The phase diagram of the intergalactic medium and the entropy floor of groups and clusters: are clusters born warm?

We point out that two problems of observational cosmology, namely the facts (i) that ≳60 per cent of the baryonic content of the Universe is not observed at   z ∼ 0  and (ii) that the properties of small clusters do not agree with simple expectations, could be closely related. As shown by recent studies, the shock heating associated with the formation of large-scale structures heats the intergalactic medium (IGM) and leads to a 'warm IGM' component for the gas. In the same spirit, we suggest the intracluster medium (ICM) to be a mixture of galaxy-recycled, metal-enriched gas and intergalactic gas, shock heated by the collapsing much larger scales. This could be obtained through two processes: (1) the late infalling gas from the external warm IGM is efficiently mixed within the halo and brings some additional entropy, or (2) the shocks generated by larger non-linear scales are also present within clusters and can heat the ICM. We show that, if assumption (1) holds, the entropy brought by the warm IGM is sufficient to explain the observed properties of clusters, in particular the entropy floor and the   L _X– T   relation. On the other hand, we note briefly that scenario (2) would require a stronger shock heating because of the larger density of the ICM as compared with filaments. Although the efficiency of these two processes remains to be checked on a quantitative level, they have the advantage of dispensing with the need to invoke any strong preheating from supernovae or quasars (which has otherwise been introduced for the sole purpose of reproducing the behaviour of clusters). Matter ejection by galaxies is included in the present calculations and, consistently with the metal-enrichment requirements, is indeed shown to yield only a quite moderate entropy increase. Our scenario of clusters being 'born warm' can be checked through the predicted redshift evolution of the entropy floor.     

塔里木河流域2000-2014年地表覆盖动态变化监测

针对塔里木河流域脆弱的生态环境,该文采用地理信息系统、遥感技术手段提取2000年、2006年、2009年、2012年以及2014年塔里木河流域地表覆盖分类数据并对其变化特征进行分析.结果表明:2000-2014年塔里木河流域除水域、荒漠与裸露地表面积减少外,其余地表类型均呈增加趋势,其中变化量最大的为荒漠与裸露地表、冰川与积雪、耕地、草地,其变化量分别为-34 558.1 km2、14 351.15 km2、6 471.79 km2、6 383.94 km2.2000-2014年塔里木河流域荒漠与裸露地表面积减小,主要转变为了草地、林地与耕地;耕地面积增加主要来自于林地、草地、荒漠与裸露地表;冰川和积雪的面积增加主要增加来源为林地、草地和荒漠与裸露地表.     

浅析地理国情监测项目的实施思路

开展地理国情监测工作,不仅有利于加快生态文明建设、促进阳光责任政府建设,也可以实现管理和决策的空间化、科学化。本文以塔里木河流域地表覆盖变化监测试点项目为例,从监测影像的选取、监测内容的确定、专题资料的收集与利用和监测技术流程等方面,全面分析了监测项目的实施思路,可为全面开展地理国情监测工作提供参考。     

Study on the characteristics and formation mechanism of the typical post-fire debris flow in Lushan area of Xichang City: A case study of 3# branch on the left bank of Xiangshuigou

On March 30, 2020, a forest fire broke out in Liangshan area of Xichang City in Sichuan Province. After the fire, the ash and burnt soil easily developed into debris flow in case of heavy rainfall, which brought potential geological hazard risks to the ecological environment of Lushan and safety of local people's lives and properties in Qionghai and Lushan areas. Taking 3^# branch on the left bank of Xiangshuigou in Anha Town as an example, the authors conducted field investigation, UAV aerial photography, geophysical exploration, field and indoor experiments to study the fluid characteristics, dynamic parameters and genetic mechanism of the post-fire debris flow on May 1, 2020. The features of movement, provenance scale and deduced precipitation were also systematically analyzed. This achievement could provide some reference for the study of the development trend of the post-fire debris flow and the mitigation of disasters in this area.     

Performance evaluation of normalized difference chlorophyll index in northern Gulf of Mexico estuaries using the Hyperspectral Imager for the Coastal Ocean

The Hyperspectral Imager for the Coastal Ocean (HICO) was used to derive chlorophyll-a (chl-a) based on the normalized difference chlorophyll index (NDCI) in two Gulf of Mexico coastal estuaries. Chl-a data were acquired from discrete in situ water sample analysis and above-water hyperspectral surface acquisition system (HyperSAS) remote sensing reflectance in Pensacola Bay (PB) and Choctawhatchee Bay (CB). NDCI algorithm calibrations and validations were completed on HICO data. Linear and best-fit (polynomial) calibrations performed strongly with R² of 0.90 and 0.96, respectively. The best validation of NDCI resulted with an R² of 0.74 and root-mean-square error (RMSE) of 1.64 µg/L. A strong spatial correspondence was observed between NDCI and chl-a, with higher NDCI associated with higher chl-a and these areas were primarily located in the northern PB and eastern CB at the river mouths. NDCI could be effectively used as a qualitative chl-a monitoring tool with a reduced need for site-specific calibration.     

