排序方式： 共有10条查询结果，搜索用时 15 毫秒
1
1.
2.
Analysis of a sediment core for hydrolysed chlorins (acidic chlorins e.g. pheophorbide a) and non-acidic chlorins, and free, bound and esterified alcohols have been performed and the results have been interpreted in terms of input and sedimentary interconversions. There is an association of the acidic chlorin input with an input of unesterified aliphatic n-alkanols (> C20), and subsequent degradation of the chlorins with depth. Input of phytol to the anoxic region of the sediment is not associated with the n-alkanols:phytol in the sediment is derived largely from chlorophyll-a input to the surface layers as intact microalgae. Degradation with depth involves conversion of the chlorophyll-a to non-chlorin, colourless phytyl esters prior to incorporation of the phytol into a bound fraction. At depth this bound phytol is hydrolysed resulting in release of free phytol. 相似文献
3.
This paper reports the initial steps in the degradation of chlorophyll-a in a temperate, sandy intertidal sediment from a low-energy coastline at Corner Inlet, SE. Victoria. The chlorophyll-a is shown to be derived primarily from diatom input into the surface layers and it is possible to show that in this environment, relative stabilities are: chlorophyll-a > chlorophyllide-C2 > chlorophyllide-C1. Traces only of chlorophyll-b are present, and little or no degradation of this pigment with depth was observed. Bacteriochlorophyll-a, bacteriopheophytin-a concentrations are inversely proportional to one another in the upper sedimentary layers and the depth profile suggests a stabilised environment. A depth profile of a range of chlorophyll-a derivatives, including pheophytin-a, provides no basis for accepting that they are intermediates on the direct degradative pathway of chlorophyll-a in this environment. Rather, the evidence favours the view that chlorophyll-a degrades primarily to colourless compounds. 相似文献
4.
Dario Alf G. David Price Michael J. Gillan 《Physics of the Earth and Planetary Interiors》1999,110(3-4):191-210
First-principles electronic structure calculations based on DFT have been used to study the thermodynamic, structural and transport properties of solid solutions and liquid alloys of iron and oxygen at Earth's core conditions. Aims of the work are to determine the oxygen concentration needed to account for the inferred density in the outer core, to probe the stability of the liquid against phase separation, to interpret the bonding in the liquid, and to find out whether the viscosity differs significantly from that of pure liquid iron at the same conditions. It is shown that the required concentration of oxygen is in the region 25–30 mol%, and evidence is presented for phase stability at these conditions. The Fe/O bonding is partly ionic, but with a strong covalent component. The viscosity is lower than that of pure liquid iron at Earth's core conditions. It is shown that earlier first-principles calculations indicating very large enthalpies of formation of solid solutions may need reinterpretation, since the assumed crystal structures are not the most stable at the oxygen concentration of interest. 相似文献
5.
ROBERT O''BRIEN BIMAL K.SINHA WILLIAM P.SMITH Statistical Policy Branch Environmental Protection Agency M St. SW Washington DC U.S.A. 《地理学报(英文版)》1991,(3)
The object of this paper is to develop a suitable statistical procedure to evaluate clean-up standards athazardous waste sites.Under the assumptions that contaminant masses at a site follow a gammadistribution and that the data from the pre-remediation baseline sample as well as from the interim orfinal sample taken after a certain period of operation are both distributed as gamma with the same shapeparameter but different scale parameters,we derive a uniformly most powerful unbiased test of thehypothesis that a specified percentage of contaminant mass has been reduced.A large-sampleapproximation of the exact test procedure and a comparison with the likelihood ratio test are provided. 相似文献
6.
