• Journal of the Korean Society for Precision Engineering
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• v.14 no.4
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• pp.38-45
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• 1997

A new dynamic model for the cutting process inb the end milling process is developed. This model, which describes the dynamic response of the end mill, the chip load geometry including tool runout, the dependence of the cutting forces on the chip load, is used to predict the dynamic cutting force during the end milling process. In order to predict accurately cutting forces and tool vibration, the model which uses instantaneous specific cutting force, inclueds both regenerative effect and penetration effect, The model is verified through comparisons of model predicted cutting force with measured cutting force obtained from machining experiments.

• Journal of Life Science
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• v.28 no.12
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• pp.1455-1460
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• 2018

Due to a rapidly expanding aging population, the incidence of degenerative bone disease has increased, and efforts to handle the issue using regenerative medicine have become more important. In order to control various bone diseases such as osteoarthritis and osteoporosis, regenerative medicine utilizing adult stem cells has been extensively studied. And it is now clear that the mitochondrial energy metabolism, oxidative phosphorylation, is important for the process of stem cell differentiation. Interestingly, a recent study reported that salicylate promotes mitochondrial biogenesis by regulating the expression of $PGC-1{\alpha}$ in murine cells. However, the possible effects of salicylate on osteogenic differentiation through increased mitochondrial biogenesis in stem cells remain unknown. Thus, here we investigated whether salicylate could influence osteogenic differentiation and mitochondrial biogenesis of periosteum-derived mesenchymal stem cells (POMSCs). We found that salicylate treatments of POMSCs undergoing osteogenic differentiation increased the activity of alkaline phosphatase, a well-known early marker of bone cell differentiation. In addition, we observed that mitochondrial mass was increased by salicylate treatments in POMSCs. Together, these results indicate that salicylate can enhance osteogenic differentiation and mitochondrial biogenesis in POMSCs. Therefore, the findings in this study suggest that small molecules augmenting mitochondrial function such as salicylate can be a novel modulator for osteogenic differentiation and regenerative medicine.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.2
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• pp.27-33
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• 2013

In this study we analyzed the on-road driving performance of two parallel-type diesel-hybrid buses which have been driven in Daegu metropolitan area. A real-time on-board data logger was facilitated to measure the vehicle information such as vehicle speed, idle stop, state of charge of battery, and engine operating conditions. These diesel-hybrid buses ran as a commuter at Daegu Exco area and Dalsung industrial complex. The driving pattern in Exco area comprised more frequent idle stop and relatively lower speed than at Dalsung area, where comprised no idle stop. Due to those different driving patterns, the fuel economy at Dalsung showed $3.7\;km/{\ell}$, which is about 8% higher than that of Exco. The main causes of this come from the higher portion of regenerative braking and higher speed which moves to the operating points of diesel engine with a lower fuel consumption.

• Development and Reproduction
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• v.12 no.1
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• pp.87-95
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• 2008

Neural stem/precursor derived from pluripotent human embryonic stem cells (hESCs) has considerable therapeutic potential due to their ability to generate various neural cells which can be used in cell-replacement therapies for neurodegenerative diseases. However, production of neural cells from hESCs remains technically very difficult. Understanding neural-tube like rosette characteristic neural precursor cells from hESCs may provide useful information to increase the efficiency of hESC neural differentiation. Generally, neural rosettes were derived from differentiating hEBs in attached culture system, however this is time-consuming and complicated. Here, we examined if neural rosettes could be formed in suspension culture system by bypassing attachment requirement. First, we tested whether the size of hESC clumps affected the formation of human embryonic bodies (hEBs) and neural differentiation. We confirmed that hEBs derived from $500{\times}500\;{\mu}m$ square sized hESC clumps were effectively differentiated into neural lineage than those of the other sizes. To induce the rosette formation, regular size hEBs were derived by incubation of hESC clumps($500{\times}500\;{\mu}m$) in EB medium for 1 wk in a suspended condition on low attachment culture dish and further incubated for additional $1{\sim}2$ wks in neuroectodermal sphere(NES)-culture medium. We observed the neural tube-like rosette structure from hEBs after $7{\sim}10$ days of differentiation. Their identity as a neural precursor cells was assessed by measuring their expressions of neural precursor markers(Vimentin, Nestin, MSI1, MSI2, Prominin-1, Pax6, Sox1, N-cadherin, Otx2, and Tuj1) by RT-PCR and immunofluorescence staining. We also confirmed that neural rosettes could be terminally differentiated into mature neural cell types by additional incubation for $2{\sim}6$ wks with NES medium without growth factors. Neuronal(Tuj1, MAP2, GABA) and glial($S100{\beta}$ and GFAP) markers were highly expressed after $2{\sim}3$ and 4 wks of incubation, respectively. Expression of oligodendrocyte markers O1 and CNPase was significantly increased after $5{\sim}6$ wks of incubation. Our results demonstrate that rosette forming neural precursor cells could be successfully derived from suspension culture system and that will not only help us understand the neural differentiation process of hESCs but also simplify the derivation process of neural precursors from hESCs.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.19-25
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• 2001

