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M. A. Adey - One of the best experts on this subject based on the ideXlab platform.
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Changes in microstructure, voids and b-fabric of surface samples of a Vertisol caused by wet/dry Cycles
Geoderma, 1998Co-Authors: J Hussein, M. A. AdeyAbstract:Abstract A finely structured (self-mulching) Vertisol from Zimbabwe was sampled to 150 mm (bulk samples) or 30 mm (undisturbed samples) in order to provide material for an investigation of the effects of wet/dry Cycles on microstructure. Bulk samples were worked in the plastic state and then taken through a number of wet/dry Cycles using flood, slow and fast capillary and simulated rainfall wetting. Thin sections were produced from the resulting clods/aggregates at different stages during the Cycles and changes in microstructure, voids and b-fabric were examined and compared to undisturbed samples of the field soil. The initial worked soil had a dense, massive structure but developed complex, blocky, crumb and platy structures during wetting and drying. Fast capillary wetting produced the finest structure in comparison to the other three wetting methods. Observable porosity (pore widths >5 μ m), at 100× magnification in horizontal thin sections, increased from 2.5% in the moist worked soil to 23.9, 13.7, 12.8 and 12.3% in the fast capillary, rainfall, slow capillary and flood wetted soils, respectively, after one wet/dry cycle. Tensile strengths of dry soils followed the converse ranking, decreasing as observable porosity increased. The shape of voids did not have a significant effect on strength. The worked soil showed predominantly planar voids but compound voids became dominant after wetting by all four methods. Changes in b-fabric during wetting and drying showed no clear trends apart from a general decrease in the proportion of oriented micromass. The b-fabric was commonly mosaic to stipple speckled with granostriations. Porostriations were rarely observed. The field soil showed ultrafine to fine crumb structure with mosaic to stipple speckled b-fabric and an observable void space at 100× magnification of 53%. This structure was approached most closely by the fast capillary wetted soil, indicating that a fine porous structure may be rapidly regenerated from an unfavourable dense structure through this method of wetting.
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changes of structure and tilth mellowing in a vertisol due to wet dry Cycles in the liquid and vapour phases
European Journal of Soil Science, 1995Co-Authors: J Hussein, M. A. AdeyAbstract:Summary Development of a fine tilth in Vertisols increases infiltration, plant-available water and ease of cultivation and produces a fine seed bed. The tilth-mellowing properties of a strongly self-mulching Vertisol from Zimbabwe were investigated by applying different types of wetting to a worked soil and examining macromorphological features, size, density, strength and friability of the resulting clods/aggregates, developed through successive wet/dry Cycles. Wetting regimes were chosen to simulate likely field conditions and included rapid flood-, slow and fast capillary-, simulated rainfall- and vapour-wetting. Tilth development was compared to that of field soils. All wetting treatments in the liquid phase resulted in decreases in aggregate density. Fast capillary wetting rapidly reduced size and strength of aggregates to below that of field soils whereas slow capillary wetting similarly rapidly decreased size but reduced strength more slowly. Flood wetting caused little change in size but aggregates showed a small decrease in strength. Rainfall wetting resulted in changes intermediate between these extremes. There was a significant linear relationship between strength and porosity of aggregates! For rainfall- and flood-wetting, friabilities were at a maximum after one wet/dry cycle but subsequently decreased. Vapour wet/dry Cycles reduced strength but not density of worked soils, implying changes in internal microstructure without measurable porosity change. Hypotheses to explain these changes are put forward.
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Changes of structure and tilth mellowing in a Vertisol due to wet/dry Cycles in the liquid and vapour phases
European Journal of Soil Science, 1995Co-Authors: J Hussein, M. A. AdeyAbstract:Summary Development of a fine tilth in Vertisols increases infiltration, plant-available water and ease of cultivation and produces a fine seed bed. The tilth-mellowing properties of a strongly self-mulching Vertisol from Zimbabwe were investigated by applying different types of wetting to a worked soil and examining macromorphological features, size, density, strength and friability of the resulting clods/aggregates, developed through successive wet/dry Cycles. Wetting regimes were chosen to simulate likely field conditions and included rapid flood-, slow and fast capillary-, simulated rainfall- and vapour-wetting. Tilth development was compared to that of field soils. All wetting treatments in the liquid phase resulted in decreases in aggregate density. Fast capillary wetting rapidly reduced size and strength of aggregates to below that of field soils whereas slow capillary wetting similarly rapidly decreased size but reduced strength more slowly. Flood wetting caused little change in size but aggregates showed a small decrease in strength. Rainfall wetting resulted in changes intermediate between these extremes. There was a significant linear relationship between strength and porosity of aggregates! For rainfall- and flood-wetting, friabilities were at a maximum after one wet/dry cycle but subsequently decreased. Vapour wet/dry Cycles reduced strength but not density of worked soils, implying changes in internal microstructure without measurable porosity change. Hypotheses to explain these changes are put forward.
