• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.92-95
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• 2011

In manufacturing optical fibers, the process starts with the glass fiber drawing from the heated and softened silica preform in the furnace, and the freshly drawn glass fiber is still at high temperature when it leaves the glass fiber drawing furnace. It is necessary to cool down the glass fiber to the ambient temperature before it then enters the fiber coating applicator, since the hot glass fiber is known to cause several technical difficulties in achieving high quality fiber coating. As the fiber drawing speed keeps increasing, a current manufacturing of optical fibers requires a dedicated cooling unit with helium gas injection. A series of three-dimensional flow and heat transfer computations are carried out to investigate the effectiveness of fiber cooling in the fiber cooling unit. The glass fiber cooling unit is simplified into the long cylindrical enclosure at which the hot glass fiber passes through at high speed, and the helium is being supplied through several injection slots of rectangular shape along the cooling unit. This study presents and discusses the effects of helium injection rates on the glass fiber cooling rates.

• Journal of Mechanical Science and Technology
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• 제14권7호
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• pp.715-721
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• 2000

Residual stress is one of the causes which makes defects in engineering components and materials. These residual stresses can occur in many engineering structures and can sometimes lead to premature failures. There are commonly used methods by which residual stresses are currently measured. But these methods have a little damage and other problems; therefore, a new experimental technique has been devised to measure residual stress in materials with a combination of electronic laser interferometry, laser heating and finite element method. The electronic laser interferometer measures in-plane deformations while the laser heating and cooling provides for very localized stress relief. FEM is used for determining the heat temperature and other parameters. The residual stresses are determined by the amount of strain that is measured subsequent to the heat-up and cool-down of the region being interrogated. A simple model is presented to provide a description of the method. In this paper, the ambiguity problem for the fringe patterns has solved by a phase shifting method.

• Progress in Superconductivity
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• 제12권1호
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• pp.57-61
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• 2010

We have developed a whole-head MEG system for basic brain research and clinical application. The sensor system consists of a 152 SQUID gradiometer array oriented and located in a suitable way to cover a whole head of the human. The system measures magnetic fields generated by neuronal currents in the brain to get information on the brain activities. For this purpose, the field sensitivity determined by the position, orientation and geometry of the pickup coil as well as amplification factor of the electronic circuits should be known precisely. However, the position and orientation of the pickup coil might be changed from the designed specifications during cool down of the dewar and it is necessary to characterize the field sensitivity. In this study, we made calibration systems to determine the actual position and orientation of the 152 pickup coils and compared the localization results of the N100m source in the auditory cortex.

• 대한물리의학회지
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• 제13권2호
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• pp.157-165
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• 2018

PURPOSE: The purpose of this study was carried out to investigate the effect of plyometric training combined with core strength training on the balance and agility of adolescent soccer players. METHODS: A total of 36 subjects participated in this study. Subjects were randomly divided 3 groups and assigned PG (plyometric training group), CSG (core strength training group) and PCG (plyometric training combined with core strength training group). Each group was assigned to 12. Intervention was performed three times a week for 4 weeks. The training was performed for 60 minutes a day. Subjects were warmed up for 10 minutes, and performed main exercise for 40 minutes. Finally, subjects performed cool-down exercise including stretching for 10 minutes. A Statistical analysis was performed the paired t-test for the comparison pre and post intervention. A comparison among the groups was using one-way ANOVA, and the LSD was used for the post-test. RESULTS: The balance and agility were statistically significant differences in all group (p<.05). There was no significant difference in the balance factors between the three groups, but there was a significant difference in the agility factor (p<.05). CONCLUSION: Plyometric training and plyometric training combined with core strength training were effective for the balance and agility of adolescent soccer players.

• 설비공학논문집
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• 제15권3호
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• pp.239-245
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• 2003

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. $textsc{k}$-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of the main flow in the duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from the main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

• 한국정밀공학회지
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• 제26권10호
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• pp.81-88
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• 2009

Bellows is used to control temperature of a Joule-Thomson micro cryocooler. It is made of Nickelcobalt alloy that retains mechanical properties from cryogenic temperature to temperature of 570K. The geometry of bellows is an axisymmetric shell and Nitrogen with high pressure was charged at temperature of 293K. During cool-down process, the pressure and volume of Nitrogen are changed and must be satisfied with state equation. At cryogenic temperature, Nitrogen can exist as a part liquid and part vapor. Pressure-density-temperature behavior under this vaporliquid phase equilibrium is closely given by the Modified-Benedict-Webb-Rubin(MBWR) state equation. To evaluate deformation of bellows for temperature change, the numerical calculation of the volume within bellows and finite element analysis of bellows under internal pressure were iteratively performed until MBWR state equation is satisfied. The numerical results show that deformation of the bellows can be analyzed by the present method in a wide range of temperature including cryogenic temperature.

