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      • Radiological Characteristics of the Havar Foil in the Cyclotron Target

        Dong gun Jang,Sang hwa Shin,Chang lak Kim,Gyeong hyeon Gwak2 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

        The cyclotron is an apparatus used for the production of radioactive isotopes through nuclear reactions, resulting in the inevitable emission of neutrons. Consequently, surrounding components become activated. The purpose of this study was to investigate the radiological characteristics of Havar foil, a periodic replacement part of the Targetry system. In this study, radioactivity and radiation dose were calculated based on the time of Havar foil replacement and equipment dismantling. The time to dismantle the equipment was set at one year after the equipment was shut down, based on the recently used 1g of Havar foil. All simulations were performed using the FLUKA program. First, in the simulation results, 11 elements (Re, W, Tc, Nb, Cu, Ni, Co, Fe, Mn, Cr, V) were converted into 36 radioisotopes by activation based on the replacement period. Based on radioactivity levels, major isotopes included 52Mn (77.63%), 56Co (13.36%), 96Tc (2.4%), and 95Tc (1.80%). Based on radiation dose rates, 52Mn (82.66%) and 56Co (13.45%) exhibited the highest levels. Furthermore, the dose rates at distances of 10 cm, 50 cm, and 100 cm were found to be 1.36E+1 mSv/hr, 2.24E+00 mSv/hr, and 8.80E-01 mSv/hr, respectively. Second, as of the time the equipment was dismantled, 20 radioactive isotopes of 10 elements, excluding short-lived nuclides, were generated. In terms of radioactivity, 56Co (45.83%), 55Fe (19.73%), 57Co (14.48%), and 54Mn (13.50%) were prominent. Regarding radiation dose rates, 56Co (92%) and 54Mn (7.32%) exhibited higher levels. Dose rates at distances of 10 cm, 50 cm, and 100 cm were calculated at 5.31E-01 mSv/hr, 8.80E-02 mSv/hr, and 3.47 E-02 mSv/hr, respectively. Third, according to the radioactive waste classification standards in the replacement and decommissioning stages, Havar foil was predicted to be low-level radioactive waste in terms of radioactivity. In addition, it was derived that a cooling period of approximately 12 years is necessary to satisfy the allowable dose for clearance level waste. In conclusion, Havar foil, which is periodically generated as radioactive waste, can cause radiation exposure to replacement workers. Therefore, special and careful management is required for the Havar foil of the cyclotron.

      • KCI등재

        Comparison of Shoulder Total Rotational Range of Motion and External to Internal Rotation Strength Ratio between Assembly Line Workers with and without Subacromial Pain Syndrome

        Gyeong-tae Gwak(Gyeong-tae Gwak),Young-soo Weon(Young-soo Weon),Jun-hee Kim(Jun-hee Kim) KEMA학회 2022 근골격계과학기술학회 Vol.6 No.1

        Background Subacromial pain syndrome (SAPS) is one of the causes of shoulder pain in workers performing repetitive upper extremity movements. However, there have been no studies on physical characteristics such as shoulder total rotational range of motion (ROM) and external to internal rotation muscle strength ratio of workers. Purpose The purpose of this study was to compare the total rotational ROM and external to internal rotation muscle strength ratio in workers with and without SAPS. Study design A cross-sectional study Methods This study included 35 workers with SAPS and 32 workers without SAPS. The total rotational ROM were measured using Smart KEMA motion sensor, and external to internal rotation muscle strength were measured using Smart KEMA pulling sensor. Results The results showed that there were significant differences in the total rotation ROM between the groups (p<0.05). However, no significant difference was found in the external to internal rotation muscle strength ratio (p>0.05). Conclusions Assembly line workers with SAPS had limited total rotational ROM. However, the ratio of external to internal rotation muscle strength ratio was not different for workers without SAPS. These characteristics can be considered factors that should be considered in evaluating workers with SAPS and establishing a treatment plan.

      • Economic evaluation of synthetic ethanol production by using domestic biowastes and coal mixture

        Gwak, You Ra,Kim, Ye Bin,Gwak, In Seop,Lee, See Hoon Elsevier 2018 Fuel Vol.213 No.-

        <P><B>Abstract</B></P> <P>Biowastes, such as cow manure, waste paper, and wood waste, are recognized as an essential source of renewable energy, and their importance increased significantly over time. However, the insufficient supply of biowastes for commercial thermochemical conversion processes is a major problem that needs to be addressed. Therefore, the co-utilization of biowastes and coal has been developed globally. In this study, we investigated the feasibility of biowaste and coal mixtures in an ethanol conversion process. A commercial-scale thermochemical process consisting of a dual fluidized bed gasifier, compressor, tar reformer, catalytic reactor, and auxiliary facilities was used and analyzed. In particular, the effects of material costs including both transportation and collection costs of biowastes and mix percentages on the economic value of synthetic ethanol were analyzed. In addition to the limitations of biowaste collection, the scale of co-utilization processes could be a critical factor for the commercialization of converting biowaste and coal mixtures to ethanol.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Biowaste-coal mixtures to synthetic ethanol conversions were investigated. </LI> <LI> The economic efficiency of synthetic ethanol process increased due to increasing final products. </LI> <LI> Mixing coal could be a solution for biowastes to energy conversion. </LI> </UL> </P>