In metal cutting, chatter is an unstable cutting phenomenon which is due to the interaction of the dynamics of the chip removal process and the structural dynamics of machine tool. When chatter occurs, it reduces tool life and results in poor surface roughness and low productivity of the machining process. In this study, the experiments have been conducted to investigate phenomenon of the chatter in CNC lathe without cutting fluid. In the experiments, two accelerometers were attached at the tail stock and tool holder and the signals were caught. In order to observe the effect of chatter on the surface roughness profiles, surface roughness profiles were generated under the ideal condition and the occurrence of the chatter based on the surface simulation model using surface-shaping system. Finally, the result of experiment and simulation have been compared.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1327-1331
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• 2004

In this paper constant power models for electric trains have been used to analyze the steady states of the AT feeding systems. There are some previous studies utilizing constant impedance models or constant current models. These mentioned models are easy to use, but even so they don't yield exact results because of the innate restraints of the models since linear models cannot represent the characteristic of constant power in inverter-driven trains. It is reasonable that the train be considered as a constant load model when it drives or as a constant source model when it applies regenerative brake. Nonlinear equations which reflect constant power model for train have been developed by considering mutual impedances between wires and AT's turn-ratio of 1:1, then these equations have been solved by N-R iterative method. The proposed method doesn't need any specific assumptions through either the process of developing equations or the process of acquiring solutions, so it can be said to be stricter than other conventional methods.

• Animal cells and systems
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• v.12 no.1
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• pp.1-9
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• 2008

In the developing limb, chondrogenesis is an important prerequisite for the formation of cartilage whose template is required for bone formation. Chondrogenesis is a tightly regulated multi-step process, including mesenchymal cell recruitment/migration, prechondrogenic condensation of the mesenchymal cells, commitment to the chondrogenic lineage, and differentiation into chondrocytes. This process is controlled exquisitely by cellular interactions with the surrounding matrix and regulating factors that initiate or suppress cellular signaling pathways and transcription of specific genes in a temporal-spatial manner. Understanding the cellular and molecular mechanisms of chondrogenesis is important not only in the context of establishing basic principle of developmental biology but also in providing research direction toward preventive and/or regenerative medicine. Here, I will overview the current understanding of cellular and molecular mechanisms contributing to prechondrogenic condensation processes, the crucial steps for chondrogenesis, focusing on cell-cell and cell-matrix interactions.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.5
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• pp.49-54
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• 2004

In order to evaluate the stability of chatter vibration in turning precess, the micro-positioning cutting test with artificial tool vibration by piezoelectric actuation were carried out. In experiment, the phase lags between cutting forces and chip thickness variations were measured, and the dimensionless penetration-rate coefficient（$\overline{K^*}$） which is the most important parameter on the stability for chatter vibration was calculated. The results show that$\overline{K^*}$ can be applicable to the stability criterion for regenerative chatter vibration.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.620-624
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• 2011

In recent years, the study of self-assembly peptide used in drug delivery system has been attracted great interest from scientists. In the category are self-assembly peptides in the structure either with one hydrophobic surface and another hydrophilic or a hydrophobic head and a hydrophilic tail. Here, we focus on a novel designed peptide EYK with double amphiphilic surfaces, investigating on the capability of peptide as a carrier for hydrophobic compound model pyrene. The fluorescence data presented the dynamic process of the transfer, showing that the pyrene was in the crystalline form in peptide solution, and molecularly migrated from its peptide encapsulations into the membrane bilayers when the peptide-pyrene suspension was mixed with liposome vesicles. The results indicated that the peptide EYK could stabilize hydrophobic pyrene in aqueous solution and delivered it into EPC liposome as a potential carrier.

• Journal of Embryo Transfer
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• v.32 no.3
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• pp.81-86
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• 2017

The Somatic cell nuclear transfer (SCNT) method can be applied to various fields such as species conservation, regenerative medicine, farming industries and drug production. However, the efficiency using SCNT is very low for many reasons. One of the troubles of SCNT is that it is highly dependent on the researcher's competence. For that reason, four somatic cell nuclear injection methods were compared to evaluate the effect of hole-sealing process and existence of cytochalasin B (CB) on efficiency of murine SCNT protocol. As a results, the microinjection with the hole-sealing process, the oocyte plasma membrane is inhaled with injection pipette, in HCZB with CB was presented to be the most efficient for the reconstructed in SCNT process. In addition, we demonstrated that the oocytes manipulated in Hepes-CZB medium (HCZB) with CB does not affect the developmental rate and the morphology of the blastocyst during the pre-implantation stage. For this reason, we suggest the microinjection involving hole-sealing in HCZB with CB could improve SCNT process efficiency.