• Kyungpook Mathematical Journal
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• v.61 no.4
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• pp.831-843
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• 2021

In this paper we look at the three dimensional stagnation point flow problem over a rough rotating disk. We study the theoretical behaviour of the stagnation point flow, or forced flow, in the presence of a slip factor in which convective instability stationary modes appear. We make a numerical investigation of the effects of slip on the behaviour of the flow components of the stagnation point flow where the disk is rough. We provide, for the first time in the literature, a complete convective instability analysis and an energy analysis. Suitable similarity transformations are used to reduce the Navier-Stokes equations and the continuity equation into a system of highly non-linear coupled ordinary differential equations, and these are solved numerically subject to suitable boundary conditions using the bvp4c function of MATLAB. The convective instability analysis and the energy analysis are performed using the Chebyshev spectral method in order to obtain the neutral curves and the energy bars. We observe that the roughness of the disk has a destabilising effect on both Type-I and Type-II instability modes. The results obtained will be prominently treated as benchmarks for our future studies on stagnation flow.

• Journal of the Semiconductor & Display Technology
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• v.22 no.1
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• pp.18-22
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• 2023

We have investigated the effect of the concentration of oxygen vacancies on the characteristics of Mo-doped ZnO (MZO) thin films for the TCO (transparent conducting oxide). For this purpose, MZO thin films were deposited by RF magnetron sputtering at different substrate temperature from room temperature to 300℃. The electrical resistivity of the MZO films decreases with increasing substrate temperature up to 100℃ and then gradually increases at higher temperatures. To investigate the influences of the ambient gases, the flow rate of oxygen and hydrogen in argon was varied from 0.1 sccm to 0.5 sccm. The MZO thin films were preferentially oriented to the (002) direction, regardless of the ambient gases used. The electrical resistivity of the MZO thin films increased with increasing O₂ flow rates, whereas the electrical resistivity decreased sharply under an Ar+H₂ atmosphere and was nearly the same, regardless of the H₂ flow rate used. As the oxygen vacancy concentration increases, the resistivity intended to decrease. In conclusion, Oxygen vacancy affects the MZO thin film's electrical characteristics. All the films showed an average transmittance of over 80% in the visible range.

• Journal of Korean Society of Water and Wastewater
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• v.35 no.6
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• pp.477-487
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• 2021

Due to the global climate change, Korean peninsula is has been experiencing flooding and drought severely. It is hard difficult to manage water resources sustainably, because due to intensive precipitation in short periods and severe drought has increased in Korea. Reused water from the wastewater treatment plant (WWTP) could be a sustainable and an alternative water source near the urban areas. In order to understand the patterns of water reuse in Korea, annual water reuses data according to the times and regional governments were investigated from 2008 to 2019. The reused water from WWTP in Korea has been mainly used for river maintenance flow and industrial use, while agricultural use of water reuse has decreased with time. Metropolitan cities in Korea such as Seoul, Busan, Daegu, Ulsan, and Incheon have been mainly used reused reusing water for river maintenance flow. Industrial water reuse has been limitedly applied recently for the planned industrial districts in Pohang, Gumi, Paju, and Asan. By using the collected annual water reuse data from the domestic sewerage statistics of sewerage, the optimistic and pessimistic future estimations of for future annual water reuse were suggested from 2020 to 2040 on a five year interval for every five years.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.5
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• pp.31-40
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• 2020

This study investigates whether other comprehensive income (OCI) reported in the statement of comprehensive income (one of the main financial statements after the adoption of K-IFRS) predicts a firm's future performance. Using the quarterly data of Korean listed companies, we examine the association between OCI estimates and future earnings. First of all, we find that OCI is positively associated with earnings in both 1- and 2-quarter ahead, supporting the predictive value of OCI. When we break down OCI into its individual components, our results suggest that the net unrealized gains/losses on available-for-sale (AFS) investment securities are positively associated with future earnings, while the other components (e.g., net unrealized gains/losses on valuation of cash flow hedge derivatives) present insignificant results. In addition, we investigate whether the reliability in OCI estimates enhances the predictive value of OCI to predict future performance. We find that the predictive ability of OCI, in particular the net unrealized gains/losses on available-for-sale (AFS) investment securities, becomes more pronounced when firms are audited by the Big 4 audit firms. Overall, our study suggests that information content embedded in OCI can provide decision-useful information that is helpful for the prediction of future firm performance.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.21-24
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• 2000

End-to-end congestion control mechanism have been critical to the robustness and stability of the Internet. Most of today's Internet traffic is TCP, and we expect this to remain so in the future. TCP/IP is the intermediate transport layer candidate for today's applications. TCP uses an adaptive window-based flow control. The congestion avoidance and control algorithms deployed by TCP aims at using the available network bandwidth. This paper compares different congestion control policies, and proposes the new design mechanism for future public networks

