• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.139-148
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• 2003

In this study, biodegradable base Li-greases were prepared by using Li-soap thickener and vegetable oils such as soybean oil, rapeseed oil, castor oil and synthetic ester. Also, EP-greases were formulated by blending base Li-greases, anti-wear additives, EP additives, anti-oxidants and corrosion inhibitor etc. And EP-greases were characterized by analysing physical properties such as worked penetration, dropping point, 4-ball wear, extreme pressure, thermal properties etc. Biodegradability of base Li-greases and EP-greases were evaluated by CEC-L-33-A-93 method using several inoculums of domestic sewage treatment plant. As the results, biodegradability of vegetable oils were shown at the range of 97.1 to $98.4\%$. And biodegradability of base Li-greases and EP-greases were $86.2\%\;\~\;89.3\%\;and\;83.4\%\;\~\;90.0\%$ which were lower value than those o( vegetable oils due to effect of Li-soap thickener, respectively. Therefore, the EP-greases prepared in this study were easily biodegraded by microorgnism.

• 설비공학논문집
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• 제14권4호
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• pp.341-349
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• 2002

Heat and mass transfer characteristics of a surfactant-added LiBr-$H_2O$ solution flowing over a single horizontal tube were examined experimentally. The parameters considered were surfactant (2-ethyl-1-hexanol) concentration, solution temperature at the top of the tube and absorber pressure. Even with an amount of the surfactant below the solubility limit, heat and mass transfer performances were enhanced tremendously. The Nusselt and Sherwood numbers increased by about 70% and 340%, respectively, when 10 ppm of the surfactant was added. However, an excess amount of the surfactant in the solution did not bring a further enhancement. The absorption performance deteriorated when the non-condensable gases were extracted from the system (by a vacuum pump) since the vaporized surfactant was also extracted during the process. Therefore, it is desirable to add a sufficient amount of the surfactant (more than 10 ppm) to maintain high performance of absorption.

• Wind and Structures
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• 제35권4호
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• pp.243-253
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• 2022

The conformal mapping method (CMM) has been broadly exploited in the study of fluid flows over airfoils and other research areas, yet it's hard to find relevant research in bridge engineering. This paper explores the feasibility of CMM in streamlined box girder bridges. Firstly, the mapping function transforming a unit circle to the streamlined box girder was solved by CMM. Subsequently, the potential flow solution of aerostatic pressure on the streamlined box girder was obtained and was compared with numerical simulation results. Finally, the aerostatic pressure attained by CMM was utilized to estimate the aerostatic coefficient and flutter performance of the streamlined box girder. The results indicate that the solution of the aerostatic pressure by CMM on the windward side is satisfactory within a small angle of attack. Considering the windward aerostatic pressure and coefficient of correction, CMM can be employed to estimate the rate of change of the lift and moment coefficients with angle of attack and the influence of the geometric shape of the streamlined box girder on flutter performance.

• 분석과학
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• 제8권2호
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• pp.131-138
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• 1995

가온 가압법으로 합성한 리튬-흑연섬유간화합물(Li-Graphite Fiber Intercalation Compounds, Li-GFICs)과 리튬-석유코크스층간화합물(Li-Petroleum Cokes Intercalation Compounds, Li-PCICs)을 공기 순환에 의하여 자발적으로 deintercalation시키고, 이 deintercalation의 분해 과정으로 나타나는 Li-GFDICs와 Li-PCICs의 구조를 전기적 성질에 미치는 영향에 대하여 논의하였다. 이에 대한 분석은 X-선 회절과 전기 비저항 측정에 의해 수행되었다. X-선 회절 분석에 의하면 Li-GFDICs의 경우 주로 2 stage가 형성되었고 Li-PCICs의 경우에는 1 stage와 2 stage가 주된 회절선으로 나타났다. 또한 deintercalatlon 반응 결과에 의하면 Li-GFDICs의 경우 5주 이후에, Li-GFDICs의 경우 3주 후에 deintercalation 반응이 각각 멈췄다. 전기 비저항 측정 결과에 의하면 Li-GFDICs의 경우 3주까지는 거의 변화가 없었고 그 후 완만한 상승곡선을 나타내었으며, Li-PCDICs의 경우에는 3주를 정점으로 하향곡선을 나타내었다. 따라서 본 연구결과에 의하면 기질로 사용된 흑연섬유와 석유 코크스의 경우 리튬의 원활한 intercalation-deintercalation 작용이 잘 이루어지므로 두 물질 모두 전지의 양극재로 사용될 수 있을 것으로 기대되어진다.

• Journal of Acupuncture Research
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• 제19권1호
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• pp.147-158
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• 2002

Objective : The aim of the present study is to investigate the effect of stimulation on different sites of the body on MBP(mean blood pressure) and HR(heart rate). Methods : Six healthy men have participated in this study. Before and after 10 min, exercise on a running machine of l0km/hr, acupressure, plain acupuncture and electroacupuncture(50Hz) stimulation was practiced on GV20, LI4, ST36, BL40 and non-acupoints on T4 and T10 respectively for 20 min. and in a control group without any treatment. The changes of MBP and HR after exercise have been observed for 20 min. at 5 minute intervals. Results : Compared with control, no significant difference was observed in research of the blood pressure measurement regardless of methods nor sites of stimulation. But there were trends of reduction in the heart rates in all experimental groups. Especially, in the group of acupressure on T10 before exercise, GV20, T10 after exercise and electroacupuncture on GV20, LI4, BL40 after exercise there was statistically significant decreases in heart rates. Conclusion : From the present experiment, it is concluded that somatic stimulation has effect on the heart rates but not on the blood pressures, and the presence of effective sites on the decreases of heart rates suggest that this effect may depend on sites of stimulation.

