• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.287-293
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• 1999

Effect of heat-treatment on the microstructure and recrystallization behavior of pure Zr was studied. The specimens were prepared under the various annealing temperatures from $400^{\circ}C$ to $800^{\circ}C$ and times from 300 to 5000 minutes after vacuum arc remelting. The recrystallization behavior was observed by a polarized optical microscope, TEM and micro-vickers hardness tester. With increasing the annealing time, the temperature region of hardness drop moved to the lower temperature region due to the recovery and recrystallization behaviors at the lower temperature. The recrystallization of cold-worked pure Zr was completed between 450 and $600^{\circ}C$. The size of recrystallized grain increased at $700^{\circ}C$ for 600min. Activation energy(Q) of pure Zr measured by the time for constant fraction technique was 78 KJ/mol.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.1-10
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• 2016

For the active control of a combustion instability, a change should be made in pressure fluctuation or heat release fluctuation using an acoustic driver or a secondary fuel injection. Also, to determine the location and timing of a secondary fuel injection, one needs to know the distribution of heat release fluctuation under combustion instability. In the present research, the distribution of heat release fluctuation has been experimentally measured by changing hydrocarbon fuel, inlet velocity, equivalence ratio, and acoustic forcing condition. It was confirmed that heat release fluctuation with regards to vortex shedding was significantly affected by the $Damk{\ddot{o}}hler$ number. Under the cases of the $Damk{\ddot{o}}hler$ number above approximately 4 - 5, hot spot region was generated in the leading edge of vortex and cold spot region was in the trailing edge. On the contrary, the cases of the $Damk{\ddot{o}}hler$ number below 3 showed the opposite trend.

• Journal of Environmental Science International
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• v.12 no.5
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• pp.521-527
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• 2003

To study the intruded phenomena of North Pacific Ocean around Boso peninsular, water property distribution in the adjacent seas to Japan is studied using the hydrographic data obtained by Japan Maritime Agency and Japan Fisheries Agency from 1973 to 1996, The scattering of water type in T-5 diagram is relatively small in the Kuroshio Region. Both the envelopes of saline side and of fresh side of the scattered data points shifts gradually from saline side to fresh side as the observation Line moves from southwest to northeast. In mixed water region, the scattering of water type increases rapidly as the observation line moves north; the envelope of fresh cold side moves towards fresh cold side much faster than that of saline side. This suggests that the water does not advect along the salinity minimum layer, but the salinity minimum layer can be understood as a boundary of two different waters aligned vertically, We defined the typical water masses as the Oyashio Water and the Kuroshio Water. The water mass below the salinity minimum layer may be created by isopycnal mixing of these two water masses with a fixed mixing rate. While the water mass above the salinity minimum cannot be created simply by isopycnal mixing. The salinity minimum layer may be eroded from upper side due to active minxing processes in the surface layer, while the water of the salinity minimum layer moves gradually southward. This appears to give an explanation why the thermosteric anomaly value at salinity minimun decereases towards south.

• Journal of the Korean GEO-environmental Society
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• v.18 no.11
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• pp.35-40
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• 2017

The rearside of concrete lining of tunnels constructed in cold region might experience on freezing due to the low temperature. This causes damage of concrete lining resulting in adverse affect on the durability as well as integrity of tunnel structure by causing damage to the concrete lining. In order to prevent the rearside of tunnel lining from freeing, the temperature change inside the concrete lining was measured by attaching a heating element to the tunnel lining surface and generating heat for a certain period of time. A special freezing chamber was developed to conduct the experiments considering in-situ environment. The carbone nanotube (CNT) was used as a heating element in this study. The temperature distribution of the concrete lining was measured by applying the heat to the heating element. The effect of the outside temperature and heating duration were analyzed.

