• International Journal of Highway Engineering
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• v.11 no.1
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• pp.105-115
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• 2009

According to the accident statistics published by the National Police Agency in 2007, the number of commercial vehicle(city, suburb and other buses) accidents consumes 3.5 percent of the total number of traffic accidents in this year. Since the commercial vehicles are responsible for not only the drivers but also the passengers, it leads more serious social and economic problems. There have been various forms of systems such as a digital speedometer or a black box to meet the social requirement for reducing traffic accidents and safe driving. however the system based on the data after accident control the driver by analyze dangerous drive behaviors, so there is a limit to control driver in real-time. Also speedometer currently managed provide the driver warning information in real-time, but using only the speed of vehicle and RPM information regardless of actual dangerous drive behaviors, disappear the effectiveness. In this study performed a simulation for drivers in general using a simulator programed with dangerous driving types we had developed in the previous study and judging the types. It'd be more effective system to provide the drivers warning information using weight valued in this study. However in this study is limited to apply weight as a result of simulation of drivers in general in actual situation should be made up the deficit based on information of driving type of actual commercial vehicles.

• Korean Journal of Applied Biomechanics
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• v.24 no.2
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• pp.139-149
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• 2014

The purpose of this study was to evaluate the effect of angle change of forefoot's adhesive outsole on the electromyographic activity (EMG) of the erector spinae and selected lower limbs muscle during downhill walking over $-20^{\circ}$ ramp. Thirteen male university students (age: $25.4{\pm}3.9$ yrs, height: $176.2{\pm}5.1$ cm, weight: $717.4{\pm}105.0$ N) who have no musculoskeletal disorder were recruited as the subjects. To assess the myoelectric activities of selected muscles, six of surface EMG electrodes with on-site pre-amplification circuitry were attached to erector spinae (ES), rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), lateral gastrocnemius (LG), and medial gastrocnemius (MG). To obtain maximum EMG levels of the selected muscles for normalization, five maximum effort isometric contraction were performed before the experimental trials. Each subject walked over $0^{\circ}$ and $20^{\circ}$ ramp with three different forefeet's EVA outsole (0, 10, $20^{\circ}$) in random order at a speed of $1.2{\pm}0.1$ m/s. For each trial being analyzed, five critical instants and four phases were identified from the recording. The results of this study showed that the average muscle activities of MG and LG decreased in $20^{\circ}$ shoes compared to $0^{\circ}$ and $10^{\circ}$ ones in the initial double limb stance (IDLS). In initial single limb stance (ISLS) phase, the average muscle activities of ES increased with the angle of forefoot's adhesive outsole, indicating that the increment of shoes' angle induce upper body to flex anteriorly in order to maintain balance of trunk. In terminal double limb stance (TDLS) phase, average muscle activities of TA significantly increased in $20^{\circ}$ outsole compared to $0^{\circ}$ and $10^{\circ}$ ones. There was no external forces acting on the right foot other than the gravity during terminal single limb stance (TSLS) phase, all muscles maintained moderate levels of activity.

• Journal of Korean Society of Transportation
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• v.33 no.6
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• pp.584-597
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• 2015

A considerable amount of literature has been published on pedestrian LOS. So far, however, there is a limitation that LOS analysis methodologies has concentrated on quantitative variables such as pedestrian flow rate, speed and space. This paper intended to suggest the accessibility variable which can not be considered on previous study. The factor was defined and quantified using public transport attributes in particular. This study was carried out in three phases: 1. defined accessibility employing public mode location and service information. 2. investigated the relationship between accessibility and pedestrian flow rate 3. developed the model to establish the factors affected to pedestrian LOS. The results showed that accessibility, walkway attribute and land use type affected the pedestrian LOS. Especially, accessibility and commercial area ratio had negative relationship with LOS. Futhermore, pedestrian LOS declined when obstacle of bus station located on the walkway. On the contrary, LOS was upgraded when sufficient effective width or residential area was secured. These results can receive considerable critical attentions related to determination of pedestrian LOS or effective walkway width.

