• Journal of Information Processing Systems
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• v.13 no.5
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• pp.1320-1330
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• 2017

Wireless sensor networks for forest monitoring are typically deployed in fields in which manual intervention cannot be easily accessed. An interesting approach to extending the lifetime of sensor nodes is the use of energy harvested from the environment. Design constraints are application-dependent and based on the monitored environment in which the energy harvesting takes place. To reduce energy consumption, we designed a power management scheme that combines dynamic duty cycle scheduling at the network layer to plan node duty time. The dynamic duty cycle scheduling is realized based on a tier structure in which the network is concentrically organized around the sink node. In addition, the multi-paths preserved in the tier structure can be used to deliver residual packets when a path failure occurs. Experimental results show that the proposed method has a better performance.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.10 no.3
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• pp.185-219
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• 1981

To analyze two dimensional incompressible laminar natural convection in a rectangular enclosure heated from below and cooled by a horizontal ceiling and two vertical walls, he primitive Navier-Stokes equations and the energy equation were solved numerically in time dependent form by a marker and cell method. A successive over-relaxation method for the elliptic portion of the problem and an explicit method for the parabolic portion were applied for the range of Grashoff number of $5{\times}10^3\;to\;5{\times}10^4$ to get the transient and steady state dimensionless temperature and velocity profiles. For the range of aspect ratio $L/H{\leqq}2.4$ in which only a pair of convection rolls exists mean Nusselt number calculated are as follows : $$N_{NU}0.89\;N_{Gr}^{0.2}(H/L)^{0.45}$$ By path lines drawn by marker particle trajectories roll number of cellular motion were observed for various aspect ratio of the enclosure.

• Progress in Superconductivity and Cryogenics
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• v.21 no.3
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• pp.18-21
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• 2019

We studied the effect of Fe ion irradiation on the upper critical field ($H_{c2}$) of 410 nm single-crystalline $MgB_2$ thin films. The irradiation energy was fixed at 140 keV when we increased the irradiation doses from $1{\times}10^{14}ion/cm^2$ to $4{\times}10^{14}ion/cm^2$. We found that $H_{c2}$ significantly increase with increasing irradiation dose, despite the low irradiation energy. The enhancement of $H_{c2}$ could be explained by the reduction of electron mean free path caused by defects induced from irradiation, leading to a decrease of coherence length (${\xi}$). We also discussed the effect of irradiation on temperature-dependent resistivity in details.

• Geomechanics and Engineering
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• v.25 no.4
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• pp.283-294
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• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• The Journal of the Acoustical Society of Korea
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• v.35 no.4
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• pp.295-302
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• 2016

Underwater acoustic communication channel is often defined as a multipath fading channel since the multipath arrivals from various paths interfere with each other and cause frequency dependent constructive or destructive interference in received signals. Therefore signal-to-noise ratio (SNR) of received signal fluctuates as a function of frequency. In addition, sea surface fluctuation induces frequency dependent time variant signal fading due to coherent component variation of surface bounce path. The frequency shift keying (FSK) system is known to be less sensitive and more robust under these interference and fading, and M-ary frequency shift keying (MFSK) system is adopted to increase a data rate. In this study, a bit error rate (BER) of 4 channels 4FSK system are examined in shallow sea multipath channel. Experimental results show that RS code reduces efficiently the BER of 4FSK system since frequency dependent time-varying fading is characterized to give burst errors. The BER of a different data rate or different source-to-receiver range depends on not only the channel coherent bandwidth but also frequency dependent multipath fading.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.225-233
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• 2003

Even though a lot of advanced researches on analysis, design, and performance evaluation of reinforced concrete (RC) under seismic action have been carried out, there has been only a few study on seismic analysis of underground RC structures surrounding soil medium. Since the underground RC structures interact with surrounding soil medium, a path-dependent soil model which can predict the soil response is necessary for analyzing behavior of the structure inside soil medium. The behavior of interfacial zone between the RC structure and the surrounding medium should be also considered for more accurate seismic analysis of the RC structure. In this paper, an averaged constitutive model of concrete and reinforcing bars for RC structure and path-dependent Ohsaki's model for soil are applied, and an elasto-plastic interface model having thickness is proposed for seismic analysis of underground RC structures. A finite element analysis technique is developed by applying aforementioned constitutive equations and is verified by predicting both static and dynamic behaviors of RC structures. Then, failure mechanisms of underground RC structure under seismic action are numerically derived through seismic analysis of underground RC station structure under different seismic forces. Finally, the changes of failure mode and the damage level of the structures are also analytically derived for different design cases of underground RC structures.