• Journal of Dairy Science and Biotechnology
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• 제18권1호
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• pp.38-46
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• 2000

Since generalization of cold storage of raw and processed milk, psychrotrophic bacteria has become more important. The number present in raw milk is related to sanitary conditions during pro-duction and to length and temperature of storage before pasteurization. Growth of psychrotrophs In raw milk often reduces the quality of pasteurized products. Recently, some pathogenic bacteria like Listeria monocytogenes, Yersinia enterocolitica, Bacillus cereus are reported to grow at low temperature and cause food poisoning. The presence of gram positive psychrotrophic bacteria which can survive pasteurization can limit the shelf life of pasteurized milk during extended storage and the survival of heat stable proteases and lipases produced by gram negative psychrotrophic bacteria often brings about proteolytic damage to milk protein in the products. Therefore, in order to prevent the deteorioration of milk and milk products by the growth of psychrotrophs, it is necessary to cool down the temperature of raw milk as soon as possible after milking and to keep the temperature below 5t during storage at farm. As psychrotrophic bacteria become readily predominant in raw milk under refregeration, it can be considered to change the traditional incubating temperature for SPC from 30${\sim}$32$^{\circ}C$ to 25${\sim}$27$^{\circ}C$ at which the psychrotrophs prefer to grow. The psychrotrophic bacterial count(PBC) is of limited use in dairy industry, because of the 10 days incubation period. Although estimates of psychrotrophic bacteria may provide an acceptable shelf-life prediction, there is no single, generally acceptable rapid method for replacing the PBC at the moment. Consequently, faster method for esmating psychrotrophic bacteria has to be developed.

• 생명과학회지
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• 제14권4호
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• pp.573-576
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• 2004

The purpose of the present study is to investigate the lipid peroxidation, creatine kinase activity and cortisol hormone levels following the training intensity in elite judo players. Six elite Judo players participated in the experiments (3h repetition judo program), which include stretching, judo skill practice and cool down without recess. Blood sampling were taken at the judo gymnasium at the time of resting, 1h training, 2h training, 3h training, 2h recovery, and 24h recovery time and this were analyzed for CK, MDA and Cortisol levels. The results obtained were analyzed via repeated measures of ANOVA using SPSS package program (ver.10.0) and a value of p<.05 was considered statistically significant. The results from this study were as follows. In the CK levels, which reflect the contribution of creatine phosphate and muscle damage degree, there was a significant difference (p<.05) after judo training in every period. Recovery 24h showed the highest level. In the MDA levels, which reflect lipid peroxidation, there was a significant difference (p<.05) after judo training. Recovery 2h showed the lowest level. In the cortisol hormone levels, which reflect stress status, there was a significant difference (p<.05). In this study, we can conclude that For the trained athletes, MDA level was lower at the time of exercise compare to the other period, this is caused by the increased antioxidant defence mechanism.

• 수산해양교육연구
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• 제26권3호
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• pp.525-534
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• 2014

This study has examined the effect of after-school physical activity on body composition and health related fitness of middle school students. The duration of after-school physical activity training program of this study is 12 weeks, the training time in 1 hours warming-up 10 minutes, the skill training 45 minutes and cool down did in 5 minutes. Exercise frequency is 5 time per week. Height basketball class, soccer class, subject class showed statistically meaningful increase between group variance showed statistically meaningful. Weight basketball class, soccer class, showed statistically meaningful decrease. Muscle mass basketball class showed statistically meaningful increase, soccer class showed statistically meaningful decrease. Cardiopulmonary basketball class, soccer class, showed statistically meaningful decrease. Explosive muscular strength basketball class, soccer class, showed statistically meaningful decrease. subject class showed statistically meaningful increase, between group variance showed statistically meaningful. Flexibility basketball class showed statistically meaningful increase, soccer class. Muscular strength basketball class, soccer class, subject class showed not statistically meaningful different.

• 설비공학논문집
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• 제5권3호
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• pp.198-206
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• 1993

Experimental results of two stage Gifford-McMahon cryorefrigerator are described. In-prototype experiments, drive mechanism is Scotch Yoke type driven by stepping motor, copper meshes and lead balls are used for regenerator's materials in the first stage and the second stage, respectively. To find optimal conditions of the cryopump, no load temperature and refrigeration capacity according to the variation of cycle frequency and operating pressure are measured, and the cool down and load characteristics at particular cycle frequencies are presented. In general, as the cycle frequency is lowered, no load temperature is dropped but refrigeration capacity is diminished. As the representative result, in a case that the cycle frequency is 70rpm and steady state pressure is 14 atm, no load temperature of second stage is lowered to 10.5K in 55 minuters, and in this situation the refrigeration capacity of the first stage is 42W at 80K, that of the second stage is 11 W at 20K.