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81.
This study applies entrepreneurship theory and social capital perspective to IT freelancing to facilitate a better understanding of it. Our model hypothesizes that both IT self-efficacy and social capital obtained through social media interactions contribute to IT freelancers’ entrepreneurial behavior and then this entrepreneurial behavior influences their performance. We collected primary data from one of the leading online freelancing marketplaces, oDesk.com (currently Upwork.com). Our empirical findings confirm the core assertion of our research model. The implications of these findings for research and practice are discussed. Directions for future research are also provided. 相似文献
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为了探究结晶器电磁搅拌(M EMS)对大圆坯结晶器内综合冶金行为的影响。以大断面圆坯连铸结晶器冶金行为为研究对象,基于电磁热流体与凝固传输理论建立三维耦合数值模型。揭示大圆坯连铸常用五孔水口浇注条件下结晶器内电磁场、流场、传热与凝固等综合冶金行为,提出电磁搅拌对结晶器冶金性能影响的多参量评价方法。以中碳铬钼齿轮钢650 mm大圆坯连铸为例,指出结晶器电磁搅拌存在最佳搅拌电流,可获得相对较好的综合冶金效果。具体表现为弯月面保持一定的切向速度和过热度,有利于保护渣的熔化和夹杂物的上浮去除;液面波动幅度在控制范围内,可避免卷渣、改善表面质量;结晶器内钢液过热得到有效耗散,有利于等轴晶形核改善铸坯内部质量;侧孔出流钢液速度得到有效控制,可抑制注流对初凝坯壳的冲刷,提高了初生坯壳生长的均匀性。此外,电磁搅拌产生的水平旋流强度也可得到有效控制,有利于避免常见的皮下白亮带现象。 相似文献
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针对人体攻击性行为识别问题,提出一种基于人体关节点数据的攻击性行为识别方法。首先,利用OpenPose获得单帧图像中的人体关节点数据,并通过最近邻帧特征加权法和分段多项式回归完成由人体自遮挡和环境因素所导致缺失值的补全;然后,对每个人体定义动态"安全距离"阈值,如果两人真实距离小于阈值,则构建行为特征矢量,其中包括帧间人体重心位移、人体关节旋转角角速度和发生交互时的最小攻击距离等;最后,提出改进的LightGBM算法w-LightGBM,并对攻击性行为进行识别。采用公共数据集UT-interaction对所提出的攻击性行为分类识别方法进行测试实验,准确率达到95.45%。实验结果表明,所提方法能够有效识别各种角度的攻击性行为。 相似文献
88.
Pressure-assisted infiltration was used to synthesize SiC/Al 6061 composites containing high weight percentages of SiC. A combination of PEG and glass water was used to fabricate SiC preforms and the effect of the presence of glass water on the microstructure and mechanical properties of the preforms was evaluated by performing compression tests on the preforms. Also, the compressive strength and the hardness of the SiC/Al composites were investigated. The results revealed that the glass water improved the compressive strength of the preforms by about five times. The microstructural characterization of the composites showed that the penetration of the aluminum melt into the preforms was completed and almost no porosity could be seen in the microstructures of the composites. Moreover, the composite containing 75 wt% SiC exhibited the highest compressive strength as well as the maximum hardness. The results of the wear tests showed that increasing the SiC content reduces the wear rate so that the Al-75 wt% SiC composite has a lower wear rate and a lower coefficient of friction than those of Al-67 wt% SiC composite. This indicated higher wear resistance in these composites than the Al alloy due to the formation of a tribological layer on the surface of the composites. 相似文献
89.
Aqeel Ahmad Hamayoun Mahmood Nurlidia Mansor Tanveer Iqbal Muhammad Moniruzzaman 《应用聚合物科学杂志》2021,138(14):50159
Reinforcement of PEEK by nanoparticles such as multiwalled carbon nanotubes (MWCNTs), is a promising technique to prepare PEEK nanocomposites with improved properties for promising biomedical applications. However, proper dispersion of MWCNTs in the polymer matrices is a primary processing challenge. The present study reports a novel and environmentally beneficial approach for homogeneous dispersion of MWCNT in PEEK by using ionic liquid (IL) 1-ethyl-3-methylimidazolium hydrogen sulfate ([EMIM][HSO4]). Neat PEEK, PEEK-MWCNTs (using conventional organic solvent dimethylformamide), and PEEK-MWCNTs-IL (using [EMIM][HSO4]) nanocomposites were fabricated via melt-compounding and compression molding techniques. The fabricated composites were characterized for morphological, thermal, and mechanical properties and compared to those of neat PEEK and PEEK-MWCNTs. Ionic liquid provoked proficient dispersion of the MWCNTs in PEEK, as confirmed by FESEM and optical micrographs. The thermal stability of PEEK-MWCNTs-IL composite was significantly superior to that of the neat PEEK and PEEK-MWCNTs. Analysis of tensile strength and nanoindentation depicted that the modulus of elasticity of PEEK-MWNCTs-IL was significantly increased by 76% as compared to that of neat PEEK. We believe that the present work could provide a new and green platform for the manufacturing of PEEK nanocomposites with enhanced dispersion of nanofillers for biomedical applications. 相似文献
90.
A. M. Patki 《Polymer-Plastics Technology and Engineering》2021,60(1):70-83
ABSTRACT Poly(ether-ketone)/hexagonal boron nitride (h-BN) composites reinforced with micrometer-sized h-BN particles were investigated. The composites exhibited glass transition temperature (Tg) and thermal stability over 160°C and 560°C, respectively. The melting point and peak crystallization temperatures of the composites decreased up to 17°C and 12°C, respectively. The linear CTE of the composites decreased both below and above the Tg. The storage modulus increased with increasing h-BN content at all temperatures (50–250°C). The composites possessed excellent dielectric properties with insignificant dispersion with increasing frequency. Thus, resultant composites are promising candidates for the printed circuit boards/electronic substrates. 相似文献