• International Journal of Oral Biology
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• v.34 no.1
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• pp.15-20
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• 2009

In our present study, total methanol extracts prepared from B. platyphylla var. japonica showed a significant increase in cell proliferation upon the induction of oxidative stress by hydrogen peroxide or $\gamma$-ray irradiation. Total methanol extracts were fractionated into five separate preparations i.e. n-hexane, dichloromethane, ethylacetate, n-butanol and water fractions. Among these, the ethylacetate and butanol fractions of B. platyphylla var. japonica showed the highest protective effects against oxidative stress induced by hydrogen peroxide. These fractions also showed strong protective effects against $\gamma$-ray irradiation. When we evaluated the cytotoxicity of these fractions, the butanol fraction showed no effects in a colony formation assay. In addition, the butanol fraction showed a cell proliferation activation effect evidenced by significant increase in the colony formation of $\gamma$-ray irradiated cells. Both a radical scavenging activity and clonogenic activity assay suggested that the mechanism behind this protective effect against reactive oxygen species may be due to the radical scavenging and cell proliferation activity of B. platyphylla var. japonica extracts.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.42-47
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• 2009

The propagation of an intense laser pulse through an upward density-gradient plasma in a self-modulated laser wakefield acceleration (SM-LWFA) is investigated by using particle-in-cell (PIC) simulations. In the fully relativistic and kinetic PIC simulations, the relativistic and kinetic effects including Landau damping enhance the electron dephasing. This electron dephasing is the most important factor for limiting the energy of accelerated electrons. However, the electron dephasing, which is enhanced by relativistic and kinetic effects in the homogeneous plasma, can be forestalled through the detuning process arising from the longitudinal density gradient. Simulation results show that the detuning process can effectively maintain the coherence of the laser wake wave in the spatiotemporal wakefield pattern, hence considerable energy enhancement is achievable. The spatiotemporal profiles are analyzed for the detailed study on the relativistic and kinetic effects. In this paper, the optimum slope of the density gradient for increasing electron energy is presented for various laser intensities.

• Polymer(Korea)
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• v.30 no.1
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• pp.10-13
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• 2006

The effects of antioxidants and thermal treatment on the radiation resistance of the gamma-ray irradiated polypropylene (PP) were studied. The PP was blended with various antioxidants and was fabricated into a sheet. The PP sheet was irradiated with gamma-ray to a dosage of 25kGy in the nitrogen atmosphere. The differences in both color and mechanical strength were investigated for the gamma-ray irradiated PP depending on the kind and the content of antioxidant. The residual amount of free radical and the variation of oxidation index were investigated for the gramma-ray irradiated PP with thermal treatment after irradiation. The PP having phosphite antioxidant showed little difference in color after gamma-ray irradiation compared with the PP having phenolic or mine antioxidant. Sufficient amount of free radical could be removed from the gamma-ray irradiated PP by the thermal treatment at $130\;^{\circ}C$ for 30 min. Thermally treated PP showed lower oxidation index than the PP without thermal treatment.

• Proceedings of the Safety Management and Science Conference
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• 2010.11a
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• pp.103-112
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• 2010

This study was done to provide basic data on the safety of professionals in medical imaging system by measuring the electromagnetic waves generated in the medical imaging system being used in medical organization. The studied medical imaging systems were general X-ray system, computed tomography(CT), ultrasonographic system, magnetic resonance imaging(MRI), PET-CT and fluoroscopic system, and through these devices, electric field and magnetic field were measured and analyzed. As a result of the analysis, the measured values classified by the medical organizations were not much significant, but in the measurement by the medical imaging systems, there were high hazard elements in the sequential order of electric field PET-CT($17.7{\pm}22.9$)v/m, CT($10.3{\pm}8.7$)v/m, general X-ray system ($8.8{\pm}8.8$)v/m, magnetic field general X-ray system($5.06{\pm}8.26$)mG, CT($2.71{\pm}4.53$)mG and PET-CT($0.74{\pm}0.34$)mG, the systems that adopted X-ray as main ray source, and the more aged the medical imaging systems, the greater the effects of electro-magnetic waves($10.6{\pm}15.93v/m$ for 5 years or more, $6.14{\pm}5.60v/m$ for 5 years or less). The effects of electromagnetic waves on medical imaging systems or facilities were not much when the notification of ministry of knowledge economy is considered, but in the overall perspective considering all the equipments and facility of the medical organization, such effects were significant. It is determined that sustainable safety managements of electric field and magnetic field must be done during process from medical imaging system installation to maintenance to rule out such factors.

