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181.
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183.
High-performance liquid chromatography-size exclusion chromatography (HPLC-SEC) coupled with a multiple wavelength absorbance detector (200-445 nm) was used in this study to investigate the apparent molecular weight (AMW) distributions of dissolved organic matter (DOM). Standard DOM, namely humic acid, fulvic acid and hydrophilic acid, from the Suwannee River were tested to ascertain the performance and sensitivity of the method. In addition to four compounds groups: humic substances (Peak 1, AMW 16 kD), fulvic acids (Peak 2, AMW 11 kD), low AMW acids (Peak 3, AMW 5 kD), and low AMW neutral and amphiphilic molecules, proteins and their amino acid building blocks (Peak 4, AMW 3 kD), an new group that appears to include low AMW, 6-10 kD, humic substances was found based on investigating the spectra at various elution times. The spectroscopic parameter S>365 (slope at wavelengths >365 nm) was determined to be a good predictor of the AMW of the DOM. The detector wavelength played an important role in evaluating the AMW distribution. For some fractions, such as the humic and low AMW non-aromatic substances, the error in measurement was ±30% as determined by two-dimensional chromatograms detected at an artificially selected wavelength. HPLC-SEC with multiple wavelength absorbance detection was found to be a useful technique for DOM characterization. It characterized the AMW distributions of DOM more accurately and provided additional, potentially important information concerning the properties of DOM with varying AMWs. 相似文献
184.
Receptor modeling for source apportionment of polycyclic aromatic hydrocarbons in urban atmosphere 总被引:1,自引:0,他引:1
Singh KP Malik A Kumar R Saxena P Sinha S 《Environmental monitoring and assessment》2008,136(1-3):183-196
This study reports source apportionment of polycyclic aromatic hydrocarbons (PAHs) in particulate depositions on vegetation
foliages near highway in the urban environment of Lucknow city (India) using the principal components analysis/absolute principal
components scores (PCA/APCS) receptor modeling approach. The multivariate method enables identification of major PAHs sources
along with their quantitative contributions with respect to individual PAH. The PCA identified three major sources of PAHs
viz. combustion, vehicular emissions, and diesel based activities. The PCA/APCS receptor modeling approach revealed that the
combustion sources (natural gas, wood, coal/coke, biomass) contributed 19–97% of various PAHs, vehicular emissions 0–70%,
diesel based sources 0–81% and other miscellaneous sources 0–20% of different PAHs. The contributions of major pyrolytic and
petrogenic sources to the total PAHs were 56 and 42%, respectively. Further, the combustion related sources contribute major
fraction of the carcinogenic PAHs in the study area. High correlation coefficient (R
2 > 0.75 for most PAHs) between the measured and predicted concentrations of PAHs suggests for the applicability of the PCA/APCS
receptor modeling approach for estimation of source contribution to the PAHs in particulates. 相似文献
185.
在我国进一步加强城市治理、大力开展环境与资源保护工作中,提出相关部门需要通力合作,实现"多规合一"的要求。而在"多规合一"中,资源环境承载力及其约束发挥了重要的作用。本文立足于此背景,在阐明资源环境承载力与"多规合一"基本内涵的基础上,结合相关研究资料,重点围绕资源环境承载力约束下的"多规合一"思路进行简要分析研究。 相似文献
186.
Agricultural causes of desertification risk in Minqin, China 总被引:1,自引:0,他引:1
This study uses statistical modeling techniques to develop a desertification risk index (RI) for Minqin County, Gansu Province, China. Twenty socio-economic factors were selected and compared with the RI results to explore the spatial and temporal variability of desertification risk in the study area and to identify possible local driving forces behind desertification risk. The explanatory factors were different in 1988, 1992 and 1997, possibly reflecting the role of temporal variation as a contributor to desertification. The average number of sheep per-household was found to be an important indicator of change in desertification risk, while changes in ridge crop planting area explained the distribution of the rate of change in desertification risk in 1988-1992. The results suggests that the RI was useful in expanding the understanding of spatial temporal desertification issues in Minqin County, as well as identifying a current set of agricultural activities related to desertification risk. Further, given the limited nature of consistent data and observations for the area, development of the RI also served to establish a baseline for future investigations into desertification change and the risks such change might pose for the region. 相似文献
187.
