Log-det approximation based on uniformly distributed seeds and its application to Gaussian process regression

Maximum likelihood estimation (MLE) of hyperparameters in Gaussian process regression as well as other computational models usually and frequently requires the evaluation of the logarithm of the determinant of a positive-definite matrix (denoted by C hereafter). In general, the exact computation of is of O(N³) operations where N is the matrix dimension. The approximation of could be developed with O(N²) operations based on power-series expansion and randomized trace estimator. In this paper, the accuracy and effectiveness of using uniformly distributed seeds for approximation are investigated. The research shows that uniform-seed based approximation is an equally good alternative to Gaussian-seed based approximation, having slightly better approximation accuracy and smaller variance. Gaussian process regression examples also substantiate the effectiveness of such a uniform-seed based log-det approximation scheme.     

32×64元硅化铂肖特基势垒红外焦平面列阵的物理设计

本文介绍了国内首见报导的32×64元硅化铂肖特基势垒红外焦平面的物理设计方法。作者从计算探测目标的辐射能量出发,综合考虑了器件的结构、材料和工艺参数,电参数,光学系统参数和响应率的非均匀性,以信嗓比作为焦平面的品质因数进行了性能优化计算。根据系统参数和现有工艺条件,预计焦平面对室温景物成象的温度分辨率优于1°K,这同器件的热象测试结果符合得相当好。     

Discrete-time ZD, GD and NI for solving nonlinear time-varying equations

A special class of neural dynamics called Zhang dynamics (ZD), which is different from gradient dynamics (GD), has recently been proposed, generalized, and investigated for solving time-varying problems by following Zhang et al.’s design method. In view of potential digital hardware implemetation, discrete-time ZD (DTZD) models are proposed and investigated in this paper for solving nonlinear time-varying equations in the form of $f(x,t)=0$ . For comparative purposes, the discrete-time GD (DTGD) model and Newton iteration (NI) are also presented for solving such nonlinear time-varying equations. Numerical examples and results demonstrate the efficacy and superiority of the proposed DTZD models for solving nonlinear time-varying equations, as compared with the DTGD model and NI.     

Controllable growth of nanocomposite films with metal nanocrystals sandwiched between dielectric superlattices

Nanocomposite films, with Ni nanocrystals (NCs) (5–8 nm) embedded within SrTiO₃/BaTiO₃ superlattice (period: 30 nm), were prepared by laser molecular beam epitaxy. In situ reflection high-energy electron diffraction was employed to study the role of lattice strain in the self-organization of NCs and the epitaxial growth of SrTiO₃/BaTiO₃ superlattice. It was found that the strain from large lattice mismatch drove the self-organization of Ni NCs. Also the SrTiO₃/BaTiO₃ epitaxial growth was achieved on the NC-dotted irregular interface, because the epitaxial growth occurred preferably at sites with low strain. The fine alternation of the two processes would provide a possible route to engineer controllably the nanocomposite microstructure.     

A bipolar metal phthalocyanine complex for sodium dual-ion battery

Dual-ion batteries (DIBs) have attracted immense interest as a new generation of energy storage device due to their low cost,environmental friendliness and high...