Minoru Ikeda

Faceted dendrite growth of silicon from undercooled melt of Si–Ni alloy

Abstract Two-dimensional faceted dendrite growth of silicon from undercooled melt of Si–6 wt%Ni alloy was experimentally investigated, in which molten alloy film from 10 to 20 mm in thickness was undercooled up to 115 K and growing dendrites were observed in situ. Both the in situ observation of dendrite morphology and the EBSP crystallographic analysis for solidified samples showed that both a ‹211› twin dendrite and a ‹100› twin-free dendrite grew in the range of undercooling from50 to 115 K. Dendrite growth velocity was also measured for different undercooling conditions. The growth velocity of ‹211› dendrites was slightly larger than that of ‹100› dendrites. It is concluded that the upper envelope of the data provide the correct dendrite growth velocity and it is compared with that obtained by phase-field simulations. Growth velocity in both follows power relationships to undercooling and the linear kinetic coefficient is estimated to be 0.01 m/s K.

Identification of spawning sites of the tiger puffer Takifugu rubripes in Nanao Bay, Japan, using DNA analysis

There are two possible spawning sites of the tiger puffer Takifugu rubripes near Nanao Bay in the Sea of Japan: one near Hachiro Lagoon, approximately 390xa0km northeast of Nanao Bay, and another in Wakasa Bay, approximately 170xa0km west of Nanao Bay. Tagging research suggests that these two spawning sites represent different subpopulations. In the present study, Nanao Bay spawning sites were identified by mitochondrial DNA control region sequencing of eggs collected using a sledge net in May and June of 2009. The spawning sites were distributed in a small region with a sandy bottom at a depth of 17.5–20.5xa0m (water temperature 13.07–16.56xa0°C, salinity 33.95–34.12). The population structure of T. rubripes around Nanao Bay was also investigated using DNA analysis of mature adult samples from three locations. Genetic differentiation was not significant among the adults, suggesting the presence of gene flow resulting from broad dispersal of individuals from the three locations.

Novel microsatellite marker development from the unassembled genome sequence data of the marbled flounder Pseudopleuronectes yokohamae

Various genome-scale data have been increasingly published in diverged species, but they can be reused for other purposes by re-analyzing in other ways. As a case study to utilize the published genome data, we developed microsatellite markers from the genome sequence data (assembled contigs and unassembled reads) of the marbled flounder Pseudopleuronectes yokohamae. No microsatellites were identified in the contig sequences, whereas the computer software found 781,773 sequences containing microsatellites with di- to hexa-nucleotide motif in the unassembled reads. For 86,732 unique sequences among them, a total of 331,368 primer pairs were designed. Screening based on PCR amplification, polymorphisms and accurate genotyping resulted in sixteen primer sets, which were later characterized using 45 samples collected in Onagawa Bay, Miyagi, Japan. The presence of null alleles was suggested at four loci in the studied population but no evidence of allelic dropout was found. The observed number of alleles and heterozygosity was 2-20 and 0-0.88889, respectively, indicating polymorphisms and usefulness for population genetic analyses of this species. In addition, a large number of the microsatellite primers developed in this study are potentially applicable also for kinship estimation, individual fingerprint and linkage map construction.