• The Journal of the Acoustical Society of Korea
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• v.42 no.1
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• pp.7-15
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• 2023

Recently, as interest in air quality in vehicles increases, the use of fine dust detection sensors for air quality measurement is becoming common. An axial-flow fan is inserted in the fine dust sensor installed in the air conditioning system in the vehicle to prevent dust from sinking directly on the sensor. When the sensor operates, the flow noise caused by the rotation of the axial-flow fan acts as a major noise source of the fine dust sensor. flow noise is recognized as one of the product competitiveness of fine dust sensors. In this study, the noise was gradually reduced at the same flow rate by improving the flow performance of the small axial flow fan. First, a virtual fan performance tester consisting of about 20 million grids was developed to analyze the aerodynamic performance of the target small axial-flow fan. In addition, the flow field was simulated by using compressible Large Eddy Simulation for direct computation of flow noise as well as high-accurate prediction of flow rate. The validity of numerical method are confirmed through the comparison of predicted results with experimental ones. After the effects of pitch angle on flow performance were analyzed using the verified numerical method, the pitch angle was determined to maximize the flow rate. It was found that the flow rate was increased by 8.1 % and noise was reduced by 0.8 dBA when the axial-flow fan with the optimum pitch angle was used.

• Journal of the Institute of Convergence Signal Processing
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• v.23 no.4
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• pp.228-233
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• 2022

This study is an experimental study on how to use phase change materials(PCM) to generate electrical energy for long-term operation of underwater unmanned vehicles. The electrical energy generation method is a volume change and a pressure change that occur as a phase change material changes to a solid or liquid state according to temperature, and the change in pressure creates a flow of fluid to create electrical energy. Polyethylene glycol was used as a phase change material considering the temperature of the ocean. In addition, an electrical energy generating device that converts volume change into pressure at low temperature (1℃~2℃) in solid state and high temperature (21℃~25℃) in liquid state was fabricated. As a result of the experiment, the pressure change according to the phase change rapidly changed between 1 hour and 2 hours, and maintained a pressure of about 24MPa after 4 hours. Through this, it was confirmed that it can be used as a power source for underwater unmanned vehicles using phase change materials and temperature differences. In addition, it was found that a more improved design should be made in order to apply the phase change material to an underwater unmanned vehicle.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6D
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• pp.693-702
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• 2009

In the Seoul metropolitan area (SMA), transportation sector is the largest source of air pollutant emissions. Of the total amount of air pollutant emissions in the SMA, about 52% of the particulate matter emissions and 59% of the nitrogen oxide emissions are from superannuated heavy diesel vehicles. To lessen the air pollutant emissions from superannuated heavy vehicles in the SMA, this study devised several strategies for operating Environmental Zone (EZ) program, which requires superannuated heavy diesel vehicles to install reduction equipments as well as restricts them entering part of the SMA, and evaluated the effects of different strategies on air pollution in the SMA. By using the Korean traffic statistics, an evaluation has been made of six EZ scenarios, which were devised by different target areas and vehicles. The results showed that the EZ program with retrofitting a DPF (Diesel Particulate Filter) equipment to 7-year-old heavy diesel vehicles and early scrapping of pre-1998 heavy diesel vehicles is the most efficient alternative in terms of air pollution reduction. In addition, the results showed that the magnitude of air pollution reduction increases when implementing the EZ program to all entering superannuated heavy diesel vehicles to the SMA rather than registered ones in the SMA.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.17 no.2
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• pp.195-205
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• 2022

This study aims to investigate the relationship between Corporate Venture Capital(CVC) investments and firm innovation, exploring the moderating effect of corporate ESG risk on this relationship. First, adopting the organizational learning theory, I theorize a process in which a firm's relationship with a venture through CVC investments acts as an external innovation source for learning and ultimately short-term innovation. Also, based on the discussion of the stakeholder theory, I argue that when a firm is evaluated as having high ESG risk externally, this may have a negative moderating effect that weakens the relationship between CVC investments and innovative performance. In order to verify these hypotheses, panel data analysis was performed using CVC investments data, patent application data, and ESG risk scores of US high-tech firms from 1993 to 2018. As a result of the analysis, as expected, it was found that the more the firm invests in ventures through CVC, the more the firm's innovative performance increases. In addition, the social aspect of ESG risk of a firm, related to the local community and employees, were found to weaken the association between CVC investments and innovative performance. This study expands the understanding of existing research on CVC investments as a vehicle for learning and innovation. Focusing on the importance of relationship with ventures rather than the size of CVC investments, I empirically examined that the formation of CVC relationships with ventures is directly related to the short-term innovation of investing firms. Additionally, this study contributes to the CVC literature by including stakeholders in the current discussion in addition to investing firms and portfolio ventures. Finally, this study investigated how ESG issues, which are attracting attention as playing an important role in firm activities, are related to CVC investments.

