• Journal of Power Electronics
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• v.15 no.4
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• pp.1035-1046
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• 2015

This study presents a practical implementation of a multi-mode two-phase interleaved boost converter for fuel cell electric vehicle application. The main operating modes, which include two continuous conducting modes and four discontinuous conducting modes, are discussed. The boundaries and transitions among these modes are analyzed with consideration of the inductor parasitic resistance. The safe operational area is analyzed through a comparison of the different operating modes. The output voltage and power characteristics with open-loop or closed-loop operation are also discussed. Key performance parameters, including the DC voltage gain, input ripple current, output ripple voltage, and switch stresses, are presented and supported by simulation and experimental results.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.3-8
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• 2000

Chemical nature of nascent metal surfaces which is one of the important active sources for tribochemical reactions was investigated using a newly developed method. Some enhanced activities were observed. For example, organic compounds chemisorbed on nascent gold surfaces and aromatic compounds decomposed on nascent nickel surfaces resulting in hydrogen evolution. Non-polar compounds such as organic sulfides had a higher chemisorption activity on nascent steel surfaces than polar compounds such as fatty acids and phosphates. Organic sulfides reacted directly with nascent steel surfaces and the surface was covered with metal sulfides. The activity for the chemisorption of organic compounds was closely dependent on the electronic structure of metals. Although benzene chemisorbed very easily on nascent surfaces of transition metals, it did not chemisorb ell nascent surfaces of simple metals. Boundary lubricating behaviors of extreme pressure additives were explained on the bases of the chemical activities of nascent surfaces obtained in this investigation. Under mild conditions, polar compounds such as fatty acids and phosphates were effective for boundary lubrication, because surfaces are covered with oxide layers. On the other hand, sulfides were more effective under severe conditions where the oxide layers were removed and the nascent surfaces were formed.

• Bulletin of the Korean Chemical Society
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• v.15 no.1
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• pp.64-74
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• 1994

The nonstoichiometric chalcogenides with NaCl-type structure were prepared and the physical and structural properties were studied. The homogeneous range and the structural change were studied based on X-ray powder diffractions using Rietveld-type full-profile fitting technique. Wide homogeneous ranges were observed in Y-S and Y-Se systems, and relatively narrow homogeneous ranges were observed in Yb-S and Yb-Se systems. Both in $Yb_{1-x}S\;and\;Yb_{1-x}Se$, a vacancy ordering transition occurred in (111) plane direction. The ordered superstructure had cubic symmetry(Fm$\bar{3}m) with doubled unit cell "a" parameter compared to the original NaCl-type. The superlattice developed in a continuous second-order transitiion was characterized by the reduced waved vector k= $(a^*+b^*+c^*)/2$. Y-S system had metallic, and YSe, YbSe system had semiconducting properties in their homogeneous ranges. It was observed that the change of electronic transport properties in extended homogeneous range did not depend on the relativeratio of metal to nonmetal, but on the quantities of vacancies.

• Bulletin of the Korean Chemical Society
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• v.10 no.2
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• pp.142-147
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• 1989

Fluorescence enhancements of ethidium bromide (EB) by solution species of low molecular weights such as DNA base molecules and nucleosides in water are reported. The degree of enhancements was determined by intensity as well as lifetime measurements for EB fluorescence. Experiments including solvent effects on absorbance and fluorescence spectra of EB, effects of protonation on the EB absorbance spectrum, and determination of equilibrium constants for EB-DNA bases have been performed to help explain the fluorescence enhancement. The results suggest that the excited state stabilization in the hydrophobic environment, the loss of torsional/vibrational energy of amino groups, and the change in the electronic transition characteristics are all responsible for the fluorescence enhancement.

