• The KIPS Transactions:PartD
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• v.10D no.4
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• pp.655-660
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• 2003

The cache used by mobile host is an important device that recovers the weak points of limited power and bandwidth, in mobile computing environments. However, it has to stand and maintain the consistency with the server data. In this paper, we propose a 'Selective Cache Consistency Scheme'. The server allows an effective broadcasting by selecting data of high usability using 'Cache State Table' and 'Data Access Table'. Moreover, this scheme prevents the loss of data that nay occur by a long period of disconnection, by asynchronous broadcasting and transmitting those broadcast data preserved in the server. This also allows user to possess the latest data. Through experiments, we have found that the enlargement of autonomy is possible by reducing the dependence of server.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.291-298
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• 2013

In this paper a new hybrid-type control system is proposed which reduces the pump speed of an electro-hydraulic actuator consisting of a pressure-compensated variable displacement piston pump and a valve-controlled hydraulic cylinder, whenever the flow rate demand is low. In order to avoid interfering with the pressure regulator which also has an effect on swash plate angle, the pump speed is changed in proportion to the mean value of the speed component of position commands. Additionally a pressure switch is employed to prevent the system pressure from getting lower than a reference value. Based on computer simulation & experimental results, it is shown that the hybrid control can save the idling power up to 44% at a stand-by mode by reducing the pump speed from 1,800 rpm to 600 rpm without affecting the dynamic response of the electro-hydraulic actuator.

• Journal of Advanced Navigation Technology
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• v.14 no.1
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• pp.33-40
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• 2010

In this paper, the bit-error-ratio (BER) performances of Digital Radio Mondiale Plus (DRM+) system which stand for the European standard to bring analogue FM radio to digital radio in Band-II(30-170 MHz) are evaluated under multipath fading channel models used in Band-II and the adjacent channel interference (ACI) caused by FM signal. From the simulation results, the DRM+ system shows robust performances under time-varying channel environments even though the speed of a vehicle is equal to 300km/h. And it is shown that the frequency diversity, determined by delay spread of multipath fading channel, increases the coding gain of the DRM+ system with an increase of delay spread. In addition, to guarantee the BER performance of 10-4 for DRM+ system with ACI due to FM signal, the simulation results show that the desired signal-to-ACI power ratio must be more than -30 dB when the carrier frequency distance is 150 kHz.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.2
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• pp.121-128
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• 2008

Modularized GPS software defined radio (SDR) has many advantages of applying and modifying algorithm. Hardware based GPS receiver uses many hardware parts (such as RF front, correlators, CPU and other peripherals) that process tracked signal and navigation data to calculate user position, while SDR uses software modules, which run on general purpose CPU platform or embedded DSP. SDR does not have to change hardware part and is not limited by hardware capability when new processing algorithm is applied. The weakness of SDR is that software correlation takes lots of processing time. However, in these days the evolution of processing power of MPU and DSP leads the competitiveness of SDR against the hardware GPS receiver. This paper shows a study of modulization of GPS software platform and it presents development of the GNSS software platform using MATLAB Simulink™. We focus on post processing SDR platform which is usually adapted in research area. The main functions of SDR are GPS signal acquisition, signal tracking, decoding navigation data and calculating stand alone user position from stored data that was down converted and sampled intermediate frequency (IF) data. Each module of SDR platform is categorized by function for applicability for applying for other frequency and GPS signal easily. The developed software platform is tested using stored data which is down-converted and sampled IF data file. The test results present that the software platform calculates user position properly.

• The Journal of Korean Association of Computer Education
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• v.12 no.3
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• pp.41-51
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• 2009

In this thesis, we suggested an e-learning model, which is named 'goal driven personalized e-learning system' to improve educational effects, and implemented it. The system makes the learner choose the learning goal which could be a motivational power for learning, so it enabled self-directed learning. In order to implement the system, we proposed new standards related to personalization by modifying SCORM 2004 standard. New standards stand for the statistics on learning objects usage, a goal for driving learning. and information of the contents model and the sequencing information model, which are parts of the system previously suggested. We implemented the system, and then proved that personalize e-learning is possible by showing that the system could offer a learning path individually to learners who have different characteristics.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.4
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• pp.226-232
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• 2015

