Enhanced optical confinement and lasing characteristics of individual urchin-like ZnO microstructures prepared by oxidation of metallic Zn

We prepared urchin-like micron-sized ZnO cavities with high optical quality by oxidizing metallic Zn and proposed the mechanism that resulted in the growth of the urchin-like microstructures. The photoluminescence spectra of the ZnO microstructures had a predominant excitonic emission at room temperature. The lasing properties of the urchin-like ZnO microstructures were investigated systematically through excitation power- and size-dependent photoluminescence measurements. The results showed that a low lasing threshold with high quality factors could be achieved because of the high reflectivity of the optical reflectors formed by the tapered nanowires. The unique optical characteristics may facilitate the development of high-efficiency random lasers.     

Influence of pretilt angle on disclination lines of liquid crystal lens

This article investigates the effect of pretilt angle on disclination lines of liquid crystal (LC) lenses. When the pretilt angle of LCs is higher than 7°, the disclination lines are reduced and are moved to the boundary of the LC lens. The disclination lines at the boundary do not influence the focused beam profile of the LC lens. As the pretilt angle of LCs further increases, the disclination lines at the boundary become almost invisible. However, the interference rings become asymmetrical. The response time of an LC lens with a pretilt angle higher than 7° is ～60% of the conventionally homogeneous LC lens. This value is a result of the decrease in the rotation angle of the LCs and the reduced disclination lines.     

Polymer blends with modified coupling agent. I. Preparation and thermal properties of LICA 44 grafted styrene–maleic anhydride copolymer

Neopentyl(diallyl)oxy, tri(N-ethyleneamino)ethyl titanate (LICA 44) was grafted to the styrene/maleic anhydride (SMA) copolymer for the purpose of obtaining a new interfacial coupling agent for flame retardant ABS blends. The graft reaction was proceeded in DMSO under 80°C and reduced pressure. Samples were prepared under various amine/anhydride ratios (AAR) in feed and reaction time. The verification of reaction was based on FTIR spectra and the results of elemental analysis. The reaction percentages were high but decreased with the rising AAR. Both combination types, amide acid and imide, of SMA and LICA 44 were found, and the ratio of amide acid and imide is related to the AAR and reaction time. After the graft reaction, both the initial pyrolysis temperature (T_pi) and the char yield at 800°C of SMA increased significantly. LICA 44 is believed to cause the char promoting effect on SMA-g-L44. And the dealcohol phenomenon of trimethylolpropane diallyl ether (TMPDE) away from SMA-g-L44 was observed during the thermal analysis. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:37–44, 1998     

Learner attending auto-monitor in distance learning using image recognition and Bayesian Networks

Distance learning is one of the common education methods. Its advantage lies in that the student can learn at anytime or anyplace. However, such a learning mode relies highly on the dependence of the student. Under different environments and conditions, not all the students can be attentive. In this research, an auto-detection system has been designed, using image processing and recognition technique, for defining the facial expressions and behavior easily found when a learner is inattentive or in bad mentality under distance learning environment. From the learner’s facial expressions and behavior features, the attentiveness of the student during distance learning can be determined by Bayesian Networks Model.After implementing the system of this research, and performing practical test, it is found that the accuracy of identifying the features of bad mentality and inattentive behavior is high. From Bayesian Networks assessment and inference, the learning attentiveness of the student can be determined precisely to have the teacher control the learning condition of the student explicitly.     

Nanosized strontium aluminate phosphors prepared via a reverse microemulsion route

Nanosized strontium aluminate phosphors co-activated by Eu²⁺ and Dy³⁺ were prepared via a novel reverse microemulsion process. This new synthesis technique lowered the synthesis temperature of SrAl₂O₄: Eu²⁺, Dy³⁺ phosphors to as low as 900 °C, and also reduced the particle size to the nanometer scale (around 40 nm). In the microemulsion process, the constituent cations were trapped by numerous nano-scaled micelles, leading to a shortening of the inter-diffusion length and enhancement of the precursor reactivity. The excitation intensity and emission peaks of nanosized SrAl₂O₄: Eu²⁺, Dy³⁺ phosphors significantly increased with increasing heating temperatures.     

Evaluation of radiation dose and positioning accuracy on X-ray volume imaging system for image-guided radiotherapy

Linear accelerators equipped with X-ray volumetric cone-beam Imaging (XVI) system enable verification of location of patients and displacement of tumors for image-guided radiotherapy (IGRT). The objective of this study is to evaluate the positioning accuracy using the XVI system for image-guided patient setup and to establish a lower-dose imaging protocol without sacrificing positioning accuracy for routine treatment courses. Several low-dose imaging protocols are proposed by modifying tube voltage from 120 to 100 kV and lowering tube current from 40 to 10 mA. The positioning accuracy of both bone and gray value registration methods provided by XVI system were also evaluated. Phantom study revealed that the gray value algorithm was more accurate than the bone algorithm in position and registration. However, both translational and rotational accuracies were less than 0.15 mm and 0.8^° at all dimensions, which were considered negligible in clinical applications. In addition, the lower-dose protocol (100 kV, 10 mA) produced relative much less radiation dose compared to the default CBCT protocol in the XVI system. In conclusion, our proposed lower-dose protocol results in significant radiation dose reduction without compromising positioning accuracy and may have the potential to be adopted for clinical usage in the future.     

