• Journal of the Korean Society of Visualization
• /
• v.13 no.1
• /
• pp.43-48
• /
• 2015

Collective cell migration is a fundamental phenomenon observed in various biological processes such as development, wound healing, and cancer metastasis. During the collective migration, cells undergo changes in their phenotypes from those of stable to the migratory state via the process called epithelial-mesenchymal transition (EMT). Recent findings in biology and biochemistry have shown that EMT is closely related to the cancer invasion or metastasis, but not much of the correlations in kinematics and physical forces between the neighboring cells are known yet. In this study, we aim to understand the cell migration and stress distribution within the expanding cell cluster. We constructed the in vitro cell cluster on the hydrogel, employed traction force microscopy (TFM) and monolayer stress microscopy (MSM) to visualize the physical forces within the expanding cell monolayer. During the expansion, cells at the cluster edge exhibited enhanced motility and developed focal adhesions that are the essential features of EMT while cells at the core of the cluster maintained the epithelial characteristics. In the aspect of mechanical stress, the cluster edge had the highest traction force of ~90 Pa directed toward the cluster core, which means that cells at the edge actively pull the substrate to make the cluster expansion. The cluster core of the tightly confined cells by neighboring cells had a lower traction force value (~60 Pa) but the highest intercellular normal stress of ~800 Pa because of the accumulation of traction from the edge of the monolayer.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.130-135
• /
• 2007

The mechanical characteristics of three types of core with two-dimensional isotropic patterns-triangular, hexagonal and starcell-were studied in applications to sandwich structures. The Young's modulus and shear modulus were calculated for the three core types in the direction normal to the faces. The compressive buckling strength and shear buckling strength were calculated by modeling each cell wall of the core as a plate under compressive or shear load. To verify this model, tests were conducted on scaled specimens to measures the compressive buckling strength of each core. The bending flexibilities of the three cores were also studied. Compliances for the three cores were measured using biaxial flexural tests. The three isotropic core patterns exhibited distinct characteristics. In the direction normal to the faces, all three cores had the same stiffness. However, the starcell core exhibited high flexibility compared to the other cores, indicating potential for application to curved sandwich structures.

• Proceedings of the Korean Society of Plant Biotechnology Conference
• /
• 2005.11a
• /
• pp.197-197
• /
• 2005

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.2105-2110
• /
• 2004

Plate-fin type recuperators for the gas turbine/fuel cell hybrid power generating system were designed using commercial design software, MUSE. Heat transfer efficiency and total pressure drop in the recuperator were calculated to confirm required recuperator performance. Both counter flow and cross flow type plate-fin recuperators were designed. Results show that the counter flow type has higher efficiency and short core length, but the cross flow type is simpler to construct because the cross flow type does not need additional distributors. Two or three headers for the each recuperator core will be designed and tested to evaluate best header design. The designed recuperators and headers which will be designed later will be constructed, tested, and used in gas turbine/fuel cell hybrid power generating system.

• Korean Journal of Microbiology
• /
• v.28 no.1
• /
• pp.1-5
• /
• 1990

The coding sequence of hepatitis B viral core antigen (HBcAg) (subtype adr) contains two in-phase initiation codons, one for precore and the other for core antigen gene. To study the expression of core antigen and the role of precore region, the coding sequence of HBcAg with or without precore (pre-C) region were subcloned into yeast expression vector containing phosphoglycerate kinase (PGK) promoter. To study the role of upstream region in the expression of the core antigen, a series of 5' deletion mutants were also subcloned into the vector. After transformation into various host strains, the expression of HBcAg were analysed by radio-immunoassat. Under optimal condition of core antigen gene expression in yeast, the highest amount of antigen was detected in the cell line SHY4 containing pGKHBc plasmid composed of the yeast PGK gene promoter, terminator and C-gene. Regardless of the presence of precore region, core antigen was not detected in the medium but in cell extract. These results suggest that precore region cannot affect the secretion of core antigen in Saccharomyces cerevisiae.

• Composites Research
• /
• v.18 no.1
• /
• pp.30-37
• /
• 2005

The bending strength characteristics and local deformation behaviors of honeycomb sandwich composites were investigated using three-point bending experiment and finite element simulation with a real model of honeycomb core. Two kinds of cell sizes of honeycomb core, two kinds of skin layer thicknesses, perfect bonding specimen as well as initial delamination specimen were used for analysis of stress and deformation behaviors of honeycomb sandwich beams. Various failure modes such as skin layer yielding, interfacial delamination, core shear deformation and local buckling were considered. Its simulation results were very comparable to the experimental ones. Consequently, cell size of honeycomb core and skin layer thickness had dominant effects on the bending strength and deformation behaviors of honeycomb sandwich composites. Specimens of large core cell size and thin skin layer showed that bending strength decreased by $30\~68\%$.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.16 no.1
• /
• pp.37-44
• /
• 2008

