Coupled dynamics of flow, microstructure, and conductivity in sheared suspensions

We propose a model for the evolution of the conductivity tensor for a flowing suspension of electrically conductive particles. We use discrete particle numerical simulations together with a continuum physical framework to construct an evolution law for the suspension microsutructure during flow. This model is then coupled with a relationship between the microstructure and the electrical conductivity tensor. The parameters of the joint model are fit experimentally using rheo- electrical conductivity measurements of carbon black suspensions under flow over a range of shear rates. The model is applied to the case of steady shearing as well as time-varying conductivity of unsteady flow experiments. We find that the model prediction agrees closely with the measured experimental data in all cases.Comment: 5 pages, 4 figure

Celebrating Soft Matter's 10th Anniversary: Chain configuration and rate-dependent mechanical properties in transient networks

Numerical solution of a coupled set of Smoluchowski convection-diffusion equations of associating polymers modelled as finitely extensible dumbbells enables computation of time-dependent end-to-end distributions for bridged, dangling, and looped chains in three dimensions as a function of associating end-group kinetics. Non-monotonic flow curves which can lead to flow instabilities during shear flow result at low equilibrium constant and high association rate from two complementary phenomena: a decrease in the fraction of elastically active chains with increasing shear rate and non-monotonic extension in the population of elastically active chains. Chain tumbling leads to reformation of bridges, resulting in an increased fraction of bridged chains at high Deborah number and significant reduction in the average bridge chain extension. In the start-up of steady shear, force-activated chain dissociation and chain tumbling cause both stress overshoot and stress ringing behaviour prior to reaching steady state stress values. During stress relaxation following steady shear, chain kinetics and extension mediate both the number of relaxations and the length of time required for system relaxation. While at low association rate relaxation is limited by the relaxation of dangling chains and the rate of dangling chain formation, at high association rate coupling of dangling and bridged chains leads to simultaneous relaxation of all chains due to a dynamic equilibrium between dangling and bridged states

A statistical gap-filling method to interpolate global monthly surface ocean carbon dioxide data

We have developed a statistical gap-filling method adapted to the specific coverage and prop-erties of observed fugacity of surface ocean CO2(fCO2). We have used this method to interpolate the Sur-face Ocean CO2Atlas (SOCAT) v2 database on a 2.5832.58 global grid (south of 708N) for 1985–2011 atmonthly resolution. The method combines a spatial interpolation based on a ‘‘radius of influence’’ to deter-mine nearby similar fCO2values with temporal harmonic and cubic spline curve-fitting, and also fits long-term trends and seasonal cycles. Interannual variability is established using deviations of observations fromthe fitted trends and seasonal cycles. An uncertainty is computed for all interpolated values based on thespatial and temporal range of the interpolation. Tests of the method using model data show that it performsas well as or better than previous regional interpolation methods, but in addition it provides a near-globaland interannual coverage

Nonuniform ocean acidification and attenuation of the ocean carbon sink

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 44 (2017): 8404–8413, doi:10.1002/2017GL074389.Surface ocean carbon chemistry is changing rapidly. Partial pressures of carbon dioxide gas (pCO2) are rising, pH levels are declining, and the ocean's buffer capacity is eroding. Regional differences in short-term pH trends primarily have been attributed to physical and biological processes; however, heterogeneous seawater carbonate chemistry may also be playing an important role. Here we use Surface Ocean CO2 Atlas Version 4 data to develop 12 month gridded climatologies of carbonate system variables and explore the coherent spatial patterns of ocean acidification and attenuation in the ocean carbon sink caused by rising atmospheric pCO2. High-latitude regions exhibit the highest pH and buffer capacity sensitivities to pCO2 increases, while the equatorial Pacific is uniquely insensitive due to a newly defined aqueous CO2 concentration effect. Importantly, dissimilar regional pH trends do not necessarily equate to dissimilar acidity ([H+]) trends, indicating that [H+] is a more useful metric of acidification.2018-02-1

Contribution of ocean, fossil fuel, land biosphere, and biomass burning carbon fluxes to seasonal and interannual variability in atmospheric CO2

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): G01010, doi:10.1029/2007JG000408.Seasonal and interannual variability in atmospheric carbon dioxide (CO2) concentrations was simulated using fluxes from fossil fuel, ocean and terrestrial biogeochemical models, and a tracer transport model with time-varying winds. The atmospheric CO2 variability resulting from these surface fluxes was compared to observations from 89 GLOBALVIEW monitoring stations. At northern hemisphere stations, the model simulations captured most of the observed seasonal cycle in atmospheric CO2, with the land tracer accounting for the majority of the signal. The ocean tracer was 3–6 months out of phase with the observed cycle at these stations and had a seasonal amplitude only ∼10% on average of observed. Model and observed interannual CO2 growth anomalies were only moderately well correlated in the northern hemisphere (R ∼ 0.4–0.8), and more poorly correlated in the southern hemisphere (R < 0.6). Land dominated the interannual variability (IAV) in the northern hemisphere, and biomass burning in particular accounted for much of the strong positive CO2 growth anomaly observed during the 1997–1998 El Niño event. The signals in atmospheric CO2 from the terrestrial biosphere extended throughout the southern hemisphere, but oceanic fluxes also exerted a strong influence there, accounting for roughly half of the IAV at many extratropical stations. However, the modeled ocean tracer was generally uncorrelated with observations in either hemisphere from 1979–2004, except during the weak El Niño/post-Pinatubo period of the early 1990s. During that time, model results suggested that the ocean may have accounted for 20–25% of the observed slowdown in the atmospheric CO2 growth rate.We acknowledge the support of NASA grant NNG05GG30G and NSF grant ATM0628472

