Dependence on pressure of conduction by hopping of small polarons in minerals of the Earth's lower mantle   总被引：1，自引：0，他引：1  

A. Goddat  J. Peyronneau  J. P. Poirier 《Physics and Chemistry of Minerals》1999,27(2):81-87

Electrical conductivity of the lower mantle-like assemblage (Mg,Fe)SiO₃ perovskite-(Mg,Fe)O magnesiowüstite is usually analyzed using the quasi-chemical Arrhenian approach of diffusion. The conductivity of this assemblage has often been attributed to hopping of small polarons, because of the low value of the activation energy and the small negative activation volume. However, the solid-state physics approach can provide more arguments, for or against conduction by polarons. We have tried to bridge the gap between the two approaches and identify the physical quantities entering the phenomenological activation parameters. In particular, we have investigated the pressure dependence of the activation energy, and the physical meaning of the activation volume. Hopping is controlled by the binding energy of the polaron and by the value of the exchange integral, which increases with pressure causing the observed decrease of the activation energy. From the physical theory and the results of experiments at pressures up to 40 GPa and temperatures up to 400 ^∘C, we have estimated the values of parameters characteristic of polarons: radius, mobility, time between jumps and adiabaticity. These values are compatible with conduction by small adiabatic polarons. The consequences for extrapolations to lower mantle conditions of the presence of a temperature dependent preexponential term in the expression for conductivity have been examined. It was found that the extrapolations are not significantly different from those using the Arrhenius equation. Received: 5 November 1998 / Revised, accepted: 4 May 1999  相似文献   

CT引导下肺部穿刺活检的应用分析     

曹林德 《CT理论与应用研究》1999,8(2):19-22

本文的目的是分析和评价ＣＴ引民下肺部穿刺活检中体位的选择,穿刺点定位,穿刺针及穿刺方式等因素对本项检查结果的影响。所用材料与方法：回顾性分析分析３６例完整的病例,分别统计了切割法和抽吸法的阳笥率,假阳性率,假阴性率,气胸率及局部出血发生率组织诊断率。得到结论为切割法较抽吸法能获得更高的阳性率和组织学诊断率,但局部少量出血发生率略高  相似文献   

螺旋CT原理,扫描参数和图像重建   总被引：6，自引：0，他引：6  

林曰增  张雪林 《CT理论与应用研究》1999,8(2):23-25

螺旋ＣＴ最显著的特征是Ｘ线球管围绕病人旋转时,扫描床上病人连续通过机架,由于滑环技术的发明螺旋ＣＴ于１９８９年投入临床应用,它被广泛接受并成功地应用于人体各个部位的检查。由于产生容积数据,螺旋ＣＴ产生较少的呼吸遣漏扫描且可行允许重建,提高了Ｚ轴的分辨率。  相似文献   

螺旋CT对肺癌气管支气管改变的分析研究     

郭秀琴  曹介枢 《CT理论与应用研究》1999,8(4):26-28

目的是探讨肺癌改变要注意观察其支气管改变,全面评价病灶部位,大小,形态及浸润范围。方法采用了螺旋ＣＴ薄层扫描（ＳＶＣＴ）后,再做增强ＣＴ扫描,然后对６８例肺癌气管支气管进行分析研究,结果明确指出了６８例病人均进行ＣＴ检查,其中５４例经手术病理,支气管镜或细胞学检查证实,从而明确了螺旋ＣＴ是诊断支气管肺癌的重要方法之一,非常有益于临床方案的选择和设计。  相似文献   

肺部良性肿块的CT表现     

苑青龙  陈燕萍 《CT理论与应用研究》1999,8(4):29-31

目的是分析了肺部良好性肿块的ＣＴ表现,探讨病变的鉴别诊断,方法用１０例病人中,硬化性血管瘤１例,孤立性肺囊肿２例,１０例均行常规胸部ＣＴ扫描,其中８例行增强扫描。结果得到硬化性血管瘤边缘光滑锐利,密度致密均匀,增强扫描强化特别明显,错构瘤呈爆花米样钙化或梅花瓣样钙化,呈浅分叶状,可有血管连接征,曲菌球,２例在空洞内呈游离状态,１例菌球占满空腔呈分叶状,形似肺癌,但增强扫描无强化,２例肺隔离症分别位  相似文献   

