Synthesis of V-doped SiC powder for growth of semi-insulating SiC crystals

V-doped semi-insulating (VDSI) SiC crystal is a promising substrate for high-frequency electronic devices achieved using GaN epitaxial films. However, V doping in a SiC crystal is difficult to control owing to the different sublimation temperatures of VC and SiC. The amount of V changes depending on the growth sequence, which has been a significant concern in VDSI SiC substrates in terms of wafer reliability.In this study, therefore, we aimed to synthesize a single source by vaporizing Si, C, and V under the same conditions to improve the doping issue in VDSI SiC. We synthesized V-doped SiC powder as the starting material for VDSI SiC substrate based on thermodynamic modeling, and the synthesized powder was used to grow a VDSI SiC crystal via physical vapor transport.Finally, considering the homogeneous V concentration in the grown crystal, the synthesized V-doped SiC was observed to be effective to grow VDSI SiC independent of the growth sequence.     

Micro scale fracture strength of grains and grain boundaries in polycrystalline La-doped β-Si3N4 ceramics

Micro scale fracture strength of grains and grain boundaries in polycrystalline La-doped β-Si₃N₄ ceramics were investigated and compared with theoretically predicted values. The fracture behaviour of SiO₂-La₂O₃ intergranular glassy phase (IGP) between β-Si₃N₄ grains was modelled by ab initio simulations. Microcantilevers were FIB-milled both from polycrystalline regions and single grains of β-Si₃N₄ and were tested in bending using a nanoindenter. The fracture strength of β-Si₃N₄ grains which fractured at fixing was 10.6 ± 0.8 GPa while the strength of the beams that failed at defects was 5.9 ± 2.3 GPa. Polycrystalline β-Si₃N₄ samples showed intergranular fracture with decreasing strength values in the range of 2.9 ± 0.4 – 2.1 ± 0.5 GPa. The comparison of single grain results with theoretical values in the literature revealed a correlation between theoretical and experimental results, which was used to convert our ab initio simulations from subnano to micro size samples. The converted strength for IGP showed quantitative agreement with micro-bending experiments.     

A longitudinal study of the association between Compulsive Internet use and wellbeing

ObjectiveCompulsive Internet Use (CIU) has been linked to lower wellbeing, especially among adolescents. Yet, questions regarding the directionality of this association remain unanswered: CIU may influence wellbeing and vice versa. Theoretically, both directions are plausible, yet so far no studies have examined the directionality of these effects among adults. This article aims to shed light on the directionality of the relation between CIU and both positive and negative wellbeing, using a prospective, longitudinal sample of adults (n = 398).MethodsOver the course of four years, participants completed five assessments of their CIU and both positive and negative indicators of wellbeing. Participants were married couples who were recruited in the municipalities where they were married.ResultsCIU predicted increases in depression, loneliness and stress over time, and a decrease in happiness. No effect of CIU on the change in self-esteem was found. Further, happiness predicted a decrease in CIU over time.ConclusionsThe results suggest CIU lowers wellbeing. This is important given that lowered wellbeing may affect health. Happiness is suggested to be a buffer for developing CIU.     

冲击钻机钻孔遇孤石的处理方法

结合广珠城际轨道交通工程ZH-3标段前山车站特大桥钻孔灌注桩施工中遇孤石的处理方法,对冲击钻机钻孔处理孤石的方法进行总结分析,供同类施工参考.     

Finite element analysis of concrete filled tube column to flat plate slab joint

For high-rise buildings, the storey height is an important factor influencing the economic efficiency of buildings. The structural system consisting of concrete filled tube columns and flat plate slabs is relatively new. However, the structural behavior of the connection between the concrete filled tube column and the flat plate slab has not yet been fully explored. The finite element analysis is therefore used to examine the stress concentration, load flow, and excessive deformation acting on the connection. Three types of connection details were compared. The analytical parameters are width, thickness of steel tube, length, thickness of wing plate, strength of steel, and eccentricity of rebar. 84 models were analyzed to find the appropriate design equation of the final connection detail. The corresponding proposed design equation showed a good agreement with the finite element analysis results.     

