• Bulletin of the Korean Mathematical Society
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• v.61 no.2
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• pp.381-399
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• 2024

In this paper, we introduce a class of Moran measures generated by quasi periodic sequences, and consider power decay of the Fourier transforms of this kind of measures.

• Bulletin of the Korean Mathematical Society
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• v.57 no.6
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• pp.1393-1408
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• 2020

In this paper we mainly study existence and regularity of mild solutions to the parabolic-elliptic system of drift-diffusion type with small initial data in Fourier-Besov spaces. To be more detailed, we will explain that global-in-time mild solutions are well-posed and Gevrey regular by means of multilinear singular integrals and Fourier localization argument. Furthermore, we can get time decay rate estimate of mild solutions in Fourier-Besov spaces.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.169-173
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• 2001

This study presents the results of decoupling of free decay roll test data by discrete wavelet transform. Free roll decay test was performed to decide the coefficients of damping terms in equation of motion. During the experiment, a slight yaw motion was found while the model was in the free roll decay motion. Discrete wavelet transform was applied to the signal to extract the pure roll motion. The results were compared to those of the Fourier transform. DWT was able to decouple the two signals efficiently while the Fourier transform was not.

• Bulletin of the Korean Mathematical Society
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• v.61 no.3
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• pp.637-669
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• 2024

The goal of this paper is to study decay properties of weak solutions to Cauchy problem of the non-stationary fractional Navier-Stokes equations. By using the Fourier splitting method, we give the time L²-decay rate of weak solutions, which reveals that L²-decay is generally determined by its linear generalized Stokes flow. In second part, we establish various decay results and the uniqueness of the two dimensional fractional Navier-Stokes flows. In the end of this article, as an appendix, the existence of global weak solutions is given by making use of Galerkin' method, weak and strong compact convergence theorems.

• The Korean Journal of Ceramics
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• v.4 no.1
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• pp.28-32
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• 1998

This paper reports on photoluminescence (PL), luminescence decay curves, and compositional analysis of porous silicon(PS) which is aged under air ambient by Fourier transform infrared vibrational spectroscopy (FTIR) and by Auger electron spectroscopy (AES). Porous silicos which has been aged under air ambient yields two PL band structures, i.e. blue/violet PL and red PL. The evolution of a blue/violet band is pronounced, especially for thin PS film which is prepared in dilute HF solution. The blue/violet PL band has been observed initially to increrase rapidly with aging, then saturated with further atmospheric aging. The ambient air aged PS exhibits a fast decay time of sub-nanosecond at room temperature and shows appreciably faster decay time than that at 20K. Atmospheric aging of this thin blue/violet luminescing PS yield non-stoichiometric oxide judging from the vibrational spectra of Si-O and AES analysis.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.26 no.4
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• pp.224-243
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• 2022

In this paper, we prove the global existence of classical solutions to the 2D incompressible Boussinesq equations for the micropolar fluid. Furthermore, applying the Fourier splitting methods, we obtain the lager time decay properties.

• KIEE International Transactions on Power Engineering
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• v.5A no.2
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• pp.138-143
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• 2005

During faults, the voltage and current signals available to the relay are affected by the decaying dc component and harmonics. In order to make appropriate and accurate decisions, most of the relaying algorithms require the fundamental frequency phasor information that is immune to decaying dc effect and harmonics. The conventional Fourier ph as or estimation algorithm is affected by the presence of decaying-exponential transients in the fault signal. This paper presents a modified Fourier algorithm, which effectively eliminates the decaying dc component and the harmonics present in the fault signal. The decaying dc parameters are estimated by means of an out-of-band filtering technique. The decaying dc offset and harmonics are removed by means of a simple computational procedure that involves the design of two sets of Orthogonal digital OFT filters tuned at different frequencies and by creating three off-line look-up tables. The technique was tested for different decay rates of the decaying dc component. It was also compared with the conventional mimic plus the full cycle OFT algorithm. The results indicate that the proposed technique has a faster convergence to the desired value compared to the conventional mimic plus OFT algorithms over a wide range of decay rates. In all cases, the convergence to the desired value was achieved within one cycle of the power system frequency.

• Journal of the Korean Wood Science and Technology
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• v.47 no.1
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• pp.21-32
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• 2019

In order to investigate the decay process of wood treated with preservative, waterproofing agent and their compound systems, a full-cell process was applied to impregnate the sapwood of poplar (Populus cathay) at paraffin wax emulsion concentrations of 0.5% and 2.0%, Copper Azole (CA) concentrations of 0.3% and 0.5%, and their four compound systems, respectively. Leaching tests and laboratory decay resistance against the white-rot fungus Corious versicolor (L.) Murrill for treated wood were carried out according to the America Standard E11-06 and China Standard GB/T 13942.1-2009. At certain time intervals during the decay test, samples were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction technique (XRD) to investigate the time-dependent changes of chemical components and crystalline structure, thus clarifying the decay mechanisms. The results suggested that white-rot fungi degrade hemicellulose and lignin in the wood cell wall first, followed by a simultaneous degradation of polysaccharides and lignin. Besides, CA could not only slower the decomposition of both hemicellulose and lignin, but also reduce the degradation amount of hemicellulose. However, paraffin wax emulsion at high concentration had a negative effect on the impregnation of CA for the compound system treated wood.

• Journal of the Korean Geophysical Society
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• v.6 no.1
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• pp.25-29
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• 2003

We suggest a method that vectorially composes 3-component earthquake records in the frequency domain, to reduce the uncertainties in the analysis of the Fourier amplitude spectrum. The use of the Fourier amplitude spectrum composed from 3 components has two advantages. First, it provides a more accurate estimate of seismic moment by eliminating the vector-partition term that appears in individual component. Second, it provides more accurate estimates of seismic moment, corner frequency, high-frequency decay constant($χ$) .etc., by enhancing the shape of the Fourier amplitude spectrum. The latter is especially useful in the analysis of small earthquakes with low signal-to-noise ratios.

• Steel and Composite Structures
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• v.38 no.5
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• pp.523-531
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• 2021

The generalized thermoelastic analysis problem of a two-dimension porous medium with and without energy dissipation are obtained in the context of Green-Naghdi's (GNIII) model. The exact solutions are presented to obtain the studying fields due to the pulse heat flux that decay exponentially in the surface of porous media. By using Laplace and Fourier transform with the eigenvalues scheme, the physical quantities are analytically presented. The surface is shocked by thermal (pulse heat flux problems) and applying the traction free on its outer surfaces (mechanical boundary) through transport (diffusion) process of temperature to observe the analytical complete expression of the main physical fields. The change in volume fraction field, the variations of the displacement components, temperature and the components of stress are graphically presented. Suitable discussion and conclusions are presented.