• Journal of Astronomy and Space Sciences
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• v.21 no.2
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• pp.141-152
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• 2004

Optics fabrication process for precision space optical parts includes bound abrasive grinding, loose abrasive lapping and polishing. The traditional bound abrasive grinding with bronze bond cupped diamond wheel leaves the machine marks of about $20{mu}m$ rms in height and the subsurface damage of about 1 ${mu}m$ rms in height to be removed by subsequent loose abrasive lapping. We explored an efficient quantitative control of precision CNC grinding. The machining parameters such as grain size, work-piece rotation speed and feed rate were altered while grinding the work-piece surfaces of 20-100 mm in diameter. The input grinding variables and the resulting surface quality data were used to build grinding prediction models using empirical and multi-variable regression analysis. The effectiveness of such grinding prediction models was then examined by running a series of precision CNC grinding operation with a set of controlled input variables and predicted output surface quality indicators. The experiment achieved the predictability down to ${pm}20$ nm in height and the surface roughness down to 36 nm in height. This study contributed to improvement of the process efficiency reaching directly the polishing and figuring process without the need for the loose abrasive lapping stage.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.9
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• pp.1020-1026
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• 2007

The control of pathogenic microorganisms is important issue in human environments, especially in surface area. However, surface disinfection has not been fully researched. In this study, the surface disinfection under UV irradiation was performed to investigate the quantitative kinetics for Bacillus subtilis spore inactivation in several experimental conditions, such as light intensity, temperature and surface roughness. This study reports that UV light would apparently inactivates the microorganisms and the required IT value for 2 log (99%) Bacillus subtilis spore inactivation was found to be 14.5 $mJ/cm^2$ in plain surface, as predicted by the Delayed Chick-Watson model. When UV was irradiated, there were no significant temperature effects. However, the experimental result shows that the more increased IT values are required at larger surface roughness.

• Journal of the Korean Geotechnical Society
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• v.39 no.8
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• pp.17-28
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• 2023

Laboratory-scale hydraulic fracturing experiments were conducted on granite specimens at various viscosities and injection rates of the fracturing fluid. A series of cross-sectional computed tomography (CT) images of fractured specimens was obtained via a three-dimensional X-ray CT imaging method. Pixel-level fracture segmentation of the CT images was conducted using a convolutional neural network (CNN)-based Nested U-Net model structure. Compared with traditional image processing methods, the CNN-based model showed a better performance in the extraction of thin and complex fractures. These extracted fractures extracted were reconstructed in three dimensions and morphologically analyzed based on their fracture volume, aperture, tortuosity, and surface roughness. The fracture volume and aperture increased with the increase in viscosity of the fracturing fluid, while the tortuosity and roughness of the fracture surface decreased. The findings also confirmed the anisotropic tortuosity and roughness of the fracture surface. In this study, a CNN-based model was used to perform accurate fracture segmentation, and quantitative analysis of hydraulic stimulated fractures was conducted successfully.

• Journal of Astronomy and Space Sciences
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• v.22 no.1
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• pp.13-20
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• 2005

Bound abrasive grinding is used for the initial fabrication phase of the precision aspheric mirrors for both space and ground based astronomical telescopes. We developed a new grinding optimization process that determines the input grinding variables for the target surface roughness, checks the grinding error magnitude in resulting surface roughnesses, and minimizes the required machining time. Using the machining data collected from the previous grinding runs and subsequently fed into the multivariable regression engine, the process has the evolving controllability that suggests the optimum set of grinding variables for each target surface roughness. The process model was then used for ten grinding experiments that resulted in the grinding accuracy of $=-0.906{\pm}3.38(\sigma)\;nm(Ra)$ for the target surface roughnesses of Zerodur substrate ranging from 96.1 nm (Ra) to 65.0 nm (Ra) The results imply that the quantitative process optimization technique developed in this study minimizes the machining time and offers the nanometric surface roughness controllability superior to the traditional, qualitative, craftsman based grinding process for the astronomical optical surfaces.

• Wind and Structures
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• v.31 no.4
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• pp.363-371
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• 2020

Proper understanding of offshore wind speed variability is of essential importance in practice, which provides useful information to a wide range of coastal and marine activities. In this paper, long-term wind speed data recorded at various offshore stations are analyzed in the framework of fractal dimension analysis. Fractal analysis is a well-established data analysis tool, which is particularly suitable to determine the complexity in time series from a quantitative point of view. The fractal dimension is estimated using the conventional box-counting method. The results suggest that the wind speed data are generally fractals, which are likely to exhibit a persistent nature. The mean fractal dimension varies from 1.31 at an offshore weather station to 1.43 at an urban station, which is mainly associated with surface roughness condition. Monthly variability of fractal dimension at offshore stations is well-defined, which often possess larger values during hotter months and lower values during winter. This is partly attributed to the effect of thermal instability. In addition, with an increase in measurement interval, the mean and minimum fractal dimension decrease, whereas the maximum and coefficient of variation increase in parallel.

