• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.79-86
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• 2005

The role of the injector as an acoustic resonator is studied for the high performance rocket engine adopting the gas-liquid scheme injector. Acoustic behavior in the combustor with single injector is investigated numerically adopting linear acoustic analysis for cold condition. Acoustic-damping effect of the injector is evaluated by damping factor as a function of the injector length. From the numerical results, it is found that the injector can play a significant role in acoustic damping and the optimum length of the injector corresponds to half of a full wavelength of the longitudinal mode with the acoustic frequency to be damped in the chamber. In baffled chamber, the optimum lengths of the injector are calculated as a function of baffle length for both cold and hot conditions.

• Journal of the Korean Magnetics Society
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• v.5 no.3
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• pp.165-170
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• 1995

NMR measurement has been studied for protons in pre-polarized flowing water by a separated detector working at high field far away from the measured field region where the transition of protons is occurred by the pertur-bation of RF energy. The conditions for NMR signal were optimized on the amplitude and frequency of modulation field, the RF field of detector, water speed, and RF field at the measured field region. The NMR signal with the full width of 320 nT at the half maximum in Lorentzian curve and with signal to noise ratio of 10.5 was measured in the range from a few ${\mu}T$ to mT, and its shape and amplitude were independent of the measured field intensity and its uniformity.

• Korean Journal of Optics and Photonics
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• v.25 no.2
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• pp.95-101
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• 2014

When voltage is applied on the metal layer of a surface plasmon resonance (SPR) sensor, electric field excitation causes charge accumulation on the metal surface. This alters not only the optical properties of the metal but also the SPR angle. In this study we investigate this effectby performing experiments using solutions of various pH values, and we obtain the relation between total surface charge and SPR angle. The curves for the various pH conditions become coincident. We compare our results to those from an earlier space charge layer (SCL) model, and suggest a modified SCL model which explains our result well. This result will be useful in applications of SPR sensors, and in studying the optical properties of thin metal layers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.6
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• pp.490-496
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• 2014

The thickness of knee joint cartilage causes most diseases of knee. Therefore, an articular cartilage segmentation of knee magnetic resonance imaging (MRI) is required to diagnose a knee diagnosis correctly. In particular, fully automatic segmentation method of knee joint cartilage enables an effective diagnosis of knee disease. In this paper, we analyze a well-known level-set based segmentation method in brain MRI, and apply that method to knee MRI with solving some problems from different image characteristics. The proposed method, a fully automatic segmentation in whole process, enables to process faster than previous semi-automatic segmentation methods. Also it can make a three-dimension visualization which provides a specialist with an assistance for the diagnosis of knee disease. In addition, the proposed method provides more accurate results than the existing methods of articular cartilage segmentation in knee MRI through experiments.

• Proceedings of the Optical Society of Korea Conference
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• 2004.07a
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• pp.54-55
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• 2004

• Computational Structural Engineering
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• v.11 no.1
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• pp.58-69
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• 1998

본 기사에서는 진동을 유발하는 기계장치의 지지 형태에 따른 해석 모델링 기법을 소개하는데 중점을 두었다. 다양한 해석 모델등 중 어느 것을 사용할 것인가는 주어진 조건이나 정보, 요구되는 정확도, 효율성 등을 고려하여 설계 엔지니어가 판단하여야 한다. 또한 진동 하중을 받는 구조물에 대한 설계 및 해석을 하기 위해서는 기계장치에 대한 사양 및 요구사항, 지반의 물리적 성질, 외부 환경적 요인 등을 파악하여야 한다. 종합적인 판단하에 구조물을 모델링하여 얻어진 결과들을 가지고 실제 설계 요구 조건과 비교, 검토를 하여야 하며, 이러한 설계 조건들은 다음과 같은 사항들을 포함한다. 1) 지반이나 구조물의 파괴, 과도한 처짐 등에 대한 정적 강도를 검토한다. 2) 진동 응답에 대한 최대 변위, 최대 속도, 최대 가속도를 검토한다. 3) 최대 확대계수, 최대 동적하중 계수, 공명조건, 최대 전달계수 등을 포함한 동적 거동을 검토한다. 4) 실제 구조물에서 일어날 수 있는 모든 모드들에 대한 검토를 한다. 5) 기계, 구조물, 연결부 등에 대한 파괴 가능성을 고려한다. 6) 사람이나 기계장치의 작동 등에 대한 환경적 요구조건의 만족 여부를 검토한다.

