• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.53.2-53.2
• /
• 2015

Fiber Bragg gratings (FBGs) are the most compact and reliable method of suppressing atmospheric emission lines in the infrared for ground-based telescopes. It has been proved that real FBGs based filters were able to eliminate 63 bright sky lines with minimal interline losses in 2011 (GNOSIS). Inscribing FBGs on multi-core fibers offers advantages. Compared to arrays of individual SMFs, the multi-core fiber Bragg grating (MCFBG) is greatly reduced in size, resistant to damage, simple to fabricate, and easy to taper into a photonics lantern (PRAXIS). Multi-mode fibers should be used and the number of modes has to be large enough to capture a sufficient amount of light from the telescope. However, the fiber Bragg gratings can only be inscribed in the single-mode fiber. A photonic lantern bi-directionally converts multi-mode to single-mode. The number of cores in MCFBGs corresponds to the mode. For a writing system consisting of a single ultra-violet (UV) laser and phase mask, the standard writing method is insufficient to produce uniform MCFBGs due to the spatial variations of the field at each core within the fiber. Most significant technical challenges are consequences of the side-on illumination of the fiber. Firstly, the fiber cladding acts as a cylindrical lens, narrowing the incident beam as it passes through the air-cladding interface. Consequently, cores receive reduced or zero illumination, while the focusing induces variations in the power at those that are exposed. The second effect is the shadowing of the furthest cores by the cores nearest to the light source. Due to a higher refractive index of cores than the cladding, diffraction occurs at each core-cladding interface as well as cores absorb the light. As a result, any core that is located directly behind another in the beam path is underexposed or exposed to a distorted interference pattern from what phase mask originally generates. Technologies are discussed to overcome the problems and recent experimental results are presented as well as simulation results.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.69.1-69.1
• /
• 2015

Classical T Tauri star DG Tau is suggested as the driving source of parsec-scale jet which expands up to 650" (0.4 pc). To investigate the kinematics and physical properties of the jet, we have obtained the optical emission lines of $H{\alpha}$, [O I] ${\lambda}{\lambda}$6300, 6363, [N II] ${\lambda}{\lambda}$6548,6584, and [S II] ${\lambda}{\lambda}$6716, 6731 from HH 158 ad HH 702. The radial velocity of HH 158 is in the range of -50 to $-250km\;s^{-1}$. For HH 702, located at 650" from the source, it shows ~ $-80km\;s^{-1}$. In HH 158, the electron density ($n_e$) close to the star is ${\sim}10^4cm^{-3}$ and it decreases to ${\sim}10^2cm^{-3}$ at 14" away from the star. Electron temperature ($T_e$) is decreasing from >15,000 K to ~5,000 K with distance. Ionization fraction ($x_e$) is increasing from almost zero to > 0.4 along the distance. In HH 702, the values of $n_e$, $T_e$, and $x_e$ are similar to those estimated at 14" from source, where knot C of HH 158 is located. This may imply that the physical properties of the knot could persist through such a long distance in the space, and the gas could be re-excited by the shock during propagation of the jet. On the other hand, we cannot avoid the possibility that HH 702 is driven by another source rather than DG Tau because HH 158 and HH 702 show somewhat large difference in their inclination angles (${\Delta}i=21-35^{\circ}$).

• Journal of Environmental Science International
• /
• v.23 no.2
• /
• pp.249-259
• /
• 2014

This paper investigates the characteristics of high $PM_{2.5}$ episodes occurred at Anmyeondo area in spring time, 2009. The monthly mean $PM_{2.5}$ concentration during April was the highest in the year and especially, high levels of $PM_{2.5}$ exceeding standard regulation level were sustained consecutively during 5 to 13 April. To analyze more detailed $PM_{2.5}$ characteristics, numerical simulations were carried out using CMAQ(Community Multi-scale Air Quality) with IPR(Integrated Process Rate) and DDM-3D(Decoupled Direct Method). $PM_{2.5}$ level was lower in daytime than that in nighttime due to vigorous vertical mixing during daytime. The chemical composition was showed that ratio of primary ion components such as sulfate($SO_4{^{2-}}$), nitrate($NO_3{^-}$) and ammonium($NH_4{^+}$) were nearly half of total amount of $PM_{2.5}$. Aerosol and transport process dominantly contributed to $PM_{2.5}$ concentration in Anmyeondo area and contribution rate of local emissions was nearly zero since Anmyeondo area has rare anthropogenic PM emission sources. DDM-3D analysis result showed that $PM_{2.5}$ in Anmyeondo area was influenced by emissions from Shanghai and Shandong region of China.

