A 2-D numerical model was developed to predict the shape of weld pool in stationary GTA welding of commercial pure aluminium, without considering fluid flow in the weld pool. A Gaussian current density and heat input ...A 2-D numerical model was developed to predict the shape of weld pool in stationary GTA welding of commercial pure aluminium, without considering fluid flow in the weld pool. A Gaussian current density and heat input distribution on the surface of the workpiece were considered. The parameters of Gaussian distribution were modified by comparing calculated results with experimental ones. It was found that these distribution parameters are fimctions of applied current and arc length. Effects of arc length, applied current and welding time on the geometry of the weld pool were investigated. To check the validity of the model, a series of experiments were also conducted. In general, the agreement between calculated overall shape of the weld pool and the experimental one was acceptable, especially in low applied currents. Therefore, it can be concluded that in pure aluminium, the heat conduction is dominant mechanism of heat transfer in the weld pool.展开更多
An experimental study on the heating of a mixture of aluminum and lithium hydroxide （LiOH） powders in a reductive bed under air atmosphere is reported. The formation of aluminum nitride （A1N） during this process w...An experimental study on the heating of a mixture of aluminum and lithium hydroxide （LiOH） powders in a reductive bed under air atmosphere is reported. The formation of aluminum nitride （A1N） during this process was the focus of this study. The formation of A1N was achieved using LiOH as an additive and heating the sample in a resistance furnace in a specially designed double crucible within a bed of a mixture of coke and filamentous calcium. The temperature range of the reaction was between 700℃ and 1100℃. The optimum temperature of 1100℃ and the optimum LiOH amount （Swt%） required to achieve maximum yield were determined by powder X-ray diffraction （XRD） analysis. Scanning electron microscopy （SEM） micrographs clearly indicated the transformation of grain structures from rods （700℃） to cauliflower shapes （1100℃）.展开更多
We study the adsorption of a methanol molecule on single-walled carbon nanotubes （SWCNTs） with various diameters and chiral angles by using the density functional theory based calculations. We find that methanol pre...We study the adsorption of a methanol molecule on single-walled carbon nanotubes （SWCNTs） with various diameters and chiral angles by using the density functional theory based calculations. We find that methanol prefers to be adsorbed physically on the exterior surface of chiral nanotubes in comparison to the armchair and zigzag tubes with binding energy of about -2.76 kcal/mol, which is consistent with recent experimental and theoretical investigation results. We further consider the adsorption of methanol on the exterior surface and edge site of functionalized SWCNTs. The obtained results indicate that the binding energy of methanol is significantly increased for adsorption on the sidewall of functionalized nanotubes. It is also found that the adsorption of methanol at the edge site of both functionalized and pristine SWCNT is remarkably different （chemisoption process） in comparison to the exterior sidewall of the tubes. Furthermore, the electronic structures and Mulliken charge population of the considered complexes at their ground state are discussed within the context.展开更多
We study the materials that are composed of metals and insulators.These plasmonic and non-plasmonic materials are ordered in geometric arrangements with dimensions that are fractions of the wavelength of light.A theor...We study the materials that are composed of metals and insulators.These plasmonic and non-plasmonic materials are ordered in geometric arrangements with dimensions that are fractions of the wavelength of light.A theoretical model is developed to simulate the refractive index of these nano-structured electromagnetic materials which support surface plasmon resonances.Factors contributing to the refractive index sensitivity are explored phenomenologically.Particles with size parameters smaller by much less than 1 have optical properties accurately predicted by the quasi-electrostatic theory while particles with larger size parameters necessitate electrodynamics.We simulate a type of refractive index material composed of metal and insulating dielectric nano-spheres,which are able to sustain the propagation of infrared or visible frequency electromagnetic waves known as surface plasmon polaritons.展开更多
文摘A 2-D numerical model was developed to predict the shape of weld pool in stationary GTA welding of commercial pure aluminium, without considering fluid flow in the weld pool. A Gaussian current density and heat input distribution on the surface of the workpiece were considered. The parameters of Gaussian distribution were modified by comparing calculated results with experimental ones. It was found that these distribution parameters are fimctions of applied current and arc length. Effects of arc length, applied current and welding time on the geometry of the weld pool were investigated. To check the validity of the model, a series of experiments were also conducted. In general, the agreement between calculated overall shape of the weld pool and the experimental one was acceptable, especially in low applied currents. Therefore, it can be concluded that in pure aluminium, the heat conduction is dominant mechanism of heat transfer in the weld pool.
文摘An experimental study on the heating of a mixture of aluminum and lithium hydroxide （LiOH） powders in a reductive bed under air atmosphere is reported. The formation of aluminum nitride （A1N） during this process was the focus of this study. The formation of A1N was achieved using LiOH as an additive and heating the sample in a resistance furnace in a specially designed double crucible within a bed of a mixture of coke and filamentous calcium. The temperature range of the reaction was between 700℃ and 1100℃. The optimum temperature of 1100℃ and the optimum LiOH amount （Swt%） required to achieve maximum yield were determined by powder X-ray diffraction （XRD） analysis. Scanning electron microscopy （SEM） micrographs clearly indicated the transformation of grain structures from rods （700℃） to cauliflower shapes （1100℃）.
文摘We study the adsorption of a methanol molecule on single-walled carbon nanotubes （SWCNTs） with various diameters and chiral angles by using the density functional theory based calculations. We find that methanol prefers to be adsorbed physically on the exterior surface of chiral nanotubes in comparison to the armchair and zigzag tubes with binding energy of about -2.76 kcal/mol, which is consistent with recent experimental and theoretical investigation results. We further consider the adsorption of methanol on the exterior surface and edge site of functionalized SWCNTs. The obtained results indicate that the binding energy of methanol is significantly increased for adsorption on the sidewall of functionalized nanotubes. It is also found that the adsorption of methanol at the edge site of both functionalized and pristine SWCNT is remarkably different （chemisoption process） in comparison to the exterior sidewall of the tubes. Furthermore, the electronic structures and Mulliken charge population of the considered complexes at their ground state are discussed within the context.
文摘We study the materials that are composed of metals and insulators.These plasmonic and non-plasmonic materials are ordered in geometric arrangements with dimensions that are fractions of the wavelength of light.A theoretical model is developed to simulate the refractive index of these nano-structured electromagnetic materials which support surface plasmon resonances.Factors contributing to the refractive index sensitivity are explored phenomenologically.Particles with size parameters smaller by much less than 1 have optical properties accurately predicted by the quasi-electrostatic theory while particles with larger size parameters necessitate electrodynamics.We simulate a type of refractive index material composed of metal and insulating dielectric nano-spheres,which are able to sustain the propagation of infrared or visible frequency electromagnetic waves known as surface plasmon polaritons.
