• Proceedings of the KSME Conference
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• 2007.05a
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• pp.54-59
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• 2007

In order to establish detailed plans for fire protection and reduce the possible fire accidents in the future, a study on the shock wave caused by VCE(Vapor Cloud Explosion) is very important. Destruction phenomena of structure by gas explosion is due to the explosion pressure and heat. Explosion pressure is a kind of energy converted from the gas mixture explosion. Therefore, the propagation progress of shock wave and flame is very important. This study investigated the shock wave caused by VCE in enclosure with opened vent port. From a result, the vent port of top at the straight line of ignition and leak location was opened most rapidly, and the vertical vent port not opened.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.362-364
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• 2010

Shock wave interaction with droplet-gas medium is investigated in this paper. In the present computation, the shock wave is initially started in a pure gas and reflected from the wedge to interact with the droplet-ridden gas flows. We used the compressible two-fluid two-phase model that is solved by the two-fluid version of the HLL scheme. The interfacial drag force and heat transfer were included to model the interaction between continuous and dispersed phases. The parametric effect of void fraction on the shock wave reflection in the two-phase media was investigated.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.214-215
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• 2005

Naval equipments are installed and used for naval vessel with different environmental conditions comparing to the commercial vessel, for example, high engine power per ship displacement size, severe vibration and shock due to high running speed and explosion from naval gun's bombardment and underwater weapons. Therefore, those equipments must be installed on shipboard with small spaces, high ambient temperature around engine room and which are required be fabricated with high resistances of vibration, shock and heat resources. But in case of commercial vessel, the performances of their recent equipments naval have been improved continuously due to the technology development of domestic shipbuilding and shipboard equipment industries, together with the related fundamental industries i.e, metal, steel and electronic industries, to an international level since 1970. With these results, it became possible to unify the specifications of shipboard equipments for the commercial and military vessels(Dual-Use). In this study, vibration and shock test standards for the commercial and military vessels will be compared and reviewed technically.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.45.1-45.1
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• 2011

Shock waves form in the intergalactic medium as a consequence of accretion, merger, and turbulent motion during the structure formation of the universe. They not only heat gas but also govern non-thermal processes through the acceleration of cosmic rays (CRs), production of magnetic fields, and generation of vorticity. We examine diffusive shock acceleration of the pre-existing as well as freshly injected populations of nonthermal, CR particles at weak cosmological shocks. Since the injection is extremely inefficient at weak shocks, the pre-existing CR population dominates over the injected population. If the pressure due to pre-existing CR protons is about 5 % of the gas thermal pressure in the upstream flow, the downstream CR pressure can absorb typically a few to 10 % of the shock ram pressure at shocks with the Mach number M<3. Yet, the re-acceleration of CR electrons can result in a substantial synchrotron emission behind the shock. The implication of our findings for observed bright radio relics is discussed.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.367-373
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. Activation energy is used as parameter as 10, 20, 27 and 35, and the specific heat ratio and the heat release are fixed as 1.2 and 50. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable pitch at Ea=10, periodical unstable pitch at Ea=20 and 27 and unstable pitch consisting of stable, periodical unstable and weak modes at Ea=35, respectively. In the weak mode, there is no Mach leg on the shock front, where the pressure level is much lower than the other modes. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of these stable and unstable modes. In the stable pitch at Ea=10, the maximum pressure history on the tube wall remained nearly constant, and the steady single Mach leg on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the periodical unstable pitch at Ea=20 and 27 of the maximum pressure history. The high frequency was one cycle of a self-induced oscillation by generation and decay in complex Mach interaction due to the variation in intensity of the transverse wave behind the shock front. Eventually, sequential high frequency oscillations formed the low frequency behavior because the frequency behavior was not always the same for each cycle. In unstable pitch at Ea=35, there are stable, periodical unstable and weak modes in one cycle of the low frequency oscillation in the maximum pressure history, and the pressure amplitude of low frequency was much larger than the others. The pressure peak appeared after weak mode, and the stable, periodical unstable and weak modes were sequentially observed with pressure decay. A series of simulations of spinning detonations clarified that the unsteady mechanism behind the shock front depending on the activation energy.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.367-373
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. Activation energy is used as parameter as 10, 20, 27 and 35, and the specific heat ratio and the heat release are fixed as 1.2 and 50. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable pitch at Ea=10, periodical unstable pitch at Ea=20 and 27 and unstable pitch consisting of stable, periodical unstable and weak modes at Ea=35, respectively. In the weak mode, there is no Mach leg on the shock front, where the pressure level is much lower than the other modes. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of these stable and unstable modes. In the stable pitch at Ea=10, the maximum pressure history on the tube wall remained nearly constant, and the steady single Mach leg on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the periodical unstable pitch at Ea=20 and 27 of the maximum pressure history. The high frequency was one cycle of a self-induced oscillation by generation and decay in complex Mach interaction due to the variation in intensity of the transverse wave behind the shock front. Eventually, sequential high frequency oscillations formed the low frequency behavior because the frequency behavior was not always the same for each cycle. In unstable pitch at Ea=35, there are stable, periodical unstable and weak modes in one cycle of the low frequency oscillation in the maximum pressure history, and the pressure amplitude of low frequency was much larger than the others. The pressure peak appeared after weak mode, and the stable, periodical unstable and weak modes were sequentially observed with pressure decay. A series of simulations of spinning detonations clarified that the unsteady mechanism behind the shock front depending on the activation energy.

