Groundwater flow path determination during riverbank filtration affected by groundwater exploitation: a case study of Liao River,Northeast China

The groundwater flow path plays an important role in maintaining hydrological and ecological quality and security, which are important in the comprehensive management and use of both groundwater and surface water. In this study, an integrated multi-tracer-constrained framework was used to determine the groundwater flow path. The results show that there are shallow and deep flow paths in riverbank filtration, controlled by the different permeabilities of riverbed sediments and aquifers at different depths. The contribution of river water to shallow groundwater is less than that to deep groundwater because of the low permeability of the riverbed sediment in the dense muddy layer in the shallow slope of the river valley. This contribution decreases with increasing distance from the Liao River. The shallow groundwater quality is better than the deep groundwater quality because of its longer residence time.     

基于地理核心素养培养的教学案例设计——以“大规模海水运动”第一课时为例

随着教育改革深入推进,地理核心素养成为课程总目标,预示着地理教育进入新的发展阶段。本文以“大规模海水运动”第一课时为例,以Boyan Slat主人公保护海洋的故事为主线,融合Earth Null School软件及模拟洋流小实验,归纳出洋流分布规律,最后升华海洋保护的主题,从中渗透地理核心素养的培育。     

粒度和磁化率记录的毛乌素沙地东缘全新世气候变化

通过对毛乌素沙地东缘大柳塔剖面地层沉积物粒度及磁化率特征的分析,结合光释光测年结果,探讨了毛乌素沙地全新世气候变化。结果表明:(1)剖面沉积物粒度组成以中砂、粗砂为主,古土壤中黏粒组分含量高(3.32%),风成砂中几乎不含黏粒组分(0.01%),粒度参数的平均粒径M_z和分选系数σ也表现为古土壤高值、风成砂低值;(2)磁化率在全剖面呈有规律的变化,低频、高频磁化率在古土壤中呈高值,湖沼相、弱成壤次之,风成砂最小;低频磁化率χ_lf与黏粒(<2μm)含量、平均粒径M_z呈显著正相关,垂向剖面上变化规律一致,指示了相似的气候环境意义;(3)毛乌素沙地在10.39 ka BP附近存在明显的3次冷干-暖湿气候波动; 10.39～9.34 ka BP,气候冷干,风沙活动盛行; 9.34～8.68 ka BP,冬季风衰退,夏季风增强,成壤作用强烈; 8.68～8.29 ka BP,气候寒冷干燥; 8.29～2.72 ka BP,气候整体温暖湿润,在6.55～3.80 ka BP达到鼎盛后转向冷干; 2.72～1.34 ka BP,冬季风占主导,沙丘活化,沙漠扩张; 1.34 ka BP至今,逐渐接近现代气候。毛乌素沙地的全新世气候变化是东亚冬、夏季风此消彼长作用下全球气候变化的区域响应。     

毒品贸易与国家主权破碎：基于缅甸北部的政治地理学分析

与中国云南省接壤的缅甸北部少数民族自治邦,包括掸邦和克钦邦,构成全球第二大非法毒品生产地的金三角核心区。通过借助历史档案和学术文献,聚焦缅甸北部,基于政治地理的视角,理清缅甸北部毒品贸易的历史起源,探讨了自缅甸1948年独立后毒品贸易给该国带来的政治与经济危机,以及相应的地缘政治冲突和外部干预。文章试图回答的问题有：为什么毒品贸易能够在缅北扎根?毒品贸易如何影响缅甸政府在其北部山区的主权完整和领土控制?文章的核心观点是毒品成为缅甸国内破碎主权和外部势力干预的原因和结果,毒品贸易以及与毒品相关的犯罪活动已经渗入缅北,严重危害了缅甸的主权完整。毒品贸易也为外部势力介入缅甸国内事务提供了契机。由于主体民族缅族控制的中央政府同缅北的少数民族地方武装间缺乏足够的信任,民族和解缺乏基础,也无法为全面禁毒创造有利的政治条件。因而,缅北的毒品贸易和缅甸的国家建设相互影响,导致国家主权破碎化和外部干预,导致缅北成为亚洲最贫穷落后的地区。文章分析以毒品为核心的开源权力机制与非正式或者非法全球化,丰富了Agnew有关主权的理论,在实践方面有助于认识中缅边境安全的复杂性,促进云南同东南亚的跨国区域化。     