The global warming potential (GWP) of $CO_2$ refrigerant is 1/1300 times lower than that of R134a. Furthermore, the size and weight of the automotive heat pump system can decrease because $CO_2$ operates at high pressure with significantly higher discharge temperature and larger temperature change. The presented $CO_2$ heat pump system was designed for both cooling and heating in fuel cell vehicles. In this study, the performance characteristics of the heat pump system were analyzed for heating, and results for performance were provided for operating conditions when using recovered heat from the stack coolant. The performance of the heat pump system with heater core was compared with that of the conventional heating system with heater core and that of the heat pump system without heater core, and thus the heat pump system with heater core showed the best performance among the selected heating systems. On the other hand, the heating performance of two different types of coolant/air heat pump systems with heater core was compared each other at various coolant inlet temperatures. Furthermore, to use exhausted thermal energy through the radiator, experiments were carried out by changing the arrangement of a radiator and an outdoor evaporator, and quantified the heating effectiveness.

• Journal of Technologic Dentistry
• /
• v.40 no.2
• /
• pp.63-69
• /
• 2018

Purpose: The purpose of this study is to investigate the non-precious metal core materials used in the dental laboratory to fabricate the implant superstructure by CAD / CAM method. And to observe and compare the morphology and distribution of the osteoblasts in relation to implant osseointegration. Methods: In this study, the mandibular right first molar tooth model was selected as an international standard to produce a single core. Using this model, the impression was made with the silicone rubber, the tooth model was scanned, and a single core was designed and 5-axis milling was performed. The materials used were Cobalt-Chromium and Nickel-Chromium, and the cores for dental implant top structures were fabricated according to the procedures of the dental labs. After the fabrication, the marginal area of the core was separated and cell culture experiment was performed. The osteoblast cells used MC3T3-E1, which is currently widely used. For morphological analysis of osteoblasts, cells were posttreated and observed using CLSM (Confocal Laser Scanning Microscope) and compared. Results: The cell adhesion behavior of the specimen surface measured by CLSM was uniformly distributed in specimen A (Cobalt-Chromium) than in specimen B (Nickel-Chromium). The distribution and changes of the cells were different in the two specimens. Conclusion : It is possible to confirm that specimen A (Cobalt-Chromium) is suitable for the living body through adhesion and proliferation of osteoblasts related to implant osseointegration in the non-precious metal superstructure used after implantation. It is considered that it is preferable to use Co-Cr when fabricating the superstructure.

• Journal of Energy Engineering
• /
• v.24 no.3
• /
• pp.89-95
• /
• 2015

Carbon felts manufactured by (Co)CNF were subjected to heat treatment under different temperatures to use for the electrode of a redox-flow battery. BET and weight loss were tested to investigate the physical properties of the carbon felt according to the heat treatment conditions. SEM and XPS were also analyzed to characterize their surface area. In addition, electrical resistance, CV (cyclic voltammetry) and RFB charge on the electrode properties were examined in accordance with the heat treatment conditions with the discharge performance. The changes of physical properties on the carbon felt surface was confirmed via SEM and BET analysis, The most addition of oxygen functional groups on the carbon felt surface was obtained when one hour heat treatment at $550^{\circ}C$ and it was confirmed by XPS analysis. After resulting the CV tests, the active area of the electrode was the largest at $550^{\circ}C$ heat treatment. The heat treatment experiment of vanadium redox flow battery using the carbon felts were tested at $400^{\circ}C$, $500^{\circ}C$ and $550^{\circ}C$. As a result, the charge-discharge energy efficiency of the heat treatment electrode was 72.9% and 79.8%, at $400^{\circ}C$ and $500^{\circ}C$, respectively. The efficiency of the heat treatment electrode at $550^{\circ}C$ was the best as 79.8% at $550^{\circ}C$.

• Journal of the Korea Convergence Society
• /
• v.8 no.9
• /
• pp.199-209
• /
• 2017

This study was carried out to confirm a convergent research pattern and researchers' role in stem cell sector by social network analysis. Articles were extracted from 1996 to 2012 in PubMed, 515 authors of 270 embryonic stem cell and induced pluripotent stem cell articles and 1,515 authors of 580 adult stem cell and mesenchymal stem cell articles. Degree(D) and betweenness(B) centrality was measured and co-author network was generated for researcher's role. As a result, Core researcher and Intermediary researcher was identified in co-author network. Core researcher had high D. centrality, otherwise high B. centrality or not. Intermediary researcher for convergent research had high B. centrality and low D. centrality. Conclusively, co-author network will be used as objective data not only to find core researchers in subject area for improving achievement but also to select experts for research project evaluation.