• 약학회지
• /
• 제26권2호
• /
• pp.105-110
• /
• 1982

The antihypertensive effect of clonidine administered concurrently with labetalol or metoprolol were studied with spontaneously hypertensive rats (SHR). The changes of heart rate were also observed in the same rats. Every drug was orally administered single dose after prechecking the systolic blood pressure and heart rate of SHR. The blood pressure of SHR in concurrently administered group was more significantly decreased than in alone administered group. The effective and stable decrease of blood pressure was maintained at the group of clonidine with labetalol (0.05+50mg/kg) for 9 hours. The group of clonidine with metoprolol (0.05+100mg/kg) manifested more marked decrease of blood pressure than the group of metoprolol (100mg/kg) alone for 9 hours. The diminishing effect of heart rate was enhanced in group of administering clonidine with labetalol, decreasing the dose of labetalol from 50mg/kg via 25mg/kg to 12.5mg/kg. On the other hand, in the group that clonidine was administered concurrently with metoprolol, the diminishing effect of heart rate was decreased with decreasing doses of metoprolol from 100mg/kg via 50mg/kg to 25mg/kg.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2002년도 춘계학술대회 논문집
• /
• pp.271-276
• /
• 2002

Continuous loading is applied the sample has been developed to overcome some of the problems associated with the incremental loading consolidation test. Therefore, it is able to reduce the test time and provide a well defined the curve of effective stress versus strain due to continuous stress-strain points. Also, the constant rate of strain consolidation(CRSC) test has been accepted widely as a standard method in foreign countries because of its many advantages. However, in Korea the CRSC test has not been used in engineering practice and experimentally verified. Because there is not a precise criterion of testing despite consolidation characteristics are influenced on strain rate and Pore pressure ratio. Consequently, it is difficult to apply in engineering practice. In this study, artificial neural networks are applied to the estimation of th proper strain rate and pore pressure ratio of the CRSC test. This study shows the possibility of utilizing the artificial neural networks model of estimation of the strain rate and pore pressure ratio in the CRSC test.

• 한국안전학회지
• /
• 제23권5호
• /
• pp.49-53
• /
• 2008

Glow discharge has lots of attractive properties, such as lower discharge sustaining voltage, no generation of ozone, and so on. And more, ionizer was developed recently using an atmospheric pressure glow discharge. On the other hand, ionizer needs a compressed or blown air to transport ion for charged objects. This air is very useful in explosive hazardous area to prevent the explosion of flammable gas and/or vapor by ignition sources, e.g. electrical spark. In this paper, we investigated the ionizing characteristic of atmospheric pressure glow discharge by controlled air flow rate from 5 liters to 60 liters a minute, and compared with decay time between the corona discharge and glow discharge as a function of some direction and distance from discharge ion source. We confirmed that an air flow rate needs 25 liters a minute to sustain the most suitable atmospheric pressure glow discharge and to increase an ionizing efficiency.

• 설비공학논문집
• /
• 제16권5호
• /
• pp.414-420
• /
• 2004

The heat transfer and pressure drop characteristics associated with the gas cooling of the supercritical carbon dioxide in a horizontal tube have been investigated experimentally. This problem is of particular interest in the design of a gas cooler of cooling systems using $CO_2$refrigerant. The test section is consisted of 6 series of 455 mm in length, 4.15 mm ID copper tube, respectively. The effects of the inlet temperature, pressure and mass flow rate on the heat transfer and pressure drop of $CO_2$in a horizontal tube is studied in detail. The heat transfer coefficient of $CO_2$is varied by temperature, inlet pressure, and mass flow rate of $CO_2$. This has maximum value at near the pseudocritical temperature. The pressure drop is changed by inlet pressure and mass flow rate of $CO_2$. The results have been compared with those of previous work. The heat transfer correlation at the supercritical gas cooling process is also suggested.

