• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.53-62
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• 1987

High power lasers provide a controllable and precise energy source in surface transformation hardening. A careful control of the process is needed in order that the surface layer of the material reaches the austenizing temperature, but that it does not melt. In order to achieve this the results of theoretical and experimental studies on the laser surface hardening of a medium carbon steel are described. A two-dimensional computer program, which can be used generally for the determination of transient temperature distributions in welding and heat treatment, was established on the basis of the finite element method. For the confirmation of the accuracy of the numerical analysis, a medium carbon steel (SM 45C) of 5mm thickness was heat-treated with a 1kW CW CO$_{2}$ laser machine, while the traverse speed and the distance from the focal point (defocused distance) were varied. Experimental and numerical results showed a similar tendency in correlations between the hardened zone shape and the process parameters. With increasing beam spot diameter the width and depth of the hardened zone increased for relatively small beam spot diameters, but decreased rapidly after reaching the maximum value, while with increasing traverse speed the width and depth of the hardened zone decreased monotonously. Too small beam spot diameters are to be avoided, since the surface melting would lower the surface hardness and produce an uneven surface which may be unacceptable because of the possible requirement for subsequent machining. It could be observed that for a given traverse speed and laser power input there exists a optimal range of the beam spot diameter, which produce a large width of the hardened zone but no melting on the surface.

• Information Systems Review
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• v.7 no.2
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• pp.257-276
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• 2005

The most distinctive characteristic in Maeil's outsourcing strategy was the rapid decision process done by CEO. At first, Maeil made a contract with a outsourcing vendor based on 50% investment for 5 years. However, 3 years later Maeil changed their outsourcing strategy from 10% share to 100% outsourcing. This is for the efficiency improvement and cost reduction. Also, Maeil organized separate TFT which could control IS quality. This TFT reviewed the feasibility of requirement analysis and IS planning process. Through this cooperation between TFT and the outsourcing vendor, Maeil could get the stable IT development and operation. During last 5 years, Maeil achieved great performance in the area of IT development and operation from the outsourcing. The present issue related to outsourcing strategy is whether Maeil will continue the current contract or change the vendor due to the anxiety of becoming a captive customer.

• Fire Science and Engineering
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• v.32 no.2
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• pp.57-66
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• 2018

The most urgent requirement in the event of disaster and fire in a skyscraper is to establish a system that enables people inside to evacuate safely. Hence, a practical direction needs to give evacuees confidence in the evacuation by reducing the psychological anxiety caused by the relatively large number of people inside and at the same time, the physically prolonged evacuation travel line. Evacuation tests with large numbers of people were conducted three times to solve these challenges and identify phenomena and issues that occurred during the experiment. The results revealed the factors that could cause a delay in evacuation and suggested improvements. The study results of this paper are as follows. First, a recent fire at a multipurpose high-rise resulted in a number of casualties due to a lack of experience with the disaster prevention system. To prevent such cases from occurring in advance, adaptability was achieved by conducting evacuation tests. Second, the data collected in the evacuation simulation statistics and the actual escape drills were compared and analyzed. Third, in the evacuation experiment, a large number of people could not participate in the experiment. The reasons for not participating were analyzed and their impact on the actual evacuation time was confirmed. Fourth, equipment aids were purchased to establish the optimal response measure to the causes of a delay in escape time and the standards for ensuring the safety of the evacuee were specified by developing improvements to minimize the evacuation delay time through comparative before and after analysis of the experiment. These results can be used for fire safety control of skyscrapers to improve the efficiency of evacuation.

• The Korean Journal of Community Living Science
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• v.18 no.1
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• pp.161-175
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• 2007

