• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.7 no.1
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• pp.41-58
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• 2007

A compact and broadband $4{\times}1$ array antenna was developed for 3G smart antenna system testbed. The $4{\times}1$ uniform linear array antenna was designed to operate at 1.885 to 2.2GHz with a total bandwidth of 315MHz. The array elements were based on the novel broadband L-probe fed inverted hybrid E-H (LIEH) shaped microstrip patch, which offers 22% size reduction to the conventional rectangular microstrip patch antenna. For steering the antenna beam, a commercial variable attenuator (KAT1D04SA002), a variable phase shifter (KPH350SC00) with four units each, and the corporate 4-ways Wilkinson power divider which was fabricated in-house were integrated to form the beamforming feed network. The developed antenna has an impedance bandwidth of 17.32% ($VSWR{\leq}1.5$), 21.78% ($VSWR{\leq}2$) with respect to center frequency 2.02GHz and with an achievable gain of 11.9dBi. The design antenna offer a broadband, compact and mobile solution for a 3G smart antenna testbed to fully characterized the IMT-2000 radio specifications and system performances.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1549-1551
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• 1998

We have designed and developed narrow bandpass multipole filters for satellite communication using $YBa_2Cu_3O_{7-x}$(YBCO) thin films on MgO substrates. The superconducting film used in this study was prepared by laser ablation on one side polished MgO (100) substrates. A Nd:YAG laser was used to fabricate YBCO thin films. The wave length of the laser was 355 nm. The laser beam was focused onto a YBCO target rotating linearly to avoid deep craters that may eject macroscopic YBCO particles. The YBCO films were grown at $750^{\circ}C$ in the oxygen partial pressure of 200 mTorr. The deposited YBCO thin films were patterned by conventional wet-etching method. The transition temperatures of YBCO thin films were 85 - 88 K and the film thicknesses were about 5,000 $\AA$. By comparing the performances of normal-metal filters and YBCO filters, we observed that superconducting YBCO multipole filters have been showed superior performances at 77 K.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.7
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• pp.36-42
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• 2000

Some polarization characteristics of reflection type photopolymer are investigated. Photopolymer on a Mylar substrate alters an incoming linearly polarized laser beam to an elliptical polarization. Due to the rotation of the polarization, the recording gratings show different diffraction efficiencies. The rotation angle is of order of 10-50% for the tested samples. It is found that the polymer layer does not changes the polarization direction but the Mylar substrate alone distorts the incoming polarization to a comparable degree. As align the polarization states of photopolymers to be parallel with a laser using a He-Ne laser(633nm), which is not sensitive to that material, it was possible to make high diffraction efficiency gratings.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.44 no.5
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• pp.543-549
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• 2011

An underwater speaker was developed for use as an acoustic deterrent device that transmits acoustic energy through the water omnidirectionally over a broadband frequency range to eliminate marine mammal attacks and to prevent physical damage to the inshore and coastal fishing grounds of Korea. The underwater speaker was constructed of two vibration caps machined from 6061-T6 aluminum alloy and a stack of PZ 26 piezoelectric ceramic rings (Ferroperm Piezoceramics A/S) connected mechanically in series and electrically in parallel. The performance characteristics of the underwater speaker were measured and analyzed in an experimental water tank of $5\;m{\times}5\;m{\times}6\;m$. The peak transmitting voltage response (TVR) was measured at 11.16 kHz with 163.45 dB re $1\;{\mu}Pa$/V at 1m. The underwater speaker showed a near omnidirectional beam pattern at the peak TVR resonance frequency. The usable frequency range was 4-25 kHz with a lower TVR limit of approximately 140 dB. We conclude that this underwater speaker could be satisfactorily used as an acoustic deterrent device against marine mammals, particularly the bottlenose dolphin, to protect catches and fishing grounds as well as the mammals themselves, for example, by keeping them away from fishing gear and/or vessels.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.239-240
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• 2006

For longer than picosecond pulses, bulk damage inside defect-free dielectrics involves the heating and multiplication of spurious electrons by the incident laser beam and transfer of this energy to the lattice. The situation is quite different for femtosecond pulses which are shorter than the time scale for electron energy transfer to the lattice. Damage caused by these pulses is produced with smaller statistical uncertainty and is controllable on a microscopic scale. These properties can be exploited to produce laser devices such as arrays of damage dots for all optical memories with high data storage density or arrays of parallel grooves to form transmission gratings. In this work, we observed characteristic of the femtosecond laser machining in BK7 and fused silica.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.324-329
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• 2010

Fuel rods using in nuclear power plants consist of uranium dioxide pellets enclosed in zirconium alloy(zircaloy) tubes. It is vitally important for the pellet surface to remain free from pits, cracks and chipping defects after it is loaded into the tubes to prevent local hot spots during reactor operation. This paper investigates the feasibility study for detecting surface flaws of pellets contained within nuclear fuel rod through X-ray tomography simulation. Reconstructed images used by parallel and fan-beam filtered back projection method were presented and confirmed the accessibility between simulation data and MPS(missing pellet surface) image data.

