• Transactions on Electrical and Electronic Materials
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• v.8 no.4
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• pp.182-187
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• 2007

The use of the pulsed electro acoustic (PEA) method allowed us to perform the direct observations of spatio-temporal charge distributions in Electric double layer capacitors (EDLCs) based on polarizable nanoporous carbonaceous electrode. The negative charge density became the maximum, about $205C/m^3$ at the region where was near to collector layer in EDLCs for case $V_{DC}=2.5V$, while the positively charged density became the maximum, about $61.1C/m^3$ at the region where it was located around the cathode layer. The performance of the best sample was found to be better in terms of the charge density (Cs) and specific energy ($E_s$) with a maximum value of ${\sim}8.4F/g$ and 26 Wh/kg. The $C_s$ obtained from the PEA method agreed well with that from the energy conversion method. The PEA measurement used here is a very useful method to quantitively investigates the spatio-temporal charge distribution in EDLCs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.12 s.255
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• pp.1218-1227
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• 2006

In this paper a parametric study using an immersed boundary method has been carried out to investigate the effects of stable density stratification on the wakes past two identical three-dimensional hills aligned in tandem. The Reynolds number based on the uniform inlet velocity and twice the hill height was fixed at Re=300 while the Froude number based on the inlet velocity and the hill height was retained at Fr=0.2. Neutral flow without density stratification was also computed for comparison. Under a strong stratification, vertical motion of fluid particles over the three-dimensional hills is suppressed and the wake structures behind the hills become planar. Depending on the distance between the two hills, the flow pattern of each wake is significantly affected by the stratification. There is a critical hill distance at which flow characteristics drastically change. Qualitative and quantitative features of the wake interaction are reported.

• Structural Engineering and Mechanics
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• v.32 no.5
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• pp.621-634
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• 2009

A numerical method is developed to investigate the effects of some geometric parameters and density variation on frequency characteristics of the circular and annular membranes with varying density. The discrete singular convolution method based on regularized Shannon's delta kernel is applied to obtain the frequency parameter. The obtained results have been compared with the analytical and numerical results of other researchers, which showed well agreement.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.436-444
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• 1991

A computational method has been developed to analyze the bone-remodeling induced by external fixator. The method was based on the Finite Element Method (FEM) in combination with numerical formulation of adaptive bone-remodeling theories. As a feed-back control variable, compressive strain and effective stress were used to determine the surface remodeling and internal (density) remodeling respectively. Surface remodeling and internal remodeling were combined at each time step to predict the rel situation. A noticeable shape and density change were detected at the region between two pins and density change was decreased with time increment. At final time step, the shape and density distribution were converged closely to its original intact bone model. Similar change was detected in stress distribution. The altered stress distribution due to the pin and external fixator converged to the intact stress distribution with time.

• International Journal of Aeronautical and Space Sciences
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• v.1 no.2
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• pp.1-8
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• 2000

The flow in low-density plumes expanding into a region of finite pressure shows a quite different behavior from that observed in low-density plumes expanding into a vacuum. The flow structure in the plume varies depending on applied ambient and stagnation chamber conditions. In the present study, the direct simulation Monte-Carlo (DSMC) method based on molecular gas dynamics is employed in the analysis of low-density gas flows expanding through a small converging/diverging nozzle. Special attention has been paid to the effect of non-zero ambient and stagnation pressures on the flow structure which has rarely been studied using the DSMC method.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1996.06c
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• pp.792-801
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• 1996

A thinning algorithm -based image analysis technique was developed to measure corn root lengths. The root length measurement method was evaluated by comparing thread lengths measured by the image analysis system with actual thread lengths. The length measurement method accurately estimated actual thread lengths (less than 2% calculated error). Also, a rapid root length density measurement procedure, which utilizes the above root length measurement method, was developed to estimate corn root length density without washing the roots. Root length densities estimated from the cut soil surface of core samples taken from the field were paired with the root length densities determined from washed roots from the same soil core sample. A linear relationship between these two values was expected and was found. Eliminating the root washing procedure reduces the time required for measuring corn root length density substantially.

