高铁酸盐稳定性研究进展

高铁酸盐具有强氧化性和无毒性,是一种多用途化学试剂,可作为氧化剂、混凝剂、消毒剂和电池阴极材料使用.但高铁酸盐水溶液极易分解及固态高铁酸盐制备成本高,从而限制了它的实际应用.本文概述了高铁酸盐稳定性方面的研究进展,介绍了溶液浓度、pH、温度、高铁酸盐纯度和离子掺杂等因素对其稳定性的影响,以及改善高铁酸盐稳定性的各种研究...     

Efficient integration for a class of highly oscillatory integrals

This paper presents some quadrature methods for a class of highly oscillatory integrals whose integrands may have singularities at the two endpoints of the interval. One is a Filon-type method based on the asymptotic expansion. The other is a Clenshaw-Curtis-Filon-type method which is based on a special Hermite interpolation polynomial and can be evaluated efficiently in O(N log N) operations, where N + 1 is the number of Clenshaw-Curtis points in the interval of integration. In addition, we derive the corresponding error bound in inverse powers of the frequency ω for the Clenshaw-Curtis-Filon-type method for the class of highly oscillatory integrals. The efficiency and the validity of these methods are testified by both the numerical experiments and the theoretical results.     

A parameterized proximal point algorithm for separable convex optimization

In this paper, we develop a parameterized proximal point algorithm (P-PPA) for solving a class of separable convex programming problems subject to linear and convex constraints. The proposed algorithm is provable to be globally convergent with a worst-case O(1 / t) convergence rate, where t denotes the iteration number. By properly choosing the algorithm parameters, numerical experiments on solving a sparse optimization problem arising from statistical learning show that our P-PPA could perform significantly better than other state-of-the-art methods, such as the alternating direction method of multipliers and the relaxed proximal point algorithm.     

An exact algorithm for graph partitioning

An exact algorithm is presented for solving edge weighted graph partitioning problems. The algorithm is based on a branch and bound method applied to a continuous quadratic programming formulation of the problem. Lower bounds are obtained by decomposing the objective function into convex and concave parts and replacing the concave part by an affine underestimate. It is shown that the best affine underestimate can be expressed in terms of the center and the radius of the smallest sphere containing the feasible set. The concave term is obtained either by a constant diagonal shift associated with the smallest eigenvalue of the objective function Hessian, or by a diagonal shift obtained by solving a semidefinite programming problem. Numerical results show that the proposed algorithm is competitive with state-of-the-art graph partitioning codes.     

Bregman operator splitting with variable stepsize for total variation image reconstruction

This paper develops a Bregman operator splitting algorithm with variable stepsize (BOSVS) for solving problems of the form $\min\{\phi(Bu) +1/2\|Au-f\|_{2}^{2}\}$ , where ? may be nonsmooth. The original Bregman Operator Splitting (BOS) algorithm employed a fixed stepsize, while BOSVS uses a line search to achieve better efficiency. These schemes are applicable to total variation (TV)-based image reconstruction. The stepsize rule starts with a Barzilai-Borwein (BB) step, and increases the nominal step until a termination condition is satisfied. The stepsize rule is related to the scheme used in SpaRSA (Sparse Reconstruction by Separable Approximation). Global convergence of the proposed BOSVS algorithm to a solution of the optimization problem is established. BOSVS is compared with other operator splitting schemes using partially parallel magnetic resonance image reconstruction problems. The experimental results indicate that the proposed BOSVS algorithm is more efficient than the BOS algorithm and another split Bregman Barzilai-Borwein algorithm known as SBB.     

