• Proceedings of the KSME Conference
• /
• 2001.06d
• /
• pp.408-413
• /
• 2001

Numerical analysis on the three-dimensional laminar flows (Re=1000) and heat transfer in a rectangular channel with punched longitudinal vortex generator have been conducted to explore the heat transfer enhancement and the combined effect of the angle of attack ${\alpha}$ and the lovour angle ${\beta}$. Rectangular winglets have been used as vortex generators. Velocity and temperature fields and spanwise averaged Nu and friction factor were presented. Enhancement of heat transfer and flow loss penalty are evidenced. The results show performance characteristics allowing a reduction in heat transfer surface area of 62% for fixed heat duty and for fixed pumping power compared with that of channel flow without vortex generator. However, adding lovour angle to the vortex generator shows no positive effect on the heat transfer enhancement.

• KSTLE International Journal
• /
• v.3 no.2
• /
• pp.95-100
• /
• 2002

Electrochemical discharge machining is a very recent technique for non-conducting materials such as ceramics and glasses. ECDM is conducted in the NaOH solution and the cathode electrode is separated from the solution by H$_2$ gas bubble. Then the discharge is appeared and the non-conductive material is removed by spark and some chemical reactions. In the ECDM technology, the H$_2$ bubble control is the most important factor to stabilize the discharging condition. In this paper we proposed the discharge peak monitoring/discharging duty feedback algorithms fur the discharge stabilization and the feasibility of this algorithm is verified by various pattern machining in the constant preload conditions for the cathode electrode.

• Journal of the Korean Society for Precision Engineering
• /
• v.21 no.12
• /
• pp.44-51
• /
• 2004

In a micro-EDM, it is well known that an RC circuit is suitable as a discharge circuit because of its low pulse width and relatively high peak current. To increase machining speed without changing unit discharge energy, charge resistance should be decreased. But, when the resistance is very low, continuous (or normal) arc discharge occurs, electrode wear increases and machining speed is reduced remarkably. In this paper, an RC circuit with transistors is used in a micro-EDM. Experimental results show that the RC circuit with transistors can cut off a continuous (o. normal) arc discharge effectively if the duty factor and switching period of the transistor are set up optimally. Through experiments with varying charge resistances, it is shown that the RC circuit with transistors has about two times faster machining speed than that of an RC circuit.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.961_962
• /
• 2009

A novel, two-inductor, interleaved power-factor-corrected (PFC) boost converter that exhibits voltage-doubler characteristic when it operates with a duty cycle greater than 0.5 is introduced. The voltage-doubler characteristic of the proposed converter makes it quite suitable for universal-line (90~265VRMS) PFC applications. Because the proposed PFC boost rectifier operates as a voltage doubler at low line, its low-line range efficiency is greatly improved compared to that of its conventional counterpart. The performance of the proposed PFC rectifier was evaluated on an experimental 300W PFC prototype.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.11
• /
• pp.1925-1930
• /
• 2016

Fuel cell power generation system, unlike conventional energy sources, converts chemical energy into electrical energy through electrochemical reaction of hydrogen and oxygen. This paper presents the control of interleaved multi-phase boost converter as the feasibility study on small-scale prototype electric railway vehicle application using fuel cell generation system. PSIM simulation program is to be used to implement the modeling of the electrical fuelcell as well as traction motor control with interleaved multi-phase boost converter. Comparing the input current ripple rate, two-phase interleaved boost converter is less than the boost converter. But the more multi-phase not less proportional to the ripple factor. we confirmed that the amplitude of the input current ripple rate of converter depend on duty ratio.

• Journal of Distribution Science
• /
• v.3 no.1
• /
• pp.43-67
• /
• 2005

Recently retail market has been rapidly expanded in the large cities of in Korea and the competition among individual companies in retail market is also being increased. Tenant MD of mixing is one of the most important factor for the company to continuously operate or to fail. The aim of this study is to examine the processes of systematically evaluating the merchandising of the established companies in retail market a part of chain operation in discount store. The basic problem of decision making in general and tenant MD of mixing in particular is to choose a best one in a set of competing alternatives that are evaluated under conflicting criteria. The purpose of research of a paper carries out a duty searching examination with making a tenant MD include by retail research, simultaneously defined when I will show an example for the tenant mix of the profitability side of the domestic discount store market which is tenant MD importance proposing the existing problem arrangement by chain operation management, and is intensifying - tenant MD of standardization in discount store of T-company.

• The Korean Nurse
• /
• v.29 no.1
• /
• pp.72-83
• /
• 1990

The purpose of this study was to identify role conflict and professional attitude of Health Center nurses for health nursing administration. The data were obtained from 151 nurses of 7 Health Centers in S from July 15 to July 22 1989 using the questiennaires which consisted of 2 scales of role conflict and profess" ional attitude. The data were analyzed by percentage, mean, t-test, ANOVA and Cronbach's $\alpha$ reliability test. The results were as follows. 1) Institutional factor had the highest mean score for the degree of role conflict. The relationship between the degree of role conflict and general characteristics was found to be statistically significant for duty position. (F=2.61, p<.05) 2) Professional educational level had the highest mean score for the professional attitude. The relationship between professional attitude and general characteristics was found to be statistically significant for educational background. (F=4.91, p<.00l), p<.00l)

• Proceedings of the KIEE Conference
• /
• 2001.07b
• /
• pp.1117-1119
• /
• 2001

This paper describes the forward type pulse power supply using a Power-MOSFET in the view of commercialization. The principle of basic operating and the operating characteristics of the forward type pulse power supply are estimated by the switching frequency, coupling factor and duty ratio. It is shown that theoretical and experimental results are in good agreement by comparing simulation and experimental results when a lamp type ozonizer can be used as a load. Also, experimental results indicate that the discharge and ozone concentration characteristics of the manufactured pulse power supply is more improved compare to the conventional pulse power supply[5]. This proposed supply show that it can be practically used as a pulse power supply in various environment improvement facilities.

• Proceedings of the KIPE Conference
• /
• 2012.11a
• /
• pp.193-194
• /
• 2012

The bidirectional boost-buck chopper type AC voltage regulator is presented in this paper. The main characteristic of the AC chopper is the fact that it generates an output AC voltage larger or lower than the input AC one, depending of the instantaneous duty-cycle. Boost-buck chopper type AC voltage regulator, derived from the DC chopper modulated method, is a kind of direct AC-AC voltage converter and has many advantages: such as fast response speed, low harmonics and high power factor. It adopts high switching frequency AC chopper technique and can do wide range step less AC voltage regulation.

• Korean Journal of Child Studies
• /
• v.33 no.5
• /
• pp.221-246
• /
• 2012

This study was conducted in order to develop an aptitude test for child care teachers (ATCCT) and to analyze it in terms of both validity and reliability. The main participants in this study consisted of 710 pre-service child care teachers. The results of factor analysis identified 7 factors and 56 items which were selected from 121 items in the original scale. The seven factors were as follows; interpersonal relationship management abilities, receptiveness and responsiveness to children, creativity and personal development, the ability to form close relationships with children, the ability to supervise child safety, the sense of duty, and positive emotions. The four factors were related to social relationship. Criterion-related validity was established by using correlations between the ATCCT and the TSES (Teacher Self-efficacy Scale). The internal consistency was found to be relatively high (Cronbach's ${\alpha}$ = .94) and test-retest reliability was also established (r = .53). In addition, there were differences among pre-service child care teacher groups according to both relative levels of education and courses taught.