No abstract

We report high-performance visible-blind ultraviolet (UV) phototransistors (PTs) based on an enhanced HEMT structure. In dark conditions, the conduction channel was depleted, and the dark current density was suppressed to 2.63 × 10 −10 mA/mm. Under 345 nm UV illumination, the depletion region shrinks, and the two-dimensional electron gas (2DEG) recovers. A high photocurrent density of 37.39 mA/mm, a peak responsivity of 6.80 × 10 4 A/W, a large photo-to-darkcurrent ratio (PDCR) of 1.42 × 10 11 , and a superior UV-to-visible rejection ratio (UVRR) of 4.84 × 10 7 are exhibited. Most importantly, the device presents an ultrafast response time of 11.33 μs/65.52 μs, which is due to the significant suppression of the persistent photoconductivity effect by the built-in electric field in the p−n junction. The results suggest that the p-GaN/AlGaN/GaN PT is a brand-new device model that combines the advantages of photoconductors with high responsivity and photodiodes with low dark current and fast response time.

In this study maximum power point tracking (MPPT) is applied to the photovoltaic (PV) system to harvest the maximum power output. The output power of the PV effect changes according to external solar irradiation and ambient temperature conditions. In the existing MPPT strategies, most of them only take variations in radiation level into account, rarely considering the impact of temperature changes. However, the temperature coefficients (TC) play an important role in the PV system, especially in applications where ambient temperature changes are relatively large. In this paper, an MPPT method is presented for a PV system that considers the temperature change by using variable universe fuzzy logic control (VUFLC). By considering the ambient temperature change in PV modules, the proposed control method can regulate the contraction and expansion factor of VUFLC, which eliminates the influence of temperature variability and improves the performance of MPPT, therefore achieving fast and accurate tracking control. The proposed method was evaluated for a PV module under different ambient conditions and its control performance is compared with other MPPT strategies by simulation and experimental results.

Recent studies suggest reactive oxygen species (ROS) induced in mammalian cells exposed to multi-walled carbon nanotubes (MWCNTs) could mediate the cytotoxicity. This study was conducted to determine the mechanisms responsible for MWCNTs-induced ROS production in human primary macrophages. Our results showed that superoxide levels were significantly increased in a time-dependent manner in blood monocyte-derived macrophages treated with 100 microg/ml MWCNTs for 12 h. Concomitantly, MWCNTs induced membrane translocation of the NADPH oxidase subunits p47phox and p67phox, a signature event for NADPH oxidase activation. Pre-incubation with apocynin, a selective inhibitor of NADPH oxidase, prevented both membrane translocation of p47phox and superoxide production. Treatment with MWCNTs also resulted in an increased cytotoxicity in human primary macrophages that was significantly attenuated by both apocynin and antioxidants. These findings demonstrate that MWCNTs activate NADPH oxidase in human macrophages, which may contribute to ROS generation in MWCNTs treated-macrophages.