• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 1999년도 Pre-symposium of the 10th ISWPC Recent Advances in Paper Science and Technology
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• pp.296-301
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• 1999

Different papers such as toilet and towel tissue, newsprint and copy paper made from reclaimed fibres were characterized using UV-VIS reflectance and fluorescence spectroscopy. The emission properties of the extracts of the papers were also evaluated. Photochemical irradiation at ambient temperatures, and thermal aging of the copy papers at 105$^{\circ}C$ and 150$^{\circ}C$ were performed. Post-colour numbers (PC) were calculated from the reflectance values measured from the corresponding UV-VIS reflectance spectra. Light absorption coefficient spectra were calculated before and after irradiation, and the changes in absorption coefficient were related to the content of chromophores in the papers. Photochemical and thermal discolouration of the copy papers, similar to that of virgin fibres, was readily observed. The influence of changes in the concentrations of fluorescent brightening agents and dyes on the spectral properties was also assessed. Photostabilization studies of the copy papers were performed with the use of polymer additives polyethylene glycol (PEG) and polytetrahydrofuran (PTHF).

• 한국전자파학회논문지
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• 제21권8호
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• pp.905-910
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• 2010

본 논문에서는 조명용 LED(Light Emitting Diode)의 스위칭 구동 회로를 이용한 변조 기법으로 조명 기능과 무선 통신 기능을 동시에 수행하는 가시광 통신(VLC: Visible Light Communication) 시스템을 제안하였다. 본 방식은 기존의 선형 영역에서 동작하는 LED 구동 회로를 갖는 가시광 통신 시스템에 비해 고효율이므로 고출력의 조명용 LED 시스템에 적용할 수 있는 장점이 있다. 제안된 시스템의 유용성을 입증하기 위하여 디지틀 방식의 오디오 시스템을 채용하여 가시광 통신 시스템을 구현하고, 그 실험 결과를 제시함으로써 제안된 방식의 우수성을 검증하였다. 실험 결과, 제안 회로의 시작품은 특별한 광필터 없이 20 W급 조명을 사용해서 약 1.5 m의 반경에서 최대 10 Mbps의 데이터 전송률을 달성하였다.

• 대한기계학회논문집B
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• 제39권11호
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• pp.853-859
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• 2015

본 연구에서는 모의 생체조직에 광을 조사하고 그에 따른 조직 내의 열전달 현상을 분석하였으며 이를 이용하여 수치해석 시 필요한 표면 경계조건에 대한 관계식을 도출하였다. 세 가지 서로 다른 파장의 광을 높이를 바꾸면서 조사하여 표면에서부터 깊이방향으로 조직 내의 온도를 측정하였다. 그 결과 파장과 조사 시간이 길수록 한천조직의 온도는 높아졌으나 붉은 색 파장과 근적외선은 큰 차이를 나타내지 않았다. 도출된 경계조건을 사용한 수치해석 결과는 측정된 온도와 잘 일치하였다.

• Current Applied Physics
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• 제18권11호
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• pp.1381-1387
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• 2018

One dimensional (1D) grating has been fabricated (using focused ion beam) on 50 nm gold (Au) film deposited on higher refractive index Gallium phosphate (GaP) substrate. The sub-wavelength periodic metal nano structuring enable to couple photon to couple with the surface plasmons (SPs) excited by them. These grating devices provide the efficient control on the SPs which propagate on the interface of noble metal and dielectric whose frequency is dependent on the bulk electron plasma frequency of the metal. For a fixed periodicity (${\Lambda}=700 nm$) and slit width (w = 100 nm) in the grating device, the efficiency of SPP excitation is about 40% compared to the transmission in the near-field. Efficient coupling of SPs with photon in dielectric provide field localisation on sub-wavelength scale which is needed in Heat Assisted Magnetic recording (HAMR) systems. The GaP is also used to emulate Vertical Cavity Surface emitting laser (VCSEL) in order to provide cheaper alternative of light source being used in HAMR technology. In order to understand the underlying physics, far-and near-field results has been compared with the modelling results which are obtained using COMSOL RF module. Apart from this, grating devices of smaller periodicity (${\Lambda}=280nm$) and slit width (w = 22 nm) has been fabricated on GaP substrate which is photoluminescence material to observe amplified spontaneous emission of the SPs at wavelength of 805 nm when the grating device was excited with 532 nm laser light. This observation is unique and can have direct application in light emitting diodes (LEDs).

• 한국기계가공학회지
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• 제12권6호
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• pp.152-158
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• 2013

The purpose of this study is to investigate cooling performance of high power LEDs from 100 to 200 W class by using a jet impingement cooling module. The numerical analysis of forced convection cooling inside cooling module is carried out using a multi-purpose CFD software, FLUENT 6.3. In the experiments, the LED cooling system consists of jet impingement module, heat exchanger, water reservoir, and pump. In the present study, the cooling performance of jet impingement cooling module is investigated to determine the effect of the heat sink types on the impinging surface, the space and length of fins. Numerical and experimental studies show the reasonable agreement of LED metal PCB temperature between those results and give the optimized design parameters such as the space of fin and the length of fin. Also, the pin fin type of heat sink is found to be more efficient than the plate type heat sink in jet impingement cooling.

