Real surface effects on radiative heat transfer

Radiative heat transfer for system of radiatively interacting opaque surfaces separated by radiatively transparent mediu

Natural attenuation of arsenic by sediment sorption and oxidation

Arsenic sorption onto aquifer sediments was investigated in anaerobic laboratory batch and column uptake experiments and characterized by As, Fe, and Mn X-ray absorption spectroscopy (XAS) to estimate the extent and mechanism of abiotic sorption and oxidation of As(III). Batch experiments at pH 6 showed that the amount of As(III) or As(V) sorption from synthetic background porewater to sediments was similar as a function of total As concentration, but slightly more As(V) was sorbed than As(III) with increasing As concentrations. Column experiments with As(III) solutions in the absence and presence of dissolved Fe^2+ showed more As uptake in the presence of Fe but also more Fe desorption during flushout with As-free solutions such that net As uptake was similar to, or less than that of, the Fe-free experiment. Fits to bulk Fe X-ray absorption near-edge spectroscopy (XANES) spectra showed no change between unreacted and reacted sediments. Manganese XANES revealed small increases in absorption in the spectral region associated with Mn(II) after reaction, indicating sediment Mn reduction. However, XANES spectra showed that Mn is not present as Mn^(IV)O_2(s) but is probably substituted into other sediment minerals as a mixture of Mn(II,III). Quantitative analyses of As XANES spectra, which indicated mixtures of As(III) and As(V) after reaction with As(III) solutions, were used to estimate a fraction of As(V) in excess of native As(V) in the sediment (0.2 mmol kg^−1) that corresponds to sorbed As(III) oxidized to As(V). The spectroscopic and solution data indicate that the aquifer sediments have a limited abiotic capacity to oxidize As(III), which did not exceed 30% of the total amount of As sorbed and was estimated in the range of 0.025−0.4 mmol kg^−1 sediment. In the presence of dissolved Fe^2+, the precipitation of Fe(III) hydrous oxide phases will be an effective mechanism for As scavenging only if there exists sufficient dissolved oxygen in groundwater to oxidize Fe. Once the aqueous oxidative capacity is exhausted, dissolved Fe^2+ may compete with As(III) for the limited abiotic oxidation supplied by sediment Mn-bearing phases

The Influence of Emotional Material on Encoding and Retrieving Intentions: An ERP Study in Younger and Older Adults

Prospective memory is a cognitive process that comprises the encoding and maintenance of an intention until the appropriate moment of its retrieval. It is of highly relevance for an independent everyday life, especially in older adults; however, there is ample evidence that prospective memory declines with increasing age. Because most studies have used neutral stimuli, it is still an open question how emotional factors influence age-related differences in prospective remembering. The aim of the study was to investigate the influence of emotional material on prospective memory encoding, monitoring, maintaining, and retrieval in younger and older adults using behavioral and electrophysiological measures. We tested 24 younger adults (M = 26.4 years) and 20 older adults (M = 68.1 years) using a picture one-back task as ongoing activity with an embedded prospective memory instruction. The experimental task consisted of three sessions. In each session, participants had to encode series of images that represented the prospective memory cues for the consecutive block. The images were either of pleasant, unpleasant, or neutral valence. The pictures used in the ongoing task were likewise of pleasant, unpleasant, or neutral valence. Event-related potentials (ERPs) were recorded to assess the neural correlates of intention encoding, maintenance, and self-initiated retrieval. We did not find age differences between younger and older adults on the behavioral level. However, the ERP results revealed an interesting pattern that suggested for both age groups elevated attentional processing of emotional cues during encoding indicated by an elevated LPP for the emotional cues. Additionally, younger adults showed increased activity for unpleasant cues. During the maintenance phase, both age groups engaged in strategic monitoring especially for pleasant cues, which led to enhanced sustained positivity. During retrieval, older adults showed increased activity of ERP components related to cue detection and retrieval mainly for pleasant cues indicating enhanced relevance for those cues. In conclusion, emotional material may influence prospective remembering in older adults differently than in younger adults by supporting a mixture of top-down and bottom-up controlled processing. The results demonstrated a negativity bias in younger adults and a positivity bias in older adults

Theoretical Study of Radiant Heat Exchange for Non-gray Non-diffuse Surfaces in a Space Environment Semiannual Status Report No. 2, Aug. 1965 - Feb. 1966

Bi-directional reflectance models for describing distribution of reflected energy from rough metallic spacecraft surface

A Gel Probe Equilibrium Sampler for Measuring Arsenic Porewater Profiles and Sorption Gradients in Sediments: I. Laboratory Development

