Granulites record the tectonic evolution from collisional thickening to extensional thinning of the Tongbai orogen in central China

A combined study of petrology and geochemistry was carried out for granulites from the Tongbai orogen in central China. The results reveal the tectonic evolution from collisional thickening to extensional thinning of the lithosphere at the convergent plate boundary. Petrographic observations, zircon U–Pb dating, and pseudosection calculations indicate that the granulites underwent four metamorphic stages, which are categorized into two cycles. The first cycle occurred at 490–450 Ma and involves high-P (HP) metamorphism (M1) at 785–815°C and 10–14 kbar followed by decompressional heating to 840–880°C and 8–9 kbar for medium-pressure granulite facies metamorphism (M2), defining a clockwise P–T path. The high pressure is indicated by the occurrence of inclusions of rutile+kyanite+K-feldspar in the garnet mantle. The second cycle occurred at c. 440 Ma and shows an anticlockwise P–T path with continuous heating to ultrahigh-temperature (UHT) metamorphism (M3) at 890–980°C and 9–11 kbar, followed by decompressional cooling to 740–880°C and 7–9 kbar (M4) till 405 Ma. The HP metamorphism is synchronous with the ultrahigh-pressure eclogite facies metamorphism in the Qinling orogen, indicating its relevance to the continental collision in the Cambrian. The UHT metamorphism took place at reduced pressures, indicating thinning of the collision-thickened orogenic lithosphere. Therefore, the Tongbai orogen was initially thickened by the collisional orogeny and then thinned, possibly as a result of foundering of the orogenic root. Such tectonic evolution may be common in collisional orogens where compression during continental collision switched to extension during continental rifting.     

基于稳定同位素技术的光背团水虱食性分析

为了探究光背团水虱的食性特征，本研究利用碳、氮稳定同位素技术于2015年冬季和2016年夏季对广西北海廉州湾红树林中光背团水虱及其食物来源的碳、氮稳定同位素比值（δ13C值和δ15N值）进行分析。结果显示，冬季和夏季光背团水虱的δ13C值大小范围为-22.85‰~-21.87‰，平均值为（-22.46±0.35）‰；δ15N值大小范围为11.02‰~12.85‰，平均值为（11.88±0.56）‰；光背团水虱的δ13C值、δ15N值变化范围较小，表明其食物来源较为简单。单因素方差分析结果显示，冬季与夏季光背团水虱的平均δ13C值差异不显著（P>0.05），而夏季的δ15N值普遍高于冬季δ15N值，差异显著（P<0.05）；不同生长阶段的光背团水虱δ13C值、δ15N值会随着体长的增长而增大，差异显著（P<0.05），表明光背团水虱在生长的过程中可能发生了食性转变。光背团水虱的δ13C值与浮游生物的δ13C值相近，而与红树植物δ13C值差距较远，说明光背团水虱主要以浮游生物为食物来源。基于R语言稳定同位素混合模型（SIAR）计算结果显示，冬季和夏季各粒径级别浮游生物对不同生长阶段的光背团水虱的贡献率趋势基本一致，表现为1.2~25 μm粒级的浮游生物对光背团水虱平均贡献率最高，其次为25~50 μm粒级，粒径大于100 μm的浮游生物对体长小于5.5 mm的光背团水虱贡献率较低，对体长大于5.5 mm的光背团水虱的贡献率随着体长增大而相应增大，说明不同生长阶段的光背团水虱食性有差异。对光背团水虱食性分析的结果可为深入研究团水虱爆发的原因及危害红树林的作用机理提供基础资料。     

Numerical Simulation on Flow Past Two Side-by-Side Inclined Circular Cylinders at Low Reynolds Number

A series of three-dimensional numerical simulations is carried out to investigate the effect of inclined angle on flow behavior behind two side-by-side inclined cylinders at low Reynolds number Re=100 and small spacing ratio T/D=1.5 (T is the center-to-center distance between two side-by-side cylinders, D is the diameter of cylinder). The instantaneous and time-averaged flow fields, force coefficients and Strouhal numbers are analyzed. Special attention is focused on the axial flow characteristics with variation of the inclined angle. The results show that the inclined angle has a significant effect on the gap flow behaviors behind two inclined cylinders. The vortex shedding behind two cylinders is suppressed with the increase of the inclined angle as well as the flip-flop gap flow. Moreover, the mean drag coefficient, root-mean-square lift coefficient and Strouhal numbers decrease monotonously with the increase of the inclined angle, which follows the independent principle at small inclined angles.

