The wave numbers of supercritical surface tension driven Benard convection

The cell size or the wave numbers of supercritical hexagonal convection cells in primarily surface tension driven convection on a uniformly heated plate was studied experimentally in thermal equilibrium in thin layers of silicone oil of large aspect ratio. It was found that the cell size decreases with increased temperature difference in the slightly supercritical range, and that the cell size is unique within the experimental error. It was also observed that the cell size reaches a minimum and begins to increase at larger temperature differences. This reversal of the rate of change of the wave number with temperature difference is attributed to influences of buoyancy on the fluid motion. The consequences of buoyancy were tested with three fluid layers of different depth

Experimental studies of self-sustaining thermal aquifer remediation (STAR) for non-aqueous phase liquid (NAPL) sources

Self-sustaining Thermal Aquifer Remediation (STAR) is a novel technology that employs smouldering combustion for the remediation of subsurface contamination by non-aqueous phase liquids (NAPLs). Smouldering is a form of combustion that is slower and less energetic than flaming combustion. Familiar examples of smouldering involve solid fuels that are destroyed by the reaction (e.g., a smouldering cigarette or peat smouldering after a wildfire). In STAR, the NAPL serves as the fuel within an inert, porous soil medium. Results from experiments across a range of scales are very promising. Detailed characterisation has focused on coal tar, a common denser-than-water NAPL (DNAPL) contaminant. Complete remediation is demonstrated across this range of scales. Visual observations are supported bychemical extraction results. Further experiments suggest that STAR can be self-sustaining, meaning that once ignited the process can supply its own energy to propagate. Costly energy input is reduced significantly. Comparison of large scale to small scale laboratory experiments, a volume increase by a factor of 100, suggests that STAR process efficiency increases with scale. This increase in efficiency results from reduced heat losses at larger scales while maximum the temperature achieved by STAR is unaffected. The research also demonstrates the controllability of STAR, where the termination of airflow to the reaction terminates the STAR process. The scale-up process provides important guidance to the development of full scale STAR for ex situ remediation of NAPL-contaminated soil

Scaling-up experiments of smouldering combustion as a remediation technology for contaminated soil

Self-sustaining Treatment for Active Remediation (STAR) is a novel, patent-pending process that uses smouldering combustion as a remediation technology for land contaminated with hazardous organic liquids. Compounds such as chlorinated solvents, coal tar and petroleum products, called Non-Aqueous Phase Liquids (NAPLs) for their low miscibility with water, have a long history of use in the industrialised world and are among the most ubiquitous of contaminants worldwide. These contaminants are toxic and many are suspected or known carcinogens. Existing remediation technologies are expensive and ineffective at reducing NAPL source zones sufficiently to restore affected water resources to appropriate quality levels. STAR introduces a self-sustaining smouldering reaction within the NAPL pool in the subsurface and allows that reaction to provide all of the post-ignition energy required by the reaction to completely remediate the NAPL source zone in the soil. Results from laboratory and field experiments have been very promising. Laboratory experiments have demonstrated STAR across a wide range of NAPL fuels and focused on coal tar to identify key parameters for successful remediation. Modelling has suggested that STAR efficiency will improve with scale as effects such as heat losses from boundaries become less significant. Observations from field experiments support the modelling theory - significantly lower relative air flow in a smouldering field experiment (330L) led to faster smouldering front propagation than observed in laboratory experiments (1L and 3L). Preliminary emissions monitoring by Fourier Transform Infrared (FTIR) spectroscopy has suggested that STAR emissions might be low enough to meet regulatory requirements, but further study is necessary. As emissions are expected to vary with each contaminant, activated carbon filters are being developed and tested in case emissions filtration is necessary. Experiments at all scales have demonstrated that STAR is controllable and self-terminating. Pilot-scale (2500L) field trials are underway to demonstrate STAR on excavated contaminated soil. The materials that will be studied in these trials are manufactured coal tar in coarse sand (which is the same material as used in the laboratory and field experiments) as well as two soils obtained from coal tar contaminated sites. This poster focuses on the scale-up to these field trials, including small scale characterisation, large scale performance, emissions monitoring and post-treatment soil analysis

Primordial helium recombination III: Thomson scattering, isotope shifts, and cumulative results

Upcoming precision measurements of the temperature anisotropy of the cosmic microwave background (CMB) at high multipoles will need to be complemented by a more complete understanding of recombination, which determines the damping of anisotropies on these scales. This is the third in a series of papers describing an accurate theory of HeI and HeII recombination. Here we describe the effect of Thomson scattering, the $^3$He isotope shift, the contribution of rare decays, collisional processes, and peculiar motion. These effects are found to be negligible: Thomson and $^3$He scattering modify the free electron fraction $x_e$ at the level of several $\times 10^{-4}$. The uncertainty in the $2^3P^o-1^1S$ rate is significant, and for conservative estimates gives uncertainties in $x_e$ of order $10^{-3}$. We describe several convergence tests for the atomic level code and its inputs, derive an overall $C_\ell$ error budget, and relate shifts in $x_e(z)$ to the changes in $C_\ell$, which are at the level of 0.5% at $\ell =3000$. Finally, we summarize the main corrections developed thus far. The remaining uncertainty from known effects is $\sim 0.3$ in $x_e$.Comment: 19 pages, 15 figures, to be submitted to PR

