• 대한수학회보
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• 제39권2호
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• pp.333-346
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• 2002

Let $F={F^v:S^1->S^1,v\in\; V$ and $g={G^v:S^1->S^1,v\in\; V$ be disjoint flows defined on the unit circle $S^1$, that is such flows that each their element either is the identity mapping or has no fixed point ((V, +) is a 2-divisible nontrivial abelian group). The aim of this paper is to give a necessary and sufficient codition for topological conjugacy of disjoint flows i.e., the existence of a homeomorphism $\Gamma:S^1->S^1$ satisfying $$\Gamma\circ\ F^v=G^v\circ\Gamma,\; v\in\; V$$ Moreover, under some further restrictions, we determine all such homeomorphisms.

• 대한화학회지
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• 제48권3호
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• pp.243-248
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• 2004

실제 기체 및 dense gas나 액체영역까지 영역의 점성까지 두루 점성 계산에 성공적이었던 brake 점성이론을 사용하여 이성분기체의 점성을 계산하였다. Adjustable parameter가 없었으나 낮은 압력에서는 물론 고압하에서도 계산된 값은 실험치와 잘 일치하였다. Redlich-Kwong 방정식을 사용하여 점성에 관한 대응상태방정식을 구성할 수 있었으며 이로부터 초임계유체의 다양한 공업적 활용가능성을 기대할 수 있게 되었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권11호
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• pp.5400-5418
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• 2016

Femtocells are envisioned as a key solution to embrace the ever-increasing high data rate and thus are extensively deployed. However, the dense and random deployments of femtocell access points (FAPs) induce severe intercell inference that in turn may degrade the performance of spectral efficiency. Hence, unrestrained proliferation of FAPs may not acquire a net throughput gain. Besides, given that numerous FAPs deployed in ultra-dense networks (UDNs) lead to significant energy consumption, the amount of FAPs deployed is worthy of more considerations. Nevertheless, little existing works present an analytical result regarding the optimal FAP density for a given User Equipment (UE) density. This paper explores the realistic scenario of randomly distributed FAPs in UDN and derives the coverage probability via Stochastic Geometry. From the analytical results, coverage probability is strictly increasing as the FAP-to-UE ratio increases, yet the growing rate of coverage probability decreases as the ratio grows. Therefore, we can consider a specific FAP-to-UE ratio as the point where further increasing the ratio is not cost-effective with regards to the requirements of communication systems. To reach the optimal FAP density, we can deploy FAPs in line with peak traffic and randomly switch off FAPs to keep the optimal ratio during off-peak hours. Furthermore, considering the unbalanced nature of traffic demands in the temporal and spatial domain, dynamically and carefully choosing the locations of active FAPs would provide advantages over randomization. Besides, with a huge FAP density in UDN, we have more potential choices for the locations of active FAPs and this adds to the demand for a strategic sleeping policy.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권9호
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• pp.4122-4143
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• 2018

Because of the increment in network scale and test expenditure, simulators gradually become main tools for research on key problems of wireless networking, such as radio resource management (RRM) techniques. However, existing simulators are generally event-driven, causing unacceptably large simulation time owing to the tremendous number of events handled during a simulation. In this article, a mass-processing framework for RRM simulations is proposed for the scenarios with a massive amount of terminals of Internet of Things accessing 5G communication systems, which divides the time axis into RRM periods and each period into a number of mini-slots. Transmissions within the coverage of each access point are arranged into mini-slots based on the simulated RRM schemes, and mini-slots are almost fully occupied in dense scenarios. Because the sizes of matrices during this process are only decided by the fixed number of mini-slots in a period, the time expended for performance calculation is not affected by the number of terminals or packets. Therefore, by avoiding the event-driven process, the proposal can simulate dense scenarios in a quite limited time. By comparing with a classical event-driven simulator, NS2, we show the significant merits of our proposal on low time and memory costs.