• Journal of Energy Engineering
• /
• v.20 no.1
• /
• pp.8-12
• /
• 2011

For reducing greenhouse gas emissions, the short-term strategy is of existing energy-efficient appliances to facilitate the spread of energy efficiency improvements to improve energy efficiency, energy saving projects that will include investments to enable. R&D is at the core of the long-term strategy. To reduce energy demand, the equipments and processes improved energy efficiency should be developed. In terms of energy supply, the policies for greenhouse gas reduction is to replace fossil fuels by expanding the supply of renewable energy such as solar, wind, geothermal, biomass and nuclear power as nearly zero-emission of greenhouse gas. In terms of energy consumption, measures to reduce greenhouse gas emissions is in line with the policy for efficiency improvement. The buildings & work-site of high-energy consumption in the building & Industry sectors, should implement a policy to strengthening the voluntary agreement on energy-saving facilities and expand to invest in energy saving facilities.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.2
• /
• pp.498-503
• /
• 2012

It happens that the fuel is not injected when the driver doesn't push the acceleration pedal of vehicle with engine speed higher than 1,500rpm above the mid range of vehicle speed. This is called "fuel-cut function" and almost every modern vehicle is equipped with this function. This is activated frequently on the downhill area of highway and the quantity of vehicle-exhausted $CO_2$ gas can be zero on this area. With this fuel-cut function on the test highway, $CO_2$ gas from passenger car(2,000cc engine volume) can be reduced up to 4%. The fuel-cut function with CRUISE made in company AVL is simulated to find the most effective driving pattern on the downhill area. By simulating with CRUISE software, it is found that the lower limit of vehicle speed for fuel-cut should be raised to improve the fuel economy on the steeper downhill road. The fuel economy can be most economical when fuel-cut driving and reacceleration are completed on the section of downhill road.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.5
• /
• pp.1379-1384
• /
• 2014

${\alpha}-Fe_2O_3$ spherical particles having an average diameter of ca. 420 nm and ${\alpha}-Fe_2O_3$ fine particles (< 10 ${\mu}m$ particle size) were prepared to examine as catalysts for CO oxidation. Kinetic studies on the catalytic reactions were performed in a flow reactor using an on-line gas chromatography system operated at 1 atm. The apparent activation energies and the partial orders with respect to CO and $O_2$ were determined from the rates of CO disappearance in the reaction stage showing a constant catalytic activity. In the temperature range of $150-275^{\circ}C$, the apparent activation energies were calculated to be 13.7 kcal/mol on the ${\alpha}-Fe_2O_3$ spherical submicron clusters and 15.0 kcal/mol on the ${\alpha}-Fe_2O_3$ fine powder. The Pco and $Po_2$ dependencies of rate were investigated at various partial pressures of CO and $O_2$ at $250^{\circ}C$. Zero-order kinetics were observed for $O_2$ on both the catalysts, but the reaction order for CO was observed as first-order on the ${\alpha}-Fe_2O_3$ fine powder and 0.75-order on the ${\alpha}-Fe_2O_3$ spherical submicron clusters. The catalytic processes including the inhibition process by $CO_2$ on the ${\alpha}-Fe_2O_3$ spherical submicron powder are discussed according to the kinetic results. The catalysts were characterized using XRD (X-ray powder diffraction), FE-SEM (field emission-scanning electron microscopy), HR-TEM (high resolution-transmission electron microscopy), and $N_2$ sorption measurements.

• Transactions of the Korean hydrogen and new energy society
• /
• v.28 no.1
• /
• pp.56-62
• /
• 2017

Although most electricity production contributes to air pollution, the vehicle organizations and environmental agency categorizes all EVs as zero-emission vehicles because they produce no direct exhaust or emissions. Currently available EVs have a shorter range per charge than most conventional vehicles have per tank of gas. EVs manufacturers typically target a range of 160 km over on a fully charged battery. The energy efficiency and driving range of EVs varies substantially based on driving conditions and driving habits. Extreme outside temperatures tend to reduce range, because more energy must be used to heat or cool the cabin. High driving speeds reduce range because of the energy required to overcome increased drag. Compared with gradual acceleration, rapid acceleration reduces range. Additional devices significant inclines also reduces range. Based on these driving modes and climate conditions, this paper discusses the performance characteristics of EVs on energy efficiency and driving range. Test vehicles were divided by low / high-speed EVs. The difference of test vehicles are on the vehicle speed and size. Low-speed EVs is a denomination for battery EVs that are legally limited to roads with posted speed limits as high as 72 km/h depending on the particular laws, usually are built to have a top speed of 60 km/h, and have a maximum loaded weight of 1,400 kg. Each vehicle test was performed according to the driving modes and test temperature ($-25^{\circ}C{\sim}35^{\circ}C$). It has a great influence on fuel efficiency amd driving distance according to test temperature conditions.

