• Smart Structures and Systems
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• 제15권6호
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• pp.1463-1479
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• 2015

Lamb waves have been a promising candidate for quantitative damage identification for various engineering structures, taking advantage of their superb capabilities of traveling for long distances with fast propagation and low attenuation. However, the application of Lamb waves in damage identification so far has been hampered by the fact that the characteristic signals associated with defects are generally weaker compared with those arising from boundary reflections, mode conversions and environmental noises, making it a tough task to achieve satisfactory damage identification from the time series. With awareness of this challenge, this paper proposes a time reversal-based technique to enhance the strength of damage-scattered signals, which has been previously applied to bulk wave-based damage detection successfully. The investigation includes (i) an analysis of Lamb wave propagation in a plate, generated by PZT patches mounted on the structure; (ii) an introduction of the time reversal theory dedicated for waveform reconstruction with a narrow-band input; (iii) a process of enhancing damage-scattered signals based on time reversal focalization; and (iv) the experimental investigation of the proposed approach to enhance the damage identification on a composite plate. The results have demonstrated that signals scattered by delamination in the composite plate can be enhanced remarkably with the assistance of the proposed process, benefiting from which the damage in the plate is identified with ease and high precision.

• 한국환경과학회지
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• 제17권9호
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• pp.957-968
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• 2008

The purpose of this study is to analyze the characteristics of hydraulic behavior of the natural channel flow according to the temporal classification mode, and thus propose the hydraulic analysis method for future channel design. For analysis, the temporal flow characteristics of the channel section was divided into the steady flow and the unsteady flow. For hydraulic analysis, the HEC-RAS model, which is a one-dimensional numerical analysis model, and the SMS-RAM2 model, which is a two-dimensional model, were used and the factors used for analysis of hydraulic characteristics were flood elevation and flow rate. The flow state was analyzed on the basis of the one-dimensional steady flow and unsteady flow for review. In the unsteady flow analysis the flow rate changed by $(-)0.16%{\sim}(+)0.26%$, and the flood elevation varied by $(-)0.35%{\sim}(+)0.51%$ as compared to the values in the steady flow analysis. Given these results, in the one-dimensional flow analysis based on the unsteady flow the flood elevation and flow rate were greater than when the analysis was done on the basis of the steady flow. The flow state was analyzed on the basis of the two-dimensional steady flow and unsteady flow. In the unsteady flow analysis the flow rate varied by $(-)0.16%{\sim}(+)1.08%$, and the flood elevation changed by $(-)0.24%{\sim}(+)0.41%$ as compared to the values in the steady flow analysis. Given these analysis results, in the two dimensional flow analysis based on the unsteady flow, the flood elevation and flow rate were greater than when the analysis was done on the basis of the steady flow.

• 대한치과기공학회지
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• 제32권4호
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• pp.327-335
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• 2010

Purpose: The purpose of this study was to investigate the correlation between zirconia core thickness and color tone blocking of discolored tooth and metal post. Methods: For this study, we made 20-porcelain sample and 4-metal sample( liechtenstein IPS e.max) bonded to zirconia core of different thickness with cement(Relyx ARC-3M USA)for produce discolored. We measured the color-spectral characteristics, using Shadepilot equipment(Degudent USA).We measured it with Shadepilot equipment set by automated average mode in 3 times And applied the average value obtained from 2 times of measurement in the middle of each sample. Results: As a result of analysing color-spectral characteristics on zirconia core sample, Depending on the thickness of zirconia core, the value of brightness(${\Delta}L*$:color-spectral characteristic) was increased within limited range, value of ${\Delta}a*$, ${\Delta}b*$ was decrease. Conclusion: Consequently, we obtained the following results: Changes of sample color were observed depending on the thickness of zirconia, but the range of change did not exceed the scope range of shade guide. The case of metal posts, shade guide color D2 were observed in 0.5mm of zirconia core thickness. As a result, in case of porcelain, increasing the zirconia thickness of 0.3mm or more is unnecessary for color blocking effect, in case of metal post, considering the discolored tooth, thickness of zirconia with at least 0.5mm or more is recommended.

