• ETRI Journal
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• v.39 no.1
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• pp.76-86
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• 2017

In this study, we propose an automatic contrast enhancement method based on transfer function modification (TFM) by histogram equalization. Previous histogram-based global contrast enhancement techniques employ histogram modification, whereas we propose a direct TFM technique that considers the mean brightness of an image during contrast enhancement. The mean point shifting method using a transfer function is proposed to preserve the mean brightness of an image. In addition, the linearization of transfer function technique, which has a histogram flattening effect, is designed to reduce visual artifacts. An attenuation factor is automatically determined using the maximum value of the probability density function in an image to control its rate of contrast. A new quantitative measurement method called sparsity of a histogram is proposed to obtain a better objective comparison relative to previous global contrast enhancement methods. According to our experimental results, we demonstrated the performance of our proposed method based on generalized measures and the newly proposed measurement.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.328-334
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• 2000

The hybrid catalytic(catalytic+thermal) combustor of a lean methane-air mixture on platinum catalyst was investigated numerically using a 2-D boundary layer model with detailed homogeneous and heterogeneous chemistries. For the more accurate calculations, the actual surface site density of monolith coated with platinum was decided by the comparison with experimental data. It was found that the homogeneous reactions in the monolith had little effect on the change of temperature profile, methane conversion rate and light off location. However, the radicals such as OH and CO were produced rapidly at exit by homogeneous reactions. Thus the homogeneous reactions were important to predict the productions of CO and NOx exactly. In thermal combustor, the production of $N_2O$ was more dominant than that of NO due to the relative important of the reaction $N_2+O(+M){\to}N_2O(+M)$. Finally the production of CO and NOx by amount of methane addition were studied.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.257-260
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• 1999

It is very important to design the shape of container in HIPing process since the final shape and relative density distribution of the product are decisively dependent on the shape of container. A derivative based approach to determine the shape of container in HIPing process is presented. In this approach the optimal design problem is formulated on the basis of the finite element process. The process model the formulation for process optimal design and the schemes for the evaluation of the design sensitivity and an iterative procedure for optimization are described. In comparison with finite difference scheme the validity of the schemes for the evaluation of the design sensitivity is examined.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.12
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• pp.1041-1047
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• 2001

In this paper, reduction characteristics of the ac flashover voltage in the horizontal air gap of sphere-sphere/needle-needle electrode system were investigated when the combustion flame was present near the high-voltage electrodes. The voltage and current waveforms were measured, when the flashover is occurred, in order to examine the flashover polarity by flame. The reduction characteristics of ac flashover voltage were discussed with the thermal ionization process, the relative air density and the deflection phenomena in the shape of flames that changed by the corona wind and coulomb\`s force. As the results of an experimental investigation, It was found that the reduction of flashover voltages in sphere-sphere system, in comparison with the no-flame case, are 79.9 [%] for k=0, 82.9 [%] for k=0.5, 87.5 [%] for k=1.0, 85.0 [%] for h=0 [cm], 40.8 [%] for h=5 [cm] and 28.2 [%] for h=9 [cm] when ac voltage is applied.

• Journal of Energy Engineering
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• v.24 no.2
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• pp.79-83
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• 2015

Hydrogen has long been recognized as a fuel having some unique and highly desirable properties, for application as a fuel in engines. Hydrogen has some remarkably high values of the key properties for transport processes, such as kinematic viscosity, thermal conductivity and diffusion coefficient, in comparison to those of the other fuels. Such differences together with its extremely low density and low luminosity help to give hydrogen its unique diffusive and heat transfer characteristics. The thermodynamic and heat transfer characteristics of hydrogen tend to produce high compression temperatures that contribute to improvements in engine efficiency and lean mixture operation.

• Journal of Power System Engineering
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• v.15 no.5
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• pp.5-9
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• 2011

The hydraulic piston using a hydrostatic bearing has been used widely due to its satisfying performance at very high pressurized circumstance and relative higher power density in comparison to conventional one. For high pressurization, enhanced efficiency and long durability of the hydraulic piston, the design of hydrostatic bearing is at issue, which is installed between piston shoe and swash plate. The performance of the hydrostatic bearing is influenced significantly by the assembly of the piston shoe consisting of circular land and recess. In this study, to estimate the performance of the hydrostatic bearing, the characteristics for lubrication of the assembly of the piston shoe were investigated by measuring a leakage rate of hydraulic fluid under an experimental condition, where a rotating velocity of the piston, hydraulic pressure and temperature of the hydraulic fluid were changed systematically. In addition, a film thickness of the hydraulic fluid on the piston shoe was measured and compared to theoretical one.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.43 no.3
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• pp.223-230
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• 2010

