• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.4
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• pp.160-166
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• 2019

Cerium oxide ($CeO_2$, often called as Ceria) is one of the valuable rare earth oxide materials, which has been widely used for high temperature applications such as solid oxide fuel cells, automotive three-way catalysts and oxygen storage capacity. Considering those application, it is important to improve high redox and thermal stability with high surface morphology because the high surface area of $CeO_2$ could improve the catalytic reactivity at high temperature conditions. Herein we successfully fabricated hierarchical flower-like $CeO_2$ deposited via controlling pathway of precipitation reaction to supply carbonate ion lead to the flower-like morphology. The hexagonal lattice system of precipitated precursor shows better thermal stability then orthorhombic one during thermal cycling condition.

• Journal of Advanced Engineering and Technology
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• v.10 no.3
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• pp.285-290
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• 2017

Molding of body with ribs is the most difficult during flow molding process. The rib area is easy to be deformed at the rear side due to wall thickness variation. In this study, relationships between molding condition and deflection of rib-shaped part is investigated during the compression molding of fiber reinforced plastic composites, and the following results are derived. Polypropylene(PP), Polystyrene(PS), and stampable sheet(SS 40wt%) show the increment of deflection along with releasing temperature. For the correlation between incremental holding pressure load and deflection, stampable sheet exhibits lower deflection along with higher holding pressure, while PS shows significant increase of deflection with higher holding pressure, PP shows completely different characteristic, significant reduction of deflection along with higher holding pressure. Regarding to mold temperature and deflection, deflection amount of SS is the biggest, and PS shows the smallest. In addition, all three kinds shows the highest amount of deflection at 173C. Deflection is reduced when mold closing speed is increased. Amount of deflection in SS is larger and is not highly dependent on molding conditions like holding pressure and cooling parameters, compared with single component material like PP. This can be elucidated by anisotropic and inhomogeneous characteristics of glass fiber during filling process of stampable sheet composite.

• Progress in Medical Physics
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• v.25 no.2
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• pp.100-109
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• 2014

In stereotactic body radiotherapy (SBRT), the accurate location of treatment sites should be guaranteed from the respiratory motions of patients. Lots of studies on this topic have been conducted. In this letter, a new verification method simulating the real respiratory motion of heterogenous treatment regions was proposed to investigate the accuracy of lung SBRT for Volumetric Modulated Arc Therapy. Based on the CT images of lung cancer patients, lung phantoms were fabricated to equip in $QUASAR^{TM}$ respiratory moving phantom using 3D printer. The phantom was bisected in order to measure 2D dose distributions by the insertion of EBT3 film. To ensure the dose calculation accuracy in heterogeneous condition, The homogeneous plastic phantom were also utilized. Two dose algorithms; Analytical Anisotropic Algorithm (AAA) and AcurosXB (AXB) were applied in plan dose calculation processes. In order to evaluate the accuracy of treatments under respiratory motion, we analyzed the gamma index between the plan dose and film dose measured under various moving conditions; static and moving target with or without gating. The CT number of GTV region was 78 HU for real patient and 92 HU for the homemade lung phantom. The gamma pass rates with 3%/3 mm criteria between the plan dose calculated by AAA algorithm and the film doses measured in heterogeneous lung phantom under gated and no gated beam delivery with respiratory motion were 88% and 78%. In static case, 95% of gamma pass rate was presented. In the all cases of homogeneous phantom, the gamma pass rates were more than 99%. Applied AcurosXB algorithm, for heterogeneous phantom, more than 98% and for homogeneous phantom, more than 99% of gamma pass rates were achieved. Since the respiratory amplitude was relatively small and the breath pattern had the longer exhale phase than inhale, the gamma pass rates in 3%/3 mm criteria didn't make any significant difference for various motion conditions. In this study, the new phantom model of 4D dose distribution verification using patient-specific lung phantoms moving in real breathing patterns was successfully implemented. It was also evaluated that the model provides the capability to verify dose distributions delivered in the more realistic condition and also the accuracy of dose calculation.