• The Journal of the Acoustical Society of Korea
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• v.26 no.7
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• pp.361-365
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• 2007

Aero-pulsation noise, generally caused by geometric asymmetry of a rotating device, is one of considerable sources of annoyance in passenger cars using the turbocharged diesel engine. Main source of this noise is the compressor wheel in the turbocharger system, and can be reduced by after-treatment devices such as silencers, but which may increase the manufacturing cost. More effective solution is to improve the geometric symmetry over all, or to control the quality of components by sorting out inferior ones. The latter is more simple and reasonable than the former in view of manufacturing. Thus, an appropriate discrimination method should be needed to evaluate aero-pulsation noise level at the production line. In this paper, we introduce the accurate method which can measure the noise level of aero-pulsation and also present its evaluation criteria. Besides verifying the reliability of a measurement system - a rig test system-, we analyze the correlation between the results from rig tests and those from vehicle tests. The gage R&R method is carried out to check the repeatability of measurements over 25 samples. From the result, we propose the standard specification which can discriminate inferior products from superior ones on the basis of aero-pulsation noise level.

• Electrical & Electronic Materials
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• v.12 no.7
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• pp.7-11
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• 1999

Fully sealed field emission display in size of 4.5 inch has been fabricated using single-wall carbon nanotubes-organic vehicle com-posite. The fabricated display were fully scalable at low temperature below 415$^{\circ}C$ and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1V/${\mu}{\textrm}{m}$ and field emis-sion current of 1.5mA at 3V/${\mu}{\textrm}{m}$ (J=90${\mu}{\textrm}{m}$/$\textrm{cm}^2$)were observed. Brightness of 1800cd/$m^2$ at 3.7V/${\mu}{\textrm}{m}$ was observed on the entire area of 4.5-inch panel from the green phosphor-ITO glass. The fluctuation of the current was found to be about 7% over a 4.5-inch cath-ode area. This reliable result enables us to produce large area full-color flat panel dis-play in the near future. Carbon nanotubes (CNTs) have attracted much attention because of their unique elec-trical properties and their potential applica-tions [1, 2]. Large aspect ratio of CNTs together with high chemical stability. ther-mal conductivity, and high mechanical strength are advantageous for applications to the field emitter [3]. Several results have been reported on the field emissions from multi-walled nanotubes (MWNTs) and single-walled nanotubes (SWNTs) grown from arc discharge [4, 5]. De Heer et al. have reported the field emission from nan-otubes aligned by the suspension-filtering method. This approach is too difficult to be fully adopted in integration process. Recently, there have been efforts to make applications to field emission devices using nanotubes. Saito et al. demonstrated a car-bon nanotube-based lamp, which was oper-ated at high voltage (10KV) [8]. Aproto-type diode structure was tested by the size of 100mm $\times$ 10mm in vacuum chamber [9]. the difficulties arise from the arrangement of vertically aligned nanotubes after the growth. Recently vertically aligned carbon nanotubes have been synthesized using plasma-enhanced chemical vapor deposition(CVD) [6, 7]. Yet, control of a large area synthesis is still not easily accessible with such approaches. Here we report integra-tion processes of fully sealed 4.5-inch CNT-field emission displays (FEDs). Low turn-on voltage with high brightness, and stabili-ty clearly demonstrate the potential applica-bility of carbon nanotubes to full color dis-plays in near future. For flat panel display in a large area, car-bon nanotubes-based field emitters were fabricated by using nanotubes-organic vehi-cles. The purified SWNTs, which were syn-thesized by dc arc discharge, were dispersed in iso propyl alcohol, and then mixed with on organic binder. The paste of well-dis-persed carbon nanotubes was squeezed onto the metal-patterned sodalime glass throuhg the metal mesh of 20${\mu}{\textrm}{m}$ in size and subse-quently heat-treated in order to remove the organic binder. The insulating spacers in thickness of 200${\mu}{\textrm}{m}$ are inserted between the lower and upper glasses. The Y\ulcornerO\ulcornerS:Eu, ZnS:Cu, Al, and ZnS:Ag, Cl, phosphors are electrically deposited on the upper glass for red, green, and blue colors, respectively. The typical sizes of each phosphor are 2~3 micron. The assembled structure was sealed in an atmosphere of highly purified Ar gas by means of a glass frit. The display plate was evacuated down to the pressure level of 1$\times$10\ulcorner Torr. Three non-evaporable getters of Ti-Zr-V-Fe were activated during the final heat-exhausting procedure. Finally, the active area of 4.5-inch panel with fully sealed carbon nanotubes was pro-duced. Emission currents were character-ized by the DC-mode and pulse-modulating mode at the voltage up to 800 volts. The brightness of field emission was measured by the Luminance calorimeter (BM-7, Topcon).

