• Korean Journal of Optics and Photonics
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• v.1 no.2
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• pp.155-161
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• 1990

A Continous wave tunable $CO_2$ laser which is the slow axial flow type was construccted for the optical pumping of methyl alcohol ($CH_3OH$) laser. The reflective grating of 100 grooveslmm and 10.6$\mu\textrm{m}$ blaze wavelength was used to select wavelength. We have investigated continous outpu: power characteristics, and then have compared tuned output power profile with the gain curve of $CO_2$ laser. The optimum condition for maxium power was found at the gas mixing ratio 1 : 3 : 10 for $CO_2: N_2$ and He. under this condition the flow rate, pressure of lasing gas and discharge current are 9.5 llmin. 14 torr, and 55 mA respectively. The maxium output power was 55 Wlm. Output power of single wavelength operation was measured on 60 individual rotation vibration transitions in the P and K branches of the 9.5$\mu\textrm{m}$ band and 10.4$\mu\textrm{m}$ band in $CO_2$. The output power profile obtained from each band is well consistent with the gain curve of $CO_2$ laser and maxium tuned output power was 20 watt.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.446-456
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• 2006

The effect of relative position of the stationary turbine blade for the fixed vane has been investigated on blade tip and shroud heat transfer. The local mass transfer coefficients were measured on the tip and shroud fur the blade fixed at six different positions within a pitch. A low speed stationary annular cascade with a single turbine stage was used. The chord length of the tested blade is 150 mm and the mean tip clearance of the blade having flat tip is 2.5% of the blade chord. A naphthalene sublimation technique was used for the detailed mass transfer measurements on the tip and the shroud. The inlet flow Reynolds number based on chord length and incoming flow velocity is fixed to $1.5{\times}10^5$. The results show that the incoming flow condition and heat transfer characteristics significantly change when the relative position of the blade changes. On the tip, the size of high heat/mass transfer region along the pressure side varies in the axial direction and the difference of heat transfer coefficient is up to 40% in the upstream region of the tip because the position of flow reattachment changes. On shroud, the effect of tip leakage vortex on the shroud as well as tip gap entering flow changes as the blade position changes. Thus, significantly different heat transfer patterns are observed with various blade positions and the periodic variation of heat transfer is expected with the blade rotation.

• Journal of Korean Neurosurgical Society
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• v.53 no.6
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• pp.331-336
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• 2013

Objective : The offset connector can allow medial and lateral variability and facilitate intralaminar screw incorporation into the construct. The aim of this study was to compare the biomechanical characteristics of C7 intralaminar screw constructs with and without offset connector using a three dimensional finite element model of a C6-7 cervical spine segment. Methods : Finite element models representing C7 intralaminar screw constructs with and without the offset connector were developed. Range of motion (ROM) and maximum von Mises stresses in the vertebra for the two techniques were compared under pure moments in flexion, extension, lateral bending and axial rotation. Results : ROM for intralaminar screw construct with offset connector was less than the construct without the offset connector in the three principal directions. The maximum von Misses stress was observed in the C7 vertebra around the pedicle in both constructs. Maximum von Mises stress in the construct without offset connector was found to be 12-30% higher than the corresponding stresses in the construct with offset connector in the three principal directions. Conclusion : This study demonstrated that the intralaminar screw fixation with offset connector is better than the construct without offset connector in terms of biomechanical stability. Construct with the offset connector reduces the ROM of C6-7 segment more significantly compared to the construct without the offset connector and causes lower stresses around the C7 pedicle-vertebral body complex.

• Journal of Aerospace System Engineering
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• v.15 no.1
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• pp.72-79
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• 2021

In this study, as part of the development of an autonomous flying personal aircraft, an equivalent model of the main wing assembly of an Optionally Piloted Personal Air Vehicle (OPPAV) was developed. Reliability of the developed equivalent model was verified by eigenvalue analysis. The main wing assembly consisted of a main wing, an inboard pod, and an outboard pod. First, for developing an equivalent model of each component, components to produce the equivalent model were divided into several sections. Nodes were then created on the axis of the equivalent model at both ends of each section. In addition, static analysis with unit force and unit moment was performed to calculate the deformation or the amount of rotation at the node to be used in the equivalent model. Equivalent axial, bending, and torsional stiffness of each section were calculated by applying the beam theory. Once the equivalent stiffness of each section was calculated, information of a mass and moment of inertia for each section was entered by creating a lumped mass in the center of each section. An equivalent model was developed using beam element. Finally, the reliability of the developed equivalent model was verified by comparison with results of mode analysis of the fine model.

