共查询到20条相似文献,搜索用时 828 毫秒
1.
2.
对于预处理共轭梯度法,本文给出其迭代矩阵AM-1与三对角阵Bs之间的关系,并对Bs的特征值分布作了分析,进而得到关于AM-1特征值的一些性质。通过算例对两者的特征值及条件数进行了探讨。 相似文献
3.
4.
5.
6.
7.
利用密度泛函理论(DFT)的B3PW91方法,在6-311G水平上对BMgn,AlMgn(n=1—12)团簇进行了几何结构优化和电子性质分析. 发现随着原子个数的增加, B原子进入镁团簇的内部, 而AlMgn和镁团簇有相似的生长模式. B,Al原子的掺杂均能使镁团簇的平均结合能增大,稳定性增强, BMgn,AlMgn关键词:
密度泛函理论
最低能量结构
n和AlMgn团簇')" href="#">BMgn和AlMgn团簇
NBO电荷布居 相似文献
8.
9.
利用基于密度泛函理论的全势能线性糕模轨函法研究了闪锌矿(B3),NiAs(B8)和岩盐(B1)结构的AlAs的相变、结构性质以及热动力学性质.对B3-B8和B3-B1结构的能量体积曲线做公切线,得到了B3→B8相变压力为5.44 GPa,并预测到B3→B1相变压力为6.46 GPa.同时计算了高压下B8相的结构性质,结果显示当V/V0≈0.7—1.05时,c/a基本保持恒定(仅有约 0.2%的波动);当V/V0≈0.4—0.7,c/a随着V/V0的减小而近似线性地增大.通过状态方程拟合,得到了AlAs的相对体积V/V0与压强P的函数关系,B8相的状态方程与实验结果符合很好.最后利用准谐德拜模型得到了AlAs的体弹模量B随压力P的变化关系以及不同压强下热容CV与温度T的关系.
关键词:
相变
热力学性质
第一性原理 相似文献
10.
建立了梯度磁场下金属熔体中晶粒迁移的一般动力学模型,导出了磁场对导电熔体黏度的影响规律,得到了迁移速度的解析解和迁移距离的分析解.导电熔体的有效黏度随磁场强度的平方成线性递增关系.迁移速度达到终极速度的时间为10-3s数量级.终极速度随着磁场强度的增加而迅速减小,表明强磁场对晶粒迁移有抑制作用.迁移距离和迁移率与磁场分布密切相关.为观察初晶硅的迁移状况,将Al-18wt%Si合金在650℃保温60min后,施加强梯度磁场(Bz=5 T,BzdBz/dz=-224T2·m-1)对熔体作用不同时间并淬火,结果表明,晶粒半径大于等于40μm的初晶硅在120s内大部分完成迁移,与理论计算符合.
关键词:
强梯度磁场
析出相
迁移
刚体动力学 相似文献
11.
The room temperature u.v. reflectance of 1000 Å Germanium films (evaporated onto smooth amorphous substrates) has been measured and observed to vary with substrate deposition temperature Ts. Changes with increasing Ts are ascribed to gradual elimination of highly anisotropic voids for Ts 160°C, and to gradual film crystallization for Ts 200°C. 相似文献
12.
A. I. Tovstolytkin N. A. Belous I. V. Lezhnenko 《Journal of magnetism and magnetic materials》1994,130(1-3):293-296
We present here the detailed analysis of the magnetic behavior of the Co0.53Ga0.47 alloy, especially at temperatures above the freezing temperature Tf = 10 K. Low field static magnetization measurements were performed by using the SQUID magnetometer in the temperature range 5–65 K and magnetic fields up to 100 Oe. The temperature dependence of the field cooled susceptibility πFC(T) at T > Tf has an anomaly, which is displayed in the double change of the curvature near Ts = 24 K. The data of magnetization MFC in an external field H lie on a universal curve MFC(H/T) at temperatures Tf < T < Ts. The plots of π-1FC(T) and non-linear magnetic susceptibility πnlFC(T-3) are linear lines in the temperature range Tf−Ts. The strong deviation of π-1FC(T) and πnlFC(T-3) from straight line, taking place at T Ts, indicates that Ts is an upper temperature limit of the classical superparamagnetic behavior with the constant cluster moment. The results suggest that such phenomena may be fairly universal for spin glasses. 相似文献
13.
Fractal Aggregation Under Rotation 总被引:1,自引:0,他引:1
WUFeng-Min WULi-Li LUHang-Jun LIQiao-Wen YEGao-Xiang 《理论物理通讯》2004,42(6):909-912
By means of the Monte Carlo simulation, a fractal growth model is introduced to describe diffusion-limited aggregation (DLA) under rotation. Patterns which are different from the classical DLA model are observed and the fractal dimension of such clusters is calculated. It is found that the pattern of the clusters and their fractal dimension depend strongly on the rotation velocity of the diffusing particle. Our results indicate the transition from fractal to non-fractal behavior of growing cluster with increasing rotation velocity, i.e. for small enough angular velocity ω; thefractal dimension decreases with increasing ω;, but then, with increasing rotation velocity, the fractal dimension increases and the cluster becomes compact and tends to non-fractal. 相似文献
14.
