西藏措勤地区典中组火山岩同位素特征及地质意义

西藏冈底斯岩浆岩带西段北侧的林子宗群火山岩含有从板块俯冲机制向大陆碰撞机制转变的丰富信息。将措勤地区典中组火山岩与冈底斯岩浆岩带东段林周盆地的典中组火山岩在同位素地球化学、演化特征方面进行对比,探讨冈底斯岩浆岩带西段与东段在演化过程中的异同性。结果表明,措勤地区典中组火山岩的87Sr/86Sr初始比值变化范围为0.710352~0.713423,具较高的87Sr/86Sr比值;143Nd/144Nd初始比值为0.512293~0.512407,具较低的143Nd/144Nd比值;林周盆地典中组火山岩的87Sr/86Sr初始比值为0.7057~0.7063之间,143Nd/144Nd初始比值范围为0.5125~0.5126。同位素特征显示措勤地区典中组源区物质可能来自于富集Ⅱ型地幔,即源区为俯冲和再循环的大陆地壳物质与地幔岩发生了混合作用的产物,源区受控于冈底斯地壳基底。林周盆地典中组火山岩源区物质可能与富集Ⅰ型地幔有关。     

岱海地区近400年来的"尘暴"事件——来自岱海沉积物粒度的证据

根据高分辨率的岱海沉积物粒度分布的中值粒径和粗颗粒含量,结合区域降水、历史记载资料,重建了内蒙古岱海地区近４００年来发生的尘暴事件。结果表明,尘暴事件是受冬、夏季风的相对强弱制约的,大量尘暴事件频发于小冰期干冷的气候条件下,表现为中值粒径大,粗颗粒含量高,在转暖的现代气候下,尘暴事件很少,中值粒径也随之降低,但是近十几年尘暴事件又呈上升趋势,部分可能与人类活动造成的土地荒漠化有关。     

Microseismicity and faulting geometry in the Gulf of Corinth (Greece)

During the summer of 1993, a network of seismological stations was installed over a period of 7 weeks around the eastern Gulf of Corinth where a sequence of strong earthquakes occurred during 1981. Seismicity lies between the Alepohori fault dipping north and the Kaparelli fault dipping south and is related to both of these antithetic faults. Focal mechanisms show normal faulting with the active fault plane dipping at about 45° for both faults. The aftershocks of the 1981 earthquake sequence recorded by King et al . (1985 ) were processed again and show similar results. In contrast, the observations collected near the western end of the Gulf of Corinth during an experiment conducted in 1991 ( Rigo et al . 1996 ), and during the aftershock studies of the 1992 Galaxidi and the 1995 Aigion earthquakes ( Hatzfeld et al . 1996 ; Bernard et al . 1997 ) show seismicity dipping at a very low angle (about 15°) northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30°. We suggest that the 8–12 km deep seismicity in the west is probably related to the seismic–aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed. The difference in the seismicity and focal mechanisms between east and west of the Gulf could be related to the difference in the recent extension rate between the western Gulf of Corinth and the eastern Gulf of Corinth, which rotated the faults dipping originally at 45° (as in the east of the Gulf) to 30° (as in the west of the Gulf).     

南方冬小麦三叶——抽穗期干物重与叶面积动态耦合计算探讨

根据实测资料,尝试性地提出了一种南方麦区冬小麦三叶到抽穗期的干物重与叶面积动态的耦合计算方法,经检验效果尚好。另外,初值灵敏度试验表明苗期生长状况的优劣对于其后生育阶段的干物重与叶面积动态影响似乎不大。     

Influence of fines content on the anti-frost properties of coarse-grained soil

This paper aims to determine the optimal fines content of coarse-grained soil required to simultaneously achieve weaker frost susceptibility and better bearing capacity. We studied the frost susceptibility and strength properties of coarse-grained soil by means of frost heaving tests and static triaxial tests, and the results are as follows:(1) the freezing temperature of coarse-grained soil decreased gradually and then leveled off with incremental increases in the percent content of fines; (2) the fines content proved to be an important factor influencing the frost heave susceptibility and strength properties of coarse-grained soil. With incremental increases in the percent content of fines, the frost heave ratio increased gradually and the cohesion function of fines effectively enhanced the shear strength of coarse-grained soil before freeze-thaw, but the frost susceptibility of fines weakened the shear strength of coarse-grained soil after freeze-thaw; (3) with increasing numbers of freeze-thaw cycles,the shear strength of coarse-grained soil decreased and then stabilized after the ninth freeze-thaw cycle, and therefore the mechanical indexes of the ninth freeze-thaw cycle are recommended for the engineering design values; and (4) considering frost susceptibility and strength properties as a whole, the optimal fines content of 5% is recommended for railway subgrade coarse-grained soil fillings in frozen regions.     

