• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2552-2559
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• 2000

Most of ferrous b.c.c weld materials have martensitic transformation during rapid cooling after welding. It is well known that volume expansion due to the phase transformation could influence on the relaxation of welding residual stress. To apply this effect practically, it is necessary to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. For this purpose, the analysis is carried out in two regions, i.e., heating and cooling, because the variation of material properties following a phase transformation in cooling is different in comparison with the case in heating, even at the same temperature. The variation of material properties following phase transformation is considered by the adjustment of specific heat and thermal expansion coefficient, and the distribution of residual stress in analysis is compared with that of experiment by previous study. In this study, simplified numerical procedures considering phase transformation, which based on a commercial finite element package was established through comparing with the experimental data of residual stress distribution by other researcher. To consider the phase transformation effect on residual stress relaxation, the transition of mechanical and thermal property such as thermal expansion coefficient and specific heat capacity was found by try and error method in this analysis. In addition to, since the transformation temperature changes by the kind and control of alloying elements, the steel with many kinds of transformation temperature were selected and the effect of transformation on stress releasement was investigated by the numerical procedures considering phase transformation.

• Applied Microscopy
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• v.31 no.3
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• pp.245-256
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• 2001

The morphological characteristics of spermatogenic cells during the spermiogenesis of Paradoxornis webbiana were studied by transmission electron microscope. Spermiogenesis of P. webbiana was divided into ten phase. The chromatin granules became fibrous granules at the Golgi phase, gradually condensed at the cap phases, condensed as a stick at the acrosomal phase, and finally, a perfect nucleus was formed at the maturation phase. The formation of sperm tail began at the early Golgi phase, and completed at the late maturation phase. In particular, the dense materials existed in the sperm neck, which is wedged between the tip of segmented columns and the first mitochondria of the middle piece. The axone in the neck were surrounded by the dense materials. The axonema in spermatozoon contains a 9+2 arrangement of microtubules: 9 doublets, and 2 central single microtubules. Mitochondrial bundles of middle piece were composed of a pair of arms, which surrounded the axone of the middle piece by the $15^{\circ}$ angled-helical structure. The outer membrane of mitochondria were surrounded by microtubules in plasma membrane of the sperm. The undulating membrane had a helical structure, and the sperm plasma membrane was surrounded by undulating membrane.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.858-868
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• 1995

Texture development and martensitic phase transformation, on rolling, are compared in two Hadfield's steels, one having low carbon content(0.65wt% C), the other high carbon content(1.35wt%). In spite of small difference in stacking fault energy(about 2 mJm$^{-2}$ ) between two Hadfield's steels, the differences in texture development are observed. In low carbon steel, the textures developed are similar to those of low stacking fault energy metals in low strain range. However, the abnormal textures such as {111} , {110} <001> are strongly developed at high strain, which are due to the disturbance of u martensite in the development of textures formed at the packets of shear bands or at the grain boundaries. In contrast to low carbon Hadfield's steel( LCHS), the texture development of high carbon Hadfield's steel(HCHS) is simitar to those of low stacking fault energy metals in the whole strain range. This may be due to the fact that the amount of deformation induced martensite was small, as observed by A.C. magnetic susceptibility and iron particle tests.

• Applied Microscopy
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• v.31 no.2
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• pp.129-141
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• 2001

To investigate the spermiogenesis of the Saghalien Pygmy shrew (Sorex minutus gracillimus), the testis obtained from mature male shrew was studied by electron microscopy, and the following results obtained based on the morphological characteristics of cell differentiation of the seminiferous epithelium in the testis. According to the fine structural differentiation, spermiogenesis of S. minutus gracillimks was divided into Golgi, cap, acrosome, maturation and spermiation phases. Beside, the Golgi and cap phases were subdivided into three steps of early, middle and late phase respectively, and acrosome phase into two steps of early and late phase , and maturation and spermiation phases has only one step respectively. Thus, the spermiogenesis of S. minutus gracillimus was divided into a total of ten steps. The chromatin granules begin to be condensed in the acrosome phase, and a perfect nucleus of sperm was formed at the spermiation phase. Mancette were appeared from the late acrosome phase to the maturation phase. The formation of sperm tail began to develop in the late Golgi phase, and completed at the spermiation phase. Multivesicular bodies were appeared from the Golgi phase to the maturation phase, recognized with pale, pale and moderate, and dense at Golgi, cap and acrosomal and matulation phases respectively.

• The Korean Journal of Zoology
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• v.38 no.3
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• pp.395-404
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• 1995

In order to study the process of spermiogenesis of the korean striped field mouse Apodemus agrorfus coreae, the cell differentiation of seminiferous epithelium and morphological features of mature sperm in cauda epididymis was examined and the results are as follows: Spermiogenesis was divided, according to the features of cell structure; Golgi, cap, acrosome and spermiation phases were further subdivided into two steps of early and late phases respectively, and maturation phase has only one step. Hence, the spermiogenesis consists of nine phases. in the changes of the chromatin in nucleus, the chromatin granules began to be condensed in the cap phase and the condensation proceeded to form a globular of nucleus at the acrsome phase. Finally, the chromatin regularization was completed and perfect nucleus of sperm was formed at the maturation phase. Sperm head had the falciform, and the outer dence fibers of middle piece were arranged in a horseshoe fashion. The outer dence fiber number 1, 5, 6 and 9 was larger than other fiber number 2, 3, 4, 7, 8.

