基于相位调制本振的相干检测系统

提出了一种简化的相干检测系统,通过在时域上交替探测信号的同向(Ⅰ)及正交(Q)信息分量,实现了基于单个平衡光电探测器(BPD)的相位分集接收.仿真结果表明,25 Gbit/s的非归零信号经过25 km标准单模光纤传输时,在10-3误码率门限下,其接收灵敏度为 39.97 dBm.用Gram-Schmidt正交化过程算法对信号光与本振(LO)光之间频率偏移引起的I、Q分量失配角进行补偿,当频率偏移小于符号速率的1/5(±5 GHz)时,灵敏度代价约为3.2 dB.此外,当LO光功率较高时,用单PD取代BPD的灵敏度损失约为3 dB.本方案为实现低成本的相干检测提供了一种解决方法.     

Quasi-two-dimensional threshold voltage model for junctionless cylindrical surrounding gate metal-oxide-semiconductor field-effect transistor with dual-material gate

Based on the quasi-two-dimensional(2D) solution of Poisson’s equation in two continuous channel regions, an analytical threshold voltage model for short-channel junctionless dual-material cylindrical surrounding-gate(JLDMCSG) metal-oxide-semiconductor field-effect transistor(MOSFET) is developed. Using the derived model, channel potential distribution, horizontal electrical field distribution, and threshold voltage roll-off of JLDMCSG MOSFET are investigated. Compared with junctionless single-material CSG(JLSGCSG) MOSFET, JLDMCSG MOSFET can effectively suppress short-channel effects and simultaneously improve carrier transport efficiency. It is also revealed that threshold voltage rolloff of JLDMCSG can be significantly reduced by adopting both a small oxide thickness and a small silicon channel radius. The model is verified by comparing its calculated results with that obtained from three-dimensional(3D) numerical device simulator ISE.     

Dynamic characteristics of resonant gyroscopes study based on the Mathieu equation approximate solution

Dynamic characteristics of the resonant gyroscope are studied based on the Mathieu equation approximate solution in this paper.The Mathieu equation is used to analyze the parametric resonant characteristics and the approximate output of the resonant gyroscope.The method of small parameter perturbation is used to analyze the approximate solution of the Mathieu equation.The theoretical analysis and the numerical simulations show that the approximate solution of the Mathieu equation is close to the dynamic output characteristics of the resonant gyroscope.The experimental analysis shows that the theoretical curve and the experimental data processing results coincide perfectly,which means that the approximate solution of the Mathieu equation can present the dynamic output characteristic of the resonant gyroscope.The theoretical approach and the experimental results of the Mathieu equation approximate solution are obtained,which provides a reference for the robust design of the resonant gyroscope.     

Implementation of LDA+DMFT with the pseudo-potential-plane-wave method

We propose an efficient implementation of combining dynamical mean field theory(DMFT) with electronic structural calculation based on the local density approximation(LDA).The pseudo-potential-plane-wave method is used in the LDA part,which enables it to be applied to large systems.The full loop self consistency of the charge density has been reached in our implementation,which allows us to compute the total energy related properties.The procedure of LDA+DMFT is introduced in detail with a complete flow chart.We have also applied our code to study the electronic structure of several typical strong correlated materials,including cerium,americium and NiO.Our results fit quite well with both the experimental data and previous studies.     

Goal-oriented error estimation applied to direct solution of steady-state analysis with frequency-domain finite element method

Based on the concept of the constitutive relation error along with the residuals of both the origin and the dual problems,a goal-oriented error estimation method with extended degrees of freedom is developed.It leads to the high quality local error bounds in the problem of the direct-solution steady-state dynamic analysis with a frequency-domain finite element,which involves the enrichments with plural variable basis functions.The solution of the steady-state dynamic procedure calculates the harmonic response directly in terms of the physical degrees of freedom in the model,which uses the mass,damping,and stiffness matrices of the system.A three-dimensional finite element example is carried out to illustrate the computational procedures.     

