• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.9
• /
• pp.1255-1263
• /
• 2000

In this study, the modification of turbulent boundary layer flow by local wall vibration is investigated. The wall is locally vibrated using a wall deformation actuator, which moves up and down at the frequencies of 100Hz and 50Hz. Simultaneous measurements of the streamwise velocities in the spanwise direction are performed at several wall-normal and streamwise locations using an in-house multi-channel hot wire anemometer and a spanwise hot-wire-probe rake. The mean velocity is reduced in most places due to the wall vibration and its reduced amount becomes small as flow goes downstream. Interestingly, the mean velocity is found to increase very near the wall and near the actuator. This is due to the motion induced by the streamwise vortices which are generated by the downward motion of the actuator. In case of the streamwise velocity fluctuations, their magnitude increases as compared to the unperturbed turbulent boundary layer, and the increased amount becomes small as the flow moves downstream. The modified flow field at the forcing frequency of 50Hz is not much different from that of 100Hz, except the reduced amount of modification.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.15 no.6
• /
• pp.49-57
• /
• 2001

This paper analyzed PFC of active clamp ZVS flybark converter by adding two method PFC (Power Factor Correction) circuit-two-stage and single-stage. The addition of active clamp circuit also provide a mechanism fur achieving ZVS of both the primary and auxiliary switches. ZVS also limits the turn off di/dt of the output rectifier, reducing rectifier switching loss and switching noise, due to diode reverse recovery. As a results, the proposed converters have characteristics of the reduced switching noise and high efficiency in comparison to conventional flyback converter. The simulation and experimental results show that the proposed converters improve the input PF of 300[W] ZVS flyback converter by adding single-stage two-stage PFC circuit.

• Journal of Surface Science and Engineering
• /
• v.22 no.2
• /
• pp.69-77
• /
• 1989

Codeposion of inert particles particles in a metallic mateix by electroless plating process involves two phenomena. Firstly, the adsorption of inercles and secondly, the adsorption of inert particles on the cathode. In the present paper the first adsorption phenomenon and in the next paper the second ane are studied in greaterdetail for the Ni-SiCc, Ni-Al2AO3 and Ni-WC systems. Measurements of the Zeta potentials for the SiC and Al2AO3 particles have been in different electrolyte solutions and the ionic species adsorbed on the Particles studied. The addition of sodium acetate, trisodium citrate and sodium phosphinate to nikel sulface sruomotes the zeta potential of SiC and Al2O3 particles, but zeta phosphinate to nickel is more positive than Al2O3 particles although the amount of nickel ion adsorbrd on the Al2O3 particles become greater than that of SiC particles. It is suggested that this is due to adsortion of Na ion onto the surface SiC particles.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.05a
• /
• pp.609-614
• /
• 2001

This paper is to explain reasonable shear behavior that can apply usually to reinforced concrete beams on the basic concepts of existent analysis and experimental research information. This study is succession $paper^{2) 3) 4) 5)}$ of treatise announced in existing and main control variable of reinforced concrete beams with stirrups used internal force state factor($\alpha$). Shear failure of reinforced concrete beams with stirrups is Influenced greatly because of the actual geometrical shape(a/d) of the concrete and flexural reinforcement steel ratio, stirrup reinforcement ratio and concrete compression strength, size effect etc. Therefore, shear behavior of reinforced concrete beams with stirrups that flexural crack is happened can be explained easily through proper extent proposal of internal force state factor($\alpha$) that express internal force state flowing. Use existent variable truss model by analysis model to explain arch action. Also, wish to compose each failure factors and correlation with internal force state factor by function, and when diagonal cracks happens, internal force state factor($\alpha$) study whether shear stress and some effect are.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.284-289
• /
• 2003

As growing importance and concern of waterfront, we have tried to study its landscape, accessibility, landuse and so on as well as its environmentally sound and sustainable development. In fact we had been under the false thought that it always what we wanted, and it was neglected in its economic value. This paper/ looks at on alternative, the non-market value generated by management of waterfront as public resource. We consider the question : how much are people willing to pay to improve, how much are people want to improve? The contigent valuation method was implemented during Sep. 9 to 14 in 3 beaches ; haeundae, Gwanganri, Songjeong. They are representative waterfronts which have been widely known and visited. We find out that households are willing to pay about $12,000{\sim}16,000$ won per year for improving nature elements and inviting more valuable functions about 3 beaches. Especially we pay attention to defference between cognitive and comprehensive satisfaction 3 beaches and their substructural factors satisfaction such as natural environment, public facilities, recreational facilities and etc.

