• 한국세라믹학회지
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• 제30권10호
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• pp.823-828
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• 1993

The performance of ferrite composite microwave absorber has been evaluated as the matching frequency, the matching thickness and the band width. Especially, matching frequency is very important in application of microwave absorber because it determines operating frequency range. In this study, the ferrite composite microwave absorbers consisted Ni-Zn ferrite and Zn2Y ferroxplana were prepared in order to control matching frequency. Then, the variation of the material constants and microwave absorbing characteristics were investigated with various ferrite mixing ratio. The material constants of ferrite composite microwave absorber could be controlled by variation ferrite mixing ratio. Therefore, it was confirm that matching frequency of microwave absorber could be shifted by control of material constants.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.485-488
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• 2003

The results of an experiment on the sound absorption of the porous concrete using recycled aggregates and its influence on the compressive strength are reported in this paper. The content of recycled aggregate of 0, 10, 30, 50 and 70%, and the design void ratio of 30 percent for a given size of aggregate were used. In the compressive strength, an aggregate of the size of 5~13mm is much higher strength than that of the 13~20mm, In sound absorption experiment, the sound absorption ratio was is subjected to decreased as the content of recycled aggregates was increased. As a result, Porous concrete using recycled aggregates and by-products sufficiently have the performance of sound absorption.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1355-1357
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• 1997

In this study, the ferrite/rubber composite microwave absorbers mixed Ni-Zn ferrite and $Ni_2Y$ ferroxplana were prepared in order to control matching condion. The variation of the material constants($\dot{\varepsilon}$, $\dot{\mu}$) and microwave absorbing characteristics were investigated with various ferrite mixing ratio. The material constants of ferrite/rubber composite microwave absorber could be controlled by variation ferrite mixing radio. The matching frequency and thickness could be controlled with various ferrite mixing ratio.

• Bulletin of the Korean Chemical Society
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• 제30권8호
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• pp.1821-1826
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• 2009

Liquid crystal display (LCD) devices contain a colour filter which can visualise colour images by transmitting or absorbing light. Colour properties of LCD mainly depend on colour materials such as pigments and polymeric binders. In this paper, colour properties were studied to improve colour quality of LCD. Generally, the colour properties can be classified into three categories which are colour purity, brightness and contrast ratio. For this study, photo resists were prepared by treatment of pigments and synthesis of polymeric binder. The treated pigments were dispersed and formulated with additives for preparing a photo resist that could be used for manufacturing colour filters. As a result of what we studied, type, mixture ratio and concentration of pigments were very important to improve colour purity of LCD device.

• EDISON SW 활용 경진대회 논문집
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• 제5회(2016년)
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• pp.228-233
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• 2016

Auxetic material is a material which has negative Poisson's ratio(NPR). Auxetic material shows some distinctive property like high energy absorbing property and high shear modulus. Among these, synclastic curvature is very interesting characteristic. When synclastic-curvature-material bends, it changes its shape like dome, contrary to non-auxetic material which changes its shape like saddle(anticlastic). This distinctive property could make it easy to manufacture curved structure like nose cone or wing panel in aerospace engineering. In this study, we studied a quantitative analysis about synclastic curvature of re-entrant panel with finite element model. We suggested a concept 'Degree of Synclasticity(DOS)', which means a ratio of curvature of load-direction and load-orthogonal direction. We studied the variation of DOS with two factor, unit cell inner angle(${\theta}$) and load position angle(${\phi}$). DOS decreases as ${\theta}$ increases because the unit cell goes out of auxetic-shape. As ${\phi}$ varies, DOS changes in a large range. So proper optimization of ${\phi}$ would be needed for application.

• 한국광학회지
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• 제13권4호
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• pp.340-346
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• 2002

초기투과도 0.48과 0.38인 포화흡수체 $Cr^{4+}$: YAG를 사용한 수동 큐스위칭 Nd:YAG 공진기에서 포화흡수의 초기 광흡수 효과로 낮은 Q-상태에서 나타나는 포화흡수체의 투과 광손실 변화와 더불어 레이저 매질의 펌핑된 밀도반전 상태를 분석하였다. 포화흡수체의 초기 광흡수로 수동 큐스위칭 열림동작때 나타나는 포화흡수체의 투과도는 각각 0.70$\pm$0.01과 0.62$\pm$0.01이었다. 이는 큐스위칭 레이저 공진기의 초기 광손실이 간소함을 의미한다. 큐스위칭 열림동작 시점에서 측정된 두 $Cr^{4+}$:YAG의 기저상태 $Cr^{4+}$ 밀도수는 약 1.4${\times}{10^{17}}$$cm^{-3}$이고 기저상태에 대한 여기상태의 $Cr^{4+}$이온밀도수의 비는 약 44%이었다. 또, 큐스위칭 펄스 발생을 위해 펌핑된 최소 반전밀도수는 각각 3.6${\times}{10^{17}}$과 3.9${\times}{10^{17}}$ $cm^{-3}$이고 양자추출효율은 두 경우 모두 약 0.32였다. 낮은 Q-상태에서 나타나는 포화흡수체의 광흡수 효과를 고려한 수동 큐스위칭 레이저 출력에너지의 수정 이론값은 각각 18과 18.5 mJ로 측정된 실험값 약 17$\pm$1과 18$\pm$1.5mJ과 잘 일치함을 보였다.

