• The KIPS Transactions:PartA
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• v.18A no.2
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• pp.75-80
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• 2011

Recently, many cleaning robots have been made with various algorithms for efficient cleaning. One of them is a DmaxCoverage algorithm which efficiently clean for the situation when the robot has a time limit. This algorithm uses Rectangle Tiling method for finding the biggest rectangle that doesn't have any obstacle. When the robot uses grid map, Rectangle Tiling method can find the optimal value. Rectangle Tiling method is to find all of the rectangles in the grid map. But when the grid map is big, it has a problem that spends a lot of times because of the large numbers of rectangles. In this paper, we propose Four Direction Rectangle Scanning(FDRS) method that has similar accuracy but faster than Rectangle Tiling method. FDRS method is not to find all of the rectangle, but to search the obstacle's all directions. We will show the FDRS method's performance by comparing of FDRS and Rectangle Tiling methods.

• Journal of Korean Society for Geospatial Information Science
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• v.23 no.2
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• pp.69-77
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• 2015

In Korea, local governments have decided the location of shelters as part of their disaster planning. However, no quantitative standards, such as assuming different hazard and shelter types, shelters' capacity, are specified in that planning. To propose the direction of disaster evacuation policy, first of all, the current state of shelters' location and evacuation area is needed to be analyzed. In addition, considering topographical condition such as road slope and physical strength by age are important factors to measure optimal evacuation route. The purpose is to suggest a new methodology of estimating optimal evacuation route considering resistance of road slope and difference of walking speed by age. Moreover, as a case study of Seoul, Korea, using coverage analysis of GIS analysis tool, the accessible area (or vulnerable area) to the shelters is evaluated based on the spatial distribution of disaster evacuation shelters and their accommodation capacity, according to evacuation time within 7.5, 15 and 30 minutes. The main results are summarized as follows: 1) The average area of disaster evacuation shelter per person is calculated as 0.45 square meters. Considering that the minimum shelters' area per person is 1 square meters, only 45% of people in Seoul can be accommodated. 2) The ratio of inhabitants who live in accessible area within 7.5 minutes presents only 33% of all. Furthermore, the ratio of inhabitants by age group of 5~9 or over 65 years old shows significantly lower percentage in comparison with 15~49 years old people.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.2
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• pp.618-633
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• 2014

Relay technology is becoming more important for mobile communications and wireless internet of things (IoT) networking because of the extended access network coverage range and reliable quality of service (QoS) it can provide at low power consumption levels. Existing mobile multihop relay (MMR) technology uses fixed-point stationary relay stations (RSs) and a divided time-frame (or frequency-band) to support the relay operation. This approach has limitations when a local fixed-point stationary RS does not exist. In addition, since the time-frame (or frequency-band) channel resources are pre-divided for the relay operation, there is no way to achieve high channel utilization using intelligent opportunistic techniques. In this paper, a different approach is considered, where the use of mobile/IoT devices as RSs is considered. In applications that use mobile/IoT devices as relay systems, due to the very limited battery energy of a mobile/IoT device and unequal channel conditions to and from the RS, both minimum energy consumption and QoS support must be considered simultaneously in the selection and configuration of RSs. Therefore, in this paper, a mobile RS is selected and configured with the objective of minimizing power consumption while satisfying end-to-end data rate and bit error rate (BER) requirements. For the RS, both downlink (DL) to the destination system (DS) (i.e., IoT device or user equipment (UE)) and uplink (UL) to the base station (BS) need to be adaptively configured (using adaptive modulation and power control) to minimize power consumption while satisfying the end-to-end QoS constraints. This paper proposes a minimum transmission power consuming RS selection and configuration (MPRSC) scheme, where the RS uses cognitive radio (CR) sub-channels when communicating with the DS, and therefore the scheme is named MPRSC-CR. The proposed MPRSC-CR scheme is activated when a DS moves out of the BS's QoS supportive coverage range. In this case, data transmissions between the RS and BS use the assigned primary channel that the DS had been using, and data transmissions between the RS and DS use CR sub-channels. The simulation results demonstrate that the proposed MPRSC-CR scheme extends the coverage range of the BS and minimizes the power consumption of the RS through optimal selection and configuration of a RS.

