• The Journal of Korean Society for Radiation Therapy
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• v.29 no.2
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• pp.43-51
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• 2017

Purpose: The purpose of this study is to evaluate the dosimetric effects of couch attenuation and air gaps using 3D phantom for prone breast radiation therapy. Materials and method: A 3D printer(Builder Extreme 1000) and computed tomography (CT) images of a breast cancer patient were used to manufacture the customized breast phantom. Eclipse External Beam Planning 13.6 (Varian Medical Systems Palo Alto, CA, USA) was used to create the treatment plan with a dose of 200 cGy per fraction with 6 MV energy. The Optically Stimulated Luminescence Detector(OSLD) was used to measure the skin dose at four points (Med 1, Med 2, Lat 1, Lat 2) on the 3D phantom and ion-chamber (FC65-G) were used to perform the in-vivo dosimetry at the two points (Anterior, Posterior). The Skin dose and in-vivo dosimetry were measured with reference air gap (3 cm) and increased air gaps (1, 2, 3, 4, 5, 6 cm) from reference distance between the couch and 3D phantom. Results: As a result, measurement for the skin dose at lateral point showed a similar value within ${\pm}4%$ compared to the plan. While the air gap increased, skin dose at medial 1 was reduced. And it was also reduced over 7 % when the air gap was more than 3 cm compared to radiation therapy plan. At medial 2 it was reduced over 4 % as well. The changes of dose from variety of the air gap showed similar value within ${\pm}1%$ at posterior. As the air gap was increased, the dose at anterior was also increased and it was increased by 1 % from the air gap distance more than 3 cm. Conclusion: Dosimetrical measurement using 3D phantom is very useful to evaluate the dosimetric effects of couch attenuation and air gaps for prone breast radiation therapy. And it is possible to reduce the skin dose and increase the accuracy of the radiation dose delivery by appling the optimized air gap.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.3
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• pp.122-128
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• 2009

DBD(Dielectric Barrier Discharges) plasma is often used to clean the surface of semiconductor. The cleaning performance is affected mainly by plasma density and duration time. In this study, the plasma density is predicted by coupled simulation of flow, chemistry mixing and reaction, plasma, and electric field. 13.56 MHz of RF source is used to generate plasma. The effect of dielectric thickness, gap distance, and flow velocity on plasma density is investigated. It is shown that the plasma density increases as the dielectric thickness decreases and the gap distance increases.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.1
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• pp.15-21
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• 2002

We investigated effects of electrical, physical, and chemical parameters on energy transfer, NO conversion, and light emission in the dielectric barrier discharge (DBD) process. As gap distance between electrodes increased, discharge onset voltage increased. However, as gap distance between electrodes increased, electric field which initiates discharge showed approximately the same value, 30kV/cm. The discharge onset voltage of the coarse surface electrode was lower than that of the smooth surface electrode. And, energy transfer was slightly enhanced in the coarse electrode condition. However, NO conversion rate decreased with the coarse surface electrode because more uniform discharge can be obtained on the smooth surface electrode. The NO conversion rate increased with decreasing the initial concentration, so the DBD process is more feasible in the lower concentration condition. The variation of gas residence time tested at the same energy density in the experiment did not affect on the NO conversion. The result shows that the NO conversion rate mainly depends on the energy density. The DBD process is able to adjust on plasma-photocatalyst process because it emits the short wavelength light in the range of ultraviolet. The intensity of light emission increased with the increase of the energy transfer to the reactor and the gas flow rate.

• Nuclear Engineering and Technology
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• v.33 no.3
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• pp.298-306
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• 2001

As fuel burnup proceeds, thermal gradients, differential swelling, and inter-assembly loading may induce assembly duct bowing. Since duct bowing affects the reactivity, such as long or short term power-reactivity-decrement variations, handling problem, caused by top end deflection of the bowed assembly duct, and the integrity of the assembly duct itself. Assembly duct bowing were first observed at EBR-ll in 1965, and then several designs of assembly ducts and core restraint system were used to accommodate this problem. In this study, NUBOW-2D KMOD was used to analyze the bowing behavior of the assembly duct under the KALIMER(Korea Advanced Liquid MEtal Reactor) core restraint system conditions. The mechanical behavior of assembly ducts related to several design parameters are evaluated. ACLP(Above Core Load Pad) positions, the gap distance between the ducts, and the gap distance between the duct and restraint ring were selected as the sensitivity parameter for the evaluation of duct deflection.

