• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.3
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• pp.232-239
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• 2013

This paper proposes an improved stator flux estimator through ensuring conventional PLPF to act as a pure integrator for sensorless control of induction motors. Conventional PLPF uses the estimated synchronous speed as a cut-off frequency and has the gain and phase compensators. The gain and phase compensators are determined on the assumption that the estimated synchronous angular speed is coincident with the real speed. Therefore, if the synchronous angular speed is not same as the real speed, the gain and phase compensation will not be appropriate. To overcome the problem of conventional PLPF, this paper analyzes the relationship between the synchronous speed error and the phase lag error of the stator flux. Based on the analysis, this paper proposes the synchronous speed error compensation scheme. To achieve a start-up without speed sensor, the current model is used as the stator flux estimator at the standstill. When the motor starts up, the current model should be switched into the voltage model. So a stable transition between the voltage model and the current model is required. This paper proposes the simple transition method which determines the initial values of the voltage model and the current model at the transition moment. The validity of the proposed schemes is proved through the simulation results and the experimental results.

• Korean Journal of Health Education and Promotion
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• v.12 no.2
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• pp.120-138
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• 1995

In order to find smoking status and its related factors for female students, a survey was conducted for 1,045 female students of a women's university in Seoul from 22nd of May to 18th of June, 1995. The results were as follows: 1. Of the 1,045 respondents, 7.4% of them were current smokers and 20.6% of them were ex-smokers. The rate of smoking by the major field of study was 18.5% in art and physical education, 10.6% in liberal art and social science, 1.9% in natural science, and 1.2% in medical science. The rate of smoking by the grade was 4.1% in the freshman, 5.9% in the sophomore, 10.9% in the junior, and 10.0% in the senior grade. 2. 7.2% of respondents experienced first smoking at junior high school, 16.8% at senior high school, 4.1% after high school, and 69.2% at college. 3. The major motivation to start smoking was 'curiosity'(57.9%), 'releasing stress'(21.6%), and 'temptation from friend or senior'(12.0%). 4. The first smoking place was 'entertainment place'(49.6%), 'own room'(20.5%), and 'school '(11.3%). And the first smoking companion was 'friend'(62.3%), 'alone'(19.9%), and 'senior or junior'(5.1%). 5. The average quantity of a daily smoking was 6.16±5.29 cigarettes in current smokers and 31.2% of them had experience to quit smoking at least one or more time. 6. Most of the reasons to quit smoking in ex-smoker were due to 'bad taste '(60.5%), 'health concern'(27.4%) and 'religion'(2.3%). 7. Current smoker and ex-smoker had more positive attitude for the female smoking than nonsmoker. And 76.7% of nonsmokers answered that they would not smoke in the future. 8. Most correspondents(89.8% of nonsmoker, 83.7% of ex-smoker, 80.5% of current smoker) strongly supported the antismoking movement. 9. The major information source in smoking were from 'radio, TV'(51.0%), 'newspaper, magazine'(38.8%) and 'school'(7.7%). 10. The multiple logistic regression analysis showed that the related factors for smoking status were satisfaction of home life, coffee intake, alcohol drinking, sister's smoking, girl friend's smoking, and knowledge about smoking.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.1
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• pp.207-212
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• 2017

The cables installed to deliver high electric power from a generator at a thermoelectric power station are XLPE (or CV) cables. Depending on the installation and usage conditions, the cables in operation start deteriorating from the time of initial operation. Some cables can cause accidents due to faulty construction or other environmental factors. In order to prevent cable accidents, regular auditing of power cables is required. We have invented a measuring device for systematic surveillance and prevention of accidents, and installed the device at Korean Western Power Co. Ltd. which measures load currents through the cables. In this paper, we present the load current measured using our device, analyze the load characteristics by measures current, compare the ampacity defined by IEC standard, and present a basic data to obtain the temperature of cable conductors.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.518-525
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• 2001

As steam generator (SG) tubes have aged, new and subtle flaws have appeared. Most of them start growing from outside the tubes. Since signals from outer diameter (OD) defects are very weak compared to those from inner diameter (ID) defects in the conventional eddy current testing due to skin effect, this paper studies the feasibility of using remote field eddy current (RFEC) technique, which has shown equal sensitivity to ID and OD defects in the ferromagnetic pipe inspection. Finite element modeling studies show that the operating frequency needs to be increased up to a few hundred kHz in order for RFEC effects to occur in the nonmagnetic SG tube. The proper distance between exciter and sensor coils is also found to be about 1.5 OD, which is half the distance used in the ferromagnetic pipe inspection. Defect signals obtained by the designed RFEC probe show equal sensitivity to ID and OD defects and the existence of linear relationship between defect depth and phase signal strength. These results tell us that RFEC inspection is feasible even in nonmagnetic steam generator tubes.

• Journal of the Korean Society of Safety
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• v.24 no.4
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• pp.28-33
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• 2009

This study examined the mounting status of cigar lighter receptacles for vehicles and analyzed the tracking phenomenon that occurs when foreign material entered a cigar lighter receptacle to obtain data for the analysis of accident investigation. Regardless of the vehicle's output, cigar lighter receptacles are mounted in a vehicle horizontally, vertically, or at tilting or inclined angle. The tilting type cigar lighter receptacle is much easier to use but current leakage resulting from foreign materials (coffee, beverages, water, etc.) falling into the cigar lighter receptacle may cause a fire to start. This study used a vehicle battery (DC 12V) as a power supply for the tracking test and configured its circuit in the same way as that of an electrical device in a vehicle. The tracking phenomenon that occurred in the standby mode of the vehicle exhibited a fine flame and an irregular occurrence of smoke. While this tracking phenomenon was occurring, the leakage current and the reaching distance of the flame were measured to be approximately 930mA and $20{\sim}50cm$, respectively. It is thought that the resultant flame may ignite toluene, dust, cigarettes, etc. It was observed that as the tracking progressed, the internal metal socket melted and a hole was created, the surface of which was also severely carbonized. In addition, the electrical resistance of the carbonized conductive path was measured to be approximately $30{\Omega}$. It is thought that this much resistance may cause local heating when leakage current flows and could ignite any nearby flammable material.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.43 no.4
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• pp.161-167
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• 2020

