24,095 research outputs found
Hepatitis C virus genotypes in Korea and their relationship to clinical outcome in type C chronic liver diseases.
No full textOBJECTIVES: The relationship between HCV genotype and the development of more serious liver disease has not been clearly established. This study was to investigate the distribution pattern of HCV genotypes in Korea and their relationship to the viremic level and to progression of chronic liver disease. METHODS: Study population was 217 patients with type C chronic liver disease. They were divided into 4 groups; 83 patients with near-normal ALT (group 1), 64 patients with elevated ALT (group 2), 20 patients with decompensated liver cirrhosis (group 3) and 50 patients with hepatocellular carcinoma (group 4). HCV genotypes were determined by reverse transcription polymerase chain reaction (RT-PCR) using mixed primer sets, and then the fidelity of genotyping was confirmed by cloning and sequencing. HCV RNA concentration was measured by quantitative competitive RT-PCR for 23 patients in group 2. RESULTS: The genotypes could be determined in 166 (76%) out of 217 patients. Type 1b and type 2a were predominantly occurring over the other types in somewhat similar frequency (45% and 51%, respectively). The genotype distribution of type 1b and 2a among four different groups showed 42% and 54% in group 1, 49% and 45% in group 2, 53% and 47% in group 3 and 41% and 57% in group 4; thus there was no significant difference in genotype distribution among 4 different disease groups. However, the viremia levels in patients with genotype 1b infection were significantly higher than those with genotype 2a. CONCLUSION: Genotype 2a infection is as prevalent as genotype 1b in Korea, and genotype 2a infection may pose no less risk for progression of disease despite lower replication level than genotype lb infection
Adsorption and reaction of 4-nitrobenzoic acid on omega-functionalized alkanethiol monolayers on powdered silver: Infrared and Raman spectroscopy study
No full textWe have investigated the stability of w-functionalized alkanethiol monolayers anchored on 2 mu m-sized silver particles by means of infrared and Raman spectroscopy. Although the alkyl chains of dodecanethiol (DDT) monolayers were deduced to have a trans-zigzag conformation by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), those of 11-mercapto-1-undecanol (11-MUD) and 12-mercapto-1-dodecylamine (12-MDA) monolayers seemed to assume strongly disordered conformations on the powdered silver surface. We also found by DRIFTS that 4-nitrobenzoic acid (4-NBA) can be incorporated nearly equally into the hydrophilic(11-MUD and 12-MDA) and hydrophobic (DDT) group-terminated monolayers by forming Ag--COO- bond(s). This seemed to be best understood by presuming that the hydrophobic interchain interaction is less optimal on a microscopically rough surface than on a smooth surface when monolayers of 11-MUD and 12-MDA are assembled on Ag. It was also found by surface-enhanced Raman scattering (SERS) that photoreaction of 4-NBA more readily occurs at the 11-MUD-derivatized Ag particles than at the 12-MDA- and DDT- derivatized Ag particles. Invoking the role of water in such photoreactions, the hydroxyl-terminated monolayers appeared to be more labile to water than the amine-terminated monolayers. The present observations clearly illustrate that commercially available powdered silver is an efficient substrate for the characterization of self-assembled monolayers on silver substrates by the simultaneous use of DRIFTS and SERS
Adsorption and stability of phthalic acid on a colloidal silver surface: surface-enhanced Raman scattering study
No full textThe adsorption characteristics of phthalic acid on a silver surface were investigated by means of surface-enhanced Raman scattering (SERS). For a reliable analysis of the SER spectrum, we also performed an ab initio vibrational wavenumber calculation, The SER spectral features dictated that the phthalic acid molecules should be bound to silver as dicarboxylate, but in contrast with earlier reports, with a strongly tilted orientation with respect to the surface normal. The degree of tilt appeared to increase with increase in the bulk pH, Such a tilted orientation was presumed to occur by the simultaneous sigma- and pi-type coordination of carboxylate groups to silver caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups. Probably owing to the latter effects, phthalic acid on silver was easily displaced with aromatic mono-acids that could be bound to silver by forming only sigma-type coordination. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for an aromatic carboxylic acid derivative to assemble a robust monolayer on a silver surface. Copyright (C) 2000 John Whey & Sons, Ltd.This work was supported by the Korea Science and Engineering Foundation(KOSEF) through the Center for Molecular Catalysis at Seoul