To compare seed collection and the growth of Anadara subcrenata in Suncheon and Boseong Bays, environmental factors and the growth of larvae and spats were investigated from August 2008 to July 2009 in commercial farming sites in both bays. The variation in water temperature in both bays was similar, but the salinity was lower in Suncheon Bay than in Boseong Bay. The chlorophyll-a content was higher in Suncheon Bay due to the large inflow of freshwater. The density and shell length of A. subcrenata larvae did not differ significantly between the two bays. However, the relative growth of shell height to shell length was significantly higher in Suncheon Bay (P<0.05). The growth of A. subcrenata spats attached to a collector was significantly faster in Suncheon Bay (P<0.05). The spats in Suncheon and Boseong Bays grew to 24.3 and 21.0 mm in shell length, respectively, within 1 year after spawning, and the shell length reached 35.6 and 34.8 mm, respectively, within 2 years of spawning. The initial spats density was higher in Boseong Bay, but the growth of spats was better in Suncheon Bay. The faster growth of A. subcrenata in Suncheon Bay can be explained by the high chlorophyll-a content in this bay. Based on the low survival (%) and slower growth rate of spats in Boseong Bay, the commercial culture density of A. subcrenata in Boseong Bay should be reduced to the optimum level of the carrying capacity.

• Korean Journal of Biological Psychiatry
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• v.10 no.2
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• pp.168-176
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• 2003

Objectives:We investigated the characteristics of P300 generators in obsessive-compulsive disorder(OCD) patients by using voxel-based statistical parametric mapping of current density images. Methods:P300 generators, produced by a rare target tone of 1500Hz under a frequent non-target tone of 1,000Hz, were measured in 15 right-handed OCD patients and 15 controls. Low Resolution Electromagnetic Tomography(LORETA), using a realistic head model of the boundary element method based on individual MRI, was applied to the 128-channel EEG. Statistical parametric mapping(SPM) was applied for the statistical analysis. Results:We found that both groups had the mean current density of P300 in the parietal, temporal and prefrontal lobe. There was a trend for decreased current density in the prefrontal area in OCD patients. The statistical comparison showed current density increase in the supraparietal area, a statistically significant longer P300 latency and a trend for reduced P300 amplitude in OCD patients. Conclusion:It suggests that P300 source of both groups exists in multiple brain regions at the same time. And both groups had no statistically significant differences in the current density of P300 except for increased current density in the supraparietal area in OCD patients. But, considering the statistically significant longer P300 latency, a trend for reduced P300 amplitude and relative mean current density reduction in the prefrontal area in OCD patients, this study suggests that the frontal lobe may have a reduced normal inhibitory process in OCD patients.

• Korean Journal of Ecology and Environment
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• v.42 no.1
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• pp.124-133
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• 2009

Effects of substrates on the relative immigration activities (RIAs) of epilithic diatoms were examined in Sum River, a tributary of South Han River, Korea. Two hundreds of tile substrates coated with 5% agar were deposited at seven study stations (30 tiles per site) for one month from March 7 to April 7, 2008. Water sampling, physico-chemical factor measurement, and diatom analysis were performed in the field and laboratory. Over the study, major epilithic diatom species were Nitzschia amphibia, Navicula subminuscula, Cymbella minuta in both the natural and artificial substrates. Two dominant species, Nitzschia amphibia and Cymbella minuta often found at seven stations. Among all observed taxa, Nav. subminuscula and Caloneis silicula showed the highest RIA, with the value over 15 throughout the study. Regarding the algal morphology, the biraphe type species showed higher RIA than any other morph, while they comprised over 55% of total biomass, indicating a density effect. Additionally, a significant relationship between RIA and 20-day deposited substrate (p<0.05) showed in two diatom species, Nitzschia fonticola, Gomphonema quadripunctatum, which showed relatively high RIAs. These results indicate that the relative immigration activities of epilithic diatom species can be influenced by algal density in the water and substrate, nutrients, and deposited time at least 20 days.

• Journal of the Korean Society of Radiology
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• v.13 no.7
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• pp.987-994
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• 2019

Low energy x-rays that occur in the low tube voltage radiography of general radiography are absorbed strongly in the body and do not aid image quality enhancement. This study maintains titer in general radiography while using tube current that are proportional to density and the tube voltage 15% principle according to density to reduce patient exposure doses, and area doses and entrance surface doses were measured to compare patient exposure doses. In hand, knee, abdomen, and skull radiography, kVp was increased to 115% and mAs was decreased to 50% and kVp was decreased to 85% while mAs was increased to 200% and area doses and entrance surface doses were measured to compare relative doses. Also, 5 places in each image were set, density was measured, and Kruskal wallis H test was conducted to observe significance probabilities between groups. To fix density, kVp was increased to 115% and mAs was decreased to 50% and after measurements of mean area doses and entrance surface doses were made by each part, each decreased to 58.68% and 59.85% when standard doses were set to 100%, and each increased to 147.28% and 159.9% when kVp was decreased to 85% and mAs was increased to 200%. Comparisons of density changes showed that hand, knee, abdomen, and skull radiography all displayed significance probabilities>0.05, showing no changes in concentration. Radiography that increases kVp and lowers mAs through reasonable calculations within ranges that don't affect resolution and contrast seems to be a simple way to decrease patient exposure doses.