• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.277-277
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• 2013

The epitaxial graphene on the 4H- or 6H-SiC(0001) surface has been intensively studied due to the possibility of wafer-scale growt. However the existence of interface layer (zero layer graphene) and its influence on the upper graphene layer have been considered as one of the main obstarcles for the industrial application. Among various methods tried to overcome the strong interaction with the substrate through the interface layer, it has been proved that the hydrogen intercalation successfully passivate the Si dangling bond of the substrate and can produce the quasi-free standing epitaxial graphene (QFEG) layers on the siC(0001) surface. In this study, we report the results of the angle-resolved photoemission spectroscopy (ARPES) and Raman spectroscopy for the QFEG layers produced by ex-situ and in-situ hydrogen intercalation.From the ARPES measurement, we confirmed that the Dirac points of QFEG layers exactly coincide with the Fermi level. The band structure of QFEG layer are sustainable upon thermal heating up to 1100 K and robust against the deposition of several metals andmolecular deposition. We also investigated the strain of the QFEG layers by using Raman spectroscopy measurement. From the change of the 2D peak position of graphene Raman spectrum, we found out that unlike the strong compressive strain in the normal epitaxial graphene on the SiC(0001) surface, the strain of the QFEG layer are significantly released and almost similar to that of the mechanically exfoliated graphene on the silicon oxide substrate. These results indicated that various ideas proposed for the ideal free-standing graphene can be tested based on the QFEG graphene layers grown on the SiC(0001) surface.

• Journal of the Korean Society of Visualization
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• v.15 no.3
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• pp.47-51
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• 2017

In this study, we investigate the wake characteristics in laminar inflow and two different turbulent inflow cases. To solve the flow with wind turbines and its wake, we use large eddy simulation (LES) technique with actuator line method (ALM) and turbulent inflow of Turbsim. We perform the quantitative analysis of velocity deficit and turbulent intensity in laminar inflow case and turbulent inflow case with different turbulent intensity. In turbulent inflow, unsteady strong wake recovery which is highly fluctuated in time. Normalized power in turbulent inflow case is also highly fluctuated with unsteady wake recovery, while that in laminar inflow has quasi steady characteristic in power generation.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.103-107
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• 2009

Intramolecular association is an important contribution to the overall hydrogen bonding in supercritical fluid systems, especially in systems of colloidal and biological interest. Amphiphile systems, especially micelle and microemulsion systems, showed highly non-ideal behavior due to the intermolecular association and intramolecular association. The objective of this research is to present a lattice fluid equation of state that combines the quasi-chemical nonrandom lattice fluid model with modified Veytsman statistics for intra + inter molecular association to calculate phase behavior for mixture containing surfactant systems. The present EOS could correlate the literature data well for mixtures containing nonionic surfactant systems.

• Proceedings of the KAIS Fall Conference
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• 2012.05a
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• pp.177-181
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• 2012

Association is an important contribution to the overall hydrogen bonding in surfactant systems, especially in systems of colloidal and biological interest. Amphiphile systems, especially micelle and microemulsion systems, showed highly non-ideal behavior due to the intermolecular association and intramolecular association. The objective of this research is to present a lattice fluid equation of state that combines the quasi-chemical nonrandom lattice fluid model with modified Veytsman statistics for intra + inter molecular association to calculate phase behavior for mixture containing surfactant systems. The present EOS could correlate the literature data well for mixtures containing nonionic surfactant systems.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.10
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• pp.830-839
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• 1991

The correlation between electrical (derivativer) characteristics and electro-optical conversion characteristics of laser diodes has been investigated both theoretically and experimentally with emphasis on the nonideal behavior. Laser diodes are electrically pumped devices with the current resulting from the carrier recombination dynamics, and their junction voltage is given by the separation of the quasi-Fermi levels which are determined by the injected carrier concentration. Thus most of the informaiton related to laser diode operation characteristics is reveraled in the electrical characteristics which are relatively simple to measure with sufficient accuracy. Therefore the measurement of electrical characteristics and their derivatives is a very useful tool of laser diode characteristion.

• Bulletin of the Korean Mathematical Society
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• v.43 no.4
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• pp.723-735
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• 2006

In [2] it was shown that a 1-generator quasi-cyclic code C of length n = ml of index l over $\mathbb{Z}_4$ is free if C is generated by a polynomial which divides $X^m-1$. In this paper, we prove that a necessary and sufficient condition for a cyclic code over $\mathbb{Z}_pk$ of length m to be free is that it is generated by a polynomial which divides $X^m-1$. We also show that this can be extended to finite local rings with a principal maximal ideal.

• Journal of Communications and Networks
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• v.16 no.6
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• pp.620-626
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• 2014

In this paper, we propose a parallel collaborative sphere decoder with a scalable architecture promising quasi-maximum likelyhood performance with a relatively small amount of computational resources. This design offers a hardware-friendly algorithm using a modified node operation through fixing the variable complexity of the critical path caused by the sequential nature of the conventional sphere decoder (SD). It also reduces the computational complexity compared to the fixed-complexity sphere decoder (FSD) algorithm by tree pruning using collaboratively operated node operators. A Monte Carlo simulation shows that our proposed design can be implemented using only half the parallel operators compared to the approach using an ideal fully parallel scheme such as FSD, with only about a 7% increase of the normalized decoding time for MIMO dimensions of $16{\times}16$ with 16-QAM modulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.6
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• pp.1453-1462
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• 1996

A numerical simulation is carried out on the directiveity synthesis of ultrasonic transducers by point source array. Directive method with combined LMS(Least-Mean-Square) method is practiced by means of a iterative method to realize the desired directivity. The directiviey of quasi-ideal beam with a beam width and a directive arbitrary specified was chosen. On the numerical resut, Proposed algorithm shows higher speed of clculating simulation than that of LMS method, and make adaptive control, which enables the desired directivity. Numerical simulations are carried out by PC(CPU:80486 DX2, RAM 16Mbyte).

• Journal of electromagnetic engineering and science
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• v.13 no.4
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• pp.259-262
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• 2013

This paper analyzes the effects of metamaterial slabs with negative permeability when applied to a two-loop wireless power transmission (WPT) system, both in theory and electromagnetic (EM) simulations. The analysis of magnetic flux focusing provided here assumes quasi-magnetostatics or magnetostatics. The slab structures with negative permeability have been realized using the periodically arrayed ring resonators (RRs) at 13.36MHz. Some examples with ideal lossless slabs of -1, -2, and -3 showed a great enhancement of WPT efficiencies when compared with the free space cases. However, practical lossy slabs made of planar copper RRs did not show significant enhancement of WPT efficiencies due to the relatively high losses in the ring resonator (or in the slab consisting of RRs) near the resonant frequency.

• Communications of the Korean Mathematical Society
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• v.37 no.2
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• pp.399-407
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• 2022

In this paper, we continue to study the von Neumann regularity of rings whose essential maximal right ideals are GP-injective. It is proved that the following statements are equivalent: (1) R is strongly regular; (2) R is a 2-primal ring whose essential maximal right ideals are GP-injective; (3) R is a right (or left) quasi-duo ring whose essential maximal right ideals are GP-injective. Moreover, it is shown that R is strongly regular if and only if R is a strongly right (or left) bounded ring whose essential maximal right ideals are GP-injective. Finally, we prove that a PI-ring whose essential maximal right ideals are GP-injective is strongly π-regular.