When two or more pool fires happen to burn so close to each other that they interact, they are termed ‘multiple pool fires’ (MPF). Past accident analysis reveals that MPFs occur quite frequently in chemical process industries. Controlled experiments done so far to study MPFs have indicated that MPFs lead to increase in the fuel burning rate, flame height and heat release rate (HRR) but the nature and the extent of the impacts of different factors on these manifestations is as yet poorly understood. In this context computational fluid dynamics (CFD) appears to be a tool which can enable more detailed and realistic simulation of MPFs than other possible approaches, especially due to its ability to closely approximate the underlying physical phenomena. In tank farms there are situations where different storage tanks are placed at different elevations yet close to each other. If such tanks happen to catch fire, the resulting fires may influence each other in a manner that may be a function of the difference in the tanks’ elevation. However no CFD study has been carried out which addresses this type of situation. Hence an attempt has been made to employ CFD to study MPFs involving two pools with fuel surfaces are at different elevations. Results reveal that good correlation is possible between the experimental findings and the CFD simulations. 相似文献
188.
GIS and multiple-criteria evaluation for the optimisation of tsetse fly eradication programmes 总被引:1,自引:0,他引:1
Tsetse flies are the vectors of trypanosomes, the causal agent of trypanosomiasis, a widespread disease of livestock and people
in Africa. Control of tsetse may open vast areas of land to livestock-keeping, with the associated benefits of developing
mixed crop-livestock production systems. However, as well as possible positive impacts there are also risks: bush clearing
would accelerate and cattle numbers would rise, leading to a reduction of vegetation cover, and an increase in runoff and
erosion; there may also be increased pressure on conserved areas and reductions in biodiversity. The objective of this study
is to show how remotely sensed and other environmental data can be combined in a decision support system to help inform tsetse
control programmes in a manner that could be used to limit possible detrimental effects of tsetse control. For Zambia, a methodology
is developed that combines a tree-based decision-support approach with the use of Multiple-Criteria Evaluation (MCE), within
a Geographical Information System (GIS), in order to target areas for tsetse control. The results show clear differentiation
of priority areas under a series of hypothetical scenarios, and some areas (e.g. northwest of Petauke in the Eastern Province
of Zambia) are consistently flagged as high priority for control. It is also demonstrated that priority areas do not comprise
isolated tsetse populations, meaning that disease control using an integrated approach is likely to be more economically viable
than local eradication. 相似文献
189.
Vanessa L. Bonanno Albrecht I. Schulte-Hostedde 《Behavioral ecology and sociobiology》2009,63(6):835-846
Sperm competition is widespread in mammals and occurs when ejaculates from two or more males compete within the female’s reproductive
tract to fertilize the ova. Enlarged testes are associated with sperm competition because they produce sperm, but the accessory
glands produce fluids and proteins that are also important for fertilization success. Sperm morphology can also have consequences
for fertilization success because of its influence on sperm motility. Red squirrels engage in multiple mating, and thus sperm
competition is likely. Here, we assess levels of multiple paternity in a natural population of red squirrels, test the prediction
that testis size is correlated with size of the accessory glands and sperm morphometry, and test the prediction that ejaculate
investment is condition-dependent. Five of six litters (83%) showed evidence of multiple paternity, indicating that sperm
competition is likely to have occurred. Testis size was correlated with the size of all three accessory glands (prostate,
seminal vesicle, epididymides), and there was a generally positive relationship between the size of the accessory glands and
sperm length. Sperm morphology showed significant variation in size and shape among individual male squirrels. There was no
evidence of condition dependence of testis size or the size of the accessory glands, but sperm midpiece length was negatively
related to body condition. Further work should include determining the fitness consequence of variation in sperm morphometry,
testis size, and accessory gland size, and determining the effects of variation in ejaculate investment on sperm motility. 相似文献
190.
Female control of reproductive skew in cooperatively breeding brown jays (<Emphasis Type="Italic">Cyanocorax morio</Emphasis>) 总被引:2,自引:0,他引:2
Brown jays (Cyanocorax morio) are long-lived, social corvids that live in large, stable, territorial groups (mean = 10 individuals). In this study, I determined the distribution of reproductive success within groups using multi-locus DNA fingerprinting. Breeding females produced virtually all (99%) of the young within their own nests. Reproduction within groups was highly skewed towards a single primary female, although long term data indicate that secondary females (female breeders that were usually younger and subordinate to the primary female) were sometimes successful. The high reproductive skew observed for females was associated with primary female aggression. Successful reproduction by secondary females may have been due to parental facilitation or the inability of primary females to completely suppress secondary females. Multiple paternity occurred in 31–43% of broods and extra-group paternity occurred in a minimum of 22% of broods. Patterns of paternity also varied between years, since females often switched or included new genetic mates. Although male consorts of nesting females fathered relatively few offspring (20%), they still had a higher chance of fathering offspring than any other single group male. Reproduction was less skewed for males than females as a result of female mating patterns. Female reproductive patterns are consistent with some of the predictions and assumptions from optimal skew models, while male reproductive patterns are not. The factors affecting skew in species with complex social systems such as incomplete control by breeders over subordinate reproduction, female control of paternity, and resource inheritance have not been well incorporated into reproductive skew models.Communicated by: J. Dickinson 相似文献