A gel probe equilibrium sampler has been developed to study arsenic (As) geochemistry and sorption behavior in sediment porewater. The gels consist of a hydrated polyacrylamide polymer, which has a 92% water content. Two types of gels were used in this study. Undoped (clear) gels were used to measure concentrations of As and other elements in sediment porewater. The polyacrylamide gel was also doped with hydrous ferric oxide (HFO), an amorphous iron (Fe) oxyhydroxide. When deployed in the field, HFO-doped gels introduce a fresh sorbent into the subsurface thus allowing assessment of in situ sorption. In this study, clear and HFO-doped gels were tested under laboratory conditions to constrain the gel behavior prior to field deployment. Both types of gels were allowed to equilibrate with solutions of varying composition and re-equilibrated in acid for analysis. Clear gels accurately measured solution concentrations (±1%), and As was completely recovered from HFO-doped gels (±4%). Arsenic speciation was determined in clear gels through chromatographic separation of the re-equilibrated solution. For comparison to speciation in solution, mixtures of As(III) and As(V) adsorbed on HFO embedded in gel were measured in situ using X-ray absorption spectroscopy (XAS). Sorption densities for As(III) and As(V) on HFO embedded in gel were obtained from sorption isotherms at pH 7.1. When As and phosphate were simultaneously equilibrated (in up to 50-fold excess of As) with HFO-doped gels, phosphate inhibited As sorption by up to 85% and had a stronger inhibitory effect on As(V) than As(III). Natural organic matter (>200 ppm) decreased As adsorption by up to 50%, and had similar effects on As(V) and As(III). The laboratory results provide a basis for interpreting results obtained by deploying the gel probe in the field and elucidating the mechanisms controlling As partitioning between solid and dissolved phases in the environment

Theoretical study of radiant heat exchange for non-gray non-diffuse surfaces in a space environment Semiannual status report no. 3, Feb. - Jul. 1966

Radiant heat exchange for nongray nondiffuse surfaces in space environmen

Hydrous Manganese Oxide Doped Gel Probe Sampler for Measuring In Situ Reductive Dissolution Rates. 2. Field Deployment

In situ rates of reductive dissolution in submerged shoreline sediments at Lake Tegel (Berlin, Germany) were measured with a novel hydrous manganese (Mn) oxide-doped gel probe sampler in concert with equilibrium gel probe and sequential extraction measurements. Rates were low in the top 8 cm, then showed a peak from 8 to 14 cm, with a maximum at 12 cm depth. This rate corresponded with a peak in dissolved porewater iron (Fe) at 11 cm depth. Below 14 cm, the reductive dissolution rate reached an intermediate steady value. Lower rates at depth corresponded with increases in operationally defined fractions of carbonate-bound and organic- and sulfide-bound Mn and Fe as detected by sequential extraction. Observed rates of reductive dissolution, which reflect a capacity for Mn reduction rather than actual rates under ambient conditions, appear to correlate with porewater chemistry and sequential extraction fractions as expected in early sediment diagenesis, and are consistent with previous measurements of in situ reductive dissolution rates. Significant downward advection in this bank filtration setting depletes the Mn and Fe oxides in the sediments and enhances the transport of dissolved Fe and Mn into the infiltrating water

Radiant heat exchange in a space environment Scientific technical report, 1 Feb. - 31 Jul. 1969

Analytical methods development for predicting radiant heat transfer and temperature of engineering surfaces in space environmen

A neutral low-coordinate heterocyclic bismuth-tin species

The reaction of distannadiazane bearing bulky RAr*-groups (RAr* = C6H2{C(H)Ph2}2R-2,6,4; R = iPr, tBu) with ECl3 (E = Sb, Bi) was studied resulting in the isolation of previously unknown N,N-bis(dichloropnictino)amines (3) and a novel heterocyclic carbenoid bismuth species (4) bearing a Bi(III) and a Sn(IV) center. The structure and bonding was investigated by means of X-ray structure elucidations and DFT calculations

TiO_2-Photocatalyzed As(III) Oxidation in a Fixed-Bed, Flow-Through Reactor

Compliance with the U.S. drinking water standard for arsenic (As) of 10 μg L^(-1) is required in January 2006. This will necessitate implementation of treatment technologies for As removal by thousands of water suppliers. Although a variety of such technologies is available, most require preoxidation of As(III) to As(V) for efficient performance. Previous batch studies with illuminated TiO_2 slurries have demonstrated that TiO_2-photocatalyzed As(III) oxidation occurs rapidly. This study examined reaction efficiency in a flow-through, fixed-bed reactor that provides a better model for treatment in practice. Glass beads were coated with mixed P25/sol gel TiO_2 and employed in an upflow reactor irradiated from above. The reactor residence time, influent As(III) concentration, number of TiO_2 coatings on the beads, solution matrix, and light source were varied to characterize this reaction and determine its feasibility for water treatment. Repeated usage of the same beads in multiple experiments or extended use was found to affect effluent As(V) concentrations but not the steady-state effluent As(III) concentration, which suggests that As(III) oxidation at the TiO_2 surface undergoes dynamic sorption equilibration. Catalyst poisoning was not observed either from As(V) or from competitively adsorbing anions, although the higher steady-state effluent As(III) concentrations in synthetic groundwater compared to 5 mM NaNO_3 indicated that competitive sorbates in the matrix partially hinder the reaction. A reactive transport model with rate constants proportional to incident light at each bead layer fit the experimental data well despite simplifying assumptions. TiO_2-photocatalyzed oxidation of As(III) was also effective under natural sunlight. Limitations to the efficiency of As(III) oxidation in the fixed-bed reactor were attributable to constraints of the reactor geometry, which could be overcome by improved design. The fixed-bed TiO_2 reactor offers an environmentally benign method for As(III) oxidation