• Journal of the Korea Institute of Building Construction
• /
• v.9 no.1
• /
• pp.57-64
• /
• 2009

CWS I method developed to overcome the problems of frequent occurrence in the application of existing downward construction methods has demonstrated excellent efficiency. However, in the case of using slurry wall instead of SCW or CIP as a retaining wall, the improvements in connecting steel beams with the wall were demanded. Therefore, the study of CWS II method was carried out in order to accomplish the CWS I method reflecting its strong points and to ensure the settlement of a steel beam and to induce the diaphragm effect of a slab while reducing the degree of difficulty and the term of works and the cost of construction. In this paper, the concept and features of CWS II method as well as the progress of execution was discussed by comparing with existing methods.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.6 no.3
• /
• pp.431-438
• /
• 1996

Transmission electron microscopy has been used to investigate the microstructure of hot-pressed $TiB_{2}$. Thin foil specimens, prepared by conventional ion beam thinning, revealed many features which originated from the crystallographic anisotropy of hexagonal $TiB_{2}$. It was observed that in these specimens Fe-impurities are precipitated to form secondary Fe-rich phases at grain triple edges, in grain boundaries and sometimes in-grain. These Fe-rich precipitates were characterised by their coherence or semi-coherence to a favourably oriented grain at a grain triple edge or grain boundaries or to the matrix $TiB_{2}$ phase.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.05b
• /
• pp.74-77
• /
• 2000

A pulsed Nd:YAG laser has been used in a wide variety of fields : measuring, material processing and so on. In a material processing, it is very important to control the laser energy density. A pulse repetition rate and a pulse width are regarded as the most dominant factors to control the energy density of laser beam. In this study, pulsed Nd:YAG laser system was designed and manufactured to control the laser output usefully and easily. This system adopted the sequential charge and discharge circuit is controlled by 80196 micro- processor. As a result, it is found that laser output is controlled minutely by changing laser input and pulse repetition rate, and usefully by using 80196 microprocessor.

• Smart Structures and Systems
• /
• v.14 no.4
• /
• pp.569-594
• /
• 2014

Damage detection methods based on modal analysis have been widely studied in recent years. However the calculation of mode shapes in real structures can be time consuming and often requires dedicated software programmes. In the present paper the combined application of proper orthogonal decomposition and gapped smoothing method to structural damage detection is presented. The first is used to calculate the dynamic shapes of a damaged structural element using only the time response of the system while the second is used to derive a reference baseline to which compare the data coming from the damaged structure. Experimental verification is provided for a beam case while numerical analyses are conducted on plates. The introduction of a stiffener on a plate is investigated and a method to distinguish its influence from that of a defect is presented. Results highlight that the derivatives of the proper orthogonal modes are more effective damage indices than the modes themselves and that they can be used in damage detection when only data from the damaged structure are available. Furthermore the stiffened plate case shows how the simple use of the curvature is not sufficient when analysing complex components. The combined application of the two techniques provides a possible improvement in damage detection of typical aeronautical structures.

• Journal of Advanced Marine Engineering and Technology
• /
• v.20 no.5
• /
• pp.93-102
• /
• 1996

Laser-induced plume and laser-target interaction during pulsed laser deposition are demonstrated for a lead zirconate titanate (PZT). A KrF excimer laser (wavelength 248nm) was used and the laser was pulsed at 20Hz, with nominal pulse width of 20ns. The laser fluence was~$16J/cm^2,$ with 100mJ per pulse. The laser-induced plasma plume for nanosecond laser irradiation on PZT target has been investigated by optical emission spectra using an optical multichannel analyzer(OMA) and by direct observation of the plume using an ICCD high speed photography. OMA analysis showed two distinct ionic species with different expansion velocities of fast or slow according to their ionization states. The ion velocity of the front surface of the developing plume was about $10^7$cm/sec and corresponding kinetic energy was about 100eV. ICCD photograph showed another kind of even slower moving particles ejected from the target. These particles considered expelled molten parts of the target. SEM morphologies of the laser irradiated targets showed drastic melting and material removal by the laser pulse, and also showed the evidence of the molten particle ejection. The physics of the plasma(plume) formation and particle ejection has been discussed.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.11
• /
• pp.1840-1848
• /
• 2003

This paper presents the structural analysis and optimum design of a vertical micro-gyroscope with decoupled 2 degrees of freedom (DOF), driven by electrostatic force. Simplified beam models were presented to derive the structural stiffness of the driving spring of the U shape and the sensing spring of I shape. A finite element analysis (FEA) was performed to validate each derivation. A total mass and a polar mass moment of inertia were also obtained and used in calculating the resonance frequency at each mode of the 2 DOF. The resonance frequencies of the total system were calculated using the proposed models and it has been found that they were in excellent agreement with those of the FEA. Finally, the developed analysis program was then linked to an optimum design module, and an optimum design of the micro-gyroscope was successfully performed.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
• /
• v.10 no.1
• /
• pp.57-61
• /
• 1980

