Simulation of the newtonian flow through an abruptly contracted tube using a mixed finite element method

The solutions of the Navier-Stokes equation for a Newtonian flow through a 4/1 contraction tube were obtained numerically using the Galerkin finite element method with the nine-node Lagrangian element which was believed to be one of the most accurate tools for mixed-type interpolating formulations. It was proved from this study that the vortex occurrence in the entrance corner region were confirmed but its size was gradually decreased with the increase of Reynolds numbers, and that the velocity profiles and pressure distributions along the applied mesh layers were in agreement with the experimental and the previously reported numerical results.     

Experiments on formation of the adiabatic shear band in sheet metal

Formation of the adiabatic shear band in sheet metal is investigated with experiments for high strength steel sheets, 60 C and 60 TRIP. Since the adiabatic shear band is formed as a result of adiabatic shear failure with a narrow band of concentrated shear strain, the adiabatic shear band plays an important role in the analysis of high speed deformation phenomena. For shear band experiments with a tension split Hopkinson bar, specimens are designed to induced large shear strain. The experimental results show that the shear deformation modes of two sheet metals, 60 TRIP and 60 C, are quite different from each other in that the adiabatic shear band is observed only in 60 C. The shear deformation in 60 TRIP is restrained by the abrupt increase of strength due to the plastic strain, which interferes with propagation of the shear crack. Instead, a tensile crack developed at the corner where the shear crack should have been initiated. As a result, the load-displacement curves show that the tensile load of 60 TRIP specimens becomes higher than that of 60 C at the same displacement.     

Nanoscale Investigation of Grain Growth in RF-Sputtered Indium Tin Oxide Thin Films by Scanning Probe Microscopy

This work studied the electronic characteristics of the grains and grain boundaries of indium tin oxide (ITO) thin films using electrostatic and Kelvin probe force microscopy. Two types of ITO films were compared, deposited using radiofrequency magnetron sputtering in pure argon or 99% argon + 1% oxygen, respectively. The average grain size and surface roughness increased with substrate temperature for the films deposited in pure argon. With the addition of 1% oxygen, the increase in the grain size was inhibited above 150°C, which was suggested to be due to passivation of the grains by the excess oxygen. Electrostatic force microscopy and Kelvin probe force microscopy (KPFM) images confirmed that the grain growth was defect mediated and occurred at defective interfaces at high temperatures. Films deposited at room temperature with 1% oxygen showed crystalline nature, while films deposited with pure argon at room temperature were amorphous as observed from KPFM images. The potential drop across the grain and grain boundary was determined by taking surface potential line profiles to evaluate the electronic properties.     

Synthesis of polyaniline-gold/graphene oxide composite and microwave absorption characteristics of the composite films

This paper describes the synthesis of polyaniline-gold nanocomposite by an in situ polymerization of aniline hydrochloride with graphene oxide using hydrogen tetrachloroaurate as an oxidant. The synthesized nanocomposites were characterized by FT-IR and UV–vis spectroscopy, and their surface morphology was studied by scanning and transmission electron microscopy. Microwave absorption property of the composite films was studied at 2–12 GHz, and the effects of sample thickness on the microwave absorption were investigated. The electromagnetic interference shielding effectiveness of PANI-GNP has been enhanced due to the inclusion of GO.     

Morphology-dependent antibacterial activities of Cu2O

Cubic and octahedral Cu₂O microcrystals were synthesized by the reduction of a copper-ligand complex solution with glucose under microwave irradiation using ethylenediaminetetraacetic acid (EDTA) and N,N,N′,N′-tetramethyl ethylenediamine (TMEDA) as ligands. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirmed that the surfaces of the cubic and octahedral of Cu₂O microcrystals had {100} and {111} lattice planes. The antibacterial activity of the Cu₂O microcrystals against E. coli was examined using optical density (OD) methods. The antibacterial activity of the cubic Cu₂O crystals was superior to that of the octahedral Cu₂O crystals. The mechanism of the specific morphology-controlled synthesis of Cu₂O and their morphology-dependent antibacterial activity are discussed.     

