• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.550-553
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• 2001

In this study, unity current gain frequency f$\_$T/ of GaAs MESFET is predicted with different temperatures up to 400 $^{\circ}C$. Temperature dependence parameters of the device including intrinsic carrier concentration n$\_$i/ effective mass, depletion width are considered to be temperature dependent. Small signal parameters such as gate-source, gate dran capacitances C$\_$gs/ C$\_$gd/ are correlated with transconductance g$\_$m/ to predict the unity current gain frequency. The extrinsic capacitance which plays an important roles in high frequency region has been taken into consideration in evaluating total capacitance by using elliptic integral through the substrate. From the results, f$\_$T/ decreases as the temperature increases due to the increase of small signal capacitances and the mobility degradation. Finally the extrinsic elements of capacitances have been proved to be critical in deciding f$\_$T/ which are originated from the design rule of the device.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2000.05a
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• pp.5-5
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• 2000

In the severe accident case like LOCA, Zircaloy(Zry) claddings are oxidized not only in high temperature but also in high pressures. It is a concem whether the safety of high bum up fuels can be maintained during severe accident. The effects of steam pressure on Zry-4 oxidation, and the effect of prc-existing oxide layer on the cladding in the high temperature-high pressure oxidation of Ziy-4 were investigated. The experimental temperature range was $700-900^{\circ}C$, and the pressures were between 0.1 and l5.0MPa. Partial pressure of steam tumed out to be the important one rather than total gas pressure. The higher the steam pressure was applied, the thicker the oxide became. nle effect of st,earn pressure on the oxidation of claddings with preexisting oxide was about 40-60% less effective than that of pickled cladding. Aocelerated oxidation in highpressure slean1 seems to be originated from the formation of microcracks produced during the transformation of tetragonal zirconia to monoclinic phase. Steam pressure seems to affect the stability of tetragonal phase.

• Korean journal of applied entomology
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• v.62 no.4
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• pp.385-388
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• 2023

Gypsy moth (Lymantria dispar), a polyphagous insect pest belonging to the family Lymantriidae, is widely distributed in Korea, Japan, Siberia, Europe, and North America. They pose a threat to various host plants including pear trees, apple trees, and blueberries. Traditionally considered a forest pest, the increasing incursion of gypsy moths into agricultural land near forested areas has intensified damage to crops lacking effective control methods. This study aimed to investigate the temperature-dependent development of gypsy moths to enhance outbreak prediction and advance technology development. The effects of temperature on development of each life stage were investigated under constant temperature conditions of 18, 21, 24, 27, 30, and 33℃ (14L:10D, RH 60±5%) utilizing egg masses collected in Jeollanam-do Jangheung-gun in 2021. The results revealed that higher temperatures accelerated the development rate of the gypsy moth larvae with optimal development occurring at 30℃. However, the survival rate was lowest at 33℃. At the favorable temperature of 30℃, the total development period was 43.8 days for females and 42.5 days for males. The developmental threshold temperature were 13.1℃ for females and 12.5℃ for males, with effective accumulated temperature of 641.1 DD and 657.8 DD, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.3
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• pp.194-199
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• 2001

The turbulent flow resistance of water solution with polymer is reduced as compared with that of pure water. This effects is named th drag reduction and offers the significant reduction of the pumping power and the energy consumption. But the intense shear forces and the high temperature experienced by the polymer solution when passing through the pipes cause the degradation a loss of drag reduction effectiveness. Especially, the degradation behavior is found to be strongly dependent on temperature. This mechanical and thermal degradation can be avoided by adding materials such as surfactant to the polymer solution, which enhance the bonding force between molecules. In the present study, Copolymer and SDS were utilized and they were mixed in 10 different mixture ratios, while total concentration was fixed as 100wppm. Degradation of Copolymer-SDS mixture solutions was investigated experimentally in closed loop at the temperature of $10^{\circ}C\; and\; 80^{\circ}C$ with various flow average velocities of 1.5 m/sec, 3.0m/sec, and 4.5m/sec. Degradation characteristics of polymer solution without surfactant show a radical loss of drag reduction effectiveness at high temperature. Degradation alleviation ability of surfactant is especially effective at high temperature. Consequently, this results show that the addition of surfactant to the polymer solution can control unfavorable degradation phenomena for high temperature systems.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2019.04a
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• pp.106-106
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• 2019

Human needs energy to maintain metabolisms, and these energy sources were uptake foods or nutritions. The most effective source was known for glucose among the nutrients, furthermore the glucose is an important source of energy for blood cells and control brain maintenences cells. But as food is plentiful and eating habits become more westernized, fast food and irregular meal times by works. Nowadays, diabetes were rapidly increased by malnutriton and obesity. Diabetes was the sixth highest on the list of causes of death in Korea, released by the Statistics Korea in 2015, which is considered a serious social problem for adult diseases. Therefore, this study aims to establish the optimal hot water extraction conditions of mixed herbs extract mixture compounds that are effective in diabetes. The independent factors were extraction temperature (X1: $40-120^{\circ}C$), extraction time (X2: 2-10 hrs.), and the ratio of water to sample (X3: 40-200 mg/mL). Their effects were assessed on dependent variables of the extract properties, which included soluble solid contents, Brix of sample extract, total polyphenols content, total flavonoids content and DPPH Radical scavenging activity. As a result, the content of total polyphenol content was the highest in No.12(6 hrs, $120^{\circ}C$, 67 mg/mL) and the highest total flavonoid contents was found in No.16(6 hrs, $80^{\circ}C$, 40 mg/mL). DPPH Radical scavenging activity showed the highest activity in No.7(8 hrs, $100^{\circ}C$, 100 mg/mL).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.267-273
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• 2013

