• Journal of The Korean Astronomical Society
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• v.29 no.2
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• pp.137-156
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• 1996

NGC 6716 is an intermediate-age open cluster in Sagittarius. In this paper, we present the new UBV CCD photometry of the stars in the cluster, which is deeper than previous ones. From the color-color diagram and the color-magnitude diagram, we derived a reddening $E_{B- V} = 0.17\pm0.03$ and a distance modulus of the cluster, $(V - Mv)_o = 9.2\pm0.1$. An age of the cluster is estimated as $8\pm10^7 yrs$ from the latest isochrone. Luminosity function and mass function of the cluster are derived. The gradient of the mass function of bright stars is a bit steep, $\Gamma = -1.85\pm0.05$, and there is no distinct bump and dip in the mass function.

• Communications of the Korean Mathematical Society
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• v.21 no.3
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• pp.419-428
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• 2006

The Berezin transform is the analogue of the Poisson transform in the Bergman spaces. Dyakonov characterize the holomorphic weighted Lipschitz function in the unit disk in terms of the Possion integral. In this paper, we characterize the harmonic weighted Lispchitz function in terms of the Berezin transform instead of the Poisson integral.

• Polymer(Korea)
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• v.24 no.2
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• pp.259-267
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• 2000

Gel polymer electrolytes were prepared from poly(vinylidene fluoride-co-hexafluoro propylene)[P(VdF-co-HFP)] that had higher mechanical properties as well as higher dielectric constant ($\varepsilon$=8~13) than other polymeric matrix. Mechanical properties and ionic conductivities have been investigated as a function of blend ratio of electrolyte solution and polymer matrix. Ethylene carbonate (EC)/${\gamma}$-butyrolactone (${\gamma}$-BL) and lithium triflate (LiCF$_3$SO$_3$) were used as solvent and salt, respectively. The mechanical properties such as tensile strength, tensile modulus, compression modulus, and dynamic shear modulus were evaluated. The highest ionic conductivity was 1.09$\times$10$^{-3}$ S/cm for PVH40 containing 28.6 wt% of P(VdF-co-HFP) at $25^{\circ}C$. Tensile strength, tensile modulus and compression modulus were increased with P(VdF-co-HFP) content and abruptly changed between PVH70 and PVH80. Dynamic shear moduli showed a typical gel behavior and changed with shear strain.

• Journal of the Korean Wood Science and Technology
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• v.34 no.1
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• pp.32-39
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• 2006

The acoustic properties of various coatings for stringed musical instruments made were investigated. The applied coatings were urethane topcoat, oil stain and UV-curable epoxy coating. Acoustic properties of coatings inferred from the elastic modulus and the shear modulus that ware calculated from a resonance frequency and a damping measured by FFT analyzer. The relationship between elastic modulus and density and the relationship between elastic modulus and shear modulus of coatings for stringed musical instruments ware investigated as a function of coating thickness.

• Communications of the Korean Mathematical Society
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• v.26 no.1
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• pp.67-77
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• 2011

We find some Eisenstein series related to modulus 4 using a theta function identity of McCullough and Shen and residue theorem for elliptic functions.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.371-379
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• 2008

In this study, seismic elastic wave and dynamic elastic modulus properties are investigated by down-hole seismic tests that were applied to the 11 gneiss area. The research results show that the realtionship between the two properties are $V_s=0.5589{\times}V_p$ in gneiss. The relationship between the two properties are separated into two groups. Group 1 is influenced mainly by the specific gravity of rock, but group 2 is influenced mainly by the joint aperture. As weathering progresses, group 1 clearly shows a decreasing tendency. In fresh and slightly weathered rock-mass, correlations between $V_p$ and dynamic elastic modulus is expressed in linear line but in moderately-highly weathered rock-mass, correlations between $V_p$ and dynamic elastic modulus is expressed curve as a quadratic function. Correlations between $V_s$ and dynamic elastic modulus are analyzed similar with a $V_p$ case.