Using two contrasting methods with the same tracers to trace the main sediment source in a mountainous catchment

Assessing the contribution of sediments from different sources is essential to understand erosive processes and formulate further soil conservation strategies to address environmental problems.In this study,we combined the source fingerprinting approach with geochemistry,including comparison of potential sources,and distribution pattern of major elements,to estimate the different land-use relative contributions to streambed sediment in the Luowugou catchment(13.5 km~2)located on the Heishui River,the first branch of the Jinsha River,China.A total of 57 samples from stream bank,cropland,grassland,forest land,and sediments were collected,and then,15 elements were analyzed foreach sample.The fingerprinting results demonstrated that the stream bank(62.4%)had the greatest relative contribution to the bed sediment yield,while cropland,grassland,and forest land contributed 18.6%,14.9%,and 4.1%to the bed sediments,respectively.In comparison to the fingerprinting method,even though the results upon geochemistry only provide a qualitative assessment,the ranking of sediment contributions based on geochemistry was consistent with the sediment fingerprinting ranking,that is,stream bankcroplandgrasslandforest land.Our findings suggest that the focal point for sediment control practices should be the stream bank rather than cropland in the region.Geochemistry can result in an important means in validating the fingerprinting results.     

Searching for GeV gamma-ray emission from the bulge of M31

The three major large-scale, diffuse γ-ray structures of the Milky Way are the Galactic disk,a bulge-like GeV excess towards the Galactic center, and the Fermi bubble. Whether such structures can also be present in other normal galaxies remains an open question. M31, as the nearest massive normal galaxy, holds promise for spatially-resolving the γ-ray emission. Based on more than 8 years of Fermi-LAT observations, we use(1) disk,(2) bulge, and(3) disk-plus-bulge templates to model the spatial distribution of the γ-ray emission from M31. Among these, the disk-plus-bulge template delivers the best-fit, in which the bulge component has a TS value 25.7 and a photon-index of 2.57 ± 0.17, providing strong evidence for a centrally-concentrated γ-ray emission from M31, that is analogous to the Galactic center excess. The total0.2–300 GeV γ-ray luminosity from this bulge component is(1.16 ± 0.14) × 1038 erg s-1, which would require ～ 1.5 × 105 millisecond pulsars, if they were the dominant source. We also search for a Fermi bubble-like structure in M31 using the full dataset(pass8), but no significant evidence has been found.In addition, a likelihood analysis using only photons with the most accurate reconstructed direction(i.e.,PSF3-only data) reveals a 4.8 σ point-like source located at ～10 kpc to the northwest of the M31 disk, with a luminosity of(0.97 ± 0.27) × 1038 erg s-1 and a pho@ton-$i·nd3 ex of 2.31 ± 0.18. Lacking a counterpart on the southeast side of the disk, the relation between this point-like source and a bubble-like structure remains elusive.     

Dynamic behaviour of weathered red mudstone in Sichuan (China) under triaxial cyclic loading

