• Journal of applied mathematics & informatics
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• v.35 no.3_4
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• pp.241-260
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• 2017

An analysis is made to study the solute transport in a Casson fluid flow through an annulus in presence of oscillatory flow field and determine how this flow influence the solute dispersion along the annular region. Axial dispersion coefficient and the mean concentration expressions are calculated using the generalized dispersion model. Dispersion coefficient in oscillatory flow is found to be a function of frequency parameter, Schmidt number, and the pressure fluctuation component besides its dependency on yield stress of the fluid, annular gap and time in the case of steady flow. Due to the oscillatory nature of the flow, the dispersion coefficient changes cyclically and the amplitude and magnitude of the dispersion increases initially with time and reaches a non - transient state after a certain critical time. This critical value varies with frequency parameter and independent of the other parameters. It is found that the presence of inner cylinder and increase in the size of the inner cylinder inhibits the dispersion process. This model may be used in understanding the dispersion phenomenon in cardiovascular flows and in particular in catheterized arteries.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1398-1406
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• 2024

The control rod worth is a key safety parameter required to be measured in commercial pressurized water reactors (PWRs). Conventionally, the control rod worth is measured after reaching the critical state, which occupies the considerable time in the zero-power physics test. In this study, an efficient control-rod worth measurement technique has been proposed based on the improved neutron-source multiplication method, which can be implemented with the source-range detector count rates in the subcritical states. Moreover, the noise reduction technique has been adopted to smooth the large fluctuation existing in the original signals. In order to verify the engineering performance of the proposed measurement technique, the measured source-range detector count rates during the rod withdrawal process before reaching critical state in a CNP1000 reactor have been employed. It demonstrated that almost all estimated results of control rod worth satisfy the engineering acceptance criteria, except one control rod with the relative difference over 10 %, which indicates the capability of the proposed method in estimating control rod worth.

• 한국HCI학회:학술대회논문집
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• 2006.02a
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• pp.931-936
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• 2006

This paper presents different issues of the real-time compression algorithms without compromising the video quality in the distributed environment. The theme of this research is to manage the critical processing stages (speed, information lost, redundancy, distortion) having better encoded ratio, without the fluctuation of quantization scale by using IP configuration. In this paper, different techniques such as distortion measure with searching method cover the block phenomenon with motion estimation process while passing technique and floating measurement is configured by discrete cosine transform (DCT) to reduce computational complexity which is implemented in this video codec. While delay of bits in encoded buffer side especially in real-time state is being controlled to produce the video with high quality and maintenance a low buffering delay. Our results show the performance accuracy gain with better achievement in all the above processes in an encouraging mode.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.291-295
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• 2009

Economic and environmental concerns over fossil fuels encourage the development of photovoltaic(PV) energy systems. Due to the intermittent nature of solar energy. energy storage is needed in a stand-alone PV system for the purpose of ensuring continuous power flow. Grid-connected PV system that supply power in a critical load demand require to curb power fluctuation. In this case. SCB is a effectiveness in controlling power variation due to intrinsic PV system. We propose the Matlab/Simulink dynamic model and power flow characteristics of a hybrid energy system with PV and SCB.

• Journal of the Korean Data and Information Science Society
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• v.21 no.3
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• pp.493-502
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• 2010

For establishing forecasting confidence interval for exchange rate, it is critical to estimate distribution of the exchange rate properly. In this thesis, we use block bootstrap method to estimate the distribution of the exchange rate via sum of its daily ratios. As a result, an easier and more accurate forecasting method is provided.

• The Korean Journal of Ecology
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• v.20 no.4
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• pp.251-258
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• 1997

Few attempts have been made to discover the ecological function of coarse woody debris (CWD) despite its importance to small mammal population. Twenty-five pitfall traps and a hundred live traps were placed in three sites with high amounts of CWD and three sites with low amounts of CWD. Eleven species were caught, and Peromyscus maniculatus was the most abundant (45.6%, n=605). Among 11 speices, abundance of Tamias townsendii and Clethronomys gapperi were higher in sites with high amounts of CWD than in sites with low amounts of CWD. Home range size was larger in breeding season than in non-breeding season indicating mating search. Resident time of Peromyscus maniculatus was longer in sites with high amounts of CWD implying better stability in population. The increasing amount of coarse woody debris (CWD) enhanced the habitat use by small mammals, and animals in high amounts of CWD were more abundant and stable in population fluctuation. This study, therefore, concludes that CWD is a critical habitat element for small mammals in forest ecosystem.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.8
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• pp.353-362
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• 1986

This paper shows that 6 pulse converter instead of 12 pulse converter can be used for the control of Superconducting Magnet Energy Storage(SMES) to improve the stability and to suppress the voltage fluctuation of power system. In order to prevent the commutation failure, when 6 pulse converter used for simultaneous control of real power and reactive power is asymmetrically controlled, stable control region has been presented by analyzing the commutation phenomena at critical points which distinguish the stable control region from the unstrol control region. Harmonic components of line current and output voltage have been calculated. Finally, computer simulation of power system stabilization has been presented to show the effectiveness of the proposed method. According to the computation results, SMES controlled by the 6 pulse converter is an effective measure in reducing the oscillation and the transient instability of the power system.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.1
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• pp.15-23
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• 1998

Characteristics of turbulence beneath the free surface around a blunt bow are numerically-investigated. Three dimensional wavier-Stokes and continuity equations are solved for the simulations.. The Large Eddy Simulation(LES) with the external disturbance is performed to simulate the turbulent free surface flow called sub-breaking wave. The result shows that the free surface fluctuates beyond a certain critical condition and the characteristics of the fluctuation are similar to the turbulent boundary layer flow around a solid body.

• Journal of the Korea Safety Management & Science
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• v.21 no.2
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• pp.1-8
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• 2019

Most of gas turbine combined cycle power plants are located in urban areas to provide peak load and district heating. However, NOx(nitrogen oxides) of exhaust gas emission from the power plants cause additional fine dust and thus it has negative impact on the urban environment. Although DLN(dry low NOx) and multi-stage combustors have been widely applied to solve this problem, they have another critical problem of damages to combustors and turbine components due to combustion dynamic pressure. In this study, the effect of different fuel ratio on NOx emission and pressure fluctuation was investigated regarding two variable conditions; combustor stages and power output on M501J gas turbine.

• Investigative Magnetic Resonance Imaging
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• v.23 no.1
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• pp.17-25
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• 2019

We discuss recent advances in Gd-based $T_1$-weighted MR contrast agents for the mapping of cellular pH. The pH plays a critical role in various biological processes. During the past two decades, several MR contrast agents of strategic importance for pH-mapping have been developed. Some of these agents shed light on the pH fluctuation in the tumor microenvironment. A pH-responsive self-assembled contrast agent facilitates the visualization of tumor size as small as $3mm^3$. Optimization of various parameters is crucial for the development of pH-responsive contrast agents. In due course, the new contrast agents may provide significant insight into pH fluctuations in the human body.