Grounding line proximal sediment characteristics at a marine‐based,late‐stage ice stream margin     

《第四纪科学杂志》2017,32(4):463-474

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X-ray reflection in accreting stellar-mass black hole systems     

R. R. Ross  A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2007,381(4):1697-1701

The X-ray spectra of accreting stellar-mass black hole systems exhibit spectral features due to reflection, especially broad iron Kα emission lines. We investigate the reflection by the accretion disc that can be expected in the high/soft state of such a system. First, we perform a self-consistent calculation of the reflection that results from illumination of a hot, inner portion of the disc with its atmosphere in hydrostatic equilibrium. Then, we present reflection spectra for a range of illumination strengths and disc temperatures under the assumption of a constant-density atmosphere. Reflection by a hot accretion disc differs in important ways from that of a much cooler disc, such as that expected in an active galactic nucleus.  相似文献   

Erratum: Voigt profile fitting to quasar absorption lines: an analytic approximation to the Voigt–Hjerting function     

《Monthly notices of the Royal Astronomical Society》2007,382(3):1375-1375

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A Multi-Wavelength Study of the 3B/X1.2 Flare Observed on 2003 October 26     

Brigitte Schmieder  Arkadiusz Berlicki 《中国天文和天体物理学报》2005,5(6):645-664

We report results from a multi-wavelength study of the 3B/X1.2 two-ribbon disk flare (S15E44), which was well observed by both ground-based and space-borne instruments. Two pairs of conjugate kernels - K1 and K4, and K2 and K3 - in the Ha images are identified. These kernels are linked by two different systems of EUV loops. Kl and K4 correspond to the two 17 GHz and 34 GHz microwave sources observed by the Nobeyama Radioheliograph (NoRH), while K2 and K3 have no corresponding microwave sources. Optical spectroscopic observations suggest that all the four kernels are possible precipitating sites of non-thermal electrons. Thus the energy of electron deposited in K2 and K3 should be less than 100 keV. Two-dimensional distributions of the full widths at half maximum (FWHM) of the Ha profiles and the line-of-sight (LOS) velocities derived from the Ca Ⅱ 8542 (?) profiles indicate that the largest FWHM and LOS velocity tends to be located near the outer edges of Ha kernels, which is consistent with the scenario of current two-ribbon flare models and previous results. When non-thermal electron bombardment is present, the observed Ha and Ca Ⅱ 8542 (?) profiles are similar to previous observational and theoretical results, while the He I 10830 A profiles are different from the theoretical ones. This puts some constraints on future theoretical calculation of the He I 10830 (?) line.  相似文献   

A theory of loosening earth pressure above a shallow tunnel in unsaturated ground     

Xu Fang  Mamoru Kikumoto  Ying Cui 《国际地质力学数值与分析法杂志》2020,44(10):1495-1508

A theory is proposed to evaluate the loosening earth pressure (vertical earth pressure after excavation) acting on a shallow tunnel in unsaturated ground with an arbitrary groundwater level. The theory is developed based on the limit equilibrium theory, combining soil–water characteristic curves, Mohr–Coulomb failure criteria, and effective stress for unsaturated soils. The proposed theory is applied to predict the vertical distribution of loosening earth pressure in unsaturated ground, which shows a significant difference from that in saturated ground. In unsaturated ground, suction contributes to the increase in effective loosening earth pressure and shear resistance. The remarkable effects of groundwater depth, soil type, and scale of overburden height and trapdoor width on loosening earth pressure are also revealed. Based on the soil–water characteristic curve, the degree of saturation decreases, which causes wet density to decrease and the total and effective loosening earth pressures to have contrary tendencies. Moreover, effective loosening earth pressures vary with soil type as the degree of saturation varies. The total loosening earth pressures are, however, very similar regardless of soil type, because wet density and shear resistance have similar tendencies. The proposed theory provides a valid model for loosening earth pressure in unsaturated ground that will be useful for shallow tunnel excavations.  相似文献   

Social equity and the probability of success of biodiversity conservation     

《Global Environmental Change》2015

Conservation actions generally benefit some groups more than others, and this inequity is thought to affect the probability of achieving conservation objectives. This has led to the common assumption that triple bottom line solutions – those that are effective, efficient, and equitable – are best and most likely to achieve each individual objective. Although this may be true, it has been little tested, and importantly lacks a conceptual foundation for understanding, predicting and evaluating how equity affects conservation outcomes. We describe types of equity relevant to conservation and explore how they may affect the probability of successfully achieving conservation outcomes. Depending on the equity type and context, the relationship between equity and conservation success varies. We find that the best conservation outcome is often achieved without perfect equity; highlighting the risk of ignoring the relationship between equity and success. We offer a conceptual foundation for better addressing this important issue in future research and application.  相似文献   

