• Composites Research
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• 제22권5호
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• pp.37-42
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• 2009

온도, 수분 및 자외선과 같은 자연환경을 모사할 수 있는 가속노화시험장치를 적용하여 복합적인 환경인자에 노출된 탄소섬유/에폭시 복합재의 열분석 특성과 화학구조분석을 수행하였다. 복합적인 환경인자의 최대 노출시간은 3000시간으로 노출시간에 따른 복합재의 열분석 특성과 화학구조는 Modulated DSE와 FTIR을 통해 조사하였다. Modulated DSC 시험을 통한 연우-결과에 따르면 노출시간이 증가할수록 복합재 내에 치밀한 망사 구조가 형성되어 유리전이온도는 증가함을 알 수 있었다. 또한 노출시간이 증가할수록 복합재의 특성에 영향을 미치는 물리시효가 발생하여 엔탈피 완화현상을 나타내는 흡열 피크가 관찰되었다. 아울러 FTIR 시험을 통해 관찰된 피크의 위치는 노출시간에 큰 영향을 받지 않지만 피크의 세기는 노출시간이 증가할수록 에폭시기에 발생되는 경화 반응으로 인해 점차 감소함을 알 수 있었다.

• 한국지역사회생활과학회지
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• 제18권4호
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• pp.599-607
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• 2007

We analyzed the effects of regular Jjimjilbang (Korean sauna) exposure on the cold tolerance in young and elderly females. Subjects were young (n=7) and elderly (n=7) females who had never had Jjimjilbang exposure experience. The Jjimjil training group was exposured in the Jjimjilbang 19 times per week. Jjimjibang exposure was limited to three times per day. Jjimjil activity was taken freely. To prove the effects of the cold tolerance, subjects were exposed to cold air ($12{\pm}1^{\circ}C,\;60{\pm}10%$RH). In these conditions, subjects were exposed for 30 minutes at which time rectal temperature, skin temperatures, clothing microclimate, energy expenditure, blood pressure and subjective sensation were measured. To prove the effects of the local cold tolerance, vascular hunting reaction was observed measuring the finger skin temperature while the left middle finger tip was immersed in cold water of $0^{\circ}C$ for 30 minutes. The results are as follows. According to repeated Jjimjil exposure, rectal temperature changes, peripheral temperature and energy expenditure were increased gradually in the cold climate chamber. Blood pressure, subjective sensation and vascular hunting reactions did not show any significant difference. In conclusion, regular Jjimjilbang exposure has negative effects on the ability of the body to improve its regulation of temperature especially in cold tolerance.

• 대한기계학회논문집B
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• 제28권4호
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• pp.493-499
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• 2004

Variations of temperature and velocity fields in a Hele-Shaw convection cell (HSC) were investigated using a holographic interferometry and 2-D PIV system with varying Rayleigh number. To measure quasi-steady variation of temperature field, two different measurement methods of holographic interferometry, double-exposure method and real-time method, were employed. In the double-exposure method, unwanted waves were eliminated effectively using a digital image processing technique. The reconstructed images are clear, but transient flow cannot be reconstructed clearly. On the other hand, transient convective flow can be reconstructed well using the real-time method. However, the fringe patterns reconstructed by the real-time method contain more noises, compared with the double-exposure method. Experimental results show a steady flow pattern at low Rayleigh numbers and a time-dependent periodic flow structure at high Rayleigh numbers. The periodic flow pattern at high Rayleigh numbers obtained by the real-time holographic interferometer method is in a good agreement with the PIV results.

• 한국주조공학회지
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• 제36권5호
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• pp.159-166
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• 2016

The microstructural evolution of a cast Ni base superalloy, IN738LC, has been investigated after long term exposure at several temperatures. Most of the fine secondary ${\gamma}^{\prime}$ particles resolved after 2000 hour exposure at $816^{\circ}C$. At higher temperatures of $871^{\circ}C$ and $927^{\circ}C$, secondary ${\gamma}^{\prime}$ resolved after 1000 hours of exposure, and cuboidal primary ${\gamma}^{\prime}$ grew with exposure time. During the thermal exposure, ${\sigma}$ phase formed at all tested temperatures, and ${\eta}$ phase was observed around interdendritic regions due to carbide degeneration. The influence of microstructural evolution during thermal exposure on the mechanical properties has been analyzed. The effects of ${\gamma}^{\prime}$ particle growth are more pronounced on the high temperature creep properties than on the room temperature tensile properties.

• ETRI Journal
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• 제42권6호
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• pp.837-845
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• 2020

The objective of this study was to implement an in vitro exposure system for 28 GHz to investigate the biological effects of fifth-generation (5G) communication. A signal source of 28 GHz for 5G millimeter-wave (MMW) deployment was developed, followed by a variable attenuator for antenna input power control. A power amplifier was also customized to ensure a maximum output power of 10 W for high-power 28-GHz exposure. A 3-dB uniformity over the 80 mm × 80 mm area that corresponds to four Petri dishes of three-dimensional cell cultures can be obtained using a customized choke-ring-type antenna. An infrared camera is employed for temperature regulation during exposure by adjusting the airflow cooling rate via real-time feedback to the incubator. The reported measurement results confirm that the input power control, uniformity, and temperature regulation for 28-GHz exposure were successfully accomplished, indicating the possibility of a wide application of the implemented in vitro exposure system in the fields of various MMW dose-response studies.