NiFe Alloy Nanoparticles with hcp Crystal Structure Stimulate Superior Oxygen Evolution Reaction Electrocatalytic Activity

Tuning the crystal phase of metal alloy nanomaterials has been proved a significant way to alter their catalytic properties based on crystal structure and electronic property. Herein, we successfully developed a simple strategy to controllably synthesize a rare crystal structure of hexagonal close‐packed (hcp) NiFe nanoparticle (NP) encapsulated in a N‐doped carbon (NC) shell (hcp‐NiFe@NC). Then, we systemically investigated the oxygen evolution reaction (OER) performance of the samples under alkaline conditions, in which the hcp‐NiFe@NC exhibits superior OER activity compared to the conventional face‐centered cubic (fcc) NiFe encapsulated in a N‐doped carbon shell (fcc‐NiFe@NC). At the current densities of 10 and 100 mA cm^?2, the hcp‐NiFe@NC with Fe/Ni ratio of ≈5.4 % only needs ultralow overpotentials of 226 mV and 263 mV versus reversible hydrogen electrode in 1.0 m KOH electrolyte, respectively, which were extremely lower than those of fcc‐NiFe@NC and most of other reported NiFe‐based electrocatalysts. We proposed that hcp‐NiFe possesses favorable electronic property to expedite the reaction on the NC surface, resulting higher catalytic activity for OER. This research provides a new insight to design more efficient electrocatalysts by considering the crystal phase correlated electronic property.     

沙丘背风侧不同铁路结构形式对风沙环境的适应性分析

当铁路穿越大风沙漠地区时,风沙灾害会对铁路工程及其正常运营产生严重威胁,而设计一种合理的铁路结构形式能够减小风沙沉积对铁路工程的危害. 在本文中,以敦煌至格尔木铁路沙山沟段落为研究对象,采用多相流的方法对越过沙丘的风沙运动过程进行数值模拟,分别讨论了风沙运动对位于沙丘背风坡的铁路路基工程和桥梁工程的影响. 主要的模拟结果显示:路基工程明显降低了风速并且将沙丘后的回流区分成了两部分,而桥梁工程的导流效应则压缩了沙丘背风坡的回流区;轨道间的道碴增大了铁路表面的粗糙度,在轨道间有少量沙粒沉积,而路基工程两侧则有大量积沙;铁路表面的积沙量与摩阻风速呈现出非线性关系,随着摩阻风速的增大,路基工程沙粒沉积的增加速度大于风蚀能力的增加速度,而桥梁工程则正好相反. 在防止风沙危害铁路方面,设置桥梁工程明显优于路基工程. 本研究为风沙运动对铁路工程的影响提供了理论支持,也为今后的铁路工程设计提供了新的思路与研究工具.      

氰基亚胺与亚甲基二氢苯并呋喃二酮类化合物的[3+2]环加成反应:螺吡唑类化合物的合成

采用具有环外双键的二氢苯并呋喃二酮类化合物和氰基亚胺的[3+2]环加成反应,在温和条件下,以高产率(78%~94%)和高非对映选择性(>20∶1dr)构建了一系列具有螺环结构的吡唑类化合物.     

Enhancement of the electrocatalytic oxidation of dyeing wastewater (reactive brilliant blue KN-R) over the Ce-modified Ti-PbO2 electrode with surface hydrophobicity

Journal of Solid State Electrochemistry - Rational hydrophobic anode has been considered as a promising approach for water pollution remediation. However, the construction method of the hydrophobic...     

Self-adaptive inexact proximal point methods

We propose a class of self-adaptive proximal point methods suitable for degenerate optimization problems where multiple minimizers may exist, or where the Hessian may be singular at a local minimizer. If the proximal regularization parameter has the form where η∈[0,2) and β>0 is a constant, we obtain convergence to the set of minimizers that is linear for η=0 and β sufficiently small, superlinear for η∈(0,1), and at least quadratic for η∈[1,2). Two different acceptance criteria for an approximate solution to the proximal problem are analyzed. These criteria are expressed in terms of the gradient of the proximal function, the gradient of the original function, and the iteration difference. With either acceptance criterion, the convergence results are analogous to those of the exact iterates. Preliminary numerical results are presented using some ill-conditioned CUTE test problems. This material is based upon work supported by the National Science Foundation under Grant Nos. 0203270, 0619080, and 0620286.