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101.
102.
An increase in the transmission of solar radiation in the UV-B region (specifically, 290–320 nm) is expected to occur as a result of anthropogenic degradation of stratospheric ozone. The potential impact of increased levels of UV-B radiation upon the biosphere is of ecological concern. In a previous study a community of estuarine organisms received a daily exposure to a simulated solar spectrum enhanced in UV-B radiation for a period of six weeks. A dominant species of diatom growing at the surface of these communities was isolated and identified to beMelosira nummuloides. Short chains of this diatom were irradiated for a four-hour period on each of three consecutive days. Fluorescent sunlamps filtered by a 290 nm cut-off filter (0.13–0.50 mm cellulose acetate) or a 315 nm cut-off filter (0.13mm Mylar ‘S’) provided a range of fluence which closely approximated natural fluence levels. A least squares regression analysis of the number of cell divisions on the biologically weighted fluence indicated a significant depression in the growth of this species by radiation in the 290–320 nm waveband. 相似文献
103.
C. L. Brogan T. R. Hunter R. Indebetouw C. J. Chandler Y. L. Shirley R. Rao A. P. Sarma 《Astrophysics and Space Science》2008,313(1-3):53-57
We describe results from recent Submillimeter Array observations of massive protostellar objects (CepheusA-East, NGC7538 IRS1,
and G5.89-0.39) with resolutions ranging from 0.8″ to 2″. A wide range of spectral and continuum properties are observed,
with one unifying theme: at these resolutions all of the studied sources reveal multiple submillimeter cores. Some are observed
to have cm-wavelength counterparts, and others not, suggesting a range of evolutionary stages coexisting in close proximity.
In the presence of such complexity and multiplicity of sources, these data suggest that the interpretation of diagnostics
such as kinematic velocity gradients and temperatures that are strongly dependent on spatial resolution should be approached
cautiously. 相似文献
104.
105.
Hydroxyl and Peroxy Radical Chemistry in a Rural Area of Central Pennsylvania: Observations and Model Comparisons 总被引:2,自引:0,他引:2
Xinrong?RenEmail author William?H.?Brune Christopher?A.?Cantrell Gavin?D.?Edwards Terry?Shirley Andrew?R.?Metcalf Robert?L.?Lesher 《Journal of Atmospheric Chemistry》2005,52(3):231-257
Atmospheric hydroxyl (OH), hydroperoxy (HO2), total peroxy (HO2 and organic peroxy radicals, RO2) mixing ratios and OH reactivity (first order OH loss rate) were measured at a rural site in central Pennsylvania during
May and June 2002. OH and HO2 mixing ratios were measured with laser induced fluorescence (LIF); HO2
+ RO2 mixing ratios were measured with chemical ionization mass spectrometry (CIMS). The daytime maximum mixing ratios were up
to 0.6 parts per trillion by volume (pptv) for OH, 30 pptv for HO2, and 45 pptv for HO2 + RO2. A parameterized RACM (Regional Atmospheric Chemistry Mechanism) box model was used to predict steady state OH, HO2 and HO2 + RO2 concentrations by constraining the model to the measured OH reactivity and previously measured volatile organic compound
(VOC) distributions. The averaged model calculations are generally in good agreement with the observations. For OH, the model
matched the observations for day and night, with an average observed-to-modeled ratio of 0.80. In previous studies such as
PROPHET98, nighttime NO was near 0 pptv and observed nighttime OH was significantly larger than modeled OH. In this study,
nighttime observed and modeled OH agree to within measurement and model uncertainties because the main source of the nighttime
OH was the reaction HO2 + NO → OH + NO2, with the NO being continually emitted from the surrounding fertilized corn field. The observed-to-modeled ratio for HO2 is 1.0 on average, although daytime HO2 is underpredicted by a factor of 1.2 and nighttime HO2 is over-predicted by a factor of ∼2. The average measured and modeled HO2 + RO2 agree well during daytime, but the modeled value is about twice the measured value during nighttime. While measured HO2 + RO2 values agree with modeled values for NO mixing ratios less than a few parts per billion by volume (ppbv), it increases substantially
above the expected value for NO greater than a few ppbv. This observation of the higher-than-expected HO2 + RO2 with the CIMS technique confirms the observed increase of HO2 above expected values at higher NO mixing ratios in HO2 measurements with the LIF technique. The maximum instantaneous O3 production rate calculated from HO2 and RO2 reactions with NO was as high as 10–15 ppb h−1 at midday; the total daily O3 production varied from 13 to 113 ppbv d−1 and was 48 ppbv d−1 on average during this campaign. 相似文献
106.
The locations of seven principal coronal features observed in projection at the 7 March 1970 eclipse are established from synoptic coronagraphic measurements.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
107.
David Gladwell Michael Thompson Shirley J. Wood 《Journal of Geochemical Exploration》1981,16(1):41-48
Cassiterite tin is determined after sample decomposition with ammonium iodide. The sublimate, collected in a separate condenser, is dissolved in tartaric acid solution and the tin is reduced to tin hydride in a continuous flow system by means of sodium tetrahydroborate. Atomisation is effected in a shielded hydrogen-argon diffusion flame to provide a high sensitivity determination. Interferences are negligible and the precision (12% R.S.D.) and detection limit (0.2 μ/g-1) obtained, as well as the throughput (60 samples per hour), are suitable for geochemical exploration. 相似文献
108.
Shirley M. Pierce 《Estuarine, Coastal and Shelf Science》1983,16(3):241-254
Net aerial production of Spartina maritima (Curtis) Fernald, in a warm temperature estuary in Algoa Bay, South Africa, occurring possibly as an exotic, was estimated as 523–680 g dry weight m?2 year?1. The method of production measurement designed here used community structure data and accounted for the species' extremely slow shoot production (3.1–6.7 dry g m?2 year?1) and continuous leaf turnover (516–676 dry g m?2 year?1). Standard methods of production measurement for other Spartina species failed by not accounting for the non-seasonal growth of S. maritima. N, C, organic and energy content of live and dead shoots remained constant through the seasons. The P : B ratio is 1.1, which is lower than for other Spartina species, but agrees with the low vigour shown by negligible regrowth a year after clipping. Decomposition rates were 90 mg g?1 month?1 in winter and 305 mg g?1 month?1 in summer. Monthly decomposition values showed significant correlation with air temperature (r = 0.86; P < 0.01), and water temperature (r = 0.80; P < 0.01), suggesting that monthly litterbag losses are a valid means of determining decomposition rate. 相似文献
109.
Because of the progressive decrease in rotation rate of the solar plasma at increasing latitudes, the photospheric foot-points of large-scale closed magnetic structures in the corona, which are originally widely separated in longitude, may ultimately be brought into proximity. Magnetic mergers and reconnections between magnetic fields of opposite polarity are presumed to occur, producing major structural changes in the corona and in the locations of underlying filaments. Thus we believe that the differential rotation phenomenon is essential to understanding both gradual (evolutionary) and sudden (transient) changes in the corona, and that they can occur without any observable change in the photospheric magnetic flux. A process is suggested for the splitting or bifurcation of a high-latitude magnetic structure, producing two separate components at the same latitude, whose rotation rates are influenced by their respective magnetic linkages to other regions on the Sun.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
110.