• The Journal of the Acoustical Society of Korea
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• v.21 no.2
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• pp.150-159
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• 2002

The possibility of a broadband noise reduction of piezoelectric smart panels is experimentally studied. Piezoelectric smart panel is basically a plate structure on which piezoelectric patch with shunt circuits is mounted and sound absorbing material is bonded on the surface of the structure. Sound absorbing materials can absorb the sound transmitted at mid frequency region effectively while the use of piezoelectric shunt damping can reduce the transmission at resonance frequencies of the panel structure. To be able to tune the piezoelectric shunt circuit, the measured electrical impedance model is adopted. Resonant shunt circuit composed of register and inductor in stories is considered and the circuit parameters are determined based on maximizing the dissipated energy through the circuit. The transmitted noise reduction performance of smart panels is investigated using an acoustic tunnel. The tunnel is a square crosses sectional tunnel and a loud speaker is mounted at one side of the tunnel as a sound source. Panels are mounted in the middle of the tunnel and the transmitted sound pressure across the panels is measured. Noise reduction performance of a double smart panel possessing absorbing material and air gap shows a good result at mid frequency region except the first resonance frequency. By enabling the piezoelectric shunt damping, noise reduction is achieved at the resonance frequency as well. Piezoelectric smart panels incorporating passive method and piezoelectric shunt damping are a promising technology for noise reduction in a broadband frequency.

• Journal of Astronomy and Space Sciences
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• v.17 no.1
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• pp.53-66
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• 2000

We developed low light CCD imaging system using thermoelectric cooling method collaboration with a company to design a commercial model. It consists of Kodak KAF-0401E(768$\times$512 pixels) CCD chip, thermoelectric module manufactured by Thermotek. This TEC system can reach an operative temperature of $-25^{\circ}C$. We employed an Uniblitz VS25s shutter and it has capability a minimum exposure time 80ms. The system components are an interface card using a Korea Astronomy Observatory (hereafter KAO) ISA bus controller, image acquisition with AD9816 chip, that is 12bit video processor. The performance test with this imaging system showed good operation within the initial specification of our design. It shows a dark current less than 0.4e-/pixel/sec at a temperature of $-10^{\circ}C$, a linearity 99.9$\pm$0.1%, gain 4.24e-/adu, and system noise is 25.3e-(rms). For low temperature CCD operation, we designed a TEC, which uses a one-stage peltier module and forced air heat exchanger. This TEC imaging system enables accurate photometry($\pm$0.01mag) even though the CCD is not at 'conventional' cryogenic temperatures(140k). The system can be a useful instrument for any other imaging applications. Finally, with this system, we obtained several images of astronomical objects for system performance tests.

• Journal of Korean Society of Transportation
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• v.26 no.5
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• pp.117-127
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• 2008

After the deregulation of the aviation market in the United States in 1978, airlines took advantage of the possibilities of the liberalized market and reorganized their networks. Then, the hub-and-spoke networks became widely used in the aviation market. The framework of hub-and-spoke network made it feasible to amplify flight networks. Thus, a number of airlines were able to fly to more destinations than ever before through the networks. Amplification of networks can be implementing through the transfer of passengers, transshipment of cargo, or both most researches have been concentrated on the passenger aspect at airports worldwide. Air cargo, however, has become one of the most significant areas at hub airports to keep their leading position in terms of the provision of services and handling volumes. This paper investigates the connectivity of airfreight networks as the temporal concentrations in current network at Incheon International Airport. In order to evaluate airline flight schedule effects to stimulate hubbing at an airport, the indirect connectivity can be considered to be the number of direct frequencies, the minimum connecting times and the quality of the connection determine indirect connectivity. Therefore the connectivity of freight transshipment depends on both the quality of the connection at the hub airport and the quality of the indirect flight compared to the direct flight. In addressing these issues, this paper analyzes the connectivity of flight schedules using a temporal wave-system structure and estimates the degree of connectivity and quality of connectivity applying the NETSCAN model.

• Journal of Bio-Environment Control
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• v.19 no.4
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• pp.189-194
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• 2010

A multi line electric tube consisted of XL pipes contained with 2~4 hot wires and water in it. The specification of one meter length multi-line electric tube was investigated and the proper number in the multi-line electric tube was determined. A multi line electric tube with three hot wires were found to be the most efficient for the media heating control system. Temperature rise of medium in the rice hulls media was faster than that in the perlite media, showed better insulation effect of rice hulls media. Temperature rise of medium with mulching on the top of the bed was faster than without mulching, resulted in the beneficial effect of temperature rise with mulching. The regression model for the rice hulls media with mulching air temperature of $5^{\circ}C$ were a = -0.1458 and b = -0.1088. Using the model, the temperature rise of medium during low temperature season can be predicted for the various media according to the different depths.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2150-2158
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• 1992

This study was carried out to investigate the flow structure and mixing process of a cross mixing flow formed by two round jets with respect to the ratio of mass flow rate. This flow configuration is of great practical relevance in a variety of combustion systems, and the flow behaviour of a cross jet defends critically on the ratio of mass flow rate and the cross angle. The mass flow rate ratios of two different jets were controlled as 1.0, 0.8, 0.6, and 0.4, and the crossing angle of two round jets was fixed at 45 degree. The velocities issuing from jet nozzle with an exit diameter of 20mm were adjusted to 40m/s, 32m/s, 24m/s, and 16m/s, and the measurements have been conducted in the streamwise range of $1.1X_0$to $2.5X_0$ by an on-line measurement system consisted of a constant temperature type two channel hot-wire anemometry connected to a computer analyzing system. The original air flow was generated by a subsonic wind tunnel with reliable stabilities and uniform flows in the test section. For the analysis of the cross mixing flow structure in the downstream region after the cross point, the mean velocity profiles, the resultant velocity contours, and the three-dimensional profiles depending upon the mass flow rate ratio have been concentrately studied.

