• Progress in Medical Physics
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• v.9 no.2
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• pp.105-113
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• 1998

Accurate radiation dosimetric characters is very important to determine of dose to a radiotherapeutic patient. Medical linear accelerators have been developed not only its new quality of convenient operation but also electric moderation. It is reliable to measure more detail physical parameter that linac's internal ability. Typically, radiation dosimetric tool is classified ionization chamber, film, thermoluminescence dosimeter, etc. Nowaday, Electronic Portal Imaging Device is smeared in radiation field to verification of treatment region. EPID's image was focused that using both on-line image verification and absolutely minimum absorbed dose during radiotherapy. So, Electronic Portal Imaging was tested for quality evaluation of medical linear accelerator had its pure conditional flash. This study has performed symmetry, Light/Radiation field congruence, and energy check, geometry difference on wedge filter using a liquid filled ion chamber (EPID). Prior to irradiated on EPID, high energy photon beam is checked with ion chamber. Using these results more convenient dosimetric method is accomplished by EPID that taken digital image. Medical image is acquired with EPID too. Therefore, EPID can be analyzed by numerical information for what want to see or get more knowledge for natural human condition.

• Journal of Radiation Protection and Research
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• v.42 no.4
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• pp.212-221
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• 2017

Background: This study aims to calculate detector positions as a design of a radioactive source localizing radiation portal monitor (RPM) system using an improved genetic algorithm. Materials and Methods: To calculate of detector positions for a source localizing RPM system optimization problem is defined. To solve the problem, a modified iterative genetic algorithm (MIGA) is developed. In general, a genetic algorithm (GA) finds a globally optimal solution with a high probability, but it is not perfect at all times. To increase the probability to find globally optimal solution rather, a MIGA is designed by supplementing the iteration, competition, and verification with GA. For an optimization problem that is defined to find detector positions that maximizes differences of detector signals, a localization method is derived by modifying the inverse radiation transport model, and realistic parameter information is suggested. Results and Discussion: To compare the MIGA and GA, both algorithms are implemented in a MATLAB environment. The performance of the GA and MIGA and that of the procedures supplemented in the MIGA are analyzed by computer simulations. The results show that the iteration, competition, and verification procedures help to search for globally optimal solutions. Further, the MIGA is more robust against falling into local minima and finds a more reliably optimal result than the GA. Conclusion: The positions of the detectors on an RPM for radioactive source localization are optimized using the MIGA. To increase the contrast of the measurements from each detector, a relationship between the source and the detectors is derived by modifying the inverse transport model. Realistic parameters are utilized for accurate simulations. Furthermore, the MIGA is developed to achieve a reliable solution. By utilizing results of this study, an RPM for radioactive source localization has been designed and will be fabricated soon.

• The Journal of Korean Society for Radiation Therapy
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• v.22 no.2
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• pp.105-111
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• 2010

Purpose: There are various beam parameter in intensity modulated radiation therapy (IMRT). The aim of this study is to investigate how various dose rate affect the parotid in treatment plan of IMRT. Materials and Methods: The study was performed on 10 nasopharyngeal carcinoma patients who have undergone IMRT. CT images were scanned 3 mm of thickness in the same condition and the treatment plan was performed by Eclipse (Ver.7.1, Varian, Palo Alto, USA). The parameters for planning used 6 MV energy and 8 beams under the same dose volume constraint. The variation of dose rates were used 300, 400, 500 MU/min. The mean dose of both parotid was accessed from the calculated planning among the 10 patients. The mean dose of parotid was verificated by 2D diode array (Mapcheck from Sun Nuclear Corporation, Melbourne, Florida). Also, Total monitor unit (MU) and beam-on time was analysed. Results: According to the dose rate, the mean dose of parotid was increased by 0.8%, 2.0% each, when dose rate was changed from 300 MU/min to 400, 500 MU/min, moreover Total MU was increased by 5.4% and 10.6% each. There was also a dose upward trend in the dose measurement of parotid by 2D diode array. However, beam - on time difference of 1~2 minutes was no signigicant in the dose rate increases. Conclusion: From this study, when the dose rates increase, there was a signigicant increase of Total MU and the parotid dose accordingly, however the shortened treatment time was not significant. Hence, it is considered that there is a significant decrease of late side effect in parotid radiation therapy, if the precise dose rate in IMRT is used.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 1996.11a
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• pp.53-56
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• 1996

In order to propose the method of the consequence analysis for fire accidents by the heavy gas release and to obtain optimum conditions of parameter selections, the consequence analysis for jet fire by the accident of xylene vapor release were performed. And the effect and the sensitivity analysis of parameters affecting the consequence were investigated. Simulation results showed that important parameters affecting results of the xylene vapor release accident were mainly hole diameter, interested distance, wind speed, and so on. For the jet fire, the accident result and the sensitivity of thermal radiation were increased with the decrease of interested distance and the increase of hole diameters, and the accidental result was increased as the increase wind speed, but the sensitivity of thermal radiation was decreased.

