Confined states and spin polarization on a topological insulator thin film modulated by an electric potential

We study the electronic structure and spin polarization of the surface states of a three-dimensional topological insulator thin film modulated by an electrical potential well. By routinely solving the low-energy surface Dirac equation for the system, we demonstrate that confined surface states exist, in which the electron density is almost localized inside the well and exponentially decayed outside in real space, and that their subband dispersions are quasilinear with respect to the propagating wavevector. Interestingly, the top and bottom surface confined states with the same density distribution have opposite spin polarizations due to the hybridization between the two surfaces. Along with the mathematical analysis, we provide an intuitive, topological understanding of the effect.     

Electronic states and spin-filter effect in three-dimensional topological insulator Bi_2Se_3 nanoribbons

We study the electronic band structure, density distribution, and transport of a Bi_2Se_3 nanoribbon. We find that the density distribution of the surface states is dependent on not only the shape and size of the transverse cross section of the nanoribbon, but also the energy of the electron. We demonstrate that a transverse electric field can eliminate the coupling between surface states on the walls of the nanoribbon, remove the gap of the surface states, and restore the quantum spin Hall effects. In addition, we study the spin-dependent transport property of the surface states transmitting from top and bottom surfaces(x-y plane) to the side surfaces(z-x plane) of a Bi_2Se_3 nanoribbon. We find that transverse electric fields can open two surface channels for spin-up and-down Dirac electrons, and then switch off one channel for the spin-up Dirac electron. Our results may provide a simple way for the design of a spin filter based on topological insulator nanostructures.     

双热源型复叠式高温热泵系统性能研究

设计了以热源型冷凝蒸发器为核心部件的双热源复叠式高温热泵系统,该复叠式高温热泵系统能够同时对中、低温两种热源进行复合利用。搭建了试验台,按照国家标准规定的高温热泵的额定供热工况对系统性能进行了实验研究。研究结果表明,低温热源工况不变时,随着中温热源进口温度、流量的升高,复叠式高温热泵系统性能均呈升高趋势,但与中温热源流量的升高相比,中温热源进口温度的升高对复叠式高温热泵系统性能的改善程度较大,为复叠式高温热泵技术的高效化提供了借鉴作用。     

作业车间调度的非合作博弈模型与混合自适应遗传算法

采用博弈理论,建立了一种基于非合作博弈的作业车间任务调度模型.在该任务调度模型中,将源于不同客户的制造任务映射为非合作博弈模型中的局中人,并将与制造任务包含的工序集所对应的可选加工设备映射为可行方案集,使各制造任务的加工完成时间和成本组合形成的多目标综合指标映射为收益函数,从而将对任务调度模型的求解转换为寻求非合作博弈模型的Nash均衡点.通过设计的爬山搜索混合自适应遗传算法、自适应交叉和变异算子,实现了对该任务调度非合作博弈模型的Nash均衡点的有效求解,同时算例仿真结果也验证了所提出的调度方法的正确性.     

Spin-dependent transport for a two-dimensional electron gas with magnetic barriers

The spin-dependent conductance and magnetoresistance ratio (MRR) for a semiconductor heterostructures consisting of two magnetic barriers with different height and space have been investigated by the transfer-matrix method. It is shown that the splitting of the conductance for parallel and antiparallel magnetization configurations results in tremendous spin-dependent MRR, and the maximal MRRs reach 5300\% and 3800\% for the magnetic barrier spaces W=81.3 and 243.9~nm, respectively. The obtained spin-filtering transport property of nanostructures with magnetic barriers may be useful to magnetic-barrier-based spintronics.     

椭圆形百叶窗翅片传热强化数值分析

提出了一种新型椭圆形百叶窗翅片,采用CFD方法对其阻力特性及传热特性进行了模拟研究,并与传统矩形百叶窗翅片进行比较,分析了雷诺数对两种结构内流体的流动与传热性能的影响,同时对两种结构内流场与温度场的协同性也进行了研究。结果表明:新提出的椭圆形百叶窗翅片与矩形百叶窗翅片相比,阻力因子f降低了16%~20%,传热因子j提高了5%~7%,且雷诺数Re在225.7~451.3范围内,椭圆形翅片综合评价因子j/f1/3比矩形百叶窗翅片的提高了11%~15%,且椭圆形百叶窗翅片的速度与温度场的协同性优于矩形百叶窗翅片,椭圆形百叶窗翅片的综合换热性能高于矩形百叶窗翅片。     

L型混沌流道流动与传热特性的数值分析

采用周期性模型对L型混沌流道内流体流动与传热性能进行数值模拟,并与普通平直流道相对比,分析得到了两种流道内流体流场与温度场分布的细观信息,同时还讨论了不同Re数对混沌流道内流体传热与流动的影响。设计制作了测试流体流动性能的冷模试验装置,采用激光多普勒测速仪对L型混沌流道中流道内特殊点的速度进行测量,并将试验测量结果与数值模拟计算结果进行对比。结果标明:试验测量结果与数值模拟计算结果总体变化趋势基本一致,主流方向上速度相对误差最大为13.8%,在工程允许的误差范围之内,由此验证了数值模拟计算的可靠性。     

太阳能辅助空气源热泵空调低温特性研究

为了改善和提高空气源热泵空调冬季低温环境下的工作性能,设计了以翅片-套管复合式换热器为核心部件,以太阳能低温热水作为辅助热源的太阳能辅助空气源热泵空调,并对该热泵空调进行了低温工况性能测试。实验结果证明,当室外环境温度低至-15℃时,太阳能辅助空气源热泵空调与单一空气源热泵空调相比,系统性能得到明显改善,COP提高50%以上。     

Photon-Assisted Electron Transport for a λ-shaped Carbon Nanotube Junction

We theoretically study the electron transport properties for two coupled single-walled caxbon nanotube quantum dots connected to metallic electrodes under the irradiation of an external electromagnetic field at low tempera- tures. Using the standaxd nonequilibrium Green＇s function techniques, we examine the time-averaged transmission coefficient and linear conductance. It is shown that by some numerical examples, the photon-assisted inter-dot coupling causes Fano resonance and the conductance of the system is sensitive to the external field parameters. The transport dependence on the external field parameters may be used to detect the high-frequency microwave irradiation.     

介观耗散电容耦合电路量子化中的正则变换

针对介观耗散电容耦合RLC电路提出一种一般的正则变换, 并证明了其正确性和合理性. 用这种正则变换研究了双回路介观耗散电容耦合电路的量子化问题, 得出的对角化哈密顿量比文献中多出一非线性项. 这种具有普遍性的一般正则变换可能对研究介观多回路耗散系统的量子涨落、量子噪声等性质具有重要的意义. 关键词： RLC电路')" href="#">RLC电路 量子化 正则变换