• 한국결정성장학회지
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• 제31권2호
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• pp.84-88
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• 2021

레이저, 광학센서 등에 사용되고 있는 La2O3-CaF2-Al2O3-SiO2 계 유리에 희토류 물질을 첨가하였을 때, 열처리 온도에 따른 결정화유리의 발광 특성 변화에 대하여 연구하였다. 결정화유리를 얻기 위한 열처리 조건은 비등온 열분석을 통해 얻었으며, 열처리 온도에 따른 결정성장 정도 및 생성된 결정상 종류를 파악하기 위해 XRD 분석을 진행하였다. Scherrer's equation을 이용한 결과, 결정화유리 내부에 25~40 nm 크기의 결정들이 생성된 것으로 계산되었다. Photoluminescence (PL) 분석결과, 660~670℃에서 1시간 열처리 된 시편이 가장 우수한 PL 강도를 보였으며, CIE 색좌표계 분석결과, 열처리 유무와 관계없이 모든 결정화유리 시편들은 red-orange 빛을 발광하는 것으로 나타났다.

• Asian Journal of Atmospheric Environment
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• 제9권1호
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• pp.86-90
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• 2015

Temperature was considered to estimate the minimum detectable absorption coefficient of aerosol particles from photothermal spectroscopy. Light energy absorbed by subsequent emission from the aerosol results in the heating of the aerosol sample and consequently causes a temperature change as well as changes in thermodynamic parameters of the sample. This thermal effect is the basis of photothermal spectroscopy. Photothermal spectroscopy has several types of techniques depending on how the photothermal effects are detected. Photothermal interferometry traces the photothermal effect, refractive index, using an interferometer. Photoacoustic spectroscopy detects the photothermal effect, sound wave, using a microphone. In this study, it is suggested that the detection limit for photothermal spectroscopy can be influenced by the introduction of a slip correction factor when the light absorption is determined in a high temperature environment. The minimum detectable absorption coefficient depends on the density, the specific heat and the temperature, which are thermodynamic properties. Without considering the slip correction, when the temperature of the environment is 400 K, the minimum detectable absorption coefficient for photothermal interferometry increases approximately 0.3% compared to the case of 300 K. The minimum detectable absorption coefficient for photoacoustic spectroscopy decreases only 0.2% compared to the case of 300 K. Photothermal interferometry differs only 0.5% point from photoacoustic spectroscopy. Thus, it is believed that photothermal interferometry is reliably comparable to photoacoustic spectroscopy under 400 K.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 춘계학술대회 논문집(한국공작기계학회)
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• pp.422-428
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• 2001

The term High Speed Machining has been used for many years to describe end milling with small diameter tools at high rotational speeds, typically 10,000 - 100,000 rpm. The process was applied in the aerospace industry for the machining of light alloys, notably aluminium. In recent year, however, the mold and die industry has begun to use the technology for the production of components, including those manufactured from hardened tool steels. With increasing cutting speed used in modern machining operation, the thermal aspects of cutting become more and more important. It not only directly influences in rate of tool wear, but also will affect machining precision recognized as thermal expansion and the roughness of the surface finish. Hence, one needs to accurately evaluate the rate of cutting heat generation and temperature distributions on the machining surface. To overcome the heat generation, we used to cutting fluid. Cutting fluid play a roles in metal cutting process. Mechanically coupled effectiveness of cutting fluids affect to friction coefficient at tool-work-piece interface and cutting temperature and chip control, surface finish, tool wear and form accuracy. Through this study, we examined the behavior of heat generation in high-speed machining and the cooling performance of various cooling methods.

• Nuclear Engineering and Technology
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• 제41권7호
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• pp.929-944
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• 2009

The present study is concerned with the extension of the Effective Convectivity Model (ECM) to the phase-change problem to simulate the dynamics of the melt pool formation in a Light Water Reactor (LWR) lower plenum during hypothetical severe accident progression. The ECM uses heat transfer characteristic velocities to describe turbulent natural convection of a melt pool. The simple approach of the ECM method allows implementing different models of the characteristic velocity in a mushy zone for non-eutectic mixtures. The Phase-change ECM (PECM) was examined using three models of the characteristic velocities in a mushy zone and its performance was compared. The PECM was validated using a dual-tier approach, namely validations against existing experimental data (the SIMECO experiment) and validations against results obtained from Computational Fluid Dynamics (CFD) simulations. The results predicted by the PECM implementing the linear dependency of mushy-zone characteristic velocity on fluid fraction are well agreed with the experimental correlation and CFD simulation results. The PECM was applied to simulation of melt pool formation heat transfer in a Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) lower plenum. The study suggests that the PECM is an adequate and effective tool to compute the dynamics of core melt pool formation.

• BMB Reports
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• 제40권1호
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• pp.107-112
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• 2007

To study the functioning of HSP70 in Escherichia coli, we selected NtHSP70-2 (AY372070) from among three genomic clones isolated in Nicotiana tabacum. Recombinant NtHSP70-2, containing a hexahistidine tag at the amino-terminus, was constructed, expressed in E. coli, and purified by $Ni^{2+}$ affinity chromatography and Q Sepharose Fast Flow anion exchange chromatography. The expressed fusion protein, $H_6NtHSP70$-2 (hexahistidine-tagged Nicotiana tabacum heat shock protein 70-2), maintained the stability of E. coli proteins up to 90$^{\circ}C$. Measuring the light scattering of luciferase (luc) revealed that NtHSP70-2 prevents the aggregation of luc without ATP during high-temperature stress. In a functional bioassay (1 h at 50$^{\circ}C$) for recombinant $H_6NtHSP70$-2, E. coli cells overexpressing $H_6NtHSP70$-2 survived about seven times longer than those lacking $H_6NtHSP70$-2. After 2 h at 50$^{\circ}C$, only the E. coli overexpressing $H_6NtHSP70$-2 survived under such conditions. Our NtHSP70-2 bioassays, as well as in vitro studies, strongly suggest that HSP70 confers thermo-tolerance to E. coli.