      • An intracellular antifreeze protein from an Antarctic microalga that responds to various environmental stresses

        Gwak, Yunho,Jung, Woongsic,Lee, Yew,Kim, Ji Sook,Kim, Chul Geun,Ju, Ji-Hyun,Song, Chihong,Hyun, Jae-Kyung,Jin, EonSeon The Federation of American Societies for Experimen 2014 The FASEB Journal Vol.28 No.11

        <P>The structure and function of the Antarctic marine diatom <I>Chaetoceros neogracile</I> antifreeze protein (Cn-AFP), as well as its expression levels and characteristics of the ice-binding site, were analyzed in the present study. <I>In silico</I> analysis revealed that the <I>Cn-AFP</I> promoter contains both light- and temperature-responsive elements. Northern and Western blot analyses demonstrated that both Cn-AFP transcript and protein expression were strongly and rapidly stimulated by freezing, as well as temperature and high light stress. Immunogold labeling revealed that Cn-AFP is preferentially localized to the intracellular space near the chloroplast membrane. Recombinant Cn-AFP had clear antifreeze activity. Protein-folding simulation was used to predict the putative ice-binding sites in Cn-AFP, and site-directed mutagenesis of the Cn-AFP b-face confirmed their identification.—Gwak, Y., Jung, W., Lee, Y., Kim, J. S., Kim, C. G., Ju, J.-H., Song, C., Hyun, J.-K., Jin, E. An intracellular antifreeze protein from an Antarctic microalga that responds to various environmental stresses.</P>

      • Upper Limit of Radiation from Coalescence of Rotating Hayward Black Holes

        Gwak, Bogeun,Gwak, B.,Kang, G.,Kim, C.,Kim, H.-C.,Lee, C.-H.,Lee, J.,Lee, S.,Lee, W. EDP Sciences 2018 The European Physical Journal Conferences Vol.168 No.-

        <P>We review the upper limit of the gravitational radiation thermally allowed under the collision of two rotating Hayward black holes. The upper limit is dependent on the gravitational spin interaction between black holes and is useful to determine one of the parameters for consistency with Laser Interferometer Gravitational-Wave Observatory (LIGO) data.</P>

      • KCI등재

        Drying characteristics of low rank coals in a pressurized flash drying system

        Gwak, In Seop,Gwak, You Ra,Kim, Ye Bin,Lee, See Hoon THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.57 No.-

        <P><B>Abstract</B></P> <P>Drying characteristics of low rank coals were examined and determined using a pressurized flash drying system which consisted of a pressurized feeder, rolled tubes (maximum of 6m), a cyclone, and a back pressure regulator. The effect of the operating conditions, such as pressure (maximum of 40bar), gas outlet temperature (maximum of 300°C), particle sizes (212–300 and 300–355μm) and residence time (maximum of 1s) on the drying ratio was investigated and analyzed. The study results show that temperature is a more effective factor than pressure. A correlation equation to predict the drying ratio of coals was suggested based on operation conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The characteristics of pressurized flash drying of low rank coal were investigated. </LI> <LI> The drying ratio mostly increased with temperatures and pressures. But the drying ratio did not increase at high pressure conditions because of increasing boiling temperature. </LI> <LI> The empirical equation to predict drying ratio was suggested as follows: <SUB> D r </SUB> = 2.82 × <SUP> R 0.63 </SUP> × <SUP> S 0.02 </SUP> × <SUP> P 0.28 </SUP> × <SUP> T 0.65 </SUP> . </LI> </UL> </P>

      • KCI등재

        가압 마이크로 수송관을 이용한 저급탄의 건조 특성 연구

        곽인섭 ( In Seop Gwak ),곽유라 ( You Ra Gwak ),김예빈 ( Ye Bin Kim ),이시훈 ( See Hoon Lee ) 한국공업화학회 2017 공업화학 Vol.28 No.3

