• Smart Structures and Systems
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• v.8 no.3
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• pp.303-320
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• 2011

Comparing to active damage monitoring, impact localization on composite by using time reversal focusing method has several difficulties. First, the transfer function of the actuator-sensor path is difficult to be obtained because of the limitation that no impact experiment is permitted to perform on the real structure and the difficulty to model it because the performance of real aircraft composite is much more complicated comparing to metal structure. Second, the position of impact is unknown and can not be controlled as the excitation signal used in the active monitoring. This makes it not applicable to compare the difference between the excitation and the focused signal. Another difficulty is that impact signal is frequency broadband, giving rise to the difficulty to process virtual synthesis because of the highly dispersion nature of frequency broadband Lamb wave in plate-like structure. Aiming at developing a practical method for on-line localization of impact on aircraft composite structure which can take advantage of time reversal focusing and does not rely on the transfer function, a PZT sensor array based phase synthesis time reversal impact imaging method is proposed. The complex Shannon wavelet transform is presented to extract the frequency narrow-band signals from the impact responded signals of PZT sensors. A phase synthesis process of the frequency narrow-band signals is implemented to search the time reversal focusing position on the structure which represents the impact position. Evaluation experiments on a carbon fiber composite structure show that the proposed method realizes the impact imaging and localization with an error less than 1.5 cm. Discussion of the influence of velocity errors and measurement noise is also given in detail.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.4
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• pp.19-22
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• 2017

In this study, wavelength-free $1{\times}N$ optical splitter using a tapered polymer waveguide was studied to realize the transmission network of high-speed information communication network. Based on the evaluation of mode converting characteristics of splitter having two tapered multi-mode interference structures, an optimized structure of the $1{\times}N$ splitter was proposed for wide-range of input wavelength. 2D-BPM analysis $1{\times}8$ model showed that insertion loss of the proposed splitter is less than 10 dB for wavelength of input source from 1260 nm to 1650 nm.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.16 no.3
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• pp.290-302
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• 1994

This study was aimed to clarify the histopathological changes in the experimental animal model subjcted to rigid fixation performed across the frontonasal sutrue in growing rabbits. Sixteen rabbits aged 6 weeks used. In experimental group(n=12), rigid fixation with miniplates and screws was performed across the frontonasal suture. Control group(n=4) was those with periosteal elevation only. Experimental animals were sacrificed on the 2nd, 4th, 8th, and 12th week after operation, and frontonasal suture area was excised for light microscopic and scanning electron microscopic examination. The results obtained were as follows : 1. In control groups, collagen fiber bundles ran in the midportion of bone sutrue and cambial layers were seen at bone surface. Sutural surfaces are beveled and external and internal bony projected portions were observed. 2. In experimental groups, distance of bone suture was decreased by new bone formation on the 2nd week, while increased by bone resorption at the miniplate applied area and bone formation in the adjacent bone on the 4th week. 3. In experimental groups, the original bone surface was almost resorbed and new bone formation was found on the 8th week. Regulary-run collagen fibers, smooth and dense bone surfaces were similar to the bone patterns of control groups on the 12th week. Above results suggest that bone formation is restricted where the miniplate is applied, while compensatory growth is appeared in the adjacent bont. It is considered that rigid fixation with miniplates and acrews results in a little disturbance of sutural growth of the craniofacial bone in infancy and children when applied for short duration.

• Carbon letters
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• v.24
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• pp.82-89
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• 2017

In this study, composite PAN-based ACNFs embedded with MgO and $MnO_2$ were prepared by the electrospinning method. The resultant pristine ACNFs, ACNF/MgO and $ACNF/MnO_2$ were characterized in terms of their morphological changes, SSA, crystallinity and functional group with FESEM-EDX, the BET method, XRD and FTIR analysis, respectively. Results from this study showed that the SSA of the ACNF/MgO composite ($1893m^2g^{-1}$) is significantly higher than that of the pristine ACNFs and $ACNF/MnO_2$ which is 478 and $430m^2g^{-1}$, respectively. FTIR analysis showed peaks of 476 and $547cm^{-1}$, indicating the presence of MgO and $MnO_2$, respectively. The FESEM micrographs analysis showed a smooth but coarser structure in all the ACNFs. Meanwhile, the ACNF/MgO has the smallest fiber diameter ($314.38{\pm}62.42nm$) compared to other ACNFs. The presence of MgO and $MnO_2$ inside the ACNFs was also confirmed with EDX analysis as well as XRD. The adsorption capacities of each ACNF toward $CH_4$ were tested with the volumetric adsorption method in which the ACNF/MgO exhibited the highest $CH_4$ adsorption up to $2.39mmol\;g^{-1}$. Meanwhile, all the ACNF samples followed the pseudo-second order kinetic model with a $R^2$ up to 0.9996.

