• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.475-483
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• 2012

High capacitance X5R MLCCs based on $BaTiO_3$ ceramic dielectric layers exhibit a single broad, asymmetric arc shape impedance and modulus response over the wide frequency range between 1 MHz to 0.01 Hz. Analysis according to the conventional brick-layer model for polycrystalline conductors employing a series connection of multiple RC parallel circuits leads to parameters associated with large errors and of little physical significance. A new parametric impedance model is shown to satisfactorily describe the experimental spectra, which is a parallel network of one resistor R representing the DC conductivity thermally activated by 1.32 eV, one ideal capacitor C exactly representing bulk capacitance, and a constant phase element (CPE) Q with complex capacitance $A(i{\omega})^{{\alpha}-1}$ with ${\alpha}$ close to 2/3 and A thermally activated by 0.45 eV or ca. 1/3 of activation energy of DC conductivity. The feature strongly indicate the CK1 model by J. R. Macdonald, where the CPE with 2/3 power-law exponent represents the polarization effects originating from mobile charge carriers. The CPE term is suggested to be directly related to the trapping of the electronic charge carriers and indirectly related to the ionic defects responsible for the insulation resistance degradation.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.3
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• pp.51-56
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• 2015

It has been used various pad finish materials to enhance the reliability of solder joint and recently Electroless Ni Electroless Pd Immersion Gold (the following : ENEPIG) pad has been used more than others. This study is about reliability according to being used in commercial Electrolytic Ni pad and ENEPIG pad, and was observed behavior of various Cu contents. After reflow, the inter-metallic compound (IMC) between solder and pad is composed of $Cu_6Sn_5$ (Ni substituted) by using EDS, and in case of ENEPIG, between IMC and Ni layer was observed the dark layer ($Ni_3P$ layer). Additional, it could be controlled the thickness of dark layer according to Cu contents. Investigated the different fracture mode between electrolytic Ni and ENEPIG pad after drop shock test, in case of soft Ni, accelerated stress propagated along the interface between $1^{st}$ IMC and $2^{nd}$ IMC, and in case of ENEPIG pad, accelerated stress propagated along the weaken surface such as dark layer. The unstable interface exists through IMC, pad material and solder bulk by the lattice mismatch, so that the thermal and physical stress due to the continuous exterior impact is transferred to the IMC interface. Therefore, it is strongly requested to control solder morphology, IMC shape and thickness to improve the solder reliability.

• Korean Journal of Applied Biomechanics
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• v.25 no.1
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• pp.113-122
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• 2015

Objective : The purpose of this study was to analyze the foot-pressure distribution of 2D(2 dimensional form) & 3D(3 dimensional form; a customized arch-fit for posture correction) insoles for assessing their biomechanical functionality. Background : Recently there has been increased interest in both foot health and foot pain patients. Analysis of the plantar pressure was often used to solve the problems of the foot displayed by such people as rheumatoid arthritis patients. Method : Subjects who participated in this study were 17 female university students who had no previous injury experience in lower limbs and a normal gait pattern. The shoe size of all subjects was 240 mm. Two models of insoles of 2D(typical flat insole - 2 dimensional form) and 3D(special production - 3 dimensional form) were selected for the test. Using the Pedar-X system and Pedar-X insoles, 4.0 km/h of walking speed, and a compilation of 50 steps walking stages were used to analyze foot-pressure distribution. Results : Results of the foot-pressure distribution and biomechanical functionality on each insole were as follows; analyses of mean plantar pressure, maximum plantar pressure, maximum vertical GRF, and plantar pressure curve shape all showed overall low plantar pressure and GRF. Conclusion : This can be evaluated as an excellent insole for low levels on the plantar pressure and GRF. Therefore, it is possible to conclude that according to this analysis the 3D Customized Arch-fit Insole was better than 2D insole on the basis of these criteria.

