• The Journal of Engineering Geology
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• v.14 no.4 s.41
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• pp.461-468
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• 2004

In order to characterize hydraulic property dependant on join roughness in rock mass, this study computed permeability coefficients on each range of joint roughness coefficient (JRC) suggested by Barton(1976). For a quantitative analysis of roughness components spectral analysis using the fast fourier transform was performed to select effective frequencies on each PC range. The results of spectral analyses show that low ranges of the JRC are mainly composed of low frequency domain, while high ranges of the JRC have dominant components at high frequency domain. The inverse Fourier transform made it possible to generate joint models of each JRC range using the effective frequencies of roughness spectrum. The homogenization analysis was applied to calculate permeability coefficient at homogeneous microscale, and then, computes a homogenized permeability coefficient (C-permeability coefficient) at macro scale. Therefore, it is possible to analyze accurate characteristics of permeability reflected with local effect of facture geometry. According to the calculation results, permeability coefficients were distributed between $10^{-3}m/sec\;and\;10^{-4}/sec$. In cases of sheared joint models permeability coefficients were plotted between $10^{-4}m/sec\;and\;10^{-5}/sec$, showing irregular distribution of permeability coefficients on each IRC range. The differences of permeability coefficients for the same aperture models or for the sheared joint models indicate that changes of roughness pattern influence on permeability coefficients. Therefore, the effect of joint roughness should be considered to characterize hydraulic properties in rock joints.

• The Journal of Korean Society for School & Community Health Education
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• v.3
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• pp.35-58
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• 2002

This research attempted to investigate the real state of adolescent smoking and drinking, and to study how stress influences on smoking and drinking of high school students. This data was collected from 837 first and second grade students in a vocational high school in Go-yang city, Gyeonggi province. Data analysis consisted of frequency, percentage, Chi-square, T-test, step-wise regression analysis, using SPSSWIN. The results of analysis were as follows: First, 51.7% of the students have never smoked, while 48.3% have experienced smoking. Most students started smoking in the second year of the middle school, though 17.6% of the smokers already started in the elementary school. The strongest motive of initial smoking was curiosity, next the inducement of friends, and 10.9% of them smoked to get rid of stress. Their favorite place for smoking was in the order of the entertainment centers, schools, and private academies. They personally purchased cigarettes mostly at the store. Most of them smoked less than 5 cigarettes a day, but 3.7% smoked more than a pack of cigarettes a day, usually with friends rather than alone. Second, the ratio of drinking was relatively high 78.1%, and their initial drinking experience was most frequent at the third year of the middle school. The initial motive of drinking was mostly curiosity and the inducement of friends, but 10.7% of them started drinking to reduce stress and anxiety. The places for buying alcohol and drinking were bars or restaurants. The ratio of habitual drinking was 45.1%, and the ratio of irregular drinking was 53.3%. 1.8% of the drinking students enjoyed drinking everyday. The amount of drinking varied from half a bottle to two bottles of Soju, and the drinking problem was serious to see that 11% of them drank more than two bottles at a time. Because 84.4% drank in groups with friends, a thorough and systematic supervision and education of the peer group drinking is essential. Third, as for the relationship between personal matters and smoking, it was found that there was a positive relation between smoking and sex, but there was no correlation between smoking and school years. Adolescent smoking was also related with scholastic achievement, the number of friends, and the existence of parents. Fourth, as for the relationship between personal matters and drinking, it was found that there was no correlation between drinking and sex, but there was a positive relation between drinking and school years. Fifth, the average index of stress was students themselves(2.58), school life(2.53), family life(2.19), friends(2.00), and the total index of stress was 2.33. Sixth, there appeared a marginal negative correlation between stress and 'drinking and smoking' in Pearson coefficient of correlation r to see the influence of stress on smoking and drinking. The difference of the average index of stress according to smoking and drinking bears meaningful difference for all students, smokers and non-smokers, drinkers and abstainers in students themselves, school life, family life, friends, and total stress. Smoking has an effect on family life most, school life next, and drinking has an effect on school life most, family life next, with the explanation power of 11% and 9% respectively, in a regression analysis to analyze the factors influencing on smoking and drinking among the factors of stress.

• Journal of Oral Medicine and Pain
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• v.30 no.1
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• pp.131-140
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• 2005

The purpose of this study was to examine the ablation rate of Er: YAG laser irradiation on dentin and enamel and to observe the microscopic structures of cavities formed after ablation of enamel and dentin in using a bur and cavities formed after ablation using laser. Er:YAG laser irradiated at 200 mJ, 250mJ, 300mJ at the frequency of 20Hz, 15Hz. The following results were obtained : 1. The ablation rate of dentin groups at power of 3 W-6 W was about $1.103{\sim}2.639mm^3/sec$ and there were no significant differences between power of 4.5 W$\sim$6 W. 2. The ablation rate of enamel groups at power of 3 W-6 W was about $0.413{\sim}0.969mm^3/sec$ and there were no significant differences between power of 4 W$\sim$6 W. 3. With SEM examination of the cavity surface treated with the conventional high speed bur revealed relatively flat appearance almost covered with a debris like smear layer. 4. With SEM examination of the lased surface of dentin groups revealed no smear layer and no debris and openings of dentinal tubules were clearly opened. But the lased surfaces of the groups over 3 W were irregular and particles were loosely attached on it. 5. With SEM examination of the lased surface of enamel groups revealed severely destructed surface at the 6 W group and melting drop materials at the 3 W group. But the lased surface of 4 W group revealed clearly ablated surface. Therefore when cutting teeth using Er:YAG laser, the lasing power which can make effective ablation rate and minimize the thermal effect could be 3W at dentin and 4W at enamel. But, further studies and additional data collection will be necessary for appropriate lasing condition of Er:YAG laser.

