Coupling copper and hydrogenated TiO2 to bare TiO2 structures for improved photocatalytic performance

Coupling of metals and hydrogenated TiO₂ (HT) to bare TiO₂ may improve synergistically the photocatalytic activity of TiO₂ for pollutant decomposition. Herein, we address this issue by investigating the photocatalytic performances of Cu‐loaded HT (CuHT)/bare TiO₂ (CuHTT) heterojunction nanocomposites for the degradation of harmful n‐butanol under simulated solar light illumination. CuHTT with a CuHT‐to‐TiO₂ composition ratio of 0.1 showed a photocatalytic efficiency exceeding those of four reference photocatalysts, exhibiting the advantages of improved visible light absorption efficiency, charge carrier separation, and adsorption capacity. Increasing the CuHT‐to‐TiO₂ ratio from 0.01 to 0.1 improved the photocatalytic efficiency of CuHTT, whereas a further increase to 0.9 resulted in a decreased photocatalytic efficiency. Moreover, the photocatalytic efficiency improved as relative humidity increased from 20% to 70%, decreasing upon its further increase to 95%. The efficiencies of n‐butanol to CO₂ conversion over CuHTT were lower than the corresponding decomposition efficiencies. Incompletely oxidized CO and three organic vapors (butanal, propanal, and 1‐propanol) were determined as major intermediates. A possible mechanism for CuHTT‐catalyzed photodegradation under simulated solar illumination was proposed.     

Reconstruction of the rose of directions from a digital microhologram of fibres

Digital holography makes it possible to acquire quickly the interference patterns of objects spread in a volume. The digital processing of the fringes is still too slow to achieve on line analysis of the holograms. We describe a new approach to obtain information on the direction of illuminated objects. The key idea is to avoid reconstruction of the volume followed by classical three-dimensional image processing. The hologram is processed using a global analysis based on autocorrelation. A fundamental property of diffraction patterns leads to an estimate of the mean geometric covariogram of the objects projections. The rose of directions is connected with the mean geometric covariogram through an inverse problem. In the general case, only the two-dimensional rose of the object projections can be reconstructed. The further assumption of unique-size objects gives access with the knowledge of this size to the three-dimensional direction information. An iterative scheme is suggested to reconstruct the three-dimensional rose in this special case. Results are provided on holograms of paper fibres.     

卫星通信中频谱反转的成因与处理

变频的目的是为了使信号能够在特定的信道内利用合适的频率对信号进行有效传输,是无线通信系统中需要经常涉及到的问题。频谱反转一般是在传输过程中由于变频而造成的接收端所收与发射端所发的信号频谱相反的现象。本文对频谱反转产生的原因以及如何在基带系统中处理的方法进行了分析和介绍。     

Use of Mesoscopic Host Matrix to Induce Ferrimagnetism in Antiferromagnetic Spinel Oxide

Despite the advances in the methods for fabricating nanoscale materials, critical issues remain, such as the difficulties encountered in anchoring, and the deterioration in their stability after integration with other components. These issues need to be addressed to further increase the scope of their applicability. In this study, using epitaxial mesoscopic host matrices, materials are spatially confined at the nanoscale, and are supported, anchored, and stabilized. They also exhibit properties distinct from the bulk counterparts proving their high quality nanoscale nature. ZnFe₂O₄ and SrTiO₃ are used as the model confined material and host matrix, respectively. The ZnFe₂O₄ phases are spatially confined by the SrTiO₃ mesoscopic matrix and have strongly enhanced ferrimagnetic properties as compared to bulk and plain thin films of ZnFe₂O₄, with a Curie temperature of ≈500 K. The results of a series of control experiments and characterization measurements indicate that cationic inversion, which originates from the high interface‐to‐volume ratio of the ZnFe₂O₄ phase in the ZnFe₂O₄–SrTiO₃ nanocomposite film, is responsible for the magnetization enhancement. An exchange bias is observed, owing to the coexistence of ferrimagnetic and antiferromagnetic regions in the confined ZnFe₂O₄ phase. The magnetic properties are dependent on the ZnFe₂O₄ crystallite size, which can be controlled by the growth conditions.     

Synergistic effect of amino silane functional montmorillonite on intumescent flame‐retarded SEBS and its mechanism

A functional modified montmorillonite (F‐OMMT) was prepared by intercalating pristine montmorillonite using phosphonium salt and subsequent grafting through alkyl amino silane coupling. The synergistic effect of F‐OMMT on the flame retardancy and char‐forming mechanism of intumescent flame‐retarded polystyrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS) composite (SEBS/IFR) was investigated. When 2 wt % F‐OMMT was introduced to the SEBS/IFR composite, the limited oxygen index (LOI) value of the composite increased from 24.9% to 26.9%, and the peak heat release rate significantly reduced according to microscale combustion calorimeter (MCC) test. The outer char demonstrated that F‐OMMT produced dense and intact nanoparticles with a stabilised graphite structure. Meanwhile, F‐OMMT helped form a crosslinking network containing large amounts of P, O, N, and Si in the char layer. Along with IFR, the amino functional group on the clay released nonflammable ammonia in the gaseous phase, the enhanced blowing effect can overcome the high‐viscosity resistance of SEBS, more intumescent coating with strengthened clay platelets was then produced. In addition, the tensile properties of SEBS/IFR/F‐OMMT composite increased evidently for the good dispersion effect. F‐OMMT can serve as an effective and environmentally friendly additive for SEBS/IFR composite. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44953.     

