• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1284-1291
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• 2002

Combustion instabilities are an important concern associated with lean premixed combustion. Laboratory-scale dump combustor was used to understand the underlying mechanisms causing combustion instabilities. Experiments were conducted at atmospheric pressure and sound level meter was used to track the pressure fluctuations inside the combustor. Instability maps and phase-resolved OH chemiluminescence images were obtained at several conditions to investigate the mechanism of combustion instability and relations between pressure wave and heat release rate. It showed that combustion instability was susceptible to occur at higher value of equivalence ratio (>0.6) as the mean velocity was decreased. Instabilities exhibited a longitudinal mode with a dominant frequency of ∼341.8 Hz, which corresponded to a quarter wave mode of combustor. Heat release and pressure waves were in-phase when instabilities occurred. Rayleigh index distribution gave a hint about the location where the strong coherence of pressure and heat release existed. These results also give an insight to the control scheme of combustion instabilities. Emission test revealed that NOx emissions were affected by not only equivalence ratio but also combustion instability.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.55.3-55.3
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• 2017

The L1641 cloud in Orion is an active site of star formation. We mapped a square region of 60 arcmin by 60 arcmin in the continuum emission from 0.89 mm to 2.0 mm wavelength using MUSIC mounted on the Caltech Submillimeter Observatory 10.4 m telescope. Eight sources were detected in at least two wavelength bands, and all the detected emission comes from thermal dust continuum radiation of dense cloud cores. Their spectral energy distributions were characterized. The dust emissivity spectral index is beta = 1.3 on average, within the range of typical cores in nearby star-forming regions. Two cores, V380 Ori NE and HH 34 MMS, have unusually low emissivity index of beta = 0.3. These cores may contain millimeter-sized dust grains, which suggests that the lifetime of some dense cores can be much longer than the free-fall timescale.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.210-217
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• 1998

This paper describes the method for detection of the misfired cylinder using the pressure fluctuations occurred in the exhaust system on an MPI gasoline engine. If misfire is occurred in the cylinder of the gasoline engine, the power of engine gets lost, the fuel consumption and the exhaust emission are increased and the vibration is caused by unsteady torque. Therefore early detection and correction of misfire play a very important role in the proper performance and the exhaust emission. This paper suggests method of misfire detection which affect engine performance. The method is a comparison of average pressure index during the displacement period. Experimental results showed that the method using the pressure fluctuations in the exhaust system is proven to be effective in the detection of misfire on gasoline engine regardless loads and revolutions of the engine. In addition, this method, using the pressure fluctuations in exhaust system is easier than other methods and is not a need of additional reconstruction of engine.

• Journal of Climate Change Research
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• v.8 no.4
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• pp.357-367
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• 2017

Electricity generation in Korea mainly depends on thermal power and nuclear power. Especially the coal power has led to the increase in $CO_2$ emissions. This paper intends to analyze the current status of $CO_2$ emissions from electricity generation in Korea during the period 1990~2016, and apply the logarithmic mean Divisia index (LMDI) technique to find the nature of the factors influencing the changes in $CO_2$ emissions. The main results as follows: first, $CO_2$ emission from electricity generation has increased by $165.9MtCO_2$ during the period of analysis. Coal products is the main fuel type for thermal power generation, which accounts about 73% $CO_2$ emissions from electricity generation. Secondly, the increase of real GDP is the most important contributor to increase $CO_2$ emissions from electricity generation. The carbon intensity and the electricity intensity also affected the increase in $CO_2$ emission, but the energy intensity effect and the dependency of thermal power effect play the dominant role in decreasing $CO_2$ emissions.

• Korean Journal of Optics and Photonics
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• v.22 no.1
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• pp.53-57
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• 2011

In this paper, we improved the light extraction efficiency by considering an additional upper layer on the top surface of a conventional LED. We simulated the LED's light emission as functions of the thickness and the refractive index of the upper layer, and analyzed how the condition improved the light efficiency. When the refractive index's range was from 1.05 to 1.40, the LED emission increased. For that case, the emission also increased as the thickness increased. We experimentally showed that the light extraction efficiency was improved about 22% by forming the upper layer on the top surface of an LED using material with refractive index 1.30 at 589.3 nm. It is expected that forming the upper layer on an LED can easily improve the extraction efficiency.

