Characterizations of TiO2/SiO2/Ni–Cu–Zn Ferrite Composite for Magnetic Photocatalysts

The TiO₂/SiO₂/Ni–Cu–Zn ferrite composite for magnetic photocatalysts with high photocatalytic activity is successfully prepared in this study. The composite are composed of spherical or elliptical Ni–Cu–Zn ferrite nanoparticles about 20–60 nm as magnetic cores, silica as barrier layers with thickness of 15 nm between the magnetic cores and titania shells with thickness approximately 1.5 nm. Photodegradation examination of TiO₂/SiO₂/ Ni–Cu–Zn ferrite composite was carried out in methylene blue (MB) solutions illuminated under a Xe arc lamp with 35 W and color temperature of 6000 K. The results indicated that about 47.1% of MB molecules adsorbed on the TiO₂/SiO₂/Ni–Cu–Zn ferrite composite within 30 min mixing due to it higher pore volume of 0.034 cm³/g, and after 6 h Xe lamp irradiation, 83.9% of MB 16.1% was photodegraded. Compared with the TiO₂ /Ni–Cu–Zn ferrite composite, the TiO₂/SiO₂/Ni–Cu–Zn ferrite composite with silica barrier layer prohibited the photodissolution and enhanced the photocatalytic ability. The magnetic photocatalyst shows high photocatalytic efficiency that the apparent first‐order rate constant k_obs is 0.18427 h^?1, and good magnetic property that the saturation magnetization (M_s) of is 37.45 emu/g, suggesting the magnetic photocatalyst can be easily recovered by the application of an external magnetic field.     

The Effects of Annealing Atmosphere on the Electrical Properties of MgNb2O6/ITO Heterostructures

The effects of annealing atmosphere (N₂, air and O₂) on the electrical properties of sol–gel‐derived MgNb₂O₆/ITO heterostructures are discussed in this work. All samples exhibited the amorphous phase and were highly transparent. The percentage of Nb⁴⁺ content increased when the films were annealed in the oxygen‐deficient conditions, which could lead to semiconducting films. In addition, the results show that the electrical properties of sol–gel‐derived MgNb₂O₆ thin films could be tuned based on the annealing atmosphere. Moreover, the conduction mechanisms of MgNb₂O₆/ITO heterostructures are also discussed in this study. The results show that MgNb₂O₆ thin films have potential for use in multifunctional optoelectronic applications, due to their flexible electrical properties and good transparency.     

Preparation and characterization of methoxy‐poly(ethylene glycol) side chain grafted onto chitosan as a wound dressing film

Chitosan has received extensive attention as a biomedical material; however, the poor solubility of chitosan is the major limiting factor in its utilization. In this study, chitosan‐based biomaterials with improved aqueous solubility were synthesized. Two molecular weights (750 Da and 2000 Da) of methoxypoly(ethylene glycol) (mPEG) were grafted onto chitosan (mPEG‐g‐chitosan) to form a ～100‐μm‐thick plastic film as a wound dressing. The chemical structures of the mPEG‐g‐chitosan copolymers were confirmed using Fourier transform infrared spectroscopy (FTIR), and the thermal properties were characterized using thermogravimetry analysis (TGA). Their microstructures were observed using scanning electron microscopy (SEM). The other properties were analyzed via the swelling ratio, tensile strength, elongation, and water vapor transmission rate (WVTR). Biocompatibility evaluations through biodegradability, cytotoxicity, and antimicrobial effect studies were also performed. The obtained mPEG‐g‐chitosan copolymers were soluble in slightly acidic aqueous solutions (pH～6.5) at a concentration of 10 wt %. The optimal mPEG‐g‐chitosan hydrogels had swelling ratios greater than 100% and WVTRs greater than 2000 g/m²/day. Their performance against Staphylococcus aureus will be subjected to further improvements with respect to medical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42340.     

