• Structural Engineering and Mechanics
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• v.74 no.1
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• pp.1-18
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• 2020

For the large deformation of shear walls under vertical and horizontal loads, there are difficulties in obtaining accurate simulation results using the response analysis method, even with fine mesh elements. Furthermore, concrete material nonlinearity, stiffness degradation, concrete cracking and crushing, and steel bar damage may occur during the large deformation of reinforced concrete (RC) shear walls. Matrix operations that are involved in nonlinear analysis using the traditional finite-element method (FEM) may also result in flaws, and may thus lead to serious errors. To solve these problems, a planar four-node element was developed based on vector mechanics. Owing to particle-based formulation along the path element, the method does not require repeated constructions of a global stiffness matrix for the nonlinear behavior of the structure. The nonlinear concrete constitutive model and bilinear steel material model are integrated with the developed element, to ensure that large deformation and damage behavior can be addressed. For verification, simulation analyses were performed to obtain experimental results on an RC shear wall subjected to a monotonically increasing lateral load with a constant vertical load. To appropriately evaluate the parameters, investigations were conducted on the loading speed, meshing dimension, and the damping factor, because vector mechanics is based on the equation of motion. The static problem was then verified to obtain a stable solution by employing a balanced equation of motion. Using the parameters obtained, the simulated pushover response, including the bearing capacity, deformation ability, curvature development, and energy dissipation, were found to be in accordance with the experimental observation. This study demonstrated the potential of the developed planar element for simulating the entire process of large deformation and damage behavior in RC shear walls.

• Publications of The Korean Astronomical Society
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• v.27 no.3
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• pp.71-80
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• 2012

We have developed superconducting mixer receivers for 129 GHz VLBI observation in Korean VLBI Network (KVN). The developed mixer has a radial waveguide probe with simple transmission line L-C transformer as a tuning circuit to its 5 series-connected junctions, which can have 125 - 165 GHz as the operation radio frequency (RF). For intermediate frequency (IF) signal path a high impedance quarter-wavelength line connects the probe to one end of symmetric RF chokes. The double side band (DSB) receiver noise of the mixer was about 40 K over 4 - 6 GHz IF band, whereas we achieved the uncorrected single side band (SSB) noise temperature of about 70 K and better than 10 dB image rejection ratio in 2SB configuration with 8 - 10 GHz IF band. Insert-type receiver cartridges employing the mixers have been under commission for KVN stations.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.39-45
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• 2011

This study presents the thermal behaviors of glass beads-rubber mixtures depending on the volumetric fraction of each constituent and relative size between them. The transient plane source method is used to measure the effective thermal conductivity of mixtures. The discrete element method (DEM) and the thermal network model are integrated to investigate the particle-scale mechanism of heat transfer in granular packings. Results show that 1) the effective thermal conductivity decreases as the rubber fraction increases, and 2) the relative size between two solid particles dominates the spatial configuration of inter-particle contact condition that in tum determines the majority of heat propagation path through particle contacts. For the mixtures whose volumetric fraction of rubber is identical, the less conductive materials (e.g., rubber particles) with a large size facilitate heat transfer in granular materials. The experimental results and particle-scale observation highlight that the thermal conduction behavior is dominated not only by the volumetric fraction but also the spatial configuration of each constituent.

• The Journal of the Korean dental association
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• v.55 no.5
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• pp.328-338
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• 2017

Introduction: The aim of the current study was to describe the prevalence and treatment of mandibular first molar eruption disturbances. Methods: A total of 38 mandibular first molars(M1mn) from 36 patients(17 males and 19 females; aged 9 years 2 months?35 years 10 months) were identified from the 13,391 patients that received orthodontic treatment from 1983?2012. The subjects were classified into 3 categories based on panoramic radiographic examination: impaction due to ectopic position of the tooth germ relative to the contra-side same tooth(Group 1), impaction due to obstruction of the eruption path with cyst or calcium mass (Group 2), and primary and secondary retention due to defects in the follicle or periodontal ligament(PDL; Group 3). The treatment outcomes were evaluated into four categories: no treatment(A), orthodontic traction(B), autotransplantation(C), and extraction due to orthodontic traction failure(D). Results: The prevalence rate of M1mn eruption disturbances in this sample was 0.27%. In Groups 1 and 2, most of the impacted M1mn were erupted successfully by orthodontic traction. In Group 3, most of the retained M1mn were failed to erupt and recommended for extraction. Conclusions: Treatment prognosis was favorable on Group 1 & 2 than Group 3. After removing an element of the cause in case of Group 1 & 2, orthodontic traction or periodic observation will be recommended.

