• 대한기계학회논문집A
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• 제24권5호
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• pp.1323-1330
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• 2000

Recently, injection molding process became more popular than ever to produce large quantities of high precision products or optical products. Especially, optical disk that was made by injection mol ding process has been used for many years as a music play media or computer sub-device. The density of data in disk media has been increased continuously. But those optical disks can cause sensorial problems because of high birefringence or deformation from the residual stresses in the media. Therefore, it is necessary to study the effects of various process conditions on the final bireffingence structure in injection-molded disks for producing precision injection-molded products. In the present paper we have focussed on the effect of holding and compression pressures on the optical anisotropy remaining in the MOD by examining the gapwise distribution of birefringence and extinction angle. The effect of holding pressure was found to form the inner two bireffingence peaks. But the effect of compression pressure on the bireffingence distribution was found to make the uniform distribution near the center in the gapwise direction. Finally, the value of the birefringence near the wall decreased as the mold temperature increased.

• 천문학회지
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• 제38권2호
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• pp.241-244
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• 2005

We have analysed near-infrared JHKL observations of the members of the $\approx$9 Myr-old $\eta$ Chamaeleontis cluster. Using (J - H)/(K - L) and (H - K)/(K - L) IR colour-colour diagrams for the brightest 15 members of the cluster, we find the fraction of stellar systems with near-IR excess emission was 0.60 $\pm$ 0.13 (2$\sigma$). For the CTT and WTT star population, we also find a strong correlation between the IR excess and Ha emission which is also known as an accretion indicator. The (K - L) excess of these stars appears to indicate a wide range of star-disk activity; from a CTT star with high levels of accretion, to CTT - WTT transitional objects with evidence for some on-going accretion, and WTT stars with weak or absent IR excesses. Among the brightest 15 members, four stars (RECX 5, 9, 11 and ECHA J0843.3-7905) with IR excesses ${\Delta}$(K - L) > 0.4 mag and strong or variable optical emission were identified as likely experiencing on-going mass accretion from their circumstellar disks which we confirmed their accretion disks from the optical high-resolution echelle spectroscopic study. The result-ing accretion fraction of 0.27 $\pm$ 0.13 (2$\sigma$) suggests that the accretion phase, in addition to the disks themselves, can endure for at least ${\~}$10 Myr.

• 천문학회지
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• 제29권spc1호
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• pp.231-232
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• 1996

The local instabilities of accretion disks were extensively studied, with the considerations of radial advection, thermal diffusion and different disk geometry, dominated pressure and optical depth. Two inertial-acoustic modes in a geometrically thin, radiative cooling dominated disk depart from each other if very little advection is included. A geometrically slim, advection-dominated disk is found to be always stable if it is optically thin. However, if it is optically thick, the thermal diffusion has no effect on the stable viscous mode but has a significant contribution to enhance the thermal instability.

• 한국정밀공학회지
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• 제18권4호
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• pp.19-24
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• 2001

• 대한치과보철학회지
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• 제42권3호
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• pp.261-266
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• 2004

Statement of problem. The effects of surface roughness have not or insufficiently been analyzed on earlier events such as cell adhesion though cell behavior most germane to implant performance is cell adhesion. Purpose. The purpose of this study was to evaluate cell adhesion of osteoblast-like cells (MG63) onto three types of titanium disks with varying roughness using the Elisa assay. Materials and methods. Representative disks from each group (SLA, HA, machined) were subjected to surface analysis and surface roughness was measured by the optical interferometer (Accura 2000, Intekplus Co., Seoul, Korea). Following this, MG63 cells were cultured on the titanium disks and released. Cell adhesion measurements using the Elisa assay were performed specifically at three points: after 24, 48, and 72 hours of culture. Results. Among the 3 types of surface analyzed, the SLA surface was the roughest with a Ra value of $1.114{\mu}m$ followed by HA coated surface and machined surface, consecutively. The optical density values for the SLA surface group was significantly higher than that of the machined and HA coated surface groups following 24 and 48 hours of culture. The cell culture on HA coated surface showed significantly higher values compared to the machined surface following 24, 48 and 72 hours of culture. Conclusion. The results suggest that surface treatment of titanium surfaces enhanced cell adhesion of human osteoblast-like cells (MG63).