• Geophysics and Geophysical Exploration
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• v.1 no.1
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• pp.25-30
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• 1998

Time-lapse crosswell seismic data, recorded before and after the cavity filling, showed that the filling increased the velocity at a known cavity zone in an old mine site in Inchon area. The seismic response depicted on the tomogram and in conjunction with the geologic data from drillings imply that the size of the cavity may be either small or filled by debris. In this study, I attempted to evaluate the filling effect by analyzing velocity measured from the time-lapse tomograms. The data acquired by a downhole airgun and 24-channel hydrophone system revealed that there exists measurable amounts of source statics. I presented a methodology to estimate the source statics. The procedure for this method is: 1) examine the source firing-time for each source, and remove the effect of irregular firing time, and 2) estimate the residual statics caused by inaccurate source positioning. This proposed multi-step inversion may reduce high frequency numerical noise and enhance the resolution at the zone of interest. The multi-step inversion with different starting models successfully shows the subtle velocity changes at the small cavity zone. The inversion procedure is: 1) conduct an inversion using regular sized cells, and generate an image of gross velocity structure by applying a 2-D median filter on the resulting tomogram, and 2) construct the starting velocity model by modifying the final velocity model from the first phase. The model was modified so that the zone of interest consists of small-sized grids. The final velocity model developed from the baseline survey was as a starting velocity model on the monitor inversion. Since we expected a velocity change only in the cavity zone, in the monitor inversion, we can significantly reduce the number of model parameters by fixing the model out-side the cavity zone equal to the baseline model.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.10 no.3
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• pp.154-163
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• 2005

Irregular discharges of freshwater through the water gates of the Keum River Estuarine Weir, Korea, whose construction had been completed in 1998 with its water gates being operated as late as August 1994, drastically modified the estuarine environment. Sharp decrease of salinity along with the altered concentrations of inorganic nutrients are accompanied with the irregular discharges of freshwater into the estuary under the influence of regular semi-diurnal tidal effect. Field sampling was carried out on the time of high tide at 2 fixed stations(St.1 near the Estuarine Weir and St.2 off Kunsan Ferry Station) every other day for 4 months from mid-February 2004 to investigate into the semi-weekly variation of spring phytoplankton community in relation to the freshwater discharges from Keum River Estuarine Weir. CV(coefficient of variation) of salinity measurements was roughly 2 times greater in St.1 than that in St.2, reflecting extreme salinity variation in St.1 Among inorganic nutrients, concentrations of N-nutrients($NO_3^-,\;NO_2^-$ and $NH_4^+$) were clearly higher in St.1, to imply the more drastic changes of the nutrient concentrations in St.1. than St.2 following the freshwater discharges. As a component of phytoplankton community, diatoms were among the top dominants in terms of species richness as well as biomass. Solitary centric diatom, Cyclotella meneghiniana, and chain-forming centric diatom, Skeletonema costatum, dominated over the phytoplankton community in order for S-6 weeks each (Succession Interval I and II), and the latter succeeded to the former from the time of <$10^{\circ}C$ of water temperature. Cyanobacterial species, Aphanizomenon Posaquae and Phormidium sp., which might be transported into the estuary along with the discharged freshwater, occupied high portion of total biomass during Succession Interval III(mid-April to late-May). During this period, freshwater species exclusively dominated over the phytoplankton community except the low concentrations of the co-occurring 2 estuarine diatoms, Cyclotella meneghiniana and Skeletonema costatum. During the 4th Succession Interval when the water temperature was over $18^{\circ}C$, the diatom, Guinardia delicatula, was predominant for a week with the highest dominance of $75\%$ in discrete samples. To summarize, during all the Succession Intervals other than Succession Interval III characterized by the extreme variation of salinity under cooler water temperature than $18^{\circ}C$, the diatoms were the most important dominants for species succession in spring. If the scale and frequency of the freshwater discharge could have been adjusted properly even during the Succession Interval III, the dominant species would quite possibly be replaced by other estuarine diatom species rather than the two freshwater cyanobacteria, Aphanizomenon flosaquae and Phormidium sp.. The scheme of field sampling every other day for the present study was concluded to be the minimal requirement in order to adequately explore the phytoplankton succession in such estuarine environment as in Keum River Estuary: which is stressed by the unpredictable and unavoidable discharges of freshwater under the regular semi-diurnal tide.