• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.699-705
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• 2007

Recent experimental data shows that the noticeable feature of irregular roughened spots on the fuel surface occurs during the combustion test with PMMA/GOX in the hybrid rocket motor. The generation of these unexpected patterns is likely to be resulted from the disturbed boundary layer due caused by wall blowing which is intented to simulate the process of fuel vaporization. LES technique was implemented to investigate both the flow characteristics near fuel surface and the subsequent evolution of turbulence modified by the wall blowing. Simple channel geometry instead of circular grain configuration was used for the investigation without chemical reactions in order to allow for a focused examination on the near-wall behavior at the Reynolds number of 22,500. It was shown that the wall blowing pushed turbulent structures upwards making them tilted and this skewed displacement, in effect, left the foot prints of the structures on the surface. This change of kinematics may explain the formation of irregular isolated spots on the fuel surface observed in the experiment.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.210-213
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• 2010

Recent experimental data shows that the noticeable feature of irregular roughened spots on the fuel surface occurs during the combustion test. The generation of these unexpected patterns is likely to be resulted from the disturbed boundary layer due caused by wall blowing which is intended to simulate the process of fuel vaporization. LES without chemical reaction was conducted to investigate the flow characteristics at the near-fuel surface and the behavior of turbulent structures which is evolved by the wall blowing at the Reynolds number of 23,000. Cylindrical geometry was considered to get the most reality of the calculation results because real hybrid rocket motor is circular grain configuration. It was shown that the wall blowing pushed turbulent structures upwards making them tilted and this skewed displacement, in effect, left the foot prints of the structures on the surface. This change of kinematics may explain the formation of irregular isolated spots on the fuel surface observed in the experiment.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.3
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• pp.12-21
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• 2022

Directed energy deposition (DED) was adopted as a metal additive manufacturing method to develop a mold for the hot stamping process. The test piece was machined from Heatvar laminate material, and results were obtained through microstructure and defect observations, as well as hardness, tensile strength, and joint strength tests. 1) Spherical pores and irregular-shaped cavities were observed as lamination defects, and columnar dendrites formed in the structure, which tended to become coarse upon heat treatment. 2) The hardness of the heat-treated material (480HV) was slightly lower than that of the non-heat-treated material (500HV). 3) In the tensile test, the maximum tensile stress and strain of the heat-treated material were 1392 MPa and 15%, respectively, which were slightly higher than the values of 1381 MPa and 13%, respectively, for the non-heat-treated material. 4) In the case of the early final fracture in the tensile test, in most cases, pores or irregularly shaped cavities were observed at the fracture surface or near the surface. 5) In the joint strength test, most of the specimens finally fractured in the laminated metal area, and the fracture surface was intragranular. In addition, dimples formed over the entire area on the fracture surface of the fractured specimen after sufficient elongation.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.174-186
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• 2009

When we apply a propagation model to the ocean with boundaries, we can calculate reflected wave using reflection coefficient suggested by Rayleigh assuming the boundaries are flat. But boundaries in ocean such as sea surface and sea bottom have an irregular rough surface. To calculate the reflection loss for an irregular boundary, it is needed to compute the coherent reflection coefficient based on an experimental formula or scattering theory. In this article, we derive the coherent reflection coefficients for a fluid-fluid interface using perturbation theory, Kirchhoff approximation and small-slope approximation respectively. Based on each formula, we can calculate coherent reflection coefficients for a rough sea surface or sea bottom, and then compare them to the Rayleigh reflection coefficient to analyze the reflection loss for a random rough surface. In general, the coherent reflection coefficient based on small-slope approximation has a wide valid region. Comparing it with the coherent reflection coefficients derived from the Kirchhoff approximation and perturbation theory, we discuss a valid region of them.

• Korean Journal of Veterinary Service
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• v.22 no.4
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• pp.405-410
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• 1999

A 7 month old male shepherd was presented with anorexia, diarrhea, and salivation, and euthanized due to no clinical improvement. Grossly, ulcers were seen on ventral surface of tongue and stomach. The mineralization was obvious in the intercostal space, lung and inner surface of aorta. Kidney was pale, firm and irregular. Histopathology confirmed uremic pneumonitis, end stage kidney and hyperplasia of parathyroid. This case was the typical uremic condition of juvenile dog, which was characterized the diffuse soft tissue mineralization due to hyperparathyroidism secondary to chronic renal failure.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.395-400
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• 2002

Epoxy coating and sealing used in nuclear plants for the protection of radiation degrades with aging and hazardous atmosphere. In order to evaluate the degradation of the epoxy, dependence of the acoustic impedance on the change of mechanical properties has been used. Unlike metals, the surface of the epoxy coating on a concrete liner is so wavy that the acoustic impedance is difficult to measure by using the reflectivity of the ultrasound on the interface surface because of the irregular reflection and propagation from the epoxy surface. SA(simulated annealing) algorithm is applied to calculate the acoustic impedance using a reflection wave from the rough epoxy surface. The surface waviness and acoustic impedance are taken into account and determined by SA method to evaluate the state of degradation quantitatively.

