• Bulletin of the Korean Chemical Society
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• 제20권11호
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• pp.1269-1276
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• 1999

Metallocenes, whether using a cocatalyst or not, act as catalysts in ethylene polymerization. The positive charge on the transition metal of a metallocene might have an important role in polymerization as an active site in our model approach. Using semiempirical calculations in the absence of cocatalyst, we show one of the possibilities that the positive charge on a metallocene might be more easily transferred through the Cp ring of a ligand to the ethylene than to transfer directly from the transition metal to the ethylene. In these calculations, the charge on titanium in an eight C2H4 system is transferred and a polymer chain is produced. This reaction takes place only when ethylenes are arranged in a particular direction with respect to the ring, but does not take place for ethylenes near Ti or Cl atoms. The same mechanism is shown for a metallocene ligand which is sterically hindered or where the Cp ring is replaced by fluorenyl. These results suggest an entirely new polymerization mechanism in the absence of a cocatalyst in which the Cp ring is the active site.

• 한국자기공명학회논문지
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• 제22권4호
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• pp.144-148
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• 2018

Catalytic enzyme Pyrazinamidase (PncA) from Mycobacterium tuberculosis can hydrolyze substrate pyrazinamide (PZA) to pyrazoic acid (POA) as active form of compound. Using NMR spectroscopy, pH-dependent catalytic properties were monitored including metal binding mode during converting PZA to POA. There seems to be a conformational change through zinc binding in active site from the perturbation of peak intensities in series of 2D HSQC spectra the conformation changes through zinc binding.

• Mass Spectrometry Letters
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• 제14권3호
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• pp.79-90
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• 2023

Natural goods, especially therapeutic plants, are abundant in the World. Because they have the ability to provide all humanity with countless advantages as a source of medicines, medicinal plants are presently receiving more attention than ever. These plants' therapeutic efficacy is based on bioactive phytochemical components that have clear physiological effects on the human body. The drying process is crucial for the preparation of plant materials prior to extraction since freshly harvested plant materials include active enzymes that create active components, intermediates, and metabolic processes. Many of the phytoconstituents may be extracted using the semi-polar solvent methanol. The goal of the current work is to use the GC-MS gas chromatography- mass spectrometry technology to identify the phytochemicals and review their biological activity. In methanol leaf extract, 5 phytocompounds were found in Ricinus communis, 5 phytocompounds in Pongamia pinnata, 12 phytocompounds in Datura metal, 7 phytocompounds in Azadirachta indica, 11 phytocompounds in Acalypha indica.

• Journal of Microbiology and Biotechnology
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• 제8권5호
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• pp.471-477
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• 1998

Taq DNA polymerase from Thermus aquaticus is very useful in the polymerase chain reaction. Taq DNA polymerase is classified in the pol I family, represented by E. coli DNA polymerase I. The three-dimensional structural alignment of 3'-5'exonuclease domains from the pol I family DNA polymerases explains why Taq DNA polymerase does not carry out proofreading in polymerase chain reactions. Three sequence motifs, Exo I, II, and III, must exist to carry out 3'-5'exonuclease activity for proof- reading by a 3'-5'exonuclease reaction, but these are abolished in Taq DNA polymerase. The key catalytic module in 3'-5'exonuclease is two metal ions chelated by four active-site carboxylic amino acids. Taq DNA polymerase was mutagenized to construct the catalytic module in the active site. The circular dichroism technique supported the formation of the catalytic module, and the radioactive assay showed that the 3'-5'exonuclease activity doubled in the mutant Taq DNA polymerase.

• 센서학회지
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• 제27권3호
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• pp.160-164
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• 2018

In this paper, a wide dynamic range complementary metal-oxide-semiconductor (CMOS) image sensor with the adjustable sensitivity by using cascode metal-oxide-semiconductor field-effect transistor (MOSFET) and inverter is proposed. The characteristics of the CMOS image sensor were analyzed through experimental results. The proposed active pixel sensor consists of eight transistors operated under various light intensity conditions. The cascode MOSFET is operated as the constant current source. The current generated from the cascode MOSFET varies with the light intensity. The proposed CMOS image sensor has wide dynamic range under the high illumination owing to logarithmic response to the light intensity. In the proposed active pixel sensor, a CMOS inverter is added. The role of the CMOS inverter is to determine either the conventional mode or the wide dynamic range mode. The cascode MOSFET let the current flow the current if the CMOS inverter is turned on. The number of pixels is $140(H){\times}180(V)$ and the CMOS image sensor architecture is composed of a pixel array, multiplexer (MUX), shift registers, and biasing circuits. The sensor was fabricated using $0.35{\mu}m$ 2-poly 4-metal CMOS standard process.

