• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.3
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• pp.288-294
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• 2018

Recently, as the speed and performance of the launcher and the missile have been improved, it is necessary to consider the acoustic load of launching and flight in initial design step. In this paper, an experimental study on acoustic absorption and transmission characteristics of aluminium vs. sandwich composite structures were conducted. The overall noise reduction was evaluated by performing an acoustic test in the reverberation room, and the acoustic absorption and transmission loss of the structures were analyzed by conducting the sound absorption test inside the structure.

• Journal of the Korean Wood Science and Technology
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• v.47 no.5
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• pp.644-654
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• 2019

In this study, the gas permeability, sound absorption coefficient, and sound transmission loss of the Paulownia tomentosa wood were estimated using capillary flow porometry, transfer function method, and transfer matrix method, respectively. The longitudinal specific permeability constant of the Paulownia tomentosa wood with a thickness of 20 mm was 0.254 for the control sample and 0.279, 0.314, and 0.452 after being subjected to heat treatments at $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$, respectively. The gas permeability was observed to be slightly increased by the heat treatment. The mean sound absorption coefficients of 20-mm thick Paulownia tomentosa log cross-section for the control sample and after being subjected to heat treatments at $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$ were 0.101, 0.109, 0.096 and 0.106, respectively. Further, the noise reduction coefficients of 20-mm thick Paulownia tomentosa log cross-section of the control sample and after being subjected to heat treatment at temperatures of $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$ were 0.060, 0.067, 0.062 and 0.071, respectively. The mean of sound transmission loss of the 20-mm thick Paulownia tomentosa log cross-section was approximately 36.93 dB. Furthermore, the gas permeability and sound absorption coefficient of the heat-treated Paulownia tomentosa discs slightly increased depending on the heat treatment temperature; however, the rate of increase was insignificant.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.26 no.3
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• pp.43-55
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• 2023

The railway project is an essential green transportation tool that is considered suitable for the domestic and foreign policy direction of carbon neutrality, but there are some limitations, such as damaging important carbon absorption sources during construction. This study analyzed the environmental impact assessment related to carbon absorption sources of greenhouse gas evaluation items conducted during the railway project, and limitations and implications were derived. The analysis of environmental impact assessment guidelines related to railway projects and carbon absorption sources dealt with prediction and reduction methods related to carbon absorption sources, but guidelines, including environmentally friendly railway construction guidelines, lacked descriptions. Since the greenhouse gas environmental impact assessment, 83 railway project environmental impact assessments have been reviewed, but in some cases, carbon absorption-related predictions have not been implemented, or carbon absorption-related reduction measures have been insufficient. In addition, there were cases where there was a limit to calculating emissions and reduction or where the reduction value was insignificant compared to emissions. In order to supplement the environmental impact assessment in the field of carbon absorption sources related to railway construction projects, alternatives such as quantitative emission and low reduction calculation, review of the no net loss system using the total environmental resource system, and linkage with climate change impact assessment are needed.

• Journal of the Korea Society of Computer and Information
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• v.25 no.2
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• pp.189-195
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• 2020

In this study, the inlet duct and guide vane of the gas floating absorption tower were redesigned to improve the desulfurization efficiency so that the exhaust gas can be uniformly introduced into the absorption tower. In order to reduce the sulfur oxide pollutants among the main sources of air pollutants in industrial boilers, the existing equipment is redesigned and solved. For this purpose, change the exhaust gas, the slurry and recycling the adsorbent to improve the removal efficiency of SOx component in the exhaust gas inside the gas floating absorption tower so as to uniformly contact. And the initial design value and CFD value for the pressure loss from the boiler outlet to the gas floating absorption tower outlet are verified. Also, the velocity distribution of the exhaust gas, the concentration distribution of the recycled adsorbent, the liquid slurry behavior, and the pressure loss were compared. The results confirmed that the desulfurization efficiency was improved because the pressure loss from the boiler outlet to the absorption tower outlet was reduced and the deflection of the exhaust gas was minimized.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.656-661
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• 2013

In this study, the moisture content, charge discharge current, electrostatic capacity and dielectric loss tangent are measured for the specimen of bisphenol type epoxy resin which is mixed with squared amorphous silica filler and dipped in hot water of $50^{\circ}C$ for 169 days. The results of this study are listed below. The longer of deposition day, the charge and discharge current was increased. It is considered that the reason is because there was water attack through the squared silica surface. The longer of deposition day, the absorption rate of all specimens was increased. It found that the absorption rate reached saturated state after 100 days. The higher frequency and the longer of deposition day, the $tan{\delta}$ was decreased. Also, It found that the $tan{\delta}$ and electrostatic capacity of the specimen which is mixed with squared filler are greater.