• 한국전자파학회논문지
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• 제15권12호
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• pp.1184-1189
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• 2004

본 논문에서는 직교신호를 발생할 수 있는 새로운 구조의 전압제어 발진기를 설계 제작하였다. 정확한 직교 신호 특성과 낮은 위상잡음 특성을 동시에 얻기 위하여 결합 증폭기의 source단자에 저항 궤환을 이용하여 차동 발진기를 결합시켰다. 발진기는 0.18 um 표준 CMOS 공정을 이용하여 제작하였다. 제작한 발질기의 위상잡음 특성은 -120 dBc/Hz @ 1 MHz 0$\~$1.8 V 전압을 가변하였을 때, 2.34 GHz$\~$2.55 GHz의 210 MHz 주파수 가변을 얻었다. 또한 낮은 IF 주파수 혼합기와 결합하여 측정한 결과 직교신호의 위상 오차는 0.5도, 진폭 오차는 0.2 dB 이하를 보였다. 바이어스 전류는 1.8 V 공급전압에 대해 전압제어발진기의 Core 부분 5 mA를 포함하여 전체적으로는 19 mA를 요구한다.

• 방송공학회논문지
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• 제18권4호
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• pp.647-650
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• 2013

HEVC RExt(High Efficiency Video Coding Range Extension)는 RGB/YUV 4:2:2 4:4:4 색 샘플링 영상과 10비트 심도 이상의 영상 지원을 목표로 한다. RGB 영상은 YUV 4:2:0 색 샘플링 영상과는 달리 색평면 간 높은 상관도를 갖고 있으며, 이를 이용하여 화소값을 예측하는 기법들이 JCT-VC 표준화 회의에서 기고되었다. 하지만 일반적으로 RGB 영상의 고주파수 성분은 색평면 간 낮은 상관도를 갖고 있으며, 이는 색평면 간 예측 시 부호화 효율 저하의 원인이 된다. 따라서 본 논문에서는 색평면 간 예측 시 고주파수 성분을 저역통과필터를 통해 적응적으로 제거하는 기법을 제안한다. HEVC RExt의 RGB 영상을 통한 실험 결과, 본 논문에서 제안하는 기법은 기존 색평면 간 예측 기법에 비해 큰 복잡도의 증가 없이 평균 0.6%의 BD(Bjontegaard Distortion)-율 이득을 얻을 수 있었다.

• 대한기계학회논문집B
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• 제26권11호
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• pp.1622-1629
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• 2002

To enhance isothermal characteristics of glass-farming surface, a rectangular parallelepiped heat pipes was fabricated, tested, and analyzed. The working fluid was sodium and the wall material was stainless steel 304. The dimension of the heat pipe was 210 (L) $\times$ 140(W) $\times$ 92(H)mm. A lattice structure covered with screen mesh was inserted to promote return of working fluid. The bottom side of heat pipe was heated electrically and the top side was cooled by liquid circulation. The temperature distribution at the bottom surface was of major concern and was monitored to determine isothermal characteristics. A frozen start-up of rectangular parallelepiped liquid metal heat pipe was tested. The operating mode of the sodium heat pipe was affected by the temperature of cooling zone, input heat flux, and the operating temperature of heat pipe. The heat pipe operated in a normal fashion as long as the heat flux was over 5.78W/cm$^2$, and the inside wall temperature of condenser part was above 95$^{\circ}C$ The maximum temperature difference at the bottom surface was observed to be 32$^{\circ}C$ when the operating temperature of the heat pipe was operating normally around 50$0^{\circ}C$. The result showed that a sodium heat pipe was very effective in reducing significantly the temperature difference in the glass-forming surface.

• 무역상무연구
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• 제27권
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• pp.183-213
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• 2005

This study is achieving overseas investment to be kept and manages important position in business scope because Korean Company achieves business in major market in world and goes forward. under proposition that development(foreign direct investment) previous engagement can not but differ with advanced nation enterprise's model in over sea direct investment achievement. Grasp ramification(pattern change substance) of overseas direct investment since the 1990 to korean manufacture Firm(enterprise). Seek political consultation by analyzing change of factor and investment decision factor by year in dimension by industry investment winter season by year affecting in oversea direct investment and was attained in purpose to verify existent theory's explanation power connected with investment previous engagement. This is that can develop and procure competitive advantage of enterprise peculiarity by making overseas direct investment adversely with existent theory that can make foreign country direct investment though there is high position of enterprise characteristic's competitive advantage and move of knowledge and information is important in korean firm's overseas direct investment in globalization roadbed in at least own field through change and renovation establish experiment model under proposition that should grope more active previous engagement than advanced nation enterprise and arranged subject of study if it is korean's firm that wish to become universal guidance enterprise. and examine trend of direct investment and actual conditions invested first in the foreign countries as examples by investment department, by investment industry inside of investment scale etc..., establish korean firm's invest area selection and decision and investment very important person and effect analysis Circumstance-model that is based in strategic adaptedness by year. Circumstance-variable have influenced how in overseas direct investment and decision and what variable will be considered first in over sea direct investment did Empirical analysis in here after