• Steel and Composite Structures
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• 제15권6호
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• pp.705-724
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• 2013

The behaviour of steel column at elevated temperature is significantly different than that at ambient temperature due to its changes in the mechanical properties with temperature. Reported literature suggests that steel column may become vulnerable when exposed to fire condition, since its strength and capacity decrease rapidly with temperature. The present study aims at investigating the lateral load resistance of non-insulated steel columns under fire exposure through finite element analysis. The studied parameters include moment-rotation behaviour, lateral load-deflection behaviour, stiffness and ductility of columns at different axial load levels. It was observed that when the temperature of the column was increased, there was a significant reduction in the lateral load and moment capacity of the non-insulated steel columns. Moreover, it was noted that the stiffness and ductility of steel columns decreased sharply with the increase in temperature, especially for temperatures above $400^{\circ}C$. In addition, the lateral load capacity and the moment capacity of columns were plotted against fire exposure time, which revealed that in fire conditions, the non-insulated steel columns experience substantial reduction in lateral load resistance within 15 minutes of fire exposure.

• 한국패류학회지
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• 제22권2호
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• pp.151-155
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• 2006

Proportion of Tegillarca granosa surviving after 2-6 hrs air exposure with 12 hrs interval at $20^{\circ}C$ and $28^{\circ}C$ for 20 days showed 85-100%, 80-100%, respectively. The survival rate was somewhat lower at high temperature but not significant (p < 0.05). Subsequent exposures for 7-9 days showed survival rate of 8.0-24.1% at $20^{\circ}C$ and $28^{\circ}C$. Oxygen consumption rates and filtration rates were significantly higher for 4 to 6 hrs exposures, compared with the preceding exposures. On the other hand, at $28^{\circ}C$, oxygen consumption rates in adult granular ark for 6 hrs exposure during 20 days had significantly decreased. Filtration rates in study groups increased a little over extended period of exposure, compared with those in control groups, and were similar irrelevant to the time of exposure and size of experimental animals. It is concluded, in view of their viability and oxygen consumption rate during air exposure, that ark shells have quite a high resistance to air exposure with their limited range of responses.

• International Journal of Railway
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• 제1권3호
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• pp.113-116
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• 2008

The long-tenn exposure of polymeric composite materials to extreme-use environments, such as pressure, temperature, moisture, and load cycles, results in changes in the original properties of the material. In this study, the effect of combined environmental factors such as ultraviolet ray, high temperature and high moisture on mechanical and thermal analysis properties of glass fabric and phenolic composites are evaluated through a 2.5 KW accelerated environmental aging tester. The environmental factors such as temperature, moisture and ultraviolet ray applied of specimens. A xenon-arc lamp is utilized for ultraviolet light and exposure time of up to 3000 hours are applied. Several types of specimens - tensile, bending, and shear specimens that are warp direction and fill direction are used to investigate the effects of environmental factors on mechanical properties of the composites. Mechanical degradations for tensile, bending and shear properties are evaluated through a Universal Testing Machine (UTM). Also, storage shear modulus, loss shear modulus and tan a are measured as a function of exposure time through a Dynamic Mechanical Analyzer (DMA). From the experimental results, changes in material properties of glass fabric and phenolic composites are shown to be slightly degraded due to combined environmental effects.

• 대한수의학회지
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• 제59권2호
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• pp.101-104
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• 2019

This study examined the disinfection conditions (exposure time, 0-30 min; exposure temperature, $4^{\circ}C-65^{\circ}C$) of hypochlorous acid water (HOCl) in automobile disinfection equipment. The study tested poliovirus type 1 (PV1), low pathogenic avian influenza virus (AIV, H9N2), and foot and mouth disease virus (FMDV, O type). As a result, the PV1 and FMD viruses were inactivated easily (virus titer 4 log value) by HOCl (> 100 ppm) but the AIV required higher exposure temperatures (> $55^{\circ}C$). In conclusion, the exposure temperature and time are important factors in deactivating AIV and FMDV.

• Restorative Dentistry and Endodontics
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• 제8권1호
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• pp.115-121
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• 1982

Sodium hypochlorite solution has been widely used as endodontic irrigant due to its ability to dissolve pulp tissue debris and its antimicrobial action. This in vitro study was conducted to evaluate the solvent action of sodium hypochlorite solution on vital pulp tissue under various conditions include concentration, exposure time, and temperature. The percentage of weight loss due to pulp tissue dissolution was calculated with weight difference of lyophilized specimens before and after the exposure to test solutions. The results were as follows; Statistical analysis indicated that the ability of both 5.0% and 2.5% sodium hypochlorite solutions to dissolve pulp tissue was significantly greater than that of distilled water, but no significant difference was found between 5.0% and 2.5% sodium hypochlorite solutions. There was no significant increase in the pulp tissue dissolving ability of sodium hypochlorite solutions; as exposure time increased 2 minutes, 5 minutes, and 10 minutes. Of the given temperatures, no significant difference was found in the solvent aciton of sodium hypochlorite solution on pulp tissue between $20^{\circ}C$ (room temperature) and $37^{\circ}C$(body temperature).