• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.6
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• pp.543-550
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• 2003

In order to saving the energy for HVAC system of buildings, utilization of wind-induced cross ventilation is thought to be promising. However, utilization of natural ventilation alone is not sufficient for maintaining the human thermal-comfort such as in hot and humid regions. A hybrid air conditioning system with a controlled natural ventilation system, or combination of natural ventilation with mechanical air conditioning is thought to overcome the deficiency of wind-driven cross ventilation and to have significant effects on energy reduction. This paper describes a concept of hybrid system and propose a new type of hybrid system using radiational cooling with wind-induced cross ventilation. Moreover, a radiational cooling system is compared with an all-air cooling system. The characteristics of the indoor environment will be examined through CFD (Computational Fluid Dynamics) simulation, which is coupled with a radiation heat transfer simulation and with HVAC control in which the PMV value for the human model in the center of the room is controlled to attain the target value.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.1
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• pp.27-31
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• 2012

In this paper, we constructed an array of speaker system with directivity by using FXLMS(Filtered-X LMS) algorithm and confirmed its directivity. The front $0^{\circ}$ characteristics of the controlled speaker was suppressed by interfering it with the control signal produced with filter coefficients optimized with respect to the $180^{\circ}$ characteristics of the rear speakers. The directivity of the array of rear speakers was measured and the damping effect of the signal from the front speaker array was confirmed. The frequency characteristics and directivity was investigated by using the adaptive filter coefficients on damping, the damping on the control point was verified in all the frequency range. In 100Hz, 200Hz, 1000Hz regime, the damping effect was observed in the range of front $60^{\circ}{\sim}100^{\circ}$.

• Journal of the korean Society of Automotive Engineers
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• v.8 no.4
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• pp.43-55
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• 1986

In the studies of noise reduction, it is important to know the generation mechanism of noise in order to identify the noise source. The relation between the structural vibration and the radiated sound is very complex and so this paper deals with a simplified radiation model that was originally developed as a verification tool for the acoustic intensity measurement procedure. As the first step for the identification of the noise source, this study deals with the noise evaluation by measuring sound pressure. On the next step, the acoustic radiational pattern is determined by the acoustic intensity method and this paper established that the acoustic intensity method is effective on the detection of noise. In the study, furthermore, the method could be used to predict the change in the sound radiational characteristics with the attachment of absorber and could be used in determining the attachment position.

• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.614-622
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• 2006

A Study on the characteristics of $Ta/Ta_2O_5/MnO_2$ capacitor applied $MnO_2$ by means of pyrolysis of manganese nitrate solution was carried out. Single phase of $MnO_2$ was obtained in the pyrolysis temperature range of 230 to $250^{\circ}C$ by TG/DSC analysis on manganese nitrate solution. Temperature of pyrolysis, concentration of manganese nitrate solution and the number of pyrolysis were selected for the basic parameters of embodying $MnO_2$ solid electrolyte and then the effects of these parameters on the characteristics of capacitor were estimated. The characteristics of capacitor pyrolyzed radiationally was superior to that of capacitor pyrolyzed convectionally on the basis of these optimized parameter conditions. It was verified that radiational pyrolysis formed smaller spherical $MnO_2$ particles than those of convectional one relatively and these facts resulted in forming uniform and dense solid electrolyte layer into the microporous sintered body of capacitor.

• Journal of IKEEE
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• v.16 no.4
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• pp.290-296
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• 2012

In this study, an effective echo-suppression and cancellation technique using reflectors in semi-anechoic chamber and time-domain measurement is proposed. By using the proposed technique, the uniformity of electric field in QZ(Quiet Zone) could be improved and the antenna test environments similar to the fully anechoic chamber could be accomplished. The performances of the proposed test environments is verified with the simulated and measured data. And it is demonstrated that this test environment is possible to use the measuring the radiational characteristics of a small antenna in VHF band.

