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排序方式: 共有138条查询结果,搜索用时 15 毫秒
61.
N. M. Smith S. E. Chambers V. R. Billson I. Laing C. P. West J. E. Bell 《黑龙江环境通报》1993,13(10):945-952
Epignathi are unusual congenital tumours presenting as oropharyngeal masses, often resulting in rapid asphyxia following birth. Occasionally, intracranial extension of the tumour is present, and two such cases are described. The presence of this complication, diagnosable by ultrasound examination, indicates that aggressive surgical treatment is inappropriate. 相似文献
62.
Christopher D. Klingshirn Zachary J. West Matthew J. DeWitt Ashil Higgins John Graham Edwin Corporan 《Journal of the Air & Waste Management Association (1995)》2019,69(8):1003-1013
The use of a two-step thermal-oxidative analysis (TOA) technique for quantification of the mass of total carbon (TC) and elemental carbon (EC) of turbine engine-borne particulate matter (PM) has been evaluated. This approach could be used in lieu of analysis methods which were developed to characterize diluted PM. This effort is of particular interest as turbine engine PM emissions typically have a higher EC content than ambient aerosols, and filter sample mass loadings can be significantly greater than recommended for existing analysis techniques. Analyses were performed under a pure oxygen environment using a two-step temperature profile; reference carbon and actual PM samples were used to identify appropriate analysis conditions. Thermal gravimetric analysis (TGA) methods were used to provide guidance on the nature of the carbon in several of the materials. This was necessary as a standard reference material does not exist for determination of the EC fraction in PM. The TGA also assisted in identifying an appropriate temperature range for the first-stage of the TOA method. Quantification of TC and EC for turbine engine PM samples using TOA was compared to results obtained using the NIOSH 5040 thermal-optical method. For first-stage TOA temperatures of 350°C and 400°C, excellent agreement between the techniques was observed in both the quantified TC and EC, supporting the viability for using TOA for analysis of turbine engine PM samples. A primary benefit of using TOA for these types of PM samples is that filters with relatively high PM mass loadings (sampled at the emission source) can be readily analyzed. In addition, an entire filter sample can be evaluated, as compared to the use of a filter punch sample for the NIOSH technique. While the feasibility of using a TOA method for engine PM samples has been demonstrated, future studies to estimate potential OC charring and oxidation of EC-type material may provide additional data to assess its impact on the OC/EC fractions for other carbon-type measurements.
Implications: This work presents results and procedures of an analytical method for the determination of total and elemental carbon, i.e., TC and EC present in combustion source particulate matter samples. In general, it is shown that the LECO TOA methodology is as reliable and comprehensive as NIOSH 5040 for determining TC and EC carbon types in particulate matter present in turbine emission sources, and should be considered as an alternative. Principles of the methodology, differences, and corresponding agreement with the standard NIOSH 5040 method and TGA analysis are discussed. 相似文献
63.
Size regulation in larvae of the crustacean Balanus eburneus (Cirripedia: Thoracica) 总被引:1,自引:0,他引:1
We tested the hypothesis that larval size in the acorn barnacle Balanus eburneus Gould (Cirripedia Thoracica) varies in relation to food availability. In March–November 1980, and March–July 1981, larvae were obtained from adult Balanus eburneus collected in the Newport River, North Carolina, USA. Carapace length and width of larvae reared at three different food concentrations were measured. Mean naupliar instar size was independent of food concentration. Mean size of the cypris instar increased with increasing food level. Greater cypris size could be attributed to increased food reserves in the preceding naupliar stage, and was coinciden with inmarked increase in metamorphic success. Variation in instar size remained constant or declined during naupliar development, but increased sharply at the molt to the cyprid. Naupliar size regulation involved: (1) conservation of a molt increment specific for each naupliar-naupliar molt, (2) an inverse relationship between premolt size and the molt increment during the first five naupliar instars, and (3) an increase in the precision of the molt increment at the molt to the sixth naupliar instar. Experimental evidence implies that size regulation in Balanus eburneus limits variation about a fixed final naupliar size (e.g. volume). Measurement of naupliar size, accumulated energy reserves, survival and development time, and cypris metamorphic success indicated that naupliar cuticular growth is the most conservative feature of larval development. The data suggest that maximum naupliar size is limited by escalating metabolic costs during development, while minimum naupliar size is limited by size-related feeding effectiveness. 相似文献
64.
