光纤激光共孔径光谱合成实现5 kW高效优质输出

采用多层介质膜衍射光栅实现多路高功率光纤激光共孔径光谱合成有望成为光纤激光同时实现高功率、高效率和高光束质量的最具发展潜力的技术途径。搭建了一套基于双光栅色散补偿设计的5 kW共孔径光谱合成系统。采用国产多层介质膜衍射光栅实现了5路kW级窄谱子束激光的高效优质共孔径光谱合成,最大输出功率达5.07 kW,光束质量因子(M2)小于3,合成效率达到91.2%。初步研究表明：多层介质膜衍射光栅在较高功率水平、较宽光谱范围内均能保持较高衍射效率,是实现高功率光纤激光高效率光谱合成的重要器件;参与合成的子束自身的光束质量水平和线宽是影响合成输出光束质量的重要因素,光谱合成系统的输出功率主要受限于窄谱子束的输出功率和合成路数,增加窄谱子束的功率或合成路数均可进一步提升系统的输出功率。     

一类灰色动态投入产出优化模型的设计及其在农业经济发展规划中的应用

本文应用灰色系统理论和方法，把动态Ｌｅｏｎｔｉｅｆ投入产出模型和线性规划结合起来，建立一种灰色动态投入产出优化模型，在山东省农业经济发展规划定量研究中，应用该模型取得比较满意的结果．     

The Minimum Rank of a 3 × 3 Partial Block Matrix

After recalling the definition and some basic properties of finite hypergroups—a notion introduced in a recent paper by one of the authors—several non-trivial examples of such hypergroups are constructed. The examples typically consist of n n×n matrices, each of which is an appropriate polynomial in a certain tri-diagonal matrix. The crucial result required in the construction is the following: ‘let A be the matrix with ones on the super-and sub-diagonals, and with main diagonal given by a ₁…a _n which are non-negative integers that form either a non-decreasing or a symmetric unimodal sequence; then A_k =P_k (A) is a non-negative matrix, where p_k denotes the characteristic polynomial of the top k× k principal submatrix of A, for k=1,…,n. The matrices A_k as well as the eigenvalues of A, are explicitly described in some special cases, such as (i) a_i =0 for all ior (ii) a_i =0 for i<n and a_n =1. Characters ot finite abelian hypergroups are defined, and that naturally leads to harmonic analysis on such hypergroups.     

Spatial, temporal and spectral emission characteristics from electron oscillation driven by an intense circularly polarized few-cycle laser pulse

The spatial, temporal and spectral emission characteristics of radiation generated from electron oscillations driven by an intense circularly polarized few-cycle laser pulse have been investigated theoretically and numerically using a single electron model. For a femtosecond driving laser pulse with duration of one optical cycle, the maximal radiation emitted by the electron comprises only one electromagnetic pulse having durations much shorter than the optical cycle and belonging to the attosecond range. It is discovered that the influence of the initial phase on the process of full spatial characteristics of the radiation is apparent for intense few-cycle laser pulse. The characteristics can be used to measure the initial phase of intense circularly polarized few-cycle laser pulse in experiments.     

Nonexistence of axially symmetric,stationary solution of Einstein Vacuum Equation with disconnected symmetric event horizon

In this short note, we prove that if an axially symmetric, asymptotically flat, stationary solution of the Einstein Vacuum Equation admits an involution interchanging the components of the event horizons, then the force between at least two of the event horizons must be positive. The proof is based on an observation that in this case the force can be expressed as a line integral with positive integrand.     

X-ray absorption investigation of the site occupancies of the copper element in nominal Cu_3Zn(OH)_6FBr

With Zn substitution to the three-dimensional antiferromagnetically ordered barlowite Cu_4(OH)_6 FBr,Cu_3 Zn(OH)_6 FBr shows no magnetic phase transition down to 50 mK,and the system is suggested to be a two-dimensional kagome quantum spin liquid [Chin.Phys.Lett.34 077502(2017)].A key issue to identify such phase diagram is the exact chemical formula of the substituted compound.With Cu L-edge x-ray absorption spectrum(XAS) combined with the MultiX XAS calculations,we evaluate the Cu concentration in a nominal Cu_3 Zn(OH)_6 FBr sample.Our results show that although the Cu concentration is 2.80,close to the expected value,there is 34% residual Cu occupation in intersite layers between kagome layers.Thus the Zn substitution of the intersite layers is not complete,and likely it intrudes the kagome layers.     

光学介质表面波度的计算机模型

任一光学介质表面波度对光散射具有不可忽视的影响.本文对用激光轮廓仪所测物体表面曲线进行研究,运用傅里叶级数和最小二乘法拟合光学介质表面波形形态分布,建立了光学介质表面波度的计算机一维模型.     

Hitting Time Problems of Sticky Brownian Motion and Their Applications in Optimal Stopping and Bond Pricing

This paper investigates the hitting time problems of sticky Brownian motion and their applications in optimal stopping and bond pricing. We study the Laplace transform of first hitting time over the constant and random jump boundary, respectively. The results about hitting the constant boundary serve for solving the optimal stopping problem of sticky Brownian motion. By introducing the sharpo ratio, we settle the bond pricing problem under sticky Brownian motion as well. An interesting result shows that the sticky point is in the continuation region and all the results we get are in closed form.

     

Single-channel color image encryption using phase retrieve algorithm in fractional Fourier domain

A single-channel color image encryption is proposed based on a phase retrieve algorithm and a two-coupled logistic map. Firstly, a gray scale image is constituted with three channels of the color image, and then permuted by a sequence of chaotic pairs generated by the two-coupled logistic map. Secondly, the permutation image is decomposed into three new components, where each component is encoded into a phase-only function in the fractional Fourier domain with a phase retrieve algorithm that is proposed based on the iterative fractional Fourier transform. Finally, an interim image is formed by the combination of these phase-only functions and encrypted into the final gray scale ciphertext with stationary white noise distribution by using chaotic diffusion, which has camouflage property to some extent. In the process of encryption and decryption, chaotic permutation and diffusion makes the resultant image nonlinear and disorder both in spatial domain and frequency domain, and the proposed phase iterative algorithm has faster convergent speed. Additionally, the encryption scheme enlarges the key space of the cryptosystem. Simulation results and security analysis verify the feasibility and effectiveness of this method.     

THE NUMERICAL STABILITY OF THE BLOCK θ-METHODS FOR DELAY DIFFERENTIAL EQUATIONS

This paper focuses on the numerical stability of the block θ-methods adapted to differential equations with a dday argument. For the block θ-methods, an interpolation procedure is introduced which leads to the mumerical processes that satisfy an important asymptotic stability condition related to the class of test problems y＇ (t)=ay(t)+by(t-r) with a,b∈C, Re(a)＜- ｜b｜ and τ>0. We prove that the block θ-method is GP-stable if and only if the method is A-stable for ordinary differential equations. Furthermore, it is proved that the P-and GP-stability are equivalent for the block θ-method.