• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.5
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• pp.79-89
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• 1984

In this paper we present development of microprocessor-based 8-channel statistical multiplexer (SMUX). The hardware design includes one Z-80A CPU board with the clock rate of 4 MHz, one 16 Kbyte ROM board for program storage, one 16 Kbyte dynamic RAM board and three I/O boards, all connected through an S-100 compatible tristate bus. The SMUX can presently multiplex 8 channels with data rates ranging 50 bps to 9600 bps, but can be reduced to accommodate 4 channels by having a slight modification of software and removing one terminal I/O board. The system specifications meet CCITT recommendations X.25 link level, V.24, V.28, X.3 and X.28. Significant features of the SMUX are its capability of handling 4 input codes (ASCII, EBCDIC, Baudot, Transcode), the use of a dynamic buffer management algorithm, a diagnostic facility, and the efficient use of a single CPU for all system operation. Throughout the paper, detailed explanations are given as to how the hardware and software of the SMUX system have been designed efficiently.

• The KIPS Transactions:PartA
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• v.17A no.2
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• pp.63-72
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• 2010

Recently, the need for multimedia devices, such as digital TV, and camcorder has increased. These devices provide many services on multimedia files such as playing, recording, and editing. Throughout these services, in case of storing edited large-scaled multimedia files, existing file system have several capability problems that are taking too much time and requiring disk I/O. In this paper, we propose the use of Linux Ext2 file system based 'Block-Link file (BL-file) system' in order to solve these problems. For the BL-file system, when editing and storing large-scaled files, there is no data input or output but only modification of the metadata. Additionally, by sharing data blocks between multimedia files, we can save disk spaces. Moreover, because the managing of data block sharing information is more convenient than the existing FWAE technique, we can lessen system overhead. The BL-file system is based on Ext2 file system and implemented in a Linux environment, and the usefulness of the proposed technique is validated by applying the Linux multimedia file-editing tool 'Avidemux'.

• Journal of Communications and Networks
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• v.6 no.4
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• pp.376-386
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• 2004

In ad hoc networks, loss-based congestion window progression by the traditional means of duplicate ACKs and timeouts causes high network buffer utilization due to large bursts of data, thereby degrading network bandwidth utilization. Moreover, network-oriented feedbacks to handle route disconnection events may impair packet forwarding capability by adding to MAC layer congestion and also dissipate considerable network resources at reluctant intermediate nodes. Here, we propose a new TCP scheme that does not require the participation of intermediate nodes. It is a purely end-to-end scheme using TCP timestamps to deduce link conditions. It also eliminates spurious reductions of the transmission window in cases of timeouts and fast retransmits. The scheme incorporates a receiver-oriented rate controller (rater), and a congestion window delimiter for the 802.11 MAC protocol. In addition, the transient nature of medium availability due to medium contention during the connection time is addressed by a freezing timer (freezer) at the receiver, which freezes the sender whenever heavy contention is perceived. Finally, the sender-end is modified to comply with the receiver-end enhancements, as an optional deployment. Simulation studies show that our modification of TCP for ad hoc networks offers outstanding performance in terms of goodput, as well as throughput.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.6
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• pp.100-108
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• 2005

In this paper deals with the frequency control of the HVDC scheme linking Haenam to Cheju Island. The primary aim of the study is to develop and evaluate a new frequency control that can be employed without having to utilise the existing Synchronous Compensators(Gas Turbines). Transient condition studies are performed utilising the detailed control strategies for the HVDC link, implemented in PSCAD/EMTDC. Study cases are completed involving synchronous compensators trip and load ripping events and study plots presented. It is demonstrated that the existing frequency measurement can be replaced by one derived from the AC network alone, incorporated into a new frequency control algorithm and gives effective frequency control and dynamic performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.6
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• pp.1137-1147
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• 1997

I propose a RZETA network consisted of switching elements(SEs) that have regular links and alternate links. A modified Zeta nework used for the RZETA network's regular links and a MIN used for its alternate links are generated using the graph theory. The RZETA network is driven from merging the formaer and latter MINs. A necessary and sufficient condition for modified Zeta network to be a nonblocking network is also presented. This condition is a ufficient condition for RZETA network with a faulty link or a faulty SE to be nonblocked. Performance of the RZETA network is analyzed by modification of the model of 2-dilated Banyan network and its performance is compared with existing redundant path networks, when packet arrival rate of each source is 1.

