• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.893-897
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• 2006

Structures with additional frictional damping system have strong nonlinearity that the dynamic behavior is highly affected. by the relative magnitude between frictional force and excitation load. In this study, normalized response spectra of the structures with non-dimensional friction force are obtained through nonlinear time history analyses of the mass-normalized single degree of freedom systems using 20 ground motion data recorded on rock site. The variation of the control performance of frictional damping system is investigated in terms of the dynamic load and the structural natural period, of which effects were not considered in the previous studies. Least square curve fitting equations are presented for describing those normalized response spectrum and optimal non-dimensional friction forces are obtained for controlling the peak displacement and absolute acceleration of the structure based on the derivative of the curve fitted design spectrum.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.5
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• pp.314-320
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• 2015

The present study investigates the thermal characteristics of a nanoscale superconductor material. A thin-film of $YBa_2Cu_3O_7-x$ was deposited on a $SrTiO_3$ substrate by using a pulsed-laser deposition technique and characterized using an ultrafast laser system. In order to extract a thermal conductivity value, a numerical solution for a transient one-dimensional heat conduction equation was obtained using a finite-difference method. The curve-fit shows a value 1.2 W/mK, which is relatively lower than those of bulk materials. This research provides a material property of superconductor thin-film required for the thermal design of micro or nanodevices.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.1 s.118
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• pp.88-94
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• 2007

Structures with additional frictional damping system have strong nonlinearity that the dynamic behavior is highly affected by the relative magnitude between frictional force and excitation load. In this study, normalized response spectra of the structures with non-dimensional friction force are obtained through nonlinear time history analyses of the mass-normalized single degree of freedom systems using 20 ground motion data recorded on rock site. The variation of the control performance of frictional damping system is investigated in terms of the dynamic load and the structural natural period, of which effects were not considered in the previous studies. Least square curve fitting equations are presented for describing those normalized response spectrum and optimal non-dimensional friction forces are obtained for controlling the peak displacement and absolute acceleration of the structure based on the derivative of the curve-fitted design spectrum.

• Journal of Biomedical Engineering Research
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• v.18 no.4
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• pp.499-505
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• 1997

A non-invasive technique to measure absorption and scattering coefficients was investigated The reflected backscattered light from the surface of phantom and biological tissue was obtained by using a time-correlated single photon counting system in pico-second time domain. The absorption and scattering coefficients were acquired by the time of peak and asymptotic behavior of the time-resolved reflectance curve and agreed well the ones that is obtained with deconvolution method It was found that the approximation method was good for biological medium to calculate optical properties due to its convenience and accuracy.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.2
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• pp.128-134
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• 2012

Purpose: The purpose of this study was to compare the screw joint stability between the CADCAM custom-made implant abutment and the prefabricated implant abutment by measuring the reverse torque value after cyclic loading. Materials and methods: Twelve screw type implants (Implantium, Dentium Co., Seoul, Korea) were embedded in aluminum cylinder with acrylic resin. The implant specimens were equally divided into 3 groups, and connected to the prefabricated titanium abutments (Implantium, Dentium Co., Seoul, Korea), CADCAM custom-made titanium abutments (Myplant, Raphabio Co., Seoul, Korea) and CADCAM custom-made zirconia abutments (Zirconia Myplant, Raphabio Co., Seoul, Korea). The CAD-CAM milled titanium crown (Raphabio Co., Seoul, Korea) was cemented on each implant abutment by resin cement. Before cyclic loading, each abutment screw was tightened to 30 Ncm and the reverse torque value was measured about 30 minutes later. After the crown specimen was subjected to the sinusoidal cyclic loading (30 to 120 N, 500,000 cycles, 2 Hz), postloading reverse torque value was measured and the reverse torque loss ratio was calculated. Kruskal-Wallis test was used for statistical analysis of the reverse torque loss ratio. Results: The CADCAM custom-made titanium abutments presented higher values in reverse torque loss ratio without statistically significant differences than the prefabricated titanium abutments ($P$>.05). Reverse torque loss ratio of the custom-made zirconia abutments was significantly higher compared to that of the prefabricated titanium abutments ($P$=.014). Conclusion: Within the limitation of the present $in-vitro$ study, it was concluded that there was no significant difference in screw joint stability between the CADCAM custom-made titanium abutments and the prefabricated titanium abutments. On the other hand, the CADCAM custom-made zirconia abutments showed lower screw joint stability than prefabricated titanium abutments.

