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We propose a scheme for the effective polarization and manipulation of electron spin by using a quantum dot with both charge and spin bias. Using the equation of motion for Keldysh nonequilibrium Green function, we study the spin accumulation and polarization for the system. Through analytical analysis and a few numerical examples, it is demonstrated that fairly large spin accumulation and polarization can be produced due to the breakingsymmetry of the chemical potential for different electron spin in the leads. Moreover, the direction and the strength of the spin polarization can be conveniently controlled and tuned by varying the charge bias or the gate voltage. 相似文献
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设计了蒸发器盘管排列密度可以改变的直接蒸发冰盘管蓄冷装置,在高、中、低三种盘管排列密度情况下,进行了蓄冷槽内载冷剂在自然对流和强制对流下的静态和动态蓄冷实验,研究了盘管排列密度和蓄冷状态对蓄冷速率的影响。结果显示:高密度系统平均蓄冷速率较低密度系统提高27.9%以上,动态系统平均蓄冷速率较静态系统提高2%左右。 相似文献
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We study analytically the moving nonlinear localized vibrational modes (discrete breathers) for a one-dimensional Klein-Gordon diatomic lattice in the whole ω(q) plane of the system by means of a semi- discrete approximation, in which the carrier wave of the modes is treated explicitly while the envelope is described in the continuum approximation. We find that both pulse and kink envelope moving modes for this lattice system can occur with certain carrier wave vectors and vibrational frequencies in separate regions of the ω(q) plane. However, the kink envelope moving modes have not been reported previously for this lattice system. 相似文献
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提出了一种以地下水辅助空气源热泵的新型双热源复合热泵装置,并设计出实验样机。针对夏季工况研究了地下水侧流量的变化对复合热泵系统性能参数的影响。实验结果表明,在最大负荷制冷工况时,采用少量的地下水作为辅助热源,可使系统制冷量提高约20%,系统能效比EER提高近65%。 相似文献
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针对电动客车用热泵空调器在低温工况下压缩比大、排气温度高、容积效率偏低、系统性能降低等突出问题,提出了带经济器的补气技术,并对系统循环过程进行理论分析,测试了在-15℃的环境温度、不同压缩机转速下,补气技术对电动客车用低温变频空调器的性能影响。结果表明:与不补气的热泵空调器相比,采用补气技术可显著降低压缩机排气温度,使系统安全可靠运行,特别是压缩机转速为5000r/min时,不补气时排气温度高达116.7℃,而补气时排气温度为99.6℃,相比下降了14.7%;采用补气技术提升了系统制热量和制热性能系数COP,且随着压缩机转速的提高,其效果更加显著,当压缩机转速由2000r/min提高到5000r/min时,与不补气的热泵空调器相比,系统制热量提升了16.2%~22.7%,COP提升了2.8%~14.2%。 相似文献
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Electronic states and spin-filter effect in three-dimensional topological insulator Bi_2Se_3 nanoribbons 下载免费PDF全文
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. 相似文献
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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。 相似文献