• Bulletin of the Korean Chemical Society
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• 제35권6호
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• pp.1659-1664
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• 2014

A porous metal-organic framework (MOF), MIL-101, was synthesized in the presence of sulfated zirconia (SZ) to produce acidic SZ/MIL-101 composites for the first time. The composites were characterized with XRD, nitrogen adsorption, FT-IR, scanning electron microscope, chemical analysis and so on. The composites (SZ/MIL-101s) were successfully applied in a liquid-phase esterification for a high yield of ester. This catalytic result of SZ/MIL-101, compared with that of pure SZ or MIL-101 (showing a negligible yield of ester), suggests that the SZ in the composite is highly active in the acid catalysis probably because of the well-dispersed active species of SZ. Moreover, the esterification is catalyzed in heterogeneous mode as confirmed by negligible esterification after filtration of the catalyst. Finally, microwaves can be efficiently applied both in the synthesis of the composites and the esterification reaction to accelerate the two processes of synthesis and esterification by about 5 times.

• 대한조선학회 특별논문집
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• 대한조선학회 2006년도 특별논문집
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• pp.128-133
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• 2006

Generally, porosity which was formed by pyrolysis of the primer is usually generated in the weld metal in respect of increase of the welding speed. in order to analyze the cause of porosity generation, this study was performed using FCAW(flux cored arc welding) process for three kinds of inorganic.zinc primer. in addition the evaluation by influence of welding method on porosity generation is conducted to compare between FCAW and MAG(metal active gas) welding with the same inorganic zinc primer. As the result of this investigation, not only primer of lower organic binder and zinc but also FCAW process than MAG in fillet welding have been verified the excellent resistance to the porosity generation for horizontal fillet welding.

• Nuclear Engineering and Technology
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• 제48권5호
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• pp.1096-1108
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• 2016

Metal fuel is being developed for the prototype generation-IV sodium-cooled fast reactor (PGSFR) to be built by 2028. U-Zr fuel is a driver for the initial core of the PGSFR, and U-transuranics (TRU)-Zr fuel will gradually replace U-Zr fuel through its qualification in the PGSFR. Based on the vast worldwide experiences of U-Zr fuel, work on U-Zr fuel is focused on fuel design, fabrication of fuel components, and fuel verification tests. U-TRU-Zr fuel uses TRU recovered through pyroelectrochemical processing of spent PWR (pressurized water reactor) fuels, which contains highly radioactive minor actinides and chemically active lanthanide or rare earth elements as carryover impurities. An advanced fuel slug casting system, which can prevent vaporization of volatile elements through a control of the atmospheric pressure of the casting chamber and also deal with chemically active lanthanide elements using protective coatings in the casting crucible, was developed. Fuel cladding of the ferritic-martensitic steel FC92, which has higher mechanical strength at a high temperature than conventional HT9 cladding, was developed and fabricated, and is being irradiated in the fast reactor.

• 전자공학회논문지B
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• 제33B권4호
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• pp.52-62
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• 1996

In this paper, a new continuous-time current-mode integrator as basic building block of the low-voltage analog current-mode active filters was proposed. Compared to the current-mode integrator which was proposed by Zele, the proposed current-mode integrator had higher unity gain frequency and output impedance in addition to lower power dissipation. And also, a current-mode third-order lowpass active filter was designed with the proposed current-mode integrator. The designed circuits were fabricated using the ORBIT's 1.2.mu.m double-poly double-metal CMOS n-well process. The experimental resutls of the active filter designed and fabricated for this research have shown that it has the performance of 44.5MHz cutoff frequency, 3.3mW power dissipation and the third-order active filter area was 0.12mm$^{2}$.

• Journal of Welding and Joining
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• 제32권5호
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• pp.26-31
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• 2014

Conventional TIG(C-TIG) welding process guarantees higher quality weldment when compared with other processes. However, C-TIG with inherent low penetration shows disadvantages in productivity, especially for thick-walled structure. To overcome these handicaps, active-flux TIG(A-TIG) welding has been introduced and studied widely in a motivation to improve both quality and productivity. Present study made a focus on optimum combination of oxide components to enhance arc contraction and penetration. Results indicated that arc contraction inducing enhancement of penetration could be possible when composition of active fluxes was well matched with base metal.