Physical Review B
Longitudinal electron transport is investigated for a long-period semiconductor superlattice in the presence of a magnetic field applied along the growth direction of the superlattice. It is shown that the longitudinal magnetoresistance exhibits a complicated dependence on the magnetic-field strength. In contrast with the conventional Shubnikov-de Haas oscillations, the magnetoresistance shows periodic oscillations only in the region of low reciprocal magnetic field.
关键词:
magnetoresistance
F.M.Chu David P.Pope Dept.of Materials Science and Engineering
,
University of Pennsylvania
,
Philadelphia
,
PA 19104
,
USA
材料科学技术（英文）
In this paper the geometric description and general theory of mechanical twinning are reviewed, the twins in general lattices and superlattices are summarized, and the kinetic process by which mechanical twins form is revisited. A case study of mechanical twinning of HfV2+Nb, (cubic) Laves phase, is presented and the synchroshear of selected atomic layers is proposed to explain the physical process of twin formation. If the twins form in this way, then long shear vectors and / or atomicshuffles are not really necessary.
关键词:
twin
,
null
,
null
,
null
J.M. Gong
,
S.T. Tu
,
J. Xia and X. Ling (School of Mechanical Engineering
,
Nanjing University of Chemical Technology
,
Nanjing 210009
,
China)
金属学报(英文版)
Creep deformation localization is generally found in structures at high temperamture,typically in weldments. As the heat affected zone (HAZ) in a weldment is very narrow, deformation in HAZ region can hardly be measured by conventional displacement gauge. A new method for measuring long-term local creep deformation was developed by quartz optical fiber and technique of digital image analysis. The creep deformations of base metal, weld metal and HAZ in weldments are thereby determined with crossweld specimens.
关键词:
creep deformation
,
null
,
null
,
null
刘国栋
,
张利英
,
王艳丽
,
郭丹
,
程翠然
高分子材料科学与工程
采用前期提出的共聚物Tg-组成关系方程研究了MA-EA、MA-n-BA二元共聚物的Tg,新方程中的周期共聚物Tg通过最小二乘法由无规共聚物Tg数据求取,相关周期共聚物的Tg为:Tg[ME]=274.6K、Tg[MB]=246.3K、Tg[MME]=286.3K、Tg[MMB]=262.8K、Tg[EEM]=262.3K、Tg(BBM]=236.7K,由此计算得到的理论值与实验值偏差极小,说明新方程能够更好地解释丙烯酸甲酯二元共聚物Tg与其组成及序列结构之间的关系.进一步预测了不同取代基时有序取代密度对聚丙烯酸甲酯Tg的影响规律,发现与对聚甲基丙烯酸甲酯Tg的影响规律不同,取代基的影响在高取代密度时才能显现.
关键词:
二元共聚物
,
玻璃化温度
,
组成
,
取代基
材料科学技术（英文）
A new type of long periodic structure has been found in ZrO2-Y2O3 ceramics in annealed states. High resolution electron microscopy (HREM), selected area electron diffraction, and computer simulation have been used to reveal the presence of the long periodic structure. The unit cell of the long periodic structure consists of a cubic ZrO2 unit cell and L1(0)- like phase one.
关键词:
ceramics;electron diffraction;electron microscopy;crystal structure;microstructure
Jiancun RAO
,
Yu ZHOU
,
Douxing LI
材料科学技术（英文）
A new type of long periodic structure has been found in ZrO2-Y2O3 ceramics in annealed states. High resolution electron microscopy (HREM), selected area electron diffraction, and computer simulation have been used to reveal the presence of the long periodic structure. The unit cell of the long periodic structure consists of a cubic ZrO2 unit cell and L10- like phase one.
关键词:
Ceramics
,
null
,
null
,
null
,
null
Applied Physics Letters
The dipole configuration of relaxor ferroelectrics (RFs) is investigated by numerically solving the time-dependent Ginzburg-Landau equation based on the dipole defect model. The domain structure of RFs is revealed to consist of dipole ordered clusters embedded in the paraelectric matrix. We demonstrate that the role of long-range elastic energy in RFs is much less important than in normal ferroelectrics, although the shape of the dipole clusters depends on the elastic energy. Based on the numerical results, a phase diagram of temperature-defect density for RFs is constructed, which identifies four distinct phase regimes. (c) 2006 American Institute of Physics.
关键词:
monte-carlo-simulation;dielectric-properties;computer-simulation;domain formation;defects;field;model;glass
Physical Review A
This paper investigates the motion of a Brownian particle experiencing both a friction (biased) force and a randomly fluctuating force with a long-time-correlation function C(f)(t) approximately t(-B), 0 < beta < 1, 1 < beta < 2, and beta = 1, instead of a Dirac delta-function. The generalized Langevin equation and Fokker-Planck equation and corresponding solution are presented. It is shown that when 0 < beta < 1 or 1 < beta < 2, the diffusion motion of the Brownian particle is the anomalous diffusion that is related to fractal Brownian motion (FBM). But when beta = 1 the diffusion motion is anomalous diffusion with no connection to FBM. The effects of friction retardation result in a probability density function for finding the particle at displacement X at time t that depends on the initial value of velocity of the particle. The approach in this paper may provide a systematic method for the study of particles diffusing in fractal media.
关键词:
disordered media;brownian-motion