Highly stable hydrophobic SiNCO nanoparticle‐modified silicon nitride membrane for zero‐discharge water desalination

Membrane distillation water desalination can attain a significantly higher water recovery than reverse osmosis, while the lack of stable hydrophobic membranes limits its commercial applications. This article presents the preparation of a new hydrophobic membrane by modifying a porous Si₃N₄ substrate with vesicular SiNCO nano‐particles. The membrane had a water contact angle of 142°, due to the presence of –Si–CH₃ terminal groups and the high surface roughness. The contact angle remained nearly the same after exposures of the membrane to boiling water, aqueous solutions with pH ranging from 2 to 12, and benzene. The membrane exhibited satisfactory water desalination performance on highly concentrated NaCl solutions and simulated seawater. With the highly stable membrane, it is promising to develop a zero‐discharge water desalination process for simultaneous production of fresh water for daily uses and brine for industrial uses. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1272–1277, 2017     

大规模MIMO系统低复杂度混合迭代信号检测

在大规模MIMO系统上行链路信号检测算法中,最小均方误差(MMSE)算法能获得接近最优的线性检测性能.但是,传统的MMSE检测算法涉及高维矩阵求逆运算,由于复杂度过高而使其在实际应用中难以快速有效地实现.基于最速下降(steepest descent,SD)算法和高斯一赛德尔(Gauss-Seidel,GS)迭代的方法提出了一种低复杂度的混合迭代算法,利用SD算法为复杂度相对较低的GS迭代算法提供有效的搜索方向,以加快算法收敛的速度.同时,给出了一种用于信道译码的比特似然比(LLR)近似计算方法.仿真结果表明,通过几次迭代,给出的算法能够快速收敛并接近MMSE检测性能,并将算法复杂度降低一个数量级,保持在O(K2).     

多频点同时反演策略在频域全波形反演中的应用和实现

频域全波形反演能够获得高分辨率的反演结果,具有较高的计算效率,因此得到广泛应用.在传统单频点串行反演策略的基础上,提出一种多频点同时反演策略,并推导出一种新的目标函数表达式,应用于频域全波形反演算法中.该策略能够同时反演所有的频率分量,对于一组频点中的每个频点进行加权求和处理,从而避免了高频分量在反演结果中占据主导,同时避免反演结果中存在噪声干扰.分别用三种不同的模型进行验证.实验表明,相对于传统的单频点策略,多频点策略的反演结果具有更好的稳定性、正确性和鲁棒性;而且对于模型中明显介质边界的位置,它的反演结果更接近于目标模型.     

电离层垂直剖面建模方法改进研究

垂测电离图反演对研究电离层结构、电离层波传播等具有重要意义,受到广泛的重视.模式法是垂测电离图反演较为普遍的方法,基于Reinisch和黄雪钦根据IRI模型建立的电离层垂直剖面模型,Carlo Scotto提出了一种反演电离层剖面的方法.文章基于这种反演方法对Reinisch和黄雪钦模型进行了改进,把高斯模型应用于F₁层模型,使反演后F₁层临频与实测F₁层临频基本吻合,同时应用F₁层模型的反模型——反高斯模型作为连接层以保证F₁层与F₂层剖面连续,并通过仿真分析对算法的有效性进行了验证。     

纳米α–Fe_2O_3协同膨胀阻燃EP材料的阻燃和抑烟性能

使用原位聚合的方法制备含α–Fe_2O_3的磷酸季戊四醇三聚氰胺盐(PPMS–Fe_2O_3),并对其结构和性能进行表征。利用傅立叶变换红外光谱、热重分析(TG)、锥形量热仪测试和烟密度实验研究PPMS–Fe_2O_3对EP树脂阻燃和抑烟性能的影响。结果表明:PPMS–Fe_2O_3的阻燃和抑烟效果随纳米α–Fe_2O_3增加呈现先增加后降低的趋势,其中PPMS–5%Fe2O3试样的阻燃及抑烟性能最佳。此外,相同添加量下的PPMS–Fe_2O_3纳米复合材料相比于PPMS与纳米α–Fe_2O_3的物理共混物具有更好的阻燃和抑烟效率。TG分析表明,添加适量的纳米α–Fe_2O_3能显著提高PPMS在EP树脂中的热稳定性和成炭性能,其中PPMS–5%Fe_2O_3阻燃EP树脂的热稳定性和成炭能力最佳。炭层分析表明,α–Fe_2O_3在燃烧过程中能促进形成更多的P—N—C和P—O—C网状交联结构,以增强炭层致密性,进而达到较好的协效阻燃和抑烟作用。