• Korean Journal of Optics and Photonics
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• v.31 no.5
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• pp.218-222
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• 2020

In this paper, we have experimentally demonstrated a 2-kW-class spectrally-beam-combined laser with high beam quality, using narrow-linewidth ytterbium-doped polarization-maintaining fiber amplifiers. Five fiber amplifiers with different center wavelengths were implemented for the spectrally-beam-combined laser. The center wavelengths of the five amplifiers were 1062, 1063, 1064, 1065, and 1066 nm, respectively. A phase-modulated laser diode was used as a seed source for each amplifier. The seed sources were modulated by filtered pseudorandom-bit-sequence (PRBS) signals 5 GHz in linewidth. The polarization-maintaining large-mode-area fiber with a core size of 30 ㎛ was used as a delivery fiber to mitigate the stimulated Brillouin scattering (SBS) effect. The laser beams from five amplifiers were spectrally combined by a multilayer dielectric diffraction grating. The maximum output power and beam quality M² of the combined laser were measured to be 2.3 kW and 1.74, respectively.

• Korean Journal of Remote Sensing
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• v.26 no.2
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• pp.123-131
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• 2010

In this paper we applied Ground-Based Synthetic Aperture Radar(GB-SAR) interferometry to detect artificial displacement of a reflector and performed an atmospheric humidity correction to improve the accuracy. A series of GB-SAR images were obtained using a center frequency of 5.3 GHz with a range resolution of 25 cm and a azimuth resolution of $0.324^{\circ}$, all in full-polarization (HH, VV, VH, HV) modes. A triangular trihedral corner reflector was located 160 m away from the system, and the artificial displacements of 0-40 mm was implemented during the GB-SAR image acquisition. The result showed that the RMS error between the actual and measured displacements, averaged in all polarization data, was 1.22 mm, while the maximum error in case of the 40 mm displacement was 2.72 mm at HH-polarization. After the atmospheric correction with respect to the humidity, the RMS error was reduced to 0.52 mm. We conclude that a GB-SAR system can be used to monitor the possible displacement of artificial/natural scatterers and the stability assessment with sub-millimeter accuracy.

• Restorative Dentistry and Endodontics
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• v.16 no.1
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• pp.6-15
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• 1991

The purpose of this study was to observe in vitro chloride corrosion behavior from 5 kinds of amalgam (Caulk spheracal, Amalcap, Dispersalloy, Tytin, Sybralloy) as a function of time after tritruration by using potentiostat. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by the mechanical amalgamator, the triturated mass was inserted the cyrindrical matal mold ($12{\times}10mm$) and was condensed by using routine manner. The specimen was removed from the mold and was stored at room temperature for 1 week, 1 month and 3 months, and standard surface preparation was routine carried out. The 0.9% saline solution was used as electrolyte in pH 6.8~7.0 at $30{\pm}0.5.^{\circ}C$. The open circuit potential was determined after 30 minutes' immersion of 1 week, 1 month and 3 month old specimens. The scan rate was 1 mV/sec and the surface area of amalgam exposed to the solution was $0.65\;Cm^2$ for each specimen. All potentials reported are with respect to a silver / silver chloride electrode (SSE). The following result was obtained. 1. All amalgam specimens became more noble corrosion potentials which represent the improved corrosion resistance as the time elapsed. 2. Three kinds of high copper amalgam always exhibited more noble potential than low copper amalgam at 1 week, 1 month and 3 months. 3. Two kinds of low copper amalgam had the similar polarization curve pattern with 3 current peaks at each time period and current densities associated with these peaks were decreased as aging especially in caulk spherical amalgam. 4. All kinds of high copper amalgam had the similar polarization curve pattern with absence of prominent current peak at each time period, but the polarization curve of D amalgam had one apparent current peak at 1 week.

• Journal of the Korean institute of surface engineering
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• v.34 no.3
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• pp.195-205
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• 2001

The surface characteristics of Ti/TiN films coated on sintered stainless steels (SSS) by electron beam physical vapour deposition (EB-PVD) were investigated. Stainless steel compacts containing 2, 4, and 10wt%Cu were prepared by the electroless Cu-plating method, which results in increased homogenization in the alloying powder. The specimens were coated with Ti and TiN with a 1.0$\mu\textrm{m}$ thickness respectively by EB-PVD. The microstructures were investigated using scanning electron microscopy (SEM). The corrosion behaviors were investigated using a potentiosat in 0.1 M $H_2$$SO_4$, and 0.1M HCl solutions and the corrosion surface was observed using SEM and XPS. The Ti coated specimens showed rough surface compared to Ti/TiN coated specimens. Ti and Ti/TiN coated SSS revealed a higher corrosion and pitting potential from anodic polarization curves than that of Ti and Ti/TiN uncoated SSS. In addition, Ti/TiN coated SSS containing 10wt% Cu exhibited good resistance to pitting corrosion due to the formation of a dense film on the surface and the decrease in interconnected porosity by electroless coated Cu.