Microwave Dielectric Properties of Nd(Zn1/2Ti1/2)O3 Ceramics with V2O5 Additives

The microwave dielectric properties and the microstructures of V₂O₅-doped Nd(Zn_1/2Ti_1/2)O₃ ceramics prepared by conventional solid-state route have been studied. Doping with V₂O₅ (up to 6 wt.%) can effectively promote the densification of Nd(Zn_1/2Ti_1/2)O₃ ceramics with low sintering temperature. At 1300 °C, Nd(Zn_1/2Ti_1/2)O₃ ceramic when added with 6 wt.% V₂O₅ possesses a dielectric constant of 29.9, a quality factor (Q × f) value of 105000 GHz (at 8 GHz), and a temperature coefficient of resonant frequency of ?45 ppm/°C. These V₂O₅-doped Nd(Zn_1/2Ti_1/2)O₃ ceramics can be used in microwave devices.     

A study of bulk current mechanism in P3HT-based thin film transistors and approach for current suppression

In this article, poly(3-hexylthiophene) (P3HT) based thin film transistors with Ti capped source and drain electrodes (S/D) was employed to have an insight into the mechanism of bulk current effect, which led to poor subthreshold swing and large off current. Our newly developed PTFTs do show greater characteristics in the aspects of on/off current ratio and subthreshold swing than those with the conventional Au/Ti S/D. In order to explain the results, we propose that the bulk current is composed of two components, i.e., side-wall and top-face injections. We ascribe the improvements to the reduction of top-face injection bulk current due to the larger injection barrier between the P3HT and Ti. As comparing the PTFTs with Ti capped laterally grown multi-wall carbon nanotube (MWCNT) S/D with the PTFTs with MWCNT S/D, we also observe similar tendency of bulk current reduction. From the viewpoint of device operation, better subthreshold swing and smaller off current result in faster device switching and lower power consumption. By this new approach of S/D structure, there are two and 20 times improvements on the subthreshold swing and off current, respectively, although the reduction of the bulk current also leads to a slight decrease of the on-current.     

Efficient and stable photocatalytic hydrogen production from water splitting over ZnxCd1–xS solid solutions under visible light irradiation

A simple co-precipitation method was employed to synthesize a series of cubic zinc-blende phase of Zn_xCd_1−xS photocatalysts using Na₂S as the S source. Structural, morphological and optical properties of the samples have been investigated by XRD, SEM, EDS, XRF, ICP, N₂ physisorption and UV–vis diffuse reflectance techniques. The Zn_xCd_1−xS solid solution is not a simple compound mixture of ZnS and CdS, its XRD patterns show new structural peaks instead of mixture of original peaks. The lattice parameter a measured from the XRD patterns of the Zn_xCd_1−xS samples exhibits a slightly nonlinear relationship with the Zn mole fraction, which is slightly inconsistent with Vegard's law, thus suggesting that a nonhomogeneous alloy structure exists in Zn_xCd_1−xS solid solution. The photocatalytic H₂ evolution from water splitting in the sacrificial reagents of 0.25 M Na₂S/0.35 M K₂SO₃ under visible light at 30 °C and 55 °C were also examined in the study. It is found that Zn_xCd_1−xS solid solution with composition x = 0.4–0.5 shows the highest photocatalytic H₂ production performance. The studied Zn_xCd_1−xS exhibits at least 50 h stable photocatalytic activity under outdoor sunlight irradiation.     

Pulsed laser deposition of (WO3)1 − x(Nb2O5)x thin films: Characterization and gasochromic studies

A series of (WO₃)_{1 − x}(Nb₂O₅)_x (x = 0, 0.05, 0.1 and 0.15) mixed oxide films were fabricated by pulsed laser deposition (PLD) at 27 Pa oxygen partial pressure on ITO glass substrates. The thickness of the (WO₃)_{1 − x}(Nb₂O₅)_x thin films is about 350 ± 30 nm and their surface has a uniform morphology. A layer of platinum (Pt) was then sputtered onto the surface of the film. The hydrogen gas sensing performance of Pt catalyst activated (WO₃)_{1 − x}(Nb₂O₅)_x thin films were investigated. The cycling of the coloration was obtained from UV–vis spectra. Gasochromic coloration of (WO₃)_{1 − x}(Nb₂O₅)_x thin films were investigated at room temperature in H₂–N₂ mixtures containing 1–100 mol% of H₂. The results show that the shortest response time of (WO₃)_{1 − x}(Nb₂O₅)_x/Pt hydrogen sensor is within 30 s and the highest transmittance change (ΔT) varies from 20% to 30%.