• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1105-1111
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• 2011

The objective of this study is to investigate the influence of surface roughness on the morphology of aluminum 6061-T6 alloy after irradiation with a Nd:YAG pulsed laser. The test specimen was prepared by a polishing process using a diamond paste ($1{\mu}m$) and emery polishing papers (#100, #220, #600, #2400) to obtain different initial surface roughness. After irradiation with ten pulsed-laser shots, the surface morphology was examined by using scanning electron microscopy (SEM), optical microscopy (OM), and atomic force microscopy (AFM). The diameter of the melted zone increased with the surface roughness because the multiple reflections and absorption of the laser beam occurred on the surface because of the surface roughness, so that the absorptance of the laser beam changed. This result was verified using the relative absorptance calculated from the diameter of the melted zone with the surface roughness and the diameter increased with the average surface roughness.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.4
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• pp.140-144
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• 2014

Co-(0.7 wt%) and Pr-(2.0, 3.5 or 5.0 wt%) doped cubic zirconia ($ZrO_2:Y_2O_3=50:50wt%$) single crystals grown by a skull melting method were heat-treated in $N_2$ at $1150^{\circ}C$ for 5 hrs. The brown colored as-grown single crystals were changed into either dark brownish green, greenish blue and light green color after the heat treatment. Before and after the heat treatment, the YSZ (yttria-stabilized zirconia) single crystals were cut for wafer form (${\phi}7.5mm{\times}t3mm$). The optical and structural properties were examined by UV-VIS spectrophotometer and X-ray diffraction. Absorption by $Co^{2+}$(${\fallingdotseq}589nm$: ${\Gamma}_8[^4A_2(^4F)]{\rightarrow}{\Gamma}_8+{\Gamma}_7[^4T_1(^4F)]$, ${\fallingdotseq}610nm$: ${\Gamma}_8[^4A_2(^4F)]{\rightarrow}{\Gamma}_8[^4T_1(^4F)]$], ${\fallingdotseq}661nm$: ${\Gamma}_8[^4A_2(^4F)]{\rightarrow}{\Gamma}_6[^4T_1(^4F)]$]) and $Pr^{3+}$(${\fallingdotseq}450nm$: ${^3}H{_4}-{^3}P{_2}$, ${\fallingdotseq}473nm$: ${^3}H{_4}{\rightarrow}{^3}P{_1}$, ${\fallingdotseq}484nm$: ${^3}H{_4}{\rightarrow}{^3}P{_0}$), change of ionization energy and lattice parameter were confirmed.

• Journal of the Korean Society of Radiology
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• v.3 no.4
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• pp.35-38
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• 2009

Flat-panel x-ray detectors using a phosphor and photoconductor material have been used for application in various medical modalities. In this study, the monte carlo simulation, optical and x-ray response characteristics were investigated in the conversion structure obtained by a columnar CsI:Na scintillation layer with a photosensitive amorphous selenium layer. Firstly, from the measurement of luminescent spectrum of CsI:Na and absorption spectrum of a-Se layer, the signal conversion characteristics are analysed. And also, the x-ray sensitivity is measured and compared with conventional a-Se($500{\mu}m$) as a function of electrical field. From the experimental result, the x-ray sensitivities of the CsI:Na($180{\mu}m$)/a-Se($30{\mu}m$) detector and the a-Se($500{\mu}m$) detector were $7.31nC/mR-cm^{2}$ and $3.95nC/mR-cm^{2}$at an electric field of $10V/{\mu}m$, respectively.

• Polymer(Korea)
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• v.25 no.3
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• pp.399-405
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• 2001

Poly[3-octylthiophene-co-3-(4-fluorophenyl)thiophene]s were synthesized in 2:1, 1:1, and 1:2 mole ratios, and organic electroluminescent devices were fabricated using the copolymers. The opto-electrical properties of the copolymers were studied by PL, EL spectra, I-V, and V-L curves of the organic electroluminescent devices in conjunction with the energy band diagrams which were obtained from the cyclic voltammogram and the electronic absorption spectra. The LUMO energy level of P(OT/FPT)(1:1) is the lowest as -3.35 eV. In the copolymers P(OT/FPT)(2:1) and P(OT/FPT)(1:1) the ${\lambada}_{max}$ in the PL and EL spectra red-shifted as the mole ratio of fluorophenyl group increased while in P(OT/FPT)(1:2) it showed a blue-shift. This indicates that the backbone chain is twisted due to the steric hinderance of the fluorophenyl group leading to shorter ${\pi}$-conjugation length. P(OT/FPT)(1:1) showed the highest EL intensity and the highest power efficiency among the three copolymers. In P(OT/FPT)(1:2) the roughness of the film surface causes unusually high local leakage current leading to the low efficiency of electroluminescence.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.28-34
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• 1999

