• Korean Journal of Materials Research
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• v.16 no.7
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• pp.408-411
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• 2006

An effective wet-chemical approach is demonstrated for growing large-area, selectively-patterned, and low-temperature-synthesized ZnO nanorods (ZNRs). The growth of ZNRs was enhanced on a Co layer. The selectivity and density were readily controlled by the control of the temperature when the substrate transfers into aqueous solution. The cross-sectional transmission electron microscopy image shows that single crystalline ZNRs grown along [0001] have good adhesion at interface between ZNRs/substrate. The turn-on field was 4 $V/{\mu}m$ at the emission current density of 1 ${\mu}A/cm^2$. The stable emission was obtained at 0.11 $mA/cm^2$ under 7.2 $V/{\mu}m$ over 10 hr. These results suggest that selectively-patterned ZNRs have the potential for use as field emitters in large-area field emission displays.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.937-939
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• 2007

Carbon nanotubes (CNTs) have used as an electron field emitter of the field emission display (FED) due to their characteristics of high-electron emission, rapid response and low power consumption. However, to commercialize the FED with CNT emitter, some fundamental problems regarding life time and emission efficiency have to be solved. In this study, we investigated the $TiO_2$ coated CNT as a field emitter. $TiO_2$ nanoparticles can coated on CNT surface by chemical solution method. $TiO_2$ nanoparticles had uniform size with the average size of about 2.4 nm to 3.1 nm. Field emission performance of CNT coated with $TiO_2$ nanoparticles was evaluated and discussed.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.10-16
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• 2004

The Homogeneous Charge Compression Ignition (HCCI) engine has advantage for reducing the NOx and P.M. simultaneously. Therefore, HCCI engine is receiving attention as a low emission diesel engine concept. This study was carried out to investigate the characteristics of combustion and exhaust emission for operating conditions in a direct injection type of HCCI engines such as supercharged and naturally aspirated using diesel fuel and additive. From the experimental result, we found that cool flame was always appeared and also it was difficult to control combustion characteristics by changing the injection timing in HCCI. In addition, at the lean air-fuel ratio and high speed range, it was observed that charging air pressure, additive or increasing intake air temperature is effective to increase combustion performance and reduce exhaust emission. We concluded that chemical reaction by the increasing intake air temperature or additive without physical improvement has limitation for reduction of exhaust emission.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.181-185
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• 2014

This paper describes the effect of canola biodiesel blended fuel on the combustion and emission characteristics in a four cylinder CRDI(Common-rail direct injection) diesel engine. In this study, using the biodiesel fuel(20%,40% of biodiesel-canola oil and 80%, 60% of ULSD(ultra low sulfur diesel) by volume ratio with change of engine speed and injection pressure. The experiment results of increasing biodiesel ratio fuel show that NOx emissions increased. However, soot emission were reduced BC fuels compared to ULSD. Soot emissions largely increased at low injection pressure.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.125-128
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• 2005

In this paper, we argue that the gigahertz peaked spectrum (GPS) quasars are special blazars, blazars in dense and dusty gas enviornment. The ROSAT detection rate of GPS quasars is similar to that of flat spectrum radio quasars (FSRQs), suggesting that the relativistic jets in GPS quasars are oriented at small angle to the line of sight. Due to strong inverse Compton scattering off infrared photons from dense and dusty nuclear interstellar media in GPS quasars, most of them may have significant soft gamma-ray and X-ray emission, which is consistent with ASCA X-ray observations. Because Compton cooling in GPS quasars is stronger than that in FSRQs, synchrotron emission in GPS quasars may less dominate over thermal emission of the accretion disk and hot dust, hence most GPS quasars show low optical polarization and small variability, consistent with observations. We suggest that it is the significant radio emission of electron/positron pairs produced by the interaction of gamma-rays with the dense gas and dust grains in GPS quasars that makes GPS quasars show steep radio spectra, low radio polarization, and relatively faint VLBI/VLBA cores. Whether GPS quasars are special blazars can be tested by gamma-ray observations with GLAST in the near future, with the detection rate of GPS quasars being similar to that of FSRQs.

