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We used a dynamic mixed layer model to determine carbon export by the oxygen mass balance method from a time series of O2/Ar, N2/Ar and Ne measurements collected at station ALOHA near Hawaii from July 2000 to June 2001. The inert gas measurements constrain the flux of oxygen into the mixed layer from small, collapsing bubbles (injection) to be greater than or equal to the flux from larger bubbles (exchange), with mean estimates of the ratio in the range of 1–2. We also show that monthly observations of temperature and inert gases cannot constrain the rate of diapycnal mixing at this location, because of uncertainties in air-sea heat flux estimates and bubble dynamics. Organic carbon export from the mixed layer calculated from our dataset was 1.1 ± 0.5 mol C m–2 yr–1, with most of the error deriving from uncertainties in the parameterization of diffusive gas exchange with wind speed. Our estimates of carbon export from the zone beneath the mixed layer but still in the euphotic zone ranged from 0 to 0.6 mol C m–2 yr–1 as the rate of background diapycnal mixing was increased from 0.1 to 1.0 cm2 s–1. We conclude that the oxygen mass balance method has errors of about a factor of two in areas similar to the subtropical North Pacific, with the main uncertainties deriving from mixing rates and the parameterization of diffusive gas exchange.

We describe an analytical method with improved precision for measuring the concentration of neon dissolved in water. Measurements were calibrated by isotope dilution, with addition of a Ne-22 spike directly to the evacuated sample flask prior to water collection. The use of glass flasks for water sampling, with flushing of air from the system by CO2, greatly reduced the chance of contamination. Dissolved gases were extracted from the water sample by equilibration with a headspace and cryogenically processed to remove interferences. The Ne-22/Ne-20 ratio was then measured on a quadrupole mass spectrometer operated in static mode. Mass fractionation by the system was accounted for by frequent analyses of the Ne-22/Ne-20 ratio in air. We routinely obtained precisions of +/-0.13% based on the standard deviation of duplicate field samples. Accuracy of the method, in the form of possible systematic offsets that could skew all the data, was assessed to be +/-0.18%, excluding a possible +/-0.2% error in the estimate of the Ne concentration of air. (C) 2004 Elsevier B.V. All rights reserved.

Past studies of noble gas concentrations in the deep ocean have revealed widespread, several percent undersaturation of Ar, Kr, and Xe. However, the physical explanation for these disequilibria remains unclear. To gain insight into undersaturation set by deep‐water formation, we measured heavy noble gas isotope and elemental ratios from the deep North Pacific using a new analytical technique. To our knowledge, these are the first high‐precision seawater profiles of 38Ar/36Ar and Kr and Xe isotope ratios. To interpret isotopic disequilibria, we carried out a suite of laboratory experiments to measure solubility fractionation factors in seawater. In the deep North Pacific, we find undersaturation of heavy‐to‐light Ar and Kr isotope ratios, suggesting an important role for rapid cooling‐driven, diffusive air‐to‐sea gas transport in setting the deep‐ocean undersaturation of heavy noble gases. These isotope ratios represent promising new constraints for quantifying physical air‐sea gas exchange processes, complementing noble gas concentration measurements. Plain Language Summary: The deep ocean inherits its dissolved gas content from exchange with the atmosphere at high latitudes and from biological and chemical processes. Noble gases, which are unaffected by biology and chemistry, are useful tools for understanding physical gas exchange. Past observations of dissolved noble gases throughout the deep ocean have revealed that Ar, Kr, and Xe concentrations fall below expected concentrations for water at solubility equilibrium with the atmosphere. However, a physical explanation for this well‐documented undersaturation of noble gases remains unclear. Here we have measured the isotope ratios of Ar, Kr, and Xe in the deep North Pacific as new tools to investigate physical mechanisms of disequilibrium. Our findings suggest that rapid cooling and sinking of surface water at high latitudes, driving air‐to‐sea gas transport with insufficient time for equilibration, is a key process in setting the observed deep‐ocean undersaturation of noble gases. Key Points: Ar, Kr, and Xe isotope ratios were measured in the deep North Pacific to investigate mechanisms of solubility disequilibriumSeawater solubility fractionation factors of heavy noble gas isotope ratios were determined, indicating a weak dependence on salinityObserved isotopic disequilibria point to incomplete cooling‐driven diffusive gas uptake prior to deep‐water formation [ABSTRACT FROM AUTHOR]