• 한국광학회:학술대회논문집
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• 한국광학회 1989년도 제4회 파동 및 레이저 학술발표회 4th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.26-31
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• 1989

Optical working machines are developed. the machines are to be used in the preparation of Nd-phosphate glass amplifier rod and elliptical disk amplifier plate of the high power Nd-YLF-phosphate glass laser amplifier system. In this report, the working principles of the machines are presented, and several results are shown by photographes, design drawing and the disks actually fabricated by using the machines.

• 한국소음진동공학회논문집
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• 제19권5호
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• pp.537-544
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• 2009

In order to increase the critical speed of rotating disks of which functional material could not be changed such as in optical and magnetic data storage disks, a new disk with a rim reinforced by composite material is proposed and its concept is verified by numerical analysis. Stress distributions are found for the rotating disk composed of two annular disks of which materials are isotropic inside and orthotropic outside. Dynamic equation is formulated in order to calculate the natural frequency and critical speed. For the solution of lateral vibration, a rotational symmertry condition is applied along circumferential direction and a finite element interpolation with Hermite polynomial is performed along the radial direction to obtain a proper solution. According to the results, reinforcing a disk at rim makes critical speeds drastically increased, and induces a buckling phenomenon in mode (0,0) which occurs over the lowest critical speed.

• 대한기계학회논문집A
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• 제32권2호
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• pp.135-142
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• 2008

Experimental studies on the aerodynamic coupling effect on natural frequencies, critical speed and flutter instability of rotating disks are investigated in this paper. The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and damping and stiffness components. The experiments performed using a vacuum chamber and ASMO/DVD disks rotating in vacuum, open and enclosure in several gaps with stationary wall give three main results. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency of disks rotating in open air is larger than that in enclosure. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

• 도시과학
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• 제10권1호
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• pp.11-20
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• 2021

In this study, the vibration characteristics were theoretically analyzed by modeling a free isotropic rotating disk with an outer periphery with a fixed inner periphery, paying attention to disks used as storage devices for information devices, especially magnetic disks, magneto-optical disks, and compact disks in which the head and disk are non-contact. Iluminate with Composite materials represented by fiber-reinforced plastics (FRP) have high specific strength (strength/density) and specific stiffness (narrowness/density). It is used in the elements, and its use is rapidly expanding. Under this circumstance, the disk currently manufactured using an isotropic material made of various plastic materials such as aluminum or polycarbonate as a base material is an extremely anisotropic material made of a composite material, and the circumferential stiffness of the disk is made of reinforcing fibers in the circumferential direction. It is modeled as an anisotropic rotating disk with increased, and its influence on the vibration characteristics is revealed.

• Applied Microscopy
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• 제29권4호
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• pp.493-498
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• 1999

기억저장매체로서 광디스크의 개발이 활발히 진행되고 있으며 최근의 레이저 기술의 발전, 제조기술의 발전에 따른 기억밀도의 증가로서 기존의 자기기록매체와 경쟁을 하고 있다. 기록밀도의 증대와 신뢰성의 향상을 위하여 다층박막 구조를 가지는 광디스크의 미세구조는 더욱 복잡하며 소형화되고 있다. 이종의 물질로 구성된 다층박막형 광디스크의 미세구조 관찰 및 분석을 위해서는 투과전자현미경과 같은 미소영역 분석법이 필수적이며 비교적 간단하고 신뢰성 높은 시편준비법의 확립이 선행되어야 한다. 본 연구에서는 투과전자현미경 분석을 위한 광디스크의 평면 및 단면시료 제작법을 제시하고 제조된 시편으로부터 얻어진 광디스크의 미세구조 분석결과를 보고한다.