A global evaluation of the regional spatial variability of column integrated CO 2 distributions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95294/1/jgrd14612.pd

An assessment of the Atlantic and Arctic sea–air CO2 fluxes, 1990–2009

© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 10 (2013): 607-627, doi:10.5194/bg-10-607-2013.The Atlantic and Arctic Oceans are critical components of the global carbon cycle. Here we quantify the net sea–air CO2 flux, for the first time, across different methodologies for consistent time and space scales for the Atlantic and Arctic basins. We present the long-term mean, seasonal cycle, interannual variability and trends in sea–air CO2 flux for the period 1990 to 2009, and assign an uncertainty to each. We use regional cuts from global observations and modeling products, specifically a pCO2-based CO2 flux climatology, flux estimates from the inversion of oceanic and atmospheric data, and results from six ocean biogeochemical models. Additionally, we use basin-wide flux estimates from surface ocean pCO2 observations based on two distinct methodologies. Our estimate of the contemporary sea–air flux of CO2 (sum of anthropogenic and natural components) by the Atlantic between 40° S and 79° N is −0.49 ± 0.05 Pg C yr−1, and by the Arctic it is −0.12 ± 0.06 Pg C yr−1, leading to a combined sea–air flux of −0.61 ± 0.06 Pg C yr−1 for the two decades (negative reflects ocean uptake). We do find broad agreement amongst methodologies with respect to the seasonal cycle in the subtropics of both hemispheres, but not elsewhere. Agreement with respect to detailed signals of interannual variability is poor, and correlations to the North Atlantic Oscillation are weaker in the North Atlantic and Arctic than in the equatorial region and southern subtropics. Linear trends for 1995 to 2009 indicate increased uptake and generally correspond between methodologies in the North Atlantic, but there is disagreement amongst methodologies in the equatorial region and southern subtropics.U. Schuster has been supported by EU grants IP 511176-2 (CARBOOCEAN), 212196 (COCOS), and 264879 (CARBOCHANGE), and UK NERC grant NE/H017046/1 (UKOARP). G. A. McKinley and A. Fay thank NASA for support (NNX08AR68G, NNX11AF53G). P. Landsch¨utzer has been supported by EU grant 238366 (GREENCYCLESII). N. Metzl acknowledges the French national funding program LEFE/INSU. Support for N. Gruber has been provided by EU grants 264879 (CARBOCHANGE) and 283080 (GEO-CARBON) S. Doney acknowledges support from NOAA (NOAA-NA07OAR4310098). T. Takahashi is supported by NOAA (NAO80AR4320754)

Strengthening seasonal marine CO2 variations due to increasing atmospheric CO2

The increase of atmospheric CO2 (ref. 1) has been predicted to impact the seasonal cycle of inorganic carbon in the global ocean2,3, yet the observational evidence to verify this prediction has been missing. Here, using an observation-based product of the oceanic partial pressure of CO2 (pCO2) covering the past 34 years, we find that the winter-to-summer difference of the pCO2 has increased on average by 2.2 ± 0.4 μatm per decade from 1982 to 2015 poleward of 10° latitude. This is largely in agreement with the trend expected from thermodynamic considerations. Most of the increase stems from the seasonality of the drivers acting on an increasing oceanic pCO2 caused by the uptake of anthropogenic CO2 from the atmosphere. In the high latitudes, the concurrent ocean-acidification-induced changes in the buffer capacity of the ocean enhance this effect. This strengthening of the seasonal winter-to-summer difference pushes the global ocean towards critical thresholds earlier, inducing stress to ocean ecosystems and fisheries4. Our study provides observational evidence for this strengthening seasonal difference in the oceanic carbon cycle on a global scale, illustrating the inevitable consequences of anthropogenic CO2 emissions

Research potential and limitations of trace analyses of cremated remains

Human cremation is a common funeral practice all over the world and willpresumably become an even more popular choice for interment in thefuture. Mainly for purposes of identification, there is presently agrowing need to perform trace analyses such as DNA or stable isotopeanalyses on human remains after cremation in order to clarify pendingquestions in civil or criminal court cases. The aim of this study was toexperimentally test the potential and limitations of DNA and stableisotope analyses when conducted on cremated remains.For this purpose, tibiae from modern cattle were experimentally crematedby incinerating the bones in increments of 100 degrees C until a maximumof 1000 degrees C was reached. In addition, cremated human remains werecollected from a modern crematory. The samples were investigated todetermine level of DNA preservation and stable isotope values (C and Nin collagen, C and O in the structural carbonate, and Sr in apatite).Furthermore, we assessed the integrity of microstructural organization,appearance under UV-light, collagen content, as well as the mineral andcrystalline organization. This was conducted in order to provide ageneral background with which to explain observed changes in the traceanalyses data sets. The goal is to develop an efficacious screeningmethod for determining at which degree of burning bone still retains itsoriginal biological signals. We found that stable isotope analysis ofthe tested light elements in bone is only possible up to a heat exposureof 300 degrees C while the isotopic signal from strontium remainsunaltered even in bones exposed to very high temperatures. DNA-analysesseem theoretically possible up to a heat exposure of 600 degrees C butcan not be advised in every case because of the increased risk ofcontamination. While the macroscopic colour and UV-fluorescence ofcremated bone give hints to temperature exposure of the bone’s outersurface, its histological appearance can be used as a reliable indicatorfor the assessment of the overall degree of burning