• Korean Journal of Optics and Photonics
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• v.28 no.1
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• pp.16-21
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• 2017

A systematic understanding of the effects of high-intensity flash sources on the human eye is strongly needed, not only for proper use of the sources, but for human eye health. In this study, the exposure-limit distance (ELD), indicating the minimal safe distance in case of seeing by chance a high-intensity flash, is proposed. The optical procedures to determine the ELD of a high-intensity flash are clarified, and the dependence of ELD on its parameters such as luminous intensity, duration, and radius of a flash are thoroughly investigated. From this investigation it is obvious that, while being weakly dependent on duration, the ELD is nearly proportional to the luminous intensity and the radius of a flash. The proposed ELD as an intuitive safety-indicating parameter is more useful and intuitive than the other characteristic parameters of a high-intensity flash. The ELD is expected to be an essential parameter as a safety indicator, to characterize the performance of a high-intensity flash and to promote the safety of the human eye.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.283-288
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• 2016

A non-lethal weapon is a device that can subdue targets without causing death or mortal wounds. A high-intensity flash generator can negate electro-optical sensors and cause temporal flash blindness with a high intensity of light. In this study, we derive the design parameters of an explosive-driven high-intensity flash generator that uses the interaction of plasma caused by the detonation of explosives with surrounding inert gas. To determine the design parameters of the flash generator, we analyze test results measured using optical sensors. The experimental results show that the light intensity of xenon gas is about four times higher than that of air. In addition, the intensity increases with the weight of the explosive, and the inert gas cross-sectional area encountered a shock wave in the airframe. The light intensity caused by a double-initiation generator is about two times higher than that of the single-initiation generator.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.7
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• pp.1225-1230
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• 2016

Since a flash light produces enormous amount of photon energy in short time, not only electro-optic and infrared(EO/IR) systems utilized for Intelligence Surveillance Target Acquisition and reconnaissance(ISTAR) activities but also the people of a combat field can be severely influenced by a high flash light bursting in front of them. The people who bumped into a flash could not escape such enormous amount of photon energy, resulting in being blind temporarily or even permanently. In order to investigate the effect of a high flash source on a human eye, it is essential to know how much photon energy be incident into an eye from the flash source. In this paper, the model of irradiated photon energy to individuals from some flashes is proposed. The proposed irradiated photon energy per unit area of retina is based on taking the situation to be modeled as a simple EO system in front of a flash light. The validity of proposed model was proved by the application of the model to human on the surface of the earth with the well known light source, the Sun. The model of this study can be utilized to simulate the retinal intensity and energy of a flash for various conditions such as the illumination levels, the distance from a flash busting site, luminous intensity and time of a flash.

• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.3
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• pp.57-67
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• 2023

A flash drought is a rapid-onset drought that develops over a short period of time as weather and environmental factors change rapidly, unlike general droughts, due to meteorological abnormalities. Abnormally high evapotranspiration rates and rapid declines in soil moisture increase vegetation stress. In addition, crop yields may decrease due to flash droughts during crop growth and may damage agricultural and economic ecosystems. In this study, Flash Drought Intensity Index (FDII) based on soil moisture data from Gravity Recovery Climate Experiment (GRACE) was used to analyze flash drought. FDII, which is calculated using soil moisture percentile, is expressed by multiplying two factors: the rate of intensification and the drought severity. FDII was developed for domestic flash drought events from 2014 to 2018. The flash drought that occurred in 2018, Chungcheongbuk-do showed the highest FDII. FDII was higher in heat wave flash drought than in precipitation deficit flash drought. The results of this study show that FDII is reliable flash drought analysis tool and can be applied to quantitatively analyze the characteristics of flash drought in South Korea.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.138-138
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• 2021

