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131.
Determination by neutron activation of 6 trace elements retained in Allende (C3) samples heated at 400–1000°C for 1 week in a low-pressure (initially ~10?5 atm H2) atmosphere reveals loss of small proportions of Ga and Se and large proportions of Bi, In and Tl-Co being unaffected. The retentivity patterns for the 5 volatile elements differ and in no way duplicate a step-function. In contrast to these trace elements, sulfur is initially present in discrete mineral(s) and visually it appears to be released over a narrow temperature range. Elements are lost more easily from powder than from chips but the difference is ≤35 per cent. Above 600°C, the process of loss appears due to process(es) with apparent activation energies of 2 kcal/mole (Bi, Tl), 4 kcal/mole (Se) and 22 kcal/mole (In). Loss of Bi, Se and Tl below 600°C involves higher apparent activation energies. Two-element correlation diagrams involving Bi, In and Tl are consistent with the idea that trends among highly-volatile elements in enstatite chondrites arise from metamorphism. 相似文献
132.
John Van Sickle Walter C. Weimer David P. Larsen 《Geochimica et cosmochimica acta》1983,47(12):2189-2197
Rates of surficial sediment mixing and sediment burial are measured in Shagawa Lake, Minnesota, using radionuclide tracers. Based on 106Ru profiles in 16 cores, mixing rates average 13 cm2/yr within the upper 9 cm of sediment. Two other nuclides, 210Pb and 137Cs, provide further evidence for calculation of mixing rates. In addition, 210Pb profiles estimate sediment burial rates (about 0.4 cm/yr). Mixing estimates are shown to be fairly insensitive both to uncertainties in sediment burial rates and to temporal patterns of 106Ru deposition. 相似文献
133.
134.
S.V.S. Murty P.S. Goel D.Vu. Minh Yu.A. Shukolyukov 《Geochimica et cosmochimica acta》1983,47(6):1061-1068
Total nitrogen, measured by neutron activation analysis, is highly enriched in residues from iron meteorites obtained by dissolution of the metal in dilute H2SO4, relative to the bulk value. On the average, the residues, representing 3% mass, contain 22% of total N. Group IA has more dissolved N than IIIA. Lithium and Ir show a distribution pattern parallel to N. Total Xe has been measured in several residues and its isotopic composition is, similar to atmospheric Xe for mass numbers 131 to 136 but not for 124Xe and 126Xe which are strongly depleted in the non-magnetic residues. It is suggested that iron meteorites have trapped in their micro-inclusions, some pre-solar nebular matter which is isotopically heterogeneous. 相似文献
135.
The distributions of steroid and triterpenoid hydrocarbons in crude oils and sedimentary rock extracts can be routinely determined by the direct injection of the sample into a gas chromatograph coupled to a mass spectrometer (GC-MS). The mass spectrometer is operated at a resolution of about 2500 (10% valley), and only the ion intensities at selected accurate mass values, diagnostic of the structural types of interest, are monitored throughout the analysis. The distributions, so obtained, find application in the assessment of the source and thermal maturity of crude oil accumulations in the subsurface. This technique eliminates chromatographic separation steps and combines two analyses in one. Thus, more geological samples and reference mixtures may be analyzed in a given time. 相似文献
136.
B. Gururaj J.P. Sharma A. Baldawa S.C.D. Arora N. Prasad A.K. Biswas 《International Journal of Mineral Processing》1983,11(4):285-302
Studies have been made on the separability of clay minerals such as kaolinite, illite and montmorillonite from hematite in dispersant-starch flocculant systems. The grossly different dispersibility of hematite from that of clay minerals aided separation by selective dispersion and flocculation. Moderate success has been achieved with a selectivity index nearing 4.0 (average recovery values around 80%).The studies have been extended to hematite recovery and clay rejection from the slimes of the Barsua iron ore washing plant owned by Rourkela Steel Plant, India. Limited success achieved in the starch selective flocculation method has been attributed to the difficulties associated with fine grain size, clay mineraloty and liberation.The ore exhibits the phenomenon of differential grinding. Hematite-rich coarser particles in the slime can be separated by differential settling in dispersant systems followed by selective flocculation in low-starch systems. 相似文献
137.
John K. Volkman Robert Alexander Robert Ian Kagi Garry Wayne Woodhouse 《Geochimica et cosmochimica acta》1983,47(4):785-794
Analyses of some Australian crude oils show that many contain varying concentrations of A/ B-ring demethylated hopanes. These range from C26 to C34 and have been identified from their retention times and mass spectral data as 17α(H)-25-norhopanes. Comparison of hopane and demethylated hopane concentrations and distributions in source-related, biodegraded oils suggests that demethylated hopanes are biotransformation products of the hopanes. Further, it appears that the process occurs at a late stage of biodegradation, after partial degradation of steranes has occurred. Demethylated hopanes are proposed as biomarkers for this stage of severe biodegradation. The presence of these compounds in apparently undegraded crude oils is thought to be due to the presence of biodegraded crude oil residues which have been dissolved by the undegraded crude oil during accumulation in the reservoir sands. The timing of hopane demethylation, relative to the degradation of other compounds, has been assessed and the progressive changes in crude oil composition with increasing extent of biodegradation have been identified. The use of demethylated hopanes as maturity parameters for severely biodegraded crude oils, and the applicability of established biomarker maturity parameters to such oils, are also discussed. 相似文献
138.
Christine Milligan 《New Zealand geographer》2005,61(3):213-224
Abstract: To date, narrative correspondence has been relatively neglected as a geographical research method. This is particularly true within the subdiscipline of health geography. Drawing on the literature on narrative approaches, as well as a qualitative study of informal carers' experiences of transitions in the place of care for older people in New Zealand, this paper highlights the valuable insights this approach can offer into the interrelationship between people, place and care. More specifically, it explores how caring identities and care related behaviour are constructed and reconstructed over time and space. 相似文献
139.
测绘市场的依法管理,是促进测绘事业健康发展的重要工作,因此要充分分析测绘工作的基本特征和发展趋势,使测绘市场管理走向规范、服务和促进测绘事业发展的正常轨道。 相似文献
140.
对南充—万州四川段500 kV送电线路工程建设诱发、加剧地质灾害的可能性及工程建设本身遭受的地质灾害以及对建设用地的适宜性作了评价,并提出防治措施建议。 相似文献