J Hussein - One of the best experts on this subject based on the ideXlab platform.
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Changes in microstructure, voids and b-fabric of surface samples of a Vertisol caused by wet/dry Cycles
Geoderma, 1998Co-Authors: J Hussein, M. A. AdeyAbstract:Abstract A finely structured (self-mulching) Vertisol from Zimbabwe was sampled to 150 mm (bulk samples) or 30 mm (undisturbed samples) in order to provide material for an investigation of the effects of wet/dry Cycles on microstructure. Bulk samples were worked in the plastic state and then taken through a number of wet/dry Cycles using flood, slow and fast capillary and simulated rainfall wetting. Thin sections were produced from the resulting clods/aggregates at different stages during the Cycles and changes in microstructure, voids and b-fabric were examined and compared to undisturbed samples of the field soil. The initial worked soil had a dense, massive structure but developed complex, blocky, crumb and platy structures during wetting and drying. Fast capillary wetting produced the finest structure in comparison to the other three wetting methods. Observable porosity (pore widths >5 μ m), at 100× magnification in horizontal thin sections, increased from 2.5% in the moist worked soil to 23.9, 13.7, 12.8 and 12.3% in the fast capillary, rainfall, slow capillary and flood wetted soils, respectively, after one wet/dry cycle. Tensile strengths of dry soils followed the converse ranking, decreasing as observable porosity increased. The shape of voids did not have a significant effect on strength. The worked soil showed predominantly planar voids but compound voids became dominant after wetting by all four methods. Changes in b-fabric during wetting and drying showed no clear trends apart from a general decrease in the proportion of oriented micromass. The b-fabric was commonly mosaic to stipple speckled with granostriations. Porostriations were rarely observed. The field soil showed ultrafine to fine crumb structure with mosaic to stipple speckled b-fabric and an observable void space at 100× magnification of 53%. This structure was approached most closely by the fast capillary wetted soil, indicating that a fine porous structure may be rapidly regenerated from an unfavourable dense structure through this method of wetting.
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changes of structure and tilth mellowing in a vertisol due to wet dry Cycles in the liquid and vapour phases
European Journal of Soil Science, 1995Co-Authors: J Hussein, M. A. AdeyAbstract:Summary Development of a fine tilth in Vertisols increases infiltration, plant-available water and ease of cultivation and produces a fine seed bed. The tilth-mellowing properties of a strongly self-mulching Vertisol from Zimbabwe were investigated by applying different types of wetting to a worked soil and examining macromorphological features, size, density, strength and friability of the resulting clods/aggregates, developed through successive wet/dry Cycles. Wetting regimes were chosen to simulate likely field conditions and included rapid flood-, slow and fast capillary-, simulated rainfall- and vapour-wetting. Tilth development was compared to that of field soils. All wetting treatments in the liquid phase resulted in decreases in aggregate density. Fast capillary wetting rapidly reduced size and strength of aggregates to below that of field soils whereas slow capillary wetting similarly rapidly decreased size but reduced strength more slowly. Flood wetting caused little change in size but aggregates showed a small decrease in strength. Rainfall wetting resulted in changes intermediate between these extremes. There was a significant linear relationship between strength and porosity of aggregates! For rainfall- and flood-wetting, friabilities were at a maximum after one wet/dry cycle but subsequently decreased. Vapour wet/dry Cycles reduced strength but not density of worked soils, implying changes in internal microstructure without measurable porosity change. Hypotheses to explain these changes are put forward.
