• Management Science and Financial Engineering
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• 제4권2호
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• pp.1-13
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• 1998

The Shortest Path Problem in Time-dependent Networks, where the travel time of each link depends on the time interval, is not realistic since the model and its solution violate the Non-passing Property (NPP:often referred to as FIFO) of real phenomena. Furthermore, solving the problem needs much more computational and memory complexity than the general shortest path problem. A new model for Time-dependent Networks where the flow speeds of each link depend on time interval, is suggested. The model is more realistic since its solution maintains the NPP. Solving the problem needs just a little more computational complexity, and the same memory complexity, as the general shortest path problem. A solution algorithm modified from Dijkstra's label setting algorithm is presented. We extend this model to the problem of Minimum Expected Time Path in Time-dependent Stochastic Networks where flow speeds of each link change statistically on each time interval. A solution method using the Kth-shortest Path algorithm is presented.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 추계 학술논문 발표대회
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• pp.170-171
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• 2015

Resource procurement and material handling are considered as a significant part of construction project especially in large or tall building construction site. There are multiple variables that must be considered in a construction site during finishing work such as movement of materials, equipments, and workers. Therefore, it is difficult for construction workers to find the material handling path solely by intuition. The aim of this study is to propose a real-time path finding model suitable for complicated logistics flow in the field. The model explores the optimal transport path of finishing material with its basis on optimization algorithm, and it determines the direction of the Smart Sign. The proposed model is expected to be utilized for planning of efficient finishing material handling.

• Management Science and Financial Engineering
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• 제11권2호
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• pp.85-103
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• 2005

In this paper, we consider the routing and wavelength assignment problem in survivable WDM transport network without wavelength conversion. We assume the single-link failure and a path protection scheme in optical layer. When a physical network and a set of working paths are given, the problem is to select a link-disjoint protection path for each working path and assign a wavelength for each working and protection path. We give an integer programming formulation of the problem and propose an algorithm to solve it. Though the formulation has exponentially many variables, we solve the linear programming relaxation of it by using column generation technique. We devise a branch-and price algorithm to solve the column generation problem. After solving the linear programming relaxation, we apply a variable fixing procedure combined with the column generation to get an integral solution. We test the proposed algorithm on some randomly generated data and test results show that the algorithm gives very good solutions.

• Journal of information and communication convergence engineering
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• 제7권3호
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• pp.241-246
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• 2009

Advances in mobile and wireless networking technologies have enabled mobile ad hoc networks applicable to a wide range of areas. Many cases of even such ad hoc networks demand to be accessible to the global network. Owing to be diversified in features depending on applications, however, some those networks may consist of devices or nodes which do not facilitate all the same transport protocols. This results in unreachable situations of establishing ad hoc network: such as non-existence of all required access points, faults or contention in a path of particular protocol communication. Interworking between different transport protocols can alleviate such problems. This paper proposes an interworking scheme to improve data transport performance and network accessibility, especially in such a mobile ad hoc network that is applicable to data communications among ships or user's convenient u-health services. Modeling and simulation analysis are used to verify the improvement.

• Nuclear Engineering and Technology
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• 제50권5호
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• pp.731-737
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• 2018

In this research paper, the thermal transport in thorium dioxide is investigated by using nonequilibrium molecular dynamics. The thermal conductivity of bulk thorium dioxide was measured to be 20.8 W/m-K, confirming reported values, and the phonon mean free path was estimated to be between 7 and 8.5 nm at 300 K. It was observed that the thermal conductivity of thorium dioxide shows a strong dependency on temperature; the highest thermal conductivity was estimated to be 77.3 W/m-K at 100 K, and the lowest thermal conductivity was estimated to be 4.3 W/m-K at 1200 K. In addition, by simulating thorium dioxide structures with different lengths at different temperatures, it was identified that short wavelength phonons dominate thermal transport in thorium dioxide at high temperatures, resulting in decreased intrinsic phonon mean free paths and minimal effect of boundary scattering while long wavelength phonons dominate the thermal transport in thorium dioxide at low temperatures.