• 인터넷정보학회논문지
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• 제23권5호
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• pp.25-31
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• 2022

초고밀도 네트워크(Ultra dense network, UDN)는 5G 이동통신 시스템에서 많은 수의 스몰셀 기지국(Small-cell access point, SAP)이 매크로셀의 서비스 영역에 배치되기 때문에 매크로 단말(Macro user equipment, MUE)이 수신하는 간섭량이 증가하여 시스템 용량이 크게 감소한다. 따라서, 본 논문은 UDN에서 SAP의 수가 증가하여도 MUE의 성능을 보장하기 위한 상향링크 유동적 채널할당 방법을 제안한다. 제안하는 유동적 채널할당 방법은 간섭량이 높은 MUE와 동일한 부채널을 사용하지 않도록 SAP들이 사용하는 부채널을 제어하여 MUE의 신호 대 간섭 잡음비(Signal to interference and noise ratio)를 주어진 임계값 이상으로 보장하는 것을 목표한다. 시뮬레이션을 통해 제안하는 유동적 채널할당 방법이 다른 방법들과 비교해 스몰셀 사용자 단말의 성능은 크게 감소되지 않으면서 MUE의 평균 전송 용량이 향상됨을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권5호
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• pp.1540-1560
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• 2022

Latest technological innovation in the development of compact lower power radios has led to the explosion of Internet of Things. With Wi-Fi, Zigbee and other physical layer protocols offering short coverage area there was a need for a RF protocol that had a larger coverage area with low power consumption. LoRa offers Long Range with lower power consumption. LoRa offers point to point and point to multipoint connections. with Single hop communication in place the need for routing protocols are eliminated. LoRa Wide Area Network stack can accommodate thousands of nodes under a single LoRa gateway with a single hop communication between the end nodes and LoRaWAN gateway. This paper takes an experimental approach to analyze the basic physical layer parameters of LoRa and the practical coverage offered by a LoRaWAN under highly dense urban conditions with variable topography. The insights gained from the practical deployment of the LoRaWAN network, and the subsequent performance analysis is used to design a novel public utility monitoring platform. The second half of the papers is designing a robust platform to integrate both existing wired sensor water meters, current and future generation wireless water meters. The Common Automated Metering Platform is designed to integrate both wired sensors and wireless (LoRaWAN and Wi-Fi) supported water meters. This integrated platform reduces the number of nodes under each LoRaWAN gateway and thus improves the scalability of the network. This architecture is currently designed to accommodate one utility application but can be modified to integrate multi-utility applications.

• 한국경영과학회지
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• 제19권3호
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• pp.187-201
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• 1994

This paper introduces an effective hybridization of the usual simplex method and an interior point method in the convergent framework of Dembo and Sahi. We formulate a specific and detailed algorithm (HYBRID) and report the results of some preliminary testing on small dense problems for its viability. By piercing through the feasible region, the newly developed hybrid algorithm avoids the combinatorial structure of linear programs, and several other interesting and important characteristics of this algorithm are also discussed.

• 대한수학회보
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• 제52권1호
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• pp.45-56
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• 2015

In this paper, we study the relation between two dynamical systems (V, f) and (V, g) with $f{\circ}g=g{\circ}f$. As an application, we show that an endomorphism (respectively a polynomial map with Zariski dense, of bounded Preper(f)) has only finitely many endomorphisms (respectively polynomial maps) of bounded degree which are commutable with f.

• 경영과학
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• 제19권2호
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• pp.155-168
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• 2002

In this paper, some efficient implementation techniques for the multifrontal method, which can be used to compute the Cholesky factor of a symmetric positive definite matrix, are presented. In order to use the cache effect in the cache-based computer architecture, a hybrid method for factorizing a frontal matrix is considered. This hybrid method uses the column Cholesky method and the submatrix Cholesky method alternatively. Experiments show that the hybrid method speeds up the performance of the supernodal multifrontal method by 5%～10%, and it is superior to the Cholesky method in some problems with dense columns or large frontal matrices.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제6권2호
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• pp.25-30
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• 2002

Let $E/{\mathbb{Q}$ be an elliptic curve defined over rationals, P is a non-torsion rational point of E and $$S=\{[n]P{\mid}n{\in}{\mathbb{Z}}\}$$. then S is dense in the component of $E({\mathbb{R}})$ which contains the infinity in the usual Euclidean topology or in the topology defined by the invariant Haar measure and it is uniformly distributed.