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        검색결과 76

        22.
        2013.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        We present a multi-dimensional reduction method of the surveyed cube database obtained using a single- dish radio telescope in Taeduk Radio Astronomy Observatory (TRAO). The multibeam receiver system installed at the 14 m telescope in TRAO was not optimized at the initial stage, though it became more stabilized in the following season. We conducted a Galactic Plane survey using the multibeam receiver system. We show that the noise level of the first part of the survey was higher than expected, and a special reduction process seemed to be definitely required. Along with a brief review of classical methods, a multi-dimensional method of reduction is introduced; It is found that the ‘background’ task within IRAF (Image Reduction and Analysis Facility) can be applied to all three directions of the cube database. Various statistics of reduction results is tested using several IRAF tasks. The rms value of raw survey data is 0.241 K, and after primitive baseline subtraction and elimination of bad channel sections, the rms value turned out to be 0.210 K. After the one-dimensional reduction using ‘background’ task, the rms value is estimated to be 0.176 K. The average rms of the final reduced image is 0.137 K. Thus, the image quality is found to be improved about 43% using the new reduction method.
        4,000원
        24.
        2012.06 구독 인증기관·개인회원 무료
        The reactive oxygen species (ROS) generated during the somatic cell transfer nuclear (SCNT) procedures may cause the mitochondrial dysfunction and DNA damage, which may result in restricts the reprogramming of SCNT embryos and play a key direct role in apoptosis. The present study was conducted to investigate the effect of antioxidant treatment during the SCNT procedures on the inhibition of mitochondria and DNA damages in bovine SCNT embryos. The reconstituted oocytes were treated with antioxidants of 25 μM β-mercaptoethanol (β-ME) or 50 μM vitamin C (Vit. C) during the SCNT procedures. In vitro fertilization (IVF) was performed for controls. Mitochondrial morphology and membrane potential (ΔΨ) were evaluated by staining the embryos with MitoTracker Red or JC-1. Apoptosis was analyzed by Caspase-3 activity assay and TUNEL assay, and DNA fragmentation was measured by comet assay at the zygote stage. Mitochondrial morphology of non-treated SCNT embryos was diffused within cytoplasm without forming clumps, while the IVF embryos and antioxidant treated SCNT embryos were formed clumps. The ΔΨ of β-ME (1.3±0.1, red/green) and Vit. C-treated (1.4±0.2, red/green) SCNT embryos were significantly higher (p<0.05) than that of non-treated SCNT embryos (0.9±0.1, red/ green), which similar to that of IVF embryos (1.3±0.1, red/green). Caspase-3 activity was not difference among the groups. TUNEL assay also revealed that little apoptosis was occurred in SCNT embryos as well as IVF embryos regardless of antioxidant treatment. Comet tail lengths of β-ME and Vit. C-treated SCNT embryos (337.8±23.5 μm and 318.7 ±27.0 μm, respectively) were shorter than that of non-treated SCNT embryos (397.4± 21.4 μm) and similar to IVF embryos (323.3±10.6 μm). These results suggest that antioxidant treatment during SCNT procedures can inhibit the mitochondrial and DNA damages of bovine SCNT embryos.
        25.
        2012.02 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this work, the silver nanoparticles have been synthesized by electrical explosion of wire in three liquid mediums: deionized water (DIW), polyvinylpyrrolidone (PVP) and sodium dodecyl benzene sulfonate (SDBS) solutions. Absorption in the UV-visible region of these suspensions was measured in the range of 300-800 nm. A surface plasmon peak was observed at ~400 nm in all suspensions in measured wavelength range. Particle size was analyzed by transmission electron microscope. It showed that the particles had nearly spherical shape in all samples. The average particle sizes prepared in DIW, PVP and SDBS solution were 37, 31 and 27 nm, respectively. Stability of the suspensions was estimated by multiple light scattering method. The presence of PVP and SDBS surfactants in the exploding medium resulted in enhanced stability of the silver suspensions.
        4,000원
        26.
