• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.4
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• pp.216-220
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• 2018

The piezoelectric properties of $0.65Pb(Zr_{1-x}Ti_x)O_3-0.35Pb(Zn_{1/6}Ni_{1/6}Nb_{2/3})O_3$ ($PZT_x-PZNN$) ceramics with $0.530{\leq}x{\leq}0.555$ were investigated for application to piezoelectric energy harvesters. Although a morphotropic phase boundary (MPB) was found at approximately x = 0.545, the ceramic with the highest figure of merit (FOM) ($d_{33}{\times}g_{33}$) was observed at a composition of x = 0.540. Values of this figure of merit, $d_{33}{\times}g_{33}$, of $19.6pm^2/N$ and $20.2pm^2/N$ were obtained from $PZT_{0.540}-PZNN$ ceramics sintered at $920^{\circ}C$ and $950^{\circ}C$, respectively. A high output power of $937{\mu}W$ and a high power density of $3.3mW/cm^3$ were obtained from unimorph-type piezoelectric energy harvesters fabricated using $PZT_{0.540}-PZNN$ ceramic sintered at $920^{\circ}C$ for 4h.

• Transactions on Electrical and Electronic Materials
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• v.17 no.3
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• pp.159-162
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• 2016

We studied an electrolyte-dielectric metal (EDM) device based on a Si₃N₄ layer-coated anodic aluminium oxide (AAO) template for chemical sensors. The AAO templates were fabricated using a two-step anodization procedure at 0℃ and 70 V in 0.3 M oxalic acid, after which the Si₃N₄ was deposited on them using plasma enhanced chemical vapor deposition (PECVD). The average pore size was approximately 106 nm and the depth of the AAO templates was 24.6 nm to 86.5 nm. The Si₃N₄ layer-coated AAO is more stable than a single AAO template.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.269-276
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• 2009

The local preconditioning method has both robust convergence and accurate solutions by using local flow properties for parameters in the preconditioning matrix. Preconditioning methods have been very effective to low speed inviscid flows. In the viscous and turbulent flows, deterioration of convergence should be overcame on the high aspect ratio grids to get better convergence and accuracy. In the present study, the local time stepping and min-CFL/max-VNN definitions are applied to compare the results and we propose the method that switches between two methods. The min-CFL definition is applied for inviscid flow problems and the min-CFL/max-VNN definition is implemented to viscous and turbulent flow problems.

• ETRI Journal
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• v.33 no.1
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• pp.32-38
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• 2011

We investigated the light-emitting performances of blue phosphorescent organic light-emitting diodes, known as PHOLEDs, by incorporating an N,N'-dicarbazolyl-3,5-benzen interlayer between the hole transporting layer and emitting layer (EML). We found that the effects of the introduced interlayer for triplet exciton confinement and hole/electron balance in the EML were exceptionally dependent on the host materials: 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole, 9-(4-tert-butylphenyl)-3,6-ditrityl-9H-carbazole, and 4,4'-bis-triphenylsilanyl-biphenyl. When an appropriate interlayer and host material were combined, the peak external quantum efficiency was greatly enhanced by over 21 times from 0.79% to 17.1%. Studies on the recombination zone using a series of host materials were also conducted.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.670-677
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• 1998

Many of the adaptive noise control systems utilize a form of the least mean square (LMS) algorithm. In the active control of noise, it is common practice to locate an error microphone far from the control source to avoid the near-field effects by evanescent waves. Such a distance between the control source and the error microphone makes a certain level of time-delay inevitable and, hence, may yield undesirable effects on the convergence properties of control algorithms such as filtered-x LMS. This paper discusses the dependence of the convergence rate on the acoustic error path in these popular algorithms and introduces new algorithms which increase the convergence region regardless of the time-delay in the acoustic error path. Performances of the new LMS algorithms are presented in comparison with those by the conventional algorithms based on computer stimulations and experiments.

• Korean Journal of Mathematics
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• v.26 no.3
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• pp.483-501
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• 2018

In this paper, we present some recent results on weighted pointwise convergence and the rate of pointwise convergence for the family of nonlinear double singular integral operators in the following form: $$T_{\eta}(f;x,y)={\int}{\int\limits_{{\mathbb{R}^2}}}K_{\eta}(t-x,\;s-y,\;f(t,s))dsdt,\;(x,y){\in}{\mathbb{R}^2},\;{\eta}{\in}{\Lambda}$$, where the function $f:{\mathbb{R}}^2{\rightarrow}{\mathbb{R}}$ is Lebesgue measurable on ${\mathbb{R}}^2$ and ${\Lambda}$ is a non-empty set of indices. Further, we provide an example to support these theoretical results.

• Honam Mathematical Journal
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• v.36 no.3
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• pp.669-678
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• 2014

We investigate various properties of ${\kappa}$-net convergence structures and define a ${\kappa}$-net-based continuous function on ${\kappa}$-net $\mathcal{L}^+$-convergence structures, and study relationships between continuity and ${\kappa}$-net-based continuity on ${\kappa}$-net $\mathcal{L}^+$-convergence structures. We also provide some characterizations of ${\kappa}$-net-based continuity.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.895-897
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• 2008

ZnO films were fabricated using rf-magnetron sputter deposition process with different $N_2$ ambient. N-content in N-doped ZnO films was less than 1%. The wavelength of the highest intensity PL peak of N-doped ZnO was shifted to higher wavelength with increasing $N_2$ flow rate in the deposition ambient. These results indicated that the optical property of ZnO was significantly affected by the defect level created by doping with a very small amount of N.

• International Journal of Control, Automation, and Systems
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• v.6 no.4
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• pp.559-570
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• 2008

This paper proposes an improved particle swarm optimization named PSO with Controllable Random Exploration Velocity (PSO-CREV) behaving an additional exploration behavior. Different from other improvements on PSO, the updating principle of PSO-CREV is constructed in terms of stochastic approximation diagram. Hence a stochastic velocity independent on cognitive and social components of PSO can be added to the updating principle, so that particles have strong exploration ability than those of conventional PSO. The conditions and main behaviors of PSO-CREV are described. Two properties in terms of "divergence before convergence" and "controllable exploration behavior" are presented, which promote the performance of PSO-CREV. An experimental method based on a complex test function is proposed by which the proper parameters of PSO-CREV used in practice are figured out, which guarantees the high exploration ability, as well as the convergence rate is concerned. The benchmarks and applications on FCRNN training verify the improvements brought by PSO-CREV.

• The Pure and Applied Mathematics
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• v.24 no.4
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• pp.201-209
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• 2017

We prove convergence properties of the global solutions to the cooperative cross-diffusion system with the intra-specific cooperative pressures dominated by the inter-specific competition pressures and the inter-specific cooperative pressures dominated by intra-specific competition pressures. Under these conditions the $W^1_2-bound$ and the time global existence of the solution for the cooperative cross-diffusion system have been obtained in [10]. In the present paper the convergence of the global solution is established for the cooperative cross-diffusion system with large diffusion coefficients.