Stress-Focusing Effect Following Dynamically Transforming Anisotropic Strains in a Spherical Zirconia Inclusion

When an infinite elastic medium with a spherical inclusion of zirconia is suddenly subjected to an instantaneous transversely anisotropic phase transformation caused by impact cooling, stress waves occur at the surface of spherical inclusion the moment instantaneous transformation strains are applied. The stress waves in an inclusion proceeds radially inward to the center of the inclusion and show the stress-focusing effects. This paper analyzes the stress-focusing effects caused by the transversely isotropic phase transformation in the spherical inclusion of zirconia embedded in the infinite domain. By using the ray theory, the numerical results give a clear indication of the mechanism of stress-focusing effects caused by the phase transformation.     

Subcooled Flow Boiling in a Minichannel

It has been considered that dry-out occurs easily in boiling heat transfer for a small channel, a mini- or microchannel, because the channel was easily filled with coalescing vapor bubbles. In the present study, the experiments of subcooled flow boiling of water were performed under atmospheric conditions for a horizontal rectangular channel for which the size is 1 mm height and 1 mm width, with a flat heating surface of 10 mm length and 1 mm width placed on the bottom of the channel. The heating surface has a top of copper heating block and is heated by ceramic heaters. In the high heat flux region of nucleate boiling, about 70–80% of the heating surface was covered with a large coalescing bubble and the boiling reached critical heat flux as observed by high-speed video. In the beginning of transition boiling, coalescing bubbles were collapsed to many fine bubbles and microbubble emission boiling was observed at liquid subcooling higher than 30 K. The maximum heat flux obtained was 8 MW/m² (800 W/cm²) at liquid subcooling of higher than 40 K and a liquid velocity of 0.5 m/s. However, the surface temperature was very much higher than that of a centimeter-scale channel. The high-speed video photographs indicated that microbubble emission boiling occurs in the deep transition boiling region.     

Effect of treatment of activated carbon fiber cloth electrodes with cold plasma upon performance of electric double-layer capacitors

Charge/discharge behavior of electric double-layer capacitors composed of activated carbon fiber cloth (ACFC) electrodes and an organic electrolyte was investigated. The modification of the ACFC electrodes was performed using cold plasma generated in argon-oxygen atmosphere. The effect of the cold plasma treatment of the ACPC electrodes on the capacitor performance was discussed on the basis of the physical and chemical properties of the ACFC surface such as pore radius distribution and surface atom concentration.     

Evaluating the performance of forced convection heat transfer enhancement

Two methods for assessing thermal performance were evaluated for four kinds of forced convective heat transfer augmentations. On method uses the first law of thermodynamics, i.e., the heat transfer improvement at (1) constant Reynolds number, (2) constant pressure loss, and (3) constant pumping power. The other method uses the second law of thermodynamics, i.e., the entropy generation. The first method restricts the effective region and the second method supplies the condition for achieving the minimum entropy generation rate. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(2): 142–154, 1998     

Newly Developed Thyristor Chopper Equipment for Electric Railcars

In the chopper control system for electric railcars, it is effective to adopt high operational frequency of the chopper for achievement of the following: 1) decrease of higher harmonic current induced in the trolley wire, 2) reduction of weight for reactors and capacitors in the traction circuit, and 3) improvement of control response. Through development of reverse-conducting thyristors with very short turn-off time and a repulsion type two-phase chopper, we finally realized production of a new standard high-frequency chopper equipment with regenerative braking for 1500-V dc railcars. Technical achievements mentioned previously were completely realized as a result of adoption of high frequency, 660 Hz, in the equipment. The newly developed standard high-frequency chopper equipment for 30 cars were delivered to the Chiyoda Line of Teito Rapid Transit Authority in Tokyo, and they have been operated satisfactorily in revenue service since March 1971. This paper also describes: 1) the chopper circuit using fast-switching reverse-conducting thyristors and series saturable reactors, 2) analysis of commutation circuit and methods of suppressing reapplied forward voltage increasing rate (dv/dt) and shortening commutation period, 3) the composition of the traction circuit including the protection system, such as protection for overvoltage at the regenerative braking, and 4) test results on the Chiyoda Line of Teito Rapid Transit Authority.     