In order to provide effective operating conditions for the fan in a wet cooling tower with film fill, a new program to search for the minimum fan power was developed using a model of the optimal total annual cost of the tower based on Merkel's model. In addition, a type of design map for a cooling tower was also developed. The inlet water temperature and heat load were considered as key parameters. The present program was first validated using several typical examples. The results showed that for a given heat load, a three-dimensional graph of the fan power (z-axis), mass flux of air (x-axis, minimum fan power), and inlet water temperature (y-axis, maximum of minimum fan power) showed a saddle configuration. The minimum fan power increased as the heat load increased. The conventionally known fact that the most effective cooling tower operation coincides with a high inlet water temperature and low air flow rate can be replaced by the statement that there exists an optimum mass flux of air corresponding to a minimum fan power for a given inlet water temperature, regardless of the heat load.

• Journal of the Korean Solar Energy Society
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• v.32 no.5
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• pp.68-74
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• 2012

Investigation of the effective soil thermal conductivity($k$) is the first step in designing the ground loop heat exchanger(borehole) of a geothermal heat pump system. Another important factor is the borehole thermal resistance($R_b$). Thermal response tests offer a good method to determine the ground thermal properties for the total heat transport in the ground. The first step is measured for initial soil temperature. This is done by supplying a only pump power into a borehole heat exchanger. They need to supply into water unload heat power more than 30 minutes. In this study, the initial soil temperature was found to analysis $14.1{\sim}16.0^{\circ}C$,the ratio was 68.7% represented. In this case of $k$, was 2.1~3.0 $W/m{\cdot}k$, $R_b$ was 0.11~0.20 $m{\cdot}K/W$. In this work, it is also shown that the distribution of a soil thermal conductivity and borehole thermal resistance were on the influence of initial soil temperature. And soil thermal conductivity was related with factors of equation by linear least square method, borehole thermal resistance was on the influence of composite factors.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.45 no.2
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• pp.108-111
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• 2000

Osmoconditioning and hardening effects for the seed germination of normal and naturally aged rice seeds were studied through analyzing the total sugars and $\alpha$-amylase activity. The normal seeds which used to have high germination rate accelerated germination with the osmoconditioning at the suboptimal temperature of 17$^{\circ}C$. On the other hand, the aged seeds did not affect germination rate at $25^{\circ}C$, while increased germination rate and accelerated germination a little at 17$^{\circ}C$, Hardening of aged seeds increased germination rate by 10-15% compared with control seeds at both 17 and $25^{\circ}C$ and accelerated germination. Total sugar content and $\alpha$-amylase activity of normal seeds were higher than did aged seeds. The aged seeds with treatment of osmoconditioning and hardening increased total sugar content and $\alpha$--amylase activity, but hardening was more effective than osmoconditioning. The $\alpha$--amylase activity was positively correlated with the total sugar content and germination rate.

• Journal of Hydrogen and New Energy
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• v.13 no.1
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• pp.83-89
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• 2002

The goal of this research is to understand the NOx emission in direct injected diesel engine with premixed hydrogen fuel. Hydrogen fuel was supplied into the test engine through the intake pipe. Amount of hydrogen-supplemented fuel was 70 % basis on heating value of the total input fuel. The effects of intake air temperature and exhaust gas recirculation(EGR) on NOx emission were studied. The intake air temperatures were varied from $23^{\circ}C$ to $0^{\circ}C$ by using liquid nitrogen. Also, the exhaust gas was recirculated to the intake manifold and the amount of exhaust gas was controlled by the valve. The major conclusions of this work include: ( i ) nitrogen concentrations in the intake pipe were increased by 30% and cylinder gas temperature was decreased by 24% as the intake air temperature were changed from $23^{\circ}C$ to $0^{\circ}C$; ( ii ) NOx emission per unit heating value of supplied fuel was decreased by 45% with same decrease of intake air temperature; and (iii) NOx emission was decreased by 77% with 30% of EGR ratio. Therefore, it may be concluded that EGR is effective method to lower NOx emission in hydrogen fueled engine.

• 연구논문집
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• s.29
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• pp.5-15
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• 1999

Present study deals with performance analysis of an inert gas generator (IGG) which is to be used as an effective mean to suppress the fire. The IGG uses a turbo jet cycle gas turbine engine to generate inert gas for fire extinguishing. It is generally known that a lesser degree of oxygen content in the product of combustion will increase the effectiveness of fire suppressing. An inert gas generator system with water injection will bring advantages of suffocating and cooling effects which are considered as vital factors for fire extinguishing. As the inert gas is injected to the burning site, it lowers the oxygen content of the air surrounding the flame as well as reduces the temperature around the fire as the vapour in the inert gas evaporates during the time of spreading. Some important aspects of influencing parameters, such as, air excess coefficient. $\alpha$, compressor pressure ratio, $ pi_c$, air temperature before combustion chamber, $T_2$, gas temperature after combustion chamber, $T_3$, mass flow rate of water injection, $M_w$, etc., on the performance of IGG system are investigated. Calculations of total amount of water needed to reduce the turbine exit temperature to pre-set nozzle exit temperature employing a heat exchanger were made to compare the economics of the system. A heat exchanger with two step cooling by water and steam is considered to be better than water cooling only. Computer programs were developed to perform the cycle analysis of the IGG system and heat exchanger considered in the present study.