• 대한방사선기술학회지:방사선기술과학
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• 제5권1호
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• pp.21-34
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• 1982

When unattenuated x-ray radiation passes through the object it is transmitted and scattered from objectes and impinging on the film. During this process certain radiation is absorbed within the object and others transmitted in reduced scattering. The scattering radiation influence upon radiation image quality, confining x-ray beam which means scattering radiation produce increased fog on x-ray film image and as a consequence decrease contrast and less detail of the film there for the elimination of fog and for absorbing scattered radiation, the grid has been used between the object and the film in order to rid of scattering rays. Using grid is good method for the qualification of the better image as well as in using air gap technique. The grid is easy to manipulate and promote good efficiency which is defined by ICRU and JIS. It is the purpose to study for eliminating scattered radiation from the tissue equivalent acryl phantom using grid, we have studied and evaluated the grid permeability about the x-ray exposure, the selection of grid ratio according to phantom thickness, on x-ray exposure are performed as follows. 1. The penetrating ratio of primary x-ray is remarkably decreased by increasing of the grid ratio, but it is almost not influenced in KVP difference and phantom thickness. 2. The scattered radiation is proportionaly increased by thickness of the phantom, having nothing to do with grid ratios. 3. The relative between the penetration rate of primary and secondary x-ray is improved by increasing grid ratio, and decreased by phantom thickness, and slightly decreased by high tube voltage. 4. The grid of 5:1 and 10:1 ratio are adequate to the phantom of 10cm and 15cm thickness, respectively.

• 한국대기환경학회지
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• 제24권4호
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• pp.415-422
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• 2008

This study was carried out to investigate the effect of operating and design conditions of gas dispersion type of absorber on $SO_2$ removal efficiency. pH difference between upper and lower part of gas dispersing plate of absorber was 0.2, which was relatively low. This was supposed that recirculation capacity of absorbing liquid between froth zone and reaction zone of absorber be increased by oxidation air injection through liquid riser which acted as liquid pump. Test results showed that $SO_2$ removal efficiency was more sensitive than absorber ${\Delta}P$. High $SO_2$ removal even at lower pH resulted from very low concentration of $HSO_3^-$ ion in absorbing liquid because of direct supply of dissolved oxygen into froth zone. 96% of $SO_2$ removal efficiency was obtained under the condition of absorber pH 5.2, flue gas flow rate of $1,530\;Nm^3/hr$, inlet $SO_2$ concentration of 800 ppm, absorber ${\Delta}P$ of 250mmAq. The following equation by a multiple linear regression was obtained to describe the relationship between $SO_2$ removal and operating variables. $$f=1-{\exp}(-1.3939+1.060pH+0.0139{\Delta}P-0.00267G-0.000064SO_2Conc.),\;R^2=0.9719$$

• 한국전자파학회논문지
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• 제19권2호
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• pp.244-249
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• 2008

본 논문에서는 Sendust와 Mn-Zn ferrite를 이용하여 2.4 GHz ISM 대역 PCB 노이즈 제거용 전파흡수체를 설계 및 제작하였다. Sendust와 Mn-Zn ferrite를 바인더인 CPE와 혼합하여 조성비별 전파흡수체 샘플을 제작하였고, 이를 분석한 결과 최적의 조성비가 Sendust : Mn-Zn ferrite : CPE=70:5:20 wt.%임을 확인하였다. 전파흡수체 샘플로부터 계산되어진 재료 정수를 이용하여 두께에 따른 흡수능의 변화를 시뮬레이션 하였으며, 시뮬레이션 결과를 토대로 전파흡수체를 실제작하여 전파 흡수능을 비교, 분석하였다. 그 결과, 시뮬레이션 결과와 실측정 결과는 잘 일치하였으며, 중심 주파수 2.4 GHz에서 흡수능 5.4 dB, 1.4$\sim$4.1 GHz 대역에서 3 dB 이상의 흡수능을 보였으며, 이때 두께는 0.85 mm이었다.

• 산업경영시스템학회지
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• 제39권2호
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• pp.1-10
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• 2016

In this paper, we present a new way to derive the mean cycle time of the G/G/m failure prone queue when the loading of the system approaches to zero. The loading is the relative ratio of the arrival rate to the service rate multiplied by the number of servers. The system with low loading means the busy fraction of the system is low. The queueing system with low loading can be found in the semiconductor manufacturing process. Cluster tools in semiconductor manufacturing need a setup whenever the types of two successive lots are different. To setup a cluster tool, all wafers of preceding lot should be removed. Then, the waiting time of the next lot is zero excluding the setup time. This kind of situation can be regarded as the system with low loading. By employing absorbing Markov chain model and renewal theory, we propose a new way to derive the exact mean cycle time. In addition, using the proposed method, we present the cycle times of other types of queueing systems. For a queueing model with phase type service time distribution, we can obtain a two dimensional Markov chain model, which leads us to calculate the exact cycle time. The results also can be applied to a queueing model with batch arrivals. Our results can be employed to test the accuracy of existing or newly developed approximation methods. Furthermore, we provide intuitive interpretations to the results regarding the expected waiting time. The intuitive interpretations can be used to understand logically the characteristics of systems with low loading.