• Korean Journal of Materials Research
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• v.11 no.7
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• pp.575-579
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• 2001

GaN buffer layer and epilayer have been grown on sapphire (0001) by metal organic chemical vapor deposition (MOCVD). GaN buffer layer ranging from 26 nm to 130 nm in thickness was grown at 55$0^{\circ}C$ prior to the 4 $\mu\textrm{m}$ thick GaN epitaxial deposition at 110$0^{\circ}C$. After GaN buffer layer growth, buffer layer surface was examined by atomic force microscopy (AFM). As the thickness of GaN buffer layer was increased, surface morphology of GaN epilayer was investigated by scanning electron microscopy (SEM). Double crystal X-ray diffraction (DCXRD) and Raman spectroscopy were employed to study crystallinity of GaN epilayers. Optical properties of GaN epilayers were measured by photoluminescence (PL). The epilayer grown with a thin buffer layer had rough surface, and the epilayer grown with a thick buffer layer had mirror-like surface of epilayer. Although the stress on the latter was larger than on the former, its crystallinity was much better. These results imply that the internal free energy is decreased in case of the thick buffer layer. Decrease in internal free energy promotes the lateral growth of the GaN film, which results in the smoother surface and better crystallinity.

• Journal of Conservation Science
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• v.22
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• pp.87-98
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• 2008

Microstructures and chemical compositions of 24 bronze mirrors recovered from the Korean peninsula were examined using the scanning electron microscope equipped with the energy dispersive spectrometer in an effort to characterize the treatments applied on their surface. Their provenance and chronology are mostly unspecified except for two objects from a Koryo burial site. In antiquity the surface of bronze mirrors was frequently finished by mere polishing when their tin content was high enough to guarantee the required reflectivity. In many cases, however, their surface was given a special treatment. The most typical treatment was to coat the surface with tin in two different processes referred to as wipe-tinning and amalgam-tinning. In wipe-tinning only tin was used, but in amalgam-tinning tin and mercury were used together. The surface was often coated with mercury in a process known as mercury-polishing. The present mirrors showed that all these techniques were in fact practiced, not only on the reflective surface but, in some cases, on the decorative surface. The detection of mercury played a crucial role in the assessment of a specific technique applied in each mirror. Mercury often remained in the substrate in the form of sulfide and thereby allowed the method of surface treatment to be estimated even when the coated layer was completely lost. The future study is expected to uncover the regional and temporal variation of the surface treatments to the better understanding of bronze mirrors with respect to provenance and chronology.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.4
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• pp.34-40
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• 2004

In this paper, we have studied the OCT(Optical Coherence Tomography) system which has been advantages of high resolution, 2-D cross-sectional images, low cost and small size configuration. The characteristics of light source determine the resolution and coherence length. The light source has a commercial SLD with a central wavelength of 1,285 ill11, 35.3 nm(FWHM). The optical delay line is necessary to make equal with the optical path length to scattered light or reflected light from a sample. In order to make equal the optical path length, the stage that is attached to a reference mirror is controled by a step motor. And the interferometer is configured with the Michelson interferometer by using a single mode fiber, and the scanner can be focused on the sample by using a reference ann Also, the 2-dimension cross-sectional images were measured with scanning the transverse direction of the sample by using a step motor. After detecting the internal signal of lateral direction, a scanner is moved to obtain the cross-sectional image of 2-dimension by using step motor. A photodiode, which has high detection sensitivity and excellent noise characteristics has been used. The detected small signal has a noise and interference. After filtering and amplifying the signal, the output signal is demodulated the waveform And then, a cross-sectional image is seen through converting this signal into a digitalized signal by using an AID converter. The resolution of the sample is about 30${\mu}{\textrm}{m}$, which corresponds to the theoretical resolution. Also, the cross-sectional images of onion cells were measured in real time scheme.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1117-1123
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• 2014

