• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.101-109
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• 2013

Recently, it is certain that the increase of heating and cooling energy consumption by radical change in climate condition has caused serious problems related to environmental and energy concerns associated with increase of fossil fuel usage and carbon dioxide production as well as global warming. So, various actions to reduce greenhouse gas exhaustion and energy consumption have been prepared by world developed countries. Our government has also been trying to seek energy control methods for houses and buildings by proclaiming political polices on low-carbon green growth and construction and performance standards for environment-friendly housing. The energy consumption by buildings approximately reaches 25% of total korea energy consumption, and the increasing rate of energy consumption by buildings is stiffer than the rate by the other industries. The greatest part in the buildings of the energy consumption is building facade. While lots of research projects for reducing energy consumption of the facade have been conducted, but a few research projects on concrete comprising more than 70% of outsider of buildings has been tried. This research presents here a study to improve the insulation property of structural concrete formed by micro form admixture (MFA) with experimentally reviewing the physical, mechanical and thermal characteristics of the concrete. As the results of this experiment, in the case of concrete mixed with MFA, slump loss has been improved. As the mixing ratio of MFA increases, the compressive strength is decreased and thermal conductivity is increased. Also it was found that water-cement ratio increases, the compressive strength is decreased and thermal conductivity is increased. but, there was not big influence by the change of fine aggregate ratio.

• Journal of Convergence for Information Technology
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• v.10 no.11
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• pp.55-63
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• 2020

The IoT technology is a field that applies and converges the technologies in the existing industrial environment, instead of new technologies. The IoT technology is releasing various application services converged with other industries such as smart home, healthcare, construction, and automobile, and it is also possible to secure the work efficiency and convenience of users of IoT-based technologies. However, the security threats occurring in the IoT-based technology environment are succeeding to the vulnerability of the existing wireless network environment. And the occurrence of new and variant attacks in the combination with the ICT convergence environment, is causing damages. Thus, in the IoT technology-based environment, it would be necessary to have researches on the safe transmission of messages in the communication environment between user and device, and device and device. This thesis aims to design a safe communication protocol in the IoT-based technology environment. Regarding the suggested communication protocol, this thesis performed the safety analysis on the attack techniques occurring in the IoT technology-based environment. And through the performance evaluation of the existing PKI-based certificate issuance system and the suggested communication protocol, this thesis verified the high efficiency(about 23%) of communication procedure. Also, this thesis verified the reduced figure(about 65%) of the issued quantity of certificate compared to the existing issuance system and the certificate management technique.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.2
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• pp.63-71
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• 2002

This paper examines the ASCE first generation benchmark problem for a seismically excited cable-stayed bridge, and proposes a new semi-active control strategy focusing on inclusion of effects of control-structure interaction. This benchmark problem focuses on a cable-stayed bridge in Cope Girardeau, Missouri, USA, for which construction is expected to be completed in 2003. Seismic considerations were strongly considered in the design of this bridge due to the location of the bridge in the New Madrid seismic zone and its critical role as a principal crossing of the Mississippi River. In this paper, magnetorheological(MR) fluid dampers are proposed as the supplemental damping devices, and a clipped-optimal control algorithm is employed. Several types of dynamic models for MR fluid dampers, such as a Bingham model, a Bouc-Wen model, and a modified Bouc-Wen model, are considered, which are obtained from data based on experimental results for full-scale dampers. Because the MR fluid damper is a controllable energy-dissipation device that cannot add mechanical energy to the structural system, the proposed control strategy is fail-safe in that bounded-input, bounded-output stability of the controlled structure is guaranteed. Numerical simulation results show that the performance of the proposed semi-active control strategy using MR fluid dampers is quite effective.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.39 no.6
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• pp.42-48
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• 2002

The design, construction and performance test of a convenient multi-purpose irradiator is described. A multi-purpose irradiator using Cesium-137 has been developed for studies of low dose radiation effects in biology and for calibration of Thermo Luminescent dosimeter(TLD). During the operation, three rods of radioactive material which are 10cm in length revolve 180 degrees and irradiate biological samples, or TLD, and return to their shielded position, after the programmed time. A programmable Logic Controller(PLC) controls the sequence of operation, interlock, motor rotation and safety system. The rotation speed of biological samples can vary up to 20 RPM. A real time monitoring system was also incorporated to check and control the operation status of the irradiator. The capacity of the irradiation chamber was 4.5 liters. The isodose distribution at arbitrary vertical planes was measured by using film dosimetry. The dose-rate was 0.13 cGy/min in air and 0.11 cGy/min in water equivalent material in the case of Cesium-137. Range of activity was 2 Ci. The homogeneity of dose distribution in the chamber was ${\pm}$7%. The actual radiation level on the surface was within permissible levels. The irradiator had a maximum 0.35 mR/min radiation leakage on its surface.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.4
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• pp.97-107
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• 2009

In image-based gait recognition systems, physical factors, such as the camera angle and the lens distortion, and environmental factors such as illumination determines the performance of recognition. In this paper we present a robust gait recognition method by compensating various types of image distortions. The proposed method is compared with existing gait recognition algorithm with consideration of both physical and environmental distortion factors in the input image. More specifically, we first present an efficient compensation algorithm of image distortion by using the projective transform, and test the feasibility of the proposed algorithm by comparing the recognition performances with and without the compensation process. Proposed method gives universal gait data which is invariant to both distance and environment. Gained data improved gait recognition rate about 41.5% in indoor image and about 55.5% in outdoor image. Proposed method can be used effectively in database(DB) construction, searching and tracking of specific objects.