• Archives of design research
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• v.18 no.4 s.62
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• pp.155-164
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• 2005

In contrast with product design field, some designers who work in furniture field tend to do their own studio works as well as typical designing part. Especially in the small furniture studios for the limited quantity batch production, custom made or handmade craft furniture which is finished with high quality, the propensity for their own production is more obvious than in the big furniture companies in this case. In this kind of small-scale furniture studios, they have more chance to create the various formative works and 'curved shape' is one of the most important elements to form creative pieces. Except by caning, it is very difficult to make curved wooden shape because of own characteristic of wood. Therefore, the special techniques of bending wood are essential to formative furniture production and vacuum press system is introduced as a main subject for the bending wood method in this study. Especially for the designers who work as makers as well at the small furniture studios, the value of vacuum press system on efficiency and productivity of work was sought by testing and improving the method of wood bending techniques. According to this practical searching, ideally sufficient condition on vacuum pressing work was founded as a result on this study.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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• pp.171-178
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• 2001

The nonlinearity of a laser interferometer usually ranges from sub-nanometer to several manometers. This nonlinearity, which has periodic characteristics, limits the accuracy of the interferometer at the sub-nanometer level. The nonlinearity error of the one-frequency homodyne interferometer with quadrature fringe detection results from a number of factors including polarization mixing by imperfect optical elements, unequal gain of photo detectors, lack of quadrature between two signals and misalignment. In this paper, we described a method for measuring and compensating the nonlinearity of homodyne interferometer using the elliptical fitting technique with least-square method. Experimental results demonstrate that $^\pm$3.5 nm nonlinearity can be reduced to $^\pm$0.2 nm level.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.79.1-79.1
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• 2010

세종 산개성단 탐사관측 연구의 일환으로 중년 산개성단 NGC 2353에 대한 UBVI CCD 측광을 수행하였다. 측광학적인 방법으로 성단 내의 구성원을 선정하였으며, 이로부터 이 성단의 성간소광과 거리를 각각 E(B-V)=$0.10\pm0.02mag$와 $d=1.17\pm0.04\;kpc$으로 얻었다. 성단 구성원의 공간적인 분포를 통해서 성단의 형태가 북서 방향에서 남동 방향을 잇는 축을 중심으로 타원의 형태를 띠고 있는 것을 발견하였다. Padova 그룹이 제시한 이론적인 등연령 곡선을 관측한 색등급도에 맞춤으로써 이 성단의 나이를 1억 3천만년으로 추정하였으며, 이는 기존 연구보다 나이가 많은 것으로 나타났다. 구성원의 거리지수 분포에서 이 성단의 거리지수보다 밝은 곳에 나타나는 쌍성의 분포를 Gaussian 분포와 맞추어 $46\pm4%$ 정도의 최소 쌍성비율을 추정하였다. 마지막으로 광도함수와 질량함수를 유도하였고, 질량함수의 기울기는 $\Gamma=-1.4\pm0.2$를 얻었다.

• Korean Journal of Optics and Photonics
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• v.2 no.2
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• pp.59-66
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• 1991

Resonance angle and optimum thinckness of various thin metal films for surface plasmon resonance were calculated using an admittance diagram and optical constants and thickness of thin Ag films and Al films were determined by fitting the measured reflectance of surface plasmon resonance. Two wavelengths of an Ar ion laser were employed to select the unique optical constants which have the same thickness at two wavelengths. Also, when these films were exposed to the air, the shift of surface plasmon resonance was measured and the optical constants of modified thin films were determined.

• Korean Journal of Optics and Photonics
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• v.3 no.1
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• pp.1-10
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• 1992

A simple formula of the envelope method, which uses two envelopes fitted to the transmittance at quarter- and half-wave optical thicknesses, is derived to determine the optical constants (refractive index and extinction coefficient) and the thickness of weakly absorbing thin films. We applied the envelope method to ZnS and SiOx films deposited in a vacuum chamber and determined the optical constants at different deposition conditions. For SiOx films, the decrease in refractive index is consistent with the increase in stoichiometry as the backfilled oxygen pressure increases.