Light emission of heavily doped AlGaN structures under optical pumping

Spectral,temporal and polarization characteristics of spontaneous and stimulated luminescence of Al0.5Ga0.5N/AlN structures grown by molecular beam epitaxy were studied at the optical pulsed pumping with λ =266 nm.Samples with a high degree of silicon doping were investigated.The vast majority of radiation falls on transitions within the band gap between the levels of defects.As a result,the radiation band embracing the whole visible range of more than 300 THz is observed in both spontaneous radiation and induced luminescence.In spontaneous radiation the band has a smooth spectral intensity distribution over the wavelengths,whereas induced radiation has its sharp peaks corresponding to the mode structure of the planar waveguide.The measured gain of the active medium is g ≈ 70 cm-1 for a weak signal.     

Redshifting and broadening of quantum-well infrared photodetector'sresponse via impurity-free vacancy disordering

The partial intermixing of the well and barrier materials offers unique opportunities to shift locally the bandgap of quantum-well (QW) structures. We have demonstrated redshifting and broadening of the wavelength responses of bound-to-continuum GaAs and InP based quantum-well infrared photodetectors (QWIP's) after growth via impurity-free vacancy disordering (IFVD). A comprehensive set of experiments is conducted on QWIP's fabricated from both as-grown and multiple-quantum-well (MQW) structures. Compared to the as-grown detector, the peak spectral responses of the disordered detectors were shifted to longer wavelengths. The peak absolute response of the disordered GaAs based QWIP is lower by almost a factor of four. However, the responsivity characteristics of the disordered InP based QWIP show no major degradation. In general, with the spectral broadening taken into account, the overall performance of the disordered QWIP's has not dropped significantly. Thus, the postgrowth control of the QW composition profiles by impurity-free vacancy disordering offers unique opportunities to fine tune various aspects of a photodetector's response. Theoretical calculations of the absorption coefficient spectrum are in excellent agreement with the experimental data     

Undoped High-Resistance GaN Buffer Layer for AlGaN/GaN High-Electron-Mobility Transistors

Technical Physics Letters - It is shown that intentionally undoped high-resistance GaN buffer layers in AlGaN/GaN heterostructures with high electron mobility for transistors can be formed by...     

How to Apply Advanced Statistical Analysis to Computational Economics: Methods and Insights

The theme of this special volume concerns advanced statistical analysis. By mining meaningful and important information, advanced statistical analysis can bring new insights to many areas, such as the development of hospitals, the environment, biology, markets, industries, and general economic systems. The contribution of this special volume is to adopt an advanced parametric and nonparametric statistical approach for the exploration of environmental and health care issues in the context of computational economics. The authors have proposed varied methods of advanced statistical analysis combined with practical applications. In terms of theory, the authors suggest designs for advanced theoretical methods. With regard to the application of professional calculation methods to everyday life, the authors have offered useful guidance for future research. The authors have also conducted empirical research by using data from Chinese regions and analyzing specific conditions. In addition, they have conducted empirical analyses of particular issues such as those related to the environment. Although this special volume has provided some methods of advanced scientific analysis for existing problems, other techniques must be applied to everyday life in order to solve the severe difficulties that human beings face.     

车用永磁同步电机三维温度场分析

为了研究车用永磁同步电机的温度场,以一台额定功率为25kW的车用永磁同步电机为研究对象,基于传热学基本理论,建立其三维求解域模型,通过仿真分析,得出了电机额定工况下的温度场及温升变化,并对连续变功率工况下的电机内关键部分的温升进行仿真分析,以研究车辆实际行驶时电机温度场的变化情况。通过搭建的实验平台,对电机工作在额定工况和连续变工况条件下的温升进行了测试。经对比分析,实验数据与仿真数据误差较小,验证了仿真的正确性。     

Chloride retention and release in a boreal forest soil: effects of soil water residence time and nitrogen and chloride loads

