• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.254-257
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• 2010

Acoustic design parameters of a Helmholtz resonator are studied experimentally and numerically for acoustic stability in a model acoustic tube. Acoustic damping is quantified by the amplitude of the fluid velocity in mass-spring-damper system. The length of an orifice, the volume of a cavity, and the diameters of an orifice and a cavity in the resonator are selected as design parameters for tuning of the resonator. It is found that acoustic damping capacity is increased by shorter orifice and longer cavity in the resonator. As the ratio of the orifice diameter to the cavity diameter increases in the resonator, the damping capacity decreases.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.236-239
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• 1998

We constructed a frequency doubler with a frequency-stabilized Nd:YAG Laser, a nonlinear crystal KTP, and an external resonant cavity. Using type II phase-making method and a resonant cavity, one usually have a serious problem that the second harmonic conversion efficiency is decreased greatly, for under usual circumstances ordinary ray and extraorninary ray cannot be resonated in a cavity simultaneously. With the change of temperature and incident angle of KTP, we found an optimized condition for the phase-matching and double-resonance. As a result we produced 26 mW of green light with 318 mW of fundamental laser power from a cw Nd:YAG laser.

• Korean Journal of Cognitive Science
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• v.18 no.2
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• pp.159-178
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• 2007

Lee & Kang (2002) showed that simultaneous phonological rehearsal significantly delayed the performance of multiplication but not subtraction, whereas holding an image in the memory delayed subtraction but not multiplication. This result indicated that arithmetic function is related to working memory in a subsystem-specific manner. The aim of the current study was to examine the neural correlates of previous finding using fMRI. For this goal, dual task conditions that required suppression or no suppression were manipulated. In general, several areas were more activated in the interference conditions than in the less interference conditions, although both conditions were dual condition. More important finding is that the specific areas activated in the phonological suppression rendition were right inferior frontal gyrus, left angular, and inferior parietal lobule, while the areas activated in the other condition were mainly in the right superior temporal gyrus and anterior cingulate gyrus. Furthermore, the areas activated in the phonological or visual less suppression condition were right medial frontal gyrus, left middle frontal gyrus, and bilateral medial frontal gyri, anterior cingulate cortices, and parahippocampal gyri, respectively. These results revealed that sharing the processing code invokes interference, and its neural basis.

• Journal of the Mineralogical Society of Korea
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• v.17 no.1
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• pp.1-9
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• 2004

Copper(II) sorbed on kaolinite (KGa-lb) was studied using electron paramagnetic resonance (EPR) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The sorbed copper(II) had an isotropic EPR signal with $g_{iso}\;=\;2.19$ at room temperature. At 77 K, the isotropic signal converted to an axially symmetric anisotropic signal with $g_{\$\mid$}\;=\;2.40,\;g_{\bot}\;=\;2.08,\;and\;A_{\$\mid$}\;=\;131\;G$. These EPR results suggest that the sorbed copper(II) forms an outer-sphere surface complex with a tetragonally distorted $CuO_{6}$ octahedral structure on the kaolinite. In the sorption measurement, the amount of sorbed copper increased with increasing pH of the solution. However, the intensity of the isotropic EPR line was not directly proportional to the amount of sorbed copper. This discrepancy was resolved by assuming the formation of a surface precipitate at higher pH that is invisible by EPR. The EXAFS data confirmed the existence of the surface precipitate. The best fit for the EXAFS of the sorbed copper showed that each copper on the kaolinite had 6.8 copper neighbors located $3.08\;{\AA}$ from it, in addition to the first shell oxygen neighbors, including 4 equatorial O at $1.96\;{\AA}$ and 2 axial O at $2.31\;{\AA}$. This work shows that the local environment of the copper sorbed on the kaolinite changes as a function of pH and surface loading, and that the EPR and EXAFS are useful in studying such changes.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.7
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• pp.915-921
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• 2020

Thermoacoustic instability caused by air conditioning in a combustion chamber has emerged as a problem that must be solved to establish a stable combustion system. Thermoacoustic instability is largely divided into primary and secondary acoustic instability. In this study, an experimental study of the effects of heat losses was conducted to investigate the mechanism of secondary acoustic instability. To generate the secondary acoustic instability, a quarter-wavelength resonator with one open end and one closed end was used, and the inside of the resonator was filled with premixed gases. Subsequently, secondary acoustic instability with downward-propagating flames could be realized via thermal expansion on the burnt side. To control heat losses qualitatively, an additional co-axial tube was installed in the resonator with air or nitrogen supply. Therefore, additional diffusion flames can be formed at the top of the resonator depending on the injection of the oxidizer into the co-axial tube when rich premixed flames are used. Consequently, secondary acoustic instability could not be achieved by increasing heat losses to the ambient when the additional diffusion flame was not formed, and the opposite result was obtained with the additional diffusion flame.

