Visual Resolution Measurement of Display using the Modified Landolt C

Visual resolution measurement method is proposed. The modified Londolt C pattern i.e. one-pixel width black square line having one-pixel white hole on a white background is shown to the observers and the threshold of hole detection viewing distance is measured. The proposed method can evaluate the display resolution more effectively

Effects of Black Luminance Level on Image Quality

The image quality is affected by the black luminance level of the image. This research aimed to investigate how low luminance levels are required to maintain image quality. The psychophysical experiment was carried out in a dark room using OLED display. Total of 6 different black luminance levels (0.003, 0.05, 0.1, 0.2, 0.3, and 1 cd/m2 ) were used in the experiment. Total of 20 participants was invited to evaluate the image quality. For the experiment, twelve test images are used and these test images categorized into three groups as dark, medium bright and bright image group by image histogram distribution. Each image is rendered by adjusting six different black luminance levels. Result found that the black level is higher than 0.1 cd/m2, the preference for the image is decreased. The best performance is achieved when the black level is 0.003 cd/m2 , but there is no big difference from 0.1 cd/m2. The final result shows that a change in black level between about 0.003 cd/m2 and 0.1 cd/m2 does not significantly affect image quality

Investigation of cut quality in fiber laser cutting of CFRP

Fiber laser cutting of CFRP sheets was investigated using a 2 kW multi-mode fiber laser, focusing on how the cut quality factors, such as kerf width, kerf depth, matrix evaporation width, matrix recession width, kerf taper angle, matrix damage zone, and cut surface morphology, change as laser power, laser scanning speed, and the number of laser passes are varied. By designing a systematic experiment on a large process window, several important parameters for kerf width, kerf depth, matrix evaporation width, and matrix recession width were identified, and using them, it was verified that the beam scanning speed is a dominant factor for minimizing thermal damages. Also, circular rings were observed in each carbon fiber at the cut surfaces, and it looked as if they were generated when each fiber was thermally fused in the radial direction. A larger number of laser passes was found to contribute to a smooth surface morphology, because of the formation of highly-fused surfaces, which prevents fiber delamination and pull-outs. Optimum process conditions were also identified by comparing various cut quality factors

Contrast-Preserved Chroma Enhancement Technique using YCbCr Color Space

The YCbCr color space is widely used in image processing techniques. The preference for YCbCr is due to the rough correspondence between the YCbCr components and visual attributes. However, image contrast decreases as the chroma value increases owing to the non-orthogonality between YCbCr components. In this study, a contrast-preserved chroma enhancement algorithm using YCbCr signals is proposed by predicting the amounts of luma change needed to compensate for the lightness change induced by chroma enhancement. Numerical and psychophysical experimental results show that the proposed algorithm can effectively enhance the perceived image chroma and details.close1

Surface roughness characterization of open and closed rock joints in deep cores using X-ray computed tomography

This research was supported by a grant from the project of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), funded by the Ministry of Trade, Industry & Energy of the Korean Government (No. 20123010110010). This work was also carried out in the framework of the European Unions Horizon 2020 research and innovation programme, DESTRESS(No 691728) and funded by the international R&D programme (No. N0002098) of Korea Institute for Advancement of Technology (KIAT).OAIID:RECH_ACHV_DSTSH_NO:T201714038RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A077915CITE_RATE:2.268DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:YCONFIRM:

Observations and analyses of the first two hydraulic stimulations in the Pohang geothermal development site, South Korea

We present key observations and analyses of the first and second stimulations conducted at the Pohang enhanced geothermal system (EGS) site in Korea in 2016. The first hydraulic stimulation was conducted in the PX-2 well of 4.3 km depth, with the maximum wellhead pressure of 89.2 MPa, the maximum injection rate of 46.8 L/s, and a total injected volume of 1970 m(3). The first stimulation showed non-linear and reversible fracture-opening behavior with injection pressure increase. The stimulation mechanism of PX-2 is interpreted as a combination of tensile fracture extension and hydraulic jacking. The second hydraulic stimulation was conducted in the PX-1 well of 4.2 km depth, with the maximum wellhead pressure of 27.7 MPa, the maximum injection rate of 18.0 L/s, and a total injected volume of 3907 m(3). The fracture-opening pressure of PX-1 was evaluated from the clear pressure peaks and the pressure at differential injectivity increase, and was drastically lower than that of PX-2. The transmissivity of PX-1 permanently increased by 6.4 times during the second stimulation. The wellhead injectivity of PX-1 was 3.6 times as high as that of PX-2 at the same injection rate. The stimulation mechanism in PX-1 is interpreted as a combination of hydraulic shearing and hydraulic jacking of unmated or shear-dilated fracture. Both stimulations in the two wells showed consistently greater seismicity rate and magnitude during the shut-in phases than during the preceding injection phases. A close correlation between the injected fluid volume and seismic magnitude was observed in both wells, and the seismic events induced by the two stimulations were in general below the maximum magnitude envelopes expected by the previous studies. Despite the close distance of approximately 600 m in the same rock formation, the two wells showed distinctly different behavior in terms of the overall pressure ranges, pressure peaks, pressure for injectivity increases, transmissivity changes, and the stimulation mechanisms due possibly to the heavy mud and lost circulation material used during the drilling and completion of PX-2. The contrasting hydromechanical responses observed in the same reservoir at the two nearby wells emphasize the importance of proper drilling and completion with close consideration of stimulation strategy.Y