• Journal of Korea Water Resources Association
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• v.47 no.9
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• pp.825-838
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• 2014

The stationary Markov chain model has been widely used as a daily rainfall simulation model. A main assumption of the stationary Markov model is that statistical characteristics do not change over time and do not have any trends. In other words, the stationary Markov chain model for daily rainfall simulation essentially can not incorporate any changes in mean or variance into the model. Here we develop a Non-stationary hidden Markov chain model (NHMM) based stochastic downscaling scheme for simulating the daily rainfall sequences, using general circulation models (GCMs) as inputs. It has been acknowledged that GCMs perform well with respect to annual and seasonal variation at large spatial scale and they stand as one of the primary sources for obtaining forecasts. The proposed model is applied to daily rainfall series at three stations in Nakdong watershed. The model showed a better performance in reproducing most of the statistics associated with daily and seasonal rainfall. In particular, the proposed model provided a significant improvement in reproducing the extremes. It was confirmed that the proposed model could be used as a downscaling model for the purpose of generating plausible daily rainfall scenarios if elaborate GCM forecasts can used as a predictor. Also, the proposed NHMM model can be applied to climate change studies if GCM based climate change scenarios are used as inputs.

• Journal of Korea Water Resources Association
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• v.46 no.10
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• pp.1029-1040
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• 2013

This study aims to develop a multivariate daily rainfall simulation model considering spatial coherence across watershed. The existing Hidden Markov Model (HMM) has been mainly applied to single site case so that the spatial coherences are not properly addressed. In this regard, HMM coupled with Chow-Liu Tree (CLT) that is designed to consider inter-dependences across rainfall networks was proposed. The proposed approach is applied to Han-River watershed where long-term and reliable hydrologic data is available, and a rigorous validation is finally conducted to verify the model's capability. It was found that the proposed model showed better performance in terms of reproducing daily rainfall statistics as well as seasonal rainfall statistics. Also, correlation matrix across stations for observation and simulation was compared and examined. It was confirmed that the spatial coherence was well reproduced via CLT-HMM model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3A
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• pp.161-169
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• 2012

This paper presents the safety and strength of simplified composite H-beam panel bridges (SCHPBs) using 3-dimentional finite-element program, ABAQUS (2007) and experimental tests. Two finite-element models (one-steel-girder-and-composite-deck model and four-steel-girder-and-wide-composite-deck model) were reviewed to predict the strength and load distribution factor (LDF) values of the composite bridges. Based on the results of the finite-element analyses, the behaviors of the two models were investigated, and deflection and strain gauges for the experimental specimens were set up to obtain the ultimate strengths and the LDF values. The ultimate strength of the one-steel-girder-and-composite-deck specimen was estimated to be 840 kN. The yield and plastic moments of the four-steel-girder-and-wide-composite-deck specimen were obtained to be 2.4 and 4.1 times the design moment based on the live loading condition of the Korea Bridge Design Specifications (2005). The SCHPB were found to have enough strength for safety under and after construction.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.19-27
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• 2010

Aging and severe environments are major causes of damage in reinforced concrete (RC) structures such as buildings and bridges. Deterioration such as concrete cracks, corrosion of steel, and deformation of structural members can significantly degrade the structural performance and safety. Therefore, effective and easy-to-use methods are desired for repairing and strengthening such concrete structures. Various methods for strengthening and rehabilitation of RC structures have been developed in the past several decades. Recently, FRP composite materials have emerged as a cost-effective alternative to the conventional materials for repairing, strengthening, and retrofitting deteriorating/deficient concrete structures, by externally bonding FRP laminates to concrete structural members. The main purpose of this study is to investigate the effectiveness of adaptive neuro-fuzzy inference system (ANFIS) in predicting behavior of circular type concrete column retrofitted with FRP. To construct training and testing dataset, experiment results for the specimens which have different retrofit profile are used. Retrofit ratio, strength of existing concrete, thickness, number of layer, stiffness, ultimate strength of fiber and size of specimens are selected as input parameters to predict strength, strain, and stiffness of post-yielding modulus. These proposed ANFIS models show reliable increased accuracy in predicting constitutive properties of concrete retrofitted by FRP, compared to the constitutive models suggested by other researchers.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.93-102
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• 2010

Recently, FRP usage for strengthening RC structures in civil engineering has been increasing. Especially, the use of FRP to strengthen structures against blast loading is growing rapidly. To estimate FRP retrofitting effect under blast loading, blast tests with nine $1,000{\times}1,000{\times}150\;mm$ RC panel specimens, which were retrofitted with carbon fiber reinforced polymer (CFRP), Polyurea, CFRP with Poly-urea and basalt fiber reinforced polymer (BFRP) have been carried out. The applied blast load was generated by the detonation of 15.88 kg ANFO explosive charge at 1.5 m standoff distance. The data acquisitions not only included blast waves of incident pressure, reflected pressure, and impulse, but also included central deflection and strains at steel, concrete, and FRP surfaces. The failure mode of each specimen was observed and compared with a control specimen. From the test results, the blast resistance of each retrofit material was determined. The test results of each retrofit material will provide the basic information for preliminary selection of retrofit material to achieve the target retrofit performance and protection level.