A Method for Individual Source Brightness Estimation in Single- and Multi-band Data

We present a method of reliably extracting the flux of individual sources from sky maps in the presence of noise and a source population in which number counts are a steeply falling function of flux. The method is an extension of a standard Bayesian procedure in the millimeter/submillimeter literature. As in the standard method, the prior applied to source flux measurements is derived from an estimate of the source counts as a function of flux, dN/dS. The key feature of the new method is that it enables reliable extraction of properties of individual sources, which previous methods in the literature do not. We first present the method for extracting individual source fluxes from data in a single observing band, then we extend the method to multiple bands, including prior information about the spectral behavior of the source population(s). The multi-band estimation technique is particularly relevant for classifying individual sources into populations according to their spectral behavior. We find that proper treatment of the correlated prior information between observing bands is key to avoiding significant biases in estimations of multi-band fluxes and spectral behavior, biases which lead to significant numbers of misclassified sources. We test the single- and multi-band versions of the method using simulated observations with observing parameters similar to that of the South Pole Telescope data used in Vieira, et al. (2010).Comment: 11 emulateapj pages, 3 figures, revised to match published versio

Small-scale forward smouldering experiments for remediation of coal tar in inert media

This paper presents a series of experiments conducted to assess the potential of smouldering combustion as a novel technology for remediation of contaminated land by water-immiscible organic compounds. The results from a detailed study of the conditions under which a smouldering reaction propagates in sand embedded with coal tar are presented. The objective of the study is to provide further understanding of the governing mechanisms of smouldering combustion of liquids in porous media. A small-scale apparatus consisting of a 100 mm in diameter quartz cylinder arranged in an upward configuration was used for the experiments. Thermocouple measurements and visible digital imaging served to track and characterize the ignition and propagation of the smouldering reaction. These two diagnostics are combined here to provide valuable information on the development of the reaction front. Post-treatment analyses of the sand were used to assess the amount of coal tar remaining in the soil. Experiments explored a range of inlet airflows and fuel concentrations. The smouldering ignition of coal tar was achieved for all the conditions presented here and self-sustained propagation was established after the igniter was turned off. It was found that the combustion is oxygen limited and peak temperatures in the range 800-1080 °C were observed. The peak temperature increased with the airflow at the lower range of flows but decreased with airflow at the higher range of flows. Higher airflows were found to produce faster propagation. Higher fuel concentrations were found to produce higher peak temperatures and slower propagation. The measured mass removal of coal tar was above 99% for sand obtained from the core and 98% for sand in the periphery of the apparatus

Longitudinal Analysis of Antibody Responses to Trachoma Antigens Before and After Mass Drug Administration.

Blinding trachoma, caused by the bacteria Chlamydia trachomatis, is a neglected tropical disease targeted for elimination by 2020. A major component of the elimination strategy is mass drug administration (MDA) with azithromycin. Currently, program decisions are made based on clinical signs of ocular infection, but we have been investigating the use of antibody responses for post-MDA surveillance. In a previous study, IgG responses were detected in children lacking clinical evidence of trachoma, suggesting that IgG responses represented historical infection. To explore the utility of serology for program evaluation, we compared IgG and IgA responses to trachoma antigens and examined changes in IgG and IgA post-drug treatment. Dried blood spots and ocular swabs were collected with parental consent from 264 1-6 year olds in a single village of Kongwa District, central Tanzania. Each child also received an ocular exam for detection of clinical signs of trachoma. MDA was given, and six months later an additional blood spot was taken from these same children. Ocular swabs were analyzed for C. trachomatis DNA and antibody responses for IgA and total IgG were measured in dried bloods spots. Baseline antibody responses showed an increase in antibody levels with age. By age 6, the percentage positive for IgG (96.0%) was much higher than for IgA (74.2%). Antibody responses to trachoma antigens declined significantly six months after drug treatment for most age groups. The percentage decrease in IgA response was much greater than for IgG. However, no instances of seroreversion were observed. Data presented here suggest that focusing on concordant antibody responses in children will provide the best serological surveillance strategy for evaluation of trachoma control programs

Measurement of 21 cm brightness fluctuations at z ~ 0.8 in cross-correlation

In this letter, 21 cm intensity maps acquired at the Green Bank Telescope are cross-correlated with large-scale structure traced by galaxies in the WiggleZ Dark Energy Survey. The data span the redshift range 0.6 < z < 1 over two fields totaling ~41 deg. sq. and 190 hours of radio integration time. The cross-correlation constrains Omega_HI b_HI r = [0.43 \pm 0.07 (stat.) \pm 0.04(sys.)] x 10^-3, where Omega_HI is the neutral hydrogen HI fraction, r is the galaxy-hydrogen correlation coefficient, and b_HI is the HI bias parameter. This is the most precise constraint on neutral hydrogen density fluctuations in a challenging redshift range. Our measurement improves the previous 21 cm cross-correlation at z ~ 0.8 both in its precision and in the range of scales probed.Comment: 5 pages, 2 figures. As published in Ap