• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.4
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• pp.12-17
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• 2004

The PSP technique has been used to measure pressure distribution on model surfaces ins high-speed flows. The objective of this study is to develop a PSP technique which can be applied to low-speed aerodynamic flows. Four different PSP formulations including two porphyrins (PtOEP and PtTFPP) and two polymers (Poly(TMSP) and RTV-118) were tested and the performance of each combination was evaluated. In a static calibration, the luminescent intensity of the PSP coatings was measured from 0kPa to 11kPa with 0.5, 1, 2kPa increments. Among 4 PSP formulations tested, the combination of PtOEP and RTV-118 shows the best performance. The developed PSP technique was applied to an oblique impinging jet to measure the pressure field distribution on the impinging plate.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.3
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• pp.199-214
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• 2011

A crack is the main cause to affect the integrity of tunnel lining as well as leakage, spalling, exposed rebar, corrosion, carbonation and so on. Since the 1980, NATM has prevailed on excavation method and geotechnical philosophy in tunnel. Although the pattern of cracks has been reported by several engineers' effort, it was only focused on longitudinal cracks of lining. Eleven operational NATM tunnels have been conducted with the precise inspection for safety and diagnosis by KISTEC (Korea Infrastructure Safety and Technology Incorporation). With those results, the crack patterns by the spatial distribution and appearance for each tunnel have been analyzed and the cause of occurrence for seven common types of cracks in NATM tunnels was classified. Additionally, the longitudinal crack on lining above duct slab was figured out by numerical simulation and field inspection. Each crack has been analyzed by CCD (Charge-Coupled Device) scanner image with 3D configuration. Each type of cracks is also explained with output of experimental and condition of construction. Defined cracks on NATM tunnels will be good example for periodical inspection and precise inspection for safety and diagnosis.

• Journal of the Korean Society of Clothing and Textiles
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• v.34 no.5
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• pp.819-830
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• 2010

This study proposes medical gowns for interns and residents that address the functions of utility and activity. Based on the questionnaires, the prototype focused on the pockets for practical use and movement adaptability. Functional pockets were made by increasing pocket sizes and separating pockets with sections according to use. An inside pocket and a loop for an identification tag was placed on the chest pocket and the side seam pocket were oblique lined. To resolve horizontal stress on the back of the gown,6 cm action pleats were added at both ends of the bladebone. The elbow area was tucked up to improve the workplace activities. To reduce hamper on the gown hemline, slits were added along the gown side seam. The front button was changed into an inside button closure. The cuffs, belt, and back waist belt were removed due to occupational cases of inconvenience. The length of the sleeves was adjusted with belts to improve the movement of the arms. In accordance with design preference, the gown was designed to be knee-length with wrist length sleeves. Blue colored (2.5PB 3/12: by Munsell) material was inserted to reduce the contamination on the neck, cuffs, front closure, and hemline area. The planning cloth of the experimental gown was designed to improve activity function, cleaning, and comfort from light materials. The field test (with 30 doctors at university hospitals and the objective assessment with 9 subject groups)were done by the valuation between the existing gown and the prototype. The results showed that the prototype had to be modified by decreasing the pocket size, expanding the usage of the penholder, and simplify front pockets in order to maintain unity. The loop for the identification tag, inside pocket, and the blue colored material had to be removed. The front closure of the gown had to return to its original state.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.4
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• pp.228-233
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• 1998

This study presents a close-range photogrammetry that is applicable to beach profile estimation using a non-metric camera. Based on the analysis of oblique video image in which the video camera was installed on a horizontal plane and the field of view was fixed, a new equation to analyze a photograph was developed considering the following aspects: (1) camera is allowed to be rotated about its optical axis and (2) a simple error model is adopted to correct lens distortion and other systematic errors associated with the non-metric camera, which improves accuracy of non-metric imageries. To test the modified technique, photographs of the beach were taken near the Donghae City in February, 1998. In addition, beach profiles were surveyed with conventional dumpy level and surveying staff. RMS error between the estimated and measured beach profiles is less than 10 cm in elevation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.6
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• pp.477-483
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• 2016

