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排序方式: 共有1166条查询结果,搜索用时 15 毫秒
61.
Guillaume Jouvet Matthias Huss Heinz Blatter Marco Picasso Jacques Rappaz 《Journal of computational physics》2009,228(17):6426-6439
Due to climatic change, many Alpine glaciers have significantly retreated during the last century. In this study we perform the numerical simulation of the temporal and spatial change of Rhonegletscher, Swiss Alps, from 1874 to 2007, and from 2007 to 2100. 相似文献
62.
《Comptes Rendus Chimie》2017,20(2):116-124
Heavy alkali metal-arsenic alloys intercalate easily into graphite, leading to the formation of a new family of ternary graphite intercalation compounds (GICs). Pure phases formulated as MAsxC4s (M = K, Rb or Cs; s = stage; x ≤ 1) have been synthesized at the laboratory. This article aims to expose all physical measurements performed on these intercalation compounds to get an idea about their electronic properties.Electrical conductivity measurements have been performed both parallel and perpendicular to the basal planes, between 4.2 and 295 K. Room temperature resistivity values lie between 16 and 35 μΩ cm and the anisotropic resistivity takes a value of an order of magnitude of 104. Dynamic magnetic susceptibility measurements, carried out at low temperature on some phases, showed that they do not exhibit superconducting transition up to 1.3 K. Raman spectroscopy investigation, which is a useful tool to study the electronic and the chemical stability of GICs, highlighted a significant up-shift of the G-band of the carbon intra-layer vibration frequency, compared to the pure graphite vibration mode. Undoubtedly, this is related to the electronic charge transfer established between graphite layers and intercalated species. 相似文献
63.
Magnetic and transport properties of Tm2Co7B3 compound have been studied. This compound crystallizes in the hexagonal Ce2Co7B3 type structure. The coercivity (H
c) of the compound was determined from hysteresis measurements in fields up to 4 T. The temperature dependence of coercivity has been explained by a thermally activated process of domain wall motion. The resistivity at low temperatures shows a T
2 dependence. At higher temperatures the resistivity is not a linear function of temperature, which indicates an electron-phonon interaction in the presence of a small s-d scattering. 相似文献
64.
Masahiro FujiwaraNaoya Tajima Tatsuro ImakuboMasafumi Tamura Reizo Kato 《Journal of solid state chemistry》2002,168(2):396-407
This article reports preparation, structure, and conducting property of several cation radical salts of organic donors tetramethyltetrathiafulvalene (TMTTF), ethylenedithiotetrathiafulvalene (EDT-TTF), bis(ethylenedithio)tetrathiafulvalene (ET), bis(ethylenedithio)tetraselenafulvalene (BETS) and hexamethylenetetraselenafulvalene (HMTSF) with two novel planar Te-based dianions, TeI42− and Te2I62−. (ET)5Te2I6 1 and (BETS)5Te2I6 2 are isostructural. In these Te2I62− salts, intermolecular short I···I contacts form a supramolecular corrugated anion sheet. Donor arrangement is similar to the θ-type. With lowering temperature, the resistivity of 1 shows a gradual increase followed by a sharp upturn at 110 K. 2 is metallic down to 120 K and shows a gradual increase of the resistivity followed by a clear transition to an insulating state around 60 K. Crystal structure of (ET)4TeI4 3 is based on the “herring bone” arrangement of ET molecules similar to the α-type. 3 shows a semiconductive behavior around room temperature followed by a transition to an insulating state at 210 K. (EDT-TTF)4TeI4 4, a semiconductor, exhibits a unique two-dimensional arrangement of dimerized EDT-TTF molecules. 相似文献
65.
利用复合靶共溅射法制备了半磁性半导体 Pb1- x Cox Se 薄膜.研究了薄膜的成分结构以及电阻率温度特性和磁化率温度特性间的关系.结果表明:由于 Co 离子介入, Pb1- x Cox Se 发生了由金属特性向半导体特性的转变,在充分低的温度下,并伴有磁相转变.磁相转变温度与磁性离子浓度相关,磁化率的相对变化幅度与磁性离子浓度有关 相似文献
66.
