• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.235-239
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• 2005

A 30-tonf-class fullscale thrust chamber for the application to a LEO SLV has been combustion tested over the wide ranges of a mixture ratio and a chamber pressure. The thrust chamber designed for an open cycle engine with a turbopump was tested with a ablative combustion chamber instead of a regenerative chamber to first evaluate its performance and function. The test results revealed stable combustion characteristics. The hardware survived the harsh environment and showed very sound functional characteristics. The estimated combustion efficiency of the chamber turned out to be 95% and a specific impulse at sea level was estimated as 254sec, which are comparable to or above the predicted design values.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.55-55
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• 2008

압전폴리머 PVDF(polyvinylidene difluoride)의 기판소재를 기반으로 한 디스플레이 소자를 연구하였다. 압전 폴리머 PVDF의 양면은 두께 300nm정도의 ITO(Indium Tin Oxide)를 TCO(Transparent conducting oxide)로 R2R(roll to roll)증착하였으며, 이를 적외선 계열 Pulsed Laser로 상온 건식 에칭을 통해 패턴해내고, 이후 고진공 환경에서 Alq3 를 기반의 유기발광소자를 제작하였다. 전기적 신호에 대해서 기계적인 작동이 가능한 투명 압전 폴리머 재료를 디스플레이 발광소자의 기판 소재로 사용함으로써, 궁극적으로 발광기능과 더불어 압전효과에 의한 스피커 기능이 한 개의 개체내에서 독립적으로 구현될 수 있도록 설계하고, 기술적으로 실현시켰다는 점이 본 연구의 의의라고 할 수 있다. 이를 위해서, 섭씨 80도 이상의 온도에서 압전 성질을 상실하는 것으로 알려진 PVDF에 대해서 투명산화전극을 레이져를 이용한 비가열식 승화방법을 통해 패턴화하는 것을 사용했으며, 밀리미터 단위에서 수십 마이크로미터 수준까지 패턴화할 수 있었다. 제작된 복합형 유연 OLED소자는 기계적으로 휘어진 상태에서도 발광 성능과 스피커 성능을 각각 독립적으로 보였으며, Alq3에 의한 녹색발광을 보임을 확인하였고, 이 경우 양자효율은 약 3%이하의 값을 보였다. 또한 각주파수별 음압(SPL: Sound Pressure Level)측정 결과는 압번폴리머가 가청주파수 영역에서 작동함을 보였으며, 고주파영역에서의 SPL값이 증가하는 전형적인 PVDF사용 필름 스피커의 특성을 보였다. 이로부터 제작된 복합형 소자는 본 연구에서 제안된 목적에서 보인 것과 같이, 두 개의 기능이 서로간의 간섭없이 독립적으로 한 개의 개체 내에서 작동함을 확인할 수 있었다. 본 연구 결과로부터 새로운 유연 전자 소자에 대한 디자인 개념을 제시하고, 기타 다른 기능이 접합된 형태의 신개념 전자 소자를 제안하는 것도 가능할 것으로 기대된다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.601-607
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• 2016

Piezoelectric thick films of soft $Pb(Zr,Ti)O_3$ (PZT) based commercial material (S55) were fabricated using a conventional tape casting method. Ag-Pd electrodes were printed on the piezoelectric film at room temperature and all 5 layered films with a dimension of $12mm{\times}16mm$ were successfully laminated for a multi-layered piezoelectric ceramic actuator. The laminated specimens were co-fired at $1,100^{\circ}C$ for 1 h. A flat layered and dense microstructure was obtained for the $112{\mu}m$ thick piezoelectric actuator after sintering process. Thereafter, a prototype piezoelectric speaker was fabricated using the multi-layered piezoelectric ceramic actuator which can operate as a bimorph. Its SPL (sound pressure level) characteristic was also evaluated for speaker application. Frequency response revealed that the output SPL with a root mean square voltage of 10 V increased gradually to the highest peak of 87.5 dB for 1.5 kHz and exhibited a relatively stable behavior over the measured frequency range (${\leq}20kHz$) at a distance of 10 cm, implying that the fabricated piezoelectric speaker is potential for speaker applications.

