Ultrathin GaN film and AlGaN/GaN heterostructure grown on thick AlN buffer by MOCVD

High-quality AlGaN/GaN/AlN heterostructures with thin GaN channel and thick AlN buffer layer were grown by metal organic chemical vapor deposition (MOCVD) on SiC substrate. By analyzing growth modes of GaN films on AlN buffer layers with different thicknesses, it is revealed that film-forming point of GaN grown on AlN buffer increases with the increase in AlN buffer thickness. Accordingly, new growth model of GaN on AlN buffer was proposed, which shows that there is an optimal matching value between Ga source flow rate and AlN thickness when GaN is grown on AlN buffer of different thicknesses. Under optimal conditions, AlGaN/GaN/AlN heterostructures with 120 nm thin GaN channel layer and thick AlN buffer show excellent carrier-limited domain, high crystalline quality, and good transport properties. Results in this work would be useful for preparing high-quality heterostructures on AlN buffer and high electron mobility transistor (HEMT) devices. Moreover, these findings can also be applied to the growth of other hyperfine structures (quantum wells, superlattices, and digital alloys) in the future.     

The evolution characteristic of sulfur-containing gases during coal thermal conversion

In this study, the evolution characteristics of sulfur-containing gases during thermal conversion of two coals under different atmospheres were studied through temperature-program decomposition (TPD) and rapid-heating decomposition (RHD) coupled with online mass spectrum (MS). The releasing profiles of H₂, CH₄ and CO were also measured. Results showed that the effect of atmosphere and heating rate on evolution of sulfur-containing gases was very significant. It was found that Ar atmosphere was more favorable to the formation of sulfur-containing gases than CO₂ atmosphere by using TPD-MS. In CO₂, the formation of H₂S and SO₂ was restrained in 260–650 °C, but was promoted in 880–980 °C; the formation of COS was promoted during the whole process. In Ar, high releasing intensity of H₂ and CH₄ could stabilize sulfur-containing radicals which led to high amount of H₂S and SO₂; while high releasing intensity of CO in CO₂ resulted in high amount of COS. By using RHD-MS, it was found that the steam atmosphere was highly favorable for the transformation of H₂S, SO₂ and COS during the entire reaction period. However, the CO₂ atmosphere was disadvantageous to the transformation of H₂S, SO₂ and COS at the initial stage, but slight favorable for the transformation of H₂S, SO₂ and COS during the later stage. These was resulted from the gasification reaction of steam/CO₂ with coal. The key factor was the releasing amount of H₂ and CO, which promoted the formation and transformation of H₂S, SO₂ and COS.     

Influence of strain-induced martensite in the anodic dissolution of austenitic stainless steels in acid medium

The anodic dissolution of austenitic stainless steel bars in an acid medium (0.5 M HCl + 2 M H₂SO₄) under different polarizations is studied. The material comes from bars formed by hot working (HW) and by cold working (CW). UNS S30403 and S31603 grades are considered. The determining effect of alloying elements and working method are proved. The morphology of the attack at different anodic potentials is analyzed. The important influence of the amount and distribution of strain-induced martensite on corrosion is demonstrated. The effect of the martensite on the anodic polarization curves is quantified using specifically designed software.     

A weighted mean filter with spatial-bias elimination for impulse noise removal

In this paper, we propose Unbiased Weighted Mean Filter (UWMF) for removing high-density impulse noise. Asymmetric distribution of corrupted pixels in the filtering window creates a spatial-bias towards the center of uncorrupted pixels. UWMF eliminates this bias by recalibrating the contribution factor (weight) of each uncorrupted pixel in such a way that the center shifts back to the center of the filtering window. The restoration process involves three sequential operations while convolving a filtering window over a contaminated image. Noise is detected, weights are recalibrated and the new intensity value is replaced by weighted mean using the recalibrated weights. Compared to the state-of-the-art impulse noise removal methods, UWMF provides superior performance, without requiring a fine-tuning for its parameters, in terms of both objective measurements and subjective assessments.     

