Paul Andrew Northrup

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We investigated H2S attenuation by dissimilatory perchlorate-reducing bacteria (DPRB). All DPRB tested oxidized H2S coupled to (per)chlorate reduction without sustaining growth. H2S was preferentially utilized over organic electron donors resulting in an enriched (34S)-elemental sulfur product. Electron microscopy revealed elemental sulfur production in the(More)
Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy was performed on phosphate mineral specimens including (a) twelve specimens from the apatite group covering a range of compositional variation and crystallinity; (b) six non-apatite calcium-rich phosphate minerals; (c) 15 aluminium-rich phosphate minerals; (d) ten phosphate minerals(More)
Sulfate adsorption on mineral surfaces is an important environmental chemical process. However, the structure of sulfate adsorption complexes has remained uncertain. In this study, we have determined the S−Fe distance of sulfate inner-sphere adsorption complexes on iron (Fe) oxyhydroxide (ferrihydrite) surfaces under air-dried conditions using sulfur K-edge(More)
Synchrotron Radiation (SR) presents itself as a "play-ground" with a large range of methods and techniques suitable to unveil the mysteries of life. Here we attempt to present a few of these methods that complement those employed in the home laboratory. SR diffraction, spectroscopy and imaging methods relevant to the atomic structure determination and(More)
The integration of synthetic, experimental and theoretical tools into a self-consistent data analysis methodology allowed us to develop unique new levels of detail in nanoparticle characterization. We describe our methods using an example of Au13 monolayer-protected clusters (MPCs), synthesized by ligand exchange methods. The combination of atom counting(More)
Significant nanoscale disorder of Cu and Ca atomic substitution is observed in CaCu(3)Ti(4)O(12), based on our integrated study using quantitative electron diffraction and extended x-ray absorption fine structure. Unambiguous identification of this previously omitted disorder is made possible by the unique sensitivity of these probes to valence-electron(More)
To investigate the effect of P surface loading on the structure of surface complexes formed at the goethite/water interface, goethite was reacted with orthophosphate at P concentrations of 0.1, 0.2, and 0.8 mmol L(-1) at pH 4.5 for 5 days. The P concentrations were chosen to ensure that P loadings at the surface would allow one to follow the transition(More)
X-ray absorption measurements from relatively high concentrations of Er ~.0.1 at. %! doped in GaN films show that Er occupies the Ga site with an unprecedentedly short Er–N bond length. Electroluminescence intensities from these GaN:Er films correlate with the concentration of Er atoms that replace Ga, not with the abundantly present O impurities in the(More)
Electron channeling experiments performed on individually scanned, single columns of atoms show that in highly n-type Si grown at low temperatures the primary electrically deactivating defect cannot belong to either the widely accepted class of donor-vacancy clusters or a recently proposed class of donor pairs. First-principles calculations suggest a new(More)
The "tender" energy range of 1 to 5 keV, between the energy ranges of most "hard" (>5 keV) and "soft" (<1 keV) synchrotron X-ray facilities, offers some unique opportunities for synchrotron- based X-ray absorption fine structure spectroscopy in life sciences. In particular the K absorption edges of Na through Ca offer opportunities to study local structure,(More)