• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1053-1058
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• 2008

Porous medium was considered in the present study for the heat transfer enhancement. This was attributed to its high surface area to volume ratio as well as intensive flow mixing by tortuous flow passages. But when the air or water flow through in the porous medium, it is occurred the pressure drop between inlet and outlet. So in the present study investigated simulation result about the pressure drop in the porous medium before apply to heat exchanger. In this simulation, the thickness of the solid inside the porous medium region was varied 0.2 mm to 0.4 mm. And then the simulation result were compared the pressure drop in the same unit cell ($0.5\;mm{\times}0.5\;mm{\times}0.5\;mm$). To make the analysis model, it was assumed the 14-sided tetrakaidecahedron cell which has long been considered the optimal packing cell first proposed by the Lord Kelvin in 1887. And then the simulation is carried out using by STAR-CCM+ which is commercial software. The simulation result can be showed quantified pressure drop by solid effect in the porous medium.

• Journal of Intelligence and Information Systems
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• v.24 no.4
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• pp.111-136
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• 2018

In this paper, we propose a methodology to extract answer information about queries from various types of unstructured documents collected from multi-sources existing on web in order to expand knowledge base. The proposed methodology is divided into the following steps. 1) Collect relevant documents from Wikipedia, Naver encyclopedia, and Naver news sources for "subject-predicate" separated queries and classify the proper documents. 2) Determine whether the sentence is suitable for extracting information and derive the confidence. 3) Based on the predicate feature, extract the information in the proper sentence and derive the overall confidence of the information extraction result. In order to evaluate the performance of the information extraction system, we selected 400 queries from the artificial intelligence speaker of SK-Telecom. Compared with the baseline model, it is confirmed that it shows higher performance index than the existing model. The contribution of this study is that we develop a sequence tagging model based on bi-directional LSTM-CRF using the predicate feature of the query, with this we developed a robust model that can maintain high recall performance even in various types of unstructured documents collected from multiple sources. The problem of information extraction for knowledge base extension should take into account heterogeneous characteristics of source-specific document types. The proposed methodology proved to extract information effectively from various types of unstructured documents compared to the baseline model. There is a limitation in previous research that the performance is poor when extracting information about the document type that is different from the training data. In addition, this study can prevent unnecessary information extraction attempts from the documents that do not include the answer information through the process for predicting the suitability of information extraction of documents and sentences before the information extraction step. It is meaningful that we provided a method that precision performance can be maintained even in actual web environment. The information extraction problem for the knowledge base expansion has the characteristic that it can not guarantee whether the document includes the correct answer because it is aimed at the unstructured document existing in the real web. When the question answering is performed on a real web, previous machine reading comprehension studies has a limitation that it shows a low level of precision because it frequently attempts to extract an answer even in a document in which there is no correct answer. The policy that predicts the suitability of document and sentence information extraction is meaningful in that it contributes to maintaining the performance of information extraction even in real web environment. The limitations of this study and future research directions are as follows. First, it is a problem related to data preprocessing. In this study, the unit of knowledge extraction is classified through the morphological analysis based on the open source Konlpy python package, and the information extraction result can be improperly performed because morphological analysis is not performed properly. To enhance the performance of information extraction results, it is necessary to develop an advanced morpheme analyzer. Second, it is a problem of entity ambiguity. The information extraction system of this study can not distinguish the same name that has different intention. If several people with the same name appear in the news, the system may not extract information about the intended query. In future research, it is necessary to take measures to identify the person with the same name. Third, it is a problem of evaluation query data. In this study, we selected 400 of user queries collected from SK Telecom 's interactive artificial intelligent speaker to evaluate the performance of the information extraction system. n this study, we developed evaluation data set using 800 documents (400 questions * 7 articles per question (1 Wikipedia, 3 Naver encyclopedia, 3 Naver news) by judging whether a correct answer is included or not. To ensure the external validity of the study, it is desirable to use more queries to determine the performance of the system. This is a costly activity that must be done manually. Future research needs to evaluate the system for more queries. It is also necessary to develop a Korean benchmark data set of information extraction system for queries from multi-source web documents to build an environment that can evaluate the results more objectively.