     

航空重力垂直梯度探测潜艇方法研究

航空重力梯度测量属于被动探测,抗干扰能力强,如果能和其他探潜手段相配合将极大地提高航空搜潜的效率。针对航空重力梯度测量是否能够用于探测潜艇的问题,依据俄亥俄级弹道导弹核潜艇的结构特点,建立了适用于重力梯度计算的潜艇模型,分别给出了潜艇外壳、内部质量亏损产生的重力垂直梯度的计算方法,并对不同精度重力梯度仪可探测的潜艇重力垂直梯度值进行了计算,从航空反潜的角度对探测潜艇效果进行了分析。经计算表明,如航空重力梯度仪精度达到10~(-2) E,将具备一定的实际探潜效能;如精度达到10~(-4) E,反潜机搜索宽度可与现有航空磁性探潜相当。     

英国高中地理教材编写特色简析--以《Geography B Evolving Planet》为例

英国是重视地理课程传统的发达国家,拥有丰富的地理教材编写经验。本文以《Evolving Planet》为范本,在阅读与分析的基础上,归纳得出该教材的四大编写特色:设置"以学为中心"的教材栏目,精选多类型优质的地理图像,重视对学生学习方法的引导和注重对学生地理技能的培养。简析该教材的编写特色,以期为未来我国中学地理教材的编写提供启示与借鉴。     

纳滤分离铝锂过程研究

本文探讨了纳滤分离Al~(3+)和Li~+的可行性,研究了含盐量和铝锂比对分离效率的影响,提出了从锂云母浸出液中分离回收锂的新方法。实验结果表明,纳滤膜对Al~(3+)和Li~+的截留率随含盐量的升高而降低,其中Li~+始终呈现负浓度梯度扩散的趋势,而Al~(3+)的截留率始终稳定在99%以上。当含盐量为45 g/L时,铝锂分离因子最高可达248.33,膜面相应Zeta电位的绝对值达到最大。随着溶液中铝锂比的变化,Al~(3+)和Li~+的截留率分别在不同铝锂比的条件下出现拐点,溶液的pH呈现先下降后上升最后下降的复杂趋势。本实验研究发现,DK膜能够在酸性环境下实现高效的铝锂分离和锂的浓缩,从而为锂云母浸出液中锂的提取提供新的思路。     

Coupling numerical simulation with remotely sensed information for the study of frozen soil dynamics

The acquisition of spatial-temporal information of frozen soil is fundamental for the study of frozen soil dynamics and its feedback to climate change in cold regions. With advancement of remote sensing and better understanding of frozen soil dynamics, discrimination of freeze and thaw status of surface soil based on passive microwave remote sensing and numerical simulation of frozen soil processes under water and heat transfer principles provides valuable means for regional and global frozen soil dynamic monitoring and systematic spatial-temporal responses to global change. However, as an important data source of frozen soil processes, remotely sensed information has not yet been fully utilized in the numerical simulation of frozen soil processes. Although great progress has been made in remote sensing and frozen soil physics, yet few frozen soil research has been done on the application of remotely sensed information in association with the numerical model for frozen soil process studies. In the present study, a distributed numerical model for frozen soil dynamic studies based on coupled water-heat transferring theory in association with remotely sensed frozen soil datasets was developed. In order to reduce the uncertainty of the simulation, the remotely sensed frozen soil information was used to monitor and modify relevant parameters in the process of model simulation. The remotely sensed information and numerically simulated spatial-temporal frozen soil processes were validated by in-situ field observations in cold regions near the town of Naqu on the East-Central Tibetan Plateau. The results suggest that the overall accuracy of the algorithm for discriminating freeze and thaw status of surface soil based on passive microwave remote sensing was more than 95%. These results provided an accurate initial freeze and thaw status of surface soil for coupling and calibrating the numerical model of this study. The numerically simulated frozen soil processes demonstrated good performance of the distributed numerical model based on the coupled water-heat transferring theory. The relatively larger uncertainties of the numerical model were found in alternating periods between freezing and thawing of surface soil. The average accuracy increased by about 5% after integrating remotely sensed information on the surface soil. The simulation accuracy was significantly improved, especially in transition periods between freezing and thawing of the surface soil.     

