• Imaging Science in Dentistry
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• v.37 no.3
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• pp.157-163
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• 2007

Purpose: To evaluate the characteristics of (widely used) cone beam computed tomography (CBCT) images. Materials and Methods: Images were obtained with CT performance phantoms (The American Association of Physicists in Medicine; AAPM). CT phantom as the destination by using PSR $9000N^{TM}$ dental CT system (Asahi Roentgen Ind. Co., Ltd., Japan) and i-CAT CBCT (Imaging Science International Inc., USA) that have different kinds of detectors and field of view, and compared these images with the CT number for linear attenuation, contrast resolution, and spatial resolution. Results: CT number of both PSR $9000N^{TM}$ dental CT system and i-CAT CBCT did not conform to the base value of CT performance phantom. The contrast of i-CAT CBCT is higher than that of PSR $9000N^{TM}$ dental CT system. Both contrasts were increased according to thickness of cross section. Spatial resolution and shapes of reappearance was possible up to 0.6 mm in PSR $9000N^{TM}$ dental CT system and up to 1.0 mm in i-CAT CBCT. Low contrast resolution in region of low contrast sensitivity revealed low level at PSR $9000N^{TM}$ dental CT system and i-CAT CBCT. Conclusion: CBCT images revealed higher spatial resolution, however, contrast resolution in region of low contrast sensitivity was the inferiority of image characteristics.

• Progress in Medical Physics
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• v.27 no.3
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• pp.125-130
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• 2016

Dual energy computed tomography (DECT) is used to classify two materials and quantify the mass density of each material in the human body. An energy modulation filter based DECT could acquire two images, which are generated by the low- and high-energy photon spectra, in one scan, with one tube and detector. In the case of DECT using the energy modulation filter, the filter should perform the optimization process for the type of materials and thicknesses for generating two photon spectra. In this study, Geant4 Monte-Carlo simulation toolkit was used to execute the optimization process for determining the property of the energy modulation filter. In the process, various materials used for the energy modulation filter are copper (Cu, $8.96g/cm^3$), niobium (Nb, $8.57g/cm^3$), stannum (Sn, $7.31g/cm^3$), gold (Au, $19.32g/cm^3$), and lead (Pb, $11.34g/cm^3$). The thickness of the modulation filter varied from 0.1 mm to 1.0 mm. To evaluate the overlap region of the low- and high-energy spectrum, Geant4 Monte-Carlo simulation is used. The variation of the photon flux and the mean energy of photon spectrum that passes through the energy modulation filter are evaluated. In the primary photon spectrum of 80 kVp, the optimal modulation filter is a 0.1 mm lead filter that can acquire the same mean energy of 140 kVp photon spectrum. The lead filter of 0.1 mm based dual energy CBCT is required to increase the tube current 4.37 times than the original tube current owing to the 77.1% attenuation in the filter.

• Journal of the Korea Institute of Building Construction
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• v.20 no.2
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• pp.129-135
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• 2020

The purpose of this research is to analyze the gamma ray shielding effect of heavy concrete containing magnetic aggregate and to confirm the applicability to the military protective facilities. In general, a military concrete structure protects combatants from bullets, and also it provides some radiation shielding. In this research, experiments were conducted using a Cs-137 source to check the gamma ray shielding effect. In addition, the Monte Carlo N-Particle(MCNP) modeling was applied to evaluate the gamma ray shielding effect of a military structure. As a result, as the concrete thickness increased, the shielding performance improved according th the linear attenuation law. With that, as the ratio of magnetic aggregate was increased, gamma ray shielding performance was also improved. Therefore, this research verified that the application of magnetic aggregate concrete to military facilities for radiation shielding purposes would be useful.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.7
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• pp.97-104
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• 2006

The spray and breakup characteristics of swirling liquid sheet were investigated by measuring the spray angle and breakup length as the axial Weber number Wel was increased up to 1554 and the ambient gas pressure up to 4.0MPa. As Wel and ambient gas density increased, the disturbances on the annular liquid sheet surface were amplified by the increase of the aerodynamic forces, and thus the liquid sheet disintegrated near from the injector exit. The measured spray angles according to the ambient gas density were different before and after the sheet breaks. Before the liquid sheet breaks, the spray angle was almost constant, but once the liquid sheet started to breakup, the spray angle decreased. And the breakup length decreased because of the increase of the aerodynamic force as the ambient gas density and Wel increased. Lastly, the measured breakup length according to the ambient gas density and Wel was compared with the result by the linear instability theory. We found that the corrected linear instability theory considering the attenuation of sheet thickness agrees well with our experimental results.

• Archives of Plastic Surgery
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• v.35 no.2
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• pp.201-204
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• 2008

Purpose: Now the CT scanner and PACS program proved to be an excellent instrument for detection and localization of most facial foreign bodies above certain minimum levels of detectability. The severity of injury in penetrating trauma on the face is often underestimated in physical examination. Wood, with its porous consistency and organic nature, provides a good medium for microbial agents. This is a report of our recent experience with wooden foreign bodies in the parotid gland imaged with CT. Methods: A 9-year-old boy was referred for evaluation of possible retained foreign body within his face. One day earlier, he had fallen, face down approximately 1 miter onto ground. He had subsequently undergone an exploration of his right parotido-masseteric area at an outside hospital with repair of a right facial laceration. Enhanced 2 mm axial and coronal CT scans were obtained through the face. Axial and coronal CT images were obtained with a General Electric(Milwaukee, Wis) 9800 CT scanner at 130 kV, 90 mA, with a 2 mm section thickness. Results: We finally decided the linear "gas" attenuation was a foreign body because of its linear configuration, which did not conform to that of an anatomic structure, and on the basis of articles that described a wood foreign body in the orbit as having the appearance of air. We found that wood was hypoattenuating($-464{\pm}27HU$). Conclusion: We recommend this type of software program for CT scanning for any patient with an injury on the face in which a foreign body is suspected.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.1
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• pp.73-79
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• 2001

