The flooding characteristics of hydrofoil impeller were systematically investigated in a two-and three-phase 383 mm i.d. stirred tank operated on air, water and spherical glass beads. The volumetric solid concen-trati...The flooding characteristics of hydrofoil impeller were systematically investigated in a two-and three-phase 383 mm i.d. stirred tank operated on air, water and spherical glass beads. The volumetric solid concen-tration Cs was varied from 0 to 25%. And the superficial gas velocity Ug was at the range of 0-0.096 m·s-1. A fast and objective method for identifying flooding point NF is developed based on the statistical analysis of the pressure fluctuation signals. It is found, the effect of solid concentration on the flooding point NF depends on the gas velocity. At the lower gas velocity (Ug = 0.010 m·s-1), the solid concentration has only a minor effect. However, it displays a very significant effect on the flooding point NF at the medium and high gas velocity. The flooding point NF linearly increases with the gas velocity Ug, at lower solid concentration (Cs = 0, 10%). When Cs = 20%, the behavior of NF versus Ug becomes more complex. The correlations of the flooding characteristics in the slurry stirred tank are proposed by considering the solid concentration effect.展开更多
Hunter-gatherer communities in the American Southeast reached an apogee of social and political complexity in the period between ca. 4200 and 3000 cal yr BP. In the lower Mississippi Valley(LMV) the Poverty Point cult...Hunter-gatherer communities in the American Southeast reached an apogee of social and political complexity in the period between ca. 4200 and 3000 cal yr BP. In the lower Mississippi Valley(LMV) the Poverty Point culture defined this period of socio-political elaboration. However, following a significant period of climate change that led to exceptional flooding and a major reorganization of the course of the Mississippi River, this culture collapsed beginning ca. 3300–3200 cal yr BP and the LMV was abandoned for the subsequent 500 years. In this study, we use data from the Jaketown site in the Yazoo Basin of west-central Mississippi to refine the chronology of the climate event that caused the collapse of the Poverty Point culture. A large flood buried Poverty Point-era occupation deposits at Jaketown around 3310 cal yr BP. Lateral migration of the Mississippi River during flooding led to inundation of the Yazoo Basin and re-occupation of ancient river courses. A coarse sand stratum topped by a more than a meter-thick fining upward sediment package marks a crevasse deposit caused by a rupture of the natural levee at Jaketown. This levee breach was part of a larger pattern of erratic flooding throughout the LMV and is associated with major landscape evolution and the abandonment of Poverty Point sites within the valley. Early Woodland peoples re-colonized the crevasse surface after ca. 2780 cal yr BP. Following this event, the Jaketown site and the eastern Yazoo Basin witnessed a period of landscape stability that lasts to this day. These archaeological data demonstrate how climate change and natural disasters can lead to socio-political dissolution and reorganization even in relatively small-scale hunter-gatherer populations.展开更多
The Gounti Yéna valley is the main watercourse that divides the left bank of the city of Niamey into two unequal parts. The area of its watershed is estimated at about 62 km<sup>2</sup>. The objective...The Gounti Yéna valley is the main watercourse that divides the left bank of the city of Niamey into two unequal parts. The area of its watershed is estimated at about 62 km<sup>2</sup>. The objective of this study is on the one hand to evaluate the current state of the physico-chemical and bacteriological quality of the water of the Gounti Yéna basin and on the other hand to define the risks of water pollution and its origin in the face of the phenomenon of the rise in the water table of this basin by defining some health risks linked to these impacts. In order to properly carry out this work, we carried out a study of the evolution of the physicochemical and bacteriological parameters of the water of the Gounti Yéna basin during the period from November 2020 to October 2021, at three sampling points chosen from upstream to downstream of the basin then entomological surveys and among the health centers of the capital. The results obtained showed that the physico-chemical quality of water in the Gounti Yéna basin is influenced by climatic factors (precipitation and temperature) and anthropogenic actions. This study also highlighted the presence of faecal contamination in the water of the Gounti Yéna basin with a greater degree during the rainy season. This contamination remains worrying and constitutes a health risk causing waterborne diseases. The stagnation of the various bodies of water is also a favorable place for the development and spread of vector-borne diseases.展开更多
文摘The flooding characteristics of hydrofoil impeller were systematically investigated in a two-and three-phase 383 mm i.d. stirred tank operated on air, water and spherical glass beads. The volumetric solid concen-tration Cs was varied from 0 to 25%. And the superficial gas velocity Ug was at the range of 0-0.096 m·s-1. A fast and objective method for identifying flooding point NF is developed based on the statistical analysis of the pressure fluctuation signals. It is found, the effect of solid concentration on the flooding point NF depends on the gas velocity. At the lower gas velocity (Ug = 0.010 m·s-1), the solid concentration has only a minor effect. However, it displays a very significant effect on the flooding point NF at the medium and high gas velocity. The flooding point NF linearly increases with the gas velocity Ug, at lower solid concentration (Cs = 0, 10%). When Cs = 20%, the behavior of NF versus Ug becomes more complex. The correlations of the flooding characteristics in the slurry stirred tank are proposed by considering the solid concentration effect.