Methane hydrate formation comparisons in media with and without a water source supply

Water is a necessary element during gas hydrate formations. Therefore, by analyzing water depletion changes in media, the reaction characteristics of methane hydrate in media can be studied. In this study, two water sources supplying some liquid water which may be consumed by the methane hydrate formation reactions were designed and assembled. Using them, the full formation processes of methane hydrate was studied. Experimental results show the following： If heat released from nucleation reaction of methane hydrate is diffused rapidly, the nucleation ratios will be enhanced discernibly. While the hydrate is formed, a force is generated that sucks fresh water from the source into the vicinity of the hydrate, slowing down the cementation process and causing some hydrate grain dissociation. As a result of cementation differences, the hydrate reaction processes with different water sources present linear or quadratic equation characteristics. After a few repeated dissociation and formation processes of some hydrate grains caused by the fresh water, the gas amounts contained in hydrate will be significantly enhanced.     

Groundwater and surface water interactions in an alluvial plain, Tuul River Basin, Ulaanbaatar, Mongolia

Drinking water supplies in Ulaanbaatar, the capital of Mongolia, are completely dependent on groundwater sourced from pumping wells located in an alluvial plain of the Tuul River which flows through Ulaanbaatar. The interaction between groundwater in the alluvial plain and river surface water was investigated using a hydrological and multi-tracers approach. The observed groundwater contour map clearly shows that the Tuul River recharges the floodplain groundwater and groundwater flows from east to west. The similarity of chemical and stable isotopic compositions suggests that groundwater is mainly recharged by Tuul River water in the vicinity of the river. In addition, considering groundwater contours and chemical composition, groundwater in the northern and southern mountain sides contribute to floodplain groundwater. Stable isotopic information suggests that winter season precipitation also contributes to the groundwater, because groundwater in a specific region has a considerably lower isotopic ratio. Using the End Member Mixing Analysis applying oxygen-18, SiO₂ and HCO₃ ^- as tracers, the contribution ratios of the Tuul River, groundwater in the northern and southern mountain regions, and winter season precipitation to floodplain groundwater are estimated to be 58% to 85%, 1% to 54%, 0% to 16%, and 0% to 12%, respectively.     

不同无机晶须/PVC复合材料力学性能的研究

采用溶液共混法制备出硼酸镁晶须(MBOw)、硼酸钙晶须(Ca BOw)、硼酸铜铝晶须(Cu Al BOw)、碱式硫酸镁晶须(MOSw)、碳酸钙晶须(Ca CO3w)及硫酸钙晶须(Ca SO4w)增强的PVC复合材料,研究不同晶须对PVC力学性能的影响。采用扫描电镜分析PVC复合材料的拉伸断面及晶须分散情况。结果表明,除MOS外其它晶须对PVC的拉伸强度和弹性模量有不同程度的提高,MBOw对PVC复合材料的增强效果最显著,当MBOw含量为20%时,所得复合材料力学性能最佳,拉伸强度和弹性模量与纯PVC比较分别提高了38.08%和71.43%。     

古村落社区旅游参与度及影响因素——西递、宏村、南屏比较研究

以社区家庭为视角,建立基于利益导向的社区旅游参与水平测度指标,以皖南古村落西递、宏村、南屏为实证研究对象,揭示了古村落社区旅游参与度异同及其影响机理。研究结果表明:① 古村落内部、古村落之间的旅游参与度均有不同程度的差异,归因为家庭微观因子与社区中观因子交互作用所致。② 通过家庭微观因子对家庭人均旅游收入影响的通径系数分析,得出三个景区相应的直接通径系数和间接通径系数,发现古村落家庭微观因子的影响方向趋同而影响程度分异,与问卷调查结果分析的一致性也显示了该方法的较强解释力和潜在应用价值。③ 提高古村落社区旅游参与整体水平、缓解参与度空间差异的根本途径在于"让利于民",增强社区分利能力,政府在其中扮演着重要的引导角色。     

Effect of removing small (<150?μm) chironomids on inferring temperature in cold lakes

Sieving samples for chironomid analysis with a 150 μm mesh was shown to greatly reduce sample preparation time, and use of only larger specimens did not affect chironomid-inferred salinities in African lakes. Here, we tested if this method is suitable for temperature reconstruction in colder lakes at higher latitudes. Removal of specimens <150 μm in two training sets, one from Canada and one from Sweden, had little impact on the performance statistics of the calibration models. Chironomid abundance, however, decreased greatly because more than half of the head capsules in assemblages were <150 μm. This had major impacts on the temperature reconstructions. Inferences were on average 2°C warmer with the modified models (all specimens >150 μm) than those obtained with the full model (all specimens >100 μm). General patterns of temperature change were also altered. For Lake 7 on Southampton Island, Canada, a cooling trend was reconstructed with the full Canadian model while the modified Canadian model yielded a warming trend. When only specimens >150 μm were used, two to three times more wet sediment was needed to obtain a sufficient number of head capsules. These results indicate that, in cold lakes (mean July/August air temperature ≤11°C), large proportions of head capsules are <150 μm, and sieving the samples in a 150 μm mesh leads to altered temperature reconstructions.