• The Korean Journal of Ecology
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• v.25 no.2
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• pp.93-100
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• 2002

In order to analyze the life cycle of A. artemisiifolia var. elation dormancy and some environmental factors inducing germination of the seeds were examined. The results were as follows : Dormancy of fertile seeds was broken in part within a month after seed collection in case of adequate moisture and alternating temperature was also effective in breaking dormancy. The temperature range, which allow germination was 12℃ ∼ 32℃. Optimum temperature for germination was 24℃. The seed of A. artemisiifolia var. elatior was light-independent. The difference of storage period appeared to have no particular effect on the viability of seeds at any time during the 9-month storage period. In the increasing temperature(IT) regime, A artemisiifolia var. elatior seeds started to germinate at 16℃, showing the higher temperature the greater germination rate, the final germination percentage was 99.34%. On the other hand, in the decresing temperature(DT) regime, seeds began to germinate at 20℃ with the 1.34% germination. An induced dormancy occurred at 12℃ making the 5.34% fecal germination in the DT regime. Low temperature was more effective to break dormancy than higher temperature Seeds of A. artemisiifolia var. elatior seems to be germinated in mid to late autumn or germination delayed until following spring. The above results suggest these variation of germination response in diverse environmental factors seems to be a physiological strategy to maintain their existence and to reproduce in the extreme thermal variation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.1049-1061
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• 2013

In this paper, a relative heat exchange rate is numerically compared for cast-in-place concrete energy piles with different heat exchange pipe configurations, and a new design method for energy piles is proposed. An equivalent heat exchange rate was estimated for the W-type (one series loop), multiple U-type (four parallel loops), and coil-type heat exchanger installed in the same large-diameter drilled shaft. In order to simulate a cooling operation in summer by a CFD analysis, the LWT (leaving water temperature) into a energy pile was fixed at $35^{\circ}C$ and then the EWT (entering water temperature) into a heat pump was monitored. In case of continuously applying the artificial maximum cooling load for 100 hours, all of the three types of heat exchangers show the marginally similar heat exchange rate. However, in case of intermittently applying the cooling load with a cycle of 8 hours operation-16 hours off for 7 consecutive days, the coil type heat exchanger exhibits a heat exchange rate only 86 % of the multiple U-type due to measurable thermal interference between pipe loops in the energy pile. On the other hand, the W-type possesses the similar heat exchange rate to the multiple U-type. The equivalent heat exchange rates for each configuration of heat exchangers obtained from the CFD analysis were adopted for implementing the commercial design program (PILESIM2). Finally, a design method for cast-in-place concrete energy piles is proposed along with a design chart in consideration of typical design factors.

• Tunnel and Underground Space
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• v.21 no.6
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• pp.518-525
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• 2011

In this study, the natural ventilation pressure resulting from the large altitude difference which is a characteristic of high radioactive waste repository and the caloric value of the heat emitted by wastes was calculated and based on the results, natural ventilation quantities were calculated. A high radioactive waste repository can be considered as being operated through closed cycle thermodynamic processes similar to those of thermal engines. The heat produced by the heating of high radioactive wastes in the underground repository is added to the surrounding air, and the air goes up through the upcast vertical shaft due to the added heat while working on its surroundings. Part of the heat added by the work done by the air can be temporarily changed into mechanical energy to promote the air flow. Therefore, if a sustained and powerful heat source exists in the repository, the heat source will naturally enable continued cyclic flows of air. Based on this assumption, the quantity of natural ventilation made during the disposal of high radioactive wastes in a deep geological layer was mathematically calculated and based on the results, natural ventilation pressure of $74{\sim}183$Pa made by the stack effect was identified along with the resultant natural ventilation quantity of $92.5{\sim}147.7m^3/s$. The result of an analysis by CFD was $82{\sim}143m^3/s$ which was very similar to the results obtained by the mathematical method.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.9 no.4
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• pp.237-245
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• 2011