Synthesis and characterization of soluble polypyrrole–poly(ɛ-caprolactone) polymer blends with improved electrical conductivities

Polypyrrole–poly(?-caprolactone) (PPy–PCL) blends were prepared through an in situ deposition technique wherein different amounts of poly(?-caprolactone) were added during the polymerization of pyrrole. Ammonium persulfate was used as an oxidant in the polymerization of polypyrrole (PPy). Compared with pure PPy, the blends showed higher solubility in many organic solvents. The composition and structural characteristics of PPy–PCL were determined by Fourier transform infrared, ultraviolet–visible, and X-ray photoelectron spectroscopic methods. Scanning electron and transmission electron microscopic methods were performed to observe the morphology of the PPy–PCL blends. The temperature-dependent conductivity of the PPy–PCL blends was measured at 300–500 K. The conductivity increased with increasing PCL concentration in the blends, which can be explained by the increased mobility of charge carriers at high PCL concentrations. Based on the temperature dependence of the electrical conductivity, hopping may be the conduction mechanism involved in the PPy–PCL blending process.     

Highly sensitive hydrogen detection of catalyst-free ZnO nanorod networks suspended by lithography-assisted growth

We have successfully demonstrated a ZnO nanorod-based 3D nanostructure to show a high sensitivity and very fast response/recovery to hydrogen gas. ZnO nanorods have been synthesized selectively over the pre-defined area at relatively low temperature using a simple self-catalytic solution process assisted by a lithographic method. The conductance of the ZnO nanorod device varies significantly as the concentration of the hydrogen is changed without any additive metal catalyst, revealing a high sensitivity to hydrogen gas. Its superior performance can be explained by the porous structure of its three-dimensional network and the enhanced surface reaction of the hydrogen molecules with the oxygen defects resulting from a high surface-to-volume ratio. It was found that the change of conductance follows a power law depending on the hydrogen concentration. A Langmuir isotherm following an ideal power law and a cross-over behavior of the activation energy with respect to hydrogen concentration were observed. This is a very novel and intriguing phenomenon on nanostructured materials, which suggests competitive surface reactions in ZnO nanorod gas sensors.     

Quantitative analysis of vehicle particle emission by using calibrated CPC system

Particle size distribution and particle number concentration from diesel engines are subjects of significant environmental concerns especially in the EU. A few years ago, the UN-ECE PMP proposed a method for measuring particle emissions in the diluted exhaust of internal combustion engine vehicles, which has become a key method used in new dilution systems and sampling condition. This paper describes the effects of parameters such as condensation particle counter (CPC) according to test procedures, test fuel and vehicle test mode, including NEDC and CVS-75 mode. The main results obtained from this study can be summarized as follows: (1) Periodic calibration of the CPC system is essential because the long-term usage of a CPC leads to an underestimation in the measurements of small particles. (2) Particle emissions measured by the UN-ECE PMP method were found to exhibit comparable repeatability as compared to other regulated emissions. (3) In particle number concentration emitted from different-fueled vehicles, the sources of particle emissions in an ascending order of magnitude are as follows: DPF equipped diesel passenger vehicles, gasoline and LPG fueled vehicles, and DPF unequipped diesel passenger vehicles. Also, we found that the particle numbers of DPF equipped diesel passenger vehicles, gasoline and LPG-fueled vehicles can meet the EU regulation limit (<6.0×10¹¹#/km), while DPF unequipped diesel passenger vehicles do not meet the EU limit.     

Optimization of a roller levelling process for Al7001T9 pipes with finite element analysis and Taguchi method

This paper is concerned with the optimization of process parameters for a roller leveller that is an indispensable piece of equipment to eliminate the undesirable curvature of a thin-walled aluminum pipe. Optimization of process parameters has been carried out for a multi-staggered-type 14-roller leveller. A finite element model of a multi-staggered 14-roller leveller was constructed for numerical analysis. The analysis is carried out with the fractional model and the Taguchi method for evaluation of the effect of process parameters such as the intermesh and the slanted angle of rollers. The response variable is set to the plastic strain along the pipe length. The optimum combination of process parameters is determined from the numerical result and confirmed by experiments. The comparison of the numerical result with the experimental one shows good coincidence for its validity and reliability.