Laboratory testing and numerical simulation of properties and thermal-induced cracking of Eibenstock granite at elevated temperatures

The knowledge about thermo-mechanical properties of granite is still limited to some extent. Individual measurements are necessary to obtain reliable properties for specific granite types. A reliable numerical model of thermal cracking behaviours of granite exposed to extreme high temperatures (e.g. 800–1000 °C) is missing. In this study, the impact of temperature up to 1000 °C on physical, mechanical, and thermal properties as well as thermo-mechanical coupled behaviour of Eibenstock granite was investigated by laboratory testing and numerical simulations. The physical properties including mineral composition, density, P-wave velocity, and open porosity are measured to be temperature dependent. Uniaxial compression and Brazilian tests were carried out to measure uniaxial compressive strength (UCS), Young’s modulus, stress–strain relationship, and tensile strength of Eibenstock granite before and after thermal treatment, respectively. Thermal properties including specific heat, thermal conductivity, thermal diffusivity, and linear thermal expansion coefficient are also measured and found to be temperature dependent, especially the expansion coefficient which shows a steep increase around 573 °C as well as at 870 °C. The numerical simulation code FLAC^3D was used to develop a numerical scheme to simulate the thermal-induced damage of granite at high temperatures. Statistical methods combined with real mineral composition were used to characterize the heterogeneity of granite. The numerical model is featured with reliable temperature-dependent parameters obtained from laboratory tests. It can well reproduce the laboratory results in form of thermal-induced micro- and macrocracks, as well as the stress–strain behaviour and the final failure pattern of Eibenstock granite after elevated temperatures up to 1000 °C. The simulation results also reveal that the thermal-induced microcracks are randomly distributed across the whole sample. Although most thermal-induced damages are tensile failures, shear failure begins to develop quickly after 500 °C. The obvious UCS reduction in granite due to heating is mainly caused by the increase in shear failure. The simulation also shows that the dominant impact of α–β quartz transition is widening pre-existing cracks rather than the formation of new microcracks.

     

柴达木盆地盐湖卤水及其沉积物硼同位素地球化学研究进展

综述了柴达木盆地盐湖卤水及其沉积物的硼同位素研究成果,并从pH值、离子浓度、物源补给等几方面对盐湖卤水及其沉积物的硼同位素组成进行了探讨。强烈的蒸发作用可以导致盐湖卤水的pH值降低,从而使δ¹¹B值相应地升高;卤水中的B可能会随碳酸盐的析出而进入到固相中,因此Ca²⁺浓度和Ca/Cl比值较高的湖泊,其卤水的δ¹¹B值一般都比较高;盐湖卤水及其补给水源的δ¹¹B值与B/Cl比值具有中等程度的负相关关系,这种特性也可以用来指示河水中硼的来源;当易风化的硅酸盐矿物经剥蚀迁移并最终在湖泊中沉积时,盐湖沉积物的δ¹¹B值会因这些低δ¹¹B值的物源加入而变低;此外,强烈的化学风化会使湖泊中沉积较多的细粒粘土矿物,由于粘土矿物的吸附作用也会使得盐湖沉积物中的δ¹¹B值偏低。关于柴达木盆地盐湖硼同位素的研究,不仅可以为盐湖的形成、演化及成盐成矿规律的研究提供可靠依据,而且可以为盐湖资源评价及合理开发提供科学依据。     

京津冀地区AOD时空变化及影响因子的地理探测

基于MODIS 3 km AOD遥感数据,利用空间自相关模型及地理探测器对2010—2016年京津冀地区AOD的时空变化特征及其影响因子进行探测。结果表明：（1） 2010—2016年京津冀地区年平均AOD值为0.83,其中天津市年均AOD值为研究区最高,河北省次之,北京市最低。研究区及各分区AOD的7 a变化趋势大体一致,呈现先下降后上升再小幅波动的状态。（2） 空间自相关分析表明京津冀地区AOD空间分布呈现显著正相关。局部高高聚集区主要集中在北京市东南部、天津市南部及河北省的中南部,低低聚集区集中分布在西北部山区。研究区高低聚集区面积均呈减小趋势,不显著区呈扩大态势。（3） 地理探测器结果表明不同区域的主导影响因子不同,北京市首要影响因子为NDVI,其次为人口密度,且二者交互作用明显。天津市主导因子为风速,人口密度、第二产业生产总值等人为因子的作用力也较大,风速与其交互作用较强。河北省主导因子为人口密度,GDP与第二产业生产总值等的作用力次之,整体交互作用偏弱。通过地理探测器解析京津冀地区AOD空间分异的影响机理,其结果对我国大气污染治理具有重要意义。     

地方院校师范生教材分析能力评价与现状分析——以地理科学专业为例

教材分析能力是师范生专业技能之一,文章选取教材分析能力指标,采用专家打分法构建评价量表,通过对某地方院校地理专业师范生实训报告的诊断,揭示师范生教材分析能力现状,发现存在以下问题:课标解读缺乏深度,忽视其对教学的指导作用;对教材重难点把握不准,分析缺乏依据;对教材知识内在逻辑与外部联系分析不到位,欠缺对教材学科思想方法的分析意识与能力;对教材表述结构及教学意图的分析较为薄弱。     