• Journal of Korea Foundry Society
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• v.15 no.3
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• pp.283-290
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• 1995

Molybdenum ingot of 50mm in diameter were obtained from sintered Mo bars by EB drip melting technique. Macroscopic observation of EB remelted ingot indicates that coarse and columnar grains grow in the direction parallel to ingot pulling direction. This can be explained by slow solidification (3mm/min), large temperature gradient and heat flow to this direction. The orientation of columnar structure was found to be <110>, <200> and <211> by the analysis of X-ray diffraction patterns. The contents of typical metallic impurities in Mo sintered bar are 1.2ppm Cr, 3ppm Fe, 44ppm Zr, 150ppm W. Most of metallic impurities were reduced below the order of ppm except zirconium and tungsten by the selective evaporation. In the removal of nonmetallic impurities, oxygen and carbon impurities were lowered from 120 to 6ppm and from 157 to 106ppm, respectively, after first melting. Although the purification effect was not significant with the number of remelting, Vickers hardness was reduced from 217 to 195 and 184 in sequence with increasing the number of remelting.

• Nuclear Engineering and Technology
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• v.38 no.4
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• pp.383-390
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• 2006

Having its roots in medical applications, industrial gamma ray CT has opened up new roads far investigating and modeling industrial processes. Using a line of research related to industrial gamma ray CT, the authors set up a system of single source and detector gamma transmission tomography for wood timber and a packed bed phantom. The hardware of the CT system consists of two servo motors, a data logger, a computer, a radiation source and a radiation detector. One motor simultaneously moves the source and the detector for a parallel beam scanning, whereas the other motor rotates the scan table at a preset projection angle. The image is reconstructed from the measured projections by the filtered back projection method. The phantom was designed to simulate a cross section of a packed bed with a void. The radiation source was 20mCi of Cs-137 and the detector was a 1 inch $\times$ 1 inch NaI (TI) scintillator shielded by a lead collimator. The experimental gamma ray CT image has sufficient resolution to reveal air holes and the density distribution inside the phantom. The system could possibly be applied to a packed bed column or a pipe flow in a petrochemical plant.

• Nuclear Engineering and Technology
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• v.30 no.5
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• pp.452-461
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• 1998

The pin power distribution is determined by analyzing the rotational gamma scanning data for 36 element fuel bundle of HANARO. A fission monitor of Nb$^{95}$ is chosen by considering the criteria of the half-life, fission yield, emitting ${\gamma}$-ray energy and probability. The ${\gamma}$-ray spectra were measured in Korea Atomic Energy Research Institute(KAERI) by using a HPGe detector and by rotating the fuel bundle at steps of 10$^{\circ}$. The counting rates of Nb$^{95}$ 766 keV ${\gamma}$-rays are determined by analyzing the full absorption peak in the spectra. A 36$\times$36 response matrix is obtained from calculating the contribution of each rod at every scanning angle by assuming 2-dimensional and parallel beam approximations for the measuring geometry. In terms of the measured counting rates and the calculated response matrix, an inverse problem is set up for the unknown distribution of activity concentrations of pins. To select a suitable solving method, the performances of three direct methods and the iterative least-square method are tested by solving simulation examples. The final solution is obtained by using the iterative least-square method that shows a good stability. The influences of detection error, step size of rotation and the collimator width are discussed on the accuracy of the numerical solution. Hence an improvement in the accuracy of the solution is proposed by reducing the collimator width of the scanning arrangement.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.387-394
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• 1999

Artificial Neural Network (ANN) is a computational model inspired by the structure and operations of the brain. It is massively parallel system consisting of a large number of highly interconnected and simple processing units. The purpose of this paper is to verify the applicability of ANN to predict experimental results through the use of measured experimental data. Although there have been accumulated data based on hysteretic characteristics of structural element with cyclic loading tests, it is difficult to directly apply them for the analysis of elastic and plastic response. Thus, simple models with mathematical formula such as Bi-Linear Model, Ramberg-Osgood Model, Degrading Tri Model, Takeda Model, Slip type Model, and etc, have been used. To verify the practicality and capability of this study, ANN is adapted to several models with mathematical formula using numerical data To show the efficiency of ANN in nonlinear analysis, it is important to determine the adequate input and output variables of hysteretic models and to minimize an error in ANN process. The application example is Beam-Column joint test using the ANN in modeling of the linear and nonlinear hysteretic behavior of structure.