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        검색결과 9,514

        6821.
        2001.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Several fabrication processes, corresponding nanostructural features and multifunctionality as well has been investigated for oxide ceramic based nanocomposites with metal nanodispersion (i.e., ceramic/metal nanocomposites). Transition metal (Ni, Co, etc) dispersed alumina and zirconia based nanocomposites have been synthesized by reducing and hot-press sintering of ceramic and metal oxide mixtures prepared by several method. Improved fracture strength (1.1 and 1.9 GPa for and nanocomposites, respectively) of these composites have been achieved according to their nanostructures. In addition, ferromagnetic characteristic has been kept. The variation of magnetization with an applied stress has found to be more sensitive as smaller as the magnetic metal dispersion is. This result thus suggests the possibility of fracture and/or stress sensing of the composites by simple magnetic measurement.
        4,000원
        6822.
        2001.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Through the observation of wear scar of two ceramic materials, microstructural wear mechanisms was investigated. As for the -5 vol% SiC nanocomposite, the grain boundary fracture was suppressed by the presence of SiC nano-particles. The intragranular SiC particles have inhibited the extension of plastic deformation through the whole grain. Part of plastic deformation was accommodated around SiC particles, which made a cavity at the interface between SiC and matrix alumina. On the other hand, gas-pressure sintered silicon nitride showed extensive grain boundary fracture due to the thermal fatigue. The lamination of wear scar was initiated by the dissolution of grain boundary phase. These two extreme cases showed the importance of microstructures in wear behavior.
        4,000원
        6823.
        2001.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        A bulk porous composite with plantinum nano-dispersion was synthesized in air atmosphere through the combination of several in situ reactions, including the pyrolysis of . A mixture of (dolomite), , and LiF (0.5 wt%, as an additive) was cold isostatically pressed at 200 MPa and sintered at for 2 h. The porous composite ( : Pt=99 : 1 in volume) had a uniformly open-porous structure (porosity: 56%) with three-dimensional (3-D) network and a narrow pore-size distribution, similarly to the porous composites reported before. Catalytic Properties (viz., NO direct decomposition and NO reduction by ) of the composite were investigated up to . In the absence of oxygen, the NO conversion rate reached ~52% for the direct decomposition and ~100% for the reduction by , respectively. The results suggest the possibility of the porous composite as a multifunctional filter, i.e., simultaneous hot gas-filtering and in one component.
        4,000원
        6824.
        2001.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        An optimum route to fabricate the ferrous alloy dispersed nanocomposites such as /Fe-Ni and /Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded , forming nanocomposite powder. The sintered /Fe-Ni composite showed the formation of Fe phase, while the reaction phases were not observed in /Fe-Co composite. Hot-pressed /Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.
        4,000원
        6826.
        2001.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        5,100원
        6828.
        2001.06 구독 인증기관 무료, 개인회원 유료
        Twelve species of the genus Nola, including a new species, Nola longicosta sp. nov. are recognized from Korea. Among them, six species, Nola cristatula(Hubner), N. yoshinensis(wileman & West), N. japonibia(Strand), N. nami(Inoue), N. ebatoi(Inoue), and N. okanoi(Inoue) are reported for the first time from Korea. Genital characteristics of the species are briefly described with illustration, and all available collecting data are given.
        4,800원
        6829.
        2001.06 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        In the present study we have determined the distance moduli for seven globular clusters M2, M3, Ml0, M12, NGC 2808, NGC 6229, and NGC 6752, whose metallicities are in the range -1.54 < [Fe/H] < -1.10. We have derived distances for them by the main-sequence fitting method using a sample of local subdwarfs, whose accurate parallaxes are taken from the Hipparcos Catalog. The derived distance moduli are 15.52 for M2, 14.98 for M3, 14.23 for Ml0, 14.03 for M12, 15.56 for NGC 2808, 17.34 for NGC 6229, and 13.29 for NGC 6752.
        4,200원
        6830.
        2001.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Partial mesophase (PM) pitch precursor was prepared from fluidized catalytic cracking-decant oils (FCC-DO) by chemical reaction in the presence of Br2. The PM pitch heated-treatment at 420℃ for 9 h exhibited the softening point of 297℃ with 23% yield, and 55% anisotropic content. The PM pitch precursor was melt-spun through circular nozzle by pressurized N2, stabilized at 310℃, carbonized at 700℃, 1000℃, and 1200℃. The enough stabilization introduced 16.4% of the oxygen approximately. The stacking height (Lc002) and interlayer spacing (d002) of the as-spun fibers were 4.58 nm and 3.45a and the value became minimum and maximum at 700℃ respectively in the carbonization procedure. The tensile strength increased with an increase in the heat treatment temperature exhibiting highest value of 750 MPa at 1200℃ carbonization.
        4,000원
        6831.
        2001.06 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        In this paper, we investigate the correlation between the radial ultraviolet color distribution and the shapes of the ultraviolet isophote for elliptical galaxies (M32, NGC 1399) and spiral bulges (of M31, M81) by using their archival UIT images. For M31, M81, and NGC 1399, the radial ultraviolet color distributions show a two-component trend; as the distance from the galactic center increase the color becomes redder in the inner region while it becomes bluer in the outer region. On the other hand, the color of M32 continues to become bluer with the increasing galactocentric distance. We also find, unlike the optical/IR images, significant variations of the position angle and the ellipticity in the ultraviolet isophotes of M31, M81, and NGC 1399 through the inner regions. For M32, the variation is significant in the outer region. Since these variation implies the triaxiality of their intrinsic shapes, we suggest that the early-type galaxies and spiral bulges with a radial color gradient in ultraviolet tend to have a triaxiality. On the other hand, the shape parameter characterized by the fourth order cosine Fourier coefficient of the isophote, a(4)/a, indicates that the systematic deviations of the ultraviolet isophotes of the four galaxies are smaller than ~0.2% in units of the semi-major axis. The latter result implies that the ultraviolet isophotes of the galaxies have a pure elliptical shape rather than the boxy or disky shapes. Therefore, there is no clear evidence of correlation between the radial ultra-violet color gradient and the boxy/disky shapes of isophotes.
        4,000원
        6833.
        2001.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        이 논문은 미국의 교정조직과 사법부의 관계의 변화에 대한 것이다. 사법부의 교정활동에 대한 개입은 3단계로 나누어 지며, 교정철학의 변화는 일곱 개의 시기로 나누어 지는 데, 이러한 변화들을 연방과 주정부 수준에서 일어난 교정활동의 결정에 있어서의 자율성과 관련시켜 설명하고 있다. 그리고 현재 미국의 교정과 텍사스주의 교정제도에 대한 간단한 소개를 한다.
        8,100원