• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.197-205
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• 2017

We investigate the slat noise generation mechanism by using large-eddy simulation (LES) and simple source modeling based on linearized Euler equations. An incompressible LES of an MD 30P30N three-element airfoil in the high-lift configuration is conducted at $Re_c=1.7{\times}10^6$. Using the total derivative of the hydrodynamic pressure (DP/Dt) acquired from the incompressible LES, representative noise sources in the slat cove region are characterized in terms of simple sources such as frequency-specific monopoles and dipoles. Acoustic radiation around the 30P30N multi-element airfoil is effectively computed using the Brinkman penalization method incorporated with the linearized Euler equation. The directivity pattern of $p^{\prime}_{rms}$ at $r=20c_{slat}$ in the multiple sources is closely compared to that obtained by the application of the LES/Ffowcs-Williams and Hawking's methods to the entire flow field. The power spectrum of p' at ${\theta}=290^{\circ}$ is in good agreement with the data reported in BANC-III, especially the broadband part of the spectrum with a decaying slope ${\propto}f^{-3}$.

• 기술혁신연구
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• 제11권2호
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• pp.151-173
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• 2003

This paper analyses the efficiency and productivity of R&D system across time (1991${\sim}$2000) and 16 OECD countries using multi-output and multi-input non-parametric frontier methods such as DEA (data envelopement analysis) and Malmquist productivity indexes. Malmquist productivity indexes are decomposed into two components measures, namely technical change and efficiency change. To calculate R&D efficiency and productivity, we used R&D stock and the number or researchers as R&D input proxies and the number of adjusted SCI papers and U.S. patent applications as R&D output proxies. Empirical result shows that Switzerland, Canada, U.S., Australia's R&D efficiencies are the highest and Korea's R&D productivity growth is the highest in the sample for the period. Technical efficiency growth was a more important source of productivity growth than technological innovation.

• 정보처리학회논문지A
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• 제11A권5호
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• pp.325-332
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• 2004

CDN(Contents Delivery Network)과 달리 P2P 네트워크에서는 컨텐츠를 제공하는 주체가 고정되어있지 않으므로 컨텐츠 분배는 매우 중요한 서비스이다. 그리고 P2P 미디어스트리밍에서 수신피어는 미디어 데이터를 재생함과 동시에 저장하고, 스트리밍이 끝나면 다른 피어에게 미디어 파일을 제공하는 새로운 소스피어로 동작한다 따라서 P2P 네트워크를 통해 컨텐츠를 분배하기 위해서는 미디어 스트리밍과 파일의 저장을 동시에 수행할 수 있어야한다. 본 논문은 기존의 컨텐츠 공유 모델이 미디어 데이터를 모두 다운로드 한 후에 재생을 하기 때문에 응답시간이 길고 P2P 멀티소스 미디어스트리밍에서 컨텐츠 분배가 어려운 점을 해결하여, 컨텐츠를 다운로드하면서 재생이 가능한 P2P 멀티소스 미디어스트리밍 시스템을 제안, 구현한다. 제안된 시스템에서는 수신피어가 데이터 스트리밍과 동시에 소스피어의 역할을 하므로 사용자 응답시간이 단축되고, 미디어스트리밍에 참여하는 소스피어의 수가 늘어나면 비트전송률이 증가되어 동시수요자 수도 증가된다. 또한, 피어가 가진 미디어파일의 일부분을 전송하는 메커니즘을 제공하여 컨텐츠 분배가 빨라진다

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.150-152
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• 2006