Yuping Wu Walter W. Piegorsch R. Webster West Dengfang Tang Maureen O. Petkewich Wei Pan 《Environmental and Ecological Statistics》2006,13(1):125-141
We develop and study multiplicity adjustments for low-dose inferences in environmental risk assessment. Application is intended
for risk analysis studies where human, animal, or ecological data are used to set safe levels of a hazardous environmental
agent. A modern method for making inferences in this setting is known as benchmark analysis, where attention centers on the
dose at which a fixed benchmark level of risk is achieved. Both upper confidence limits on the risk and lower confidence limits
on the “benchmark dose” are of interest. In practice, a number of possible benchmark risks may be under study; if so, corrections
must be applied to adjust the limits for multiplicity. In this note, we discuss approaches for doing so with continuous, nonquantal
response data. 相似文献
65.
Martha L. Sykes Hsueh-Wen Yeh Ian F. West R. W. Gauldie Charles E. Helsley 《Journal of Polymers and the Environment》1994,2(3):201-209
A new method for evaluating biodegradability of starch-based and certain other polymer blends uses the pre- and postexposure stable carbon isotope composition of material coupled with weight loss data to determine which components have degraded. The naturally occurring stable isotope of carbon.13C, is enriched in corn starch (13C, approx. –11) compared to petroleum-derived synthetic polymers (13C, approx. –32). Results on starch-synthetic polymer blends indicate that the 13C signatures of these blends are near-linear mixtures of their component 13C. Values of a 13C for starch-synthetic polymer blends exposed to biologically active laboratory soil and artificial seawater conditions are depleted in13C compared to unexposed samples, suggesting loss of the starch component. Combined with weight loss data for the exposed samples, the 13C values are statistically consistent with models requiring loss of the soluble component glycerin, followed by loss of starch, then petrochemical polymer, or simultaneous loss of starch and petrochemical polymer. Replicate 13C analyses of starch-synthetic polymer blends increase the statistical power of this relatively inexpensive, accessible technique to discriminate between degrading components. 相似文献
66.
Angela M. Leung D. Matthew McDonough C. David West 《Environmental monitoring and assessment》1998,50(1):85-94
The extent of contamination by endosulfans in soil samples collected from the Point Mugu watershed near Oxnard, California was determined using capillary gas chromatography/mass selective detection (GC/MSD). The study was designed to detect three organochlorinated pesticides: endosulfan , endosulfan and endosulfan sulfate. Thirteen sets of two soil samples each were taken from various sites in the region. Our results show that the endosulfan levels in these soils range from trace amounts to nearly 30 ppm, with endosulfan being the most abundant and endosulfan sulfate the least. Two sites of the study, Hueneme and Revolon and Farm and Revolon, showed high amounts of endosulfans and , with concentrations between 20 and 30 ppm. The majority of the other sites studied in this research produced concentrations of less than 10 ppm for each of the three endosulfans monitored. At five areas in particular, Pleasant Valley and Creek, Laguna and Creek, Etting and Creek, Road and Creek and Hueneme and Creek, less than 2 ppm or only trace amounts of endosulfans , and sulfate were detected. 相似文献
67.
D. Jones A.G. Scarlett C.E. West R.A. Frank R. Gieleciak D. Hager J. Pureveen E. Tegelaar S.J. Rowland 《Chemosphere》2013
‘Naphthenic acids’ (NAs) in petroleum produced water and oil sands process water (OSPW), have been implicated in toxicological effects. However, many are not well characterized. A method for fractionation of NAs of an OSPW was used herein and a multi-method characterization of the fractions conducted. 相似文献
68.
69.
Korte NE West OR Liang L Gu B Zutman JL Fernando Q 《Waste management (New York, N.Y.)》2002,22(3):343-349
This report describes the application of palladized iron (Pd/Fe) to the dechlorination of polychlorinted biphenyls (PCBs) at ambient temperature. Experiments supported by congener-specific analyses demonstrated that dechlorination occurs in a step-wise fashion with the meta-chlorines being more reactive than ortho-chlorines. Over the course of the laboratory experiments, complete conversion to biphenyl was observed. The process was also tested with PCBs dissolved in high (40-60%) concentrations of ethanol and isopropanol as a means of simulating solutions generated by commercial soil and solid waste extraction processes. The reaction rate was sensitive to the percentage of solvent but complete dechlorination was still indicated. Tests with soil extracts from a contaminated site demonstrated that there were no apparent interferences from asphalt and other miscellaneous debris. Short-duration tests with highly contaminated PCB solutions from a hazardous waste site demonstrated efficient dechlorination although there was a reduction in reaction rate with time. 相似文献
70.