• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.76-80
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• 1989

Spatial filters were designed for 1 TW high power phosphate glass laser development. Laser beam should be expanded from 1 mm diameter to 200mm diameter. Pin hole size should be determined and most of incident energy should be transmitted through out to final spatial filter. Each pin hole size is determined by calculating encircled energy for Gaussian beam from the oscillator. The optical tube length of each spatial filter is corrected to have the best collimating quality by scew raytracing through the total system.

• Imaging Science in Dentistry
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• v.49 no.2
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• pp.139-151
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• 2019

Purpose: This study was performed to investigate the effect of exposure parameters on image quality obtained using a cone-beam computed tomography (CBCT) scanner and the relationship between physical factors and clinical image quality depending on the diagnostic task. Materials and Methods: CBCT images of a SedentexCT IQ phantom and a real skull phantom were obtained under different combinations of tube voltage and tube current (Alphard 3030 CBCT scanner, 78-90 kVp and 2-8 mA). The images obtained using a SedentexCT IQ phantom were analyzed technically, and the physical factors of image noise, contrast resolution, spatial resolution, and metal artifacts were measured. The images obtained using a real skull phantom were evaluated for each diagnostic task by 6 oral and maxillofacial radiologists, and each setting was classified as acceptable or unacceptable based on those evaluations. A statistical analysis of the relationships of exposure parameters and physical factors with observer scores was conducted. Results: For periapical diagnosis and implant planning, the tube current of the acceptable images was significantly higher than that of the unacceptable images. Image noise, the contrast-to-noise ratio (CNR), the line pair chart on the Z axis, and modulation transfer function (MTF) values showed statistically significant differences between the acceptable and unacceptable image groups. The cut-off values obtained using receiver operating characteristic curves for CNR and MTF 10 were useful for determining acceptability. Conclusion: Tube current had a major influence on clinical image quality. CNR and MTF 10 were useful physical factors that showed significantly associations with clinical image quality.

• Imaging Science in Dentistry
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• v.53 no.4
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• pp.325-333
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• 2023

Purpose: The objective of this study was to evaluate and compare the accuracy and image quality of root surface area (RSA) measurements obtained with various cone-beam computed tomography (CBCT) protocols, relative to the gold standard of micro-computed tomography (CT), in an in vitro setting. Materials and Methods: Four dry human skulls were scanned using 8 different protocols, with voxel sizes of 0.15 mm, 0.3 mm, and 0.4 mm. Three-dimensional models of the selected teeth were constructed using CBCT and microCT protocols, and the RSA was automatically measured by the image-processing software. The absolute difference in the percentage of the RSA(%ΔRSA) was calculated and compared across the 8 CBCT protocols using repeatedmeasures analysis of variance. Finally, image quality scores of the RSA measurements were computed and reported in terms of percent distribution. Results: No significant differences were observed in the %ΔRSA across the 8 protocols (P>0.05). The deviation in %ΔRSA ranged from 1.51% to 4.30%, with an increase corresponding to voxel size. As the voxel size increased, the image quality deteriorated. This decline in quality was particularly noticeable at the apical level of the root, where the distribution of poorer scores was most concentrated. Conclusion: Relative to CBCT protocols with voxel sizes of 0.15mm and 0.3mm, the protocols with a voxel size of 0.4 mm demonstrated inferior image quality at the apical levels. In spite of this, no significant discrepancies were observed in RSA measurements across the different CBCT protocols.

• Korean Journal of Agricultural Science
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• v.39 no.3
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• pp.341-347
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• 2012

The objective of this study was to investigate the combined effect of electron beam irradiation (EB) and onion peel extracts and selected flavorings on microbiological and sensory quality of pork jerky. Total aerobic bacteria were detected in the range of $3.87{\pm}0.30{\sim}4.60{\pm}0.12$ log CFU/g in all samples. Addition of both onion peel extract and flavoring showed the decrease of total aerobic bacterial count in pork jerky. No viable cells were observed after EB at 4 kGy. Sensory evaluation indicated that the EB-treated pork jerky with 0.5% barbecue flavoring did not show any difference in overall acceptability compared with the control. Therefore, combined use of EB with onion peel extracts and barbecue flavoring may enhance the safety of pork jerky with proper sensory quality.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.6
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• pp.569-577
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• 2010

Nonplanar surface geometries of components are frequently encountered in real ultrasonic inspection situations. Use of rigid array transducers can lead to beam defocusing and reduction of defect image quality due to the mismatch between the planar array and the changing surface. When a flexible array is used to fit the complex surface profile, the locations of array elements should be known to compute the delay time necessary for adaptive heam focusing. An alternative method is to employ the time reversal focusing technique that does not require a prior knowledge about the properties and structures of the specimen and the transducer. In this paper, a time reversal method is applied to simulate beam focusing of flexible arrays and imaging of point-like defects contained in specimens with nonplanar surface geometry. Quantitative comparisons are made for the performance of a number of array techniques in terms of the ability to focus and image three point-like reflectors positioned at regular intervals. The sinusoidal profile array studied here exhibits almost the same image quality as the flat, reference case.

