• Journal of Radiation Protection and Research
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• v.39 no.2
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• pp.81-88
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• 2014

Recently, a new imaging method, gamma vertex imaging (GVI), was proposed for the verification of in-vivo proton dose distribution. In GVI, the vertices of prompt gammas generated by proton induced nuclear interaction were determined by tracking the Compton-recoiled electrons. The GVI system is composed of a beryllium electron converter for converting gamma to electron, two double-sided silicon strip detectors (DSSDs) for the electron tracking, and a scintillation detector for the energy determination of the electron. In the present study, the modules of a charge sensitive preamplifier (CSP) and a shaping amplifier for the analog signal processing of DSSD were developed and the performances were evaluated by comparing the energy resolutions with those of the commercial products. Based on the results, it was confirmed that the energy resolution of the developed CSP module was a little lower than that of the CR-113 (Cremat, Inc., MA), and the resolution of the shaping amplifier was similar to that of the CR-200 (Cremat, Inc., MA). The value of $V_{rms}$ representing the magnitude of noise of the developed system was estimated as 6.48 keV and it was confirmed that the trajectory of the electron can be measured by the developed system considering the minimum energy deposition ( > ~51 keV) of Compton-recoiled electron in 145-${\mu}m$-thick DSSD.

• Journal of the Korean Society of Radiology
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• v.13 no.2
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• pp.253-260
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• 2019

Radiation dose enhancement is a method of increasing the cross section of interaction, thus increasing the deposited dose. This can contribute to linear energy transfer, LET and relative biological effectiveness, RBE. Previous studies on dose enhancement have been mainly focused on X, ${\gamma}-rays$, but in this study, the dose enhancement was analyzed for proton using Monte Carlo simulation using MCNP6. Based on the mathematical modeling method, energy spectrum and relative intensity of spread out Bragg-peak were calculated, and evaluated dose enhancement factor and dose distribution of dose enhancement material, such as aurum and gadolinium. Dose enhancement factor of 1.085-1.120 folds in aurum, 1.047-1.091 folds in gadolinium was shown. In addition, it showed a decrease of 95% modulation range and practical range. This may lead to an uncertain dose in the tumor tissue as well as dose enhancement. Therefore, it is necessary to make appropriate corrections for spread out Bragg-peak and practical range from mass stopping power. It is expected that Monte Carlo simulation for dose enhancement will be used as basic data for in-vivo and in-vitro experiments.

• Progress in Medical Physics
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• v.6 no.2
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• pp.61-70
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• 1995

The picosecond time resolved fluorescence spectra of Hematoporphyrin Derivative (HPD) in both solutions and cancer cell are measured by a time correlated single photon counting system with a synchronously mode locked dye laser. Two exoponential decay components in the fluorescence spectra were observed. The slow decay(6.3 ㎱)and the fast one(350 ㎰)are attributed to be originated from monomers and dimers, respectively. The absorption and fluorescence measurements in steady state also showed the presence of a monomeric and dimeric forms of HPD molecules. The monomer lifetime in the cancer cell was measured to be longer than that in solution, which was expected from the blue shift and narrowing of the absorption spectra for HPD-treated in vitro. The relative amplitude of the fast component was found to be enhanced in cancer cell, strongly indicating the higher affinity of the dimer for the cancer cell.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.320-320
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• 2012

III-V 화합물 태양전지는 실리콘, CdTe, CIGS, 염료, 및 유기 등 다른 태양전지에 비해 1sun 상 30% 이상의 고효율을 갖고 있고 앞으로도 계속 증가할 수 있는 가능성을 갖고 있다. 그 이유는 직접천이형 밴드갭, 높은 이동도 등의 고성능 물질특성과 더불어 3족과 5족의 비율을 조절함으로써 같은 결정구조를 갖고 에너지 밴드갭이 다른 물질들을 만들기에 용의하여, 태양전지 스펙트럼의 넓은 영역을 흡수할 수 있는 장점이 있기 때문이다. 그러나, 셀자체의 물질이 실리콘에 비하여 고가이므로, 고성능이 요구되는 우주 인공위성등에 적용이 되었지만, 2000년대 이후로 집광에 적용가능한 태양전지의 연구를 거듭하여 2005년부터는 값싼 프레넬 렌즈를 이용하여 1sun에 비해 500배 해당하는 빛을 셀에 집광하여 보다 효율을 증가시킴으로써 지상발전용에도 적용가능한 셀을 형성하게 되었다. 더불어 태양전지의 효율을 증가시키기 위한 개선된 구조적 변화의 시도도 많이 이루어지고 있다. 최근 보고에 의하면 실리콘 태양전지의 표면에 texture 또는 나노 구조를 주어 높은 흡수율과 낮은 반사율을 갖게 함으로써 효율을 증가시키는 사례가 많아지고, III-V 화합물 태양전지도 texturing에 의해 증가된 효율을 발표한바 있다. 본 연구에서는 태양전지의 효율을 증가시키기 위하여 III-V 화합물 태양전지 표면에 micro-hole array texture 구조를 형성한 후 나노 particle을 이용한 나노 texture 구조를 형성하였다. Photo-lithography와 chemical wet etching으로 micro-hole array texture 구조를 형성하였으며 micro-hole의 직경은 $5{\sim}20{\mu}m$, hole과 hole의 간격은 $3{\sim}15{\mu}m$로 다양하게 변화를 주었다. 형성된 micro-hole array texture 구조위에 수십 nm 크기의 particle을 만들어 chemical wet etching으로 나노 texture 구조를 형성하였다. 태양전지 표면에 texture 구조가 있는 경우와 없는 경우에 각각 효율을 측정, 비교 분석하였다.

