• Korean Journal of Food Science and Technology
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• v.22 no.6
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• pp.686-689
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• 1990

For the monitoring of kimchi fermentation states, pressure detecting sensor and monitoring device were designed and fabricated. The system was consisted of an air tight fermenting tube(31.5 ml), strain gauge type pressure sensor and signal processing device built with operational amplifier and A/D converter, and interfaced to personal computer. Chiness cabbage kimchi was fermented in the plastic container($150{\times}220{\times}160mm$) at $25^{\circ}C\;and\;30^{\circ}C$. The fermentation was monitored with fermenting tubes containing kimchi. The pressure based kimchi fermentation curve was constructed and showed a typical kimchi curing curve having 2 stepwise pressure increasing pattern.

• Smart Structures and Systems
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• v.33 no.3
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• pp.189-199
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• 2024

To properly extract the strain components under varying operational conditions is very important in bridge health monitoring. The abnormal sensor readings can be correctly identified and the expected operational performance of the bridge can be better understood if each strain components can be accurately quantified. In this study, strain components under varying load conditions, i.e., temperature variation and live-load variation are evaluated based on field strain measurements collected from a real concrete box-girder bridge. Temperature-induced strain is mainly regarded as the trend variation along with the ambient temperature, thus a smoothing technique based on the wavelet packet decomposition method is proposed to estimate the temperature-induced strain. However, how to effectively extract the vehicle-induced strain is always troublesome because conventional threshold setting-based methods cease to function: if the threshold is set too large, the minor response will be ignored, and if too small, noise will be introduced. Therefore, an autoencoder framework is proposed to evaluate the vehicle-induced strain. After the elimination of temperature and vehicle-induced strain, the left of which, defined as the model error, is used to assess the operational performance of the bridge. As empirical techniques fail to detect the degraded state of the structure, a clustering technique based on Gaussian Mixture Model is employed to identify the damage occurrence and the validity is verified in a simulation study.

• Steel and Composite Structures
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• v.35 no.6
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• pp.779-788
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• 2020

Multi-Walled Carbon nanotubes (MWCNT) coupled with Silicone Rubber (SR) can represent applicable strain sensors with accessible materials, which result in good stretchability and great sensitivity. Employing these materials and given the fact that the combination of these two has been addressed in few studies, this study is trying to represent a low-cost, durable and stretchable strain sensor that can perform excellently in a high number of repeated cycles. Great stability was observed during the cyclic test after 2000 cycles. Ultrahigh sensitivity (GF>1227) along with good extensibility (ε>120%) was observed while testing the sensor at different strain rates and the various number of cycles. Further investigation is dedicated to sensor performance in the detection of human body movements. Not only the sensor performance in detecting the small strains like the vibrations on the throat was tested, but also the larger strains as observed in extension/bending of the muscle joints like knee were monitored and recorded. Bearing in mind the applicability and low-cost features, this sensor may become promising in skin-mountable devices to detect the human body motions.

• Journal of Microbiology
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• v.40 no.4
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• pp.274-281
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• 2002

The competitive quantitative PCR method targeting pcbC gene was developed for monitoring 4-chlorobiphenyl(4CB)-degrading bacteria, Pseudomonas sp. strain DJ-12, in soil microcosms. The method involves extraction of DNA from soil contaminated with 4CB, PCR amplification of a pcbC gene fragment from the introduced strain with a set of strain-specific primers, and quantification of the elec-trophoresed PCR product by densitometry. To test the adequacy of the method, Pseudomonas sp. strain DJ-12 was introduced into both contaminated and non-contaminated soil microcosms amended with 4CB. Pseudomonas sp. strain DJ-12 was monitored and quantified by a competitive quantitative PCR in comparison with 4CB degradation and the result was compared to those obtained by using the conventional cultivation method. We successfully detected and monitored 4CB-degrading bacteria in each microcosm and found a significant linear relationship between the number of 4CB-degrading bacteria and the capacity for 4CB biodegradation. The results of DNA spiking and cell-spreading experiments suggest that this competitive quantitative PCR method targeting the pcbC gene for monitoring 4CB- degrading bacteria appears to be rapid, sensitive and more suitable than the microbiological approach in estimating the capacity of 4CB biodegradation in environmental samples.