• Composites Research
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• v.30 no.4
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• pp.247-253
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• 2017

In this study, the mechanical behavior and interface properties of boron nitride nanotube-poly(methyl methacrylate) nanocomposites are predicted using the molecular dynamics simulations and the double inclusion model. After modeling nanocomposite unit cell embedding single-walled nanotube and polymer, the stiffness matrix is determined from uniaxial tension and shear tests. Through the orientation average of the transversely isotropic stiffness matrix, the effective isotropic elastic constants of randomly dispersed microstructure of nanocomposites. Compared with the double inclusion model solution with a perfect interfacial condition, it is found that the interface between boron nitride nanotube and polymer matrix is weak in nature. To characterize the interphase surrounding the nanotube, the two step domain decomposition method incorporating a linear spring model at the interface is adopted. As a result, various combinations of the interfacial compliance and the interphase elastic constants are successfully determined from an inverse analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.1
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• pp.80-90
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• 1996

The efficienty of ATM is based on the statical multiplexing of fixed-length packets, which are called cells. The most important technical point for realizing ATM switching network is an arrangement of the buffers and switches. Current most ATM switching networks are being achieved by using the switching modules based on the unit switch of $8{\times}8$ 150Mb/s or $16{\times}16$ 150Mb/s, the unit switch of $32{\times}32$150Mb/s for a large scale system is under study in many countries. In this paper, we proposed a new $32{\times}32$(4.9Gb/s throughput) ATM switch using Shared buffer memory switch which provides superior traffic characteristics in the cell loss, delay and throughput performance and easy LSI(Large Scale Integrated circuit). We analytically estimated and simulated by computer the buffer size into it. We also proposed the configuration of the large capacity ATM switching network($M{\times}M$.M>1,000) consisting of multistage to improve the link speed by non-blocking.

• Journal of Preventive Medicine and Public Health
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• v.47 no.1
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• pp.57-63
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• 2014

Objectives: We established a Wistar rat model of asthma caused by toluene diisocyanate (TDI) exposure, and investigated the relationship between TDI exposure concentrations and respiratory hypersensitivity, airway inflammation, and cytokine secretions in animals, to better understand the mechanism of TDI induced occupational asthma. Methods: Wistar rats were exposed to two different concentrations of TDI vapor four hours a day for five consecutive days. Bronchoalveolar lavage (BAL) was performed, and differential leucocytes from the BAL fluid were analyzed. Lung histopathological examination was carried out to investigate the inflammatory status in the airways. Production of cytokines interleukin (IL)-4 and IL-5 productions in the BAL fluid in vivo was determined with enzyme-linked immunosorbent assay kits. Results: The TDI-exposed rats exhibited greater airway hypersensitivity symptoms than the control rats. The BAL differential cell count and lung histopathological examination demonstrated that inflammation reactions were present in both the central and peripheral airways, characterized with marked infiltration of eosinophils in the TDI-exposed rats. The cytokine assay showed that IL-4 and IL-5 were predominantly produced in the BAL fluid in vivo. Conclusions: These findings imply that TDI exposure concentrations may greatly affect the occurrence and extent of inflammatory events and that Th2 type cytokines may play an important role in the immunopathogenesis of TDI-induced occupational respiratory hypersensitivity.

