基于LBM方法的风力发电机尾流结构仿真

针对传统CFD数值计算方法难以实现风力机动态旋转及其旋转状态下的流固耦合计算,本文结合格子玻尔兹曼(LBM)方法易于处理动态复杂边界的特点及大涡模拟(LES)方法在非稳态涡流结构捕捉上的优势,采用LBM-LES联合方法进行三维风力发电机整机气动性能及尾流结构仿真研究,同时采用尺度自适应方法对尾涡结构进行跟踪和精细化计算。针对NREL PhaseⅥ型试验机进行模拟,得到了与实验结果吻合的流动形态及尾流结构演变规律,分析了尾流区速度演变规律并对比了不同亚格子湍流模型对计算结果的影响.     

不同构型(In,Al)GaN合金发光机理的第一性原理研究

基于第一性原理的密度泛函理论，研究了纤锌矿（In，Al）GaN合金的4种构型（均匀、短链、小团簇、团簇-链共存模型）的电子结构和发光微观机理。结果表明，在InGaN合金中，短In-N-链和小In-N团簇都局域电子在价带顶（VBM）态。当小团簇与短链共存时，前者局域电子的能力明显强于后者，是辐射复合发光中心。然而，在AlGaN合金中，电子在VBM态的局域受短Al-N链和小Al-N团簇的影响并不显著。合金微观结构的不同会引起电子局域的改变，从而影响材料的发光性能，并对带隙和弯曲系数有重要影响。     

BOUND POLARONS IN ASYMMETRIC QUANTUM WELLS IN AN ELECTRIC FIELD

We have proposed the Hamiltonian of a polaron bound to a donor impurity in semiconductor quantum wells (QWs) in the presence of an electric field. The couplings of an electron with the confined bulk like longitudinal optical (L₀) phonons, halfspace L₀ phonons and interface phonons are considered. In particular, the interaction of the impurity with the various phonon modes is also included. We have calculated the ionization energy of a bound polaron in Al_xl Ga_1-xl As/GaAs/Al_xr Ga_1-xr As asymmetric and symmetric QWs. Results are obtained as a function of the barrier height (or equivalently of Al concentration x),the well width, the electric field intensities and the position of impurity in the QWs. Our numerical calculations show clearly that the interaction between the impurity and the phonon field plays an important role in screening the Coulomb interaction. It is shown that for at hin well (＜12nm), the cumulative effects of the electronphonon coupling and the impurityphonon coupling can contribute appreciably to the donor ionization energy and polarizability.     

四层异质结构的表面和界面光学声子模

用连续介电模型研究了有限厚度四层异质结构的表面和界面光学声子模。精确得到本征失量、色散关系和面电荷密度。前人关于介电平板、双层、三层以及无限四层结构等所有已得结果，都可从此文普遍关系重新推出。另外，还给出了有限阶梯量子阱等有趣而实用结构的色散关系及其数值显示。本研究可视为文献［８］的推广。 关键词：     

Electronic Structures of Wurtzite GaN with Ga and N Vacancies

The electronic band structures of wurtzite GaN with Ga and N vacancy defects are investigated by means of the first-principles total energy calculations in the neutral charge state. Our results show that the band structures can be significantly modified by the Ga and N vacancies in the GaN samples. Generally, the width of the valence band is reduced and the band gap is enlarged. The defect-induced bands can be introduced in the band gap of GMV due to the Ga and N vacancies. Moreover, the GaN with high density of N vacancies becomes an indirect gap semiconductor. Three defect bands due to Ga vacancy defects are created within the band gap and near the top of the valence band. In contrast, the N vacancies introduce four defect bands within the band gap. One is in the vicinity of the top of the valence band, and the others are near the bottom of the conduction band. The physical origin of the defect bands and modification of the band structures due to the Ga and N vacancies are analysed in depth.     

