• Carbon letters
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• v.15 no.1
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• pp.25-31
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• 2014

A microstructure analysis is carried out to optimize the process parameters of a randomly oriented discrete length hybrid carbon fiber reinforced carbon matrix composite. The composite is fabricated by moulding of a slurry into a preform, followed by hot-pressing and carbonization. Heating rates of 0.1, 0.2, 0.3, 0.5, 1, and $3.3^{\circ}C/min$ and pressures of 5, 10, 15, and 20 MPa are applied during hot-pressing. Matrix precursor to reinforcement weight ratios of 70:30, 50:50, and 30:70 are also considered. A microstructure analysis of the carbon/carbon compacts is performed for each variant. Higher heating rates give bloated compacts whereas low heating rates give bloating-free, fine microstructure compacts. The compacts fabricated at higher pressure have displayed side oozing of molten pitch and discrete length carbon fibers. The microstructure of the compacts fabricated at low pressure shows a lack of densification. The compacts with low matrix precursor to reinforcement weight ratios have insufficient bonding agent to bind the reinforcement whereas the higher matrix precursor to reinforcement weight ratio results in a plaster-like structure. Based on the microstructure analysis, a heating rate of $0.2^{\circ}C/min$, pressure of 15 MPa, and a matrix precursor to reinforcement ratio of 50:50 are found to be optimum w.r.t attaining bloating-free densification and processing time.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1903-1908
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• 2008

This paper presents a characteristics of linear induction motor considering airgap variation for railway transit in order to achieve high performance of the vehicle. The operating principle of a LIM(Linear induction motor) is identical to a rotary induction motor. Space-time variant magnetic fields are generated by the primary part across the airgap and induce the electro-motive force(EMF) in the secondary part, a conducting sheet. This EMF generates the eddy currents, which interact with the airgap flux and so produce the thrust force known as Loren's force. Even though the operating principal is exactly same as a rotary motor, the linear motor has a finite length of the primary or secondary parts and it causes static and dynamic end-effect which is the discontinuous airgap flux phenomenon. This end-effect causes the deterioration of the system performance, especially in high-speed operation. Another problem is that construction tolerance restricts the minimum airgap in order to prevent a collision between the primary part and the secondary reaction plate. More over, as the airgap length is getting smaller, the attraction force between the primary part and secondary parts is getting larger dramatically and the attraction force would be another friction against propulsion. Therefore, it is necessary to figure out the characteristics of linear induction motor considering airgap variation in order to achieve high performance of the vehicle. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction and thrust force according to the airgap variation is analyzed. The simulation results are presented to show the effect of the LIM according to the airgap variation.

• Journal of Conservation Science
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• v.26 no.4
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• pp.459-465
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• 2010

The 5th century kiln that produced pottery coffins was found for the first time in Korea, located in the Oryang-dong remains in the city of Naju. This kiln, located in the central area of the Yeongsan River, provides important data for research on mortuary practices in prehistoric society, including the structure of production and patterns of distribution and consumption. For this study, the remains of five ancient tombs and pottery coffins excavated from the 4th century Mandong archaeological site were chosen to determine the area of consumption of pottery coffins produced at the Oryang-dong kiln. The samples from each area of remains were analyzed for minor elements using neutron activation analysis method, and from these results, the identities of the corresponding production areas were investigated using the multi-variant statistical analysis of discriminant analysis. The evidence strongly suggests that pottery coffins produced at the Oryang-dong kiln in Naju were used in ancient tombs of the Bannam mound in Naju, the Okyari mound in Yeongam, and the Banam mound in Hampyeong, reaching those sites through trade and distribution. The findings also suggest that pottery coffins from the Mandong archeological site in Gochang and the Inpyeong mound in Muan were not produced at the Oryang-dong kiln in Naju, but rather were brought from pottery kilns in different production areas, through trade and distribution.

• Journal of the Korea Society of Computer and Information
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• v.10 no.4 s.36
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• pp.191-201
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• 2005

In this paper, we propose a method to calculate camera motion parameter, which is based on efficient invariant features irrelevant to the camera veiwpoint. As feature information in previous research is variant to camera viewpoint. information content is increased, therefore, extraction of accurate features is difficult. LM(Levenberg-Marquardt) method for camera extrinsic parameter converges on the goat value exactly, but it has also drawback to take long time because of minimization process by small step size. Therefore, in this paper, we propose the extracting method of invariant features to camera viewpoint and two-stage calculation method of camera motion parameter which enhances accuracy and convergent degree by using camera motion parameter by 2D homography to the initial value of LM method. The proposed method are composed of features extraction stage, matching stage and calculation stage of motion parameter. In the experiments, we compare and analyse the proposed method with existing methods by using various indoor images to demonstrate the superiority of the proposed algorithm.

• Journal of the Korea Society for Simulation
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• v.27 no.3
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• pp.45-52
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• 2018

We consider the busy period of an M/G/1/K queueing system with queue-length-dependent overload control policy. A variant of an oscillating control strategy that was recently analyzed by Choi and Kim (2016) is considered: two threshold values, $L_1({\leq_-}L_2)$ and $L_2({\leq_-}K)$, are assumed, and service rate and arrival rate are adjusted depending on the queue length to alleviate congestion. We investigate the busy period of an M/G/1/K queue with two overload control policies, and present the formulae to obtain the expected length of a busy period for each control policy. Based on the numerical examples, we conclude that the variability and expected value of the service time distribution have the most influence on the length of a busy period.