• Journal of Environmental Science International
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• v.9 no.4
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• pp.295-302
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• 2000

This study was conducted to investigate the characteristics of surface ozone concentration and occurrence of high ozone concentration using hourly ozone, nitrogen dioxide and meteorological data for 1997~1998 in Pusan coastal area. Monthly mean ozone concentration was the highest at Dongsamdong in Spring(35.4ppb), at Kwangbokdong in Fall(25.1ppb) and the lowest Dongsamdong(22.2ppb) and Kwangbokdong(16.0ppb) in Winter. Relative standard deviation indicating clearness of observation site was 0.42 at Dongsamdong and 0.49 at Kwangbokdong that is similar to urban area. The diurnal variation of ozone concentration of Dongsamdong and Kwangbokdong showed maximum at 1500~1600LST and minimum 0700~0800LST that typical pattern of ozone concentration. In ozone episode period(Sept. 10~15, 1998), diurnal change of ozone concentration was very high, and ozone concentration was related to meteorological parameters such as temperature, relative humidity, wind speed, cloud amount and radiation on a horizontal surface. During the episode days peak ozone concentrations are much higher than the normal values, wind speeds are always lower, and solar radiation is high with the exception of the September episode.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1672-1675
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• 2003

Microstrip antennas have many applications in wireless communication system. This paper propose a analytical far-field pattern of radiation for application of the wireless communication. The triangular slot antenna fed by micorstrip line is proposed at resonance frequency 10 GHz. The simulation results of the electromagnetic field radiation pattern, S parameter, characteristic of input impedance are obtain by using the finite difference time domain (FDTD) method. The analytical space in FDTD analysis are $50{\times}171{\times}120$ cells with the cell dimension ${\Delta}x=0.152\;mm$, ${\Delta}y={\Delta}z=0.15\;mm$.

• Journal of Korean Society for Atmospheric Environment
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• v.17 no.1
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• pp.31-38
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• 2001

Ambient ge-phase $H_2O$$_2$(Hydrogen Peroxide) concentrations were measured at four sites in downtown Seoul Korea. These measurements were mad during winter and summer, February 14~19 and 12~17, 1997. $H_2O$$_2$concentrations were quantified by fluorescence using enzyms. $H_2O$$_2$ concentrations in winter were below the limit of detection and was much higher concentrations in summer. The mean of all observations was 264 ppt and the range measured was 23ppt~1856ppt. The results from the correlation analysis showed that the concentration of gasous $H_2O$$_2$is dependent on the other air pollutants(O$_3$, NO$_2$) and meteorological parameter(solar radiation).

• Journal of electromagnetic engineering and science
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• v.7 no.3
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• pp.116-121
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• 2007

Novel design of a wideband monopole antenna for DVB-H service is presented. The proposed antenna is designed based on a monopole antenna. It consists of folded monopole and parallel parasitic element. The folded segment of the folded monopole makes the antenna shorter. The length of the parasitic element obtains additional resonance frequencies. The gap distance between the folded monopole and the parasitic element is a key parameter to control impedance matching for wideband operation. The antenna has wide band performance, good impedance and radiation characteristics from 470 MHz to 870 MHz. The measured return loss for operating frequencies over DVB-H band is better than 10 dB. Good radiation patterns are also obtained. The measured results are compared with calculated results using Ansoft HFSS(High Frequency Structure Simulator).

• Journal of computational fluids engineering
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• v.15 no.3
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• pp.87-94
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• 2010

Hydromagnetic flow in a cavity under a uniform magnetic field is studied numerically. The cavity is comprised of four radiatively active surfaces. Due to large temperature difference inside a cavity, the radiative interaction between walls is taken into account. The coupled momentum and energy equations are solved by SIMPLER algorithm while the radiant heat exchanges are obtained by the finite volume method for radiation. A Wide range of Grashof numbers is examined as a controlling parameter. Resultant flow and heat transfer characteristics are investigated as well.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1639-1644
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• 2003

A hybrid genetic algorithm is developed for estimating the wall emissivities for an absorbing, emitting, and scattering media in a two-dimensional irregular geometry with diffusely emitting and reflecting opaque boundaries by minimizing an objective function, which is expressed by the sum of square errors between estimated and measured temperatures at only four data positions. The finite-volume method was employed to solve the radiative transfer equation for a two-dimensional irregular geometry. The results show that a developed hybrid genetic algorithms reduce the effect of genetic parameters on the performance of genetic algorithm and that the wall emissivities are estimated accurately without measurement errors.