• Journal of Ocean Engineering and Technology
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• v.10 no.2
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• pp.69-76
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• 1996

In-process quality control and high reliability of the weld are the major concerns in applying friction welding to the economical and qualified mass-production. Experimental examinations and quantitative analysis were performed for the optimiaztion of similar friction welding of hydraulic valve spool steels(SNCM220, SCM435, SACM645, SCM415, ${\varphi}24). The quantitative correlations were found between the initial cumulative counts of acoustic emission(AE) occurring during plastic deformation periods of the welding and the fatigue life as well as weld strength and welding conditions. A real-time evaluation system was developed for the friction weld quality by AE.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.66-73
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• 1999

This paper presents the experimental examinations and statistical quantitative analysis of the correlation between the cumulative counts of acoustic emission(AE) during plastic deformation periods of the welding and the tensile strength and other properties of the tube-to-tube welded joints of O.D. 30mm (I.D 18mm) nozzle steel. This is a new approach which attempts finally to develop real-time quality monitoring system for friction welding. And this study results in practical possiblility of real-time quality control more than 100% joint efficiency showing good weld no micro structural defects.

• Journal of the Korean Society of Safety
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• v.16 no.3
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• pp.19-25
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• 2001

The friction-welding SM25C is a substitute for the suing steel that is utilized in the machinery, airplane, and automobile, ok. This substitution would provide reduction of material and weight of welding parts. From the result we found that the strength of the friction welded joint was 529-617MPa and the toughness 1.2 times higher than that of the base metal. The optimal condition of friction welding was found as follows : n=2000rpm, $P_1$=68㎫, $P_2$=137MPa, $t_2$=2sec, $t_1$=2-4sec, Considering the strength, the hardness, and the reduction of area in the friction welding, the fiction welding using SUP9A and SM25C was found to cause no problem in on-the-job application.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04a
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• pp.127-129
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• 2003

현재 데이터의 양은 인터넷 관련 비즈니스/전자상거래 등 인터넷 프로토콜(IP) 네트워크를 이용한 저장 장치의 데이터 증가를 가져오게 되었다. 본 논문에서는 펜티엄 프로세서, 고속 이더넷 IDE RAID 시스템 (IDE RAID Controller와 IDE 디스크로 구성)과 iSCSI(Internet Small Computer System Interface) 프로토콜을 이용하여 저렴한 비용으로 비교적 우수한 성능의 리눅스 기반의 저장장치 시스템을 설계 구현하였다. 또한 저장장치 시스템의 벤치마크 프로그램인 ioZone을 사용하여 SCSI RAID 시스템으로 구성된 저장 장치 시스템과의 성능을 비교 분석하여 가격대비 성능이 비교적 우수함을 보여준다. 끝으로. 향후 SATA(Serial ATA)를 이용한 저장장치 시스템의 전망을 가늠해본다.

• Bulletin of the Korean Space Science Society
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• 1993.10a
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• pp.22-22
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• 1993

We developed the low energy electron detector (LEED) for KITSAT-B which was launched on September 26, 1998. The sensor head is mounted on the top of the satellite so that it can measure the precipitating electron flux along the Magnetic field line in the auroral zone at 820 km altitude. The detector system is composed of 4 parts : the electrostatic analyzer, the spira10on detector, the discriminator / Preamplifier, and the interface to the spacecraft. The analyzer limits the access to the spiraltron only to the electrons of certain energies which are determined by the electrostatic field across the two coaxial cylindrical analyzer plates. The energy spectrum of the detector in consideration is about 100 eV to 6.7 KeV, which is swept in 1.6 seconds and divided into 16 bins. It 81so is 1.6 second reset period after each swept, We will discuss the technical features of the system as well as the future observational schedule.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.181-185
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• 2008

Recently, location based service(LBS) expended based on personal specialized service, however since commercialized GPS based emergency rescue service comes with shadow zone for GPS signal such as inside building, the accuracy and reliability are not guaranteed. Therefore to improve such problem, we propose an active location detecting algorithm using RFID-TAG and Yagiantenna. To track the location of RFID-TAG where signal is generated, location tracking device in which Yagi-Antenna is installed moves around. Since directed wave and reflected wave co-exist during signal reception, final signal generated location is searched by setting up multiple of locations where signal can be generated on the map and moving location tracking device along minimum length of path. The algorithm proposed in this paper was verified of its technical validity through simulator.

