• Atmosphere
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• v.20 no.3
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• pp.261-271
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• 2010

Carbon isotopic compositions of the YC-2 stalagmite in Yongcheon Cave were analyzed to delineate paleoclimatic variations near Korean peninsula for the past historical period. The YC-2 stalagmite is about 68 mm long and annual growth laminae are distinctively identified. Because the number of growth laminae is at least 242, the stalagmite can be estimated to be at least 241 years old. At about 15 mm from the bottom, one thick brown growth lamina is observed, and this lamina was likely to have been formed when the stalagmite ceased to grow, making the hiatus. High resolution, carbon isotope data indicate past fluctuations of East Asia monsoonal intensity (intimately related to the amount of precipitation). Based on the carbon isotope trend, the stalagmite can be divided into three stages (Stages I, II and III). The highest carbon isotopic compositions of Stage I (${\delta}^{13}C$=-3.3~0.4‰, PDB) indicate that the stalagmite grew during the Little Ice Age when cold and dry climate prevailed with less vegetation. Stage II is characterized by a transitional period from cold and dry to warm and wet climate with a increasing trend of carbon isotopic compositions (${\delta}^{13}C$=-9.6~-0.6‰) and this period indicates the weakening of the Little Ice Age climate. This decreasing trend also suggests that Little Ice Age was terminated near middle 1870's around Korean peninsula. Relatively low carbon isotopic compositions during Stage III (${\delta}^{13}C$=-11.0~-8.0‰) indicates that the climate was changed to warm and wet conditions which are similar to the present.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.19
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• pp.100-131
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• 1975

To obtain basic information on the improvement of naked barley production. and to clarify the relation-ships between yield or yield components and some meteorogical factors for yield prediction were the objectives of this study. The basic data used in this study were obtained from the experiments carried out for 16 years from 1958 to 1974 at the Chon-nam Provincial Office of Rural development. The simple correlation coefficients and multiple regression coefficients among the yield or yield components and meteorogical factors were calculated for the study. Days to emergence ranged from 8 to 26 days were reduced under conditions of mean minimum air temperature were high. The early emergence contributed to increasing plant height and number of tillers as well as to earlier maximum tillering and heading date. The plant height before wintering showed positive correlations with the hours of sunshine. On the other hand, plant height measured on march 1st and March 20th showed positive correlation with the amount of precipitation and negative correlation with the hours of sunshine during the wintering or regrowth stage. Kernel weights were affected by the hours of sunshine and rainfall after heading, and kernel weights were less variable when the hours of sunshine were relatively long and rainfalls in May were around 80 to 10mm. It seemed that grain yields were mostly affected by the climatic condition in March. showing the negative correlation between yield and mean air temperature, minimum air temperature during the period. In the other hand, the yield was shown to have positive correlation with hours of sunshine. Some yield prediction equations were obtained from the data of mean air temperature, mean minimum temperature and accumulated air temperature in March. Yield prediction was also possible by using multiple regression equations, which were derived from yield data and the number of spikes and plant height as observed at May 20th.

• Journal of Korean Society on Water Environment
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• v.25 no.6
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• pp.821-831
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• 2009

The study was aimed to assess the expected impact of climate change on the water cycle and soil losses in Daecheong Reservoir watershed, Korea using the Soil and Water Assessment Tool (SWAT) that was validated for the watershed in a previous study. Future climate data including precipitation, temperature and humidity generated by introducing a regional climate model (Mesoscale Model Version 5, MM5) to dynamically downscale global circulation model (European Centre Hamburg Model Version 4, ECHAM4) were used to simulate the hydrological responses and soil erosion processes in the future 100 years (2001~2100) under the Special Report on Emissions Scenario (SRES) A1B. The results indicated that the climate change may increase in the amount of surface runoff and thereby sediment load to the reservoir. Spatially, the impact was relatively more significant in the subbasin Bocheongcheon because of its lower occupation rate of forest land compared to other subbasins. Seasonally, the increase of surface runoff and soil losses was more significant during late summer and fall season when both flood control and turbidity flow control are necessary for the reservoir and downstream. The occurrence of extreme turbidity flow events during these period is more vulnerable to reservoir operation because the suspended solids that remained water column can be resuspended by vertical mixing during winter turnover period. The study results provide useful information for the development of adaptive management strategy for the reservoir to cope with the expected impact of future climate change.