• Journal of Korean Society of Transportation
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• v.31 no.5
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• pp.48-59
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• 2013

Normally the benefits concerned in the feasibility study for highway constructions are travel time saving, vehicle operation cost, etc. which can be calculated using the simulation tool(EMME3). However, there must be extra benefits of driving amenity improvement that drivers can perceive through decreasing driving fatigue and improving driving comfortability. In this study, the definition of driving amenity was established and a method of estimation for the benefit of driving amenity improvement was developed. Highway type (urban/rural highway) and highway density was considered to estimate the driving amenity. And Double-bounded Dichotomous Choice among Contingent Valuation Method(CVM) was applied to survey the willingness-to-pay of drivers when highway density decreases. Finally the value of driving amenity was estimated using the results of survey and logit medel. As the existing highway density is high, willingness-to-pay increases in both urban and rural highways. Even though the changing rates of highway density are same, willingness-to-pay is different based on the existing highway density.

• Journal of the Korean Society of Radiology
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• v.17 no.7
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• pp.1017-1023
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• 2023

The purpose of this study was to improve the accuracy of effective atomic number (EAN) and relative electron density (RED) using a polynomial-based calibration method using dual-energy CT images. A phantom composed of 11 tissue-equivalent materials was acquired with dual-energy CT to obtain low- and high-energy images. Using the acquired dual-energy images, the ratio of attenuation of low- and high-energy images for EAN was calibrated based on Stoichiometric, Quadratic, Cubic, Quartic polynomials. EAN and RED were extracted using each calibration method. As a result of the experiment, the average error of EAN using Cubic polynomial-based calibration was minimum. Even in the RED image extracted using EAN, the error of the Cubic polynomial-based RED was minimum. Cubic polynomial-based calibration contributes to improving the accuracy of EAN and RED, and would like to contribute to accurate diagnosis of lesions in CT examinations or quantification of various materials in the human body.

• Journal of Computing Science and Engineering
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• v.11 no.2
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• pp.39-48
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• 2017

Main content extraction of web pages is widely used in search engines, web content aggregation and mobile Internet browsing. However, a mass of irrelevant information such as advertisement, irrelevant navigation and trash information is included in web pages. Such irrelevant information reduces the efficiency of web content processing in content-based applications. The purpose of this paper is to propose an automatic main content extraction method of web pages. In this method, we use two indicators to describe characteristics of web pages: text density and hyperlink density. According to continuous distribution of similar content on a page, we use an estimation algorithm to judge if a node is a content node or a noisy node based on characteristics of the node and neighboring nodes. This algorithm enables us to filter advertisement nodes and irrelevant navigation. Experimental results on 10 news websites revealed that our algorithm could achieve a 96.34% average acceptable rate.

• Journal of Power Electronics
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• v.15 no.1
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• pp.65-77
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• 2015

Resonant converters are well suited for induction heating (IH) applications due to their advantages such as efficiency and power density. The control systems of these appliances should provide smooth and wide power control with fewer losses. In this paper, a simple phase locked loop (PLL) based variable duty cycle (VDC) pulse density modulation (PDM) power control scheme for use in class-D inverters for IH loads is proposed. This VDC PDM control method provides a wide power control range. This control scheme also achieves stable and efficient Zero-Voltage-Switching (ZVS) operation over a wide load range. Analysis and modeling of an IH load is done to perform a time domain simulation. The design and output power analysis of a class-D inverter are done for both the conventional pulse width modulation (PWM) and the proposed PLL based VDC PDM methods. The control principles of the proposed method are described in detail. The validity of the proposed control scheme is verified through MATLAB simulations. The PLL loop maintains operation closer to the resonant frequency irrespective of variations in the load parameters. The proposed control scheme provides a linear output power variation to simplify the control logic. A prototype of the class-D inverter system is implemented to validate the simulation results.