• The Journal of Korea Robotics Society
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• v.16 no.2
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• pp.112-121
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• 2021

Unlike a typical small-sized robot navigating in a free space, an autonomous vehicle has to travel in a designated road which has lanes to follow and traffic rules to obey. High-Definition (HD) maps, which include road markings, traffic signs, and traffic lights with high location accuracy, can help an autonomous vehicle avoid the need to detect such challenging road surroundings. With space constraints and a pre-built HD map, a new type of path planning algorithm can be conceived as a substitute for conventional grid-based path planning algorithms, which require substantial planning time to cover large-scale free space. In this paper, we propose an obstacle-avoiding, cost-based planning algorithm in a continuous space that aims to pursue a globally-planned path with the help of HD map information. Experimentally, the proposed algorithm is shown to outperform other state-of-the-art path planning algorithms in terms of computation complexity in a typical urban road setting, thereby achieving real-time performance and safe avoidance of obstacles.

• Journal of the Korean Geographical Society
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• v.40 no.5 s.110
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• pp.514-532
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• 2005

The purpose of this study is to critically examine conventional spatial measures of individual accessibility, which are based on the notion of spatial proximity, the single reference location, and the unlinked travel model. Using space-time accessibility measures with the travel-activity diary data set of Portland Metro, US, three expectations from spatial measures on spatial patterns of individual accessibility were empirically examined: (1) does individual accessibility decrease with an increase of distance from the CBD?; (2) does the spatial pattern of accessibility resemble that of urban opportunity density pattern?; and (3) are spatial patterns of individual accessibility of different socio- demographic population groups basically similar as people in the same area share the same geographic characteristics regardless of gender, race, age, and so on? First of all, the results showed that spatial variations in individual accessibility were not directly determined by spatial proximity and opportunity density as suggested by previous accessibility measures. The spatial pattern of individual accessibility was dramatically different from that of urban opportunity density High peaks of accessibility level were found far away from the CBD and regional centers. This finding might be associated with the importance of multi-reference locations and linked travels in shaping accessibility in reality. Furthermore, this study found that spatial patterns of accessibility clearly differ between men and women. These findings suggest that access requires more than proximity, and that the interaction between person-specific space-time constraints and the consequential availability of urban opportunities in space-time renders different accessibility experiences to people even in the same region, which would be one of the key ingredients missing from conventional spatial measures of accessibility.

• Journal of Korean Society of Transportation
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• v.27 no.2
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• pp.179-187
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• 2009

Currently, the signalized intersections in Korea are operated without providing an emergency vehicle preemption control strategy. Thus, it might threaten the safety of the pedestrians and drivers on highways when an emergency vehicle faces congested traffic conditions. The existing preemption control is activated when an emergency vehicle is detected along a path. This enables emergency vehicles to progress uninterrupted, but it also increases the delay of other vehicles. In this paper, a revised preemption control strategy considering queue length restrictions is proposed to make both a progressive movement of an emergency vehicle and reduce delay of other vehicles simultaneously. By applying the preemption control strategy through a simulation study, it was shown that delay of an emergency vehicle decreased to 44.3%-96.1% and speed increased to 8.8%-42.0% in all 9 cases as compared with a conventional signal control. The existing preemption control is superior for oversaturated conditions (v/c >1.0) or a link length less than 200m. However, the preemption control considering queue length constraints shows better performance than the existing preemption control when the v/c is less than 0.8 and a link length is longer than 500m.

• Journal of the Korean Institute of Landscape Architecture
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• v.42 no.3
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• pp.25-34
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• 2014

The purposes of this study are two folds: (a) to identify the influences of tourism on subjective well-being, and (b) to understand the roles of travel motivation, constraint and personal value in subjective well-being. A polling agency was employed to select 500 respondents by quota sampling, and data was collected by online survey. ANOVA and regression results showed that tourism participants, compared to the non-participants, have a tendency to select tourism as a mean to enhance their subjective well-being because they are more self-motivated people. Their high motivation to take a trip lead to set up their feasible goals to achieve by the tourism experience and their relatively few constraints help them to have trip easily. The people's satisfaction in tourism contributes to the satisfaction in his/her leisure life, which in turn contributes to his/her subjective well-being. It is also revealed that tourism participation and subjective income level are significant variables affecting subjective well-being, which explain 21.1 percent of the variance. The research suggests various managerial implications to reduce constraints and several ideas for future researches.

