Improvement of InGaN/GaN laser diodes by using a Si-doped In/sub 0.23/Ga/sub 0.77/N/GaN short-period superlattice tunneling contact layer

InGaN/GaN multiple-quantum-well laser diode (LD) structures, including an Si-doped n/sup +/-In/sub 0.23/Ga/sub 0.77/N/GaN short-period superlattice (SPS) tunneling contact layer, are grown on c-face sapphire substrates by metalorganic vapor-phase epitaxy. The In/sub 0.23/Ga/sub 0.77/N/GaN(n/sup +/)-GaN(p) tunneling junction, which uses a low-resistivity n/sup +/-In/sub 0.23/Ga/sub 0.77/N/GaN SPS instead of a high-resistivity p-type GaN as a top contact layer, allows the reverse-biased tunnel junction to form a "quasi-ohmic" contact. Experimental results indicate that LDs with n/sup +/-In/sub 0.23/Ga/sub 0.77/N/GaN SPS contacting layers can achieve a lower threshold current and longer lasing duration under pulsed operation. Moreover, when the input pulse width is lengthened from 300 ns to 2 /spl mu/s, the lasing duration of the LD with Pt ohmic contact is three times longer than that of the LD with Ni/Au ohmic contacts. Therefore, we conclude that nitride-based LDs with an SPS reversed-tunneling contact layer may significantly reduce the contact resistance of an anode electrode and thereby increase the thermal stability of the device reliability.     

Nitrogen removal in a fluidized bed bioreactor by using mixed culture under oxygen-limited conditions.

Nitrogen removal involving nitrification and denitrification was investigated in a fluidized bed bioreactor by using mixed culture sludge under oxygen-limited conditions. Methane was used as a sole carbon source for denitrification. In this study, optimal nitrification and denitrification rates were examined by varying methane and oxygen gas dissolution flow rates, 90 ml/min, 400 ml/min and 650 ml/min, in each. Simultaneously nitrification and denitrification was achieved. The total nitrogen removal rate was 15-mg N/g VSS. d, 21-mg N/g VSS. d and 26.4-mg N/g VSS. d at gas dissolution flow rate 90 ml/min, 400 ml/min and 650 ml/min, respectively. No significant accumulation of nitrite was found in this experiment. Nitrogen removal rates depend on gas dissolution flow rates. DO concentration was at 0.5-2 mg/L.     

Effect of defects on the burst failure of butt fusion welded polyethylene pipes

With the increasing demand of Medium density polyethylene (MDPE) pipes for gas transmission, the safety concern related with welding defects is becoming a serious matter. In this paper, experimental burst tests and finite element analyses were employed to study butt fusion welded MDPE pipe joints with spherical and planar defects of various sizes. These defects were used to simulate lack of bonding during the welding. Test results showed that in all pipe test cases, the failure location originated from pipe substrates, even though the defect size was increased to 45% of the pipe’s wall thickness. The burst pressure could be estimated by the expression employed in the ASME BPVC, and in the burst pressure, the hoop stress was 20.28 MPa. Simulation results showed that the failure position was not only affected by the defect size, but also by the welding bead. It can be argued that a single welding defect whose maximum size is smaller than 15% of the thickness can be used without failure during short-term usage, even when there is no welding bead in the welded joint.     

A system of automatic control of motion speed of a city transport system electric train

An adaptive system of automatic control of the electric train motion speed permitting one to take into account the specific requirements imposed by the control object is proposed. Such requirements include limitation of the level of the index of the movement smoothness during the transient movement modes characterizing the degree of comfort for the passengers, as well as the possibility of implementing accelerations (delays) differing from nominal ones. The methods of automatic control and simulation modeling theory are used while solving the problem. The required control quality is provided by the fact that the input drive signal for the speed control circuit is smoothed by means of an operator, which is based on integration with saturation. The speed control circuit parameters are determined as a result of solving the task of the parametrical synthesis. The result of the work is an operation algorithm of the automatic control system (ACS) of the electric train speed, application of which provides limitation of the level of the movement smoothness index within the transient movement modes. As a result of solving the task of the parametrical synthesis the analytical dependences are also obtained connecting the ACS control law parameters with the train weight, use of which provides independence of the control quality on the train weight.     