The current standard of electronic devices and data storage media has reached a level such that magnetic materials have to be fabricated on a nanometer scale. In particular, the emerging concept of spintronics, which is based on fact that current carriers have not only charge but also spin, requires the assembling of nanometer-sized magnetic structures with desired magnetic properties. It is this background that motivates scientists and engineers to attempt to grow and characterize magnetic objects at smaller and smaller length scales, from 2D films and multilayers to 1D wires and eventually to 0D dots. In this article, some of the most significant progress in recent years in the effort of growing artificially structured magnetic materials are reviewed. The new structural and magnetic properties of these materials are discussed, with an emphasis on the correlation between structure and magnetism, which also serves as guidance for improving their magnetic properties. The emerging emphasis is on converting the existing knowledge into growing and studying low-dimensional complex materials, which promise to have considerably higher “tuning” ability for desired properties. 相似文献
67.
The electronic structure of substitutional non-magnetic impurities Cu, Ag, Cd, Mg, Zn, Ga, In, Ge, Si and Sn in Al is studied
using density functional theory. A simple physical model is proposed to calculate the effective charges on impurities in trivalent
metal Al. A linear relation is found between the effective charges on impurities and impurity vacancy capture radii. The spherical
solid model (SSM) is used to account for discrete nature of the host. The impurity-induced change in charge density, scattering
phase shifts, host-impurity potential, residual resistivity and impurity self-energy are calculated. Higher order scattering
phase shifts are found significant and the host-impurity potential is found proportional to effective charge on impurity in
its vicinity. The self-consistently calculated potential is used to calculate the electric field gradients (EFGs) at the first
and second nearest neighbours (1NNs, 2NNs) of impurity. The calculated values are in agreement with the experimental results. 相似文献
68.
The establishment of atomic short-range order (SRO) has been investigated in CuMn alloys (5, 8,13,16,20 at. % Mn) by measurement of the electrical resistivity during isochronal and isothermal annealing. An increasing degree of SRO is accompanied by a reduction of resistivity; this effect increases with Mn concentration. For 8,13 and 16 at. % Mn SRO kinetics turn out to deviate significantly from single exponential behavior with a maximum at 13 at. % Mn, whereas at 5 and 20 at. % Mn SRO is adjusted in a single exponential process. For data analysis three methods are used: a sum of two and three exponentials as well as a log-normal spectrum of relaxation times. The strong interaction between second-nearest-neighbor atoms in CuMn seems to be essential for SRO kinetics but of minor importance for the value of SRO-induced resistivity change. 相似文献
69.
The effect of simultaneous Sr substitution at the Ba and Y sites has been studied in the Sr0.75Y0.75Ba1.5Cu3O7–dsystem. Attempts to replace 25% Y and 25% Ba have been successful and superconductivity was observed above 78 K for Sr0.75Y0.75Ba1.5Cu3O7–d compound with high oxygen content, i.e., O6.76, and having orthorhombic crystal symmetry. The compound was treated in argon gas at 800°C to reduce the oxygen content and to induce some structural changes. The Sr0.75Y0.75Ba1.5Cu3O6.1 compound thus obtained has tetragonal symmetry and low oxygen content, O6.1. It has also shown superconductivity at 28 K. The paper presents a careful comparison of the structural and electrical properties and infrared absorbance spectra of the two compounds with the same metallic composition, Sr0.75Y0.75Ba1.5Cu3, but with different oxygen content and crystal symmetry. The study clearly establishes the occurrence of superconductivity in tetragonal Sr-substituted (both at Y and Ba sites in) YBCO. 相似文献
70.
BaoQiangWU 《数学学报(英文版)》2004,20(1):71-80
In this paper,we study the infinity behavior of the bounded subharmonic functions on a Ricci non-negative Riemannian manifold M.We first show that limr→∞r^2/V(r)∫B(r)△hdv=0if h is a bounded subharmonic function.If we further assume that the Laplacian decays pointwisely faster than quadratically we show that h approaches its supremun pointwisely at infinity,under certain auxiliary conditions on the volume growth of M.In particular,our result applies to the case when the Riemannian manifold has maximum volume growth.We also derive a representation formula in our paper,from which one can easily derive Yau‘s Liouville theorem on bounded harmonic functions. 相似文献