• Journal of Powder Materials
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• v.22 no.4
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• pp.234-239
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• 2015

Electronic products are a major part of evolving industry and human life style; however most of them are known to emit electromagnetic waves that have severe health hazards. Therefore, different materials and fabrication techniques are understudy to control or limit transfer of such waves to human body. In this study, nanocomposite powder is dispersed into epoxy resin and shielding effects such as absorption, reflection, penetration and multiple reflections are investigated. In addition, nano size powder (Ni, $Fe_2O_3$, Fe-85Ni, C-Ni) is fabricated by pulsed wire evaporation method and dispersed manually into epoxy. Characterization techniques such as X-ray diffraction, Scanning electron microscopy and Transmission electron microscopy are used to investigate the phase analysis, size and shape as well as dispersion trend of a nano powder on epoxy matrix. Shielding effect is measured by standard test method to investigate the electromagnetic shielding effectiveness of planar materials, ASTM D4935. At lower frequency, sample consisting nano-powder of Fe-85%Wt Ni shows better electromagnetic shielding effect compared to only epoxy, only Ni, $Fe_2O_3$ and C-Ni samples.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1082-1089
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• 1998

To obtain fine dispersion of Ag particles in $YBa_2$$Cu_3$$O_{7-y}$ (123) superconductors, 123 samples were made by pyrophoric synthetic method using malic acid and the subsequent solid- state reaction. As the pyrophoric synthetic powder was used as a precursor material, fine 123 powder of submicron size was produced in a short reaction time. The added $Ag_2$O was converted to metallic Ag during Pyrophoric reaction and it accelerated both the formation of 123 phase and the grain growth via the enhanced mass transfer. The Ag particles of the sample sintered using the pyrephoric synthetic powder were more finely dispersed in the 123 matrix, compared to those of the sample sintered using the mechanically mixed powder, attributing to the improvement of the superconducting properties.

• Bulletin of the Society of Naval Architects of Korea
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• v.13 no.1
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• pp.1-9
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• 1976

Using the computer programs for calculation of natural vibrations of ship's hull developed by the authors et al., an investigation into influences of various parameters on the accuracy of calculation was done through example calculations of a 30,000 DWT petroleum products carrier M/S Sweet Brier built by Korea Shipbuilding and Engineering Corporation. The methodical principles employed for the computer program development are as follows; (a) the ship system is reduced to an equivalent discrete elements system conforming to Myklestad-Prohl model, (b) the problem formulation is of transfer matrix method, and (c) to obtain solutions an extended $G\ddot{u}mbel's$ initial value method is introduced. The scope of the investigation is influences of number of discrete elements, choice of significant system parameters such as rotary inertia, bending stiffness and shear stiffness, and simplification of distributions of added mass and stiffness as trapezoidal ones referred to those of midship section on the calculation accuracy. From the investigation the followings are found out; (1) To obtain good results for the modes up to the seven-noded thirty or more divisions of the hull is desirable. For fundamental mode fifteen divisions may give fairly good results. (2) The influence of rotary inertia is negligibly small at least for the modes up to the 5- or 6- noded. (3) In the case of assuming either bending modes or shear modes the calculation results in considerably higher frequencies as compared with those based on Timoshenko beam theory. However, the calculation base on the slender beam theory surprisingly gives frequencies within 10% error for fundamental modes. (4) It is proved that to simplify distributions of added mass and stiffness as trapezoidal ones referred to those of midship section is a promising approach for the prediction of natural frequencies at preliminary design stage; provided good accumulation of data from similar type ships, we may expect to obtain natural frequencies within 5% error.

• Korean Journal of Materials Research
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• v.32 no.11
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• pp.508-514
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• 2022

Piezoelectric composite films which are enabled by inorganic piezoelectric nanomaterials-embedded polymer, have attracted enormous attention as a sustainable power source for low powered electronics, because of their ease of fabrication and flexible nature. However, the absorption of applied stress by the soft polymeric matrices is a major issue that must be solved to expand the fields of piezoelectric composite applications. Herein, a flexible and porous piezoelectric composite (piezoelectric sponge) comprised of BaTiO₃ nanoparticles and polydimethylsiloxane was developed using template method to enhance the energy conversion efficiency by minimizing the stress that vanishes into the polymer matrix. In the porous structure, effective stress transfer can occur between the piezoelectric active materials in compression mode due to direct contact between the ceramic particles embedded in the pore-polymer interface. The piezoelectric sponge with 30 wt% of BaTiO₃ particles generated an open-circuit voltage of ~12 V and a short-circuit current of ~150 nA. A finite element method-based simulation was conducted to theoretically back up that the piezoelectric output performance was effectively improved by introducing the sponge structure. Furthermore, to demonstrate the feasibility of pressure detecting applications using the BaTiO₃ particles-embedded piezoelectric sponge, the composite was arranged in a 3 × 3 array and integrated into a single pressure sensor. The fabricated sensor array successfully detected the shape of the applied pressure. This work can provide a cost-effective, biocompatible, and structural strategy for realizing piezoelectric composite-based energy harvesters and self-powered sensors with improved energy conversion efficiency.