• Journal of the korean Society of Automotive Engineers
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• v.11 no.1
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• pp.57-67
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• 1989

Acoustic intensity method is applied to a 4-cylinder gasoline engine in order to identify the noise sources and the response characteristics. Acoustic intensity is analyzed by 1/3 octave band filter for each center frequency. Radiational characteristics of acoustic intensity at overall and the maximum intensity level are represented by using the contour and three-dimensional plot. It is verified that this method is effective to the assessment of engine noise. It can be found that the maximum intensity is radiated from the front side of the engine under idling condition and the right side of it under 2, 000 rpm running with no loading condition at overall level, and also that the maximum intensity is radiated from the oil pan and the intake and exhaust manifold at the center frequency of 100 Hz.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.1
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• pp.9-23
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• 1997

A numerical study of a two-layer, stratified flow is investigated, using the implicit finite difference method in one dimension. The results of computational method have been tested and, in case of lock exchange flow, compared with the results of experimental data. The results of model experiments with various interfacial, bottom friction coefficients along with various time weighting factor of numerical scheme and dissipative interface are shown and discussed. Two-layer model experiment has been also carried out to investigate the generation and propagation characteristics of internal tidal wave over the steep bottom topography under stratified condition. The internal wave seems to well radiate through the downstream boundary under the experiments adopting radiation conditions both at two layers and only at upper layer, confirming the applicability of radiational boundary condition in stratified flows. It is also shown that the internal wave through the downstream boundary propagates more actively with increasing thickness of lower layer in the downstream. This implies that the potential tidal energy in the interface will depend upon the thickness of lower layer for the constant thickness of upper layer.

• Journal of the Korean Graphic Arts Communication Society
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• v.19 no.2
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• pp.12-21
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• 2001

For the purpose of determining characteristics of widely used commercial medical x-ray films, which are used for obtaining the Linac-grams for radiational treatment of cancers, we placed several commercial x-ray films at a fixed distance form the linear accelerator. After varying the exposed amount of radiation step by step, we could obtain a continually increasing density image for each film whose densities were determined by microdensitometer readings. The characteristic curves of the films were obtained by plotting the densities vs. the exposed radiation amounts, and their ${\gamma}$ values were determined. These values can be used to suggest a minimum necessary amount of exposed radiation to get a useful Linac-gram. The measured ${\gamma}$ values of the characteristic curves of the Kodak-DVP/RA-1 film were 1.73 when used 6MV x-ray, 1.70 when used 15MV of intensity. For the Konica-AX film, ${\gamma}$ values were 1.29 and 1.18 respectively. The result suggests that the effective conditions for high resolution of a L-gram be 6 MV of x-ray intensity and about 3 rad of exposed dose on a Kodak-DVP/RA-1 film.

• Journal of the Korean association of regional geographers
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• v.21 no.3
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• pp.608-617
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• 2015

This paper synthetically analyzes micrometeorological data and geomorphological features of Doeksan-ri Eoreumgol(ice valley) Yeongdeok-gun in order to investigate occurrence characteristics of the ice valley and a mechanism for freezing in summer. This ice valley is located in the distal end of a talus and intensity of cooling and freezing in summer seems to be related to morphology and dimensions of talus. Cooling in the ice valley is generated by cold air flows that move down to the bottom of talus from high mountains through pores and voids, then debris in talus is supercooled by the cold air. For it forms a stable state in and around voids cold air is stagnating in the lower end of talus. This causes freezing in summer at outpour points. Furthermore humidity condition of external air and vaporization heat is a key factor when freezing.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.257-262
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• 1999

The selective area growth of GaN by metal organic chemical vapor deposition has been carried out on GaN/ sapphire substrate using $SiO_2$ mask. We investgated the effect of growth parameters such as flow rate of $NH_3$(500­~1300sccm) and the growth temperature(TEX>$950~1060^{\circ}C$) on the growth selectivity and characteristics of GaN using the Scanning Electron Microscopy(SEM). The selectivity of GaN improved as flow rate of NH, and growth temperature in­creased. But the grown GaN shapes on the substrate windows was independent of the flow rate of $NH_3$. On the pattern shapes such as circle, stripe, and radiational pattern(rotate the stripe pattern by $30^{\circ}, 45^{\circ}$), we observed the hexagonal pyramid, the lateral over growth on the mask layer, and the difference of the lateral growth rate depending on growth condition.