• Journal of radiological science and technology
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• v.35 no.2
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• pp.119-124
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• 2012

Recently, Glass Dosimeter (GD) with thermoluminescent Dosimeter (TLD) are comprehensively used to measure absorbed dose from diagnostic field to therapy field that means from low energy field to high energy field. However, such studies about dose characteristics of GD, such as reproducibility and energy dependency, are mostly results in high energy field. Because characteristic study for measurement devices of radiation dose and radiation detector is performed using 137Cs and 60Co which emit high energy radiations. Thus, this study was evaluated the linearity according to Piranha dose which measured by changing tube voltage (50kV, 80kV and 100kV which are low energy radiations), reproducibility and reproducibility according to delay time using GD. Measurement of radiation dose is performed using internal detector of Piranha 657 which is multi-function QA device (RTI Electronic, Sweden). Condition of measurement was 25mA, 0.02sec, 2.5mAs, SSD of 100 cm and exposure area with $10{\times}10cm^2$. As above method, GD was exposed to radiation. Sixty GDs were divided into three groups (50kV, 80kV, 100kV), then measured. In this study, GD was indicated the linearity in low energy field as high energy existing reported results. The reproducibility and reproducibility according to delay time were acceptable. In this study, we could know that GD can be used to not only measure the high energy field but also low energy field.

• Journal of the Korean Society of Radiology
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• v.11 no.7
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• pp.547-553
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• 2017

In the current medical field, lead is widely used as a radiation shield. However, the lead weight is very heavy, so wearing protective clothing such as apron is difficult to wear for long periods of time and there is a problem with the danger of lethal toxicity in humans. Recently, many studies have been conducted to develop substitute materials of lead to resolve these problems. As a substitute materials for lead, barium(Ba) and iodine(I) have excellent shielding ability. But, It has characteristics emitting characteristic X-rays from the energy area near 30 keV. For patients or radiation workers, shielding materials is often made into contact with the human body. Therefore, the characteristic X-rays generated by the shielding material are directly exposured in the human body, which increases the risk of increasing radiation absorbed dose. In this study, we have developed the FLUKA transport code, one of the most suitable elements of radiation transport codes, to remove the characteristic X-rays generated by barium or iodine. We have verified the reliability of the shielding fraction of the structure of the structure shielding by comparing with the MCPDX simulations conducted as a prior study. Using the MCNPX and FLUKA, the double layer shielding structures with the various thickness combination consisting of barium sulphate ($BaSO_4$) and bismuth oxide($Bi_2O_3$) are designed. The accuracy of the type shown in IEC 61331-1 was geometrically identical to the simulation. In addition, the transmission spectrum and absorbed dose of the shielding material for the successive x-rays of 120 kVp spectra were compared with lead. In results, $0.3mm-BaSO_4/0.3mm-Bi_2O_3$ and $0.1mm-BaSO_4/0.5mm-Bi_2O_3$ structures have been absorbed in both 33 keV and 37 keV characteristic X-rays. In addition, for high-energy X-rays greater than 90 keV, the shielding efficiency was shown close to lead. Also, the transport code of the FLUKA's photon transport code was showed cut-off on low-energy X-rays(below 33keV) and is limited to computerized X-rays of the low-energy X-rays. But, In high-energy areas above 40 keV, the relative error with MCNPX was found to be highly reliable within 6 %.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.263-271
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• 2005

HPFRCC(High Performance Fiber Reinforced Cementitious Composite) is a class of FRCCs(Fiber Reinforced Cementitious Composites) that exhibit multiple cracking. Multiple cracking leads to improvement in properties such as ductility, toughness, fracture energy, strain hardening, strain capacity, and deformation capacity under tension, compression, and bending. These improved properties of HPFRCCs have triggered unique and versatile structural applications, including damage reduction, damage tolerance, energy absorption, crack distribution, deformation compatibility, and delamination resistance. These mechanical properties of HPFRCCs become different from the kinds and shapes of used fiber, and it is known that the effective size of fiber in macro crack is different from that in micro crack. This paper reports an experimental findings on the mechanical properties of HPFRCCs reinforced with the micro fiber(PP50, PVA100 and PVA200) and macro fiber(PVA660, SF500). Uniaxial compressive tests and three point bending tests are carried out in order to compare with the mechanical properties of HPFRCCs reinforced with micro fibers or hybrid fibers such as compressive strength, ultimate bending stress, toughness, deformation capacity and crack pattern under bending, etc.,