As necessity of safety re-evaluation for spent fuel storage facility has emphasized after the Fukushima accident, accuracy improvement of heat load evaluation has become more important to acquire reliable thermal-hydraulic evaluation results. As groundwork, parametric and sensitivity analyses of various storage conditions for Kori Unit 4 spent fuel storage pool and spent fuel depletion parameters such as axial burnup effect, operation history, and specific heat are conducted using ORIGEN2 code. According to heat load evaluation and parametric sensitivity analyses, decay heat of last discharged fuel comprises maximum 80.42% of total heat load of storage facility and there is a negative correlation between effect of depletion parameters and cooling period. It is determined that specific heat is most influential parameter and operation history is secondly influential parameter. And decay heat of just discharged fuel is varied from 0.34 to 1.66 times of average value and decay heat of 1 year cooled fuel is varied from 0.55 to 1.37 times of average value in accordance with change of specific power. Namely depletion parameters can cause large variation in decay heat calculation of short-term cooled fuel. Therefore application of real operation data instead of user selection value is needed to improve evaluation accuracy. It is expected that these results could be used to improve accuracy of heat load assessment and evaluate uncertainty of calculated heat load.

• Korean Journal of Materials Research
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• v.25 no.5
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• pp.226-232
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• 2015

High temperature plasma coating technology has been applied to recover damaged aluminum dies from wear by spraying pure aluminum and alumina powder. However, the coated mixed powder layer composed of aluminum and alumina often undergoes a detachment from the substrate, making the coated substrate die unable to maintain its expected life span. In this study, in order to increase the bonding strength between the substrate and the coating layer, a pure aluminum layer was applied as an intermediate bond layer. In order to prepare the specimen with variable bond coating conditions, the bond coat layers with a various gun speed from 10 cm/sec to 30 cm/sec were prepared with coating cycle variations ranging from three to nine cycles. The specimen with a bond coat layer coated with a gun speed of 20 cm/sec and three coating cycles exhibited ~13MPa of adhesion strength, while the specimen without a bond coat layer showed ~6 MPa of adhesion strength. The adhesion strength with a variation of bond coat layer thickness is discussed in terms of coating parameters.

• Applied Chemistry for Engineering
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• v.28 no.5
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• pp.534-538
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• 2017

In this study, the molecular weight controlled pitches derived from pyrolyzed fuel oil (PFO) were prepared using solvent extraction and were carbonized. Electrochemical characteristics of lithium battery anode materials were investigated using these petroleum pitches. Three pitch samples prepared by the thermal reaction were 3903 (at $390^{\circ}C$ for 3 h), 4001 (at $400^{\circ}C$ for 1 h) and 4002 (at $400^{\circ}C$ for 2 h). The prepared hexane insoluble pitches were analysed by XRD, TGA, SEM and Gel permeation Chromatography (GPC). The electrochemical characteristics of the PFO-derived pitch as an anode material were investigated by constant current charge/discharge, cyclic voltammetry and electrochemical impedance tests. The coin cell using pitch (4001) and the electrolyte of $LiPF_6$ in organic solvents (EC : DMC = 1 : 1 vol%, VC 3 wt%) has better initial capacity (310 mAh/g) than that of other pitch coin cells. Also, this carbon anode showd a high initial efficiency of 82%, retention rate capability at 2 C/0.1 C of 90% and cycle retention of 85%. It was found that modified pitches improved the cycling and rate capacity performance.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.3
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• pp.304-311
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• 2014

In this study, to apply hydrogen energy to ship engine and to generate effective hydrogen production, we investigated the effects of high temperature $H_2SO_4$ feed rate and cooling water rate to pump parts with fixed frequency needed to reciprocate motion and a simulation was conducted at each condition. In the fixed frequency and cooling water inlet flow rate of 0.5 Hz and 3.9 kg/s, we changed the high temperature $H_2SO_4$ flow rate to 47.46 kg/s (it is 105 % of 45.2 kg/s), 49.72 kg/s (110 %), and 51.98 kg/s (115 %). Also, at 0.5 Hz and 45.2 kg/s of frequency and high temperature $H_2SO_4$ flow, the thermal hydraulic analysis was performed at the condition of 95 % (3.705 kg/s), 90 % (3.51 kg/s), and 85 % (3.315 kg/s). In overall simulation cases, the physical properties of materials are more influential to the temperature increase in the pump part rather than the changes on the feed rate of high temperature $H_2SO_4$ and cooling water. A continuous operation of pump was also capable even if the excess feed of high temperature $H_2SO_4$ of about 15 % or the less feed of cooling water of about 15 % were performed, respectively. When the increasing feed of high temperature $H_2SO_4$ of up to 5 %, 10 %, and 15 % were compared with base flow (45.2 kg/s), the deviation of time period rose to a certain temperature and ranged from 0 to 4.5 s in the same position (same material). In case of cooling water, the deviation of time period rose to a certain temperature and ranged from 0 to 5.9 s according to the decreasing feed changes of cooling water at 5 %, 10 %, and 15 % compared to a base flow (3.9 kg/s). Finally, the additional researches related to the two different materials (Teflon and STS for Pitch and End-plate), which are concerned about the effects of temperature changes to the parts contacting different materials, are needed, and we have a plan to conduct a follow-up study.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.3
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• pp.239-256
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• 2017

