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361.
Photosynthetic responses of selected Antarctic plants to solar radiation in the southern maritime Antarctic 总被引:1,自引:0,他引:1
The effects of UV-B exclusion and enhancement of solar radiation on photosynthesis of the two phanerogams which occur in the maritime Antarctic, Deschampsia antarctica and Colobanthus quitensis , and the moss Sanionia uncinats were investigated. Data on air temperature and solar radiation illustrate a drastic seasonal variation. Daily O3 column mean values and UV-B measured at ground level document the occurrence of the O3 "hole" in the spring of 1997, with a concomitant increase in UV-B. The grass, D. antarctica , exhibited a broad temperature optimum for photosynthesis between 10–25°C while photosynthesis did not saturate even at high irradiance. The high water use efficiencies measured in the grass may be one of the features explaining the presence of this species in the maritime Antarctic. The net photosynthesis response to intercellular CO2 (A/ci ) for D. antarctica was typical of a C3 plant. Exposure to a biologically effective UV-B irradiance of 0.74 W M-2 did not result in any significant change in either the maximum rate of photosynthesis at saturating CO2 and light, or in the initial carboxylation efficiency of Rubisco. (Vc,max ). Furthermore while ambient (or enhanced) solar UV-B did not affect photochemical yield, measured in the field, of C. quitensis and D. antarctica , UV-B enhancement did affect negatively photochemical yield in S. uncinata . In D. antarctica plants, exposure to UV-B at low irradiances elicited increased flavonoid synthesis. The observed effects of UV-B enhancement on the moss (decreased photochemical yield) and the grass (increase in flavonoids) require further, separate investigation. 相似文献
362.
Experimental characterization,design and modelling of the RBRL seismic‐isolation system for lightweight structures
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The Rolling‐Ball Rubber‐Layer (RBRL) system was developed to enable seismic isolation of lightweight structures, such as special equipment or works of art, and is very versatile, a great range of equivalent natural frequencies and coefficients of damping being achievable through choice of the system parameters. The necessity to have a simple and effective design procedure has led to a new parametric experimentation at Tun Abdul Razak Research Centre (TARRC) on the rolling behaviour of the RBRL system and load–deflection behaviour of the recentering springs. The experimental results, together with theories for the rolling resistance of a loaded steel ball on a thin rubber layer and the lateral load–deflection behaviour of cylindrical rubber springs, are used to develop a general design method for the RBRL system, which allows the system to be tailored to the specific application. Sinusoidal test results are presented for the small‐deflection behaviour of the system, influenced by the presence of a viscoelastic depression on the rubber tracks beneath each ball, and an amplitude‐dependent time‐domain model is proposed, based on these results and on the steady‐state behaviour of the system. The model is validated through comparison with previously performed shaking‐table tests. Attention is here restricted to uniaxial behaviour. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
363.
Don P. Chambers Anny Cazenave Nicolas Champollion Habib Dieng William Llovel Rene Forsberg Karina von Schuckmann Yoshihide Wada 《Surveys in Geophysics》2017,38(1):309-327
Evaluating global mean sea level (GMSL) in terms of its components—mass and steric—is useful for both quantifying the accuracy of the measurements and understanding the processes that contribute to GMSL rise. In this paper, we review the GMSL budget over two periods—1993 to 2014 and 2005 to 2014—using multiple data sets of both total GMSL and the components (mass and steric). In addition to comparing linear trends, we also compare the level of agreement of the time series. For the longer period (1993–2014), we find closure in terms of the long-term trend but not for year-to-year variations, consistent with other studies. This is due to the lack of sufficient estimates of the amount of natural water mass cycling between the oceans and hydrosphere. For the more recent period (2005–2014), we find closure in both the long-term trend and for month-to-month variations. This is also consistent with previous studies. 相似文献
364.
Don G. Wyckoff 《Geoarchaeology》1993,8(1):35-58
Alibates silicified dolomite is one of the principal knappable lithic materials indigenous to the Southern High Plains. Prehistorically, this material was extensively quarried along the Canadian River in Potter County, Texas. Some of these quarries are preserved in what is now the Alibates National Monument. Archaeologists working in Oklahoma traditionally interpret artifacts of Alibates silicified dolomite as evidence for long distance trade. However, a survey of three transects across the Canadian's valley in western Oklahoma reveals the persistent, but minor, presence of Alibates clasts in gravel deposits. Thirty-nine gravel exposures yielded 1365 clasts of the dolomite. The abundance, size, shape, and knappability of this material is comparable to most flakes and implements found on western Oklahoma archaeological sites, especially those of prehistoric and protohistoric Plains Villagers. © 1993 John Wiley & Sons, Inc. 相似文献
365.
Sixteen basic and intermediate composition igneous glacial erratics from Anglian (pre-423,000 years) deposits in Hertfordshire and Buckinghamshire, southern Britain, were selected for chemical and petrographic analysis in order to determine their original source outcrops. Major and trace element compositions suggest that seven samples (plus two uncertain) originated in the Lower Carboniferous volcanics of the Scottish Midland Valley (SMV), four came from the Upper Carboniferous quartz dolerite association which crops out in Scotland, northern England (Whin Sill) and extends to Norway, and one came from the northern England Cleveland Dyke. One sample of altered dolerite is ambiguous but has some similarity to the Old Red Sandstone (Devonian) age lavas of the SMV, and one meta-basalt sample may be from southwest Scotland or Scandinavia. These results identify specific outcrops which provided glacial erratics within currently accepted ice trails in the United Kingdom, and provide the first supporting evidence based on geochemistry, rather than petrography, for these ice movements. The distribution and provenance of glacial erratics are of importance in archaeological studies, because erratics provided a potential source of raw material for stone implement production. There is a marked geographical correlation between the distribution of prehistoric stone implements of quartz dolerite in the United Kingdom, and directions of ice movements from quartz dolerite outcrops within Britain. This correlation lends support to the hypothesis that prehistoric man made extensive use of glacial erratics for implement manufacture, as an alternative to quarrying at outcrops and subsequent long-distance trade. © 1999 John Wiley & Sons, Inc. 相似文献