Structural, electronic and optical properties of orthorhombic distorted perovskite TbMnO₃     

蔡鲁刚  刘发民  钟文武 《海洋学报(英文版)》2010,29(9)

This paper calculates the structural parameters, electronic and optical properties of orthorhombic distorted perovskite-type TbMnO₃ by first principles using density functional theory within the generalised gradient approximation. The calculated equilibrium lattice constants are in a reasonable agreement with theoretical and experimental data. The energy band structure, density of states and partial density of states of elements are obtained. Band structures show that TbMnO₃ is an indirect band gap between the O 2p states and Mn 3d states, and the band gap is of 0.48 eV agreeing with experimental result. Furthermore, the optical properties, including the dielectric function, absorption coefficient, optical reflectivity, refractive index and energy loss spectrum are calculated and analysed, showing that the TbMnO₃ is a promising dielectric material.  相似文献   

Unconventional geometric phase gate and multiqubit entanglement for hot ions with a frequency-modulated field     

钟文学  程广玲  陈爱喜 《海洋学报(英文版)》2010,29(11)

We present an alternative scheme for implementing the unconventional geometric two-qubit phase gate and preparing multiqubit entanglement by using a frequency-modulated laser field to simultaneously illuminate all ions. Selecting the index of modulation yields selective mechanisms for coupling and decoupling between the internal and the external states of the ions. By the selective mechanisms, we obtain the unconventional geometric two-qubit phase gate, multiparticle Greenberger--Horne--Zeilinger states and highly entangled cluster states. Our scheme is insensitive to the thermal motion of the ions.  相似文献   

Fluoride enrichment in aquifers of the Thar Desert: controlling factors and its geochemical modelling     

Chander Kumar Singh  Rina Kumari  Neha Singh  Javed Mallick  Saumitra Mukherjee 《水文研究》2013,27(17):2462-2474

The groundwater is the only source of drinking water in the Jaisalmer district of Rajasthan, India. The study area is a part of the Thar Desert. It has low and scattered population and no industries; hence, the possibility of anthropogenic input of fluoride is almost negligible. Thus, the enrichment of fluoride is only possible due to geochemical processes taking place in the groundwater of the region. A total of 100 groundwater samples, 34 samples from Jaisalmer and 66 samples from the Pokharan administrative blocks, were collected. It was observed that the concentration of fluoride ranged from 0.08 mg/l to 4.56 mg/l in the groundwater of Jaisalmer and from 0.56 mg/l to 6.60 mg/l in the samples of the Pokharan block. The alkaline condition (average pH, 7.7 ± 0.22 and 8.01 ± 0.25 in Jaisalmer and the Pokharan administrative block, respectively) in the region favours fluorite dissolution. Ion exchange, dissolution of calcite, semi‐arid climate, alkaline conditions and weathering are responsible for fluoride enrichment in the groundwater of the study area. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Influence of fluid chemistry on shear-wave attenuation and velocity in sedimentary rocks   总被引：2，自引：0，他引：2  

Dung Vo-Thanh 《Geophysical Journal International》1995,121(3):737-749

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Palaeomagnetism and rock magnetism of the Deccan traps     

C. Radhakrishnamurty  K. V. Subbarao 《Journal of Earth System Science》1990,99(4):669-680

Extensive work on the palaeomagnetism of the Deccan traps by several workers has revealed only one reversal (normal-reverse-normal) of the geomagnetic field during the period of eruption of these flows. The scatter in the natural remanent magnetic directions of different flows in a sequence of these traps is rather large and it persists even after magnetic cleaning. Generally this large scatter of directions is attributed to the geomagnetic secular variation during formation of the traps. Recent studies of the magnetic properties of the trap samples indicate that the presence of multidomain magnetite in a lava sequence differs from locality to locality in the Deccan trap province and so the stability of their natural remanent magnetization. While these features can be clearly perceived, an understanding of the same seems to be quite difficult. However, it appears that part of the scatter in directions could be due to the alteration of the magnetic minerals in the Deccan traps and hence it would not be proper to relate the entire scatter to the secular variation.  相似文献   

The rate of bedrock weathering by frost action: Field measurements and a predictive model   总被引：1，自引：0，他引：1  

Norikazu Matsuoka 《地球表面变化过程与地形》1990,15(1):73-90

Shattering rate, surface temperature, moisture content, and the physical and strength properties of bedrock were measured in four rockwall sites of the Japanese Alps. Five-year observations revealed that the bedrock shattering rate was usually much higher in the freeze-thaw period from October to next May than in the frost-free period from June to September. This indicates that frost action is the most important shattering process, although unusual heavy rainstorms in summer are also responsible for the shattering. A combination of some empirical relationships derived from recent laboratory experiments leads to a predictive model of the frost shattering rate. This model shows that the annual shattering rate is dependent on the annual freeze-thaw frequency on the rock surface, and the degree of saturation and tensile strength of the rock masses. The coefficients involved in the model were determined using the field data.  相似文献   

一种新的计算冰面饱和水汽压方法   总被引：1，自引：0，他引：1  

刘公波  胡志晋 《气象》1994,20(1):24-26

综述了国内外近似计算平面饱和水汽压公式。给出了较为精确、简单的平冰面饱和水汽压计算式，并与Ｗｅｘｌｅｒ等的计算结果进行了比较。  相似文献   

干法毛管压力试验新技术及其在判别储层水饱和度中的应用   总被引：1，自引：0，他引：1  

向阳  单钰铭  赵冠军 《矿物岩石》1994,(2)

根据毛细管压力理论研制的ＹＢ－１型岩石水饱和度仪，广泛应用于油气勘探开发中测定储集岩石的含水饱和度，测定误差小于５％，该方法为不受取心条件、样品大小、物性和岩性限制快速的新方法，实际应用证明效果较好  相似文献   

电阻率-孔隙度、电阻率-含油（气）饱和度关系的一般形式及其最佳逼近函数类型的确定（Ⅰ）   总被引：4，自引：0，他引：4       下载免费PDF全文

李宁 《地球物理学报》1989,32(5):580-592

本文导出了电阻率-孔隙度、电阻率-含油（气）饱和度关系的一般形式--两个对称的表达式,并给予了实验证明。同时,本文指出,Archie公式、Winsauer公式和双水公式都是一般形式在一定条件下的特例。在一般情况下,本文给出了14个能够逼近这两个表达式的函数类型,通过岩芯数据进行选优,可以得到适合不同地区或地层的最优方程。根据本文理论建立的解释方法和研制的软件已经在油田生产中推广应用并取得了良好效果。 由于涉及内容较多,全文分两部分撰写。以下是本文的第（Ⅰ）部分,即一般形式的导出及实验验证;而最佳函数类型的确定及其在生产中的应用将作为本文的第（Ⅱ）部分发表。  相似文献   

Frost weathering and the saturation of coastal rocks     

A. S. Trenhaile  D. W. Mercan 《地球表面变化过程与地形》1984,9(4):321-331

Measurements were made of the water content in coastal rocks, by simulating tidal oscillations in the laboratory, and by field measurement in eastern Canada. If rapid freezing takes place upon exposure to the air, saturation levels may be high enough to permit frost weathering in fine grained rocks in the lower portions of the intertidal zone. Near the high tidal level, however, it may be dependent upon a supply of water from the ice foot and from melting snow. If freezing is slow, frost action may be inhibited by desorption of the rocks while they are exposed by the ebb tide. There was no evidence of a level of permanent sea water saturation within the intertidal zone. Ambient temperature and humidity may affect the rate of rock desorption.  相似文献