• Journal of the Korean Ceramic Society
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• v.45 no.3
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• pp.139-141
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• 2008

The piezoelectric properties of tetragonal 0.88Pb$(Zn_{1/3}Nb_{2/3)O_3-0.12PbTiO_3$ single crystals are characterized along the <111> direction, which composed the engineering domain configuration in the tetragonal phase. The <111>-oriented crystal possessed smaller $d_{33}$ values compared to the crystal along the <001> spontaneous polarization direction. Based on phenomenological theory, it is shown that the engineering domain configuration does not enhance the piezoelectric constant in tetragonal 0.88Pb$(Zn_{1/3}Nb_{2/3)O_3-0.12PbTiO_3$ single crystals. In addition, the electrostrictive coefficients of $Q_{12}=-0.03706m^4/C^2,\;Q_{11}=0.10765m^4/C^2,\;and\;Q_{44}=0.02020m^4/C^2$ of tetragonal 0.88PZN-0.12PT single crystals were calculated.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.50.2-50.2
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• 2017

Spatial distribution of atmosphereless bodies in the solar system provides an important clue as to their origins, namely asteroids from Mainbelt or comets from outer solar system. It is, however, difficult to distinguish asteroids and dormant comets due to their similar appearances. In this study, we conducted a unique observation to differentiate asteroids and dormant comets in terms of 'polarimetry'. We observed (331471) 1984 QY1 (hereafter QY1) at large phase angles using the Multi-Spectral Imager (MSI) on the 1.6-m Pirka Telescope from UT 2016 May 25 to June 24. QY1 is a dormant comet candidate in terms of the dynamical properties (i.e. the Tisserand parameter with respect to Jupiter, TJ = 2.68). We analyzed the polarization degree of QY1 as a function of phase angle and found its maximum polarization degree, $Pmax=8.68{\pm}0.28%$ and $8.72{\pm}0.38%$, in RC-and V-band, respectively, around the phase angle of ${\alpha}=100^{\circ}$. In addition, we obtained the geometric albedo, $pV=0.16{\pm}0.02$ by means of an empirical slope-albedo law. The polarimetric properties and the albedo value we acquired are similar to those of S-type asteroids rather than cometary nuclei. In this presentation, we introduce our observation and findings. In addition, we further discuss a dynamical transportation process from Mainbelt to the current orbit.

• Journal of the Korean Vacuum Society
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• v.15 no.1
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• pp.64-72
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• 2006

We demonstrated organic light-emitting devices (OLEDs) based on the organic thin-film materials such as tris-(8-hydroxyquinoline) aluminum $(Alq_3)$. The structure of OLEDs was vacuum deposited upon transparent and thin glass substrates pre-coated with a transparent, conducting indium tin oxide thin film. The luminance characteristics, current, capacitance, and dispersion factor for degraded OLEDs, which were made by various bias currents $(0.5mA\;{\leq}\;I_{Bias}\;{\leq}9mA)$, are studied. The current dependences of lifetime were divided at approximately 2mA, and they represented nearly linear behaviors but had different slopes in a logarithmic plot of lifetime versus bias current. With lighting OLEDs, the anomaly of capacitance, as shown in the CV curve, occurred because of two factors, polarization in the bulk of organic materials and the interface between the metal and organic layers. In decayed OLEDs that had lower bias currents of less than 2mA, it was found that the degradation of luminance was related to both the decrease of polarization and to the lowering of the injection barrier.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.2
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• pp.344-350
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• 2001

This paper was studied on the characteristics of galvanic corrosion and its protection on heat exchanger tube plate in the sea water. In this paper, behavior of pitting corrosion of Ni-al bronze connected with Ti tube was measured af flow velocity of 0 m/s and 2.4 m/s. To protect galvanic corrosion, the protection characteristics of Ni-Al bronze connected with Ti tube by Zn-base alloys galvanic anode and hexagonal nylon insert was investigated. Main results obtained asre al follows: 1) The galvanic corrosion of Ni-Al bronze connected with Ti-tube is more active than single Ni-al bronze. 2) As the circuit resistance increase under the cathodic protection employing Zn-base alloys galvanic anode, Ni-al bronze connected with Ti tube is cathodically unpolarized. 3) The corrosion of Ni-Al bronze connected with Ti tube by nylon insert controls approximately 73% than not nylon insert.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.2
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• pp.345-345
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• 2001

This paper was studied on the characteristics of galvanic corrosion and its protection on heat exchanger tube plate in the sea water. In this paper, behavior of pitting corrosion of Ni-al bronze connected with Ti tube was measured af flow velocity of 0 m/s and 2.4 m/s. To protect galvanic corrosion, the protection characteristics of Ni-Al bronze connected with Ti tube by Zn-base alloys galvanic anode and hexagonal nylon insert was investigated. Main results obtained asre al follows: 1) The galvanic corrosion of Ni-Al bronze connected with Ti-tube is more active than single Ni-al bronze. 2) As the circuit resistance increase under the cathodic protection employing Zn-base alloys galvanic anode, Ni-al bronze connected with Ti tube is cathodically unpolarized. 3) The corrosion of Ni-Al bronze connected with Ti tube by nylon insert controls approximately 73% than not nylon insert.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.595-599
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• 2003

We have studied the phase transition to look for molecular structure by using several different techniques for new banana-shaped liquid crystals shown in Fig. 1. Based on the similarities to recently observed fluro-contaning materials (switching involves layer structure rearrangement, increasing threshold with increasing temperature) for HC sample (where x is H), we assume that the phase C has a triclinic symmetry corresponding to the double tilted $smC_G$ Phase. The observation that the polarization peak appears at lower field ($E_o{\sim}15V/{\mu}m$) than the amplitude of the threshold ($E_{th}$) can be explained assuming a field induced $SmC_G$ - SmCP (or SmAP) transition at $E_{th}$