• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.2
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• pp.139-147
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• 2003

In this paper we proposed system parameter values of M-ary PPM/TH(Pulse Position Modulation/Time Hopping) ultra-wideband systems having data rate of 100 Mbps for the frequency band, which is allocated by Federal Communications Commission(FCC). We also analyzed performance of the proposed system in the AWGN channels. According to the results of performance analysis, It is observed that available pulse duration is very limitative for this system. In case of constant data rate, if M and the pulse repetition numbers are increased, then the system performance is improved and the user number is decreased.

• Korean Journal of Materials Research
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• v.14 no.9
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• pp.664-669
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• 2004

Anodic aluminum oxide (AAO) with pores of various diameter, density, and thickness values was obtained through control of the anodization parameters including voltage, temperature, pore widening time, anodization time, etc. The pore diameter was controlled by a pore widening in an etchant, and alumina templates having stepped nano-channels were fabricated by repetition of anodization and pore widening processes. Stepped carbon nanotubes (CNTs) were then grown on the stepped AAO templates by pyrolysis of acetylene without using the catalyst. High-resolution transmission electron microscopy images revealed that CNTs have a multi-wall structure made of graphite flakes of several nm sizes. The current-voltage characteristic of the sloped and linear CNTs were also examined.

• Proceedings of the KIPE Conference
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• 2001.12a
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• pp.164-165
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• 2001

An IGBT driver for serially connected pulse switching IGBTS was contructed and tested. The IGBT driver has ten output pulses with 1 ${\mu}ysec$ pulse width Its pulse repetition-rate can adjusted from 0 to 20 kHz. The output pulses was insulated from 10 kV high voltage by a pulse transformer. Their voltage amplitude are 18 V, voltage rising time 250 nsec., and voltage falling time 200 nsec when IGBT gates with 12 nF input capacitance are connected.

• Journal of the Korean Vacuum Society
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• v.8 no.3B
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• pp.327-332
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• 1999

High speed real-time spectroscopic ellipsometry was employed in order to characterize the growth of chromium thin film. This instrument can collect 512 points of {$\Delta$(hv), $\Psi$(hv)} spectra from 1.3 to 4.5 eV with acquisition and repetition rates of 20 msec or less. When this instrument was integrated into the chromium thin film growth, we could obtain not only the information on film properties but also the details of the processes. We deduced the growth rates and the evolution of the optical properties of chromium thin films under several preparation conditions. We also demonstrated the contamination process of chromium thin films caused by air exposure.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.116-116
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• 2001

Purpose： PRESS is one of the representative sequences in MRS, but still, we do not have the formul describing the steady state magnetization of it. So, we derive the equation of th magnetization as a function of the echo time and the repetition time, and compare it wit phantom experiments. Method： PRESS consists of three 180 pulses and the additional crusher gradients whic destroy the unwanted coherences of the magnetization. Using the simple vector model, w derive a formula which describes the behaviour of the magnetization In PRESS and compa the results with the phantom experiment. Also, we explore the results of the T1 from STEAM, PRESS and the simple exponential.

• Proceedings of the SCSK Conference
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• 2003.09b
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• pp.480-507
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• 2003

A rapid and efficient method for analyzing the nonionic surfactants and silicone polymers, which control the shape and characteristics of cosmetic products and give influence on product quality, has been developed using Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI- TOF IMS). The MALDI-TOF/MS could easily and effectively determine the molecular weight distribution and monomer units of nonionic surfactants. As a result, creating a library of mass spectrum data of surfactants used in cosmetic products using MALDI-TOF/MS and analyzing surfactants extracted from the products may become a useful method for detailed structural characterization of the surfactants. Furthermore, the MALDI-TOF/MS analysis was effective in obtaining the spectrum of silicone polymers from which the molecular weight distribution could be determined. The repetition units and structural data could also be obtained through molecular mass peaks. Additionally, the monomer ratio and terminal groups as properties of silicone copolymers could be determined

• Korean Journal of Child Studies
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• v.21 no.2
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• pp.135-146
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• 2000

This study compared the effectiveness of various prevention methods(1-time video viewing; repeated video viewing; participation-enriched video viewing) used in delivering awareness of sexual abuse and coping skills to preschool children. All of the experimental groups performed better than the control group. The participation-enriched viewing group displayed higher levels of coping skills than the control and the 1-time viewing groups. Repeated viewing and participation-enriched viewing approaches were most effective in long-term understanding. The repeated viewing group showed superiority in long-term coping skills. Direct participation, interaction, and reinforcement by means of repetition are important for optimal results in sexual abuse prevention education.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.5
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• pp.268-272
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• 2004

A high voltage pulse generator with a rotator airhole spark gap instead of a rotary ball spark gap has been proposed and investigated. Its feasibility as a high voltage pulse generator is compared with the rotary ball spark gap type one. Parametric studies showed that proposed the rotary airhole type spark gap had a very stable breakdown voltage and reliable pulse repetition time compared with the conventional rotary ball type spark gap. This however showed that the proposed pulse generator with a rotary airhole spark gap instead of a rotary ball spark gap could be potentially used as a very stable and reliable pulse generator in the various fields of applications.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.04b
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• pp.1239-1242
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• 2002

In this paper, the implementation of MAI(multiple access interference)-cancelled SSMA(spread spectrum multiple access) system using orthogonal carriers was presented. Employing the pseudo periodic spreading codes and orthogonal carriers frequency offset, proposed system have the features no MAI during a certain local time-duration. Spreading signals designed by pseudo periodic method and repetition, have zero correlation duration(ZCD) by orthogonal frequency shift method. The SSMA modem has been designed and implemented using surface-acoustic-wave(SAW) device as the matched filter of receiver. The effects of frequency offset on stability have been evaluated using computer simulation.

• Textile Coloration and Finishing
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• v.12 no.5
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• pp.280-287
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• 2000

For thousands of years, dyes were obtained from natural sources, such as plants and animals. Although synthetic dyes have replaced many natural dyes for commercial use but natural dyes with their fascinating color are still used extensively by some people. To investigate the dyeing properties of chestnut bur, which is most widely found in our country, some experiments were performed under the several dyeing conditions with silk and cotton fabrics. It was found that $\lambda_{max}$ of chestnut but extract was 410nm and the color of the fabric dyed is Yellow Red. The K/S value of silk and cotton fabrics increased when the dyeing temperature was higher than $60^\circ{C}$ and the dyeing time was more than 30 minutes. Optimal dyeing pH was between 5 and 6, and repetition of dyeing increased K/S value of the sample fabrics. K/S value of silk fabric dyed with chestnut bur extract was higher than that of cotton. Post-mordanting method showed higher color yield compared with pre-mordanting, and higher temperature and increased time in mordanting increased the dye-uptake.