• The Journal of the Acoustical Society of Korea
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• v.21 no.2
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• pp.150-159
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• 2002

The possibility of a broadband noise reduction of piezoelectric smart panels is experimentally studied. Piezoelectric smart panel is basically a plate structure on which piezoelectric patch with shunt circuits is mounted and sound absorbing material is bonded on the surface of the structure. Sound absorbing materials can absorb the sound transmitted at mid frequency region effectively while the use of piezoelectric shunt damping can reduce the transmission at resonance frequencies of the panel structure. To be able to tune the piezoelectric shunt circuit, the measured electrical impedance model is adopted. Resonant shunt circuit composed of register and inductor in stories is considered and the circuit parameters are determined based on maximizing the dissipated energy through the circuit. The transmitted noise reduction performance of smart panels is investigated using an acoustic tunnel. The tunnel is a square crosses sectional tunnel and a loud speaker is mounted at one side of the tunnel as a sound source. Panels are mounted in the middle of the tunnel and the transmitted sound pressure across the panels is measured. Noise reduction performance of a double smart panel possessing absorbing material and air gap shows a good result at mid frequency region except the first resonance frequency. By enabling the piezoelectric shunt damping, noise reduction is achieved at the resonance frequency as well. Piezoelectric smart panels incorporating passive method and piezoelectric shunt damping are a promising technology for noise reduction in a broadband frequency.

• Asian Journal of Turfgrass Science
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• v.20 no.1
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• pp.83-91
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• 2006

This research was initiated to enhance the tilth of fine-textured soil for turf growth by incorporation of crumb rubber shredded from used tires. A specific objective was to determine the physical properties of soil mixes amended with different grade and amount of crumb rubber in soils. Two soils and three different grades(3.5, 6.5 and 9.5 mm) of crumb rubber were used. The soils selected were an Arenzville silt loam(coarse-silty, mixed, nonacid, mesic Typic Udifluvents) and a Hosmer silty clay loam(fine-silty, mixed, mesic Typic Fragiudalfs). The amount of crumb rubber mixed in soil ranged from 0 to 0.4 $g{\cdot}g^{-1}$(using 0.05 $g{\cdot}g^{-1}$) increments and 0 as a control. For each treatment, soil cores were constructed following the recommendation by the United States Golf Association Green Section Record. Results indicated that porosity of the mixes decreased as the amount of crumb rubber increased. Regardless of the grade of crumb rubber, mixes with less than 0.15 $g{\cdot}g^{-1}$ of crumb rubber in fine-textured soil could not enhance their macro-porosity and hydraulic conductivity. However, as the amendment increased over 0.15 $g{\cdot}g^{-1}$, the tilth of the mixes had improved significantly macro-porosity, hydraulic conductivity and air permeability, as compared with a control.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.288-289
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• 2000

