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N. R. Khisina D. A. Khramov M. V. Kolosov A. A. Kleschev Lawrence A. Taylor 《Physics and Chemistry of Minerals》1995,22(4):241-250
Olivine samples (Fa 11) have been oxidized in air (f O2 = 0.2 atm) at temperatures ranging from 350–700 °C and examined by Mössbauer spectroscopy, transmission electron microscopy, X-ray powder diffraction and thermomagnetic analysis. Oxidation of olivine was found to result in ferriolivine, magnesioferrite (major oxide phase) and magnetite (minor oxide phase) formation. Ferriolivine forms planar (001) precipitates, 0.6 nm in thickness, in the olivine host; the composition is likely to be Mg0.5 v 0.5(Fe3+)1.0SiO4. Magnesioferrite MgFe2O4 exsolves as fine-grained precipitates (5–6 nm in size) filling interstices between the ferriolivine planar precipitates. Oxidation kinetic data at 700 °C show two stages of oxidation corresponding to formation of ferriolivine in the first stage and magnesioferrite in the second stage. The linear rate law with a rate constant k Fol = 1.23 · 10-3 s-1 was found for the first stage whereas a parabolic rate-law with a constant of k oxi = 3.28 · 10-3 s-1 was determined for the second stage of oxidation. It was found that ferriolivine is not an intermediate metastable phase in the oxidation process, terminated by magnesioferrite formation. The ferriolivine and magnesioferrite are considered to have formed by independent reactions which do not necessarily proceed simultaneously. 相似文献
144.
Environmental impact of salmon net-pen culture on marine benthic communities in Maine: A case study 总被引:1,自引:0,他引:1
The environmental impacts of salmon net-pen aquaculture on the benthic environment were investigated at a commercial fish farm located in coastal Maine waters. This site has a sandy mud bottom and low current velocities, is subjected to episodic sediment resuspension, and way in production for 3 yr prior to this study: We examined both the increase in carbon flux to the benthos caused by the net-pen and the effects of the elevated flux on sediment biogeochemistry and the microbenthic communities. The experimental design involved the establishment of two study sites, an ambient site ca. 100 m from the net-pen and a treatment site around the pen. Sediment traps deployed 1 m above the sediment-water interface indicated that carbon flux to the benthos was increased 1-fold to 6-fold (to a maximum of 5 g m?2d?1) at the edge of the net-pen with little or no increase in carbon flux 10 m from the pen. Unlike carbon flux rates, sediment organic matter inventories showed a complex pattern of change over time. Mineral surface area, organic carbon and nitrogen, digestible protein, and sterol content were initially (April 1991) lower beneath the pen than in ambient sediments. During 1991 ambient sediment accumulated organic matter until July after which it decreased, to a low during November. In contrast, organic matter inventories of sediment beneath the pen remained low until July and then increased to a high during November. These latter gains were associated with the development of bacterial mats at the sediment-water interface. Beneath the pen, microbial and macrofaunal communities were shifted toward those commonly associated with organic enrichment but seasonal trends and storm-related resuspension events also significantly affected these sediment communities. When abundant, most epibenthic organisms were more numerous near the pen than in adjacent ambient areas. These results suggest that net-pen aquaculture can alter the benthic ecosystem in Maine Coastal waters but indicate that the effects are spatially limited. 相似文献
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应用模式识别定量划分潜在震源区 总被引:2,自引:0,他引:2
本文以陕西关中及部分邻区为例,考虑地质构造、地震活动及地球物地场等因素,采用不同的模式识别方法和多种计算方案,以定量判定潜在震源区。其结果表明,模式识别方法有利于地质、地震活动及地球物理场等多种因素综合应用,并能选择和显示判定潜有震源区的主要特征。不同模式识别方法的比较和多种试验方案的综合,则可提高潜在震源区判定的可靠性和稳定性。 相似文献
149.
Lawrence R. Heaney 《Climatic change》1991,19(1-2):53-61
Tropical rain forest in Southeast Asia has developed within an extensive archipelago during the past 65 million years or more. During the Miocene (beginning 25 million years BP), rain forest extended much further north (to southern China and Japan); since that time it has contracted. During the Pleistocene (beginning 2.0 million years BP), development of continental glaciers at high latitudes was associated in Southeast Asia with lowered sea level, cooler temperatures, and modified rainfall patterns. Fossil pollen records demonstrate that Southeast Asian vegetation during the last glacial maximum (ca. 18 000 BP) differed substantially from that of today, with an increase in the extent of montane vegetation and savannah and a decline in rain forest. These data show that the distribution and extent of rain forest in Southeast Asia has historically been quite sensitive to climatic change. 相似文献
150.
Yutaka Ishizaka Peter V. Hobbs Lawrence F. Radke 《Journal of Atmospheric Chemistry》1989,9(1-3):149-159
Airborne measurements made during August 1985 over Greenland and its environs show that both accumulation-mode (0.1 m D2.0 m) and giant (D2 m) particles were present in relatively high concentrations in arctic haze layers and that the accumulation-mode particles dominated light scattering. Particles with diameters (D) between 1 and 4 m consisted predominately of mixed materials, small and dense inclusions, and probably organic compounds containing sulfur. Many of the particles from 0.1 to 1 m in diameter were also of mixed composition, with sulfuric acid, ammonium sulfate and organics probably the dominant constituents. 相似文献