• Korean Journal of Crystallography
• /
• v.14 no.2
• /
• pp.56-61
• /
• 2003

Nanocrystalline hydrogenated silicon (nc-Si : H) thin films were deposited at room temperature by plasma enhanced chemical vapor deposition (PECVD): a mixture of SiH₄ and H₂ gas was introduced into the evacuated reaction chamber. When the H₂ gas flow rate was low, the density of Si-H₃ bonds was high in the films. On the other hand, when the H₂ gas flow rate was high, e.g., 100 sccm, a large number of Si-H bonds contributed to the passivation of the surface of the large volume of Si nanocrystallites. The relative fraction of the Si-H₃ and Si-H₂ bonds in the amorphous matrix varied sensitively with the H₂ gas flow rate. The variation was associated with the change in the intensity as well as the wavelength of the main PL peaks, indicating the change in the total volume as well as the size of the Si nanocrystallites in the films.

• International Journal of Vascular Biomedical Engineering
• /
• v.1 no.2
• /
• pp.13-19
• /
• 2003

Endothelial release of nitric oxide (NO) contributes to the regulation of vascular tone by inducing vascular relaxation. To estimate the blood flow-dependent nitric oxide level and half-life (T1/2) of nitric oxide in vivo state, we investigated the change of aortic NO currents during the change of aortic blood flow rate using NO-selective electrode system and electromagnetic flowmeter in the aorta of anesthetized rats. Resting mean aortic blood flow rate was $49.6{\pm}5.6ml/min$ in the anesthetized rats. NO currents in the aorta were increased by the elevation of blood pressure and/or blood flow rate. When the aortic blood flow was occluded by the clamping, aortic NO currents were decreased. The difference of NO concentration between resting state and occluded state was $1.34{\pm}0.26{\mu}M$ (n=7). This NO concentration was estimated as blood flow-dependent nitric oxide concentration in the rats. Also, while the aortic blood flow was occluded, NO currents were decreased with exponential pattern with $12.84{\pm}2.15$ seconds of time constant and $7.70{\pm}1.07$ seconds of half-life. To summarize, this study suggested that blood flow-dependent NO concentration and half-life of nitric oxide were about $1.3{\mu}M$ and 7.7 seconds, respectively, in the aorta of anesthetized rats. The nitric oxide-selective electrode system is useful for the direct and continuous measurement of NO in vivo state.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.19 no.2
• /
• pp.109-120
• /
• 2017

Groundwater seepage into a tunnel is one of the main causes triggering tunnel collapse and the consequent ground subsidence. Thus, it is important to estimate adequately the groundwater inflow rate and porewater pressure change during tunneling with time elapse. In current practice, Goodman's analytical solution (or image tunnel method) assuming homogeneous ground condition around a tunnel is commonly used for estimating groundwater inflow rate. However, the generally-used analytical solution for estimating groundwater inflow rate does not consider groundwater level drawdown and permeability change with depth, and the inflow rate can be overestimated in design phase. In this study, parametric study was performed in order to investigate the effect of groundwater level drawdown and permeability reduction with depth, and transient flow analysis was carried out for studying the inflow rate change as well as groundwater level and porewater pressure change around a tunnel with time elapse.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.2141-2145
• /
• 2004

As part of study on thermal hydraulic behavior in the reactor cavity under external vessel cooling in the APR (Advanced Power Reactor) 1400, one dimensional two phase flow of steady state in the reactor cavity have been analyzed to investigate a coolant circulation mass flow rate in the annulus region between the reactor vessel and the insulation material using the RELAP5/MOD3 computer code. The RELAP5/MOD3 results have shown that a two phase natural circulation flow of 300 - 600 kg/s is generated in the annulus region between the reactor vessel and the insulation material when the external vessel cooling has been applied in the APR 1400. An increase in the heat flux of the inner vessel leads to an increase of the coolant mass flow rate. An increase in the coolant outlet area leads to an increase in the coolant circulation mass flow rate, but the coolant inlet area does not effective on the coolant circulation mass flow rate. The change of the lower coolant outlet to a lower position affects the coolant circulation mass flow rate, but the variation trend is not consistent.

• The Korean Journal of Nuclear Medicine
• /
• v.11 no.1
• /
• pp.33-37
• /
• 1977

To evaluate the diagnostic significance of the blood disappearance rate of $^{198}Au$-colloid and to evaluate the change of hepatic blood flow during position change from supine to erect, we measured the half time of blood disappearance rate of $^{198}Au$-colloid using external counting method in 94 normal persons and in 77 patients with various hepatic diseases. The results obtained were as follows: 1. In normal control, the mean blood disappearance half time of $^{198}Au$-colloid in supine position was $2.7{\pm}0.4$ minutes. There was no significant difference of hepatic blood flow in age and sex. 2. In acute hepatitis, chronic hepatitis and hepatic cirrhosis, the mean blood disappearance half times in supine position were $3.0{\pm}0.45,\;3.5{\pm}0.74,\;7.2{\pm}3.6$ minutes respectively. The hepatic blood flow of the patients with chronic hepatitis and hepatic cirrhosis were significantly decreased than that of normal control. 3. In the normal control and acute hepatitis, the decreaces of the hepatic blood flow during the position change from supine to erect were 27.7% and 22.6% respectively.

