A recipe for why and how to set up and sustain an experimental catchment

Experimental catchments are fundamental elements in hydrological sciences as they provide key data for putting forward and testing hypotheses, developing theories, constraining models, and making predictions. Significant progress in catchment hydrology stemmed from field measurements but increasing costs and risks associated with field work and the availability of big data based on remote sensing, machine learning, and a plethora of models, as well as observations deriving from previous and current sites, raises questions on whether running an experimental catchment still provides individual and community benefits as in the past. In this commentary, I highlight the advantages of keeping experimental catchments alive and propose a personal 10-step “recipe” to set up a new experimental catchment and manage and sustain it in the long term. These suggestions can be useful both to young and less young researchers who are open to facing the challenge of measuring processes in the field and are willing to offer the scientific community new experimental evidence for advancing our current knowledge in catchment hydrology.     

被动型氢钟流量变化对长期频率稳定度的影响分析

为提高系统的长期频率稳定度(它是被动型氢钟的一个重要指标),设计了一种实验,用以分析在不同微波腔谐振频率下,氢气流量变化对输出频率的影响。通过实验发现微波腔的控制电压存在一个调谐点,在调谐点附近,流量变化对输出频率的影响变小。但是对于单频系统,如何将微波腔锁定在调谐点附近以及如何减小流量的影响和提高系统的长期频率稳定度还需要进一步探索。     

一类生化反应动力系统极限环的存在唯一性

研究微分方程定性理论的应用,利用定性分析的方法,讨论了一类在生化反应中的动力系统,证明了其极限环的存在性、不存在性及极限环的存在唯一性,从而得到了完整的结果。     

水-岩作用下单裂隙灰岩渗流特性演化规律研究

针对某水电站地下洞室裂隙灰岩的渗漏问题,现场采集岩样和库水,设计进行了两种方案的水-岩作用试验,历时360 d,其中,方案1在浸泡过程中定期更换浸泡溶液,模拟地下水的长期浸泡和流动更新现象,方案2主要模拟长期浸泡过程。综合水-岩作用下裂隙面微观形貌特征以及浸泡溶液中离子浓度变化,分析水-岩作用下裂隙灰岩的渗流特性变化特征及机制。研究结果表明：在浸泡过程中,单裂隙灰岩的渗透系数呈“先快后慢”的增大趋势,浸泡360 d后,2.5、3.0、3.5、4.0 MPa等4种侧向应力在两种方案下单裂隙灰岩的渗透系数分别增大了729.90%～384.17%、549.04%～297.45%,侧向应力越小,裂隙岩样的渗透系数增大趋势越明显,增长趋势分别在120 d和90 d后趋于稳定。比较而言,方案1裂隙灰岩的渗透系数增长速率和幅度明显较大,为方案2的1.34～2.07倍。方案1定期更换浸泡库水,保持了浸泡溶液的不平衡状态,使得岩样与浸泡溶液间形成了较大的浓度梯度,增加了反应化学势,加快了裂隙表面矿物溶解、溶蚀速率,而方案2中,长期浸泡使得溶液中离子浓度逐渐接近平衡状态,导致裂隙面矿物溶解、溶蚀速率明显低于方案1。长期水-岩作用使得裂隙面粗糙度和波动性明显减小,局部坡度和起伏度逐渐减小,整体溶蚀深度逐渐增加,据此,建立了水-岩作用下单裂隙灰岩渗流通道演化模型,在长期水-岩作用下裂隙岩样的渗流通道逐渐向吻合度低、开度大的方向演化,从而导致了裂隙岩样等效水力开度及渗透系数的大幅度增长。相关研究思路和成果为裂隙岩体的水-岩作用模拟提供了较好的参考。     

湖南新化煤系石墨结构演化及其热反应行为

为了探究煤系石墨形成过程中结构演化及不同石墨化程度无烟煤和石墨的热反应行为,选取湖南新化系列变质程度无烟煤和煤系石墨为研究对象,通过X射线衍射（XRD）和高分辨率透射电子显微镜（HRTEM）对其结构进行表征,并结合程序控制升温法（TPO）分析不同变质程度无烟煤和煤系石墨的热反应行为。结果表明,随变质程度的增加,碳结构由无烟煤中的无定形态转变成石墨的三维有序C原子点阵。系列石墨化煤是由多种有序度不同的碳结构相组成,体现了其结构非均质性,碳结构相含量及分布随变质程度而逐渐变化,石墨化程度最高的煤系石墨中主要为石墨微晶集合体,但依旧含有结构缺陷。无烟煤和煤系石墨中碳结构的多相性和不均匀分布是影响其热反应行为的重要原因。      

Preliminary study on the sea level change and its long-term prognostic method for Shanghai

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Metamorphism and Isotopic Evolution of Granulites of Southern India: Reference to Neoproterozoic Crustal Evolution

