• Structural Engineering and Mechanics
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• v.44 no.5
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• pp.601-609
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• 2012

Effect of different crack sizes on fracture criterion of some engineering materials was investigated in this work. Using finite element (FE) method coupled with a newly developed algorithm, J-integral values for different crack sizes were obtained for single-edge notched bend (SENB) and compact type (CT) specimen. Specimens with initial a/W ratio from 0.25 to 0.75 varying in crack size in steps of 0.125 were investigated. Several different materials, like 20MnMoNi55, 42CrMo4 and 50CrMo4, usually used in engineering structure, were investigated. For one of mentioned materials, numerical results were compared with experimental and their compatibility is visible.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.5
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• pp.160-167
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• 2000

In this research, the fatigue behaviors of carbonitrided Cr-Mo(SCM415) steel are examined. From fatigue test results, we propose a modified fatigue strength evaluation model and modified formulae. That is, we develop improved models fur evaluating and predicting the fatigue strength of carbonitrided SCM415 by modifying specific terms in the Murakami and Endo's model which is the representative fatigue strength evaluation formulae fur high strength steel.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.6
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• pp.95-100
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• 2005

Since air pollution has become a globally critical issue and exhaust emissions from automobiles cause a major source of air pollution, many countries including advanced countries have stipulated stringent emission regulations. This research focused on engine performance characteristics with the application of a continuous regeneration diesel particulate filter and EGR together in a heavy duty vehicle, and gives some suggestions on the direction of designing points of view by comparing the experimental data with numerical results which were obtained through KIVA-3V.

• Journal of the Korean Physical Society
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• v.73 no.10
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• pp.1550-1554
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• 2018

The spin cutoff parameters of $^{50-57}Cr$ isotopes have been calculated using a superconducting Hamiltonian with the inclusion of the pairing effect. Their energy and temperature dependences have been studied through comparison with some well-known semi-empirical formulae. This study shows that the microscopic calculation results converge to the Fermi gas model prediction at higher energies. Also, an even-odd effect is evident in the spin cutoff parameters at low temperatures and disappears after the pairing phase transition.

• Journal of Environmental Science International
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• v.24 no.9
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• pp.1131-1138
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• 2015

Radon exhalation rates have been determined for samples of concrete, gypsum board, marble, and tile among building materials that are used in domestic construction environment. Radon emanation was measured using the closed chamber method based on CR-39 nuclear track detectors. The radon concentrations in apartments of 100 households in Seoul, Busan and Gyeonggi Provinces were measured to verify the prediction model of indoor radon concentration. The results obtained by the four samples showed the largest radon exhalation rate of $0.34314Bq/m^2{\cdot}h$ for sample concrete. The radon concentration contribution to indoor radon in the house due to exhalation from the concrete was $31.006{\pm}7.529Bq/m^3$. The difference between the prediction concentration and actual measured concentration was believed to be due to the uncertainty resulting from the model implementation.

• ETRI Journal
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• v.42 no.2
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• pp.258-271
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• 2020

A correlation exists between luminance samples and chrominance samples of a color image. It is beneficial to exploit such interchannel redundancy for color image compression. We propose an algorithm that predicts chrominance components Cb and Cr from the luminance component Y. The prediction model is trained by supervised learning with Laplacian-regularized least squares to minimize the total prediction error. Kernel principal component analysis mapping, which reduces computational complexity, is implemented on the same point set at both the encoder and decoder to ensure that predictions are identical at both the ends without signaling extra location information. In addition, chrominance subsampling and entropy coding for model parameters are adopted to further reduce the bit rate. Finally, luminance information and model parameters are stored for image reconstruction. Experimental results show the performance superiority of the proposed algorithm over its predecessor and JPEG, and even over JPEG-XR. The compensation version with the chrominance difference of the proposed algorithm performs close to and even better than JPEG2000 in some cases.

• Clinical and Experimental Pediatrics
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• v.50 no.4
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• pp.369-375
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• 2007

