• Title/Summary/Keyword: Determination of Defects

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Distribution Characteristics of Bending Properties for Visual Graded Lumber of Japanese Larch (육안등급으로 구분된 낙엽송 제재목의 휨성능 분포 특성)

  • Lee, Jun Jae;Kim, Gwang Chul;Kim, Kwang Mo;Oh, Jung Kwon
    • Journal of the Korean Wood Science and Technology
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    • v.31 no.5
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    • pp.72-79
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    • 2003
  • In reliability based design(RBD) method, the distribution characteristics of mechanical properties of material are basic input variable. Therefore, distribution type and parameters of mechanical properties should be determined accurately. Until now, the properties were derived from tests with small, clear specimens. However, the test conditions should emulate as nearly as possible the way in which the timber would be used in practice and the test results should, as closely as possible, reflect the structural end use conditions to which the timber products would be subjected. In this study, structural timbers (38mm by 140mm, 3.0m long) were graded by visual assessment of growth characteristics and defects. And then bending tests were conducted on 498 structural size timbers. For each grade, the distribution type and the parameters of mechanical properties were determined for each grade. For the determination of best-fit distribution type, comparing of square error between distribution types and KS test were conducted. Best-fit distribution type of bending strength(MOR) is weibull distribution for all grade. In case of MOE, normal distribution is best-fit.

Reliability Evaluation for Prediction of Concrete Compressive Strength through Impact Resonance Method and Ultra Pulse Velocity Method (충격공진법과 초음파속도법을 통한 콘크리트 압축강도 예측의 신뢰성 평가)

  • Lee, Han-Kyul;Lee, Byung-Jae;Oh, Kwang-Chin;Kim, Yun-Yong
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.4
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    • pp.18-24
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    • 2015
  • Non-destructive testing (NDT) methods are widely used in the construction industry to diagnose the defects/strength of the concrete structure. However, it has been reported that the results obtained from NDT are having low reliability. In order to resolve this issue, four kinds of NDT test (ultrasonic velocity measurements by P-wave and S-wave and the impact resonance methods by longitudinal vibration and deformation vibration) were carried out on 180 concrete cylinders made with two kinds of mix proportions. The reliability of the NDT results was analyzed and compared through the measurement of the actual compressive strength of the concrete cylinders. The statistical analysis of the results was revealed that the ultrasonic velocity method by S-wave is having lowest coefficient of variation and also most capable of stable observation. Analytical equations were established to estimate the compressive strength of the concrete from the obtained NDT results by relating the actual compressive strength. Moreover the equation established by the ultrasonic velocity method by S-wave had the highest coefficient of determination. Further studies on the stability of non-destructive testing depending on various mixing conditions will be necessary in the future.

Folate: 2020 Dietary reference intakes and nutritional status of Koreans (엽산: 2020 영양소 섭취기준과 한국인의 영양상태)

  • Han, Young-Hee;Hyun, Taisun
    • Journal of Nutrition and Health
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    • v.55 no.3
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    • pp.330-347
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    • 2022
  • Folate, a water-soluble vitamin, acts as a coenzyme for one-carbon metabolism in nucleic acid synthesis and amino acid metabolism. Adequate folate nutritional status during the periconceptional period is known to prevent neural tube defects. In addition, insufficient folate intake is associated with various conditions, such as anemia, hyperhomocysteinemia, cardiovascular disease, cancer, cognitive impairment, and depression. This review discusses the rationale for the revision of the 2020 Korean dietary reference intakes for folate, and suggestions for future revisions. Based on the changes in the standard body weight in 2020, the adequate intake (AI) for infants (5-11 months) and the estimated average requirements (EARs) for 15-18 years of age were revised, but there were no changes in the recommended nutrient intakes (RNIs) and tolerable upper intake levels (ULs) for all age groups. Mean folate intake did not reach RNI in most age groups and was particularly low in women aged 15-29 years, according to the results of the 2016-2018 Korea National Health and Nutrition Examination Survey (KNHANES). The percentages of folate intake to RNI were lower than 60% in pregnant and lactating women, but serum folate concentrations were higher than those in other age groups, presumably due to the use of supplements. Therefore, total folate intake, from both food and supplements, should be evaluated. In addition, the database of folate in raw, cooked, and fortified foods should be further expanded to accurately assess the folate intake of Koreans. Determination of the concentrations of erythrocyte folate and plasma homocysteine as well as serum folate is recommended, and quality control of the analysis is critical.

