基于遗传算法(GA)的地应力有限元反演研究

由于地应力的反演是一个不断逼近最优解的过程，计算量较大，收敛速度较慢。为解决该问题，本文引入遗传算法确定地应力反演中的边界条件，从而提高收敛速度。本文利用改进的反演算法确定河北平原区的边界条件，并在此基础上采用有限元方法计算出该地区的地应力。结果表明，本文提出的算法计算速度快、且其计算结果与地震机制解及活动断裂的分布具有良好的一致性。     

藻酸双酯钠(PSS)遗传毒理学效应的初步研究

本研究是用紫露草微核技术检测新药藻酸双酯钠(PSS)的遗传毒理学效应。实验结果表明,PSS没有遗传毒性,却有保护染色体免受损伤的作用。其表现是使汞离子所产生的微核率明显下降。因而为扩大PSS的临床应用范围和使用安全提供了实验依据。     

云南斑岩型多金属金矿的嵌布特征及赋存状态研究

云南西部有大量低品位金矿资源,且具有嵌布粒度不均匀、矿石结构复杂、解离不完全等特点,传统工艺矿物学分析不易快速、准确测定金赋存状态及载金矿物的嵌布特征。本文利用矿物自动分析系统(MLA)、化学分析等方法对滇西多金属金矿进行系统的工艺矿物学研究,查明了该矿的矿物组成、嵌布粒度、连生及包裹关系,同时阐明了载金矿物的工艺矿物学性质对金回收率的影响。结果表明:金主要以游离态自然金的形式存在,嵌布粒度极细,主要集中在0.01~0.02 mm粒度级别;小于0.074 mm粒级的金占原矿总金量的50.08%,其余金以微细包裹体分散于黄铁矿、磁铁矿、黄铜矿等载金矿物中。但载金矿物粒度较细,解离性差,嵌布不均匀,因此提高载金矿物解离度是提高金回收率的一个重要参考方向。     

On species distribution modelling,spatial scales and environmental flow assessment with Multi–Layer Perceptron Ensembles: A case study on the redfin barbel (Barbus haasi; Mertens, 1925)

Inconsistent performance of Species Distribution Models (SDMs), which may depend on several factors such as the initial conditions or the applied modelling technique, is one of the greatest challenges in ecological modelling. To overcome this problem, ensemble modelling combines the forecasts of several individual models. A commonly applied ensemble modelling technique is the Multi–Layer Perceptron (MLP) Ensemble, which was envisaged in the 1990s. However, despite its potential for ecological modelling, it has received little attention in the development of SDMs for freshwater fish. Although this approach originally included all the developed MLPs, Genetic Algorithms (GA) now allow selection of the optimal subset of MLPs and thus substantial improvement of model performance. In this study, MLP Ensembles were used to develop SDMs for the redfin barbel (Barbus haasi; Mertens, 1925) at two different spatial scales: the micro–scale and the meso–scale. Finally, the potential of the MLP Ensembles for environmental flow (e–flow) assessment was tested by linking model results to hydraulic simulation. MLP Ensembles with a candidate selection based on GA outperformed the optimal single MLP or the ensemble of the whole set of MLPs. The micro–scale model complemented previous studies, showing high suitability of relatively deep areas with coarse substrate and corroborating the need for cover and the rheophilic nature of the redfin barbel. The meso–scale model highlighted the advantages of using cross–scale variables, since elevation (a macro–scale variable) was selected in the optimal model. Although the meso–scale model also demonstrated that redfin barbel selects deep areas, it partially contradicted the micro–scale model because velocity had a clearer positive effect on habitat suitability and redfin barbel showed a preference for fine substrate in the meso–scale model. Although the meso–scale model suggested an overall higher habitat suitability of the test site, this did not result in a notable higher minimum environmental flow. Our results demonstrate that MLP Ensembles are a promising tool in the development of SDMs for freshwater fish species and proficient in e–flow assessment.     