National University (SNU) and by the Korea Research Foundation through the Research Institute for Basic Sciences at SNU. S.W.J. thanks the KOSEF for an Intern Research Fellowship
Mixed mode excitation and low cost control IC for electronic ballast
No full textThis paper introduces a gate-driven mixed mode excitation that is applicable to dimmable electronic ballasts. The proposed approach combines the characteristics of self-oscillating mode and external excitation. In the mixed mode excitation, the metal oxide semiconductor field effect transistors in an electronic ballast are turned on by the resonant current and turned off by the gate driver, which is triggered by a low voltage control integrated circuit (IC). By adjusting this triggering point, the low voltage control IC controls the switching frequency of the electronic ballast. In the electronic ballast with mixed mode excitation, filament preheating, dimming, and protection are all implemented by the low voltage control IC, which is fabricated in a 3.3-V standard CMOS process. The proposed approach allows for the realization of a low cost and high performance electronic ballast
BONDING STRUCTURE AND OPTICAL BANDGAP OF RF-SPUTTERED HYDROGENATED AMORPHOUS-SILICON CARBIDE ALLOY-FILMS
No full textHydrogenated amorphous silicon carbide (a-Si1-xCx:H) alloy films were deposited by radio frequency (rf) magnetron sputtering at room temperature with variable rf powers. Effects of deposition parameters on the bonding structure and optical properties of the films were measured. Infrared (IR) absorption and optical transmittance measurements of films deposited under methane gas flow rates of 2 and 3 sccm showed that they differed. In the case of 2 sccm flow rate, the optical bandgaps gradually decreased with increasing rf power and slopes, B, of the Tauc plot increased up to a power of 5 W/cm2. In the case of 3 sccm flow rate, optical bandgaps increased and the slopes were invariant with power. This difference is attributed to the differences in the bond structure of the films. Under the condition of flow methane gas flow rate as in the former case, the Si-C bonding concentration is saturated and those of Si-H(n) bonds still increase while those of C-H(n) bonds decrease with power. However in the latter, both concentrations of Si-C and Si-H(n) bonds increase and those of C-H(n) bonds decrease. As a result, optical bandgaps of rf sputtered films which have a high fraction of carbon, greater than 0.65, are more influenced by the Si-C bonds than by the hydrogen-related bonds
Field emission characteristics of CoSi2/TiN-coated silicon emitter tips
No full textA CoSi2/TiN bilayer was coated on Si emitter tips and the emission characteristics of the tips were investigated. The CoSi2 layer was grown in situ by a reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt at 650 degreesC and then the TiN was deposited on the CoSi2 layer at 550 degreesC by a reactive sputtering of Ti with gas a reactive gas. The CoSi2 layer was conformally coated on the Si tips and the TiN layer adhered well to the CoSi2 layer. The CoSi2/MN-coated emitters showed a low turn-on voltage due to the low work function by TiN and a steep current increase caused by CoSi2. The current fluctuation of the CoSi2/TiN-coated Si emitter was smaller than that of the TiN-coated emitter. The long-term emission stability of the CoSi2/TiN-coated Si emitter was also greatly improved compared to the CoSi2-coated emitter because of the superior high temperature stability of the TiN layer. (C) 2002 Elsevier Science B.V. All rights reserved
Growth of in situ CoSi2 layer by metalorganic chemical vapor deposition on Si tips and its field-emission properties
No full textWe prepared Si emitters coated with a metalorganic chemical vapor deposited CoSi2 layer to improve emission properties. The CoSi2 layer was grown in situ by reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt at 650 degreesC. The CoSi2 layer was conformally deposited on the Si emitter tips and had a twinned structure at the epitaxial CoSi2/Si interface in the partial region. The CoSi2-coated Si emitters showed an enhanced emission due to the increase in the number of emitting sites from the Fowler-Nordheim plot. The fluctuation of emission current was reduced by the CoSi2 coating. But the long-term stability was not much improved, which may be due to the decrease of the field enhancement factor and the number of emitting sites of the CoSi2-coated Si tip. (C) 2001 American Vacuum Society
- …