• Journal of Microbiology and Biotechnology
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• v.27 no.9
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• pp.1593-1601
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• 2017

Vibrio species are generally recognized as pathogens predominant in seafood along coastal areas. The food industry has sought to develop efficient microbial detection methods. Owing to the limits of conventional methods, this study aimed to establish a rapid identification method for Vibrio isolated from Korea, based on matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Four different preparation procedures were compared to determine the appropriate means to pretreat Vibrio species, using 17 isolates and five reference strains. Extended direct transfer and full formic acid extraction methods using bacterial colonies on agar plates revealed very low identification rates. Formic acid and trifluoroacetic acid (TFA) extractions using bacterial broth cultures were also performed. All Vibrio isolates and reference strains prepared by TFA extraction were successfully identified to the species level (17/22, 77.3%) and to the genus level (5/22, 22.7%). Thus, TFA extraction was considered the most appropriate method to pretreat Vibrio species for MALDI-TOF MS. The remaining 33 isolates and two reference strains were prepared by TFA extraction and analyzed by MALDI-TOF MS. Overall, 50 isolates were identified to the species level (40/50, 80%) and to the genus level (10/50, 20%). All isolates were identified as 43 V. alginolyticus, six V. parahaemolyticus, and one V. vulnificus species. V. alginolyticus and V. parahaemolyticus were isolated from fish offal (87.5% and 12.5%, respectively), seawater (91.3%, 8.7%), and shellfish (62.5%, 37.5%), whereas V. alginolyticus and V. vulnificus were isolated from sediment (90.9% and 9.1%, respectively). This study established a reliable system of MALDI-TOF MS preparation and analysis for Vibrio identification.

• Composites Research
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• v.36 no.1
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• pp.1-15
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• 2023

Demand for energy consumption reduction is increasing according to the development expectations of future mobility. Lightweight structural materials are known as a method to reduce greenhouse gas emissions and improve energy efficiency. In particular, fiber reinforced polymer composite (FRP) is attracting attention as a material that can replace existing metal alloys due to its excellent mechanical properties and light weight. In this paper, industrial applications and research trends of carbon fiber reinforced composites (CFRP, carbon FRP) and self-reinforced composites (SRC) were reviewed based on the reinforcement, polymer matrix, and manufacturing process. In order to overcome the expensive process cost and long manufacturing time of the epoxy resin-based autoclave method, which is mainly used in the aircraft field, mass production of CFRP-applied electric vehicles has been reported using a high-pressure resin transfer molding process including fast-curing epoxy. In addition, thermoplastic resin-based CFRP and interface enhancement methods to solve the recycling issue of carbon fiber composites were reviewed in terms of materials and processes. To form a perfect matrix-reinforcement interface, which is known as the major factor inducing the excellent mechanical properties of FRP, studies on SRC impregnated with the same matrix in polymer fibers have been reported. The physical and mechanical properties of SRC based on various thermoplastic polymers were reviewed in terms of polymer orientation and composite structure. In addition, a copolymer matrix strategy for extending the processing window of highly drawn polypropylene fiber-based SRC was discussed. The application of CFRP and SRC as lightweight structural materials can provide potential options for improving the energy efficiency of future mobility.

• Journal of Korea Multimedia Society
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• v.13 no.5
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• pp.641-650
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• 2010

Color image sensors (CIS) output color images through image sensors and image signal processing. Image sensors that convert light to electrical signal are divided into CMOS image sensor and CCD image sensor according to transferring method of signal charge. In general, a CIS has RGB output signals from tri-stimulus XYZ of the scene through image signal processing. This paper presents an adaptive colorimetric analysis method to obtain chromaticity and luminance using CIS under various environments. An image sensor for the use of colorimeter is characterized based on the CIE standard colorimetric observer. We use the method of least squares to derive a colorimetric characterization matrix between camera RGB output signals and CIE XYZ tristimulus values. We first survey the camera characterization in the standard environment then derive a SGL(shutter-gain-level) function which is relationship between luminance and auto exposure (AE) characteristic of CIS, and read the status of an AWB(auto white balance) function. Then we can apply CIS to measure luminance and chromaticity from camera outputs and AE resister values without any preprocessing. Camera RGB outputs, register values, and camera photoelectric characteristic are used to analyze the colorimetric results for real scenes such as chromaticity and luminance. Experimental results show that the proposed method is valid in the measuring performance. The proposed method can apply to various fields like surveillant systems of the display or security systems.