• Applied Chemistry for Engineering
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• v.10 no.7
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• pp.1028-1034
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• 1999

Poly(lactic acid) is expected to be one of the most promising biodegradable polymers. However, the high molecular weight polymer could be obtained by ring-opening polymerization process conventionally, which raises the production cost and decreases the final yield. In this study, linear and star-shaped poly(L-lactic acid)s were prepared by direct solution polycondensation method and their physical and thermal properties were examined. Tin compounds were found to be effective catalyst for the preparation of high molecular weight polymers. When 0.2g (0.5 wt % of monomer) of $SnCl_2$ and 100 mL of p-xylene were used, the polymer yield and molecular weight were relatively high. As a means to obtain higher molecular weight polymer easily in the direct polycondensation system, dipentaerythritol(dipet) or pentaerythritol(pet) was introduced as a multifunctional branching monomer to provide a star-shaped poly(lactic acid). Moderately high molecular weight polymers with the inherent viscosity values up to 1.14 dL/g(weight-average molecular weight of about 140000 by GPC) were obtained and could be cast strong and transparent films.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.21 no.2
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• pp.55-60
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• 2015

Packaging of export cut lilies reduces physical damage during distribution like dropping, shock, vibration, compression and serves to protect from necrosis, microbial contamination and decomposition. Study on which packaging materials must be selected is necessary because it serves to direct effect maintaining quality and the degree of freshness. newspaper, perforated OPP film, Oriented Nylon film (ON), punched OPP film, OPP films are used in this study. Plant senescence of lilies was happened rapidly during storage at $25^{\circ}C$ rather than at $5^{\circ}C$. Also, water absorption, fresh weight at during storage $25^{\circ}C$ rather than at $5^{\circ}C$ In addition, fresh weight of lilies storage at $25^{\circ}C$ appears higher than at $5^{\circ}C$ all of the packaging materials except OPP because water absorption of lily storage at $5^{\circ}C$ appears higher than at $25^{\circ}C$, thereby suppressing the fresh weight reducing Also, effect on biological activity of lilies from shape of packaging material appears higher during storage at $5^{\circ}C$ than at $25^{\circ}C$. Compared with each packaging materials, newspaper packaging is the smallest effect on changes in biological activity of cut lilies during storage. Thus, the results demonstrate that flowering date are affected mainly by the storage temperature rather than packaging materials.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.30 no.1
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• pp.52-59
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• 2008

The geometric design of an implant surface may play an important role in affecting early osseointegration. It is well known that the porous surfaced implant had much benefits for the osseointegration and the early stability of implant. However, the porous surfaced implant had weakness from the transgingival contamitants, and it resulted in alveolar bone loss. The other problem identified with porous surface implant is the loss of physical properties resulting from the bead sintering process. In this study, we developed the new bead coating implant to overcome the disadvantages of porous surfaced implant. Ti-6Al-4V beads were supplied from STARMET (USA). The beads were prepared by a plasma rotating electrode process (PREP) and had a nearly spherical shape with a diameter of 75-150 ${\mu}m$. Two types of titanium implants were supplied by KJ Meditech (Korea). One is an external hexa system (External type) and the other is an internal system with threads (Internal type). The implants were pasted with beads using polyvinylalcohol solution as a binder, and then sintered at 1250 $^{\circ}C$ for 2 hours in vacuum of $10^{-5}$ torr. The resulting porous structure was 400-500 ${\mu}m$ thick and consisted of three to four bead layers bonded to each other and the implant. The pore size was in the range of 50-150 ${\mu}m$ and the porosity was 30-40 % in volume. The aim of this study was to evaluate the osseointegration of the newly developed dental implant. The experimental implants (n=16) were inserted in the unilateral femur of 4 mongrel dogs. All animals were killed at 8 weeks after implantation, and samples were harvested for hitological examination. All bead coated porous implants were successfully osseointegrated with peripheral bone. The average bone-implant contact ratios were 84.6 % (External type) and 81.5 % (Internal type). In the modified Goldner's trichrome staining, new generated mature bones were observed at the implant interface at 8 weeks after implantation. Although, further studies are required, we could conclude that the newly developed vacuum sintered Ti-6Al-4V bead coating implant was strong enough to resist the implant insertion force, and it was easily osseointegrated with peripheral bone.