• Journal of the Korean Vacuum Society
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• v.12 no.4
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• pp.251-256
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• 2003

Indium aluminum arsenide(InAlAs) was grown by molecular beam epitaxy on (001) indium phosphide (InP) substrate and the effects of growth temperature on the properties of epitaxial layers were studied. In the temperature range of 370-$400 ^{\circ}C$, we observed that the surface morphology, optical quality and structural quality of InAlAs epilayers were improved as growth temperature increased. However, the InAlAs epilavers grown at $430 ^{\circ}C$ have the bad surface morphology and show the same trends as structural and epical quality. As a result of these measurements, it is suggested that the InAlAs epilayers of very good properties can be grown at $400 ^{\circ}C$.

• Korean Journal of Optics and Photonics
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• v.32 no.2
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• pp.55-61
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• 2021

The lateral-mode characteristics of 850-nm GaAs/(Al,Ga)As multiple-quantum-well laser diodes and their influence on the kinks in output optical power are investigated. For the investigation, self-consistent electro-thermal-optical simulation and measurement of fabricated devices are used. From this investigation, the optimal P-cladding thickness that provides single-lateral-mode operation is determined, so that high beam quality can be achieved even at high output powers.

• Journal of the Korean Physical Society
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• v.73 no.12
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• pp.1814-1820
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• 2018

With the publication of TRS-483 in late 2017 the IAEA has established an international code of practice for reference dosimetry in small and non-standard fields based on a formalism first suggested by Alfonso et al. in 2008. However, data on beam quality correction factors ($k^{f_{msr},f_{ref}}_{Q_{msr},Q_0}$) for the Leksell Gamma $Knife^{(R)}$ $Perfexion^{TM}$ is scarce and what little data is available was obtained under conditions not necessarily in accordance with the IAEA's recommendations. This study constitutes the first systematic attempt to calculate those correction factors by applying the new code of practice to Monte Carlo simulation using the GEANT4 toolkit. $k^{f_{msr},f_{ref}}_{Q_{msr},Q_0}$ values were determined for three common ionization chamber detectors and five different phantom materials, with results indicating that in most phantom materials, all chambers were well suited for reference dosimetry with the Gamma $Knife^{(R)}$. Similarities and differences between the results of this study and previous ones were also analyzed and it was found that the results obtained herein were generally in good agreement with earlier PENELOPE and EGSnrc studies.

• Progress in Medical Physics
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• v.21 no.1
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• pp.120-125
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• 2010

For the measurements of an absorbed dose using the standard dosimetry based on an absorbed dose to water the variety of factors, whether big, small, or tiny, may influence the accuracy of dosimetry. The beam quality correction factor ${\kappa}_{Q,Q_0}$ of an ionization chamber might also be one of them. The cylindrical type of ionization chamber, the PTW30013 chamber, was chosen for this work and 9 chambers of the same type were collected from several institutes where the chamber types are used for the reference dosimetry. They were calibrated from the domestic Secondary Standard Dosimetry Laboratory with the same electrometer and cable. These calibrated chambers were used to measure absorbed doses to water in the reference condition for the photon beam of 6 MV and 10 MV and the electron beam of 12 MeV from Siemens ONCOR. The biggest difference among chambers amounts to 2.4% for the 6 MV photon beam, 0.8% for the 10 MV photon beam, and 2.4% for the 12 MeV electron beam. The big deviation in the photon of 6 MV demonstrates that if there had been no problems with the process of measurements application of the same ${\kappa}_{Q,Q_0}$ to the chambers used in this study might have influenced the deviation in the photon 6 MV and that how important an external audit is.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.10
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• pp.1089-1095
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• 2012

Laser beam machining (LBM) using nanosecond pulsed laser is widely known to be rapid and non-wear process for micromachining. However, the quality itself cannot meet the precision standard due to the recast layer and heat affected zone. In this paper, a fabrication method for machining micro features in stainless steel using a hybrid process of LBM using nanosecond pulsed laser and electrochemical etching (ECE) is reported. ECE uses non-contacting method for precise surface machining and selectively removes the recast layer and heat affected zone produced by laser beam in an effective way. Compared to the single LBM process, the hybrid process of LBM and ECE enhanced the quality of the micro features.