• Research in Mathematical Education
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• v.7 no.3
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• pp.139-150
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• 2003

The purpose of this paper is to review the gifted education from a reflective perspective. Especially, this research touches upon the issues of selection process from a critical point of view. Most of the problems presented in the mathematics competition or in the programs for preparing such competitions share the similar characteristic: the circumstances that are given for questions are too artificial and complicated; problem solving processes are superficially and fragmentally related to mathematical knowledge; and the previous experience with the problem very much decides whether a student can solve the problem and the speed of problem solving. In contrast, the problems for selecting students for Gifted Education Center clearly show what the related mathematical knowledge is and what kind of mathematical thinking ability these problems intend to assess. Accordingly, the process of solving these problems can be considered an important criterion of a student's mathematical ability. In addition, these kinds of problems can encourage students to keep further interest, and can be used as tasks for mathematical investigation later. We hope that this paper will initiate further discussions on issues derived from the mathematically gifted student selection process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4460-4467
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• 2010

Recent advances in computer technology have brought more dependence on software to railway systems and changed to computer systems. Hence, the reliability and safety assurance of the vital software running on the embedded railway system is going to tend toward very critical task. Accordingly, various software test and validation activities are highly recommended in the international standards related railway software. In this paper, we presented an automated analysis tool and standard for software testing coverage in railway system, and presented its result of implementation. We developed the control flow analysis tool estimating test coverage as an important quantitative item for software safety verification in railway software. Also, we proposed judgement standards due to railway S/W Safety Integrity Level(SWSIL) based on analysis of standards in any other field for utilizing developed tool widely at real railway industrial sites. This tool has more advantage of effective measuring various test coverages than other countries, so we can expect railway S/W development and testing technology of real railway industrial sites in Korea.

• Korean Journal of Construction Engineering and Management
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• v.21 no.5
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• pp.55-63
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• 2020

Earthwork automation has emerged as a promising technology in the construction industry, and the application of earthwork automation technology is starting from the acquisition and processing of point cloud data of the site. Point cloud data has more than a million data due to vast extent of the construction site, and the processing time of the original point cloud data is critical because it takes tens or hundreds of hours to generate a Digital Terrain Model (DTM), and enhancement of the processing time can largely impact on the efficiency of the modeling. Currently, a benchmark program (BP) is actively used for the purpose of both point cloud data processing and BIM design as an integrated program in Korea, however, there are some aspects to be modified and refined. This study modified the BP, and developed an updated program by adopting a compile-based development environment, newly designed UI/UX, and OpenGL while maintaining existing PCD processing functions, and expended compatibility of the PCD file formats. We conducted a comparative test in terms of loading speed with different number of point cloud data, and the results showed that 92 to 99% performance increase was found in the developed program. This program can be used as a foundation for the development of a program that reduces the gap between design and construction by integrating PCD and earthwork BIM functions in the future.

• KIPS Transactions on Computer and Communication Systems
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• v.8 no.6
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• pp.127-138
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• 2019

The data response speed is a critical issue of cloud services because it directly related to the user experience. As such, the in-memory database is widely adopted in many cloud-based applications for achieving fast data response. However, the current implementation of the in-memory database is mostly based on the linked list-based hash table which cannot guarantee the constant data response time. Thus, cuckoo hashing was introduced as an alternative solution, however, there is a disadvantage that only half of the allocated memory can be used for storing data. Subsequently, bucketized cuckoo hashing (BCH) improved the performance of cuckoo hashing in terms of memory efficiency but still cannot overcome the limitation that the insert overhead. In this paper, we propose a data management solution called Wall Cuckoo which aims to improve not only the insert performance but also lookup performance of BCH. The key idea of Wall Cuckoo is that separates the data among a bucket according to the different hash function be used. By doing so, the searching range among the bucket is narrowed down, thereby the amount of slot accesses required for the data lookup can be reduced. At the same time, the insert performance will be improved because the insert is following up the operation of the lookup. According to analysis, the expected value of slot access required for our Wall Cuckoo is less than that of BCH. We conducted experiments to show that Wall Cuckoo outperforms the BCH and Sorting Cuckoo in terms of the amount of slot access in lookup and insert operations and in different load factor (i.e., 10%-95%).

• Tribology and Lubricants
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• v.35 no.1
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• pp.44-51
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• 2019