Granulites are important component of high-grade metamorphic rocks reflecting intense conditions observed for crustal rocks in terms of temperature, and pressure. This review paper demonstrates how these high-grade granulites are critical to understanding the evolution of the lower continental crust with special reference to southern India. Geothermobarometric traverse across different granulite blocks in southern India shows wide ranging P-T conditions of metamorphism (700–1000 ° C, and 5–10 kbar). The sapphirine-, orthopyroxene-sillimanite, and spinel -bearing quartz-deficient granulites recognised from parts of southern granulite terrain (Ganguvarpatti, Kiranur, and Palani hill ranges etc.) show oriented sillimanite aggregates pseudomorph after course twinned kyanite, staurolite + kyanite assemblages, and corroded blebs of gedrite within orthopyroxene, suggesting a prograde stage of a clockwise P-T evolution. Evidence of ITD history comes from the textures in which an early Mg-rich garnet (X_Mg 52–60) with orthopyroxene (up to 10% Al₂O₃) involving sillimanite breakdown forming variety of symplectites having combinations of orthopyroxene, sapphirine, cordierite, and spinel. These spectacular reaction textures, and mineralogic sensors from the high-grade rocks establish a prograde clockwise P-T-t path with notable decompressive history (ITD) in the southern granulite terrain. The inferred P-T-t paths have been further integrated with the recent geochronological, and isotopic data to constrain the timing, and duration of metamorphism, emplacement of the magmatic protolith for characterising the evolution of the granulites, and their bearing on the geodynamic implications. Based on the emerging evidence for Neoproterozoic tectonothermal imprints in the southern granulite terrain, history of the assembly of dispersed fragments is also addressed within the East Gondwana framework.     

成岩作用中的地下水碳酸体系与方解石溶解度

方解石在沉积岩成岩环境中的溶解度与地下水化学特征、温度等有着极为密切的关系。地下水碳酸体系中各碳酸组分的比例是溶液pH值的函数,可溶性CO2、HCO3-和CO32-分别在pH≤pK1的酸性介质、pK1≤pH≤pK2的弱酸至中性介质和pH≥pK2的碱性介质中具有绝对数量。而地下水体系中碳酸总量及各组分的变化受到pH值、气相CO2分压PCO2及固相方解石的溶解-沉淀效应的控制。通过限定溶液中离子的电价平衡和质量守恒约束条件可以确定各种温压环境中的地下水组成及方解石的溶解度特征。溶液pH值和温度是方解石溶解度的最直接的控制因素,且方解石的溶解随pH值不同分别在强酸、弱酸和碱性介质中表现出不同的反应方式。基于质量守恒条件,溶液中初始[ΣCO2]-[Ca2+]值对中性至碱性介质中的方解石溶解度带来很大的影响,当[ΣCO2]0<[ca2+]0有利于方解石的溶解,当[σco2]0>[Ca2+]0时有利于方解石的沉淀。如果CO2—H2O—CaCO3体系同时受到电价平衡和质量守恒条件的约束,则方解石只在酸性介质中溶解,碱性介质中沉淀。新疆塔里木盆地库车坳陷克拉2气田及相关储层中方解石分布特征表明,该区碎屑岩储层中方解石的大量沉淀发生于重碳酸钠型地下水环境中,而孔隙度极好、次生孔隙发育的储集段则出现于氯化型的地下水环境,从而验证了成岩作用中地下水类型对方解石溶解—沉淀的控制机制。      

Lost City低温热液场--一种新的海底热液活动类型

综述了新近发现的海底热液活动的新类型——Lost C ity低温热液场。该低温热液场坐落于距洋中脊15 km远的轴外洋底上,下伏的橄榄石经蛇纹石化反应所产生的热能是驱动该热液场的热源。低温热液场烟囱结构的矿物组分主要为方解石、文石和水镁石,热液流的温度为40~75℃,并以高pH值以及高氢、高甲烷含量为特征。Lost C ity低温热液场,为研究者们了解早期地球热液过程与它们所支撑的生命系统关系,探讨蛇纹石化、碳酸盐沉淀、微生物活动之间关系提供了天然实验室。     

宁夏南部地区水质形成机制研究

宁夏南部地区是中国严重缺水地区之一,该地区地下水类型可分为松散岩类孔隙水、碎屑岩类裂隙-孔隙水、基岩裂隙水和碳酸盐类岩溶水。受到当地特殊的气候条件、地貌特征、地层岩性和地质构造的影响,各类地下水水质普遍比较差。含水介质中大量的石膏、芒硝等矿物成分进人地下水中是水质恶劣的根本原因;封闭的蓄水构造使得当地地下水循环不畅,蒸发浓缩作用使得浅层水中聚集高盐分,也是水质变差的重要原因。