• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.146-146
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• 2003

If rare earth ions could be activated by electrical means after introducing into an appropriate semiconductor host, it might be possible to achieve the electrically-driven optical amplifier. Futhermore, some groups report that rare earth doped semiconductor nanoparticls show the sensitized emission. In this study, we try to prepare the Er/PbS nanoparticles encaupsulated by phenyl modified silica shell via sol-gel process. Er/PbS nanoparticles were characterized by UV-vis absorption, XRD, FT-IR and TEM etc. Finally we will present the luminescence properties of Er doped PbS nanoencapsulation.

• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.16-21
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• 2005

The effect of additive composition, using AlN and $Er_{2}O_{3}$ as sintering additives, on the mechanical properties of liquid-phase-sintered, and subsequently annealed SiC ceramics was investigated. The microstructures developed were quantitatively analyzed by image analysis. The average thickness of SiC grains increased with increasing the $Er_{2}O_{3}/(AlN + Er_{2}O_{3})$ ratio in the additives whereas the aspect ratio decreased with increasing the ratio. The mechanical properties versus $Er_{2}O_{3}/(AlN + Er_{2}O_{3})$ ratio curve had a maximum; i.e., there was a small composition range at which optimum mechanical properties were realized. The best results were obtained when the ratio ranged from 0.4 to 0.6. The flexural strength and fracture toughness of the SiC ceramics were $550\~650\;MPa$ and $5.5\~6.5$ MPa${\cdot}m^{1/2}$, respectively.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04b
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• pp.142-144
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• 2002

데이터 웨어하우스는 기업의 의사 결정을 지원하기 위해 기업의 운영 데이터베이스로부터 추출한 데이터의 집합으로써 OLAP 분석에 이용된다. OLAP은 이들 데이터를 다양하게 분석할 수 있도록 다차원 데이터로 표현하고 이를 활용하여 복잡한 분석 질의 처리 및 다차원 데이터 분석에 활용한다. 이러한 OLAP의 다차원 데이터를 관계형 데이터베이스에서 표현하기 위해 스타 스키마가 널리 사용된다. 또한 다차원 데이터와 데이터 웨어하우스는 방대한 분량를 갖는 전체 기업의 데이터를 표현하고 있어 이를 설계하는 것이 매우 복잡하고 많은 노력이 소요된다. 따라서 이를 설계하기 위한 체계적인 설계 방법론이 필요하다. 데이터 웨어하우스의 원천 데이터가 되는 운영 데이터베이스는 현재 ER 도형을 이용하여 개념적인 방법으로 널리 설계되고 있다. 따라서 이 논문에서는 ER 도형으로 설계된 운영 데이터베이스로부터 데이터 웨어하우스를 설계하는 개념적인 방법론을 제시한다. 이에 따라 OLAP 분석을 위해 사용할 수 있는 다양한 유형의 스타 스키마에 대해 ER 도형으로 표현/변환하는 방법을 제시한다. 이를 통해 자신이 원하는 다차원 데이터를 얻기 위해 유지해야 할 데이터 웨어하우스를 ER 도형을 이용하여 개념적으로 편리하게 설계하는 방법/지침을 제공하며, 나아가 해당 유형의 스타 스키마가 갖는 의미를 개념적으로 쉽게 전달할 수 있도록 하였다.

• Journal of KSNVE
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• v.11 no.2
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• pp.301-306
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• 2001

Electro-Rheological (ER) fluid is applied to a controllable squeeze film damper (SFD) for stabilizing a flexibly supported rotor system. ER fluid is a class of functional fluid whose yield stress varies according to the applied electric field strength, which is observed as viscosity variation of the fluid. In applying ER fluid to a SFD, a pair of rings of the damper can be used as electrodes. When the electrodes are divided into a horizontal pair and a vertical one, the SFD can produce damping force in each direction independently. A prototype of the directionally controllable SFD was constructed and its performance was experimentally and numerically investigated in the present work.

• KSTLE International Journal
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• v.2 no.1
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• pp.71-74
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• 2001

The electrorheological(ER) performance of a chitosan sebaciate suspension in silicone oil was investigated by varying the electric fields, volume fractions of particles, and shear rates, respectively. The chitosan sebacicate susepnsion showed a typical ER response caused by the polarizability of an amide polar group and shear yield stress due to the formation of multiple chains upon application of an electric field. The shear stress for the suspension exhibited a linear dependence on the volume fraction of particles and an electric field power of 1.88. On the basis of the results, the newly synthesized chitosan sebacicate suspension was found to be an anhydrous ER fluid.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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• pp.53-60
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• 2001

This paper presents a position control of a platform at the seaport cargo handling system. After brief description of the operating principles of the cargo handling system, the governing equation of the moving platform is derived. The equation is described in the state space model, and a robust H$_{\infty}$ controller to achieve position tracking of the moving platform. which can carry 200ton of containers, is formulated. In the synthesis of the controller, the weight of the container is treated as uncertain parameter. Both regulating and tracking control responses are analyzed for the loading and unloading procedures of the proposed automatic cargo handling system.

• Korea-Australia Rheology Journal
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• v.18 no.1
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• pp.25-30
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• 2006

To enhance the stability of dispersed polyaniline (PANI) particles in a silicone oil system, a nonionic surfactant was adopted, and its effect on the electrorheological (ER) performance was investigated under an applied electric field. In the presence of a nonionic surfactant, the PANI based ER fluid exhibited not only an improved sedimentation stability based on the estimated sedimentation ratio but also an enhanced maximum yield stress behavior. Furthermore, the surfactant added ER suspension was applied to an ER damper system, and its damping performance was compared with the ER suspension without a surfactant.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.348.2-348
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• 2002

ER mount is often used instead of rubber mount in cylindrical shell to improve the vibration and noise performanec. The noise radiated by cylindrical shell will be reduced by reducing the force transmitted to the cylindrical shell through ER mount. In this paper, LQ control theory is used to reduce the transmitted force to the cylindrical shell. The finite element method of cylindrical shell is formulated by NASTRAN and its vibrating shape is calculated in frequency domain. (omitted)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1119-1126
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• 2000

This paper is concerned with the design and application of an Electro-Rheological(ER) fluid damper to suppress the vibration of a rotor system. The system is flexible with a slender shaft and a thin disk, being supported by two ball bearings. In addition, to investigate the system performances also in the high speed range, the driving torque is made transmit through a speed increasing gear train. Along with the experiments, to predict and compare the ER damper effect, the rotor system is simulated as to its free and forced vibration characteristics by means of a finite element method code, which is assembled with the mathematical model of the designed ER damper.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1286-1291
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• 2000

A new electro-rheological squeeze film damper (ER SFD) has been sealed with slotted piston rings which have electrodes at the inside of the constant gap. The slotted ER SFD can prevent the problem of electric discharge which might be occurred in the previous configuration of an ER SFD. The current paper presents the extraction of linearized dynamic coefficients within small orbit where these coefficients are controlled by the application of electric strength. Test rig has been modified to isolate the damper section for dynamic coefficient extraction. The results show that rotordynamic coefficients, damping and inertia terms, increase with increasing supply voltages, while stiffness coefficients decrease with increasing supply voltages. Rotating speed of rigid Shaft does not affect these coefficients.