• The Bulletin of The Korean Astronomical Society
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• 제43권2호
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• pp.40.3-40.3
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• 2018

This dissertation presents the results on two-dimensional Redshift space distortion (hereafter RSD) analyses of the large-scale structure of the universe using spectroscopic data and on improvement of modeling of the RSD effect. RSD is an effect caused by galaxies' peculiar velocity on their clustering feature in observation along the line of sight and is thus intimately connected to the growth rate of the structure in the universe, from which we can test the origin of cosmic acceleration and Einstein's theory of gravity at cosmic scales in the end. However, there are several challenges in modeling precise and accurate RSD effect, such as non-linearities and the existence of an exotic component, e.g. massive neutrino. As part of endeavors for modeling more precise and accurate galaxy clustering in redshift space, this dissertation includes a series of works for this issue. (More detailed descriptions were omitted.)

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제28권9호
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• pp.8-13
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• 2014

Currently it is major problem of electric railway with increasing drive speed such as the arc generated by the pantograph detachment and the distortion current in the motor-block high speed switching. When physical contact between the pantograph and the catenary line is separated, the pantograph detachment arcing occurs and it makes up the conductive noise to the return feeder. We made the EMTP modeling of the railway traction system and the pantograph arc by circuit elements and switches. The influence of pantograph detachment frequency is investigated by changing some frequencies. The over-current occurs in each detachment and it oscillates some time at beginning and stabilizes gradually. The magnitude of over-current is decided by instantaneous value of existing traction return current. If the detachment occurs at a point of peak value or distortion current, the over-current will be more harmful to the power systems connected with the return feeder and will become to arise with increasing detachment frequency.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제44권10호
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• pp.185-190
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• 2007

In this paper, minimum sampling rates and method of nonlinear characterization were suggested for low power, quasi-memoryless PAs. So far, the Nyquist rate of the input signal has been used for nonlinear PA modeling, and it is burdening Analog-to-digital converters for wideband signals. This paper shows that the input Nyquist rate sampling is not a necessary condition for successful modeling of quasi-memoryless PAs. Since this sampling requirement relives the bandwidth requirements for Analog-to-digital converters (ADCs) for feedback paths in digital pre-distortion systems, relatively low-cost ADcs can be used to identify nonlinear PAs for wideband signal transmission, even at severe aliasing conditions. Simulation results show that a generic memoryless nonlinear RF power amplifier with AMAM and AMPM distortion can be successfully identified at any sampling rates. Measurement results show the modeling error variation is less than 0.8dB over any sampling rates.

• JSTS:Journal of Semiconductor Technology and Science
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• 제4권3호
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• pp.141-148
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• 2004

We discuss and develop a compact MOSFET modeling scheme in order to obtain accurate descriptions of the drain current and its derivatives up to the 5th order. We have analyzed the physical effects which govern the behaviour of the 3rd derivative in long and deep-subrnicron channel MOSFETs. Our modeling agrees well with experimental data and describes continuous transitions between operating regimes, thanks to the use of continuous functions, which do not introduce any artificial peaks.

• Transactions on Electrical and Electronic Materials
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• 제14권6호
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• pp.283-290
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• 2013

This paper illustrates the possibilities of using the program ATP-Draw (Alternative Transient Program) for the modeling of power networks to study power quality problems with highly detailed analyses. The Program ATP-Draw is one of the most widespread and oldest programs. A unique characteristic of this program is its public domain and the existence of forums and study committees where new application cases and modification are presented and shared publicly. In this paper, to study the propagation of harmonics through a power network, a part of an industrial power network was modeled. The network contains different types of electric components, such as transformers, transmission lines, cables and loads, and there is a source of harmonics that injects $3^{rd}$, $5^{th}$, $7^{th}$, $9^{th}$ and $11^{th}$ harmonic currents into the network, causing a distortion of the wave form of the currents and voltages through the power network.

• Journal of electromagnetic engineering and science
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• 제8권1호
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• pp.17-22
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• 2008

It is presented that sampling rates for behavioral modeling of quasi-memory less nonlinear devices can be far less than the Nyquist rate of the input signal. Although it has been believed that the sampling rate of nonlinear device modeling should be at least the Nyquist rate of the output signal, this paper suggests that far less than the Nyquist rate of the input signal can be applied to the modeling of quasi-memoryless nonlinear devices, such as frequency multipliers. To verify, a QPSK signal at 820 MHz were applied to a frequency tripler, whereby the device can be utilized as an up-converting mixer into 2.46 GHz with the aid of digital predistortion. AM-AM, AM-PM and PM-PM can be successfully measured regardless of sampling rates.

• Journal of Welding and Joining
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• 제30권6호
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• pp.120-125
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• 2012

Because ships and offshore structures have very large dimensions and complicated shapes, it is difficult to determine the deformation or internal stress in the structure by simple lab tests. Thus, a rigorous analysis by using the computer simulation technology is essential for obtaining their distortions by considering the entire production process characteristics. The rapid development of computer technology made it possible to analyze the heat transfer phenomena, deformation and phase transformation in the welded joint. For large shell structures, shell elements modeling contributed primarily to this development. But if a welding is done by multi-pass, shell elements whose thickness are unchangeable can hard to describe the local situation. Recently, it was researched how to introduce the imaginary temperature for V grooved multi-layer butt welding in strain-boundary method (a kind of shrinkage methodologies). In the present study, we formulated the imaginary temperature for the double bevel and double V groove by considering the thickness change of each pass through the bead and the thickness directions simultaneously and also demonstrated the feasibility of the formula by applying it to the thermal distortion analysis of the erection process of crane pedestal.

• Journal of the Institute of Electronics Engineers of Korea SD
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• 제41권4호
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• pp.101-112
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• 2004

In this paper, we developed a numerical analysis model by using ADI-FDTD method to analyze three-dimensional interconnect structure. We discretized maxwell's curl equation by using ADI-FDTD. Using ADI-FDTD method, a sampler circuit designed from 3.3 V CMOS technology is simplified to 3-metal line structure. Using this simplified structure, the time delay and signal distortion of complex interconnects are investigated. As results of simulation, 5∼10 ps of delay time and 0.1∼0.2 V of signal distortion are measured. As demonstrated in this paper, the full-wave analysis using ADI-FDTD exhibits a promise for accurate modeling of electromagnetic phenomena in high-speed VLSI interconnect.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제16권10호
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• pp.1010-1019
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• 2005

In this paper, we used neural network technique to model memory effects of RF power amplifier which is fed by two-tone input signals. The memory effects in power amplifier were identified by observing the unsymmetrical distribution of IMD(Inter-Modulation Distortion) measurements with the change of tone spacings and power levels. Different asymmetries of IMD were also found at different center frequencies. We applied TDNN technique to model LDMOS power amplifier based on two tone IMD data, and the accuracy was very high compared to other modeling methods such as the(memoryless) adaptive modeling method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제18권5호
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• pp.151-155
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• 2004

Millimeterwave OFDM wireless LAN system has been modeled for ACPR analysis. With simple AM-to-PM modeling for power amplifier and system simulation technique, power amplifier ACPR is simulated for OFDM modulation, Also, amplifier back-off value satisfying the required ACPR and the ACPR degradation have been predicted with the measured and modeled AM-tn-PM distortion.