• ETRI Journal
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• v.32 no.5
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• pp.831-834
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• 2010

This paper proposes a new joint channel coding algorithm based on principal component analysis. A conventional joint channel coder using passive downmixing undergoes a reduction of both the primary-to-ambient energy ratio (PAR) of the downmix signal and the panning gain ratio of the primary source. The proposed system preserves the PAR of the downmix signal by using active downmixing which reflects spatial characteristic. The proposed system also improves the accuracy of the panning gain ratio estimation. Computer simulations and subjective listening tests verify the performance of the proposed system.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.3
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• pp.93-98
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• 2011

To analyze and evaluate the performance of developing air to water multi heat pump, the heat pump was installed and tested at low energy house in Daejeon, korea. Heating capacity of heat pump is 16.5KW and cooling capacity is 14.0KW. Space heating/cooling, floor heating and hot water is available. The results performance evaluation of heat pump in lab test showed that the coefficient of performance (cop) was 3.75, and heating capacity was 16.0KW in ambient temperature $7^{\circ}C$. Also at ambient temperature $-15^{\circ}C$, the COP was 1.69. At a low energy house, floor heating is controled by a floor heating water temperature and a room temperature. The COP of heat pump is decreased with frequent on/off operation for controlling of floor heating water temperature.

• Journal of Wind Energy
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• v.14 no.3
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• pp.91-99
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• 2023

In research conducted on a southwestern Korean offshore meteorological tower, acceleration datasets were gathered over half a year with time-history sensors. To enhance data credibility, a parallel measurement system was used for verification. A model of the tower was configured using beam elements, and with modifications accounting for added stiffness from auxiliary structures. Ground interactions were considered as calibrated springs based on soil layer properties. The tower's dynamic attributes and mass sensitivity were discerned using eigenvalue analysis. The structural natural frequency was consistent, with variations primarily due to new equipment adding approximately 1400 kgs. With free vibration damping assumptions, a damping ratio of roughly 1 % was derived.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1320-1327
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• 2013

In this paper, two different electromagnetic energy harvesters using bulk micromachined silicon spiral springs and Polydimethylsiloxane (PDMS) packaging technique have been fabricated, characterized, and compared to generate electrical energy from ultra-low ambient vibrations under 0.3g. The proposed energy harvesters were comprised of a highly miniaturized Neodymium Iron Boron (NdFeB) magnet, silicon spiral spring, multi-turned copper coil, and PDMS housing in order to improve the electrical output powers and reduce their sizes/volumes. When an external vibration moves directly the magnet mounted as a seismic mass at the center of the spiral spring, the mechanical energy of the moving mass is transformed to electrical energy through the 183 turns of solenoid copper coils. The silicon spiral springs were applied to generate high electrical output power by maximizing the deflection of the movable mass at the low level vibrations. The fabricated energy harvesters using these two different spiral springs exhibited the resonant frequencies of 36Hz and 63Hz and the optimal load resistances of $99{\Omega}$ and $55{\Omega}$, respectively. In particular, the energy harvester using the spiral spring with two links exhibited much better linearity characteristics than the one with four links. It generated $29.02{\mu}W$ of output power and 107.3mV of load voltage at the vibration acceleration of 0.3g. It also exhibited power density and normalized power density of $48.37{\mu}W{\cdot}cm-3$ and $537.41{\mu}W{\cdot}cm-3{\cdot}g-2$, respectively. The total volume of the fabricated energy harvesters was $1cm{\times}1cm{\times}0.6cm$ (height).

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.49 no.1
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• pp.58-66
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• 2013

Most of steam power plant in Korea are heating the feed water system to prevent freezing water flowing in the pipe in winter time. The heating system is operated whenever the ambient temperature around the power plant area below 5 degree Centigrade. But this kind of heat supplying system cause a lot of energy consuming. If we think about the method that the temperature of the each pipe is controled by attaching the temperature measuring sensor like RTD sensor and heat is supplied only when the outer surface temperature of the pipe is under 5 degree Centigrade, then we can save a plenty of energy. In this study, the computer program package for simulation is used to compare the energy consumption load of both systems. Energy saving rate is calculated for the location of Youngweol area using the data of weather station in winter season, especially the January' severe weather data is analyzed for comparison. Various convection heat transfer coefficients for the ambient air and the flowing water inside the pipe was used for the accurate calculation. And also the various initial flowing water temperature was used for the system. Steady state analysis is done previously to approximate the result before the simulation. The result shows that the temperature control system using RTD sensor represents the high energy saving effect which is more than 90% of energy saving rate. Even in the severe January weather condition, the energy saving rate is almost 60%.