• Journal of The Korean Astronomical Society
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• v.48 no.5
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• pp.257-265
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• 2015

We present results of long-term multi-wavelength polarization observations of the powerful blazar 3C 279 after its γ-ray flare on 2013 December 20. We followed up this flare with single-dish polarization observations using two 21-m telescopes of the Korean VLBI Network. Observations carried out weekly from 2013 December 25 to 2015 January 11, at 22 GHz, 43 GHz, 86 GHz simultaneously, as part of the Monitoring Of GAmma-ray Bright AGN (MOGABA) program. We measured 3C 279 total flux densities of 22–34 Jy at 22 GHz, 15–28 Jy (43 GHz), and 10–21 Jy (86 GHz), showing mild variability of ≤ 50 % over the period of our observations. The spectral index between 22 GHz and 86 GHz ranged from −0.13 to −0.36. Linear polarization angles were 27°–38°, 30°–42°, and 33°–50° at 22 GHz, 43 GHz, and 86 GHz, respectively. The degree of linear polarization was in the range of 6–12 %, and slightly decreased with time at all frequencies. We investigated Faraday rotation and depolarization of the polarized emission at 22–86 GHz, and found Faraday rotation measures (RM) of −300 to −1200 rad m⁻² between 22 GHz and 43 GHz, and −800 to −5100 rad m⁻² between 43 GHz and 86 GHz. The RM values follow a power law with a mean power law index a of 2.2, implying that the polarized emission at these frequencies travels through a Faraday screen in or near the jet. We conclude that the regions emitting polarized radio emission may be different from the region responsible for the 2013 December γ-ray flare and are maintained by the dominant magnetic field perpendicular to the direction of the radio jet at milliarcsecond scales.

• Geomechanics and Engineering
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• v.13 no.5
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• pp.861-879
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• 2017

Coal and gas outburst is a serious dynamic disaster that occurs during coal mining and threatens the lives of coal miners. Currently, coal and gas outburst is commonly predicted using single indicator and its critical value. However, single indicator is unable to fully reflect all of the factors impacting outburst risk and has poor prediction accuracy. Therefore, a more accurate prediction method is necessary. In this work, we first analyzed on-site impacting factors and precursors of coal and gas outburst; then, we constructed a Fisher discriminant analysis (FDA) index system using the gas adsorption index of drilling cutting ${\Delta}h_2$, the drilling cutting weight S, the initial velocity of gas emission from borehole q, the thickness of soft coal h, and the maximum ratio of post-blasting gas emission peak to pre-blasting gas emission $B_{max}$; finally, we studied an FDA-based multiple indicators discriminant model of coal and gas outburst, and applied the discriminant model to predict coal and gas outburst. The results showed that the discriminant model has 100% prediction accuracy, even when some conventional indexes are lower than the warning criteria. The FDA method has a broad application prospects in coal and gas outburst prediction.

• The Journal of Sustainable Design and Educational Environment Research
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• v.12 no.1
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• pp.35-45
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• 2013

The purpose of this study is to suggest improvement plans of school green building certification system in the concept of the Green Building Index by comparing items of domestic system with those of foreign system. School is a public facility for students. So Green Building Certification System for School must have educational point of view adding to energy saving, reduction of greenhouse gas emission, etc. Also school is forming a large part with the apartment house in the green building certification system. So we need to manage the green building certification system for school to meet carbon reduction policy.

• Journal of The Korean Astronomical Society
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• v.47 no.5
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• pp.195-199
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• 2014

We present a GUI-based interactive Python program, VIMAP, which generates radio spectral index maps of active galactic nuclei (AGN) from Very Long Baseline Interferometry (VLBI) maps obtained at different frequencies. VIMAP is a handy tool for the spectral analysis of synchrotron emission from AGN jets, specifically of spectral index distributions, turn-over frequencies, and core-shifts. In general, the required accurate image alignment is difficult to achieve because of a loss of absolute spatial coordinate information during VLBI data reduction (self-calibration) and/or intrinsic variations of source structure as function of frequency. These issues are overcome by VIMAP which in turn is based on the two-dimensional cross-correlation algorithm of Croke & Gabuzda (2008). In this paper, we briefly review the problem of aligning VLBI AGN maps, describe the workflow of VIMAP, and present an analysis of archival VLBI maps of the active nucleus 3C 120.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.6
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• pp.597-600
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• 1999

By periodically varying the current density and etching time during anodic oxidation of crustalline silicon wafers in 15% HF-ethanol solution, we obtained porous silicon multilayers which have periodically varying refractive index. We fabricated the porous silicon microcavity (PSM) which consist of porous silicon multilayers (I), active layer of porous silicon, and porous silicon multilayers (II) and investigated its physical properties. The AFM (Atomic Force Microscope) measurement from the cross section of multilayers (I and II) shows uniformity of high refractive index and low index layers as well as the active layer. We observed the characteristics of Bragg reflector when the thickness of layers was 1/4 and the thickness of active layer was twice of the effective wavelength, which can be used as a filter for specific wavelength. We found the emission characteristic from the PSM, which FWHM (full width half maximum) was considerably decreased and emission intensity was increased.