Low-temperature combustion synthesis of CuCr2O4 spinel powder for spectrally selective paints

CuCr₂O₄ spinel powder with high quality black hue, investigated as solar-absorbing pigment for spectrally selective paint, was synthesized by an environmental friendly sol–gel combustion process using citric acid as the fuel and metal nitrates as oxidizers. Single-phase CuCr₂O₄ spinel crystals were obtained after heat treatment of the as-burnt powder at a low temperature (600 °C) and the average crystallite size of the CuCr₂O₄ powders increased with the calcining temperature. Morphological analysis of powders calcined at various temperatures was done by field emission scanning electron microscopy. CuCr₂O₄ powder calcined at 700 °C was chosen as pigment to fabricate thickness sensitive spectrally selective paint coatings by simple spray-coating technique. For the sake of comparison, the as-burnt powder composed of mixed metal oxides (i.e., CuO and Cr₂O₃) was also used as pigment. The results reveal that the spinel CuCr₂O₄ based paint coatings exhibit much higher spectral selectivity (α _s = 0.88–0.91, ε ₁₀₀ = 0.27–0.35) which is depending on the coating thicknesses than that of coatings using as-burnt powder as pigment (α _s = 0.83–0.88, ε ₁₀₀ = 0.60–0.66). The CuCr₂O₄-based paint coatings showed no visible degradation after 600 h of condensation test and the performance criterion value is 0.04, indicating that the coatings have excellent long term stability.     

不同磁路下微型ECR中和器电子引出的模拟研究

电子回旋共振(ECR)中和器是微型ECR离子推力器的重要组成部分,其引出的电子用于中和ECR离子源的离子束流,避免了航天器表面电荷堆积,并且电子引出性能对推力器的整体性能起着重要作用.为了分析影响微型ECR中和器电子引出的因素,本文建立了二维轴对称PIC/MCC计算模型,通过数值模拟研究不同磁路结构对中和器的电子引出,及不同腔体长度对壁面电流损失的影响.计算结果表明, ECR区位置和引出孔附近磁场构型对中和器的电子引出性能至关重要.当ECR区位于天线上游,电子在迁移扩散中易损失,并且电子跨过引出孔前电势阱所需的能量更高.如果更多磁力线平行通过引出孔,中和器引出相同电子电流所需电压较小.当ECR区被天线切割或位于下游时,电子更易沿磁力线迁移到引出孔附近,从而降低了收集板电压.研究了同一磁路结构下不同腔体长度对电子引出的影响,发现增加腔体长度,使得更多平行轴线的磁力线通过引出孔从而避免电子损失在引出板表面,增加了引出电子电流.研究结果有助于设计合理的中和器磁路和腔体尺寸.     

Magnetic properties and large cryogenic low-field magnetocaloric effect of HoCo<Subscript>2</Subscript> nanoparticles without core/shell structure

The HoCo₂ nanoparticles are found to be stable in air without any shell protection. The HoCo₂ nanoparticles display superparamagnetic properties between their blocking temperature of 40 K and Curie temperature of 78 K. The magnetic-entropy change increases with decreasing temperature at a certain magnetic-field change, which is ascribed to the competition between the Zeeman energy and thermal-agitation energy at low temperatures. A large magnetic-entropy change of 19.4 J kg⁻¹ K⁻¹ was found at 7.5 K in an applied-field change from 1 to 7 T, while 6.1 J kg⁻¹ K⁻¹ was achieved in a low field change of 1 T. HoCo₂ nanoparticles are useful for application of magnetic refrigeration at low temperatures.     

面向客户群的服务方案配置规则挖掘方法

产品/服务配置规则获取的主要方式是用数据挖掘技术从设计实例数据库中提取.客户化服务方案配置规则为服务功能需求和方案特征间的关联规则.考虑到常用关联规则挖掘算法Apriori具有运算复杂的缺点,提出基于PIETM(Principle of Inclusion—Exclusion and Transaction Mapping)算法的配置规则挖掘方法,考虑置信度和有趣度指标,提取强关联规则.针对配置实例数据库数据量较大时,配置规则挖掘的效率会降低且会产生大量冗余规则的问题,采用二元语义模型表达定性的服务功能需求,将同类客户群的功能需求进行合并,替换多样化的功能需求,减少规则的冗余.最后以一工程机械制造企业服务方案配置规则挖掘为例,验证了所提方法的有效性.     

A Superacid-catalyzed Synthesis of Fluorescent Covalent Triazine Based Framework Containing Perylene Tetraanhydride Bisimide for Sensing to O-nitrophenol with Ultrahigh Sensitivity

Abstract

A mesoporous covalent triazine framework, PCPDI, was synthesized via an aromatic nitrile trimerization reaction of N,N′-di(4-cyanphenyl)- 3,4,9,10-tetracarboxydiimide (CPDI) by CF₃SO₃H catalyzed at 40?°C and this method avoids the use of noble metal catalyzers or high temperature reaction. PCPDI exhibits high thermal stability and strong fluorescence. The PCPDI shows ultrahigh sensitivity to tracing o-nitrophenol in chloroform with K_SV constant of 1.74?×?10⁵ L mol^?1 and detection limit (LOD) of 1.72?×?10^?11?mol L^?1.     

Facile electrochemical synthesis of a conducting copolymer from 5-aminoindole and EDOT and its use as Pt catalyst support for formic acid electrooxidation

5-Aminoindole and 3,4-ethylenedioxythiophene (EDOT) were copolymerized electrochemically on a carbon cloth (CC) electrode in an aqueous sulfuric acid solution. The as-prepared copolymer was characterized by cyclic voltammogram, SEM, and UV-vis and FT-IR spectra through which the electrochemical properties, structure, and composition of the as-obtained copolymer were determined. The electrochemical activity and stability of the as-formed copolymer are significantly improved in comparison with poly(5-aminoindole) due to the incorporation of EDOT units into the conjugated chain. The copolymer film-modified CC electrode was used as substrate for Pt particle deposition (denoted as Pt/copolymer/CC), and then, its catalytic activity towards formic acid electrooxidation was studied. Experimental results indicate that the catalytic activity of Pt/copolymer/CC towards formic acid electrooxidation is enhanced in comparison with that of Pt/homopolymer/CC, which can be attributed to the homogeneous distribution of Pt nanoparticles on the copolymer/CC substrate and the improved electrochemical activity of the copolymer film.     

From electronic excited state theory to the property predictions of organic optoelectronic materials

We introduce here a work package for a National Natural Science Foundation of China Major Project. We propose to develop computational methodology starting from the theory of electronic excitation processes to predicting the opto-electronic property for organic materials, in close collaborations with experiments. Through developing methods for the electron dynamics, considering superexchange electronic couplings, spin-orbit coupling elements between excited states, electron-phonon relaxation, intermolecular Coulomb and exchange terms we combine the statistical physics approaches including dynamic Monte Carlo, Boltzmann transport equation and Boltzmann statistics to predict the macroscopic properties of opto-electronic materials such as light-emitting efficiency, charge mobility, and exciton diffusion length. Experimental synthesis and characterization of D-A type ambipolar transport material as well as novel carbon based material will provide a test ground for the verification of theory.     

Multicomponent Reaction for Synthesis of 2-(Indol-3-yl)pyridine Derivatives Under Microwave Irradiation

A short, practical, and efficient preparation of 2-(indol-3-yl)pyridine derivatives via a one-pot procedure of 3-cyanoacetylindole, chalcones, and ammonium acetate under microwave irradiation was described. All these compounds were obtained in good yield, and their structures were confirmed by ¹H NMR, infrared, and elementary analysis.