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231.
The crystallisation of soluble salts within the pores of the stone is widely recognised as a major mechanism causing the deterioration
of the stone-built architectural heritage. Temperature, in turn, is one of the main controls on this process, including salt
precipitation, the pressure of crystallisation and the thermal expansion of salts. Most laboratory experiments on decay generated
by salts are just carried out with convective heating regimes, while in natural environments building stones can undergo radiative
and convective heating regimes. The thermal response of stone to these different heating regimes is noticeably different and
might influence the crystallisation patterns of a salt within a stone. The aim of this work is to raise awareness on the different
patterns of crystallisation of NaCl within a porous stone tested with different heating regimes (convection and radiation)
and the implications that this could have on the design of experimental modelling of natural weathering conditions in laboratory
simulations. Results show that heating regime affects the sodium chloride distribution within a stone with high percentage
of microporosity. In this case, radiation heating facilitates the generation of subefflorescences, while convection heating
promotes efflorescences. This has a clear implication both on the stone decay in natural environments and on the methodologies
for testing salt decay, as subefflorescences are more destructive than efflorescences. In this sense, the use of convective
heating in laboratory experimentation might underestimate the potential damage that sodium chloride may generate. This counsels
the use of radiation heating test methods in addition to convection for the laboratory study of salt crystallisation. 相似文献
232.
The Caturrita Formation is a lithostratigraphic unit that comprises the Ladinian–Eonorian sequence of the Paraná Basin. It has been interpreted as deposits of alluvial plains and meandering rivers. Purported fossil tracks found in this formation at Faxinal do Soturno County, Rio Grande do Sul State, Brazil, are concave circular-shaped structures, with a laminar deformation. Some show digitiform projections, and at least three are aligned. They are interpreted as a disruption of the substrate homogeneity caused by bioturbation of tetrapods. In some of these there is a distinct color pattern — more reddish than the surrounding substrate. This is interpreted as a result of differential diagenesis. The features remain enigmatic tracks but were probably made by prosauropod dinosaurs, the dominant terrestrial herbivore group from the end of the Triassic in Gondwana strata. 相似文献
233.
Three juvenile Brazilian sharpnose sharks (Rhizoprionodon lalandii) caught in gillnets in southeast Brazil, southwest Atlantic, were found with plastic debris rings around their gill or mouth region. The rings caused severe abrasion on the sharks' tissues as the animal grew, the collars probably hampering normal feeding and/or ventilation since two of the collared individuals were emaciated. The rings were identified as detachable lid parts from plastic bottles, likely thrown overboard by fishery and/or recreation boats. As several carcharhinid shark species dwells and reproduce in shallow waters, the impact of discarded plastic debris likely is greater on this shark type. 相似文献
234.
Rafael A. Kascheev 《Earth, Moon, and Planets》1988,41(1):89-94
A new approach is discussed for determination of lunar gravity parameters. Estimations were made with the line-of-sight (LOS) accelerations of artificial satellites. Tests indicate the advantages of such an approach over the classical one. 相似文献
235.
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239.
Large-scale fields of soil moisture are forced by atmospheric precipitation and radiative forcing. When these forcing factors
are themselves influenced by surface and soil moisture processes, the result is a nonlinear land-atmosphere system with inherent
feedback mechanisms that may strongly modulate variability in climate. Given such feedbacks, simple randomness in the forcing
factors may be manifested as a complex statistical signature in the surface hydrology. In this paper, we investigate the impacts
of non-Gaussian and colored-noise on the probability distribution of soil moisture resulting from the statistical-dynamical
land-atmosphere interaction model of Rodriguez-Iturbe et al. (1991). Persistence of hydroclimatologic anomalies as characterized
by the correlation time scale of soil moisture is discussed. 相似文献
240.