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51.
Laser microprobe for the study of noble gases and nitrogen in single grains: A case study of individual chondrules from the Dhajala meteorite 总被引:1,自引:0,他引:1
A laser microprobe capable of analysing nitrogen and noble gases in individual grains with masses less than a milligram is
described. It can be used in both continuous wave (CW) mode, useful for stepwise heating of an individual grain, as well as
in pulsed mode, useful for ablating material from a small selected area of a sample, for gas extraction. We could achieve
low blanks (in ccSTP units) for 4He(4.8 x 10{-12}),22Ne(1.0 x 10{-12}),36Ar(1.0 x10
-13),84Kr(2.9 x 10{-14}),132 Xe(2.6 x 10{-14}), and N (87 pg), using this system. Preliminary data for individual chondrules from the Dhajala meteorite show that noble
gases and nitrogen from grains as small as 170 microgram can be analysed using the present laser microprobe setup. The amount
of trapped neon in Dhajala chondrules is very small, and nitrogen in the chondrules is isotopically heavier as compared to
the bulk meteorite. 相似文献
52.
利用光谱反射率估算叶片生化组分和籽粒品质指标研究 总被引:2,自引:0,他引:2
对可见光至短波红外波段(350—2500nm)冬小麦田间冠层光谱反射率与叶片含氮量间的关系进行了相关分析。结果表明,820—1100nm波段的光谱反射率与叶片含氮量极显著正相关;1150—1300hm波段的光谱反射率与叶片含氮量显著正相关,以上两波段为叶片全氮的敏感波段。对各生育时期叶片全氮与其他生化组分的关系进行了回归分析,并建立了相关的回归方程,显著性检验结果表明,方程具有较高的可靠性。小麦的叶片含氮量可以估算其它生化组分及干物质指标含量,开花期叶片含氮量可用来估测籽粒蛋白质和干面筋等品质指标含量。 相似文献
53.
R. G. Derwent W. J. Collins M. E. Jenkin C. E. Johnson D. S. Stevenson 《Journal of Atmospheric Chemistry》2003,44(1):57-95
A global 3-D Lagrangian chemistry-transport model STOCHEM is used to describe the tropospheric distributions of four components of the secondary atmospheric aerosol: nitrate, sulphate, ammonium and organic compounds. The model describes the detailed chemistry of the formation of the acid precursors from the oxidation of SO2, DMS, NOx, NH3 and terpenes and their uptake into the aerosol. Model results are compared in some detail with the available surface observations. Comparisons are made between the global budgets and burdens found in other modelling studies. The global distributions of the total mass of secondary aerosols have been estimated for the pre-industrial, present day and 2030 emissions and large changes have been estimated in the mass fractions of the different secondary aerosol components. 相似文献
54.
S. Solberg T. Krognes F. Stordal OØ Hov H. J. Beine D. A. Jaffe K. C. Clemitshaw S. A. Penkett 《Journal of Atmospheric Chemistry》1997,28(1-3):209-225
Simultaneousindependent measurements of NOy and NOx(NOx= NO + NO2) by high-sensitivitychemiluminescence systems and of PAN (peroxyacetylnitrate) and PPN (peroxypropionyl nitrate) by GC-ECDwere made at Spitsbergen in the Norwegian Arcticduring the first half year of 1994. The average mixingratio of the sum of PAN and PPN (denoted PANs)increased from around 150 pptv in early winter to amaximum of around 500 pptv in late March, whereasepisodic peak values reached 800 pptv. This occurredsimultaneously with a maximum in ozone which increasedto 45–50 ppbv in March–April. The average NOxmixing ratio was 27 pptv and did not show any cyclethrough the period. The NOy mixing ratio showeda maximum in late March, while the difference betweenNOy and PAN decreased during spring. This is anindication of the dominance of PAN in the NOybudget in the Arctic, but possible changes in theefficiency of the NOy converter could alsocontribute to this. Although most PAN in theArctic is believed to be due to long range transport,the observations indicate local loss and formationrates of up to 1–2 pptv h-1 in April–May.Measurements of carbonyl compounds suggest thatacetaldehyde was the dominant, local precursor ofPAN.Now at 1. 相似文献
55.
