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981.
Dr. Qingsong Dong Prof. Xiao‐Juan Yang Shida Gong Dr. Qiong Luo Prof. Qian‐Shu Li Prof. Ji‐Hu Su Dr. Yanxia Zhao Prof. Biao Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(45):15240-15247
A nickel? nickel‐bonded complex, [{Ni(μ‐L.?)}2] ( 1 ; L=[(2,6‐iPr2C6H3)NC(Me)]2), was synthesized from reduction of the LNiBr2 precursor by sodium metal. Further controllable reduction of 1 with 1.0, 2.0 and 3.0 equiv of Na, respectively, afforded the singly, doubly, and triply reduced compounds [Na(DME)3] ? [{Ni(μ‐L.?)}2] ( 2 ; DME=1,2‐dimethoxyethane), [Na(Et2O)]Na[(L.?)Ni? NiL2?] ( 3 ), and [Na(Et2O)]2Na[L2?Ni? NiL2?] ( 4 ). Here L represents the neutral ligand, L.? denotes its radical monoanion, and L2? is the dianion. All of the four compounds feature a short Ni? Ni bond from 2.2957(6) to 2.4649(8) Å. Interestingly, they display two different structures: the perpendicular ( 1 and 2 ) and the coaxial ( 3 and 4 ) structure, in which the metal? metal bond axis is perpendicular to or collinear with the axes of the α‐diimine ligands, respectively. The electronic structures, Ni? Ni bonding nature, and energetic comparisons of the two structure types were investigated by DFT computations. 相似文献
982.
Composite hydrogels were prepared from pineapple peel cellulose with the combinations of polyethylene glycol (PEG), polyvinyl alcohol (PVA), к-carrageenan (CN), or soluble starch (SH) in 1-allyl-3-methylimidazolium chloride solvent. Impacts of these macromolecules on the texture profile analysis (TPA) parameters, equilibrium swelling ratio (ESR), and sodium salicylate (NaSA) load of the prepared hydrogels were studied. The NaSA release kinetics of the composite hydrogels were also compared. The composite hydrogels exhibited differences in Fourier transform infrared spectroscopy (FTIR), TPA parameters, ESR, NaSA load ratio, and release kinetics. CN addition increased the hardness of the hydrogels, while PEG played an opposite role. SH and PVA could decrease hardness, gumminess, and resilience, and SH could increase the springiness and cohesiveness of the hydrogels. Most of the composite hydrogels exhibited the same basic FTIR features as the simple hydrogel. Freeze-dried composite hydrogels exhibited a markedly higher ESR than the oven-dried ones, and additions of PEG, PVA, CN, and SH showed the same effect. Addition of the PEG and PVA combination could lower the ESR of the hydrogels, whereas additions of the PEG and CN combination or PEG and SH combination could markedly increase the ESR of the hydrogels. Addition of PEG, PVA, CN, and SH respectively could increase the NaSA load ratio of the hydrogels. Oven-drying treatment, additions of the PEG and PVA combination or PEG and CN combination were propitious for extending the NaSA fast-release phase of the hydrogels. 相似文献
983.
984.
Tao Cai Zhen Yang Haijiang Li Hu Yang Aimin Li Rongshi Cheng 《Cellulose (London, England)》2013,20(5):2605-2614
In this present work, a series of hydrolyzed polyacrylamide grafted carboxymethyl cellulose (CMC-g-HPAM) was prepared. The structure and solution properties of CMC-g-HPAM were characterized by FTIR, 1H-NMR, elemental analysis and zeta potential measurements. The graft copolymers were applied as flocculants to remove methylene blue (MB), a cationic dye, from aqueous solutions. In comparison with its precursors, carboxymethyl cellulose (CMC) and polyacrylamide CMC-g-PAM, CMC-g-HPAM exhibited higher removal efficiencies. Furthermore, the flocculation performance of the copolymers was significantly improved with the increase of the hydrolysis degree, and the MB removal efficiency was more than 90 % when the hydrolysis degree of CMC-g-HPAM was higher than 80 %. More importantly, image analysis in combination with fractal theory demonstrated that the graft copolymers could produce notably denser and larger flocs, which was of great significance in practical water treatment. The improved flocculation performance was ascribed to both charge neutralization and bridging effects. 相似文献
985.
