• The Journal of the Acoustical Society of Korea
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• v.24 no.2
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• pp.68-77
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• 2005

The purpose of a spatial audio system is to give a listener an impression as if he were present in a recorded environment when its sound is reproduced. For this purpose a dummy head microphone is generally used. Because of its human-like shape, dummy head microphone can reproduce spatial images through headphone reproduction. However, its shape and size are restriction to public use and it is difficult to convert the output signal of dummy head microphone into a multi-channel signal for multi-channel environment. So, in this paper, we propose a multi-channel 3D microphone technology. The multi-channel 3D microphone acquire a spatial audio using five microphones around a horizontal plane of a rigid sphere and through post processing, it can reproduce various reproduction signals for headphone, stereo, stereo dipole, 4ch and 5ch reproduction environments. Because of complex computation, we implemented H/W based post processing system. To verily the Performance of the multi-channel 3D microphone, localization experiments were Performed. The result shows that a front/back confusion, which is the one of common limitations of conventional dummy head technology, can be reduced dramatically.

• The Korean Journal of Pesticide Science
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• v.14 no.3
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• pp.191-198
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• 2010

To predict and design of new potent insecticidal compounds, the two dimensional quantitative structure-activity relationships (2D-QSARs) and molecular hologram quantitative structure-activity relationships (HQSARs) between the various physicochemical parameters as descripters of N'-phenyl-N-methylformamidine analogues (1-22) and their insecticidal activity against the two spotted spider mite (Tetranychus urticae) were discussed quantitatively. From 2D-QSAR models (1 & 3), the width ($B_2$) of $R_3$-group as sterically factor and optimal total dipole moment (TDM=2.025D) of $R_4$-group were mainly influenced to increase the activity. Therefore, the activities were depend upon the $R_3$- and $R_4$-groups. Particularly, it is predicted that the activity of newly designed potent compound (PI; $EC_{50}$=0.516 ppm) by 2D-QSAR models (3) and HQSAR model F2 was about 34.3 fold higher than that of the commercialized insecticide, Amitraz ($EC_{50}$=17.7 ppm).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.663-669
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• 2016

A terahertz asymmetric split-loop resonator (ASLR) was analyzed for use in high-sensitivity sensing applications. Its structural asymmetricity induces an asymmetric Fano resonance which has a high quality factor compared to the symmetric eigen-resonance. The variations of the resonant frequency, transmission coefficient, and quality factor of the ASLR in the eigen and Fano resonances are analyzed as a function of its structural asymmetricity. Also, the surface current densities on the ASLR in both resonances are calculated to analyze the main cause of the variations of its transmission characteristics. The surface current of the ASLR in the eigen resonance shows a dipole resonance, which increases the radiation loss and reduces the quality factor. On the other hand, the surface current of the ASLR in the Fano resonance shows a trapped or quadrupole mode which has a low radiation loss. Therefore, the ASLR operated in the Fano resonance has a high quality factor. Terahertz, high-performance filters and high sensitivity sensors can be developed based on our analysis results of the ASLR having a high quality factor. These high-performance devices based on terahertz metamaterials could increase the adoption of terahertz industrial applications.

• Journal of the Korean Vacuum Society
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• v.21 no.5
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• pp.264-272
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• 2012

In this paper, we report THz generation and detection characteristics investigated by InGaAs semiconductor epilayers, as results of a basic study obtained from the InGaAs-based THz transmitter/receiver (Tx/Rx). High-temperature and low-temperature (LT) grown InGaAs epilayers were prepared by the molecular beam epitaxy technique for the characterization of THz generation and detection, respectively, and the surface emission based on the photo-Dember effect was tried for THz generation. THz wave was generated by irradiation of a Ti:Sapphire fs pulse laser (60 ps/83 MHz), and a LT-GaAs Rx was used for the THz detection. The frequency band shown in the spectral amplitudes Fourier-transformed from the measured current signals was ranging in 0.5~2 THz, and the signal currents were exponentially increased with the Tx beam power. The THz detection characteristics of LT-InGaAs were investigated by using an Rx with dipole (5/20 ${\mu}m$) antenna, and the cutoff frequency was ~2 THz.

• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.86-89
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• 2007

[ $FeCr_2Se_4$ ] prepared under the high pressure (3 GPa) has been studied with x-ray, neutron diffraction techniques, superconducting quantum interference device (SQUID) magnetometer, resistance, and Mossbauer spectroscopy. The temperature dependence of resistance is explained by Mott-VRH and small polaron model for the regions I (T<20 K) and II (T>42 K), respectively. Neutron diffraction results show an antiferromagnetic spin-lattice coupling near the Neel temperature. So finally the distance of atom is enlarged in region (110$FeCr_2Se_4$ shows convex type of temperature dependence.