• Composites Research
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• v.31 no.2
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• pp.69-75
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• 2018

In this study, a grid panel structure in which the woven CFRP composites were stacked in the orthogonal array was proposed and the mechanical properties were analyzed and studied. The grid parts were fabricated by cutting prepregs and laminating them. The grid panel structure was fabricated by co-curing with lower laminate plate in auto-clave process. The behavior of the proposed grid panel structure was evaluated by tests under tensile, compressive, shear, and bending loads. The effect of increasing the stiffness of the orthogonal grid structure was verified through these tests. In addition, the finite element model was constructed and compared with the test results, confirming the validity and reliability of the test and analysis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.2
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• pp.76-83
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• 2015

This paper aims at developing an environmentally friendly modular dome structure system with highly filled extrusion wood-plastic composite (WPC) member, and manufacturing a real-size specimen by modularizing members and nodes. The member used in the model is the WPC member with 70% wooden fiber contests, which is higher then previous WPC one. Its members and nodes are modularized by analyzing geometric characteristics of icosahedral-based geodetic dome. Applicapability of the 6ea prototype nodes and 3ea prototype members to the modular dome is examined with the results of the modulaization and the making process for the real-size specimen. Besides, from the analysis results, the lowest buckling mode is expected to be a nodal buckling on a node near the boundary.

• Advances in nano research
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• v.9 no.1
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• pp.1-13
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• 2020

In this work, the electrical potential (EP) technique with an artificial neural networks (ANNs) for monitoring of nanostructures are used for the first time. This study employs an expert system to identify size and localize hidden nano-delamination (N.Del) inside layers of nano-pipe (N.P) manufactured from Basalt Fiber Reinforced Polymer (BFRP) laminate composite by using low-cost monitoring method of electrical potential (EP) technique with an artificial neural networks (ANNs), which are combined to decrease detection effort to discern N.Del location/size inside the N.P layers, with high accuracy, simple and low-cost. The dielectric properties of the N.P material are measured before and after N.Del introduced using arrays of electrical contacts and the variation in capacitance values, capacitance change and node potential distribution are analyzed. Using these changes in electrical potential due to N.Del, a finite element (FE) simulation model for N.Del location/size detection is generated by ANSYS and MATLAB, which are combined to simulate sensor characteristic, therefore, FE analyses are employed to make sets of data for the learning of the ANNs. The method is applied for the N.Del monitoring, to minimize the number of FE analysis in order to keep the cost and save the time of the assessment to a minimum. The FE results are in excellent agreement with an ANN and the experimental results available in the literature, thus validating the accuracy and reliability of the proposed technique.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.159-169
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• 2014

This study generalizes the lateral load-displacement relationship of reinforced concrete shear walls from the section analysis for moment-curvature response to straightforwardly evaluate the flexural capacity and ductility of such members. Moment and curvature at different selected points including the first flexural crack, yielding of tensile reinforcing bar, maximum strength, 80% of the maximum strength at descending branch, and fracture of tensile reinforcing bar are calculated based on the strain compatibility and equilibrium of internal forces. The strain at extreme compressive fiber to determine the curvature at the descending branch is formulated as a function of reduction factor of maximum stress of concrete and volumetric index of lateral reinforcement using the stress-strain model of confined concrete proposed by Razvi and Saatcioglu. The moment prediction models are simply formulated as a function of tensile reinforcement index, vertical reinforcement index, and axial load index from an extensive parametric study. Lateral displacement is calculated by using the moment area method of idealized curvature distribution along the wall height. The generalized lateral load-displacement relationship is in good agreement with test result, even at the descending branch after ultimate strength of shear walls.

• Preventive Nutrition and Food Science
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• v.17 no.4
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• pp.245-253
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• 2012

Collagen tripeptide (CTP) is a functional food material with several biological effects such as improving dry skin and wound and bone fracture healing. This study focused on the anti-photoaging effects of CTP on a hairless mouse model. To evaluate the effects of CTP on UVB-induced skin wrinkle formation in vivo, the hairless mice were exposed to UVB radiation with oral administration of CTP for 14 weeks. Compared with the untreated UVB control group, mice treated with CTP showed significantly reduced wrinkle formation, skin thickening, and transepidermal water loss (TEWL). Skin hydration and hydroxyproline were increased in the CTP-treated group. Moreover, oral administration of CTP prevented UVB-induced MMP-3 and -13 activities as well as MMP-2 and -9 expressions. Oral administration of CTP increased skin elasticity and decreased abnormal elastic fiber formation. Erythema was also decreased in the CTP-treated group. Taken together, these results strongly suggest that CTP has potential as an anti-photoaging agent.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.503-509
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• 2013

Carbon fiber reinforced plastics (CFRPs), a composite material, are generally vulnerable to compressive load and impact damage in a direction perpendicular to the surface of the material. In particular, during the operation of an aircraft, impact damages caused by bird collisions or falling tools reduce the strength of the aircraft structure. In this study, after impact damages were applied to CFRP specimens with various impact energies and impactor diameters, the compressive residual strength of the impact-damaged specimen was evaluated by performing a compression test. Furthermore, a prediction model for the compressive residual strength is proposed according to the variation in the impact energy by comparing the test results.