• Restorative Dentistry and Endodontics
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• v.24 no.2
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• pp.265-285
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• 1999

The purposes of this investigation were to observe the reaction kinetics of five commercial dual cured resin cements (Bistite, Dual, Scotchbond, Duolink and Duo) when cured under varying thicknesses of porcelain inlays by chemical or light activation and to evaluate the effect of the porcelain disc on the rate of polymerization of dual cured resin cement during light exposure by using thermal analysis. Thermogravimetric analysis(TGA) was used to evaluate the weight change as a function of temperature during a thermal program from $25{\sim}800^{\circ}C$ at rate of $10^{\circ}C$/min and to measure inorganic filler weight %. Differential scanning calorimetry(DSC) was used to evaluate the heat of cure(${\Delta}H$), maximum rate of heat output and peak heat flow time in dual cured resin cement systems when the polymerization reaction occured by chemical cure only or by light exposure through 0mm, 1mm, 2mm and 4mm thickness of porcelain discs. In 4mm thickness of porcelain disc, the exposure time was varied from 40s to 60s to investigate the effect of the exposure time on polymerization reaction. To investigate the effect on the setting of dual cured resin cements of absorption of polymerizing light by porcelain materials used as inlays and onlays, the change of the intensity of the light attenuated by 1mm, 2mm and 4mm thickness of porcelain discs was measured using curing radiometer. The results were as follows 1. The heat of cure of resin cements was 34~60J/gm and significant differences were observed between brands (P<0.001). Inverse relationship was present between the heat of reaction and filler weight % the heat of cure decreased with increasing filler content (R=-0.967). The heat of reaction by light cure was greater than by chemical cure in Bistite, Scotchbond and Duolink(P<0.05), but there was no statistically significant difference in Dual and Duo(P>0.05). 2. The polymerization rate of chemical cure and light cure of five commercially available dual cured resin cements was found to vary greatly with brand. Setting time based on peak heat flow time was shortest in Duo during chemical cure, and shortest in Dual during light cure. Cure speed by light exposure was 5~20 times faster than by chemical cure in dual cured resin cements. The dual cured resin cements differed markedly in the ratio of light and chemical activated catalysts. 3. The peak heat flow time increased by 1.51, 1.87, and 3.24 times as light cure was done through 1mm, 2mm and 4mm thick porcelain discs. Exposure times recommended by the manufacturers were insufficient to compensate for the attenuation of light by the 4mm thick porcelain disc. 4. A strong inverse relationship was observed between peak heat flow and peak time in chemical cure(R=0.951), and a strong positive correlations hip was observed between peak heat flow and the heat of cure in light cure(R=0.928). There was no correlationship present between filler weight % or heat of cure and peak time. 5. The thermal decomposition of resin cements occured primarily between $300^{\circ}C$ and $480^{\circ}C$ with maximum decomposition rates at $335^{\circ}C$ and $440^{\circ}C$.

• Journal of Magnetics
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• v.20 no.3
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• pp.215-220
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• 2015

The PVDF fibrous composite filled with iron oxide nanoparticles were prepared by using the electrospinning technique. The electrospun composite have the thickness in the range of $60-80{\mu}m$ with the average fibrous diameters of 500-900 nm. The magnetizations of PVDF fibrous composite filled with iron oxide nanoparticles showed 4.5 emu/g, 3.1 emu/g and 1.6 emu/g at 1.5 T of external magnetic field for 20 wt.%, 10 wt.% and 5 wt.% iron oxide nanoparticles, respectively. The heat elevation of the magnetic composite were measured under various AC magnetic fields, frequency and the ambient temperatures. The temperature reached up to $46.3^{\circ}C$ from $36^{\circ}C$ at 128 Oe and 355 kHz for 20 wt.% iron oxide nanoparticles filled in PVDF fibrous composite sheet. The specific absorption rate of theses sheets increased from 0.041 W/g to 0.236 W/g with the increment of AC magnetic field from 90 Oe to 167 Oe at 190 kHz, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.1
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• pp.47-52
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• 2009