• Journal of the Korean Chemical Society
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• v.51 no.5
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• pp.447-458
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• 2007

The purpose of this study was to explore high school teacher's and students' perceptions of learning difficulties of the ‘chemical bond' unit of the Chemistry II in the 7th national curriculum. The participants in this study were consisted of a teacher and his students(85) from the Chemistry II classrooms: they all answered to the questionnaire, and then some students and the teacher were interviewed individually. The results showed that there were big differences between the teacher's and his students' perceptions of 1) the most difficult unit for understanding; 2) concepts they learned; and 3) the most difficult concept for understanding in the classroom. Students thought that electro-negativity unit was the most difficult to understand while teacher thought molecular structure unit was the hardest unit to teach. And teacher taught all 32 subjects of chemical bond unit to students, but some students could not remember they learned all of them. Most difficult parts for students to understand were ‘Coulomb force' and ‘dipole moment', while the most difficult part for the teacher to teach was ‘the conceptual difference between atomic bond and intermolecular force'. The reasons caused the students' learning difficulties were analyzed and discussed based on the interview data, and then further study was presented.

• Geophysics and Geophysical Exploration
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• v.4 no.1
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• pp.8-18
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• 2001

To delineate the inhomogeneities including fractures and to estimate the freshness of rock borehole radar consisting of the reflection and tomography methods, and GPR surveys were conducted at a granite quarry mine. The borehole reflection survey using the direction finding antenna was also conducted to get the spatial orientations of reflectors. 20 MHz was adopted as the central frequency for the borehole radar reflection and tomography surveys and 100 MHz was for GPR. Through the interpretation of borehole reflection data using dipole and direction finding antenna as well as GPR images, which are good agreement with each other, we could determine the orientation of the major fractures in three dimensional way. Parts of travel time curves of tomography data showed the anisotropy, which is uncommon in granite quarry. By comparing the tomography data and TeleViewer images, the anisotropy effect in this area are closely related to fine fissures aligned in the same direction. The area confined by the two fractures, MF2 and MF5, might consist of the most fresh granite in the surveyed area, which was concluded from the borehole radar tomography, and GPR images as well as the distribution of anisotropy.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.3 s.94
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• pp.246-252
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• 2005

A RF microstrip balun having low transmission loss for the balanced receiving dipole antenna is designed and fabricated using a three-section Wilkinson divider and two 3-dB quadrature couplers. It considers two types of the three-section Wilkinson dividers, the Cohn's optimum three-section structure and the miniaturized three-section structure, for wideband power splitting. Also, two 3-dB quadrature couplers for 180 degrees of phase difference adopt a twist-wire coaxial cable. The fabricated first balun having the Cohn's optimum three-section Wilkinson divider has 0.5 dB of transmission loss, $\pm$0.2 dB of amplitude imbalance, and 180$\pm$2.3 degrees of phase imbalance over 400 to 1000 MHz by measurement. The second one using the miniaturized three-section Wilkinson divider shows 1.0 dB of transmission loss, $\pm$0.7 dB of amplitude imbalance, and 180$\pm$8.8 degrees of phase imbalance over the same frequency band.

• Journal of the Korean Chemical Society
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• v.28 no.4
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• pp.210-216
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• 1984

Solvatochromic comparison methods were applied to determine Taft's solvent parameters, ${\pi}^{\ast}$(solvent polarity-polarizability), ${\alpha}$(solvent hydrogen bond donor acidity) and ${\beta}$ (solvent hydrogen bond acceptor basicity) for MeOH-MeCN solvent mixtures. Swain's solvent parameters A(anion solvation scale) and B(cation solvation scale) were also determined by least square fitting of kinetic data in the same binary solvent mixtures. It was found that: (i)${\beta}$ depends on the basicity of the solvent and increases with the MeOH content owing to the increase in polymeric structure of methanol; (ii) ${\pi}^{\ast}$depends on the dipole moment of the solvent and increases with the MeCN content of the solvent; (iii) ${\alpha}$ increases rapidly with the MeOH content as the hydrogen bond donor acidity of the solvent mixtures increases. Taft's reaction constants a and s and Swain's reaction constants a and b were determined for the reactions reported from our laboratory previously using solvent parameters determined in this work. No meaningful inter-relationship was found between the two set of reaction parameters, but a good linear correlation was found between the ratios a/s and a/b. Solvent effect on the reaction mechanism, substituent effect and leaving group ability were examined in the light of these reaction constants ratios.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.5
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• pp.197-203
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• 2016

In this paper, the dipole antenna that can control a beam steering were designed for attaching on LEO(Low Earth Orbit) small satellite. The proposed antenna was based on Yagi-Uda antenna. The parasitic element was proposed as a T-shape. Depending on the state of open or short at the end of a vertical element, we can choose a characteristic of the parasitic element with fixing a vertical element length of the parasitic element. Using this characteristic, we designed the director element and reflector element. The proposed antenna was designed to receive UHF 436.5 MHz. Antenna gain was chosen by link budget between one satellite and the other satellite or between the satellite and the ground station. By changing a vertical element length which is the largest variable that chooses an antenna characteristic, we confirmed that ${\lambda}/2$ length transformer has a result that improve 0.5 dB in comparison ${\lambda}/4$ length transformer from maximum gain direction. In production, we made an on/off switch composed of a diode, capacitor, and inductor control an open and short at the end of the parasitic element. As a result, the gain of antenna used in a link between one satellite and the other satellite had average 5.92 dBi. And the gain of antenna used in a link between the satellite and the ground station had average 0.99 dBi.