• Journal of the Korean Society of Combustion
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• v.7 no.4
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• pp.29-35
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• 2002

[$CO_2$] is a well-known greenhouse gas, which is the major source of global warming. Many researchers have studied to reduce $CO_2$ emission in combustion processes. The central method of low $CO_2$ emission is Oxygen/CxHy combustion. Theoretically Oxygen/CxHy combustion only produces $CO_2\;and\;H_2O$ and allows convenient recovery of $CO_2$. The combustion characteristics, flame stability, composition in the flame zone and temperature profile were studied experimentally for various compositions of oxidant by substituting $CO_2\;for\;N_2$ with the constant $O_2$ concentration. Results showed that flame became unstable due to the high heat capacity, low transport rate and strong radiation effect of $CO_2$ in comparison with those of $N_2$. The reaction zone was quenched and broadened, as the ratio of $CO_2\;to\;N_2$ was increased. The emission of NOx in flue gas decreased due to the decreased temperature of the reaction zone. As the conversion ratio of $CO_2\;to\;N_2$ was increased, the emission of CO and the higher temperature zone increased due to decrease of reaction rate by the a quenching effect.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.1
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• pp.44-50
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• 2007

Diesel engines have high thermal efficiency, and they have less CO & HC emissions than another engines. while NOx & Soot emissions are very much. compared with exhaust emission standards. However, the limit level is more and more strengthened yearly due to the importance of environmental protection. So, the optimal countermeasures for the reduction of NOx & Soot emissions below limit level are required. Therefore. the author has investigated the effects of emulsified fuel on the characteristics of exhaust emissions. using an four-cycle, four-cylinder and direct injection diesel engine because the using of emulsified fuel among various methods for reducing NOx & Soot emissions is simple in installation low in cost and high in efficiency. The results of investigation according to various operating conditions are as follows : 1) Specific fuel consumption increase maximum 19.8% at low load. but is not affected at full load. 2) In case of emulsion ratio 25%, NOx emission decrease 32% at 75% load. 30% at full load. 3) In case of emulsion ratio 25%, Soot emission decrease 84% at 75% load, 59% at full load.

• Computers and Concrete
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• v.20 no.5
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• pp.595-603
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• 2017

Piezoceramic transducers have been widely used in the health monitoring of civil structures. However, in most cases, they are used as sensors either to measure strain or receive stress waves. This paper proposes a method of using piezoelectric transducers as strain gauges and acoustic emission (AE) sensors simultaneously. The signals received by piezoceramic transducers are decomposed into different frequency components for various analysis purposes. The low-frequency signals are used to measure strain, whereas the high-frequency signals are used as acoustic emission signal associated with local damage. The b-value theory is used to process the AE signal in piezoceramic transducers. The proposed method was applied in the bending failure experiments of two reinforced concrete beams to verify its feasibility. The results showed that the extracted low-frequency signals from the piezoceramic transducers had good agreement with that from the strain gauge, and the processed high-frequency signal from piezoceramic transducers as AE could indicate the local damage to concrete. The experimental results verified the feasibly of structural health monitoring using piezoceramic transducers as strain gauges and AE sensors simultaneously, which can advance their application in civil engineering.

• Journal of Korean Vacuum Science & Technology
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• v.3 no.1
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• pp.38-42
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• 1999

Using the LOCOS process, we have fabricated the lateral type polysilicon field emission triodes with poly-Si/oxide/Si structure and investigated their current-voltage characteristics for three biasing modes of operation. The fabricated devices exhibit excellent electrical performances such as a relatively low turn-on anode voltage of 14 V at VGC = 0V, a stable and high emission current of 92${\mu}$A/triode over 90 hours, a small gate leakage current of 0.23 ${\mu}$A/triode and an outstanding transconductance of 57${\mu}$S/5triodes at VGC = 5V and VAC = 26V. these superior electrical operation is believed to be due to a large field enhancement effect, which is related to the sharp cathode tips produced by the LOCOS process as well as the high aspect ratio (height /radius ) of the cathode tip end.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.12S
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• pp.1248-1254
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• 2003

Carbon nanotubes(CNTs) are grown by using Co catalyst metal. CNTs fabricated by PECVD(plasma enhanced chemical vapor deposition) method are studied in terms of surface reaction and surface structure by TEM and Raman analysing method and ate analysed in its electrical field emission characteristics with variation of space between anode and cathode. Acetylene(C$_2$H$_2$) gas is used as the carbon source, while ammonia and hydrogen gas are used as catalyst and dilution gas. The CNTs grown by hydrogen(H$_2$) gas plasma indicates better vortical alignment, lower temperature process, and longer tip, compared to that grown by ammonia(NH$_3$) gas plasma. The CNTs fabricated with Co(cobalt) catalyst metal and PECVD method show the multiwall structure in mid-circle type in tip-end and the inner vacancy of 10nm. Emission properties of CNTs indicate the turn-on field to be 2.6 V/${\mu}{\textrm}{m}$ We suggest that CNTs can be possibly applied to the emitter tip of FEDs and high brightness flat lamp because of low temperature CNTs growth, low turn-on field.