Integrated distribution network expansion planning incorporating distributed generation considering uncertainties,reliability, and operational conditions

In this paper, an integrated methodology is proposed for distribution network expansion planning which considers most of the planning alternatives. The planning aims to determine the optimal reinforcement of existing medium voltage lines and high voltage/medium voltage substations, or installation of new ones to meet the load growth in the planning horizon subject to the technical and operational constraints. Also, to take the advantages of new technologies, the renewable and non-renewable distributed generations have been included in the problem as another alternative. The uncertainties related to renewable DGs, load demand, and energy price have been considered in the calculation of cost components. The load duration curve has been utilized for loads such that the results be more precise. The possibility of islanding and load transferring through the reserve feeders have been regarded in the problem to improve the reliability of the network. Also, the required condition for successful and safe operation of island considering all of uncertainty states have been checked out to accurately calculate the reliability. The genetic algorithm is employed to solve this integrated problem. Finally, the proposed method is applied to the 54-bus system and also a real large-scale distribution network, and the results are discussed. The results verify the effectiveness of the presented method.     

Redox-Active Polymer Integrated with MXene for Ultra-Stable and Fast Aqueous Proton Storage

Proton is a charge carrier with the smallest ionic size and quickest kinetics, making aqueous proton batteries (APBs), a promising technology for safe and profitable energy storage systems. Despite being potential electrode materials, organic compounds have not yet been fully investigated in terms of proton storage properties and APB applications due to their low capacity and unstable cycle life in aqueous electrolytes. Herein, a novel redox-active polymer (PDPZ) with diquinoxalino-phenazine as the structural unit has been designed, which is further integrated with MXene nanosheets to construct a flexible PDPZ@MXene electrode material with a rapid and ultra-stable proton storage behavior. In-operando monitoring techniques, i.e., in situ Raman and in situ FTIR, demonstrate the highly reversible redox reaction between CN and C N/N H bonds in electro-active PDPZ molecule with the strong proton absorption ability. Theoretical calculation further proves the electron transfer from MXene to PDPZ promotes the redox reaction of the PDPZ@MXene electrode. As a result, a flexible APB device is developed with a considerable energy density (64.3 mWh cm⁻³), a supercapacitor-level power density (6000 mW cm⁻³), and a record lifespan with ≈98.2% capacity retention over 10 000 cycles, revealing its potential applications in satisfying the various requirements of energy storage systems.     

温州吹填土的沉降特性研究

为了研究温州吹填土的沉降特性,针对温州丁山垦区的吹填土进行了沉降柱试验。首先研究了吹填淤泥的物理力学指标,然后进行了不同土水比、不同直径和材质的沉降柱实验,测定了沉降量和孔隙比。实验结果表明,温州吹填土沉降为大变形,曲线可分为三段:自重落淤阶段、自重固结阶段和平衡阶段;水土比影响总沉降和最终孔隙比的变化,并拟合出了曲线公式,呈对数关系;沉降柱试验槽的侧壁材质的不同对实验结果有显著影响,材质越光滑对沉积越有利。     

浅谈加快新建应用型本科院校的信息化教务管理

本文通过分析新建应用型本科院校教务管理工作的特点．提出做好新建应用型本科院校教务管理工作应解决的四个重要环节，并在此基础上提出了加快新建应用型本科院校信息化教务管理的必要性和措施。     

The effect of LaNiO3 buffer layer thickness on the electric properties of Pb(Zr0.53Ti0.47)O3 thin films deposited on titanium foils

Sol-gel derived Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on LaNiO₃ (LNO) buffered titanium foils. The effect of LNO buffer layer thickness on the electric properties of PZT thin films was investigated. The room temperature dielectric constant of PZT thin films increased with increasing LNO thickness. The remnant polarization of PZT thin films on 150 and 250 nm LNO was about 20 uC/cm². Curie temperatures of PZT thin films were 310, 330 and 340 °C for LNO of 250, 150 and 50 nm respectively. The current-voltage characteristics of PZT thin films were examined for different LNO buffer layer thicknesses, and the space charge limited conduction model was followed in PZT thin films on 50 nm LNO.