• Bulletin of the Korean Chemical Society
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• v.16 no.10
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• pp.929-933
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• 1995

The electronic band structure and electrical properties of KMo4O6 containing chains of condensed molybdenum octahedra are analyzed by means of the extended Hu&ckel tight-binding method. KMo4O6 has partially filled bands of 1D as well as 3D character. They also exhibit the anisotropic band dispersions with bandwidths much larger along the c* axis than along the directions perpendicular to it. Thus, conduction electrons are essentially delocalized along the c* direction (i.e., the chain of condensed molybdenum octahedra) in the solid. The 1D band of two partially filled d-block bands leads to Fermi surface nesting with the wave vector q=0.3c*. The CDW instability due to this nesting is expected to cause the phase transition associated with the resistivity anomaly at low temperature. The characteristics of metallic behavior in the crystallographic ab plane are explained on the basis of the unnested 2D Fermi surfaces.

• Bulletin of the Korean Chemical Society
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• v.12 no.4
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• pp.406-410
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• 1991

Second order rate constants have been measured spectrophotometrically for reactions of 4-nitrophenyl substituted benzoates with various aryloxides and aryl benzoates with p-chlorophenoxide. The reactivity has exhibited significant dependences on the electronic nature of the substituent in the acyl moiety of the substrate and in the nucleophilic phenoxide, while the substituent in the leaving phenoxide has little influenced the reactivity. The Bronsted coefficient $\beta$ values so obtiained support that the present acyl transfer reaction proceeds via a stepwise mechanism in which the nucleophilic attack would be the rate-determining step. Interestingly, the magnitude of the $\betaacyl$ and $\beta$ nuc increases with increasing reactivity, implying that the reactivity selectivity principle is not operative in the present system. The failure of the reactivity selectivity principle is attributed to a change in transition state structure upon the substituent variation in the present acyl transfer reaction.

• Bulletin of the Korean Chemical Society
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• v.19 no.2
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• pp.202-206
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• 1998

The p-fluorotoluene was vibronically excited in a jet with a buffer gas He in a corona excited supersonic expansion. The vibronic emission spectrum of the jet cooled p-fluorotoluene in the transition of S1 → S0 has been recorded with a Fourier transform spectrometer in the uv region. The spectrum observed was analyzed to obtain accurate vibrational frequencies in the ground electronic state by comparing with those reported previously. The origin of the low frequency sequence bands observed in this work was discussed. Also, the absence of significant intensity of hot band resulting from the excited vibrational states in the spectrum suggests extensive vibrational cooling in the source.

• Bulletin of the Korean Chemical Society
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• v.16 no.3
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• pp.226-232
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• 1995

The electronic structures of the C60, (H3P)2Pt(η2-C2H4) and (H3P)2Pt(η2-C60) are calculated by using the EHMO method with the fragment analysis. We have modified the EHT parameters so as to yield the orbital energy level correlation and to fit the optical transition gap to the previous theoretical results of C60. In Pt-derivatives, our FMO results with the modified parameters show that the carbon-carbon double bonds of C60 and ethene react like those of electron-poor arenes and alkenes, and also that C60 is more electron-susceptive than C2H4.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.5
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• pp.678-681
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• 2020

In this paper, we analyzed the noise figure of cascode low noise amplifier (LNA) based on the measured data of 65nm CMOS devices. By using the channel thermal noise model of transistors, we expanded noise figure equation and divided the equation into three parts to see its contributions to noise figure. We also varied design parameters such as bias point, transistor gate width, and operating frequency. Our results show that different noise sources dominate at the different operating frequencies. One can easily find the noise transition frequency with device models in ahead of the practical design. Therefore, this research provides a low noise design approach for different operating frequencies.

• International Journal of Computer Science & Network Security
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• v.22 no.2
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• pp.297-303
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• 2022

The main purpose of the study is to determine the main aspects of the problem of socio-economic development in the conditions of the digital economy. The post-industrial era is characterized by the development of the electronic environment and the transition to an information civilization. In this regard, the developed countries of the world pay considerable attention to the development of the digital economy. However, there are a significant number of problems associated with this process. The country cannot be successful in the development of the digital economy in the absence of the necessary legal framework, an economic development strategy based on digital technologies. The research methodology involves the use of several theoretical methods for analyzing and synthesizing information. As a result of the study, the key problems of socio-economic development in the digital economy were characterized.