Velocity profiles of laminar, transition and turbulent boundary layers were investigated by using Particle Image Velocimetry(PIV) measurements on the flat plate at Mach 2.96. The Schlieren visualization and PIV measurements are also used to confirm whether the oblique shock wave generated from the leading edge affects the flow field over the flat plate. The laminar velocity profile measured from the experiment was well matched with the compressible Blasius solution. The velocity profile of the transition boundary layer was well correlated with the theoretical turbulent velocity profile from near the wall and the transition began from Re = $1.41{\times}106$. For the turbulent boundary layer, considering compressibility effects, the Van Driest-transformed velocity satisfies the incompressible log-law. It is found that the log region is extended farther in the wall-normal direction compared to the log region in incompressible boundary layer.

• Imaging Science in Dentistry
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• v.53 no.4
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• pp.375-381
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• 2023

Purpose: This study assessed the diagnostic performance of stitched and non-stitched cross-sectional cone-beam computed tomography (CBCT) images of non-displaced ovine mandibular fractures. Materials and Methods: In this ex vivo study, non-displaced fractures were artificially created in 10 ovine mandibles (20 hemi-mandibles) using a hammer. The control group comprised 8 hemi-mandibles. The non-displaced fracture lines were oblique or vertical, <0.5 mm wide, 10-20 mm long, and only in the buccal or lingual cortex. Fracture lines in the ramus and posterior mandible were created to be at the interface or borders of the 2 stitched images. CBCT images were obtained from the specimens with an 80 mm×80 mm field of view before and after fracture induction. OnDemand software (Cybermed, Seoul, Korea) was used for stitching the CBCT images. Four observers evaluated 56 (28 stitched and 28 non-stitched) images to detect fracture lines. The diagnostic performance of stitched and non-stitched images was assessed by calculating the area under the receiver operating characteristic curve (AUC). Sensitivity and specificity values were also calculated (alpha=0.05). Results: The AUC was calculated to be 0.862 and 0.825 for the stitched and non-stitched images, respectively (P=0.747). The sensitivity and specificity were 90% and 75% for the non-stitched images and 85% and 87% for the stitched images, respectively. The inter-observer reliability was shown by a Fleiss kappa coefficient of 0.79, indicating good agreement. Conclusion: No significant difference was found in the diagnostic performance of stitched and non-stitched cross-sectional CBCT images of non-displaced fractures of the ovine mandible.

• Progress in Medical Physics
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• v.21 no.1
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• pp.86-92
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• 2010

The purpose of this study was to measure curvature contour skin dose using radiochromic film and TLD for a conventional open field. We also attempted to quantify the degradation of skin sparing associated with use of immobilization devices for high energy photon beams and to calculate the skin dose with a help of Monte Carlo (MC) simulation. To simulate head-and-neck and shoulder treatment, a cylindrical solid water phantom 11 cm in diameter was irradiated with 6 MV x-rays using $40{\times}40\;cm^2$ field at 100 cm source axis distance (SAD) to the center of the phantom. Aquaplastic mesh mask was placed on the surface of the cylindrical phantom that mimicked relevant clinical situations. The skin dose profile was obtained by taking measurements from $0^{\circ}$ to $360^{\circ}$ around the circumference of the cylindrical phantom. The skin doses obtained from radiochromic film were found to be 47% of the maximum dose of $D_{max}$ at the $0^{\circ}$ beam entry position and 61% at the $90^{\circ}$ oblique beam position without the mask. Using the mask (1.5 mm), the skin dose received was 59% at $0^{\circ}$ incidence and 78% at $80^{\circ}$ incidence. Skin dose results were also gathered using thin thermoluminescent dosimeters (TLD). With the mask, the skin dose was 66% at $0^{\circ}$ incidence and 80% at $80^{\circ}$ incidence. This method with the mask revealed the similar pattern as film measurement. For the treatments of the head-and-neck and shoulder regions in which immobilization mask was used, skin doses at around tangential angle were nearly the same as the prescription dose. When a sloping skin contour is encountered, skin doses may be abated using thinner and more perforated immoblization devices which should still maintain immoblization.

