric constant increases with temperature and reaches a local maximum of 834 at 578 K. After heating the sample to 778 K and cooling back to room-temperature, both dielectric and diffraction measurements provide evidence for a small but irreversible change in the stoichiometry.

Published
1999

38. Iron-Containing Cells in the Honey Bee (Apis mellifera).

Author

Kuterbach DA, Walcott B, Reeder RJ, and Frankel RB

Abstract

Honey bees are sensitive to earth strength magnetic fields and are reported to contain magnetite (Fe3O4) in their abdomens. We report bands of cells around each abdominal segment that contain numerous electron-opaque, iron-containing granules. The iron is principally in the form of hydrous iron oxides.

Published
1982
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results