• Journal of Distribution Science
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• v.14 no.12
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• pp.79-87
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• 2016

Purpose - Since 1990, the sudden stop in capital flows has caused the economic crisis. The purpose of this research is to suggest the policy measures to mitigate the risk of the sudden stop in capital flows. To this end, we examine the theoretical framework and analyze the case study for countries which are faced with the sudden stop. Also we examine the structural problems of the foreign exchange market in Korea and derive the policy implications to prevent the sudden stop. Research design, data, and methodology - The criteria of whether the sudden stop in capital flows occurs are based upon Calvo et al. (2008). In case the proxy variable for the balance of capital account decreases from the average by over twice standard deviation, we determine that the sudden stop occurs for that country. The sample period is from January 1990 to December 2008, as in Calvo (2014). The sample countries are 17 developed countries and 19 emerging market countries, which are different from those of the previous papers as Agosin and Huaita (2012), and Calvo (2014). When the exchange market pressure index(EMPI) is deviated from the average by over three times standard deviation, we determine that the foreign exchange market is unstable for that country. Results - We find that the characteristics of the sudden stop in capital flows are the bunching or contagion among countries, the rapid drop in real effective exchange rate, and the huge decrease in foreign exchange reserves. Many countries tried to increase foreign exchange reserves and regulate capital flows. Also the foreign exchange market in Korea are found to be the volatile exchange rate, the vulnerable external debt and careless management of the foreign exchange derivatives transaction risk. Conclusions - To lessen the risk in the sudden stop of capital flows, this research suggests the some useful policy measures. To enhance the foreign exchange and distribution market stability, we should improve the price mechanism of exchange rate, hold the appropriate level of foreign exchange reserves, prevent excessive inflows of foreign exchange and promote sound transactions of foreign exchange derivatives.

• The Journal of the Acoustical Society of Korea
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• v.20 no.6
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• pp.57-65
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• 2001

In this paper, we designed the acoustic horn for magnetostrictive ultrasonic transducers in a theoretical manner, and validity of the analysis was verified through comparison with the results of finite element analysis. Results of the two analysis methods showed good agreement with each other. The theoretical method can fairly quickly determine the horn length that satisfies given frequency specification, but also has the drawback that it is applicable only to the frequency range over the cut-off frequency. According to the results, the catenoidal horn can provide larger amplification than the exponential horn. It was also found that it is more desirable for the region having the catenoidal curvature to be as short as possible to achieve larger amplification of the transducer deformation. Based on the analysis results, a magneto-strictive transducer sample was fabricated and its performance was evaluated experimentally. The transducer has the resonance frequency of 19.3 ㎑ as well as the maximum SPL of 199 dB, and shows the omni-directional radiation pattern.

• Archives of Plastic Surgery
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• v.39 no.1
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• pp.25-30
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• 2012

Background : The soft palate functions as a valve and helps generate the oral pressure required for normal speech resonance. Speech problems and nasal regurgitation can result from a soft palatal defect. Reduction of the size of the velopharyngeal orifice is required to compensate for the lack of mobility in a reconstructed soft palate. We suggest a large volume folded free flap for reduction of the caliber and a palmaris longus tendon sling for suspension of the reconstructed palate. Methods : Six patients had total soft palate resection for tonsillar cancer and reconstruction with a large volume folded radial forearm free flap combined with a palmaris longus sling. A single surgeon and speech therapist examined the patients with three standardized speech assessment tools: nasometer test, consonant articulation test, and speech acuity test performed for speech evaluation. Results : Mean nasalance score was 76.20% for sentences with nasal sounds and 43.60% for sentences with oral sounds. Hypernasality was seen for oral sound sentences. The mean score of the picture consonant articulation test was 84% (range, 63% to 100%). The mean score of the speech acuity test was 5.84 (range, 5 to 6). These mean ratings represent a satisfactory level of speech function. Conclusions : The large volume folded free flap with a palmaris longus tendon sling for total soft palate reconstruction resulted in satisfactory prognosis for speech despite moderate hypernasality.