中国及邻区岩石层密度三维结构   总被引：4，自引：0，他引：4  

方剑  许厚泽 《地球物理学进展》1999,14(2):88-93

利用中国及邻区２×２Ｓ波速地震三维层析成像和３０’×３０’重力资料．首先采用密度差与Ｓ波速差的经验关系式,建立起中国及邻区的岩石层密度初始模型,再利用布格重力异常进行阻尼最小二乘法反演,得到该区岩石层三维密度分布结果．反演结果表明：１．中国地区密度异常分布与大地构造分区有着明显的相关性,高密度区对应古老地块,低密度区对应高原及山区,在不同块体边界存在着密度异常梯级带;２．岩石层地幔密度分布与地壳密度分布特征不一致．  相似文献   

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction     

Sinclair Buchan  Denzil Taylor Smith 《Marine Georesources & Geotechnology》1999,17(1):65-81

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.  相似文献   

面向目标自适应有限元法的带地形三维大地电磁各向异性正演模拟          下载免费PDF全文

曹晓月  殷长春  张博  黄鑫  刘云鹤  蔡晶 《地球物理学报》2018,61(6):2618-2628

传统三维大地电磁各向异性模拟均是基于规则六面体网格,计算精度有限且较难拟合复杂地质条件.本文采用面向目标自适应非结构矢量有限元法,对三维大地电磁各向异性介质进行模拟.首先从电场双旋度方程出发,利用伽辽金方法建立变分方程;然后利用电流密度连续性条件构建适合大地电磁各向异性问题的加权后验误差估计方法,实现面向目标的网格自适应正演;最后通过典型算例分析各向异性对网格自适应和大地电磁响应的影响特征以及各向异性的识别方法.本文算法能够高精度地拟合起伏地表和任意各向异性介质,适用于分析复杂地电条件大地电磁响应特征,为提高大地电磁资料解释水平提供了理论基础.  相似文献   

基于MPI并行算法的电阻率法多种装置数据的三维联合反演          下载免费PDF全文

马欢  郭越  吴萍萍  谭捍东 《地球物理学报》2018,61(12):5052-5065

由于地表电阻率法受到浅地表局部异常体的干扰,反演精度受到影响,井中装置数据资料参与反演虽然可以减小浅地表局部异常体的干扰,但是由于钻井位置的局限性,数据量得不到保障,也会导致反演精度降低.为此,本文开发了一套结合地表、地-井、井-地和井-井装置数据的三维联合反演算法.首先,利用有限差分法实现正演模拟,采用非线性共轭梯度法（NLCG）恢复电阻率结构;其次,调用Message Passing Interface（MPI）函数库加速正演模拟和灵敏度矩阵运算,当开辟12个进程时,反演程序获得最大加速比4.51;最后,通过合成数据和实测数据算例证明该反演算法的有效性,也证实了多种装置组合数据体反演结果明显优于单一地表装置数据体反演结果.  相似文献   

含碳结构对龙门山断层带电导率影响的实验探索   总被引：1，自引：1，他引：0       下载免费PDF全文

陈进宇  杨晓松  陈建业 《地球物理学报》2017,60(9):3475-3492

碳是影响岩石电导率大小的一个重要因素,可能是造成龙门山断层带电导率异常的重要原因之一.为了研究不同的碳含量、矿物颗粒粒径与碳晶体结构对断层带电导率的影响,在干燥、常温、0.2~300 MPa的压力条件下实验研究了人工模拟断层泥样品(石英粉末与含碳粉末混合的样品,简称模拟样品)和采自映秀-北川断层八角庙剖面的天然断层岩样品(简称天然样品)的电导率.实验结果显示,当模拟样品中的含碳粉末连通时,电导率与碳体积率的关系符合逾渗理论模型;而含碳粉末未连通时,电导率随总孔隙度降低而指数性升高.同时模拟样品的电导率也随石英颗粒粒径的变化而发生改变.相比于模拟样品中的含碳粉末主要分布于石英颗粒支撑的孔隙中,天然样品中的碳则主要以碳膜的形式赋存在颗粒边缘,导致碳体积率相同的条件下,模拟样品的电导率小于天然样品.此外,天然样品的电导率(9×10~(-4)S·m~(-1))也要小于野外大地电磁探测的结果(0.03~0.1 S·m~(-1)).在今后的实验中还需要考虑在动态摩擦条件下对含有完整含碳结构的天然样品进行电导率的实验研究.  相似文献