• Korean journal of food and cookery science
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• v.32 no.4
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• pp.413-425
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• 2016

Purpose: This study was conducted to understand the factors that affect the acceptance of gluten-free rice pasta samples prepared with added buckwheat, mungbean, and acorn starches, and to compare sensory characteristics of samples with those of 100% semolina pasta. Methods: Descriptive analysis of pasta was conducted by 12 trained panels. Acceptance test was carried out by 40 consumers using 7-point hedonic scale. Collected data was statistically analyzed by principal component analysis, and partial least squares regression analysis. Results: Quantitative descriptive analysis showed that increasing amount of buckwheat, mungbean, and acorn starches resulted in significant improvement in gluten-free rice pasta properties, especially texture, hardness, chewiness, roughness, and al dente with increasing amount of sample starches, and decreased adhesiveness. In acceptance test, appearance and texture of gluten-free rice pasta with mungbean starch were preferred than pasta made with 100% rice. Flavor and taste was preferred in pasta with buckwheat starch than other pasta samples. Rice pasta with 30% buckwheat starch showed the highest score in overall acceptance among rice samples. Conclusion: This study suggested that adding mungbean starch could improve texture of gluten-free pasta, and adding buckwheat starch would improve taste and flavor of gluten-free rice pasta.

• The Journal of Engineering Geology
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• v.14 no.4 s.41
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• pp.461-468
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• 2004

In order to characterize hydraulic property dependant on join roughness in rock mass, this study computed permeability coefficients on each range of joint roughness coefficient (JRC) suggested by Barton(1976). For a quantitative analysis of roughness components spectral analysis using the fast fourier transform was performed to select effective frequencies on each PC range. The results of spectral analyses show that low ranges of the JRC are mainly composed of low frequency domain, while high ranges of the JRC have dominant components at high frequency domain. The inverse Fourier transform made it possible to generate joint models of each JRC range using the effective frequencies of roughness spectrum. The homogenization analysis was applied to calculate permeability coefficient at homogeneous microscale, and then, computes a homogenized permeability coefficient (C-permeability coefficient) at macro scale. Therefore, it is possible to analyze accurate characteristics of permeability reflected with local effect of facture geometry. According to the calculation results, permeability coefficients were distributed between $10^{-3}m/sec\;and\;10^{-4}/sec$. In cases of sheared joint models permeability coefficients were plotted between $10^{-4}m/sec\;and\;10^{-5}/sec$, showing irregular distribution of permeability coefficients on each IRC range. The differences of permeability coefficients for the same aperture models or for the sheared joint models indicate that changes of roughness pattern influence on permeability coefficients. Therefore, the effect of joint roughness should be considered to characterize hydraulic properties in rock joints.

• Journal of the Korean Society of Safety
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• v.14 no.2
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• pp.109-115
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• 1999

The release of gas from the LPG storage tank by the rupture or leakage can occure explosion and this causes serious damage to people and structures. In this study, the explosion effect and damaging distance were measured for the LPG cloud explosion to perform the quantitative risk assessment for the PSM, and the effective parameters on the explosion were found. The gas dispersion and mass contaminant in the explosion limits were calculated by using DEGADIS, and it was converted to TNT equivalency and damaging distance. As a result, the wind speed was the most effective parameter on the diffusion rate and TNT equivalency, and the damaging distance were increased with decrease of wind speed and surface roughness.

• Journal of Korean Ophthalmic Optics Society
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• v.3 no.1
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• pp.259-262
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• 1998

The Anterior surface and posterior surface of rigid gas permeable(RGP) contact lenses has been studied by scanning electron microscopy. Results point out that the ultrastructure of contact lenses surface was some different on the anterior and posterior surface of RGP. The Quantitative study of surface roughness suggest that the anterior surface was more smooth than the posterior surface. These results suggest that the materials characters appeared the contact lens surface. The morphology of the anterior and posterior surface have different, Maybe, these result have a manufacture processing of the contact lenses. But some surface appeared a foreign body particles.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.289-298
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• 1992

Fouling is "a major unsolved" area in heat transfer research. Currently, fouling researches are performed in every directions-fundamental aspects, modeling and cumulating experimental data. In this study, an attempt was made to extend the knowledge in enhanced tube fouling. The Kern-Seaton fouling model which was originally proposed for smooth tube fouling was extended to repeated rib tubes. Key parameters-mass transfer coefficient and wall shear stress-were modeled for repeated rib tubes. Some critical points related with the enhanced tube fouling-uncertainties in the mass transfer rate, wall shear stress modeling, deformation of roughness shape during fouling-were discussed, and some quantitative evaluations were made.