Simplified analytical solution for point load acting behind a cantilever wall     

George Maurice Iskander 《国际地质力学数值与分析法杂志》2012,36(3):344-351

The analysis of earth pressure resulting from an applied point load behind a retaining wall is to be carried out in three dimensions as the earth pressure distribution varies both in vertical and horizontal directions. In this research, the semi‐empirical expressions developed by Terzaghi [Trans. ASCE 1954; 119 ] for earth pressure due to point load are integrated and a correction factor is introduced to develop equivalent equations for two‐dimensional analyses. A new parameter referred to as the design width, which is the horizontal distance retained by the individual vertical retaining element is introduced. The used procedure and the resulted equations are tested and verified by adopting different design width values covering the practical range. The resulted equations together with the semi‐empirical expressions of earth pressure due to line load developed by Terzaghi [Trans. ASCE 1954; 119 ] can be easily used for two‐dimensional analysis of the effect of point load. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

全吸力范围生物炭−黏土混合土的土−水特性     

李明玉  孙文静  黄强  孙德安 《岩土力学》2022,43(10):2717-2725

土−水特征曲线在研究非饱和土的水力与力学特性中发挥着重要的作用。生物炭具有多孔结构、高比表面积和强吸附的特性。将生物炭改性土应用于垃圾填埋场上覆盖层,因受自然环境因素的影响会使其水力特性发生改变。为了研究全吸力范围内生物炭掺量对生物炭−黏土混合土保水特性的影响,利用蒸汽平衡法（吸力范围 3～368 MPa）、滤纸法（吸力范围 0 ～40 MPa）和压力板法（吸力范围 0～1.5 MPa）控制土样的吸力,测定吸力平衡后土样的含水率和饱和度,得到全吸力范围内生物炭−黏土混合土的土−水特征曲线。试验结果表明：（1）3种吸力测试方法很好地表达了生物炭−黏土混合土全吸力范围内的土−水特征曲线。（2）生物炭能够影响黏土的保水性,但在一定的吸力范围内,生物炭−黏土混合土的保水性还与孔隙结构和孔隙中水的形态相关。（3）通过压力板法测得,试样的进气值随着生物炭掺量的增加而减小。当吸力值小于进气值时,曲线出现水平段,土样始终处于饱和状态,生物炭掺量越大,试样的保水性越好。（4）由生物炭−黏土混合土微观孔隙结构以及生物炭在黏土中的分布形态来解释生物炭改性黏土的保水能力随生物炭掺量的变化关系。  相似文献   

基于离散元法对边坡二维极限平衡法的探讨          下载免费PDF全文

李松 《甘肃地质》2022,(3):59-62

边坡稳定性分析的极限平衡法是要做一定假设的。本文考虑了离散元与极限平衡法基于刚体理论的相似性,用离散元法计算出极限平衡法中的各个计算分量值,然后代入到常用极限平衡法中分析计算,根据离散元法的计算结果讨论了各极限平衡法中各种假设的合理性,为极限平衡法的计算提供了一个新思路。结果表明Bishop法与离散元法的计算结果比较接近,是本文经过离散元法计算后所推荐使用的方法。  相似文献   

山东青岛灵山湾南部海滩的时空演变及其影响因素^*          下载免费PDF全文

吴闯  张晓东  许淑梅  胡日军  姜胜辉  杨作升 《古地理学报》2022,24(1):152-163

全面准确评估海滩的时空演变,是海滩侵蚀防护的前提;基于卫星图像资源全面准确评估海滩的时空演变,对于缺乏长期连续实测数据的海滩的侵蚀防护具有重要意义。本研究基于谷歌地球引擎合成并下载灵南海滩(灵山湾南部海滩)1984—2021年的880幅卫星图像,聚焦海滩剖面提取干湿线和水边线在剖面上的位置;结合模拟潮位分析海滩剖面形态,计算海滩坡度和平均高、低潮线等,采用多指标研究灵南海滩的时空演变;结合历史资料分析影响灵南海滩演变的主要因素,并利用海滩实测数据评估利用卫星图像提取的海滩岸线的误差。结果表明,大量卫星图像的应用提高了研究结果的时间分辨率、精度和可靠性。在1984—2021年间,灵南海滩部分岸段发生了阶段性快速侵蚀,侵蚀速率为5.2~60 m/a,总侵蚀量达30~78 m,持续时间为0.5~11年,该快速侵蚀主要是挖沙、养殖场改建和废弃等人为因素造成的,风暴潮起次要的辅助作用。除上述快速侵蚀时段外,灵南海滩普遍发生慢速侵蚀,侵蚀速率一般小于2 m/a,这是相对海平面上升和河流入海泥沙锐减等的结果。  相似文献