In the process of cutting large aircraft parts, the tool may be abnormally worn or damaged due to various factors such as mechanical vibration, disturbances such as chips, and physical properties of the workpiece, which may result in deterioration of the surface quality of the workpiece. Because workpieces used for large aircrafts parts are expensive and require strict processing quality, a maintenance plan is required to minimize the deterioration of the workpiece quality that can be caused by unexpected abnormalities of the tool and take maintenance measures at an earlier stage that does not adversely affect the machining. In this paper, we propose a method to indirectly monitor the tool condition that can affect the machining quality of large aircraft parts through real-time monitoring of the current signal applied to the spindle motor during machining by comparing whether the monitored current shows an abnormal pattern during actual machining by using this as a reference pattern. First, 30 types of tools are used for machining large aircraft parts, and three tools with relatively frequent breakages among these tools were selected as monitoring targets by reflecting the opinions of processing experts in the field. Second, when creating the CNC machining program, the M code, which is a CNC auxiliary function, is inserted at the starting and ending positions of the tool to be monitored using the editing tool, so that monitoring start and end times can be notified. Third, the monitoring program was run with the M code signal notified from the CNC controller by using the DAQ (Data Acquisition) device, and the machine learning algorithms for detecting abnormality of the current signal received in real time could be used to determine whether there was an abnormality. Fourth, through the implementation of the prototype system, the feasibility of the method proposed in this paper was shown and verified through an actual example.

• 한국해양학회지
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• v.25 no.2
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• pp.84-95
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• 1990

Observations by CTD castings, moored current meters and satellite imageries reveal some physical characteristics of the area around the tidal mixing front found in the mid-Yellow Sea off Korea. Tidal mixing is the greatest at the promontory of Taean Peninsula with a front around it. The front appears in April with the start of solar heating, becomes most clear in August and disappears in November with the start of surface cooling. In the north of the front, tidal fluctuations of temperature and salinity induced by tidal currents manifest the existence of the front, Differently from the usual tidal mixing front, the front in Kyunggi Bay is formed by presence of the water discharged from the Han River which meets the offshore water at the front. Near the surface cold center, vertically well-mixed zone extends to about 50 Km offshore from the coast, Farther south, this structure is generally retained but with lesser degree of vertical mixing. Within the relatively well-fixed coastal zone, the fresh water discharged from the Kum River makes another salinity front of smaller extent. At some places around this salinity front, an Upwelling-like feature is remarked.

• Journal of Energy Engineering
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• v.18 no.1
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• pp.69-73
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• 2009

The regulations for exhaust emission from vehicles have become much more stringent in recent years. These more stringent regulations require vehicle manufacturers to develop alternative fuels that reduce exhaust emission. This research is to analyze the characteristics of exhaust gas emission of same level vehicles that use gasoline, diesel, and LPG fuels. As for the test mode, we used the CVS-75 mode, which is the driving mode of the current domestic and North American emissions. The characteristics of the exhaust gas emitted under this driving condition was studied. We examined the emissions of THC, CO, and NOx of vehicles that use gasoline, diesel, and LPG fuels. As a result, vehicle exhaust gas emissions increased 9.8 % for vehicles using gasoline and it decreased 12.2 % for diesel-powered vehicles compared to vehicles using LPG fuel. Using gasoline and LPG fuel in the CVS-mode, over 80 % of THC and CO emission was produced for the cold start Phase 1.

• Journal of Information Technology and Architecture
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• v.11 no.1
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• pp.81-88
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• 2014

This study is about the suggestion of reduction method for social insurance cost of startup SMEs Based on the study abroad and the current status of Korea we suggest several methods such as direct and indirect support, exemption, deferment/loan. For the economic effect analysis, we derived benefits and costs. Employment, value added, and revenue increasing effects are considered as benefits. Costs are analyzed by each method. In case of exemption, the analysis is impossible. Analysis results show that direct and deferment/loan case have an effect of 563,469 jobs creation, added value of 26.82 trillion wons, and increase in tax revenues about 82.4 billion wons. In case of exemption, There are 105,368 jobs creation, 5.02 trillion wons of added value, and 15.4 billion wons of increase in tax revenues. And for each case, there are costs 9.58 trillion won, 5.42 trillion won, 1.79 trillion won.

• The Journal of the Korea Contents Association
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• v.14 no.10
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• pp.661-676
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• 2014

Due to current economic recessions, interest on entrepreneurship and/or business start-up is getting increased beyond sex and ages. Currently business start-up of university students and retirement to age limit in silver generation are getting increased day by day. As a part of preparation against those phenomenons, this investigation try to show the effect of characteristic factors of entrepreneurs on the will of business establishment In this study, in order to analyse effects on business establishment, survey was conducted for 328 pre and existed entrepreneurs. For collected datas, reliability analysis, factor analysis and correlation analysis were conducted via spss20 statistical program and lastly, through regression analysis, following conclusions were drawn. At first, the will of business establishment was effected by personal characteristic and environmental factor. in second, the mentoring of business establishment was effected by personal characteristic and environmental factor In particular, the will of business establishment was controlled by mentoring of business establishment which was effected by environmental factor.