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91.
Large-Eddy Simulation of Turbulent Organized Structures within and above Explicitly Resolved Cube Arrays 总被引:2,自引:12,他引:2
Large-eddy simulations have been performed for fully developed turbulent flow within and above explicitly resolved simple cube arrays. The results from our model, hereafter LES-CITY, are shown to agree with laboratory experiments. We investigated the systematic influence of cube density on turbulent flow characteristics by performing numerical experiments for cube areal densities from 0 to 44%. The following results were obtained: (1) The dispersive momentum flux was quite large within the canopy layer due to a mean stream re-circulation, whereas it was smaller above the canopy. The spatial variation of temporally averaged momentum in the roughness sub-layer was 20% or less of the total kinematic surface drag. (2) The temporally and spatially-averaged flow structure confirmed the existence of conventionally described canyon flow regimes; isolated, interfacial, and wake. However, the intermittency of the canyon flow for all cube densities was quite large and the stream patterns were never persistent. (3) Turbulent organized structures (TOS) similar to those observed in turbulent surface-layer flows were simulated, which are characterized by longitudinally-elongated low speed streaks and the corresponding shorter streamwise vortices. The streaks in sparse and dense canopy flows were likely to be aligned to the street line and to the roof lines, respectively. Such heterogeneity of TOS partially accounts for the large spatial variation of momentum flux. (4) In contrast to the mixing layer analogy of vegetation flows, the TOS and the resulting turbulent statistics of urban flow above the canopy resembled those in surface layers. The recirculation within the canopy significantly influenced the turbulent statistical properties. 相似文献
92.
Ethnic groups’ response to the 26 December 2004 earthquake and tsunami in Aceh, Indonesia 总被引:4,自引:4,他引:0
Jean-Christophe Gaillard Elsa Clavé Océane Vibert Azhari Dedi Jean-Charles Denain Yusuf Efendi Delphine Grancher Catherine C. Liamzon Desy Rosnita Sari Ryo Setiawan 《Natural Hazards》2008,47(1):17-38
The 26 December 2004 earthquake and tsunami unfairly hit the different ethnic groups of Aceh, Indonesia. About 170,000 Acehnese
and Minangkabau people died in the Northern tip of Sumatra while only 44 Simeulue people passed away in the neighbouring Simeulue
island located near the earthquake epicentre. Such a difference in the death toll does not lie in the nature of the hazard
but in different human behaviours and ethnic contexts. The present study draws on a contextual framework of analysis where
people’s behaviour in the face of natural hazards is deeply influenced by the cultural, social, economic and political context.
Questionnaire-based surveys among affected communities, key informant interviews and literature reviews show that the people
of Simeulue detected the tsunami very early and then escaped to the mountains. On the other hand, Acehnese and Minangkabau
people, respectively in the cities of Banda Aceh and Meulaboh, did not anticipate the phenomenon and were thus caught by the
waves. The different behaviours of the victims have been commanded by the existence or the absence of a disaster subculture
among affected communities as well as by their capacity to protect themselves in facing the tsunami. People’s behaviours and
the capacity to protect oneself can be further tracked down to a deep tangle of intricate factors which include the armed
conflict that has been affecting the province since the 1970s, the historical and cultural heritage and the national political
economy system. This paper finally argues that the uneven impact of the 26 December 2004 earthquake and tsunami in Aceh lies
in the different daily life conditions of the ethnic groups struck by the disaster. 相似文献
93.
94.
The 16 September 2015 Chile Tsunami from the Post-Tsunami Survey and Numerical Modeling Perspectives
95.
Yumiko Watanabe Shun'ichi Nakai Akihiro Hiruta Ryo Matsumoto Kunio Yoshida 《Earth and Planetary Science Letters》2008,272(1-2):89-96
We performed U–Th radioactive disequilibrium analyses of carbonate nodules and sediment samples recovered from methane seep sites off Joetsu, of the eastern margin of Japan Sea, to decipher the active period of the methane seep. The carbonates contain 230Th, part of which is located in detritus such as silicate and organics, at the time of precipitation. The initial 230Th renders accurate dating with U–Th radioactive disequilibrium method difficult. We assessed the feasibility of correction using radioactive disequilibrium data of ambient sediment to overcome this difficulty. A (230Th/232Th)–(234U/232Th) isochron drawn by three chips divided from a carbonate nodule (PC05-04-50) passed through data points of local sediments. We conclude that the problem of initial 230Th can be resolved by measurements of local sediments. Results show that carbonate nodules include local sediment as impurities. Furthermore, the results of trace element analyses such as Rb, Zr, Nb, REE, Pb, and Th also support the idea.In all, 18 carbonate samples were dated with correction of initial 230Th using the mean value of local sediment in this study. The U–Th correction ages show 12–35ka with an isochron age of 26 ± 3ka. Results indicate that during the time interval of U–Th ages, from 12ka to 35ka, environmental conditions must have been favorable for enhanced methane flux through sediment. The extensive methane flow period at 20ka accords with the lowest-stand sea level during the last glacial age. Results of this study also suggest that U–Th ages of carbonate are useful as a reliable chronometer with regard to methane seep activation. In order to acquire U–Th ages of carbonate at methane seep sites, however, it is important to evaluate the amount of initial 230Th accurately using the value of sediment. 相似文献
96.
