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941.
采用灰色关联度分析法对红层软岩的矿物成分、化学成分、崩解试验等数据进行了分析。分析表明, 水理特性不稳定的粘土矿物始终是影响软岩崩解的主要因素之一, 而不同的化学成分对红层软岩崩解性的影响程度不同。通过以纯水、MgCl2, FeCl3, NaCl, CaCl2盐溶液作为红层软岩岩块浸泡液的崩解试验, 说明纯水浸泡下软岩的崩解性最强, 而所选3种盐溶液对所选红层软岩样品的崩解性均有抑制作用, 其中又以CaCl2抑制作用最强。在此基础上提出公路施工中填筑前以浇水作为加快红层软岩崩解, 填筑压实中以掺入石灰作为抑制软岩崩解路用控制方法。 相似文献
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943.
The first part of this paper discusses how planet formation proceeds in the disks orbiting M dwarf stars. These environments are different from those associated with solar‐type stars in several ways: The planet forming clock (set by orbits) runs slower, the disks are more prone to evaporation, the supply of raw material is lower, the snowline is closer in, and planetary systems are more easily disrupted. Because of these considerations, red dwarfs are less likely to harbor giant planets, but can readily produce smaller planets. The second part of this paper describes stellar evolution calculations for M dwarfs, which live far longer than the current age of the universe. These diminutive stellar objects remain convective over most of their lives, continue to burn hydrogen for trillions of years, and do not experience red giant phases in their old age. Instead, red dwarfs turn into blue dwarfs and finally white dwarfs. This work also shows (in part) why larger stars become red giants. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
944.
冬春季青藏高原北麓河多年冻土活动层中气体CO2浓度分布特征 总被引:14,自引:4,他引:10
2005年1~5月在青藏高原北麓河附近的高寒干草原、高寒草甸和高寒草原3种典型草地上进行了不同深度土壤气体采样和CO2浓度分析.结果表明:土壤剖面的土壤气体CO2浓度呈现出上低下高的分布特征.在动态变化上,土壤中CO2浓度在多年冻土活动层春季升温过程中出现一个峰值,经过短暂的降低后随夏季融化过程开始而升高.土壤剖面CO2浓度与土壤有机碳、重组有机碳、轻组有机碳、水溶性有机碳、植物残体有机碳、微生物碳贮量和土壤温度呈明显的相关关系,在100 cm以上深度与土壤水分呈负相关关系.在整个观测期间,高寒干草原、高寒草原和高寒草甸植被下3种土壤剖面土壤气体CO2浓度变化范围分别为1 052~3 050 mL·m-3、3 425~39 144 mL·m-3和984~12250 mL·m-3,高于我国塿土CO2浓度变化范围,也远远高于青藏高原五道梁地区高寒草原土壤气体CO2浓度变化范围.石灰简育寒冻雏形土和石灰寒冻砂质新成土CO2浓度变化范围低于国外报道的草地和农田CO2浓度变化范围;石灰草毡寒冻雏形土CO2浓度变化范围明显高于国外报道的草地和农田CO2浓度变化范围.活动层冻结期,土壤CO2的闭蓄作蓄作用比较明显.由于微地形导致土壤水分条件的差异,夏季融化过程各观测点土壤CO2浓度开始升高时间存在差异. 相似文献
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946.
947.
The effective stress principle has been efficiently applied to saturated soils in the soil mechanics and geotechnical engineering practice; however, its applicability to unsaturated soils is still under debate. The appropriate selection of stress state variables is essential for the construction of constitutive models for unsaturated soils. Owing to the complexity of unsaturated soils, it is difficult to determine the deformation and strength behaviors of unsaturated soils uniquely with the previous single‐effective‐stress variable theory and two‐effective‐stress‐variable theory in all the situations. In this paper, based on the porous media theory, the specific expression of work is proposed, and the effective stress of unsaturated soils conjugated with the displacement of the soil skeleton is further derived. In the derived work and energy balance equations, the energy dissipation in unsaturated soils is taken into account. According to the derived work and energy balance equations, all of the three generalized stresses and the conjugated strains have effects on the deformation of unsaturated soils. For considering these effects, a principle of generalized effective stress to describe the behaviors of unsaturated soils is proposed. The proposed principle of generalized effective stress may reduce to the previous effective stress theory of single‐stress variable or the two‐stress variables under certain conditions. This principle provides a helpful reference for the development of constitutive models for unsaturated soils. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
948.
Development of pan coefficients for estimating evapotranspiration from riparian woody vegetation
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Tanya M. Doody Richard G. Benyon S. Theiveyanathan Vijay Koul Leroy Stewart 《水文研究》2014,28(4):2129-2149
The long‐term ‘Millennium Drought’ has put significant pressure on water resources across Australia. In southeastern Australia and in particular the Murray‐Darling Basin, removal of exotic, high‐water‐use Salix trees may provide a means to return water to the environment. This paper describes a simple model to estimate evapotranspiration of two introduced Salix species under non‐water‐limited conditions across seven biogeoclimatic zones in Australia. In this study, Salix evapotranspiration was calculated using the Penman–Monteith model. Field measurements of leaf area index and stomatal conductance for Salix babylonica and Salix fragilis were used to parameterize the models. Each model was validated using extensive field estimates of evapotranspiration from a semi‐arid (S. babylonica, r2 = 0.88) and cool temperate (S. fragilis, r2 = 0.99) region. Modelled mean annual evapotranspiration showed strong agreement with field measurements, being within 32 and 2 mm year?1 for S. babylonica and S. fragilis, respectively. Monthly pan coefficients (the ratio of mean evapotranspiration to mean pan evaporation) were developed from 30 years of meteorological data, for 30 key reference sites across Australia for both species using the validated Penman–Monteith models. Open‐water evaporation was estimated from field measurements and was used to develop a simple linear regression model for open‐water evaporation across the 30 reference sites. Differences between modelled evapotranspiration and open‐water evaporation at each site provide an indication of the amount of water that might be returned to the environment from removal of in‐stream Salix species. The monthly pan coefficient method reported has application across riparian environments worldwide where measured evapotranspiration is available for model validation. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
949.
950.
Stress history plays an important role in controlling the consolidation behavior of soft clays, but few models exist that can provide quantitative estimate of its influence. In this paper, the Gibson–Lo rheological model is used to simulate the coupled processes of drainage and creep of soft soils that takes stress history into account. A hybrid combination of analytical and numerical methods is adopted to solve the governing equations of consolidation with the nonlinear rheological model. The methodology is applied to a saturated soft soil subjected to surface loading. The soil profile is separated into normally consolidated and overconsolidated layers by a boundary that is allowed to move. Comparisons of the model predictions and its simulations are used to evaluate the effects of stress history, model parameters, and loading pattern on consolidation behavior. It is shown that stress history influences the location of the moving boundary, variations of the profiles of excess pore water pressure dissipation, stress and deformation‐based average degrees of consolidation. Parametric studies conducted show that when soil is stiffer, the excess pore water pressure dissipates much more quickly, and thus the soil consolidates much faster especially at the early stages. The results also show that soil viscosity influences the deformation‐based average degree of consolidation at the latter stages. The consolidation process of soil layer under linear loading is shown to lag behind those under instantaneous loading: the longer the loading period is, the smaller the average degrees of consolidation are no matter how they are defined. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献