• Journal of Photoscience
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• v.6 no.3
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• pp.135-139
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• 1999

The ratio of dissociation rate $textsc{k}$-acversus the radiative decay rate $textsc{k}$D of the 1O2(1Δg) dimol has been determined to be $1.5\times$109 by its relaxation dynamcis in combination with a two-step O2((1Δg) sensitizing tetratert-butylphthalocoyanine luminescence. Consequently, with a known $textsc{k}$D value of 1.2 $\times$103S-1 , 10$textsc{k}$-ac has been extracted to be 1.8 $\times$1012S-1 CDCl3.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4329-4337
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• 2022

Jet impinging device is designed for decay heat removal on horizontal fuel rods in a low temperature heating reactor. An experimental system with a fuel rod simulator is established and experiments are performed to evaluate water film covering capacity, within 0.0287-0.0444 kg/ms mass flow rate, 0-164.1 kW/m² heating flux and 13.8-91.4℃ feeding water temperature. An effective method to obtain the film coverage rate by infrared equipment is proposed. Water film flowing patterns are recoded and the film coverage rates at different circumference angles are measured. It is found the film coverage rate decreases with heating flux during single-phase convection, while increases after onset of nucleate boiling. Besides, film coverage rate is found affected by Marangoni effect and film accelerating effect, and surface wetting is significantly facilitated by bubble behavior. Based on the observed phenomenon and physical mechanism, dry-out depth and initial dry-out rate are proposed to evaluate film covering potential on a heating surface. A model to predict film coverage rate is proposed based on the data. The findings would have reliable guide and important implications for further evaluation and design of decay heat removal system of new reactors, and could be helpful for passive containment cooling research.

• The Korean Journal of Ecology
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• v.9 no.1
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• pp.51-58
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• 1986

The decay rates of organic matter were investigated and the leaching rates were determined from the concentration distribution of N,P,K, Ca and Na in the soil profile at Pinus rigida stand on Mt. Gwan-ak and at Pseudosasa japonica stand on Odong-do. In order to determine the leaching rates θo/W wazs substituted with KL in Towner's equation. Decay rates were 0.191 at Pinus stand on Mt. Gwan-ak and 0.234 at Pseudosasa stan don Odong-do. Concentration distributions of N,P, K and Na in soil profiles were corresponed with Towner's model curve. Leaching rates determined from concentration distributions were 0.086, 0.079, 0.041, 0.029, 0.096 on Mt. Gwan-ak and 0.080, 0.056, 0.051, 0.008, 0.028 on Odong-do. The soil of Pseudosasa stand showed on the whole lower leaching rates than that of Pinus stand. The soil of Pseudosasa stand showing higher decay rate and lower leaching rates contained more concentration of each nutrient than that of Pinus stand.

• 전자공학회논문지 IE
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• v.44 no.3
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• pp.6-11
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• 2007

In this study, which was performed to identify a degradation mechanism in macromolecular insulating material, the contact angle, surface potential decay, surface resistance rate and XPS analysis were compared after exposure of fibre-glass-reinforced polymer laminate to plasma discharge. In the case of chemical changes arising from plasma treatment, carboxyl radicals were generated mainly in the plasma-treated surface, which was rapidly changed to a hydrophilic surface. In the corona potential decay study to determine the electrical changes, leading to a negative surface for the untreated specimen. However, in the case of the hydrophilic surface, a lot of carboxy radicals(-COO) acting as positive polarity were generated, resulting in a positive surface. Owing to such a positive surface, the charges of applied negative polarity were decreased rapidly.

• The Korean Journal of Ecology
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• v.13 no.1
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• pp.51-58
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• 1990

The rates of litter production and decomposition of litters from grasslands and forests in Mt. Guryong were studied. The annual litter production of Glycine soja showed the highest value 1950.88 g/$m^2$/yr in the grasslands and that in Quercus acutissima, as 2202.38 g/$m^2$/yr in the forests. The highest decay rate of the grasslands was found in G. soja as k=0.713 and that of the forests was in Salix koreensis as k=0.319. The Z values of k in the grasslands was higher than that in the forests. The shortest half-time of the litter decay in the grasslands was 0.9 years in G. soja and the longest one of the forests was S. koreensis as 2.1 years and the longest of all was Q. mongolica as 5.2 years. In the amount of total nitrogen of litters, G. soja was the highest of the grasslands and S. koreensis was the highest of the forest. The content of the total nitrogen in litters was directly propotional to the decay rates.

• Journal of Aerospace System Engineering
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• v.9 no.2
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• pp.57-62
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• 2015

The satellite orbit is continuously changing due to space environment. Especially for low earth orbit, atmospheric drag plays an important role in the orbit altitude decay. Recently, solar activities are expected to be high, and relevant events are occurring frequently. In this paper, analysis on the impact of geomagnetic storm on LEO satellite orbit is presented. For this, real flight data of KOMPSAT-2, KOMPSAT-3, and KOMPSAT-5 are analyzed by using the daily decay rate of mean altitude is calculated from the orbit determination. In addition, the relationship between the solar flux and geomagnetic index, which are the metrics for solar activities, is statistically analyzed with respect to the altitude decay. The accuracy of orbit prediction with both the fixed drag coefficient and estimated one is examined with the precise orbit data as a reference. The main results shows that the improved accuracy can be achieved in case of using estimated drag coefficient.

