• Journal of the Korean Society of Safety
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• v.17 no.4
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• pp.66-70
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• 2002

The transient soot distributions within the region bounded by the droplet surface and the flame were measured using a full-filed light extinction technique and subsequent tomographic inversion using Abel transforms. The soot volume fraction results for n-heptane droplets represent the first quantitative assessment of the degree of sooting for isolated droplets burning under microgravity condition. The absence of buoyancy(which produces longer residence times) and the effects of thermophoresis produce a situation in which a significant concentration of soot is produced and accumulated into a soot-cloud. Results indicate that indeed the soot concentration within the microgravity droplet flames(with maximum soot volume fractions as high as ~60ppm) are significantly higher than corresponding values that are reports for normal-gravity flames. This increase in likely due to longer residence times and thermophoretic effects that manifested under microgravity conditions.

• Korean Journal of Optics and Photonics
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• v.35 no.1
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• pp.1-8
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• 2024

Explicit expressions for the transmission pseudo-ellipsometric constants and transmittance of a semi-transparent glass substrate coated with thin films are presented to determine the optical constants of a very weakly absorbing thin film coated on a glass substrate. The intensity of the multiply reflected light inside the semi-transparent substrate is superposed incoherently and the light absorption by the substrate is properly treated, so that modeling analysis of thin films coated on a semi-transparent substrate can be performed with increased accuracy. The extinction coefficient derived from transmittance analysis is compared to that from ellipsometric analysis in the weakly absorbing region, and the difference between the two extinction coefficients is discussed in relation to the sensitivities of the transmittance and ellipsometric constants. This transmittance analysis, together with ellipsometric analysis, is applied to a glass substrate coated with a SiN thin film, and it is shown that the thickness and complex refractive index of the SiN thin film can be determined accurately, even though the extinction coefficient is very small.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2008.10a
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• pp.357-358
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• 2008

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1796-1804
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• 1992

Profiles of soot volume fraction, average diameter and particle number density have been measured using a light scattering and extinction technique in a coannular propane diffusion flame at atmosperic pressure. Temperature profiles were also obtained using a thermocouple technique. Measurements show that soot is first observed to form low in the flame in an annular region inside the main reaction zone. At higher locations this annular region widen until entire flame is observed to contain particles. Soot volume fraction and particle diameter profiles peak some 1mm on the fuel side of peak temperature and increase with height to oxidation region. Number density of the flame core drop steeply from formation region to growth region and relatively invariant to some height and decay out at flame tip.

• Fire Science and Engineering
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• v.29 no.3
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• pp.43-47
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• 2015

Water mist was sprayed on small compartment areas filled with smoke that formed from two different combustibles. The water-mist injection pressure and time were varied, and changes in the light extinction coefficient were measured over time. The smoke removal effect was analyzed with a light sensing smoke meter in different experimental conditions. Using the meter, the changes in smoke density were converted to changes in DC voltage over time to obtain the changes in the light extinction coefficient. The water mist was more effective in eliminating the smoke formed from glowing compared to flaming combustion. The smoke removal effect was significantly better with greater injection pressure and injection time.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.468-480
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• 1998

The temporal and spatial distributions of soot volume fractions were measured for single toluene droplet flames as a function of pressure under the normal-gravity condition. In order to characterize the transient nature of the flame and sooting regions, a full-field light extinction and subsequent tomographic inversion technique was used. The reduction in sooting as a function of pressure was assessed by comparison of the maximum soot volume fractions at several vertical positions along the axis above the droplet. The maximum soot volume fraction was reduced by 70% when the pressure was reduced by 60% from 1 atm to 0.4 atm. The reduction in sooting is attributed to variation of the geometric configuration of flame which reduces the system Grashof number as well as only the change in the adiabatic flame temperature as the pressure decreases. The gravimetrically-measured total soot yield was also compared to the optically-measured soot volume fraction to obtain a correlation between the two measurements. As a result, the total soot yield was linearly proportional to the optically-measured maximum soot volume fraction and linearly reduced as the pressure decreased. Accordingly, the non-intrusive full-field light extinction-measurements were able to be calibrated not only to measure soot volume fraction, but to simultaneously evaluate the total soot yield emitted from the toluene droplet flame (which is useful in the practical application).