• Journal of the Korean Ceramic Society
• /
• v.41 no.9
• /
• pp.653-656
• /
• 2004

We report the magnetic properties, microstructures, and crystal orientations of the CrO$_2$ thin films on TiO$_2$ single crystals. CrO$_2$ thin films were deposited by thermal decompositions with CrO$_3$ source materials. The microstructure of (110) oriented CrO$_2$ thin films deposited on (110) TiO$_2$ single crystals were uniform. As the oxygen flow rates increased, the resistivity, coercive field, and remnant magnetization of the CrO$_2$ thin films on TiO$_2$ single crystals decreased.

• Journal of the Korean Geographical Society
• /
• v.35 no.5
• /
• pp.665-680
• /
• 2000

본 연구의 목적은 미국의 산타아나 강 상류 유역분지 내 잠재적 퇴적물 생산량의 공간적 분포 패턴을 고찰하는데 있다. 이를 위해 산타아나 강 상류지역을 42개의 하부 유역분지로 나눈 후에 각 유역분지에 퇴적물 생산량에 영향을 주는 지형 기복 요소, 면적-형태 요소, 지질 요소, 기후 요소와 관련하여 20개의 변수를 GIS를 이용하여 추출하였다. 이러한 20개의 변수들을 기초로 군집분석하여 42개 하부 유역분지들의 잠재적 퇴적물 생산량을 평가한 결과 4개 지역으로 구분되었다. 평가 결과 <발톤> 평기자 포함된 제2지역이 산타아나 강 상류 유역분지에서 가장 퇴적작용이 왕성한 지역으로 나타났다. 이 지역은 낮은 기복 및 고도와 미고화된 물질로 피복된 지역이 97%를 차지하고 있다. 잠재적 퇴적물 생산량이 가장 높은 지역은 제 2지역의 상류부에 분포하는 유역분지들(제 4지역)로서 높은 기복과 고도뿐만 아니라 침식 면적이 넒으며, 과거의 빙하작용이 있었던 지역이다. 특히 단층선이 퇴적작용이 크게 이루어지고 있는 지역(제2지역)과 잠재적 퇴적물 생산량이 가장 높은 지역(제4지역) 사이에 분포하고 있어, 사면경사의 급변으로 제 2 지역의 퇴적작용은 더욱 가속화 될 것이다.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 2005.11a
• /
• pp.471-474
• /
• 2005

For the purpose of objective and scientific inspection, traffic accidents should be appraised and inspected by righteous material evidences, computer simulation, and studies such as automobile engineering, traveling and collision accident dynamics, road and traffic engineering. In this paper, it displays the results of studying cases with the reasons of traffic accidents by analyzing and studying automobile kinetics, real traffic accidents and the results of in scientific and objective ways. In this paper, it is proved that with compared by dry and wet road surface condition, the transient brake time of wet condition is longer than dry road condition. Moreover, compared with unpacked road condition and packed road condition. unpacked road condition is shorter than packed road condition using computer simulation.

• Journal of Periodontal and Implant Science
• /
• v.23 no.1
• /
• pp.1-15
• /
• 1993

P. gingivalis has been implicated as a strong pathogen in periodontal disease and known to have three serotypes of P. gingivalis. The purpose of this study is to investigate on the relationship between virulence, metabolic acids and genetic heterogeneity of P. gingivalis. P. gingivalis W50 standard strain and five strains of P. gingivalis serotype b Korean isolates were used in this study. For in vitro virulence test, lyophilized whole cell P. gingivalis were suspended, and sonicated with ultrasonic dismembranometer. Sonicated samples were applied to cultured cells derived from periodontal ligament, and cell activity was assayed with growth and survival assay. The metabolic acids were also extracted, and determined by High Performance Liquid Chromatography. Pst I-digested bacterial genomic DNA was electrophoresed, and densitometric analysis was performed to study the genetic heterogeneity. All of the P. gingivalis serotype b produced butyric acid. In cell activity study, butyric acid inhibited the cell activity irrespective of its concentration. Densitometric analysis showed restriction fragment length polymorphism. These results suggested that there existed heterogeneity of the metabolic acids and the virulence of P. gingivalis and such heterogeneity might be related to genetic heterogeneity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.5
• /
• pp.369-375
• /
• 1996

This paper described the miniaturization of microstrip bandpss filter in UHF using S-plane Prototype. Modern microwave receiver system requires smaller size and better filter performance. The design of filters using bandpass S-plane prototype is made to satisfy these requirements. Bandpass S-plane prototypes are made by exact-synthesis technique using transmission zero locations at wanted frequency bandwidth, and the calculation of prototype values was performed by computer.