肯尼亚交通优势度及其空间分异格局分析

基于2018年肯尼亚铁路、公路、机场、港口等交通基础设施数据,设定交通优势度指数及交通网络连接度指数和交通对外通达度指数2个分指数,采用探索性数据分析法对肯尼亚交通优势度及其空间分异格局进行分析,并对其影响因素进行探讨。研究发现：① 肯尼亚交通优势度空间差异十分显著,以内罗毕、蒙巴萨和基苏木为主要交通节点的铁路沿线地区交通优势度水平明显高于其他地区;② 肯尼亚交通优势度空间分异格局总体上呈现出较强的非均衡性,交通网络连接度呈现出以内罗毕为核心,以铁路沿线为轴带呈圈层状向四周递减的空间分异格局,而交通对外通达度呈现出北部和西北部较低而南部和东南部较高的空间分异格局。③ 地形地貌、气候、水文、人口集聚、经济发展等是形成肯尼亚交通优势度空间分异的主要影响因素。对交通基础设施空间分布进行优化调整,积极引导经济空间合理布局,是推动肯尼亚经济健康持续发展的重要途经。     

北斗三号短基线相对定位精度分析

我国北斗卫星导航系统（BDS）已经进入第三阶段北斗三号（BDS-3）的建设,其定位精度问题一直是全球关注的热点．本文基于IGS连续跟踪站2018年第227天多模全球卫星导航系统（GNSS）数据,对短基线进行动态处理,将BDS-3的相对定位精度与北斗二号(BDS-2)的相对定位精度进行分析．结果表明,目前BDS-3短基线相对定位精度E方向优于3 cm,N方向优于3.5 cm,U方向优于10 cm,三个方向精度略高于BDS-2短基线相对定位精度．      

基于拉格朗日分析法的中尺度涡精细三维结构研究及其误差估计

在前人的工作中,拉格朗日分析法被用来演示大尺度环流,同时拉格朗日拟序结构可以较好的演示中尺度涡两维结构的发展过程。然而,很少研究关注怎么利用拉格朗日分析法针对中尺度涡三维结构进行演示。与以往利用欧拉方法研究中尺度涡三维结构的工作不同,我们利用拉格朗日分析法,从另一个视角来研究涡旋结构。我们在海山上方模拟出一个理想的气旋涡,涡旋内的下沉流和涡旋旁的上升流形成一个闭合的环流。这种结构很难从欧拉角度来演示。然而,粒子的运动轨迹很好地展示了整个循环:流体在涡旋中旋转下沉,汇聚到底层的上升流区,并通过上升流返回到海表面。我们也将拉格朗日分析法应用于真实的模拟结果中。作为中国南海的一个重要现象,靠近越南中部的海域中的偶极子（反气旋涡/气旋涡）,关于其结构的研究已经比较成熟了,但这些研究主要关注的是海面过程。通过拉格朗日分析,我们很好的演示了偶极子的三维结构:流体在反气旋涡(气旋涡)内部旋转上升(下沉)。更重要的是,粒子的轨迹表明,这两个涡旋之间不存在水团交换,因为强边界急流将它们彼此分开。以上结论均得到了计算误差估计的可信度支持。尽管在强辐散流和强垂直扩散流中,计算误差逐渐增大,但是在一定的时间步长和积分周期内,计算误差始终保持在一个较小的值。     

Nonlinear feedback synchronisation control between fractional-order and integer-order chaotic systems

This paper focuses on the synchronisation between fractional-order and integer-order chaotic systems. Based on Lyapunov stability theory and numerical differentiation, a nonlinear feedback controller is obtained to achieve the synchronisation between fractional-order and integer-order chaotic systems. Numerical simulation results are presented to illustrate the effectiveness of this method.     

Modification of the spontaneous emission of quantum dots near the surface of a three-dimensional colloidal photonic crystal

This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal. In experiments, semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated. The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements. The modification of the spontaneous emission rate, which is reflected in the change of spectral shape and PL lifetime, is clearly observed. While an obvious increase in the PL lifetime is found at most wavelengths in the band gap, a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge. Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal. It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously. This finding provides a simple and effective way for improving the performance of light emitting devices.     

Regulation of water quality and growth characteristics of indoor raceway culture of <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis>

Two modes of regulating the water quality of experimental ponds in indoor raceway culture of Litopenaeus vannamei were evaluated using simple water treatment facilities. A self-made water purifying net, aeration stone, composite microbe preparation, and Ceratophyllum demersum were placed in the experimental ponds and the culture water was circulated along the raceway inside the pond using a paddle wheel aerator. In addition, the water quality in the experimental pond was improved by draining effluent from the pipeline at the bottom of ponds 7 and 8 (mode I) and exchanging the circulating water in pond 10 (mode II) with the reservoir water in pond 9 using a pump and pipeline. The water quality in the experimental ponds was similar in response to regulation using mode I or mode II. Water quality parameters in the experimental ponds were controlled within a suitable range by simple facilities during culture period without using any chemical treatments. The rich content of dissolved oxygen was maintained by the circular flow and continuous aeration of the pond water. The respective average values of the main water parameters in experimental ponds 7 and 10 in response to regulation of the water quality using modes I and II were as follows: pH 8.17 and 7.99; DO 5.16 mg/L and 5.97 mg/L; COD_Mn 18.45 and 12.61 mg/L; TAN (NH₃-N) 0.854 mg/L (0.087 mg/L) and 0.427 mg/L (0.012 mg/L); NO₂-N 0.489 mg/L and 0.337 mg/L. Moreover, the average body length and body weight of harvested shrimp of pond 7 and pond 10 were 7.56 cm and 8.99 cm, 5.10 g and 8.33 g, respectively. Furthermore, the survival rate, average biomass yield and average condition factor of the shrimp harvested were 70% and 60%, 2.54 kg/m² and 2.14 kg/m², and 0.675 g/cm and 0.927 g/cm, respectively. Linear equations describing the relationship between body length and culture time and cubic or power functions describing the relationship between body weight and body length were obtained based on evaluation of the growth data of shrimps throughout the culture period.