• Current Research on Agriculture and Life Sciences
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• v.17
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• pp.15-20
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• 1999

To investigate the function of the chloroplast small heat shock protein (small HSP), transgenic tobacco plants (Nicotiana tabacum L., cv. SRI) that show constitutive expression of the chloroplast small HSP were generated. Effects of constitutive expression of the introduced gene on thermotolerance were first probed with the chlorophyll fluorescence. After a 5-min incubation of leaf discs at high temperatures, an increase in the Fo level and a decrease in the Fv level, indications of separation of LHCII from PSII and inactivation of electron transport reactions in PSII, were mitigated by constitutive expression of the small HSP. When tobacco plantlets grown in Petri dishes were incubated at $52^{\circ}C$ for 45 min and subsequently incubated at $25^{\circ}C$, leaf color of nontransformants was gradually became white and all plantlets finally were died. Under conditions in which all nontransformants were dying, more than 80% of the transformants remained green and survived. These results suggest that the chloroplast small HSP plays an important role in protecting photosynthetic machinery during heat stress.

• Journal of Ginseng Research
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• v.43 no.2
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• pp.252-260
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• 2019

Background: Increases in the average global temperature cause heat stress-induced disorders by disrupting homeostasis. Excessive heat stress triggers an imbalance in the immune system; thus protection against heat stress is important to maintain immune homeostasis. Korean ginseng (Panax ginseng Meyer) has been used as a herbal medicine and displays beneficial biological properties. Methods: We investigated the protective effects of Korean ginseng extracts (KGEs) against heat stress in a rat model. Following acclimatization for 1 week, rats were housed at room temperature for 2 weeks and then exposed to heat stress ($40^{\circ}C$/2 h/day) for 4 weeks. Rats were treated with three KGEs from the beginning of the second week to the end of the experiment. Results: Heat stress dramatically increased secretion of inflammatory factors, and this was significantly reduced in the KGE-treated groups. Levels of inflammatory factors such as heat shock protein 70, interleukin 6, inducible nitric oxide synthase, and tumor necrosis factor-alpha were increased in the spleen and muscle upon heat stress. KGEs inhibited these increases by down-regulating heat shock protein 70 and the associated nuclear $factor-{\kappa}B$ and mitogen-activated protein kinase signaling pathways. Consequently, KGEs suppressed activation of T-cells and B-cells. Conclusion: KGEs suppress the immune response upon heat stress and decrease the production of inflammatory cytokines in muscle and spleen. We suggest that KGEs protect against heat stress by inhibiting inflammation and maintaining immune homeostasis.

• Korean Journal of Microbiology
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• v.37 no.3
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• pp.221-227
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• 2001

Heat shock proteins serve as chaperone by preventing the aggregation of denatured proteins and promote survival of pathogens in harsh environments. In bacteria, ethanol shock induced the major chaperone GroEL and DnaK, but in Streptococcus pneumoniae, it induced neither GroEL nor DnaK but alcohol dehydrogenase (ADH). In this study, ADH gene encoding a 104-kDa (p104) protein was identified and characterized. The deduced amino acid sequence of pneumococcal ADH shows homology with other members of the ADH family, and particularly with Entamoeba histolytica ADH2 and E. coli ADH. S. pneumoniae adh is composed of 883 amino acids and its estimated isoelectric point is 6.09. Although ADH is conserved between S. pneumoniae and E. coli, immunoblot analysis employing antisera raised against pneumococcus ADH demonstrated no cross-reactivity with ADH analog in Eschericha coli, Staphylococcus aureus and human HeLa cells. Also secretion of ADH was demonstrated by subcellular fractionation and immunoblot analysis of proteins. These results suggest that S. pneumoniae ADH could be a highly feasible candidate for both diagnostic marker and vaccine.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.951-958
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• 2002

Rapid expansion of a moist air or a stream through a supersonic nozzle often leads to non-equilibrium condensation shock wave, causing a considerable energy loss in flow field. Depending on amount of latent heat released due to non-equilibrium condensation, the flow is highly unstable or a periodical oscillation accompanying the condensation shock wave in the nozzle. The unsteadiness of the condensation shock wave is always associated with several kinds of instabilities as well as noise and vibration of flow devices. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for the purpose of alleviation of the condensation shock oscillations in a transonic nozzle. A droplet growth equation is coupled with two-dimensional Navier-Stokes equation system. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft wind tunnel is made to validate the present computational results. The results show that the oscillations of the condensation shock wave are completely suppressed by the current passive control method.