• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.27 no.4
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• pp.296-310
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• 2023

In this paper, we derive the Γ-limit of functionals pertaining to some optimal material distribution problems that involve a variable exponent, as the exponent goes to infinity. In addition, we prove a relaxation result for supremal optimal design functionals with respect to the weak-∗ L^∞(Ω; [0, 1])× W^1,p0 (Ω;ℝ^m) weak topology.

• Journal of the Korean Mathematical Society
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• v.49 no.6
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• pp.1123-1138
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• 2012

We study some anisotropic boundary value problems involving variable exponent growth conditions and we establish the existence and multiplicity of weak solutions by using as main argument critical point theory.

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2237-2242
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• 2011

Anomalous scaling behaviors such as significantly large growth exponent (${\beta}$) and small reciprocal of dynamic exponent (1/z) values for many molecular crystalline thin films have been reported. In this study, the variation of scaling exponent values and consequent growth behaviors of molecular thin films were more quantitatively analysed using a (1+1)-dimensional surface lateral diffusion model. From these simulations, influence of step edge barriers and grain boundaries of molecular thin films on the various scaling exponent values were elucidated. The simulation results for the scaling exponents were also well consistent with the experimental data for previously reported molecular thin film systems.

• Transactions of Materials Processing
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• v.19 no.7
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• pp.393-398
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• 2010

This paper investigates the effect of material properties on the formability of sheet metals based on the Marciniak-Kuczynski model (M-K model). The hardening behavior of the material is modeled as the Hollomon model with the strain rate effect. The yield surfaces are constructed with Hosford79 yield function. The material properties considered in this study include the R-value, the strain hardening exponent, the strain rate hardening exponent, and the crystal structure of the material. The effect of the crystal structure on formability is roughly expressed as the change of the yield surface by varying the value of the exponent in Hosford79 yield function. Results show that the R-value affects neither the magnitude nor the shape of right hand side of forming limit diagrams (FLDs). Higher strain hardening exponent and higher strain rate hardening exponent improve the formability of sheet metals because they stabilize the forming processes.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.336-339
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• 2008

Monthly mean data of Angstrom exponent and Aerosol optical thickness (AOT) from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) measurements over the East Asian waters were analyzed. Increasing trend of the satellite-derived Angstrom exponent was found over 1998-2006 while AOT mean was observed stable during the same period. Statistical test showed that annual increase in Angstrom exponent of about 0.01 is statistically significant over three study sub-areas out of six surrounding waters of Japan. Comparison with Aqua/MODIS-derived Angstrom exponent time series over June 2002 through June 2008 showed consistent correlation, with similar statistical significance. The trend of Angstrom exponent was interpreted as increase in fraction of small aerosol particles to give quantitative estimates on the variability of aerosols. The mean increase is evaluated to be about +0.35%/yr or more in terms of the contribution of small particles to the total AOT, or sub-micron fraction (SMF).

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.523-528
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• 2001

In this study we tried to determine the work-hardening exponent using continuous indentation test. Work-hardening exponent, which was determined by Hollomon equation, in tensile test, is an important parameter to determine plastic deformation and brittle/ductile property of materials. For using Hollomon equation, true stress and true strain were defined by indentation depth and indentation load. Using them the new equation, which is constituted by indentation depth, indentation load and work-hardening exponent, was induced. Indentation depth was calibrated because of elastic deflection and pile-up/sink-in phenomena. Work-hardening exponents of various steels derived by it showed good agreement to the results of tensile tests. In addition to experiments, FEM simulation was accomplished to investigate changes of real contact depth with materials properties changes. Through this simulation it is concluded that the real contact depth is changed by Y/E value which affect the early stage of indentation, and work-hardening exponent which the latter stage.

