• Journal of Photoscience
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• 제9권2호
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• pp.170-173
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• 2002

Space is full of energetic events emitting high-energy radiations which may be fatal to all living things unless protected. The present paper briefly describes high-energy photons and particles incident on Earth surface and their common properties toward living things. Role of radiation played in evolution of life and earth environment will be presented.

• BMB Reports
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• 제40권5호
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• pp.644-648
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• 2007

Exposure of algae or plants to irradiance from above the light saturation point of photosynthesis is known as high light stress. This high light stress induces various responses including photoinhibition of the photosynthetic apparatus. The degree of photoinhibition could be clearly determined by measuring the parameters such as absorption and fluorescence of chromoproteins. In cyanobacteria and red algae, most of the photosystem (PS) II associated light harvesting is performed by a membrane attached complex called the phycobilisome (PBS). The effects of high intensity light (1000-4000 ${\mu}mol$ photons $m^{-2}s^{-1}$) on excitation energy transfer from PBSs to PS II in a cyanobacterium Spirulina platensis were studied by measuring room temperature PC fluorescence emission spectra. High light (3000 ${\mu}mol$ photons $m^{-2}s^{-1}$) stress had a significant effect on PC fluorescence emission spectra. On the other hand, light stress induced an increase in the ratio of PC fluorescence intensity of PBS indicating that light stress inhibits excitation energy transfer from PBS to PS II. The high light treatment to 3000 ${\mu}mol$ photons $m^{-2}s^{-1}$ caused disappearance of 31.5 kDa linker polypeptide which is known to link PC discs together. In addition we observed the similar decrease in the other polypeptide contents. Our data concludes that the Spirulina cells upon light treatment causes alterations in the phycobiliproteins (PBPs) and affects the energy transfer process within the PBSs.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.600-603
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• 2003

Energy spectrum modulation of X-ray source in digital mammography has been studied. In this study, we calculated various filtered spectra using the scattering data. Primary spectra were generated by Molybdenum (Mo) and Tungsten (W) targets. The materials of added filters are Molybdenum and Rhodium (Rh) for 40 kVp Mo. primary spectrum, the amounts of photons over whole energy ranges are attenuated to 0.43 with 0.03 mm Mo filter and 0.38 with 0.06 mm Mo filter while the photons of energy ranged from 17 keV to 20 keV. The photons of low energy ranged below 17 keV are considerably attenuated. This effect brings out reducing the scattered radiation and dose to the patient, and enhancing subject contrast in the image. The results show that filtered spectra are not seriously affected by X-ray tube loadability. Because the energy range from 17 keV to 20 keV is directly transmitted although low and high energies are mainly filtered.

• Asian Pacific Journal of Cancer Prevention
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• 제16권17호
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• pp.7785-7788
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• 2015

Utilization of high energy photons (>10MV) with an optimal weight using a mixed energy technique is a practical way to generate a homogenous dose distribution while maintaining adequate target coverage in intact breast radiotherapy. This study represents a model for estimation of this optimal weight for day to day clinical usage. For this purpose, treatment planning computed tomography scans of thirty-three consecutive early stage breast cancer patients following breast conservation surgery were analyzed. After delineation of the breast clinical target volume (CTV) and placing opposed wedge paired isocenteric tangential portals, dosimeteric calculations were conducted and dose volume histograms (DVHs) were generated, first with pure 6MV photons and then these calculations were repeated ten times with incorporating 18MV photons (ten percent increase in weight per step) in each individual patient. For each calculation two indexes including maximum dose in the breast CTV ($D_{max}$) and the volume of CTV which covered with 95% Isodose line ($V_{CTV,95%IDL}$) were measured according to the DVH data and then normalized values were plotted in a graph. The optimal weight of 18MV photons was defined as the intersection point of $D_{max}$ and $V_{CTV,95%IDL}$ graphs. For creating a model to predict this optimal weight multiple linear regression analysis was used based on some of the breast and tangential field parameters. The best fitting model for prediction of 18MV photons optimal weight in breast radiotherapy using mixed energy technique, incorporated chest wall separation plus central lung distance (Adjusted R2=0.776). In conclusion, this study represents a model for the estimation of optimal beam weighting in breast radiotherapy using mixed photon energy technique for routine day to day clinical usage.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
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• pp.23.1-23.1
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• 2008

