Geochemistry of arsenic in uranium mill tailings, Saskatchewan, Canada

The Rabbit Lake in-pit tailings body consisted of alternating layers of ice, frozen tailings and unfrozen tailings which varied in consistency from a slurry to a firm silty sand. The tailings solids are predominately composed of quartz (16 to 36%), calcium sulphate (0.3 to 54%) and illite (3 and 14%). Arsenic and Ni concentrations in the tailings showed similar patterns with depth, which were strongly related to historical changes in As and Ni concentrations in the mill feed. Mineralogy of the ore bodies indicated that As and Ni in the mill feed occurred primarily as 1:1 molar ratio arsenides such as niccolite and gersdorffite. SEM analysis suggested that solubilized arsenic is precipitated as Ca, Fe and Ni arsenates during the neutralization process. Dissolved arsenic concentrations in rive monitoring wells installed within the tailing body ranged from 9.6 to 71 mg/L. Sequential extraction analyses of tailings samples showed that As above 34 in depth was primarily associated with amorphous iron and metal hydroxides while the As below 34 m depth was primarily amorphous calcium arsenate precipitates. The high Ca/As ratio during tailings neutralization would likely preferentially precipitate Ca4(OH)2(AsO4)2:4H2O. Geochemical modeling suggested that the pore fluid calcium arsenate equilibrium As concentrations would range between 13 and 81 mg/L. The predicted pH and speciation of arsenic in the filter sand was dependent on the redox conditions (oxidizing or reducing) assigned to the regional groundwater. Reducing conditions in the regional groundwater cause As, the dominant species in the tailings, to be reduced to As 34 as arsenic diffuses from the tailings into the filter sand. Under reducing conditions, iron as Fe2+ in the filter sand is oxidized to Fe3+ as the sulphate (S6+) present in the tailings diffuses into the filter sand and is reduced to sulphide (S2). The pH in the tailings will decrease as the high concentrations of protons (lower pH) in the filter sand diffuse into the tailings. As the solubility of calcium arsenate minerals present in the tailings are pH dependent, the decrease in pH in the tailings causes an increase in solubility of the calcium arsenate minerals resulting in the dissolution of calcium arsenate minerals

The Accessory Minerals of some Granitic Rocks of the Boulder Batholith

Although the position of the Boulder batholith in space and time is well known, the modes of occurrence of various rock types and the inter-relationships between the petrographic types are not known in detail

Design, setup of an optically accessible internal combustion engine for study of gasoline direct injection combustion

Gasoline direct injection (GDI) engines are becoming attractive options for automobiles. The precise control over fuel delivery increases the potential for better fuel efficiency and higher performance. In this study, a single-cylinder optically-accessible engine was built to visualize GDI combustion. The optical engine was originally designed and used as a compression ignition engine for study of diesel combustion, but was extensively modified for GDI. The cylinder head was modified to include a spark plug, and a new ignition system was designed. In addition, a lowered compression ratio, new piston geometry, and new fuel injector were employed. In the experiment, combustion of a 20 percent ethanol/80 percent pure 90-octane gasoline fuel blend was studied. Experiments were conducted at 1200 rpm, and intake air and fuel were independently controlled. A metal version of the optical piston was made, and preliminary tests were conducted using the metal configuration. From these tests, engine performance, stability, and emissions were measured. Following the metal engine testing, an optical study was performed. Using a high-speed camera at 12,000 frames per second, images of fuel injector spray as well as combustion were recorded. A 3-dimensional Mie scattering technique was used to image the interaction of the fuel spray with the piston and cylinder walls, and natural flame luminosity was used to capture combustion images. From the experiments, it was concluded that in this configuration, a double injection with a first injection timing of 180° BTDC and a 90 percent/10 percent first/second injection split gave the best results with respect to engine stability and emissions. The combustion and spray imaging paired with corresponding performance and emissions data provide a broad picture of GDI combustion characteristics

Pahs, Ionized Gas, and Molecular Hydrogen in Brightest Cluster Galaxies of Cool Core Clusters of Galaxies