• Journal of KSNVE
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• v.8 no.6
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• pp.1113-1120
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• 1998

For an analysis of some Helmholtz resonators, it is likely to be more appropriate to consider acoustic field within cavity than just the 1-DOF analogous model. However, a design method that considers increased parameters than the lumped model. is not a trivial process due to the trade-off effect among the parameters. In this paper. the genetic algorithm. one of the optimization technique that rapidly converges to global fittest solution and robust convergence. is applied to the design process of Helmholtz resonators. Results show that the genetic algorithm can be successfully and efficiently used to find the resonant frequencies for both lumped model and distributed model.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.224-225
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• 2011

전자 사이클로트론 공명 이온원(Electron Cyclotron Resonance Ion Source; ECR 이온원)을 사용하여 다가(multi-charged) 이온빔을 인출하고 이온들을 분리하였다. 사용된 ECR 이온원은 그림 1과 같은 구조를 가진다. 그림 1에서 축자장을 만드는 자석(axial magnet)은 세 뭉치의 상전도 전자석으로, 그리고 육극자장을 만드는 자석(hexapole magnet)은 영구자석으로 되어 있으며 14.5 GHz 고주파는 도파관을 통하여 용기의 축과 평행한 방향으로 입사된다. 헬륨, 아르곤, 메탄(CH4), 이산화탄소(CO2)를 사용하여 빔 인출 및 이온 분리 실험을 진행하였으며, 본 논문에서는 운전조건의 최적화 과정을 수행하기 전에 진행된 초기 실험결과들에 대하여 논의한다. 그림 2는 헬륨을 사용한 경우의 질량 스펙트럼이다.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.39.1-39.1
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• 2009

중성입자가 함께 존재하는 불균일한 플라즈마 내로 입사하는 전파들은 플라즈마의 전자 밀도와 전자-중성입자 충돌에 의해 영향을 받게 된다. 특히 전자들의 운동이 중요한 높은 주파수 파동들은 상위 혼합 공명(Upper Hybrid Resonance)과 주변 자기장 현상에 의한 파동 모드 변환(mode conversion)으로 전파의 성질이 변하게 된다. 그리고 전자-중성입자에 의한 충돌은 에너지의 감쇄 등의 영향을 미치게 된다. 이러한 조건을 모두 고려한 유체 수치 모델을 이용하여 지구의 전리층이나 약한 자기권을 가지고 있는 행성 대기와 같이 플라즈마와 중성입자가 섞여있는 매질에서의 전자기파 파동의 특성을 조사하였다. 주파수, 중성대기 밀도 및 입사 각도에 따라 파동의 공명 흡수량과 감쇄량을 각각 알아본다.

• Journal of KSNVE
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• v.10 no.1
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• pp.33-40
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• 2000

With the increased requirement for automobile noise, a design fo mufflers with higher performances becomes more important in recent days. For a design of some mufflers, it must satisfy both minimizing back pressure and maximizing sound attenuation in broad range of frequecny. Even for a simple Helmholtz resonator, an important element in a muffler, a resonator design with accurate resonant frequency is difficult if one want to consider standing waves within the cavity. In this paper, the genetic algorithm, one of the optimization technique with high capability of global fittest solution and robust convergence, is applied to the design process of mufflers. Results show that the genetic algorithm can be successfully and efficiently used to find the fittest model for both mufflers and Helmoltz resonators.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.19-22
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• 2004

In the future engine with high performance, the gas-liquid scheme injectors will be adopted and the role of the injector as an acoustic resonator is investigated as an advanced study The injector can play a significant role in acoustic damping and the optimum length of the injector to maximize the damping capacity is calculated as a function of baffle length.