• Journal of Korean Society of Environmental Engineers
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• v.30 no.3
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• pp.302-313
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• 2008

The purposes of this study are to investigate the concentration levels of fine particles, so called PM$_{2.5}$, to identify the affecting sources, and to estimate quantitatively the source contributions of PM$_{2.5}$. Ambient air sampling was seasonally carried out at two sites in Pohang(a residential and an industrial area) during the period of March to December 2003. PM$_{2.5}$ samples were collected by high volume air samplers with a PM$_{10}$ Inlet and an impactor for particle size segregation, and then determined by gravimetric method. The chemical species associated with PM$_{2.5}$ were analyzed by inductively coupled plasma spectrophotometery(ICP) and ion chromatography(IC). The results showed that the most significant season for PM$_{2.5}$ mass concentrations appeared to be spring, followed by winter, fall, and summer. The annual mean concentrations of PM$_{2.5}$ were 36.6 $\mu$g/m$^3$ in the industrial and 30.6 $\mu$g/m$^3$ in the residential area, respectively. The major components associated with PM$_{2.5}$ were the secondary aerosols such as nitrates and sulfates, which were respectively 4.2 and 8.6 $\mu$g/m$^3$ in the industrial area and 3.7 and 6.9 $\mu$g/m$^3$ in the residential area. The concentrations of chemical component in relation to natural emission sources such as Al, Ca, Mg, K were generally higher at both sampling sites than other sources. However, the concentrations of Fe, Mn, Cr in the industrial area were higher than those in the residential area. Based on the principal component analysis and stepwise multiple linear regression analysis for both areas, it was found that soil/road dust and secondary aerosols are the most significant factors affecting the variations of PM$_{2.5}$ in the ambient air of Pohang. The source apportionments of PM$_{2.5}$ were conducted by chemical mass balance(CMB) modeling. The contributions of PM$_{2.5}$ emission sources were estimated using the CMB8.0 receptor model, resulting that soil/road dust was the major contributor to PM$_{2.5}$, followed by secondary aerosols, vehicle emissions, marine aerosols, metallurgy industry. Finally, the application and its limitations of chemical mass balance modeling for PM$_{2.5}$ was discussed.

• Clinical and Experimental Pediatrics
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• v.52 no.7
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• pp.824-831
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• 2009