Purpose : There have been numerous researches on urine ${\beta}_2$-microglobulin (${\beta}_2$-M) concerned with primary nephrotic syndrome and other glomerular diseases, but not much has been done in relation to pediatric age groups. Thus, our hospital decided to study the relations between the analysis of the test results we have conducted on pediatric patients and renal functions. Methods : Retrospective data analysis was done to 102 patients of ages 0 to 4 with renal diseases with symptoms such as hematuria, edema, and proteinuria who were admitted to Chung-Ang Yongsan Hospital and who participated in 24-hour urine and urine ${\beta}_2$-M excretion test between January of 2003 and January of 2006. Each disease was differentiated as independent variables, and the statistical difference of the results of urine ${\beta}_2$-M excretion of several groups of renal diseases was analyzed with student T-test by using test results as dependent variables. Results : Levels of urine ${\beta}_2$-M excretion of the 102 patients were as follows : 52 had primary nephrotic syndrome [MCNS (n=45, $72{\pm}45{\mu}g/g$ creatinine, ${\mu}g/g-Cr$), MPGN (n=3, $154{\pm}415{\mu}g/g-Cr$), FSGS (n=4, $188{\pm}46{\mu}g/-Cr$], six had APSGN ($93{\pm}404{\mu}g/g-Cr$), seven had IgA nephropathy ($3,414{\pm}106{\mu}g/g-Cr$), 9 had APN ($742{\pm}160{\mu}g/g-Cr$), 16 had cystitis ($179{\pm}168{\mu}g/g-Cr$), and 12 had HSP nephritis ($109{\pm}898{\mu}g/g-Cr$). IgA nephropathy (P<0.05) and APN (P<0.05) were significantly higher than in other renal diseases. Among primary nephrotic syndrome, FSGS with higher results of ${\beta}_2$-microglobulin test had longer treatment period (P<0.01) when compared to the lower groups, but no significant differences in Ccr, BUN, or Cr were observed. Conclusion : IgA nephropathy and APN groups showed significantly higher level of ${\beta}_2$-M excretion value than other groups. Although ${\beta}_2$-microglobulin value is not appropriate as an indicator of general renal function and pathology, it seems to be sufficient in the differential diagnosis of the UTI and in the prediction of the treat-ment period of nephrotic syndrome patients.

• The Korean Journal of Rheology
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• v.11 no.2
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• pp.128-134
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• 1999

Rheological characterization was examined for two different types of magenetic particle (rod-like $\gamma$-$Fe_{2}O_{3}$, $CrO_2$ )suspension in this study. The measured suspension viscosity (viscosity vs. concentration or shear rate) is used to obtain the dependence of viscous energy dissipation on the microstructural states of magnetic particle dispersions as well as the microstructural shape effects which are related to magnetic particle orientation. The empirical formulas from mean field theory and the Mooney equation are used to relate suspension viscosity to particle concentration. Intrinsic viscosities of these two different types of rod-like magnetic particle suspensions are found to exceed the prediction of hydrodynamic theory for dilute suspensions and support the existence of flocs containing significant amounts of immobilized suspending medium due to native attraction forces among particles in the microstructures.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.18-26
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• 2000

Boiler high-temperature pipelines such as main steam pipe, header and steam drum in fossil power plants are degraded by creep damage due to severe operating conditions such as high temperature and high pressure for an extended period time. Conventional measurement techniques(replica method, electric resistance method, and hardness test method) for measuring creep damage have such disadvantages as complex preparation and measurement procedures, too many control parameters. And also these techniques have low practicality and applied only to component surfaces with good accessibility. In this paper, artificial creep degradation test and ultrasonic measurement for their creep degraded specimens(Cr-Mo alloy steels) were carried out for the purpose of evaluation for creep damage. Absolute measuring method of quantitative ultrasonic measurement for material degradation was established, and long term creep degradation tests using life prediction formula were carried out. As a result of ultrasonic tests for crept specimens. we conformed that both the sound velocity decreased and attenuation coefficient linearly increased in proportion to the Increase of creep life fraction($\Phi$c).

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.61-75
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• 1997

The social demand urges us to use some equipments and structures in high temperature environment. By this occasion, the necessity of studying the fatigue crack growth is an important aspect of new materials. However, the present situation is rarely to accumulate the fatigue data. Especially, 1Cr-1Mo-0.25V steel and 304 stainless steel have been increased to be used under the severe condition of high temperature. And so, the fatigue estimation of those materials is important and appropriate. Fatigue tests have been carried out to examine the crack initiation, growth behaviour for the small fatigue crack of 1Cr-1Mo-0.25V steel and 304 stainless steel at room temperature and 538^{\circ}C$. The remote measurement system which has many merits of checking and saving the image for detailed examination was applied to closely detect the crack length. Generally, the fatigue crack initiated in the form of multiple cracks and grew each other. And then it coalesced to become a major crack. The major crack governed the rest of the fatigue life. In the growing process, each peripheral cracks interact and grow for a certain period. After then, it coalesced and fractured. On the basis of the above experimental data for the small crack, a simulation program was developed to predict the residual life time and to estimate the integrity of machine elements and structures. At the same time, the simulation was extended to 1Cr-1Mo-0.25V steel. The simulation results have shown a good agreement to those of the experimental ones for both materials of 1Cr-1Mo-0.25V steel and 304 stainless steel with small cracks. The NASCRAC has applied to compare the fatigue life with the experimental results. And so, it can be said that the simulation program is valuable tools to the industrial fields.