• 한국산학기술학회논문지
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• 제16권11호
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• pp.7745-7753
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• 2015

텔레비전의 가스 스프링은 롱 스트로크 (200 ~ 300mm, TV 상승 변위) 하에서 작동 할 때 피스톤 속도의 제어가 가능하다. 이 원리에 의해서 사용자는 높낮이 조절이 가능하다. 먼저 피스톤의 흐름 해석을 수행하였다. 정확한 관형 단면을 위한 피스톤 속도 조절기술을 조사하였다. 유동률 제어 및 높낮이 작용을 위한 피스톤 구조를 제안되었다. 본 연구는 대형 텔레비전 스탠드를 통해 50 인치 이상 TV의 가스 스프링의 개발을 위한 것이다. 최적 피스톤 로드 제어를 위한 중공축(외경 19.9mm, 내경 13.9mm)에 질소 개스(0.3m/s)를 주입하였다. 그 결과, 유동율이 증대함에 따라 피스톤 로드의 압력강하는 외력의 변화 없이 증대되었다. 결과적으로, 가스스프링을 통한 변위의 제어는 가능하다.

• Journal of Chest Surgery
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• 제17권4호
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• pp.565-573
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• 1984

The increasing use of cardioplegic solution for the reduction of ischemic tissue injury requires that all cardioplegic solution be carefully assessed for any protective or damaging properties. This study describes functional assessment of the efficiency of steroid in cardioplegic solution by using a Langendorffs perfusion model. Isolated rat heart were subject to a 2 minute period of coronary infusion with the steroid mixed cold cardioplegic solution immediately before and also at the midpoint of a 60 minutes period of hypothermic [10\ulcorner\ulcorner] ischemic arrest. The result of this study were as follows: 1.Spontaneous heart beat after ischemic arrest occurred 14 second later Langendorffs reperfusion in the steroid mixed Young & GIK group and 16 second later in the control group. [Young & GIK without steroid] A good recovery state of spontaneous heart beat was shown in both groups. 2.The percentage of recoveries of heart rate during the 30 minute after postischemic Langendorffs reperfusion was; at first 5 minute 106.3\ulcorner.7% [P<0.05] in the steroid mixed Young & GIK group. This percentage of recovery of steroid mixed Young & GIK group was significantly greater than the control group during the first 5 minute course. 3.The percentage of recovery of coronary flow during the 30 minute after postischemic Langendorffs reperfusion was; at first 5 minute 101\ulcorner.2% in the steroid mixed Young & GI K group. This percentage of recovery of the steroid mixed Young & GIK group was not significantly than the control group during the first 5 minute.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.855-864
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• 2017

The control rod assembly controls reactor power by adjusting its position during normal operation and shuts down chain reactions by its free drop under scram conditions. Therefore, the drop performance of the control rod assembly is important for the safety of a nuclear reactor. In this study, the drop performance of the conceptually designed control rod assembly for the prototype generation IV sodium-cooled fast reactor that is being developed at the Korea Atomic Energy Research Institute as a next-generation nuclear reactor was experimentally investigated. For the performance test, the test facility and test procedure were established first, and several free drop performance tests of the control rod assembly under different flow rate conditions were then carried out. Moreover, performance tests under several types and magnitudes of seismic loading conditions were also conducted to investigate the effects of seismic loading on the drop performance of the control rod assembly. The drop time of the conceptually designed control rod assembly for 0% of the tentatively designed flow rate was measured to be 1.527 seconds, and this agrees well with the analytically calculated drop time. It was also observed that the effect of seismic loading on the drop time was not significant.

• 한국응용약물학회:학술대회논문집
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• 한국응용약물학회 2003년도 Annual Meeting of KSAP : International Symposium on Pharmaceutical and Biomedical Sciences on Obesity
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• pp.108-108
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• 2003

