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181.
Geological and geotechnical aspects of underground coal mining methods within Australia 总被引:1,自引:1,他引:0
B. Scott P. G. Ranjtih S. K. Choi Manoj Khandelwal 《Environmental Earth Sciences》2010,60(5):1007-1019
About one quarter of the coal produced in Australia is by underground mining methods. The most commonly used underground coal
mining methods in Australia are longwall, and room and pillar. This paper provides a detailed review of the two methods, including
their advantages and disadvantages, the major geotechnical and operational issues, and the factors that need to be considered
regarding their choice, including the varying geological and geotechnical conditions suited to a particular method. Factors
and issues such as capital cost, productivity, recovery, versatility and mine safety associated with the two methods are discussed
and compared. The major advantages of the longwall mining method include its suitability for mining at greater depth, higher
recovery, and higher production rate compared to room and pillar. The main disadvantages of the room and pillar method are
the higher risks of roof and pillar collapse, higher capital costs incurred as well as lower recovery rate. 相似文献
182.
Multi-zone fusion crust formation and classification of the 2004 Auckland meteorite (L6, S5, and W0)
James M. Scott Marianne Negrini Kevin Faure Marshall C. Palmer Derek R. Knaack Matthew I. Leybourne 《Meteoritics & planetary science》2023,58(3):328-340
On June 12, 2004, a meteorite passed through Earth's atmosphere and landed under the television in the living room of a house in Auckland, New Zealand. Textural characteristics, the chemistry of olivine (Fa23–24) and orthopyroxene (Fs20.7), and the bulk rock triple oxygen isotopes (δ17O + 3.1; δ18O + 4.2‰) from the interior of the completely unweathered (W0) 1.3 kg meteorite, hereafter referred to as Auckland, suggest it to be a strongly metamorphosed fragment from the interior of a low iron ordinary chondrite (L6) parent asteroid. The occurrence of maskelynite but shock fracturing of olivine and pyroxene indicates Auckland experienced extreme shock metamorphism (S5), likely during Ordovician fragmentation of the asteroid parent. The fusion crust consists of three zones: (1) an innermost zone containing narrow Fe-Ni-S-bearing veins that migrated along pre-existing shock fractures in olivine and pyroxene; (2) a middle zone in which the meteorite partially melted to form a silicate glass and immiscible blebs of metal and troilite, and is accompanied by unmelted silicate minerals; and (3) an approximately 0.1 mm wide vesicular-rich outermost layer that largely melted, volatilizing sulfides, before quenching to form glass and olivine. Oxygen isotope values of the bulk rock and/or maskelynite of melted rim and modified substrate are 2–3‰ greater than the meteorite interior and indicate that up to 19% of terrestrial atmospheric O2 was incorporated into the fusion crust during the formation. The fusion crust migrated inwards as ablation occurred, enabling melting, migration, and re-precipitation ± loss of sulfide and metal components, with the prominent glassy rim therefore forming from an already chemically modified zone. 相似文献
183.
Phillip H. Larson Ronald I. Dorn R. Evan Palmer Zack Bowles Emma Harrison Scott Kelley 《自然地理学》2014,35(5):369-389
The Sonoran Desert portion of the Basin and Range physiographic province contains a number of streams that now flow across once-closed basins. We explore here the research questions of if and how granitic rock pediments respond to the transition from rimming endorheic basins to bordering through-flowing streams. Granitic rock pediments of the northern Usery and eastern McDowell Mountains once graded to the closed Miocene–Pliocene Pemberton basin that occupied the present-day location of the confluence of the Salt and Verde Rivers. The process of lake overflow, which integrated these rivers, first aggraded fill terraces that, in turn, caused aggradation of a mantle of transported grus on bedrock pediments. Subsequent episodic incision of the Salt and Verde rivers lowered the base level; this led to the development of erosional features such as rolling topography of a degrading pediment mantle; exposure of the former piedmont angle and its associated zones of enhanced bedrock decay and regolith carbonate; and exposure of spheroidally weathered bedrock and emerging tors, some of which experienced 20th century erosion. The granitic pediments of the former Pemberton Basin, which now transport grus to the Salt and Verde rivers, have actively adjusted to aggradational and degradational events associated with drainage integration and do not appear to be inherited from an ancient wet climatic interval. 相似文献
184.