• Composites Research
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• v.13 no.1
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• pp.1-10
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• 2000

During the compression molding process of the continuous fiber-reinforced polymeric composites, two main problems such as fiber-matrix separation and fiber orientation are produced by the difference of flow velocity. Molded parts are lead to be nonhomogeneous and anisotropic. As the mechanical property of the products are dependent on the separation and orientation, it is important to research the fiber mat structure and molding condition. If the fiber mat structure is changed by the increment of needling, the separation decreases and after compression molding the orientation is easily aligned. As it were, the compression moldability is good. But the defects as tears, thin thickness are produced in the products. Therefore, it is important to clarify the moldability in relation to the usage of products and the expenses of produce on the actual process. Therefore we must make the measurement methods that can define the moldability of products. In this research, the effects of the fiber mat structure(NP = 0, 5, 10, 25, 50 punches/$cm^2$) and the mold geometry($r_p$ = 1, 25, 50 mm) on the moldability of products were discussed. We investigated the case of one-dimensional flow in order to obtain the degree of nonhomogeneity and the fiber orientation function. In result, we could gain the correlation coefficient of the continuous fiber-reinforced polymeric composites. Also we experimented on the cup-type compression molding which was appeared the wrinkle on the flange part by the complex stress condition in order to gain the degree of nonhomogeneity and area ratio. In result, the moldability of products was expressed as the correlation coefficient and area ratio.

• Journal of the Korean GEO-environmental Society
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• v.1 no.1
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• pp.5-12
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• 2000

Mudstone, found Du-Ho Dong and around there in Po-Hang, is used as construction material. When it is exposed to the air and contacts with water, the strength is decreased rapidly and then it causes a lot of problems. In the field, clay soils with $K_o$ condition have anisotropic characteristics which behave differently according to the change of principal stress direction. In this study, $K_o$ consolidation is performed to make the completely weathered mudstone under the same conditions of construction place. Then, the triaxial compression test is performed at different shear velocity and anisotropy by sampling degree and the stress - strain behavior is shown the strain softening behavior. The stress - strain relationship from triaxial compression test is compared with the prediction value of Cam-clay model. From the results of tests, $K_o$ value decreases with the increase of sampling degree. Generally the behavior of $K_o$ consolidated specimen shows work-softening characteristic. The trend of behaviour of the measured is nearly to same to the predicted by Cam-clay model. But the measured value of deviator stress is very higher than the predicted. Therefore, Cam-clay model was not appropriate to the completely weathered mudstone consolidated with $K_o$ condition in Pohang region.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1182-1182
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• 2001

In this study, the newly constructed optical measurement system, which was mainly composed of a parametric tunable laser and a near infrared photoelectric multiplier, was introduced to clarify the optical characteristics of wood as discontinuous body with anisotropic cellular structure from the viewpoint of the time-of-flight near infrared spectroscopy (TOF-NIRS). The combined effects of the cellular structure of wood sample, the wavelength of the laser beam λ, and the detection position of transmitted light on the time resolved profiles were investigated in detail. The variation of the attenuance of peak maxima At, the time delay of peak maxima Δt and the variation of full width at half maximum Δw were strongly dependent on the feature of cellular structure of a sample and the wavelength of the laser beam. The substantial optical path length became about 30 to 35 times as long as sample thickness except the absorption band of water. Δt ${\times}$ Δw representing the light scattering condition increased exponentially with the sample thickness or the distance between the irradiation point and the end of sample. Around the λ=900-950 nm, there may be considerable light scattering in the lumen of tracheid, which is multiple specular reflection and easy to propagate along the length of wood fiber. Such tendency was remarkable for soft wood with the aggregate of thin layers of cell walls. When we apply TOF-NIRS to the cellular structural materials like wood, it is very important to give attention to the difference in the light scattering within cell wall and the multiple specular-like reflections between cell walls. We tried to express the characteristics of the time resolved profile on the basis of the optical parameters for light propagation determined by the previous studies, which were absorption coefficient K and scattering coefficient S from Kubelka-Munk theory and n from nth power cosine model of radiant intensity. The wavelength dependency of the product of K/S and n, which expressed the light-absorbing and -scattering condition and the degree of anisotropy, respectively, was similar to that of the time delay of peak maxima Δt. The variation of the time resolved profile is governed by the combination of these parameters. So, we can easily find the set of parameters for light propagation synthetically from Δt.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.10a
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• pp.49-49
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• 1999