        2011.10 구독 인증기관·개인회원 무료
        Bacterial contamination reduces the semen quality, semen preservation, and cause of disease spread as well. Sperm fertility is essential factor of reproductive performance in swine. Sperm fertility is affected by semen quality such as sperm motility, abnormality, morphology, and rate of bacterial contamination. This study was conducted to determine the relationship between elapsed time after semen preservation on the changes of bacteria and semen quality. Semen was diluted with BTS extender without antibiotic for 7 days and sperm parameter and fertility were measured. Sperm motility was measured by CASA and total bacteria number was counted after 22 24 hr incubation from counting agar plate in which sperm dilute to 10 106 in 0.9% saline solution and inoculate to agar. Acrosomal integrity was measured by Chlortetracycline (CTC) staining. CTC patterns were uniform fluorescence over the whole head (pattern A), characteristic of uncapacitated acrosome-intact spermatozoa; fluorescence-free band in the post-acrosomal region (pattern B), characteristic of capacitated acrosome-intact spermatozoa; and almost no fluorescence over the whole head except for a thin band in the equatorial segment (pattern C), characteristic of acrosome reacted spermatozoa. Total number of bacteria was significantly increased (p<0.0001) 3 days after preservation. Sperm motility, viability, and morphological abnormality on elapsed time after preservation were lower from 5 (77.24±6.47, p<0.001) and 7 days (77.24±6.47, p< 0.001) after preservation compared to 1 (15.71±7.18) and 3 days(18.39±7.22) after preservation, respectively. Sperm viability was significantly lower (53.25±35.03, p<0.0001) at 7 days after preservation. Mohological abnormality of sperm was lower (p<0.001) at 1 (15.71±7.18) and 3 (18.39±7.22) days compared to (5 21.84±7.91) and 7 (22.59± 9.93) days after preservation. Acrosomal integrity and capacitation rate (pattern A) were significantly lower (p<0.001) from 5 days after preservation.
        27.
        2010.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The Cu nanofluid in ethylene glycol was prepared by electrical explosion of wire, a novel one-step method. The X-ray diffraction, field emission scanning electron microscope and transmission electron microscope were used to study the properties of Cu nanoparticles. The results showed that the nanoparticles were consisted of pure face-centered cubic structure and near spherical shape with average grain size of 65 nm. Ultraviolet-visible spectroscopy (UV-Vis) confirmed Cu nanoparticles with a single absorbance peak of Cu surface plasmon resonance band at 600 nm. The nanofluid was found to be stable due to high positive zeta potential value, +51 mV. The backscattering level of nanofluid in static stationary was decreased about 2% for 5 days. The thermal conductivity measurement showed that Cu-ethylene glycol nanofluid with low concentration of nanoparticles had higher thermal conductivity than based fluid. The enhancement of thermal conductivity of nanofluid at a volume fraction of 0.1% was approximately 5.2%.
        4,000원
        30.
        2010.02 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In present work, amorphous TiCuNi powders were fabricated by mechanical alloying process. Amorphization and crystallization behaviors of the TiCuNi powders during high-energy ball milling and subsequent microstructure changes were studied by X-ray diffraction and transmission electron microscope. TEM samples were prepared by the focused ion beam technique. The morphology of powders prepared with different milling times was observed by field-emission scanning electron microscope and optical microscope. The powders developed a fine, layered, homogeneous structure with milling times. The crystallization behavior showed that glass transition, , onset crystallization, , and super cooled liquid range were 628, 755 and 127K, respectively. The as-prepared amorphous TiCuNi powders were consolidated by spark plasma sintering process. Full densified TiCuNi samples were successfully produced by the spark plasma sintering process. Crystallization of the MA powders happened during sintering at 733K.
        4,000원
        31.
        2010.02 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this work, effect of various process-control agents (PCAs) on the mechanical alloying of amorphous alloy of has been investigated. The dependence of the particle shape, size and crystallization behavior of the amorphous alloy powders on the type of PCAs and their concentrations was investigated by using X-ray diffraction, field-emission scanning electron microscopy and differential scanning calorimetry. It was found that the additive of toluene could affect positively the amorphization and thermally induced crystallization processes, as well as the size refinement, morphology and particle-size distribution of as-milled powders in comparison with alloy obtained without PCA.
        4,000원
        32.
        2009.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        TiCuNiAl quaternary amorphous alloy was prepared by high-energy ball milling process. A complete amorphization was confirmed for the composition of TiCuNiAl after milling for 30hrs. Differential scanning calorimetry showed a large super-cooled liquid region (T = T T, T and T: glass transition and crystallization onset temperatures, respectively) of 80 K. Prepared amorphous powders of TiCuNiAl were consolidated by spark-plasma sintering. Densification behavior and microstructure changes were investigated. Samples sintered at higher temperature of 713 K had a nearly full density. With increasing the sintering temperature, the compressive strength increased to fracture strength of 756 MPa in the case of sintering at 733 K, which showed a 'transparticle' fracture. The samples sintered at above 693 K showed the elongation maximum above 2%.
        4,000원
        38.
        2006.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Multi-walled carbon nanotube-poly methyl methacrylate (MWNT/PMMA) nanocomposite has been prepared by in situ polymerization of MMA dispersed with MWNTs. The MWNTs were functionalized by nitric acid and sulfuric acid treatment, and this was confirmed by FTIR spectrometer. The solution mixture of MWNTs and MMA was partially polymerized at 80℃, followed by the addition of AIBN and polymerization at 50℃. The MWNT-PMMA composite was prepared by casting the pre-polymer on the glass plate, and the optical properties have been studied using UV-vis spectrometer. The acid treated MWNTs were well dispersed in MMA with fairly good dispersion stability, while flocculation and sedimentation was observed from raw MWNTs in MMA.
        4,000원
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