• The Korean Journal of Physiology and Pharmacology
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• 제22권4호
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• pp.363-368
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• 2018

Hypotension is one of the potential causes of dizziness. In this review, we summarize the studies published in recent years about the electrophysiological and pharmacological mechanisms of hypotension-induced dizziness and the role of the vestibular system in the control of blood pressure in response to hypotension. It is postulated that ischemic excitation of the peripheral vestibular hair cells as a result of a reduction in blood flow to the inner ear following hypotension leads to excitation of the central vestibular nuclei, which in turn may produce dizziness after hypotension. In addition, excitation of the vestibular nuclei following hypotension elicits the vestibulosympathetic reflex, and the reflex then regulates blood pressure by a dualcontrol (neurogenic and humoral control) mechanism. In fact, recent studies have shown that peripheral vestibular receptors play a role in the control of blood pressure through neural reflex pathways. This review illustrates the dual-control mechanism of peripheral vestibular receptors in the regulation of blood pressure following hypotension.

• Structural Engineering and Mechanics
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• 제81권4호
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• pp.523-527
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• 2022

The objective of this study is to simulate the flow in pipes with various boundary conditions. Free-pressure fluid model, is used in the pipe based on Navier-Stokes equation. The models are solved by using the numerical method. A problem called "stability of pipes" is used in order to compare frequency and critical fluid velocity. When the initial conditions of problem satisfied the instability conditions, the free-pressure model could accurately predict discontinuities in the solution field. Employing nonlinear strains-displacements, stress-strain energy method the governing equations were derived using Hamilton's principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The results of this paper are analyzed by hyperbolic numerical method. Results show that the level of numerical diffusion in the solution field and the range of well-posedness are two important criteria for selecting the two-fluid models. The solutions for predicting the flow variables is approximately equal to the two-pressure model 2. Therefore, the predicted pressure changes profile in the two-pressure model is more consistent with actual physics. Therefore, in numerical modeling of gas-liquid two-phase flows in the vertical pipe, the present model can be applied.

• 대한한의학회지
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• 제42권4호
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• pp.164-175
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• 2021

Objectives: The LI11 (Quchi) acupuncture point has always been included in the Seven acupoints for stroke; however, additional LI11 acupuncture research is needed. In this study, the effect of LI11 acupuncture on cerebral blood flow of the anterior cerebral arteries (ACA) and middle cerebral arteries (MCA) was investigated. Method: This study included 10 healthy young male subjects. Cerebral blood flow velocity and cerebrovascular reactivity were measured using transcranial Doppler sonography. Changes in hyperventilation-induced carbon dioxide (CO₂) reactivity and modified ACA and MCA blood flow velocity at 40 mmHg (CV40), blood pressure, and heart rate were observed before and after LI11 acupuncture treatment. Results: A statistically significant increase in contralateral anterior cerebral artery CO₂ reactivity (p=0.036) and decrease in contralateral middle cerebral artery CV40 (p=0.047) were observed. No significant difference in mean blood pressure was shown. A statistically significant increase in heart rate occurred after LI11 acupuncture; however, it was not clinically significant as there were negligible changes in the heart rhythm. Conclusions: LI11 acupuncture treatment could improve cerebral blood flow velocity. These results might be explained by regulating endothelium-dependent vessel dilation in the anterior cerebral artery region. Trial registration: This trial has been registered with Clinical Research Information Service, a service of the Korea Centers for Disease Control and Prevention: KCT0004494 (retrospectively registered). https://cris.nih.go.kr/cris/search/search_result_st01.jsp?seq=15359

• Korean Chemical Engineering Research
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• 제46권1호
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• pp.175-183
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• 2008

흡착제 Li-X 제올라이트(UOP)에서 $CO_2$, CO, $CH_4$, $H_2$에 대한 단일성분 및 혼합성분의 흡착평형 실험을 정적부피법에 의해 수행하였다. 실험 데이터는 압력범위 0~20 bar와 온도범위 293.15 K, 303.15 K, 313.15 K에서 실시하였다. 각각 등온식의 파라미터들은 단일성분 실험을 통해 결정했고, 결정한 파라미터로 혼합성분의 흡착 평형을 예측하였으며 실험값과 비교하였다. Li-X 제올라이트에서의 $H_2/CO_2$, $H_2/CO$, $H_2/CH_4$ 혼합성분의 흡착평형 실험 결과는 extended langmuir-freundlich(L-F) 등온식, dual-site langmuir(DSL) 등온식을 이용해 예측하였으며 실험값과 비교하였다. L-F 등온식은 다른 모델들에 비해 $CH_4$와 $H_2$에서 좋은 예측 결과를 보여주었다. 또한 DSL 등온 식은 $CO_2$와 CO에서 좋은 예측 결과를 보여주었다.

• Journal of Advanced Marine Engineering and Technology
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• 제30권4호
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• pp.483-493
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• 2006

A model for a pressure drop of water vapor flow across tube banks in a horizontal tube absorber of an absorption chiller/heater using LiBr solution as a working fluid has been developed based on a commercial 20RT(70kW) absorption chiller/heater. The numerical results show that the characteristic of the pressure drop in the shell side of the horizontal tube absorber is completely different from that in a conventional shell and tube heat exchanger. Especially, solution film thickness has significant influence on the vapor pressure drop in the horizontal tube absorber. In addition, the effects by the tube diameters, the longitudinal pitch to diameter ratio, and Reynolds number of the vapor flow, on the vapor pressure drop have been studied to evaluate the compactness of tube absorber. It was found that the vapor pressure drop decreases as tube diameter increases, the longitudinal pitch to diameter ratio increases, and Reynolds number of the vapor flow decreases. A comparison of the present study results with well-established experimental and numerical results showed a good overall agreement.