最小二乘法分段拟合标定反应谱方法

反应谱的标定方法直接关系到反应谱特征参数的确定,合理的反应谱标定方法得到的设计反应谱能够真实地表达地震动的特性,是确定地震动输入的重要环节。提出了基于坐标变换的最小二乘法分段拟合方法,通过对汶川大地震不同场地典型强震记录反应谱的标定,对比了反应谱不同的标定方法,根据反应谱标定图形的对比及误差分析认为,最小二乘法分段拟合方法是操作简便且标定结果合理的反应谱标定方法。     

非饱和岩石中的纵波频散与衰减: 双重孔隙介质波传播方程

本文采用Rayleigh理论描述纵波激励下非饱和岩石中气泡的局域流体流动,从经典力学的哈密顿原理导出了双重孔隙介质中的波传播方程,即Biot-Rayleigh方程.方程的格式简洁,参数少,所有相关参数物理可测,因此,方程具有较好的物理可实现性.基于相同的岩石与前人理论对比,初步验证了本理论的有效性.对三个地区的砂岩储层进行了分析,结果显示:地震频段内纵波对储层是否含气非常敏感,但对含气饱和度指示性不佳,且随着孔隙度降低,纵波频散与衰减在中低频段更为显著;含甲烷与含二氧化碳的砂岩储层均呈第三类AVO响应特征,很难从叠前分析技术中鉴别;理论预测的纵波频散随饱和度与频率变化的趋势与特征,与多频段实验观测结果一致.     

冈底斯成矿带谢通门县梅巴切勤早白垩世高分异A型花岗岩的地球化学特征与钨锡成矿作用研究

高分异花岗岩因其特殊的成矿专属性而受到广泛关注。谢通门县梅巴切勤复式岩体出露于冈底斯成矿带,由黑云母正长花岗岩、二云母正长花岗岩和白云母正长花岗岩构成,钨锡矿体处于白云母正长花岗岩内部或外接触带。在详细地质研究的基础上,用LA-ICP-MS方法获得了129.7±0.9Ma（黑云母正长花岗岩）、128.4±1.6Ma（二云母正长花岗岩）与129.5±0.5Ma（白云母正长花岗岩）的206Pb/238U加权平均年龄。花岗岩具有高SiO2、K2O、K2O+Na2O,低Al2O3、CaO、MgO的特点,相对富集Zr、Nb、Ce、Y、Hf等元素,亏损Ti、Ba、Sr、P等元素,具有较高的10000Ga/Al、全岩Zr饱和温度和明显的Eu负异常,显示其为高分异A型花岗岩,形成于碰撞后的伸展环境。白云母正长花岗岩是分异演化的最终产物,为稀有金属花岗岩,存在较明显的稀土元素四分组效应,其更为强烈的熔体-流体作用造成W、Sn、Nb、Ta等稀有金属进一步富集,碰撞后的伸展环境以及热扰动在提供通道和热源的同时,也延长了岩浆分异演化时间,有利于成矿物质在岩浆演化的晚期阶段富集和品位高、规模大的稀有金属矿床的形成。梅巴切勤地区良好的成矿地质条件预示着其具有形成大-超大型矿的潜力,该研究对于冈底斯成矿带W、Sn、Nb、Ta等稀有金属找矿有着重要的引导和参考意义。     

基于声发射实验结果讨论大震前地震活动平静现象的机制

基于岩石变形声发射实验结果讨论了大震前地震活动平静现象的机制。在双轴压缩、等位移速率加载条件下 ,挤压型雁列断层、含宏观凹凸体断层、Ⅲ型剪切断层等非连续断层在临近滑动失稳前 ,声发射活动均出现了明显的相对平静现象 ,表现为声发射事件的发生率和应变能释放水平显著降低。与此阶段相对应 ,断层带 (特别是非连续部位上新形成的一小段断层 )发生了蠕滑和匀阻化作用 ,并使得标本的差应力开始下降。根据实验结果提出 ,大地震前断层的“蠕滑 -匀阻化”过程是造成地震活动平静现象的可能机制