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51.
In order to investigate the microstructure and mechanical properties of small sized Sn–Bi bump, the eutectic Sn–Bi bumps with a diameter of 25 μm and a height of less than 20 μm after reflow were fabricated by electroplating and reflow. The reflow temperature of the Sn–Bi bumps was 170 °C, and the reflow times were varied from 5 to 20 min. The experimental results showed that a eutectic Sn–Bi composition was obtained by plating at a current density of 30 mA/cm2 for 15 min. The average height and diameter of the bumps reflowed for 5 min were 16.1 ± 0.7 μm and 25.2 ± 0.7 μm, respectively. The microstructure of the reflowed bumps consisted of Sn- and Bi-rich phases. The thickness of the IMC of Cu6Sn5 increased from 1.17 to 2.25 μm with increasing reflow time from 5 to 20 min. The shear strength of the reflowed Sn–Bi bump increased with increasing reflow time, and reached approximately 11 gf at 15 and 20 min. The elastic modulus and hardness of eutectic Sn–Bi bump by nanoindentation were 53.5 and 0.43 GPa. Those of Cu6Sn5 were found to be 121.1 and 6.67 GPa. 相似文献
52.
Young-Sam Oh Hyun-Seog Roh Ki-Won Jun Young-Soon Baek 《International Journal of Hydrogen Energy》2003,28(12):1387-1392
The steam treatment effect has been investigated over the doubly impregnated catalyst, Ni/Ce–ZrO2/θ-Al2O3, in steam methane reforming (SMR). The catalyst was remarkably deactivated by steam treatment but reversibly regenerated by H2-reduction. XRD results showed that the steam treatment resulted in the formation of NiAl2O4 which is inactive for SMR but it was reversibly converted to Ni by the reduction. The reversible oxidation-reduction of Ni state was also evidenced by XPS and it was observed that the formation of NiAl2O4 is more favorable at higher temperature. It is most likely that the alumina support is only partially covered with Ce–ZrO2 and most Ni directly interacts with θ-Al2O3 which would probably make easy formation of NiAl2O4 in the presence of steam alone. The results imply that, during the start-up procedure in SMR, too high concentration of steam could deactivate seriously Al2O3 supported Ni catalysts. 相似文献
53.
Yoola Hwang Byoung‐Sun Lee Young‐Rok Kim Kyoung‐Min Roh Ok‐Chul Jung Haedong Kim 《ETRI Journal》2011,33(4):487-496
Korea Multi‐Purpose Satellite‐5 (KOMPSAT‐5) is the first satellite in Korea that provides 1 m resolution synthetic aperture radar (SAR) images. Precise orbit determination (POD) using a dual‐frequency IGOR receiver data is performed to conduct high‐resolution SAR images. We suggest orbit determination strategies based on a differential GPS technique. Double‐differenced phase observations are sampled every 30 seconds. A dynamic model approach using an estimation of general empirical acceleration every 6 minutes through a batch least‐squares estimator is applied. The orbit accuracy is validated using real data from GRACE and KOMPSAT‐2 as well as simulated KOMPSAT‐5 data. The POD results using GRACE satellite are adjusted through satellite laser ranging data and compared with publicly available reference orbit data. Operational orbit determination satisfies 5 m root sum square (RSS) in one sigma, and POD meets the orbit accuracy requirements of less than 20 cm and 0.003 cm/s RSS in position and velocity, respectively. 相似文献
54.
Jeong-il Kang Chung-Wook Roh Gun-Woo Moon Myung-Joong Youn 《Industrial Electronics, IEEE Transactions on》2002,49(3):649-652
A new phase-shifted parallel-input/series-output dual converter is proposed. It features a low-output voltage ripple, a low rms current in the output capacitor, and a greatly reduced constant switch turn-off stress, whereby the efficiency is significantly improved. This converter is considered to be well suited to high-power step-up applications 相似文献
55.
KH Park SY Rha CH Kim TS Kim NC Yoo JH Kim JK Roh SH Noh JS Min KS Lee BS Kim HC Chung 《Canadian Metallurgical Quarterly》1998,13(3):489-495
For the cancer cells which have overcome the second mitotic clock (M2), activated telomerase is essential and used as another marker of immortality. Many trials had been initiated to target telomerase, which is known to be specific to tumors. To determine the best in vitro cell system for testing the efficacy of telomerase inhibitors, we evaluated the telomerase activity of various cancer cell lines and measured their telomere lengths. We also treated some cancer cell lines with adriamycin and measured the changes of telomerase activity. Telomerase activity was evaluated in various cell lines with the TRAP (telomeric repeat amplification protocol) assay. Telomerase activity was calculated and translated into arbitrary units by computer-assisted densitometry with the control of telomerase activity in the 293 control cell line. Also, terminal restriction fragment lengths were measured using Southern blotting. We also measured telomerase activity and telomere lengths in 11 benign breast tumor tissues and 19 paired stomach cancer and normal tissues. Cancer cell lines treated with adriamycin we evaluated for changes of telomerase activity and the cell proliferation by MTT assay and dye exclusion test. Telomerase activity of cell lines was 95.3 24.1 unit with a range of 27.6-129.6 unit, while the telomere lengths of those cell lines were variable from 5.0 to 10.4 kbp with a median of 6 kbp. In 11 cancer cell lines which were not yet firmly established, we could not detect any telomerase activity. Low telomerase activity was detected in only 2 benign tumor tissues of breast with a median telomere length of 8.8 (7-10.5) kbp. Among paired 19 gastric cancer and normal tissues, only 7 cancer tissues showed weak telomerase activity. After adriamycin treatment, telomerase activity in YCC-S-1, YCC-S-3, MCF-7 and MCF-7/ADR was decreased in accordance with the changes of the cell numbers. Telomerase is specific to cancer tissues and is expressed differently from organ to organ. Telomerase activity by TRAP assay could be used as a chemosensitivity assay. 相似文献
56.