Real‐time calculation of power system bus voltage using a hybrid approach combining the Newton–Raphson method and dynamic programming

The calculation of the magnitudes and phase angles of the bus voltage is a challenging task in real‐time applications for power systems. Voltage profile, which denotes the present conditions of a power system, is determined by executing the traditional AC power flow program or by searching the supervisory control and data acquisition system. The AC power flow program is not suitable for several real‐time applications, such as contingency analysis and security control calculations, because of its complexity and convergence problems. Fast computation is the major concern in such applications. In this paper, a new method based on sensitivity factors, referred to as Jacobian‐based distribution factors (JBDFs), is proposed for calculating the magnitudes and phase angles of bus voltages. This method requires setting up JBDFs and deriving optimal solution paths of bus voltage for non‐swing buses through dynamic programming under base‐case loading conditions. Under real‐time conditions, the proposed method initially calculates real and reactive power line flows via JBDFs, and then computes the voltage magnitudes and phase angles of non‐swing buses through the derived optimal solution paths. The excellence of the proposed hybrid calculation method is verified by IEEE test systems. Simulation results demonstrate that the proposed method exhibits fast computation and high accuracy. Thus, the method is suitable for real‐time applications. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A unified spectrum sensing and throughput analysis model in cognitive radio networks

Cognitive radio (CR) is a newly developed technology for increasing spectral efficiency in wireless communication systems. In the CR networks, there exist two traditional spectrum‐sharing technologies called spectrum overlay and spectrum underlay. A new hybrid overlay/underlay paradigm has also been discussed in the literature. In this work, we create a unified spectrum sensing and throughput analysis model, which is suitable for overlay, underlay, and hybrid overlay/underlay paradigms in the CR networks. In the proposed model, the energy detection scheme is employed for the spectrum sensing in the network in which the co‐channel interference is present among primary users and secondary users (SUs). The SUs' throughput in the proposed CR system model is then analyzed. The simulations are also carried out for demonstrating the performance of overlay, underlay, and hybrid overlay/underlay paradigms. Copyright © 2013 John Wiley & Sons, Ltd.     

A channel reservation and preemption model using overlapping regions in sector‐based cellular networks

This paper presents a channel reservation and preemption (CRP) model using overlapping regions in a cellular network with multiple sectors. To fully exploit and reuse the frequencies, directional antennas are installed on base stations (BSs) to divide the coverage into a number of equal‐sized sectors. When traffic is unevenly distributed across the sectors in a BS, channel utilization in every sector may become very different; low‐traffic sectors may be underutilized while high‐traffic sectors may be overutilized. A CRP scheme is thus proposed to more efficiently utilize free channels among sectors. CRP aims at reducing the dropping probabilities of handoff calls. Specifically, when free channels in a sector are not available, a handoff call, instead of being dropped, is allowed to preempt an ongoing call residing in the overlapping region of two adjacent sectors or two neighbor cells. Under CRP, the preempted ongoing call will not be disconnected, because it can switch over its service to the BS of a neighbor cell or to another directional antenna of an adjacent sector. For the purpose of evaluation, we build an analytical model for the proposed CRP using six‐tuple Markov chains. Analytical results show that the proposed CRP can significantly reduce the dropping probabilities of inter‐sector handoff calls, particularly when traffic between two sectors is not evenly distributed. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermoplastic polyvinyl alcohol/multiwalled carbon nanotube composites: Preparation,mechanical properties,thermal properties,and electromagnetic shielding effectiveness

This study uses the solution mixing method to combine plasticized polyvinyl alcohol (PVA) as a matrix, and multiwalled carbon nanotubes (MWCNTs) as reinforcement to form PVA/MWCNTs films. The films are then laminated and hot pressed to create PVA/MWCNTs composites. The control group of PVA/MWCNTs composites is made by incorporating the melt compounding method. Diverse properties of PVA/MWCNTs composites are then evaluated. For the experimental group, the incorporation of MWCNTs improves the glass transition temperature (T_g), crystallization temperature, T_c), and thermal stability of the composites. In addition, the test results indicate that composites containing 1.5 wt % of MWCNTs have the maximum tensile strength of 51.1 MPa, whereas composites containing 2 wt % MWCNTs have the optimal electrical conductivity of 2.4 S/cm, and electromagnetic shielding effectiveness (EMI SE) of ?31.41 dB. This study proves that the solution mixing method outperforms the melt compounding method in terms of mechanical properties, dispersion, melting and crystallization behaviors, thermal stability, and EMI SE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43474.