The common assumption that chloride (Cl-) is conservative in soils and can be used as a groundwater tracer is currently being questioned, and an increasing number of studies indicate that Cl- can be retained in soils. We performed lysimeter experiments with soil from a coniferous forest in southeast Sweden to determine whether pore water residence time and nitrogen and Cl- loads affected Cl- retention. Over the first 42 days there was a net retention of Cl- with retention rates averaging 3.1 mg CI- m(-2) d(-1) (68% of the added Cl- retained over 42 days). Thereafter, a net release of Cl- at similar rates was observed for the remaining experimental period (85 d). Longer soil water residence time and higher Cl- load gave higher initial retention and subsequent release rates than shorter residence time and lower Cl- load did. Nitrogen load did not affect Cl transformation rates. This study indicates that simultaneous retention and release of Cl- can occur in soils, and that rates may be considerable relative to the load. The retention of Cl- observed was probably due to chlorination of soil organic matter or ion exchange. The cause of the shift between net retention and net release is unclear, but we hypothesize that the presence of O2 or the presence of microbially available organic matter regulates Cl- retention and release rates.     

流化床-化学气相沉积技术的应用及研究进展

流化床-化学气相沉积(FB-CVD)技术是一种多学科交叉的材料制备技术,兼有流化床传热传质性能良好以及化学气相沉积均匀、产物单一等优点,在工业生产中有着广泛的应用,但因其属于交叉学科,散见于各种研究,没有进行专门的进展评述。本文拟对FB-CVD的工业应用进行专题综述,分析其发展和研究趋势。首先探讨了FB-CVD的基本原理,分别综述了其在颗粒包覆、一维纳米材料、多晶硅制备、颗粒表面改性及粉体制备等方面的应用,介绍了FB-CVD的过程模拟及反应器结构优化方面的研究进展。通过以上讨论,梳理了FB-CVD研究的科学内涵。可以看出,该过程具有明显的多尺度特征,即材料制备的微观层次、颗粒流化均匀性的介观层次以及反应器结构设计的宏观尺度。总结得出:FB-CVD技术的未来发展取决于3个尺度的耦合分析,其研究重点也应关注尺度间的相互影响效应,如材料制备的均相成核、非均相成核和颗粒流化及运动规律的相互耦合等。     

Oxygen Activity Calculations of Molten Steel: Comparison With Measured Results

This study sets out to find some model/s that could calculate the closest oxygen activity of molten steel to the measured oxygen activity in an ASEA‐SKF ladle furnace. Ten steel heats grade SAE 52100 were chosen, the oxygen activities of the molten steel after vacuum degassing process were measured, then by means of two different equations and one computer programs the theoretical oxygen activities were calculated and compared to the measured results. In order to calculate the activities of Al₂O₃ in the top slag four different models and two different constants were applied. Both Wagner and Turkdogan's equations were found to be useful. It was seen that increasing the wt% Al from 0 up to 0.05 in molten steel, increasing CaO/Al₂O₃ ratio in top slag, and reducing equilibrium temperature of slag‐steel could contribute to reduction of oxygen activity of molten steel. The scanning electron microscope observations revealed that the main types of observed non‐metallic inclusions in these samples were spinels and calcium aluminates and by increasing the CaO content of the inclusions their equivalent circle diameters grew.     

Fibre-rich additives--the effect on staling and their function in free-standing and pan-baked bread

BACKGROUND: The use of dietary fibre in bread products is increasing because of consumer demand for healthier products. However, an increase in dietary fibre level changes the rheological properties of the dough and also the quality properties of the final bread product. In this study, effects on dough and bread staling were followed after replacing 3% of wheat flour by fibre‐rich additives (fine durum, oat bran, rye bran and wheat bran). Free‐standing and pan‐baked loaves were baked to compare the influence of baking method and loaf shape. RESULTS: All additives increased dough stability, with oat bran giving the greatest stability and longest development time. Parameters measured during storage were distribution, migration and loss of water, cutability, crumbliness, firmness and springiness. Furthermore, amylopectin retrogradation and amylase‐lipid complex formation were assessed. Oat bran provided similar or better results than the control for all staling parameters, while other additives gave no general improvements. Cutability reached a plateau when crumb firmness was ≥ 4 N. CONCLUSION: Small amounts of fibre‐rich additives had a significant influence on staling. However, the baking method (free‐standing or pan‐baked bread) had a greater impact on staling than the additives, thus displaying the importance of the baking method. Cutability was found to be related to firmness. Copyright © 2011 Society of Chemical Industry