It is important for young adults to establish good dietary behavior for healthy life. The prevalence of obesity in college students has increased gradually. The obesity is one of the most prevalent health problems in S. Korea. Moreover, obesity is closely related with the disease such as cardiovascular disease, diabetes mellitus. The purpose of this study was to evaluate health practice, serum components and nutrient intake of the college students according to Body Mass Index (BMI) level. 400 male and female freshmen students in 4 year university located near to Seoul metropolitan area were surveyed respectively through the health check-up procedure for college entrance in February. Survey was carried out for them by questionnaires, including a 24-hour dietary recall and anthropometric measurements. Blood samples were obtained while fasting. Nutrient intake was expressed by DDS(Dietary Diversity Score by 5 food groups) and DVS(Dietary Variety Score). Nutrition level was analyzed by Can-Pro (Korea Nutrition Association). And for the quantity intake, percentage ratio against daily requirement(by KDRIs) and MAR(Mean Adequacy Ratio) were calculated. Underweight group($BMI<18.5kg/m^2$), normal weight group($18.5) and overweight group($BMI<23.0 kg/m^2$) were 18.5%, 61.2% and 19.3% respectively. Nutrient intake levels and food intake status were not significantly different among three groups. The mean nutrient adequacy ratio (MAR) was not significantly different by BMI status. Nutrient intakes of calcium, iron, and riboflavin were especially low for all the students. Overweight group showed high blood pressure(120.9/79.3 mmHg) compared with the underweight group (116.4/ 75.8mmHg) but the difference was not significant. The serum triglyceride level in overweight group (94,0mg%) was higher than that in normal (70.9mg%) or underweight group(70.8mg%)(p<0.05). HDL-cholesterol level in overweight (43.8 mg%) group was not significantly different from that in underweight group (45.9mg%). BMI was positively correlated with blood pressure, hemoglobin, and the intake of total fat and cholesterol. But it was negatively correlated with HDL-cholesterol level. With these results overweight group is closely related with the cardiovascular disease risks, such as high blood pressure and high triglycerides and cholesterol. Thus, a health intervention program including weight control is required for young adults.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.4
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• pp.795-804
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• 1999

The increasing number of users of mobile communication systems and the corresponding need for increased system capacity require the use of a modulation scheme which is both power and spectrally efficient. In this paper, we numerically calculate the BER performance of DS/CDMA-BPSK system in different fading channel (Rayleigh, Rician, Shadow Rician). Also, we calculate BER performance and the channel capacity of DS/CDMA-BPSK system which is constant or nearly constant envelopes in 3-state fading channel model. The Shadow Rician fading model described in this paper apply the parameters of the Canadian Mobile Satellite (MSAT). And we assume that the 3-state fading channel model is consist of Rayleigh fading state, Rician fading state, and shadow Rician fading state. This model can be used as a basis for the simulation of the land mobile satellite channel. The dynamic 3-state fading channel model is considered corresponding to different environments and the transitions between these environments. From the numerically calculate results, the DS/CDMA-BPSK system with MUI-20, PG-511 can not achieve the BER performance ($P_b\leq10^{-5}$). And the channel capacity did not meet the system requirement. Also, we know that the BER performance is depend m the occupancy probability of radio channel and the degree of shadow. From the results, we how that during shadowed time intervals it is necessary to use some form of error control coding and receiver diversity in order to support reliable data communication.

• The KIPS Transactions:PartC
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• v.18C no.1
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• pp.51-60
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• 2011

In this paper, we propose a P4P based P2P system for live multimedia streaming services. In order to satisfy the strict requirement of delay in live multimedia streaming, in the proposed scheme, the P4P server of network provider provides the network status information related to delay and congestion links to P2P system in addition to the information to optimize the network resource utilization. The P2P system server, then, makes the peering suggestion based on the information from the network server. Also, we propose a playback synchronization mechanism that enable each peer to start the playback within the limited variation from the playback positions of source peer. Through the simulation results, it is shown that the proposed scheme not only deals with the original objective of the P4P framework, i.e., effective network utilization, but also the live multimedia streaming requirements. It enhances the playback continuity, and reduces the playback start-up latency and the control overhead. In addition, the proposed scheme reduces the variation in playback positions of the peers.

• Journal of Yeungnam Medical Science
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• v.13 no.2
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• pp.225-233
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• 1996

From August 1992 to July 1996, 63 consecutive patients underwent coronary artery bypass surgery. The mean age of these patient was 57 years(range form 30 to 71years). There were 44 men and 19 women. Preoperative 12 patients had stable angina pectoris and 23 patients were unstable angina pectoris. 8 patients had previous myocardial infarctation history and emergency or urgent myocardial revascularization were performed in 9 cases. In the risk factors of coronary atherosclerosis, 25 patients(40%) were hypercholesterolemia, 38 patients(60%) have smoking history and 19 patients(30%) have hypertension history. In the patterns of disease, 9 patients were single vessel disease, 18 patients were two vessele disease and 33 patients were three vessel disease. We performed total 284 distal anastomosis(mean 3.5 anastomosis per patient) and performed one case of ascending aorta graft interposition, two cases of mitral valve replacement, one case of aortic valve replacement, one case of ventricular septal defect repair and one case of atrial septal defect repair and the mean aortic cross clamp time was 115.3 minutes. The common complications were arrhythmia(7cases), wound infection(5cases), perioperative myocardial infarction(4cases), reoperation for bleeding control(4cases) and stroke(4cases). There were six hospital deaths due to low cardiac output syndrome, ventricular arrhythmia and respiratory failure. In the evaluation of operative risk factors, preoperative intravenous nitroglycerin requirement and prolonged aortic cross clamp tirne(>2hours) were found to be predective factor of morbidity and old age(>65years) was found to be predective factor of mortality.