• Communications for Statistical Applications and Methods
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• v.15 no.4
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• pp.563-585
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• 2008

This paper presents how to improve the efficiency and accuracy in the pricing and sensitivity evaluation for derivatives, since the need for the evaluation of complicated derivatives is increased. The Monte Carlo(MC) simulation using the quasi random number instead of pseudo random number can improve the elapsed time and accuracy for the valuation of European-type derivatives. However, the quasi MC simulation method has its limit for applying it in the multi-dimensional case such as American-type and path-dependent options due to the increased correlation between dimensions as the dimension of random numbers is increased. In order to complement this problem, we develop a modified method in which correlation values are controlled to be below a pre-specified value. Thus, this method is applicable for the pricing of either derivatives ill which underlying assets or risk factors are several or derivatives having path-dependent or early redemption property. Furthermore, we illustrate that it is important to take an appropriate grid interval for the use of finite difference method(FDM) by applying the FDM to one example of non-symmetrical butterfly spreads.

• Korean Journal of Social Welfare
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• v.35
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• pp.319-344
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• 1998

The endeavor to reveal reasons and backgrounds of juvenile's being delinquent has been continuing. Most of them, however, are not multi-dimensional and integrative, but one-dimensional which has had just focused on the factor of family or individual. One of the main purposes of this. study is to get implications on practical programs through the ecological-systematic analysis on factors and processes of juvenile delinquency. In this study, region has separated into two, one is of poor and the other is non, and then informations on factors and process of being delinquent were gathered by comparing between them. Eleven hundreds and sixteen cases were sampled from six junior-high schools which have met the purpose of this study. The survey had been committed with structured questionnaire which had been consisted in several variables; personal; familial; school and peer related; delinquent characteristics. Reliability and validity of each variables had been tested through pilot test. Effects of independent variables on dependent variables were analyzed according to the region through path analysis. In the analysis, remarkable differences on the processes of being delinquent had been found and three path models of being delinquent had been made on the basis of those differences. Each of them has shown different effecting patterns of personal, familial, and school and peer related variables on one's degree of delinquency. In Pattern 1, peer related variables have committed more powerful effects on the degree of delinquency than the others have. School related variables, in Pattern 2, commit most striking effects on the dependent variables. The degree of delinquency in Pattern 3 is most strongly effected by familial variables. The limitations that personal behavior oriented approach might be confronted in the field of juvenile delinquency have been proved by these results of this study. These results have given many implications to us on the needs of distinctive and integrative approaches to the problems of juvenile delinquency.

• Journal of the Korean Home Economics Association
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• v.36 no.9
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• pp.49-62
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• 1998

This paper investigates the parenting stress of fathers who have preschooler. At first, a causal model constructed, including the parenting stress as a dependent variable and the psychological characteristics of paternal self-esteem and parenting efficacy as parameters. Based on the change of parenting stress, self-esteem and parenting efficacy according to various pertinent to fathers, the causal effect of various variables effecting on the paternal parenting stress is analyzed. The SPSS PC program was used for the statistical analysis, where fully exploited were frequencies, percentages, means, standard deviations, Cronbach α, one-way analysis(ANOVA), path analysis. The results can be summarized into 3 parts, in conclusion: 1) The younger a father is, the higher paternal self-esteem becomes. Paternal self-esteem trend was there, for a father who is a member of large family, and for a father whose education level is high, and for a father whose occupation is professional. Regarding parenting sense of competence, a father shows confidence when he has more income, more educated and less children. 2) The variable analysis effecting on the parenting stress dut to the paternal environment shows that a father feels more stress when his income is less and his spouse is working. The sub-factor analysis on the parenting stress shows that 'typical stress dut to the parenting' increases when his income is less and his spouse is working, and 'pressures pertaning to the parental role and distress' increases for a father with less income, working spouse, less educated and non-professional job. Further 'guilty to the parenting by others' shows higher for a father with less income and a working spouse. 3) The path analysis, which were performed to check the causality of the parenting stress dut to various variables, shows that the self-esteem and the parenting efficacy are significant factors directly effecting on the paternal parenting stress, and the job-satisfaction and marriage-satisfaction are significantly effecting on the parenting stress both directly and indirectly.

• Journal of the Korean Society for Railway
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• v.13 no.2
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• pp.222-228
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• 2010

In this paper, we propose a optimization approach for the Electric Locomotive Overhaul Maintenance Facility (ELOMF), which aims at the simulation optimization so as to meet the design specification. In simulation design, we consider the critical path and sensitivity analysis of the critical (dependent) factors and the design (independent) parameters for the parameter selection and reduction of the metamodel. Therefore, we construct the multi-objective non-linear programming. The objective function is normalized for the generalization of design parameter while the constraints are composed of the simulation-based regression metamodel for the critical factors and design factor's domain. Then the effective solution procedure based on the pareto optimal solution set is proposed. This approach provides a comprehensive approach for the optimization of Train Overhaul Maintenance Facility(TOMF)'s design parameters using the simulation and metamoels.