SBN, BSKNN KNSBN 등의 tungsten-bronze 계열에 속하는 광굴절 결정은 짧은 파장에서 좋은 감광도와 빠른 응답시간을 갖는다. 이중에서도 KNSBN 결정은 큰 크기의 결정 성장 및 도핑이 용이하고 광굴절 결정에서 중요한 특성 중 하나인 열 안정성(thermal stability)이 좋기 때문에 빠른 응답특성이 요구되는 응용분야에서 촉망받는 매질이다. 본 논문에서는 광정보저장, 광정보처리, 광컴퓨터, 광통신과 같은 다양한 분야에서 응용가능성을 가지는 Cu가 0.04wt.%도핑된 5mm$\times$5mm$\times$5mm 크기의 KNSBN 결정을 이용한 광신호의 증폭기술에 대하여 연구하였다. 먼저 Cu-KNSNB 결정의 2광파 결합 특성을 분석하기 위하여, 기록 파장에 따른 지수이득계수의 외부입사각의존성, 최대 지수이득계수를 나타내는 외부입사각에서 입사빔의 세기비에 따른 2광파 결합 이득을 측정하였다. 또한, 632.8nm파장 영역에서 기록 및 삭제시간 상수, 회절 효율의 입사빔 세기비 의존성을 측정하였다. 그리고, 음향-광학 변조기(AOM: acousto-optic modulator)에 의해 진폭 변조된 신호빔을 이용하여 광신호 증폭특성을 분석하고 그 결과를 제시하였다. 이때 두 빔의 입사각은 최대 지수이득계수를 나타내는 입사반각 12$^{\circ}$로 고정하고, 감쇄기를 이용하여 신호빔의 세기를 조절하면서 신호빔의 차동이득을 측정하였다. 투과된 신호빔은 같은 주파수에서 차동 이득(diffrerential gain)을 보였으며, 이는 moving grating과 시간-변조된 신호빔(또는 펌프빔)사이의 새로운 상호작용은 광굴절 결정의 시간 적분 특성에 의한 것이다. (중략) 경우는 상온에서 펌프 펄스의 유지시간이 0.5% 인 경우 레이저가 동작하는 것을 보여주었다. 이는 구조내에서 열전도가 문제가 된다는 것을 의미하는데 위아래가 공기로 둘러 싸여 있어 발생한 열이 가는 유전체 네트웍을 통해서만 전달 될 수 있기 때문이다. (중략)$^4$A$_2$에 의한 nophonon line R$_1$, R$_2$(680.4, 678.5 nm) 및 $^2$T$_1$$\longrightarrow$$^4$A$_2$(655.7, 649.3, 645.2 nm)의 형광방출 스펙트럼을 얻었으며, 형광수명은 0.264 ms로 조사되었다. 제조된 레이저 발진봉은 직경 6.3 m, 길이 45 nm이었다.\pm$0.06kHz Ge $F_4$; -1.84$\pm$0.04kHz$0.04kHz/TEX>0.04kHz 모국어 및 관련 외국어의 음운규칙만 알면 어느 학습대상 외국어에라도 적용할 수 있는 보편성을 지니는 것으로 사료된다.없다. 그렇다면 겹의문사를 [-wh]의리를 지 닌 의문사의 병렬로 분석할 수 없다. 예를 들어 누구누구를 [주구-이-ν가] [누구누구-이- ν가]로부터 생성되었다고 볼 수 없다. 그러므로 [-wh] 겹의문사는 복수 의미를 지닐 수 없 다. 그러면 단수 의미는 어떻게 생성되는가\ulcorner 본 논문에서는 표면적 형태에도 불구하고 [-wh]의미의 겹의문사는 병렬적 관계의 합성어가 아니라 내부구조를 지니지 않은 단순한 단어(minimal $X^{0}$ elements)로 가정한다.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.214-219
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• 1997

The mechanical seals, which are installed in rotating machines like pump and compressor, are generally used as sealing devices in the many fields of industries. The failure of mechanical seals such as leakage, crack, breakage, fast and severe wear, excessive torque, and squeaking results in big problems. To identify abnormal phenomena on mechanical seals and to propose the proper monitoring parameter for the failure of mechanical seals, sliding wear experiments were conducted. Acoustic emission, torque, and temperature were measured during experiments. Optical microstructure was observed for the wear processing after every 10 minute sliding at rotation speed of 1750 rpm and scanning electron microscopy was also observed. Except for the initial part of every experiment, the variation of acoustic emission was well coincided with torque variation during the experiments. This study concludes that acoustic emission and torque are proper monitoring parameters for the failure of mechanical seals. The intensity of acoustic emission signals is measured in root mean square voltage. Temperature of sealing face will be used as a parallel parameter for increasing the reliability of monitoring system.

• Journal of Chest Surgery
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• v.30 no.8
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• pp.739-746
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• 1997

A variety of experiments concerning the development of ideal prosthetic grafts for correcting circumferential tracheal defects have been performed. The requirements for an ideal tracheal prosthesis are impermeability to air, consistency to prevent collapse, and acceptance by the host tissue causing a minimum inflammatory reaction, allowing fibroblastic infiltration and epithelialization. The synthetic material, polyurethane(PU), is known as a biocompatible polymer with an inert component. In this study, the tracheal prosthesis was made from microporous PU(30 micrometer in diameter) coated with gelatin and reinforced with isoplastic rings. This procedure provides the prosthesis with a compression strength. The out side diame er of the prosthesis was 20 mm with a length of 30 mm. The gelatin used in the study was obtained from pig skin and immobilized and cross-linked by irradiation(60 Co gamma ray) to promote host tissue incorporation and render the prosthesis epithelization after implantation. Animal experiments using 10 mongrel dogs were performed to compare three kinds of prosthesis; gelatin coated polyurethane graft, uncoated polyurethane graft, and prosthesisf pericadium complex graft. After 6 weeks of implantation, the epithelialization of implants was seen on the gelatin-coated and prosthesisfpericadium complex grafts. Implanted prosthesis were complicated by airway obstruction due to anastomosis granuloma. Early tracheal stenosis was found in the uncoated graft group. Two kind of anastomosis techniques were tested on the gelatin-coated prosthesis. Everted anastomosis resulted severe granuloma than the inverted anastomosis. In the prosthesislpericadium complex graft, bacteria and inflammation at a anastomotic site was found. Based on these results, gelatin coated porous polyurethane trachea prosthesis is biocompatible and may be useful in clinical application with further investigation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.83-91
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• 2015