• Journal of Microbiology and Biotechnology
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• v.16 no.11
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• pp.1690-1698
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• 2006

In order to investigate the effect of dissolved oxygen (DO) level on AVM $B_{1a}$ production by a high yielding mutant of Streptomyces avermitilis, five sets of bioreactor cultures were performed under variously controlled DO levels. Using an online computer control system, the agitation speed and aeration rate were automatically controlled in an adaptive manner, responding timely to the oxygen requirement of the producer microorganism. In the two cultures of DO limitation, the onset of AVM $B_{1a}$ biosynthesis was observed to casually coincide with the fermentation time when oxygen-limited conditions were overcome by the producing microorganism. In contrast, this phenomenon did not occur in the parallel fermentations with DO levels controlled at around 30% and 40% throughout the entire fermentation period, showing an almost growth-associated mode of AVM $B_{1a}$ production: AVM $B_{1a}$ biosynthesis under the environments of high DO levels started much earlier than the corresponding oxygen-limited cultures, leading to a significant enhancement of AVM $B_{1a}$ production during the exponential stage. Consequently, approximately 6-fold and 9-fold increases in the final AVM $B_{1a}$ production were obtained in 30% and 40% DO-controlled fermentations, respectively, especially when compared with the culture of severe DO limitation (the culture with 0% DO level during the exponential phase). The production yield ($Y_{p/x}$), volumetric production rate (Qp), and specific production rate (${\bar{q}}_p$) of the 40% DO-controlled culture were observed to be 14%, 15%, and 15% higher, respectively, than those of the parallel cultures that were performed under an excessive agitation speed (350 rpm) and aeration rate (1 vvm) to maintain sufficiently high DO levels throughout the entire fermentation period. These results suggest that high shear damage of the high-yielding strain due to an excessive agitation speed is the primary reason for the reduction of the AVM $B_{1a}$ biosynthetic capability of the producer. As for the cell growth, exponential growth patterns during the initial 3 days were observed in the fermentations of sufficient DO levels, whereas almost linear patterns of cell growth were observed in the other two cultures of DO limitation during the identical period, resulting in apparently lower amounts of DCW. These results led us to conclude that maintenance of optimum DO levels, but not too high to cause potential shear damage on the producer, was crucial not only for the cell growth, but also for the enhanced production of AVM $B_{1a}$ by the filamentous mycelial cells of Streptomyces avermitilis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.11
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• pp.1006-1015
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• 2016

This paper presents preliminary design and performance analysis of a fast and high precision Tracking Mount for 1m Satellite Laser Ranging(SLR) which is development by Korea Astronomy and Space science Institute(KASI). SLR is considered to be the most accurate technique currently available for the precise orbit determination of Earth satellites. The SLR technique measures the time of flight between pulses emitted from laser transmitter and pulses returned from satellites with laser retro-reflector array. It provides millimeter level precision of range measurements between SLR stations and satellites. A fast and high precision Tracking Mount for SLR which is proposed in this research should be capable of day and nighttime laser tracking about the satellites with laser reflectors from 200 km to 36,000 km altitude(geosynchronous orbit). In order to meet this requirement, we performed mechanical design and structural analysis for Tracking Mount. Also we designed the motion control system and conducted pre-performance analysis to obtain good performance results for a fast and high precision Tracking Mount.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.681-688
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• 2018

As environmental regulations have been strengthened and high fuel efficiency has been in demand in recent years, the number of ships using natural gas as a fuel is increasing. The demand for ships using LPG or methanol, which are emerging as eco-friendly vessel fuels, is also increasing. In this perspective, ME-LGI engines using LPG or methanol as a fuel have attracted considerable attention. Ships equipped with an ME-LGI engine are required to check the reliability of the fuel injection valve during shipping. This means that the development of a fuel injection valve tester is essential for the commercialization of ME-LGI engine. This study conducted the conceptual design of a fuel injection valve tester for ME-LGI engines using a system engineering process in the order of requirements analysis, functional analysis, and design synthesis. In the requirement analysis stage, the operating process of fuel injection valve was analyzed, and the necessity of checking the sealing oil leakage was then derived. In the functional analysis stage, the functions and flow of them were defined at each functional level. In the design synthesis stage, the equipment for each function was set and the process block diagram based on it was derived. In addition, preliminary risk analysis was performed as a part of system analysis and control, and safety measures were added to the conceptual design. This study is expected to be a good reference material for the concept design of other systems in the future because it shows the application process of a system engineering process to the conceptual design in detail.