In the process of site selection for a radioactive waste disposal, site characterization must be carried out to obtain input parameters to assess the safety and feasibility of deep geological repository. In this paper, methodologies of site characterization for radioactive waste disposal in Korea were suggested based on foreign cases of site characterization. The IAEA recommends that site characterization for radioactive waste disposal should be performed through stepwise processes, in which the site characterization period is divided into preliminary and detailed stages, in sequence. This methodology was followed by several foreign countries for their geological disposal programs. General properties related to geological environments were obtained at the preliminary site characterization stage; more detailed site characteristics were investigated during the detailed site characterization stage. The results of investigation of geology, hydro-geology, geochemistry, rock mechanics, solute transport and thermal properties at a site have to be combined and constructed in the form of a site descriptive model. Based on this site descriptive model, the site characteristics can be evaluated to assess suitability of site for radioactive waste disposal. According to foreign site characterization cases, 7 or 8 years are expected to be needed for site characterization; however, the time required may increase if the no proper national strategy is provided.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.1
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• pp.33-38
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• 2007

We studied a bonding at low temperature using polymer bump and Non-Conductive Adhesive (NCA), and studied the reliability of the polymer bump/Al pad joints. The polymer bumps were formed on oxidized Si substrates by photolithography process, and the thin film metals were formed on the polymer bumps using DC magnetron sputtering. The substrate used was AL metallized glass. The polymer bump and Al metallized glass substrates were joined together at $80^{\circ}C$ under various pressure. Two NCAs were applied during joining. Thermal cycling test ($0^{\circ}C-55^{\circ}C$, cycle/30 min) was carried out up to 2000 cycles to evaluate the reliability of the joints. The bondability was evaluated by measuring the contact resistance of the joints through the four point probe method, and the joints were observed by Scanning Electron Microscope (SEM). The contact resistance of the joints was $70-90m{\Omega}$ before the reliability test. The joints of the polymer bump/Al pad were damaged by NCA filler particles under pressure above 200 MPa. After reliability test, some joints were electrically failed since thinner metal layers deposited at the edge of bumps were disconnected.

• Journal of the Korean Society of Food Science and Nutrition
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• v.30 no.6
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• pp.1095-1101
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• 2001

Spinach was minimally processed into the unseasoned side dish to be used for Korean food service industry, using the techniques of cook-chill and sous vide. Spinach was blanched at 10$0^{\circ}C$ for 6 minutes, vacuum-packaged in the unit of 500 g by plastic film of low gas permeability, pasteurized at 9$0^{\circ}C$ and then cooled rapidly at 3$^{\circ}C$. The chilled products were then stored at 3 and 1$0^{\circ}C$ with measurement in their quality. Six log cycle (6D) inactivation of Listeria monocytogenes and 13 log (13D) thermal destruction of Streptococcus faecalis were compared as two pasteurization conditions, which corresponded to heating for 22.8 and 30.0 minutes at 9$0^{\circ}C$, respectively. Milder heat processing based on 6D process of L monocytogenes gave better quality of color, texture, ascorbic acid and chlorophyll than the conditions of 13D process of S. faecalis. Any microbial growth in total aerobic, psychrophilic and anaerobic bacteria was not observed until 8 days at 1$0^{\circ}C$ and 14 days at 3$^{\circ}C$, which might be regarded as strict guidelines of shelf life. Storage times based on the changes in physical and chemical quality were longer than those based on strict microbial quality in case of the products pasteurized by 6D process of L. monocytogenes. The seasoned vegetables prepared from sous vide processed spinach were found to be inferior in sensory quality to those from freshly blanched one.