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The concept of compositional bimodality in carbonatites has become widely accepted and has been used to impose restrictions on the composition of carbonatite magmas. We agree that mineralogical bimodality exists in carbonatites (most are either calcitic or dolomitic/ankeritic), but we argue that there is no compositional bimodality. The idea of bimodality is based on the interpretation of a variety of element distribution diagrams which were compiled only from chemical analyses in which SiO2 is < 10 wt.%. All others were rejected. Even with such a restricted data set the case for compositional bimodality is extremely weak, but the inclusion of analyses with higher SiO2 content destroys it completely. Yet these more siliceous compositions must be included, for many carbonatites contain substantial amounts of Fe–Mg silicates which are an essential part of the magmatic mineralogy of the rocks. They account for much of the Mg in carbonatites that are otherwise calcitic. Many such carbonatites contain well in excess of 10 wt.% SiO2. Supporters of the bimodality concept argue that liquids having compositions between calcite and dolomite can precipitate neither calcite nor dolomite because the minimum on the solid solution loops in the system calcite–dolomite permits only a carbonate of intermediate composition. Therefore, it is argued, liquids of such intermediate composition cannot be parental to calcitic and dolomitic carbonatites; their parent magmas must be calcitic and dolomitic. This deduction is incorrect. It is well established that dolomitic liquids have calcite as the liquidus phase over substantial temperature intervals, and that this is followed by dolomite precipitation. Mixed calcite–dolomite carbonatites are explicable in this way. Therefore, dolomitic liquids can be parental to calcitic carbonatites. However, dolomitic carbonatites cannot crystallize from a calcitic liquid. We suggest that intermediate composition carbonatite magmas are probably common. Bimodality in carbonatites is solely mineralogical, not compositional. 相似文献
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无人机与卫星影像的叶面积指数遥感反演研究 总被引：1，自引：0，他引：1
针对卫星遥感影像获取的叶面积指数精度较低的问题,该文结合无人机低空航拍影像和卫星影像,基于最小二乘法建立了一种叶面积指数遥感反演方法,并与卫星影像像元二分模型进行了比较。结果表明:从单一植被类型到整体植被叶面积指数的反演,新方法均优于卫星影像的像元二分法,两者整体相对误差分别为27%和35%。4种植被类型中,草本植物对模型的反演精度影响较大,两者相对误差分别为32%和56%。使用该方法准确计算了长汀县相关区域叶面积指数分布,与他人结果一致。该方法提高了卫星遥感影像获取叶面积指数的精度,为大面积高精度估算区域植被提供了一种方法。 相似文献
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Ship floating condition in regular waves is calculated. New equations controlling any ship＇s floating condition are proposed by use of the vector operation. This form is a nonlinear optimization problem which can be solved using the penalty function method with constant coefficients. And the solving process is accelerated by dichotomy. During the solving process, the ship＇s displacement and buoyant centre have been calculated by the integration of the ship surface according to the waterline. The ship surface is described using an accumulative chord length theory in order to determine the displacement, the buoyancy center and the waterline. The draught forming the waterline at each station can be found out by calculating the intersection of the ship surface and the wave surface. The results of an example indicate that this method is exact and efficient. It can calculate the ship floating condition in regular waves as well as simplify the calculation and improve the computational efficiency and the precision of results. 相似文献