• Current Industrial and Technological Trends in Aerospace
• /
• v.7 no.2
• /
• pp.95-105
• /
• 2009

Fuel cells are applied to the propulsion system of aircraft based on environmental-friendly characteristics with low noise and zero emission of CO2, currently many kinds of UAV and small manned aircraft equipped with fuel cells are being developed. Fuel cells for aircraft typically classified into PEMFC(Proton Exchange Membrane Fuel Cell) type and SOFC(Solid Oxide Fuel Cell) type and the system is developed to adapt missions and operational conditions of aircraft. For UAV, various types of aircraft mostly based on PEM fuel cell technology are investigated for military or commercial uses, and the stability and endurance of system will be improved. For small manned aircraft, many researches are carried out to substitute the propulsion system by fuel cell, also some developments for the higher performance of APU of large commercial aircraft to apply fuel cells are in progress. In the future, a fuel cell aircraft will be expected to improve the reliability and efficiency with higher power density.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.544-545
• /
• 2013

Recently, low-temperature atmospheric-pressure plasmas have been investigated [1,2] for biomedical applications and surface treatments. Experiments for improving hydrophilicity of stainless steel (SUS 304) plate with atmospheric microwave argon and H2O2 mixture plasma jet [3] were carried out and experimental measurements and plasma simulations were conducted for investigating the characteristics of plasma for the process. After 30 s of low power (under 10 W) and low temperature (under $50^{\circ}C$) plasma treatment, the water contact angle decreased rapidly to around $10^{\circ}$ from $75^{\circ}$ and was maintained under $30^{\circ}$ for a day (24 hours). The surface free energy, calculated from the contact angles, increased. The chemical properties of the surface were examined by X-ray Photoelectron Spectroscopy (XPS) and the surface morphology and roughness were examined by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) respectively. The characteristics of plasma sources with several frequencies were investigated by Optical Emission Spectroscopy (OES) measurement and one-dimensional Particle-in-Cell (PIC) simulation and zero-dimensional global simulation [4]. The relation between plasma components and the efficacy of the surface modification were discussed.

• Journal of Environmental Science International
• /
• v.21 no.11
• /
• pp.1321-1331
• /
• 2012

To date, carbon and nitrogen co-doped photocatalysts (CN-$TiO_2$) for environmental application focused mainly on the aqueous phase to investigate the decomposition of water pollutants. Accordingly, the present study explored the photocatalytic performance of CN-$TiO_2$ photocatalysts for the purification of indoor-level gas-phase aromatic species under different operational conditions. The characteristics of prepared photocatalysts were investigated using X-ray diffraction, scanning emission microscope, diffuse reflectance UV-VIS-NIR analysis, and Fourier transform infrared (FTIR) analysis. In most cases, the decomposition efficiency for the target compounds exhibited a decreasing trend as input concentration (IC) increased. Specifically, the average decomposition efficiencies for benzene, toluene, ethyl benzene, and xylene (BTEX) over a 3-h process decreased from 29% to close to zero, 80 to 5%, 95 to 19%, and 99 to 32%, respectively, as the IC increased from 0.1 to 2.0 ppm. The decomposition efficiencies obtained from the CN-$TiO_2$ photocatalytic system were higher than those of the $TiO_2$ system. As relative humidity (RH) increased from 20 to 95%, the decomposition efficiencies for BTEX decreased from 39 to 5%, 97 to 59%, 100 to 87%, and 100 to 92%, respectively. In addition, as the stream flow rates (SFRs) decreased from 3.0 to 1.0 L $min^{-1}$, the average efficiencies for BTEX increased from 0 to 58%, 63 to 100%, 69 to 100%, and 68 to 100%, respectively. Taken together, these findings suggest that three (IC, RH, and SFR) should be considered for better BTEX decomposition efficiencies when applying CN-$TiO_2$ photocatalytic technology to purification of indoor air BTEX.