对现行土地征用制度的几点建议

土地征用是指国家因进行经济、文化、国防建设以及兴办社会公共事业的需要,依法将农民集体所有土地变为国有土地并给予补偿的行为。近几年来,随着我国工业化、城市化进程加快,大量农民集体土地经征收、征用转为国有建设用地,由于现行的土地征用制度基本形成于计划经济时期,因此在土地征用过程中产生了大量的矛盾。     

东天山西滩浅成低温热液型金矿成矿地质地球化学动力学

西滩金矿床位于塔里木板块北缘晚古生代火山岛弧带,属典型的浅成低温热液石英脉型金矿。矿床控矿构造为破火山口放射状和环状断裂系统。成矿流体主要由大气降水热液组成,其运动状态表现为沿较宽大断裂裂隙快速（上涌）流动。沸腾作用是主要的一种动力成矿机制,成矿方式以充填作用为主。成矿反应系统包含成矿反应、控制反应及缓冲控制反应３类,动力学条件对成矿起主导作用     

近地小行星轨道演化的研究

本文主要阐述了近年来我们在近地小行星轨道演化研究所获得的一些基本结果,即合理的力学模型和相应的有效算法,并以实际预报算例与有关权威性的结果作了比较,证实这些研究结果确实是可信的。     

Evidence of two-stage magnetic reconnection in the 2005 January 15 X2.6 flare

We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using multiwavelength observations. There are several interesting properties of the flare that reveal possible two-stage magnetic reconnection similar to that in the physical picture of tether-cutting, where the magnetic fields of two separate loop systems reconnect at the flare core region, and subsequently a large flux rope forms, erupts, and breaks open the overlying arcade fields. The observed manifestations include: (1) remote Hα brightenings appear minutes before the main phase of the flare; (2) separation of the flare ribbons has a slow and a fast phase, and the flare hard X-ray emission appears in the later fast phase; (3) rapid transverse field enhancement near the magnetic polarity inversion line (PIL) is found to be associated with the flare. We conclude that the flare occurrence fits the tether-cutting reconnection picture in a special way, in which there are three flare ribbons outlining the sigmoid configuration. We also discuss this event in the context of what was predicted by Hudson et al. (2008), where the Lorentz force near the flaring PIL drops after the flare and consequently the magnetic field lines there turn to be more horizontal as we observed.     

苏鲁豫皖接壤地区的环境特征及水环境问题

苏鲁豫皖四省接壤地区环境受人为干扰和黄泛影响严重,环境问题和自然灾害较多,尤其是围绕水环境的旱涝和水体污染问题更为突出,针对四省接壤的特定区位和水环境状况,要通过加强跨地区水资源管理,落实有关法规和实行综合治理等对策进行整治。     

苏里格气田西区盒8下亚段辫状河沉积论证与分析

鄂尔多斯盆地苏里格气田西区盒₈^下亚段主力含气层段相的研究观点较多,不同认识导致各个沉积相域内砂体对比和预测存在着较大的差异,从而给勘探井位部署增加了难度。笔者在前人研究成果基础上,充分利用钻井、测井、岩心、地震、分析化验和野外露头等多种资料和手段,采用岩石学特征分析、岩心沉积构特征观察、古生物化石证据、研究区柳林成家庄野外露头沉积序列揭示、测井相特征和河流相地震特殊反射结构观察等多种研究手段和方法,对该区盒₈^下亚段的沉积相进行了详细论证、分析和描述。研究结果表明,辫状河沉积是苏里格西区盒₈^下亚段主要的相类型;干旱与潮湿气候的频繁交替变化,是导致砂体研究区目的层垂向砂体厚度大、非均质性强和砂体横向变化快的主控因素。     