• 한국소음진동공학회논문집
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• 제13권10호
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• pp.798-804
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• 2003

One of the methods that are used to compare and verify the supporting performance of the spacer grids developed is the vibration characteristic test. A modal test in this paper is performed for a dummy rod 3,847 mm tall supported by eight New Doublet (ND) spacer grids. For the vibration test in air, nine accelerometers, one displacement sensor and one shaker are used for acquiring signals, and an I-DEAS TDAS software Is employed for analyzing the signals. Also, a finite element (FE) analysis is performed by a beam-spring simple model and a contact model simulating the contact phenomenon between the rod and the ND spring. And then, the results of the modal testing are compared with those of the FE analysis. The natural frequencies as well as the mode shapes obtained by the experiment have a greater similarity to the results by the contact model than the previous beam-spring model. In audition, for grasping whether or not the modal parameters are influenced by where shaking spot is, two kinds of tests are performed : one is for the shaker attached at the fourth span (center), the other is for the shaker at the fifth span that is one span nearer to the bottom of the rod. The latter shows higher MAC than the former Finally, the vibration displacements are measured in the range of 0.l12∼0.214 mm for the excitation force of 0.25∼0.75 N.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권8호
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• pp.3295-3311
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• 2020

With the wide application of hyperspectral images, it becomes more and more important to compress hyperspectral images. Conventional recursive least squares (CRLS) algorithm has great potentiality in lossless compression for hyperspectral images. The prediction accuracy of CRLS is closely related to the correlations between the reference bands and the current band, and the similarity between pixels in prediction context. According to this characteristic, we present an improved CRLS with adaptive band selection and adaptive predictor selection (CRLS-ABS-APS). Firstly, a spectral vector correlation coefficient-based k-means clustering algorithm is employed to generate clustering map. Afterwards, an adaptive band selection strategy based on inter-spectral correlation coefficient is adopted to select the reference bands for each band. Then, an adaptive predictor selection strategy based on clustering map is adopted to select the optimal CRLS predictor for each pixel. In addition, a double snake scan mode is used to further improve the similarity of prediction context, and a recursive average estimation method is used to accelerate the local average calculation. Finally, the prediction residuals are entropy encoded by arithmetic encoder. Experiments on the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) 2006 data set show that the CRLS-ABS-APS achieves average bit rates of 3.28 bpp, 5.55 bpp and 2.39 bpp on the three subsets, respectively. The results indicate that the CRLS-ABS-APS effectively improves the compression effect with lower computation complexity, and outperforms to the current state-of-the-art methods.

• 천문학회지
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• 제48권5호
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• pp.313-323
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• 2015

Active galactic nuclei (AGN) are known for irregular variability on all time scales, down to intra-day variability with relative variations of a few percent within minutes to hours. On such short timescales, unexplored territory, such as the possible existence of a shortest characteristic time scale of activity and the shape of the high frequency end of AGN power spectra, still exists. We present the results of AGN single-dish fast photometry performed with the Korean VLBI Network (KVN). Observations were done in a “anti-correlated” mode using two antennas, with always at least one antenna pointing at the target. This results in an effective time resolution of less than three minutes. We used all four KVN frequencies, 22, 43, 86, and 129 GHz, in order to trace spectral variability, if any. We were able to derive high-quality light curves for 3C 111, 3C 454.3, and BL Lacertae at 22 and 43 GHz, and for 3C 279 at 86 GHz, between May 2012 and April 2013. We performed a detailed statistical analysis in order to assess the levels of variability and the corresponding upper limits. We found upper limits on flux variability ranging from ~1.6% to ~7.6%. The upper limits on the derived brightness temperatures exceed the inverse Compton limit by three to six orders of magnitude. From our results, plus comparison with data obtained by the University of Michigan Radio Astronomy Observatory, we conclude that we have not detected source-intrinsic variability which would have to occur at sub-per cent levels.