A New Equation of State for CCS Pipeline Transport: Calibration of Mixing Rules for Binary Mixtures of CO2 with N2, O2 and H2

One of the aspects currently holding back commercial scale deployment of carbon capture and storage (CCS) is an accurate understanding of the thermodynamic behaviour of carbon dioxide and relevant impurities during the pipeline transport stage. In this article we develop a general framework for deriving pressure-explicit EoS for impure CO2. This flexible framework facilitates ongoing development of custom EoS in response to new data and computational applications. We use our method to generalise a recent EoS for pure CO2 [Demetriades et al. Proc IMechE Part E, 227 (2013) pp. 117] to binary mixtures with N2, O2 and H2, obtaining model parameters by fitting to experiments made under conditions relevant to CCS-pipeline transport. Our model pertains to pressures up to 16MPa and temperatures between 273K and the critical temperature of pure CO2. In this region, we achieve close agreement with experimental data. When compared to the GERG EoS, our EoS has a comparable level of agreement with CO2 -N2 VLE experiments and demonstrably superior agreement with the O2 and H2 VLE data. Finally, we discuss future options to improve the calibration of EoS and to deal with the sparsity of data for some impurities

Contaminant trends in US National Estuarine Research Reserves

Inputs of toxic chemicals provide one of the major types of anthropogenic stress threatening our Nation's coastal and estuarine waters. To assess this threat, the National Oceanic and Atmospheric Administration's (NOAA’s) National Status and Trends (NS&T) Program Mussel Watch Project monitors the concentrations of more than 70 toxic chemicals in sediments and on the whole soft-parts of mussels and oysters at over 300 sites around the U.S. Twenty of the 25 designated areas that comprise NOAA's National Estuarine Research Reserve System (NERRS) have one or more Mussel Watch monitoring sites. Trace elements and organic contaminants were quantified including As, Ag, Cd, Cu, Hg, Ni, Pb, Zn, ΣPCBs, ΣPAHs, DDT and its metabolites, and butyltins. The Mussel Watch sites located in or near the 20 Reserves provide for both status and trends. Generally the Reserves have trace element and organic contaminant concentrations that are at or below the median concentration determined for all NS&T Mussel Watch monitoring data. Trends were derived using the Spearman-rank correlation coefficient. It was possible to determine if trends exist for sites at which six or more years of data are available. Generally no trends were found for trace elements but when trends were found they were usually decreasing. The same general conclusion holds for organic contaminants but more decreasing trends were found than for trace elements. The greatest number of decreasing trends were found for tributyltin and its metabolites. (PDF contains 203 pages

Bayesian Analysis of Hot Jupiter Radius Anomalies: Evidence for Ohmic Dissipation?

The cause of hot Jupiter radius inflation, where giant planets with $T_{\rm eq}$ $>1000$ K are significantly larger than expected, is an open question and the subject of many proposed explanations. Rather than examine these models individually, this work seeks to characterize the anomalous heating as a function of incident flux, $\epsilon(F)$, needed to inflate the population of planets to their observed sizes. We then compare that result to theoretical predictions for various models. We examine the population of about 300 giant planets with well-determined masses and radii and apply thermal evolution and Bayesian statistical models to infer the anomalous power as a function of incident flux that best reproduces the observed radii. First, we observe that the inflation of planets below about M=0.5 \;\rm{M}_\rm{J} appears very different than their higher mass counterparts, perhaps as the result of mass loss or an inefficient heating mechanism. As such, we exclude planets below this threshold. Next, we show with strong significance that $\epsilon(F)$ increases with $T_{\rm{eq}}$ towards a maximum of $\sim 2.5\%$ at $T_{\rm{eq}} \approx 1500$ K, and then decreases as temperatures increase further, falling to $\sim0.2\%$ at T_\rm{eff}= 2500 K. This high-flux decrease in inflation efficiency was predicted by the Ohmic dissipation model of giant planet inflation but not other models. We also explicitly check the thermal tides model and find that it predicts far more variance in radii than is observed. Thus, our results provide evidence for the Ohmic dissipation model and a functional form for $\epsilon(F)$ that any future theories of hot Jupiter radii can be tested against.Comment: 14 pages, 14 figures, accepted to The Astronomical Journal. This revision revises the description of statistical methods for clarity, but the conclusions remain the sam