First-principles Study on the Magnetic Properties of Gd doped Bithmuth-Telluride (Gd 도핑된 비스무스 텔루라이드의 자기적 성질에 대한 제일원리 계산 연구)

  • Van Quang, Tran;Kim, Miyoung
    • Journal of the Korean Magnetics Society
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    • v.26 no.2
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    • pp.39-44
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    • 2016
  • Determination of the structural, electronic, and magnetic properties of the magnetically doped bismuth-telluride alloys are drawing lots of interest in the fields of the thermoelectric application as well as the research on magnetic interaction and topological insulator. In this study, we performed the first-principles electronic structure calculations within the density functional theory for the Gd doped bismuth-tellurides in order to study its magnetic properties and magnetic phase stability. All-electron FLAPW (full-potential linearized augmented plane-wave) method is employed and the exchange correlation potentials of electrons are treated within the generalized gradient approximation. In order to describe the localized f-electrons of Gd properly, the Hubbard +U term and the spin-orbit coupling of the valence electrons are included in the second variational way. The results show that while the Gd bulk prefers a ferromagnetic phase, the total energy differences between the ferromagnetic and the antiferromagnetic phases of the Gd doped bismuth-telluride alloys are about ~1meV/Gd, indicating that the stable magnetic phase may be changed sensitively depending on the structural change such as defects or strains.

Determination of PEG Concentration and Solvent Selection for Freeze-Drying of Highly-Degraded Waterlogged Woods (고함수율 수침고목재의 동결 건조를 위한 PEG 전처리 농도 및 용매 설정)

  • Kim, Soo-Choul;Park, Won-Kyu;Yi, Yong-Hee
    • Journal of Conservation Science
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    • v.9 no.1
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    • pp.40-47
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    • 2000
  • Dimension stability was examined after PEG pretreatment and post freeze-drying treatment in order to determine the PEG(#3350) concentration and solvent for pre-treatment of freeze-drying of highly-degraded waterlogged ash woods(Fraxinus spp.; ca. 5,700 BP) excavated from peat lands at Pyungtack, Kyounggi-do. At the low concentration (<30-40%) of PEG soaking in both water and t-butanol, the weight increases abruptly, but at high concentration (>50%) gradually, consequently, taking longer treatment time. PEG loading was higher in t-butanol solution than in water. However, the best dimesional stability was obtained from freeze-drying after lower PEG solution (40% in water) soaking. Low dimensional stability, found in the samples treated with higher PEG solutions (60%-70% in t-butanol), might come from incomplete freezing and excess PEG absorbing moisture. The samples air-dried after 70% PEG treatment had collapse defects. In conclusion, the use of low concentration (about 40% in water) PEG solution was the most suitable pretreatment for freeze drying of highly-degraded waterlogged ash woods.

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The Defect Characterization of Luminescence Thin Film by the Positron Annihilation Spectroscopy (양전자 소멸 측정을 이용한 발광 박막 구조 결함 특성)

  • Lee, Kwon Hee;Bae, Suk Hwan;Lee, Chong Yong
    • Journal of the Korean Vacuum Society
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    • v.22 no.5
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    • pp.250-256
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    • 2013
  • It is described that the proton beam induces micro-size defects and electronic deep levels in luminescence Thin Film. Coincidence Doppler Broadening Positron Annihilation Spectroscopy (CDBPAS) and Positron lifetime Spectroscopy were applied to study of characteristics of a poly crystal samples. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S-parameter value. The samples were exposed by 3.0 MeV proton beams with the intensities ranging between 0 to ${\sim}10^{14}$ particles. The S-parameter values decreased as increased the proton beam, that indicates the protons trapped in vacancies. Lifetime ${\tau}_1$ shows that positrons are trapped in mono vacancies. Lifetime ${\tau}_2$ is not changed according to proton irradiation that indicate the cluster vacancies of the grain structure.