The current study was performed to observe the effects of Panax ginseng (PG) and P. quinquefolia (PQ) on hemodynamics such as blood flow rate (BF), blood flow velocity (BV), heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP, and body temperature (BT) in healthy young men. After testing equality of variance, Student's t-test using PROC TTEST was examined to. prove statistical differences between control and ginseng conditions at each time point. It was found that the BF data were fluctuated by personal deviation. In order to minimize the deviation, the results obtained for 6 hrs were reconstituted after dividing them into two periods of the first half from 1 to 3 hrs and of the latter half from 3.5 to 6 hrs. And then the reconstitution data and dose-response curves were obtained. Blood flow such as BF and BV shows significant increases both two periods in the dose of PG 2.25 and PG 9.0, whereas significant decrease in the dose of PG 4.5. However, in the PQ groups, the middle dose PQ 4.5 shows the highest significant increase among the three doses. Except for PG 2.25 in HR, other doses show significant decreases both in the first half and latter half. SBP of PQ 9.0 shows only a significant decrease in the first half; on the other hand, in the latter half, PG 4.5, PG 9.0 and PQ 9.0 significantly increase SBP. In addition, DBP of PG 2.25 and PG 4.5 show significant increase in the both periods. In the BT, PQ groups show gradual decrease from PQ 2.25 to PQ 9.0; however, PG groups show differently. PG 4.5 shows significant decrease, but PG 9.0 shows a increase without statistical meanings. In summary, PG is more effective in respect to keeping homeostasis of hemodynamics.

• 한국물환경학회지
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• 제20권5호
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• pp.415-421
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• 2004

Litter wastes on highway runoff are gradually being considered one of the major pollutants of concern in protecting the integrity of receiving waters for beneficial use. The California State Water Resources Control Board has identified in their 303(d) list at least 36 water bodies where trash or litter is considered a pollutant of concern. The first TMDL adopted by the Region 4 (Los Angeles area) of the California State Water Quality Control Board was for trash in the Los Angeles River. The first flush characteristic study was developed to obtain first flush water quality and litter data from representative stormwater runoff from standard highway drainage outfalls in the Los Angeles area. Total captured gross pollutants in stormwater runoff were monitored at six Southern California highway sites over two years. The gross pollutants were 90% vegetation and 10% litter. Approximately 50% of the litter was composed of biodegradable materials. The event mean concentrations show an increasing trend with antecedent dry days and a decreasing trend with total runoff volume or total rainfall. Event mean concentrations were ranged 0.0021 to 0.259g/L for wet gross pollutants and 0.0001 to 0.027g/L for wet litters. The first flush phenomenon was evaluated and the impacts of various parameters such as rainfall intensity, drainage area, peak flow rate, and antecedent dry period on litter volume and loading rates were evaluated. First flush phenomenon was generally observed for litter concentrations, but was not apparent with litter mass loading rates. Litter volume and loading rates appear to be directly related to peak storm intensity, antecedent dry days and total flow volume.

• 한국기계가공학회지
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• 제18권8호
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• pp.51-59
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• 2019

Flow forming is an eco-friendly and high-efficiency plastic deformation process with fewer chips during a process which is specifically used to manufacture seamless tubular products like tire wheels, rocket motor cases etc. On the development of mortar barrel using Inconel718 tube, some flow formed products had dimensional errors on their thickness. In this study, our purpose is to optimize the process conditions with the smallest dimensional error. In order to find an optimum process condition, 2D axisymmetric FEM simulation analyses with Taguchi method were conducted. Geometric variables (attack angle, flatting angle, roller nose radius) and operating parameters (depth of forming, feed rate) are considered as control factors. Forward flow forming with single roller was first analyzed to determine the effective factors using AFDEX software and attack angle of the roller was identified as the most influential factor. Also, the nose radius of the rollers was confirmed as a significant factor in multi-rollers flow forming system. The effect of rollers offset values are also studied and finally, we proposed optimal conditions to improve the accuracy of flow forming process with Inconel718 tube for mortar barrel manufacturing.

• Bulletin of the Korean Chemical Society
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• 제27권2호
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• pp.224-230
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• 2006