• The KIPS Transactions:PartC
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• v.16C no.2
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• pp.143-150
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• 2009

In trust-based networks, it is very important how to decide a node is trustworthy when one node performs communications with other node. In current networks based on trust, a node creates a new trust value from observation and then establishes an intercommunication path through the process of evaluating a targeted communication node. In our paper, we propose four trust models in which a new node enters a cluster and finds a target node to create a communication in ad-hoc networks. The proposed models have been classified according to the existence of reputation server and the trust evaluation functions. Through the proposed model, we found that new node finds target node more quickly in which there exists a reputation server in the cluster and considers neighbor node's recommendation as well as own experience information when calculates trust values. As our performance analysis, we focus the communication delay time to generate a final trust value for each trust model.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.33 no.4
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• pp.305-316
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• 2015

The GPS signal delays in troposphere, which are along the signal path between a transmitting satellite and GPS permanent station, can be used to retrieve the precipitable water vapor. The GPS remote sensing technique of atmospheric water vapor is capable of monitoring typhoon and detecting long term water vapor for tracking of earth’s climate change. In this study, we analyzed GPS precipitable water vapor variations during the heavy snowstorm event occurred in the Yeongdong area, 2014. The results show that the snowfall event were occurring after the GPS precipitable water vapor were increased, the maximum fresh snow depth was recorded after the maximum GPS precipitable water vapor was generated, in Kangneug and Wuljin, respectively. Also, we analyzed that the closely correlation among the GPS precipitable water vapor, the K-index and total index which was acquired by the upper air observation system during this snowstorm event was revealed.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
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• 2013.11a
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• pp.28-29
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• 2013

We have been measuring $CH_4$ flux in a rice paddy in Gimje using the eddy covariance method since July 2011. In order to measure the fast fluctuations of $CH_4$ concentration, an innovative LI-7700 open-path laser spectrometer is used. This high-precision, low power, light weight, low maintenance sensor enables us to operate it on a continuous and long-term basis. One particular feature, among other things, is the self-cleaning lower mirror which decreases maintenance requirements while ensuring more robust, continuous, high-quality dataset. Its cleaning is initiated at user-specified time intervals or a signal strength threshold, and its status is recorded as a diagnostic index. We have noticed that the operation of LI-7700 at Gimje site is quite challenging particularly due to its frequent mirror cleaning requirement and the associated sensitivity of the instrument. In this presentation, we present some field observation data regarding the mirror cleaning and their analysis, thereby suggesting the pertinent operation options for high-quality, maximum data retrieval in the field.

• The Journal of the Korea Contents Association
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• v.19 no.9
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• pp.376-387
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• 2019

The role of local decentralization and balanced regional development becomes important due to the concentration of population due to urbanization, and the development of tourism contents in local governments is actively being attempted. However, this is largely due to quantitative growth, and it does not offer tourist content that offers a different experience while utilizing regional characteristics. This means that it is important to develop programs and contents that emphasize the identity of the region by cultivating local characteristics and build a different image. However, most of the small regions where characteristic resources are difficult to find have a problem that it is difficult to develop different programs and contents due to relatively few development opportunities and financial constraints. In this study, it was considered that it is effective to analyze characteristic features of the region and utilize the possessed assets as much as possible. Therefore, we propose a service design process that effectively supports ecotourism, one of the regional revitalization plan using local eco - assets. In the process, Venn Diagram Position and Context Map methodology was developed and verified through Sutonggol Observation Path.

• Journal of Aerospace System Engineering
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• v.13 no.2
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• pp.66-72
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• 2019

The observation satellites which uses high heat-dissipating equipment such as synthetic aperture radar (SAR) satellites require a radiator to transmit heat from the equipment into outer space. However, during cold conditions it requires a heater to maintain the temperature of equipment within the allowable minimum limit when it is not in operation. In this study, we proposed a variable conductivity radiator that changes its thermal conductivity value through movement of the liquid metal between two reservoirs based on the temperature condition. This reduces the power consumption of the heater by limiting heat transfer path to the radiator in cold condition, while effectively transferring heat to the radiator during hot condition. The feasibility of the proposed radiator was validated through comparison of the thermal control performance with the conventional fixed conductivity radiator via a thermal analysis.

• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.28-38
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• 2010

High temperature high cycle and low cycle fatigue deformation behavior of automotive heat resistant aluminum alloys (A356 and A319 based) were investigated in this study. The microstructures of both alloys were composed of primary Al-Si dendrite and eutectic Si phase. However, the size and distribution for eutectic Si phase varied: a coarse and inhomogeneous distributed was observed in alloy B (A319 based). A brittle intermethallic phase of ${\alpha}-Fe\;Al_{12}(Fe,Mn)_3Si_2$ was detected only in B alloy. Alloy B exhibited high fatigue life only under a high stress amplitued condition in the high cycle fatigue results, whereas alloy A showed high fatigue life when stress was lowered. With regard to the low-cycle fatigue result ($250^{\circ}C$) showing higher fatigue life as ductility increased, alloy A demonstrated higher fatigue life under all of the strain amplitude conditions. Fractographic observations showed that large porosities and pores near the outside surface could be the main factor in the formation of fatigue cracks. In alloy B. micro-cracks were formed in both the brittle intermetallic and coarse Si phasese. These micro-cracks then coalesced together and provided a path for fatigue crack propagation. From the observation of the differences in microstructure and fractography of these two automotive alloys, the authors attempt to explain the high-temperature fatigue deformation behavior of heat resistant aluminum alloys.