• Journal of The Korean Society of Grassland and Forage Science
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• v.17 no.1
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• pp.43-50
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• 1997

The aim of the study is to describe the fate and transformation of nitrogen in grassland ecosystems. Field experiments were conducted using sandyloam soil under variabling conditions: Zen, fertilization, reduced slurry application(l20kg N $ha^{-1}\;yr^{-1}$), usual sluny application (240 kg N $ha^{-1}\;yr^{-1}$).Soil water samples were gathered with 120cm ceramic cups with initial pressure of 0.5 bar. Samples were collected twice a month and analysed for NO, colormetrically. Percolation was calculated as the difference between precipitation and potential evapotranspiration, and leaching as the product of percolation and nitrate content of the water h m the ceramic cups. The N$H_4$-N content in soil had no significant effect on slurry application, but high slurry application on grassland resulted in high N$O_3$-N content in soil. The NO, concentration in soil water was remarkably variable during the year. The average N$O_3$, concentration during experiment became the lowest(8.5 mg/e ) without slurry application and highest with 240kOa cattle sluny(25.3 mg4 ). For each of the three different amounts of cattle sluny applied (0, 120, and 240kOa), the amount of N$O_3$-N leached per year were 12, 23 and 29kg/ha respectively. On grassland under the climatic conditions of Allgau showed enormous nitrate leaching, which has a p a t potential of polluting the ground water. The high pool of mineral N in the soil are the source for N$O_3$ leaching. The leaching of N$O_3$ cannot be avoided completely, but minimized by optimizing N fertilization rate.

• Research in Plant Disease
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• v.7 no.2
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• pp.102-106
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• 2001

Currently the rice false smut caused by Ustilaginoidea virens (Cooke) Takah. has occurred widely in Korea. A survey on the disease incidence at rice fields in 8 inland provinces was carried out in 2000, showing that the disease occurred at 104 (7.5%) out of 1,152 rice fields examined, ranging from 1.5% to 13.7% in provincial average. It was found that the disease incidence was greatly affected by local weather conditions and rice cultivars. In case of the most susceptible cultivar Namchunbyeo, the disease incidence was only about 1.3% in Icheon, while it was over 20% in Namwon which had weather conditions of the shorter sunshine period (about 64%) and the higher amount of precipitation (about 130%) during the rice cultivation than Icheon. In Icheon, artificial inoculation of the pathogen failed to induce the disease, probably because of the weather conditions unfavorable to the disease development, which also suggests that its incidence may be dependent on the weather conditions. Susceptibility of rice cultivars to the disease varied greatly; eight resistant cultivars including Heukjinjubyeo were not damaged by the disease, but 2 cultivars including Geumnambyeo and Namchunbyeo were severely damaged, having more than 20% of the disease incidence. Among chemicals tested fur the control of the rice false smut tebuconazole WP showed the highest control efficacy of 83∼88% on cvs. Geumnambyeo and Namchunbyeo. Other chemicals such as azoxystrobin WP and ferimzone WP also effectively suppressed the disease development in the field trials.

• Journal of Sericultural and Entomological Science
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• v.29 no.1
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• pp.12-19
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• 1987

This study was carried out to investigate the effects of climatic conditions on the budding of buds and the growth of shoots of mulberry (Morus alba L.) at Suwon for the period of six years from 1978 to 1983. The results are summarized as follows. 1. The period that influenced most greatly on mulberry budding and foliating of it's buds was from late part of March to middle part of April in the district of Suwon, Korea. 2. Temperatures in soil 20cm deep during the period from late part of March to middle part of April had high correlations with budding dates. 3. It was disclosed that the budding date had high correlations with the date of bud shaped swallow-bill (r=0.9861**), date of the third leaf(r=0.97**), and date of the fifth leaf(r=0.96**), respectively. 4. The higher the average temperature of April became, the longer the length of shoots became. 5. The earlier the budding date and foliating date came, the larger the leaf yield became. However, with excessive amount of precipitation after early budding and foliating, the leaf yield was not increased in proportional. 6. The longer the growing period of the shoots became, the larger the leaf yield became.