• Progress in Medical Physics
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• v.10 no.3
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• pp.133-140
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• 1999

In this paper, as a preliminary study for developing a full 3D electron dose calculation algorithm, We developed 2.5D electron dose calculation algorithm by extending 2D pencil-beam model to consider three dimensional geometry such as air-gap and obliquity appropriately. The dose calculation algorithm was implemented using the IDL5.2(Research Systems Inc., USA), For calculation of the Hogstrom's pencil-beam algorithm, the measured data of the central-axis depth-dose for 12 MeV(Siemens M6740) and the linear stopping power and the linear scattering power of water and air from ICRU report 35 was used. To evaluate the accuracy of the implemented program, we compared the calculated dose distribution with the film measurements in the three situations; the normal incident beam, the 45$^{\circ}$ oblique incident beam, and the beam incident on the pit-shaped phantom. As results, about 120 seconds had been required on the PC (Pentium III 450MHz) to calculate dose distribution of a single beam. It needs some optimizing methods to speed up the dose calculation. For the accuracy of dose calculation, in the case of the normal incident beam of the regular and irregular shaped field, at the rapid dose gradient region of penumbra, the errors were within $\pm$3 mm and the dose profiles were agreed within 5%. However, the discrepancy between the calculation and the measurement were about 10% for the oblique incident beam and the beam incident on the pit-shaped phantom. In conclusions, we expended 2D pencil-beam algorithm to take into account the three dimensional geometry of the patient. And also, as well as the dose calculation of irregular field, the irregular shaped body contour and the air-gap could be considered appropriately in the implemented program. In the near future, the more accurate algorithm will be implemented considering inhomogeneity correction using CT, and at that time, the program can be used as a tool for educational and research purpose. This study was supported by a grant (＃HMP-98-G-1-016) of the HAN(Highly Advanced National) Project, Ministry of Health & Welfare, R.O.K.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.8-23
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• 1997

Steady and unsteady numerical simulations are conducted for the comparison with the experiments performed to investigate the ram accelerator flow field by using an expansion tube facility in Stanford University. Wavier-Stokes equations for chemically reacting flows are analyzed by fully implicit and time accurate numerical methods with Jachimowski's detailed chemistry model for hydrogen-air combustion involving 9 species and 19 reaction steps. Although the steady state numerical simulation shows a good agreement with the experimental schlieren and OH PLIF images for the case of $2H_2$＋$O_2$＋$17N_2$ fails in reproducing the combustion region behind the shock intersection point shown in the case of $2H_2$＋$O_2$＋$12N_2$ mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. From the result of unsteady numerical simulation, the experimental result seems to be an instantaneous state during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.

• Journal of the Korean earth science society
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• v.32 no.2
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• pp.161-169
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• 2011

Focal mechanism solutions in the central and western areas of the Korean Peninsula (36-37.8$^{\circ}N$, 126-128$^{\circ}E$) were obtained from the analysis of the recent seventeen earthquakes (M${\geq}$2.2) which occurred from January, 2005 to May, 2010. The spatial differences between the epicenters recalculated by this study and those announced by the Korea Meteorological Administration are less than $0.03^{\circ}$, indicating a small deviation. Focal mechanism solutions were obtained from the analysis of P wave polarities, SH wave polarities and SH/P amplitude ratios. The focal mechanism solutions show dominant strike-slip faulting or oblique slip faulting with strike-slip components. The P-axes trends are mainly ENE-WSW or E-W directions. The direction of fault plane and auxillary fault plane with NNE-SSW and WNW-ESE are almost parallel to the general trends of lineaments in the study area. The results also show that focal mechanism solutions and the main axis of stress field in the Kyonggi massif and Okchon belt are almost same.