• Membrane and Water Treatment
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• v.5 no.2
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• pp.109-122
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• 2014

Polyvinylidene fluoride (PVDF) hollow fiber membrane is widely used for water treatment. However, the weak mechanical strength of PVDF limits its application. To enhance its tensile strength, a double-layer composite hollow fiber membrane, with PVDF and polyetherimide as the external and inner layers, respectively, was successfully prepared through phase inversion technique. The effects of additive content, air gap distance, N,N-dimethyl-acetamide content in the inner core liquid, and the temperature of external coagulation bath on the membrane structure, permeation flux, rejection, tensile strength, and porosity were determined. Experimental results showed that the optimum preparation conditions for the double-layer composite hollow fiber membrane were as follows: PEG-400 and PEG-600, 5 wt%; air gap distance, 10 cm; inner core liquid and the external coagulation bath should be water; and temperature of the external coagulation bath, 40 C. A single layer PVDF hollow fiber membrane (without PEI layer) was also prepared under optimum conditions. The double-layer composite membrane remarkably improved the tensile strength compared with the single-layer PVDF hollow fiber membrane. The permeation flux, rejection, and porosity were also slightly enhanced. High-tensile strength hollow fiber PVDF ultrafiltration membrane can be fabricated using the proposed technique.

• Transactions on Electrical and Electronic Materials
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• v.9 no.1
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• pp.16-19
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• 2008

In this study, it was investigated about optical simulation in direct-type backlight design. Direct-type backlight has been used high-brightness backlight such as medical LCD application. The key parameter in designing direct-type backlight was consists of three geometrical dimension such as the distance of two lamps, the gap of lamp and reflection plate and the number of lamps. It has many of variations in optical design and it causes the different properties in backlight system. It shows the best values of above parameters; 26 mm of the distance of two lamps, 4.5 mm of the gap of lamp and reflection plate and 16 lamps. And we produced the specimen as above condition, and acquired good result in backlight such as the value of the brightness is 6423 nit in center of emission area and less than 5 % in brightness uniformity. It shows the effective ways of designing backlight system using optical simulation method for medical LCD application.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1334-1335
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• 2008

Although many studies have been carried out about binary gas mixtures with $SF_6$, few studies were presented about breakdown characteristics of $SF_6/CF_4$ mixtures. At present study the breakdown characteristics of $SF_6/CF_4$ mixtures in uniform and nonuniform field was performed. The experiments were carried out under AC voltages. The sphere-sphere electrode whose gap distance was 1 mm was used and the point-plane electrode whose gap distance was 3 mm was used in a test chamber. $SF_6/CF_4$ mixture contained 20% $SF_6$ and 80% $CF_4$ and the experimental gas pressure ranged from 0.1 to 0.5 MPa. The results show that addition of $SF_6/CF_4$ mixtures increase AC breakdown voltages. In uniform field the breakdown voltages of gas were linearly increased according to the pressure. However in nonuniform field the breakdown voltages of gas were increased nonlinearly.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.7 no.1
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• pp.36-39
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• 2014

MFC(microbial fuel cell) is the device to produce the electricity by using the microbes which are living in the waste water. In this paper, the electric characteristics of the MFC were investigated according to each different structure and electrode materials. The voltage being reversed phenomenon was observed in the MFC which uses the cupper plate as the cathode material. This result comes from the oxidation reaction of the cupper plate electrode in this MFC. And this MFC has lower output voltage than one that has a platinum plate electrode. The smaller gap distance of the cupper plate electrode of the MFC showed the higher output voltage. The larger electrode area of the cupper plate electrode showed that the reaching time of the output voltage to the maximum value was delayed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.415-415
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• 2007

In this study. it was investigated about optical simulation in direct-type backlight design. Direct-type backlight has been used high-brightness backlight such as LCD television application. The key parameter in designing direct-type backlight was consists of three geometrical dimension such as the distance of two lamps. the gap of lamp and reflection plate and the number of lamps. It has many variation in optical design and it causes the different properties in backlight system. It shows the best values of above parameters; 26mm of the distance of two lamps. 4.5mm of the gap of lamp and reflection plate and 16 lamps. And we produced the specimen as above condition. and acquired good result in backlight such as the value of the brightness is 6436 nit in center of emission area and less than 5% in brightness uniformity. It shows the effective ways of designing backlight system using optical simulation method.

• The Journal of Asian Finance, Economics and Business
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• v.9 no.8
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• pp.1-6
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• 2022

This paper uses the gravity model estimated by the random effect method to analyze the factors affecting Vietnam's coffee export turnover for the period 2007-2020 major markets according to statistics from the General Statistics Office and the General Department of Customs. Coffee export turnover was collected from the General Statistics Office, General Department of Customs, and Vietnam Cacao Coffee Association. The authors calculated the price of coffee based on output and export value from data on coffee export turnover; the authors calculated the economic gap based on population and Gross Domestic Product data (reference: geographic distance metrics on the website: http://www.distancefromto.net/countries.php) and other data was collected based on the databases of the Food and Agriculture Organization of the United Nations, the International Monetary Fund, and World Bank organizations. The results of the study show that from 2007 to 2020, the factors of Vietnam's export price of coffee, geographical distance, Gross Domestic Product of the importing country and Gross Domestic Product of Vietnam, the population of Vietnam, the economic gap between Vietnam and the importing country, the openness of the economy, all have an impact on Vietnam's coffee export turnover. Finally, some conclusions about the policy's impact are made based on the empirical results of the paper.