• Ecology and Resilient Infrastructure
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• v.7 no.4
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• pp.262-273
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• 2020

Amending biopolymers such as β-glucan (BG) and Xanthan gum (XG) generally enhances soil strength by ionic and hydrogen bonds between soil particles. Thus, biopolymers have been studied as eco-friendly construction materials in levees. However, physiological responses of plants grown on soil amended with biopolymers are not fully understood. This study focuses on the effects of biopolymers on the growth of Camelina sativa L. (Camelina) under excess zinc (Zn) stress. The optimal concentrations of BG and XG were confirmed to have a 0.5% ratio in soil depending on the physiological parameters of Camelina under excess Zn stress. The Zn binding capacity of biopolymers was investigated using 1,5-diphenylthiocarbazone (DTZ). The reduction of Zn damage in Camelina was evaluated by analyzing the Zn content and expression of heavy metal ATPase (HMA) genes under excess Zn stress. Amendments of BG and XG improved Camelina growth under excess Zn stress. In DTZ staining and ICP-OES analysis, Camelina grown on BG and XG soil showed less Zn uptake than normal soil under excess Zn stress. The Zn-inducible CsHMA3 gene was not stimulated by either BG or XG amendment under excess Zn stress. Moreover, both BG and XG amendments in soil exhibit Zn-stress mitigation similar to that of Zn-tolerant CsHMA3 overexpres sed Camelina. These results indicate that biopolymer-amended soils may influence the prevention of Zn absorption in Camelina under excess Zn stress. Thus, BG and XG are proven to be suitable materials for levee construction and can protect plants from soil contamination by Zn.

• Korean Journal of Food Science and Technology
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• v.30 no.5
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• pp.1222-1228
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• 1998

Stress will induce various changes in human metabolism. The remarkable phenomenon of these changes is increased energy metabolism that can induce many reactive oxygen species (ROS) production. ROS can peroxidize cellular macromolecules including lipid and protein. The object of this study was to investigate that stress may induce cellular damage by producing ROS and that Rooibos tea can protect cells against reactive oxygen species by immobilization stress in SD rat. The stress group significantly increased in 5-hydroxyindole acetic acid (5-HIAA), one of the stress hormone. Rooibos tea treatment had no effects on 5-HIAA contents, but body weight of Rooibos tea treated rat more increased than that of only the stress group. It was suggested that Rooibos tea colud not affect stress response itself, but protect against the another mechanism. We thought that the oxidative damage was caused by increased energy metabolism. Protein degradation level and lipid peroxide formation on index of oxidative damage significantly increased in the stress group. But the stress-induced activity change could not be observed in antioxidative enzymes such as superoxide dismutase, glutathione peroxidase and glutathione reductase. But the catalase activity of the brain significantly was inhibited by the stress. From these results, it was suggested that the immobilization stress induce the brain oxidative damage. However the oxidative damage was inhibited by feeding Rooibos tea containing various antioxidants, such as polyphenol, flavonoid and so on. Therefore, Rooibos tea have the protective effects against the stress caused by the ROS mediated cellular damage.

• Journal of radiological science and technology
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• v.30 no.2
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• pp.113-119
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• 2007

It is important to consider the contrast of object in Mammography because an absorption gap between tissues of body and breast in breast is low. This study is to evaluate MTF image with resolution chart according to change of combination of target and filter. The results were as follows : 1. There were significant differences in X-ray energy according to combination of filter(Mo/Mo, Mo/Rh. Mo/Al, Rh/Rh, Rh/Al) and acrylic thickness(2 cm, 3 cm, 4 cm). 2. The value of lp/mm on MTF to 0.5 showed that the sharpness in MTF curve was 2.4 compared to Mo/Mo and 2cm acryl, 2.63 in Mo/Rh and 4 cm acryl, and 2.9 in Rh/Rh and 6cm acryl. 3. The value of lp/mm on MTF showed that the resolution in MTF curve was 6.0 compared to Mo/Mo and 2 cm acryl, 4.60 in Rh/Al and 4cm acryl, and 6.03 in Rh/Al and 6 cm acryl. 4. The value of MTF on 2.5 lp/mm distinguishable visually was 0.48 compared to Mo/Mo and 2 cm acryl, 0.53 in Mo/Rh and 4cm acryl, and 0.59 in Rh/Rh and 6cm acryl. 5. For the evaluation of an image of the mammo-phantom, the score of Mo/Mo was 12 points, Mo/Rh 11, Rh/Rh 10.5, Mo/Al 10, Rh/Al 9.0, respectively.