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Changes of structure and tilth mellowing in a Vertisol due to wet/dry Cycles in the liquid and vapour phases
European Journal of Soil Science, 1995Co-Authors: J Hussein, M. A. AdeyAbstract:Summary Development of a fine tilth in Vertisols increases infiltration, plant-available water and ease of cultivation and produces a fine seed bed. The tilth-mellowing properties of a strongly self-mulching Vertisol from Zimbabwe were investigated by applying different types of wetting to a worked soil and examining macromorphological features, size, density, strength and friability of the resulting clods/aggregates, developed through successive wet/dry Cycles. Wetting regimes were chosen to simulate likely field conditions and included rapid flood-, slow and fast capillary-, simulated rainfall- and vapour-wetting. Tilth development was compared to that of field soils. All wetting treatments in the liquid phase resulted in decreases in aggregate density. Fast capillary wetting rapidly reduced size and strength of aggregates to below that of field soils whereas slow capillary wetting similarly rapidly decreased size but reduced strength more slowly. Flood wetting caused little change in size but aggregates showed a small decrease in strength. Rainfall wetting resulted in changes intermediate between these extremes. There was a significant linear relationship between strength and porosity of aggregates! For rainfall- and flood-wetting, friabilities were at a maximum after one wet/dry cycle but subsequently decreased. Vapour wet/dry Cycles reduced strength but not density of worked soils, implying changes in internal microstructure without measurable porosity change. Hypotheses to explain these changes are put forward.
Carla Conti - One of the best experts on this subject based on the ideXlab platform.
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Corrosion resistance of galvanized steel reinforcements in carbonated concrete: effect of wet–dry Cycles in tap water and in chloride solution on the passivating layer
Cement and Concrete Research, 2014Co-Authors: G. Roventi, Tiziano Bellezze, G. Giuliani, Carla ContiAbstract:The effect of wet–dry Cycles in tap water and in 3.5% NaCl solution on the passivating products of galvanized steel after concrete carbonation was investigated. The results show that carbonation destroys the passivating layer of calcium hydroxyzincate with the formation of the amorphous products ZnCO3 and Zn5(CO3)2(OH)6, which are also protective. The exposure to wet–dry Cycles in tap water after concrete carbonation does not significantly increase the corrosion rate of the galvanized steel with respect to the values measured in non-carbonated concrete. On the contrary, the exposure to chloride solution after concrete carbonation leads to a marked decrease in the chloride threshold for galvanized steel corrosion with respect to that found in non-carbonated concrete.
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corrosion resistance of galvanized steel reinforcements in carbonated concrete effect of wet dry Cycles in tap water and in chloride solution on the passivating layer
Cement and Concrete Research, 2014Co-Authors: G. Roventi, Tiziano Bellezze, G. Giuliani, Carla ContiAbstract:The effect of wet–dry Cycles in tap water and in 3.5% NaCl solution on the passivating products of galvanized steel after concrete carbonation was investigated. The results show that carbonation destroys the passivating layer of calcium hydroxyzincate with the formation of the amorphous products ZnCO3 and Zn5(CO3)2(OH)6, which are also protective. The exposure to wet–dry Cycles in tap water after concrete carbonation does not significantly increase the corrosion rate of the galvanized steel with respect to the values measured in non-carbonated concrete. On the contrary, the exposure to chloride solution after concrete carbonation leads to a marked decrease in the chloride threshold for galvanized steel corrosion with respect to that found in non-carbonated concrete.
Thomas Carell - One of the best experts on this subject based on the ideXlab platform.
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Wet-Dry Cycles enable the parallel origin of canonical and non-canonical nucleosides by continuous synthesis.
Nature communications, 2018Co-Authors: Sidney Becker, Christina Schneider, Hidenori Okamura, Antony Crisp, Tynchtyk Amatov, Milan Dejmek, Thomas CarellAbstract:The molecules of life were created by a continuous physicochemical process on an early Earth. In this hadean environment, chemical transformations were driven by fluctuations of the naturally given physical parameters established for example by Wet-Dry Cycles. These conditions might have allowed for the formation of (self)-replicating RNA as the fundamental biopolymer during chemical evolution. The question of how a complex multistep chemical synthesis of RNA building blocks was possible in such an environment remains unanswered. Here we report that geothermal fields could provide the right setup for establishing Wet-Dry Cycles that allow for the synthesis of RNA nucleosides by continuous synthesis. Our model provides both the canonical and many ubiquitous non-canonical purine nucleosides in parallel by simple changes of physical parameters such as temperature, pH and concentration. The data show that modified nucleosides were potentially formed as competitor molecules. They could in this sense be considered as molecular fossils.