Flash floods are one of the types of natural hazards which has severe consequences. Flash floods cause high mortality, about 5,000 deaths a year worldwide. Flash floods usually occur in mountainous areas in conditions where the soil is highly saturated and also when heavy rainfall happens in a short period of time. The magnitude of a flash flood depends on several natural and human factors, including: rainfall duration and intensity, antecedent soil moisture conditions, land cover, soil type, watershed characteristics, land use. Among these rainfall intensity and antecedent soil moisture, play the most important roles, respectively. Flash Flood Guidance is the amount of rainfall of a given duration over a small stream basin needed to create minor flooding (bank-full) conditions at the outlet of the stream basin. In this study, the Sejong University Rainfall-Runoff model (SURR model) was used to calculate soil moisture along with FFG in order to identify flash flood events for the Geum basin. The division of Geum river basin led to 177 head-water catchments, with an average of 38 km². the soil moisture of head-water catchments is considered the same as sub-basin. The study has measured the threshold of flash flood generation by GIUH method. Finally, the flash flood events were used for verification of FFG. The results of the validation of seven past independent events of flash flood events are very satisfying.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.366-366
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• 2020

The drought is one of the extreme natural disasters observed in any climate zone and it is due to the deficiency in moisture. The flash drought is identified recently as a subdivision of drought and it is an extreme event distinguished by sudden onset and rapid intensification of drought conditions with severe impacts. The main cause for the flash drought is coupled situation due to precipitation deficit and high evapotranspiration. Hence, heat waves plays major role in identification of flash drought. Therefore, this study focused on identifying changes in distribution of heat waves for Korean Peninsula. The daily maximum and minimum temperature data were used in this study. The heat wave, heat wave intensity and heat wave intensity index were derived. The results of the study would be an input for the future studies on identification of flash drought in Korean Peninsula.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.380-385
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• 2000

In this study, geometric shape and crack in welded interface of the air cooled heat exchanger Fin-Tube of Dissimilar Meterials was analysed. The object of study is to understand the behavior of Stress Intensity Factor for fin length, flash thickness, flash length, symmetric and asymmetric cracks of comming from the manufacturing process. Stress Intensity Factor was analysed by BEM. Kelvin's solution was used as a fundamental solution in BEM analysis and stress extrapolation method was used to determine Stress Intensity Factor.

• The Korean Journal of Food And Nutrition
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• v.11 no.3
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• pp.267-271
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• 1998

The photochemical carcinogenic reaction mechanism and molecular carcinogenic intensity through the reaction of dibromo carbene and diazomethane with dehydroacetic acid and coumarin have been studied under the two kinds of photolysis. The reaction intensities show the degree of carcinogenic activity. Under the condition of UV/vis light source, the yield of high toxic carcinogenetic carbene intermediate is produced less than those of the laser flash photolysis.

• Journal of ILASS-Korea
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• v.29 no.2
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• pp.91-97
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• 2024

When investigating the droplet, spray, and impact of liquid on a solid plate, backlight imaging has been widely used to understand these phenomena. However, some previous studies have suffered from poor image quality. In this study, various combinations of image processing algorithms, such as white image correction, histogram equalization, CLAHE, Otsu's binarization, and multi-Otsu's binarization, have been applied to flash boiling spray images to enhance image quality for qualitative observation and semi-quantitative spray angle evaluation. To acquire images with high contrast for qualitative observation, applying CLAHE was effective, making small droplets and detailed shapes of the jet noticeable. However, when images were averaged to determine spray angle or penetration length based on intensity, this method induced artifact unphysical patterns, thus requiring careful consideration. Based on the algorithm proposed in this study, the spray angle variation according to injection pressure and temperature has been calculated, showing a reasonable trend.

• International conference on construction engineering and project management
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• 2005.10a
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• pp.539-543
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• 2005

The research presented in this paper enables real-time 3D modeling to help make construction processes ultimately faster, more predictable and safer. Initial research efforts used an emerging sensor technology and proved its usefulness in the acquisition of range information for the detection and efficient representation of static and moving objects. Based on the time-of-flight principle, the sensor acquires range and intensity information of each image pixel within the entire sensor's field-of-view in real-time with frequencies of up to 30 Hz. However, real-time working range data processing algorithms need to be developed to rapidly process range information into meaningful 3D computer models. This research ultimately focuses on the application of safer heavy equipment operation. The paper compares (a) a previous research effort in convex hull modeling using sparse range point clouds from a single laser beam range finder, to (b) high-frame rate update Flash LADAR (Laser Detection and Ranging) scanning for complete scene modeling. The presented research will demonstrate if the FlashLADAR technology can play an important role in real-time modeling of infrastructure assets in the near future.