• Management Science and Financial Engineering
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• v.8 no.1
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• pp.39-51
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• 2002

Special structure of flow networks can reduce the order of the relative existent algorithms. In this paper a special structure of flow network called self-similar f1ow networks is introduced, After describing such networks an efficient algorithm for finding maximum flow is presented. It is shown that this algorithm runs in O(m) time.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.12
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• pp.777-784
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• 2016

All-vanadium redox flow batteries (VRFBs) are used as energy storage systems for multiple intermittent power sources. The performance of the VRFBs depends on the materials and operating conditions. Hence, performance characterization is of great importance in the development of the VRFBs. This paper proposes a method for determining the maximum current density based on stoichiometric ratios. A laboratory-scaled VRFB with a projected electrode area of $25cm^2$ is electrically charged when the state of the charge has begun from 0.6. The operating conditions, such as current density and volumetric flow rate are important in the test, and the maximum current density is influenced by the mass transfer coefficient. The results show that increasing the electrolyte flow rate from 5 mL/min to 60 mL/min enhances the maximum current density up to $520mA/cm^2$.

• Journal of Korea Water Resources Association
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• v.31 no.3
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• pp.291-301
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• 1998

The objective of this study is to analyze the characteristics of flow and bed topography with changing bed material in a 180-degree, with constant-radius curved experimental channel. Sand($D_{50}$ = 0.56 mm, s = 2.65) and anthracite($D_{50}$ = 0.26 mm, s = 1.54) were selected as bed materials. The maximum scour depth was found to be about two times for the mean flow depth at the outer bank of bend angle $30^{\circ}~60^{\circ}$, and in case of anthracite, it was found upper part of bend angle $5^{\circ}~15^{\circ}$ than that of sand. Regardless of bed materials the path of maximum streamwise velocity is skewed inwards in the upper part of the bend, the maximum velocity shifts outwards, and it lagged downward as bed roughness increases. The maximum skewed angle of flow grows faster in the smooth bottom than in the rough one, and its value also increases. The secondary flow in anthracite bottom was measured larger than that of sand one, and two cells of secondary flow was found in this experiment.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.3
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• pp.158-166
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• 2005

The present study investigated experimentally and numerically the enhancement of absorption performance due to the waviness of falling film in the vertical absorber tube. The momentum, energy and mass diffusion equations were utilized to find out temperature and concentration profiles at both the interfaces of liquid solution and refrigerant vapor and the wall. Flow visualization was performed to find out the wetting characteristics of the falling film. The maximum heat transfer coefficient was obtained for the wavy flow using spring as an insert device through both numerical and experimental studies. Based on the numerical and experimental results, the maximum absorption rate was found for the wavy-flow using spring as the insert device. The differences between experimental and analytical results ranged from $5.0\;to\;25\%\;when\;Re_j>100$.

• Journal of Chest Surgery
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• v.24 no.12
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• pp.1167-1172
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• 1991

Since March 1988 we have performed 133 arteriovenous fistulae for hemodialysis in 121 patients with chronic renal failure. Of the 133 cases of arteriovenous fistulae, follow-up evaluation was possible for 80 cases which performed in 69 patients. The relation between blood flow and patency rate and duration of arteriovenous fistula was examined. The overall 6 - 12 - 18 -, and 24 - month patency rates of arteriovenous fistulae were 82%, 64%a, 62%, and 57%, respectively. The maximum blood flow was 150 ~ 350ml /min[mean 217.1$\pm$44.27]. The patency duration was evaluated in patients divided into three groups owing to maximum blood flow through the fistulae. The range of maximum blood flow was 150 ~ 200ml /min for group A, 200 ~ 250ml /min for group B, and above 250ml /min for group C. The mean duration of the patency was 10.7$\pm$7.60 months in group A, 14.9$\pm$9.82 months in group B, and 21.6$\pm$11.16 months in group C[p<0 05]. With increased maximum blood flow, the duration of the patency was longer in group A than group B and C [r=0.39, p<0. 05]. The maintenance blood flow was 100 ~ 250ml /min[mean 179.2$\pm$37.26 ml/min]. When the maintenance blood flow was above 200ml /min, long-term patency rate was higher than the group below 200ml /min[r=0.48, p<0.01]. In the same range of blood flow, patency duration of the patients with using their own blood vessels were longer than the patients with using vascular graft for A-V fistula. We concluded that the patency of the arteriovenous fistulae was closely correlated with the blood flow through the fistulae.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2189-2195
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• 1992

