• Journal of Communications and Networks
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• v.4 no.3
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• pp.221-229
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• 2002

Adaptability is the most promising feature to be applied in future robust multimedia applications. In this paper, we propose the Direct Algorithm to improve the degree of satisfaction at heterogeneous receivers in multi-layered multicast video environments. The algorithm relies on a mechanism that dynamically controls the rates of the video layers and is based on feedback control packets sent by the receivers. The algorithm also addresses scalability issues by implementing a merging procedure at intermediate nodes in order to avoid packet implosion at the source in the case of large multicast groups. The proposed scheme is optimized to achieve high global video quality and reduced bandwidth requirements. We also propose the Direct Algorithm with a virtual number of layers. The virtual layering scheme induces intermediate nodes to keep extra states of the multicast session, which reduces the video degradation for all the receivers. The results show that the proposed scheme leads to improved global video quality at heterogeneous receivers with no cost of extra bandwidth.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.5
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• pp.61-69
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• 2021

On-demand broadcast is an effective data dissemination technique in mobile computing environments. This paper explores the issues for scheduling multi-data queries in on-demand broadcast environments, and proposes a new broadcast scheduling scheme named CASS. The proposed scheme prioritizes queries by reflecting the characteristics of multi-data queries, and selects the data that has not been broadcast in the query for the longest time as the broadcast data according to the query priority. Simulation is performed to evaluate the performance of CASS. The simulation results show that the proposed scheme outperforms other schemes in terms of the average response time since it can show highly desirable characteristics in the aspects of query data adjacency and data conflict rate.

• Journal of the Korean Institute of Educational Facilities
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• v.28 no.5
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• pp.3-8
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• 2021

The purpose of this study was exploring perceptions of people in community towards community use and multiple-use of special school facilities and providing implications for connecting school to the communities. Survey was conducted to special education teachers, parents of children receiving special education, and local residents. Total 5,702 people participated in this study and general finds were as following: (1) All 3 groups of study participants reported that there was a generally positive perception of special schools within the community, however, at the same time, almost quarter of parents having children with disabilities reported negative perceptions of special schools in the community; (2) among the special school facilities, sports facilities appeared to be the most open to the community and difficulties related to the community-open of school facilities included facility management and safety issues, and inteference with students' school activities; (3) facilities suitable for the multi-use of special schools facilities included sports facilities, cultural and creative spaces, and commercial areas, and those facilities could be open to community during non-class hours such as after-school, weekends, and vacations. Based on the results from survey, implications for planning, designing, and implementing multi-use facilities of special schools were provided.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.42 no.1
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• pp.8-20
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• 2019

The vehicle routing problem is one of the vibrant research problems for half a century. Many studies have extensively studied the vehicle routing problem in order to deal with practical decision-making issues in logistics. However, developments of new logistics strategies have inevitably required investigations on solution methods for solving the problem because of computational complexity and inherent constraints in the problem. For this reason, this paper suggests a simulated annealing (SA) algorithm for a variant of vehicle routing problem introduced by a previous study. The vehicle routing problem is a multi-depot and multi-trip vehicle routing problem with multiple heterogeneous vehicles restricted by the maximum permitted weight and the number of compartments. The SA algorithm generates an initial solution through a greedy-type algorithm and improves it using an enhanced SA procedure with three local search methods. A series of computational experiments are performed to evaluate the performance of the heuristic and several managerial findings are further discussed through scenario analyses. Experiment results show that the proposed SA algorithm can obtain good solutions within a reasonable computation time and scenario analyses show that a transportation system visiting non-dedicated factories shows better performance in truck management in terms of the numbers of vehicles used and trips for serving customer orders than another system visiting only dedicated factories.

• ETRI Journal
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• v.43 no.2
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• pp.221-231
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• 2021

To resolve energy depletion issues in massive Internet of Things sensor networks, we developed a set of distributed energy beamforming methods with one-bit feedback and clustering for multi-node wireless energy transfer, where multiple singleantenna distributed energy transmitters (Txs) transfer their energy to multiple nodes wirelessly. Unlike previous works focusing on distributed information beamforming using a single energy receiver (Rx) node, we developed a distributed energy beamforming method for multiple Rx nodes. Additionally, we propose two clustering methods in which each Tx node chooses a suitable Rx node. Furthermore, we propose a fast distributed beamforming method based on Tx sub-clustering. Through computer simulations, we demonstrate that the proposed distributed beamforming method makes it possible to transfer wireless energy to massive numbers of sensors effectively and rapidly with small implementation complexity. We also analyze the energy harvesting outage probability of the proposed beamforming method, which provides insights into the design of wireless energy transfer networks with distributed beamforming.

