• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.5
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• pp.260-270
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• 2014

In this paper, we first analyze the delay performance of Dynamic Space-time Subframe (DSTS)-based frame structure which has been proposed to support the real-time service as well as non real-time service, using Ad hoc Self-Organizing Time Division Multiple Access (ASO-TDMA) MAC protocol, especially when transmitting a MAC SDU with two or more MAC PDUs, in a multi-hop ad-hoc maritime communication network. We propose two key transmission schemes: contiguous DSTS reservation which guarantees the end-to-end delay for the multiple PDUs, and adaptive transmission probability control schemes to maximize the system throughput. Our simulation results show that the proposed schemes outperform the system throughput of the existing transmission schemes, while supporting the real-time requirement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.5
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• pp.280-292
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• 2014

Recently, heterogeneous networks consisting of small-cells on top of traditional macro-cellular network has attracted much attention, because traditional macro-cellular network is not suitable to support more demanding mobile data traffic due to its limitation of spatial reuse. However, due to the transmit power difference between macro- and small-cells, most users are associated with macro-cells rather than small-cells. To solve this problem, enhanced inter-cell interference coordination (eICIC) has been introduced. Particularly, in eICIC, the small-cell coverage is forcibly expanded to associate more users with small-cells. Then, to avoid cross-tier interference from macro-cells, these users are allowed to receive the data during almost blank subframe (ABS) in which macro-cells almost remain silent. However, this approach is not sufficient to balance the load between macro- and small-cells because it only expands the small-cell coverage. In this paper, we propose a load balance scheme improving proportional fairness for heterogeneous networks employing eICIC. In particular, the proposed scheme combines the greedy-based user association and the ABS rate determination in a recursive manner to perform the load balance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.314-317
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• 2007

Automotive rear subframe of aluminum tube was developed by using hydroforming process, based on the numerical analysis and physical tryouts. In the previous study, the effect of prebending was evaluated on the basis of forming limit diagram which had been obtained from free bulging, T-shape forming and cross-shape forming, using the developed tube hydroformability testing system. In order to get the sound products, appropriate internal pressure is to be imposed corresponding to the axial feeding. In this study, the loading path, the combination of internal pressure and axial feeding during the process, was optimized to ensure minimum thickness variation and dimensional accuracy, by using response surface method.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2017.06a
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• pp.155-157
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• 2017

본 논문에서는 ATSC(Avanced Television Systems Committee) 3.0 물리계층에서 다양한 서비스 시나리오별 가능한 프로파일을 도출하기 위한 MATLAB GUI(graphical user interface)기반의 ATSC 3.0 시뮬레이터를 구현한다. 개발된 시뮬레이터는 ATSC 3.0 에서 지원하는 다양한 종류의 BICM(bit interleaved and coded modulation) 및 OFDM(orthogonal frequency division multiplexing) 파라미터 조합과 다중화 방식을 지원할 수 있고, 그에 따른 프레임 길이와 전송률을 계산할 수 있다. 개발된 시뮬레이터에서는 4 개의 PLP(physical layer pipe)까지 지원할 수 있고, 최대 4 개의 부프레임(subframe)까지 구성이 가능하다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.402-408
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• 2003

Currently tube hydroforming has many studies and applications in manufacturing industry, especially in automotive industry. But tube hydroforming was applied to the automotive component with simple shape. So the manufacturer and the researcher proposed additional processes to form the automotive component with complex shape. It is prebending and preforming. Prebending is to crush bend or rotary draw bend a tubular blank into a shape that facilitates placement into the next forming tool. Preforming is where the prebent tube is crushed into a shape that facilitates placement into the final forming tool. This paper analyzed and compared to the tube hydroforming process to using of general and preformed bending tube, also explained the importance of tube bending and preforming process. The explicit finite element program PAM-STAMP$\^$TM/ was used to simulate the tube hydroforming operations.

• Korean Journal of Mathematics
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• v.15 no.2
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• pp.87-100
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• 2007

We introduce a concept of countably strong inclusions ${\triangleleft}$ and that of ${\triangleleft}-{\sigma}$-ideals and prove that the subframe $S({\triangleleft})$ of the frame ${\sigma}IdL$ of ${\sigma}$-ideals is a Lindel$\ddot{o}$fication of a frame L. We also deal with conditions for which the converse holds. We show that any countably approximating regular $D({\aleph}_1)$ frame has the smallest countably strong inclusion and any frame which has the smallest $D({\aleph}_1)$ Lindel$\ddot{o}$fication is countably approximating regular $D({\aleph}_1)$.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.4
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• pp.223-228
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• 2005

Tube hydroforming provides a number of advantages over conventional stamping process, including fewer secondary operation, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength and stiffness. It can produce wide range of products such as subframe, engine cradle, and exhaust manifold. In this study, the effect of the heat treatment conditions such as post seam annealing (PSA) and bright annealing (BA) on the ovality and hydro-formability of steel tubes has been investigated. Hydroformabilities have been estimated by the bulging heights obtained at various processing parameters such as internal pressure, axial feeding and heat treatment conditions. The ovality and forming height are strongly influenced by material properties after heat treatments.

• Korean Journal of Mathematics
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• v.29 no.3
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• pp.493-499
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• 2021

Every closed subset of a compact topological space is compact. Also every compact subset of a Hausdorff topological space is closed. It follows that compact subsets are precisely the closed subsets in a compact Hausdorff space. It is also proved that a topological space is maximal compact if and only if its compact subsets are precisely the closed subsets. A locale is a categorical extension of topological spaces and a frame is an object in its opposite category. We investigate to find whether the closed sublocales are exactly the compact sublocales of a compact Hausdorff frame. We also try to investigate whether the closed sublocales are exactly the compact sublocales of a maximal compact frame.

• Journal of the Korean Society for Railway
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• v.19 no.1
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• pp.20-28
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• 2016

Curved squeal noise may result when railway vehicles run on curved tracks. Contact between the wheels and the rails causes a stick-slip phenomenon, which generates squeal noise. In order to identify the mechanism of the squeal noise systematically, a scaled test rig has been fabricated. Knowledge of the contact forces between the wheels and the rail rollers is essential for investigating the squeal noise characteristics; however, it is difficult to measure there contact force. In this study, contact forces have been calculated indirectly according to the modal behavior of the subframe that supports the rail roller and the responses at specific positions of that subframe. In order to verify the estimated contact forces, the displacements at the contact points between the wheels and rail rollers have been calculated from the estimated forces; the resulting values have been compared with the measured displacement values. The SPL at the specific location has been calculated using the estimated contact forces and this also has been compared with the SPL, measured in a semi-anechoic chamber. The comparisons in displacements and SPLs show good correlation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.851-863
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• 2002

Recent industrial requirements for highly precise shape processing have brought the electric discharge machining (EDM) in great need. High precision in EDM is primarily achieved by high performance controllers. However there exists inherent precision loss due to structural micro-deformation. On this background, we study structural deformation characteristics of wire cut EDM via finite element (FE) analysis and axiomatic design. Two different wire cut EDMs are selected as analysis models. 3D CAD package I-Deas is first used to construct FE models of wire cut EDMs, and then ABAQUS FE code is used for following structural analysis. Pertinency of FE mesh refinement is discussed in terms of η -factor. It is shown that performance accuracy of EDM depends strongly on the structural characteristics. Some design enhancements are suggested in an axiomatic design point of view. Finally we provide weight and temperature induced displacement discrepancies between wire end points as position functions of each subframe.