Effect of static magnetic field on a thermal conductivity measurement of a molten droplet using an electromagnetic levitation technique

Recently, a novel method of measuring the thermophysical properties, particularly thermal conductivity, of high-temperature molten materials using the electromagnetic levitation technique has been developed by Kobatake et al. [H. Kobatake, H. Fukuyama, I. Minato, T. Tsukada, S. Awaji, Noncontact measurement of thermal conductivity of liquid silicon in a static magnetic field, Appl. Phys. Lett. 90 (2007) 094102]; this method is based on a periodic laser-heating method, and entails the superimposing of a static magnetic field to suppress convection in an electromagnetically levitated droplet. In this work, to confirm the fact that a static magnetic field really suppresses convection in a molten silicon droplet in an electromagnetic levitator, numerical simulations of convection in the droplet and periodic laser heating in the presence of convection have been carried out. Here, the convections driven by buoyancy force, thermocapillary force due to the temperature dependence of the surface tension on the melt surface, and electromagnetic force in the droplet were considered. As a result, it was found that applying a static magnetic field of 4 T can suppress convection in a molten silicon droplet enough to measure the real thermal conductivity of molten silicon.     

Deformation-induced martensitic transformation behavior in cold-rolled and cold-drawn type 316 stainless steels

We investigate deformation-induced martensitic transformation behavior in cold-rolled and cold-drawn specimens of type 316 stainless steel. Deformation-induced martensite preferentially nucleates at the twin boundary between the austenite matrix and a deformation twin. In the cold-rolled specimen, martensite formed at the twin boundary has a Kurdjumov–Sachs (K–S) relationship with both the austenite matrix and the deformation twin (“double K–S relationship”). In the cold-drawn specimen, two kinds of deformation twins with different twin planes are typically formed, and therefore deformation-induced martensites are formed where the deformation twin boundaries intersect: martensite thus has an imperfect “triple K–S relationship” with the austenite matrix and the two deformation twins. The complicated crystallographic orientation relationship between austenite and martensite grains strongly restricts the formation of some variants of deformation-induced martensites. Because of the difference in number of nucleation sites in the cold-drawn and cold-rolled specimens, martensitic transformation is more enhanced in the former than in the latter.     

Dependence of ion selectivity on ordered orientation of neutral carriers in ion-sensing membranes based on thermotropic liquid crystals

Thermotropic liquid-crystalline compounds were applied as membrane materials (membrane solvent and neutral carrier) for neutral carrier-type ion sensors to investigate how the ordered arrangement of neutral carriers affects the property of the resulting ion sensors. Nematic, smectic, and cholesteric liquid-crystalline compounds were used as the membrane solvents and crown ether derivatives with a molecular structure similar to the liquid-crystalline solvent as the K+ neutral carriers. Polarized IR spectroscopy and X-ray diffraction experiments confirmed that the highly ordered arrangement of membrane components was retained in the liquid-crystal-based ion-sensing membranes containing a neutral carrier and a lipophilic salt. The ordered arrangement of neutral carriers in the liquid-crystalline membranes enhanced the ion selectivity significantly, probably due to the efficient cooperation of two adjacent crown ether moieties in the highly ordered and aggregated state.     

Effect of applied voltage frequency on swarming pulsive microdischarges in closed voids

The extinction of the partial discharge (PD) pulse has frequently been observed in an epoxy specimen with a closed void during voltage endurance tests using a CIGRE Method-II electrode. The individual discharge pulse becomes so small that the discharges cannot be detected by conventional pulse detection methods. Such discharges are known as “swarming pulsive microdischarges” (SPMD). In this paper, the SPMD characteristics are investigated by varying the frequency of the applied voltage from 0.1 to 240 Hz. As a result, the SPMD are found to occur less frequently as the frequency is lowered. To seek this cause, one-shot voltages were applied repeatedly at constant intervals. By varying the interval from 0.02 to 100 s, the PD off an electrically aged specimen was measured. It was revealed that the discharge magnitude increases as the interval becomes longer. The onset of SPMD was found to depend on the preceding discharge. The results explain the reason why swarming is harder to occur at lower frequency with a longer discharge interval. Hence, in the conventional pulse detection, it is useful to employ the very low frequency for diagnosis of machine insulation containing enclosed voids.     

The Oxidation behavior of an iron-chromium alloy containing yttrium or rare earth elements between 900° and 1200°C

The oxidation behavior of an Iron-15 wt pct Chromium alloy, some containing small additions of yttrium or rare earth elements, have been observed using a TG and an EPMA method at temperatures between 900° and 1200°C. Yttrium or rare earth element additions to the Iron-Chromium alloy result in a rapid initial oxidation rate, but decrease the total weight gain of the Iron-Chromium alloy at the final time of exposure. The line trace obtained indicates that the increased segregation of chromium content in the inner oxide layer of the alloy containing yttrium or rare earth elements and also shows that the enriched concentration of yttrium or lanthanum is detected within the chromium oxides which exist near the oxide scale/alloy matrix interface. Yttrium or rare earth element oxides serve as the sites for the protective chromium oxide scales.     

Study on anisotropy of growth rate of ice crystal in supercooled water

The purpose of this research was to investigate the ice growth of a single crystal in three dimensions. Three-dimensional pattern of ice crystal growth in supercooled water was observed using Mach–Zehnder spectro-interferometer. Temperature was varied from −0.3 to −1.6 °C. It was found that the ice crystal began to grow as a single crystal at the tip of the capillary tube and propagated freely in supercooled water. Time variation of the shape of dendrite on a–c plane was obtained. It was found that half parabola fits the shape very closely, and the coefficient of squared term, a, of a quadratic function was calculated. The coefficient, a varied in time but at quasi steady state it was found to be depending mostly upon the degree of supercooling. Furthermore, the growth velocity in c-axis at the flat surface was calculated from the thickness measured. It was found that the velocity in c-axis is independent of the degree of supercooling but depends upon time, in other words, the thickness in c-axis.     

Occurrence,horizontal transfer and degeneration of VDE intein family in Saccharomycete yeasts

VDE is a homing endonuclease gene originally discovered as an intervening element in VMA1s of Saccharomyces cerevisiae. There have been two independent subfamilies of VDE, one from S. cerevisiae strain X2180-1A and the other from Saccharomyces sp. DH1-1A in the host VMA1 gene, and they share the identity of 96.3%. In order to search the occurrence, intra/interspecies transfer and molecular degeneration of VDE, complete sequences of VMA1 in 10 strains of S. cerevisiae, eight species of saccharomycete yeasts, Candida glabrata and Kluyveromyces lactis were determined. We found that six of 10 S. cerevisiae strains contain VDEs 99.7-100% identical to that of the strain X2180-1A, one has no VDE, whereas the other three harbour VDEs 100% identical to that of the strain DH1-1A. S. carlsbergensis has two VMA1s, one being 99.8% identical to that of the strain X2180-1A with VDE 100% identical to that of the strain DH1-1A and the other containing the same VMA1 in S. pastorianus with no VDE. This and other evidence indicates that intra/interspecies transmissions of VDEs have occurred among saccharomycete yeasts. Phylogenetic analyses of VMA1 and VDE suggest that the S. cerevisiae VDEs had branched earlier than other VDEs from an ancestral VDE and had invaded into the host loci as relatively late events. The two VDEs seemed to degenerate in individual host loci, retaining their splicing capacity intact. The degeneration of the endonuclease domains was distinct and, if compared, its apparent rate was much faster than that of the protein-splicing domains.