• International conference on construction engineering and project management
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• 2022.06a
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• pp.1032-1039
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• 2022

Evaluating infrastructure's impact on social equity is an emerging area of research in transportation construction engineering. Transportation agencies have been trying to include sustainable development. The three components of sustainable development are environmental protection, social equity, and economic development. Although social equity is one of the essential components of sustainable development, most transportation agencies do not consider this component. The research publications in this area are limited. The principal objective of this study is to synthesize existing studies related to the impact of transportation infrastructures on social equity. This study will also identify social equity indicators, the correlation between social equity and transportation infrastructures and their services, and the impact of transportation infrastructures' on social equity. In addition, this study will identify current issues of social equity and will provide some recommendations. This synthesis study revealed that transportation infrastructures impacted social equity in various ways. Some effects are positive, such as new job creation on the market. Other effects are adverse, such as diminishing socio-economic and environmental degradation. Studies also showed that the current practices evaluated infrastructures' impact on a case-by-case basis. The authors recommend adopting a multi-disciplinary holistic for assessing infrastructure's effects on social equity. The multi-disciplinary fields of study include civil engineers, construction engineers/managers, public policy researchers, environmentalists, and social scientists.

• Journal of the Korea Society of Computer and Information
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• v.14 no.12
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• pp.33-40
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• 2009

We study Interpreted Systems, ATL, and ATEL to capture the notion of time, knowledge, and strategy which are important in the analysis of multi-agent systems and propose strategic constraints based on subgame perfect Nash equilibrium of game theory as one of the solutions for the issues of ATEL which an agent can access the current state of the whole system when making up his strategy even when he should be uncertain about the state, and no explicit representation of actions in ATEL models makes some natural situations harder to model. Also, we present strategic constraints-based Interpreted Systems for model checking of multi-agent systems.

• The Journal of Korea Robotics Society
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• v.18 no.2
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• pp.189-196
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• 2023

An abdominal brace is a recommended treatment for patients with lumbar spinal disorders. However, due to the nature of the static brace, it uniformly compresses the lumbar region, which can weaken the lumbar muscles or create a psychological dependence that worsens the condition of the spine when worn for an extended period of time. Due to these issues, doctors limit the wearing time when prescribing it to patients. In this paper, we propose a device that can dynamically provide abdominal pressure and support according to the lumbar motion. The proposed device is a wearable robot in the form of a brace, with actuators and a driving unit mounted on the brace. To enhance wearability and reduce the weight of the device, worm gears actuator and a multi-pulley mechanism were adopted. Based on the spinal motion of the wearer measured by the Inertia measurement unit sensors, the drives wire by driving pulley, which provide tension to the multi-pulley mechanism on both sides, dynamically tightening or loosening the device. Finally, the device can dynamically provide abdominal pressure and support. We describe the hardware and system configuration of the device and demonstrate its potential through basic control experiments.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.10a
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• pp.524-526
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• 2021

As the video wall controller market is growing rapidly, issues that have not been addressed so far are raised. One of them is a phenomenon in which a black screen is displayed on a multi-screen. Black screen is displayed due to an error in the video being displayed in the video wall controller. Human intervention is inevitable to recognize and solve the black screen. However, it is impossible for the operator to monitor the multi-screen 24 hours a day. In this paper, we propose a model that detects the black screen being displayed on the video wall controller. We propose a CNN based architecture to detect a black screen.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.873-879
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• 2024

A sodium-cooled fast reactor (SFR) core has a potential of prompt criticality due to a change of core material distribution during a severe accident, and the resultant energy release has been one of the safety issues of SFRs. In this study, the safety assessment of an unprotected loss-of-flow (ULOF) in a small SFR (SSFR) has been performed using the SIMMER-IV computer code, which couples the models of space- and time-dependent neutronics and multi-component, multi-field thermal hydraulics in three dimensions. The code, therefore, is applicable to the simulations of transient behaviors of extended disrupted core material motion and its reactivity effects during the transition phase (TP) of ULOF, including a potential of prompt-criticality power excursions driven by fuel compaction. Several conservative assumptions are used in the TP analysis by SIMMER-IV. It was found out that one of the important mechanisms that drives the reactivity-inserting fuel motion was sodium vapor pressure resulted from a fuel-coolant interaction (FCI), which itself was non-energetic local phenomenon. The uncertainties relating to FCI is also evaluated in much conservative way in the sensitivity analysis. From this study, the ULOF characteristics in an SSFR have been understood. Occurrence of recriticality events under conservative assumptions are plausible, but their energy releases are limited.