• Tribology and Lubricants
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• v.39 no.5
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• pp.183-189
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• 2023

A bearing is a mechanical component that transmits rotation and supports loads. According to the type of rotating mechanism, bearings are categorized into ball bearings and tapered roller bearings. Tapered roller bearings have higher load-bearing capabilities than ball bearings. They are used in applications where high loads need to be supported, such as wheel bearings for commercial vehicles and trucks, aircraft and high-speed trains, and heavy-duty spindles for heavy machinery. In recent times, the demand for reducing the driving friction torque in automobiles has been increasing owing to the CO₂ emission regulations and fuel efficiency requirements. Accordingly, the research on the driving friction torque of bearings has become more essential. Researchers have conducted various studies on the lubrication, friction, and contact in tapered roller bearings. Although researchers have conducted numerous studies on the friction in the lips and on roller misalignment and skew, studies considering the influence of roller shape, specifically roller shape errors including lips, are few. This study investigates the driving friction torque of tapered roller bearings considering roller geometric uncertainties. Initially, the study calculates the driving friction torque of tapered roller bearings when subjected to axial loads and compares it with experimental results. Additionally, it performs Monte Carlo simulations to evaluate the influence of roller geometric uncertainties (i.e., the effects of roller geometric deviations) on the driving friction torque of the bearings. It then analyzes the results of these simulations.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.1
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• pp.61-69
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• 2008

Purpose: Micro-pinhole SPECT system with conventional multiple-head gamma cameras has the advantage of high magnification factor for imaging of rodents. However, several geometric factors should be calibrated to obtain the SPECT image with good image quality. We developed a simplified geometric calibration method for rotating triple-head pinhole SPECT system and assessed the effects of the calibration using several phantom and rodent imaging studies. Materials and Methods: Trionix Triad XLT9 triple-head SPECT scanner with 1.0 mm pinhole apertures were used for the experiments. Approximately centered point source was scanned to track the angle-dependent positioning errors. The centroid of point source was determined by the center of mass calculation. Axially departed two point sources were scanned to calibrate radius of rotation from pinhole to center of rotation. To verify the improvements by the geometric calibration, we compared the spatial resolution of the reconstructed image of Tc-99m point source with and without the calibration. SPECT image of micro performance phantom with hot rod inserts was acquired and several animal imaging studies were performed. Results: Exact sphere shape of the point source was obtained by applying the calibration and axial resolution was improved. Lesion detectibility and image quality was also much improved by the calibration in the phantom and animal studies. Conclusion: Serious degradation of micro-pinhole SPECT images due to the geometric errors could be corrected using a simplified calibration method using only one or two point sources.

• Progress in Medical Physics
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• v.19 no.4
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• pp.209-218
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• 2008

According to improved radiation therapy technology such as IMRT and proton therapy, the accuracy of patient alignment system is more emphasized and IGRT is dominated research field in radiation oncology. We proposed to study the feasibility of cone-beam CT system using simple x-ray imaging systems for image guided proton therapy at National Cancer Center. 180 projection views ($2,304{\times}3,200$, 14 bit with 127 ${\mu}m$ pixel pitch) for the geometrical calibration phantom and humanoid phantoms (skull, abdomen) were acquired with $2^{\circ}$ step angle using x-ray imaging system of proton therapy gantry room ($360^{\circ}$ for 1 rotation). The geometrical calibration was performed for misalignments between the x-ray source and the flat-panel detector, such as distances and slanted angle using available algorithm. With the geometrically calibrated projection view, Feldkamp cone-beam algorithm using Ram-Lak filter was implemented for CBCT reconstruction images for skull and abdomen phantom. The distance from x-ray source to the gantry isocenter, the distance from the flat panel to the isocenter were calculated as 1,517.5 mm, 591.12 mm and the rotated angle of flat panel detector around x-ray beam axis was considered as $0.25^{\circ}$. It was observed that the blurring artifacts, originated from the rotation of the detector, in the reconstructed toomographs were significantly reduced after the geometrical calibration. The demonstrated CBCT images for the skull and abdomen phantoms are very promising. We performed the geometrical calibration of the large gantry rotation system with simple x-ray imaging devices for CBCT reconstruction. The CBCT system for proton therapy will be used as a main patient alignment system for image guided proton therapy.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.783-788
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• 2012