Lee W.H. Dong-Kyu Lee Young-Ho Na Keon-Soo Kim Kun-Ok Ahn Kang-Deog Suh Yonghan Roh 《Electron Device Letters, IEEE》2002,23(8):476-478
We report the effects of plasma process-induced damage during floating gate (FG) dry-etching process on the erase characteristics of NOR flash cells. As compared to flash cells processed in a stable plasma condition, it is found that flash cells processed in the nonoptimized ambient show significantly degraded erase characteristics under a negative gate Fowler-Nordheim (FN) bias, exhibiting a fast-erasing bit in the distribution of erased bits. However, little differences are found in their tunneling characteristics under a positive gate biasing. The gate bias polarity dependence of FN tunneling indicates that positive charges are created near the poly-Si/SiO/sub 2/ interface during the FG dry-etching, prior to the backend processes such as metal- or via-etch. 相似文献
57.
58.
N.S. Baek Y.H. Kim S.‐G. Roh B.K. Kwak H.K. Kim 《Advanced functional materials》2006,16(14):1873-1882
A series of inert and photostable encapsulated lanthanide(III) complexes—based on dendritic anthracene ligands—is shown for the first time to exhibit strong near‐IR emission bands via efficient energy transfer from the excited states of the peripheral antenna to the Ln3+ ions (Er3+, Yb3+, and Nd3+). A significant decrease in the fluorescence of the anthracene ligand is accompanied by a strong increase in the near‐IR emission of the Ln3+ ions. The near‐IR emission intensities of Ln3+ ions in the encapsulated Ln3+–dendrimer complexes are dramatically enhanced on increasing the generation number (n) of dendrons, owing to site‐isolation and light‐harvesting effects. Furthermore, a first attempt is made to distinguish between the site‐isolation and light‐harvesting effects in the present complexes. Photophysical studies indicate the sensitization of Ln3+ luminescence by energy transfer through the excited singlet state of the anthracene ligands, and the energy‐transfer efficiency between the dendritic anthracene ligands and the Ln3+ ion is evaluated to be in the range of 90 to 97 %. Their energy‐transfer efficiency is in good agreement with the result that the biexponential decays contain a radiative decay of anthracene units (< ca. 10 %) and an energy‐transfer component (> ca. 90 %) from the excited state of anthracene ligands to the Ln3+ ions. Time‐resolved luminescence spectra show monoexponential decays with a lifetime of 2 μs for the Er3+ ion 11 μs for the Yb3+ ion and 0.7 μs for the Nd3+ ion in thin films, and calculated intrinsic quantum yields of the Ln3+ ions are in the range of ca. 0.025 to 0.55 %. 相似文献
59.
Seungin Baek Sookyoung Roh Yoonchan Jeong Byoungho Lee 《Photonics Technology Letters, IEEE》2006,18(5):700-702
A long-period fiber grating (LPFG) was inscribed in a single-mode fiber and was spliced with a ytterbium (Yb)-doped double-clad fiber in order to couple pump radiation of the inner cladding into the core in a cladding-pumped fiber laser. The use of an LPFG permits a partial core-pumping scheme in a cladding-pumping fiber laser because a portion of the pump radiation can be coupled to the core by LPFG. The enhancement of the pump absorption of a Yb-doped cladding-pumped fiber laser as the result of pump coupling by LPFG was 35%, and the maximal output power increased by up to 55% when a 20-W pump source is used. 相似文献
60.
SY Rha WI Yang JH Kim JK Roh JS Min KS Lee BS Kim HC Chung 《Canadian Metallurgical Quarterly》1998,5(4):875-879
The role of nitric oxide (NO) in activation of cGMP is well established. It has been proposed that the ratio of cAMP to cGMP may be important in the regulation of preimplantation embryonic growth and differentiation. Therefore, we determined the ability of murine preimplantation embryos to produce NO. In addition, NO as an endogenous smooth muscle relaxant and vasodilator is a candidate for involvement in embryo implantation because this process requires increased vascular permeability and uterine quiescence at the sites of blastocyst apposition. Nitrite assays, an indirect measure of NO production, indicate that preimplantation murine embryos produce NO. This production was reversibly inhibited by culture of embryos in medium containing a nonspecific NO synthase (NOS) inhibitor (NG-nitro-L-arginine). Additionally, inhibition of normal development was observed in embryos cultured with NOS inhibitor. NO levels increased in culture medium when ovariectomized progesterone-treated animals were exposed to estrogen for 1 h in utero. Such hormonal treatment induces implantation. These data indicate that NO levels are regulated by estrogen and may be important in regulation of implantation. In addition, these data demonstrate for the first time that NO production appears to be required for normal embryonic development. 相似文献