• Journal of Astronomy and Space Sciences
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• v.33 no.2
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• pp.109-117
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• 2016

We explain the results of Yu et al. (2015b) of the novel sharpness angle measurement to a large number of spectra obtained from the Fermi gamma-ray burst monitor. The sharpness angle is compared to the values obtained from various representative emission models: blackbody, single-electron synchrotron, synchrotron emission from a Maxwellian or power-law electron distribution. It is found that more than 91% of the high temporally and spectrally resolved spectra are inconsistent with any kind of optically thin synchrotron emission model alone. It is also found that the limiting case, a single temperature Maxwellian synchrotron function, can only contribute up to 58⁺²³₋₁₈% of the peak flux. These results show that even the sharpest but non-realistic case, the single-electron synchrotron function, cannot explain a large fraction of the observed spectra. Since any combination of physically possible synchrotron spectra added together will always further broaden the spectrum, emission mechanisms other than optically thin synchrotron radiation are likely required in a full explanation of the spectral peaks or breaks of the GRB prompt emission phase.

• Journal of The Korean Astronomical Society
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• v.47 no.1
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• pp.15-39
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• 2014

Polarization is a basic property of light and is fundamentally linked to the internal geometry of a source of radiation. Polarimetry complements photometric, spectroscopic, and imaging analyses of sources of radiation and has made possible multiple astrophysical discoveries. In this article I review (i) the physical basics of polarization: electromagnetic waves, photons, and parameterizations; (ii) astrophysical sources of polarization: scattering, synchrotron radiation, active media, and the Zeeman, Goldreich-Kylafis, and Hanle effects, as well as interactions between polarization and matter (like birefringence, Faraday rotation, or the Chandrasekhar-Fermi effect); (iii) observational methodology: on-sky geometry, influence of atmosphere and instrumental polarization, polarization statistics, and observational techniques for radio, optical, and $X/{\gamma}$ wavelengths; and (iv) science cases for astronomical polarimetry: solar and stellar physics, planetary system bodies, interstellar matter, astrobiology, astronomical masers, pulsars, galactic magnetic fields, gamma-ray bursts, active galactic nuclei, and cosmic microwave background radiation.

• Journal of Radiation Protection and Research
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• v.36 no.4
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• pp.190-194
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• 2011

After the first report that electrons with sub-ionization energy of DNA could cause single strand breaks or double strand breaks to DNA, there have been various studies to investigate the mechanisms of DNA damage by low-energy electrons. In this paper, we examined the possibility of using X-ray photoelectron spectroscopy (XPS) to analyze the dissociation patterns of the molecular bonds by electron irradiation on DNA thin films and tried to establish the method as a general tool for studying the radiation damage of biomolecules by low energ yelectrons. For the experiment, pBR322 plasmid DNA solution was formed into the films on tantalum plates by lyophilization and was irradiated by 5-eV electrons. Un-irradiated and irradiated DNA films were compared and analyzed using the XPS technique.

• Journal of The Korean Astronomical Society
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• v.45 no.6
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• pp.147-156
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• 2012

We present a test of the emission statistics of active galactic nuclei (AGN), probing the connection between the red-noise temporal power spectra and multi-modal flux distributions known from observations. We simulate AGN lightcurves under the assumption of uniform stochastic emission processes for different power-law indices of their respective power spectra. For sufficiently shallow slopes (power-law indices (${\beta}{\leq}1$), the flux distributions (histograms) of the resulting lightcurves are approximately Gaussian. For indices corresponding to steeper slopes (${\beta}{\geq}1$), the flux distributions become multi-modal. This finding disagrees systematically with results of recent mm/radio observations. Accordingly, we conclude that the emission from AGN does not necessarily originate from uniform stochastic processes even if their power spectra suggest otherwise. Possible mechanisms include transitions between different activity states and/or the presence of multiple, spatially disconnected, emission regions.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.16
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• pp.6649-6655
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• 2014

Radiation therapy is an important treatment for head and neck squamous cell carcinoma (HNSCC). However, how to promote radiation sensitivity in HNSCC remains a challenge. This study aimed to investigate the radiosensitizing effects of fenofibrate on HNSCC and explore the underlying mechanisms. HNSCC cell lines CNE-2 and KB were subjected to ionizing radiation (IR), in the presence or absence of fenofibrate treatment. Cell growth and survival, apoptosis and cell cycle were evaluated. In addition, CNE-2 cells were xenografted into nude mice and subjected to IR and/or fenofibrate treatment. The expression of cyclinB and CDK1 was detected by Western blotting. Our results showed that fenofibrate efficiently radiosensitized HNSCC cells and xenografts in mice, and induced apoptosis and G2/M arrest via reducing the activity of the CDK1/cyclinB1 kinase complex. These data suggest that fenofibrate could be a promising radiosensitizer for HNSCC radiotherapy.

