• 정보저장시스템학회논문집
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• 제1권1호
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• pp.78-83
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• 2005

The Blu-ray disc as a next generation high density optical medium uses an objective lens of high numerical aperture(NA 0.85) and blue laser in order to increase the recording density. The double layer is also useful for doubling the density. The spherical aberration of Blu-ray disc is very sensitive to the thickness of the disk because of high numerical aperture. This paper suggests a method to compensate the spherical aberration caused by the change of disk thickness, by using the Liquid Crystal lens instead of the Liquid Crystal panel. It was possible to develop both the LC panel generating the optical phase difference and LC lens changing the optical power. In this paper, we analyzed the aberration performance and a position sensitivity of the two type LC elements when the samples deviate from the optical axis of the objective lens. The results of applying this analysis show that the LC lenses rather than the LC panels have a significant assembling tolerance. The theoretical characteristics of the two elements are calculated and compared with the measurement data.

• Korea-Australia Rheology Journal
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• 제13권1호
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• pp.47-54
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• 2001

Prediction of the maximum packing volume fraction with non-spherical particles has been one of the important problems in powder technology. The sphericity of fly ash particles depending on the particle diameter was measured by means of a CCD image processing instrument. An algorithm to predict the maximum packing volume fraction with non-spherical particles is proposed. The maximum packing volume fraction is used to predict the slurry viscosity under well dispersed conditions. For this purpose, Simha's cell model is applied for concentrated slurry with wide particle size distribution. Also, Usui's model developed for aggregative slurries is applied to predict the non-Newtonian viscosity of dense fly ash - water slurry. It is certified that the maximum packing volume fraction for non-spherical particles can be successfully used to predict slurry viscosity. The pressure drop in a pipe flow is predicted by using the non-Newtonian viscosity of dense fly ash-water slurry obtained by the present model. The predicted relationship between pressure drop and flow rate results in a good agreement with the experimented data obtained for a test rig with 50 mm inner diameter tube. Base on the design procedure proposed in this study, a feasibility study of fly ash hydraulic transportation system from a coal-fired power station to a controlled deposit site is carried out to give a future prospect of inexpensive fly ash transportation technology.

• 한국세라믹학회지
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• 제51권4호
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• pp.243-247
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• 2014

Spherical NiO-YSZ particles were synthesized by ultrasonic spray pyrolysis (USP). The morphology of the synthesized particles can be modified by controlling parameters such as precursor pH, carrier-gas flow-rate, and temperature of the heating zone. The synthesized spherical NiO-YSZ particles have rough surface morphology at high carrier-gas flow-rates due to rapid gas exhaustion and insufficient particle ordering. The Ni-YSZ cermet anode synthesized by ultrasonic spray pyrolysis at a flow rate of l L/min, with precursor solution at pH4, showed a higher maximum power density of 256 $mW/cm^2$ compared to a conventionally mixed Ni-YSZ anode (185 $mW/cm^2$) at $800^{\circ}C$. While the area-specific resistance of conventionally mixed Ni-YSZ anodes increases gradually with operation time (indicating performance degradation), the Ni-YSZ anode synthesized by USP does not exhibit any performance degradation, even after 500 h.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1177-1184
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• 2002

In this paper, power flow analysis method on the various types of thin shell has been developed to solve vibrational Problems in the medium to high frequency ranges. Energy governing equations have been derived both for out-of plane and in-plane waves in thin shell. These results have been numerically applied to predict the vibrational energy density and intensity distributions of cylindrical, spherical and doubly-curved shells.

• 한국안광학회지
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• 제17권1호
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• pp.53-58
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• 2012

목적: 최적구면굴절상태에서 진용한 시력표로 측정한 logMAR 시력에 의한 난시예상량을 파악해 보고, 투영식 소수시력표와 비교해 보고자 하였다. 방법: 대학생 150명 300안을 대상으로 logMAR 시력과 소수시력을 측정하여 완전교정 때의 난시량과 비교하였다. 결과: 진용한 시력표가 투영식 시력표에 비해 시표 줄 간의 차이가 0.25 D이상으로 비교적 구별이 뚜렷하였다. 또한 난시량과의 상관성은 logMAR 시력이 r = 0.8578로 소수시력 r = -0.7199 보다 높았다. 결론: 최적구면굴절상태에서 logMAR 시력을 통하여 난시량을 예측할 수 있었고, 투영식 시력표 보다 진용한 시력표가 단계별 난시예상량을 예측하는 것이 쉬운 것으로 판단된다.

