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131.
To improve the scaling parameter controlling the impact crater formation in the strength regime, we conducted impact experiments on sintered snow targets with the dynamic strength continuously changed from 20 to 200 kPa, and the largest crater size formed on small icy satellites was considered by using the revised scaling parameter. Ice and snow projectiles were impacted on a snow surface with 36% porosity at an impact velocity from 31 m s−1 to 150 m s−1. The snow target was sintered at the temperature from −5 °C to −18 °C, and the snow dynamic strength was changed with the sintering duration at each temperature. We found that the mass ejected from the crater normalized by the projectile mass, πV, was related to the ratio of the dynamic strength to the impact pressure, , as follows: , where the impact pressure was indicated by P = ρtC0tvi/2 with the target density of ρt, when the impact velocity, vi, was much smaller than the bulk sound velocity C0t (typically 1.8 km s−1 in our targets). The ratio of the largest crater diameter to the diameter of the target body, dmax/D, was estimated by calculating the crater diameter at the impact condition for catastrophic disruption and then compared to the observed dmax/D of jovian and saturnian small satellites, in order to discuss the formation condition of these large dmax/D in the strength regime. 相似文献
132.
Sulfur isotope effects produced by microbial dissimilatory sulfate reduction are used to reconstruct the coupled cycling of carbon and sulfur through geologic time, to constrain the evolution of sulfur-based metabolisms, and to track the oxygenation of Earth’s surface. In this study, we investigate how the coupling of carbon and sulfur metabolisms in batch and continuous cultures of a recently isolated marine sulfate reducing bacterium DMSS-1, a Desulfovibrio sp., influences the fractionation of sulfur isotopes.DMSS-1 grown in batch culture on seven different electron donors (ethanol, glycerol, fructose, glucose, lactate, malate and pyruvate) fractionates 34S/32S ratio from 6‰ to 44‰, demonstrating that the fractionations by an actively growing culture of a single incomplete oxidizing sulfate reducing microbe can span almost the entire range of previously reported values in defined cultures. The magnitude of isotope effect correlates well with cell specific sulfate reduction rates (from 0.7 to 26.1 fmol/cell/day). DMSS-1 grown on lactate in continuous culture produces a larger isotope effect (21-37‰) than the lactate-grown batch culture (6‰), indicating that the isotope effect also depends on the supply rate of the electron donor and microbial growth rate. The largest isotope effect in continuous culture is accompanied by measurable changes in cell length and cellular yield that suggest starvation. The use of multiple sulfur isotopes in the model of metabolic fluxes of sulfur shows that the loss of sulfate from the cell and the intracellular reoxidation of reduced sulfur species contribute to the increase in isotope effects in a correlated manner. Isotope fractionations produced during sulfate reduction in the pure culture of DMSS-1 expand the previously reported range of triple sulfur isotope effects (32S, 33S, and 34S) by marine sulfate reducing bacteria, implying that microbial sulfur disproportionation may have a smaller 33S isotopic fingerprint than previously thought. 相似文献
133.
Death tolls from tornadoes in Bangladesh are the highest in the world due to lack of storm warnings, poor communication, weak
housing, and lack of shelters from strong winds in tornadoes and nor’westers. Based on surveys of housing types and designs
in the Tangail district, a household tornado shelter is proposed to be placed in the elevated storage platform that is common
in houses. The shelter is 2 m tall, 1.2 m wide, and 2–4 m long (4.8–9.6 m3 in volume) with the floor of the shelter placed one meter below the floor of the house. Walls are 7–10 cm thick and made
of concrete or an earthen wall stabilized with cement or strengthened with bamboo or bricks. A survey of 200 residents of
the region found nearly universal acceptance for the shelter design, and residents were eager for installation of the household
shelters. The shelter cost is 2,500–10,000 taka (US50 to50 to 200) depending on local material and labor costs but residents
were willing to pay an average of only 1,071 taka (US$21) toward the cost of the shelter. Families with greater income and
land holdings and families in villages with recent tornado experience were willing to spend more for a shelter. A pilot project
to install household tornado shelters in selected villages and monitor their use, along with continued efforts to issue storm
warnings, communicate the warnings, and improve education about storm hazards, will prevent injuries and save lives in Bangladesh
and reduce the descent into poverty that results from losses in severe local storms. 相似文献
134.
Koichi Shiraishi Masahiko Hayashi Motowo Fujiwara Takashi Shibata Masaharu Watanabe Yasunobu Iwasaka Roland Neuber Takashi Yamanouchi 《Polar Science》2011,5(4):399-410
Solid polar stratospheric cloud (PSC) layers observed by lidar and a balloon-borne optical particle counter (OPC) on 17 December 1995 are reexamined in a comparative analysis framework. The typical radius of solid particles in the observed PSC is determined through the comparative analysis to have been approximately 2.3 μm. A backward trajectory analysis for the air mass in which the solid particles were observed shows that the air mass had experienced temperatures 2–3 K below the frost point of nitric acid tri-hydrate (NAT) during the 4 days preceding the observations. The back-trajectory analysis traces the air mass back to northern Greenland and Ellesmere Island on 16 December, one day before the observations. A microphysical box model is used to investigate possible mechanisms of formation for the observed solid particles. The results of this model suggest that the solid particles formed under mesoscale temperature fluctuations associated with mountain lee wave activity induced by the relatively high terrestrial elevations of northern Greenland and Ellesmere Island. 相似文献
135.
