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排序方式: 共有116条查询结果,搜索用时 15 毫秒
31.
32.
Rogers F Arnott P Zielinska B Sagebiel J Kelly KE Wagner D Lighty JS Sarofim AF 《Journal of the Air & Waste Management Association (1995)》2005,55(5):583-593
Particulate-phase exhaust properties from two different types of ground-based jet aircraft engines--high-thrust and turboshaft--were studied with real-time instruments on a portable pallet and additional time-integrated sampling devices. The real-time instruments successfully characterized rapidly changing particulate mass, light absorption, and polycyclic aromatic hydrocarbon (PAH) content. The integrated measurements included particulate-size distributions, PAH, and carbon concentrations for an entire test run (i.e., "run-integrated" measurements). In all cases, the particle-size distributions showed single modes peaking at 20-40nm diameter. Measurements of exhaust from high-thrust F404 engines showed relatively low-light absorption compared with exhaust from a turboshaft engine. Particulate-phase PAH measurements generally varied in phase with both net particulate mass and with light-absorbing particulate concentrations. Unexplained response behavior sometimes occurred with the real-time PAH analyzer, although on average the real-time and integrated PAH methods agreed within the same order of magnitude found in earlier investigations. 相似文献
33.
James W. Falco Pat C. Kerr Michael B. Barron Donald L. Brockway 《Ecological modelling》1975,1(2):117-131
A model is proposed to account for mass transport limitation to the uptake of major nutrients. A thin film diffusion resistance layer is hypothesized. In an example using Cyclotella nana (a diatom), diffusion resistance was calculated to result in a maximum decrease of 40% in phosphorus uptake rate. Transport limitation was demonstrated experimentally. The growth of Chlorella pyrenoidosa (a green alga) was found to be stimulated by shaking the cultures.Using similar mathematical techniques, the internal resistance to the uptake of nutrients in algal cell aggregates was also modeled. 相似文献
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35.
Pat M. Fidopiastis Daniel J. Bezdek Michael H. Horn Judith S. Kandel 《Marine Biology》2006,148(3):631-642
The zebraperch, Hermosilla azurea Jenkins and Evermann, a warm-temperate marine fish species with a strictly macroalgal diet, has a relatively long digestive
tract with an enlarged hindgut and an associated blind caecum (HC). In zebraperch sampled off Santa Catalina Island, California
(33°19′42′′N; 118°18′37′′W) in years 1995 through 2001, direct cell counts, gut epithelium assessment of bacterial attachment,
and short-chain fatty acid (SCFA) analyses verified that the zebraperch HC possesses a dense and morphologically diverse,
fermentative microbiota. Bacterial cell counts and morphological diversity were significantly higher in HC contents compared
to anterior gut regions, suggesting that microbial populations were growing along the digestive tract. Similarly, electron
micrographs of the HC epithelium revealed attached microbes, further supporting the possibility that these organisms constitute
resident microbiota. Five different SCFAs were detected in all three regions of the digestive tract, but levels were up to
three times greater in HC contents. Acetate was consistently the prevailing SCFA in all gut regions. Sequence analysis of
bacterial 16S rDNA was used to identify predominant bacterial groups in HC contents. Of the seven main bacterial types identified,
Enterovibrio spp. were the dominant bacteria in HC contents followed by species of Bacteroides,Faecalibacterium, and Desulfovibrio. Taken together, our findings show that the zebraperch HC harbors a consortium of microbes that appears to assist in the
breakdown of algal polysaccharides in the herbivorous diet of the fish. 相似文献
36.
Koh YK Chiu TY Boobis AR Cartmell E Pollard SJ Scrimshaw MD Lester JN 《Chemosphere》2008,73(4):551-556
This paper presents a method for the determination of alkylphenols, alkylphenol polyethoxylates (APEO) and alkylphenol ethoxycarboxylates (APEC) in the aqueous and particulate phase of wastewater samples. Quantification was achieved by liquid chromatography-tandem mass spectrometry. The sensitivity of the method is demonstrated by low detection limits, in the dissolved phase 1.2-9.6ngl(-1) for alkylphenol, AP(1-3)EO and APEC and 0.1-4.1ngl(-1) for longer chain alkylphenol polyethoxylates. The method detection limit for particulate phase samples ranged from 6 to 60ngg(-1) for AP, AP(1-3)EO and APEC; with the longer chain APEO being from 0.5 to 20ngg(-1). Matrix effects were noted in complex matrix rich samples. There was a distinct change in the distribution of alkylphenol ethoxylates during biological treatment of the wastewater, with the major biotransformation products observed being carboxylated derivatives at concentrations of up to 1768ngl(-1). Shorter chain APEO were present in higher proportions in the suspended solids, due to their higher affinity to particulate matter compared to the long-chain oligomers. 相似文献
37.
Spatial concentration distribution of a chemical in an indoor environment is an important factor in the evaluation of chemical nuisances. However, straightforward techniques for the determination of this distribution are not very common and usually limited in their application. Sorptive sampling using polydimethylsiloxane-coated stir bars and the combination of active and diffusive sampling were shown to allow uncomplicated spatial concentration profiling of multiple compounds in an indoor environment. The validity of the approach was demonstrated in the analysis of the spatial concentration distribution of a pyrethroid insecticide in a common bedroom. The relative concentrations of allethrin and piperonyl butoxide were profiled throughout the room upon the application of an insecticide vaporizer. 相似文献
38.
Jack Charteris Pat A. Scott 《International journal of occupational safety and ergonomics》2013,19(4):336-346
Occupational back stress among manual workers in South Africa is now a cause of governmental concern. Yet no data on the back strength of the South African workforce have been published. This study represents a first step in reporting the trunk strength of Xhosa workers in South Africa, in absolute and size-relative terms. Thirty-five male manual workers were tested isometrically while making maximal extension and flexion efforts at 0°, 23°, 46°, 69°, and 92° of stoop. The results show nonlinearity of the extensor-to-flexor (E/F) ratio of the trunk musculature. The E/F ratio increases in deep stoop because of a drop in flexor torques. The data suggest that predictions of flexor from extensor torques or vice versa can confidently be made so long as testing is done away from the fully flexed position. Significant differences between morphologically gracile and robust workers in this sample are discussed. The study has implications for occupational rehabilitation and for prophylaxis, for whereas muscular strength alone may not protect the spine from occupational injury, muscular weakness certainly predisposes it. 相似文献
39.
The biological action of ionizing radiation 总被引:1,自引:0,他引:1
E C Pollard 《American scientist》1969,57(2):206-236
40.
The humanitarian system has grown organically over the course of a generation to become a complex system bound by a common primary mandate. Its guiding principles provide it with a unique identity and separate humanitarian actors from other aid-related stakeholders. However, all of the evidence suggests that humanitarian actors will extend their reach and engage in new and unprecedented ways with an expanded mandate in years to come. Now, more than ever, they are challenged to retain the moral high ground and to put disaster-affected people at the centre of humanitarian action. Consequently, this paper proposes that the humanitarian system introduce a new principle: humanitarian subsidiarity. It moves the conception of subsidiarity beyond meanings ascribed by the Catholic Church and the European Union and links it instead to the attributes of agency, accountability, and trust to find accommodation with the core humanitarian principles of humanity, impartiality, neutrality, and independence. 相似文献