显生宙脉型铀矿床成矿理论的几个基本问题

显生宙铀矿地质的一个重要特征就是大量脉型铀矿床(或称热液铀矿床)的发育。本文以中国显生宙脉型铀矿床的研究成果为基础,综合西欧、中欧、苏联和美国同类矿床的资料,概要地阐述了这类矿床的基本地质和地球化学特征,讨论和评述了其成矿理论的几个基本问题。根据对世界主要铀矿区的大地构造背景分析,提出区域性铀源主要来自褶皱带的中心地块和活动大陆边缘基底古老硅铝壳中的富铀地质体,铀的活化和向上部构造层转移的主要因素是深熔作用和酸性岩浆怍用。显生宙热液铀成矿省形成的可能原因在于遭受深熔的部位存在着足够多的富铀地质体。提出了成矿热液形成的可能机制和“双混合”成因模式。强调指出拉张型构造运动和裂陷作用对脉型铀矿床形成的重要作用。     

The ‚loess’︁ section at Borden,Kent, SE England

A 5.3m profile originally described as loess with a buried interglacial soil is reinterpreted from petrographic evidence and thermoluminescence dating as a Holocene colluvial accretionary soil. Mineralogical analyses of coarse silt (16–63 μm) fractions suggest that most of the silty colluvium was derived from weathered Thanet Beds upslope, though some loess was incorporated during the final depositional phase. Thin sections show that clay illuviation occurred penecontem-poraneously with deposition of colluvium. Thermoluminescence properties suggest partial optical bleaching of the grains during rapid deposition, which is consistent with a Holocene colluvial origin.     

Polysynthetic feldspar twin-width distributions: Models for inversion twinning

The lamella-width distribution of the transformation polysynthetic twins produced in volcanic anorthoclases during cooling reflects certain aspects of twin nucleation and growth kinetics. An analysis of simple hypothetical statistical models for the kinetics of the transformation process outlines the range and type of twin-width distributions possible. The general characteristics of these distributions, particularly at small twin widths, are sensitive to whether twin boundaries or twin centers nucleate. The rates of twin nucleation and growth during transformation also influence the general form, particularly the skewness, of the final twin-width distribution. The generally exponential nature of the upper tails to the distributions studied is apparently quite insensitive to kinetic details.     

Trend-surface analysis of distribution of some heavy minerals in shelf sediments off Mangalore, India

The mineralogy of the 0.062–0.125 and 0.125–0.25 mm fractions of 58 selected samples from a set of 78 samples collected at a spacing of 1–2 km in the inner shelf of Mangalore were studied. Trend-surface analysis of distribution of the heavy minerals, hornblende, muscovite, garnet, and sillimanite, were made to determine the various factors controlling the mineral-distribution patterns in the area. Parts of the area showing contrasting environments were analyzed separately to determine the relationship of the regional and local trends and the various factors controlling the trends. The linear, quadratic and cubic trends for hornblende, garnet, and sillimanite were controlled by the source, westerly river flow and southerly currents; for mica, the response to processes has been the main factor. The mineral distribution in this area is mainly the result of dynamic interaction of process and response elements and a process-response model is suggested.Published with permission of the Director General, Geological Survey of India.     

Mathematical prediction of lead removal from carbonate-rich illite

The interaction between heavy metal contaminants and surface forces associated with the reactive surfaces of soil particles was studied with the aim of developing an analytical tool that would permit the prediction of heavy metal and soil sorption–desorption phenomena. The predictive model developed in this study considers the energy of the interaction developed between a lead contaminant and illitic soil. Since these energy calculations include both inner and outer sphere complexes, energy balance requirements can be realistically evaluated with respect to environmental mobility. For a comparison between the calculated values obtained from the predictive model and experimentally obtained measurements, laboratory batch equilibrium tests and electro–kinetic tests were used. These were concerned with the sorption–desorption determination of illitic soil samples with the lead contaminant in the form of a lead nitrate solution. The force balance of lead ions indicates that lead ions in the so-called Stern layer, i.e. the first two layers of a water molecule, are non-removable. Good correlations between calculated and measured values were obtained.