采用软模板法制备了氮化钨-钨/掺氮有序介孔碳复合材料(WN-W/NOMC),作为一种高比表面积且价格低廉的阴极氧还原反应催化剂。通过适量添加尿素来改变复合材料中的氮含量,在掺氮量为7%(w/w)时,实验发现材料能够保持完整有序介孔结构,测试其比表面积高达835 m2·g-1,透射电子显微镜(TEM)测试结果显示其催化颗粒均匀地分散在氮掺杂有序介孔碳载体上。在O2饱和的0.1 mol·L-1 KOH溶液中测试了材料的氧还原催化性能(ORR),显示其起始电位为0.87 V(vs RHE),极限电流密度为4.49 mA·cm-2,氧还原反应的转移电子数为3.4,接近于20%(w/w)商业Pt/C的3.8,说明该材料表现出近似4电子的氧还原反应途径。研究结果表明,WN-W/NOMC的催化性能虽然稍弱于商业铂碳(0.99 V,5.1 mA·cm-2),但其具有远超铂碳的循环稳定性和耐甲醇毒化能力。 相似文献
986.
987.
988.
Zhi-Hua?Hu Yingxue?ZhaoEmail author Sha?Tao Zhao-Han?Sheng 《Annals of Operations Research》2015,235(1):37-49
This work addresses a new transportation problem in outbound logistics in the automobile industry: the finished-vehicle transporter routing problem (FVTRP). The FVTRP is a practical routing problem with loading constraints, and it assumes that dealers have deterministic demands for finished vehicles that have three-dimensional irregular shapes. The problem solution will identify optimal routes while satisfying demands. In terms of complex packing, finished vehicles are not directly loaded into the spaces of transporters; instead, loading patterns matching finished vehicles with transporters are identified first by mining successful loading records through virtual and manual loading test procedures, such that the packing problem is practically solved with the help of a procedure to discover loading patterns. This work proposes a mixed-integer linear programming (MILP) model for the FVTRP considering loading patterns. As a special class of routing models, the FVTRP is typically difficult to solve within a manageable computing time. Thus, an evolutionary algorithm is designed to solve the FVTRP. Comparisons of the proposed algorithm and a commercial MILP solver demonstrate that the proposed algorithm is more effective in solving medium- and large-scale problems. The proposed scheme for addressing the FVTRP is illustrated with an example and tested with benchmark instances that are derived from well-studied vehicle routing datasets. 相似文献
989.
990.
Numerical discretization-based kernel type estimation methods for ordinary differential equation models 下载免费PDF全文
We consider the problem of parameter estimation in both linear and nonlinear ordinary differential equation(ODE) models. Nonlinear ODE models are widely used in applications. But their analytic solutions are usually not available. Thus regular methods usually depend on repetitive use of numerical solutions which bring huge computational cost. We proposed a new two-stage approach which includes a smoothing method(kernel smoothing or local polynomial fitting) in the first stage, and a numerical discretization method(Eulers discretization method, the trapezoidal discretization method,or the Runge–Kutta discretization method) in the second stage. Through numerical simulations, we find the proposed method gains a proper balance between estimation accuracy and computational cost.Asymptotic properties are also presented, which show the consistency and asymptotic normality of estimators under some mild conditions. The proposed method is compared to existing methods in term of accuracy and computational cost. The simulation results show that the estimators with local linear smoothing in the first stage and trapezoidal discretization in the second stage have the lowest average relative errors. We apply the proposed method to HIV dynamics data to illustrate the practicability of the estimator. 相似文献