• Korean Journal of Environmental Biology
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• v.38 no.1
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• pp.197-205
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• 2020

With the purpose of designing companion planting of groundcover plants for ornamental uses, this study identified the yearly growth characteristics of nine species of different life forms, analyzed the coverage characteristics of individual plants, and suggested combinations of plants suitable for each life form. Polygonatum odoratum var. pluriflorum, Liriope platyphylla and Hosta capitata, as short-grained plants that can grow to more than 20 cm, tended to grow for 60 days after planting in April and maintain their shape thereafter. Their aerial parts started to wither and enter dormancy after September. Saxifraga stolonifera, Dianthus chinensis and Sedum middendorffianum tended to continuously grow until September after planting in April and their growth declined after September. Lysimachia nummularia, as a creeping plant that grows creeping on the ground, started to show a rapid growth three months after planting. Sedum sarmentosum grew slowly until August and the aerial parts started to wither from September when the temperature decreases. The coverage characteristics of these nine species that grow differently after companion planting were surveyed and the growth of Sedum sarmentosum showed the highest number of companions. It was found that Hosta capitata can be companion planted with Sedum middendorffianum, Saxifraga stolonifera, and Lysimachia nummularia. These results indicate that among different shoot growth types species propagated with their stems creeping on the ground or those that can grow vegetatively with non-rhizome parts are more suitable for companion planting with others than those of which rhizomes branch.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.10
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• pp.664-673
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• 2014

This paper analyzes the power allocation scheme to maximize the sum-rate for heterogeneous networks based on asynchronous time division duplex. We consider heterogeneous networks where a small cell exists in the macro cell coverage and the small cell and the macro cell share the same time-frequency resources. We formulate the optimization problem which maximizes the sum-rate of the heterogeneous network subject to the target signal-to-interference-plus-noise ratio. We analyze the feasible region in order for the optimal solution to exists and the optimal power allocation scheme for maximizing the sum-rate. Simulation results show that the proposed power allocation schemes outperform the maximum power transmission scheme.

• The Journal of Korean Medicine
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• v.38 no.3
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• pp.143-159
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• 2017

Objectives: The aim of this study was to investigate the current status of and seek for measures to activate Korean medicine in stroke care. Methods: This is an e-mail survey targeting the members of Korean medical doctors registered at the association of Korean medicine. The project team of the society of stroke on Korean medicine for the development of clinical practice guideline for stroke has devised the items for the questionnaire. The survey was conducted for 15 days in November 2016. Results: The percentage of the respondents who have treated patients with stroke for the past month was 11.2% in the acute phase, 20.5% in the convalescent phase, and 32.4% in the chronic phase. Approximately 80% of the respondents answered they had a decrease in the number of patients compared to 10 years ago, regardless of the stroke phase. Most of the respondents were using Western medicine together with traditional Korean medicine for physical examination. Acupuncture and herbal medicine were the main therapeutic interventions. The two measures chosen by the most respondents to activate the Korean medicine usage for stroke care were the expansion of the insurance coverage (34.9%) and the generation of evidence on the effectiveness of traditional Korean medicine (25.1%) Conclusion: It is necessary to actively show the role of the Korean medicine through the establishment of the evidence on the effectiveness of Korean medicine and the promotion based on the evidence. In addition, optimal treatment methods should be derived based on the traditional knowledge and modern scientific research and the methods should be educated to every Korean medical clinics and hospitals so that they can be implemented in clinical practice. At the same time, the government should provide policy support to ensure that the optimal treatment can be timely and appropriately implemented.