• Journal of the Korean Ceramic Society
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• v.41 no.12 s.271
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• pp.921-928
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• 2004

Calcium phosphate powders have been prepared by using $Ca(OH)_2\;and\;H_{3}PO_4$ solution under various conditions such as pH, calcination temperature, and reaction time. ${\beta}-TCP({\beta}-tricalcium phosphate)$and HAp(hydroxyapatite) were synthesized at pH=5.21 and pH > 7.62, respectively. From XRD results, $Ca(OH)_2\;and\;H_{3}PO_4$ solution reacted quickly to form HAp, which was structurally stable up to 16h. Calcination temperature having good crystallinity is revealed to be at $1200^{\circ}C$. SEM analysis showed that ${\beta}-TCP$ and HAp with needle type were synthesized at pH 5.21 and pH 7.62, respectively. However, at pH 9.16, tiny and homogeneous HAp having sphere was prepared and rearranged to show needle morphology. HAp synthesized at pH 9.16 was utilized as bonechina body and calcined. The sample was analyzed its crystallinity, water absorbtion, color, and shape to check physical properties.

• Journal of the Korean GEO-environmental Society
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• v.9 no.6
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• pp.21-29
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• 2008

As household and industrial wastes continue to rapidly increase every year, the demands for landfill sites are also increasing. However, the construction of landfill sites causes many problems due to the high costs of liners, while the leachate from the landfills generates secondary contamination of surrounding lands and groundwater. The purpose of this study is to determine the proper mixing ratio to meet the liner conditions (must be less than $1{\times}10^{-7}cm/sec$), using the local soil as the main material and using fly ash, bentonite, and cement as the mixing materials. The possibility of using this mixture as the liner for landfill sites was examined. To determine the proper mixing ratio, this study conducted basic physical properties tests, compaction tests, consolidation tests, and uniaxial compression tests. It was found that the higher the ratio of bentonite, the lower the coefficient of permeability, and the higher the ratio of fly ash, the higher the coefficient of permeability. The reason for this is that, while bentonite expands and fills pores, fly ash cannot fill the pores because the particles have a round shape and do not have adhesion. In conclusion, the optimum coefficient of permeability that meets the landfill liner condition was obtained when the ratio of bentonite was 15% or higher. If fly ash was mixed, the landfill liner condition was met when the ratio of bentonite was 15% or higher and the ratio of fly ash was 20% or lower.

• Journal of the Korean Society of Food Science and Nutrition
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• v.39 no.9
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• pp.1313-1319
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• 2010

Rice cultivars of Goami2 (G2), Baegjinju (BJJ), and Sulgaeng (SG) with different amylose contents were developed by mutation breeding via N-methyl-N-nitrosourea (MNU) treatment to Ilpumbyeo (IP), high japonica rice. They were identified by different appearances such as grain size, color, and shape. In this experiment, the compositional and physical qualities of those cultivars were examined. The G2 rice classified as a high-amylose rice cultivar was significantly higher in its non-digestable carbohydrates contents. Linoleic and oleic acid were composed of 70~75% of all fatty acids composition regardless of milled and brown rice, except G2 rice in which palmitic acid was the major fatty acid followed by linoleic acid and oleic acid in order. Major amino acids were aspartic acid, glutamic acid, and hydroxy lysine. It was found that cysteine contents were higher in the cultivars of endosperm mutant rice. The DSC analysis revealed that enthalpy was the highest in BJJ followed by SG, IP, and G2 rice. The lowest enthalpy of G2 might be attributable to the higher amylose content. Ilpumbyeo in its cooked rice form showed the highest in Toyo value and less in hardness, but G2 was vise versa. Results of gelatinization and cooked rice properties suggest that G2 was less suitable for cooked rice, but has a potential for functional ingredients from nutritional point of view. The BJJ and SG could be used for traditional cooking as well as for processed foods.

• Composites Research
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• v.18 no.4
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• pp.27-34
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• 2005

Salt water spray and immersion tests were experimentally conducted for over 6 months to investigate the durability of glass fabric/phenolic composites under salt water environment. Mechanical properties such as tensile properties, flexural properties, and shear properties were evaluated and thermal analysis properties such as storage shear modulus, loss shear moduls, and tan 6 were obtained through a DMA. A change in chemical structures was analyzed through a FTIR. According to the results, mechanical properties and thermal analysis properties were sensitive to salt water environment and these properties began to degrade in increasing in exposure times. However, tensile and flexural moduli started to decrease and then slightly increase as increasing in exposure times due to plasticization and crosslinking in matrix as well as physical swelling in composites. Beyond a certain exposure times, these properties began to decrease as further increasing in exposure times. Also the shape and location of peaks in FTIR curves were insensitive to exposure times, but the intensity of peaks would be. finally we found that the durability of glass fabric/phenolic composites were affected on salt water immersion environment rather than salt water spray environment.