Scott A. Reinemann David F. Porinchu Mae Sexauer Gustin Bryan G. Mark 《Journal of Paleolimnology》2014,52(4):405-418
The geochemistry of lake sediments was used to identify anthropogenic factors influencing aquatic ecosystems of sub-alpine lakes in the western United States during the past century. Sediment cores were recovered from six high-elevation lakes in the central Great Basin of the United States. The proxies utilized to examine the degree of recent anthropogenic environmental change include spheroidal carbonaceous particle (SCP), mercury (Hg), and sediment organic content estimated using loss-on-ignition. Chronologies for the sediment cores, developed using 210Pb, indicate the cores span the twentieth century. Mercury flux varied between lakes but all exhibited increasing fluxes during the mid-twentieth century. The mean ratio of modern (post-A.D. 1985) to preindustrial (pre-A.D. 1880) Hg flux was 5.2, which is comparable to the results from previous studies conducted in western North America. Peak SCP flux for all lakes occurred between approximately A.D. 1940 and A.D. 1970, after which time the SCP flux was greatly reduced. The reduction in SCP input is likely due to better controls on combustion sources. Measured Hg concentrations and calculated sedimentation rates suggest atmospheric Hg flux increased in the early 1900s, from A.D. 1920 to A.D. 1990, and at present. Atmospheric deposition is the primary source of the anthropogenic inputs of Hg and SCPs to these high elevation lakes. The input of SCPs, which is largely driven by regional sources, has declined with the implementation of national pollution control regulations. Mercury deposition in the Great Basin has most likely been influenced more by regional inputs. 相似文献
185.
Global climate change has evolved from a scientific problem into an economic and political problem oI worlOwloe rater- est. National perspectives play a crucial role in addressing climate change. Mutual understanding of perspectives is nec- essary to result in rational policies and a consensus among stakeholders with divergent interests. Conceptual frameworks for understanding the problem of climate change in China, the largest developing country and the largest greenhouse gas emitter, are of great significance to national and international efforts to address the problems of climate change. Chinese perceptions of climate change as a sustainable development problem have recently been in tension with an emerging Western perspective that frames climate change as a security issue. This paper explores Chinese perceptions of climate change as expressed in recent governmental policy statements, public opinion surveys, and academic scholarship with a focus on publications in Chinese-language journals, often unfamiliar in the West. It looks at the relationship between Chinese research and policy and finds that the Chinese policy frame of climate change as a sustainable development problem draws from the body of domestic research and is reflective of the perspectives and multidisciplinary approach of Chinese researchers in areas of climate change. 相似文献
186.
Scott H. Ensign Cliff R. Hupp Gregory B. Noe Ken W. Krauss Camille L. Stagg 《Estuaries and Coasts》2014,37(5):1107-1119
Sediment accretion was measured at four sites in varying stages of forest-to-marsh succession along a fresh-to-oligohaline gradient on the Waccamaw River and its tributary Turkey Creek (Coastal Plain watersheds, South Carolina) and the Savannah River (Piedmont watershed, South Carolina and Georgia). Sites included tidal freshwater forests, moderately salt-impacted forests at the freshwater–oligohaline transition, highly salt-impacted forests, and oligohaline marshes. Sediment accretion was measured by use of feldspar marker pads for 2.5 year; accessory information on wetland inundation, canopy litterfall, herbaceous production, and soil characteristics were also collected. Sediment accretion ranged from 4.5 mm year?1 at moderately salt-impacted forest on the Savannah River to 19.1 mm year?1 at its relict, highly salt-impacted forest downstream. Oligohaline marsh sediment accretion was 1.5–2.5 times greater than in tidal freshwater forests. Overall, there was no significant difference in accretion rate between rivers with contrasting sediment loads. Accretion was significantly higher in hollows than on hummocks in tidal freshwater forests. Organic sediment accretion was similar to autochthonous litter production at all sites, but inorganic sediment constituted the majority of accretion at both marshes and the Savannah River highly salt-impacted forest. A strong correlation between inorganic sediment accumulation and autochthonous litter production indicated a positive feedback between herbaceous plant production and allochthonous sediment deposition. The similarity in rates of sediment accretion and sea level rise in tidal freshwater forests indicates that these habitats may become permanently inundated if the rate of sea level rise increases. 相似文献
187.