Corporate Bond Rating Using Various Multiclass Support Vector Machines (다양한 다분류 SVM을 적용한 기업채권평가)

  • Ahn, Hyun-Chul;Kim, Kyoung-Jae
    • Asia pacific journal of information systems
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    • v.19 no.2
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    • pp.157-178
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    • 2009
  • Corporate credit rating is a very important factor in the market for corporate debt. Information concerning corporate operations is often disseminated to market participants through the changes in credit ratings that are published by professional rating agencies, such as Standard and Poor's (S&P) and Moody's Investor Service. Since these agencies generally require a large fee for the service, and the periodically provided ratings sometimes do not reflect the default risk of the company at the time, it may be advantageous for bond-market participants to be able to classify credit ratings before the agencies actually publish them. As a result, it is very important for companies (especially, financial companies) to develop a proper model of credit rating. From a technical perspective, the credit rating constitutes a typical, multiclass, classification problem because rating agencies generally have ten or more categories of ratings. For example, S&P's ratings range from AAA for the highest-quality bonds to D for the lowest-quality bonds. The professional rating agencies emphasize the importance of analysts' subjective judgments in the determination of credit ratings. However, in practice, a mathematical model that uses the financial variables of companies plays an important role in determining credit ratings, since it is convenient to apply and cost efficient. These financial variables include the ratios that represent a company's leverage status, liquidity status, and profitability status. Several statistical and artificial intelligence (AI) techniques have been applied as tools for predicting credit ratings. Among them, artificial neural networks are most prevalent in the area of finance because of their broad applicability to many business problems and their preeminent ability to adapt. However, artificial neural networks also have many defects, including the difficulty in determining the values of the control parameters and the number of processing elements in the layer as well as the risk of over-fitting. Of late, because of their robustness and high accuracy, support vector machines (SVMs) have become popular as a solution for problems with generating accurate prediction. An SVM's solution may be globally optimal because SVMs seek to minimize structural risk. On the other hand, artificial neural network models may tend to find locally optimal solutions because they seek to minimize empirical risk. In addition, no parameters need to be tuned in SVMs, barring the upper bound for non-separable cases in linear SVMs. Since SVMs were originally devised for binary classification, however they are not intrinsically geared for multiclass classifications as in credit ratings. Thus, researchers have tried to extend the original SVM to multiclass classification. Hitherto, a variety of techniques to extend standard SVMs to multiclass SVMs (MSVMs) has been proposed in the literature Only a few types of MSVM are, however, tested using prior studies that apply MSVMs to credit ratings studies. In this study, we examined six different techniques of MSVMs: (1) One-Against-One, (2) One-Against-AIL (3) DAGSVM, (4) ECOC, (5) Method of Weston and Watkins, and (6) Method of Crammer and Singer. In addition, we examined the prediction accuracy of some modified version of conventional MSVM techniques. To find the most appropriate technique of MSVMs for corporate bond rating, we applied all the techniques of MSVMs to a real-world case of credit rating in Korea. The best application is in corporate bond rating, which is the most frequently studied area of credit rating for specific debt issues or other financial obligations. For our study the research data were collected from National Information and Credit Evaluation, Inc., a major bond-rating company in Korea. The data set is comprised of the bond-ratings for the year 2002 and various financial variables for 1,295 companies from the manufacturing industry in Korea. We compared the results of these techniques with one another, and with those of traditional methods for credit ratings, such as multiple discriminant analysis (MDA), multinomial logistic regression (MLOGIT), and artificial neural networks (ANNs). As a result, we found that DAGSVM with an ordered list was the best approach for the prediction of bond rating. In addition, we found that the modified version of ECOC approach can yield higher prediction accuracy for the cases showing clear patterns.