基于局部结构张量的红外图像背景抑制

文中将局部结构张量与双边滤波相结合,提出了一种基于局部结构张量的红外图像结构化背景抑制算法。该算法采用局部结构张量的标准差作为双边滤波的执行判定,并利用双边滤波加权系数实现背景估计,从而实现结构化背景抑制和目标信息增强。实验结果显示,与二维最小均方滤波和偏微分方程算法相比,该算法对含有弱小目标的复杂背景具有良好抑制效果。     

A density functional study of plutonium dioxide

The electronic and geometric structures of bulk PuO₂ and its (110) surface have been studied using a periodic model within the generalized gradient approximation (GGA) of density functional theory (DFT). The sixty core electrons of the Pu atom have been represented by a relativistic effective core potential and scalar relativistic effects have been incorporated on the valence orbitals. For bulk PuO₂, we predict an equilibrium lattice constant of 10.10 a.u. and a cohesive energy of 17.28 eV, in good agreement with experimental data. For the (110) surface, upon relaxation, the distance between the top layer and the next layer is found to decrease by 0.12 ?, i.e. 5.3% of the corresponding interlayer distance in the bulk. The distance between the two oxygen atoms on the top layer is found to increase by 0.15 ?, i.e. 5.6% of the corresponding bulk value. The small surface relaxation energy of 0.268 eV per unit cell indicates the fair stability of this surface. The effective charges on Pu and O atoms show that the chemical bonding in this system is not purely ionic. Together with the metallic feature of the density of states (DOS) on the surface, the effective charge distribution provides some basis for understanding surface reactivity and corresponding support for catalysis. Received 16 June 2000     

The Wigner Band Random Matrix Model: Studied from the View Point of a Generalization of Brillouin- Wigner Perturbation Theory

The Wigner band random matrix model is studied by making use of a generalization of Brillouin-Wigner perturbation theory. Energy eigenfunctions are shown to be divided into perturbative and nonperturbative parts. A relation between the average shape of eigenstates and that of the so-called local spectral density of states (LDOS) is derived by making use of some properties of energy eigenfunctions drawn from numerical results. Several perturbation strengths predicted by the perturbation theory are found to play important roles in the variation of the shape of the LDOS with perturbation strength.     

Estimating Magic Numbers Larger Than 126 by Fermi—Yang Liming Method

The Fermi-Yang Liming method is followed and developed to estimate new magic numbers in nuclei with a Woods-Saxon density function.The calculated results predict that the magic number next to 126 should be around 184 and 258.     

An Elementary Approach to Exponential Spaces

In 1970, Day and Kelly characterized exponential spaces by a condition (C). Eight years later, Hofmann and Lawson pointed out that this is equivalent to quasi-local compactness, i.e. every neighborhood V of a point contains a smaller one W such that any open cover of V admits a finite subcover of W. These characterizations work with topologies on topologies and may be felt to be not really elementary. This note instead offers an elementary approach which applies to quotient-reflective subcategories as well and includes a natural generalization of the compact-open topology on function spaces.     

A633D斗杆的疲劳裂纹形成寿命

分析了A633D钢焊接接头在循环哉荷下的疲劳特性,进行了疲劳特性和静态拉伸实验,得到了该材料的静力参数,常规机械性能,焊接接头的循环σ-ε曲线以及焊接接头的应变寿命曲线,将局部应力－应变法用于该材料的10m3斗杆的裂纹形成寿命的估算,采用Miner法则结合概率的方法计算了不同可靠度下的疲劳寿命,其间考虑了焊接残余应力的影响,得出了焊接残余应力的存在使斗杆的裂纹形成寿命降低约10％。     

Efficient 2 and 3-Flip Neighborhood Search Algorithms for the MAX SAT: Experimental Evaluation

For problems SAT and MAX SAT, local search algorithms are widely acknowledged as one of the most effective approaches. Most of the local search algorithms are based on the 1-flip neighborhood, which is the set of solutions obtainable by flipping the truth assignment of one variable. In this paper, we consider r-flip neighborhoods for r = 2, 3, and examine their effectiveness by computational experiments. In the accompanying paper, we proposed new implementations of these neighborhoods, and showed that the expected size of 2-flip neighborhood is O(n + m) and that of 3-flip neighborhood is O(m + t ² n), compared to their original size O(n ²) andO(n ³), respectively, where n is the number of variables, m is the number of clauses and t is the maximum number of appearances of one variable. These are used in this paper under the framework of tabu search and other metaheuristic methods, and compared with other existing algorithms with 1-flip neighborhood. The results exhibit good prospects of larger neighborhoods.     

Geometric Integration of Ordinary Differential Equations on Manifolds

This article illustrates how classical integration methods for differential equations on manifolds can be modified in order to preserve certain geometric properties of the exact flow. Projection methods as well as integrators based on local coordinates are considered. The central ideas of this article have been presented at the 40th anniversary meeting of the journal BIT.This revised version was published online in October 2005 with corrections to the Cover Date.     

Local and Parallel Finite Element Algorithms Based on Two-Grid Discretizations for Nonlinear Problems

In this paper, some local and parallel discretizations and adaptive finite element algorithms are proposed and analyzed for nonlinear elliptic boundary value problems in both two and three dimensions. The main technique is to use a standard finite element discretization on a coarse grid to approximate low frequencies and then to apply some linearized discretization on a fine grid to correct the resulted residual (which contains mostly high frequencies) by some local/parallel procedures. The theoretical tools for analyzing these methods are some local a priori and a posteriori error estimates for finite element solutions on general shape-regular grids that are also obtained in this paper.     

Slow ester side‐group flips in glassy poly(alkyl methacrylate)s characterized by centerband‐only detection of exchange nuclear magnetic resonance

Slow side‐group dynamics in a series of five poly(alkyl methacrylate)s with various side‐group sizes [poly(methacrylic acid) (PMAA), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(isobutyl methacrylate) (PiBMA), and poly(cyclohexyl methacrylate), with ? H, ? CH₃, ? CH₂CH₃, ? CH₂CH(CH₃)₂, and ? cyclohexyl alkyl substituents (CODEX), respectively] were studied quantitatively by centerband‐only detection of exchange nuclear magnetic resonance (NMR). Flips and small‐angle motions of the ester groups associated with the β relaxation were observed distinctly in the CODEX NMR data, and the fraction of slowly flipping groups was measured with a precision of 3%. In PMMA, 34% of the side groups flipped on a 1‐s timescale, whereas the fraction was 31% in PEMA at 25 °C. Even the large isobutylether and cyclohexylester side groups flipped in the glassy state, although the flipping fraction was reduced to 22 and about 10%, respectively. In PMAA, no slow side‐group flips were detected on the 1‐s timescale. A striking difference in the temperature dependence of the flipping fraction in PMMA versus PEMA and PiBMA was observed. In PMMA, the flipping fraction was temperature‐independent between 25 and 80 °C, whereas in PEMA, it increased continuously from 31 to 60% between 25 and 60 °C. A similar doubling was also observed in PiBMA. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2444–2453, 2001