• 한국통신학회논문지
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• 제27권1B호
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• pp.108-113
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• 2002

ITS(Intelligent Transport System: 지능형교통시스템)에서 노변장치 및 차량 단말기사이의 근거리통신은 매우 중요한 역할을 차지한다. 노변통신은 통신 환경이 근거리이고 데이터의 전송 속도가 빠르며 통신 가능 시간이 짧다는 독특한 특성이 있고, 도로 환경에 따라 전파의 전파특성이 매우 다르다. 따라서 원하는 통신 성능을 얻기 위해서는 도로변에서의 전파 다중경로 전파특성의 분석이 필수적이다.

• 한국ITS학회 논문지
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• 제7권1호
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• pp.84-91
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• 2008

본 논문은 다중경로 채널에 따른 채널왜곡을 보상하여 복조하는 주파수 영역 기반 BPM-UWB수신기를 제안한다. 시간영역 BPM-UWB수신기로부터 주파수 영역 기반 BPM-UWB 수신 방식을 유도하였으며 다중경로 채널 환경에서도 성능을 최적화 시킬 수 있는 matched 필터 방식 수신기 구조를 제시하였다. 수학적인 분석에 의해서 시스템 성능을 유도하였으며 시뮬레이션에 의해서 제안한 채널 보상 시스템에 의해 성능이 획기적으로 개선됨을 보인다.

• 한국ITS학회 논문지
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• 제20권1호
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• pp.1-9
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• 2021

본 논문은 안전한 보행 경로 정보를 제공하는 IoT 기반 고령자용 교통안전 보행자 시스템을 제안한다. 제안하는 시스템은 고령자 안전 변수의 요인분석을 수행하고 분석결과를 사용하여 고령자에게 최적의 경로를 제공한다. 이 시스템의 성능을 검증하기 위해 고령 보행자 경로에 대한 성능 측정을 실험하였습니다. 그 결과 모바일 내비게이션보다 안전 성능이 더 나은 성능 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4787-4807
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• 2016

Although the dense interconnection datacenter networks (DCNs) (e.g. FatTree) provide multiple paths and high bisection bandwidth for each server pair, the single-path TCP (SPT) and ECMP which are widely used currently neither achieve high bandwidth utilization nor have good load balancing. Due to only one available transmission path, SPT cannot make full use of all available bandwidth, while ECMP's random hashing results in many collisions. In this paper, we present OFPT, an OpenFlow based Parallel Transport framework, which integrates precise routing and scheduling for better load balancing and higher network throughput. By adopting OpenFlow based centralized control mechanism, OFPT computes the optimal path and bandwidth provision for each flow according to the global network view. To guarantee high throughput, OFPT dynamically schedules flows with Seamless Flow Migration Mechanism (SFMM), which can avoid packet loss in flow rerouting. Finally, we test OFPT on Mininet and implement it in a real testbed. The experimental results show that the average network throughput in OFPT is up to 97.5% of bisection bandwidth, which is higher than ECMP by 36%. Besides, OFPT decreases the average flow completion time (AFCT) and achieves better scalability.

• Ocean Systems Engineering
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• 제12권3호
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• pp.359-384
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• 2022

We develop in this work a new well-balanced preserving-positivity path-conservative central-upwind scheme for Saint-Venant-Exner (SVE) model. The SVE system (SVEs) under some considerations, is a nonconservative hyperbolic system of nonlinear partial differential equations. This model is widely used in coastal engineering to simulate the interaction of fluid flow with sediment beds. It is well known that SVEs requires a robust treatment of nonconservative terms. Some efficient numerical schemes have been proposed to overcome the difficulties related to these terms. However, the main drawbacks of these schemes are what follows: (i) Lack of robustness, (ii) Generation of non-physical diffusions, (iii) Presence of instabilities within numerical solutions. This collection of drawbacks weakens the efficiency of most numerical methods proposed in the literature. To overcome these drawbacks a reformulation of the central-upwind scheme for SVEs (CU-SVEs for short) in a path-conservative version is presented in this work. We first develop a finite-volume method of the first order and then extend it to the second order via the averaging essentially non oscillatory (AENO) framework. Our numerical approach is shown to be well-balanced positivity-preserving and shock-capturing. The resulting scheme could be seen as a predictor-corrector method. The accuracy and robustness of the proposed scheme are assessed through a carefully selected suite of tests.