Microscopic calcite dendrites in cold-water tufa: implications for nucleation of micrite and cement

Dendritic calcite forms in an active cold-water tufa system in association with extracellular polymeric substances (EPS) that discontinuously coat bryophytes and cyanobacteria. Dendrites consist of 100–200 nm thick calcite fibres that form 3D lattice-like domains. In each dendrite domain, fibres have three structurally equal orientations, which correspond in disposition to radii from the centre of a calcite unit cell to the convex triple face junctions on its surface. Fibres do not form in the orientation of the c-axis. The external form of each dendrite has the shape of half of a shortened octahedron, with an upper triangular surface parallel to the substrate. Dendrite nucleation takes place on or in microbial EPS, whether microbial cells are present or not, and is probably effected by attraction of Ca²⁺ cations to negatively charged EPS, together with CO₂-degassing and concomitant pH increase of supersaturated spring water in stream splash zones. Ensuing dendrite growth is abiogenic and controlled by diffusion. Dendrite c-axes are perpendicular to the substrate, probably because the negative charge of EPS forces the orientation of Ca²⁺ and CO planes within the developing dendrite crystal to be parallel to the EPS film surface. Dendrites are eventually filled and overgrown by solid, syntaxial calcite, which gradually and completely obliterates the dendrites as more familiar calcite crystal forms develop. No trace of the dendritic nucleus remains in the rock record. Calcite crystal nucleation may take place by this mechanism in many marine and meteoric settings, given that microbial EPS is now assumed to be virtually ubiquitous in these environments. This phenomenon could contribute to the development of familiar fabrics such as marine micrite cement and fibrous calcite cement, radial ooids, peloids, ‘abiogenic’ stromatolites, sea floor precipitates, microbialites, tufa, travertine, speleothems, and some meteoric cements. It may also contribute to the substrate-normal orientation of c-axes of common cement fabrics.     

BIOGENIC INFLUENCES ON THE FORMATION AND LONG-TERM DYNAMICS OF COHESIVE SEDIMENTS

1 wrRonvCTIoxToday it is widely accepted that the PrOcesses involved in cohesive sediment transpoft are stronglyinfluenced by the biological achvity of planctic (flocculation and sedimentahon) and benthic(consolldation and erosion) orgedsms (SPOrk et al. l997; PrOchnow et al. l999). Furthennre it can notbe neglected that particulary the ProCesses of sediment aging in teW of comPosition, pore-water content,stickiness of particles and aggregates and threshold of sediment motion are affected…     

不同数据模型间空间数据的对象转换方法--以EPS地图数据转换到GeoDatabase为例

通过对EPS和GeoDatabase数据模型的分析和比较，提出了从对象到对象的数据转换思想，并就其实现方法和过程进行较为详细地描述，针对实现过程中采用的关键技术加以说明。     

基于EPS2008平台的地理国情普查内业数据生产质检模块设计与实现

主要叙述了在地理国情内业数据生产时,基于EPS2008地理信息工作站实现系统、自动化对数据进行质量检查的过程,主要包括数据合法性检查、空间逻辑关系检查、属性取值范围、国情地表约束检查等质检功能的设计和组合,最终以模块化运行质检功能,提高了数据质检效果和效率。     

基础测绘产品元数据及附属产品的快速自动化生产

元数据是基础地理信息数据库中的重要组成部分,本文结合工作中的实例,简要地叙述了基于EPS平台,应用VBS语言进行脚本二次开发,自动化生产基础地理信息元数据及其他附属产品的技术方案设计与实现过程,并针对其中的关键技术问题进行了阐述。     

基于EPS的线状地物自动连线的编程实现

分析了清华山维EPS编码对照机制及EPS脚本语言规则,利用VBScript编程技术编写EPS脚本函数,实现线状地物的自动连线。实例运用表明,利用自动连线编程测图可减少勾绘错误,大大提高了测图效率。     

浅谈清华山维在地形图数据质量控制方面的应用

总结地形图数据生产过程中常见质量问题及形成原因的基础上,简要介绍了工作中利用清华山维软件进行数据质量控制的方法及其优点。     

海洋放线菌胞外多糖发酵工艺及其条件研究

以具有明显海洋特性的、产胞外免疫活性多糖的链霉菌2305菌株作为发酵菌种，对其胞外多糖的发酵工艺及其条件进行了研究，考察了不同碳源、氮源、水质、培养基初始pH值、发酵温度、通气量等因素对发酵菌种的生物量及胞外多糖产量等的影响，建立和优化了胞外多糖摇瓶发酵培养基配方、发酵工艺及发酵条件，胞外多糖产量达到4．58g／L，转化率达到6．90％。研究了发酵过程中菌体生物量、底物糖残余量、pH值、产物多糖积累量等的动态变化，分析讨论了2305菌株胞外多糖发酵的动力学类型。     

EPS平台下图形的分层分色方法

介绍了以数据库为核心构建的EPS平台下数据生产的分层分色方法,探讨了EPS平台作为GIS前端数据采集时的数据标准化自动控制和一图多用方面的灵活运用。