• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.1
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• pp.47-60
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• 2021

Hydrogen is a next-generation energy source, and according to the roadmap for activating the hydrogen economy, it is expected that industries to stably produce, store, and transport of hydrogen as well as the supply of hydrogen fuel cell vehicles will be made rapidly. Accordingly, safety measures for accidents of hydrogen vehicles in confined spaces such as tunnels are required. In this study, as part of a study to ensure the safety of hydrogen fuel cell vehicles in road tunnels, a basic investigation and research on the risk of fire and explosion due to gas leakage and hydrogen tank rupture among various hazards caused by hydrogen fuel cell vehicle accidents in tunnels was conducted. The following results were obtained. In the event of hydrogen fuel cell vehicle accidents, the gas release rate depends on the orifice diameter of TPRD, and when the gas is ignited, the maximum heat release rate reaches 3.22~51.36 MW (orifice diameter: 1~4 mm) depending on the orifice diameter but the duration times are short. Therefore, it was analyzed that there was little increase in risk due to fire. As the overpressure of the gas explosion was calculated by the equivalent TNT method, in the case of yield of VCE of 0.2 is applied, the safety threshold distance is analyzed to be about 35 m, and number of the equivalent fatalities are conservatively predicted to reach tens of people.

• Animal Bioscience
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• v.37 no.5
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• pp.896-907
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• 2024

Objective: The potential of aqueous extract of Christ's thorn jujube (Ziziphus spina-christi) leaves (SLAE) to reduce the negative impacts of heat stress on production performance and physiological traits was investigated in dual-purpose layers under subtropical farming. Methods: A total of 200, 25-week-old laying hens (Inshas strain) were randomly assigned to four dietary treatments including SLAE at 0, 2.5, 5.0, and 7.5 mL/kg, respectively. The average temperature-humidity index value was 26.69 during the experimental period. The SLAE contained saponin (0.045%), total flavonoid content of 17.9 mg of quercetin equivalent/100 g and overall antioxidant capacity concentration of 17.9 mg of ascorbic acid equivalent/100 g. Results: The maximum final body weight (BW), BW gain, egg weight, number, and mass occurred at the level of SLAE7.5 inclusion. The egg quality was significantly higher in SLAE groups than in control, and overall, SLAE7.5 had the most favorable influence at 28 and 32 weeks. Liver and kidney function, as well as lipids profile, improved significantly by SLAE inclusion; the lowest concentrations of these parameters were in SLAE7.5 hens. Treatment with SLAE7.5 increased total antioxidant capacity and endogenous antioxidant enzymes compared to control, whereas no effect on superoxide dismutase was noticed. Conclusion: The addition of SLAE at 7.5 mL/kg diet improved egg laying performance and quality, metabolic profiles, and antioxidant status during hyperthermia conditions.

• Journal of Biosystems Engineering
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• v.43 no.1
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• pp.21-29
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• 2018

Purpose: The objective of this study is to evaluate the performance of the conical solar concentrator (CSC) system, whose design is focused on increasing its collecting efficiency by determining the optimal conical angle through a theoretical study. Methods: The design and thermal performance analysis of a solar concentrator system based on a $45^{\circ}$ conical concentrator were conducted utilizing different mass flow rates. For an accurate comparison of these flow rates, three equivalent systems were tested under the same operating conditions, such as the incident direct solar radiation, and ambient and inlet temperatures. In order to minimize heat loss, the optimal double tube absorber length was selected by considering the law of reflection. A series of experiments utilizing water as operating fluid and two-axis solar tracking systems were performed under a clear or cloudless sky. Results: The analysis results of the CSC system according to varying mass flow rates showed that the collecting efficiency tended to increase as the flow rate increased. However, the collecting efficiency decreased as the flow rate increased beyond the optimal value. In order to optimize the collecting efficiency, the conical angle, which is a design factor of CSC, was selected to be $45^{\circ}$ because its use theoretically yielded a low heat loss. The collecting efficiency was observed to be lowest at 0.03 kg/s and highest at 0.06 kg/s. All efficiencies were reduced over time because of variations in ambient and inlet temperatures throughout the day. The maximum efficiency calculated at an optimum flow rate of 0.06 kg/s was 85%, which is higher than those of the other flow rates. Conclusions: It was reasonable to set the conical angle and mass flow rate to achieve the maximum CSC system efficiency in this study at $45^{\circ}$ and 0.06 kg/s, respectively.

