• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1996.11a
• /
• pp.37-39
• /
• 1996

A hydride vapor phase epitaxy (HVPE) method was performed to prepare the GaN thick-films on c-plane sapphire substrates. The full-width at half maximum of double crystal X-ray rocking curve from 350${\mu}{\textrm}{m}$ thick GaN was 576 arcsecond. The photo- luminescence spectrum measured (at room temperature) show the narrow bound exciton(I$_2$) line and weak donor-acceptor pair recombination peak, however, there was not observed deep donor-acceptor pare recombination indicate the GaN crystals prepared in this study are of high purity and high crystalline quality.

• Proceedings of the KIEE Conference
• /
• 1998.07e
• /
• pp.1702-1704
• /
• 1998

In order to establish the usefulness of ultrasonic techniques for detecting corona discharges in high-voltage power apparatus, it is first necessary to determine the relationship between electrical and ultrasonic signals of corona discharges in air. In this paper, various characteristics of ultrasonic signal detection for point-to-plane corona discharges using a 200[kHz] ultrasonic sensor are examined. In regard to the attenuation and directivity of ultrasonic signals, the signals were inversely proportional to the distance between corona sources and ultrasonic receiving sensors, and half attenuation angles were approximately 7.0 degree. Ultrasonic signals of positive polarities were first obserbed at corona inception voltages. and the signals were increased with increasing the applied voltages.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.10 no.1
• /
• pp.21-26
• /
• 1973

A simple matrix method to analyze the ship's transverse frame ring is proposed. In this approach, the frame ring is treated as a plane frame of uniform slender members. The loadings on the frame consist of buoyancy loads, deck loads and cargo loads. The hatch coaming are considered to deflect under the loads. Because of symmetry, only the half of the frame is analyzed. The method is to obtain the forces and moments on each member. The deformation of the frame can be determined from the nodal displacements. For a sample calculation, a frame ring of a 10,000 ton class cargo liner is analyzed on the IBM 1130 computer. The numerical results obtained are proved to be resonable.

• Honam Mathematical Journal
• /
• v.31 no.4
• /
• pp.463-478
• /
• 2009

Let k be an imaginary quadratic field, ℌ the complex upper half plane, and let ${\tau}{\in}k{\cap}$ℌ, q = exp(${\pi}i{\tau}$). And let n, t be positive integers with $1{\leq}t{\leq}n-1$. Then $q^{{\frac{n}{12}}-{\frac{t}{2}}+{\frac{t^2}{2n}}}{\prod}^{\infty}_{m=1}(1-q^{nm-t})(1-q^{nm-(n-t)})$ is an algebraic number [10]. As a generalization of this result, we find several infinite series and products giving algebraic numbers using Ramanujan's $_{1{\psi}1}$ summation. These are also related to Rogers-Ramanujan continued fractions.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.8
• /
• pp.1715-1718
• /
• 2009

A series of sitting-atop (SAT) complexes, [(ZrO)$H_2t(X)pp(NO_3)_2$], have been prepared via the reactions of free base meso-tetraarylporphyrins, $H_2$t(X)pp, with zirconyl nitrate hydrate, ZrO(N$O_3)_2{\cdot}xH_2$O. The products have been characterized by a variety of methods including $^1H\;NMR,\;^{13}C$ NMR, IR and UV-Vis spectroscopies, elemental analysis and conductance measurements. The data indicate that the meso-tetraarylporphyrins coordinate with two pyrrolenine nitrogen atoms to the zirconyl cation located above the distorted porphyrin plane and two protons remain on the pyrrole nitrogens. Such half sandwich-type sitting-atop complexes may be considered as models for the initial steps of the metallation of the macrocycles.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1996.10a
• /
• pp.213-217
• /
• 1996

The electrochemical methods of early detection and analysis of corrosion related deterioration in concrete reinforcement structures are very useful techniques. The generally using procedure for corrosion monitoring of reinforced structures employs a method of half-cell potential measurement. Whilst the technique has provided a useful means of delineating areas of high or low corrosion risk, there are difficulties in its use and interpretation, particularly when assessing corrosion rates of reinforcement. The aim of this study is to describe the AC-impedance method being employed to monitor and assess corrosion rates, to estimate corrosion mechanism of reinfrocement in laboratory conditions. The AC-impedance monitoring technique applies a small amplitude(20mV) AC signal to embedded steel in concrete and reference electrode (Cu/$CuSo_4$). We obtained over a wide frequency range(10MHz~1mHz) to produce a complex plane plot or Nyquist plot.

