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

Bog birds of Cheboygan County.

http://deepblue.lib.umich.edu/bitstream/2027.42/51731/1/157.pd

Inflight and ground-based simulation of handling qualities of very large airplanes in landing approach

Inflight and ground based simulation of Boeing 367-80 variable stability aircraft handling qualities during landing approac

Linearized inverse scattering based on seismic Reverse Time Migration

In this paper we study the linearized inverse problem associated with imaging of reflection seismic data. We introduce an inverse scattering transform derived from reverse-time migration (RTM). In the process, the explicit evaluation of the so-called normal operator is avoided, while other differential and pseudodifferential operator factors are introduced. We prove that, under certain conditions, the transform yields a partial inverse, and support this with numerical simulations. In addition, we explain the recently discussed 'low-frequency artifacts' in RTM, which are naturally removed by the new method

Swimming Eastern Chipmunks, Tamias striatus, and Hairy-tailed Mole, Parascalops breweri, in Kawartha Highlands Provincial Park, Ontario

We report swimming Eastern Chipmunks, Tamias striatus, and a swimming Hairy-tailed Mole, Parascalops breweri, in southern Ontario in Kawartha Highlands Provincial Park. Although naturally swimming Eastern Chipmunks have been seen before, they have never been previously documented in the literature. Ours appears to be the first photograph of a swimming Hairy-tailed Mole and the first report of one successfully and apparently voluntarily swimming

Introducing the concept of Potential Aerosol Mass (PAM)

International audiencePotential Aerosol Mass (PAM) can be defined as the maximum aerosol mass that the oxidation of precursor gases produces. In the measurement, all precursor gases are rapidly oxidized with extreme amounts of oxidants to low volatility compounds, resulting in the aerosol formation. Oxidation occurs in a small, simple, flow-through chamber that has a short residence time and is irradiated with ultraviolet light. The amount of the oxidants ozone (O3), hydroxyl (OH), and hydroperoxyl (HO2) were measured directly and can be controlled by varying the UV light and the relative humidity. Maximum values were 40 ppmv for O3, 500 pptv for OH, and 4 ppbv for HO2. The oxidant amounts are 100 to 1000 times troposphere values, but the ratios OH/O3 and HO2/OH are similar to troposphere values. The aerosol production mechanism and the aerosol mass yield were studied for several controlling variables, such as temperature, relative humidity, oxidant concentration, presence of nitrogen oxides (NOx), precursor gas composition and amount, and the presence of acidic seed aerosol. The measured secondary organic aerosol (SOA) yield of several natural and anthropogenic volatile organic compounds and a mixture of hydrocarbons in the PAM chamber were similar to those obtained in large, batch-style environmental chambers. This PAM method is being developed for measuring potential aerosol mass in the atmosphere, but is also useful for examining SOA processes in the laboratory and in environmental chambers