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        검색결과 64

        41.
        2009.10 구독 인증기관·개인회원 무료
        45.
        2007.12 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        The spectroscopic properties of bright extragalactic planetary nebulae are reviewed, considering primarily their chemical abundances and their internal kinematics. Low-resolution spectroscopy is used to investigate how the precursor stars of bright planetary nebulae modify their original composition through nucleosynthesis and dredge up. At present, the evidence indicates that oxygen and neon abundances usually remain unchanged, helium abundances are typically enhanced by less than 50%, while nitrogen enhancements span a very wide range. Interpreting these changes in terms of the masses of their progenitor stars implies that the progenitor stars typically have masses or order 1.5M⊙ or less, though no models satisfactorily explain the nitrogen enrichment. High-resolution spectroscopy is used to study the internal kinematics of bright planetary nebulae in Local Group galaxies. At first sight, the expansion velocities are remarkably uniform, with a typical expansion velocity of 18 km/s and a range of 8-28 km/s, independent of the progenitor stellar population. Upon closer examination, bright planetary nebulae in the bulge of M31 expand slightly faster than their counterparts in M31's disk, a result that may extend generally to the planetary nebulae arising from old and young stellar populations. There are no very strong correlations between expansion velocity and global nebular properties, except that there are no large expansion velocities at the highest Hβ luminosities (i.e., the youngest objects never expand rapidly). These results independently suggest that bright planetary nebulae arise from a similar mass range in all galaxies. Nonetheless, there are good reasons to believe that bright planetary nebulae do not arise from identical progenitor stars in all galaxies.
        3,000원
        48.
        2005.10 구독 인증기관·개인회원 무료
        50.
        2004.06 구독 인증기관 무료, 개인회원 유료
        In anticipation of starting a new online journal in the field of educational technology, we conducted a review of existing journals, dividing them into two categories-online-only and online +print. The 30 journals in the review were analyzed with respect t frequency of publication; their content emphases, goals, and audiences; policies on subscription and copyright,· and technical functions, such as search and discussion. We were looking for the features that made the online journals distinctive from the others, which were based in the print paradigm. The aspects that yielded significant differences were subscription policy, redistribution policy, and search function. The online-only journals were more liberal in their subscription and redistribution policies, but the online + print journals had more extensive search capabilities. In addition, we identified gaps in the topical coverage of the existing journals, in the areas of educational technology management, educational systems design/reform, policy issues, and cultural issues.
        4,000원
        56.
        2020.12 KCI 등재 SCOPUS 서비스 종료(열람 제한)
        This study provides an assessment on a proposed method for separation of cesium, strontium, and barium using electrochemical reduction at a liquid bismuth cathode in LiCl-KCl eutectic salt, investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS). CV studies were performed at temperatures of 723-823 K and concentrations of the target species up to 4.0wt%. Redox reactions occurring during potential sweeps were observed. Concentration of BaCl2 in the salt did not seem to influence the diffusivity in the studied concentration range up to 4.0wt%. The presence of strontium in the system affected the redox reaction of lithium; however, there were no distinguishable redox peaks that could be measured. Impedance spectra obtained from EIS methods were used to calculate the exchange current densities of the electroactive active redox couple at the bismuth cathode. Results show the rate-controlling step in deposition to be the mass transport of Cs+ ions from the bulk salt to the cathode surface layer. Results from SEM-EDS suggest that Cs-Bi and Sr-Bi intermetallics from LiCl-KCl salt are not thermodynamically favorable.
        57.
        2020.03 KCI 등재 SCOPUS 서비스 종료(열람 제한)
        Molten salt solutions consisting of eutectic LiCl-KCl and concentrations of samarium chloride (0.5 to 3.0 wt%) at 500℃ were analyzed using both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV technique gave the average diffusion coefficient for Sm3+ over the concentration range. Equipped with Sm3+ diffusion coefficient, the Randles-Sevcik equation predicted Sm3+ concentration values that agree with the given experimental values. From CV measurements; the anodic, cathodic, and half-peak potentials were identified and subsequently used as a parameter to acquire EIS spectra. A six-element Voigt model was used to model the EIS data in terms of resistance-time constant pairs. The lowest resistances were observed at the half-peak potential with the associated resistance-time constant pairs characterizing the reversible reaction between Sm3+ and Sm2+. By extrapolation, the Voigt model estimated the polarization resistance and established a polarization resistance-concentration relationship.
        58.
        2019.11 KCI 등재 SCOPUS 서비스 종료(열람 제한)
        The purpose of this research is to review historical development of Islamic finance in individual East Asian economies, including China, Japan, South Korea and Hong Kong, and examine the success factors of the Hong Kong Sukuk issuances in 2014-2017. The research is a qualitative study applying case study method. It is found that the East Asian economies do play efforts to develop their Islamic capital markets although they have very limited size of Muslim population. Their progress on this development generally remains to be slow. The Hong Kong Sukuk is a breakthrough, carrying a total issuance value of US$3 billion. The Sukuk issuances, treated as a kind of asset-backed securities with restrictions on financing purposes, are distributed to international investors by investment banks from Hong Kong, Middle East and Malaysia. Success factors of these issuances include involvement of an issuer with high credit quality, recognition by central bank for using the Sukuk in its discount facility for commercial banks, centralized clearing services for the Sukuk and global banking network for underwriting the Sukuk. The lessons from the Hong Kong Sukuk are good references for other economies to develop their regional Islamic capital markets and to integrate the markets into the global capital market.
        60.
        2018.03 KCI 등재 SCOPUS 서비스 종료(열람 제한)
        A simplified flowsheet for pyroprocessing commercial spent fuel is proposed in which the only salt treatment step is actinide drawdown from electrorefiner salt. Actinide drawdown can be performed using a simple galvanic reduction process utilizing the reducing potential of gadolinium metal. Recent results of equilibrium reduction potentials for Gd, Ce, Nd, and La are summarized. A description of a recent experiment to demonstrate galvanic reduction with gadolinium is reviewed. Based on these experimental results and material balances of the flowsheet, this new variant of the pyroprocessing scheme is expected to meet the objectives of minimizing cost, maximizing processing rate, minimizing proliferation risk, and optimizing the utilization of geologic repository space.
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