We present measurements of 5-25 {\mu}m emission features of brightest cluster galaxies (BCGs) with strong optical emission lines in a sample of 9 cool-core clusters of galaxies observed with the Infrared Spectrograph on board the Spitzer Space Telescope. These systems provide a view of dusty molecular gas and star formation, surrounded by dense, X-ray emitting intracluster gas. Past work has shown that BCGs in cool-core clusters may host powerful radio sources, luminous optical emission line systems, and excess UV, while BCGs in other clusters never show this activity. In this sample, we detect polycyclic aromatic hydrocarbons (PAHs), extremely luminous, rotationally-excited molecular hydrogen line emission, forbidden line emission from ionized gas ([Ne II] and [Ne III]), and infrared continuum emission from warm dust and cool stars. We show here that these BCGs exhibit more luminous forbidden neon and H2 rotational line emission than star-forming galaxies with similar total infrared luminosities, as well as somewhat higher ratios of 70 {\mu}m / 24 {\mu}m luminosities. Our analysis suggests that while star formation processes dominate the heating of the dust and PAHs, a heating process consistent with suprathermal electron heating from the hot gas, distinct from star formation, is heating the molecular gas and contributing to the heating of the ionized gas in the galaxies. The survival of PAHs and dust suggests that dusty gas is somehow shielded from significant interaction with the X-ray gas.Comment: 27 preprint pages, 18 figures, accepted by Astrophysical Journa

When Should One Substract Background Fluorescence in Two Color Microarrays?

Two color microarrays are a powerful tool for genomic analysis, but have noise components that make inferences regarding gene expression inefficient and potentially misleading. Background fluorescence,whether attributable to non-specific binding or other sources,is an important component of noise. The decision to subtract fluorescence surrounding spots of hybridization from spot fluorescence has been controversial, with no clear criteria for determining circumstances that may favor, or disfavor, background subtraction. While it is generally accepted that subtracting background reduces bias but increases variance in the estimates of the ratios of interest, no formal analysis of the bias-variance trade off of background subtraction has been undertaken. In this paper, we use simulation to systematically examine the bias-variance trade off under a variety of possible experimental conditions. Our simulation is based on data obtained from two self versus self microarray experiments and is free of distributional assumptions. Our results identify factors that are important for determining whether to background subtract, including the correlation of foreground to background intensity ratios. Using these results we develop recommendations for diagnostic visualizations that can help decisions about background subtraction

Star formation and UV colors of the brightest Cluster Galaxies in the representative XMM-Newton Cluster Structure Survey

We present UV broadband photometry and optical emission-line measurements for a sample of 32 Brightest Cluster Galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM Optical Monitor, supplemented by existing archival GALEX photometry. We detected H\alpha and forbidden line emission in 7 (22%) of these BCGs, in optical spectra. All of the emission-line BCGs occupy clusters classified as cool cores, for an emission-line incidence rate of 70% for BCGs in cool core clusters. Significant correlations between the H\alpha equivalent widths, excess UV production in the BCG, and the presence of dense, X-ray bright intracluster gas with a short cooling time are seen, including the fact that all of the H\alpha emitters inhabit systems with short central cooling times and high central ICM densities. Estimates of the star formation rates based on H\alpha and UV excesses are consistent with each other in these 7 systems, ranging from 0.1-8 solar masses per year. The incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat lower than in other X-ray selected samples (-35%), and somewhat higher than but statistically consistent with optically selected, slightly lower redshift BCG samples (-10-15%). The UV-optical colors (UVW1-R-4.7\pm0.3) of REXCESS BCGs without strong optical emission lines are consistent with those predicted from templates and observations of ellipticals dominated by old stellar populations. We see no trend in UV-optical colors with optical luminosity, R-K color, X-ray temperature, redshift, or offset between X-ray centroid and X-ray peak ().Comment: 19 pages, 18 figures, 6 tables. Submitted, with minor revisions, to ApJ

Stable reduction of CCR5 by RNAi through hematopoietic stem cell transplant in non-human primates

RNAi is a powerful method for suppressing gene expression that has tremendous potential for therapeutic applications. However, because endogenous RNAi plays a role in normal cellular functions, delivery and expression of siRNAs must be balanced with safety. Here we report successful stable expression in primates of siRNAs directed to chemokine (c-c motif) receptor 5 (CCR5) introduced through CD34+ hematopoietic stem/progenitor cell transplant. After hematopoietic reconstitution, to date 14 months after transplant, we observe stably marked lymphocytes expressing siRNAs and consistent down-regulation of chemokine (c-c motif) receptor 5 expression. The marked cells are less susceptible to simian immunodeficiency virus infection ex vivo. These studies provide a successful demonstration that siRNAs can be used together with hematopoietic stem cell transplant to stably modulate gene expression in primates and potentially treat blood diseases such as HIV-1