• Advances in materials Research
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• v.12 no.4
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• pp.273-286
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• 2023

The fracture mechanics make it possible to characterize the behavior with cracking of structures using parameters quantifiable in the sense of the engineer, in particular the stress field, the size of the crack, and the resistance to cracking of the material. Any structure contains defects, whether they were introduced during the production of the part (machining or molding defects for example). The aim of this work is to determine numerically by the finite element method the stress concentration factor Kt of a plate subjected to a tensile loading containing a lateral form defect with different sizes: a semicircle of different radii, a notch with different opening angles and a crack of different lengths. The crack propagation is then determined using the extended finite element technique (X-FEM). The modeling was carried out using the ABAQUS calculation code.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.6
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• pp.246-251
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• 2014

Recent studies have shown methods of improving solar cell efficiency. Especially on single crystalline silicon wafer which is high-efficiency solar cell material that has been widely studied. Interstitial oxygen (Oi) is the main impurity in the Czochralski (Cz) growing method, and excess of this can form precipitates during cell fabrication. We have demonstrated the effect of Oi impurity and oxygen precipitation concentration of the wafer on Cz-silicon solar cell efficiency. The result showed a decrease in cell efficiency as Oi and oxygen precipitation increase. Moreover, we have found that the critical point of [Oi] to bring higher cell efficiency is at 14.5 ppma in non-existent Bulk Micro Defect (BMD).

• Korean Journal of Materials Research
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• v.21 no.12
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• pp.644-649
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• 2011

[ $A_{3-2x/3}Al_{1-z}In_{z}O_4F:Eu_x^{3+}$ ](A = Ca, Sr, Ba, x = -0.15, z = 0, 0.1) oxyfluoride phosphors were simply prepared by the solid-state method at $1050^{\circ}C$ in air. The phosphors had the bright red photoluminescence (PL) spectra of an $A_{3-2x/3}Al_{1-z}In_{z}O_4F$ for $Eu^{3+}$ activator. X-ray diffraction (XRD) patterns of the obtained red phosphors were exhibited for indexing peak positions and calculating unit-cell parameters. Dynamic excitation and emission spectra of $Eu^{3+}$ activated red oxyfluoride phosphors were clearly monitored. Red and blue shifts gradually occurred in the emission spectra of $Eu^{3+}$ activated $A_3AlO_4F$ oxyfluoride phosphors when $Sr^{2+}$ by $Ca^{2+}$ and $Ba^{2+}$ ions were substituted, respectively. The concentration quenching as a function of $Eu^{3+}$ contents in $A_{3-2x/3}AlO_4F:Eu^{3+}$ (A = Ca, Sr, Ba) was measured. The interesting behaviors of defect-induced $A_{3-2x/3}Al_{1-z}In_{z}O_{4-{\alpha}}F_{1-{\delta}}$ phosphors with $Eu^{3+}$ activator are discussed based on PL spectra and CIE coordinates. Substituting $In^{3+}$ into the $Al^{3+}$ position in the $A_{3-2x/3}AlO_4F:Eu^{3+}$ oxyfluorides resulted in the relative intensity of the red emitted phosphors noticeably increasing by seven times.

• Journal of IKEEE
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• v.28 no.1
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• pp.104-109
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• 2024

In this research, we explored the influence of post-annealing atmospheres on the electrical properties of Ga₂O₃/SiC heterojunction diodes. We fabricated Ga₂O₃/SiC heterojunction diodes by RF sputtering and after the fabrication the post-annealing in various gas atmospheres was performed. We measured the changes in deep-level defects using Deep Level Transient Spectroscopy (DLTS) and we conducted an electrical characteristic of J-V measurement and Hall measurement to analyzed the effects of annealing atmosphere on Ga₂O₃/SiC heterojunction diode. In the N₂ annealed devices, the highest on-state current was measured as 3.06 × 10^-2 A/cm^2, and an increase in carrier concentration of 3.8 × 10¹⁴ cm^-3 was observed. This confirms that the variations in deep level defects due to the post-annealing atmosphere can influence the electrical properties.