The DISCOVER Project (${\underline{D}}istributed$ ${\underline{I}}nformation$ ${\underline{S}}ervices$ for ${\underline{C}}limate$ and ${\underline{O}}cean$ products and ${\underline{V}}isualizations$ for ${\underline{E}}arth$ ${\underline{R}}esearch$) is a NASA funded Earth Science REASoN project that strives to provide highly accurate, carefully calibrated, long-term climate data records and near-real-time ocean products suitable for the most demanding Earth research applications via easy-to-use display and data access tools. A key element of DISCOVER is the merging of data from the multiple sensors on multiple platforms into geophysical data sets consistent in both time and space. The project is a follow-on to the SSM/I Pathfinder and Passive Microwave ESIP projects which pioneered the simultaneous retrieval of sea surface temperature, surface wind speed, columnar water vapor, cloud liquid water content, and rain rate from SSM/I and TMI observations. The ocean products available through DISCOVER are derived from multi-sensor observations combined into daily products and a consistent multi-decadal climate time series. The DISCOVER team has a strong track record in identifying and removing unexpected sources of systematic error in radiometric measurements, including misspecification of SSM/I pointing geometry, the slightly emissive TMI antenna, and problems with the hot calibration source on AMSR-E. This in-depth experience with inter-calibration is absolutely essential for achieving our objective of merging multi-sensor observations into consistent data sets. Extreme care in satellite inter-calibration and commonality of geophysical algorithms is applied to all sensors. This presentation will introduce the DISCOVER products currently available from the web site, http://www.discover-earth.org and provide examples of the scientific application of both the diurnally corrected optimally interpolated global sea surface temperature product and the 4x-daily global microwave water vapor product.

• Journal of Communications and Networks
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• 제9권3호
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• pp.296-311
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• 2007

Mobile multi-robot teams are useful in many critical applications such as search and rescue. Explicit communication among robots in such mobile multi-robot teams is useful for the coordination of such teams as well as exchanging data. Since many applications for mobile robots involve scenarios in which communication infrastructure may be damaged or unavailable, mobile robot teams frequently need to communicate with each other via ad hoc networking. In such scenarios, low-overhead and energy-efficient routing protocols for delivering messages among robots are a key requirement. Two important primitives for communication are essential for enabling a wide variety of mobile robot applications. First, unicast communication (between two robots) needs to be provided to enable coordination and data exchange. Second, in many applications, group communication is required for flexible control, organization, and management of the mobile robots. Multicast provides a bandwidth-efficient communication method between a source and a group of robots. In this paper, we first propose and evaluate two unicast routing protocols tailored for use in ad hoc networks formed by mobile multi-robot teams: Mobile robot distance vector (MRDV) and mobile robot source routing (MRSR). Both protocols exploit the unique mobility characteristics of mobile robot networks to perform efficient routing. Our simulation study show that both MRDV and MRSR incur lower overhead while operating in mobile robot networks when compared to traditional mobile ad hoc network routing protocols such as DSR and AODV. We then propose and evaluate an efficient multicast protocol mobile robot mesh multicast (MRMM) for deployment in mobile robot networks. MRMM exploits the fact that mobile robots know what velocity they are instructed to move at and for what distance in building a long lifetime sparse mesh for group communication that is more efficient. Our results show that MRMM provides an efficient group communication mechanism that can potentially be used in many mobile robot application scenarios.

• 한국인터넷방송통신학회논문지
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• 제22권6호
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• pp.91-97
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• 2022

사이클 검출 문제에 대해, 단일 출발(SS)을 갖는 단일 연결 리스트(SLL)에 한해 O(n) 복잡도의 거북이와 토끼 경주법(HTA)이 제안되었으며, 다중 출발지-다중 종착지, 다중 분기(MSMDMB)를 갖는 일반 그래프에 대해서는 빠른 방법이 알려져 있지 않고 있다. 본 논문에서는 MSMDMB를 갖는 주어진 무 방향과 방향 그래프의 최대 사이클을 선형시간 복잡도로 검출할 수 있는 방법을 제안하였다. 제안된 방법은 주어진 원 그래프 G에는 사이클 형성 조건을 충족시키지 못하는 다수의 정점(또는 노드)가 존재한다는 사실에 기반하여 이들 정점(또는 노드)들을 제거한 축소된 그래프 G'를 얻었다. 이 축소된 그래프에 대해 선형시간 복잡도인 선형탐색으로 사이클 집합 C와 사이클 길이 λ를 찾았다. 제안된 알고리즘을 실험 데이터에 적용한 결과 모든 데이터들에 대해 최대 사이클을 찾을 수 있음을 보였다.