Stern tube bearing is a shaft device playing important roles to reduce the friction of axial rotation and to support the weight of shaft. However, because there is no domestic producer of stern tube bering, imported stern tube bearings have many practical problems including prices, delivery and after services. This is why stern tube bearing should be localization. For the purpose of development of polyurethane resin for stern tube bearings, the effect of additives on the hardness, tensile strength and elongation of the polyurethane resin were systematically investigated. For the preliminary researches, depending on the type of curing agent, MOCA type and non-MOCA type polyurethanes were synthesized. Preliminary researches concluded that MOCA type polyurethane resin has more excellent mechanical properties than non-MPCA type for stern tube bearings that Tensile strength and Hardness of non-MOCA type investigated 23 D, 4.3 Mpa. Therefore, MOCA type polyurethane was adapted as base resin of this research. Silica, calcium carbonate and graphite were selected as additives for the enhancement of mechanical properties of polyurethane resin. Effect of the type and the dosage of these additives on the hardness, tensile strength, elongation of the polyurethane resin were experimentally examined. However, addition of calcium carbonate and graphite showed only minor effect on the hardness of the resin. Polyurethane resin with silica showed relatively excellent hardness, tensile strength and improved elongation.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.683-692
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• 2011

In piloti-type low-rise RC residential buildings, severe damages have been usually concentrated at piloti stories under the earthquake. In this study, a piloti story was retrofitted by installation of buckling-restrained braces (BRB's) to increase strength and stiffness of piloti story and by application of fiber reinforced polymer (FRP) sheet on columns to avoid the brittle shear and axial failure of columns. To verify this retrofit performance, reversed cyclic lateral load tests were performed on 1:5 scale bare and retrofitted frames. The test results showed that yield strength (43.2 kN) appeared to be significantly larger than design value (30 kN) due to the increase of strength in the compression side, but the stiffness value (11.6 kN/mm) turned out to be approximately one-half of the design value (24.2 kN/mm). The reasons for this difference in stiffness were due to slippage at joint between the frame and the BRB's, displacement and rotation at footing. The energy absorption capacity of the retrofitted frame was 7.5 times larger than that of the bare frame. The change of the number of load cells under the footing from 2 to 1 reduced lateral stiffness from 11.6 kN/mm to 6 kN/mm, which was only three times larger than that of the bare frame (2.1 kN/mm).

• The Journal of the Korea Contents Association
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• v.11 no.12
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• pp.814-821
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• 2011

The purpose of this study was to evaluate of resolution parameter and reconstitution filter in the 256 multi detector computed tomography(MDCT) by using the head phantom. We used 256 MDCT, and head phantom of philips system. We evaluated to image quality by using Extended Brilliance Workspace. The protocol were axial scan method with 120 kVp, 0.5 sec of rotation time, 5 mm of slice thickness and increment, 250 mm of field of view(FOV), $512{\times}512$ of matrix size, 1.0 of pitch, $128{\times}0.625$ mm of collimations. The resolution parameter was applied for 'Standard', 'High' and 'Ultrahigh'. The reconstitution filters were changed to seven type of 'A', 'B', 'C', 'D', 'UA', 'UB', 'UC'. The assesment factors of image quality were the uniformity, the noise, the linearity and 50% and 10% of the modulation transfer function(MTF). Finally The good image quality in 'High' resolution parameter showed at the uniformity, the linearity and 50% and 10% of MTF. The 'UA', 'UB' reconstitution filter showed at the good image quality of the uniformity and the noise and 'C' reconstitution filter showed at the same result of the linearity and 50% and 10% of MTF.