Biological markers from Green River kerogen decomposition

Isoprenoid and other carbon skeletons that are formed in living organisms and preserved essentially intact in ancient sediments are often called biological markers. The purpose of this paper is to develop improved methods of using isoprenoid hydrocarbons to relate petroleum or shale oil to its source rock. It is demonstrated that most, but not all, of the isoprenoid hydrocarbon structures are chemically bonded in kerogen (or to minerals) in Green River oil shale. The rate constant for thermally producing isoprenoid, cyclic, and aromatic hydrocarbons is substantially greater than for the bulk of shale oil. This may be related to the substantial quantity of CO₂ which is evolved coincident with the isoprenoid hydrocarbons but prior to substantial oil evolution. Although formation of isoprenoid alkenes is enhanced by rapid heating and high pyrolysis temperatures, the ratio of isoprenoid alkenes plus alkanes to normal alkenes plus alkanes is independent of heating rate. High-temperature laboratory pyrolysis experiments can thus be used to predict the distribution of aliphatic hydrocarbons in low temperature processes such as in situ shale oil production and perhaps petroleum formation. Finally, we demonstrate that significant variation in biological marker ratios occurs as a function of stratigraphy in the Green River formation. This information, combined with methods for measuring process yield from oil composition, enables one to relate time-dependent processing conditions to the corresponding time-dependent oil yield in a vertical modified-in situ retort even if there is a substantial and previously undetermined delay in drainage of shale oil from the retort.     

Shock waves in a dusty plasma having q-nonextensive electron velocity distribution

The dust-acoustic shock waves have been theoretically investigated using reductive perturbation technique. An unmagnetized four-component dusty plasma system consisting of nonextensive q-distributed electrons, Boltzmann distributed ions, and negatively as well as positively charged dust particles has been considered. The solution of Burgers equation in planar geometry is numerically analyzed. It has been observed that the nonextensive q-distribution of electrons has a significant role in the formation of shock waves. The relevance of our results to astrophysics as well as laboratory plasmas are briefly discussed.     

Squeezing information from regional climate change projections - results from a synthesis of CMIP5 results for south-east Queensland, Australia

We present a synthesis of CMIP5 model results for projected rainfall changes for a single region (south-east Queensland, Australia) and note that, as was evident in CMIP3 results, the multi-model mean projected changes for the late 21st century are not statistically significant for any season nor annually. Taking account of the number of statistically significant changes to mean rainfall, we find some evidence favouring a decrease in both spring and annual rainfall, but this is not compelling. In almost all cases the most frequent result is for no significant change. However, if we consider the number of results where there is a statistically significant change in the distributions of rainfall amounts, there appears to be slightly more information available for risk assessment studies. These numbers suggest an increase in the frequency of both wet and dry events during summer and spring, and a shift towards more frequent dry events during winter. There is no evidence for any significant changes to the distributions for either autumn or annually. The findings suggest that, in one respect, multi-model rainfall projections may contain more information than is evident from syntheses which focus on changes to the means and that, for some regions where changes in the frequency of wet and dry seasons/years have known impacts, the model projections may be more valuable than previously thought.     

Numerical Study on Coalescence of Pre-Existing Flaw Pairs in Rock-Like Material

The present numerical study, which is an extension of our previous numerical analysis on cracking processes of a single pre-existing flaw, focuses on the coalescence of two pre-existing parallel open flaws in rock subjected to a uniaxial compressive loading. To facilitate a systematic investigation, the arrangements of the flaw pair are classified into 11 categories. Simulations engaging AUTODYN are conducted on each category. The numerical results are compared with some published physical experimental test results. Eleven typical coalescence patterns are obtained, which are in good agreement with the experimental results, which include two coalescence patterns obtained in flaw pair arrangements (II) and (VIII″) not being reported in previous studies. The information gathered in the simulations helps identify the type (tensile/shear) of each crack segment involved in the coalescence. Most of the coalescence cracks initiate at or around the flaw tips, except those in flaw pair arrangements (II) and (IX′) with a very short ligament length, in which the coalescence cracks initiate on the flaw surfaces away from the flaw tip regions. Based on the numerical simulation results, the properties of the 11 coalescence patterns are obtained. Except those in flaw pair arrangements (II) and (IX′), the other coalescence patterns can be interpreted with respect to the basic crack types—tensile wing crack, horsetail crack and anti-wing crack. In addition, based on the type of crack segments involved in coalescence, namely tensile and shear, the coalescence can be classified into T mode (tensile mode), S mode (shear mode) and TS mode (mixed tensile–shear mode).     

Microbial fuel cell operation using nitrate as terminal electron acceptor for simultaneous organic and nutrient removal

A double-chambered biocathode microbial fuel cell with carbon felt employed as electrodes was developed for wastewater treatment and bioelectricity generation simultaneously. The system was operated in fed-batch mode for over eight batches. The effect of circuit connections on organic and nitrate reduction was investigated. The maximum power density recorded was 21.97 mW/m² at current density of 88.57 mA/m². The Coulombic efficiency and internal resistance of the system were 5% and 100 Ω. Up to 89.9 ± 5.9% of chemical oxygen demand reduction efficiency achieved with an influent of 1123 ± 28 mg/L. There was no significant difference in the chemical oxygen demand reduction when system operated in either open or closed circuit. This study clearly showed that higher nitrate reduction efficiency obtained in closed circuit (74.7 ± 7.0%) due to bio-electrochemical denitrification compared to only 41.7% in the open circuit. The result also successfully demonstrated nitrate as terminal electron acceptor for the cathodic nitrate reduction.