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1.
We have analysed X-ray spectra of 13 solar flares as obtained by the Bent Crystal Spectrometer (BCS) on the Solar Maximum Mission. In particular, we have examined the observed ratio of T
Fe/T
Ca where T
Fe and T
Ca are the temperatures obtained from the Fexxv and Caxix spectra, respectively. In order to simplify the investigation we have analysed only flares which reach quasi-steady-state during the decay. It turned out that the observed ratios cannot be explained by a model consisting of a single, uniformly heated loop, with a constant or variable cross-sectional area. We propose that this problem may be solved by introducing some distribution of the heating function across the flaring loop. This model has been tested by detailed calculations. 相似文献
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Kristine L. Delong Suyapa Gonzalez Jeffrey B. Obelcz Jonathan T. Truong Samuel J. Bentley Sr Kehui Xu Carl A. Reese Grant L. Harley Alicia Caporaso Zhixiong Shen Beth A. Middleton 《Boreas: An International Journal of Quaternary Research》2021,50(3):871-892
Approximately 13 km south of Gulf Shores, Alabama (United States), divers found in situ baldcypress (Taxodium distichum) stumps 18 m below the ocean surface. These trees could have only lived when sea level fell during the Pleistocene subaerially exposing the tectonically stable continental shelf. Here we investigate the geophysical properties along with microfossil and stratigraphical analyses of sediment cores to understand the factors that lead to this wood’s preservation. The stumps are exposed in an elongated depression (~100 m long, ~1 m deep) nested in a trough of the northwest–southeast trending Holocene sand ridges and troughs with 2–5 m vertical relief and ~0.5 km wavelength. Radiocarbon ages of the wood were infinite thus optically stimulated luminescence (OSL) dating was used to constrain the site’s age. Below the Holocene sands (~0.1–4 m thick), separated by a regional erosional unconformity, are Late Pleistocene mud-peat (72±8 ka OSL), mud-sand (63±5, 73±6 ka OSL), and palaeosol (56±5 ka OSL) facies that grade laterally from west to east, respectively. Foraminiferal analysis reveals the location of the terrestrial-marine transitional layer above the Pleistocene facies in an interbedded sand and mud facies (3940±30 (1σ) 14C a BP), which is part of a lower shoreface or marine-dominated estuarine environment. The occurrence of palaeosol and swamp facies of broadly similar ages and elevation suggests the glacial landscape possessed topographic relief that allowed wood, mud and peats to be preserved for ~50 ka of subaerial exposure before transitioning to the modern marine environment. We hypothesize that rapid sea-level rise occurring ~60 or ~40 ka ago provided opportunities for local flood-plain aggradation to bury the swamp thus preserving the stumps and that other sites may exist in the northern Gulf of Mexico shelf. 相似文献
4.
A group of three large curvilinear ridges, called the Barra Volcanic Ridge System, has been mapped in the acoustic basement of southern Rockall Trough. Typically, each ridge is about 2 km high and 20 km wide at its base. A crudely-layered acoustic character, moderate density but high strength of magnetisation point to a volcanic-sedimentary (ash?) composition for the ridges. Seismic continuity with the acoustic basement of the rest of Rockall Trough suggests that the trough basement is of similar composition. An age for the ridges of Lower Cretaceous is indicated by well ties and consideration of regional geology. Volumetrically, the ridges are on the scale of hot spot features such as the Wyville-Thomson Ridge. 相似文献
5.
