• Journal of Communications and Networks
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• 제11권3호
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• pp.287-296
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• 2009

Although asymptotic bounds of wireless network capacity have been heavily pursued, the answers to the following questions are still critical for network planning, protocol and architecture design: Given a three-dimensional (3D) network space with the number of active users randomly located in the space and using the wireless communication technology, what are the expected per-flow throughput, network capacity, and network transport capacity? In addition, how can the protocol parameters be tuned to enhance network performance? In this paper, we focus on the ultra wideband (UWB) based wireless personal area networks (WPANs) and provide answers to these questions, considering the salient features of UWB communications, i.e., low transmission/interference power level, accurate ranging capability, etc. Specifically, we demonstrate how to explore the spatial multiplexing gain of UWB networks by allowing appropriate concurrent transmissions. Given 3D space and the number of active users, we derive the expected number of concurrent transmissions, network capacity and transport capacity of the UWB network. The results reveal the main factors affecting network (transport) capacity, and how to determine the best protocol parameters, e.g., exclusive region size, in order to maximize the capacity. Extensive simulation results are given to validate the analytical results.

• 한국임상수의학회지
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• 제32권1호
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• pp.101-104
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• 2015

4년령의 수컷 골든 리트리버 견이 복부 팽만 및 호흡곤란을 주증상으로 내원하였으며, 신체 검사 결과 부정맥과 심잡음이 청진되었다. 흉복부 방사선 검사 결과 전반적인 심비대, 흉수 및 복수가 관찰되었다. 심초음파 검사에서 비정상적인 승모판 및 삼첨판의 움직임과 역류가 관찰되었으며, 좌심실의 편심성 비대와 좌심방 비대가 보였다. 컬러 도플러 영상에서 확장기에 승모판 입구로부터 좌심실로 유입되는 와류가 관찰되었으며, 수축기에는 좌심방 및 우심방으로의 와류가 보였다. 도플러 검사로 확장기 승모판 유입 속도가 매우 증가하였으며 pressure half time이 지연되었다는 것을 알 수 있었다. 심초음파 검사 결과에 기초하여 승모판 협착증과 병발된 승모판 이형성증과 삼첨판 이형성증을 진단하였다.

• 한국경영과학회지
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• 제22권2호
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• pp.13-29
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• 1997

This paper considers a new routing problem, successive max-min connection ratio problem (SMCRP), arised in circuit telecommunication networks such as SONET and WDM optical transport network. An optimization model for SMCRP is established based on link-flow formulation. It's first optimization process is an integral version of maximum concurrent flow problem. Integer condition does not give the same connection-ratio of each node-pair at an optimal solution any more. It is also an integral multi-commodity flow problem with fairness restriction. In order to guarantee fairness to every node-pair the minimum of connection ratios to demand is maximized. NP- hardness of SMCRP is proved and a heuristic algorithm with polynomial-time bound is developed for the problem. Augmenting path and rerouting flow are used for the algorithm. The heuristic algorithm is implemented and tested for networks of different sizes. The results are compared with those given by GAMS/OSL, a popular commercial solver for integer programming problem.n among ferrite-pearlite matrix, the increase in spheroidal ratio with increasing fatigue limitation, 90% had the highest, 14.3% increasing more then 70%, distribution range of fatigue.
ife was small in same stress level. (2) $\sqrt{area}_{max}$ of graphite can be used to predict fatigue limit of Ductile Cast Iron. The Statistical distribution of extreme values of $\sqrt{area}_{max}$ may be used as a guideline for the control of inclusion size in the steelmaking.