• Horticultural Science & Technology
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• v.32 no.4
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• pp.493-498
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• 2014

The objective of this study was to make growth and yield models for common ice plant (Mesembryanthemum crystallinum L.) using expolinear functional equations in a closed-type plant production system. Three-band radiation type fluorescent lamps with a 12-hours photoperiod were used, and the light intensity was $200{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$. Nutrient film systems with three layers were used for plant growth. Environmental conditions, such as air temperature, relative humidity and $CO_2$ concentration were controlled by an ON/OFF operation. Leaf area, shoot fresh and dry weights, light use efficiency of common ice plant as function of days after transplanting, accumulative temperature and accumulative radiation were analyzed. Leaf area, shoot fresh and dry weights per area were described using an expolinear equation. A linear relationship between shoot dry and fresh weights was observed. Light use efficiency of common ice plant was $3.3g{\cdot}MJ^{-1}$ at 30 days after transplanting. It is concluded that the expolinear growth model can be a useful tool for quantifying the growth and yield of common ice plant in a closed plant production system.

• Tunnel and Underground Space
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• v.25 no.1
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• pp.107-114
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• 2015

This study focuses on assessing risks which might occur in operation stage of CAES storage cavern and analyzing fire scenarios for the risk that have been assessed with highest risk level. Risks in operation stage were categorized into upper risk group and lower risk group. Components of upper risk group are technical risk, facility risk and natural disaster risk. Lower risk group is composed of 11 sub-risks. 20 experts were chosen to survey questionnaires. ANP model was applied to analyze the relative importance of 11 sub-risks. Results of risk analysis were compared with risk criterion to set risk priorities, and the highest risk was determined to be 'occurrence of the fire within the management opening'. Three fire scenarios were developed for the highest risk level and FDS (Fire dynamics Simulator) was used to analyze these scenarios. No. 3 scenario which air blows from tunnel into outside atmosphere represented that a rate of smoke spread was the fastest among three fire scenarios and a smoke descended most quickly below the limit line of breathing. Thus, No. 3 scenario turned out to be the most unfavorable condition when operating staffs were evacuated from access tunnel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.465-473
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• 2018

A cabinet-door integrated finite element model for a built-in side-by-side refrigerator with an ice dispenser and home bar was constructed, and its deformation was analyzed by ANSYS. As loads, the food load in the shelf and baskets, and thermal load occurring during the normal operation condition were considered. From results of the analyses, the door height difference (DHD) and door flatness difference (DFD) between the two doors, and the increase in the gap of the door gasket, which affects the sealing of cool air in the cabinet, were derived. As results of an evaluation of the differences, the DHD and DFD under the assembled condition satisfied the acceptance criteria of the manufacturer. The food and thermal loads increased the DHD and DFD due to thermal deformation, and the DFD increased significantly. In addition, the increase in the gap of door gasket located between the cabinet and doors was derived from the results of displacements under the food and thermal loads. The evaluation showed that the maximum increase in gap appeared at the left edge of the freezing compartment gasket, which satisfied the acceptance criteria of the manufacturer.

• KIPS Transactions on Software and Data Engineering
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• v.9 no.4
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• pp.129-136
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• 2020

PM2.5 which is a very tiny air particulate matter even smaller than PM10 has been issued in the environmental problem. Since PM2.5 can cause eye diseases or respiratory problems and infiltrate even deep blood vessels in the brain, it is important to predict PM2.5. However, it is difficult to predict PM2.5 because there is no clear explanation yet regarding the creation and the movement of PM2.5. Thus, prediction methods which not only predict PM2.5 accurately but also have the interpretability of the result are needed. To predict hourly PM2.5 of Seoul city, we propose a method using random forest with the adjusted bootstrap number from the time series ground data preprocessed on different sources. With this method, the prediction model can be trained uniformly on hourly information and the result has the interpretability. To evaluate the prediction performance, we conducted comparative experiments. As a result, the performance of the proposed method was superior against other models in all labels. Also, the proposed method showed the importance of the variables regarding the creation of PM2.5 and the effect of China.

• Journal of Soil and Groundwater Environment
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• v.9 no.1
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• pp.12-27
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• 2004

The contamination pattern of indoor air was simulated when groundwater dissolving benzene was used for household activities. Indoor exposure scenario consisted of inhalation, ingestion, and dermal absorption. Physiologically based pharmacokinetic (PBPK) model was used to analyze how benzene exposed to human body was distributed in internal organs. Main exposure pathways contributing total internal dose were inhalation and ingestion while the contribution of dermal absorption was very small. Man showed higher exposure rate than woman due to his higher breath rate. For a short-term exposure, benzene concentration in venous blood of SPT, RPT and liver changed rapidly while slowly did in venous blood of adipose tissue at a low concentration. For a long-term exposure, woman accumulated about 2.1 times higher than man. Most of benzene exposed to human body was removed by exhalation and metabolism at lung and liver, respectively. For inhalation and ingestion, the benzene removals by exhalation were 69.8 and 48.4%, respectively. Relative importance of removal mechanism was different according to the inflow displacement of benzene. The results obtained from this study would help understand exposure, distribution, and removal phenomena and make plans for the reduction of the health risk associated with the contaminated groundwater by various organic compounds.