Agusa T Nomura K Kunito T Anan Y Iwata H Miyazaki N Tatsukawa R Tanabe S 《Marine pollution bulletin》2008,57(6-12):807-815
Concentrations of 19 trace elements (V, Cr, Mn, Fe, Co, Cu, Zn, Se, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Tl, Hg, and Pb) were determined in the liver of the striped dolphins (Stenella coeruleoalba) collected around Japan during 1977-1982 to examine the sex difference, age dependence, and interrelationships among trace elements. Tissue distribution of trace elements was also investigated in one adult and one fetus specimens. Generally, concentrations of Se, Sr, Ag, Cd, Cs, Ba, Hg, and Pb were higher in the tissues of adult than those of fetus, whereas the opposite trend was observed for Cr and Tl. There were no significant sex differences in the trace element levels in the liver. Significant positive correlations between age (0-26.5 years) and hepatic concentrations were found for Ag, Se, Hg, V, Fe, Pb, and Sr, suggesting their age-dependent accumulation in the liver. In contrast, hepatic concentrations of Mn and Zn decreased with age. Significant positive relationships were observed between Se, and Hg, Ag, V, Fe, and Sr in the liver. 相似文献
97.
Tetsuro Agusa Kumiko Nomura Takashi Kunito Yasumi Anan Hisato Iwata Nobuyuki Miyazaki Ryo Tatsukawa Shinsuke Tanabe 《Marine pollution bulletin》2008,57(6-12):807
Concentrations of 19 trace elements (V, Cr, Mn, Fe, Co, Cu, Zn, Se, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Tl, Hg, and Pb) were determined in the liver of the striped dolphins (Stenella coeruleoalba) collected around Japan during 1977–1982 to examine the sex difference, age dependence, and interrelationships among trace elements. Tissue distribution of trace elements was also investigated in one adult and one fetus specimens. Generally, concentrations of Se, Sr, Ag, Cd, Cs, Ba, Hg, and Pb were higher in the tissues of adult than those of fetus, whereas the opposite trend was observed for Cr and Tl. There were no significant sex differences in the trace element levels in the liver. Significant positive correlations between age (0–26.5 years) and hepatic concentrations were found for Ag, Se, Hg, V, Fe, Pb, and Sr, suggesting their age-dependent accumulation in the liver. In contrast, hepatic concentrations of Mn and Zn decreased with age. Significant positive relationships were observed between Se, and Hg, Ag, V, Fe, and Sr in the liver. 相似文献
98.
Dredged spoil (DS) was used as a silt and clay additive in the construction of artificial tidal flats from mountain sand (MS). As the ratio of DS in the sediment media increased, the number of emerging macrobenthos increased. The composition of the macrobenthic community was also affected by the addition of DS, and the changes might be dependent on the ratio of DS to MS. In addition, the macrobenthos in the artificial tidal flats was more abundant than that in the control tidal flat, which was constructed with natural tidal flat sediment. With a silt and clay content of 25%, polychaetes Ceratonereis erythraeensis and Capitella sp. and the gastropod Batillaria cumingii were dominant, whereas no bivalves were present. With less silt and clay (5% and 10%), the bivalves Ruditapes philippinarum and Musculista senhousia were observed in the artificial flats, while their numbers in the control tidal flat were lower. 相似文献
99.
100.
Nitrogen isotope ratios of nitrate as a clue to the origin of nitrogen on the Pacific coast of Japan
To clarify the sources and transformation of NO3− on the Pacific coast of Japan, observations over the continental shelf were conducted during the summer in 2005 and 2006 when the Kuroshio flowed close to and away from the coastal area, respectively. Below the halocline, there are two prominent salinity peaks that originated in two different waters. In the subsurface layer, the salinity maximum (Smax) was indicative of the Kuroshio Water (KW), while the salinity minimum (Smin) in the middle layer at ∼400 m depth was indicative of the North Pacific Intermediate Water (NPIW). δ15NNO3 ranged from 4.1‰ to 5.1‰ with a mean of 4.8±0.4‰ in the deeper water around Smin. Below 50 m depth over the shelf break, δ15NNO3 values (3.1±0.8‰ in 2005 and 4.6±0.3‰ in 2006) clearly increased as contribution of NPIW increased in 2006. On the contrary, subsurface δ15N of NO3− values (−1.1±0.1‰) remained unchanged in both years, although the contribution of the KW to the subsurface water changed significantly. This suggests that the source of NO3− has little effect on the δ15N of NO3− in this layer. The negative δ15N values also coincided with the base of the chlorophyll maximum layer suggesting that these isotopic signals must be evidence of active nitrification in the upper layer. 相似文献