• Explosives and Blasting
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• v.31 no.1
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• pp.11-22
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• 2013

This study compared and analysed ground vibration, size of underwater background noise in fish farms and underwater object noise of blasting and obtained ground vibration prediction equation through a regression analysis and correlation equation between underwater object noises in order to predict degrees of underwater noise in blasting and organize underwater noise control regulations. Before the study, when background noise of fish and shellfish farms with different conditions was measured, levels of background noise were different according to environmental characteristics of each farm. Ground vibration which causes underwater noise was measured to obtain a correlation equation between ground vibration and underwater object noise. Therefore, if underwater noise is predicted for each construction with a use of a correlation and permissible standards appropriate for each condition are applied for design and construction, financial loss from damages to fish and shellfish caused by development of insufficient technological and engineering logic can be prevented and successful construction with safety of underwater creatures guaranteed can be achieved.

• The KSFM Journal of Fluid Machinery
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• v.17 no.1
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• pp.35-40
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• 2014

A multi-objective optimization of a regenerative fan for enhancing the aerodynamic and aeroacoustic performance was carried out using an integrated fan design system, namely, Total FAN-Regen$^{(R)}$. The Total FAN-Regen$^{(R)}$ was developed for non-specialists to carry out a series of design process, viz., computational preliminary design, three-dimensional aerodynamic and aeroacoustic analyses, and design optimization, for a regenerative fan. An aerodynamic analysis of the regenerative fan was conducted by solving three-dimensional Reynolds-averaged Navier-Stokes equations using the shear stress transport turbulence model. And, an aeroacoustic analysis of the regenerative fan was implemented in a finite/infinite element method by solving the variational formulation of Lighthill's analogy based on the results of the unsteady flow analysis. An optimum shape obtained by Total FAN-Regen$^{(R)}$ shows the enhanced efficiency and decreased sound pressure level as much as 1.5 % and 20.0 dB, respectively, compared to those of the reference design. The performance test was carried out for an optimized regenerative fan to validate the performance of the numerically predicted optimal design.

• Polymer(Korea)
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• v.37 no.5
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• pp.642-648
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• 2013

There is a kind of abnormal noise known to come from the stick-slip mechanism induced by frictional impulses during the sliding of two polymeric plates. In this work, quantitative analysis of abnormal noise is carried out based on experimental results. Some combinations of polymer plates, such as an ABS base-plate contacted to ABS, PP, MIPS, and POM plates, which are well-known materials used in home-appliances, are studied to obtain the best combination of polymer plates in order to reduce the abnormal noise. For the experiments, a rig for the test was set up and a methodology was proposed. In addition, the effects of the surface roughness of the plate, the normal loading force, and the relative sliding speed between the two contact plates were evaluated in order to understand the reason for the abnormal noise. Through this experimental work, the optimal combination of materials was ABS/POM system to reduce the noise in real industrial applications.

• Journal of the Korean Society of Marine Environment & Safety
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• v.12 no.3 s.26
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• pp.193-199
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• 2006

The noise levels on board ship recognized at Europe in the early 1970s and the noise regulations on the ship began to put in a statutory form. After that, in 1982 'International Code on Noise Levels on Board Ships' adopted by IMO and it became a standards to the newly built ship and it remains up to recently. Especially, the ship engine room, which have huge main engine and various kinds of subsidiary machines, is under an extremely loud condition and so the worker who works in it is easy to lose his hearing. Recently, each nation regulates the allowable noise exposure time by law to protect the industrial employee from the occupational hardness of hearing. In our country, the allowable noise exposure time is regulated by the labor. standard law but the international provisions regulated by IMO have been applied in case of the ship engine room. In this paper, the cabin's noise levels of cargo-passenger ships plies south-west coast line were investigated.