• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.1
• /
• pp.115-124
• /
• 1989

Near-threshold fatigue crack-growth behavior at room temperature for a duplex stainless steel weldments was investigated to evaluate the effect of load ratio, microstructural change, and residual stresses. Near-threshold fatigue crack propagation behavior is found to show a marked sensitivity to .alpha./.gamma. phase ratio, and little residual stress effects. Threshold values in the heat affected zones are higher than those of base metals and threshold values for crack growth decrease with increasing the load ratio in the base metals and weldments. The fractrographic features in base metals, weldments and heat affectred zones were discussed in terms mechanism of crack growth.

• Journal of Korean Society for Geospatial Information Science
• /
• v.12 no.2 s.29
• /
• pp.3-9
• /
• 2004

The Broadcasting system is very important part of human lift that preceding to people news, nation plan, sport, drama, leisure and politics. The product of maded by brocasting system conveyed the whole country by radio signal. A brocasting station operate the brocast product radio trial network in the mountain. Recently a height of new building, concrete structure is very large and higher then old one. Since one does or says, noise occur to radio and TV signal whole nation. In this study, Taejun Sikjang mountain and Cheunan-Heuksung mountain where occurred radio noise chosen as a sample, and analysis 3D simulation and plane check. Accordingly come to conclusion condition of noise occurred radio antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.9 no.2
• /
• pp.199-210
• /
• 1998

It is very important to analyze and predict the propagation characteristics of LEO communication satellite at the service area using computer simulation. In this paper, the propagation characteristics of a satellite communication system are analyzed using ray tracing technique. We predicted the receiving environment and obtain the delay profile and total received power at each position using ray tracing method by changing both the azimuth and elevation angles after establishing the imaginary receiving space. The final goal of this paper is to analyze and understand the wave propagation characteristics of the satellite communication network about 2 GHz frequency band. The prediction method presented in this paper may help us to design satellite transceiver system and to construct a satellite communication network.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.11 no.6
• /
• pp.900-906
• /
• 2000

The remarkable progress of electronics and radio communications technology has made our life abundant. On the other hand, the countermeasure of EMl/EMC becomes more important socially according to the increased use of electromagnetic waves. It had been required that the absorbing ability of an electromagnetic wave absorber is more than 20 dB, the bandwidth of which is required through 30 MHz to 1,000 MHz for satisfying the international standard about an anechoic chamber for EMl/EMS measurement. From November of 1998, however, the CISPR11 has accepted the extended frequency band to 18 GHz in the bandwidth of EMI measurement. In this paper, we proposed the cut corn type and cylinder type absorbers satisfying the above requirments and carried out broadband design using the equivalent material constants method.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.21 no.6
• /
• pp.737-743
• /
• 2015

This paper are mainly focusing on the facts influencing on RCS reductions, appling radar absorbing materials by using RCS contributions of elements and appling a metamaterials which is high-tech radar absorbing materials. RCS analysis results are given for a simplified ship model, with radar absorbing materials and metamaterials cause RCS reduction in terms of mean values.

• The Journal of the Acoustical Society of Korea
• /
• v.19 no.5
• /
• pp.41-45
• /
• 2000

The effective elastic constants of a single-crystal superlattice film have been determined by two methods based on the velocities of surface acoustic waves (SAW). One method uses formulas to calculate the effective elastic constants of a superlattice from the known elastic constants of the constituent layers. The calculated effective elastic constants are tested by comparing the corresponding SAW velocities calculated for thin-film/substrate systems with the corresponding SAW velocities measured by line-focus acoustic microscopy (LFAM). The other method determines the effective elastic constants of the superlattices by inverting the SAW velocity dispersion data measured by LFAM. The results of both methods applied to a TiN/NbN superlattice film are in good agreement.

• The Journal of the Acoustical Society of Korea
• /
• v.14 no.2E
• /
• pp.37-42
• /
• 1995

The polar parabolic equation method (Polar PE) which introduces a series of "cascaded" boundary fitting coordinates into the parabolic equation method has been verified as a good numerical method for atmospheric sound propagation over a curved surface and hills. Polar PE is applied here to underwater sound propagation over a sea mountain assuming locally reacting boundary sea bottom and pressure release water surface for the boundary conditions. Calculations are presented for underwater propagation over a 450 m high sea mountain. Feasibility of Polar PE application for underwater sound propagation over a smooth mountain is discussed.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38C no.7
• /
• pp.605-611
• /
• 2013

If an accident vehicle propagates emergency messages to other vehicles close to it, the other drivers may realize and avoid the accident spot. In this letter, we propose a broadcast scheme to propagate emergency messages fast in urban VANETs (Vehicular Ad-Hoc Networks) with the help of GPS (Global Position System). In our scheme, a transmitting vehicle chooses the farthest node as the next relay vehicle to propagate emergency messages. And, we suggest an algorithm for intersection recognition and SCF (Store-Carry-Forward) task by taking advantage of periodic hello packets to reduce the propagation time and enhance the delivery ratio.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.3
• /
• pp.449-459
• /
• 1999

The scattering problems from electromagnetic absorbers can be greatly simplified using the transmission line approximations (TLA) and effective medium theory. This method has been widely used for the absorber design because of its very simple calculation and intuitional approach, while numerical analysis needs the tremendous computation requirements, This paper examined the accuracy and limitations originated by the intrinsic approximation limits of TLA by comparison with FEM results for various absorber design examples. It was found that the TLA result is valid when λ $\geq$ 2p, where λ is the wavelength of the interested upper frequency and p is the distance between two periodic cone arrays. Therefore, the electromagnetic absorbers having high material properties and big base-area commonly do not meet this condition, and the electromagnetic scattering from those absorbers must be evaluated by the numerical analysis in those cases.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.149.2-149.2
• /
• 2012

세계전파통신회의 (WRC; World Radiocommunication Conference)회의는 국제전기통신연합 (ITU)에서 규정하는 국제 전파법 제개정을 위해, 3-4년 간격으로 개최되는 전파통신 관련 최고회의라고 할 수 있다. WRC-15회의는 2015년 11월 2일 - 11월 27일에 걸쳐 스위스 제네바에서 개최될 예정이며, 과학업무 관련 의제들은 다음과 같다. 즉, 7145-7235 MHz 또는 7-8 GHz 대역의 지구탐사위성(지구대우주)업무의 1순위 분배연구, 지구탐사위성업무용 연속 600MHz 대역 분배방안 연구 (8,700~10,500MHz대역 내), 우주선 근거리통신용 관련 규정 재검토, 윤초삭제와 관련된 세계협정시(UTC) 개정 또는 대처방안 연구가 있다. 그리고 모바일광대역 응용 실현을 위한 이동통신업무 추가 분배 및 IMT 추가 지정 연구, 7150-7250MHz (우주대지구), 8400-8500MHz (지구대우주)에서 고정위성업무 추가 분배연구, 나노 위성 및 피코 위성 규제 관련 연구들이 있다. 따라서 본 발표에서는 WRC-15회의의 과학업무 의제들 가운데, 국내전파망원경 운용에 영향을 미칠 수 있는 주파수 대역 및 윤초 관리 등과 관련된 주요 과학업무 의제를 소개하고 이에 대한 향후 대응책 검토를 하고자 한다.