The paper presents the rotordynamic performance measurements and model predictions of a fuel cell electric vehicle (FCEV) air compressor supported on gas foil bearings (GFBs). The rotor has an impeller on one end and a thrust runner on the other end. The front (impeller side) and rear (thrust side) gas foil journal bearings (GFJBs) are located between the impeller and thrust runner to support the radial loads, and a pair of gas foil thrust bearings are located on both sides of the thrust runner to support the axial loads. The test GFJBs have a partial arc shim foil installed between the top foil and bump strip layers to enhance hydrodynamic pressure generation. During the rotordynamic performance tests, two sets of orthogonally installed eddy-current displacement sensors measure the rotor radial motions at the rotor impeller and thrust ends. A series of speed-up and coast-down tests to 100k rpm demonstrates the dominant synchronous (1X) rotor responses to imbalance masses without noticeable subsynchronous motions, which indicates a rotordynamically stable rotor-GFB system. Finite element analysis of the rotor determines the rotor free-free (bending) natural modes and frequencies well beyond the maximum rotating frequency. The predicted damped natural frequencies and damping ratios of the rotor-GFB system reveal rotordynamic stability over the speeds of interest. The imbalance response predictions show that the predicted critical speeds and rotor amplitudes strongly agree with the test measurements, thus validating the developed rotordynamic model.

• Wind and Structures
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• v.28 no.2
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• pp.71-87
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• 2019

The yaw and interference effects of blades affect aerodynamic performance of large wind turbine system significantly, thus influencing wind-induced response and stability performance of the tower-blade system. In this study, the 5MW wind turbine which was developed by Nanjing University of Aeronautics and Astronautics (NUAA) was chosen as the research object. Large eddy simulation on flow field and aerodynamics of its wind turbine system with different yaw angles($0^{\circ}$, $5^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$ and $45^{\circ}$) under the most unfavorable blade position was carried out. Results were compared with codes and measurement results at home and abroad, which verified validity of large eddy simulation. On this basis, effects of yaw angle on average wind pressure, fluctuating wind pressure, lift coefficient, resistance coefficient,streaming and wake characteristics on different interference zone of tower of wind turbine were analyzed. Next, the blade-cabin-tower-foundation integrated coupling model of the large wind turbine was constructed based on finite element method. Dynamic characteristics, wind-induced response and stability performance of the wind turbine structural system under different yaw angle were analyzed systematically. Research results demonstrate that with the increase of yaw angle, the maximum negative pressure and extreme negative pressure of the significant interference zone of the tower present a V-shaped variation trend, whereas the layer resistance coefficient increases gradually. By contrast, the maximum negative pressure, extreme negative pressure and layer resistance coefficient of the non-interference zone remain basically same. Effects of streaming and wake weaken gradually. When the yaw angle increases to $45^{\circ}$, aerodynamic force of the tower is close with that when there's no blade yaw and interference. As the height of significant interference zone increases, layer resistance coefficient decreases firstly and then increases under different yaw angles. Maximum means and mean square error (MSE) of radial displacement under different yaw angles all occur at circumferential $0^{\circ}$ and $180^{\circ}$ of the tower. The maximum bending moment at tower bottom is at circumferential $20^{\circ}$. When the yaw angle is $0^{\circ}$, the maximum downwind displacement responses of different blades are higher than 2.7 m. With the increase of yaw angle, MSEs of radial displacement at tower top, downwind displacement of blades, internal force at blade roots all decrease gradually, while the critical wind speed decreases firstly and then increases and finally decreases. The comprehensive analysis shows that the worst aerodynamic performance and wind-induced response of the wind turbine system are achieved when the yaw angle is $0^{\circ}$, whereas the worst stability performance and ultimate bearing capacity are achieved when the yaw angle is $45^{\circ}$.

• Resources Recycling
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• v.29 no.6
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• pp.104-113
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• 2020

Bubble size in froth flotation has long been recognized as a key factor which affects the bubble residence time, the bubble surface area flux (Sb) and the carrying rate (Cr). This paper presents method of bubble size measurement, relationship between operating variables and gas dispersion properties in flotation column. Using high speed camera and image analysis system, bubble size has been directly measured as a function of operating parameters (e.g., superficial gas rate (Jg), superficial wash water rate (Jw), frother concentration) in flotation column. Relationship compared to measured and estimated bubble size was obtained within error ranges of ±15~20% and mean bubble size was 0.718mm. From this system the empirical relationship to control the bubble size and distribution has been developed under operating conditions such as Jg of 0.65~1.3cm/s, Jw of 0.13~0.52cm/s and frother concentration of 60~200ppm. Surface tension and bubble size decreased as frother concentration increased. It seemed that critical coalescence concentration (CCC) of bubbles was 200ppm so that surface tension was the lowest (49.24mN/m) at frother concentration of 200ppm. Bubble size tend to increase when superficial gas rate (Jg) decreases and superficial wash water rate Jw and frother concentration increase. Gas holdup is proportional to superficial gas rate as well as frother concentration and superficial wash water rate (at the fixed superficial gas rate).