We studied the electrical characteristics of low-k SiOCH interlayer dielectric(ILD) films fabricated by plasma enhanced chemical vapor deposition (PECVD). BTMSM precursor was evaporated and introduced with the flow rates from 16 sccm to 25 sccm by 1 sccm step with the constant flow rate of 60 sccm $O_2$ in process chamber. The vibrational groups of SiOCH thin films were analyzed by FT!IR absorption lines, and the dielectric constant of the low-k SiOCH thin films were obtained by measuring C-V characteristic curves. The heat treatment on SiOCH thin films reduced the FTIR absorption intensity of the Si-O-$CH_3$ bonding group and Si-$CH_3$ bonding group but increased the intensity of Si-O-Si(C) bonding group. The SiOCH ILD films could have low dielectric constant $k\;{\simeq}\;2$ and also be reduced further by decreasing the $CH_3$ group density and increasing Si-O-Si(C) group density through annealing process.

• Applied Chemistry for Engineering
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• v.21 no.5
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• pp.522-526
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• 2010

Heat storage application techniques can be categorized into the sensible heat storage and the latent heat storage according to the method of heat storage. Heat storage is the way of saving remaining heat when heating and cooling loads are light, and then using it when the heating and cooling loads are heavy. Latent heat storage is defined as the method of saving heat by using substances which have high potential heat when phase change is in the range of a certain temperature and when heat storage space is small, compared to those of sensible heat storage and it is possible that absorption and emission of heat at a certain temperature. This study is conducted to save energy when either air-conditioning or heating is operated in a building. We have tried to find out the essential properties of matter and the optimum mixing rate about cement and gypsum for building materials, which have been widely used for proper phase change materials (PCM), when thermal environment property is applied. So we obtained the result of the cooling delay effect about 19% with heat storage mortar containing 3 wt% of PCM.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.3
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• pp.56-61
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• 2010

Recently, UV pulse laser is widely used in micro machining of the research, development and industry field of IT, NT and BT products because the laser short wavelength provides not only micro drilling, micro cutting and micro grooving which has a very fine line width, but also high absorption coefficient which allows a lot of type of materials to be machined more easily. To analyze the dynamic deformation during a very short processing time, which is nearly about several tens nanoseconds, the commercial Finite Element Analysis (FEA) code, LS-DYNA 3D, was employed for the computitional simulation of the UV laser micro machining behavior for thin copper material in this paper. A finite element model considering high strain rate effect is especially suggested to investigate the micro phenomena which are only dominated by mechanically pressure impact in disregard of thermally heat transfer. From these computational results, some of dynamic deformation behaviors such as dent deformation shapes, strains and stresses distributions were observed and compared with previous experimental works. These will help us to understand micro interaction between UV laser beam and material.

• Food Science and Preservation
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• v.9 no.2
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• pp.194-199
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• 2002

This study was conducted to develop processing method for vinegar powder from natural vinegar for encapsulation applications. To optimize the spray drying process, experiment was designed by central composition method to find optimal conditions for manufacturing vinegar powder. The acidity, water absorption, solid content and heat stability of vinegar powder were selected as response variables. The optimal concentration of inclusion complex which was made with vinegar and ${\beta}$-cyclodextrin was determined on 30。bx. On increasing the concentration of ${\beta}$-cyclodextrin as a wall material, the quality of the vinegar was decreased. The optimum conditions of spray drying process for manufacturing vinegar powder were 188∼192$^{\circ}C$ and 500∼600 Lh$\^$ -1/ as inlet temperature and flow rate, respectively.

• Journal of the Korean Wood Science and Technology
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• v.30 no.3
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• pp.91-96
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• 2002

This study was carried out to estimate the property of dimensional stability of heat compression of italian poplar wood with low density. Firstly, two levels of pressure conditions were applied using the closed and open-press system. The thermal treatment temperatures were 180℃ and 200℃, respectively. Water absorption tests were conducted in water bath at 25℃ and 100℃ for 35 hours and 1 hour, respectively. The compression rates of wood were 47 percent, 60 percent, and 73 percent, respectively. From these tests, it was found that the dimensional stability of the closed-press system was superior to that of the open-press system. Furthermore, the dimensional stability of compressed wood in the closed-press system was better at 200℃ than 180℃. In compression rate, dimensional stability of 73 percent compression rate was the best result. Considering these results, the best conditions for the dimensional stability of compressed wood were those of the closed-compressing system at high temperatures above 200℃ and larger compression rate. Therefore, it was concluded that the dimensional stability of wood is improved at higher temperature and larger deformation.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.279-283
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• 2009