• Journal of Preventive Medicine and Public Health
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• v.27 no.3 s.47
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• pp.465-473
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• 1994

This study was carried out to evaluate the relations between sociodemographic, work-related factors and health related behaviors in a group of 1,042 workers in Taejeon and Chungnam area. The results were as followings: The older workers took more irregularly meals, more cigarette and more alcohol than the younger. Men had more appropriate sleeping time, more regular exercise than women, but more frequent alcohol consumption and cigarette smoking. The married had more regular sleeping habit than the unmarried. The group of married were smoking more and obese. In view of monthly income which represent the socioeconomic state of workers, the group of more than 1 million won had more frequent alcohol ingestion, more heavier body weight than another group of less than 1 million won. Workers having their work hours exceed 9 hours had inappropriate sleep duration, and shift workers took more irregularly meals. The group having poor self-rated health status showed more regular diet, exercise and overweight. Workers recently experienced chronic illness were more overweight and lesser smokers. Above results showed that the health related behaviors were related to the sociodemographic characteristics and occupation-related characteristics. The study for relationship between variant factors affecting health behavior and disease or mortality is need and it should be emphasized that the publicity and education of health related behavior for industrial workers is necessary.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.3
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• pp.281-286
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• 2012

In the growing standard of people's lives, we want desire to create eco-friendly water space what is called the Green Technology that is in the limelight. These green space is introduced the cultural contents and we use the water, music, and nature as tool of emotional verbalism. Presently, when we want to make scenario, water landscape scenario is made by director. but these systems have some disadvantages as the cost and limitation of direction. There is a growing interest in the integrated control system based on PC and Internet. In this paper, it is about fountain control system. Previous research area was only one using programmable logic controller or industrial PC. we proposed the development of intelligent green fountain culture system for healthy emotional self-concept. And we made automatic weather sensing system that is designed by the intelligent green fountain culture system to estimate the time-variant system.

• Journal of the Korean Home Economics Association
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• v.36 no.3
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• pp.173-190
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• 1998

This study reviewed both consumer movement and consumer policy of government in Japan. Their evolution since the Second World War will be reviewed and compared multiple periods, after the Second World war till the late 1960s, the period of the 1970s, the period after 1980s. In addition, firms' consumer satisfaction policies were briefly reviewed in order to fully understand consumer protection activities in japan. This study found four major characteristics of consumer protection activities led by both voluntary consumer organizations and government. First, consumer protection policy of government in Japan after the late 1960s was more active than that of consumer movement by consumer organizations. Second, major concerns for consumer protection were variant over time. The major goal in the first stage of period(during the 1960s) was to protect consumer safety from defective and dangerous goods and services, whereas the goal after the late 1970s was extended to cover various areas concerning the quality of life. Those areas refer to the quality of services, the way of sales and marketing, pollution of environment, and the quality of consuming life. Third, this study found that computer networks, aiming at collecting and analyzing the very useful to improve the consuming life of Japanese by providing sufficient consumer information to encourge rational choices of consumers. Forth, a close cooperation between the central and local administrations was crucial for the successful outcome In Japan This paper gives us useful guideline regarding how to improve consumer movement and govemments' policies for protecting consumer in Korea. In addition, other lessons on successful consumer satisfaction policies of Japanese firms may enable Korean firms to shape effective consumer policies of enhancing their competitiveness.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.58-65
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• 2016

Satellite communication is a wide area network (WAN) which provides communication service worldwide. However, the performance of TCP can be seriously degraded in the satellite networks due to limited bandwidth, long round-trip time (RTT) and high bit error rate (BER) over satellite links. In order to improve the performance of TCP, this paper proposes cross-layer Performance Enhancing Proxy (PEP) in digital video broadcasting-return channel via satellite (DVB-RCS) networks. The proposed protocol sets TCP Congestion Window (CWND) size by using satellite resource allocation information exchanged between TCP and the link-layer. we implement PEP testbed based on Linux to evaluate the performance of the proposed protocol. The simulation results show that the proposed protocol performs better than standard TCP both in single and multiple sessions in variant BER, because the proposed protocol sets TCP CWND size by using satellite resource allocation.

• Journal of Communications and Networks
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• v.13 no.5
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• pp.481-493
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• 2011

Multiple-input multiple-output (MIMO) technology provides high data rate and enhanced quality of service for wireless communications. Since the benefits from MIMO result in a heavy computational load in detectors, the design of low-complexity suboptimum receivers is currently an active area of research. Lattice-reduction-aided detection (LRAD) has been shown to be an effective low-complexity method with near-maximum-likelihood performance. In this paper, we advocate the use of systolic array architectures for MIMO receivers, and in particular we exhibit one of them based on LRAD. The "Lenstra-Lenstra-Lov$\acute{a}$sz (LLL) lattice reduction algorithm" and the ensuing linear detections or successive spatial-interference cancellations can be located in the same array, which is considerably hardware-efficient. Since the conventional form of the LLL algorithm is not immediately suitable for parallel processing, two modified LLL algorithms are considered here for the systolic array. LLL algorithm with full-size reduction-LLL is one of the versions more suitable for parallel processing. Another variant is the all-swap lattice-reduction (ASLR) algorithm for complex-valued lattices, which processes all lattice basis vectors simultaneously within one iteration. Our novel systolic array can operate both algorithms with different external logic controls. In order to simplify the systolic array design, we replace the Lov$\acute{a}$sz condition in the definition of LLL-reduced lattice with the looser Siegel condition. Simulation results show that for LR-aided linear detections, the bit-error-rate performance is still maintained with this relaxation. Comparisons between the two algorithms in terms of bit-error-rate performance, and average field-programmable gate array processing time in the systolic array are made, which shows that ASLR is a better choice for a systolic architecture, especially for systems with a large number of antennas.