• Science of Emotion and Sensibility
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• v.14 no.3
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• pp.403-414
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• 2011

The current study examined brain regions associated with aesthetic experience to fractal images using functional MRI. The aesthetic estimations of the images showed that there is a general consensus regarding the perception of beautiful images. Out of 270 fractal images, fifty images rated highest(beautiful images) and fifty images rated lowest(non-beautiful images) were selected and presented to the participants. The two conditions were presented using the block design. Frontal lobes, cingulate gyri, and insula, the areas related to the cognitive and emotional processing in aesthetic experience, were activated when beautiful images were presented. In contrast, the middle occipital gyri and precuneus, the areas associated with experience of negative emotions, were activated when non-beautiful images were presented. The conjunction analysis showed activations in temporal areas in response to beautiful images and activations in parietal areas in response to non-beautiful images. These results indicate that beautiful images elicit semantic interpretations whereas non-beautiful images facilitate abstract processes.

• Journal of the Korean Magnetics Society
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• v.24 no.1
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• pp.18-21
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• 2014

The microwave absorption ($P_{tot}$), which is the double integration value of ferromagnetic resonance signal, propositional to the saturation magnetization, and the increase of the $P_{tot}$ measured during the thermal reaction time expect the growth process of the nanoparticles. Therefore, in this work, we measured the $P_{tot}$ in order to obtain the growth time of iron oxide nanoparticles after thermal decomposition of $Fe(acac)_3$ precursor at aging temperature $T_a=273$, 300 and $324^{\circ}C$, respectively. The best condition for monodisperse nanoparticles was obtained at $T_a=300^{\circ}C$, which condition showed the most rapid increase of $P_{tot}$ with thermal reaction time. Finally, the rapid growth rate was necessary condition for the synthesis of iron-oxide monodisperse nanoparticles.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.911-915
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• 2006

가스히터의 연소로부터 발생하는 소음 및 진동의 주원인은 연소소음(combustion roar)과 연소진동음(combustion oscillation)이다. 연소음의 특징은 음압이 넓은 주파수대에 걸쳐 비교적 일정하게 분포하고 있다. 본 논문에서 언급하고 있는 가스히터 초기 조건에서 볼 수 있는 상황으로 소음레벨이 낮고 진동 문제도 발생하지 않는다. 반면 연소진동음은 연소실내 기체의 고유진동수에 대하여 버너계가 Positive Feedback을 일으켜 공진할 때 발생되는 소음 및 진동이다. 연소진동의 발생 원인은 앞서 지적한 바와 같이, 연소할 때의 연소 진동수와 연소실의 구조적 고유진동수가 일치하면 큰 진동 및 소음을 발생시킨다. 따라서 소음 및 진동을 해결 할 수 있는 방법은 두 개의 고유진동수가 일치하지 않도록 하는 방법을 강구하여야 한다. 첫 번째 방법으로는 버너에서 연료와 공기량의 비율을 변화 시켜 진동수를 변화 시키거나, 연료와 공기의 통로길이, 연소실내에서의 연료와 공기의 혼합속도를 변화 시키는 방법이 있다. 두 번째 방법으로, 연소실의 고유진동수를 변화 시키는 방법으로 연소실의 길이나 덕트의 길이를 변경시켜 고유진동수의 주파수를 변경시키는 방법이다. 본 논문에서는 연소실의 조건을 변경하여 공명을 회피하는 방법을 채택하였고, 좋은 결과를 얻을 수 있었다.

• The Journal of the Korea Contents Association
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• v.19 no.6
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• pp.418-423
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• 2019

The purpose of this study was to determine how the different number of channels of coils were related in the perceived signal intensity under identical parameters and area. Dedicated knee phantoms were scanned consecutively using both of the 16-channel and 8-channel knee coils. The T1 weighted and T2 weighted sequences were acquired using both coils to compare the signal intensities according to the number of channels. As a result, the 16-channel knee coils outperformed the 8-channel knee coils and the signal intensity was significantly increased in both of the T1 and T2 weighted images with the 16-channel coil. In conclusion, it is considered that better signal intensities and more clinical utility can be provided, when coils with more number of channels are used rather than using the coils with smaller number of channels.