• Journal of the Korean Geographical Society
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• v.42 no.5
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• pp.808-834
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• 2007

This study attempts to elucidate manifold dimensions of gendered accessibility experiences. How gender roles(household responsibilities) differentiate accessibility experiences between women and men is explored through the comparison of married dual-earner couples' parental status, using the US Portland activity-travel diary dataset with GIS-based geocomputation results of(time-geography based) space-time accessibility. First, this study shows how gender division of labor within the household still permeates current society, despite the widespread belief of the social change toward a gender-egalitarian society. Then, the study pays special attention to the way gender roles structure individual accessibility experiences of women and men differently, and, in turn, the way such accessibility experiences take a form of gendered spatiality. Gendered spatiality is examined through the analysis of accessibility space as well as activity space in order to ascertain women's home-attached and spatially entrapped characteristics. More household responsibilities throughout a day and, even more, the time constraint of picking up children at the daycare centers after work lead women's possible activity space to be more home-centered. The analysis of the spatio-temporal context of accessibility space makes gendered spatiality visible. However, the findings suggest that behavioral outcomes should be understood with an explicit awareness of constraints individuals face. It is because the revealed activity spaces can be not only an outcome of constraint but also an outcome of choice. Behavioral outcomes should not be treated as a straightforward expression of the level of constraints. It is problematic to expect that behavioral outcomes directly mirror the level of constraints. It is also problematic to suppose that the level of constraints can be straightforwardly elicited from revealed behavioral outcomes.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.356-362
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• 2011

Usually urban railways are built under ground thus the necessary condition of urban railroad, a linear-shaped track, causes a difficulty in enhancement of speed limits of urban rail. Also the underground construction of city railroad produces speed limit values reduced according to a speed code array, in case of speed decision according to the conventional block section division, thus onventionally it could not but apply speed limit values lower than actual safety speeds. In this study, The above two facts induced the author to study on a method to enhance speed limit values for CBTC within existing urban railroad sectors. Since it is possible to exchange data continuously and to control speeds in case of railroads based on CBTC, the author applied result values of speed limits, which were gained based on a railroad condition, a linear track, to the CBTC system without correction of the result values and then the author compared and analyzed, through simulation, the running times and the efficiencies of running energies between railway stations, between the existing fixed-block system and the CBTC system. As a result simulation, the improvement of speed and the deceleration distance of reduction confirmed that it was effective to reduce the time to travel between stations. A fixed block the set of constraints on the speed limit, he way the operation is optimized based CBTC speed limit by suggesting ways to reset the scheduled speed measures to improve were extracted.

• Advances in aircraft and spacecraft science
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• v.2 no.1
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• pp.95-108
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• 2015

Automatic Dependent Surveillance Broadcast (ADS-B) is quickly being adopted by aviation safety authorities around the world as the standard for aircraft tracking. The technology provides the opportunity for live tracking of aircraft positions within range of an ADS-B receiver stations. Currently these receiver stations are bound by land and local infrastructural constraints. As such there is little to no coverage over oceans and poles, over which many commercial flights routinely travel. A low cost space based ADS-B receiving system is proposed as a constellation of small satellites. The possibility for a link between aircraft and satellite is dependent primarily on proximity. Calculating the likelihood of a link between two moving targets when considering with the non-periodic and non-uniform nature of actual aircraft flight-paths is non-trivial. This analysis of the link likelihood and the performance of the tracking ability of the satellite constellation has been carried out by a direct simulation of satellites and aircraft. Parameters defining the constellation (satellite numbers, orbit size and shape, orbit configuration) were varied between reasonable limits. The recent MH370 disappearance was simulated and potential tracking and coverage was analysed using an example constellation. The trend of more satellites at a higher altitude inclined at 60 degrees was found to be the optimal solution.

