• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.377-381
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• 2006

This paper describes experimental work to control supersonic jet noise using a mesh screen that is placed at the nozzle exit plane. The mesh screen is a wire-gauze screen that is made of long stainless wires with a very small diameter. The nozzle pressure ratio is varied to obtain the supersonic jets which are operated in a wide range of over-expanded to moderately under-expanded jets. In order to perturb mainly the initial jet shear layer, the hole is perforated in the central part of the mesh screen. The hole size is varied to investigate the noise control effectiveness of the mesh screen. A schlieren optical system is used to visualize the flow fields of supersonic jet with and without the mesh screen device. Acoustic measurement is performed to obtain the OASPL and noise spectra. The results obtained show that the present mesh screen device leads to a substantial suppression of jet screech tones. The hole size is an important factor in reducing the supersonic jet noise. For over-expanded jets, the noise control effectiveness of the mesh screen appears more significant, compared to correctly and under-expanded jets

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.231-235
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• 2009

The mainly objectives of this study was a combustion dynamics and instability characteristics in a model dump type combustor which is scale down of GE 7FA+e DLN 2.6 gas turbine combustor with running at Seo-Inchon combined cycle power plant. Model gas turbine injector has 2-stage swirl vane and it's reduced 1/3 size of the original one. The shape of plenum and combustor were designed for similar acoustic characteristics. As the result, this research have been shows the peak frequency of model combustor was changed quarter-wave mode to Helmholtz resonator mode in plenum and longitudinal mode in dump combustor at unstable flame conditions caused by the different of combustor temperature and fuel-air mixture distributions.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.54-60
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• 2017

In order to identify the characteristics of the flame transfer function gain, cold-flow transfer function was introduced, which is the part of the combustion instability research. Nitrogen and carbon dioxide was used to obtain the cold-flow transfer function and input/output variables was measured by hot wire anemometry. Density and fluid flow rate affect the cold-flow transfer function gain and peak frequency. In addition, acoustic resonance frequency affects the peak frequency of gain in the fuel feeding line.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.1
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• pp.232-238
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• 2013

This paper study the position estimation of MBK system according to the non-linear filter for non-Gaussian noise in underwater sensor networks. In the filter to estimate location, recently, the extended Kalman filter (EKF) and particle filter are getting attention. EKF is widely used due to the best algorithm in the Gaussian noise environment, but has many restrictions on the usage in non-Gaussian noise environment such as in underwater. In this paper, we propose the improved One-Dimension Particle Filter (ODPF) using the distribution re-interpretation techniques based on the maximum likelihood. Through the simulation, we compared and analyzed the proposed particle filter with the EKF in non-Gaussian underwater sensor networks. In the case of both the sufficient statistical sample and the sufficient calculation capacity, we confirm that the ODPF's result shows more accurate localization than EKF's result.

• Journal of Korean Foot and Ankle Society
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• v.14 no.2
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• pp.169-172
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• 2010

Purpose: The authors have experienced various lesions that simulate ganglion of the foot on the ultrasonography. The purpose of this study is to evaluate ultrasonographic findings of soft tissue lesions, which were interpreted as ganglion but confirmed as different lesions in the foot. Materials and Methods: We reviewed a database of patients with ganglion on the ultrasonography from two different institutions. There were 109 patients who underwent both ultrasonography and surgical confirmation. Twenty one lesions were identified, of which initial interpretation on the ultrasonography included ganglion which pathology revealed to be different lesions. All images were evaluated by one musculoskeletal radiologist, regarding size, margins, internal echogenicity of lesions, and presence of posterior enhancement. Results: Of 21 lesions, there were 6 fibrous tumors including fibroma, giant cell tumor of tendon sheath, and fibromatosis, 3 hemangiomas, 2 epidermal inclusion cysts, 2 chondromas, 2 angioleiomyomas, 1 trichilemal cyst, 1 neurofibroma, 1 granular cell tumor, 1 neurilemmoma, 1 neuromyxoma, and 1 nodular hidradenoma. Mean size of the lesion was 1.1 cm. Margins were smooth in 10, mild lobulation in 8 and marked lobulation in 3 lesions. Lesions were hypoechoic in 16, anechoic in 4 and isoechoic in 1 case. Posterior acoustic enhancement was definitely present in 5 lesions. Conclusion: On the ultrasonography, various soft tissue lesions of the foot may be confused with ganglion. During surgical resection care should be given even to a simple ganglion as it might turn up to be a solid lesions such as fibrous tumors.