• Journal of Ginseng Research
• /
• v.26 no.3
• /
• pp.132-138
• /
• 2002

To study the effect of Korea red ginseng (KCG) on the skin and cerebral blood flow, we evaluated the change of skin perfusion rate and cerebral perfusion rate after the intravenous, intraperitoneal, and oral administration of crude saponin (CS) and saponin-free fraction (SFF) of KRG in the rats. The change of skin perfusion rate and cerebral perfusion rate was measured laser doppler flowmetry. The intravenous injections of CS or SFF of KRG and intraperitoneal injection of SFF of KRG did not change the relative skin and cerebral blood flow in the rats. When the rats were treated by the intraperitoneal injection of CS of KRG, relative cerebral blood flow was significantly increased with a time-dependent manner, however, relative skin blood flow was not influenced by the them. Oral administration of CS of KRG slightly increased skin blood flow in the rats. Also, the change of cerebral blood flow by transient bilateral carotid arterial clamp in the CS-treated rats was significantly decreased, compared with control groups. From the above results, it was suggested that Korea red ginseng have a increasing property of cerebral blood flow in the rats.

• Journal of Korean Society of Water and Wastewater
• /
• v.10 no.1
• /
• pp.69-77
• /
• 1996

To evaluate the change of the groundwater flow and the water table response resulting from urbanization, two cases of the transient three-dimensional numerical simulations were performed. Variations of the groundwater flow system caused by withdrawals were analyzed. Two cases of infiltration rates were applied in this study to verify the water table changes. One is the rate under the circumstance during 1994 and the other is the revised rate. The numerical results from this study indicated that groundwater flow was influenced by human impacts. Groundwater flow has been concentrated to Taegu Textile Complex area where had large amount of pumping. Water table so far decreased -2.76m a year due to withdrawals. Water tables of many points were increased more than 30cm when the surface was reformed by infiltrating the rainfall. It was appeared that the improvement of surface to recharge the precipitation was very important to preserve and manage for the groundwater.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.6
• /
• pp.792-801
• /
• 2000

The problem of phase change from liquid to solid in the inviscid plane-stagnation flow is theoretically investigated. The solution at the initial stage of freezing is obtained by expanding it in powers of time, and the final equilibrium state is determined from the steady-state governing equations. The transient solution is dependent on the three dimensionless parameters, but the equilibrium state is determined by one parameter of (temperature ratio/conductivity ratio). The effect of the fluid flow on the growth rate of the solid in the pure conduction problem can be clearly seen from the solution of the initial stage and the final equilibrium state. The characteristics of the transient heat transfer at the surface of the solid and the liquid side of the solid-liquid interface for all the dimensionless parameters are elucidated.

• 유체기계공업학회:학술대회논문집
• /
• 2003.12a
• /
• pp.174-177
• /
• 2003

The automatic temperature control valve is used to control the flow rate of heating water in the large apartment complex and buildings. It is important to have simillar heating flow rate in the apartments, even though the apartment is top or bottom floors. To achieve those purposes, the automatic flow-temperature control valve was developed. The perfromance of this control valve is effected by the catridge shape and spring length. The flow capacity of this control valve is obtained with the different shape of catridges and with change of spring length.

• Proceedings of the SAREK Conference
• /
• 2008.06a
• /
• pp.1195-1200
• /
• 2008

This study have goal with conceptual design for Offshore Structures of high pressure control valve for localization. Ball valve for development accomplished with flow analysis based on provision of ANSI B16.34, ANSI B16.10, ANSI B16.25 In order to localize the Offshore Structures high pressure control valve. Numerical simulation using CFD(Computational Fluid Dynamic) in order to predict a mass flow rate and a flow coefficient form flow dynamic point of view. The working fluid assumed the glycerin($C_3H_8O_3$). The valve inlet and outlet setup a pressure boundary condition. The outlet pressure was fixed by atmospheric pressure and calculated until increasing 1bar to 10bar. CFD analysis used STAR-CCM+ which is commercial code and Governing equations were calculated by moving mesh which is rotated 90 degrees when ball valve operated opening and closing in 1 degree interval. The result shows change of mass flow rate according to opening and closing angle of valve. Flow decrease observed open valve that equal percentage flow paten which is general inclination of ball valve. Relation with flow and flow coefficient can not be proportional according to inlet pressure when compare with mass flow rate. Because flow coefficient have influence in flow and pressure difference. Namely, flow can be change even if it has same Cv value. The structural analysis used ANSYS which is a commercial code. Stress analysis result of internal pressure in valve showed lower than yield strength. This is expect to need more detail design and verification for stem and seat structure.