• Journal of information and communication convergence engineering
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• v.18 no.2
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• pp.123-131
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• 2020

After observing that most tourists plan to complete their visits to multiple cultural heritage sites within one day, we surmised that for many museum visitors, the foremost thought is with regard to the amount of time is to be spent at each location and how they can maximize their enjoyment at a site while still balancing their travel itinerary? Recommendation systems in e-commerce are built on knowledge about the users' previous purchasing history; recommendation systems for museums, on the other hand, do not have an equivalent data source available. Recent solutions have incorporated advanced technologies such as algorithms that rely on social filtering, which builds recommendations from the nearest identified similar user. Our paper proposes a different approach, and involves providing dynamic recommendations that deploy social filtering as well as content-based filtering using term frequency-inverse document frequency. The main challenge is to overcome a cold start, whereby no information is available on new users entering the system, and thus there is no strong background information for generating the recommendation. In these cases, our solution deploys statistical methods to create a recommendation, which can then be used to gather data for future iterations. We are currently running a pilot test at Chao Samphraya national museum and have received positive feedback to date on the implementation.

• Smart Structures and Systems
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• v.26 no.5
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• pp.657-666
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• 2020

A rotational pulse-echo ultrasonic propagation imager that can inspect cylindrical specimens for material nondestructive evaluations is proposed herein. In this system, a laser-generated ultrasonic bulk wave is used for inspection, which enables a clear visualization of subsurface defects with a precise reproduction of the damage shape and size. The ultrasonic waves are generated by a Q-switched laser that impinges on the outer surface of the specimen walls. The generated waves travel through the walls and their echo is detected by a Laser Doppler Vibrometer (LDV) at the same point. To obtain the optimal Signal-to-Noise Ratio (SNR) of the measured signal, the LDV requires the sensed surface to be at a right angle to the laser beam and at a predefined constant standoff distance from the laser head. For flat specimens, these constraints can be easily satisfied by performing a raster scan using a dual-axis linear stage. However, this arrangement cannot be used for cylindrical specimens owing to their curved nature. To inspect the cylindrical specimens, a circular scan technology is newly proposed for pulse-echo laser ultrasound. A rotational stage is coupled with a single-axis linear stage to inspect the desired area of the specimen. This system arrangement ensures that the standoff distance and beam incidence angle are maintained while the cylindrical specimen is being inspected. This enables the inspection of a curved specimen while maintaining the optimal SNR. The measurement result is displayed in parallel with the on-going inspection. The inspection data used in scanning are mapped from rotational coordinates to linear coordinates for visualization and post-processing of results. A graphical user interface software is implemented in C++ using a QT framework and controls all the individual blocks of the system and implements the necessary image processing, scan calculations, data acquisition, signal processing and result visualization.

• The KIPS Transactions:PartD
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• v.13D no.7 s.110
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• pp.879-888
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• 2006

Recently many researchers have focused on management of Historical trajectories of moving objects in Euclidean spaces due to numerous sizes of accumulated data over time. However, the movement of moving objects in real applications generally has some constraints, for example vehicles on roads can only travel along connected road networks. In this paper, we propose an indexing method for trajectories of moving objects on road networks in order to process the network-based spatiotemporal range query. Our method contains the connect information of road networks to use the network distance for query processing, deals with trajectories which are represented by road segments in road networks, and manages them using multiple R-trees assigned per each road segment. Furthermore, it has a structure to be able to share R-tree among several road segments in large road networks. Consequently, we show that our method takes about 30% less in node accesses for the network-based spatiotemporal range query processing than other methods based on the Euclidean distance by experiments.