A 2000-yr reconstruction of air temperature in the Great Basin of the United States with specific reference to the Medieval Climatic Anomaly 总被引:1,自引:0,他引:1
Scott A. Reinemann David F. Porinchu Glen M. MacDonald Bryan G. Mark James Q. DeGrand 《Quaternary Research》2014
A sediment core representing the past two millennia was recovered from Stella Lake in the Snake Range of the central Great Basin in Nevada. The core was analyzed for sub-fossil chironomids and sediment organic content. A quantitative reconstruction of mean July air temperature (MJAT) was developed using a regional training set and a chironomid-based WA-PLS inference model (r2jack = 0.55, RMSEP = 0.9°C). The chironomid-based MJAT reconstruction suggests that the interval between AD 900 and AD 1300, corresponding to the Medieval Climate Anomaly (MCA), was characterized by MJAT elevated 1.0°C above the subsequent Little Ice Age (LIA), but likely not as warm as recent conditions. Comparison of the Stella Lake temperature reconstruction to previously published paleoclimate records from this region indicates that the temperature fluctuations inferred to have occurred at Stella Lake between AD 900 and AD 1300 correspond to regional records documenting hydroclimate variability during the MCA interval. The Stella Lake record provides evidence that elevated summer temperature contributed to the increased aridity that characterized the western United States during the MCA. 相似文献
188.
We report here on the observation and offline detection of the meteotsunami off the New Jersey coast on June 13, 2013, using coastal radar systems and tide gauges. This work extends the previous observations of tsunamis originating in Japan and Indonesia. The radars observed the meteotsunami 23 km offshore, 47 min before it arrived at the coast. Subsequent observations showed it moving onshore. The neighboring tide gauge height reading provides confirmation of the radar observations near the shore. 相似文献
189.
Anastasia Petrenko Anton Sizo Winchel Qian A. Dylan Knowles Amin Tavassolian Kevin Stanley Scott Bell 《Transactions in GIS》2014,18(3):351-369
The popularization of tracking devices, such as GPS, accelerometers and smartphones, have made it possible to detect, record, and analyze new patterns of human movement and behavior. However, employing GPS alone for indoor localization is not always possible due to the system's inability to determine location inside buildings or in places of signal occlusion. In this context, the application of local wireless networks for determining position is a promising alternative solution, although they still suffer from a number of limitations due to energy and IT‐resources. Our research outlines the potential for employing indoor wireless network positioning and sensor‐based systems to improve the collection of tracking data indoors. By applying various methods of GIScience we developed a methodology that can be applicable for diverse human indoor mobility analysis. To show the advantage of the proposed method, we present the result of an experiment that included mobility analysis of 37 participants. We tracked their movements on a university campus over the course of 41 days and demonstrated that their movement behavior can be successfully studied with our proposed method. 相似文献
190.
Concerns related to climate change have resulted in an increasing interest in the importance of hydrological events such as droughts in affecting biogeochemical responses of watersheds. The effects of an unusually dry summer in 2002 had a marked impact on the biogeochemistry of three watersheds in the north‐eastern USA. Chemical, isotopic and hydrological responses with particular emphasis on S dynamics were evaluated for Archer Creek (New York), Sleepers River (Vermont) and Cone Pond (New Hampshire) watersheds. From 1 August to 14 September 2002, all three watersheds had very low precipitation (48 to 69 mm) resulting in either very low or no discharge (mean 0·015, 0·15 and 0·000 mm day?1 for Archer Creek, Sleepers River and Cone Pond, respectively). From 15 September to 31 October 2002, there was a substantial increase in precipitation totals (212, 246 and 198 mm, respectively) with increased discharge. Archer Creek was characterized by a large range of SO42? concentrations (152 to 389 µeq L?1, mean = 273 µeq L?1) and also exhibited the greatest range in δ34S values of SO42? (?1·4 to 8·8 ‰ ). Sleepers River's SO42? concentrations ranged from 136 to 243 µeq L?1 (mean = 167 µeq L?1) and δ34S values of SO42? ranged from 4·0 to 9·0 ‰ . Cone Pond's SO42? concentrations (126–187 µeq L?1, mean = 154 µeq L?1) and δ34S values (2·4 to 4·3 ‰ ) had the smallest ranges of the three watersheds. The range and mean of δ18O‐SO42? values for Archer Creek and Cone Pond were similar (3·0 to 8·9 ‰ , mean = 4·5 ‰ ; 3·9 to 6·3 ‰ , mean = 4·9 ‰ ; respectively) while δ18O‐SO42? values for Sleepers River covered a larger range with a lower mean (1·2 to 10·0 ‰ , mean = 2·5). The difference in Sleepers River chemical and isotopic responses was attributed to weathering reactions contributing SO42?. For Archer Creek wetland areas containing previously reduced S compounds that were reoxidized to SO42? probably provided a substantial source of S. Cone Pond had limited internal S sources and less chemical or isotopic response to storms. Differences among the three watersheds in S biogeochemical responses during these storm events were attributed to differences in S mineral weathering contributions, hydrological pathways and landscape features. Further evaluations of differences and similarities in biogeochemical and hydrological responses among watersheds are needed to predict the impacts of climate change. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献