• 대한기계학회논문집B
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• 제20권12호
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• pp.3949-3959
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• 1996

A new interfacial instability between two vertical fluid layers of different densities is studied. The two layers are flowing between two parallel vertical plates vertically upward or downward, forming counter- or concurrent flows. In order to extend the study to highly-nonlinear regime in future studies, a nonlinear interface evolution equation is derived, and the stability analysis is performed based on the evolution equation. Among the parameters studies are the ratios of the fluid densities and layer thicknesses and the net flow rate.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1994년도 SIEMSTA94 농업과학 기계기술 심포지엄
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• pp.139-160
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• 1994

The-state-of-the-art of rice drying in the U.S.A. is presented. The U.S.A. is a minor producer but major exporter of rice. Head yield is its major criterion in evaluating rice quality . A decrease of 1 to 3 points in head yield can be expected to occur in a well-designed rice-drying system. Rice is dried on the farm in bins in the U.S. A., and n high-temperature continuous -flow dryers at the elevator level. Two relatively new rice-drying systems are discussed in some detail. : The top-bin/in -bin-counterflow bin-type on-farm dryer, and the concurrent-flow high-temperature elevator dryer.

• International Journal of Automotive Technology
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• 제7권2호
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• pp.217-226
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• 2006

To maintain competitiveness in the modern automotive market, it is important to carry out process planning concurrently with new car development processes. Process planners need to make decisions concurrently and collaboratively in order to reduce manufacturing preparation time for developing a new car. Automated generation of a simulation model by using the integrated process plan database can reduce time consumed for carrying out a simulation and allow a consistent model to be used throughout. In this research, we developed a web-based system for concurrent and collaborative process planning and flow analysis for an automotive general assembly using web, database, and simulation technology. A single integrated database is designed to automatically generate simulation models from process plans without having to rework the data. This system enables process planners to evaluate their decisions quickly, considering various factors, and easily share their opinions with others. By using this collaborative system, time and cost put into the assembly process planning can be reduced and the reliability of the process plan would be improved.

• 한국정보과학회논문지:정보통신
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• 제37권4호
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• pp.272-283
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• 2010

무선 메쉬 네트워크는 최근 주목받는 연구 주제로 부상하고 있다. 무선 메쉬 네트워크는 대규모 무선 랜 장치와 AP들이 서로 연결된 무선 기반 구조로, 무선 메쉬 네트워크의 처리량(throughput)을 향상시키는 것을 목표로 한 수많은 연구가 이루어진 바 있다. 여기에서는 동시에 생겨나는 다수의 트래픽 흐름들을 전송하기 위한 적절한 라우팅 경로를 설정하는 작업이 매우 중요하다. 본 논문에서는 IEEE 802.11 DCF하에서 전송되는 다수의 트래픽 흐름에 대해 신호 감지(Carrier Sensing), 간섭 등의 정보를 이용하여 양 말단간 (end-to-end) 처리량을 수학적으로 모델화하기 위한 방법을 제시하고자 한다. 각 단말에 성공적으로 이루어지는 평균 서비스 시간을 비교하고, 한편으로는 트래픽 흐름 가운데 병목현상이 발생하는 부분을 찾아내어 그로부터 말단간 처리량의 최대치를 계산할 수 있다. 본 논문에서 제시된 모델을 사용하여 동시에 전송되는 다수의 트래픽 흐름을 전달하기 위한 전송 경로에 대한 후보 경로를 얻어낼 수 있으며, 얻어진 경로로부터 처리량을 최대로 높일 수 있는 효율적인 경로를 찾아낼 수 있다. 제시된 모델링 기법과 최적 경로 선택 메커니즘은 무선 메쉬 네트워크에서의 다양한 트래픽 흐름을 사용한 시뮬레이션을 통해 평가하였다.

