Shrinking Sphere Kinetics for Batch Dissolution of Mixed Particles of a Single Substance at High Under-Saturation: Validation with Sodium Chloride, but with Biogenic Silica in Mind

The cubic equation recently derived for the increase in concentration of a solute with time, as the solid dissolves in batch according to the shrinking sphere model at high under-saturation, is extended to dissolutions of mixtures of differently sized particles. This problem needs to be solved if batch dissolutions are to play their part in the proposed amelioration of global warming and associated climate change by accelerated ‘re-burial’ of excess CO₂ in ocean sediment. The upgraded model was tested using sodium chloride dissolved in 50% aqueous propanone, whence the model fitted two separate runs with 500 and 212 μm, and 212 and 38 μm, diameter crystals, respectively. The key to simulating dissolution in this way lies in the dissolutions being independent of each other. It is further shown that although this condition was implicit in the recent derivation of the cubic equation, it was not recognised at the time. The work should be applicable to any batch dissolution of mixed particles at high under-saturation, and hence, may find use in many industrial and laboratory dissolutions. Simulations show how agglomerated mixtures can yield a straight line on the plot of ln(1 − C/C _T) versus time, as was reported to occur recently with sodium chloride taken ‘straight from the bottle’. It is shown that this probably explains why exponential dissolutions may have seemed appropriate to the dissolution of biogenic silica in earlier literature. This study suggests that a new round of biogenic silica dissolutions, but with sieved samples, would be worthwhile, with the likelihood that shrinking sphere behaviour might well be found to characterise the kinetics. The opportunity is taken to investigate a number of aspects of the shrinking sphere model not generally discussed before, e.g. the graph for the change in surface area with time. The limitations of using cubic salt crystals with the shrinking sphere model are discussed.     

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等距离球面高斯投影

针对传统高斯投影直接基于等角横切圆柱投影而带来的不能直接用球面坐标换算等问题,研究了一种运用等距离球面进行投影的高斯投影,即等距离球面高斯投影。借助等距离纬度正反解公式,推导了等距离球面高斯投影的正反解公式,分析了其经纬线变形情况;基于投影公式,计算和分析了等距离球面高斯投影的长度变形、角度变形、面积变形及子午线收敛角等参数;最后与传统高斯投影进行比较,说明了该投影的可用性。     

对部分简单形体产生的自然电位进行定量分析

本文提出了一种新的特征点法,并在前人的基础上改进了一种数值计算方法(最小二乘法),以此来确定部分具有自然电位异常简单地质体的形态(形态系数)、埋藏深度、极化角和电偶极矩。特征点法通过剖面上三个特殊点(两个极值点和零电位点)的值以及它们相互间的距离便可快速求取地质体各参数。改进的最小二乘法则是在前人的基础上加入了零电位点的计算及其它处理方法,以此来获得准确性更高的地质体各参数。两种方法都被用来计算加入±5%随机误差的理论模型数据,并在土耳其的一个实际野外数据中得到测试。结果表明所求的参数与实际参数具有较好的一致性。     

地史中成矿演化的趋势和阶段性

大量的地质矿产资料表明，随着地球的形成和发展，尤其是水圈、大气圈和生物圈的演化，成矿作用也呈前进的、不可逆的发展趋势，表现在成矿物质（矿种）由少到多；矿床类型由简到繁；成矿频率由低到高；聚矿能力由弱到强。受地球上重大地质事件的制约，这一成矿演化过程又表现出阶段性，可划分出７个成矿大阶段，即太古宙、古元古代、中元古代、新元古代、早古生代、晚古生代—早中生代、晚中生代—新生代等成矿期。每一期中都有特定的成矿构造环境和矿床成因类型。制约地史上成矿演化的主要因素有：①成矿物质的地球化学性质；②水圈、大气圈和生物圈的演化；③地球构造运动的演变。矿床形成后的保存条件对矿床的时空分布特征也有重要影响。     

西北地区生态环境需水估算的几个问题研讨

西北地区生态环境需水研究是生态环境建设的重要基础。但是,目前区域生态需水研究仍处在初期阶段,面临许多问题与挑战。研讨了西北地区生态环境需水估算的几个问题,目的是为西北地区水资源合理配置、生态环境建设和可持续发展问题研究,探讨一些基本的研究思路和方法论。     

黄河中上游河道生态水短缺价值损失探讨

作为生态系统中最为关键和重要的因素,黄河中上游的水资源十分短缺,而如何定量计算由于水短缺而导致的生态价值损失是一个复杂的问题。本文首先对生态价值进行分类,并对国内常用的评估方法进行介绍。根据黄河中上游的特点将生态需水分为输沙需水、基本生态需水和蒸发需水三个部分,在此基础上,利用市场价值法和影子工程法对短缺水量引起的生态价值损失进行了计算。结果显示2002年黄河中上游生态价值损失中由泥沙淤积引起的部分最大,达到了35.3亿元,其次是水质污染和渔业损失,分别为15.5亿和8.0亿元。由于数据的限制,本文未对水土保持、净化空气、科学文化功能等其他生态价值损失进行计算。最后提出跨流域调水是弥补生态损失的有效方法。