• Macromolecular Research
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• v.8 no.4
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• pp.165-171
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• 2000

Fluorinated polyimides with high thermal stability, low optical absorption loss in the optical communication wavelengths of 1.3 and 1.55㎛, and low birefringence and water absorption have been investigated for optical waveguide applications. These polyimides were prepared from 2,2-bis(3,4-dicar-boxyphenyl) hexafluoropropane dianhydride (6FDA) with 1,4-bis-(4-amino-2-trifluoromethyl-phenoxy) tetrafluorobenzene (ATPT) , 1,4-bis-(4-amino-2-trifluoromethyl-phenoxy) benzene (ATPB) , and 1,3-bis-(4-amino-2-trifluoromethyl-phenoxy ) 4,6-dichlorobenzene (ATPD ), respectively. The polyimides obtained had glass transition temperatures that ranged from 260 to 280$\^{C}$, and low water absorption less than 0.4% and low optical loss (> 0.2 dB/cm) at 1.3 and 1.55㎛. Birefringency values of polymer films ranged from 0.0041 to 0.0066.

• Journal of electromagnetic engineering and science
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• v.16 no.3
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• pp.150-158
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• 2016

This paper reports on a study of LiNiZn-ferrite composite as a radiation absorbent material (RAM). The electromagnetic (EM) wave absorbers are composed of an EM wave absorbing material and a polymeric binder. The surface morphology, chemical composition, weight percent of the ferrite composite of the toroid sample, magnetic properties, and return loss are investigated using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and network analyzer. For preparing the absorbing sheet, chlorinated polyethylene (CPE) is used as a polymeric binder. The EM wave absorption properties of the prepared samples were studied at 4 - 8 GHz. We can confirm the effects of the thickness of the samples for absorption properties. An absorption bandwidth of more than a 10-dB return loss shifts toward a lower frequency range along with an increase in the thickness of the absorber.

• Journal of Magnetics
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• v.14 no.4
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• pp.155-160
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• 2009

This study examined the effects of a decrease in thickness of magnetic alloy flakes on the electromagnetic wave absorption characteristics of nanocrystalline $Fe_{73.5}Cu_1Nb_3Si_{15.5}B_7$ (at.%) alloy flakes/polymer composite sheets available for a quasi-microwave band. The thickness of FeCuNbSiB alloy flakes decreased to 1-2 $\mu$m with increasing milling time up to 24 h, and the composite sheet including alloy flakes milled for 24 h exhibited considerably enhanced power loss properties in the GHz range compared to the sheets having non-milled alloy powders. Although a considerable increase in loss factor upon milling was observed in the narrow frequency range of 4-6 GHz, there was no correlation between the complex permeability and flake thickness. However, the complex permittivity increased with increasing milling time, and there was good agreement between the milling time and the frequency dependences of the complex permittivity and power loss.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.6
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• pp.133-143
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• 1996

The need of comfortable car and the efforts to overcoming the noise regulations on passenger cars bring about a series of studies on the ruduction of exhaust noises. In this study, acoustic characteristics of various components that compose mufflers of automobiles were analyzed theoretically, and the program which predicts the performance of mufflers was developed by the transfer matrix approach. The simulations were verified by the experiments on a real muffler. By using the developed simulation program, we investigate the effects of each component on the entire muffler system and the energy loss coefficient on absorption materials in the front muffler. Finally, we proposed two designs to improve the performance of a muffler and verified the improved performance by the experiments and simulations.

• Journal of the Optical Society of Korea
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• v.16 no.1
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• pp.80-84
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• 2012

A high reflectance mirror, which has very low absorption and scattering loss, was coated onto a crystalline substrate by ion beam sputtering and then annealed at $450^{\circ}C$. We carefully selected the mirror coating material, and designed the high reflectance mirror, in order to avoid UV degradation which comes from the He-Ne plasma. We measured the surface roughness of the Zerodur substrate using phase shift interferometry and atomic force microscopy, and compared it with the TIS scattering of the mirror. The cavity ring-down method was used to measure the absorption of the mirror, and the thin film structure was correlated to its results. We also compared the optical properties of coated mirrors before and after annealing.