Escherichia coli transcription termination factor Rho catalyzes the unwinding of RNA/DNA duplex in reactions that are coupled to ATP binding and hydrolysis. We report here the kinetic mechanism of presteady state ATP binding and hydrolysis by the Rho-RNA complex. Presteady state chemical quenched-flow technique under multiple turnover condition was used to probe the kinetics of ATP binding and hydrolysis by the Rho-RNA complex. The quenched-flow presteady state kinetics of ATP hydrolysis studies show that three ATPs are bound to the Rho-RNA complex with a rate of $4.4\;{\times}\;10^5M^{-1}s^{-1}$, which are subsequently hydrolyzed at a rate of $88s^{-1}$ and released during the initiation process. Global fit of the presteady state ATP hydrolysis kinetic data suggests that a rapid-equilibrium binding of ATP to Rho-RNA complex occurs prior to the first turnover and the chemistry step is not reversible. The initial burst of three ATPs hydrolysis was proposed to be involved in the initialization step that accompanies proper complex formation of Rho-RNA. Based on these results a kinetic model for initiation process for Rho-RNA complex was proposed relating the mechanism of ATP binding and hydrolysis by Rho to the structural transitions of Rho-RNA complex to reach the steady state phase, which is implicated during translocation along the RNA.

• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.352-359
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• 2010

In recent years, the market has shown increasing interest in pump-turbines. The prompt availability of pumped storage plants and the benefits to the power system achieved by peak lopping, providing reserve capacity, and rapid response in frequency control are providing a growing advantage. In this context, there is a need to develop pumpturbines that can reliably withstand dynamic operation modes, fast changes of discharge rate by adjusting the variable diffuser vanes, as well as fast changes from pumping to turbine operation. In the first part of the present study, various flow patterns linked to operation of a pump-turbine system are discussed. In this context, pump and turbine modes are presented separately and different load cases are shown in each operating mode. In order to create modern, competitive pump-turbine designs, this study further explains what design challenges should be considered in defining the geometry of a pump-turbine impeller. The second part of the paper describes an innovative, staggered approach to impeller development, applied to a low head pump-turbine project. The first level of the process consists of optimization strategies based on evolutionary algorithms together with 3D in-viscid flow analysis. In the next stage, the hydraulic behavior of both pump mode and turbine mode is evaluated by solving the full 3D Navier-Stokes equations in combination with a robust turbulence model. Finally, the progress in hydraulic design is demonstrated by model test results that show a significant improvement in hydraulic performance compared to an existing reference design.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1552-1564
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• 2002

Meter-in, meter-out and bleed-off circuits are widely utilized in order to adjust the speed of a hydraulic actuator by using a flow control valve and in order to regulate the pressure of a hydraulic volume by using a simple on-off valve. In these circuits, a relief valve serves either to maintain constant system pressure or to protect the system from over-pressure loading. The relief valve of a bleed-off circuit is the second case frequently undergoing on-off action during operation. It makes the analysis of the pressure control characteristics of the circuit highly difficult. In this paper, steady-state flow rate, pressure, heat loss and efficiency of the three circuits are reexamined and basic experiments far obtaining the characteristics of a pump and relief valve are conducted. Finally, simple empirical first-order dynamic models of decreasing and increasing pressure were separately proposed and verified by comparison with experiment. As the result, the basis for the theoretical analysis of the pressure control characteristics of a bleed-off circuit using a simple on-off valve is established.

• The Korean Journal of Physiology and Pharmacology
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• 제11권3호
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• pp.89-95
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• 2007

Polygala tenuifolia (PT) is one of the most well-known traditional herbal medicines in Korea which is commonly used for the treatment of cardiovascular symptoms. The anti-ischemic effects of PT in isolated rat heart was investigated by analyzing changes in blood pressure, aortic flow, coronary flow, and cardiac output. And, its underlying mechanism was examined by quantitating intracellular calcium content in rat neonatal cardiomyocytes. Rats were divided into two groups: an ischemia-induced group without any treatment, and an ischemia-induced group treated with PT. Ischemia of isolated heart was induced by stopping the supply of oxygen and buffer for 10 min. The isolated heart was exposed to PT for the first 5 min of 10 min ischemia. PT treatment significantly prevented the decreases of perfusion pressure, aortic flow, coronary flow, and cardiac output under ischemic conditions. In addition, hemodynamics (except heart rate) of the PT-treated group was significantly recovered 60 min after reperfusion compared to the control group (systolic aortic pressure: 83.3% vs. 64.9%, aortic flow volume: 69.5% vs. 48.7%, coronary flow volume: 77.7% vs. 58.4%, and cardiac output: 71.6% vs. 51.2%, p < 0.01). As for the underlying mechanism, PT significantly prevented intracellular calcium increase which was induced by isoproterenol (p < 0.01), suggesting that the anti-ischemic effect of PT is mediated by inhibition of intracellular calcium increase.