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排序方式: 共有853条查询结果,搜索用时 218 毫秒
1.
Based on the current spin density functional theory, a theoretical model of three vertically aligned semiconductor quantum dots is proposed and numerically studied. This quantum dot molecule (QDM) model is treated with realistic hard-wall confinement potential and external magnetic field in three-dimensional setting. Using the effective-mass approximation with band nonparabolicity, the many-body Hamiltonian results in a cubic eigenvalue problem from a finite difference discretization. A self-consistent algorithm for solving the Schrödinger-Poisson system by using the Jacobi-Davidson method and GMRES is given to illustrate the Kohn-Sham orbitals and energies of six electrons in the molecule with some magnetic fields. It is shown that the six electrons residing in the central dot at zero magnetic field can be changed to such that each dot contains two electrons with some feasible magnetic field. The Förster-Dexter resonant energy transfer may therefore be generated by two individual QDMs. This may motivate a new paradigm of Fermionic qubits for quantum computing in solid-state systems. 相似文献
2.
一种基于三次样条函数求离子浓度的自动算法 总被引:1,自引:0,他引:1
本文提出了一种用三次样条函数模拟双次标准加入法测量方程,直接求解离子浓度的自动算法。比较了三咱不同边界条件下用要池数计算离子浓度的结果。造出节点区间两极端点的二阶导数为零时的三次样条函数为最佳模拟函数。并讨论了该方法在实际分析中误差的来源及消除办法。经对一系列文献数据的验算对比,表明本法完全可代替传统的迭代法和查图法,且能方便地设置在智能化的电位分析系统中。 相似文献
3.
本文利用C++面向对象的特征,对三次参数样条曲线的定义和生成过程进行封装,从而极大地简化了三次参数样条曲线的定义和绘制过程 相似文献
4.
The crystallization behavior of well-defined star-shaped cubic silsesquioxane-poly(ethylene oxide) (CSSQ-PEO) and linear PEO were studied in terms of differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). It was found in DSC analysis that the glass transition temperature (Tg) and the crystallization temperature (Tc) of CSSQ-PEO are different from those of linear PEO. The presence of CSSQ in PEO reduced the overall crystallization growth rate. This effect can be ascribed to the reduction of the mobility of the PEO crystallites in the presence of CSSQ and the star structure of the polymer. The Ozawa method is qualitatively satisfactory for describing the nonisothermal crystallizations of linear PEO and CSSQ-PEO. The presence of CSSQ leads to the diffusion- and nucleation-controlled mechanisms in the crystallization process of CSSQ-PEO whilst only the nucleation-controlled mechanism was observed in the case of linear PEO. The apparent activation energy required for crystallization was calculated using the Kissinger method. The isothermal crystallization morphology of PEO and CSSQ-PEO were also examined by cross-polarizing optical microscopy (CPOM). The CPOM images indicated the spherulite growth is slower in CSSQ-PEO as compared to linear PEO. It was also investigated that more number of PEO spherulites in CSSQ-PEO were observed, which sizes are markedly smaller than the spherulites developed in linear PEO. Wide-angle X-ray scattering (WAXS) studies showed that the crystallization peaks for linear PEO and CSSQ-PEO appeared at different temperature revealing the crystallization process and crystal growth rate are different from each other. However, no significant distortion of the crystal structure of PEO was evaluated in the presence of CSSQ. 相似文献
5.
The infiltration of compacted cubic BN (cBN) with molten aluminum has been investigated as a potential route for a cheap and easy method of manufacturing cBN/metal composites. CBN compacts have been infiltrated with molten Al at a temperature between 670 and 800 °C and pressure of 15 MPa in vacuum. At these temperatures no pronounced interactions between hexagonal and cubic BN with Al was observed, allowing the complete infiltration of cBN with 12 μm mean grain size. After infiltration at 800 °C, the temperature was increased without pressure to convert aluminum into borides and AlN. The hardness of the resulting materials depends on the content of hexagonal, cubic BN and the rate of conversion of Al into borides and AlN. The infiltration height of less than 1 mm obtained from infiltrating the 3 μm cBN powder green compacts gave a hardness of 22.0 ± 0.6 GPa after heat treatment. 相似文献
6.
7.
Chi-Chang Wang 《International Communications in Heat and Mass Transfer》2005,32(10):1337-1349
This research discusses the impacts of the surface area that the wavy surface gets more than the flat plate upon the aerosol particle deposition. Starting from the full Navier–Stokes equation, the mathematical analysis takes the thermophoretic motion formed by the temperature gradient and the fluid thermal expansion into consideration, and converts the governing equations into the boundary layer equation by the simple coordinate transformation and non-similarity method, and then works out these equations by the Spline Alternating-Direction Implicit method (SADI). The numerical value result reveals that the average deposition effect of the wavy plate is greater than the flat plate and that the increasing rate is nearly equal to the value obtained by dividing the surface area that the wavy plate gets more than the flat plate by 2.2. 相似文献
8.
Daniel Ocone 《Mathematics of Control, Signals, and Systems (MCSS)》1988,1(2):183-202
This paper applies the techniques of Malliavin’s stochastic calculus of variations to Zakai’s equation for the one-dimensional
cubic sensor problem in order to study the existence of densities of conditional statistics. Let {X
t} be a Brownian motion observed by a cubic sensor corrupted by white noise, and let
denote the unnormalized conditional estimate of φ(X
i
). If φ1,...,φ
n
are linearly independent, and if
, it is shown that the probability distribution of
admits a density with respect to Lebesgue measure for anyn. This implies that, at any fixed time, the unnormalized conditional density cannot be characterized by a finite set of sufficient
statistics.
Research supported in part by NSF Grant No. MCS-8301880 and by the Institute for Mathematics and It Applications, Minneapolis,
Minnesota. 相似文献
9.
10.
Costs in precision cylindrical grinding are compared for different abrasives, machines and grinding conditions. The analysis is for repeated batch production. Account is taken of machine cost and abrasive cost. Cost comparisons were based on extensive trials to assess re-dress life against workpiece quality requirements. Experiments show that different workpiece materials require different strategies to reduce costs. Easy-to-grind AISI 52100 and difficult-to-grind Inconel 718 materials were ground at conventional speeds and at high speeds. It is shown that wheel speed affects production rate through acceptable values of re-dress life, removal rate and dwell time. Advantages were gained using vitrified CBN at conventional speed and at high speed. For both materials, vitrified CBN wheels used at high speed, gave better quality at lower cost than conventional abrasives. Wheel costs became negligible and labour costs greatly reduced. Re-dress life trials, usually neglected, are shown to be essential to reduce costs and maintain quality [1]. 相似文献