A Clostridium difficile-Specific, Gel-Forming Protein Required for Optimal Spore Germination

Clostridium difficile is a Gram-positive spore-forming obligate anaerobe that is a leading cause of antibiotic-associated diarrhea worldwide. In order for C. difficile to initiate infection, its aerotolerant spore form must germinate in the gut of mammalian hosts. While almost all spore-forming organisms use trans- membrane germinant receptors to trigger germination, C. difficile uses the pseu- doprotease CspC to sense bile salt germinants. CspC activates the related subtilisin-like protease CspB, which then proteolytically activates the cortex hy- drolase SleC. Activated SleC degrades the protective spore cortex layer, a step that is essential for germination to proceed. Since CspC incorporation into spores also depends on CspA, a related pseudoprotease domain, Csp family pro- teins play a critical role in germination. However, how Csps are incorporated into spores remains unknown. In this study, we demonstrate that incorporation of the CspC, CspB, and CspA germination regulators into spores depends on CD0311 (renamed GerG), a previously uncharacterized hypothetical protein. The reduced levels of Csps in gerG spores correlate with reduced responsiveness to bile salt germinants and increased germination heterogeneity in single-spore germination assays. Interestingly, asparagine-rich repeat sequences in GerG’s central region facilitate spontaneous gel formation in vitro even though they are dispensable for GerG-mediated control of germination. Since GerG is found exclusively in C. difficile, our results suggest that exploiting GerG function could represent a promising avenue for developing C. difficile-specific anti-infective therapies

Extending the GERG-2008 equation of state: Improved departure function and interaction parameters for (methane+butane)

The Groupe Européen de Recherches Gazières (GERG) 2008 multi-parameter equation of state (EOS) is considered the reference model for the prediction of natural gas mixture properties. However, the limited quality of thermodynamic property data available for many key binary mixtures at the time of its development constrained both its range of validity and achievable uncertainty. The data situation for the binary system (CH4 + C4H10) in particular was identified previously as limiting the ability of the GERG-EOS to describe rich natural gases at low temperatures. Recently, new vapour-liquid equilibrium (VLE) and liquid mixture heat capacity data measured at low temperatures and high pressures have been published that significantly improve the data situation for this crucial binary, allowing erroneous literature data to be identified and the predictive behaviour of the GERG-EOS when extrapolated to be tested. The 10 basis functions in the generalised departure function used by the GERG-EOS for several binaries including (CH4 + C4H10) were examined to eliminate the term causing a divergence between measured and predicted liquid mixture isobaric heat capacities at T < 150 K. With a simplified nine-term departure function, the maximum relative deviation between the measured and predicted heat capacities was reduced from nearly (110 to 7) %. The interaction parameters in the GERG equation were also re-determined by including, for the first time for this binary, reliable low temperature VLE data together with most of the other high temperature data used in the original development of the model. The new interaction parameters for (CH4 + C4H10) reduced the relative deviation of bubble point pressures measured and calculated at T = 244 K from (9 to 1.4) %, without affecting the accuracy of property predictions at higher temperature

Speeds of sound for (CH4 + He) mixtures from p = (0.5 to 20) MPa at T = (273.16 to 375) K

Producción CientíficaThis work aims to provide accurate and wide-ranging experimental new speed of sound data w(p,T) of two binary (CH4 + He) mixtures at a nominal helium content of 5 % and 10 % at pressures p = (0.5 up to 20) MPa and temperatures T = (273.16, 300, 325, 350 and 375) K. For this purpose, the most accurate technique for determining speed of sound in gas phase has been used: the spherical acoustic resonator. Speed of sound is determined with an overall relative expanded (k = 2) uncertainty of 230 parts in 106 and compared to reference models for multicomponent natural gas-like mixtures: AGA8-DC92 and GERG-2008 equations of state. Relative deviations of experimental data from model estimations are outside the experimental uncertainty limit, although all points are mostly within the AGA uncertainty of 0.2 % and GERG uncertainty of 0.5 % and worsen as the helium content increases. Absolute average deviations are better than 0.45 % for GERG and below 0.14 % for AGA models in (0.95 CH4 + 0.05 He) mixture and below 0.83 % for GERG and within 0.22 % for AGA equations in (0.90 CH4 + 0.10 He) mixture.Junta de Castilla y León (project VA280P18)Ministerio de Economía, Industria y Competitividad (project ENE2017-88474-R