东昆仑夏日哈木超大型岩浆镍钴硫化物矿床成矿特征

超大型岩浆镍钴硫化物矿床的形成多与大陆裂谷或地幔柱活动密切相关,是何种机制促使深部幔源金属元素超常富集于东昆仑造山带而形成超大型岩浆镍钴硫化物矿床呢?文章通过剖析夏日哈木岩体及矿体基本特征,发现赋矿岩体整体呈东宽西窄的楔状体,以富集轻稀土元素、贫重稀土元素以及Nb、Ta、Zr、Hf等高场强元素的亏损为特征,镍钴矿体主要富集于辉石岩和橄榄岩中,西段矿石富,东段矿石贫,矿石品位与橄榄石含量呈正相关关系.精细矿物学研究发现,寄主矿物"巨型"斜方辉石所包裹的橄榄石Fo值及Ni含量从核部到边部均增高,揭示含矿岩相侵入过程中可能存在至少2次岩浆活动.由橄榄石和铬尖晶石成分分析,推测夏日哈木母岩浆为低Ti、高Mg的拉斑玄武质岩浆,可能起源于软流圈地幔.结合区域构造演化和岩体形成时代,认为东昆仑夏日哈木镁铁-超镁铁质岩体形成于伸展环境,深部部分熔融形成的岩浆多次脉冲上涌叠加,地壳混染对硫化物达到饱和具有关键作用,于柴达木盆地南缘东昆仑造山带中构造薄弱部位成岩成矿,可能是伴随古特提斯洋演化开始大陆裂解岩浆镍钴成矿响应的表现.该认识对丰富造山带中的岩浆镍钴硫化物矿床成矿理论研究、拓宽岩浆镍钴矿床找矿空间与潜力、支撑并指导区域找矿新突破,具有重要作用.     

Comprehensive evaluation of heavy metal contamination in surface and core sediments of Taihu Lake, the third largest freshwater lake in China

The spatial and temporal variations of Fe, K, Co, V, Cr, Cu, Ni, Zn, and Pb were determined in the sediments of Taihu Lake, the third largest freshwater lake in China and categorized into natural origin (Fe, K, Co, and V) and human contamination (Cr, Cu, Ni, Zn, and Pb) groups by principal component analysis. Most of the metals were positively correlated with the clay content (<4???m) and negatively correlated with the >16???m fraction, indicating the dominant role of grain size in regulating metals concentrations. Geochemical normalization and enrichment factors (EFs) were introduced to reduce the confounding of variable grain size and to quantify anthropogenic contributions. Higher EF values for Cr, Cu, Ni, and Zn occurred in the north Zhushan, Meiliang, and Gonghu Bays, indicating a high level of human contamination from the northern cities, such as Wuxi and Changzhou. Higher EF values of Pb were also present in the southwest and east lake areas, denoting the existence of additional anthropogenic sources. Chrome, Cu, Ni, Zn, and Pb showed increasing EF values in the top layers of sediment cores, indicating enhancing contamination since 1970s with rapid economy development in the catchment. These results indicate that geochemical normalization is a necessary and effective method in quantifying heavy metals contamination, and that historic sediment should be used as background values in calculating EFs. Potential risks of the heavy metals were assessed linking the consensus-based sediment quality guidelines and human contamination. Concentrations of Ni and Cr are greater than the threshold effect concentration (TEC) values, even in the sediments before 1970s, due to higher background concentrations in terrestrial parent materials. Concentrations of Ni and Cr are generally lower than the probable effect concentration (PEC) values, and concentrations of Cu and Zn are below the TEC values in the open lake areas. Whereas, concentrations of Ni and Cr are surpassing the PEC values and Cu and Zn are surpassing the TEC values in the north bays due to the high level of human contamination, where they were with EFs over 1.2, denoting higher potential eco-risks.     

海面阻力系数的流体力学研究

利用相似理论的方法 ,把湍流问题的尼古拉兹曲线引入到风应力中 ,阐明了决定海面阻力系数的关键因素 ,并提出了阻力系数和有效波高的关系。     

Discrete element modeling of dynamic behaviors of railway ballast under cyclic loading with dilated polyhedra

The dynamic behaviors of railway ballast under cyclic loading are simulated with discrete element method (DEM). Dilated polyhedra are constructed based on the Minkowski sum operator in order to resemble the irregular shapes of ballast particles. The polyhedral particle generation, contact detection between particles and contact laws are presented. Ballast box tests with periodic lateral boundaries are conducted to simulate the dynamics of the sleeper and ballast particles. The settlement and effective stiffness of ballast bed are investigated under cyclic loadings with five distinct frequencies. The settlement of ballast bed is significant in the first several cycles and increases with the number of cycles gradually. The higher frequency loading generates larger displacement in the same simulation time. The effective stiffness of ballast bed increases gradually. To study the effect of particles' sharpness, dilated polyhedra with different dilating radii and spherical particles are also developed. Simulation results show the sharper the ballast particles are, the smaller the produced settlement. Copyright © 2016 John Wiley & Sons, Ltd.