In dental roentgenograph it is of mutual benefit to the patient and the dentist to use the minimum amount of radiation capable of producing roentgenograms with maximum interprtive informations. Recent increases in the number of diagnostic x-ray examinations made in this country have caused attention to be paid to the quantity of radiation delivered to the population and operator. The purposes of this study was to assess the quality of dental x-ray units, the amount of films, the average processing procedures and the radiation protection methods in korea. The results were as following: 1. Most of radiation generating system were used in low voltage such as 60Kvp, 10㎃. 2. High sensitivity films such as 'D' group of Kodak or Rinn were mainly used and average 14.7 films used per weeks. 3. Some dentists practiced visual processing technic in simple dark room, and others used instant films. 4. 68.26% of patient held the film themselves, but 27.30% were assisted by dentists film holding. 5. In radiation protection method, 7.85% of dentists had protection equipments such as protective barrier, 2.73% wore protective apron, 27.9% made it a rules to avoid beam, and 7.51% used to maintain a distance from the radiation source.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.470.1-470.1
• /
• 2014

InAs는 high mobility를 갖는 III-V 화합물 반도체로 최근 InAs 나노선 기반 electronic transport에 대한 연구가 활발히 진행되고 있다. 또한, InAs는 n-type의 중온 영역대의 열전물질로서 나노선이나 나노박막과 같은 저 차원 구조의 열전 특성에 대한 보고가 이루어 지고 있다. 대부분의 InAs 나노선의 성장 방법은 화학기상증착법에 의한 것으로, 상온에서 $100{\mu}V/K$ 이하의 낮은 Seebeck 계수 값을 나타내고 있다. 본 연구는 무촉매 상태에서 MBE (Molecular beam epitaxy) 성장시킨 InAs 나노선의 열전 특성을 측정하였다. MTMP (Microfabricated Thermoelectric measurement platform)를 이용하여 50 K에서 300 K까지의 온도 영역에서 전기전도도, Seebeck 계수의 측정을 진행하였다. 그 결과 Seebeck 계수 값은 상온에서 대략 $200{\mu}V/K$로 높게 나타나고 있으며, 동일한 나노선의 상온 전기전도도는 대략 9800 S/m로 많은 보고들과 비슷한 수준의 수치가 나타나고 있다. Transconductance 측정을 통한 field-effect mobility와 carrier 농도를 평가한 결과가 Mott formula에서 계산된 carrier 농도와 유사한 결과를 나타내었다. 매우 큰 Seebeck 는 carrier 농도가 낮은 것에 기인한 것으로 판단된다.

• Journal of IKEEE
• /
• v.24 no.3
• /
• pp.917-920
• /
• 2020

In this paper, we studied the derivation method of isoflux radiation for a planar array antenna. The presented array antenna was designed for considering of 1U-sized CubeSAT with Ku-band communications. For the presented array antenna, 8×8 radiating elements were arranged, and the distance between radiating elements was set of half-wavelength. The excited current weighting for each radiating elements was calculated by the signal processing technique used in the design of the low-pass filter. As a result of analysis of the method proposed in this paper, it was confirmed that a seamless isoflux pattern can be derived.

• Journal of Welding and Joining
• /
• v.12 no.3
• /
• pp.109-117
• /
• 1994

Spot welding has wide used with a high work efficiency in the automotive and aerospace industries. Up to the present, the technique mainly used to test spot welds on production lines has been entirely depended upon destructive chisel or peel testing. Therefore, it's being very important assignment to secure the NDE technique which can be evaluate spot weld quality with more efficiency and high reliability. This paper discusses the feasibility of UNDE techniques to evaluate spot weld quality. For the sake of the approach to the quantitative measurement of nugget diameter and the discrimination of a the corona bond from nugget, ultrasonic c-scan image and distribution of reflective echo amplitude was measured by immersion method with the mechanical and the electronic scanning of point-focussed ultrasonic beam(25 MHz). As the results of this study, corona bond which is the most dangerous types of interface defects can be successfully detected, as well as expulsion and voids. Ultrasonic testing results were confirmed and compared by optical microscope and SAM(Scanning Acoustic Microscope) observation of the spot-weld cross section. The results show that the nugget diameter can be successfully measured with the accuracy of 0.8 mm.