• Journal of Korea Water Resources Association
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• v.51 no.5
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• pp.451-459
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• 2018

We calculated the optimal exponent values based on the hourly rainfall data observed in South Korea by treating the exponent value as a variable without fixing it as a square in the inverse distance method. For this purpose, rainfall observation stations providing the data are classified into four groups which are located at the Han river upstream, downstream, the Geum river upstream, and the Nakdong river midstream area. A total of 52 cases were analyzed for seven stations in each group. The optimal exponent value of distance was calculated in a case including one base station and four surrounding stations in a group. We applied the golden section search method to calculating this optimum values using rainfall data for 10 years (2004~2013) and verified the optimum values for the last three years (2014~2016). We compared and analyzed two results of the conventional inverse distance method and the inverse distance method in this study. The optimal values of distance exponent obtained in this study were 3.280, 1.839, 2.181, and 2.005 respectively, in the four groups, and totally mean value was 2.326. It is shown the proposed inverse distance method applying the optimal exponent is superior to the conventional inverse distance method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.10
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• pp.2338-2356
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• 2013

In cognitive radio networks, acquiring the position information of the primary user is critical to the communication of the secondary user. Localization of primary users can help improve the efficiency with which the spectrum is reused, because the information can be used to avoid harmful interference to the network while simultaneity is exploited to improve the spectrum utilization. Despite its inherent inaccuracy, received signal strength based on range has been used as the standard tool for distance measurements in the location detection process. Most previous works have employed the path-loss propagation model with a fixed value of the path loss exponent. However, in actual environments, the path loss exponent for each channel is different. Moreover, due to the complexity of the radio channel, when the number of channel increases, a larger number of RSS measurements are needed, and this results in additional energy consumption. In this paper, to overcome this problem, we propose using the Bayesian compressive sensing method with a calibrated path loss exponent to improve the performance of the PU localization method.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.1 s.94
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• pp.141-149
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• 1999

어느 한 계가 양수의 발산지수(Lyapunov exponent)를 가질 때 이 계는 카오스계로 분류되며 그 동특성은 예측이 불가능해 진다. 감쇠 기계계(소산계)에서는 위상공간(phase space)의 초기 부피가 시간에 따라 수축한다. 발산 지수들의 합은 음수이며 그 기계계의 감쇠와 관련되며, 따라서 발산지수들의 합은 감쇠의 변화를 감시하는데 사용되어질 수 있다. 그러나 그 감쇠변화를 감시하기 위해서는 발산지수를 계산하는데 사용하는 신호(data) 부분(segment)이 짧아야 한다. 이는 문제점을 야기시키는데 그 이유는 발산지수가 아주 많은 양의 발산률(divergence rate)의 평균으로서 구해지기 때문이다. 이 문제를 극복하기 위해서, 본 저자는 '순간발산지수(Instantaneous Lyapunov Exponent)'를 도입하였으며, 이 순간발산지수들의 합이 어떻게 기계계의 감쇠와 관련되어지는 가에 대하여 기술하였다. 미분방적식과 시계열(time series)을 이용한 컴퓨터 시뮬레이션은 '순간발산지수들의 합'의 중요성을 입증하였다. 그러나 시계열(또는 실험신호)로 부터의 정확한 순간발산지수를 측정하기는 매우 힘들기 때문에 '부분발산지수(Short term averaged Lyapunov Exponent)'를 또한 도입하였다.

• Journal of the Korean Solar Energy Society
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• v.32 no.2
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• pp.87-94
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• 2012

In this study, we found a relationship between wind shear exponent, ${\alpha}$, and a few factors such as the wind speed, $V$, ruggedness index($RIX$), and the Weibull shape parameter, $k$ of sites in complex terrain in Korea. Wind shear exponents in main wind directions were calculated using wind speed data measured for one year from various heights of eleven meteorological masts in Gangwon province. It was found from the analysis that the reciprocal of the wind shear exponent can be expressed by an exponentially decaying function with respect to a multiple of $V$, $RIX$ and $k$. This result is considered useful to be used to characterize wind characteristics of specific sites in complex terrain in Korea with limited information.