Distributed generation(DG) of combined cooling, heat. and power(CCHP)has been gaining momentum in recent year as efficient, secure alternative for meeting increasing energy demands. This paper presents the energy performance of microturbine CCHP system equipped with an absorption chiller by modelling it in hospital building. The orders of study were as following. 1)The list and schedule of energy consumption equipment in hospital were examined such as heating and cooling machine, light etc. 2) Annual report of energy usage and monitoring data were examined as heating, cooling, DHW, lighting, etc. 3) The weather data in 2007 was used for simulation and was arranged by meteorological office data in Daejeon. 4) Reference simulation model was built by comparison of real energy consumption and simulation result by TRNSYS and ESP-r. The energy consumption pattern of building were analyzed by simulation model and energy reduction rate were calculated over the cogeneration. As a result of this study, power generation efficiency of turbine was about 30% after installing micro gas turbine and lighting energy as well as total electricity consumption can be reduced by 40%. If electricity energy and waste heat in turbine are used, 56% of heating energy and 67% of cooling energy can be reduced respectively, and total system efficiency can be increased up to 70%.

• Transactions of the Korean hydrogen and new energy society
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• v.5 no.2
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• pp.81-90
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• 1994

The hydrogen fuel tanks having hydrogen storing capacity of about 300g and 1200g are manufactured using $MmNi_{4.7}Al_{0.25}V_{0.05}Fe_{0.001}$ alloy. They are composed of several unit reactor made of Cu-tube(outer diameter = 50.1mm, thickness = 2mm). In order to increase the heat and mass transfer property of the hydride bed, Al-plates are inserted perpendicular to axial direction at intervals of 5mm and three arteries of diameter 8mm are installed symmetrically in each unit reactor. Hydrogen absorption is proceeded about 80% within 30 minute and is completed within 60 minute at the conditions of charging hydrogen pressure of 25atm and temperature of $22^{\circ}C$. On desorbing hydrogen at a constant rate of 30 slm at $20^{\circ}C$, discharging hydrogen pressure is sustained at 3~5atm for 120 minutes. The discharging pressure is increased upto 5~8atm as the increase of the reactor temperature to $30^{\circ}C$. From the experimental results and the brief discussions about the hydrogen absorption and disorption behaviors of the hydrogen storage tank, it is suggested that the behaviors of hydrogen charging and discharging could be controlled by adjusting the operating parameters and the reactor design parameters.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.1
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• pp.63-70
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• 1997

A study was performed to examine the aging behaviors of Al-2.1Li-2.9Cu alloy by differential scanning calorimetry and transmission electron microscopy. DSC measurements were conducted over the temperature range of $25{\sim}550^{\circ}C$ at a heating rate of $5^{\circ}C$/min. for the specimens aged at 130, 160, $190^{\circ}C$ and $220^{\circ}C$ for various times after solution treatment at $540^{\circ}C$ for 30 minutes. The peaks due to the formation of G.P.zone were not detected in the specimens aged at 130 and $160^{\circ}C$, but those at 190 and $220^{\circ}C$ appeared in DSC curves. The heat absorption due to the dissolution of ${\delta}^{\prime}$ phase was increased with increasing aging time at $130^{\circ}C$ aging. In contrast, those values for the specimens aged at 160 and $190^{\circ}C$ were initially increased and inversely decreased at the transition time of 72 and 1 hour, respectively. The heat evolution due to the formation of $T_1$ phase was nearly unchanged at $130^{\circ}C$ aging, but at $160^{\circ}C$ and $190^{\circ}C$ aging, drastically decreased after the transition time. It can be considered that the increase of $T_1$ phase results in the decrease of ${\delta}^{\prime}$ phase when aging time is longer than the transition time. The hardness of the specimen aged at $190^{\circ}C$ is initially higher compared with that at $160^{\circ}C$, however, the peak hardness shows the lower value than that at $160^{\circ}C$.