• Journal of the Korean institute of surface engineering
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• v.51 no.1
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• pp.79-85
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• 2018

We systematically investigated the optical properties of sub-micron sized methylammonium lead tribromide ($CH_3NH_3PbBr_3$) cubes in the range of 100 to 700 nm, which were prepared by a surfactant-free precipitation method. We found that despite the strong absorbance, their photoluminescence quantum yield (PLQY) is very low as 0.009~0.011 % for whole range of sizes. Surfactant-free synthesis approach results in nanocubes that has no surface passivating reagents (e.g. surfactants) on their surface. As-prepared particles contain a large number of surface defects that may cause the low PLQY. The role of the surface defects were investigated in their photoluminescence decay process, which can be correlated with the particle size. Larger particles are characterized by a slower decay rate compared to smaller particles due to a large number of surface defects in the smaller particles that trap more excitons in the fluorescence decay process. These experimental results provide new insights into the fundamental relationship between surface state and optical properties.

• Journal of Korean Society for Atmospheric Environment
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• v.12 no.3
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• pp.341-350
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• 1996

We determined 6 polycyclic aromatic hydrocarbons (PAHs) fluranthene, pyrene, benz(a)anthracene, chrysene, benzo(a)pyrene, dibenzo(a,h)anthracene). A total of 129 samples has been collected from September 1990 to September 1994 on 2 different types of filters (quartz fiber filter, glass fiber filter) by a PM-10 high volume air sampler at the Kyung Hee University-Suwon campus. The organic components in the PM-10 were extracted by an ultrasonication process with benzene:ethanol(4:1, v/v) prior to the analysis by using a GC/FID. We had also investigated the decaying quantity of 6PAHs at the room temperature. For example, chrysene was decayed by 56.7% after 4 days and benzo(a)anthracene by 84.2% after 30 days. All of PAHs were almost completely decayed after a year. We extensively estimated the decay rates by regression analyses for existing 18 raw data sets. Based on the decay rate constants $(\beta)$, pyrene was rapidly decayed by 19.0 $\times 10^{-2}$/day; on the other hand, dibenzo(a,h)anthracene slowly by 0.7 $\times 10^{-2}$/day. Applying the decay rates of PAHs on stored and dated samples, we could reasonably determine annual and seasonal concentration average of PAHs in particulate matters smaller than 10 $\mu$m.

• Journal of the Korean Society of Food Science and Nutrition
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• v.23 no.2
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• pp.315-321
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• 1994

In order to prevent the postharvest decay and to promote the freshness retention of fruits and vegetables grapefruit seed extract(GFSE), natural microorganism control agent, was applied to the preservation of fresh fruits and vegetables. Freshfruits and vegetables treated with GFSE and stored in polyethylene film (0.1mm) at 1$0^{\circ}C$-15$^{\circ}C$ of natural low temperature low kept better qualities in color and texture than the GFSE -not- treated control. The treatment using GFSE ina 250ppm to 500ppm concentration seemed to be an effective one for the control of Botrytis cinerea isolated in red wine grapes. After 4 weeks of storage the firmness rate of cucumbers treated with the dilute GFSE was four times higher than that of non-treated ones. GFSE showed effective inhibitory action towards plant pathological bacteria and fungi which were involved in the decay of fruits and vegetables. Minimum inhibitory concentrations of GFSE towards them were in the range of 250ppm to 500ppm .Direct visualization of microbial cells and spores using electron microscopy showed microbial cells and fungal spores the function of which was destroyed by treating with the dilute solutions of GFSE. It was observed that GFSE would reduced disease damages and have bactericide & fungicide properties during the storage of such fruits and vegetables as egg plant, wild edible greens , kumquat, and kiwi fruit.

• Journal of Wetlands Research
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• v.14 no.4
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• pp.537-545
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• 2012

Decay rate and nutrient dynamics during leaf litter decomposition of deciduous Quercus acutissima were compared between Gongju and Jinju for 33 months from December 2008 through March 2011. Percent remaining weight of Q. acutissima leaf litter after 33 months elapsed in Gongju and in Jinju was $41.2{\pm}0.4%$ and $28.3{\pm}0.6%$, and decay constant (k) was 0.39 and 0.61, respectively. Decomposition in Jinju was significantly faster than that in Gongju. This seemed to be related to higher temperature and precipitation in Jinju than those in Gongju during the experimental period. Initial C/N and C/P ratio of Q. acutissima leaf litter was 46.8 and 270.9, respectively. After 33 months elapsed, C/N and C/P ratios in Gongju decreased to 22.0 and 106.8, and those in Jinju decreased to 19.2 and 170.2, respectively. Initial concentration of N, P, K, Ca and Mg in Q. acutissima leaf litter was 8.31, 0.44, 4.18, 9.38, 1.37 mg/g, respectively. After 33 month elapsed, remaining N, P, K, Ca and Mg were 91.0, 85.4, 30.2, 47.9, 11.7% in Gongju, and 67.0, 54.2, 19.9, 30.0, 40.8% in Jinju, respectively. Except for Mg, remaining nutrients of decomposing leaf litter in Jinju were lower than those in Gongju. In case of N and P, initial immobilization was observed, however, only mineralization was observed in K, Ca and Mg during the whole experimental period.