PIV measurement and turbulence scale in turbulent combustion

We have investigated turbulent combustion by PIV (Particle Image Velocimetry) technique. Comparing with LDV data, the validity of PIV measurements has been confirmed. Particularly, the conditions of sampling number and spatial resolution have been shown to yield reliable data using PIV. Based on the velocity fields in cold flow and combustion, the interaction between flame and flow has been discussed. It was observed that the flow field is changed by combustion and the turbulence is reduced. In order to determine statistical quantities such as mean velocity and RMS of velocity fluctuation, a sampling number of 1000 is needed. Moreover, the velocity correlation coefficient was evaluated to obtain the integral length scale of the flow. For both cold flow and combustion, the PIV estimated scale is very close to that of LDV based on the assumption of Taylor's hypothesis. As a result, the spatial resolution in this study is about 6 times smaller than the integral length scale. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(7): 501–512, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20129     

A numerical method for natural convection and heat conduction around and in a horizontal circular pipe

Natural convection around a horizontal circular pipe coupled with heat conduction in the solid structure is numerically investigated using a preconditioning method for solving incompressible and compressible Navier–Stokes equations. In this method, fundamental equations are completely reduced to an equation of heat conduction when the flow field is static (zero velocity). Therefore, not only compressible flows but also very slow flows such as natural convection in a flow field and heat conduction in a static field can be simultaneously calculated using the same computational algorithm. In this study, we first calculated the compressible flow around a NACA0012 airfoil with conduction in the airfoil and then simulated natural convections around a horizontal circular pipe with a different heat conductivity. Finally, we numerically investigated the effect of heat conductivity of the pipe on natural convection.     

Antibiotic contamination and occurrence of antibiotic-resistant bacteria in aquatic environments of northern Vietnam

The ubiquitous application and release of antibiotics to the environment can result in bacterial antibiotic resistance, which in turn can be a serious risk to humans and other animals. Southeast Asian countries commonly apply an integrated recycling farm system called VAC (Vegetable, Aquaculture and Caged animal). In the VAC environment, antibiotics are released from animal and human origins, which would cause antibiotic-resistant bacteria (ARB). This study evaluated occurrence of ARB in the VAC environment in northern Vietnam, with quantitative analysis of antibiotic pollution. We found that sulfonamides were commonly detected at all sites. In dry season, while sulfamethazine was a major contaminant in pig farm pond (475-6662 ng/l) and less common in city canal and aquaculture sites, sulfamethoxazole was a major one in city canal (612-4330 ng/l). Erythromycin (154-2246 ng/l) and clarithromycin (2.8-778 ng/ml) were the common macrolides in city canal, but very low concentrations in pig farm pond and aquaculture sites. High frequencies of sulfamethoxazole-resistant bacteria (2.14-94.44%) were found whereas the occurrence rates of erythromycin-resistant bacteria were lower (< 0.01-38.8%). A positive correlation was found between sulfamethoxazole concentration and occurrence of sulfamethoxazole-resistant bacteria in dry season. The sulfamethoxazole-resistant isolates were found to belong to 25 genera. Acinetobacter and Aeromonas were the major genera. Twenty three of 25 genera contained sul genes. This study showed specific contamination patterns in city and VAC environments and concluded that ARB occurred not only within contaminated sites but also those less contaminated. Various species can obtain resistance in VAC environment, which would be reservoir of drug resistance genes. Occurrence of ARB is suggested to relate with rainfall condition and horizontal gene transfer in diverse microbial community.     

Electron-temperature control by varying dc voltage to a mesh grid covered by thin film in plasmas

We discuss theoretically how the resistance of a film deposited on the metal grid affects the efficiency of electron-temperature control by employing a grid-bias method, in which, by using a naked metal grid, the electron temperature decreases from 3.4 to 0.12 eV with a decrease in the grid potential from 40 to − 60 V, being accompanied by an electron-density increase from 0.6 × 10⁹ cm^− 3 to 6.0 × 10⁹ cm^− 3 at an argon gas pressure of 5.0 mTorr. The electron temperature can be varied even when the grid is covered with a film with finite resistance, although the range of electron temperature variation is restricted. This method is applicable to reactive plasmas in which grids are often covered by films with finite resistance.     