In this study, $Cl_2/BCI_3$ magnetized inductively coupled plasmas (MICP) were used to etch GaN and the effects of magnetic confinements of inductively coupled plasmas on the GaN etch characteristics were investigated as a function of $Cl_2/BCI_3$. Also, the effects of Kr addition to the magnetized $Cl_2/BCI_3$ plasmas on the GaN etch rates were investigated. The characteristics of the plasmas were estimated using a Langmuir probe and quadrupole ma~s spectrometry (QMS). Etched GaN profiles were observed using scanning electron microscopy (SEM). The small addition of $Cl_2/BCI_3$ (10-20%) in $Cl_2$ increased GaN etch rates for both with and without the magnetic confinements. The application of magnetic confinements to the $Cl_2/BCI_3$ inductively coupled plasmas (ICP) increased GaN etch rates and changed the $Cl_2/BCI_3$ gas composition of the peak GaN etch rate from 10% $BCI_3$ to 20% $BCI_3$. It also increased the etch selectivity over photoresist, while slightly reducing the selectivity over $Si0_2$. The application of the magnetic field significantly increased positive $BCI_2{\;}^+$ measured by QMS and total ion saturation current measured by the Langmuir probe. Other species such as CI, BCI, and CI+ were increased while species such as $BCl_2$ and $BCI_3$ were decreased with the application of the magnetic field. Therefore, it appears that the increase of GaN etch rate in our experiment is related to the increased dissociative ionization of $BCI_3$ by the application of the magnetic field. The addition of 10% Kr in an optimized $Cl_2/BCI_3$ condition (80% $Cl_2/$ 20% $BCI_3$) with the magnets increased the GaN etch rate about 60%. More anisotropic GaN etch profile was obtained with the application of the magnetic field and a vertical GaN etch profile could be obtained with the addition of 10% Kr in an optimized $Cl_2/BCI_3$ condition with the magnets.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.6
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• pp.589-601
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• 2008

The variation of groundwater level near the Shingok weir has been analyzed. To consider the soil inhomogeneity, coefficient of effective permeability was computed to be 0.313 m/day in the horizontal direction, and 0.0423 m/day in vertical direction. Anisotropic ratio is 7.19. The river water level drawdown (caused by the removing of the weir) causes the groundwater level drawdown, and 3 months are required for the new steady condition. and groundwater flows from Han river toward Gulpo stream before the removing of the weir, but when the weir removed, the flow direction changes. The groundwater level falls maximum 30 cm in the areas under the influence of Han river, but, in the areas near Kulpo stream, groundwater level falls about 10 cm. The amount of groundwater use in the study area was investigated to be $52m^3/day$ and in this condition, groundwater level falls maximum 1m (before or after the removing of Shingok weir). therefore, the variation of groundwater level caused by the removing of Shingok weir is less than that caused by the usual use of groundwater.

• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.81-89
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• 2008

The purpose of this study is to develop a new technique to quickly assess the quantitative stability of a tunnel by using measured displacement at the tunnel construction site. To achieve this purpose, in this study, a critical strain concept was introduced for the first time and applied to an assessment of a tunnel under construction. The new technique calculates numerically the strains of the surrounding ground by using displacements measured during tunnel excavation. The techniques considering the relative displacement, shotcrete, and anisotropic characteristics of ground were newly introduced after reinvestigating the existing analysis technique. In addition, an analysis module was developed based on the proposed analysis technique in this study, and the applicability of the developed module was verified. To verify the module, first of all, the calculated excavation displacements of a cylindrical tunnel by analytic method and commercial programs (Pentagon-3D, Flac-2D) were compared for the confirmation of applicability of commercial programs. Then, the calculated excavation displacements under the same initial condition, both with and without a shotcrete lining, by two commercial programs were compared. finally, we assess the load condition and material properties of in-situ ground by inputting tunnel excavation displacement, which was calculated by a commercial program, into the developed analysis module (FAST-Ver. 1.2, feedback Analysis System for Tunneling), and checked whether the assessed results conform to the originally assumed values.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.102-106
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• 1997

Micro gas sensors including thin film catal) tic type require stress-free memhrancs for etch stop of Si anisotropic etching and sublayer of sensing elements hecause stress is one of the main factors affecting breakdown of thin membranes. This paper reports the effects of deposition conditions on stress and refractive index of $SiN_{x}/SiO_{x}/(NON)$ films deposited by low pressure c11ernic;rl vapor deposition(L, t'CVI)) 2nd reactve sputtering. In the case of I.PCVI1, the stresses of $SiN_{x}$ and NON films arc $7.6{\times}10^{8}dyne/cm^2$ and $3.3{\times}10^{8}dyne/cm^2$, respectibely, and the refractive indices are 3.05 and 152, respectively. In the cxse oi the sputtered SiN, , compressi\e stress decreased in magnitude and then turned to tensility as increasing proc, ess pressure by lmtorr to 30mtorr and cicreasmg applied power density by $2.74W/cm^2$ to $1.10W/cm^2$. The hest value of film stress obt;~ined under condition of lOmtorr and $1.37W/cm^2$ in this' experiment was $1.2{\times}10^{9}dyne/cm^2$ cnnipressive. The refr~ict~ve index decreased from 2 05 to 1 89 as decreasing applied power density by lnitorr to 3Orntorr and increasing process pressure hy $2.74W/cm^2$ to $1.10W/cm^2$. Stresses of films deposited by both LPCVL) and sputtering decreased as incre;lsing temperature and showed plastic behavior as decreasing temperature.