Processing optimization,surface properties and wear behavior of HVOF spraying WC–CrC–Ni coating

In this work, the optimal coating process (OCP) designed by Taguchi program for high velocity oxy-fuel (HVOF) thermal spraying WC–CrC–Ni powder on Inconel 718 substrate (IN 718) is obtained by optimizing hardness (38 FMR oxygen flow rate, 53 FMR hydrogen flow rate, 25 g/min powder feed rate and 7 in. spray distance). Oxygen flow rate affects hardness mostly. The surface properties such as microstructure, crystalline phase, hardness, and porosity of WC–CrC–Ni coating have been investigated. The phase of coating has been changed during the OCP spraying because a portion of carbides, such as WC, Cr₇C₃, Ni₃C decomposes to W₂C, Cr, Ni and free carbon. Hardness (1150 ± 50 Hv) and porosity (1.2 ± 0.2%) of the OCP coating have been improved by optimization. The friction and wear behaviors of the WC–CrC–Ni coating, electrolytic hard chrome (EHC) plating and IN 718 have been studied comparatively. The lubrication due to free carbon and metal oxide debris results in a decrease of friction coefficients of the WC–CrC–Ni, compared to EHC and IN 718 at both 25 and 450 °C. It is concluded that HVOF WC–CrC–Ni coating performs more excellent anti-wear than others at both temperatures.     

Rheological property and curing behavior of poly(amide-co-imide)/multi-walled carbon nanotube composites

Poly(amide-co-imide) (PAI)/multi-walled carbon nanotube (MWCNTs) composites were prepared by using solution mixing with ultrasonication excitation in order to investigate effects of MWCNTs on rheological properties and thermal curing behavior. Steady shear viscosity of the composite showed bell shaped curves with three characteristic patterns: shear thickening, shear thinning, and Newtonian plateau behavior. Both storage modulus and complex viscosity were increased due to higher molecular interaction than that of the pure PAI resin. Especially, hydrogen peroxide treated MWCNT/PAI composites had the highest storage modulus and complex viscosity. Glass transition temperature of the PAI/MWCNT composite was increased with increasing MWCNT content and thermal curing time since the mobility of PAI molecules was reduced as more constraints were generated in PAI molecular chains. It was found that thermal curing conditions of PAI/MWCNT composites are determined by considering effects of weight fraction and surface modification of MWCNTs on internal structure and thermal properties.     

Efficient design sensitivity analysis of incompressible fluids using SPH projection method

Using the direct differentiation method, a design sensitivity analysis method for time-dependent incompressible fluids is developed. The fluid behavior is described as the motion of particles involved by the SPH method. In the SPH projection method, instead of changing the fluid density, incompressibility is enforced by the pressure Poisson equation derived from pressure projection, which enable to use larger time steps. In spite of the additional pressure Poisson equation, the computational cost for the design sensitivity is not expensive since the factorized system matrix of pressure Poisson equation can be utilized. Aforementioned computational efficiency is very beneficial for the design sensitivity computation required for every time step in explicit time integration and updated Lagrangian schemes, for which an update scheme of design velocity field is developed using the velocity sensitivity. Through demonstrative numerical examples, the developed DSA method turns out to be efficient and shows excellent agreement with finite differencing.     

Dual coupled inductor fed isolated boost converter for low inputvoltage applications

A new isolated boost DC-to-DC converter suitable for low input voltage application is proposed. It features low switch current stresses, a wide input voltage range, and inherent inrush current protection, essential for the design of a low-to-high voltage conversion circuits. A comparative analysis and experimental results are presented to demonstrate the validity of the proposed converter     

Protection against lethal Japanese encephalitis virus infection of mice by immunization with the highly attenuated MVA strain of vaccinia virus expressing JEV prM and E genes

Genes encoding the glycosylated precursor of the membrane (prM) and envelope (E) proteins of a Korean strain of Japanese encephalitis virus (JEV) were inserted into the genome of the host-range restricted, highly attenuated, and safety-tested MVA strain of vaccinia virus. MVA recombinants containing the JEV genes, under strong synthetic or modified H5 vaccinia virus promoters, were isolated. Synthesis of JEV prM and E proteins was detected by immunofluorescence microscopy, flow cytometry, and polyacrylamide gel electrophoresis. Mice inoculated and boosted by various routes with either of the MVA recombinants produced JEV neutralizing antibodies, that had titres comparable with those induced by an inactivated JEV vaccine, as well as haemagglutination-inhibiting antibodies. Mice immunized with 2 x 10(6) infectious units of MVA/JEV recombinants by intramuscular or intraperitoneal routes were completely protected against a 10(5) LD50 JEV challenge at 9 weeks of age.     