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文章从镜面反射点的定义出发,导出了在搜索镜面反射点时应满足的几何条件,分析了目前用于搜索镜面反射点算法的优点及不足;在此基础上,提出了一种二分算法;最后通过双基实验数据对这一算法进行验证,并与其他算法进行对比,结果显示出这种算法在收敛速度、搜索精度以及准确性等方面的优越性. 相似文献
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提出砂岩全应力.应变曲线的二分法原则,应用混沌动力学Lyapunov评价准则定性研究得到了曲线新的分段特征:试验曲线的所有峰前段均处于混沌状态,证明岩石节理裂隙这一复杂系统的非线性状态演化是客观存在、线性是近似的;节理裂隙系统有85%演化到峰后段时呈有序定常态,表明节理裂隙贯通后的岩石已呈现宏观破坏,线性特征明显:围压作用将延长节理裂隙的贯通过程,使之在峰后呈抵抗性破坏特征;峰后应变长度占总应变长度的2/3及以上时,该阶段节理裂隙系统的状态将主导其演化全过程的状态特征. 相似文献
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在渠道设计中,通常按明渠均匀流计算渠道底坡.当渠道较短时,不能形成均匀流,则需按恒定渐变流理论计算渠道底坡,至今尚未发现探讨该类问题的文献.因此本文结合工程实例,分析了四种类型的水面线和渠道底坡间的关系,以及相应的底坡搜索区间,最后用性能稳健的二分法计算出了渠道底坡值. 相似文献
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针对现有分布式目标通道最优极化算法存在运算量偏大等问题,以算法的实用性为目的,在理论分析的基础上提出一种求解分布式目标通道最优极化的快速算法.首先将任意通道下的天线接收功率模型统一为同极化通道下的天线接收功率拓展模型,然后对该拓展模型进行变换极化基处理,在此基础上理论确定目标最优极化在(r,θ)平面上的位置区间,从而为简化目标最优极化求解或预判目标最优极化位置等提供理论支撑.为获取目标最优极化,采用区间二分法在目标最优极化位置区间内迭代搜索.通过对比实验对算法运算速度和实现方面予以验证.Abstract： Aiming at the large mount of calculation of the traditional algorithms for polarimetric power optimization of random target in arbitrary channel, a fast algorithm is proposed in this article. Firstly, the function of received power in arbitrary channel is unified as the form of copolar power. Then based on the change of polarimetric basis,the copotar power is analyzed theoretically to obtain the minimum interval of target optimal polarization state in (r,θ)plane, which provides theoretic support for simplifying the process of obtaining optimal polarization states or anticipating their positions. In order to obtain optimal polarization states, the interval dichotomy is used to search in the minimum interval of target optimal polarization state, The experiment results have demonstrated that the proposed algorithm has better performance than the Lagrange multiplier method or the method of traversal search in algorithmic realization and computational speed. 相似文献
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现代地震学展现出了一个复杂的地球内核内部和表面结构.地球内核内部结构的主要特征表现为其地震波速度和衰减呈现各向异性,且各种结构（速度、衰减和各向异性）均呈现东西半球差异,而内核表面的新发现则包括其局部区域存在起伏的地形和固液并存的糊状层.地球内核压缩波速度和衰减均呈现以地球旋转轴为轴的柱对称各向异性,沿地球旋转轴方向传播的压缩波比沿赤道方向传播的压缩波传播更快且衰减更强烈.同时,内核各向异性结构随深度而变化：内核顶部约100~400 km接近各向同性,而在内核最深处300~600 km内则可能存在一个具有不同各向异性特征的内内核.地球内核的东西半球差异表现在多方面：在内核顶部~100 km厚度内,东半球的各向同性速度比西半球快约0.8%,东半球具有较强的衰减（Q=250）,而西半球则具有较弱的衰减（Q=600）;西半球的顶部各向同性层厚度约为100 km,而东半球顶部各向同性层厚度则约为400 km;在各向同性层底下,西半球具有较强的各向异性（~4%）,而东半球则具有较弱的各向异性（~0.7%）.地球内核边界在菲律宾海、黄海、西太平洋以及中美洲下方存在1~14 km高的地形起伏,在鄂霍次克海西南部下方存在4~8 km厚的糊状层.地球内核的这些新发现引发了对许多可能的新物理机制的探讨,也促使我们重新评估我们对外核成分、外核热化学对流、内核凝固过程和地球磁场驱动力的认识.这些结果表明内核凝固过程和地球磁场的热和化学驱动力远比传统观念认为的横向均匀分布复杂得多.内核西半球可能不断凝固并释放潜热和轻元素,而东半球则可能不断熔化并吸收潜热和轻元素,外核对流的驱动力在东西半球可能截然不同,甚至呈现相反方向.这些凝固与熔化交替过程也发生在局部地形起伏区域.在糊状层区域,地球内核凝固释放潜热和化学能,而在大部分无糊状地区,内核凝固只释放潜热. 相似文献
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悬链线剖面是大位移井轨道的经典类型,在进行设计时需要求解一个以悬链线初始井斜角为未知数的非线性方程。由于未知数包含在多个三角函数和对数函数中,计算工作量较大,而且常用的迭代求解方法存在一些问题。通过数学变换将该方程转换成一个只包含对数函数和多项式函数的新方程,对新方程的函数性态做了几何分析,进而提出了寻找求解区间的步长搜索算法和自适应步长搜索算法。利用二分法在求解区间上能够快速求出新方程的数值解。利用大位移井设计实例验证了本文算法的有效性,并对圆弧井段井眼曲率与方程解的关系进行了讨论。本文提出的算法可用于大位移井轨道设计的计算机软件开发中。 相似文献