New approach to SRM drive with six-switch converter

This paper presents novel topologies implementation for Switched Reluctance Motor (SRM) drive used in commercial applications. For effective utilization of the developed system, a novel direct current controlled PWM scheme is designed and implemented to produce the desired dynamic speed characteristic. In comparison to conventional asymmetric converter topology, it can minimize entire system costs by reducing numbers of power semiconductors. Therefore, it may open up investigation of a new way for SRM to compete with other ac motors such as induction motors, brushless dc motors, etc. The validity of the proposed method is verified through theoretical explanation and experimental results.     

Strengthening and Toughening Mechanisms of Ceramic Nanocomposites

Crack-tip bridging by particles is considered to be one of the primary strengthening mechanisms of ceramic nanocomposites. Small, brittle particulate inclusions have been shown to cause crack-tip bridging at short distances behind the crack tip. This mechanism leads to modest toughness but a very steep R -curve, and it is the latter that produces the very high fracture strength of the ceramic nanocomposite. Localized high residual stress around the particles (particularly in the case of silicon carbide-alumina material) causes the strengthening mechanism to operate effectively, even at a small volume fraction of 5%. The present study predicts the magnitude of the toughness increase and the extent of R -curve behavior for the nanocomposite.     

Synthesis and electrical properties of (Bi(1/2)Na(1/2))TiO3 (BNT) ferroelectric thin films by liquid sprayed mist chemical vapor deposition technique

This study aims to synthesize lead-free ferroelectric material, (Bi(1/2)Na(1/2))TiO3 using the Liquid Sprayed Mist Chemical Vapor Deposition (LSMCVD) technique. The mist of precursor solution was vaporized and deposited on two different substrates of Si(100) and (111)Pt/TiO2/SiO2/Si(100) in an oxygen atmosphere. The deposition temperature and time were varied in the range of 400-600 degrees C and 30-90 min. (Bi(1/2)Na(1/2))TiO3 thin film had preferred orientations of (110). The thickness of the thin film deposited was 35-162 nm. The remnant polarization (2Pr) and the dielectric constant were 4.6-16.8 microC/cm2, 325-350, respectively.     

Fabrication and magnetic characteristics of vertical feco nanowire arrayed in Al2O3 insulator of honeycomb bulkhead structure

High-density and uniform-sized FeCo alloy nanowires were prepared by electro deposition of Fe2+ and Co2+ into Anodic aluminum oxide (AAO) templates with two different diameters. These templates were fabricated with three-step anodization method. The additional anodization after the 2nd anodization step resulted in the decrease of the thickness of bottom barrier layer. It found an optimum condition to obtain a successful electrodeposition of Fe2+ and Co2+ into AAO templates. The nanowires with the diameters of 25 nm and 80 nm were homogeneously embedded in the AAO templates and their magnetic properties were strongly affected by diameters of nanowire.     

Characteristics of nano-sized (Pb, La)TiO3 powder synthesized at room temperature

We synthesized nano-sized (Pb, La)TiO3 powder using a high energy mechano-chemical technique at room temperature. By the results, nano-sized (Pb, La)TiO3 powder with perovskite structure was successfully synthesized from an oxide mixture using a high energy mechano-chemical technique without any post-annealing. The mechanically-synthesized (Pb, La)TiO3 powder consisted of nanometer sized particles and had very high homogeneity. According to increase of milling time, source phases such as Pb oxides and TiO2 disappeared and the perovskite PLT phase was formed by chemical reaction and the release of OH group.     

Role of Si on the Diffusional Interactions Between U-Mo and Al-Si Alloys at 823?K (550?��C)

U-Mo dispersions in Al-alloy matrix and monolithic fuels encased in Al-alloy are under development to fulfill the requirements for research and test reactors to use low-enriched molybdenum stabilized uranium alloy fuels. Significant interaction takes place between the U-Mo fuel and Al during manufacturing and in-reactor irradiation. The interaction products are Al-rich phases with physical and thermal characteristics that adversely affect fuel performance and result in premature failure. Detailed analysis of the interdiffusion and microstructural development of this system was carried through diffusion couples consisting of U-7 wt pct Mo, U-10 wt pct Mo and U-12 wt pct Mo in contact with pure Al, Al-2 wt pct Si, and Al-5 wt pct Si, annealed at 823 K (550 °C) for 1, 5 and 20 hours. Scanning electron microscopy and transmission electron microscopy were employed for the analysis. Diffusion couples consisting of U-Mo in contact with pure Al contained UAl₃, UAl₄, U₆Mo₄Al₄₃, and UMo₂Al₂₀ phases. Additions of Si to the Al significantly reduced the thickness of the interdiffusion zone. The interdiffusion zones developed Al- and Si-enriched regions, whose locations and size depended on the Si and Mo concentrations in the terminal alloys. In these couples, the (U,Mo)(Al,Si)₃ phase was observed throughout the interdiffusion zone, and the U₆Mo₄Al₄₃ and UMo₂Al₂₀ phases were observed only where the Si concentrations were low.     

Antimicrobial resistance observed in Escherichia coli strains isolated from fecal samples of cattle and pigs in Korea during 2003-2004

A total of 744 Escherichia coli strains isolated from 830 fecal samples of healthy cattle and pigs in all provinces of Korea were examined for resistance to 16 antimicrobials. The most frequently observed resistance in cattle isolates was to tetracycline (30.5%), followed by resistance to streptomycin (20.4%), ampicillin (12.0%) and chlorampenicol (6.9%). Prevalences of resistance to the same four antimicrobials in swine isolates were 96.3%, 66.8%, 66.1%, and 47.6%, respectively. The prevalence of resistance in pigs was much higher than that in cattle, with 98.3% of pig isolates and 37.1% of cattle isolates showing resistance to one or more of the antimicrobial agents tested.     

Fabrication of biofilm in nanoscale consisting of cytochrome f/2-MAA bilayer on Au surface for bioelectronic devices by self-assembly technique

We developed the nanoscale biofilm consisting of cytochrome f self-assembled on 2-MAA layer to apply bioelectronic devices. As cytochrome f has redox property, it can be possible to apply bioelectronic devices. The fabricated biofilm was confirmed by SPR and STM experiment. And the electrochemical property was checked by CV, CA, and STS.     

Characterization and stability of liposome-enveloped trypsin/Fe3O4 for drug delivery and drug release behavior

Liposome encapsulating Fe3O4 (liposome complexes) has been prepared for targeting a drug to a specific organ, as well as for MRI (magnetic resonance imaging) contrast agents. The objective of the present work was to investigate the Fe3O4 properties and the effects of chitosan concentration on the characteristics of chitosan-coated liposome complexes. They were characterized by DLS, FT-IR, XRD, VSM, UV-Vis spectrometer, TEM and phase-contrast microscopy. The average liposome complex size was approximately 500 nm, with individual Fe3O4 nanoparticle sizes of 10 nm. The drug incorporation efficiency of trypsin in liposome complexes was 65-69%, the drug release was sustained and the incorporated drugs had the magnetization properties of the liposome complexes. Incorporation of chitosan into the liposome bilayer decreased trypsin release from the liposome complexes due to an increased rigidity of the liposome membrane structure. Chitosan-coated liposome complexes showed a higher stability when compared with the stability of non-coated liposome complexes.