• 한국벤처창업학회:학술대회논문집
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• 한국벤처창업학회 2017년도 통합학술대회
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• pp.37-47
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• 2017

The digital multi-sided platform has led the growth of industries. Accelerating this growth, generativity allowed innovation based on boundary-less modularity. Online games are a rich source of research but most of the research is dedicated in examining only the online game itself. However, there is a growing need to understand online games in an ecosystem level for a new phase of evolution is starting based on generativity. With generativity, online game users now make new graphics and quest that can be added and shared to the already existing game environment. The ecosystem is moving towards finding an amicable multi-sided distribution platform for these user generated game contents. Preliminary data suggest the possibility of actual connection between generativity and users' game engagement. Interviews and surveys will be prepared to find out the details of the possible relationship and how the ecosystem will shape accordingly.

• Industrial Engineering and Management Systems
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• 제14권1호
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• pp.11-21
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• 2015

The purpose of this research is to develop algorithms using the Differential Evolution Algorithm (DE) to solve a multi-objective, sources and stages location-allocation problem. The development process starts from the design of a standard DE, then modifies the recombination process of the DE in order improve the efficiency of the standard DE. The modified algorithm is called modified DE. The proposed algorithms have been tested with one real case study (large size problem) and 2 randomly selected data sets (small and medium size problems). The computational results show that the modified DE gives better solutions and uses less computational time than the standard DE. The proposed heuristics can find solutions 0 to 3.56% different from the optimal solution in small test instances, while differences are 1.4-3.5% higher than that of the lower bound generated by optimization software in medium and large test instances, while using more than 99% less computational time than the optimization software.

• Journal of Communications and Networks
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• 제14권1호
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• pp.63-74
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• 2012

Multicast data communication is an efficient communication scheme, especially inmulti-hop ad hoc networks where the media access control (MAC) layer is based on one-hop broadcast from one source to multiple receivers. Compared to unicast, multicast over a wireless channel should be able to deal with varying channel conditions of multiple users and user mobility to provide good quality to all users. IEEE 802.11 does not support reliable multicast owing to its inability to exchange request-to-send/clear-to-send and acknowledgement packets with multiple recipients. Thus, several MAC layer protocols have been proposed to provide reliable multicast. However, additional overhead is introduced, as a result, which degrades the system performance. In this paper, we propose an efficient wireless multicast MAC protocol with small control overhead required for reliable multicast in multi-hop wireless ad hoc networks. We present analytical formulations of the system throughput and delay associated with the overhead.

• 한국정보통신학회논문지
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• 제26권11호
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• pp.1679-1685
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• 2022

본 논문에서는 무선전력 통신 네트워크에서 소스에서 목적지 노드까지 종단간 데이터 전송률을 최대화하기 위한 최적의 멀티홉 전송 방식을 제안한다. 에너지 하베스팅을 하면서 멀티홉 전송을 위한 프레임 구조를 제시하고, 노드간 서로 다른 에너지 수확량과 링크 품질을 고려하여 종단간 전송률을 최대화하는 각 노드의 전송 시간을 수학적 분석을 통하여 도출한다. 아울러, 고려하는 무선전력기반 멀티홉 전송의 시스템 모델링을 통하여 최적화 문제를 도출하고, 이 최적화 문제가 convex 함을 보임으로써 전역 최적해가 존재함을 증명한다. 이를 통하여 최적화 문제를 계산 가능한 형태로 변형하여 손쉽게 최적해를 찾는다. 제안한 최적 멀티홉 전송 방식은 모든 링크의 전송률이 같아지도록 노드별 전송 시간을 최적으로 할당함으로써 종단간 전송률을 최대화한다.