• Journal of the Korean Vacuum Society
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• v.16 no.4
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• pp.298-304
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• 2007

We have studied the effect of $N_2$ flow rate on the structural and optical properties of GaN nanorods grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy. The hexagonal shape nanorods with lateral diameters from 80 to 190 nm with increasing $N_2$ flow rate from 1.1 to 2.0 sccm are obtained. However, the ratio of length (thickness) and compact region increases with increasing $N_2$ flow rate up to 1.7 sccm and then saturate. From the photoluminescence, free exciton transition is clearly observed for GaN nanorods with low $N_2$ flow rate. And the PL peak energies are blue-shifted with decreasing diameter of the GaN nanorods due to size effect. Temperature-dependent photoluminescence spectra for the nanorods with $N_2$ flow rate of 1.7 sccm show an abnormal behavior like "S-shape" with increasing temperature.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.4
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• pp.285-289
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• 1997

A Held experiment was carried out to confirm the effect of underwater sound on the luring of fish school of rudder fish in a set net at the coast of Cheju Island. The effects of the acoustic emission on the luring of fish school were observed at a cage around a set net fishing ground using a manufactured underwater speaker. Underwater sounds that were emitted for the luring of fish school were the pure sounds of which frequency were 300Hz and 400Hz, engine noise and swimming sound. The results of the observation are as follows : 1. The input and output wave forms of a manufactured underwater speaker in water tank were similar to those in measurement frequencies. The result of the observation indicated that it could be used for the purpose of the sound emission in measurement frequencies. 2. The effect of the emitted pure sound of 300Hz, 400Hz was remarkable for the luring of fish school in 2 minutes after the sound emission. The reaction of fish school was more sensitive to the pure sound of 400Hz than 300Hz. 3. The effect of the emitted engine noise was more remarkable than that of the pure sound for 3 minute continuously. On the feeding sound, fish formed a shoal and swimmed, but didn't gather around the underwater speaker. 4. The feeding and swimming sound spectra on rudder Hsh showed similar sound pressure distribution each other, they appeared low sound pressure in frequencies of 200-600Hz.

• Journal of Broadcast Engineering
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• v.5 no.1
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• pp.10-22
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• 2000

In this paper, we present a texture description method as a standardization of multimedia contents description. Like color, shape, object and camera motion information, texture is one of very important information in the visual part of international standard (MPEG-7) in multimedia contents description. Current MPEG-7 texture descriptor has been designed to fit human visual system. Many psychophysical experiments give evidence that the brain decomposes the spectra into perceptual channels that are bands in spatial frequency. The MPEG-7 texture description method has employed Radon transform that fits with HVS behavior. By taking average energy and energy deviation of HVS channels, the texture descriptor is generated. To test the performance of current texture descriptor, experiments with MPEG-7 Texture data sets of T1 to T7 are performed. Results show that the current MPEG-7 texture descriptor gives better retrieval rate and fast and fast extraction time for texture feature.

• Journal of The Korean Astronomical Society
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• v.48 no.2
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• pp.155-164
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• 2015

In Kang (2015) we calculated the acceleration of cosmic-ray electrons at weak spherical shocks that are expected to form in the cluster outskirts, and estimated the diffuse synchrotron radiation emitted by those electrons. There we demonstrated that, at decelerating spherical shocks, the volume integrated spectra of both electrons and radiation deviate significantly from the test-particle power-laws predicted for constant planar shocks, because the shock compression ratio and the flux of inject electrons decrease in time. In this study, we consider spherical blast waves propagating through a constant density core surrounded by an isothermal halo with ρ ∝ r⁻ⁿ in order to explore how the deceleration of the shock affects the radio emission from accelerated electrons. The surface brightness profile and the volumeintegrated radio spectrum of the model shocks are calculated by assuming a ribbon-like shock surface on a spherical shell and the associated downstream region of relativistic electrons. If the postshock magnetic field strength is about 0.7 or 7 µG, at the shock age of ∼ 50 Myr, the volume-integrated radio spectrum steepens gradually with the spectral index from α_inj to α_inj + 0.5 over 0.1–10 GHz, where α_inj is the injection index at the shock position expected from the diffusive shock acceleration theory. Such gradual steepening could explain the curved radio spectrum of the radio relic in cluster A2266, which was interpreted as a broken power-law by Trasatti et al. (2015), if the relic shock is young enough so that the break frequency is around 1 GHz.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.04a
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• pp.89-97
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• 1998

