• Bulletin of the Korean Mathematical Society
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• v.57 no.3
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• pp.691-707
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• 2020

In this paper, we introduce and study the notions of weakly ⊕-supplemented modules, weakly D2 modules and weakly D2-covers. A right R-module M is called weakly ⊕-supplemented if every non-small submodule of M has a supplement that is not essential in M, and module M_R is called weakly D2 if it satisfies the condition: for every s ∈ S and s ≠ 0, if there exists n ∈ ℕ such that sⁿ ≠ 0 and Im(sⁿ) is a direct summand of M, then Ker(sⁿ) is a direct summand of M. The class of weakly ⊕-supplemented-modules and weakly D2 modules contains ⊕-supplemented modules and D2 modules, respectively, and they are equivalent in case M is uniform, and projective, respectively.

• Journal of applied mathematics & informatics
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• v.12 no.1_2
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• pp.395-408
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• 2003

Common Channel Signaling(CCS) networks need special controls to avoid overload of signaling networks and degradation of call process-ing rate, since they play an important role of controlling communication transfer networks. Congestion control and flow control mechanisms are well described in ITU-T recommendation on Signaling System No.7(SS7). For the practical provisions, however, we need an analysis on the relation among service objects, system requirements and implementation of congestion control algorithms. SS7 provides several options for controlling link congestion in CCS networks. In this paper we give a general queueing model of congestion control algorithm which covers both the international and national options. From the queuing model, we obtain the performance parameters such as throughput, message loss rate and mean delay for the international option. To show the performance of the algorithm, some numerical results are also given.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.567-570
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• 2002

The LVDS (Low Voltage Differential Signaling) I/O cells, fully compatible with ANSI TIA/ EIA-644 LVDS standard, are designed using a 0.35${\mu}m$ standard CMOS technology. With a single 3V supply, the core cells operate at 1.34Gbps and power consumption of the output driver and the input receiver is 10. 5mW and 4.2mW, respectively. In the output driver, we employ the DCMFB (Dynamic Common-Mode FeedBack) circuit which can control the DC offset voltage of differential output signals. The SPICE simulation result of the proposed output driver shows that the variation of the DC offset voltage is 15.6% within a permissible range. In the input receiver, the proposed dual input stage with a positive feedback latch covers rail-to-rail input common-mode range and enables a high-speed, low-power operation. 5-channels of the proposed LVDS I/O pair can handle display data up to 8-bit gray scale and UXGA resolution.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10C
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• pp.942-949
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• 2007

In this paper, we propose a new rate-control scheme, called splining, to construct low-rate codes from high-rate codes by splitting rows of the parity-check matrices of LDPC codes, which can construct rate-compatible LDPC codes having good initial transmission performance. Good low-rate codes can be constructed by making the number of distinct check node degrees as small as possible after splitting. The proposed scheme achieves good cycle property, low decoding complexity, and fast convergence speed, especially compared to the puncturing. Especially, rate-compatible repeat accumulate-type LDPC (RA-Type LDPC) code is constructed using splitting, which covers the code rates from 1/3 to 4/5. Through simulation it is shown that this code outperforms other rate-compatible RA-Type LDPC codes for all rates and can be decoded conveniently and efficiently.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.135-137
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• 2005

The body of the work covers FSW welding of Al6061 and its thermal distribution based on an analytical model for the heat input at the probe/matrix boundary of Al plates and FSW tool due to the effect of combined translation and rotational motion of the tool pin and shoulder. Finally the 2D- finite element heat transfer analysis program has been used to plot the heat distribution at the Friction Stir Welded joint in Al 6061 plate. The work concludes that the heat distribution result obtained from FE analysis has a reasonable agreement with the experimentally measured values.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.19 no.4
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• pp.417-428
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• 2015

Although, in general, the random fluctuation of interest rates gives a limited impact on portfolio optimization, their stochastic nature may exert a significant influence on the process of selecting the proportions of various assets to be held in a given portfolio when the stochastic volatility of risky assets is considered. The stochastic volatility covers a variety of known models to fit in with diverse economic environments. In this paper, an optimal strategy for portfolio selection as well as the smoothness properties of the relevant value function are studied with the dynamic programming method under a market model of both stochastic volatility and stochastic interest rates.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.9
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• pp.4280-4300
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• 2017

The fact that cloud computing services have been proposed in recent years, organizations and individuals face with various challenges and problems such as how to migrate applications and software platforms into cloud or how to ensure security of migrated applications. This study reviews the current challenges and open issues in cloud computing, with the focus on autonomic resource management especially in federated clouds. In addition, this study provides recommendations and research roadmaps for scientific activities, as well as potential improvements in federated cloud computing. This survey study covers results achieved through 190 literatures including books, journal and conference papers, industrial reports, forums, and project reports. A solution is proposed for autonomic resource management in the federated clouds, using machine learning and statistical analysis in order to provide better and efficient resource management.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.154.1-154.1
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• 2011

IGRINS (Immersion Grating Infrared Spectrometer) is a cross-dispersed high resolution near-infrared spectrograph whose primary disperser is a silicon immersion grating (SIG) and cross-dispersers are two volume phase holographic gratings (VPHG). IGRINS covers the full ranges of H and K astronomical wavelength bands at a single exposure with the spectral resolution of 40,000. The overall layout of the IGRINS Cryostat is a $960{\times}600{\times}380$ cubic millimeter rectangular box and the whole optical train is sitting on an $880{\times}520{\times}50\;mm^3$ rectangular Optical Bench. The total volume of the instrument has been revolutionarily reduced and remained compact for the spectral coverage and sensitivity of a high resolution spectrograph in infrared. We, in this presentation, introduce the design models, the structural and thermal analysis results of the mechanics and cryogenics of IGRINS.

• Journal of electromagnetic engineering and science
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• v.2 no.2
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• pp.105-111
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• 2002

New high-performance Ka-band waveguide-to-microstrip transitions for millimeter-wave transceiver applications have been developed and characterized. These transitions are probe-type, but the dielectric material completely covers the whole waveguide aperture, thus providing moisture-barrier and robustness in the probe section. The new probe transitions are also designed to be less sensitive to fabrication tolerances. Further performance enhancements have been obtained by placing vias around the waveguide aperture. Also, the resonance phenomena associated with waveguide wall-penetration have been identified. The developed probe transitions provide insertion loss less than 0.4 dB over entire Ka-band frequencies, but can be optimized for narrowband applications with insertion loss less than 0.2 dB.

• Transactions on Electrical and Electronic Materials
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• v.11 no.4
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• pp.190-193
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• 2010

This report covers an effective fabrication method of graphene nanoribbon for top-gated field effect transistors (FETs) utilizing electron beam lithography with a bi-layer resists (XR-1541/poly methtyl methacrylate) process. To improve the variation of the gating properties of FETs, the residues of an e beam resist on the graphene channel are successfully taken off through the combination of reactive ion etching and a lift-off process for the XR-1541 bi-layer. In order to identify the presence of graphene structures, atomic force microscopy measurement and Raman spectrum analysis are performed. We believe that the lift-off process with bi-layer resists could be a good solution to increase gate dielectric properties toward the high quality of graphene FETs.