• Journal of information and communication convergence engineering
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• v.12 no.3
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• pp.154-160
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• 2014

The address resolution protocol (ARP) provides dynamic mapping between two different forms of addresses: the 32-bit Internet protocol (IP) address of the network layer and the 48-bit medium access control (MAC) address of the data link layer. A host computer finds the MAC address of the default gateway or the other hosts on the same subnet by using ARP and can then send IP packets. However, ARP can be used for network attacks, which are one of the most prevalent types of network attacks today. In this study, a new ARP algorithm that can prevent IP spoofing attacks is proposed. The proposed ARP algorithm is a broadcast ARP reply and an ARP notification. The broadcast ARP reply was used for checking whether the ARP information was forged. The broadcast ARP notification was used for preventing a normal host's ARP table from being poisoned. The proposed algorithm is backward compatible with the current ARP protocol and dynamically prevents any ARP spoofing attacks. In this study, the proposed ARP algorithm was implemented on the Linux operating system; here, we present the test results with respect to the prevention of ARP spoofing attacks.

• Journal of the Korean Society for information Management
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• v.14 no.1
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• pp.77-105
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• 1997

The study confirmed that the methods for expanding headings and combined structures among the headings, subdivisions, qualifiers and inverted terms were diverse, and that the headings used for similar purposes do not have identical structural forms. It is also found that the standard symbols representing generic relationship in theasurus, which are introduced in the list of subject headings, do not show precisely the hiearchical relationship of phrase headings. MeSH in pre-coordinated system will be available for retrieval in the computer environment because it can make a link between headings and subdivisions in searching stage. The changes in retrieval circumstances and the seeking behaviors of the users demand that a new structure of subject headings be developed. It was proposed that the modification of the structure in the Hangul subject headings be essential.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.472-476
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• 2011

This paper presents the results of theoretical analysis and experimental test to verify the size effect on the fiber strength of filament wound pressure vessel. As a test method, a series of fully scaled hoop ring tests with filament wound carbon fiber-epoxy has been conducted. Test results showed remarkable size effect on fiber strength. And, as an analytical method, the WWLM(Weibull weakest link model) and SMFM(sequential multi-step failure model) were considered and compared to hoop ring test data. The analysis results showed significantly lower fiber strength value than that of test data. Through the modification of length size effect, modified SMFM is suggested. The fiber strengths from modified SMFM showed good agreement with test data.

• The Journal of Korea Robotics Society
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• v.8 no.3
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• pp.186-196
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• 2013

Since its introduction (e.g., [4, 6]), virtual coupling technique has been de facto way to connect a haptic device with a virtual proxy for haptic rendering and control. However, because of the single dependence on spring-damper feedback action, this virtual coupling suffers from the degraded transparency particularly during contact tasks when large device/proxy-forces are involved. In this paper, we propose a novel virtual coupling technique, which, by utilizing passive decomposition, reduces device-proxy position deviation even during the contact tasks while also scaling down (or up) the apparent inertia of the coordinated device-proxy. By doing so, we can significantly improve transparency between multiple degree of freedom (possibly nonlinear) haptic device and virtual proxy. In other to use passive decomposition, disturbance observer of [3] is adopted to estimate human force with some dead-zone modification to avoid "winding-up" force estimation in the presence of device torque saturation. Some preliminary experimental results are also given to illustrate efficacy of the proposed technique.

• BMB Reports
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• v.47 no.11
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• pp.609-618
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• 2014

DNA methylation at cytosines (5mC) is a major epigenetic modification involved in the regulation of multiple biological processes in mammals. How methylation is reversed was until recently poorly understood. The family of dioxygenases commonly known as Ten-eleven translocation (Tet) proteins are responsible for the oxidation of 5mC into three new forms, 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). Current models link Tet-mediated 5mC oxidation with active DNA demethylation. The higher oxidation products (5fC and 5caC) are recognized and excised by the DNA glycosylase TDG via the base excision repair pathway. Like DNA methyltransferases, Tet enzymes are important for embryonic development. We will examine the mechanism and biological significance of Tet-mediated 5mC oxidation in the context of pronuclear DNA demethylation in mouse early embryos. In contrast to its role in active demethylation in the germ cells and early embryo, a number of lines of evidence suggest that the intragenic 5hmC present in brain may act as a stable mark instead. This short review explores mechanistic aspects of TET oxidation activity, the impact Tet enzymes have on epigenome organization and their contribution to the regulation of early embryonic and neuronal development.