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Abstract. A component analysis of the sugar and lipid fraction in foam layers around kelp beds on the South African west coast showed the following trends: In the residue of foam drainage of both 12 h and 120 h old foam the sugar fraction is represented by mannose (33–41 %), galactose (4–30%), fucose (3–29%) and glucose (19–26%). With the exception of fucose, the same components could be found in foam filtration. In the lipid fraction the main fatty acids are palmitic (23.3–27.3%), oleic (14.0–5.5%) and timnodonic acid (11.2–9.1%). Selacholeinic acid was only found in 12 h old foam while lignoceric acid could not be located in foam filtration. Against expectation mannitol was not identified in quantifiable amounts in foam samples although it is the dominant component of kelp mucilage, whose presence is of major importance for foam formation. Hypotheses explaining the lack of mannitol are forwarded. Component sugar and lipid content for 11 of foam was calculated and estimation of sugar and lipid content in an average foam patch (volume of 30001) is given. The importance of foam formation as a mechanism for binding and transfer of energy in the marine environment is emphasized. 相似文献
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The genotoxic disease syndrome 总被引:1,自引:0,他引:1
Since lower animals develop neoplasia rarely or not at all, the DNA- and chromosomal-alterations observed in them after exposure to genotoxic chemicals should be correlated to some genotoxic endpoint other than neoplasia. On the basis of good correlations between induction of DNA- and chromosomal-alterations and the induction of gene mutations, this paper argues that in natural species a variety of manifestations of the mutational event may actually prove to be of much greater biological and ecological importance than induction of neoplasia. These manifestations include impairments in enzyme function, altered protein turnover, impairments in general metabolism, production of initiators of cytotoxic injuries, inhibition of growth, degenerative processes and atrophy in tissues and organs, decreased scope for growth in organisms, faster ageing, decreased fitness and well-being, impairments in immunoresponse and reproduction, increased frequency of diseases and neoplasia, impairments in adaptation, survival, and succession, and finally, extinction of species. Taken together, these ‘symptoms’ constitute a syndrome of a disease which etiologically could be named the genotoxic disease syndrome. 相似文献
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Ivan Güttler Čedo Branković Travis A. O’Brien Erika Coppola Branko Grisogono Filippo Giorgi 《Climate Dynamics》2014,43(7-8):1753-1772
This study investigates the performance of two planetary boundary layer (PBL) parameterisations in the regional climate model RegCM4.2 with specific focus on the recently implemented prognostic turbulent kinetic energy parameterisation scheme: the University of Washington (UW) scheme. When compared with the default Holtslag scheme, the UW scheme, in the 10-year experiments over the European domain, shows a substantial cooling. It reduces winter warm bias over the north-eastern Europe by 2 °C and reduces summer warm bias over central Europe by 3 °C. A part of the detected cooling is ascribed to a general reduction in lower tropospheric eddy heat diffusivity with the UW scheme. While differences in temperature tendency due to PBL schemes are mostly localized to the lower troposphere, the schemes show a much higher diversity in how vertical turbulent mixing of the water vapour mixing ratio is governed. Differences in the water vapour mixing ratio tendency due to the PBL scheme are present almost throughout the troposphere. However, they alone cannot explain the overall water vapour mixing ratio profiles, suggesting strong interaction between the PBL and other model parameterisations. An additional 18-member ensemble with the UW scheme is made, where two formulations of the master turbulent length scale in unstable conditions are tested and unconstrained parameters associated with (a) the evaporative enhancement of the cloud-top entrainment and (b) the formulation of the master turbulent length scale in stable conditions are systematically perturbed. These experiments suggest that the master turbulent length scale in the UW scheme could be further refined in the current implementation in the RegCM model. It was also found that the UW scheme is less sensitive to the variations of the other two selected unconstrained parameters, supporting the choice of these parameters in the default formulation of the UW scheme. 相似文献
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Robert J. Beare Malcolm K. Macvean Albert A. M. Holtslag Joan Cuxart Igor Esau Jean-Christophe Golaz Maria A. Jimenez Marat Khairoutdinov Branko Kosovic David Lewellen Thomas S. Lund Julie K. Lundquist Anne Mccabe Arnold F. Moene Yign Noh Siegfried Raasch Peter Sullivan 《Boundary-Layer Meteorology》2006,118(2):247-272
Results are presented from the first intercomparison of large-eddy simulation (LES) models for the stable boundary layer (SBL), as part of the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study initiative. A moderately stable case is used, based on Arctic observations. All models produce successful simulations, in as much as they generate resolved turbulence and reflect many of the results from local scaling theory and observations. Simulations performed at 1-m and 2-m resolution show only small changes in the mean profiles compared to coarser resolutions. Also, sensitivity to subgrid models for individual models highlights their importance in SBL simulation at moderate resolution (6.25 m). Stability functions are derived from the LES using typical mixing lengths used in numerical weather prediction (NWP) and climate models. The functions have smaller values than those used in NWP. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL. 相似文献
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Radiative destabilization of the nocturnal stable atmospheric boundary layer (NSABL) over homogeneous desert terrain is predicted by an analytical model based on a modified diffusion equation. The model applies late at night under calm, dry conditions when long-wave radiative transfer dominates the NSABL evolution. A three-layer structure for the NSABL is proposed: a shear sub-layer closest to the surface, a radiative sub-layer which contains the inversion top, and a coupling sub-layer which matches the NSABL with the residual layer aloft. A sub-sub-layer called the nocturnal internal boundary layer (NIBL) is nested within the radiative sub-layer and comprises the temperature maximum. The model can explain: (1) maximum cooling in the NIBL, (2) deepening of the NIBL, (3) radiative destabilization of the NSABL, and (4) possible surface warming before sunrise. An example from the Mohave Desert, USA is presented, and the observed temperature profile compares favorably with the model solution. 相似文献
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Evidence for a Long-Term Strength Threshold in Crystalline Rock 总被引:3,自引:1,他引:2
The mechanical response of brittle rock to long-duration compression loading is of particular concern in underground disposal of nuclear waste, where radionuclides must be isolated from the biosphere for periods of the order of a million years. Does the strength decrease without limit over such time, or is there, for some rock types, a lower “threshold” strength below which the rock will cease to deform? This paper examines the possibility of such a threshold in silicate crystalline rocks from several perspectives, including: (1) interpretation of the results of short-term creep tests on rock; (2) numerical analysis of the effect of decrease in fracture toughness due to stress corrosion on the strength of a crystalline rock; and (3) evidence from plate tectonics, and observations of in situ rock stress in granite quarries. The study concludes that there is clear evidence of threshold strength. The threshold is of the order of 40% of the unconfined compressive strength or higher for laboratory specimens under unconfined compressive loading, and increases rapidly in absolute value with confinement. Field evidence also leads to the conclusion that the long-term strength of crystalline rock in situ is of comparable magnitude to the laboratory value. 相似文献
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Thorsten?MauritsenEmail author Gunilla?Svensson Branko?Grisogono 《Boundary-Layer Meteorology》2005,117(2):259-273
We investigate the flow over Arctic leads using a mesoscale numerical model, typical of both summer and winter, under idealised
conditions. We find that Arctic leads may be the source of standing atmospheric internal gravity waves during both seasons.
The summertime wave may be compared with the wave generated by a small ridge, though with the phase reversed. The mechanism
for exciting the wave is found to be the internal boundary layer developing due to horizontal variations in surface temperature
and roughness length. During the more exploratory wintertime simulations, with substantial temperature difference between
the lead and the ice surface, we find that secondary circulations and intermittent wave-breaking may occur. The effects of
the lead appear far downstream. 相似文献