Two-dimensionally quantized friction observed with two-dimensional frictional force microscope

Using a two-dimensional frictional force microscope, we studied the two-dimensional nature of the atomic scale friction between a Si₃N₄ sharp tip and a cleaved graphite surface, which is composed of only C atoms and is a good conductor. As a result, we observed the two-dimensionally quantized friction with the lattice periodicity of the graphite surface, similarly to mica, MoS₂ and NaF surfaces. Thus quantized friction occurs at material surfaces which are composed of not only some elements but also of a single element, and the quantized friction does not depend on the conductivity of the surface.     

Application study of a high‐temperature superconducting fault current limiter for electric power system

Using high‐temperature superconductors, a superconducting fault current limiter (SFCL) was fabricated and tested. The superconductor and a vacuum interrupter serving as a commutation switch were connected in parallel with a bypass coil. When a fault occurs and excessive current flows, the superconductor is first quenched and the current is transferred to the bypass coil because of the voltage drop of the superconductor. At the same time, since a magnetic field is generated by the current flowing in the bypass coil, the commutation switch is immediately driven by an electromagnetic repulsion plate connected to the driving rod of the vacuum interrupter (VI), and the superconductor is separated from this circuit. Using the test model, we were able to separate the superconductor from the circuit by the movement of the VI within a half current cycle and to transfer all current to the bypass coil. Since the operation of the commutation switch is included in the current limiting operation of this test model, it will be a useful circuit in the development of SFCL in the future. Moreover, since it can make the energy consumption of the superconductor small during the fault state due to the realization of a high‐speed switch with simple composition, the burden on the superconductor is reduced compared with the conventional resistive type of SFCL and it is considered that the flexibility of SFCL design is increased. Cooperation with a circuit breaker was also considered; trial calculations of the parameters and energy of operation were conducted and a discussion of the installation of the SFCL in an electric power system is presented. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 20–29, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20265     

Preparation and properties of disyndiotactic poly(alkyl crotonate)s

Ethyl, n-propyl, iso-propyl and n-butyl crotonates were polymerized by group transfer polymerization (GTP) using ketene trialkylsilyl acetals as initiators in the presence of mercury (II) iodide as catalyst and iodotriethylsilane as co-catalyst. Predominantly disyndiotactic polymers with number-average molecular weights ranging from 56,000 to 90,000 were obtained almost quantitatively. Thermal and mechanical properties of poly(alkyl crotonate)s, such as glass transition temperature (T_g), refractive index, transmissivity, Izod impact strength, Young's modulus, hardness, tensile strength, tensile elongation at break, gas permeability coefficient and density were measured. All the polycrotonates have 65–90 °C higher T_g than the corresponding polymethacrylates.     

Phase Diagram Mapping of the Fe<Subscript>3</Subscript>Al-Cr-Mo-C Pseudo-Quaternary System at 800 °C Using a New Diffusion-Multiple Technique

A new diffusion-multiple technique was used for mapping the phase diagram in the pseudo-quaternary Fe₃Al-Cr-Mo-C system at 800 °C. The following five carbide phases were formed in an Fe₃Al matrix phase (B2) with composition gradients of Cr, Mo, and C in the diffusion-multiple samples: κ-Fe₃AlC, M₅C, M₆C, Cr₇C₃, and M₂C (M: Mo, Cr, Al, and Fe). It was assumed that B2 phase is in equilibrium with κ, M₅C, M₆C, and Cr₇C₃ but not with M₂C phase at 800 °C. Complex phase equilibria among those phases were efficiently mapped by the diffusion-multiple technique. The results from the technique were consistent with those obtained from the conventional bulk alloy method.