均匀格子气Boltzmann方程的稳定性研究

１．引言格子气的基本方程是在几何空间、速度空间和时间上都是离散的Ｂｏｌｔｚｍａｎｎ方程（Ｂ方程）．这是一个有限差分方程．在离散速度气体运动论中［１］,Ｂ方程在速度空间上是离散的,在几何空间和时间上是连续的．这是一个偏微分方程．人们对离散速度气体Ｂ方程的稳定性和渐近特性的研究已经取得了很多结果．Ｍａａｓｓ~［２］通过构造Ｌｙaｐｕｎｏｖ函数族,在分布函数在空间上均匀的条件下,证明了平衡分布的渐近稳定性．信息函数Ｈ是该函数族的一员．Ｂｅｌｌｏｍｏｅｔａｌ~［３］．采用小扰动线性化方法在初值距离平衡解足…     

Excitons in quantum—dot quantum—well nanoparticles

A variational calculation is presented for the ground-state properties of excitons confined in spherical core-shell quantum-dot quantum-well (QDQW) nanoparticles. The relationship between the exciton states and structure parameters of QDQW nanoparticles is investigated, in which both the heavy-hole and the light-hole exciton states are considered. The results show that the confinement energies of the electron and hole states and the exciton binding energies depend sensitively on the well width and core radius of the QDQW structure. A detailed comparison between the heavy-hole and light-hole exciton states is given. Excellent agreement is found between experimental results and our calculated 1s_e－1s_h transition energies.     

The 2D InSe/WS_2 Heterostructure with Enhanced Optoelectronic Performance in the Visible Region

Two-dimensional(2D)InSe and WS_2 exhibit promising characteristics for optoelectronic applications.However,they both have poor absorption of visible light due to wide bandgaps:2D InSe has high electron mobility but low hole mobility,while 2D WS_2 is on the contrary.We propose a 2D heterostructure composed of their monolayers as a solution to both problems.Our first-principles calculations show that the heterostructure has a type-Ⅱband alignment as expected.Consequently,the bandgap of the heterostructure is reduced to 2.19 eV,which is much smaller than those of the monolayers.The reduction in bandgap leads to a considerable enhancement of the visible-light absorption,such as about fivefold(threefold)increase in comparison to monolayer InSe(WS_2)at the wavelength of 490 nm.Meanwhile,the type-Ⅱ band alignment also facilitates the spatial separation of photogenerated electron-hole pairs;i.e.,electrons(holes)reside preferably in the InSe(WS_2)layer.As a result,the two layers complement each other in carrier mobilities of the heterostructure:the photogenerated electrons and holes inherit the large mobilities from the InSe and WS_2 monolayers,respectively.     

First-Principles Study on Native Defect Complexes in InN

We present first-principles calculations of the formation energy of different native defects and their complexes in wurtzite InN using density-functional theory and the pseudopotential plane-wave method. Our calculations are aimed in the three cases： N/In = 1, N/In 〉 1 （N-rich）, and N/In 〈 1 （In-rich）. Our results indicate that the antisite defect has the lowest formation energy under N/In = 1. The formation energy of nitrogen interstitial （nitrogen vacancy） defect is significantly low under the N-rich （In-rich） condition. Thus the antisite defect is an important defect if N/In = 1, and the nitrogen interstitial （nitrogen vacancy） defect is a vital defect under the N-rich （In-rich） condition. The atomic site relaxation around the nitrogen interstitial and vacancy is investigated. Our calculations show that the nitrogen vacancy cannot be observed although it is one of the most important defects in InN. Our results are confirmed by experiments.     

Effect of a Two-Dimensional Periodic Dielectric Background on Complete Photonic Band Gap in Complex Square Lattices

A two-dimensional photonic crystal model with a periodic square dielectric background is proposed. The photonic band modulation effects due to the two-dimensional periodic background are investigated in detail. It is found that periodic modulation of the dielectric background greatly alters photonic band structures, especially for the Epolarization modes. The number, width and position of the photonic band gaps sensitively depend on the dielectric constants of the two-dimensional periodic background. Complete band gaps are found, and the dependence of the widths of these gaps on the structural and material parameters of the two alternating rods/holes is studied.