• Korean Journal of Environmental Agriculture
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• v.17 no.1
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• pp.76-83
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• 1998

The most remarkable aspect in the hormesis law is that dose of harmful agents can produce effect that are diametrically opposite to the effect found with high doses of the same agent. Minute quantities of a harmful agent bring about very small change in the organism and control mechanisms appear to subjugate normal processes to place the organism in a state of albert and repair. The stimulated organism in more responsive to changes in environmental factors than it did before being alerted. Routine functions, including repair and defense, have priority for available energy and matetial. The alerted organism utilizes nutrients more efficiently, grows faster, shows improved defense, and lives longer. Accelerated germination, sprouting, growth, development, blooming and ripening, and increased crop yield and resistance to disease are found in plants. Another concept supported by the data in that low doses of ionizing radiation provide increased resistance to subsequent high doses of radiation. The hormesis varies with subject plant, variety, state of seed, environmental and cultural conditions, physiologic function measured, dose rate and total exposure. The results of hormesis are less consistently found, probably due to the great number of uncontrolled variables in the experiments. The general dosage for radiation homlesis in about 100 (10 to 1,000) times ambient or 100 (10 to 1,000) times less than a definitely harmful dose, but these must be modified to the occasion. Although little is known about most mechanisms of homzesis reaction, overcompensation of repair mechanism is offered as one mechanism.

• Journal of The Korean Astronomical Society
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• v.52 no.5
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• pp.173-180
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• 2019

We present IR flux density measurements, models of the broadband SED, and results of SED modeling for the Pulsar Wind Nebula (PWN) 3C 58. We find that the Herschel flux density seems to be slightly lower than suggested by interpolation of previous measurements in nearby wavebands, implying that there may be multiple electron populations in 3C 58. We model the SED using a simple stationary one-zone and a more realistic time-evolving multi-zone scenario. The latter includes variations of flow properties in the PWN (injected energy, magnetic field, and bulk speed), radiative energy losses, adiabatic expansion, and diffusion, similar to previous PWN models. From the modeling, we find that a PWN age of 2900-5400 yrs is preferred and that there may be excess emission at ${\sim}10^{11}Hz$. The latter may imply multiple populations of electrons in the PWN.

• Journal of the Korean Society of Food Science and Nutrition
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• v.41 no.7
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• pp.901-906
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• 2012

The purpose of this study was to elucidate the anti-proliferative effect and the mechanisms underlying apoptosis induced by a methanol extracts from Ishige sinicola (ISE) in HeLa cells. ISE treatment for 24 hr significantly inhibited cell viability in a dose-dependent manner. Apoptosis was detected by Hoechst 33258 staining and an annexin V/PI assay after 24 hr treatment. Moreover, ISE treatment triggered the cleavage of caspase-8, -9, -3, and poly(ADP-ribose) polymerase (PARP) in dose-dependent and time-dependent manners. In addition, z-VAD-fmk, a general caspase inhibitor, blocked ISE-induced cell death. Taken together, these results suggest that ISE-induced apoptosis is mediated by the activation of a caspase cascade in HeLa cells.

• Asian Pacific Journal of Cancer Prevention
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• v.14 no.11
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• pp.6197-6208
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• 2013

Cancers will continue to be a threat to health unless they can be controlled by combinations of treatment modalities. In this review, evaluate the role of resveratrol (RSV) as a radiosensitizing agent was evaluated and underlying mechanisms holistically explored in different cancer models focusing on therapeutic possibilities. The ability of RSV to modify the effect of radiation exposure in normal and cancer cells has indeed been shown quite convincingly, the combination of RSV and IR exhibiting synergistic effects on different cancer cells. This is relevant since controlled exposure to IR is one of the most frequently applied treatments in cancer patients. However, radiotherapy (XRT) treatment regimes are very often not effective in clinical practice as observed in patients with glioma, prostate cancer (PCa), melanoma, for example, largely due to tumour radioresistant properties. Sensitization of IR-induced apoptosis by natural products such as RSV is likely to be relevant in cancer control and treatment. However, all cancers do not respond to RSV+IR in a similar manner. Therefore, for those such as the radioresistant PCa or melanoma cells, the RSV+IR regime has to be very carefully chosen in order to achieve effective and desirable outcomes with minimum toxicity to normal cells. They are reports that the highest concentration of 100 ${\mu}M$ RSV and highest dose of 5 Gy IR are sufficient to kill cells by induction of apoptosis, indicating that RSV is effective in radiosensitizing otherwise radioresistant cells. In general, it has been shown in different cancer cells that RSV+XRT effectively act by enhancing expression of anti-proliferative and pro-apoptotic molecules, and inhibiting pro-proliferative and anti-apoptotic molecules, leading to induction of apoptosis through various pathways, and cell death. If RSV+XRT can suppress the signature of cancer stemness, enhance the radiosensitivity by either targeting the mitochondrial functionality or modulating the tumour necrosis factor-mediated or Fas-FasL-mediated pathways of apoptosis in different cancers, particularly in vivo, its therapeutic use in the control of cancers holds promise in the near future.

• Journal of The Korean Astronomical Society
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• v.51 no.4
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• pp.111-117
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• 2018

A numerical method is proposed to calculate the response of detectors measuring particle energies from incident isotropic fluxes of electrons and positive ions. The isotropic flux is generated by injecting particles moving radially inward on a hypothetical, spherical surface encompassing the detectors. A geometric projection of the field-of-view from the detectors onto the spherical surface allows for the identification of initial positions and momenta corresponding to the clear field-of-view of the detectors. The contamination of detector responses by particles penetrating through, or scattering off, the structure is also similarly identified by tracing the initial positions and momenta of the detected particles. The relative contribution from the contaminating particles is calculated using GEANT4 to obtain the geometric factor of the instrument as a function of the energy. This calculation clearly shows that the geometric factor is a strong function of incident particle energies. The current investigation provides a simple and decisive method to analyze the instrument geometric factor, which is a complicated function of contributions from the anticipated field-of-view particles, together with penetrating or scattered particles.