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111.

Other Index

List of Forthcoming Papers  相似文献   
112.
We have computed line profiles and curves of growth for both reflected and transmitted radiation for typical lines in CO2 bands (in the photographic infrared) which occur in the spectrum of Venus. In our model the pressure variation with altitude was considered and the base of the cloud deck was set at the 2 bar level. The temperature was held constant at 250K and a Voigt profile was used for the lineshape. We also assumed that the scale height of the cloud particles was equal to the scale height of the gas. The calculations were made for four values of the scattering optical thickness (τc = 0.1, 1.0, 10, and 100) using a continuum single scattering albedo ωc = 0.9975 (which gives a Bond albedo of 0.896 for τc = 100, the value observed for Venus at these wavelengths). Curves of growth are also presented for reflected radiation which has been averaged over the visible disk for three values of the Venus phase angle (0, 86, and 166°).  相似文献   
113.
114.
Greenhouse warming due to carbon dioxide atmospheres may be responsible for maintaining the early Earth's surface temperature above freezing and may even have allowed for liquid water on early Mars. However, the high levels of CO2 required for such warming should have also resulted in the formation of CO2 clouds. These clouds, depending on their particle size, could lead to either warming or cooling. The particle size in turn is determined by the nucleation and growth conditions. Here we present laboratory studies of the nucleation and growth of carbon dioxide on water ice under martian atmospheric conditions. We find that a critical saturation, S=1.34, is required for nucleation, corresponding to a contact parameter between solid water and solid carbon dioxide of m=0.95. We also find that after nucleation occurs, growth of CO2 is very rapid, and we report the growth rates at a number of supersaturations. Because growth would be expected to continue until the CO2 pressure is lowered to its vapor pressure, we expect particles larger than those being currently suggested for the present and past martian atmospheres. Using this information in a microphysical model described in a companion paper, we find that CO2 clouds are best described as “snow,” having a relatively small number of large particles.  相似文献   
115.
The extraordinary SN 1997cy associated with GRB 970514 has been observed photometrically and spectroscopically for nearly 2 yr. At the time of discovery, SN 1997cy was the brightest supernova (SN) ever observed (MV相似文献   
116.
New observations of fracture nucleation are presented from three triaxial compression experiments on intact samples of Westerly granite, using Acoustic Emission (AE) monitoring. By conducting the tests under different loading conditions, the fracture process is demonstrated for quasi-static fracture (under AE Feedback load), a slowly developing unstable fracture (loaded at a `slow' constant strain rate of 2.5 × 10−6 /s) and an unstable fracture that develops near instantaneously (loaded at a `fast' constant strain rate of 5 × 10−5 /s). By recording a continuous ultrasonic waveform during the critical period of fracture, the entire AE catalogue can be captured and the exact time of fracture defined. Under constant strain loading, three stages are observed: (1) An initial nucleation or stable growth phase at a rate of ~ 1.3 mm/s, (2) a sudden increase to a constant or slowly accelerating propagation speed of ~ 18 mm/s, and (3) unstable, accelerating propagation. In the ~ 100 ms before rupture, the high level of AE activity (as seen on the continuous record) prevented the location of discrete AE events. A lower bound estimate of the average propagation velocity (using the time-to-rupture and the existing fracture length) suggests values of a few m/s. However from a low gain acoustic record, we infer that in the final few ms, the fracture propagation speed increased to 175 m/s. These results demonstrate similarities between fracture nucleation in intact rock and the nucleation of dynamic instabilities in stick slip experiments. It is suggested that the ability to constrain the size of an evolving fracture provides a crucial tool in further understanding the controls on fracture nucleation.  相似文献   
117.
张远海 《中国岩溶》2006,25(Z1):71-78
大部分情况下,天坑都是现代暗河通道洞顶塌陷而成.塌陷的扩大造成暗河通道的阻塞和改道,使得水力梯度变陡,溶蚀和侵蚀增强.可以说,天坑大部分空间体积的形成都是地下河大规模搬运崩塌堆积物的结果.强烈变化的大流量是搬运崩塌堆积的最佳条件,而暗河通道的改道和扩大又进一步加强了塌陷作用.与区域裂隙模式不同,新的裂隙随着崩塌周围应力释放而扩张.与原始洞穴通道形成相比,大规模天坑的形成都是源于这些作用.  相似文献   
118.
Storm runoff in the steep watersheds in Hawaii leads to sediment and freshwater pulses to coastal waters that quickly affect nearshore water quality. This is particularly true in semi-enclosed embayments, such as Kaneohe Bay, Oahu, where water has a relatively long residence time compared to more open coastal areas of the islands. In this paper the authors discuss water quality and productivity in Kaneohe Bay after back-to-back rain events in late November and early December 2003, following a particularly dry summer. The short-term biogeochemical response of coastal waters and the ecosystem to runoff and physical forcing was evaluated through a combination of continuous in situ measurements and adaptive synoptic sampling carried out on a variety of temporal and spatial scales.  相似文献   
119.
The effect of weathering on optically stimulated luminescence dating   总被引:2,自引:0,他引:2  
Optically stimulated luminescence (OSL) dating was applied to quartz samples recovered from the gravel sediments of deformed marine terrace at the Suryum site, southeastern Korea, but has yielded stratigraphically inconsistent ages. Micromorphological, chemical, and mineralogical analyses of the gravels indicate the possible influence of chemical weathering on the apparent OSL ages. In the course of weathering after emerging from beach environments, originally permeable gravels underwent infilling by halloysite-rich clays in their voids, export and import of radioactive elements, and loss of mechanical strength with the creation of a porosity within pebbles. Calculation based on the evolution of the weathering profile showed a severe fluctuation of dose rate caused by the change of water content and radioactive element concentrations. Samples recovered from the weathering profile inevitably include quartz grains derived from mechanically weakened pebbles or illuviated from the upper layer, making it difficult to determine the equivalent dose (De) values of exclusively depositional quartz sands. Quantitative evaluation of the change of fabric and chemistry of the sediments on the basis of pedologic insight significantly aids in the derivation of OSL ages consistent with geomorphology and other independent age controls.  相似文献   
120.
Dolomitic concretions in diatomaceous hemipelagic sediments of the Miocene Pohang Basin in the southwestern East Sea (Sea of Japan) preserve distinct signals of two independent sedimentary processes, which controlled the extents of isotopic compositions. Variable δ18O (−9.1‰ to +0.7‰) and high δ13C (+3.1‰ to +17.9‰) values suggest that the concretions formed in the methanogenic zone with alteration of the residual mid-Miocene seawater by volcanogenic sediments. Remarkable δ18O and δ13C values show a strong linear relationship, indicating that distinctly independent depositional processes operated during the formation of the concretions. The degree of methanogenesis was enhanced during rapid hemipelagic sedimentation of organic-rich particles, resulting in higher δ13C values, and the effect of volcaniclastics was diluted, maintaining the original properties of ambient mid-Miocene seawater. In contrast, lower δ18O and 87Sr/86Sr values characterize the effect of volcaniclastic sediments that were transported by intermittent gravity flows and interacted with mid-Miocene seawater. The input of volcaniclastic sediment probably degraded the role of methanogenesis by lowering the contents of organic matter and thereby decreased the δ13C values within the concretions. Isotopic signals recorded within the concretions highlight understanding of the depositional environment and evolution of the pore-water chemistry.  相似文献   
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