• Computers and Concrete
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• v.8 no.4
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• pp.401-423
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• 2011

In this paper, a mesoscale model of concrete is presented, which considers particles, matrix material and the interfacial transition zone (ITZ) as separate constituents. Particles are represented as ellipsoides, generated according to a prescribed grading curve and placed randomly into the specimen. In this context, an efficient separation procedure is used. The nonlinear behavior is simulated with a cohesive interface model for the ITZ and a combined damage/plasticity model for the matrix material. The mesoscale model is used to simulate a compression and a tensile test. Furthermore, the influence of the particle distribution on the loaddisplacement curve is investigated.

• Economic and Environmental Geology
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• v.31 no.1
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• pp.21-29
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• 1998

Broadband receiver functions are developed from teleseismic P waveforms recorded at Wonju (KSRS), Inchon (IRIS), and Pohang (PHN), and are analyzed to examine the crustal structure beneath the three stations. The teleseismic receiver functions are inverted in the time domain to the vertical P wave velocity structure beneath the stations. Clear P-to-S converted phases from the Moho interface are observed in teleseismic seismograms recorded at the three stations. We estimated the crustal velocity structures beneath the stations using the receiver function inversion. The general features of inversion results are as follows: (1) For Pohang station, there is a high velocity gradient at a 4~5 km deep for SE and NW back azimuth and a low velocity zone at around 10 km deep. The Moho depth is 28 km for NW direction. (2) The shallow crustal structure beneath Wonju station is somewhat complex and there is a high-velocity zone ($V_p{\simeq}6.8km/sec$) at 3 to 4 km deep. The average crustal thickness is 33 km, and a transition zone exists at a 30~33 km deep of lower crust, of which velocity is abruptly changed 6.4 to 7.9 km/sec. (3) For Inchon station, the crustal velocity gradient monotonously increases up to the Moho discontinuity and the velocity is abruptly changed from 6.2 km/sec to 7.9 km/sec at 29 km deep.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.4
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• pp.318-331
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• 1995

The c - axis oriented single crystal of $LiNbO_3$ and $LiNbO_3$ : 5mol%MgO was success-fully grown by Floating zone method using halogen lamp as a heat source. The effects of the sintering condition of the feed rod and the atmosphere gas during the crystal growth on the be havior of the feed rod/melt interface were studied for growing crystal with the high quality, and then, the optimum growth conditions were determined by studying the experimental param eters, such as gas flow rate, pulling rate, rotation speeds of the feed rod and the seed. The grown crystals were analyzed using the chemical etching to observe the tch pattern and the ICP (Inductively Coupled Plasma) to determine the composition uniformity and the impurity content of Fe. The effects of additive (5 mol % MgO) on the transmittance and refractive index was, also, analyzed. In order to compare the nonlinear optical oharacteristics of $LiNbO_3$ with those of the other optical materials, the nonlinear optical refractive index ($n_2$) was calcu l lated using the measured refractive index.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.762-771
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• 1987

Friction welding is a fusion process in which the necessary heat is generated by clamping one of the two pieces to be welded in a stationary chuck and rotating the other at high speed with an axially applied load. It is essentially a variation of the pressure welding process but utilizes a novel heating method. In addition to the foregoing advantages, it has also been reported excellent for welding dissimilar materials. Therefore, this study reported on investigating the strength behavior for the frictionally welded domestic structural steel SM45C and SUS304. The results obtained by the experiments are as follows. (1) The highest tensile strength of the best friction welded specimen (B4) is about 3% lower than that of SM-45C base metal, and 9% lower than that of SUS304 base metal. The heat treated specimens (850.deg.C 1hr A.C) have almost same value of tensile strength. (2) The strain of SM45C base metal is 27.3% and that of SUS304 is 42%, that of the best friction welded specimen (B4) appeared as 11.9% which is about 50% lower than the base metal, so, this same phenomenon apeared in all the other welding conditions. (3) The bending strength of SM45C base metal is 123kgf/mm$^{2}$ and that of SUS304 is 127kgf/mm$^{2}$. The best specimen (B4) appeared as 121kgf/mm$^{2}$ which is almost same bending strength for both base metals. (4) The friction welded condition involving maximum strength is determined by P$_{1}$=8kgf/mm$_{2}$, P$_{2}$=22kgf/mm$_{2}$, T$_{1}$=10sec, T$_{2}$=2sec, and amount of upset 7.6mm. (5) The interface of two dissimilar materials are mixed strongly, and welded zone is about 1.03mm and also the heat affected zone is about 2.36mm at SM45C while about 1.85mm at SUS304, therefore the welded zone and heat affected zone are very narrow to compare with those of the other welding materials.