In order to predict the changing trend of the dissolved gas in the transformer oil accurately and guide the condition-based maintenance of a power transformer, a combined forecasting model based on cross-entropy is proposed and its application is analyzed. First, a combined forecasting model is established on the basis of radical basis function neural network, back propagation neural network, least squares support vector machine with two different kernel functions, and grey model. Then, the weight coefficient of each algorithm is determined by cross-entropy theory. After that, an application method of the combined forecasting model by the pattern of a variable time window is proposed for the purpose of arranging the equipment maintenance in advance. In this way, the increased budget due to emergency maintenance can be alleviated, and potential loss due to lack of timely maintenance can be reduced. Finally, the accuracy of the combination forecasting method and the effectiveness of the application method are verified by a series of examples. [ABSTRACT FROM AUTHOR]

The promotion/prevention mechanism of dissolved gases on cavitation inception is essential for many high-tech industries and research. In the present study, large-scale molecular dynamics simulations are performed to investigate the effects of water cavitation caused by different gas types by using nitrogen and oxygen gases with TIP4P/2005 water. The cavitation inception behaviour is analyzed via Mean First Passage Time method. Water with dissolved gases has a higher nucleation rate and is easier to cavitate than pure water. At the same gas concentration, the cavitation of water with nitrogen is promoted to a greater extent than that with oxygen. The number and energy of hydrogen bond (HB) are further calculated by the Acceptor-Hydrogen-Donor method to explain this promotion mechanism. The number and energy of HB in water with gases decrease compared with those in pure water. The introduction of gases weakens the HB network and promotes cavitation inception because of weaker interactions between gas and water molecules. A model is developed to describe the relationship between nucleation rate and HB energy. Gas molecules assemble on the surface of bubbles during water cavitation, which may decrease the free energy of bubble surface, maintain the existing bubble, and contribute to the growth process. [ABSTRACT FROM AUTHOR]

Gas generation and flow in soil is relevant to applications such as the fate of leaking geologically sequestered carbon dioxide, natural releases of methane from peat and marine sediments, and numerous electro‐thermal remediation technologies for contaminated sites, such as electrical resistance heating. While traditional multiphase flow models generally perform poorly in describing unstable gas flow phenomena in soil, Macroscopic Invasion Percolation (MIP) models can reproduce key features of its behavior. When coupled with continuum heat and mass transport models, MIP has the potential to simulate complex subsurface scenarios. However, coupled MIP‐continuum models have not yet been validated against experimental data and lack key mechanisms required for electro‐thermal scenarios. Therefore, the purpose of this study was to (a) incorporate mechanisms required for steam generation and flow into an existing MIP‐continuum model (ET‐MIP), (b) validate ET‐MIP against an experimental lab‐scale electrical resistance heating study, and (c) investigate the sensitivity of water boiling and gas (steam) transport to key parameters. Water boiling plateaus (i.e., latent heat), heat recirculation within steam clusters, and steam collapse (i.e., condensation) mechanisms were added to ET‐MIP. ET‐MIP closely matched observed transient gas saturation distributions, measurements of electrical current, and temperature distributions. Heat recirculation and cluster collapse were identified as the key mechanisms required to describe gas flow dynamics using a MIP algorithm. Sensitivity analysis revealed that gas generation rates and transport distances, particularly through regions of cold water, are sensitive to the presence of dissolved gases. Key Points: Coupled Macroscopic Invasion Percolation (MIP) model with continuum heat and mass models accurately reproduced lab‐scale gas production and migrationSimulation of condensation mechanisms and heat recirculation within gas clusters were key to capturing gas flow dynamics with MIPHigher concentrations of dissolved oxygen and nitrogen increased gas mobilization and decreased steam condensation rates in cold water [ABSTRACT FROM AUTHOR]

Hydrogen is an important intermediate that is produced during carbohydrate fermentation to volatile fatty acid and utilized by methanogens to produce methane in the rumen. Ruminal volatile fatty acid and dissolved methane concentrations are more than 500 times greater than dissolved hydrogen concentration. Therefore, we hypothesized that dissolved hydrogen might have a higher sensitivity in response to dietary changes compared with volatile fatty acid and dissolved methane. Using goats, we investigated the effects of increasing dietary starch content (maize replaced with wheat bran) and supplementing with rhubarb rhizomes and roots on the relationships among dissolved hydrogen, dissolved methane and other fermentation end products. The study was conducted in a replicated 4×4 Latin square with a 2×2 factorial arrangement of four treatments: two starch levels (220 v. 320 g/kg dry matter (DM)), without and with rhubarb supplement (0% v. 2.8% of total mixed ration). Increased dietary starch and rhubarb supplementation did not alter volatile fatty acid concentrations or methane emissions in terms of g/day, g/g DM intake and g/g organic matter digested. However, goats fed the high-starch diet had greater dissolved hydrogen (P =0.005) and relative abundance of Selenomonas ruminantium (P <0.01), and lower (P =0.02) copy number of protozoa than those fed the low-starch diet. Rhubarb increased ruminal dissolved H2 (P =0.03) and total volatile fatty acid concentration (P <0.001), but decreased copies of bacteria (P =0.002). In conclusion, dissolved hydrogen appears to be more sensitive to dietary changes with starch content and rhubarb supplementation, when compared with volatile fatty acid concentrations and methane production. [ABSTRACT FROM AUTHOR]