• Journal of the Korean Society of Radiology
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• v.3 no.1
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• pp.29-39
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• 2009

In this paper has proposed to the recognition of the disease on medical images using neural network. The neural network is constructed as three-layers of the input-layer, the hidden-layer and the output-layer. The training method applied for the recognition of disease region is adaptive error back-propagation. The low-frequency region analyzed by DWT are expressed by matrix. The coefficient-values of the characteristic polynomial applied are n+1. The normalized maximum value +1 and minimum value -1 in the range of tangent-sigmoid transfer function are applied to be use as the input vector of the neural network. To prove the validity of the proposed methods used in the experiment with a simulation experiment, the input medical image recognition rate the evaluation of areas of disease. As a result of the experiment, the characteristic polynomial coefficient of low-frequency area matrix, conversed to 4 level DWT, was proved to be optimum to be applied to the feature parameter. As for the number of training, it was marked fewest in 0.01 of learning coefficient and 0.95 of momentum, when the adaptive error back-propagation was learned by inputting standardized feature parameter into organized neural network. As to the training result when the learning coefficient was 0.01, and momentum was 0.95, it was 100% recognized in fifty-five times of the stomach image, fifty-five times of the chest image, forty-six times of the CT image, fifty-five times of ultrasonogram, and one hundred fifty-seven times of angiogram.

• Korean Journal of Crystallography
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• v.8 no.2
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• pp.127-131
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• 1997

The crystal structure of a bromine sorption complex of vacuum-dehydrated Ag+ and Ca2+ exchanged zeolite A(a=12,234(1) Å) has been determined by single-crystal X-ray diffraction methods in the cubic space group Pm3m. The crystal was prepared by flow method using exchange solution in which mole ratio of AgNo3 and Ca(NO3)2 was 1:150 with a total concentration of 0.05M. The crystal was dehydrated at 360℃ and 2 ×10-6 Torr for 2days, followed by exposure to 180 Torr of Br2 vapor for 20min. full-matrix least-squares refinements converged to the final error indices of R1=0.111 and R2=0.101 using 90 reflections for which I>3o(I). About 3.1 Ag+ ions and 4.45 Ca2+ ions lie on the two crystallographically nonequivalent three-fold axes associated with 6-ring oxygens. A total of six bromine molecules are sorbed per unit cell. Each bromine molecule approaches a framework oxide ions axially (Br-Br-O=171(2)', O-Br=3.25(6) Å; and Br-Br=2,61(8) Å by a charge-transfer interaction.

• Korean Journal of Crystallography
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• v.6 no.2
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• pp.118-124
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• 1995

The crystal structure of an iodine sorption complex of vacumm-dehydrated Ag+ and Ca2+ exchanged zeolite A(a=12.174(3)Å) has been determined at 21℃ by single-crystal X-ray diffraction techniques in the cubic space group Pm3m. The crystal was prepared by flow method for three days using exchange solution in solution in which mole ratio of AgNO3 and Ca(NO3)2 was 1:150 with total concentration of 0.05 M. The complex was prepared by dehydration at 360℃ and 2×10-6 Torr for 2 days, followed by exposure to about 14.3 Torr of iodine vaporat 80℃ for 24 hours. Full-matrix least-squares refinement converged to the final error indices of R1=0.082, R2=0.068 using 122 reflections for which I > 3σ(I). Two Ag+ ions, 1.1 Ag+ ions, and 4.45 Ca2+ ions per unit cell are located on three different three-fold axes associated with 6-ring oxygens. Two Ag+ ions per unit cell are in the large cavity, 1.399(4)Å from the (111) plane of three oxygens. Another 1.1 Ag+ ions are found at opposite sites. Six iodine molecules are sorbed per unit cell. Each I2 molecule approaches a framework oxide ion axially (O-I=3.43(2)Å, I-I=2.92Å, I-I-O;166.1(3)°), by a charge transfer complex interaction. Two Ag+ ions make a close approach to the iodine molecules (Ag-I ; 2.73(2)Å).