The aging of Korea is rapidly advancing in an unprecedented rate in the world. Indoor and outdoor safety accidents involving the elderly frequently occur, with elderly population increasing. Because the physical strength of elderly is decreased, it is necessary to develop devices that aid the everyday life of the elderly to prevent safety accidents. Among many activities, the motions of standing from and sitting on a chair require much physical strength from particular body parts, which causes an overload for particular body parts. To the elderly the repeating motion of standing from and sitting down on a chair is burdensome, because they do not have enough physical strength compare to young persons. As a result the elderly could be injured or falling during standing or sitting. Therefore, the development of a lift chair that considers the problems mentioned above is necessary to prevent the safety accidents of the elderly. The study designed a non-motorized lift chair that comfortably aids the standing and sitting down motion for the use of the elderly by reflecting the anthropometric data of the Korean elderly over 65 years old. Also the design was implemented to smoothly aid the standing motion by considering the knee angle of the elderly when standing. Because the regained strength to stand from a chair is depend on the knee angle. Unlike existing lift devices, this device utilizes a tilting mechanism that does not use electric power so that the product could be composed inexpensively than existing chairs released in the market.

• Journal of the Korean Society of Physical Medicine
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• v.11 no.1
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• pp.23-34
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• 2016

PURPOSE: This study aimed to assess the relationship between the severity of radiographic features and pain and function in patients with knee osteoarthritis (KOA). METHODS: Seventy-eight subjects (14 men, 64 women) with KOA, between the ages of 41 and 83 years (mean age, 61.29 years), were included. All the subjects diagnosed with KOA were scored for severity of radiographic KOA according to the Kellgren-Lawrence (K/L) grade, visual analogue scale (VAS), knee joint range of motion (ROM), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), maximum muscle power (MMP), and sit-to-stand (STS) and one-leg standing (OLS) tests. Associations among the K/L grade, diagnosis, pain, and function were examined by correlation analysis. RESULTS: There were no significant differences between the K/L grade, and the VAS, STS test time, and WOMAC scores (p>.05). There were no significant differences between the K/L grade, bilateral ROM, MMP, and left OLS test time (p>.05). However, there was a significant difference between the K/L grade and right OLS test time (p<.05). The K/L grade was negatively correlated with the left OLS test time(r=-.24, p<.05) and with the right OLS test time (r=-.307, p<.01). CONCLUSION: These results suggest that radiographic KOA was not associated with pain, knee MMP, ROM, and STS test time, but had a weak negative correlation with OLS test time.

• Journal of Korea Society of Industrial Information Systems
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• v.17 no.7
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• pp.17-24
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• 2012

As the resources and power on Ad-hoc networks are limited, new data aggregation techniques are required for energy efficiency. The current research on data aggregation techniques is actively in progress, but existing studies don't consider the density of nodes. If nodes are densely placed in a particular area, the information which the sensor nodes placed on those areas detect can be judged as very strong association. But, the energy spent transmitting this information is a waste of energy. In this paper the densely-concentrated node area is designated as Hotspot_Zone in the multi-hop clustering environment using the AMC and a key node is selected in the area. If the request message of data aggregation is transmitted, the key node among the neighboring nodes sends its environmental information to a manager to avoid duplicate sensing information. Therefore, the life of networks can be prolonged due to this.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.1
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• pp.103-112
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• 2018

To improve current transportation service, a new Seoul Metropolitan Transportation Administration (Seoul MTA), backed by Korean central government, is on the way of being established. This paper tries to answer questions such as 'What is the best type of organizational formation of the upcoming institute to deliver better, seamless transportation service?' and 'What is the most suitable scope of work of the upcoming institute to achieve the goal?' A group decision making process, a kind of AHP (Analytic Hierarchy Process) was adopted to measure the experts' preferences of alternatives in quantitative scale measurement. To evaluate the alternatives, five evaluation criteria were selected. Among them, it is revealed that 'Improvement of the transportation service' and 'Political & Administrative power to make it happen' are the two most important evaluation criteria over what types or operating costs of the administrations are. When the five evaluation criteria are applied onto the group of alternatives, it yields that a stand-alone organization, which should be independent from upper-level government body, should have an integrated and sole authority on the area-wide transportation system management.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2008.10b
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• pp.113-125
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• 2008

In developing information systems, omissions and redundancies of user requirements are too frequent to increase development cost as they need to be remedied at later stages. In order to cope with this problem, various tools describing business processes have been proposed in the past and yet fewer attempts have been made to systematically and categorically evaluate performance of individual tools describing business processes. In this paper, we offer a general framework for appraising competing tools for describing business processes, including ERD, DFD, and Use Case Diagram in terms of ease of use, completeness, chance of having omissions, and. Based on a exemplary business From the measures proposed in this paper for comparing descriptive tools, ERD turns out to stand out over other often-used methodologies. Despite its problem with poor readability, ERD proves to offer relatively higher expressive power and ease of use. Being supplemented by well-formed job descriptions, ERD would remain a better choice in developing business information systems.