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Wet-Dry Cycles enable the parallel origin of canonical and non-canonical nucleosides by continuous synthesis
Nature Communications, 2018Co-Authors: Sidney Becker, Christina Schneider, Hidenori Okamura, Antony Crisp, Tynchtyk Amatov, Milan Dejmek, Thomas CarellAbstract:How RNA building blocks have formed on an early Earth by a continuous process is still a mystery awaiting its solution. Here, the authors report that fluctuations of physical parameters like temperature and pH could have been enough to facilitate nucleoside formation from simple starting materials. The molecules of life were created by a continuous physicochemical process on an early Earth. In this hadean environment, chemical transformations were driven by fluctuations of the naturally given physical parameters established for example by wet–dry Cycles. These conditions might have allowed for the formation of (self)-replicating RNA as the fundamental biopolymer during chemical evolution. The question of how a complex multistep chemical synthesis of RNA building blocks was possible in such an environment remains unanswered. Here we report that geothermal fields could provide the right setup for establishing wet–dry Cycles that allow for the synthesis of RNA nucleosides by continuous synthesis. Our model provides both the canonical and many ubiquitous non-canonical purine nucleosides in parallel by simple changes of physical parameters such as temperature, pH and concentration. The data show that modified nucleosides were potentially formed as competitor molecules. They could in this sense be considered as molecular fossils.
Tooru Tsuru - One of the best experts on this subject based on the ideXlab platform.
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electrochemical impedance study on galvanized steel corrosion under cyclic wet dry conditions influence of time of wetness
Corrosion Science, 2004Co-Authors: Amar Prasad Yadav, Atsushi Nishikata, Tooru TsuruAbstract:Abstract Electrochemical impedance technique has been applied to study the corrosion behavior of galvanized steel under wet–dry cyclic conditions with various drying periods. The wet–dry Cycles were carried out for the period of 336 h by exposure to alternate conditions of 1 h immersion in a 0.5 M NaCl solution and drying for various time periods (11, 7 and 3 h) at 298 K and 60% RH. During the wet–dry Cycles, the polarization resistance, Rp, and solution resistance, Rs, were continuously monitored. The instantaneous corrosion rate of the coating was estimated from the obtained Rp−1 and time of wetness was determined from the Rs values. The corrosion potential, Ecorr, was also measured only during the immersion period of each wet–dry cycle. In all cases, the corrosion was accelerated by the wet–dry Cycles in the early stage, and started to decrease at a certain cycle and finally became similar to that at the initial cycle. The underlying steel corrosion commenced after the corrosion rate started to decrease. The shorter drying period in each cycle led to higher amount of corrosion of the coating because the surface was under wet conditions for longer periods. On the other hand, time to red rust appearance due to occurrence of the underlying steel corrosion became shorter as the drying period increased, although the total amount of corrosion was smaller. The corrosion mechanism of substrate steel under various drying conditions has been discussed, the galvanic coupling effect being taken into account.
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AC impedance study on corrosion of 55%Al-Zn alloy-coated steel under thin electrolyte layers
Corrosion Science, 2000Co-Authors: Gamal A. El-mahdy, Atsushi Nishikata, Tooru TsuruAbstract:Abstract The corrosion behavior of 55%Al–Zn alloy-coated steel under a chloride-containing electrolyte layer ranging from 15 to 888 μm in thickness has been investigated using electrochemical impedance spectroscopy (EIS). The interface of the coating-electrolyte layer can be represented by an equivalent circuit consisting of a solution resistance, a charge transfer resistance, a double layer capacitance and a Warburg element. The corrosion current density estimated from the polarization resistance significantly decreases as the thickness of electrolyte layer increases between 15 and 100 μm and is almost independent of the thickness up to 888 μm. Furthermore, corrosion monitoring of 55%Al–Zn alloy-coated steel has been performed under alternate conditions of 1 h-immersion in solution of 0.05 M NaCl or 0.05 M Na 2 SO 4 and 7 h-drying at 298 K and 60% RH. During the wet–dry Cycles, the instantaneous corrosion rate was monitored by AC impedance method together with the corrosion potential. The corrosion rate increases at the initial stage of the wet–dry Cycles because the native oxide on the coating surface is dissolved into the solution and converted to hydrated zinc and aluminum oxides, and then decreases slowly owing to the accumulation of the corrosion products over the coating surface. The corrosion mechanism of 55%Al–Zn coating is discussed on the basis of the monitoring results.
