• Membrane Journal
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• v.7 no.3
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• pp.142-149
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• 1997

The extended analysis on the diverging flow through asymmetric membrane pores has been performed in this study. Afore rigorous equations of velocity profile relevant to the divergent slit and cone shaped channels, which are widely used as a general pore model, have been obtained by employing a creeping flow approach of Newtonian fluids. As a degree of asymmetry (i.e., diverging angle) is increased, the predicted flow function shifts Toward the center region due to the incorporated wall effect, so that the overall velocity profile becomes decreased. It is true, as expected, that when the divergent channel is in the low diverging angle limit, the channel flow results in the Poiseuillean fashion by utilizing a lubrication approximation. The flow rate equation of each type of channel has been developed from the combined solution of velocity profile and pressure fields. The effect of diverging flow on the flow rate enhancement has been remarkably predicted, in which the flow rate increases with the increase of pore asymmetry. The advantage of our theoretical results lies in the analytical expression for the diverging flow behavior through pore channels as well as its ability to play a fundamental role on the related membrane filtrations such as microfiltration and ultrafiltration.

• Management Science and Financial Engineering
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• v.17 no.2
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• pp.99-129
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• 2011

This paper analytically studies how to choose hedging instrument for firms with steady operating cash flows from value maximization perspective. I derive a formula to determine option's optimal strike that makes hedged cash flow have the best monetary payoff given a hedger's view on the underlying asset. I find that not only the expected mean but also the expected standard deviation of the underlying asset in relation to the forward price and the implied volatility play a crucial role in making optimal hedging decision. Higher moments play a certain part in hedging decision but to a lesser degree.

• Proceedings of the Membrane Society of Korea Conference
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• 1995.10a
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• pp.5-9
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• 1995

In the dry-jet-wet-spinning process of a hollow fiber membrane, the polymer solution is pumped into a coaxial tube, jet spinneret. The threadline emerging from the spinneret is stabilized by an internal coagulating medium(liquid or gas) as it emerges from the jet orifice. The nascent hollow thread is further stabilized in a quench bath as shown in Fig. 1. In this scheme, three mechanism of formatiota(temperature gradient, solvent evaporation, and solvent-nonsotvent exchange) can be combined. The changes which promote stabilization often play a dominant role in determining the ultimate fiber wall structure as well. Hence, in pratice, hollow fiber stabilization and development of membrane structure are commonly inseparable. However, fiber dimension(the inside diameter and wall thickness of the hollow fiber) is mainly a rheological problem and is determined by dope pumping rate, spinneret diatance from the coagulation bath, inner coagulant flow rate, and fiber draw-rate. Besides rheological phenomena play a prominent part in the final properties of the hollow fiber.

• Journal of Korea Society of Digital Industry and Information Management
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• v.11 no.4
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• pp.143-154
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• 2015

This study aims to evaluate smartphone gaming controllers. Diffusion of smartphone makes its users to play smartphone games in ease and comfort and its built-in sensors deliver new gaming experience to the users. Based on the concept how the controller system is important, the current research also implies the importance of customizing service which gives users a selection to deploy a controller. To explore the interaction effect of controllers and customizing on interactivity, flow, usability, attitude, and intention, the research constructs 3(gyroscope, wheel, and button controllers) by 2(default and customizing setting) experimental design and forty college students played Gameloft's Asphalt 8: Airborne in a within subject design. The results showed that interaction effect and customizing main effect were not found, but controller main effect was statistically significant. Button controller is superior to those other two in more detail. It implies that it is still not useful to play new types of gaming controller, and a customizing service. It suggests that smartphone games should more focus on improving optimal user experience with built-in sensor controllers.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.15-25
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• 2017

Swirl flow is often found in proximal coronary arteries, because the aortic valves can induce swirl flows in the coronary artery due to vortex formation. In addition, the curvature and tortuosity of arterial configurations can also produce swirl flows. The present study was performed to investigate fractional flow reserve alterations in a post-stenotic distal part due to the presence of pre-stenotic swirl flow by computational fluid dynamics analysis for virtual stenotic models by quantifying fractional flow reserve(FFR). Simplified stenotic coronary models were divided into those with and without pre-stenotic swirl flow. Various degrees of virtual stenosis were grouped into three grades: mild, moderate, and severe, with degree of stenosis of 0 ~ 40%, 50 ~ 60%, and 70 ~ 90%, respectively. In this study, three-dimensional computational hemodynamic simulations were performed under hyperemic conditions in virtual stenotic coronary models by coupling with a zero-dimensional lumped parameter model. The results showed that the influence of pre-stenotic swirl inflow is dominant on FFR alteration in mild stenosis, whereas stenosis is dominant on FFR alteration in moderate/severe stenosis. The decrease in FFR caused by swirl flow is more significant in mild stenosis than moderate/severe stenosis. Biomechanical modeling is useful for clinicians to provide insight for medical intervention strategies. This hemodynamic-based parameter study could play a critical role in the development of a non-invasive imaging-based strategy-support system for percutaneous transluminal angioplasty in cases of mild/moderate stenosis.