• Journal of Energy Engineering
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• v.16 no.1 s.49
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• pp.46-52
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• 2007

The piecewise constant angular approximation is developed to replace the conventional angular quadrature sets in the solution of the second-order, multi-dimensional $S_{N}$ neutron transport equations. The newly generated quadrature sets by this method substantially mitigate ray effects and can be used in the same manner as the conventional quadrature sets are used. The discrete-ordinates and the piecewise-constant approximations are applied to both the first-order Boltzmann and the second-order form of neutron transport equations in treating angular variables. The result is that the mitigation of ray effects is only achieved by the piecewise-constant method, in which new angular quadratures are generated by integrating angle variables over the specified region. In other sense, the newly generated angular quadratures turn out to decrease the contribution of mixed-derivative terms in the even-parity equation that is one of the second-order neutron transport equation. This result can be interpreted as the entire elimination or substantial mitigation of ray effect are possible in the simplified even-parity equation which has no mixed-derivative terms.

• Journal of the Korea Safety Management & Science
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• v.12 no.4
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• pp.67-72
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• 2010

This study was done to provide basic data on the safety of professionals in medical imaging system by measuring the electromagnetic waves generated in the medical imaging system being used in medical organization. The studied medical imaging systems were general X-ray system, computed tomography(CT), ultrasonographic(USG) system, magnetic resonance imaging(MRI), PET-CT and fluoroscopic(R/F) system, and through these devices, electric field and magnetic field were measured and analyzed. As a result of the analysis, the measured values classified by the medical organizations were not much significant, but in the measurement by the medical imaging systems, there were high hazard elements in the sequential order of electric field PET-CT($17.7{\pm}22.9$)v/m, CT($10.3{\pm}8.7$)v/m, general X-ray system($8.8{\pm}8.8$)v/m, magnetic field general X-ray system($5.06{\pm}8.26$)mG, CT($2.71{\pm}4.53$)mG and PET-CT($0.74{\pm}0.34$)mG, the systems that adopted X-ray as main ray source, and the more aged the medical imaging systems, the greater the effects of electro-magnetic waves($10.6{\pm}15.93v/m$ for 5 years or more, $6.14{\pm}5.60v/m$ for 5 years or less). The effects of electromagnetic waves on medical imaging systems or facilities were not much when the notification of ministry of knowledge economy is considered, but in the overall perspective considering all the equipments and facility of the medical organization, such effects were significant. It is determined that sustainable safety managements of electric field and magnetic field must be done during process from medical imaging system installation to maintenance to rule out such factors.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.78.1-78.1
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• 2012

We have studied the physical properties of X-ray point sources in galaxy clusters using ~600 Chandra archival observations. The goal of this study is to investigate the density environmental effects on the physical properties of X-ray point sources by comparing the properties of X-ray point sources in galaxy clusters to those in typical blank fields. In this presentation, we show the nature of X-ray point sources which are expected to be related with galaxy clusters with different core properties. Using ~60 galaxy clusters observed with Chandra, we investigate the physical properties of X-ray point sources in cool-core and non-cool-core clusters. The cool-core clusters are known to have short central cooling time, and are characterized by low central entropy, systematic central temperature drops, and a brightest cluster galaxy at the X-ray peak. While the non-cool-core clusters have longer central cooling time, and are characterized by large central entropies and flat or centrally rising temperature profile. We show that how central core properties of galaxy clusters affect on the physical properties of X-ray point sources.

• International Journal of Safety
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• v.8 no.1
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• pp.14-17
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• 2009

The $Co^{60}$ $\gamma$-ray irradiation effects on the electrical and thermal characteristics of low density polyethylene crosslinked by Dicumyl peroxide (DCP) were investigated. We experimented on electrical properties as following; electrical tree inception and growing type for applying AC step voltage, AC breakdown strength, volume resistivity with increasing dosage. Also, chemical analyses were performed TGA, gel fraction. These electrical properties changed depending upon its crosslinking degree and byproducts from crosslinking reactions. Crosslinking reactions were considered causing by $\gamma$-ray irradiation and DCP had contained in low density polyethylene.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.102-106
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• 1999

In this study, inhomogeneous amplitude modulation effects on the imaging performance a lens system are expermentally investigated by measuring the diffraction OTF. The lens under the test is a binocular objective made in Korea. Inhomogeneous amplitude modulation is carried out by positioning the modulator cross contacted to the lens under test which is illuminated by collimated light beam. The aberration characteristics of the lens under test are examined by caculating the ray-fan through finite ray tracing. The MTFs of the lens illuminated by the homogeneous and inhomogeneous light beam are measured on the Gaussian image plane and compared with one another.

• Journal of Radiation Industry
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• v.7 no.1
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• pp.51-54
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• 2013

Chitosan is a useful natural polymer material in many application fields such as biomaterials, water-treatment, agriculture, medication, and food science. However, the poor solubility limits its application. In this study, the effects of radiation on chitosan were investigated using gamma ray and electron beam irradiation. The chemical structure and molecular weight analysis show similar degradation effects of chitosan powder in both gamma ray and electron beam irradiation. However, the radiation irradiated chitosan in $H_2O$ has a lower molecular weight, since the hydroxyl radicals attack the glycosidic bonds. This effect is more clearly shown in the electron beam irradiation results.