• 한국항공우주학회지
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• 제43권5호
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• pp.432-439
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• 2015

MEMS 고체 추력기 모듈은 MEMS 고체 추력기와 MEMS 추력기 제어보드로 구성된다. MEMS 고체 추력기는 학문적 연구개발 목적으로 개발되었기 때문에 발사환경을 고려한 설계 및 시험이 이루어지지 않아 이를 큐브위성에 탑재 및 궤도검증을 위해서는 설계 시 추력기 모듈로의 발사 하중이 최소화 되도록 하는 위성체 시스템 레벨에서의 설계노력이 요구된다. 본 논문에서는 MEMS 고체 추력기의 조립 및 시험과정에서의 탈장착 용이성 및 발사환경에서의 구조건전성 확보를 위해 브래킷을 이용한 구조설계를 제안하였으며, 준정적해석과 랜덤해석 및 진동시험을 통해 설계의 유효성을 검증하였다. 또한, 본 논문에서 제안한 스프링 핀을 이용한 MEMS 추력기와의 전기적 체결방식은 발사 진동에서의 구조건전성 확보에 유효함을 입증하였다.

• 대한금속재료학회지
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• 제47권5호
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• pp.267-273
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• 2009

Three types of structural intermetallic compounds, $Ni_3Al$, NiAl and TiAl, having each single phase structure without pores were produced by arc-melting process. Their sliding wear properties were investigated against a hardened tool steel. It was shown that the wear of the intermetallic compounds was hardly occurred against the hardened tool steel. TiAl compound showed the best wear resistance among them. In this case, wear was preferentially occurred on the surface of the hardened tool steel of the mating material which has higher hardness. It could be found that the wear mode on intermetallics without pores by arc-melting process was different from that on its porous layer coated on steel by combustion synthesis.

• Journal of Welding and Joining
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• 제21권2호
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• pp.82-88
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• 2003

The bonding phenomenon and mechanism in the transient liquid phase bonding(TLP Bonding) of directionally solidified Ni base superalloy, GTD-111 was investigated. At the bonding temperature of 1403K, liquid insert metal was eliminated by isothermal solidification which was controlled by the diffusion of B and Si into the base metal and solids in the bonded interlayer grew epitaxially from mating base metal inward the insert metal. The number of grain boundaries formed at the bonded interlayer was corresponded with those of base metal. The liquation of grain boundary and dendrite boundary occurred at 1433K. At the bonding temperature of 1453K which is higher than liquation temperature of grain boundary, liquids of the Insert metal were connected with liquated grain boundaries and compositions in each region mixed mutually. In Joints held for various time at 1453t phases formed at liquated grain boundary far from the interface were similar to those of bonded interlayer. With prolonged holding time, liquid phases decreased gradually and liquids of continuous band shape divided many island shape. But liquid phases did not disappeared after holding for 7.2ks at 1453k. Isothermal solidification process at the bonding temperature which is higher than the liquation temperature of the grain boundary was controlled by diffusion of Ti to be result in liquation than B or Si. in insert metal. (Received January 15, 2003)

• Journal of Microbiology
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• 제34권1호
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• pp.30-36
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• 1996

We have exmained the re-establishment of HIMRE mediated silencing function on the transcriptional activity of yeast heast shock gene HSP82. To test whether the onset of SIR repression can occur in growing cells in the rpesence of a potent inhibitor of DNA replication, HMRa/HSP82 strains with SIR4- and SIR4S$^{+}$ genetic backgrounds were arrested in S phase by incubation of a culture in 200 mM hydroxyurea for 120 min. It was clear that following a 20 minute heat shock, silencing of the HMRa/HSP82 allele in cells pretreated with hydroxyurea does occur in a SIR4-dependen fashion, even though the kinetics of repression appears to be substantially delayed. We also have tested whether re- establishement of silencing at the HMR/hsp82 locus can occur in G1-arrested cells. Cell cycle arrest at G1 phase was achieved by treatment of early log a cell cultures with .alpha.-factor mating pheromone, which induces G1 arrest. The result suggests that passage through S phase (and therefore DNA replication) is nor required for re-establishing silencer-mediated repression at the HMNRa/HSP82 locus. Finally, to test whether de nono protein synthesis is required for re-establishment of silencer-mediated repression, cells were pretreated with cycloheximide (500 /.mu.g/ml) 120 min. It was apparent that inhibiting protein synthesis delays, but does not prevent, re-establishment of silencer-mediated repression. Altogether, these results indicate that re-establishment of silencer-mediated repression is not dependent on the DNA replication and has no requirement for protein synthesis.s.