Purpose : We aimed to investigate the efficacy of and functional recovery after intracerebral transplantation of different doses of mouse mesenchymal stem cells (mMSCs) in immature rat brain with hypoxic-ischemic encephalopathy (HIE). Methods : Postnatal 7-days-old Sprague-Dawley rats, which had undergone unilateral HI operation, were given stereotaxic intracerebral injections of either vehicle or mMSCs and then tested for locomotory activity in the 2nd, 4th, 6th, and 8th week of the stem cell injection. In the 8th week, Morris water maze test was performed to evaluate the learning and memory dysfunction for a week. Results : In the open field test, no differences were observed in the total distance/the total duration (F=0.412, P=0.745) among the 4 study groups. In the invisible-platform Morris water maze test, significant differences were observed in escape latency (F=380.319, P<0.01) among the 4 groups. The escape latency in the control group significantly differed from that in the high-dose mMSC and/or sham group on training days 2-5 (Scheffe's test, P<0.05) and became prominent with time progression (F=6.034, P<0.01). In spatial probe trial and visible-platform Morris water maze test, no significant improvement was observed in the rats that had undergone transplantation. Conclusion : Although the rats that received a high dose of mMSCs showed significant recovery in the learning-related behavioral test only, our data support that mMSCs may be used as a valuable source to improve outcome in HIE. Further study is necessary to identify the optimal dose that shows maximal efficacy for HIE treatment.

• Journal of Korean Society for Atmospheric Environment
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• v.34 no.3
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• pp.430-446
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• 2018

To improve understanding of the sources and chemical properties of particulate pollutants on the Korean Peninsula, An Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) measured non-refractory fine particle ($NR-PM_1$) from 2013 to 2015 at Baengnyeong Island and Seoul metropolitan area (SMA), Korea. The chemical composition of $NR-PM_1$ in Baengnyeong island was dominated by organics and sulfate in the range of 36~38% for 3 years, and the organics were the dominant species in the range of 44~55% of $NR-PM_1$ in Seoul metropolitan area. The sulfate was found to be more than 85% of the anthropogenic origin in the both areas of Baengnyeong and SMA. Ratio of gas to particle partition of sulfate and nitrate were observed in both areas as more than 0.6 and 0.8, respectively, representing potential for formation of additional particulate sulfate and nitrate. The high-resolution spectra of organic aerosol (OA) were separated by three factors which were Primary OA(POA), Semi-Volatility Oxygenated Organic Aerosol (SV-OOA), and Low-Volatility OOA(LV-OOA) using positive matrix factorization (PMF) analysis. The fraction of oxygenated OA (SOA, ${\fallingdotseq}OOA$=SV-OOA+LV-OOA) was bigger than the fraction of POA in $NR-PM_1$. The POA fraction of OA in Seoul is higher than it of Baengnyeong Island, because Seoul has a relatively large number of primary pollutants, such as gasoline or diesel vehicle, factories, energy facilities. Potential source contribution function (PSCF) analysis revealed that transport from eastern China, an industrial area with high emissions, was associated with high particulate sulfate and organic concentrations at the Baengnyeong and SMA sites. PSCF also presents that the ship emissions on the Yellow Sea was associated with high particulate sulfate concentrations at the measurement sites.

• Journal of Yeungnam Medical Science
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• v.6 no.2
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• pp.159-172
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• 1989

This study was conducted to compare the date on knowledge, attitude and motivation toward blood donation between donors and nondonors. The study population included 622 donors and 322 nondonors who visited the mobile blood donation car of Taegu Red Cross Blood Center and participated the group appointed blood donation campaign managed by the center from March 1 to March 31, 1989. The donors and nondonors were questioned above mentioned items with a formulated questionnaire. Among the general characteristics of the subjects in the study, male predominace(84.1% in donors and 73.6% in nondonors) in young age group (16-24 years) was the outstanding feature. As a medium of information about blood donation, "television" was playing a dominant role(donors ; 75.2%, nondonors ; 78.9%), while "magazine"played more important roles among donors. Of the donors, 70.6% and of the nondonors, 58.1% replied that they had ever been induced to donate blood (p<0.01). Major inducers were friend and personnel of mobile blood donation vehicle. On the measuring of knowledge level, the average rates of correct answer was higher in donors (62.6%) than in nondonors (54.1%) (p<0.01). Higher the education level was presented, higher the knowledge level (p<0.05). There have been noticeable difference between donors and nondonors in blood replying the questionnaire set to measure their attitude toward blood donation. especially in the items such as "impression toward blood", "selection of transfusion blood source" and "view on the situation of blood shortage." The major motivation toward blood donation of the groups were "possible future need" and "altruism or humanitarian interest". The major reasons for not donating blood in both groups were "fear of the needle" and around to visit to mobile car or center."