• Economic and Environmental Geology
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• v.39 no.5 s.180
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• pp.607-613
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• 2006

For the reasonable use of low grade-shallow geothermal energy by Standing Column Well(SCW) system, the basic requirements are depth-wise increase of earth temperature like $2^{\circ}C$ per every 100m depth, sufficient amount of groundwater production being about 10 to 30% of the design flow rate of GSHP with good water quality and moderate temperature, and non-collapsing of borehole wall during reinjection of circulating water into the SCW. A closed loop type-vertical ground heat exchanger(GHEX) with $100{\sim}150m$ deep can supply geothermal energy of 2 to 3 RT but a SCW with $400{\sim}500m$ deep can provide $30{\sim}40RT$ being equivalent to 10 to 15 numbers of GHEX as well requires smaller space. Being considered as an alternative of vertical GHEX, many numbers of SCW have been widely constructed in whole country without any account for site specific hydrogeologic and geothermal characteristics. When those are designed and constructed under the base of insufficient knowledges of hydrgeothermal properties of the relevant specific site as our current situations, a bad reputation will be created and it will hamper a rational utilization of geothermal energy using SCW in the near future. This paper is prepared for providing a guideline of SCW design comportable to our hydrogeothermal system.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.305-313
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• 2003

The setting and hardening of concrete is accompanied with nonlinear temperature distribution caused by development of hydration heat of cement. Especially at early ages, this nonlinear distribution has a large influence on the crack evolution. As a result, in order to predict the exact temperature history in concrete structures it is required to examine thermal properties of concrete. In this study, the coefficient of air convection, which presents thermal transfer between surface of concrete and air, was experimentally investigated with variables such as velocity of wind and types of form. From experimental results, the coefficient of air convection was calculated using equations of thermal equilibrium. Finally, the prediction model for equivalent coefficient of air convection including effects of velocity of wind and types of form was theoretically proposed. The coefficient of air convection in the proposed model increases with velocity of wind, and its dependance on wind velocity is varied with types of form. This tendency is due to a combined heat transfer system of conduction through form and convection to air. From comparison with experimental results, the coefficient of air convection by this model was well agreed with those by experimental results.

• Polymer(Korea)
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• v.39 no.3
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• pp.499-505
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• 2015

Polyorganosiloxane having controlled cross-linking density and phenyl group content were prepared by dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS) and phenyltrimethoxysilane (PTMS). The effect of cross-linking density and phenyl group content on the physical properties of siloxane resin and its coated film have been invetigated. Si-NMR results confirmed that synthesized siloxane resins have equivalent D $T^{Me}$ $T^{Ph}$ structures according to applied mole ratios of DMDMS, MTMS and PTMS. Polyorganosiloxane having higher cross-linking density with high phenyl content showed the high molecular weight and increasing phenyl content resulted in higher refractive index as well as better thermal stability. Cross-linking density is more important factor than phenyl content to obtain higher pencil hardness of coated film on the glass. Our results concluded that even polyorganosiloxanes having similar siloxane structures show different physical properties as function of cross-linking density and phenyl content in polyorganosiloxane.

• Journal of Energy Engineering
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• v.20 no.1
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• pp.1-7
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• 2011

The performance and life-cycle costs of electric vehicle(EV) and hybrid electric vehicle(HEV) depend inherently on battery packs. Temperature uniformity in a pack is an important factor for obtaining optimum performance for an EV or HEV battery pack, because uneven temperature distribution in a pack leads to electrically unbalanced battery cells and reduced pack performance. In this work, a three-dimensional modeling was carried out to investigate the effects of operating conditions on the thermal behavior of a lithium-ion battery pack for an EV or HEV application. Thermal conductivities of various compartments of the battery were estimated based on the equivalent network of parallel/series thermal resistances of battery components. Heat generation rate in a cell was calculated using the modeling results of the potential and current density distributions of a battery cell.

