Char Crystalline Transformations During Coal Combustion and Their Implication for Carbon Burnout

Recent work at Sandia National Laboratories, Imperial College, and the U.K. utility PowerGen, has identified an important mechanism believed to have a large influence on unburned carbon levels from pulverized coal fired boilers. That mechanism is char carbon crystalline rearrangements on subsecond times scales at temperatures of 1800 - 2500 K, which lead to char deactivation in the flame zones of furnaces. The so-called thermal annealing of carbons is a well known phenomenon, but its key role in carbon burnout has only recently been appreciated, and there is a lack of quantitative data in this time/temperature range. In addition, a new fundamental tool has recently become available to study crystalline transformations, namely high resolution transmission electron microscopy (HRTEM) fringe imaging, which provides a wealth of information on the nature and degree of crystallinity in carbon materials such as coal chars. Motivated by these new developments, this University Coal Research project has been initiated with the following two goals: to determine transient, high-temperature, thermal deactivation kinetics as a function of parent coal and temperature history. to characterize the effect of this thermal treatment on carbon crystalline structure through high-resolution transmission electron microscopy and specialized, quantitative image analysis. Work is currently underway on the following three tasks: Task 1 Experimental technique development. The goal of this task is to develop and demonstrate an apparatus and procedure for measuring transient, high-temperature, thermal deactivation of coal chars. While peak gas temperatures in boilers are often in the range 1800 - 2000 K, peak particle temperatures can be much higher due to high rates of heat release at the particle surface due to exothermic carbon oxidation. The prototype transient heat treatment apparatus is based on an inert-gas purged graphite-rod sample holder that is subjected to rapid Joule heating to temperatures approaching 3000 o C. For the measurement of temperature histories an optical diagnostic is being developed that offers sufficient spatial resolution to distinguish the sample temperature from the substrate temperature. The optical diagnostic is based on a CID camera, a high-power lens, and movable mirrors to projecting multiple, filtered images onto a single chip. Oxidation kinetics are measured on the heat treated samples by a nonisothermal TGA technique. Task 2 Thermal deactivation kinetics. The goal of this task is to quantify thermal char deactivation as a function of temperature history and parent coal, with an emphasis on inert environments at temperatures and times found in combustion systems. The results are to be cast in the form of deactivation kinetics useful for incorporation in combustion models

Differential effects of nanoselenium doping on healthy and cancerous osteoblasts in coculture on titanium

In the present study, selenium (Se) nanoclusters were grown through heterogeneous nucleation on titanium (Ti) surfaces, a common orthopedic implant material. Normal healthy osteoblasts (bone-forming cells) and cancerous osteoblasts (osteosarcoma) were cultured on the Se-doped surfaces having three different coating densities. For the first time, it is shown that substrates with Se nanoclusters promote normal osteoblast proliferation and inhibit cancerous osteoblast growth in both separate (mono-culture) and coculture experiment. This study suggests that Se surface nanoclusters can be properly engineered to inhibit bone cancer growth while simultaneously promoting the growth of normal bone tissue

UV Imaging Polarimetry of the peculiar Seyfert 2 galaxy Mrk 477

We present the results of UV imaging polarimetry of the Seyfert 2 galaxy Mrk 477 taken by the Faint Object Camera onboard the Hubble Space Telescope (HST). From a previous HST UV image (lambda ~ 2180A), Mrk 477 has been known to have a pointlike bright UV hotspot in the central region, peculiar among nearby Seyfert 2 galaxies. There are also claims of UV/optical variability, unusual for a Seyfert 2 galaxy. Our data show that there is an off-nuclear scattering region ~ 0."6 (~ 500 pc) NE from the hotspot. The data, after the subtraction of the instrumental effect due to this bright hotspot region, might indicate that the scattered light is also detected in the central 0."2 radius region and is extended to a very wide angle. The hotspot location is consistent with the symmetry center of the PA pattern, which represents the location of the hidden nucleus, but our data do not provide a strong upper limit to the distance between the symmetry center and the hotspot. We have obtained high spatial resolution color map of the continuum which shows that the nuclear spiral arm of 0."4 scale (~ 300pc) is significantly bluer than the off-nuclear mirror and the hotspot region. The nature of the hotspot is briefly discussed.Comment: To appear in Ap