• Journal of Korean Society for Quality Management
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• v.14 no.2
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• pp.40-46
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• 1986

The decision maker has the job of torecasting capital investments and operating expenses to aid the decision making in choosing and evaluating present and future alternatives. The estimating function eventually analysis, evaluates and choose the alternatives. The analysis stemmed originally from a preliminary design of some sort, and eventually plans are started to investigate investment possibilites. This study provide the descounted cash flow and the present worth method. Despite any choice of an analytical method, there remains the problem of predicting certain future events. Therefore, these models dealing with optimum plant sizing, equipment replacement, and lease or buy will be discussed.

• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.613-622
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• 2001

Interaction of blood flow and leaflet behavior in a bileaflet mechanical heart valve was investigated using computational analysis. Blood flows of a Newtonian fluid and a non-Newtonian fluid with Carreau model were modeled as pulsatile, laminar, and incompressible. A finite volume computational fluid dynamics code and a finite element structure dynamics code were used concurrently to solve the flow and structure equations, respectively, where the two equations were strongly coupled. Physiologic ventricular and aortic pressure waveforms were used as flow boundary conditions. Flow fields, leaflet behaviors, and shear stresses with time were obtained for Newtonian and non-Newtonian fluid cases. At the fully opened phase three jets through the leaflets were found and large vortices were present in the sinus area. At the very final stage of the closing phase, the angular velocity of the leaflet was enormously large. Large shear stress was found on leaflet tips and in the orifice region between two leaflets at the final stage of closing phase. This method using fluid-structure interaction turned out to be a useful tool to analyze the different designs of existing and future bileaflet valves.

• Journal of the Korean Society of Visualization
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• v.8 no.2
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• pp.23-30
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• 2010

Regarding the aircrafts with a rotor blade system, the miniaturization of them is limited due to the rotor blade length and the tail rotor system. To miniaturize an aircraft, an equipment is required that increases thrust and also shortens the length of the rotor blade. The present study will conduct the flow analysis for miniaturizing the aircraft by applying a duct to the coaxial rotor blade system without tail rotor. First, the verification on the calculated results was conducted through the computational flow analysis on the coaxial rotor blade system without a duct. Then, the flow analysis for the coaxial rotor blade systems was performed including Ka-60 duct, Single duct, Twin duct, and Double duct, respectively. From the numerical results, the thrust coefficient appeared higher with the duct than without a duct for the coaxial rotor blade system. Especially, in the case of Double duct, the thrust was improved due to the increase of incoming flow and the extension of the wake area. These results will be used as the basic concepts for miniaturizing the aircraft with the rotor blade system. The flow analysis on the coaxial rotor blade system including the fuselage remains as a future work.

• The Journal of Korean Physical Therapy
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• v.28 no.2
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• pp.136-141
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• 2016

Purpose: In this study experiments were performed during 6 weeks with 40 adults, 20 subjects in the waist stabilization exercise with blood flow restriction group and 20 subjects in the waist stabilization exercise without blood flow restriction group, in order to determine the impact of waist stabilization exercise on White Area Index (WAI) followed by blood flow restriction. Methods: Thickness of external oblique abdominal muscle, internal oblique abdominal muscle, and transversus abdominis muscle, as well as density and WAI of external oblique abdominal muscle were measured, followed by performance of repeated ANOVA. Results: Significant difference in thickness of external oblique abdominal muscle according to periodical difference was observed between groups (p<0.05). Significant difference in thickness of internal oblique abdominal muscle and transversus abdominis muscle according to periodical difference was observed between groups (p<0.05). Significant difference in density and WAI of external oblique abdominal muscle according to periodical difference was observed between groups (p<0.05). Conclusion: In conclusion, significant difference was observed after waist stabilization exercise with blood flow restriction. These results can be used as basic data for future research on waist stabilization exercise and blood flow restriction exercise.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2423-2430
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• 1994

Several factors of the efficient combustion process are shape of combustion chamber, position of spark plug, turbulence flow and so on. the shape of combustion chamber and position of spark plug are constrained to geometrically, and then it could not make a change the shape easily. But the turlence flow in combustion chamber have a great influence on combustion phenomena, and which is much easier to control relatively. And since characteristics of turbulence flow would be very important to the stability of combustion and performances, This study is also essential to future engine-low emission and lean burn engine. This paper shows that the visualization of the turbulence flow of single cylinder engine by using 2way, $45^{\circ}$ inclined and 2 channel hot wire probe through the park plug hole. We also study the characteristics of turbulence flow by means of ensemble averaged mean velocity, turvulence intensity and integral length scale.