In this study, a submerged plate-type breakwater is considered, which is supported by elastic foundation. This breakwater makes use of wave phase interaction among the incident, diffracted and radiated waves. We apply a three-dimensional singularity distribution method within the linear potential theory in order to describe the wave field. The submerged plate is assumed to be rigid and the elastic support be a linear spring with constant stiffness. A typical rectangle plate is exemplified for numerical calculation. The thickness of the plate is carefully selected in order to guarantee the solution to be stable by checking the condition number of the system matrix. A parametric study is carried out for examining the effect of the stiffness of the elastic support on performance of the breakwater. We also examine the effect of the submerged depth.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.103.1-103.1
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• 2011

Recent observations by Hinode show weakly-attenuated coronal loop oscillations in the presence of background flow (Ofman & Wang 2008, A&A, 482, L9). We study the vertical kink oscillations in solar coronal loops, considering field aligned flows inside the loops as well as surrounding the loops environment. The two dimensional numerical model of straight slab is used to explore the excitation and attenuation of the impulsively triggered fast magnetosonic standing kink waves. A full set of time dependent ideal magnetohydrodynamics equations is solved numerically taking into account the value of flow of the order of observed flows detected by SOT/Hinode. We find that relaxing the assumption of the limited flows within the loops enhances the damping rate of the fundamental mode of the standing kink waves by 2 - 3 % as compared to flow pattern which is basically localized within the loops. We further notice that extending the flow pattern beyond the loop thickness also enhances the strength of the shock associated with slow magnetoacoustic waves, recognized as an addition feature detected in the numerical simulation. The wider out-flow pattern destroys the oscillation patterns early as compared to narrower flow pattern, in other words we can say that it affects the durability of the oscillation. However, for the typical coronal loops parameters we find that the observed durability periods of the SOT/Hinode observation can be achieved with an out-flow Gaussian patterns for which half-width is not greater than factor 2.0 of the loop-half-width. explain a possible relation between electric current structure and sigmoid observed in a preflare phase.

• Current Optics and Photonics
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• v.1 no.2
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• pp.132-137
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• 2017

To investigate the usefulness of optical coherence tomography (OCT) for imaging lymphedema, we directly compared it to other histological methods in a mouse model of lymphedema. We performed detailed imaging of the lymphedema lesion on a mouse tail. We imaged the mouse tail in vivo with OCT and created histopathological samples. We constructed a spectrometer-based OCT system using a fiber-optic Michelson interferometer. The light was directed to 50:50 couplers that split the light into reference and sample arms. Backscattered light from a reference mirror and the sample produced an interference fringe. An OCT image of the lymphedema model revealed an inflammatory reaction of the skin that was accompanied by edema, leading to an increase in the light attenuation in the dermal and subcutaneous layers. Similar to OCT image findings, histological biopsy showed an inflammatory response that involved edema, increased neutrophils in epidermis and subdermis, and lymphatic microvascular dilatation. Furthermore, the lymphedema model showed an increase in thickness of the dermis in both diagnostic studies. In the mouse tail model of lymphedema, OCT imaging showed very similar results to other histological examinations. OCT provides a quick and useful diagnostic imaging technique for lymphedema and is a valuable addition or complement to other noninvasive imaging tools.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.12
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• pp.837-842
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• 2015

In this study, the characteristics of electrostatic attenuation in plain shape glass filament sample (0.29 mm thickness, cross section of $12.25cm^2$, $16cm^2$, $20.25cm^2$) for insulator has been measured at temperature of $5^{\circ}C{\sim}38^{\circ}C$, humidity of 50%~90%. The results of this study are as follows. In case of samples that the cross section is $12.25cm^2$, $16cm^2$, $20.25cm^2$ at humidity of 50%~90%, it found that the electrification voltage of electrostatic increased with increasing temperature, with a return to decrease at $20^{\circ}C$. In case of samples that the cross section is $12.25cm^2$, $16cm^2$, $20.25cm^2$ at temperature of $5^{\circ}C{\sim}38^{\circ}C$, it found that the electrification voltage of electrostatic decreased with increasing humidity. In case of the sample at temperature of $20^{\circ}C$ and humidity of 65%, 75%, it found that the electrification voltage of electrostatic increased with increasing cross section. In case of the sample at humidity of 65% and cross section of $12.25cm^2$, the time that it takes to reduce electrification voltage of electrostatic in half decreased to 0.912s, 0.736s, 0.673s with increasing temperature to $10^{\circ}C$ $20^{\circ}C$, $30^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.13 no.5
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• pp.216-220
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• 2003

In this work, transmission characteristics of read and write signal were calculated when a MRAM (magnetic random access memory) cell is operated up to 10 GHz. Test device having long read and write lines was modeled in 3 dimensions to perform a simulation. The simulation was divided into two parts, read and write operations, and S-parameters were computed utilizing FEM (finite element method) algorithm. Transmission coefficients, S$\sub$21/, for read and write operations of MRAM device which was designed for a single cell test configuration were analyzed from DC to 1 GHz and DC to 10 GHz, respectively. When the insulator thickness between the bit and sense lines was increased from 500 to 1500 ${\AA}$, 3 dB attenuation frequency was increased by 3.3 times, from 135 to 430 MHz. The length of the bit and sense lines were 600 ${\mu}$m. In addition, access time was estimated by calculating the propagation delay utilizing S-parameters.