Innovational radiation sensor by integrating AL2O3:C optically stimulated luminescent dosemeter and GaN detectors

We report a new dosimetry concept that is built on an earlier integrated sensor concept by our group at University of Washington to integrate a radiation-dosimetry-quality Al2O3:C and a high quantum-efficiency GaN-based p-i-n photodiode on one side, and light emitting diodes (LEDs) on the opposite side as the stimulation source. The performance of the sensor has been evaluated by computer simulation, the performance of GaN photodiodes and studying the GaN films. The absorption spectrum of the GaN film was measured and indicated that the GaN photodiodes would not respond to the output wavelengths of the stimulating LEDs. The electrical properties and the performance of GaN p-i-n photodiode under irradiation were simulated. The results showed that the sensor offered comparable radiation sensitivity to current technologies and could be operated in active mode.     

Low-temperature particle synthesis of titania/silica/natural rubber composites for antibacterial properties

Composite particles of titania/silica/natural rubber (TiO₂/SiO₂/NR) were prepared and evaluated for their potential antibacterial application. All processes were restricted to a low temperature or a small heating contact time to avoid degradation of the NR. The primary NR particles were synthesized by spray drying and then SiO₂ and TiO₂ were incorporated sequentially by chemical vapor deposition and liquid phase deposition, respectively. The physical and chemical properties were characterized by X-ray diffractometry, scanning electron microscopy with energy dispersive X-ray spectrometry, Fourier-infrared spectroscopy and thermogravimetric analyses. The TiO₂/SiO₂/NR composite particles had a spherical shape with a diameter of about 10 μm, with titania on the outer layer, and showed an effective antibacterial activity of a 99.99% reduction in viable Escherichia. coli and Staphylococcus aureus within 20 min of exposure under fluorescent light. In addition, the particles could be reused with the same level of antibacterial activity for up to three cycles. The structural and antibacterial models of the composite particles are proposed in this work.     

A study on novel combined processes for preparation of high performance Pt–Co/C electrocatalyst for oxygen reduction in PEM fuel cell

The preparation of a Pt–Co/C electrocatalyst for the oxygen reduction reaction in PEM fuel cells was achieved via a novel combined process of impregnation and seeding. The effect of seeding and non-seeding approaches on the morphologies and activities of the electrocatalyst was explored. The results indicated that the seeding or non-seeding approaches provided the similar results of Pt structure and phase composition in the Pt–Co/C electrocatalyst. However, the seeding approach provided a more uniform dispersion and smaller particle size of electrocatalyst compared with that of the non-seeding approach. Also, higher values of kinetic parameters including i₀, E₀, i_0.9V and E_10mA/cm2 were obtained in case of seeding electrocatalyst. Finally, the rotating disk electrode experimental results showed that the mechanism of oxygen reduction involved the four-electron pathway.     

A novel fuzzy logic control technique tuned by particle swarm optimization for maximum power point tracking for a photovoltaic system using a current-mode boost converter with bifurcation control

This paper presents a novel fuzzy logic control technique tuned by particle swarm optimization (PSO-FLC) for maximum power point tracking (MPPT) for a photovoltaic (PV) system. The proposed PV system composes of a current-mode boost converter (CMBC) with bifurcation control. An optimal slope compensation technique is used in the CMBC to keep the system adequately remote from the first bifurcation point in spite of nonlinear characteristics and instabilities of this converter. The proposed PSO technique allows easy and more accurate tuning of FLC compared with the trial-and-error based tuning. Consequently, the proposed PSO-FLC method provides faster tracking of maximum power point (MPP) under varying light intensities and temperature conditions. The proposed MPPT technique is simple and particularly suitable for PV system equipped with CMBC. Experimental results are shown to confirm superiority of the proposed technique comparing with the conventional PVVC technique and the trial-and-error based tuning FLC.     

A systematic study on group III-nitride thin films with low temperature deposited via MOCVD

Wide bandgap semiconductor materials provide superior electrical, optical, and thermal properties that classical semiconductors, Si and GaAs, are unable to achieve. However, most commercially available substrates have large lattice and thermal expansion mismatches to III-nitrides films. Thus a high quality buffer layer, grown at low temperatures, is essential in growing high quality III-nitride films. This research provides a throughout study on III-nitrides, such as AlN, GaN and AlGaN thin films, which were grown at low temperatures (400–600 °C). Growth rate, stoichiometry and crystal structure of low temperature growth films will be reported by using several advanced post-growth analysis techniques. Temperature, pressure, and V/III molar ratio were also investigated to determine their effect on the film properties. From the study, a better understanding of the relationships between film properties and growth parameters will be achieved.     

Novel application of Hicon Black in PEMFC microporous sublayer: Effects of composition and subsequent membrane selection

This research was carried out to prepare high performance membrane electrode assemblies (MEAs) for a proton exchange membrane fuel cell (PEMFC). The MEAs were prepared by introducing a microporous sublayer (MPS) between the gas diffusion layer and the catalyst layer. Main parameters for MPS preparation, which are microporous carbon types and the polytetrafluoroethylene (PTFE) content in the MPS, were investigated. Three microporous carbon types, which are Hicon Black, RGN and Vulcan, were evaluated. Then, Nafion membranes with two thicknesses were employed to form an MEA. The preliminary results demonstrated that a high performance could be achieved with the presence of Hicon Black in the MPS and the performance was comparable to those with the presence of Vulcan XC-72, particularly in the high current density region. The optimum PTFE content was found to be 6 wt% and the thinner membrane provided a better cell performance. The highest current density was 858 mA cm^?2 at the cell potential of 0.6 V.