Thermo‐ and pH‐ responsive copolymers: Poly(n‐Isopropylacrylamide‐co‐IAM) copolymers

Poly(N‐isopropylacrylamide) (NIPAAm) is well known as a smart material with good thermal sensitivity and favorable biocompatibility. A series of new smart hydrogels, NIPAAm copolymerized with IAM (itaconamic acid; 4‐amino‐2‐methylene‐4‐oxobutanoic acid), were synthesized through radical solution polymerization in this work. Poly(NIPAAm‐co‐IAM) can respond to the changes of temperature as well as pH value. Such a characteristic is due to the fact that IAM contains not only a hydrophilic acrylic acid moiety but also an acrylamide moiety to be thermal and pH sensitive. The experimental results show that the lower critical solution temperature (LCST) of the copolymer increases as the molar fraction of IAM increases. Moreover, based on the current experimental data, 3 wt % of Poly(NIPAAm‐co‐IAM) aqueous solution in this study exhibits a phase transition temperature (37.8°C) close to the human body temperature in the buffer solution of pH 7 possibly to be useful in drug delivery. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42367.     

Enhancing strength and hardness of AZ31B through simultaneous addition of nickel and nano-Al2O3 particulates

In the present study, AZ31B-Al₂O₃-Ni composites are developed by the addition of different amounts of Ni particulates into AZ31B-1.5Al₂O₃ using disintegrated melt deposition technique followed by hot extrusion. The AZ31B-1.5Al₂O₃ nano-composite is known to exhibit excellent ductility (∼30%) matching with that of pure aluminum but its strength levels are compromised. The composites developed in the current study show a homogeneous microstructure and significant improvement in mechanical characteristics. The results of mechanical properties characterization reveal that addition of Ni led to a simultaneous improvement in 0.2% YS (up to 25%), UTS (up to 13%) and hardness (up to 62%). The ductility, however, stayed almost similar to the ductility of monolithic AZ31B in the case of AZ31B-1.5Al₂O₃-1.5Ni composite while it was compromised for AZ31B-1.5Al₂O₃-3.19Ni. The results clearly reveal the superior capability of AZ31B-Al₂O₃-Ni formulations in terms of overall mechanical response when compared to monolithic AZ31B.     

GaN-Based LEDs With AZO:Y Upper Contact

We report the fabrication of GaN-based light-emitting diodes (LEDs) with ytterbium-doped alumina-zinc-oxide (AZO:Y) upper contact. It was found that AZO and AZO:Y are both highly transparent in the visible region with good thermal stability optically. However, it was found that AZO:Y is much more thermally stable electrically, as compared with AZO. Furthermore, it was found that the output power of GaN LEDs with AZO upper contact decreased significantly from 2.80 to 2.30 mW after 700°C annealing. With the same annealing condition, it was found that output power decreased only slightly from 2.77 to 2.69 mW for the LEDs with AZO:Y upper contact.     

基于改进YOLOv4-Tiny的矿井电机车多目标实时检测

为解决煤矿巷道环境恶劣以及人工疲劳驾驶电机车导致煤矿井下有轨电机车事故频发的问题,提出一种基于改进YOLOv4-Tiny算法的YOLOv4-Tiny-4S矿井电机车多目标实时检测方法。首先,为了提高网络模型对于小目标的检测能力,将传统YOLOv4-Tiny的两尺度预测增加至四尺度预测,并且在网络模型的颈部引入空间金字塔池化（SPP）模块,以丰富特征融合信息,增大网络模型的感受野;其次,以煤矿巷道中的行人、电机车、信号灯以及碎石作为检测目标,创建矿井电机车多目标检测数据集,并分别采用K-means和K-means++聚类分析算法对数据集重新聚类,通过对比分析验证了K-means++算法具有更好的聚类效果;最后,通过对传统YOLOv4-Tiny算法的消融实验,进一步直观了不同改进措施对网络模型检测性能的影响,并在电机车运行的煤矿巷道场景中,对比分析了YOLOv4-Tiny-4S算法与其他几种算法的检测性能。实验结果表明：YOLOv4-Tiny-4S算法能够准确检测并识别出图像中的各类目标,其平均检测精度（mAP）为95.35%,对小目标“碎石”的平均检测精度（AP）为86.69%,相比传统YOLOv4-Tiny算法分别提高了12.38和41.66个百分点;改进后算法的平均检测速度达58.7帧/秒（FPS）,模型内存仅为26.3Mb,YOLOv4-Tiny-4S算法的检测性能优于其他算法。本文提出的基于YOLOv4-Tiny-4S矿井电机车多目标实时检测方法可为实现矿井电机车的无人驾驶提供技术支撑。     

钢筋砼受弯构件斜截面抗剪承载力计算方法

分析了深梁,浅梁和短梁斜截面应力分布规律和抗剪机理,得出影响砼受弯构件斜截面抗剪承载力的主要因素是剪跨ａ／ｈ０的大小,而跨高比ｌ／ｈ的大小对斜截面抗剪承载力的影响甚微,在抗剪计算中可忽略不计的新结论,在此基础上提出了以剪跨比为主要参数的 受弯构件截面抗剪承载力计算公式。