Somatic mutations in the kinase domain of the Met/hepatocyte growth factor receptor gene in childhood hepatocellular carcinomas

The MET protooncogene encodes a transmembrane tyrosine kinase identified as the receptor of a polypeptide known as hepatocyte growth factor/scatter factor. We performed PCR-based single-strand conformational polymorphism and sequencing analysis of the tyrosine kinase domain of the MET gene (exon 15-19) in 75 primary liver cancers. Three missense mutations were detected exclusively in 10 childhood hepatocellular carcinomas (HCCs), while no mutations were detected in 16 adult HCCs, 21 cholangiocarcinomas, or 28 hepatoblastomas. The extremely short incubation period from hepatitis B virus infection to the genesis of childhood HCC as compared with the adult HCC suggests that there may be an additional mechanism that accelerates the carcinogenesis of childhood HCC. Our results indicate that mutations of the tyrosine kinase domain of the MET gene may be involved in the acceleration of the carcinogenesis in childhood HCC.     

Emission mechanism of localized deep levels in BeZnO layers grown by hybrid beam method

BeZnO layers, which are new materials for ultraviolet-light-emitting devices, were grown by hybrid beam method. The mobility and the carrier concentration on the Be _x Zn_1−x O layers of x = 0.28 were confirmed to be 2.83 cm²/V s and 4.16 × 10¹⁸ cm⁻³, respectively. Also, the optical properties attributed to the thermal quenching phenomenon of BeZnO were analyzed by photoluminescence as a function of temperature. With increasing temperature, the intensities and the spectral widths on the localized deep-level emissions of 3.6230 eV exponentially reduced and tended to broaden, respectively. Therefore, the temperature dependences of the full width at half maximum and the intensity were explained in terms of a configuration coordinate model. The broad emissions of 3.6230 eV without any fine structure were acted by a strong electron-phonon coupling due to the interaction between the radical beryllium and the ZnO host lattice. In addition, the Frank-Condon shift was found out to be 78.9 meV with the associated phonon energy of 15 meV. Thus, the activation energy of the nonradiative emission participating in the thermal quenching process was estimated to be 48.6 meV. Consequently, its value corresponds to the thermal dissociation energy requiring for the recombination of the conduction electron from the exciting state to the ground state.     

Effects of rolling condition on the tensile properties of Mg-MM-Sn-Al-Zn alloy

The microstructures and mechanical properties of Mg-2MM-2Sn-1Al-1Zn (ETAZ2211) sheets fabricated under different conditions have been investigated. Two hot-rolling routes following extrusion have been carried out at 300 °C or 400 °C. One method is to roll the extruded strips parallel to the extrusion direction (ED); the other is to roll the extruded strips perpendicular to the extrusion direction (TD). The strength and the elongation-to-fracture of specimens prepared by a combination of extrusion and rolling processes are increased dramatically when compared those of the simply rolled specimens. Especially, the TD alloy sheet rolled at 300 °C exhibits the best combination of strength and ductility, i.e. yield strength of 178.5 MPa, ultimate tensile strength of 239.1 MPa, uniform elongation of 24.4 % and elongation-to-fracture of 37.9 %. Observation of texture reveals that the intensity of (0002) texture is lower for the TD alloy sheets than that for the ED alloy sheets, indicating that the texture intensity is reduced by change of the rolling direction.     

Characterization of FePt film electrodeposited with a ferric electrolyte

The electrodeposition of FePt alloy film in a novel ferric electrolyte that could be an alternative electrolyte to the usual non-stable baths was investigated. The influence of the applied current density and electrolyte temperature on the composition of the alloy was studied. It was found that co-deposition of oxygen can be reduced by deposition at higher temperature of 65 °C than room temperature. The as-deposited film had a face-centered cubic (γ-Fe,Pt) structure, and after an additional annealing process, the structure was changed to a face-centered tetragonal structure. The as-deposited FePt film also shows good resistance to corrosion and its coercivity was about 0.1T, which makes it suitable for use in applications compatible with silicon technology.