• Journal of Korea Water Resources Association
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• v.35 no.4 s.129
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• pp.345-358
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• 2002

The flow apportioning algorithms with digital elevation models have been developed to reflect reasonable flow divergence properties but they showed several defects related to the connectivity of channel cells, various divergence features along to local topography and channel cells' size etc. Topographic data used by existing flow apportioning algorithms are flow accumulation area and local slope. However, the size and location of channel cells which play the dominant role in the flow pathway were not properly considered. Therefore, a new flow apportioning algorithm considering various flow divergence characteristics in the complicate terrain is proposed. The GA optimization scheme is used to represent the location and scale of the channel pixel. Improved result can be obtained by using both a new flow apportioning algorithm and optimization.

• The Korean Journal of Community Living Science
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• v.25 no.3
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• pp.349-361
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• 2014

This study was examined the general trends in social activity participation, the flow degree, and the psychological well-being of middle-aged women in Korea and explored how psychological well-being varies according to various sociodemographic variables, social activity participation, and the flow degree. This study provided practical insights into how the psychological well-being of middle-aged women can be enhanced. Data were gathered from 302 middle-aged women between the ages of 40 and 60 by using a structural questionnaire. The statistical methods included a descriptive analysis, a t-test, and a regression analysis using SPSS WIN 18.0. According to the results of the hierarchical regression analysis, the key variables influencing the psychological well-being of middle-aged women included the flow degree in terms of social activity participation and the education level. These variables explained 30% of the psychological well-being of middle-aged women. The higher the education level and the flow degree, the stronger the psychological well-being was. Social activity participation and the flow degree had greater effects on psychological well-being than sociodemographic characteristics. In particular, an increase in the flow of social activities increased psychological well-being. This suggests a need to improve the psychological well-being of middle-aged women by providing them with an environment where they can play social roles. One way to accomplish this is by linking retraining and life-long education-related activities to employment or volunteer activities. This study demonstrates the importance of the flow degree for the psychological well-being of middle-aged women. The results have important policy and theoretical implications.

• Journal of Acupuncture Research
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• v.17 no.1
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• pp.175-187
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• 2000

PyoBon GeunGyul - one of the twelve regular meridians theory - play a important role on the principle of point selection and point prescription in acumoxibustion. PyoBon explain the connection of the concentration and diffusion of channel qi, GeunGyul explain the relation of both poles of channels flow. So, Geun and Bon means the starting point of channel qi, and Pyo and Gyul means the terminal point of channel qi. But the flow of channel qi on PyoBon GeunGyul different from today's circulation courses of twelve regular channels based on Kyungmaek(經脈) chapter of Youngchu. Thus this study investigate the contents of PyoBon GeunGyul and consider its connection with channel flow. The results are as follows : 1. PyoBon GeunGyul theory explain that the relation of the limbs and trunk at meridian and emphasize that the connection of meridian and the importance of the limb acupoints. 2. PyoBon GeunGyul theory can be understandable in the view of the primordial qi and explain that the primordial qi of twelve regular channels acts from the limbs to the trunk. 3. PyoBon GeunGyul theory is based on the system of primordial qi channel which circulates from fingers and toes facing toward heart or the head, different from today's circulation courses of twelve regular meridians. 4. PyoBon GeunGyul theory act as a basis of principle of a part or distant point selection which applicated widely in acumoxibustion.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.242-250
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• 2006

The impacts of equivalence ratio on the flow structure and flame dynamics in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.2
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• pp.152-158
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• 2007

Most of experimental visualizations and numerical results on the flow field separated form a leading edge around an unsteady foil show a continuous streakline from the leading edge and large reverse flow between the streakline and the suction surface. However, they have not exactly clarified yet the dynamic behavior of vortices separated from the leading edge because separation around an unsteady foil is very complicated phenomenon due to many parameters. In the present study the flow fields around pitching foils have been visualized by using a Schlieren method with a high speed camera in a wind tunnel at low Reynolds number regions. It has been observed that small vortices are shed discretely from the leading and trailing edge and that they stand in line on the integrated streakline of separation shear layer. By counting vortices in the VTR frames it was clarified that the number of vortex shedding from the leading and trailing edge during one pitching cycle strongly depends on the non-dimensional pitching rate. Futhermore the vortices moving up to the leading edge on the suction surface of the pitching foil are visualized. They play an important role to balance the number of vortex shedding from both edges.