• Applied Microscopy
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• 제22권2호
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• pp.97-117
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• 1992

In order to study process of spermiogenesis of the Korean greater horseshoe bat, Rhinolophus ferrumequinum korai, the cycle of seminiferous epithelium was examined by the light and electron microscope and the following results were obtained based on the epithelial cell differentiation. 1. Spermiogenesis occurred from early July to mid-Octber, and spermatogenic activity was vigorous from mid-August to late September. Spermatocytes including spermatogonia were found to be degenerated in only July. It is deduced that the degeneration serves as the mechanism to regulate effective use of energy to prepare for mating and hibernating periods, and regulation of breeding cycle. 2. Spermiogenesis of the Korean greater horseshoe bat was divided according to differentiation of the cell structure, into Golgi, cap, acrosome, maturation and spermiation phases; Golgi, cap and spermiation phases were further divided into two steps of early and late phase respectively, and acrosome phase into three steps of early, mid and late phases, and maturation phase has only one step. Hence, the spermiogenesis consists of ten phases. The first research was done in this article on the changes of chromatin with nucleus, the time of appearance and disappearance of chromatin granules, in case of Korean greater horseshoe bat (Rhinolophus ferrumequinum korai). Chromatin granule began to be condensed in late Golgi and the condensation proceeded to form an irregular mass of a electron-dense chromatin in a form of circular cylinder in the center of nucleus at the phase of maturation. Finally, the chromatin condensation proceeded and perfect nucleus of sperm with homogeneous density was formed when the sperm was separated from Sertoli cell. Therefore, appearance and disappearance of chromatin granules occurred in the period of time between late Golgi and maturation phase, The tail of sperm began to develop in early cap phase, Numerous lipid droplets were obseved in the cytoplasm of spermatids during the maturation phase, which seemed to be used as energy source necessary to make mature sperm during spermiogenesis.

• 한국해양공학회지
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• 제25권4호
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• pp.7-11
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• 2011

The installation phase for a topside module suggested can be divided into 9 stages, which include start, pre-lifting, lifting, lifted, rotating, positioning, lowering, mating, and end of installation. The transfer of the topside module from a transport barge to a crane vessel takes place in the first three stages, from start to lifting, while the transfer of the module onto a floating spar hull occurs in the last three stages, from lowering to the end. The coupled multi-body motions are calculated in both calm water and in irregular waves with significant wave height (1.52m), with suggested force equilibrium diagrams. The effects of the hydrodynamic interactions between the crane vessel and barge during the lifting stage have been considered. The internal forces caused by the load transfer and ballasting are derived for the lifting phases. The results of these internal forces for the calm water condition are compared with those in the irregular sea condition. Although the effect of pitch motion on the relative vertical motion between the deck of the floating structure and the topside module is significant in the lifting phases, the internal force induced pitch motion is too small to show its influence. However, the effect of the internal force on the wave-induced heave responses in the lifting phases is noticeable in the irregular sea condition because the transfer mass-induced draught changes in the floating structure are observed to have higher amplitudes than the external force induced responses.

• 산업경영시스템학회지
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• 제41권3호
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• pp.186-193
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• 2018

Modern manufacturing industries is to produce both precise and robust mechanical parts without failure while they are in service. In order to prevent a part failure for its lifetime, a mechanical design for a part should be examined on a basis of mechanical simulation. A nozzle plate, being a key part in steam engines, changes flow directions of steam in a turbine used in power plant. This paper is to the design and test for part safety and durability. Currently, nozzle plates are fabricated by welding nozzles to their plates. Welding causes some defects on the used materials while they are being manufactured. Another major defect is un-even pitches between welded nozzles. Welding causes phase changes because of high melting temperature of metal. This leads to decay on the welding spots, which weakens their structural strength and then, may lead to early damages on mechanical structures. This research proposes assembly-typed nozzle plate without welding. From the beginning, nozzle and plate are designed for insertion-typed assembly. Nozzle head and foot are designed in accordance with the grooves on outer ring and inner ring of a plate to make mating surfaces. Then the nozzle plate should be proved for structural and fatigue safety before they are put in manufacturing. This research adopts commercial softwares for modeling and mechanical simulation. The test result shows that the design with smaller mating area and deeper insertion produces higher safety in terms of structure and durability. From the conclusion, this paper proposes the assembly-typed nozzle plate to replace the welding typed.