氮同位素比(^15N/^14N)在地下水氮污染研究中的应用基础 总被引:25,自引:1,他引:25
华北地下水中硝态氮浓度和δ^15N值如下:在自然状态下为4.4≤+5,来自下水道粪便污染者为20-70和+10-+20,受化肥污染者为30-60和-2-+5。因此,氮同位素可用来识别氮污染来源和氮的迁移。 相似文献
56.
土壤干湿交替促进硒酸盐的还原作用 总被引:3,自引:0,他引:3
采集不同类型的新鲜土壤,经处理获得其风干、烘干的样品,重新潮湿后,加入一定量的Na2SeO4溶液,进行了培育实验(incubationexperiments)。实验结果表明,随着土壤干燥程度的增加,硒酸盐还原作用的速度也随之加快。这进一步证实,作为一种地球化学营力的土壤干湿交替,通过对土壤水势(soilwaterpotential)、微生物群落等的影响,间接地促进了硒酸盐还原作用,因而成为硒生物地球化学循环的驱动力之一。 相似文献
57.
I. A. Jaiyeoba 《Journal of Arid Environments》1996,33(4):473-482
Soil was sampled from cropping fields in radial patterns from beneathAcacia albida, Parkia bigloboza(Jacq.) Benth. andEucalyptus camaldulensisDehnh. near Zaria, Nigeria. Results of analysis show a significant coarsening of soil texture and a decrease in organic matter and cation exchange capacity with increasing distance from all three tree species at a depth of 0–15 cm. Concentrations of nitrogen and some exchangeable cations decreased significantly with increasing distance from beneath acacia and parkia, and soil pH decreased with increasing distance from eucalyptus. The implication of the results for land management are discussed in relation to increasing productivity and soil use sustainability. 相似文献
58.
59.
Rate constants for the gas-phase reactions of OH radicals, NO3 radicals and O3 with the C7-carbonyl compounds 4-methylenehex-5-enal [CH2=CHC(=CH2)CH2CH2CHO], (3Z)- and (3E)-4-methylhexa-3,5-dienal [CH2=CHC(CH3)=CHCH2CHO] and 4-methylcyclohex-3-en-1-one, which are products of the atmospheric degradations of myrcene, Z- and E-ocimene and terpinolene, respectively, have been measured at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained (in cm3 molecule–1 s–1 units) were: for 4-methylenehex-5-enal, (1.55 ± 0.15) × 10–10, (4.75 ± 0.35) × 10–13 and (1.46 ± 0.12) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; for (3Z)-4-methylhexa-3,5-dienal: (1.61 ± 0.35) × 10–10, (2.17 ± 0.30) × 10–12, and (4.13 ± 0.81) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; for (3E)-4-methylhexa-3,5-dienal: (2.52 ± 0.65) × 10–10, (1.75 ± 0.27) × 10–12, and (5.36 ± 0.28) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; and for 4-methylcyclohex-3-en-1-one: (1.10 ± 0.19) × 10–10, (1.81 ± 0.35) × 10–12, and (6.98 ± 0.40) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively. These carbonyl compounds are all reactive in the troposphere, with daytime reaction with the OH radical and nighttime reaction with the NO3 radical being predicted to dominate as loss processes and with estimated lifetimes of about an hour or less. 相似文献
60.
The absolute amounts and relative distributions of neutral nitrogen compounds in the Tabei oilfield (e. G. Blocks Ln1-Ln1 1) showed remarkable migration fractionation in the vertical direction. From Ordovician reservoirs (O) to oil legs TⅢ and T Ⅰ of Triassic reservoirs in blocks LN1-LN11, the concentrations of [a] [c] decreased from 1. 59μg/g, 0.49μg/g to 0.17 μg/g (oil). The ratios of various alkylcarbazole isomers, such as 1,8-dimethylcarbazole/nitrogenpartially shielded isomers and 1,8-dimethylcarbazole/nitrogen-exposed isomers, were adopted as the indicators of petroleum migration. The ratios increased from 0.13, 0.20 to 0.67 and from going from the south to the north of the Tabei oilfield, the absolute concentrations of neutral nitrogen compounds decreased drastically, and the nitrogen-shielded isomers were enriched relative to nitrogen-exposed isomers and nitrogen-partially shielded isomers. Crude oils in the Tabei oilfield migrated laterally from the Jilake structure to the Sangtamu fault uplift and Lunnan fault uplift, and crude oils in the same fault uplift migrated and remigrated vertically from Ordovician reservoirs, to oil legs TⅢ to TⅠ of Triassic reservoirs. 相似文献