• Korean Journal of Materials Research
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• v.33 no.11
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• pp.439-446
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• 2023

Changes in the microstructure and mechanical properties of as-roll-bonded AA6061/AA5052/AA1050 three-layered sheet with increasing annealing temperature were investigated in detail. The commercial AA6061, AA5052 and AA1050 sheets with 2 mm thickness were roll-bonded by multi-pass rolling at ambient temperature. The roll-bonded Al sheets were then annealed for 1 h at various temperatures from 200 to 400 ℃. The specimens annealed up to 250 ℃ showed a typical deformation structure where the grains are elongated in the rolling direction in all regions. However, after annealing at 300 ℃, while AA6061 and AA1050 regions still retained the deformation structure, but AA5052 region changed into complete recrystallization. For all the annealed materials, the fraction of high angle grain boundaries was lower than that of low angle grain boundaries. In addition, while the rolling texture of the {110}<112> and {123}<634> components strongly developed in the AA6061 and AA1050 regions, in the AA5052 region the recrystallization texture of the {100}<001> component developed. After annealing at 350 ℃ the recrystallization texture developed in all regions. The as-rolled material exhibited a relatively high tensile strength of 282 MPa and elongation of 18 %. However, the tensile strength decreased and the elongation increased gradually with the increase in annealing temperature. The changes in mechanical properties with increasing annealing temperature were compared with those of other three-layered Al sheets fabricated in previous studies.

• Journal of the Semiconductor & Display Technology
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• v.6 no.3
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• pp.47-53
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• 2007

Ultra thin Si p-n junctions shallower than $300{\AA}$ were fabricated and biased to the avalanche regime. The ultra thin junctions were fabricated to be parallel to the surface and exposed to the surface without $SiO_2$ layer. Those junctions emitted white light and electrons when junctions were biased in the avalanche breakdown regime. Therefore, we could observe the avalanche breakdown region visually. We could also observe the influence of electric field to the current flow visually by observing the white light which correspond to the avalanche breakdown region. Arrayed diodes emit light and electrons uniformly at the diode area. But, the reverse leakage current were larger than those of ordinary diodes, and the breakdown voltage were less than 10V.

• Journal of the Korean GEO-environmental Society
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• v.20 no.4
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• pp.11-16
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• 2019

The low temperature and temperature difference (variation) may cause to deteriorate the integrity of tunnel constructed in cold region. An insulation material was developed and applied to the tunnel lining surface to keep the temperature of tunnel lining constant in spite of temperature variation at outdoor. The lining surface where the insulation material applied showed the less sensitive to temperature variation than non-applied lining surface.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.8
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• pp.63-72
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• 1995

Closed-die forging of spur gears with hollow cylindrical billet has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent the forging die profile. In the analysis, the deformation region has been divided into nine zones. A constant frictional stress has been assumed on the contacting surfaces. Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth and friction factor, on the forging of spur gears. Hardness and accuracy of forged gears are measured. The following results have been obtained: (1) It is verified that an axisymmetric deformation zone exists between root circle and center of gear through forged gears. (2) The average relative forging pressure is predominantly dependent on the number of teeth and increases near the final filling stage as the addendum modification coefficient increases. (3) Close agreement was found between the predicted values of forging load and those obtained from experimental results.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2007.11a
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• pp.558-561
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• 2007

In this paper, non working day for the construction project in Cheongju and Chungju region considering weather condition was estimated. In Cheongju region, non working day for outside and half outside work was 157days and for interior work 144days. For Chungju region, non working day for outside and half outside work was 160days and for interior work 144days. Non working day affected by temperature was 144 days at both Chungju and Cheongju. Non working day due to low temperature was 109 days and it due to high temperature was 45 days for Choengju. In Chungju, it was 11Sdays for cold weather, while it due to hot weather was 29 days.Non working day due to rainfall was 23 days at both region. To reduce the deviation between estimated non working days and measured ones, proper selection of the duration is required.

• Journal of Appropriate Technology
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• v.6 no.2
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• pp.94-102
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• 2020

Renewable energy (RE) is essential to comprise sustainable societies, especially, in rural villages of developing countries. Furthermore, application of off-grid RE systems to health care can improve the quality of life. In this research, a RE-based vaccination supply management system was constructed to enlarge the cold-chain in developing countries for the safe storage and delivery of vaccines. The system was comprised of the construction of RE plants and development of vaccine carriers. RE plants were constructed and connected to health posts in local villages. The cooling mechanism of vaccine carriers was improved and monitoring devices were installed. The effect of the system on vaccine cold-chain was evaluated from the field test and topographical analysis in the southern village of Nepal. RE plants were normally operated for the vaccine refrigerator in the health post. The modified vaccine carriers had a longer operation time and better temperature control via monitoring and RE-based recharging functionality. The topographical analysis estimated that the system can cover larger region. The system prototype showed great potential regarding the possibility of a sustainable and enlarged cold-chain. Thus, RE-based vaccine supply management is expected to facilitate vaccine availability while minimizing waste in the supply chain.