We fabricated a planar ultra-violet photodetector whose ohmic and schottky contacts were respectively formed with evaporated Al and Pt on the GaN layer. To examine the applicability of the device to the UV sensor, we investigated its electrical and optical characteristics. The GaN layer on the sapphire waver had $7.8{\times}10^{16}cm^{-3}$ of doping concentnation and the $138 cm^2/V{\cdot}s$ of electron mobility and it absorbed the spectrum of the light below 325 nm wavelength. It had the responsivity of 2.8 A/W of at 325 nm, and the signal to noise ratio(SNR) of $4{\times}10^4$, and the noise equivalent power(NEP) of $3.5{\times}10^9$W under 5 V reverse bias. These results confirmed that the GaN schottky diode had a solar blind properly when it was applied to the UV photodetector.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.242-243
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• 2000

Erbium 첨가 광섬유(EDF) 광원은 출력 특성과 온도에 대한 파장 특성이 우수하여 Sagnac 간섭계의 원리를 이용한 광섬유 자이로스코프(이하 줄여 자이로라 함)에 많이 사용되고 있다. 이득매질인 EDF를 광원 겸 광증폭기로 사용하는 광섬유 증폭기형 광원 (Fiber Amplifier/source : FAS) 방식$^{[l-2]}$ 은 기존의 single-pass 방식$^{[3]}$ 에 비해서 구조가 단순하고 검출광 power가 크다는 장점이 있다. 그런데, 검출광 power가 큰 경우에 자이로의 SNR이 광원의 과잉잡음(excess noise)에 의해서 제한되므로 실제로 자이로의 측정감도는 개선되지 않는 문제점이 있다.$^{[4]}$ Single-pass 방식의 광원을 사용하는 경우, 적절한 신호처리를 통해 자이로 출력신호에 포함된 광원의 과잉잡음의 적정주파수 성분을 소거함으로써 자이로 신호의 SNR을 개선시킨 바 있었다.$^{[5]}$ 그러나, 일반적으로 single-pass 방식의 경우에는 검출광 power가 작아서 자이로의 SNR이 광원의 과잉잡음에 의해서 제한되는 경우는 드물다. 반면에 증폭기형 광원 방식은 자이로로부터 되돌아오는 신호광이 다시 광원으로 입사되어 EDF를 반대 방향으로 진행하는 동안 증폭되기 때문에 충분히 큰 검출광 power를 얻을 수 있다. 따라서, 자이로 신호에 포함된 광원의 과잉잡음이 소거된다면 자이로 신호의 SNR은 크게 개선될 것으로 여겨진다. 이 논문에서는 광섬유 증폭기형 광원 방식(FAS)의 자이로에 대해 위와 같은 신호처리를 이용하여 광인의 과잉잡음의 적정주파수 성분을 소거하는 실험을 하였다. (중략)한 흡수를 확인하고, $^4$T$_2$$\longrightarrow$$^4$A$_2$(650-800 nm), $^2$E$\longrightarrow$$^4$A$_2$에 의한 nophonon line R$_1$, R$_2$(680.4, 678.5 nm) 및 $^2$T$_1$$\longrightarrow$$^4$A$_2$(655.7, 649.3, 645.2 nm)의 형광방출 스펙트럼을 얻었으며, 형광수명은 0.264 ms로 조사되었다. 제조된 레이저 발진봉은 직경 6.3 m, 길이 45 nm이었다.\pm$0.06kHz Ge $F_4$; -1.84$\pm$0.04kHz$0.04kHz/TEX>0.04kHz 모국어 및 관련 외국어의 음운규칙만 알면 어느 학습대상 외국어에라도 적용할 수 있는 보편성을 지니는 것으로 사료된다.없다. 그렇다면 겹의문사를 [-wh]의리를 지 닌 의문사의 병렬로 분석할 수 없다. 예를 들어 누구누구를 [주구-이-ν가] [누구누구-이- ν가]로부터 생성되었다고 볼 수 없다. 그러므로 [-wh] 겹의문사는 복수 의미를 지닐 수 없 다. 그러면 단수 의미는 어떻게 생성되는가\ulcorner 본 논문에서는 표면적 형태에도 불구하고 [-wh]의미의 겹의문사는 병렬적 관계의 합성어가 아니라 내부구조를 지니지 않은 단순한 단어(minimal $X

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.535-541
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• 2005