Modeling of laser-diode side-pumped continuous wave Nd:YAG/KTP green laser

By reasonably assuming the distribution of the pump light in laser medium, the equations about the absorption and the gain for the end-pumped lasers are applied to the side-pumped ones, and a theoretical model for laser-diode side-pumped continuous wave intracavity-frequency-doubling lasers is given, in which the thermally induced diffraction loss and the variation of the fundamental wave radii with the pump power are considered. By using a Z-type cavity, a laser-diode side-pumped continuous wave Nd:YAG/KTP green laser is realized. The threshold pump power is 15 W, and the highest output power of the green laser is 3.75 W at the pump power of 160 W, corresponding to an optical–optical slope efficiency 2.6%. The experimental results are consistent with the numerical solutions.     

A network analysis of the Chinese stock market

In many practical important cases, a massive dataset can be represented as a very large network with certain attributes associated with its vertices and edges. Stock markets generate huge amounts of data, which can be use for constructing the network reflecting the market’s behavior. In this paper, we use a threshold method to construct China’s stock correlation network and then study the network’s structural properties and topological stability. We conduct a statistical analysis of this network and show that it follows a power-law model. We also detect components, cliques and independent sets in this network. These analyses allows one to apply a new data mining technique of classifying financial instruments based on stock price data, which provides a deeper insight into the internal structure of the stock market. Moreover, we test the topological stability of this network and find that it displays a topological robustness against random vertex failures, but it is also fragile to intentional attacks. Such a network stability property would be also useful for portfolio investment and risk management.     

Focal depth and focal splitting of truncated hyperbolic-cosine-Gaussian beam induced by phase plate

Focal depth and focal splitting of hyperbolic-cosine-Gaussian beams induced by a phase plate were investigated. The pure phase plate consists of three concentric zones: a center circle zone, an inner annular zone and an outer annular zone. The phase variance of the inner annular zone is adjustable. Simulation results show that the focal depth can be adjusted by changing the radii of zones. With the increase of the inner radius of the outer annular zone, the focal spot broadens along the optical axis and splits into two peaks. Then the two peaks combine back into one peak. There are two critical values for the inner radius of the outer annular zone, at which focal spot changes sharply. The tunable range of the focal depth varies considerably. The phase variance of the inner annular zone affects focal depth also; when the phase variance is π, the effect attains maximum. The parameters of cosh parts of the beam affect both focal splitting and focal depth evidently; focal splitting disappears with increasing parameters of cosh parts, and focal depth increases with increasing the parameters of cosh parts in both the low and the high numerical-aperture optical systems.     

Surface morphology of ZnO buffer layer and its effects on the growth of GaN films on Si substrates by magnetron sputtering

ZnO thin films were first prepared on Si(111) substrates using a radio frequency magnetron sputtering system. Then the as-grown ZnO films were annealed in oxygen ambient at temperatures of 700, 800, 900, and 1000°C , respectively. The morphologies of ZnO films were studied by an atom force microscope (AFM). Subsequently, GaN epilayers about 500 nm thick were deposited on the ZnO buffer layers. The GaN/ZnO films were annealed in NH₃ ambient at 900°C. The microstructure, morphology and optical properties of GaN films were studied by x-ray diffraction (XRD), AFM, scanning electron microscopy (SEM) and photoluminescence (PL). The results are shown, their properties having been investigated particularly as a function of the ZnO layers. For better growth of the GaN films, the optimal annealing temperature of the ZnO buffer layers was 900°C.     

Comparative study of heteroepitaxial domain growth Mg0.4Zn0.6O alloy films on LaAlO3 and MgO substrates

Cubic-phase heteroepitaxial domain Mg_0.4Zn_0.6O films have been realized on both LaAlO₃(100) and MgO (100) substrates using pulsed laser deposition. Different domain matching epitaxy relationships were obtained due to the different lattice mismatch between the films and substrates. A 45° rotated diagonal domain growth (2 diagonal units of Mg_0.4Zn_0.6O to 3 units of LAO) results in a mismatch of less than 2%. Meanwhile a perfectly matched cube-on-cube relationship is demonstrated in the Mg_0.4Zn_0.6O/MgO structure. X-ray diffraction confirms that substrates have little effects on the lattice parameters of the Mg_0.4Zn_0.6O films.