The performance of heat exchanger as an energy conversion device can be described by the available energy output and efficiency. The efficiency is defined as the ratio of the available energy output and the exergy of the heat source flow. In present study, a counterflow heat exchanger is analyzed and the conditions to obtain maximum output is numerically determined. As a result, the avilable energy obtained by the cold flow can be determined as functions of the heat capacity flow, the cold flow inlet temperature and the heat transfer capacity of heat exchanger. At the maximum output condition the heat capacity flow of the cold fluid is larger than that of the heat source, and the heat capacity flow ratio is equal to the ratio of the cold flow inlet temperature and the atmospheric temperature. And the avilable energy output increases as the heat transfer capacity of the heat exchanger become larger, but in the economic point of view there is also an optimum heat transfer capacity for a given heat source flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.920-928
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• 2003

The objective of the present study was to investigate the characteristics of flow and wall shear stress under steady and pulsatile flow in the aneurysm. The numerical simulation using the software were carried out for the diameter ratios ranging from 1.5 to 3.0, Reynolds number ranging from 900 to 1800 and Womersley number, 15.47. For steady flow, it was shown that a recirculating vortex occupied the entire bulge with its core located closer to the distal end of the bulge and the strength of vortex increased with increase of the Reynolds number and diameter ratio. The position of a maximum wall shear stress was the distal end of the aneurysm regardless of the Reynolds number and diameter ratios. For the pulsatile flow, a recirculating flow at the bulge was developed and disappeared for one period and the strength of vortex increased with the diameter ratio. The maximum values of the wall shear stress increased in proportion to the diameter ratio. However, the position of a maximum wall shear stress was the distal end of the aneurysm regardless of the diameter ratios.

• Journal of Korean Society on Water Environment
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• v.28 no.2
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• pp.224-231
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• 2012

It is necessary to develop flow duration curve (FDC) on each unit watershed in order to analyze flow conditions in the stream for the management of Total Maximum Daily Loads (TMDLs). This study investigated a simple method to develop FDC for the general use of the curve. A simple equation for daily flow estimation was derived from the regression analysis between the 8-day interval flow data of a unit watershed and the daily flow monitoring data of an adjacent upstream region. FDC can be prepared with the calculation of daily flow by the equation for each unit watershed. An annual and a full-period FDC were drawn for each unit watershed in Guem river basin. Standard flow such as low and ordinary flow can be obtained from the annual FDC. Major percentile of flow such as 10, 25, 50, 75 or 90% can be obtained from the full-period FDC. It is considered that this simple method of developing FDC can be utilized more widely for the calculation of standard flow and the assessment of water quality in the process of TMDLs.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.12 no.2
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• pp.121-125
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• 2001

Singing requires exquisite coordination between the respiratory and phonatory system to efficiently control glottal airflow. Respiratory function and vocal aerodynamics were investigated in six female professional sopranos and in six female subjects without vocal training. All sopranos had more than 15 years of formal classic vocal training. Pulmonary function test data on simple pulmonary function, flow volume curve, static lung volumes, maximum inspiratory pressure(MIP), and maximum expiratory pressure(MEP) were obtained from all subjects. Vocal aerodynamic studies of maximum phonation time(MPT), phonation quotient, and mean glottal flow rates (MFR) were also measured in all subjects. Simple pulmonary function in professional sopranos was generally the same as that of other female subjects without vocal training. However, MIP and MEP showing respiratory muscle forces were significantly elevated in professional sopranos, compared to those of other female subjects without vocal training. Maximum phonation times and phonation quotient in sopranos are longer than those of other female subjects even though there were no differences in simple pulmonary function. High-pitched tones were made with significantly higher mean glottal flow rates(GFR) in normal subjects than low-pitched tones, whereas no changes in GFR were found in sopranos. The result indicated that sopranos demonstrated significant improvements in aerodynamic measures of GFR, maximum phonation time, suggesting an increase in glottal efficiency.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.5
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• pp.1037-1049
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• 2001

Considerable interest has evolved in the flow of non-Newtonian fluids in channels of noncircular cross section in compact heat exchanges. Analytical solution was developed for prediction of the flow rate and maximum velocity in steady laminar flow of any incompressible, time-independent non-Newtonian fluids in straight closed and open channels of arbitrary, but axially unchanging cross section. The geometric parameters and function of shear describing the behavior of the fluid model were evaluated for fluid flow among a bundle of rods arranged in triangular and square array. Numerical values of dimensionless maximum velocities, mean velocities, pressure-drop-flow parameters and friction factors were evaluated as a function of porosity and pitch-to-radius ratio.