A space shuttle with a Prototype Synchrotron Radiation Detector (PSRD) was launched in 2001. PSRD was set in the Endeavour payloads and got data for 12 days. The purpose of PSRD is to measure synchrotron photons which are created by high energy charged particles near earth. Synchrotron photons are confused with background photons. We studied how to separate synchrotron photons from backgrounds.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.694-694
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• 2013

With the growing need of more effective energy harvesting, solar energy has been sought as one of the prominent candidates among the eco-friendly methods. Although many types of solar cells have been developed, the electronic conversion efficiency is limited by the material's physical properties: solar cells can only harvest solar energy from limited range in solar energy spectrum. To overcome this physical limit, we approached by using the down conversion effect, transforming the high energy photons to low energy photons, to the range the designated solar cell can convert to electronic energy. In our study, we have fabricated GaAs single junction solar cells and applied CdSe quantum dots for down-conversion. We examine the effects of such application on the solar cell efficiancy, fill-factor, JSC, VOC, etc.

• 한국의학물리학회지:의학물리
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• 제1권1호
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• pp.3-10
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• 1990

No Abstract, See Full Text

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.221-239
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• 2014

The global demand for energy has been increasing since past decades. Various technologies have been working to find a suitable alternative for the generation of sustainable energy. Photovoltaic technologies for solar energy conversion represent one of the significant routes for the green and renewable energy production. Despite of remarkable improvement in solar cell technologies, the generation of power is still suffering with lower energy conversion efficiency, high production cost, etc. The major problem in improving the PV efficiency is spectral mismatch between the incident solar spectrum and bandgap of a semiconductor material used in solar cell. Luminescent materials such as rare-earth doped phosphor materials having the quantum efficiency higher than unity can be helpful for photovoltaic applications. Quantum cutting phosphors are the most suitable candidates for the generation of two or more low-energy photons for the absorption of every incident high-energy photons. The phosphors which are capable of converting UV photon to visible and near-IR (NIR) photon are studied primarily for photovoltaic applications. In this review, we will survey various near IR quantum cutting phosphors with respective to their synthesis method, energy transfer mechanism, nature of activator, sensitizer and dopant materials incorporation and energy conversion efficiency considering their applications in photovoltaics.

• Nuclear Engineering and Technology
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• 제51권2호
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• pp.539-545
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• 2019

Yttrium-90 is a useful therapeutic radioisotope for tumor treatment because of its high-energy-emitting beta rays. However, it has been difficult to select appropriate collimators and main energy windows for Y-90 Bremsstrahlung imaging using gamma cameras because of the broad energy spectra of Y-90. We used a Monte Carlo simulation to investigate the effects of collimator selection and energy windows on Y-90 Bremsstrahlung imaging. We considered both MELP and HE collimators. Various phantoms were employed in the simulation to determine the main energy window using primary-to-scatter ratios (PSRs). Imaging performance was evaluated using spatial resolution indices, imaging counts, scatter fractions, and contrast-to-noise ratios. Collimator choice slightly affected energy spectrum shapes and improved PSRs. The HE collimator performed better than the MELP collimator on all imaging performance indices (except for imaging count). We observed minor differences in SR and SF values for the HE collimator among the five simulated energy windows. The combination of an HE collimator and improved-PSR energy window produced the best CNR value. In conclusion, appropriate collimator selection is an important component of Bremsstrahlung Y-90 photon imaging and main energy window determination. We found HE collimators to be more appropriate for improving the imaging performance of Bremsstrahlung Y-90 photons.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.662-662
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• 2013

Over the last several decades, innovative light-harvesting devices have evolved to achieve high efficiency in solar energy transfer. Research on the mechanisms for plasmon resonance is very desirable to overcome the conventional efficiency limits of photovoltaics. The influence of localized surface plasmon resonance on hot electron flow at a metal-semiconductor interface was observed with a Schottky diode composed of a thin silver layer on $TiO_2$. The photocurrent is generated by absorption of photons when electrons have enough energy to travel over the Schottky barrier and into the titanium oxide conduction band. The correlation between the hot electrons and the surface plasmon is confirmed by matching the range of peaks between the incident photons to current conversion efficiency (IPCE, flux of collected electrons per flux of incident photons) and UV-Vis spectra. The photocurrent measured on Ag/$TiO_2$ exhibited surface plasmon peaks; whereas, in contrast to the Au/$TiO_2$, a continuous Au thin film doesn't exhibit surface plasmon peaks. We modified the thickness and morphology of a continuous Ag layer by electron beam evaporation deposition and heating under gas conditions and found that the morphological change and thickness of the Ag film are key factors in controlling the peak position of light absorption.