• Advances in environmental research
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• v.2 no.1
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• pp.35-49
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• 2013

Research work on removal of fluoride from water, referred to as water defluoridation, has resulted into the development of a number of technologies over the years but they suffer from either cost or efficiency drawbacks. In this work, enhancement effects of phosphate and silicate on defluoridation of water by low-cost Plaster of Paris (calcined gypsum) were studied. To our knowledge, the influence of silicate on defluoridation was not reported. It was claimed, that the presence of some ions in the treated water samples, was decreasing the fluoride removal since these ions compete the fluoride ions on occupying the available adsorption sites, however, phosphate and silicate ions, from its sodium slats, have enhanced the fluoride % removal, hence, precipitation of calcium-fluoro compounds of these ions can be suggested. Percentage removal of $F^-$ by neat Plaster is 48%, the electrical conductance (EC) curve shows the typical curve of Plaster setting which begins at 20 min and finished at 30 min. The addition of phosphate and silicate ions enhances the removal of fluoride to high extent > 90%. Thermodynamics parameters showed spontaneous fluoride removal by neat Plaster and Plaster-silicate system. The percentage removal with time showed second-order reaction kinetics.

• Atmosphere
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• v.24 no.4
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• pp.533-540
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• 2014

Statistical forecast models for the prediction of the summertime Changma precipitation have been developed in this study. As effective predictors for the Changma precipitation, the springtime sea surface temperature (SST) anomalies over the North Atlantic (NA1), the North Pacific (NPC) and the tropical Pacific Ocean (CNINO) has been suggested in Lee and Seo (2013). To further improve the performance of the statistical prediction scheme, we select other potential predictors and construct 2 additional statistical models. The selected predictors are the Northern Indian Ocean (NIO) and the Bering Sea (BS) SST anomalies, and the spring Eurasian snow cover anomaly (EUSC). Then, using the total three statistical prediction models, a simple ensemble-mean prediction is performed. The resulting correlation skill score reaches as high as ~0.90 for the last 21 years, which is ~16% increase in the skill compared to the prediction model by Lee and Seo (2013). The EUSC and BS predictors are related to a strengthening of the Okhotsk high, leading to an enhancement of the Changma front. The NIO predictor induces the cyclonic anomalies to the southwest of the Korean peninsula and southeasterly flows toward the peninsula, giving rise to an increase in the Changma precipitation.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.241-246
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• 1999

In this research, electrokinetic remediation test was experimented with contaminated kaoline specimen at below, above the cation-exchange capacity of the mineral. The changes of the flow in electro-osmosis with open electrodes and current were presented, and lead removal results were evaluated through the extraction test. As a result, it was showed that removal efficiency was 20-30%, 67-87% In the anode As lead transport continues, the lead precipitation within a narrow zone very close to the cathode can go significantly high. This high lead precipitation near the cathode could block the flow path, decrease the conductivity, and thus the electroosmotic flow. The net effect will cause a decrease in the efficiency of electrokinetic processing. Therefore, in this study, citric acid and surfactant solution was used at the cathode as enhancement techniques.

• Transactions of Materials Processing
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• v.17 no.2
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• pp.102-106
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• 2008

Cryogenic rolling combined with warm rolling has been found more effective than a single cryogenic rolling process in improving the strength of a 5052 Al alloy. In this study, cryo-rolled 5052 Al alloys were warm-rolled at $175^{\circ}C$. A notable increase of tensile strength was achieved by the precipitation during warm rolling process. Mechanical behavior of this alloy was investigated using hardness and tensile tests. It was found that the cryogenic rolling process combined with warm rolling process was very effective in improving tensile strength.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.81-83
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• 2007

Cryogenic rolling combined with warm rolling has been found to be more effective than only cryogenic rolling procedure in improving the strength of a 5052 Al alloy. In this study, cryo-rolled 5052 Al alloys were aged at $175^{\circ}C$. Warm rolling was conducted after dipping plates into silicon oil bath. A notable increase of tensile strength is achieved by the precipitation during warm rolling. The mechanical behavior of this alloy was investigated by hardness and tensile tests. The microstructure was investigated by transmission electron microscopy. It was found that the cryogenic rolling combined with warm rolling was very effective in improving tensile strength.

• The Korean Journal of Ceramics
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• v.2 no.4
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• pp.184-187
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• 1996

Diamod nucleation by mw assisted CVD was examined various conditions namely, (1) diamond nucleation on variour substrate materials, such as Si, cubic BN, pyrolytic BN and AIN, (2) AST(Activated species transport) method which promote nucleation of diamond on single crystal and polycrystalline alumina substrate was developed. (3) Effect of bias enhancement of nucleation on single crystalline Si was examined, and finally (4) DST (Double step treatment) method was developed to enhance diamond nucleation on Ni. In this method, we separated carbon diffusing process into Ni, carbon precipitating process from the inside of Ni and diamond precipitation process.