• Restorative Dentistry and Endodontics
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• v.29 no.6
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• pp.489-497
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• 2004

Objective: The purpose of this study was to investigate the viscoelastic properties related to handling characteristics of composite resins, Methods: A custom designed vertical oscillation rheometer (VOR) was used for rheological measurements of composites. The VOR consists of three parts: (1) a measuring unit, (2) a deformation induction unit and (3) a force detecting unit, Two medium viscous composites, Z100 and Z250 and two packable composites, P60 and SureFil were tested. The viscoelastic material function, including complex modulus $E^{*}$ and phase angle ${\delta}$, were measured. A dynamic oscillatory test was used to evaluate the storage modulus (E'), loss modulus (E") and loss tangent ($tan{\delta}$) of the composites as a function of frequency ($\omega$) from 0.1 to 20 Hz at $23^{\circ}C$. Results: The E' and E" increased with increasing frequency and showed differences in magnitude between brands. The $E^{*}s$ of composites at ${\omega}{\;}={\;}2{\;}Hz$, normalized to that of Z100, were 2.16 (Z250), 4,80 (P60) and 25.21 (SureFil). The magnitudes and patterns of the change of $tan{\delta}$ of composites with increasing frequency were significantly different between brands. The relationships between the complex modulus $E^{*}$, the phase angle ${\delta}$ and the frequency \omega were represented by frequency domain phasor form, $E^{*}{\;}(\omega){\;}={\;}E^{*}e^{i{\delta}}{\;}={\;}E^{*}{\angle}{\delta}$. Conclusions: The viscoelasticity of composites that influences handling characteristics is significant different between brands, The VOR is a relatively simple device for dynamic, mechanical analysis of high viscous dental composites. The locus of frequency domain phasor plots in a complex plane is a valuable method of representing the viscoelastic properties of composites.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.48.1-48.1
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• 2021

Gaussian process regression (GPR) is a powerful method used for model-independent analysis of cosmological observations. In GPR, it is important to decide an input mean function and hyperparameters that affect the reconstruction results. Depending on how the input mean function and hyperparameters are determined in the literature, I divide into four main applications for GPR and compare their results. In particular, a zero mean function is commonly used as an input mean function, which may be inappropriate for reconstructing cosmological observations such as the distance modulus. Using mock data based on Pantheon compilation of type Ia supernovae, I will point out the problem of using a zero input and suggest a new way to deal with the input mean function.

• Journal of IKEEE
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• v.13 no.1
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• pp.1-10
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• 2009

Recently, some frequency domain CMA (Constant Modulus Algorithm) have been introduced in an effort to reduce computational complexities [1,2]. In [1], a fast algorithm that minimizing cost function designed for block input signal is employed, while in [2], a novel cost function that minimizing sample by sample input is used. Although, the two fast algorithm save computational complexities as compared to CMA, the convergence behaviors of the two fast algorithm show different results with repsect to CMA. Thus, in this paper, some analytical results on the error surface of the fast frequency domain CMA are introduced. From the analytical results, we show that the more recent algorithm [2] outperforms the previous algorithm [1]. Simulation results reveals that the recent algorithm [2] shows 50% enhanced convergence with respect to the old fast algorithm [1]. Also, we show that the recent fast algorithm [2] has comparable convergence performance with respect to conventional CMA algorithm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.11
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• pp.949-955
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• 2009

In this study, we investigated the effects of Cr dopant (1.0 at% $Cr_2O_3$ sintered at $1000^{\circ}C$ for 1 h in air) on the bulk trap (i.e. defect) and interface state levels of ZnO using dielectric functions ($Z^*$, $M^*$, $Y^*$, $\varepsilon^*$, and $tan{\delta}$), admittance spectroscopy (AS), and impedance-modulus spectroscopy (IS & MS). For the identification of the bulk trap levels, we examine the zero-biased admittance spectroscopy and dielectric functions as a function of frequency and temperature. Impedance and electric modulus spectroscopy is a powerful technique to characterize grain boundaries of electronic ceramic materials as well. As a result, three kinds of bulk defect trap levels were found below the conduction band edge of ZnO in 1.0 at% Cr-doped ZnO (Cr-ZnO) as 0.11 eV, 0.21 eV, and 0.31 eV. The overlapped defect levels ($Zn^{..}_i$ and $V^{\cdot}_0$) in admittance spectra were successfully separated by the combination of dielectric function such as $M^*$, $\varepsilon^*$, and $tan{\delta}$. In Cr-ZnO, the interfacial state level was about 1.17 eV by IS and MS. Also we measured the resistance ($R_{gb}$) and capacitance ($C_{gb}$) of grain boundaries with temperature using impedance-modulus spectroscopy. It have discussed about the stability and homogeneity of grain boundaries using distribution parameter ($\alpha$) simulated with the Z"-logf plots with temperature.