基金supported by the U.S. National Science Foundation (Grant No. #0827097) with additional support from the Edward S. and Tedi Macias fund at Washington University in St. Louis
文摘Hunter-gatherer communities in the American Southeast reached an apogee of social and political complexity in the period between ca. 4200 and 3000 cal yr BP. In the lower Mississippi Valley(LMV) the Poverty Point culture defined this period of socio-political elaboration. However, following a significant period of climate change that led to exceptional flooding and a major reorganization of the course of the Mississippi River, this culture collapsed beginning ca. 3300–3200 cal yr BP and the LMV was abandoned for the subsequent 500 years. In this study, we use data from the Jaketown site in the Yazoo Basin of west-central Mississippi to refine the chronology of the climate event that caused the collapse of the Poverty Point culture. A large flood buried Poverty Point-era occupation deposits at Jaketown around 3310 cal yr BP. Lateral migration of the Mississippi River during flooding led to inundation of the Yazoo Basin and re-occupation of ancient river courses. A coarse sand stratum topped by a more than a meter-thick fining upward sediment package marks a crevasse deposit caused by a rupture of the natural levee at Jaketown. This levee breach was part of a larger pattern of erratic flooding throughout the LMV and is associated with major landscape evolution and the abandonment of Poverty Point sites within the valley. Early Woodland peoples re-colonized the crevasse surface after ca. 2780 cal yr BP. Following this event, the Jaketown site and the eastern Yazoo Basin witnessed a period of landscape stability that lasts to this day. These archaeological data demonstrate how climate change and natural disasters can lead to socio-political dissolution and reorganization even in relatively small-scale hunter-gatherer populations.
文摘The Gounti Yéna valley is the main watercourse that divides the left bank of the city of Niamey into two unequal parts. The area of its watershed is estimated at about 62 km<sup>2</sup>. The objective of this study is on the one hand to evaluate the current state of the physico-chemical and bacteriological quality of the water of the Gounti Yéna basin and on the other hand to define the risks of water pollution and its origin in the face of the phenomenon of the rise in the water table of this basin by defining some health risks linked to these impacts. In order to properly carry out this work, we carried out a study of the evolution of the physicochemical and bacteriological parameters of the water of the Gounti Yéna basin during the period from November 2020 to October 2021, at three sampling points chosen from upstream to downstream of the basin then entomological surveys and among the health centers of the capital. The results obtained showed that the physico-chemical quality of water in the Gounti Yéna basin is influenced by climatic factors (precipitation and temperature) and anthropogenic actions. This study also highlighted the presence of faecal contamination in the water of the Gounti Yéna basin with a greater degree during the rainy season. This contamination remains worrying and constitutes a health risk causing waterborne diseases. The stagnation of the various bodies of water is also a favorable place for the development and spread of vector-borne diseases.
