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491.
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. 相似文献
492.
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). 相似文献
493.
Y.-S. Oon S.-A. Ong L.-N. Ho Y.-S. Wong Y.-L. Oon H. K. Lehl W.-E. Thung 《International Journal of Environmental Science and Technology》2017,14(11):2435-2442
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. 相似文献
494.
The issue of water shortage and related eco-environmental degradation in North China is one of the major emerging problems
in China. Precipitation is the most key factor for water resources. Based on the historical flood/dryness grade dataset during
the period of 1470–2000 obtained from 25 gauging stations in North China, the multi-scale variability and trends are analyzed
by means of power spectral and continuous wavelet transform. It is found that the precipitation is characterized by obvious
seasonal changes, quasi biennial oscillations, inter-annual 4–7 year component and inter-decadal 19-year periodicity. The
MK test results showe that step changes occurred around 1914 and 1964 in the annual precipitation. As for the historical flood/dryness
grade time series, it is characterized by 4∼5 year ENSO mode inter-annual oscillation, quasi-10 year inter-decadal variability,
quasi-24 year component and 50–80 year centurial periodicity. However, the scales of these variations have decreased significantly
since the 1970s. The trend for precipitation change in North China has been negative for last 30 years. Further research shows
that North China will continue to become dryer until 2015 and may change to a wetter regime after 2020. These findings should
be helpful for future decision-making to ensure sustainable water resource management in North China. 相似文献
495.
A.K. Burnham J.E. Clarkson M.F. Singleton C.M. Wong R.W. Crawford 《Geochimica et cosmochimica acta》1982,46(7):1243-1251
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. 相似文献
496.
摘 要 从显微煤岩学角度探讨了贵州六盘水地区晚二叠世龙潭煤系煤的生烃状况。研究表
明树皮体和基质镜质体是研究区煤岩显微组成中主要的两种富氢组分“富镜质体 较富树
皮体” 是主采煤层典型的煤岩组合特征在成烃演化过程中富氢镜质体和树皮体对生烃作
出了主要贡献。渗出沥青体充填于镜质体微裂隙或细小孔洞以及丝质体胞腔中。这些微裂隙
和胞腔对煤成油的保存、富集和运移起到关键作用。显微组分间的这种配置关系为煤成油藏
的形成提供了非常有利的条件。六盘水地区具有形成煤成油藏的母质条件同时在煤层中具
有较好的保存富集以及运移条件如果存在有利的地质背景与之相配合研究区煤成油藏的
勘探开发工作将具有十分乐观的前景。 相似文献