• Asian-Australasian Journal of Animal Sciences
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• v.5 no.3
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• pp.419-426
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• 1992

After the virtual eradication of cattle during World War II, Papua New Guinea herds were rebuilt with Shorthorn and Aberdeen Angus cattle from Australia. These, and Red Sindhi and Sahiwal, imported in 1952, were considered unsuitable breeds. In 1954, Department of Agriculture, Stock and Fisheries imported three Brahman bulls and three heifers from Texas and in 1960 began importations of Afrikaner from Queensland. In Central Province, Brahmans were crossed with Angus and at Erap (Morobe) the hottest place in Papua New Guinea, Shorthorns were crossed with Afrikaners. In 1965, Brahman and Brahman-cross were sent to Erap. Records of breeding and growth rates were collected for use in upgrading in cattle of the basis of performance, not pedigree. The data are not ideal for genetic analysis, since no control groups were maintained. Birth weights (BWT), weaning weights (WWT) and calving intervals (CI) were analysed for the period 1969-1978. After exclusion of unsatisfactory data, 2,514 calf records were used, including both breeds from 1969 to 1973, but only Brahman-cross subsequently. Breed mean BWT ranged only from 30.6 to 33.8 kg. As Brahman content increased, BWT decreased and WWT increased; within a genotype, there was a negative maternal effect of high Brahman content on BWT and a positive effect on WWT which ranged from 138 to 174 kg. Afrikaner calves had heavier BWT but lighter WWT. As expected, bulls were heaviest, heifers lightest and mature cows bore and reared heavier calves. Calving interval (405 days, equivalent to 90% calving) was unaffected by breed but 4-year old cows averaged 423 days. Breed differences in BWT and WWT are consistent with the body of literature on performance of Brahmans and Afrikaners. Since cattle tick are not present and internal parasites are insignificant at Erap, the superiority of Brahmans indicates that they were better at utilizing the mediocre quality grazing of the Markham Valley or were more heat tolerant. Performance selection over ten years resulted in the virtual elimination of Afrikaners, with the final genotype approximately 9/16 Brahman, 3/8 Shorthorn and 1/16 Afrikaner.

• International Journal of Automotive Technology
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• v.8 no.4
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• pp.421-428
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• 2007

This paper investigates the combustion and emission characteristics of a compression ignition engine fueled with neat and blended Shell's gas-to-liquid (GTL) fuel, which was derived from natural gas through the Fischer-Tropsch process. The experiments were conducted in a 6-cylinder DI diesel engine with pump timing settings of $6^{\circ},\;9^{\circ}\;and\;12^{\circ}$crank angle before TDC over ECE R49 and US 13-mode cycles separately and compared to a conventional diesel fuel. The results show that GTL exhibited almost the same power and torque output, improved fuel economy and effective thermal efficiency. It was found that GTL displayed lower peak in-cylinder combustion pressure and maximum heat release rate (HRR), the timings of the peak pressure and the maximum HRR were generally delayed, and the combustion durations were almost equivalent for diesel and GTL under the same speed-load condition. The results also indicate that, compared to diesel fuel, GTL blends showed a trend forward decreasing four regulated emissions simultaneously and a higher GTL fraction in blends contributing to further reductions in the emissions. In particular and on average, neat GTL significantly reduced HC, CO, NOx and PM by 16.4%, 17.8%, 18.3% and 32.4%, respectively, for all cases.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.155-160
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• 2002

Metal matrix composites had generated a lot of interest in recent times because of significant in specific properties. It was also highlighted as the materials of frontier industry because strength, heat-resistant, corrosion-resistant, wear-resistant were superiored. In this study the strength properties of $Al_{18}B_4O_{33}/AC4CH$ were represented mixing the binder of $Al_2O_3$ and $TiO_2$. It was also fabricated by squeeze casting. $Al_{18}B_4O_{33}/AC4CH$ was fabricated at the melt temperature of $760^{\circ}C$ the perform temperature of $700^{\circ}C$ and mold temperature of $200^{\circ}C$ under the pressure of 83.4MPa and observed SEM. Fatigue crack growth rate tests on compact tension specimen(half-size) of thickness 12.5mm were conducted by using sinusoidal waveform. Compact tension specimens(half-size) were used and fatigue crack growth rate da/dN and stress intensity factor range ${\Delta}K$ were analyzed concerning to the R value of 0.1 and 0.05. In order to find out the value of ${\Delta}K$, load amplitude constant method was applied by the standard fatigue testing method describes in ASTM E647-95a. As the results of this study, Fatigue crack growth rate increased with in creasing the load ratio, Consequently, At equivalent stress intensity factors, the fatigue crack growth rates in MMC were faster than those of AC4CH alloy. then the fatigue life and the fatigue crack growth rate was investigated using scanning election microscopy(SEM)