        지속적인 에너지 수요의 증가로 인하여 저등급 석탄이 새로운 에너지 자원으로서 인정받고 있다. 그러나 저등급 석탄의 높은 수분 함량으로 인하여 저등급 석탄의 이용 효율은 기존의 석탄 이용 플랜트들에서 이용하기에 부족하다. 따라서 저등급 석탄의 수분 함량을 낮추는 건조 공정이 요구되고 있다. 비록 다양한 건조 실험들이 진행되었으나, 고압 조건에서의 건조 특성은 크게 연구되지 않았다. 이에 본 연구에서는 높은 수분 함량을 지닌 저등급 석탄(수분 함량: 21.5 wt%)의 급속 건조 특성을 가압 마이크로 상승관을 이용하여 고찰하였다. 압력(1-40 bar), 건조 온도(200-600 ℃), 마이크로 상승관 길이(2-6 m) 등의 운전 조건 변화에 따른 저등급 석탄의 건조 특성을 분석하였다. With the continuous increase of energy demand, low-grade coal is regarded as one of new energy sources. However, due to the high water content, the utilization efficiency of low-grade coal is not good to be used in recent conversion plants. Therefore, it requires a drying process to lower the water content in low-grade coals. Although a variety of drying experiments were conducted, drying characteristics in accordance with the pressure change has not been progressed. In this study, the flash drying characteristics of low grade coal with high moisture content (21.5 wt%) were determined in a pressurized micro- riser. The effect of operation conditions such as pressure (1-40 bar), dryer temperature (200-600 ℃), and tube length (2-6 m) on drying ratios were investigated.

      • New industrial application of forward osmosis (FO): Precious metal recovery from printed circuit board (PCB) plant wastewater

        Gwak, Gimun,Kim, David Inhyuk,Hong, Seungkwan Elsevier 2018 Journal of membrane science Vol.552 No.-

        <P><B>Abstract</B></P> <P>As a promising industrial application of forward osmosis (FO), an FO-based concentration system for precious metal recovery from printed circuit board (PCB) wastewater has been newly suggested. This novel FO concentration process utilizes a dilution-needed waste solution possessing high conductivity as a draw solution, and thus an external supply of draw solution as well as a re-concentration process for the diluted draw solution are not required. An electroless (E’less) nickel (Ni) plating solution was evaluated as dilution-needed waste stream-based draw solution, and the test results confirmed that the selected Ni solution could produce an acceptable FO performance, i.e., water flux of 39.4 LMH (active layer facing draw solution (AL-DS) mode with deionized feed solution). From a series of FO experiments conducted with a palladium (Pd) catalyst as a concentration-needed feed solution, the Pd solution was effectively concentrated under an active layer facing feed solution (AL-FS) mode with a slight impact from Pd scaling. The modeling prediction based on our experimental results showed that theoretically Pd can be concentrated 17.2-times-high. The overall performance of our Pd concentration tests indicated that the FO process is promising for concentrating Pd, thereby improving the efficiency of its recycling. The newly proposed system, a recovery-free FO driven by a waste stream, offers attractive economic advantages including (1) zero cost for the supply and re-concentration of the draw solution and (2) enhanced energy efficiency in the precious metal recycling process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> FO-based precious metal recovery system from PCB plant was newly proposed. </LI> <LI> E’less Ni plating solution was assessed as representative disposable draw solution. </LI> <LI> Maximum Pd concentration yield was calculated as 17.2 through theoretical modeling. </LI> <LI> Sustainable Pd enrichment was achieved under AL-FS mode despite Pd scaling. </LI> <LI> The suggested FO system can be expended by adopting different PCB waste streams. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

      • SCISCIESCOPUS

        Instability of charged anti-de Sitter black holes

        Gwak, B.,Lee, B.H.,Ro, D. North-Holland Pub. Co 2016 Physics letters. Section B Vol.761 No.-

        We have studied the instability of charged anti-de Sitter black holes in four- or higher-dimensions under fragmentation. The unstable black holes under fragmentation can be broken into two black holes. Instability depends not only on the mass and charge of the black hole but also on the ratio between the fragmented black hole and its predecessor. We have found that the near extremal black holes are unstable, and Schwarzschild-AdS black holes are stable. These are qualitatively similar to black holes in four dimensions and higher. The detailed instabilities are numerically investigated.

      • Multi-dimensional modeling and large-scale simulation of hydrogen absorption/desorption phenomena in metal hydride vessels (MHVs)

        Gwak, Geonhui,Yun, Seongjin,Ju, Hyunchul Elsevier 2018 Fusion engineering and design Vol.130 No.-

        <P><B>Abstract</B></P> <P>In this paper, a three-dimensional (3-D) hydrogen absorption/desorption model is applied to two different real-scale metal hydride vessels (MHVs). The model is then validated against experimentally measured metal hydride temperature and H/M ratio evolution data from a hydrogen charge/discharge cycle. The two experimental vessels were designed to have identical dimensions and contain the same mass of ZrCo (125 g), but one is loaded with copper fins and the other with copper foams. Since the real-scale vessel geometries involve several million computational grid points, a parallel computational methodology has been employed to reduce the computational turnaround time. This comparison highlights this substantial improvement in agreement between simulation and experiment obtained by conducting full-scale simulations of the whole MHVs. In addition to model validation, detailed key contours are analyzed to elucidate hydrogen charge/discharge characteristics in whole-scale MHV geometries. This study demonstrates the validity of our 3-D hydrogen absorption/desorption model for optimization of practical MHV design and operating conditions.</P>

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