• Journal of Power Electronics
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• v.13 no.4
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• pp.592-599
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• 2013

This paper investigates a new isolated single-phase AC-DC converter, which integrates a modified AC-DC buck-boost converter with a DC-DC forward converter. The front semi-stage is operated in discontinuous conduction mode (DCM) to achieve an almost unity power factor and a low total harmonic distortion of the input current. The rear semi-stage is used for step-down voltage conversion and electrical isolation. The front semi-stage uses a coupled inductor with the same winding-turn in the primary and secondary sides, which is charged in series during the switch-on period and is discharged in parallel during the switch-off period. The discharging time can be shortened. In other words, the duty ratio can be extended. This semi-stage can be operated in a larger duty-ratio range than the conventional AC-DC buck-boost converter for DCM operation. Therefore, the proposed converter is suitable for universal input voltage (90~264 $V_{rms}$) and a wide output-power range. Moreover, the voltage stress on the DC-link capacitor is low. Finally, a prototype circuit is implemented to verify the performance of the proposed converter.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.3
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• pp.102-110
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• 2005

Piezoelectric transformers(PT) are expected to be small, thin and highly efficient, and which are attractive as a transformer with high power density for step down voltage. For these reasons, we have attempted to develop a step-down PT for the miniaturized adaptor. We propose a PT, operating in thickness extensional vibration mode for step-down voltage. This PT consists of a multi-layered construction in the thickness direction. In order to develop the step-down PT of 10 W class and turn ratio of 0.1 with high efficiency and miniaturization, the piezoelectric ceramics and PT designs are estimated with a variety of characteristics. The basic composition of piezoelectric ceramics consists of ternary yPb(Zr$_{x}$Ti$_{1-x}$)O$_{3}$-(1-y)Pb(Mn$_{1/3}$Nb1$_{1/3}$Sb$_{1/3}$)O$_{3}$. In the piezoelectric characteristics evaluations, at y=0.95 and x=0.505, the electromechanical coupling factor(K$_{p}$) is 58$\%$, piezoelectric strain constant(d$_{33}$) is 270 pC/N, mechanical quality factor(Qr$_{m}$) is 1520, permittivity($\varepsilon$/ 0) is 1500, and Curie temperature is 350 $^{\circ}C$. At y = 0.90 and x = 0.500, kp is 56$\%$, d33 is 250 pC/N, Q$_{m}$ is 1820, $\varepsilon$$_{33}$$^{T}$/$\varepsilon$$_{0}$ is 1120, and Curie temperature is 290 $^{\circ}C$. It shows the excellent properties at morphotropic phase boundary regions. PZT-PMNS ceramic may be available for high power piezoelectric devices such as PTs. The design of step-down PTs for adaptor proposes a multi-layer structure to overcome some structural defects of conventional PTs. In order to design PTs and analyze their performances, the finite element analysis and equivalent circuit analysis method are applied. The maximum peak of gain G as a first mode for thickness extensional vibration occurs near 0.85 MHz at load resistance of 10 .The peak of second mode at 1.7 MHz is 0.12 and the efficiency is 92$\%$.

• Journal of the Korean Institute of Gas
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• v.7 no.4 s.21
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• pp.7-13
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• 2003

This study was carried out to optimize premixed burner and heat exchanger of the condensing gas boiler which can save energy by utilizing latent heat of combustion gas and reduce pollutant in exhaust gas. The heat exchanger of the gas boiler was composed of three parts, which were an upper, lower, and coil heat exchanger. The upper heat exchanger was placed outside of the premixed burner and a lower heat exchanger was located under the upper heat exchanger. And, coil heat exchanger rounded the outer surface of an upper and lower heat exchanger. The boiler designed by this research reaches turn-down ratio 4:1 in the domain of equivalence ratio 0.75${\~}$0.8 and thermal efficiency of $97\%$. Emission of NOx and CO concentration was under 20ppm and 140ppm at equivalence ratio 0.8. When diameter of the burner is replaced from 60mm to 50mm, emission of CO was reduced about 50ppm remarkably.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.714-720
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• 1998