• Journal of Microbiology and Biotechnology
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• 제1권4호
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• pp.266-273
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• 1991

Hirudin, a 65-amino acid protein isolated from the salivary gland of the bloodsucking leech, Hirudo medicinalis, is a potent thrombin-specific inhibitor and blocks the thrombin-mediated conversion of fibrinogen to fibrin in clot formation. We have studied the gene expression and secretion of hirudin in yeast. Saccharomyces cerevisiae. A gene coding for hirudin was synthesized based on the amino acid sequence and cloned into a yeast expression vector $YEG{\alpha}-1$ containing the ${\alpha}-mating$ factor pre-pro leader sequence and galactose-inducible promoter, GALl0. Recombinant S. cerevisiae was found to secrete biologically active hirudin into the extracellular medium. The secreted recombinant hirudin was recovered from the culture medium and purified with ultrafiltration and reverse phase high performance liquid chromatography. Approximately 1 mg of hirudin per liter was produced under suboptimal culture conditions and brought to about 90% purity in two steps of purification.

• 한국균학회지
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• 제37권1호
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• pp.86-90
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• 2009

KACC에서 분양받은 C. militaris 4균주와 야생에서 채집된 6균주 그리고 교배 육성한 4균주를 대상으로 DNA분석에 의한 분류동정을 시행하였다. 표준균주 10균주와 교잡균주 4균주에서 조사된 전 부위(ITS1, 5.8S rDNA, ITS2)에서 많은 염기서열 차이를 보이고 있으나 같은 종으로 확인된 표준균주들과 수집균주들과 비교한 바 같은 균으로 분류된 것을 확인할 수 있었다. 교잡에 쓰여 졌던 표준 균주에서 교잡된 교잡균주 중 가장 우수한 교잡균주 mat1과 교잡에 사용되었던 표준균주(MPNU10306, MPNU10366)를 선택하여 RAPD 분석을 하였으며, RAPD에서 나타난 각 균주간의 다양한 유전적 변이가 관찰되었다. 이는 새로운 C. militaris종 균주로 판단되어지며, HPLC 분석에서도 교잡에 쓰여 졌던 표준균주보다 교잡한 C. militaris 균주가 cordycepin 생산량이 우수하게 나타났으며, 이는 교잡균주가 cordycepin 함량을 보다 더 높일 수 있음을 의미하고 상업적 가치가 있을 것이라 판단되어지며, 지속적인 연구가 필요할 것으로 생각된다.

• Journal of Microbiology and Biotechnology
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• 제9권2호
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• pp.179-183
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• 1999

A recombinant form of hirudin, a potent thrombin-specific inhibitor derived from the bloodsucking leech, was expressed as a secretory product in Saccharomyces cerevisiae under the control of GALl0 promoter and the mating factor $\alpha$pre-pro leader sequence. In an attempt to produce recombinant hirudin (r-Hir) of therapeutic purity in large quantities, the fed-batch fermentation was carried out by using this recombinant yeast, and subsequently downstream processing was developed with the preparative-scale column chromatography systems. About 234 mg/l of biologically active r-Hir was produced as a secretory product by the fed-batch fermentation strategy developed for an efficient downstream processing. Using a two-step chromatography process (an anion exchange chromatography followed by the reverse phase HPLC), the r-Hir was purified to>98% with an overall recovery yield of 84%. According to the N-terminal amino acid sequencing, the purified r-Hir was found to have the predicted N-terminal amino acid sequence. The biological activity of the purified r-Hir to inhibit thrombin was also identical to that of the commercial hirudin.