Porous concrete consists of cement, water and coarse aggregate and has been used for the purpose of decreasing the earth environmental load such as air and water permeability, sound absorption, etc. However, the physical and mechanical properties of porous concrete changes due to compaction load during construction. For such a reason, the purpose of this study is to investigate the physical and mechanical properties of porous concrete according to the kinds of binder, the ratio of water to binder and target void ratio. In particular, this study has been carried out to investigate the influence of compaction load on the void ratio, strength and coefficient of permeability. Aggregate used in this study are by-products generated during production of crushed gravel with a maximum size of 13mm. The results of this study showed that the target void ratio, the coefficient of permeability and compressive strength of porous concrete had a close relationship with the void ratio, and it will be possible that the void ratio is suggested by the mix design of porous concrete. The compressive strength of porous concrete was the highest at the content of the expansive admixture of 5% and compared to non-mixture, 10% mixture of silica fume improved compressive strength about 32%. And in the result of the study to change the compaction load, the compressive strength increased from the load of 15kN, the void ratio decreased from the load of 0.8kN, the coefficient of permeability decreased from the load 35kN, respectively.

• Applied Chemistry for Engineering
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• v.25 no.4
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• pp.401-408
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• 2014

In membrane bio-reactor (MBR), the aeration control is one of the important independent variables to decrease fouling and to save energy with shear stress change on the membrane surface. The paper was carried out for numerical simulation of 3-dimensional fluid flow phenomena of the cylindrical bioreactor with submerged flat membranes equipped in the center and supplied the air from the bottom by using the COMSOL program. The viscosity and temperature of solution were assumed to be constant, and the specific air demand based on permeate volume ($SAD_p$) defined as scouring air per permeate rates was used as a variable. The calculated CFD velocities were compared with those of the velocity meter measurement and video image analysis, respectively. The results were good agreement each other within 11% error. For fluid flow in the reactor the liquid velocity increased rapidly between the air diffuser and membrane module, but the velocity decreased during flowing of the membrane module. Also, the velocity increased as it was near from the reactor wall to the central axis. The calculated shear stress on the membrane surface showed the highest value at the center part of the module bottom side and increased as aeration rate increased. Especially, the wall shear stress increased dramatically as the aeration rate increased from 0.15 to 0.25 L/min.

• Korean Journal of Food Science and Technology
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• v.12 no.4
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• pp.229-234
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• 1980

Deep-fried instant noodle was prepared on a laboratory scale (150 units). A part of the noodle was packed in gas-proof laminated film bags with a small package of an oxygen scavenger made from Fe-powder and a 150 ml of air in each bag(Sample 1). Another part was packed in ordinary laminated film bags (Control), and the rest was vacuum-packed (74 mmHg) in the gas-proof film bags (Sample 2). All samples were placed in an incubator kept at $45.0{\pm}0.5^{\circ}C$ for 45 days. Oxygen-removing power of the scavenger, and peroxide and thiobarbituric acid values of the samples were determined regulary. The results of the study are as follows: 1. The residual oxygen concentration of the bags in Sample 1 decreased from the original 21% to less than 0. 5% after 48 hr. 2. POVs of Control, Samples 1 and 2 after 45 days were $12.4{\pm}0.4$, $5.7{\pm}0.2$ and $6.8{\pm}0.1\;meq/㎏$ fat respectively. It was noteworthy that the POV of Sample 1 did not change significantly during the storage period. The scavenger seemed very effective in retarding the POV development of Sample 1. 3. TBA values of Control, Sample 1 and 2 after 45 days were $1.31{\pm}0.04$, $0.60{\pm}0.04$, and $0.72{\pm}0.07$. As in the case of POVs, the samples packed with the scavengers exhibited consistently smaller TBA values than the vacuum-packed samples in later stages of the storage period.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.103-110
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• 2011