• Restorative Dentistry and Endodontics
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• v.18 no.2
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• pp.277-290
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• 1993

Dental caries is considered to be caused by demineralization by organic acid produced by microorganism. But the formation of subsurface lesion in initial caries make it diffcult to explain by simple demineralization. This study is carried out on the basis of thermodynamic concept proposed by Margolis and Moreno. The purpose of this study is to evaluate the effects of acid concentration and pH of lactate buffer system on the artificial caries lesion progress. 160 teeth without any crack, defect or opaque enamel were used and coated with nail varnish except the window ($2{\times}3$ mm). Under the constant degree of saturation(D.S.). The teeth were divided into 8 groups according to acid concentration(10mM, 25mM, 50mM, 100mM) and pH(4.3, 5.0, 6.0). Each group was immersed in buffer solution for 3, 6, 9, 18 days under controlled temperature($25^{\circ}C$). After cutting through the window and grinding, the specimens, 100-150 um in thickness, were imbibed in water or air and examined using polarilizing microscope. The depth of the surface and subsurface surface lesion were measured. 1. In the constant pH and D. S. value, the subsurface lesion progresses more rapidly as the concentration of lactic acid increases. (0.01, 0.025, 0.05, 0.1) 2. In the constant acid concentration and DS value, the subsurface lesion progresses more slowly as the pH increases. (4.3, 5.0, 5.5, 6.0) 3. The width of surface lesion seems to be constant independant of pH and acid concentration.

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.308-314
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• 2017

Anodic film formation behavior of AZ31 Mg alloy was studied as a function of NaOH concentration in 1 M $Na_2CO_3$ + 0.5 M $Na_2SiO_3$ solution under the application of a constant anodic current density, based on the analyses of voltage-time curves, surface appearances and morphologies of the anodically formed PEO (plasma electrolytic oxidation) films. The anodic film formation voltage and its fluctuations became largely lowered with increasing added NaOH concentration in the solution. Two different types of film defects, large size dark spots indented from the original surface and locally extruded white spots, were observed on the PEO-treated surface, depending on the concentration of added NaOH. The large size dark spots appeared only when added NaOH concentration is less than 0.2 M and they seem to result from the local detachments of porous PEO films. The white spots were observed to be very porous and locally extruded and their size became smaller with increasing added NaOH concentration. The white spot defects disappeared completely when more than 0.8 M NaOH is added in the solution. Concludingly it is suggested that the presence of enough concentration of $OH^-$ ions in the carbonate and silicate ion-containing electrolyte can prevent local thickening and/or detachment of the PEO films on the AZ31 Mg alloy surface and lower the PEO film formation voltage less than 70 V.

• Journal of Periodontal and Implant Science
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• v.27 no.4
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• pp.867-882
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• 1997

Safflower(Carthamus tinctorius $Linn\acute{e}$ has been traditionally used for the treatment of blood stasis, and Dipsasi Radix has been used as a drug for fracture in Chinese medicine. The purpose of present study was to examine the biologic effects of safflower extract and Disasi radix extracts on the periodontal. ligament cells and osteoblastic cells and on the wound healing of rat calvarial defect. The ethanolic extract of safflower blossom, safflower seed and Dipsasi Radix(125, 250, and 500 ${\mu}g/ml$) were prepared as test group, and PDGF-BB(lOng/ml) and unsafonifiable fraction of Zea Mays L.(125, 250, and 500 ${\mu}g/ml$) were employed as positive control. The effects of each agents on the growth and survival, ALPase activity, expression of PDGF-BB receptor, chemotactic response of PDL cell and ATCC human osteosarcoma MG63 cells in vitro were examined. The tissue regenerative effect of each extracts was evaluated by histomorphometric measuring of newly formed bone on the 8mm defect in rat calvaria after oral administration of 3 different dosages groups : 0.02, 0.1 and 0.35g/kg, per day. It was also employed the same dosages of unsaponifiable fraction of Zea Mays L. as positive controls. Safflower blossom extract, safflower seed extract, and Dipsasi Radix extract stimulate the cellular activity of MG63 cells in concentration range of $125-500{\mu}g/ml$, and safflower bolssom extract and safflower seed extract stimulate also the cellular activity of periodontal ligament cells in concentration range of $250-500{\mu}g/ml$. In activity of ALPase, $250-500{\mu}g/ml$ of safflower blossom extracts showed significant stimulating effects on MG63 cells, and the same concentration range of safflower seed extracts showed significant effect on periodontal ligament cells. In the recovery on PDGF-BB receptor expression which was depressed by $IL-1{\beta}$, $125-250{\mu}g/ml$ of safflower blossom extracts and $250-500{\mu}g/ml$ of safflower seed extracts showed significant increasing effect on MG63 cells, and $500{\mu}g/ml$ of safflower blossom extract and $250-500{\mu}g/ml$ of safflower seed extracts showed significant effect on periodontal ligament cells. In chemotactic response, among all tested group, safflower seed extracts only were chemotactic to MG63 cells and periodontal ligament cells in concentration range of $125-500{\mu}g/ml$. Also in the view of bone regeneration in rat calvarial defect model, the only group that was orally administrated 0.35g/kg, day of safflower seed extract showed significant new bone formation. These results suggested that safflower extracts might have a potential possibilities as an useful drug for adjunct to treatment for regeneration of periodontal defect.