Abstract Coupling microbial dynamics with the complete dynamics of the packaging gases is still a challenge. In this work the microbial growth kinetic parameters for Pseudomonas and Lactic Acid Bacteria (LAB) in MAP are identified based on accurate estimation of diffusivity of gases and parameter scaled sensitivity approaches. The microbial dynamics are also compared with those estimated based on partial pressure measurement. Scaled sensitivity coefficient analysis using dissolved gases as variable inputs, shows that in most cases the only coefficients large enough for estimation were those for CO 2max-diss , and for μ max. The current data showed that dissolved gases led significant differences on the microbial parameter of CO 2max values when compared with the headspace gases. On the other hand, the (so-called) dissolved specific growth rate follows a clear trend down for both microorganisms in relation to the increase of the initial headspace CO 2. Finally, current results indicate a possible correlation between CO 2max - diss , CO 2max - headspace , and μ max as functions of CO 2init. [ABSTRACT FROM AUTHOR]

Measurement of transformer remaining useful life has long been a goal for responsible asset management. Most testing laboratories offer furan concentration testing as a suitable method. The interpretive method of choice is usually the Chendong equation, expressed in practical terms as degree of polymerization of the paper with new paper at about 1000 and end of life at around 300. Typical mill transformers have thermal insulation ratings expressed as 55 °C rise for plain kraft or 65 °C, which corresponds to thermally upgraded kraft paper (TUP). It has been determined that TUP does not produce furans and, thus, provides a false indicator of the cellulose breakdown. There are several recent papers that have demonstrated that a measurement of methanol (MeOH) may be a better method to determine ageing of the TUP insulation and also better for transformers with plain kraft paper insulation. The objective of this paper is to provide an overview of the reasons why furans should not be used as the basis for measuring aging of thermally upgraded paper, why MeOH should be so used, and to compare actual furans and MeOH test data for service aged transformers in a process industry application [ABSTRACT FROM AUTHOR]

Hypothesis In literature it is stated that the stability of oil-in-water emulsions could be enhanced by decreasing the so-called “hydrophobic interactions” between surfaces through removal of dissolved atmospheric gases. Since the effect of the dissolved gases depends on the hydrophobicity of the oil phase, as well as the system pressure, we vary this effect systematically and monitor droplet coalescence in a tailor-made microfluidic device. Experiments The coalescence of oil drops in standard and degassed conditions was studied by direct observation using a microfluidic setup. Two model oils (heptane and xylene) were used to represent different hydrophobicity of the dispersed phases, together with an oil with dynamic interfacial behaviour (diluted crude oil). In addition, the effect of the volume fraction, droplet size and degassing method was studied. Findings At ambient pressure, the degassing of the continuous phase reduced the extent of coalescence for the model oils, which is in agreement with other reports. No effect of the dissolved gases was found on the drop formation process. At elevated pressures, the dissolved gases influenced only the most hydrophobic oil (heptane), while causing no effect in the other systems. The coalescence frequencies decreased upon the reduction of the drop sizes, which was justified with the theory for two interacting spheres. [ABSTRACT FROM AUTHOR]

The gravity-driven flashing of superheated water, a non-equilibrium phase change phenomenon usually associated with geysers, has not been studied yet in the specific configuration of a pool heated from below. However, this vaporization mode is tightly linked with some of the safety issues of the Spent Fuel Pool (SFP) loss-of-cooling accident. In order to fill this gap, an experiment, presented in this article, was designed and provided first results that highlighted some relevant mechanisms behind this vaporization mode. By heating up 40 L of demineralized water at a constant reduced pressure of 25 mbar with a heating power of 1000 W , it was possible to reproduce the expected phenomenology of a SFP loss-of-cooling accident at the laboratory scale. Starting the test with an initially large supersaturation in dissolved gases within the liquid, the latter, once superheated, vaporized onto the air nuclei that resulted from the liquid degassing. When the dissolved gases content dropped below a threshold value, the nucleation vanished. The liquid continued to heat-up for a while until an energetic equilibrium was reached between the heat supply and the heat removal induced by the free surface evaporation. This equilibrium substantially limited the superheats reached within the liquid. • A first study of the gravity-driven flashing of water in a heated pool. • A novel similarity approach based on system's pressure distortion. • A vaporization mechanism strongly influenced by the dissolved gases. [ABSTRACT FROM AUTHOR]