The abundance of sterols in sediment depth profiles is determined by variations in input source abundances and diagenesis. Deconvolution of these variables would permit accurate estimation of degradation rates and initial input source contributions of sterols to the sediments. In this study we have demonstrated the application of a simple mathematical approach to the estimation of the relative stabilities of a range of sterols in a microbially-poor temperate intertidal sediment. The results indicate that st-5-enols and possibly 4-methyl sterols are less stable than other sterols in this environment. Since dehydration reactions of sterols would be favoured by both a 4-methyl substituent and a C5,6 double bond, whilst other processes would not be as selective, it seems probable that this abiological process predominates in the Corner Inlet sediments. 相似文献
7.
Can the Earth's dynamo run on heat alone? 总被引：1，自引：0，他引：1
David Gubbins Dario Alfè Guy Masters G. David Price M. J. Gillan 《Geophysical Journal International》2003,155(2):609-622
8.
Links between bacterial communities in marine sediments and trace metal geochemistry as measured by in situ DET/DGT approaches 总被引：1，自引：0，他引：1
Gillan DC Baeyens W Bechara R Billon G Denis K Grosjean P Leermakers M Lesven L Pede A Sabbe K Gao Y 《Marine pollution bulletin》2012,64(2):353-362
Our current view about the relationship between metals and bacteria in marine sediments might be biased because most studies only use ex situ approaches to quantify metals. The aim of the present research was to compare ex situ and in situ methods of metal measurement (DET and DGT--diffusive equilibration or diffusive gradients in thin-films) and relate the results with two commonly used microbiological variables (bacterial biomass and bacterial diversity as revealed by DGGE). No previous studies have used such in situ approaches in microbial ecology. For biomass and most of the investigated trace metals (Ag, Cd, Sn, Cr, Ni, Cu, Pb, and Al) no significant correlations were found. The exceptions were Fe, Mn, Co, and As which behave like micronutrients. For bacterial diversity, no relevant relationships were found. We conclude that in situ methods are more adapted tools for microbial ecologists but that ex situ approaches are still necessary. 相似文献
9.
Samples from a sediment core collected in Bowling Green Bay, North Queensland have been analysed for hexane/isopropanol extractable lipids and fatty acids. These data revealed a subsurface lipid abundance maximum at 3–4 cm depth and consistent low total fatty acid abundances (ca 2 μg/g) in the deeper samples ( > 10 cm depth). Lipid phosphate was below the level of detection in all the samples. Bacterial community structure was found to vary markedly in the upper 10 cm of the core, with the 18:1Δ11 bacterial chemotype predominant in the surface sediment and trans-acid chemotypes dominating in the 3–4 cm depth sediment. Based on the fatty acid composition, the bacterial biomass was estimated to vary from 199 μg/g at 3–4 cm depth toca 8 μg/g at 11–13 cm depth, although the fatty acid distributions indicated possible interference from protozoan detritus. In order to test this possibility, a surface sediment sample from a nearby site was extracted and analysed for fatty acids in lipid fractions separated by silica column chromatography. The fatty acid distributions in lipid fractions containing wax/steryl esters, triacylglycerols, glycolipids and phospholipids were markedly different. These analyses were interpreted in terms of fatty acid contributions to the extractable lipids from bacteria, cyanobacteria, protozoan detritus and highly degraded organic matter. 相似文献
10.
J.K. Volkman R.B. Johns F.T. Gillan G.J. Perry H.J. Bavor 《Geochimica et cosmochimica acta》1980,44(8):1133-1143
A detailed study has been made of the solvent extractable monocarboxylic, dicarboxylic and hydroxylated fatty acids and n-alkanes in a surface intertidal sediment, and the distributions compared to microorganisms cultured from the sediment. Diatoms are shown to contribute most of the monocarboxylic acids, particularly the significant amounts of polyunsaturated acids present, and a small proportion of the n-alkanes. Bacteria contribute between 11 and 14% of the monocarboxylic acids and markers for this, including trans-monounsaturated acids, are proposed. Detritus from the sea-grass Zostera muelleri is a major source of the α-hydroxy-, ω-hydroxy and α,ω-dicarboxylic acids in the sediment and a minor contributor of n-alkanes and long-chain fatty acids. 相似文献
1