We report on the development of a passively mode-locked near-infrared femtosecond laser with Cr:YAG crystal that operates near room temperature. The laser wavelength could easily be tuned by using only the internal prism pair over 110 nm from 1400 nm to 1510 nm in cw and over about 30 nm in mode-locked operation, respectively Maximum cw output powers of 810 mW were obtained with $1.5 \%$ output coupler for absorbed pump powers of 7.6 W. For compensation of the internal group velocity dispersion, an IR graded prism pair was used. The Cr:YAG laser delivered nearly Fourier-transform limited pulses with a pulse duration as short as 64 fs at 100 MHz repetition rate. In the mode-locked regime, the laser was operating at 1510 nm with a spectral bandwidth of 44 nm. In order to avoid unstable mode-locking and power instabilities, self-built tubes were inserted into the beam path in the resonator and purged with N2 gas. Finally, output powers of the Cr:YAG laser were optimized to 250 mW fer long time stable mode-locked operation.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.178-184
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• 2001

Transparent and highly oriented KLN thin films have been grown by an rf- magnetron sputtering deposition method. A homogeneous and stable KLN target was prepared by calcine and sintering process. For KLN target, stoichiometry and composition excess with K of 30% and 60%, and Li of 15% and 30% respectively, was prepared. The targets were sintered at low temperature to prevent vaporization of K and Li. KLN thin films were fabricated by rf-magnetron sputtering method using those targets. In this experiment, using the target of composition excessed with K of 60% and Li of 30%, single phase KLN thin film was produced. KLN thin film has excellent crystallinity and highly c-axis oriented on Corning 1737 substrate. Transmittance of thin film in visible range was 90%, absorption edge is 333 nm and refractive index at 632.8 nm was 1.93.

• Journal of the Korean GEO-environmental Society
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• v.24 no.3
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• pp.5-14
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• 2023

The dry unit weight of the soil can be obtained by measuring the weight of the oven dried soil. According to the Korean Industrial Standards (KS F), oven dried soil at 110±5℃ continuously increases in weight when exposed to air. However, there is no regulation on the weight measurement time of oven dried soil, making it difficult to accurately measure the dry weight. In this study, a method to easily determine the dry weight was presented through the analysis of the weight singularity that appears during weight measurement. The weight singularity represents the smallest value among the measured weights, and is the weight at which the effect of moisture absorption in the air of the sample is minimized. In the course of the experiment, a container was selected using a statistical analysis method, and a photograph of the soil samples were presented using an optical microscope. In addition, the temperature of the weight singularity was measured using a non-contact infrared thermometer. As a result of analyzing the weight singularity of six types of soil, including Jumunjin sand, Naeseong stream sand, Yecheon weathered granite soil, Jeju sand, Sabkha sand, and Ulleung sand, the weight singularity of oven dried sample appeared between 8 and 27 seconds after weight measurement, and the temperature ranged from 103.4 to 108.13℃. The weight decrease rate of the singularity was 0.0066 to 0.0085% depending on the soil samples.

• The korean journal of orthodontics
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• v.28 no.2 s.67
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• pp.297-310
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• 1998

The purpose of this study was to investigate the initial tissue change, to repair on the teeth & surrounding tissue under the intrusive orthodontic forces by use of elastic chain, through the microscopic findings. For this study, three young adult mongrel dogs were used, and were divied into three group : the control group was deliveried only casting crown and the experimental group 1 was equipped with energy chain during 1 week and experimental 2 group was deliveried using energy chain during 1 week and 3 weeks observation. All experimental groups and control groups were sacrificed to make the samples for microscopic findings on premolar teeth. All samples were examed and compared the histologic changes through the microscopic with H-E stain. The obtained results were as follows. 1. In hematoxylin-eosin stain of the control group, the periodontal ligament was constant width from apical third to cervical third of the root, and the periodontal fiber arrangement was horizontal or oblique in cervical third, oblique in middle and apical third of the root. 2. In Masson Trichrome stain of the control group, osteoblast and osteoclast appeared in cervical third of root, and bone resorption and new bone formation was observed in middle and apical third of the root. 3. In experimental 1, osteoclasts were increased highly, and hyperemia of blood vessels and new bone formation and bone resorption by reversal line in apical third of the root were seen. PDL width was increased apprarently from crest to apex of the root and more in apical third. 4. In experimental 2, osteoclasts and hyperemia of blood vessels were more increased than control material in apical third of the root. PDL width was increased more than control group in root apex, and was seen less than experimental 1. PDL arrangement was similar to experimental 1 and was mixed only in root apex. Therefore, in premolar intrusion of the young adult dog, there were increased osteoclast, hyperemia and dilation of blood vessel, resorption of alveolar bone and cementum and different arrangement of PDL in initial tissue change. There was not observed complete repair after remove intrusive force.