This paper describes the petrological features and the ages of rock fractures filled mainly with carbonates at coastal outcrops of Yakushima Island, Japan. Microscopic observation and geochemical analysis were used to investigate the petrological features and the compositions of the fracture fillings. In addition, AMS 14C dating was also performed to estimate the ages of them. Microscopic study indicated that the fracture fillings contain not only cementing materials but also lithic fragments from host rock and bioclasts. SEM observation showed that the cements exhibit the characteristic textures of beachrocks. The cements were identified as Mg-calcite from XRD analysis. It was also observed from geochemical analysis that there were at least two stages of precipitation within the fractures. In addition, AMS 14C dating for seventeen samples of fracture fillings showed that the ages range from 2,460 to 5,130 years BP which is found to be younger than that of the uplifted coral at Yakushima Island (approximately 5,300–5,600 years BP). The results suggest that the fractures were solidified after the coral was uplifted. 相似文献
136.
137.
This paper presents recent results of application of the finite element models to wave overtopping and wave run-up problems in ocean dynamics. Open boundaries are prescribed as natural boundary condition obtained from the continuity equation of the Galerkin finite element formulation. The numerical results are, in general, reasonably good agreements with the histrical field data. 相似文献
138.
Masahiko Ikeda 《Astrophysics and Space Science》1975,35(2):255-268
The energy spectrum of the diffuse component of cosmic X-rays was measured with rocket-borne scintillation counters. Subtracting the environmental background unambiguously by means of the shutter method, the absolute values of the cosmic X-ray flux are obtained in a few keV band from 10 to 40 keV. The result indicates that the energy spectrum sharply changes its slope around 20–30 keV. Some trial functions for the spectrum are compared with our result; among them a thermal bremsstrahlung spectrum and a two-slope power law spectrum seem to fit very well. The former needs, however, another origin of X-rays in the lower and higher energy regions. ‘Sharpness’ of the break in the case of the latter is discussed, including a data point in high energy side from a balloon experiment. The acceptable range of the spectral index in the high energy side is 2.3–2.6, that of the break energy is 20–30 keV and the corresponding transition width is smaller than 50 keV, if the confidence level is to be better than 5%. Non-thermal X-ray generation due to the inverse Compton effect does not reproduce the X-ray spectrum, even if the electron spectrum shows a sharp break. Bremsstrahlung with the non-thermal electrons or protons with a sharp cut in the low energy side of the spectrum can reproduce our result, though such a cut seems unrealistic. Our result may suggest that current theories on the origin of the diffuse X-rays have to be revised. 相似文献
139.
Ai Hattori-Saito Jun Nishioka Tsuneo Ono R. Michael L. McKay Koji Suzuki 《Journal of Oceanography》2010,66(1):105-115
In order to detect iron (Fe) stress in micro-sized (20–200 μm) diatoms in the Oyashio region, western subarctic Pacific during
spring, immunological ferredoxin/flavodoxin assays were applied to samples collected from the surface layer in May 2005. Concomitantly,
the community composition of the micro-sized phytoplankton and hydrographic conditions, including dissolved Fe and macronutrient
concentrations, were also examined. Chlorophyll (Chl) a concentrations were <2 mg m−3 at all sampling stations, except at a station where the Chl a level was 9.0 mg m−3 and a micro-sized diatom bloom occurred. A high abundance of ferredoxin in micro-sized diatoms was detected only at a rather
near-shore station where dissolved Fe and macronutrient concentrations were higher, indicating that the micro-sized diatoms
did not suffer from iron deficiency. On the other hand, flavodoxin in micro-sized diatoms was often observed at the other
stations, including the bloom station, where macronutrients were replete but dissolved Fe concentration was low (0.31 nM).
A significant amount of chlorophyllide a, a degradation product of Chl a, was also observed at the bloom station, suggesting a decline of the diatom bloom. The micro-sized phytoplankton species
at all the stations were mainly composed of the diatoms Thalassiosira, Chaetoceros, and Fragilariopsis spp. Our study indicates that micro-sized diatoms were stressed by Fe bioavailability during the spring season in the Oyashio
region 相似文献
140.
To clarify the effect of a surface regolith layer on the formation of craters in bedrock, we conducted impact-cratering experiments on two-layered targets composed of a basalt block covered with a mortar layer. A nylon projectile was impacted on the targets at velocities of 2 and 4 km s?1, and we investigated the crater size formed on the basalt. The crater size decreased with increased mortar thickness and decreased projectile mass and impact velocity. The normalized crater volume, πV, of all the data was successfully scaled by the following exponential equation with a reduction length λ0: , where λ is the normalized thickness T/Lp, T and Lp are the mortar thickness and the projectile length, respectively, b0 and b1 are fitted parameters obtained for a homogeneous basalt target, 10?2.7±0.7 and ?1.4 ± 0.3, respectively, and λ0 is obtained to be 0.38 ± 0.03. This empirical equation showing the effect of the mortar layer was physically explained by an improved non-dimensional scaling parameter, , defined by , where up was the particle velocity of the mortar layer at the boundary between the mortar and the basalt. We performed the impact experiments to obtain the attenuation rate of the particle velocity in the mortar layer and derived the empirical equation of , where vi is the impact velocity of the projectile. We propose a simple model for the crater formation on the basalt block that the surface mortar layer with the impact velocity of up collides on the surface of the basalt block, and we confirmed that this model could reproduce our empirical equation showing the effect of the surface layer on the crater volume of basalt. 相似文献