• Smart Structures and Systems
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• v.22 no.4
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• pp.481-493
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• 2018

Ultrasonic guided waves have attracted increasing attention for non-destructive testing (NDT) and structural health monitoring (SHM) of bridge cables. They offer advantages like single measurement, wide coverage of acoustical field, and long-range propagation capability. To design defect detection systems, it is essential to understand how guided waves propagate in cables and how to select the optimal excitation frequency and mode. However, certain cable characteristics such as multiple wires, anchorage, and polyethylene (PE) sheath increase the complexity in analyzing the guided wave propagation. In this study, guided wave modes for multi-wire bridge cables are identified by using a semi-analytical finite element (SAFE) technique to obtain relevant dispersion curves. Numerical results indicated that the number of guided wave modes increases, the length of the flat region with a low frequency of L(0,1) mode becomes shorter, and the cutoff frequency for high order longitudinal wave modes becomes lower, as the number of steel wires in a cable increases. These findings were used in design of transducers for defect detection and selection of the optimal wave mode and frequency for subsequent experiments. A magnetostrictive transducer system was used to excite and detect the guided waves. The applicability of the proposed approach for detecting and locating wire breakages was demonstrated for a cable with 37 wires. The present ultrasonic guided wave method has been found to be very responsive to the number of brokenwires and is thus capable of detecting defects with varying sizes.

• Journal of the Korean Institute of Gas
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• v.19 no.6
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• pp.72-79
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• 2015

Electricity can be generated when the natural gas passes through a turbo-expander pressure reduction system at natural gas pressure reduction stations. Efficiency of the turbo-expander depends on the ratio of the natural gas flow rates to the design flow rate of the turbo-expander. Therefore, the optimal conditions for the operation of the pressure reduction system can be determined by controlling the natural gas flow rates. In this study, we have calculated the electric energy generation depending on the natural gas flow rates at the two low-pressure reduction stations when the pressure of the natural gas is reduced from 17.5 bar to 8.5 bar and have found the optimal conditions for the turbo-expander pressure reduction system through the comparison with the calculation results. The turbo-expander generates the electric power efficiently for the high natural gas flow rates which variations are slight. The determined design flow rate of the turbo-expander has the highest coverage of the natural gas flow rates. The electricity generation is calculated as much as 9 MW(B station) and 12 MW(D station) at each pressure reduction station.

• The Journal of Korea Robotics Society
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• v.18 no.1
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• pp.1-9
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• 2023

This paper presents an optimal path planning strategy for aerial searching and surveying of a user-designated area using multiple Unmanned Aerial Vehicles (UAVs). The method is designed to deal with a single unseparated polygonal area, regardless of polygonal convexity. By defining the search area into a set of grids, the algorithm enables UAVs to completely search without leaving unsearched space. The presented strategy consists of two main algorithmic steps: cellular decomposition and path planning stages. The cellular decomposition method divides the area to designate a conflict-free subsearch-space to an individual UAV, while accounting the assigned flight velocity, take-off and landing positions. Then, the path planning strategy forms paths based on every point located in end of each grid row. The first waypoint is chosen as the closest point from the vehicle-starting position, and it recursively updates the nearest endpoint set to generate the shortest path. The path planning policy produces four path candidates by alternating the starting point (left or right edge), and the travel direction (vertical or horizontal). The optimal-selection policy is enforced to maximize the search efficiency, which is time dependent; the policy imposes the total path-length and turning number criteria per candidate. The results demonstrate that the proposed cellular decomposition method improves the search-time efficiency. In addition, the candidate selection enhances the algorithmic efficacy toward further mission time-duration reduction. The method shows robustness against both convex and non-convex shaped search area.

• Journal of Advanced Navigation Technology
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• v.27 no.5
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• pp.502-509
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• 2023

This study presents a satellite constellation method that achieves optimal revisit performance by utilizing genetic algorithm techniques. The Walker method is a global coverage concept, and there are limitations to target-centered constellation considering the strategic environment of the Korean Peninsula. To overcome these limitations, targets are set in major areas of interest in North Korea, orbit elements with optimal revisit performance for each target are searched, and based on this, the number of satellites optimized for each target is derived using a genetic algorithm. The results of this study demonstrate the performance of the optimized constellation by applying phasing rules to achieve the desired revisit performance.