This study is intended to investigate the seismic responses of bridge structures considering site effects. The site effects in the seismic analysis of bridge structures were classified into two parts. At first, the seismic responses of the structures on each "soil profile types" of the code were evaluated in accordance with code-specified method and compared with results of time-history analysis method. And next, as a second stage of the study, the responses of the two different soil with considerably different soil properties, even though they are classified to the same "soil profile types" of the code, were evaluated and compared each other. The first part of study is purposed to evaluate the applicability of code-specified method, while the other part is purposed to find the variance of the seismic responses from the different soil sites in the same soil profile types of the code. For the analysis, two major methods of the code, single-mode spectral anaysis and multi-mode spectral analysis, were used and the time-history analysis method which is expected to give more accurate responses was also used for the comparison purposes. For the time-history analysis, time-domain analysis technique of the lumped-mass model with frequency-independent soil springs and dampers was adopted and artificially generated spectra of the code was used as input motion. As the results of the study, the code specified methods for the seismic responses considering the site effects were verified to give the results in conservative side for the most of the cases. However, for the structures on the site with considerable flexibility, the responses of the bridge girders or deckplates by the code methods both in section forces and horizontal movement responses, may have much smaller values than the actual responses. Therefore, more detailed analysis considering the flexibility of the base soil may be required to have more reasonable results in girder responses.in girder responses.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.461-461
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• 2013

Over the last decade, zinc oxide (ZnO) thin films have attracted considerable attention owing to large band gap of 3.37 eV and large exciton binding energy of 60 meV at room temperature [1-3]. Recent interest in ZnO related researches has been switched into the fabrication and characterization of low-dimensional nanostructures, such as nano-wires and nano-dots that can be applicable to manufacture the optoelectronic devices such as ultraviolet lasers, light-emitting-diodes and detectors. Since the optical properties of ZnO nano-structures might be distinct from those of bulk materials or thin films, the low-dimensional phenomena should be examined further. In order to utilize such advanced optoelectronic devices, one of the challenges is how to control the surface state related emissions that are drastically increased with increasing the density of the nano-structures and the surface-to-volume ratio. This paper reports the synthesis and characterization of self-assembled ZnO hexagonal nano-disks grown by radio-frequency magnetron sputtering. X-ray diffraction data and scanning electron microscopy data showed that ZnO hexagonal nano-disks were nucleated on top of the flat surfaces as the film thickness reached to 1.56 ${\mu}m$ and then the number of nano-disks increased with increasing the film thickness. The lateral size of hexagonal nano-disks was ~720 nm and height was ~74 nm. The strong photo luminescence spectra obtained at 10 K was also observed, which was assigned to a surface exciton emission at 3.3628 eV arising from the surface sites of hexagonal nano-disks.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.527-536
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• 2016