The differential pressure venturi-cone flowmeter is an advanced flowmeter which has many advantages such as wide range of measurement, high accuracy, excellent flow turn-down ratio, low headless, short installation pipe length requirement, and etc. Like other differential pressure flowmeters, the venturi-cone flowmeter uses the law of energy conservation, but its shape and position make it perform better than others. The cone acts as its own flow conditioner and mixer, fully conditioning and mixing the flow prior to measurement. For the analysis, we used Reynolds-averaged Wavier-Stokes equations and k-$\omega$ turbulence model. The equations were fully transformed into the computational domain, the pressure-velocity coupling was made through SIMPLER algorithm, and the equations were discretized using finite analytic solutions of the liberalized equations(Finite Analytic Method). To control the separation phenomenon on the cone surface, we proposed a new shape of cone, and analyzed the flowfield in the new flowmeter system, and found the improvement on the performance of the new cone flowmeter.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.271-278
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• 1987

The experimental study was carried out to investigate the pressure fluctuation, operating frequency, noise emission and combustion characteristics in an aero-valved pulsating combustor. Measurements of the pressure fluctuation, mean temperature and ion current inside the combustion chamber indicate that combustion phenomena are characteristically similar to those in the diffusion flame. The measured frequency schedue indicates that the acoustic theory of the quarter wave tube can be approximated to give the operating frequency, but correction factor must be involved to estimate the correct operating frequency. The spectral behavior of the noise emission exhibits that frequency bands with high noise intensity are narrowly restricted to the neighborhood of the operating frequency signalling the low-frequency combustion characteristics of the pulsating combustor. Measurements of the operating characteristics as variation of the fuel nozzle diameter and injection angle with 4 fuel nozzles have been made, and it was found that the system produced the stable operating conditions up to the turn down ratio of 3 when the fuel nozzle diameter is 1.2mm, and the optimum fuel injection angle is thought to be in the neighborhood of 30.deg. radially.

• Journal of the Korean Society of School Health
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• v.16 no.1
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• pp.149-160
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• 2003

The purpose of this study was to analyze the effects after having the obesity education with obese elementary school children. The subjects were made up of 31 obese children out of U elementary school in B town as experimental group, and also were selected 34 children out of S elementary school under the same circumstance as control group. They ranged from the third to sixth grades with over 30% body fat ratio. The proceeding of obesity education consisted of three stage; stage for preparation, stage for practice, and stage for finish. The stages mentioned above were put into practice in turn for eleven weeks beginning on Oct. 8, 2001 through Dec. 22, 2001, while two stages only, stage for preparation and finish, were put into practice on the control group. The contents of the education for eleven weeks obesity regulation contained counseling and taking regular exercises once a week by professional gym teacher. In order to evaluate the effects of the education, physical characteristics, body composition, physical fitness, knowledge of obesity, dietry habit and attitude were measured. The obtained data were analyzed using SPSS program, the effects of pre and post obesity education in experimintal group were measured by paired-t test. The conclusions of this study were as follows : 1. Body fat ratio was significantly reduced after obesity education in experimintal group(p=.003). 2. The height with experimental group got taller remarkably(p=.000), but weight showed no signeficance after obesity education(p=.258). 3. Triceps and subscapular skinfold thickness showed remarkable decrese after obesity education(p=.000), percentage body fat and body fat amount got down remarkably after obesity education(p=.000). Percentage lean body mass and lean body mass amount got down remarkably after obesity education(p=.000). 4. Body flexibility, agility and muscle endurance graded up remarkably after obesity education(p=.009, p=.000, p=.000). 5. The grade in obesity knowledge got up remarkably after obesity education(p.000), but dietry habits and its life showed no significance in figures after obesity education(p=.335, p=.112). Through the results shown above, the obesity education caused body fat ratio, physique, body composition to grade up and physical fitness elevated, while dietry habits and its life showed no significance.

• The Journal of Industrial Distribution & Business
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• v.12 no.11
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• pp.33-50
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• 2021

Purpose: In South Korea, two kinds of mandatory insurance, Fierce Liability Insurance and Outdoor Advertising Liability Insurance sells as of February 2021 according to relevant codes. This study analyzed third party liability and personal living liability insurance in terms of various risks not corporation side but personal side arising from normal living and life. Research design, data and methodology: Some cases of drone accident hit man and fierce dog accident were taken into analysis to verify blame ratio and insurance claim money. The former case is that on the way down the elevator, the dog, American pit bull terrier rushed in and bit the lower part of the knee against the visitor. The latter case is that while flying in the sky as usual, the drone suddenly crashed, fell, and hit the head of a young child while walking on the street. Further previous studies such as third party liabilities, liability insurance, mandatory insurance were deeply analyzed. Results: Based on some case studies and previous studies, the author suggested valuable comments in turn realization of insurer as provider, exhaustive creation and operation of mandatory insurance, realization of insured as demanded, and arrangements of laws and systems in special consideration of amendment of companion animal and exhaustive execution of mandatory insurance by the government. Conclusions: This study was about third party liability, personal living liability insurance and expansion of mandatory insurance caused by relevant laws by the government. In this study the author verified what issues were observed from two cases drone accident and fierce dog accident and then suggested some valuable comment as above both systemic plans and practical plans. First of all, the individual should get Comprehensive Property Insurance(CPI) that covers the risks of his/her own property arising from the everyday life. And then the individual should further buy Personal Living Liability Insurance(PLLI) in order to prepare 'accidents that may happen when, where, or how' and overcome the said accidents. Moreover, the individual should take a look every single insurance contract whether he/she has a special terms and conditions of Personal Living Liability Insurance(PLLI) or not.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2020.08a
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• pp.76-76
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• 2020

