• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.7
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• pp.693-701
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• 2002

In this paper, we analyze the coverage of asynchronous IMT(International Mobile Telecommunication)-2000 reverse link with a MUD(Multi-User Detector) system. The MUD system is utilized to increase the coverage of reverse link. Also we have considered a propagation loss model and an interference effect. Because it is very difficult that we have calculated the interference accurately, so a fractional cell loading factor(F) is used in this paper. We make use of a MUD efficiency($\beta$) to analyze the performance; this efficiency is presented the MAI of reduction. A simulation utilizes Hata's model, we calculated the coverage according to voice and data services. In this paper, we have assumed that the frequency of carrier has 800 MHz or 1.9 GHz, and a bandwidth is decided 3.84 MHz. We have predicted the performance of actual system by the analysis of capacity and coverage.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.61-71
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• 1993

The stress waves generated by the mechanical energies by impact or the chemical energies by the explosions are transmitted through medium. The wave propagation process through medium is a very complicated procedure due to the reflections and refractions of the waves at the free surfaces and interfaces. In this study the pressure independent Von-Mises model is employed for the wave propagation analysis in the layered systems. Governing equations of this study are conservation equations of momentum and mass in Lagrangian coordinate system which is fixed to the material. Due to the shock-front which violates the continuity assumptions inherent in the differential equations numerical artificial viscosity is used to spread the shock front over several computational zones. These equations are solved by Finite Difference Method with discretized time and space coordinates. The associate normality flow rule as a plastic theory is implemented to find the plastic strains.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.19-19
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• 1991

Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test(τ/σ= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio τ/σ. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

• Journal of the Korean Institute of Gas
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• v.3 no.2 s.7
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• pp.34-42
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• 1999

The discrete variables such as time and sequence must be considered for automating HAZOP analysis of batch processes in contrast with continuous processes. Because these variables can not be explained by the method used in the HAZOP analysis of continuous processes, we have developed the methodology for HAZOP analysis of batch processes on the basis of the relation between discrete variables and continuous ones. In this study, we have discussed the performance of the methodology on a Latex batch process to evaluate its effectiveness.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.544-545
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• 2010

전자식 안정기의 초기구동 시, 발생되는 입력단의 높은 돌입전류는 전자식 안정기 내의 전파정류다이오드 및 능동 역률보상회로의 파손원인이 되며, 제품의 신뢰성을 감소시키는 큰 요인으로 지목된다. 따라서 안정기의 입력에서 발생되는 돌입전류를 분석하고 제한하는 방법이 필요하다. 본 논문은 250W CDM(Ceramic Discharge Metal-halide) 램프용 DBI(Dual Buck Inverter) 구조의 전자식 안정기에서 초기 구동 시 높은 돌입전류가 발생되는 원인을 분석하고, 해결책을 제시하였다.

• Journal of Advanced Navigation Technology
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• v.17 no.5
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• pp.516-523
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• 2013

In this paper, The path loss model of Air Traffic Control(ATC) telecommunication radio channel has been studied at the Incheon International Airport(IIA) with the terminal with two antlers. We measured two frequencies among VHF/UHF channel bands. The transmitting site radiated the Continuous Wave(CW). The propagation measurement was taken using the moving vehicle equipped with receiver and antenna. The transmitting power, frequency and antenna height are the same as the current operating condition. The path loss exponent and intercept parameters were extracted by the basic path loss model and hata model. The path loss exponents at passager terminal areas were 3.32 and 3.10 respectively in 128.2 MHz and 269.1 MHz. The deviation of prediction error is 9.69 and 9.65. The new path loss equation at the terminal area was also developed using the derived path loss parameters. The new path loss was compared with other models. This result will be helpful for the ATC site selection and service quality evaluation.

• Journal of the Korean Society for Railway
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• v.15 no.4
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• pp.364-369
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• 2012

This paper presents an experimental study on the radio propagation characteristics in subway tunnel at 18GHz frequency band which has been assigned to video transmission between train and wayside. The radio propagation tests are carried out in the subway tunnel of Seoul Metro using the antenna and communication devices of the prototype video transmission system. The measurement results show that 18GHz radio propagation in subway tunnel has smaller path loss than that of general outdoor radio environment. It is also cleared that the arch-type tunnels have smaller radio propagation losses than rectangular tunnels, and single track tunnels have smaller pass loss than double track tunnels. From the measurements, the radio propagation coverage is worked out as 520 meters. The curved tunnels which cannot have LOS communication between transmitter and receiver have large pass losses and fluctuation profile along distance. The radio propagation coverage along curved tunnels is worked out as 300 meters. These investigation results can be used to design the 18GHz radio transmission system for subway tunnel by providing the optimized wayside transmitter locations and handover algorithm customized to the radio propagation characteristics in subway tunnels.

• Geophysics and Geophysical Exploration
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• v.25 no.4
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• pp.214-216
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• 2022

Distributed acoustic sensing (DAS), an increasingly growing acquisition technique in the oil and gas exploration and seismology fields, has been used to record seismic signals using optical cables as receivers. With the development of imaging methods for DAS data, full waveform inversion (FWI) is been applied to DAS data to obtain high-resolution property models such as P- and S-velocity. However, because the DAS systems measure strain from the phase distortion between two points along optical cables, DAS data must be transformed from strain to particle velocity for FWI algorithms. In this study, a plane-wave FWI algorithm based on the relationship between strain and horizontal particle velocity in the plane-wave assumption is proposed to apply FWI to DAS data. Under the plane-wave assumption, strain equals the horizontal particle velocity, which is scaled by the velocity at the receiver position. This relationship was confirmed using a numerical experiment. Furthermore, 4-layer and modified Marmousi-2 velocity models were used to verify the applicability of the proposed FWI algorithm in various survey environments. The proposed FWI was implemented in land and marine survey environments and provided high-resolution P- and S-velocity models.

• Economic and Environmental Geology
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• v.9 no.4
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• pp.213-223
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• 1976

Proceeding from general elementary principles to more specific abstract problems, we have attempted the rearrangement of the research results as they are known at present concerning the propagation and attennation of the elastic wave in submarine layers. We have derived the elementary equations of the elastic wave. In addition, the relationship of the propagation of the elastic waves in the sea water mass and the reflection of the waves from the water-sediment interface are treated and presented in different sections.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.2
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• pp.24-33
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• 1993

In indoor radio systems, vehicular communication systems, and land mobile systems, a very important problem is that of maintaing stable communications at all locations. Therefore solutions for the indoor propagation problem are an important aspects of the mobile communication system. Leaky coaxial cables finding increasing use in communications systems involving mines, tunnels, railroads, and highways, and in new obstacle detection, or guided radar, schemes for ground transpor- tation and perimeter surveilance. In this paper a leaky coaxial cable having periodic slots in the outer conductor is described to obtain the propagation modes in the various environments. We use an essentric cylindrical model to develop the theory for surface-wave propagation on the cable. Numerical Results are also included for the propagation constants, field distribution and impedance as functions of various parameters. First, we derive the electromagnetic equation for leaky coaxial cable having periodic slots using mode-matching method and Floguet's theorem, and then find various modes, propagation constants, field distribution, etc.