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排序方式: 共有58条查询结果,搜索用时 15 毫秒
1.
Christiaan Sterken 《Astrophysics and Space Science》2006,304(1-4):139-143
Intensive monitoring of main-sequence stars for pulsational studies continuously reveals new binaries and multiple systems. The resulting extensive data sets lead to exact orbital parameters, and to accurate masses of the components. This is also the case higher up the main sequence, though less frequently. We discuss a few examples where intensive observational efforts are necessary in order to improve our knowledge of the pulsational behaviour in the upper main-sequence instability domains, but we emphasize that observational efforts alone that turn out more and more of the same type of data, are by far insufficient, and that there is urgent need for theoretical developments. Determination of highly accurate stellar parameters is of paramount importance and is much more needed than time-series observations. 相似文献
2.
H. Hummel C. Amiard-Triquet G. Bachelet M. Desprez J. Marchand B. Sylvand J.C. Amiard H. Rybarczyk R.H. Bogaards J. Sinke Y. De Wit L. De Wolf 《Journal of Sea Research》1996,35(4):315-321
Variation in the sensitivity to stress of Macoma balthica was measured in several French and Dutch estuaries. For adult and juvenile Macoma balthica exposed to copper under conditions of starvation, differences in mortality rate, condition, glycogen, burrowing rate and copper content were assessed. No significant differences were observed between adults and juveniles; the influence of treatment and origin was always evident. Animals from the most southern estuaries, Loire and Gironde, near to the species's southern limit of distribution, showed, in the field, the strongest deviations for the ecophysiological traits measured, and were in the experiments the most sensitive to stress. 相似文献
3.
R.H.M. Eertman C.L.F.M.G. Groenink B. Sandee H. Hummel A.C. Smaal 《Marine environmental research》1995,39(1-4)
The polycyclic aromatic hydrocarbons fluoranthene and benzo(a)pyrene significantly reduced the feeding rate of mussels. For both compounds the tissue concentration resulting in a 50% reduction of the clearance rate (TEC50) was calculated. At high tissue concentrations both aromatic compounds reduced the tolerance of mussels to aerial exposure, whereas at low tissue concentrations an improved response was noticed. The activities of the antioxidant enzymes Superoxide dismutase (SOD) and catalase were elevated only at low tissue concentrations of fluoranthene and benzo(a)pyrene. At the highest measured tissue concentrations the activity of both enzymes was reduced, possibly due to a narcotic effect. The reproductive success rate of mussels appeared to be affected negatively by the investigated hydrocarbons. The results of a pilot experiment indicate that mussels can be used also for the testing of contaminated sediments. 相似文献
4.
5.
Characterisation of hydroclimatological trends and variability in the Lake Naivasha basin,Kenya 下载免费PDF全文
Vincent Omondi Odongo Christiaan van der Tol Pieter R. van Oel Frank M. Meins Robert Becht Japheth Onyando Zhongbo Su 《水文研究》2015,29(15):3276-3293
Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 106 m3 year?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
K. Hummel 《International Journal of Earth Sciences》1928,19(3):223-228
Ohne ZusammenfassungVortrag, gehalten in der Hauptversammlung der Geologischen Vereinigung in Frankfurt a. M., am 7. I. 1928. Ausführlichere Mitteilungen über dieses Thema werden im Rahmen einer größeren Abhandlung über die südalpine Mitteltrias an anderer Stelle veröffentlicht werden. 相似文献
7.
K. Hummel 《International Journal of Earth Sciences》1920,11(1-4):18-44
Ohne Zusammenfassung 相似文献
8.
K. Hummel 《International Journal of Earth Sciences》1926,17(4):281-290
Ohne Zusammenfassung 相似文献
9.
Sander Wijnhoven Vincent Escaravage Eugène Daemen Herman Hummel 《Estuaries and Coasts》2010,33(6):1261-1278
The former tidal inlet Lake Veere was turned into a stagnant brackish lake in 1961. Ever since, the system has shown a continuous
degradation. The current study shows the monitoring results for the macrozoobenthic communities and the abiotic conditions
for the period 1990–2008. This includes the first step to remediation, the restoration of the exchange between the tidal marine
Eastern Scheldt and Lake Veere in 2004. A continuous decline in water clearance co-occurring with decreasing macrofauna densities
and richness was observed till 2004. Water quality (e.g., secchi depth, nutrient levels, and oxygen conditions) improved significantly
after the measure at a higher salinity level with less variation. But the macrofauna densities, biomass, and diversity did
not improve yet. First indications of changes in the benthic communities by arrival of new and returning species are however
observed and show that restoration at macrofauna level follows the improved abiotic conditions with a delay of several years. 相似文献
10.
K. Hummel 《International Journal of Earth Sciences》1922,13(1):40-81
Ohne Zusammenfassung 相似文献