• Journal of the Korean Geographical Society
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• v.30 no.4
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• pp.333-351
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• 1995

Trend surface analysis (TSA) was selected to estimate a natural trend in precipitation and to examine urban influences on precipitation over five urban areas (Houston, Dallas, and San Antonio, TX; New Orleans, LA; and Memphis, TN) in the southern United States. TSA was applied to monthly, seasonal and annual normal precipitation data for the period of 1961-1990. Winter and spring have more trends than summer and fall and the period of November through March have more marked trends than the period of April through October in all study areas except the Houston area. Residual maps for Houston, Dallas and San Antonio have positive residuals in the city and downwind during summer indicating that urban effects on precipitation enhancement in these areas do exist during these seasons after eliminating the natural precipitation variations. Summer residual maps for New Orleans and Memphis have no distinct precipitation increases due to urban effects. The June residual map in New Orleans and the July residual map in Memphis have positive values in the city, but the magnitude of values is smaller than other cities.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2584-2594
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• 2024

A novel approach to incorporating oxide formers into ferritic ODS production has been developed using the co-precipitation technique. This method enables the tailored design of complex nano-oxides, integrated during Mechanical Alloying (MA) and precipitated during Spark Plasma Sintering (SPS) consolidation. Findings illustrate that co-precipitation effectively produces nano-powders with customised compositions, enriching Y, Ti, and Zr in the ferritic grade to condition subsequent oxide precipitation. While the addition of Y-Ti-Zr-O nano-oxides did not prevent the formation of Y-Al-O and Al-containing nano-oxides, these were refined thanks to the presence of well-dispersed Zr. Additionally, the Spark Plasma Sintering (SPS) parameters were optimised to tailor the bimodal grain size distribution of the ODS steels, aiming for favourable strength-to-ductility ratios. Comprehensive microstructural analyses were performed using SEM, EDS, EBSD, and TEM techniques, alongside mechanical assessments involving microtensile tests conducted at room temperature and small punch tests carried out at room temperature, 300 ℃, and 500 ℃. The outcomes yielded promising findings, showcasing similar or better performance with conventionally manufactured ODS steels. This reinforces the effectiveness and success of this innovative approach.

• Journal of the Korean Geographical Society
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• v.51 no.1
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• pp.23-40
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• 2016

In this study, long-term changes in means and extreme events of precipitation during summer rainy period called Changma (late June~early September) are examined based on rainfall data observed by Chukwooki during Joseon Dynasty (1777~1907) and by modern rain-gauge onward (1908~2015) in Seoul, Korea. Also, characterizations of the relevant changes in synoptic climate fields in East Asia are made by the examination of the NCEP-NCAR reanalysis I data. Analyses of 239-year time series of precipitation data demonstrate that the total precipitation as well as their inter-annual variability during the entire Changma period (late June~early September) has increased in the late 20th century and onward. Notably, since the early 1990s the means and extreme events during the summer Changma period (late June~mid-July) and Changma break period (late July~early August) has significantly increased, resulting in less clear demarcations of sub-Changma periods. In this regard, comparisons of synoptic climate fields before and after the early 1990s reveal that in recent decades the subtropical high pressure has expanded in the warmer Pacific as the advection of high-latitude air masses toward East Asia was enhanced due to more active northerly wind vector around the high pressure departure core over Mongolia. Consequently, it is suggested that the enhancement of rising motions due to more active confluence of the two different air masses along the northwestern borders of the Pacific might lead to the increases of the means and extreme events of Changma precipitation in Seoul in recent decades.

• Atmosphere
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• v.19 no.4
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• pp.297-307
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• 2009

The synoptic structures and the dynamic and thermodynamic characteristics of Changma in 2007 are investigated using the ECMWF analysis data and the radiosonde data from KEOP-2007 IOP. The enhancement of the North-Pacific High into the Korean peninsula and the retreat of the Okhotsk High are shown during the onset of Changma and the change of wind component from southwesterly to northwesterly is appeared during the end of Changma. The baroclinic atmosphere is dominant during Changma at most regions over the Korean peninsula except at Gosan and Sokcho. The quasi-barotropic atmosphere is induced at Gosan by warm air mass and Sokcho by cold air mass. Precipitation in the Korean peninsula occurs when dynamic instability is strengthened as the baroclinic and qusi-barotropic structure is weakened. An empirical orthogonal function (EOF) analysis is performed to find the dominant modes of variability in Changma. The first EOF explains the onset of Changma. The second EOF is related to the discrimination for existence and nonexistence of precipitation during Changma period according to the alternation of equivalent potential temperature between middle and lower atmosphere.