• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.31-38
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• 2003

In the present work, a nonlinear inverse perturbation method which has been used in the structural optimization, is adopted so as to identify the structural damages. Unlike the structural optimization, a larger number of constrained equations than the number of unknown parameters are often required detect structural damage. Therefore, nonlinear least squares method is utilized to solve the problem. Because only a limited number of sensors are available I real situation of damage detection, the determination of sensor location becomes one of the most important issues. Hence, this work concentrates on the issue of sensor placement in the framework of nonlinear inverse perturbation method, and the performances of various methodologies concerning to sensor placement are compared with each other. The comparisons show tat the successive elimination method gets good performance for sensor placement. From the several numerical studies, it is confirmed that the inverse perturbation method, combined with the successive elimination method, is very promising in structural damage detection.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.453-458
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• 2004

This study proposes a new two-level condensation scheme for the construction of a reduced system. In the first step, the candidate area is selected for the construction of the reduced system by energy estimation in element-level. In the second step, primary degrees of freedom are selected by sequential elimination from the candidate degrees of freedom linked to the selected elements. Numerical examples demonstrate that the proposed method saves the computational cost effectively and provides a reduced system which predicts the eigenvalues accurately. Moreover, the well-constructed reduced system can present the reliable behavior of the structure under arbitrary dynamic loads comparing to that of global system. Time integration in a reduced system can save the computing time remarkably. Through a few numerical examples, the efficiency and reliability of the proposed scheme are verified.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.439-450
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• 2008

In this study, the reduced system for the dynamic analysis is proposed and the selection criterion of the primary degrees of freedom is presented considering the relation between natural frequency and external loading frequency. A well-constructed reduced system can assure the accurate representation of the dynamic behavior under arbitrary dynamic loads. For selecting the primary degrees of freedom of the reduced system, we employ the robust two-level condensation scheme of which the reliability has been proven through previous study. In the numerical examples, the reliability of the dynamic analysis based on the reduced system is demonstrated through comparing with those of global system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.9 s.252
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• pp.1062-1069
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• 2006

Reduction schemes approximate the lower eigenvalues that represent the global behavior of the structures. But, they are not efficient to be applied to large-scaled problems because these schemes require considerable amount of computing time in constructing reduced one from the original large-scaled systems. In addition, the selection of the primary degrees of freedom might be localized to cause the excessive emphasis of the lower mode or lost of the important modes. In the present study, a new reduction method combined with the subdomain method is proposed. For the construction of the final reduced system the system of each domain subdivided into primary, slave and interface degrees of freedom. It is remarkably efficient and accurate comparable to full-scale system. Numerical examples demonstrate that the proposed method saves computational cost effectively and provides a reduced system which predicts accurate eigen-pairs of global system.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.9 no.1
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• pp.47-54
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• 1991

In this study, the accuracy of three dimensional location was improved by self calibration bundle method with additional parameter, which is to correct systematic error through detection and elimination of the gross error from updated reference variance for observation values in photogram-metry. In this study, with the result of comparing accuracy of each method, correcting systematic error is more effective after gross error detection and when observation values are contained more than two gross error the point with maximum correlation value is detected by masking effect of least square adjustment.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.3
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• pp.347-352
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• 2007

Eigenvalue reduction schemes approximate the lower eigenmodes that represent the global behavior of the structures. In the previous study, we proposed a two-level condensation scheme (TLCS) for the construction of a reduced system. In the first step, the selection of candidate elements by energy estimation, Rayleigh quotient, through Ritz vector calculation. In the second step, the primary degrees of freedom are selected by the sequential elimination method from the degrees of freedom connected to the candidate elements in the first step. In the present study, we propose TLCS combined with iterative improved reduced system (IIRS) to increase accuracy of the higher modes in the intermediate range. Also, it is possible to control the accuracy of the eigenvalues and eigenmodes of the reduced system. Finally, numerical examples demonstrate the performance of the proposed method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.1
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• pp.57-63
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• 2007

The systematic method to construct equivalent static load from a given dynamic load is proposed in the present study. Previously reported works to construct equivalent static load were based on ad hoc methods. Due to improper selection of loading position, they may results in unreliable structural design. The present study proposes the employment of primary degrees of freedom for imposing the equivalent static loads. The degrees of freedom are selected by two-level condensation scheme with reliability and efficiency. In several numerical examples, the efficiency and reliability of the proposed scheme is verified by comparison displacement for equivalent static loading and dynamic loading at the critical time.