Partitioning of heavy metals on soil samples from column tests 总被引:3,自引:0,他引:3
R. N. Yong W. Z. W. Yaacob S. P. Bentley C. Harris B. K. Tan 《Engineering Geology》2001,60(1-4):307-322
In this study, column tests were used to determine the retention capability of three types of estuarine alluvia collected adjacent to landfill sites in South Wales. Selective sequential extraction (SSE) was used to study the retention mechanisms of heavy metals in the soil columns obtained from leaching experiments. Acid digestion was later used to check the validity of the SSE results. Breakthrough curves show good retention of heavy metal ions (Pb, Cu, and Zn) by all soils, where almost 99% of heavy metals were retained with the Ce/Co values in the order of 10−3. The retention strength of these soils was observed to be constant up to five pore volumes (PV). This corresponds with the pH of the effluents and pore water of soil slices, which also show good buffering capacity against very acidic leachate up to 5PV. The heavy metal extraction profiles from SSE show very similar trends with the retention profiles from the leaching experiments, where heavy metals were retained mainly at the top part where the leachate entered the column. SSE indicates qualitatively that heavy metals precipitated with carbonates and amorphous materials (oxides/hydroxides) are higher than heavy metal retention via exchangeable mechanisms. The mass balance calculation gives range of deviation of 1–16% of the total soil extraction. The distribution of the heavy metals with various soil constituents are ranked in the following order: Carbonates>Amorphous oxides hydroxides>Organic matter>Exchangeable phases. 相似文献
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Elizabeth A. V. Mackie Jeremy M. Lloyd Melanie J. Leng Michael J. Bentley Carol Arrowsmith 《第四纪科学杂志》2007,22(6):579-591
Carbon isotopes (δ13C) and C/N ratios from bulk organic matter have recently been used as alternative proxies for relative sea‐level (RSL) reconstruction where there are problems associated with conventional biological indictors. A previous study on a single isolation basin (Upper Loch nan Eala) in northwest Scotland has shown a clear relationship between δ13C, C/N ratios and palaeosalinity from Younger Dryas and Holocene aged sediments. In this paper we present results of δ13C and C/N ratio analyses from other isolation basins in northwest Scotland over the Holocene and the Lateglacial period in order to validate this technique. The results from the Holocene sequences support the earlier findings that this technique can be used to identify RSL change from isolation basins over the Holocene in this region. The relationship between δ13C, C/N ratios and RSL change is not apparent in sediments of Lateglacial age. Other environmental variables such as atmospheric CO2 concentration, poor vegetation development and temperature influence δ13C values during this period. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
8.
Liaqat Ali Russell E. Bentley Alberto A. Gutierrez Yosmar Gonzalez 《Acta Geotechnica》2014,9(1):135-144
The use of slickline distributed temperature sensing (SL-DTS) technology is becoming widespread due to its ease of operation and ability to acquire real-time multiple temperature traces inside the wellbore. Injection of treated acid gas (TAG)—a mixture of CO2 and H2S—into geologic formations has become an attractive technical and economic option for oil and gas producers and processors who are faced with regulations concerning excess sulfur and greenhouse gas emissions. Acid gas injection (AGI) into geologic formations is more economical and more flexible in dealing with varying TAG compositions than sulfur recovery units (SRUs) using the Claus process. SRUs do not achieve air quality standards and have high operation and maintenance costs. In addition, there is low demand for sulfur and sulfur disposal costs are high. The results of the analysis of SL-DTS data acquired in conjunction with step rate and pressure falloff (PFO) tests are presented in this paper. These tests were conducted to evaluate the injection potential of geologic formations. The injection zone consisted of a carbonate formation characterized by Karst features, vugs, and natural fractures. The SL-DTS data during the initial injection flow rate for the step rate test (SRT) indicated that high permeability zones accepted fluid at lower injection rates. An increasing number of discrete zones began to accept fluid as the injection rate was increased. The results of the SRT provided the fracture pressure of the formation. This information was used to design an AGI program that would avoid fracturing the formation while allowing for the required volume of TAG to be injected. The results of the PFO test provided information on the reservoir pressure and permeability and also indicated the presence of one or more hydraulic fractures. This case study of SL-DTS measurements made during a SRT and a PFO test for the design of an AGI well provides valuable insights into the potential of DTS technology and its use in AGI and carbon capture/sequestration (CCS) operations. Its findings could be applied to analyze injection potential of geological formations not only for AGI projects but also for CCS, and CO2 enhanced oil recovery opportunities. 相似文献
9.
Peter Wilson Michael J. Bentley Christoph Schnabel Richard Clark Sheng Xu 《第四纪科学杂志》2008,23(5):461-473
Cosmogenic isotope (10Be and 26Al) surface exposure dating has been applied to valley‐axis and hillslope stone runs (relict periglacial block streams) and their source outcrops in the Falkland Islands, South Atlantic. The data indicate that stone runs are considerably older landforms than previously envisaged and afford no evidence that they are a product of the Last Glacial Maximum; the samples range in apparent 10Be age from 42k to 731k yr BP, but some of these are minima. The results indicate that valley‐axis stone runs may be up to 700–800k yr old, have simple exposure histories and are composite landforms that developed over several cold stages. Analyses of some hillslope and outcrop samples also demonstrate simple exposure histories with 10Be ages from 42k to 658k yr BP. In contrast, isotopic ratios from other hillslope and outcrop samples reveal they have had a complex exposure history involving periods of burial or shielding; the samples range in 10Be age from 59k to 569k yr BP and these are regarded as minimum age estimates. Larger stone runs may be older than smaller runs and there is a possibility that stone runs older than 800k yr exist in other parts of the Falklands. The assertion that glaciation in the Falklands was restricted to the highest uplands is supported by the data, and the potential for age determination of other boulder‐strewn and bedrock landforms, using cosmogenic isotope analysis, in order to extend the geochronology of Quaternary events and processes is noted. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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