Salinivibrio sp.YH4胞外丝氨酸蛋白酶EYHS耐盐性及生物信息学分析

摘要：目的 探讨菌株Salinivibrio sp.YH4分泌的丝氨酸蛋白酶EYHS的耐盐性及结构特征。方法 明胶底物酶谱法分析EYHS的耐盐性。应用生物信息学手段对EYHS及6种耐盐的S8家族丝氨酸蛋白酶结构特征进行分析。结果 EYHS在4 mol/L的NaCl溶液中仍具有活性，属于耐盐蛋白酶。EYHS及6种S8家族丝氨酸蛋白酶分子表面的loop区等无规则卷曲所占比例较高，α-螺旋与β-片层则主要位于酶分子内部。EYHS分子表面酸性氨基酸含量较高，且具有弱疏水内核。多序列比对发现蛋白酶的催化三联体两侧存在高度保守的基序和保守的极性氨基酸及芳香族氨基酸，并存在多个保守的Gly与Ala。同源模建和表面电荷分布显示，α螺旋和β片层围成了蛋白酶的催化腔，EYHS活性中心包含由Asp32、His65与Ser215组成的催化三联体，且催化位点区域表面静电势为负。结论 上述结构特征可能有助于耐盐丝氨酸蛋白酶EYHS在高盐环境下维持其稳定性和适度柔性，并有助于其催化功能的发挥，为深入研究耐盐丝氨酸蛋白酶的高盐环境适应性提供了一定的理论依据。     

毛乌素沙地锦鸡儿（Caragana）根系微域细菌群落多样性特征

基于16S rRNA高通量基因测序技术，对毛乌素沙地小叶锦鸡儿（Caragana microphylla)、柠条锦鸡儿（Caragana korshinskii）根系微域（即根系、根际土、根区土、灌丛间空白土）间的细菌群落多样性和结构差异性进行表征。本研究对各根系微域间细菌群落的Alpha多样性指数进行了单因素方差分析以及基于OTU水平的PCA分析，探究其在根系微域间Alpha和Beta多样性的层级变化，证实了有关植物根系微域生态位分化的报道，并发现锦鸡儿属植物根系微域间细菌群落的多样性和结构组成随着4个微域类型由外及内呈现出显著的层级差异性（P<0.05）。通过对优势细菌群组的结构组成分析，发现锦鸡儿属植物对特定细菌群组具有显著的向根系内筛选富集的作用（P<0.05）。这种植物通过根系微域对特定细菌群组的逐级筛选富集作用，是导致锦鸡儿属植物灌丛下不同生态位间细菌群落结构和组成发生层级变异的主要原因。     

江苏海岸中部近岸冬季潮汐和潮流特征

南黄海西侧的江苏海岸近岸区域,素以地形复杂、潮流强劲、悬沙输运剧烈著称,但是较长期的同步潮位和潮流观测数据仍然缺乏,尤其是在近岸(20 km)浅水(20 m)区域。2014年1月在大丰港附近开展了连续潮位和潮流观测,获得的数据揭示了一系列特征。此地潮汐潮流为正规半日潮,浅水分潮显著。平均潮差为3.05 m,最显著的两个分潮为M2和S2分潮,振幅分别为1.45 m和0.52 m。潮流最显著的半日分潮M2分潮和最显著的浅水分潮M4分潮在沿岸方向上振幅分别为0.84m/s和0.12m/s,在跨岸方向上振幅分别为0.24 m/s和0.01 m/s,沿岸方向占绝对优势。潮波的沿岸传播介于前进波和驻波之间,驻波的特征稍强。M2分潮潮流椭圆最大流(长轴)方向为南偏东7.4°。存在冬季沿岸向北的余流,垂向平均值的大小为2.2 cm/s。以上潮汐潮流特征为该区域海洋物质输运研究提供了基础资料。