A 3-dimensional in vitro model of epithelioid granulomas induced by high aspect ratio nanomaterials

<p>Abstract</p> <p>Background</p> <p>The most common causes of granulomatous inflammation are persistent pathogens and poorly-degradable irritating materials. A characteristic pathological reaction to intratracheal instillation, pharyngeal aspiration, or inhalation of carbon nanotubes is formation of epithelioid granulomas accompanied by interstitial fibrosis in the lungs. In the mesothelium, a similar response is induced by high aspect ratio nanomaterials, including asbestos fibers, following intraperitoneal injection. This asbestos-like behaviour of some engineered nanomaterials is a concern for their potential adverse health effects in the lungs and mesothelium. We hypothesize that high aspect ratio nanomaterials will induce epithelioid granulomas in nonadherent macrophages in 3D cultures.</p> <p>Results</p> <p>Carbon black particles (Printex 90) and crocidolite asbestos fibers were used as well-characterized reference materials and compared with three commercial samples of multiwalled carbon nanotubes (MWCNTs). Doses were identified in 2D and 3D cultures in order to minimize acute toxicity and to reflect realistic occupational exposures in humans and in previous inhalation studies in rodents. Under serum-free conditions, exposure of nonadherent primary murine bone marrow-derived macrophages to 0.5 μg/ml (0.38 μg/cm²) of crocidolite asbestos fibers or MWCNTs, but not carbon black, induced macrophage differentiation into epithelioid cells and formation of stable aggregates with the characteristic morphology of granulomas. Formation of multinucleated giant cells was also induced by asbestos fibers or MWCNTs in this 3D <it>in vitro </it>model. After 7-14 days, macrophages exposed to high aspect ratio nanomaterials co-expressed proinflammatory (M1) as well as profibrotic (M2) phenotypic markers.</p> <p>Conclusions</p> <p>Induction of epithelioid granulomas appears to correlate with high aspect ratio and complex 3D structure of carbon nanotubes, not with their iron content or surface area. This model offers a time- and cost-effective platform to evaluate the potential of engineered high aspect ratio nanomaterials, including carbon nanotubes, nanofibers, nanorods and metallic nanowires, to induce granulomas following inhalation.</p

UV Imaging Polarimetry of the Seyfert 2 Galaxy Mrk 3

We present UV imaging polarimetry data of the Seyfert 2 galaxy Mrk 3 taken by the Hubble Space Telescope. The polarized flux is found to be extended to ~1 kpc from the nucleus, and the position angles of polarization are centrosymmetric, confirming that the polarization is caused by scattering. We determine the location of the hidden nucleus as the center of this centrosymmetric pattern. From the polarization images taken in two broad bands, we have obtained the color distribution of the polarized flux. Some regions have blue polarized flux, consistent with optically-thin dust scattering, but some bright knots have a color similar to that of Seyfert 1 nucleus. Also, the recent Chandra X-ray observation suggests that the ratio of scattered UV flux to scattered X-ray flux is rather similar to the intrinsic UV/X-ray ratio in a Seyfert 1 nucleus, if the observed extended X-ray continuum is scattered light. While the scattered X-ray would be essentially from electron scattering, the UV slope and UV/X-ray ratio both being similar to Seyfert 1's would lead to two possibilities as to the nature of the UV scatterers. One is that the UV may also be scattered by electrons, in which case the scattering gas is somehow dust-free. The other is that the UV is scattered by dust grains, but the wavelength-independent UV scattering with low efficiency indicated by the UV slope and UV/X-ray ratio would suggest that the grains reside in UV-opaque clouds, or the dust might be mainly composed of large grains and lacks small-grain population.Comment: 15 pages, 8 figures (plus 2 color versions of grayscale figures), To appear in ApJ; minor corrections for the proofs of the manuscrip

A graphene-based hydrogel monolith with tailored surface chemistry for PFAS passive sampling