• Journal of the Korean institute of surface engineering
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• v.26 no.5
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• pp.225-234
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• 1993

Titanium nitride coatings were deposited onto SUS304 stainless steel substrates pretreated by mechanical scrubbing, chemical etching at 50% HCl solution and Ar ion etching. Adhesion strength were measured by scratch tester and confirmed by SEM with EDS. Adhesion strength of Ar ion etched substrate was 10 to 15 times higher than that of mechanical scrubbed or chemical etched substrate. Ar ion etching brought about an uniform and fine spherical shaped surface, while chemical etching gave rise to a rough and irregular surface on SEM micrograph. It was suggested that higher adhesion strength might be caused by anchoring effect of Ar ion etched surface prior to TiN deposition.

• Journal of the Korean Association of Geographic Information Studies
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• v.4 no.4
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• pp.61-71
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• 2001

In these days, surveying instruments are developing rapidly and the precision is improving continuously. The reappearance of three dimensional terrains of a great precision are possible and the calculation of the area or the volume has a high precision due to the development of the technique of the spatial information system using computer. But actually, in construction site they calculate two-dimensional area using the traditional method, plane table surveying, planimeter, and then get ground surface area through timing the slope correction factor. In this study, I show the defect and inefficiency of the calculation of the area by the traditional methods and survey the area with Electronic Distance Measuring equipment and GPS instrument. With these data, we made the three dimensional terrain model and calculated two-dimensional area and ground surface area. After that, I compared areas that calculated by algorithm method of irregular triangle and analysis of grid method with standardizing the area that calculated by the traditional method. Finally, I suggested more effective and precise method in calculating ground surface area.

• Journal of Powder Materials
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• v.11 no.6 s.47
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• pp.493-502
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• 2004

In this study, nano-sized indium oxide powder with the average particle size below 100 nm is fab-ricated from the indium chloride solution by the spray pyrolysis process. The effects of the reaction temperature, the concentration of raw material solution and the inlet speed of solution on the properties of powder were studied. As the reaction temperature increased from 850 to $1000^{\circ}C$, the average particle size of produced powder increased from 30 to 100 nm, and microstructure became more solid, the particle size distribution was more irregular, the intensity of a XRD peak increased and specific surface area decreased. As the indium concentration of the raw material solution increased from 40 to 350 g/l, the average particle size of the powder gradually increased from 20 to 60 nm, yet the particle size distribution appeared more irregular, the intensity of a XRD peak increased and spe-cific surface area decreased. As the inlet speed of solution increased from 2 to 5 cc/min., the average particle size of the powder decreased and the particle size distribution became more homogeneous. In case of the inlet speed of 10 cc/min, the average particle size was larger and the particle size distribution was much irregular compared with the inlet speed of 5 cc/min. As the inlet speed of solution was 50 cc/min, the average particle size was smaller and microstructure of the powder was less solid compared with the inlet speed of 10 cc/min. The intensity of a XRD peak and the variation of specific area of the powder had the same tendency with the variation of the average par-ticle size.

• Progress in Medical Physics
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• v.28 no.1
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• pp.33-38
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• 2017

Creating individualized build-up material for superficial photon beam radiation therapy at irregular surface is complex with rice or commonly used flat shape bolus. In this study, we implemented a workflow using 3D printed patient specific bolus and describe our clinical experience. To provide better fitted build-up to irregular surface, the 3D printing technique was used. The PolyLactic Acid (PLA) which processed with nontoxic plant component was used for 3D printer filament material for clinical usage. The 3D printed bolus was designed using virtual bolus structure delineated on patient CT images. Dose distributions were generated from treatment plan for bolus assigned uniform relative electron density and bolus using relative electron density from CT image and compared to evaluate the inhomogeneity effect of bolus material. Pretreatment QA is performed to verify the relative electron density applied to bolus structure by gamma analysis. As an in-vivo dosimetry, Optically Stimulated Luminescent Dosimeters (OSLD) are used to measure the skin dose. The plan comparison result shows that discrepancies between the virtual bolus plan and printed bolus plan are negligible. (0.3% maximum dose difference and 0.2% mean dose difference). The dose distribution is evaluated with gamma method (2%, 2 mm) at the center of GTV and the passing rate was 99.6%. The OSLD measurement shows 0.3% to 2.1% higher than expected dose at patient treatment lesion. In this study, we treated Mycosis fungoides patient with patient specific bolus using 3D printing technique. The accuracy of treatment plan was verified by pretreatment QA and in-vivo dosimetry. The QA results and 4 month follow up result shows the radiation treatment using 3D printing bolus is feasible to treat irregular patient skin.