• Journal of Digital Convergence
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• v.14 no.8
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• pp.431-439
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• 2016

Designers are implementing the trial for enhancing human happiness and quality of life. As the happiness factor experienced by each individual is diverse based on human economic growth, absolute design has reached the limitations. A tool to represent the speedy development of change in consumption and problem shooting methods is necessary. Currently, no tool exists that develops in response to changing conditions and subsequent changes. As the solution to this necessity, worm's metamorphosis would be meaningful in design whereby tools exist and necessity as well as solution methods are in advanced change. Rice continues growth following the season, and no single method exists to remove the germs and worms. This study clarified the problems to be resolved by staging the lifetime of rice in 5 stages in environmental changes and conditions. This worm in metamorphosis design is developing brilliantly in biotechnology. However, the environment and conditions that bring happiness to humans do evolve, and this study aims to be the academic research for the design which accordingly replaces the tools.

• Korean Journal of Materials Research
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• v.11 no.5
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• pp.431-437
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• 2001

This research was examined the effect of intercritical heat treatment on the mechanical Properties and retained austenite formation in 0.1C-6.5Mn steels for the development of a high strength high ductility steel. using of transformation induced plasticity due to retained austenite. The stability of retained austenite is very important for the good ductility and it depend on diffusion of carbon and manganese during reverse transformation. It is effective to heat treat at$ 645^{\circ}C$ in order to obtain over 30 vol.% of retained austenite. However, it is more desirable to heat treat at $620^{\circ}C$, considering the volume fraction and mechanical stability of retained austenite. The strength-elongation combination in cold rolled steel sheets after reverse transformed at $620^{\circ}C$ for 1hr was about 4000k9/mm7, but it decreased rapidly with increasing holding time at high temperature due to the decrease of ductility. The addition of 1.1%Si in 0.14C-6.5Mn TRIP steel does not improve the mechanical properties and retained austenite formation.

• Korean journal of applied entomology
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• v.31 no.4
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• pp.371-378
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• 1992

The ecdysteroid titers of representive developmental stages of the blackblow fly, Phormia regina, were determined by radioimmunoassay and the effect of ecdysteroid on the oocyte maturation was investigated. Prior to every molts ecdysteroid levels began to increase sharply, suggesting ecdysteroid was the major component for egg-larval, larval-larval, and larval-pupal transformation. A difference in the levels of ecdysteroid between male and female was ob¬served during adult life span. Following the protein meal, ecdysteroid in the females increased rapidly to a maximum at 96 hr of age when terminal oocyte fully matured. Effect of ecdysteroid on oocyte development was determined for control and ecdysone-treated female flies after the liver-feeding. The growth of oocyte in the flies treated by $\mu$g of ecdysone, along with the control flies, was not facilitated. When the flies treated by 5 $\mu$g of ecdysone, however, duration of oocyte maturation was shorter than those of other two groups. This can be suggested that oocyte development in P. regina is due to the critical level of ecdysone.

• Development and Reproduction
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• v.11 no.1
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• pp.31-41
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• 2007

The spermiogenesis of Crocidura shantungensis were studied by electron microscope. All process of spermiogenesis was divided into 11 phases 15 steps, based on the morphological features of the nucleus and cell organelles in cytoplasm of spermatids. The spermatids in Golgi and cap phases were a spherical shape. On the other hand, at the early acrosomal phase they changed into an oval shape, and the tail was created in this phase. In maturation phase, the shapes of spermatid head were thin and longish. Until step 7 the direction of spermatids head turned toward the lumen of the seminiferous tubule. From step 8 to step 15 their heads turned toward the basal lamina. In step 12, the nucleus and acrosome shown maximal elongation. From Step 13 the nucleus of spermatids became flat, simultaneously with flat expansion of the acrosome expanded, and the visible whole lengths of spermatids were tend to be shorten. Spermatid heading which arrived to step 14 was taken the final shape. The nucleus was doing the wedge shape, and the nuclear chromatins condensed completely and homogenized. In the spermiation phase, the spermatids were gradually disconnected from the cytoplasm of the Sertoli cell. In this phase, the acrosome of the spermatids were fully shorten and flat, and the spermatozoa completed the process of heading and the tailing. Considering all the results, the spermiogenesis may be useful information to analyze the differentiation of spermatogenic cells.

• The Korean Journal of Malacology
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• v.29 no.2
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• pp.91-96
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• 2013

Although the method of seedling production of Haliotis discus hannai is well known, the optimum benthic diatom species as a live food at early larval stage are not fully developed. In this study three Pennales diatom species, Caloneis schroederi, Rhaphoneis sp., and Cocconeis californica were examined on settlement, metamorphosis, survival, and growth of Haliotis discus hannai larvae. The larvae fed Raphoneis sp. or C. californica showed high settlement rate with 80-82% within 48 hrs, which was significantly higher than those fed C. schroederi or mixed diets with three diatom species. The larvae fed the former microalgal species also showed higher metamorphosis rate with 32-34% than the latter species with 10-12% within 4 days. With regard to survival and growth of the larvae, single diet with Rhaphoneis sp. or C. californica had better dietary value than the mixed diets for the early larvae of H. discus hannai.