• Management Science and Financial Engineering
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• 제15권1호
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• pp.51-69
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• 2009

A network model and a Genetic Algorithm (GA) is proposed to solve the simultaneous estimation of the trip distribution and traffic assignment from traffic counts in the congested networks in a logit-based Stochastic User Equilibrium (SUE). The model is formulated as a problem of minimizing a non-linear objective function with the linear constraints. In the model, the flow-conservation constraints are utilized to restrict the solution space and to force the link flows become consistent to the traffic counts. The objective of the model is to minimize the discrepancies between two sets of link flows. One is the set of link flows satisfying the constraints of flow-conservation, trip production from origin, trip attraction to destination and traffic counts at observed links. The other is the set of link flows those are estimated through the trip distribution and traffic assignment using the path flow estimator in the logit-based SUE. In the proposed GA, a chromosome is defined as a real vector representing a set of Origin-Destination Matrix (ODM), link flows and route-choice dispersion coefficient. Each chromosome is evaluated by the corresponding discrepancies. The population of the chromosome is evolved by the concurrent simplex crossover and random mutation. To maintain the feasibility of solutions, a bounded vector shipment technique is used during the crossover and mutation.

• Journal of Korean Neurosurgical Society
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• 제58권6호
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• pp.518-527
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• 2015

Objective : The treatment of complex intracranial aneurysms remains challenging. One approach is the application of surgical flow alteration to treat aneurysms that are neither clippable, trappable, or coilable. The efficacy and limitations of surgical flow alteration have not yet been established. Methods : Cases of complex aneurysms treated with surgical flow alteration (proximal occlusion with or without bypass, distal occlusion with or without bypass and bypass only) were included in this retrospective study. Results : Among a total of 16 cases, there were 7 giant aneurysms (${\geq}25mm$ diameter) and 9 large aneurysms (>10 mm diameter); 15 of 16 aneurysms were unruptured. There were 8 aneurysms located in the anterior circulation, while the other 8 were in the posterior circulation. Aneurysms were treated with proximal occlusion in 10 cases and distal occlusion in 5 cases; in 1 case, the aneurysm occluded spontaneously after bypass without parent artery occlusion. All but 2 cases underwent prior or concurrent bypass surgery. Complete obliteration of the aneurysm at the latest imaging follow-up was shown in 12 of 16 cases (75.0%). Bypass patency was confirmed in 13 of 15 cases (86.7%). Surgery-related morbidity developed in 3 cases (18.8%, Glasgow outcome scale of 4) and all were perforator infarctions. There were no mortalities. Conclusion : Surgical flow alteration resulted in a high rate of aneurysmal obliteration with acceptable morbidity. Although several limitations remained, it could represent an alternative method for treating complex aneurysms.

• 한국수자원학회논문집
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• 제36권6호
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• pp.971-984
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• 2003

본 연구에서는 보 월류시 공기 유입을 수리학적인 방법으로 분석하였다. 이를 위해 하천에 설치된 보의 형태로서 계단형 보와 래버린스 보 및 배사문 보를 선정하여 현지측정과 수리실험을 통해 산소전달 효율을 검토하였다. 산소전달 효율은 계단형 보가 크며, 배사문 보는 산소전달 효율이 그리 크지 않았다. 산소전달은 흐름의 유속, Froude 수, 유량 순으로 상관 관계를 나타내었으며 특히 흐름의 유녹과 산소전달 효율에서 높은 관계를 나타내었다. 수리실험 결과 계단형 보의 월류 흐름은 유량이 작을 경우 계단 전 구간에 걸쳐 잠입류가 발생하고, 유량 증가에 따라 잠입류와 표면류가 공존하며 이 경우 계단 상부께서 표면류 및 계단 하부에서 잠입류가 발생하였다. 잠입류의 경우 계단 끝단에서 흐름 분리에 의해 공기 유입이 시작되고, 자유낙하 nappe과 계단 안쪽의 공기 주머니 및 nappe impact와 이후의 도수 현상으로 많은 공기 유입이 발생되었다. 표면류의 경우 계단 끝단에서 공기 유입이 시작되고, 흐름이 계단과 계단을 스쳐가듯이 흐르는 과정에서 수표면의 진동에 의해 많은 공기가 유입되었지만 공기 유입은 잠입류의 경우에 비해 상대적으로 작았다.