• Proceedings of the KIEE Conference
• /
• 2000.07d
• /
• pp.2287-2289
• /
• 2000

This paper focuses on the robust pole assignment for time varying uncertain linear systems in a specified disk. Based on Linear Matrix Inequality(LMI) approach, we give two sufficient conditions, one is for the analysis and another is for the design, that guarantee the robust pole assignment in a specified disk in the left half plane(L.H.P) while satisfying the robust stability. Since these conditions are expressed as LMI forms, we can easily check their feasibility using MATLAB control toolbox. Finally, we show by an example that our results are useful for analysis and design.

• ETRI Journal
• /
• v.33 no.2
• /
• pp.163-168
• /
• 2011

A Fabry-Perot cavity (FPC) antenna producing both high-gain and circularly-polarized (CP) behavior is proposed. To increase antenna gain and obtain CP characteristics, a superstrate composed of square patches with a pair of truncated corners is placed above the linearly polarized patch antenna with an approximately half-wavelength distance from the ground plane at the operating frequency. The proposed antenna has the advantages of high gain, a simple design, and an excellent boresight axial ratio over the operating frequency bandwidth. Moreover, used in an FPC antenna, the proposed superstrate converts a linear polarization produced by a patch antenna into a circular polarization. In addition, the cavity antenna produces left-hand circular-polarization and right-hand circular-polarization when a patch antenna inside the cavity generates x-direction and y-direction polarization, respectively. The measured and simulated results verify the performance of the antenna.

• Journal of Magnetics
• /
• v.7 no.2
• /
• pp.51-54
• /
• 2002

The crystallization of amorphous Ba-ferrite/sapphire(001) thin films was studied in real-time synchrotron x-ray scattering experiments. In the sputter-grown amorphous films, we found the existence of epitaxial $Fe_3O_4$ interfacial crystallites (50-${\AA}$-thick), well aligned $[0.03^circ$full-width at half-maximum (FWHM)] to the sapphire [001] direction. The amorphous precursor was crystallized to epitaxial Ba-ferrite and \alpha-Fe_2O_3$grains in two steps; i) the nucleation of crystalline \alpha-Fe_2O_3$ phase started at $300^circ{C}$ together with the transformation of the $Fe_3O_4$ crystallites to the \alpha-Fe_2O_3$ crystallites, ii) the nucleation of Ba-ferrite phase occurred at temperature above $600^circ{C}$. In the crystallized films irrespective of the film thickness, the crystal domain size of the \alpha-Fe_2O_3$grains was about 250 ${\AA}$ in the film plane, similar to that of the Ba-ferrite grains.

• Journal of electromagnetic engineering and science
• /
• v.14 no.3
• /
• pp.314-316
• /
• 2014

This letter presents two types of metamaterial-inspired absorbers adopting resistive trumpet structures at the X band. The unit cell of the first type is composed of a trumpet-shaped resonator loading a chip resistor, a metallic back plane, and a FR4 (${\varepsilon}_r=4.4-j0.02$) substrate between them (single-layer). The absorption rate is 99.5% at 13.3 GHz. The full width at half maximum (FWHM) is 95 % at 11.2 GHz (from 5.9 to 16.5 GHz). The size of unit cell is $5.6{\times}5.6{\times}2.4mm^3$. The second type has been optimized with a $7{\Omega}$/square uniform resistive coating, removing the chip resistors but leading to results comparable to the first type. The proposed absorbers are almost insensitive to polarizations of incident waves due to symmetric geometry.