The construction of a high-speed railway (HSR) in Southwest China is being hindered by a severe shortage of high-quality subgrade materials. However, red mudstone is widely distributed in the Sichuan Basin of China. The ability to use weathered red mudstone (WRM) to fill subgrade beds by controlling its critical stress and cumulative strain would enable substantial savings in project investments and mitigate damage to the ecological environment. To better understand the dynamic behaviour of WRM, both monotonic and cyclic triaxial tests were performed. The evolution of the cumulative strain vs. increased loading cycles was measured. The influences of confining pressure and loading cycles on the dynamic modulus, damping ratio, critical cyclic stress ratio (CSR), and dynamic stress level (DSL) were investigated. The relationship between the CSR and loading cycles under different failure strain criteria (0.1%-1.0%) was analysed. The prediction model of cumulative strain was also evaluated. The results indicated that the shear strength of WRM sufficiently meets the static strength requirements of subgrade. The critical dynamic stress of WRM can thus satisfy the dynamic stress-bearing requirement of the HSR subgrade. The critical CSR decreases and displays a power function with increasing confining pressure. As the confining pressure increases, the DSL remains relatively stable, ranging between 0.153 and 0.163. Furthermore, the relationship between the dynamic strength and loading cycles required to cause failure was established. Finally, a newly developed model for determining cumulative strain was established. A prediction exercise showed that the model is in good agreement with the experimental data.     

Effect of dry density on the liquefaction behaviour of Quaternary silt

Quaternary silt is widely distributed in China and easily liquefies during earthquakes. To identify the influence of the dry density on the liquefaction behaviour of Quaternary silt, 40 cyclic triaxial liquefaction tests were performed on loose silt (dry density ρ_d=1.460 g/cm³) and dense silt (ρ_d=1.586 g/cm³) under different cyclic stress ratios (CSRs) to obtain liquefaction assessment criteria, determine the liquefaction resistance, improve the excess pore water pressure (EPWP) growth model and clarify the relationship between the shear modulus and damping ratio. The results indicate that the initial liquefaction assessment criteria for the loose and dense silts are a double-amplitude axial strain of 5% and an EPWP ratio of 1. The increase in the anti-liquefaction ability for the dense silt is more significant under lower confining pressures. The CSR of loose silt falls well within the results of the sandy silt and Fraser River silt, and the dense silt exhibits a higher liquefaction resistance than the sand-silt mixture. The relationships between the CSR and loading cycles were obtained at a failure strain of 1%. The EPWP development in the dense and loose silts complies with the “fast-stable” and “fast-gentle-sharp” growth modes, respectively. The power function model can effectively describe the EPWP growth characteristics of the dense silt. Finally, based on the liquefaction behaviour of silt, a suggestion for reinforcing silt slopes or foundations is proposed.     

Experimental Study on A Sloshing Mitigation Concept Using Floating Layers of Solid Foam Elements

A sloshing mitigation concept taking advantage of floating layers of solid foam elements is proposed in the present study. Physical experiments are carried out in a liquid tank to investigate the hydrodynamic mechanism of this concept. Effects of the foam-layer thickness, excitation amplitude, and excitation frequency on the sloshing properties are analyzed in detail. It is found that the floating layers of solid foam elements do not evidently affect the fundamental natural sloshing frequency of the liquid tank evidently among the considered cases. At the resonant condition, the maximum wave height and dynamic pressure are greatly reduced as the foam-layer thickness increases. Higher-order pressure components on the tank side gradually vanish with the increase of the foam-layer thickness. Cases with different excitation amplitudes are also analyzed. The phenomenon is observed when the wave breaking in the tank can be suppressed by solid foam elements.     

Process and Contextual Factors Supporting Action-Oriented Learning: A Thematic Synthesis of Empirical Literature in Natural Resource Management

Despite a long-term focus on learning in natural resource management (NRM), it is still debated how learning supports sustainable real-world NRM practices. We offer a qualitative in-depth synthesis of selected scientific empirical literature (N?=?53), which explores factors affecting action-oriented learning. We inductively identify eight key process-based and contextual factors discussed in this literature. Three patterns emerge from our results. First, the literature discusses both facilitated participation and self-organized collaboration as dialogical spaces, which bridge interests and support constructive conflict management. Second, the literature suggests practice-based dialogs as those best able to facilitate action and puts a strong emphasis on experimentation. Finally, not emphasized in existing reviews and syntheses, we found multiple evidence about certain contextual factors affecting learning, including social-ecological crises, complexity, and power structures. Our review also points at important knowledge gaps, which can be used to advance the current research agenda about learning and NRM.