This study is to comparatively analyze the characteristics of pH decrease in recycled fine aggregates for embankment and landfill produced from waste concrete by using natural process and artificial process. The result was as follows In case of recycled fine aggregates left outdoor, it was found that pH level was decreased if the thickness of embankment becomes thinner, or the materials left outdoors owing to high concentration of $CO_2$ in atmosphere caused by respirations of people. When the air was permeated, pH level was decreased more effectively. It was analyzed that this phenomenon was caused by efficient supply of $CO_2$ in the recycled fine aggregates owing to high-pressure ventilators. In case of water spraying treatment, sprayed water facilitated hydration of unhydrated cement to dissolve calcium hydroxides which neutralized $CO_2$ in the atmosphere during desiccation process and decrease pH level by a considerable margin. In case of Immersed treatment, decrease of pH was not sufficient. When facilitating the supply of $CO_2$, pH level of the recycled fine aggregates was decreased by the largest margin. It was analyzed that this phenomenon was caused by efficient supply of $CO_2$. From the above results, it was analyzed that the most effective method of reducing pH level of the recycled fine aggregates from the aspects of pH reduction performance, economic efficiency and workability was repeated wet-dry cycles of spraying water to the aggregates in the proportion of 1:0.5 by weight and then treating by forcefully blowing $CO_2$ gas into the aggregates.

• Journal of Haehwa Medicine
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• v.5 no.2
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• pp.497-497
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• 1997

간질성폐질변(間質性肺疾變)은 결체조직질병(結締組織疾病)의 상견(常見)되는 병발증(倂發證)이지만, 지금까지는 이상적(理想的)인 치료법(治療法)이 없었다. 본(本) 연구(硏究)는 본병(本病)의 병리기전(病理機轉)이 중의(中醫)에서의 "어혈(瘀血)"증(證) 상호(相互) 유사(類似)한 것으로부터 시작(始作)하여, 중의(中醫)의 "활혈화어법(活血化瘀法)"과 결합(結合)하여 치료(治療)하면서 환자(患者)의 폐기능(肺氣能) 검사결과(檢査結果)의 변화(變化)를 추적(追跡)해, 그 치료효과(治療效果)에 대(對)한 평가(評價)를 내리는 작업(作業)으로 이루어졌다. 먼저 풍습과(風濕科)에 의뢰(依賴)하여 결체조직질병(結締組織疾病)에 간질성폐병(間質性肺病)이 병발(倂發)한 환자(患者)를 선별(選別)한 후(後)에, 서의치료(西醫治療) 통(通)해서 그 원발성(原發性) 질병(疾病)이 은정(隱靜)한 상태(狀態)에까지 이르도록 한 후(後), 필요(必要)한 최저량(最低量)의 서의약(西醫藥)만을 유지(維持)케 하였다. 환자(患者)의 의사(意舍)에 따라서 두 개의 조(組)로 나누어, 실험군(實驗群)은 중의(中醫)에서 회진(會診)하고, Raynaud 증후군(症候群)의 유무(有無)에 따라서, 당귀사역탕(當歸四逆湯) 혹(或)은 혈부축어탕(血府逐瘀湯)을 농축분제(濃縮粉劑)로 투여(投與)하며 연속(連續)하여 6개월간(個月間) 치료(治療)하였다. 대조군(對照群)의 경우(境遇)에는 중의(中醫)가 회진(會診)하지 않았다. 14개월(個月)동안 모두 실험군(實驗群) 23례(例)와 대조군(對照群) 16례(例)를 대상(對象)으로 연구(硏究)를 하였는데, 모두 여성환자(女性患者)였다. 압축성폐용량(壓軸性肺用量)(FVC), 폐총용량(肺總用量)(TCL), carbon monoxide에 대(對)한 폐(肺)의 확산능력(擴散能力)(DLCO), 그리고 폐포공기량(肺泡空氣量)(VA)에 대(對) DCLO의 비(比)를 지표(指標)로 삼아, 폐기능(肺氣能)의 손상정도(損傷程度)에 따라서 box plot으로 분석(分析)하고, 폐기능(肺氣能)의 손상(損傷)을 측정(測定)하는 시스템을 만들었다. 실험결과(實驗結果), 실험군(實驗群)이 대조군(對照群)에 비(比)해서 치료(治療) 전(前)보다 명현(明顯)한 개선(改善)이 있었다. 폐기능(肺氣能)을 검사(檢査)한 수치(數値)들을 일반적(一般的)으로 통계처리(統計處理)한 것을 응용(應用)하고, TCL과 FVC의 모형식(模型式)을 만든 결과(結果), 실험군(實驗群)에서 FVC가 치료과정(治療過程)의 기간(其間)과 정비례(正比例)하여 향상(向上)되고, 또한 치료효과(治療效果)가 명현(明顯)하게 나타나기 시작(始作)하는 시기(時期)가 중의(中醫) 치료과정(治療過程)을 거친 실험군(實驗群)의 제(第)12개(個)에서 DLCO와 DLCO/VA의 향상(向上)이 나타나는 시기(時期)와 거의 일치(一致)하는 것을 발견(發見)하였다.