• Journal of Power System Engineering
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• v.15 no.3
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• pp.65-69
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• 2011

This paper introduces the multi-coil eddy current sensor and its characteristic in magnetic material gas turbine rotor. In the past, magnetic particle inspection method was used for qualitative defect evaluation in magnetic material gas turbine rotor. And the ultrasonic inspection method was used for quantitative defect evaluation. Nowadays, eddy current method is used in magnetic gas turbine rotor inspection due to advanced sensor design technology. We developed multi-coil eddy current sensor for the rotor dovetail inspection. At first, rotor stress is analyzed for the determination of sensor position and number. The sensor coils are designed to cover the stress concentration area of rotor dovetail. We select optimum frequency according to material standard penetration data and experiment results. The rotor mock-up and artificial defects were made for the signal detection and resolution analysis of multi-coil eddy current sensor. The results show that signal detection and resolution capabilities are enhanced in comparison to the commercialized sensor enough for the gas turbine rotor inspection. So, this developed multi-coil eddy current sensor substituted for commercialized one and it applied in real gas turbine rotor inspection.

• Korean Chemical Engineering Research
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• v.52 no.3
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• pp.340-346
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• 2014

Continuous and dense ZIF-7 membranes were successfully synthesized on ${\alpha}-Al_2O_3$ porous substrate via two-step crystallization technique. ZIF-7 seeding layer was first deposited on porous ${\alpha}-Al_2O_3$ substrate by in-situ low temperature crystallization, and then ZIF-7 membrane layer can be grown through the secondary high-temperature crystallization. Two synthesis solutions with different concentration were used to prepare ZIF-7 seeding layer and membrane layer on porous ${\alpha}-Al_2O_3$ substrate, respectively. As a result, a continuous and defect-free ZIF-7 membrane layer can be prepared on porous ${\alpha}-Al_2O_3$ substrate, as confirmed by scanning electron microscope. XRD characterization shows that the resulting membrane layer is composed of pure ZIF-7 phase without any impurity. A single gas permeation test of $H_2$, $O_2$, $CH_4$ or $CO_2$ was conducted based on our prepared ZIF-7 membrane. The ZIF-7 membrane exhibited excellent H2 molecular sieving properties due to its suitable pore aperture and defect-free membrane layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.3
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• pp.242-247
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• 1998

In this study, we have synthesized $ZnGa_2O_4$:Mn,X powder doped with Mn, MnO, $MnF_2$ and $MnCl_2$, low voltage green emitting phosphor, in vacuum atmosphere. From PL spectra, the intensity of the emission peak, the brightness with coactivator show that $ZnGa_2O_4$:Mn,Cl > $ZnGa_2O_4$:Mn,F > $ZnGa_2O_4$:Mn,O > $ZnGa_2O_4$:Mn. These improvement of the brightness are caused by the increase of the concentration of $Mn^{2+}$ ion. In case of $ZnGa_2O_4$:Mn,Cl and ZnGa$_2$O$_4$:Mn,F, the brightness is enhanced much more, which is owed to the decrease of defect of host material. For $ZnGa_2O_4$:Mn,Cl phosphor fabricated with optimized condition, the decay time becomes short from 30 ms of the $ZnGa_2O_4$:Mn and $ZnGa_2O_4$:Mn,O to 6 ms and the brightness of CL at 1 kV, 1 mA is 60 cd/$m^2$.