Aquatic contamination by per- and polyfluorinated alkyl substances (PFAS) has attracted global attention due to their environmental and health concerns. Current health advisories and surface water regulatory limits require PFAS detection in the parts per trillion (ppt) range. One way to achieve those low detection limits is to use a reliable passive sampling-based monitoring tool for PFAS, as exists for numerous nonpolar persistent organic pollutants. Here we introduce a new graphene-based hydrogel monolith and describe its synthesis, chemical functionalization, property characterization, and testing as a PFAS equilibrium passive sampler. The graphene monoliths were self-assembled by hydrothermal treatment from graphene oxide (GO) aqueous dispersions to produce free standing cylinders of ∼563 mm3 volume consisting of 4 wt% thin-walled porous graphene and ∼96 wt% water. The uptake of 23 PFAS was measured on the as-produced monoliths, and equilibrium partition coefficients (KSW), were derived for longer chain (C ≥ 8) perfluoroalkyl acids (PFAA) and neutral precursors such as sulfonamides (log KSW range 1.9–3.6). To increase the KSW for shorter chain PFAA, the monoliths were chemically modified by a new diazonium-based grafting reaction that introduces positive surface charge without damage to the graphenic backbone. Introduction of benzylamine moieties through the diazonium intermediate switches zeta potential at pH 7 from −45 mV (as-produced graphene) to +5 mV. This modification increased the sorption of short and middle chain PFAA by ten-fold (e.g. log KSW for PFBA increased from 1.3 to 2.2), thereby improving the functionality of the passive sampler device for a wider range of PFAS. Field deployments demonstrated that the graphene monoliths were capable of detecting key PFAS in the Delaware River

Nuclear Bar Catalyzed Star Formation: 13^CO, C18^O and Molecular Gas Properties in the Nucleus of Maffei 2

(Abridged) We present resolution maps of CO, its isotopologues, and HCN from in the center of Maffei 2. The J=1-0 rotational lines of 12^CO, 13^CO, C18^O and HCN, and the J=2-1 lines of 13^CO and C18^O were observed with the OVRO and BIMA arrays. The 2-1/1-0 line ratios of the isotopologues constrain the bulk of the molecular gas to originate in low excitation, subthermal gas. From LVG modeling, we infer that the central GMCs have n(H_2) ~10^2.75 cm^-3 and T_k ~ 30 K. Continuum emission at 3.4 mm, 2.7 mm and 1.4 mm was mapped to determine the distribution and amount of HII regions and dust. Column densities derived from C18^O and 1.4 mm dust continuum fluxes indicate the CO conversion factor in the center of Maffei 2 is lower than Galactic by factors of ~2-4. Gas morphology and the clear ``parallelogram'' in the Position-Velocity diagram shows that molecular gas orbits within the potential of a nuclear (~220 pc) bar. The nuclear bar is distinct from the bar that governs the large scale morphology of Maffei 2. Giant molecular clouds in the nucleus are nonspherical and have large linewidths. Dense gas and star formation are concentrated at the sites of the x_1-x_2 orbit intersections of the nuclear bar, suggesting that the starburst is dynamically triggered.Comment: 50 pages, 14 figures, accepted for publication in Ap

Near and Mid-IR Photometry of the Pleiades, and a New List of Substellar Candidate Members

We make use of new near and mid-IR photometry of the Pleiades cluster in order to help identify proposed cluster members. We also use the new photometry with previously published photometry to define the single-star main sequence locus at the age of the Pleiades in a variety of color-magnitude planes. The new near and mid-IR photometry extend effectively two magnitudes deeper than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new set of candidate very low mass and sub-stellar mass members of the Pleiades in the central square degree of the cluster. We identify 42 new candidate members fainter than Ks =14 (corresponding to 0.1 Mo). These candidate members should eventually allow a better estimate of the cluster mass function to be made down to of order 0.04 solar masses. We also use new IRAC data, in particular the images obtained at 8 um, in order to comment briefly on interstellar dust in and near the Pleiades. We confirm, as expected, that -- with one exception -- a sample of low mass stars recently identified as having 24 um excesses due to debris disks do not have significant excesses at IRAC wavelengths. However, evidence is also presented that several of the Pleiades high mass stars are found to be impacting with local condensations of the molecular cloud that is passing through the Pleiades at the current epoch.Comment: Accepted to ApJS; data tables and embedded-figure version available at http://spider.ipac.caltech.edu/staff/stauffer/pleiades07