Stachys sieboldii Miq. (chinese artichoke), which has been extensively used in oriental traditional medicine to treat of ischemic stroke; however, the role of Stachys sieboldii Miq. (SSM) in cerebral ischemia/reperfusion (I/R) injury is not yet fully understood. In the current study, the neuroblastoma cell line (SH-SY5Y) were subjected to oxygen-glucose deprivation/reperfusion (OGD/R) to simulate I/R injury in vitro model. The results showed that SSM improved OGD/R-induced inhibitory effect on cell viability of SH-SY5Y Cells. SSM displayed anti-oxidative activity as proved by the decreased levels of reactive oxygen species (ROS) and malondialdehyde (MDA), and increased activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) in OGD/R-induced SH-SY5Y Cells. In addition, cell apoptosis was markedly decreased after SSM treatment in OGD/R-induced SH-SY5Y Cells. The up-regulation of Bcl-2 and down-regulation of Bax, thus reducing the Bax/Bcl-2 ratio that in turn protected the activation of caspase-9 and -3, and inhibition of poly (ADP-ribose) polymerase cleavage, which was associated with the blocking of cytochrome c release to the cytoplasm. Collectively, SSM protected human neuroblastoma SH-SY5Y cells from OGD/R-induced injury via preventing mitochondrial-dependent pathway through scavenging excessive ROS, suggesting that SSM might be a potential agent for the ischemic stroke therapy.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.6
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• pp.645-650
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• 2010

In this research, the problem of combustion and its system in Hyundai Heavy Industries and Sachuan Unison will be analyzed in order to provide some methods of thermal efficiency improvement and help to make a positive influence on fuel savings and their productivity. In forging industries, in order to improve the material properties of the industrial heating elements which are being used, depending on different operation conditions of system equipment and combustion systems, fuel consumption and material properties can get a profound influence. Thus, analyzing about combustion system characteristics of 100 tons heating furnace and heat treatment furnace which are in operation in Hyundai Heavy Industry will be done. In usual, air-fuel ratio is proper for capacity of burner installed in each heating device, otherwise burner gets an automatic turn down ratio. It has a profound influence on heating performance and precision of temperature because it is the fixed characteristics of every industrial furnace. Even if there are some methods to improve the heating performance of a furnace installed with a large capacity burner, it is very difficult to obtain the precision of temperature in maintenance interval. Based on this, performance of burner can be drove to best by improving combustion system. Proper Combustion characteristic for each heating interval was analyzed in heating furnace in Hyundai Heavy Industry. A project plan for improving fuel savings and increasing precision of temperature was presented in this research.

• Journal of the Korean Magnetics Society
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• v.17 no.4
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• pp.162-165
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• 2007

We investigated the effects of the capping layer materials on the crystallization of the amorphous top-CoFeB (t-CoFeB) electrode and the magnetoresistance properties of the magnetic tunnel junctions (MTJs). When the hcp(002)-textured Ru capping layer was used, the amorphous t-CoFeB was crystallized to bcc-CoFe(110). The CoFe(110)/Ru(002) texture relation can be minimized the lattice mismatch down to 5.6%. However, when the fine polycrystalline but almost amorphous TiAl or amorphous ZrAl were used, the amorphous t-CoFeB was crystallized to bcc-CoFe(002). When the amorphous capping materials were used, the evolution of the t-CoFeB texture was affected mainly by the MgO(001) texture. Consequently, the M ratios of the annealed MTJ capped with the ZrAl and TiAl (72.7 and 71.8%) are relatively higher than that of the MTJ with Ru capping layer (46.7%). In conclusions, the texture evolution of the amorphous t-CoFeB during the post deposition annealing could be controlled by the crystallinity of the adjacent capping layer and in turn, it affects the TMR ratio of MTJs.