This study sintered $Si_3N_4$ with different amounts of $SiO_2$ nano-colloid. The surface of a mirror-polished specimen was coated with $SiO_2$ nano-colloid, and cracks were healed when the specimen was treated at a temperature of 1273 K for 1 h in air. Wear specimen experiments were conducted after heat treatments for 10 min at 1073, 1273, and 1573 K. The heat-treated surface that was coated with the $SiO_2$ nano-colloid was slightly rougher than the noncoated surface. The oxidation state of the surface according to the heat treatment temperature showed no correlation with the surface roughness. Moreover, the friction coefficient, wear loss, and bending strength were not related to the surface roughness. $Si_3N_4$ exhibited an abrasive wear behavior when SKD11 was used as an opponent material. The friction coefficient was proportional to the wear loss, and the bending strength was inversely proportional to the friction coefficient and wear loss. The friction coefficient and wear loss increased with increasing amounts of the $SiO_2$ nanocolloid. In addition, the friction coefficient was slightly increased by increasing the heat treatment temperature.

• Analytical Science and Technology
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• v.24 no.5
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• pp.387-394
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• 2011

This study was performed to investigate the contents and leaching characteristics of hazardous wastes from the paint industry. In order to establish a hazardous waste list, samples from industrial discharge have been analyzed for 8 non-regulated inorganic hazardous substances (i.e., Sb, Ni, F, V, Ba, Zn, Be, Se). In more detail, hazardous waste samples from a total of 64 workplaces, e.g. manufacture, formulation, supply and use (MFSU) of coatings, adhesives, sealants and printing inks processing, have been chosen and analyzed. Contents and leaching tests for inorganic metal species in samples show that the non-regulated hazardous substances satisfy all the criteria, while quantitative analyses reveal that some samples of the discharged wastes exceeded the criteria proposed by NIER (National Instituted of Environmental Research). In conclusion, we expect the outcome of this study to align the classification system of hazardous waste management in South Korea with international legislations, and consequently contribute to reduce environmental pollution as well as health risks by toxic wastes.

• Journal of Astronomy and Space Sciences
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• v.21 no.4
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• pp.329-342
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• 2004

In this paper, we present preliminary feasibility studies on three types of solar observation payloads for future Korean Science and Technology Satellite (STSAT) programs. The three candidates are (1) an UV imaging telescope, (2) an UV spectrograph, and (3) an X-ray spectrometer. In the case of UV imaging telescope, the most important constraint seems to be the control stability of a satellite in order to obtain a reasonably good spatial resolution. Considering that the current pointing stability estimated from the data of the Far ultraviolet Imaging Spectrograph (FIMS) onboard the Korean STSAT-1, is around 1 arc minutes/sec, we think that it is hard to obtain a spatial resolution sufficient for scientific research by such an UV Imaging Telescope. For solar imaging missions, we realize that an image stabilization system, which is composed of a small guide telescope with limb sensor and a servo controller of secondary mirror, is quite essential for a very good pointing stability of about 0.1 arcsec. An UV spectrograph covering the solar full disk seems to be a good choice in that there is no risk due to poor pointing stability as well as that it can provide us with valuable UV spectral irradiance data valuable for studying their effects on the Earth's atmosphere and satellites. The heritage of the FIMS can be a great advantage of developing the UV spectrograph. Its main disadvantage is that two major missions are in operation or scheduled. Our preliminary investigations show that an X-ray spectrometer for the full disk Sun seems to be the best choice among the three candidates. The reasons are : (1) high temporal and spectral X-ray data are very essential for studying the acceleration process of energetic particles associated with solar flares, (2) we have a good heritage of X-ray detectors including a rocket-borne X-ray detector, (3) in the case of developing countries such as India and Czech, solar X-ray spectrometers were selected as their early stage satellite missions due to their poor pointing stabilities, and (4) there is no planned major mission after currently operating Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) mission. Finally, we present a preliminary design of a solar X-ray spectrometer covering soft X-ray (2 keV) to gamma ray (10 MeV).