• Journal of The Korean Astronomical Society
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• v.49 no.6
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• pp.233-238
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• 2016

The missing historical record of the Cassiopeia A (Cas A) supernova (SN) event implies a large extinction to the SN, possibly greater than the interstellar extinction to the current SN remnant. Here we investigate the possibility that the guest star that appeared near Cas A in 1592-1593 in Korean history books could have been an 'impostor' of the Cas A SN, i.e., a luminous transient that appeared to be a SN but did not destroy the progenitor star, with strong mass loss to have provided extra circumstellar extinction. We first review the Korean records and show that a spatial coincidence between the guest star and Cas A cannot be ruled out, as opposed to previous studies. Based on modern astrophysical findings on core-collapse SN, we argue that Cas A could have had an impostor and derive its anticipated properties. It turned out that the Cas A SN impostor must have been bright ($M_V=-14.7{\pm}2.2mag$) and an amount of dust with visual extinction of ${\geq}2.8{\pm}2.2mag$ should have formed in the ejected envelope and/or in a strong wind afterwards. The mass loss needs to have been spherically asymmetric in order to see the light echo from the SN event but not the one from the impostor event.

• Journal of Korean Ophthalmic Optics Society
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• v.6 no.2
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• pp.11-16
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• 2001

The polariscope to measure :he stress in lens was made up quarter-wave plate polarizer and we analyzed two components of light's wave $E_1$ and $E_2$ following the steps. It is clear that the principal-stress difference ${\sigma}_1-{\sigma}_2$ can be determined in 2-D model if fringe order N is measured each point in sample moreover. the optical axes of sample coincide with the principal-stress directions. The birefringence acted to a light wave and a phase retardation were in proportioned to the principal-stressed difference (${\sigma}_1-{\sigma}_2$) and the intensity of final light wave was proportioned to $sin^2({\Delta}/2)$, when ${\Delta}/2=n^{\pi}$ (n=0, 1, 2, ...) and the extinction occurs. As a experimental result, the extinction band shifted owing to a magnitude of lens' external stress.

• Journal of ILASS-Korea
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• v.18 no.3
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• pp.132-139
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• 2013

Smoke emissions from light duty diesel vehicles were measured using light extinction method with the free acceleration test mode. The smoke emissions for each measurement cycle of the free acceleration method showed large variations according to driver's pedal pushing pattern. The smoke values for each measurement cycle initially increased and reach a peak value. Integration of the smoke emissions with time for each measurement cycle was performed to get a representative smoke value which was obtained by averaging the integrated results. Two kinds of integration time range were used. One is range over the whole measurement cycle of the free acceleration method. The other is only the acceleration range in the measurement cycle. Overall, variation of the representative smoke values obtained by the integration method was reduced comparing to the traditional representative smoke value which was obtained from a peak smoke value over the measurement cycle. Ten vehicles of the same model with 2.5 liter diesel engines, and seven vehicles of the same model with 2.7 liter diesel engines, were tested using the free acceleration test method.

• Particle and aerosol research
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• v.11 no.4
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• pp.93-98
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• 2015

Particles which generated from plasma enhanced chemical vapor deposition (PECVD) during thin film deposition process can affect to the process yield. By using light extinction method, ISPM can measure particles in the large-diameter pipe (${\leq}300mm$). In our research, in-situ particle monitor (ISPM) sensor was installed at the 300 mm diameter exhaust-line to count the particles in each size. In-house flange for mounting the transmitting and receiving parts of ISPM was carefully designed and installed at a certain point of exhaust line where no plasma light affect to the light extinction measurement. Measurement results of trend changes on particle count in each size can confirm that ISPM is suitable for real-time monitoring of vacuum process.