The low temperature (1.3–20 K) heat capacity of the weak itinerant electron ferromagnet Sc3In was measured in magnetic fields up to 10 T. The measurements were made on three different samples containing 24.1, 24.3 and 24.4 at.% In with Curie temperatures at H = 0 of 5.5, 6.0 and 6.3 K, respectively. The heat capacity peak at Tc becomes smaller with increasing fields and at 9.98 T the magnetic entropies are only 11 to 19% of the zero field value. Above Tc the spin fluctuation contribution to heat capacity, which is enhanced by the magnetic field at low fields (<≈ 5 T), is quenched at high fields ( ≈ 5 T). Our results show that the spin fluctuations in Sc3In are almost completely quenched by the magnetic fields of ≈ 10 T, and that the characteristics spin fluctuation temperature, Ts, of this itinerant electron ferromagnet is about the same as Tc. 相似文献
15.
Viscosities of pure Ga, Ga_(80)Ni_(20), and Ga_(80)Cr_(20) metallic melts under a horizontal magnetic field were investigated by a torsional oscillation viscometer. A mathematical physical model was established to quantitatively describe the viscosity of single and binary metallic melts under a horizontal magnetic field. The relationship between the viscosity and the electrical resistivity under the horizontal magnetic field was studied, which can be described as η_B = η +(2H/πΩ)B~2(η_B is the viscosity under the horizontal magnetic field, η is the viscosity without the magnetic field, H is the height of the sample,? is the electrical resistivity, and B is the intensity of magnetic field). The viscosity under the horizontal magnetic field is proportional to the square of the intensity of the magnetic field, which is in very good agreement with the experimental results. In addition, the proportionality coefficient of ηB and quadratic B, which is related to the electrical resistivity,conforms to the law established that increasing the temperature of the completely mixed melts is accompanied by an increase of the electrical resistivity. We can predict the viscosity of metallic melts under magnetic field by measuring the electrical resistivity based on our equation, and vice versa. This discovery is important for understanding condensed-matter physics under external magnetic field. 相似文献
16.
We analyze the hadronic and radiative decay modes of the recently observed DsJ(2317) meson, in the hypothesis that it can be identified with the scalar
state of
spectrum (Ds0). The method is based on heavy quark symmetries and vector meson dominance ansatz. We find that the hadronic isospin violating mode Ds0→Dsπ0 is enhanced with respect to the radiative mode Ds0→Ds*γ. The estimated width of the meson is Γ(Ds0)7 keV. 相似文献
17.
Magnetization measurements on the Fe60Mn5Ni35 and Fe50Mn15Ni35 alloy samples were carried out in the temperature range 80T300 K and in magnetic fields up to 8 kOe. The Fe60Mn5Ni35 was found to order ferromagnetically with a Curie temperature, Tc, above 300 K. From the temperature dependence of the spontaneous magnetization, Ms, it was concluded that the magnetic behavior of Fe60Mn5Ni35 follows Wohlfarth theory of weak itinerant ferromagnet. The Fe50Mn15Ni35 sample exhibits a magnetic phase transition from ferromagnetism to paramagnetism at Tc=242 K. The critical amplitudes and critical exponents (β, γ and δ) have been determined by using Arrott plots, Kouvel–Fisher method and scaling plots of the reduced magnetization and reduced magnetic field. The values of β, γ and δ are discussed and compared with the results obtained for various theoretical models and also with the experimentally determined values for related systems obtained by others. 相似文献
18.
A model based on invasion percolation was used to simulate the migration on a non-wetting fluid through a porous medium filled with an immiscible wetting fluid under the influence of a gradient such as that provided by gravity. The migrating fluid clusters undergo both fragmentation and coalescence. The fragment size distribution obtained from two-dimensional simulations in which the gradient g is slowly increased from 0 can be represented by the scaling form Ns(g)s-2ƒ(s|g|-z where z=1+(D−1)ν(ν+1). Here D is the fractal dimensionality of invasion percolation, with trapping, and ν is the ordinary percolation correlation length exponent. 相似文献
19.
20.
The Mössbauer spectra of Invar type Fe65(Ni1-xMnx)35 alloys (0 x 0.3) were analyzed to yield hyperfine field distribution (P(H)) curve. The P(H) curves of the alloy with x = 0, that is the “classical” Invar alloy, at 4.2 K is character ized by a relatively sharp main peak at 350 kOe and a weak low field component around 50 kOe. With increasing x, the low field component grows and the high field main peak spreads toward a low field. By raising temperature, the main peak exhibits a remarkable broadening as well as a decrease in the average internal field and a growth of the low field component has not been detected. On the basis of these observations, models of the Invar alloy so far proposed are discussed. 相似文献