Analysis of polymer electrolyte fuel cell performance by electrode polarization model

For development of polymer electrolyte fuel cell (PEFC) lifetime estimation method, a high accuracy PEFC electrode polarization model is required. An electrode polarization model which was previously proposed was verified. However, accuracy of the electrode polarization model was not enough to estimate PEFC performance under various conditions. A new high accuracy PEFC electrode polarization model has been developed based on electrochemical consideration and data observed at elevated pressures. In the cathode polarization model, effects of O₂ diffusion and H₂O plugging have to be considered to obtain high accuracy for long-term operation. In addition, PEFC performance degradation was analyzed by the electrode polarization model. Main factors of PEFC performance degradation are OCV drop, the cathodic activation polarization, voltage drops by O₂ diffusion and H₂O plugging.     

Poly(ethylene oxide) macromonomers

Summary p-Vinylbenzyl-terninated poly(ethylene oxide) macromonomers (M₂) were radical-copolymerized with styrene (M₁) in benzene, tetrahydrofuran, and methyl isobutyl ketone at 60°C. Relative reactivity of the macromonomer toward polystyryl radical, as estimated by l/r₁ was found to decrease with increasing number-average degree of polymerization and also in a solvent which gives a higher [] of both polystyrene and the macromonomer. The results support our previous suggestion that a repulsion between the macromonomer and the propagating polymer radical can be a factor responsible for disturbing their mutual reaction.Part 1: Ref. 1, Part 2: Ref. 2     

Water quality and transparency characteristics during the Planktothrix abundance period in shallow Lake Kasumigaura,Japan

Cyanobacterial blooms in lakes cause serious environmental problems on a global scale. Planktothrix (a filamentous cyanobacterium) blooms occurred during winter and spring from 2007 to 2011 in Lake Kasumigaura, a eutrophic lake located in Japan. This study analysed water quality during the period of Planktothrix abundance (2007–2010) at the centre of Lake Kasumigaura and compared it to that in the succeeding period, which did not have Planktothrix blooms (2012–2015). The average phytoplankton biovolume during the abundance period was larger than that in the succeeding period, which would contribute to the high chemical oxygen demand (COD_Mn; annual average of 9.7 mg/L) in the abundance period, compared to the succeeding period (7.6 mg/L). The total phosphorus concentration peaked in spring and summer in the abundance period, but only in summer in the succeeding period, whereas the seasonal variation in total nitrogen concentration between the two periods was relatively small. The annual average transparency (Secchi disc depth) increased before the abundance period due to a decrease in fixed suspended solid, which is comprised mainly of inorganic matter. It is likely that the change in irradiance conditions affected the occurrence of Planktothrix blooms.     

Tensile and impact properties of fully green composites reinforced with mercerized ramie fibers

The purpose of this study is to create a natural fiber-reinforced fully green composite with excellent toughness. By treating ramie plied yarns in a high concentration alkali solution, the reinforcements were mercerized. Results of tensile tests showed that unidirectional composites using mercerized ramie yarns exhibited two to three times larger fracture strain, without a marked decrease in strength, than composites using untreated yarns. In addition, mercerization for the ramie yarns brings a better interfacial strength to the composites. Laminated composites using mercerized ramie yarns also showed approximately twice larger impact energy than composites using untreated yarns. Thus, mercerization for natural fibers is expected for application to mechanical materials requiring a high toughness.     

Orientation of nanowires consisting of poly(3-hexylthiophene) using strong magnetic field

Nanowires consisting of regioregular poly(3-hexylthiophene) (P3HT) as a conducting polymer were prepared using p-xylene. Magnetic processing of the nanowires was carried out using two superconducting magnets with horizontal (B_max = 8 T) and vertical (B_max = 10 T) directions. The formation of the nanowires was confirmed by atomic force microscopy (AFM) measurement. The results from the AFM images and the polarized absorption spectra on glass plates indicated that the nanowires partly oriented themselves with their long axes, which are parallel to the π–π stacking direction, being perpendicular to the magnetic field. The magnetic orientation is most likely ascribed to anisotropy in the magnetic susceptibilities of the ordered P3HT in the nanowires.