• Journal of The Korean Association of Information Education
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• v.20 no.4
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• pp.323-332
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• 2016

A robot's recognition and diagnosis of pronunciation and its speech are the most important interactions in RALL(Robot Assisted Language Learning). This study is to verify the effectiveness of robot TTS(Text to Sound) technology in assisting Korean English language learners to acquire a native-like accent by correcting the prosodic errors they commonly make. The child English language learners' F0 range and speaking rate in the 4th grade, a prosodic variable, will be measured and analyzed for any changes in accent. We compare whether robot with the currently available TTS technology appeared to be effective for the 4th graders and 1st graders who were not under the formal English learning with native speaker from the acoustic phonetic viewpoint. Two groups by repeating TTS of RALL responded to the speaking rate rather than F0 range.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.539-546
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• 2003

The GaN/sapphire layered structure is a potential candidate for high frequency devices due to high acoustic velocity of sapphire. Generally, the GaN thin films are epitaxially grown on c, a, and r-plane sapphire substrates. In this study, wave equations of GaN/sapphire structure were calculated according to crystallographic relationship between GaN layer and sapphire substrate. On each plane, the shear velocity was changed by the kH of GaN layer and propagation direction on sapphire substrate. We found electromechanical coupling constant of r-plane was better than the others. As a result, elastic stiffness and electromechanical coupling constant of materials are affected by a cut and an orientation of substrate. GaN/r-plane sapphire structure is more advantageous for high frequency SAW devices.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.5
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• pp.1-6
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• 2011

LED(Light Emitting Diode) components have advantages of longer lifetime, lower power consumption and easy-to-control, compare to normal lamp and fluorescent light, according to the development of recent technologies. Thus, lots of illuminations which utilize LED components could be used. Recently, Visible Light Communication(VLC) which is a part of communication technologies, utilizing high speed response characteristic of LED components, started receiving public attention. In case of VLC, there is no need of frequency allocation due to no use of radio, but also no interference exists during data transmission, much different in ISM((Industrial Scientific Medical band). This is the reason why a lot of research results about VLC are becoming issued. In this paper, a survey of feasibility for using VLC utilizing an original LED illumination for underwater applications has been done and a primitive possibility of its application has been examined.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.42 no.3 s.303
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• pp.33-40
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• 2005

In order to successfully exploit underwater resources, the first step would be a marine environmental research and exploration on the seafloor. Traditionally one sets up a long-term underwater experimental unit on the seafloor and retrieves the unit later after a certain period time. Essential to these applications is the reliable teleoperation and telemetering of the unit. This study presents ultrasonic-wave remote control system and an underwater sound recognition algorithm that can identify the sound signal without the influence of disturbances due to underwater environmental changes. The proposed method provides a means suitable for units which require low power dissipation and long-time underwater operation. We demonstrate its ability of securing stability and fast sound recognition through experimental methods.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.8
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• pp.15-21
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• 2020

We improved the sound pressure of the speaker and allowed the speaker to rotate 360 degrees to improve the effectiveness of the acoustic type bird repellent system. The prototype of the bird repellent system was developed by evaluating sound pressure characteristics by distance and direction and installing orchards. As a result of the evaluation, the extermination sound pressure increased from a distance of about 30 m to a maximum of 60 m, and through the rotary speaker, the extermination distance could be widened in all directions without specific direction.