朝天门大桥关键临时结构的施工与监控

重庆朝天门大桥为世界最大的公轨两用钢桁架拱桥,主桁拱采用平衡悬臂拼装法施工,施工阶段中最大悬臂长度276m。为解决大悬臂施工难题,朝天门大桥建设采用新颖的带铰斜拉扣挂系统和临时系杆。通过对斜拉扣挂系统、临时系杆的施工及监控,并对索力、应力、位移进行动态监测,结果表明:主桁拱、斜拉扣挂系统和临时系杆线型和应力均处于安全受控状态。朝天门大桥已于2009年4月底建成通车,对大跨度临时结构的施工与监控具有借鉴意义。     

高原寒冷地区客专铁路高墩大跨简支梁节段拼装施工线型控制技术

节段拼装梁施工线型控制一直是桥梁施工控制的重点,兰新铁路作为国家的重点铁路工程,对桥梁线型的要求更高,其中大通河特大桥地处青海省,常年昼夜温差达15℃,给节段拼装梁施工线型控制带来不小的考验,文中对该桥节段拼装梁施工中的线型控制技术研究进行总结,为类似工程施工提供参考。     

Effects of supplementary biomass firing on the performance of combined cycle power generation: A comparison between NGCC and IGCC plants

In the present work, effects of biomass supplementary firing on the performance of fossil fuel fired combined cycles have been analyzed. Both natural gas fired combined cycle (NGCC) and integrated coal gasification combined cycle (IGCC) have been considered in the study. The efficiency of the NGCC plant monotonically reduces with the increase in supplementary firing, while for the IGCC plant the maximum plant efficiency occurs at an optimum degree of supplementary firing. This difference in the nature of variation of the efficiency of two plants under the influence of supplementary firing has been critically analyzed in the paper. The ratings of different plant equipments, fuel flow rates and the emission indices of CO₂ from the plants at varying degree of supplementary firing have been evaluated for a net power output of 200 MW. The fraction of total power generated by the bottoming cycle increases with the increase in supplementary firing. However, the decrease in the ratings of gas turbines is much more than the increase in that of the steam turbines due to the low work ratio of the topping cycle. The NGCC plants require less biomass compared to the IGCC under identical condition. A critical degree of supplementary firing has been identified for the slag free operation of the biomass combustor. The performance parameters, equipment ratings and fuel flow rates for no supplementary firing and for the critical degree of supplementary biomass firing have been compared for the NGCC and IGCC plants.     

岩溶区特大断面小净距隧道群综合探测成果分析

为保证某岩溶区特大断面小净距隧道群安全施工,采用高密度电阻率法勘探、钻探及声波测试对该隧道群围岩进行了综合探测。高密度电阻率法勘探成果显示测线内覆盖层厚度在0~1.3 m之间,强风化层厚度在4.0~21.0 m之间,基岩表面溶沟溶槽发育,并推测了存在溶洞的位置。声波测试结果显示隧道围岩为可溶岩,岩溶微发育;隧道围岩完整性系数在0.49~0.64之间。现场已施工的37个钻孔中,有2个遇溶洞/裂隙,钻孔遇洞率5%。高密度电阻率法勘探与钻孔及声波测试所得的地下地质体信息吻合。综合物探成果很好地解释了隧道群围岩的地质情况,可以作为岩溶区特大断面小净距隧道群隧道设计、施工的初步依据。     

Studies on phytohormones,vitamins and mineral element requirements of Lentinus subnudus (Berk) and schizophyllum commune (Fr. Ex. Fr) from Nigeria

The effects of phytohormones, vitamins and mineral elements on growth of Lentinus subnudus (Berk) and Schizophyllum commune (Fr. ex Fr), two Nigerian edible mushrooms, were studied. Among the phytohormones tested, 1.0 ppm of 2,4 D stimulated the best growth in L. subnudus, followed by 0.1 ppm of GA3. As for S. commune, 10.0 ppm of 2, 4 D enhanced the best growth while 1.0 ppm of GA3 was the second best. The least stimulatory hormone for the two mushrooms was GA3 at 20.0 ppm concentration. Among the vitamins, biotin was the most utilizable for L. subnudus, followed in order by thiamine and folic acid. Pyridoxine promoted best growth for S. commune while the poorest growth was supported by pantothenic acid. In both higher fungi, macroelements (Mg, K and Ca) promoted good mycelial growth but Na was least utilised. Similarly, trace elements (Zn, Fe and Mn) also supported growth to a significant level (P=0.01). The implication of the obtained results are discussed in relation to the cultivation of L. subnudus and S. commune in Nigeria.