• 대한수학회지
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• 제52권4호
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• pp.797-819
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• 2015

A trapdoor discrete logarithm group is a cryptographic primitive with many applications, and an algorithm that allows discrete logarithm problems to be solved faster using a pre-computed table increases the practicality of using this primitive. Currently, the distinguished point method and one extension to this algorithm are the only pre-computation aided discrete logarithm problem solving algorithms appearing in the related literature. This work investigates the possibility of adopting other pre-computation matrix structures that were originally designed for used with cryptanalytic time memory tradeoff algorithms to work as pre-computation aided discrete logarithm problem solving algorithms. We find that the classical Hellman matrix structure leads to an algorithm that has performance advantages over the two existing algorithms.

• 한국자동차공학회논문집
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• 제6권3호
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• pp.34-44
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• 1998

It is clear that when an automobile negotiates a curve the lateral acceleration causes an increase in tire normal load for the wheels on the outside of the curve and a decrease in load for the inside wheels. However, just how the details of the suspension linkages and the parameters of the springs and shock absorbers affect the dynamics of the load transfer os not easily understood. One even encounters the false idea that since it is the compression and extension of the main suspension springs spring body role which largely determines the changes in normal load, of roll could be reduced, the load transfer would also be reduced. Using free body diagrams, one can explain quite clearly how the load is transferred for steady state cornering, and, using complex multibody models of particular vehicles one can simulate in good fidelity how load transfer occurs dynamically. Here we adopt a middle ground by using the concept of roll center and using a series of half-car bond graph models to point out main effects. Since bond graph junction structures automatically and consistently constrain geometric and force variables simultaneously, they can be used to point out hidden assumptions of other simplified vehicle models.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2007년도 학술대회
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• pp.46-49
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• 2007

Multiple Antenna Technologies such as Multiple-Input Multiple-Output (MIMO) and Beamforming provide the increase of channel capacity and the reliability of wireless link. To obtain these advantages, WiBro, Mobile WiMAX and $4^{th}$ Generation System are employing multiple antenna technologies. There exist, however, many technical issues in considering the application of the technologies or the providing of services using them. In this paper, various technical topics are discussed and simple solutions are proposed. Beamforming has several technical issues which include coverage imbalance, difficulties in providing Multicast-Broadcast Service (MBS). In Addition, network planning is a critical point from a cell extension and initial network entry point of view. In case of MIMO, network deployment is discussed in that cellular data network such as WiBro has many repeaters. MIMO mode selection for maximizing the cell capacity is also covered.

• 대한수학회논문집
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• 제17권2호
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• pp.253-260
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• 2002

For an outer action $\alpha$ of a finite group G on a factor M, it was proved that H is a, normal subgroup of G if and only if there exists a finite group F and an outer action $\beta$ of F on the crossed product algebra M $\times$$_{\alpha}$ G = (M $\times$$_{\alpha}$ F. We generalize this to infinite group actions. For an outer action $\alpha$ of a discrete group, we obtain a Galois correspondence for crossed product algebras related to normal subgroups. When $\alpha$ satisfies a certain condition, we also obtain a Galois correspondence for fixed point algebras. Furthermore, for a minimal action $\alpha$ of a compact group G and a closed normal subgroup H, we prove $M^{G}$ = ( $M^{H}$)$^{{beta}(G/H)}$for a minimal action $\beta$ of G/H on $M^{H}$.f G/H on $M^{H}$.TEX> H/.

• 대한수학회보
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• 제57권1호
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• pp.251-274
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• 2020

We study a dynamical system that was originally defined by Romik in 2008 using an old theorem of Berggren concerning Pythagorean triples. Romik's system is closely related to the Farey map on the unit interval which generates an additive continued fraction algorithm. We explore some number theoretical properties of the Romik system. In particular, we prove an analogue of Lagrange's theorem in the case of the Romik system on the unit quarter circle, which states that a point possesses an eventually periodic digit expansion if and only if the point is defined over a real quadratic extension field of rationals.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권6호
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• pp.1982-2004
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• 2014

Wireless Mesh Networks (WMNs) are emerging as promising, convenient next generation wireless network technology. There is a great need for a secure framework for routing in WMNs and several research studies have proposed secure versions of the default routing protocol of WMNs. In this paper, we propose a security framework for Hybrid Wireless Mesh Protocol (HWMP) in WMNs. Contrary to existing schemes, our proposed framework ensures both end-to-end and point-to-point authentication and integrity to both mutable and non-mutable fields of routing frames by adding message extension fields to the HWMP path selection frame elements. Security analysis and simulation results show that the proposed approach performs significantly well in spite of the cryptographic computations involved in routing.

• 한국환경보건학회지
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• 제28권1호
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• pp.1-10
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• 2002

This study was carried out to provide environmental information using geographic information system for the environmental manager engaged in governmental office. Point and nonpoint sources were classified by each small watershed and an administrative district. ArcView and ERDAS software were used to develop environmental information system. Small watershed was extracted into the DTEM using HEC-geoHMS which is ArcView extension. Study area was divided into 7 small watershed. Point sources were constituted as cattle, milk cattle, swine, and poultry. Land use was divided into forests, rice paddies, residential sites et al. User interface was designed to search information easily for the nonprofessional GIS users.

• Journal of applied mathematics & informatics
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• 제28권5_6호
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• pp.1249-1262
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• 2010

An approximate alternating linearization decomposition method, for minimizing the sum of two convex functions with some separable structures, is presented in this paper. It can be viewed as an extension of the method with exact solutions proposed by Kiwiel, Rosa and Ruszczynski(1999). In this paper we use inexact optimal solutions instead of the exact ones that are not easily computed to construct the linear models and get the inexact solutions of both subproblems, and also we prove that the inexact optimal solution tends to proximal point, i.e., the inexact optimal solution tends to optimal solution.

• 전력전자학회논문지
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• 제22권6호
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• pp.535-542
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• 2017

This paper proposes a simple 3-level interleaved charger-discharger for the uninterruptible power supply (UPS) with various combinations of battery cells. The proposed converter not only improves charging and discharging efficiency, but also reduces the physical volume and the cost. Furthermore, the converter also offers the capability of the neutral point voltage, so that more stable operation can be obtained. In addition, the proposed converter significantly reduces the ripple current of the battery inductor, thereby providing an expected life extension of the battery. Experimental results for a 300kVA UPS prototype verify the validity of the proposed converter. The proposed charger-discharger is suitable for UPSs and energy storage systems (ESSs) with wide input battery voltage ranges.

• Journal of Power Electronics
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• 제13권6호
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• pp.1042-1050
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• 2013

This paper presents a study of maximum power point tracking (MPPT) for photovoltaic arrays with only one current sensor. Initially, a review of MPPT methods with only a current sensor is performed with extension for a variety of dc/dc converters. Furthermore, the same topology is developed to achieve better performance in the presence of sensor offset and environmental noise. The proposed method is robust, cost effective, and behaves well dynamically and in the steady state. After a theoretical analysis of presented approach, its validity and effectiveness are verified by simulation and experimental results.