• 한국안광학회지
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• 제16권2호
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• pp.167-170
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• 2011

목적: 등가구면 시력을 통한 피검자의 난시량 예측이 가능한지를 알아보고자 하였다. 방법: 평균연령 23.3세의 남녀 54명(108안)을 대상으로 굴절이상 완전교정 후 크로스실린더의 도수를 ${\pm}$0.25D씩 증가시키면서 크로스실린더의 (-)축이 $180^{\circ}$ 일 때, $90^{\circ}$ 일 때, 그리고 $45^{\circ}$ 일 때의 원거리(5m) 시력변화를 각각 측정하였다. 결과: 크로스실린더의 도수가 증가될수록 시력은 반비례하여 감소되었다. 크로스실린더 ${\pm}$2.50D ($180^{\circ}$와 $90^{\circ}$)과 ${\pm}$2.25D ($45^{\circ}$)에서 측정 최소값인 시력 0.05로 나타났다. 결론: 각각의 등가구면 시력에 대응하는 난시량에 대한 관계를 추정할 수 있었다.

• 비파괴검사학회지
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• 제28권2호
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• pp.137-143
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• 2008

안경용 구면 렌즈는 굴절력에 따라 (+)디옵터와 (-)디옵터 렌즈로 구분할 수 있다. 렌즈에 가해지는 외부 열원에 의해서 생기는 열변형은 디옵터의 종류에 따라 다르게 나타난다. 본 논문에서는 빛의 가간섭성을 이용하여 물체의 변형을 비접촉으로 정확하게 측정할 수 있는 전자처리 스페클법을 이용하여 렌즈에 발생되는 열변형을 정량적으로 측정하였다. 외부 열원에 의한 온도 분포의 측정은 실시간 비접촉으로 온도를 측정할 수 있는 적외선 열화상 카메라를 사용하였다. 실험은 총 14종의 플라스틱 상용 안경 렌즈를 대상으로 수행하였다. 동일한 온도차에서 (+)디옵터 렌즈의 경우에는 디옵터의 증가에 따라서 열변형량이 증가하였다. 반면에 (-)디옵터 렌즈는 디옵터의 증가와 관계없이 열변형량이 거의 선형적이었다. 또한 동일한 디옵터에서 (+)디옵터 렌즈의 열변형량이 (-)디옵터 렌즈의 열변형량 보다 작았다. 따라서 본 논문에서는 렌즈에 열이 가해지는 경우 렌즈의 열변형량을 정량적으로 측정할 수 있음을 확인하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.19-19
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• 2009

Recently, Light Emitting Diode(LED) has many advantages in comparison with conventional light sources; low power consumption, long lifetime, and less environmental pollution. Therefore, the use of LED is multiplying and increasing rapidly. In general, however, spherical lens is used in LED-lighting which cause many problems induces by optical aberration of spherical lens; low illumination, a yellow belt, unpleasant feeling in human eye. As a potential solution of this problem, aspherical lens can be employed. This study reports the improvement of LED-lighting performance by adopting aspherical lens. From the commercial program, $LightTools^{TM}$, the optical problem were ensured. And then, to improve this problem, optimum aspheric form was designed using Code $V^{TM}$.

• 천문학회지
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• 제27권1호
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• pp.45-53
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• 1994

We present the calculation of X -ray spectra produced through Compton scattering of soft X-rays by hot electrons in the spherical shell geometry, using fully relativistic Monte Carlo simulation. With this model, we show that the power-law component, which has been observed in the low luminosity state of low-mass X-ray binaries (LMXBs), is explained physically. From a spectral. analysis, we find that spectral hardness is mainly due to the relative contribution of scattered component. In addition, we see that Wi en spectral features appear when the plasma is optically thick, especially in the high energy range, $E{\gtrsim}100keV$. We suggest that after a number of scattering the escape probability approaches an asymptotic form depending on the geometry of the scattering medium rather than on the initial photon spectrum.

• 한국전기전자재료학회논문지
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• 제22권12호
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• pp.1033-1038
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• 2009

Recently, Light Emitting Diode (LED) has many advantages in comparison with conventional light sources; low power consumption, long lifetime, and less environmental pollution. Therefore, the use of LED is increasing rapidly. In general, however, spherical lens is used in LED-lighting which cause many problems induces by optical aberration of spherical lens; low illumination, yellow belt, unpleasant feeling in human eye. As a solution of these problem, aspherical lens can be employed. This study reported the improvement of LED-lighting performance by adopting aspherical lens. From the commercial program, $LightTools^{TM}$, the optical problem were ensured. And then, to improve these problem, optimum aspheric form was designed using Code $V^{TM}$.