• Journal of the Korean Vacuum Society
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• v.6 no.3
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• pp.206-212
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• 1997

The reflow characteristics of copper, which is expected to be used as interconnection materials in the next generation semiconductor devices, were investigated. Copper films were deposited on hole and trench patterns by metal organic chemical vapor deposition and annealed in nitrogen and oxygen ambient with the annealing temperatures ranging from $350^{\circ}C$ to $550^{\circ}C$. Copper films were not reflowed into the patterns upon the annealing in nitrogen ambient, but reflowed at the annealing temperature higher than $450^{\circ}C$ in oxygen ambient. It is considered that the reflow takes place as the heat generated by the oxidation of copper liquefies the copper film partly and the liquid copper fills the patterns for minimizing the surface energy and the potential energy. Upon the annealing in oxygen ambient, the copper oxide whose thickness was less than 300$\AA$ formed at the surface of an agglomerate and the resistivity of copper film increased drastically at an annealing temperature of $550^{\circ}C$ due to the copper agglomeration.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.1
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• pp.35-44
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• 2000

The winter case of the near-field dilution at the Masan outfalls has been studied by field measurements and CORMIX model simulations. Dilution rates of the wastewater discharge in winter were obtained by a salinity deficit method using the field data observed in the neap tidal period of February, 1999. The observed dilution rates in winter season were found to be very high in the range of 90～130 due to the isopycnal mixing of ambient density compared with the summer range of 30～40 under weak neap tidal currents. The results of CORMIX model simulations also show that the winter dilution rates under a weak ambient current(Ua=6.0ms/s) were increased by 3-fold of the summer dilution rates. However, the difference between two seasons becomes small by 30% under a strong current(Ua=15.5cm/s). This result indicates that the dilution and hydrodynamic mixing process of the effluents are more influenced by ambient crossflow condition than by ambient density stratification at the outfalls site.

• Journal of Soil and Groundwater Environment
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• v.14 no.6
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• pp.87-94
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• 2009

Surfactant-enhanced air sparging (SEAS) was developed to suppress the surface tension of groundwater prior to air sparging resulting in higher air saturation and larger contact area between NAPL and gas during air sparging. Larger contacting interface between NAPL and gas means faster mass transfer of contaminants from NAPL to gas phase. This new technique, however, is limited to relatively volatile contaminants because vaporization is its basic mechanism of mass transfer. In this study, SEAS was tested at an elevated temperature for a semi-volatile n-decane, which is expected not to be a good candidate of SEAS application due to its low vapor pressure at ambient temperature. Three sparging experiments were conducted using 1-dimensional column (5 cm id, 80 cm length) packed with sand; (1) ambient temperature ($23^{\circ}C$), column saturated with distilled water, (2) SEAS at ambient temperature ($23^{\circ}C$), for n-decane contaminated sand, (3) SEAS at elevated temperature ($73^{\circ}C$), for n-decane contaminated sand. Higher air saturation was achieved by SEAS compared to that by air sparging without surfactant application. The n-decane removal efficiency of SEAS at elevated temperature was significantly higher(> 10 times) than that of ambient SEAS. The n-decane concentrations in the gas effluent from column during SEAS at $73^{\circ}C$ are found to be 10 times of those measured at ambient temperature. Thus, SEAS technique can be applied for removal of semi-volatile contaminants provided that an appropriate technique for elevating aquifer temperature is available.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.4
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• pp.7-12
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• 2019

Ambient backscatter communication is limited to channel estimation technique through a pilot signal, which is a channel estimation method in current RF communication, due to transmission power efficiency. In a limited transmission power environment, the research of traditional ambient backscatter communication has been studied assuming that it is an ideal channel without signal distortions due to channel conditions. In this paper, we propose an expectation-maximization(EM) algorithm, one of the blind channel estimation techniques, as a channel estimation method in ambient backscatter communication system which is the state of channel following normal distribution. In the proposed system model, the simulations confirm that channel estimate through EM algorithm is approaching the lower bound of the mean square error compared with the Bayesian Cramer-Rao Boundary(BCRB) to check performance. It shows that the channel parameter can be estimated in the ambient backscatter communication system.

• Tribology and Lubricants
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• v.40 no.3
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• pp.103-110
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• 2024

Gas foil thrust bearings (GFTBs) are oil-free self-acting hydrodynamic bearings that support axial loads with a low friction during airborne operation. They need solid lubricants to reduce dry-friction between the runner and top foil and minimize local wears on their surfaces during start-up and shutdown processes. In this study, we evaluate the lift-off speeds and load capacity performance of a GFTB with Polytetrafluoroethylene (PTFE) surface coating by measuring drag torques during a series of experimental tests at increasing ambient temperatures of 25, 75 and 110℃. An electric heat gun provides hot air to the test GFTB operating in the closed booth to increase the ambient temperature. Test results show that the increasing ambient temperature delays the lift-off speed and decreases the load capacity of the test GFTB. An early developed prediction tool well predicts the measured drag torques at 60 krpm. After all tests, post inspections of the surface coating of the top foil are conducted. Scanning electron microscope (SEM) images imply that abrasive wear and oxidation wear are dominant during the tests at 25℃ and 110℃, respectively. A quantitative energy dispersive spectroscopy (EDS) microanalysis reveals that the weight percentages of carbon, oxygen, and nitrogen decrease, while that of fluorine increases significantly during the highest-temperature tests. The study demonstrates that the increasing ambient temperature noticeably deteriorates the static performances and degrades the surface coating of the test GFTB.