• Analytical Science and Technology
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• v.26 no.4
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• pp.276-286
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• 2013

This study was performed to investigate the contents characteristics of hazardous oil wastes and wastes of liquid fuels from different industrial process. In order to establish a hazardous waste list, samples of various industrial discharge have been analyzed for 16 non-regulated inorganic hazardous substances (i.e., Cu, Pb, Cd, CN, Hg, As, T-Cr, $Cr^{6+}$, Sb, Ni, F, V, Ba, Zn, Be, Se). In more detail, hazardous waste samples including waste hydraulic oils, waste engine, gear and lubricating oils, waste insulating and heat transmission oils, bilge oils, oil/water separator contents processing were collected from 37 workplaces and analyzed. We observed that the most of the inorganic substances exceeded the proposed criteria in many samples. Especially the concentration of Sb in heat transmission oil, bilge oil and gear & lubricating oils were ranged from 6 to 419 mg/kg whereas the proposed criteria is 50 mg/kg. The assessment result of hazardous waste in Korea according to the EWC showed that the out of 24 processes, 16 belongs to absolute entry and 8 belongs to mirror entry. In conclusion, we expect the outcome of this study to align the classification system of hazardous waste management in South Korea with international legislations, and consequently contribute to reduce environmental pollution as well as health risks by toxic wastes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.472-478
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• 2015

This paper describes the design of the active optical compensation movements(at focal plane, secondary mirror) for the image stabilization of a small satellite camera. The movements can correct optical misalignment on-line and directly compensate vibration disturbances in the focal plane. Since the devices are installed inside the space camera, it has an remarkable advantage to deal with the structural deformation of a space camera effectively. In this paper, the requirements of the active optical compensation movements for 1m GSD small satellite camera have been analyzed. Based on the established requirements, the design of the active compensation movements have been conducted. The designed active optical compensation system can control 5 axes movements independently to compensate micro-vibration disturbances in the focal plane and to refocus the optical misaligned satellite camera.

• Korean Journal of Cognitive Science
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• v.25 no.4
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• pp.343-384
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• 2014

In order to unravel the problems of the mind, today's cognitive science has expanded its perspective from the narrow framework of the past computer model or neuronal network model to the wider frameworks of interaction with the brain in interaction with the body in interaction with their environments. The theories of 'the extended mind', 'embodied mind', or 'enactive mind' appeared through such processes are working on a way to move into the environments while the problem to unravel the complex process of interactions between the mind, the body and the environments are left alone. This problem can be traced back as far as to Gibson and Maturana & Varela who tried at first to unravel the problem of the mind in terms of interaction between the brain, the body and there environments in 1960~70s. It's because Gibson stressed the importance of the 'affordance' provided by the environment while Maturana & Varela emphasized the 'autonomy' of auto-poiesis of life. However, it will be proper to say that there are invariants in the affordances provided by the environment as well as the autonomy of life in the state of structural coupling of the environment's variants and life's openness toward the environment. In this case, the confrontational points between Gibson and Maturana & Varela will be resolved. In this article, I propose Benjamin's theory of mimesis as a mediator of both theories. Because Benjamin's concept of mimesis has the process of making a constellation of the embodiment of the affordance and the enaction of new affordance into the environment at the same time, Gibson's concept of the affordance and Maturana & Varela's concept of embodiment and enaction will be so smoothly interconnected to circulate through the medium of Benjamin's concept of mimesis.

• Journal of the Korean Magnetics Society
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• v.19 no.2
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• pp.47-51
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• 2009

The surface structure of polycrystalline Fe films of various thicknesses on glass substrates have been studied using a Ti: Sapphire laser at 780 nm. We found that the surface structure possesses C$_s$ crystal structure close to $C_{2v}$ through symmetry consideration. We present one-fold intensity profile with one mirror plane in second harmonic (SH) intensity as a proof of $C_s$ symmetry. $C_s$ and $C_{2v}$ surface symmetries usually appear at the (110) surface of a cubic diamond single crystal [1]. Therefore this surface symmetry would be related to bcc (110) growth orientation coinciding with XRD measurement. Further we treated surface normalized SH asymmetry with various thicknesses. The SH asymmetry increases with increasing of film thickness. From these results, it is observed that the surface structure of thin polycrystalline Fe film below 5 nm is almost isotropic, while in the case of the thicker Fe films, surface structure have $C_s$ symmetry structure close to $C_{2v}$.