• Korean Journal of Materials Research
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• v.9 no.9
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• pp.905-912
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• 1999

Tensile properties of powder metallurgy (PM) processed Cu-7.5Ni-5Sn alloys, either as-received or additionally solution heat treated, were examined as a function of aging time. It was found that the as-received Cu-7.5Ni-5Sn alloys showed an abrupt increase in tensile strength after aging at $350^{\circ}C$ for 20 minutes, due to the metastable ${\gamma}$\\` precipitation and a marginal Spinodal decomposition. The resolutionized PM Cu-7.5Ni-5Sn alloys, on the other hand, showed a gradual increase in tensile strength from the very early stage of aging. The overall tensile strength of resolutionized PM Cu-7.5Ni-5Sn alloys, however, was lower than that of the as-received and aged counterparts, due to the grain growth during resolutionization. Afterprolonged aging for the as-received PM Cu-7.5Ni-5Sn alloys, a considerable amount of discontinuous precipitates formed along the grain boundaries. The formation and growth kinetics of such discontinuous precipitates appeared to be dependent on the heat treatment conditions, and affect the mechanical properties greatly.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.1-11
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• 1996

Mechanical alloying is an effective process to finely distribute inert dispersoids in an Al-TM(TM is a transition metal) system. It has been considered that high melting point aluminides are formed by precipitation from supersaturated Al(Ti) powder. This analysis is based on the fact that much higher content of TM than the solubioity can be dissolved in alpha aluminum during the high energy ball milling. Thus, decomposition behavior of Ti in the Al(Ti) was considered very important. But it is confirmed that the higher portion of Ti than Al(Ti) solid solution is existed as nano-sized Ti particles in the MA powders by high energy ball nilling from the XRD spectrum and TEM analysis in this study. Therefore, the role of undissolved TM particles affect the formation of aluminides should be suitably considered. In this study, we present experimental observation on the formation of $Al_3Ti$ fron mechanical alloyed Al-Ti alloys in the hyperperitectic region. This study showed that, in the mechanically alloyed Al-20wt%Ti specimen, intermediate phase of cubic $Al_3Ti$ and tetragonal $Al_{24}Ti_8$ formed at $300{\sim}400^{\circ}C$ and $400{\sim}500^{\circ}C$, respectively, before the MA state reaches to equilibrium at higher temperatures. The formation behavior of $Ll_2-Al_3Ti$ is interpreted by interdiffusion of Al and Ti in solid state based on the fact that large amount of nano-sized Ti particles exist in the milled powder. Present analysis indicated undissolved Ti particles of nanosize should have played an important role initiation the formation of $Al_3Ti$ phase during annealing.

• Journal of Korean Society for Atmospheric Environment
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• v.8 no.2
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• pp.93-99
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• 1992

Recently a passive $NO_2$ samplers have been frequently used for the measurement of $NO_2$ concentration in the atmosphere because of its simplicity and high accuracy. But these samplers have a defect that the amount of $NO_2$ adsorbed is increased by wind. In this study, the inlet of sampler was covered with a draft shield made by 325 mesh stainless sieve to eliminate the effect. But it was expected that $NO_2$ diffusion was interrupted by the draft shield. In order to conform this phenomenon, samplers with and without draft shield were exposed to a box filled with 1-1.1ppm $NO_2$. The result indicated that draft shield nearly did not disturb $NO_2$ diffusion. To protect samplers from dust, sunshine, precipitation and vertical wind effects, these samplers were placed into a shelter during the field test. The data obtained in this study was compared with the data from the ambient air monitoring network. The coefficient of correlation(r) between the two data was 0.9995 for the test period of up to 35days. The results of this study indicate that the type of $NO_2$ samplers with draft shield in shelter used in this study can be used for measuring $NO_2$ concentrations in the ambient air relatively for a long period over 30 days.

• Plant Resources
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• v.6 no.2
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• pp.134-139
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• 2003

This study was conducted to investigate the relationships between yearly variations of meteorological elements and yearly variations of productivity in rice. In addition, correlation coefficients among yield and yield components were used to find out the relationships between meteorological elements and productivity. Yearly variation of the mean air temperature in May was large with coefficients of variation(C.V.) of 25.0%, but the variation of the duration of sunshine in May were relative small. No. of panicles per hill and 1,000 grains wt. of brown rice were great with C.V. of 21.1, 19.7%, respectively, brown rice yield show more or less C.V. of 5.5% and milled rice show still less variation. Correlation coefficients between temperatures in period of cultivation from May and yield were positive correlations. Correlation Coefficients between precipitation in period of cultivation from Sep. to Oct. and yield are positive correlations. Correlation coefficients amount the panicle length, no. of panicles, no. of spikelets, ratio of ripened grains, 1,000 grains wt. of brown rice, milled rice yield, brown rice yield and milled rice yield were positively significant at the level of 1 %, respectively.