Simulation of structural phase transition in NaNO3 and CaCO3

 The order-disorder phase transitions in NaNO₃ and CaCO₃ are simulated by molecular dynamics. The simulations are based on the potentials calculated from the Gordon–Kim modified electron gas formalism extended to molecular ions. We successfully reproduced the transition temperature T _c and the abnormally large c axis thermal expansion observed in experiment. The phase transitions in NaNO₃ and CaCO₃ were found to be initiated by ±60 and ±180° reorientation of the NO₃ and CO₃ ions about the c axis. The orientations of NO₃ and CO₃ ions are continuous with six preferred calcite-type orientations above the phase-transition temperature. Received: 30 January 2001 / Accepted: 11 May 2001     

兰州阿干镇及其外围中生代地层

兰州阿干镇及其外围中生代地层有大西沟组、阿干镇组、铁冶沟组和河口群。我们在这四个地层单位中采到了不同丰富程度的孢粉,并在前二组中采到了丰富的植物化石。本文报道的孢粉是这一地区内的首次报道。 大西沟组 孢子以Osmundacidites Wellmanii为主,混有少量繁盛于晚三叠世的Taeniae-sporites sp.;植物属我国北方Coniopteris-Phoenicopsis植物群早期组合。时代为早侏罗世。 阿干镇组 孢粉中Cyathidites minor和Cycadopites typicus含量丰富;植物属我国北方Coniopteris phoenicopsis植物群晚期组合。时代属中侏罗世,并大致属Bathonian期。 铁冶沟群 下部的孢粉以Cycthidites minor居优势,上部没见化石。整个铁冶沟群的时代暂定为中—晚侏罗世。 河口群 下岩组内海金砂科的孢子多见,Cicatricosisporites sp.、Schinaeoisporites sp.仅少量存在。时代为早白垩世。 经过研究,我们在验证前人对四个地层单位时代归宿的同时,进一步认为阿干镇组可大致属于Bathonian期。     

Fourth Asian Urbanization Conference

Fourth Asian Urbanization Conference     

古汉山井田地下水同位素组成特征研究

根据古汉山井田地下水中~3H、D、~(18)O和~(13)C等资料,建立了该井田鉴别主要含水层地下水的同位素标志,并对冲积层水、奥陶纪石灰岩水和煤系薄层石灰岩水之间的关系,以及矿井充水条件,做出了判断,为今后矿井基建、采矿中判别突水来源,提供了依据。     

坡风热力不稳定条件的讨论

本文在文献^[1,2]的基础上,说明坡风是一种耗散结构,并对形成坡风的热力不稳定条件进行了初步讨论,给出了临界瑞利数Rc作为坡风热力不稳定的判据。     

滇西地区九种岩石的P波Q值

本文叙述了以波传播和谱振幅比法测得的滇西地区九种岩石在不同应力状态下(σ_1=σ_2=σ_3=σ)的衰减系数,P波速度及Q值。在σ≤90 MPa时,随压力增加,衰减系数减小,P波速度及Q值增大;在σ≥120 MPa以后,衰减系数、P波速度及Q值变化甚小。其中团山砂岩及砖窑村片麻岩Q值较低。     

珠江口海域主导光学因子的遥感分类及其变化特征

基于2014年5月和8月珠江口海域的现场和实验测量数据,分析了光学因子和生态参数的动态变化特征,并找出该海域的主导光学因子;基于模拟的MODIS数据,构建了水体组分特征波长处吸收系数的遥感反演模型,并结合MODIS卫星遥感影像,依据IOCCG规则对主导光学因子进行遥感分类,揭示了珠江口海域2014年逐月水体主导光学因子的动态变化特征。结果表明,珠江口海域水体以a_d、a_g以及两种共同主导类型为主,并且a_g、a_d两种光学因子主导类型所占比例最大,其次是a_g主导类型,a_d主导类型所占比例最小。同时发现a_d（442）、a_dg（442）均与无机悬浮物浓度有较好的正相关关系,说明CDOM和悬浮泥沙具有相似的来源和动力变化过程。     

Impact of the Three Gorges Dam on the spawning stock and natural reproduction of Chinese sturgeon in Changjiang River,China

Chinese sturgeon (Acipenser sinensis) is the flagship species of the Changjiang River. The migration route of this species is blocked by the first dam, the Gezhou Dam, and its reproduction is affected by the Three Gorges Dam (TGD), one of the largest dams in the world. We studied the impact of the impoundment of the Three Gorges Reservoir (TGR) since 2003 on the spawning stock and the natural reproduction of the Chinese sturgeon by using our monitoring data from 1997 to 2013. Results indicate that TGR impoundment has delayed the first spawning dates of the fish from middle-late October to late November, decreased the amount of spawning activities from twice to only once each year, and significantly reduced egg production. In particular, the fish did not demonstrate any spawning activities in 2013. Therefore, TGR impoundment significantly affects the natural reproduction of the fish downstream of the TGD. The spawning stock size of the fish is also predicted to further decrease in the future, which will lead to a risk of population extinction. Ecological regulations must be imposed on decreasing the water temperature to 20°C before mid-October and increasing water discharge downstream of the TGD in October to induce spawning of the Chinese sturgeon.