Electronic states of InAs verfically-assembled quantum disks in magnetic fields and two-electron quantum-disk qubit

We have studied the single-electron and two-electron vertically-assembled quantum disks in an axial magnetic field using the effective mass approximation. The electron interaction is treated accurately by the direct diagonalization of the Hamiltonian matrix. We calculate the six criergy levels of single-electron quantum disks and the two lowest energy levels of two-electron quantum disks in an axial magnetic field. The change of the magnetic field as an effective potential strongly modifies the electronic structures. leading to splittings and crossings between levels The results demonstrate the switching between the around states with the total spins S = 0 and S = 1. The switching results in a qubit allowed to fabricate by current growth techniques.

施肥水平对长武旱塬地冬小麦产量影响的模拟

为了在实时气象条件下确定旱塬区适宜的肥力水平和产量水平,在模拟精度验证基础上,应用WinEPIC模型模拟研究了黄土高原长武旱塬地1957～2001年期间不同肥力水平下连作冬小麦田产量效应。模型验证结果表明CK、N、NP处理产量模拟值与观测值之间的相关系数分别为0.740、0.764和0.740,均达到显著水平,WinEPIC模型对不同肥力处理下冬小麦籽粒产量模拟较为准确。模拟结果表明,无肥、低肥、中肥和高肥处理下连作冬小麦的产量均呈现波动性降低趋势,其平均值分别为1.055、1.422、2.405和3.170t/hm2,不同肥力处理间差异显著,以中肥和高肥处理增产效果最好。为黄土高原南部沟壑区旱地小麦生产的可持续发展提供了科学依据。

非对称性有利于合作行为的演化

解释合作行为的演化一直是社会行为学和进化生物学研究的核心问题之一.经典的亲选择和互惠选择理论认为,合作双方由于高度的亲缘关系(遗传相似性)或互惠关系而存在合作均衡或进化稳定策略.这些经典合作演化理论都暗含合作双方是对称的前提假设,即合作双方的实力对等.然而,在现实的合作系统中,博弈双方几乎都是实力不对等的非对称性相互关系.运用"鹰鸽博弈"模型及博弈理论发现,若博弈双方的实力不对等,博弈双方冲突的频率与博弈双方实力的对比有着密切关系,即:博弈双方实力对比越悬殊,合作的频率越大,而实力对等时发生冲突的频率最大.该结果表明,相互作用个体间的非对称性将可能是合作关系演化的关键动力之一,且非对称性合作系统并不存在稳定的纯策略Nash均衡.模型结果有效地解释了为什么在几乎所有的著名合作系统中都观测到了合作双方的冲突行为.该模型同时发现,博弈双方发生合作频率的大小与冲突的单位成本收益呈负相关,而合作方冲突行为的单位成本收益可能取决于合作个体从其系统扩散到其他系统的几率或从原有系统退出的成本大小.而扩散到其他系统几率越小,或退出成本越高,合作接受方(优势方)对合作方的不合作行为惩罚越可信,合作系统因而可能越稳定.

Intersubband absorption from In0.26Ga0.74As/GaAs quantum dot superlattice

We have grown a high-quality 20 period InGaAs/GaAs quantum dot superlattice with a standard structure typically used for quantum well infrared photodetector. Normal incident absorption was observed around 13-15 mu m. Potential applications for this work include high-performance quantum dot infrared detectors.

Effect of Si-Ge interdiffusion on the waveguide properties of SiGe-Si MQW photodetector

Because of Si-Ge interdiffusion in the Si-SiGe interface during the growth process, the square-wave refractive index distribution of a SiGe-Si multiple-quantum-web (MQW) will become smooth. In order to simulate the actual refractive index profile, a staircase approximation is applied. Based on this approach, the dispersion equation of the MQW waveguide is obtained by using a transfer matrix method, The effects of index changes caused by the interdiffusion on the optical field and the characteristics of the photodetector are evaluated by solving the dispersion equation, It is shown that the Si-Ge interdiffusion can result in a reduction of the effective absorption coefficient and the quantum efficiency.