• KSBB Journal
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• v.18 no.4
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• pp.282-288
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• 2003

For the screening of anti-inflammation and antioxidative activities, ethanolic extract of 40 species of traditional herbal medicines were examined their hyaluronidase inhibitory effect and radical scavenging activity in vitro. From the result of the hyaluronidase inhibitory activity using a Morgan-Elson assay, Astragali Radix, Eucommia Cortex, Schizandrae Fructus, Scutellaria Radix, Acanthopanacis Cortex, Chaenomelis Fructus, Amomum xanthioides Wallich and Moutan Radicis Cortex showed more than 50% hyaluronidase inhibitory effects at the concentration of 10 mg/mL. In the various solvent fractions (n-hexane, chloroform, ethyl acetate, water) prepared from ethanolic extracts, the ethyl acetate fraction of all extracts tested showed strong activity. Antioxidative activity was evaluated by assaying electron-donating ability to DPPH free radical and scavenging of hydroxyl radical (ㆍOH) generated through Fenton reaction, respectively. Rubus coreanus Miq, Moutan Radicis Cortex, Paeoniae Radix Alba, Plantaginis Semen and Sorbus commixta Hedl. showed high activity more than 90%, yet similar activity to $\alpha$-tocopherol and BHA at the concentration of 1 mg/mL in electron donating activity. The scavenging effects of ethanolic extracts on hydroxyl radical were investigated using a 2-deoxyribose oxidation method and tested all extracts showed significant radical scavenging activity. The experiment was also performed to examine whether herbal medicines having significant lipid peroxidation inhibitory activity, Schizandrae-Fructus is the strongest inhibitory activity in both linoleic acid and liposome peroxidation.

• Journal of Mushroom
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• v.19 no.3
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• pp.140-149
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• 2021

Mushroom-derived polysaccharides, which are the primary bioactive constituents, are beneficial for human health. Polysaccharides have immuno-modulation, antitumor, and antioxidant properties. Additionally, they have antiviral properties and protect against chronic radiation stress. In this study, high yield water-soluble polysaccharides were obtained from Pleurotus djamor var. roseus basidiocarps. The crude polysaccharide (CP) was extracted sequentially by hot water and ethanol precipitation. The yield of the brown CPs was 5.6% dw. Diethylaminoethyl cellulose and Sepharose-6B column chromatography of CPs generated several fractions. Total glucan content was determined in all the fractions. The F1 fraction displayed the highest sugar content and was considered as a purified polysaccharide (PP). The total glucan and β-glucan content in the four fractions ranged between 76.85-2.95% and 75.08-1.46%, respectively. The yield of the PPs was 300 mg, and it was obtained as a white powder. The PPs were characterized by Fourier-transform infrared spectroscopy (FTIR) and thin-layer chromatography. The FTIR spectral details confirmed the presence of a xylopentose polysaccharide. The antioxidant activity of the PPs was evaluated using in vitro 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging assay and superoxide radical scavenging assay. The PPs showed strong DPPH free radical and superoxide anion radical scavenging activities in a dose-dependent manner. Purified PPs free of phenolics, protein, and carbohydrates were mainly responsible for the radical scavenging activity. The data suggest the potential of PPs as natural antioxidants.

• Food Science and Preservation
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• v.22 no.3
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• pp.437-442
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• 2015

In a continuing screening of selected medicinal plants native to South Korea, the antioxidant and pancreatic lipase inhibitory activities of an aqueous methanolic extract from the heartwood of Aquilaria agallocha were investigated. Eighty percent of the methanolic extract of A. agallocha was further divided into $CH_2Cl_2$, EtOAc and n-BuOH in order to yield four solvent-soluble portions, namely $CH_2Cl_2$-soluble, EtOAc-soluble, n-BuOH-soluble and $H_2O$ residue. The antioxidant properties were evaluated by employing radical scavenging assays using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) ($ABTS^+$) radicals, while the anti-obesity efficacy of A. agallocha extracts and solvent-soluble portions were tested by porcine pancreatic lipase assay. All tested samples showed dose-dependent radical scavenging and pancreatic lipase inhibitory activities. Among the tested extracts and solvent-soluble portions, the $CH_2Cl_2$-soluble portion showed much higher radical scavenging activity and pancreatic lipase inhibitory properties when compared with other solvent-soluble portions. This result suggested that there was a significant relationship between the total phenolic content and biological efficacies, and A. agallocha extract might be considered as a new potential source of natural antioxidants and as a pancreatic lipase inhibitory source. A more systematic investigation of this biomass will be performed for further investigation of activity against antioxidative and anti-obesity effects.