• Composites Research
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• v.16 no.3
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• pp.58-67
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• 2003

To perform the realtime strain and fracture monitoring of the smart composite structures, two optical fiber sensor systems are proposed. The two types of the coherent sources were used for fracture signal detection - EDFA with FBG and EDFA with Fabry-Perot filter. These sources were coupled to EFPI sensors imbedded in composite specimens. To understand the characteristics of matrix crack signals, at first, we performed tensile tests using surface attached PZT sensors by changing the thickness and width of the specimens. This paper describes the implementation of time-frequency analysis such as short time Fourier transform (STFT) and wavelet transform (WT) for the quantitative evaluation of fracture signals. The experimental result shows the distinctive signal features in frequency domain due to the different specimen shapes. And, from the test of tensile load monitoring using optical fiber sensor systems, measured strain agreed with the value of electric strain gage and the fracture detection system could detect the moment of damage with high sensitivity to recognize the onset of micro-crack fracture signal.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.6
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• pp.607-613
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• 2008

A monitoring system for the subway structures using prestrained FBG sensors fixed with partially stripped fibers was developed. The sensor packages had pre-strain controllable fixtures. Tensile and compressive strain of the structure could be measured without slip. The FBG sensor system was applied to the concrete lining structure in Taegu subway. Near the structure, the narrow tunnel construction, for the electric power cables and telecommunication cables, started. We wanted to measure the deformations of the subway structures due to the construction by the FBG sensor. The applied sensors had the gauge length of 1 meter to overcome the inhomogeneity of the concrete material with enough length. In order to fix tightly to the structure, the partially stripped parts of the sensor glued to the package and slip phenomenon between fiber and acrylate jacket was prevented. Prestrain of the sensor was imposed by controlling the two fixed points with bolts and nuts in order to measure compressive strain as well as tensile strain. The behavior of subway lining structure could be monitored very well.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.3 s.22
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• pp.9-16
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• 2006

In structural health monitoring, the safety of structural members are assessed by the level of stress measured by various strain sensors based on different sensing mechanisms. Since most existing strain sensors used for health monitoring system can cover a relatively small range of structural members, it is very difficult to measure the maximum value of the member subjected to varying amount and types of loads with those point sensors. The reliability of assessed safety of a member may be improved by increasing the number of sensors. It may not be also realistic to increase the number of sensors to overcome these drawbacks. In this paper, a stress measuring method for beam-column members is developed by estimating the maximum stress based on the average strains obtained from long gauge sensor. The average strain from long gage fiber optic sensor is transformed into the maximum strain by multiplication of the modification factor derived in this research.

• Composites Research
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• v.22 no.6
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• pp.1-6
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• 2009

This paper presents an experimental study on the piezoresistive behavior of nanocomposite strain sensors subjected to various loading modes and their capability to detect structural deformations and damages. The electrically conductive nanocomposites were fabricated in the form of a film using various types of thermoplastic polymers and multi-walled carbon nanotubes (MWNTs) at various loadings. In this study, the nanocomposite strain sensors were bonded to a substrate and subjected to tension, flexure, or compression. In tension and flexure, the resistivity change showed dependence on measurement direction, indicating that the sensors can be used for multi-directional strain sensing. In addition, the sensors exhibited a decreasing behavior in resistivity as the compressive load was applied, suggesting that they can be used for pressure sensing. This study demonstrates that the nanocomposite strain sensors can provide a pathway to affordable, effective, and versatile structural health monitoring.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.754-760
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• 2008

For monitoring of railway structures, optical fiber sensors are very convenient. The fiber sensors are very small and do not disturb the structural properties. They also have several merits such as electro-magnetic immunity, long signal transmission, good accuracy and multiplicity of one sensor line. Strain measurement technologies with fiber optic sensors have been investigated as a part of smart structure. In this paper, we investigated the possibilities of fiber optic sensor application to the monitoring of railway structures. We expect that the fiber optic sensors have much less noises than electrical strain gauges because of electro-magnetic immunity while railways operate electric power of 22000 volts. Fiber optic sensors showed good durability and long term stability for continuous monitoring of the railway structures as well as good response to the structural behaviors during construction.

• Structural Monitoring and Maintenance
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• v.6 no.3
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• pp.255-268
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• 2019

Civil infrastructures, such as bridges and tunnels are most important assets and their failure during service will have significant economic and social impact in any country. Behavior of a bridge can be evaluated only through actual monitoring/measurements of bridge members under the loads of interest. Theoretical analysis alone is not a good predictor of the ability of a bridge. In some cases, theoretical analyses can give less effect than actual since theoretical analyses do not consider the actual condition of the bridge, support conditions, level of corrosion and damage in members and connections etc. Hence actual measurements of bridge response should be considered in making decisions on structural integrity, especially in cases of high value bridges (large spans and major crossings). This paper describes in detail the experimental investigations carried out on an open web type steel railway bridge. Strain gages and displacement transducers were installed at critical locations and responses were measured during passage of locomotives. Stresses were evaluated and extrapolated to maximum design loading. The responses measured from the bridge were within the permissible limits. The methodology adopted shall be used for assessing the structural integrity of the bridge for the design loads.