The ROTSE-I experiment has generated CCD photometry for the entire Northern sky in two epochs nightly since March 1998. These sky patrol data are a powerful resource for studies of astrophysical transients. As a demonstration project, we present first results of a search for periodic variable stars derived from ROTSE-I observations. Variable identification, period determination, and type classification are conducted via automatic algorithms. In a set of nine ROTSE-I sky patrol fields covering ∼2000 square degrees we identify 1781 periodic variable stars with mean magnitudes between m v =10.0 and m v =15.5. About 90% of these objects are newly identified as variable. Examples of many familiar types are presented. All classifications for this study have been manually confirmed. The selection criteria for this analysis have been conservatively defined, and are known to be biased against some variable classes. This preliminary study includes only 5.6% of the total ROTSE-I sky coverage, suggesting that the full ROTSE-I variable catalog will include more than 32,000 periodic variable stars.

We present a sample of 148 candidate RR Lyrae stars selected from Sloan Digital Sky Survey (SDSS) commissioning data for about 100 deg2 of sky surveyed twice with *t \ 1.9946 days. Although the faintmagnitude limit of the SDSS allows us to detect RR Lyrae stars to large Galactocentric distances (D100 kpc, or r* D 21), we Ðnd no candidates fainter than r* D 20, i.e., farther than D65 kpc from the Galactic center. On the assumption that all 148 candidates are indeed RR Lyrae stars (contamination by other species of variable star is probably less than 10%), we Ðnd that their volume density has roughly a power-law dependence on Galactocentric radius, R~2.7B0.2, between 10 and 50 kpc and drops abruptly at R D 50È60 kpc, possibly indicating a sharp edge to the stellar halo as traced by RR Lyrae stars. The Galactic distribution of stars in this sample is very inhomogeneous and shows a clump of over 70 stars at about 45 kpc from the Galactic center. This clump is also detected in the distribution of nonvariable objects with RR Lyrae star colors. When sources in the clump are excluded, the best power-law Ðt becomes consistent with the R~3 distribution found from surveys of bright RR Lyrae stars. These results imply that the halo contains clumpy overdensities inhomogeneously distributed within a smooth R~3 background, with a possible cuto † at D50 kpc.

We apply Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and pair distribution function (PDF) analysis of high-energy X-ray scattering to investigate the effects of bivalent cation-oxyanion pairs on the structure of Fe(III) precipitates formed from the oxidation of Fe(II) generated by the electrolytic dissolution of Fe(0) electrodes. We found that Fe(II) oxidation in the presence of weakly adsorbing electrolytes (NaCl, CaCl 2 , MgCl 2 ) leads to pseudo-lepidocrocite (Lp; c-FeOOH), a poorly crystalline version of Lp with low sheet-stacking coherence. In the absence of bivalent cations, P and As(V) have similar uptake behavior, but different effects on the average Fe(III) precipitate structure: pseudo-Lp dominates in the presence of P, whereas a disordered ferrihydrite-like precipitate akin to hydrous ferric oxide (HFO) is the dominant phase that forms in the presence of As(V). Despite its lower affinity for Fe(III) precipitates, Si leads to Si-HFO in all conditions tested. The presence of 1 mM Ca 2+ or Mg 2+ enhances oxyanion uptake, destabilizes the colloidally stable oxyanion-bearing particle suspensions and, in some P and As(V) electrolytes, results in more crystalline precipitates. The trends in oxyanion uptake and Fe(III) precipitate structure in the presence of Ca 2+ /Mg 2+ suggest a systematic decrease in the strength of bivalent cation:oxyanion interaction in the order of Ca 2+ > Mg 2+ and P > As(V) ) Si. Using the PDF technique, we identify the polyhedral linkages that contribute to the intermediate structures (>6 A ˚) of disordered, nanoscale oxyanion-bearing Fe(III) precipitate samples. Our results suggest that oxyanions present during Fe(III) polymerization bind to corner-sharing Fe surface sites leading to a precipitate surface deficient in corner-sharing Fe, whereas the edge-and corner-sharing Fe sites in the precipitate core likely remain intact.

Millions of people in rural South Asia are exposed to high levels of arsenic through groundwater used for drinking. Many deployed arsenic remediation technologies quickly fail because they are not maintained, repaired, accepted, or affordable. It is therefore imperative that arsenic remediation technologies be evaluated for their ability to perform within a sustainable and scalable business model that addresses these challenges. We present field trial results of a 600 L Electro-Chemical Arsenic Remediation (ECAR) reactor operating over 3.5 months in West Bengal. These results are evaluated through the lens of a community scale micro-utility business model as a potential sustainable and scalable safe water solution for rural communities in South Asia. We demonstrate ECAR's ability to consistently reduce arsenic concentrations of ~266 μg/L to <5 μg/L in real groundwater, simultaneously meeting the international standards for iron and aluminum in drinking water. ECAR operating costs (amortized capital plus consumables) are estimated as $0.83-$1.04/m(3) under realistic conditions. We discuss the implications of these results against the constraints of a sustainable and scalable business model to argue that ECAR is a promising technology to help provide a clean water solution in arsenic-affected areas of South Asia.

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