• Journal of Advanced Navigation Technology
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• v.18 no.2
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• pp.142-150
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• 2014

In this paper, the performance analysis results of time/frequency synchronization and cell search algorithm are presented for aeronautical mobile airport communication systems (AeroMACS). AeroMACS is based on IEEE 802.16e mobile WiMAX standard and uses the aeronautical frequency band of 5GHz with the bandwidth of 5MHz. The simulation model of AeroMACS is designed and the performance evaluation is conducted with the various airport channel models such as apron (APR), runway (RWY), taxiway (TWY), and park (PRK). The proposed synchronization unit was designed in hardware description language (HDL) and implemented on FPGA. Also, the real-time operation was verified and evaluated using FPGA test system.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.21 no.3
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• pp.99-110
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• 2018

Compared to yellow dust coming from China or particulate matter created naturally in spring due to Total Suspended Particulate(TSP), particulate matter in winter season have much more serious effect on human body as they penetrate cell membranes. Although such particulate matter are becoming a social issue, there are no concrete plans on how to reduce them. Air-purifying plants are limited in maintaining the indoor air quality of large area because it is usually difficult to quantify their performance. In order to improve this, a bio-filter that can be connected to air conditioner is suggested as an option. This study seeks to improve air conditioning model-based monitoring method for bio-filters from prior studies and objectify correlations between applied vegetation and growing environment into quantitative indicators. By doing so, this study seeks to provide criteria on plants applied to artificial soil-based vegetation bio-filters and basic information to set air-conditioning features. The study results confirmed significant tendency on the growing stability of each purifying plant in mechanical air-conditioning environment. Among three models selected for bio-filter vegetation models, epipremnum aureum showed high performance in quantitative indicators, including soil moisture, EC, and leaf temperature, etc., indicating that it would assure the highest growing stability in this test air-conditioning environment.

• Advances in nano research
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• v.15 no.5
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• pp.385-399
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• 2023

Hexagonal boron nitride (h-BN), commonly referred to as Boron Nitride Nanoribbons (BNNRs), is an electrical insulator characterized by high thermal stability and a wide bandgap semiconductor property. This study delves into the electronic properties of two BNNR configurations: Armchair BNNRs (ABNNRs) and Zigzag BNNRs (ZBNNRs). Utilizing the nearest-neighbour tight-binding approach and numerical methods, the electronic properties of BNNRs were simulated. A simplifying assumption, the Hamiltonian matrix is used to compute the electronic properties by considering the self-interaction energy of a unit cell and the interaction energy between the unit cells. The edge perturbation is applied to the selected atoms of ABNNRs and ZBNNRs to simulate the electronic properties changes. This simulation work is done by generating a custom script using numerical computational methods in MATLAB software. When benchmarked against a reference study, our results aligned closely in terms of band structure and bandgap energy for ABNNRs. However, variations were observed in the peak values of the continuous curves for the local density of states. This discrepancy can be attributed to the use of numerical methods in our study, in contrast to the semi-analytical approach adopted in the reference work.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.223-233
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• 2003

Sand compaction pile (SCP) is one of the ground improvement techniques which are being used for not only accelerating consolidation but also increasing bearing capacity of loose sands or soft clay grounds. In this study, laboratory model tests and 3-D finite element analyses were performed to investigate the interaction between sand compaction piles and surrounding soft soils. Based on the results obtained, as the area replacement ratio increases, the stress concentration ratio increases at the pile point, the settlement decreases, and the relative displacement between column and soil also decreases. It is also found that numerical study is illustrated by good comparison with model test results, and the numerical analysis revealed slip effects which could not be specifically identified in the model tests.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.10
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• pp.691-699
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• 2022

Large aperture antennas with long focal lengths in space have important application for telecommunications, Earth observation and science missions. This paper aims to understand the dynamics of deployment of large mesh antennas and to provide a multibody model for determining the driving forces for the design of reflectors and booms. The modular deployable reflector and boom are designed based on the deployment unit cell. A multibody dynamic model is formulated with Kane's equation and simulated using the pseudo upper triangular decomposition (PUTD) method for solving the constrained problem. Based on the multibody dynamic model, the kinetics of the deployment, the motor driving forces, and the structural dynamic deformation are investigated.