This paper investigates seismic damage potential of recent September 12 M5.8 Gyeongju earthquake from diverse earthquake engineering perspectives using the accelerograms recorded at three stations near the epicenter. In time domain, strong motion durations are evaluated based on the accelerograms and compared with statistical averages of the ground motions with similar magnitude, epicentral distance and soil conditions, while Fourier analysis using FFT is performed to identify damaging frequency contents contained in the earthquake. Effective peak ground accelerations are evaluated from the calculated response spectra and compared with apparent peak ground accelerations and the design spectrum in KBC 2016. All these results are used to consistently explain the reason why most of seismic damage in the earthquake was concentrated on low-rise stiff buildings but not quite significant. In order to comparatively appraise the damage potential, the constant ductility spectrum constructed from the Gyeongju earthquake is compared with that of the well-known 1940 El Centro earthquake. Deconvolution analysis by using one accelerogram speculated to be recorded at a stiff soil site is also performed to estimate the soil profile conforming to the response spectrum characteristics. Finally, response history analysis for 39- and 61-story tall buildings is performed as a case study to explain significant building vibration felt on the upper floors of some tall buildings in Busan area during the Gyeongju earthquake. Seismic design and retrofit implications of M5.8 Gyeongju earthquake are summarized for further research efforts and improvements of relevant practice.

• Journal of the Korean Chemical Society
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• v.48 no.3
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• pp.229-235
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• 2004

For the study of hydrogen bonding phenomenon of high energetic compounds, we have been carried out a theoretical calculations for the nitromethane with the program Gaussian-98. The calculations at levels of restricted BLYP/6-311++G(d,p), B3LYP/6-311++G(d,p) and MP2/6-311++G have been performed to obtain molecular structures, hydrogen bonding effects and vibrational spectra of nitromethane monomer and dimer. The results show nitromethane is favored to make two hydrogen bonds between molecules and the nitromethane dimer is more stable than the monomer about 15.2, 19.4 and 32.6 kJ/mol for the BLYP, B3LYP, and MP2 level calculations, respectively.

• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.93-99
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• 2007

We investigated analytically and numerically the occurrence of modulation instability in fibers with periodic changes both in dispersion and gain. Previously, it has been known that the modulation instability is suppressed in dispersion managed solitons where dispersion is managed in such a way that the local dispersion alternates between the normal and the anomalous regimes. In this work, we enhanced the advantage of the dispersion management scheme by additionally introducing proper gain/loss profiles in fibers. The gain/loss profile is given by $\Gamma(z)=0.5/D(z)*(dD/dz)$, where D(z) represents the dispersion profile. The fundamental gain spectra of the modulation instability in the dispersion and gain managed fibers have been derived analytically and confirmed by numerical calculation. Our investigation reveals that in the dispersion and gain fibers the modulation instabilities are always much more suppressed compared to the case with only dispersion managed. In practical dispersion management schemes, dispersion profiles show discontinuity. and thus. the corresponding gain/loss profiles tend to be finite. In these cases, the gain/loss profiles were approximated by lumped gains/losses of finite values. Our numerical calculations confirm that this approximation also works well.

• Bulletin of the Korean Chemical Society
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• v.30 no.11
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• pp.2595-2602
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• 2009

Hexamer cluster of N,N-dimethylformamide(DMF) based on the crystal structure was investigated for the equilibrium structure, the stabilization energies, and the vibrational properties in the density functional force field. The geometry (point group $C_i$) of fully optimized hexamer clustered DMF shows quite close similarity to the crystal structure weakly intermolecular hydrogen bonded each other. Stretching force constants for intermolecular hydrogen bonded methyl and formyl hydrogen atoms with nearby oxygen atom, methyl C–H${\cdots}$O and formyl C–H${\cdots}$O, were obtained in 0.055 $\sim$ 0.11 and $\sim$ 0.081 mdyn/$\AA$, respectively. In-plane bending force constants for hydrogen bonded methyl hydrogen atoms were in 0.25 $\sim$ 0.33, and for formyl hydrogen $\sim$ 0.55 mdynÅ. Torsion force constants through hydrogen bonding for methyl hydrogen atoms were in 0.038 $\sim$ 0.089, and for formyl hydrogen atom $\sim$ 0.095 mdynÅ. Calculated Raman and infrared spectral features of single and hexamer cluster represent well the experimental spectra of DMF obtained in the liquid state. Noncoincidence between IR and Raman frequency positions of stretching C=O, formyl C–H and other several modes was interpreted in terms of the intermolecular vibrational coupling in the condensed phase.