• 한국주조공학회지
• /
• 제15권6호
• /
• pp.566-573
• /
• 1995

In this study, the microstructural characteristics such as primary silicon, eutectic silicon, $SiC_p$ dispersion behavior, compound amount and Si solubility in $Al/SiC_p$ composite fabricated by the squeeze casting under various conditions were investigated systematically. As applied pressure(MPa) increases, cooling rate and compound amount are increased. In gravity casting, the cooling rate of hypereutectic composite is slower than of hypoeutectic composite by exothermic reaction of primary Si crystallization. But the cooling rate of hypereutectic composite is faster than that of hypoeutectic composite fabricated by same applied pressure, because amount of primary Si crystallization in hypereutectic composite was decreased, on the contrary, primary ${\alpha}-Al$ in hypoeutetic composite was increased due to increase of Si solubility in matrix by applied pressure. The crystalized primary silicon in hypereutectic composite fabricated by squeeze casting become more fine than that in non-pressure casting This is because mush zone became narrow due to increase of Si content of eutectic composition by pressure and time for growth of primary silicon got shorter according to applied pressure. It is turned out that eutectic temperature and liquidus are decreased by the increasing of squeeze pressure in all the composite due to thermal unstability of matrix owing to increasing of Si solubility in matrix by the increasing of applied pressure, as indicated in thermal anaiysis(DSC) results.

• 대한기계학회논문집B
• /
• 제21권11호
• /
• pp.1527-1537
• /
• 1997

Extinction characteristics and acoustic response of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flamelet in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such nonmonotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. The investigation of acoustic-pressure response in each regime, for better understanding of combustion instability, shows different characteristics depending on pressure. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted since flame temperature and chain branching reaction rate decreases as pressure rises. This acoustic response can be predicted properly only with detailed chemistry or proper reduced chemistry.

• 한국자동차공학회논문집
• /
• 제2권6호
• /
• pp.102-109
• /
• 1994

As a fundamental study to apply high pressure injection system to direct injection diesel engine, fuel injection system and constant volume combustion chamber were made and the behaviors of evaporating spray with the variation of injection pressure and the ambient gas temperature were observed by using high speed camera, and the combusion characteristics with the variation of injection pressure and A/F ratio were analyzed. As injection pressure increases, spray tip penetration and spray angle increase and, as a results spray volume increases. This helps an uniform mixing of fuel and air. Spray liquid core length decreases as ambient gas temperature increases, while it decreases as injection pressure increases but the effect of ambient gas temperature is dorminant. As injection pressure increases, ignition delay is shortened and combustion rate being raised, maximum heat release rate increases. It become clear that High injection pressure has high level of potential to improve the performance of DI-diesel engine.

• 한국추진공학회지
• /
• 제25권6호
• /
• pp.12-19
• /
• 2021

액체 추진제 공급 시, 하류의 압력변동과 무관하게 일정한 유량을 공급하기 위한 캐비테이션 벤츄리의 실험적 연구가 수행되었다. 캐비테이션 벤츄리의 성능을 파악하기 위해 벤츄리를 설계, 제작하여 후단의 형상, 전단압, 그리고 배압에 따른 유량과 벤츄리 전·후단 압력비를 관찰하였다. 일반적으로 캐비테이션 벤츄리의 구조적인 형상에만 종속하는 벤츄리 임계압력비는 실험결과, 후단의 형상 및 벤츄리 전단압과 관계없이 0.74로 일정함을 확인하였다.

• 오토저널
• /
• 제7권1호
• /
• pp.35-42
• /
• 1985

This paper describes an experimental study of the effect of injection timing on the combustion characteristics in four stroke cycle diesel engine with direct injection type combustion chamber. The effect of injection timing and compression ratio of engine on the combustion characteristics are investigated. Experimental results of combustion characteristics in cylinder show that the combustion pressure and the rate of pressure rise decrease in accordance with the retard of fuel injection timing. It is observed that the rate of pressure rise in cylinder is increased an increase in the compression ratio of engine. The effect of the fuel injection timing on the frequency of cylinder pressure brings about the same trend of the maximum rate of pressure rise in cylinder.

• 한국유체기계학회 논문집
• /
• 제3권2호
• /
• pp.36-43
• /
• 2000

This study presents the centrifugal compressor performance for three different vane stagger angles and wall pressure distribution within vaned diffuser channels, and is also discussed about the stability with respect to the compressor components. As the vane stagger angle decreases, the flow rate for the stall onset decreases, and higher pressure can be obtained at the low flow rate region, however, the effective operation range of the compressor decreases because of the blockage effect of the diffuser vane. Low pressure pocket within the vaned diffuser channel moves from the pressure side of leading edge to the suction side as the flow rate decreases. The compressor system stability mainly depends on that of the diffuser.