• Bulletin of the Korean Chemical Society
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• v.20 no.7
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• pp.786-790
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• 1999

Relatively inert surface of microcrystalline MgO was modified into chemically active one by carrying out controlled hydration followed by dehydration at elevated temperature under dynamic vacuum. Even though the treatment by the first cycle of hydration-dehydration did not alter the porosity of MgO, it largely enhanced surface reactivity of the MgO toward adsorbed water, turning its outer layer into brucite upon rehydration. Treatment by the second cycle of hydration-dehydration generated micropores, and slit-shaped mesopores, raising the porosity of the MgO. The overlayer of Fe2O3 of the core/shell type composite magnesium oxide enhanced this surface modification, turning its surface into more porous and more active one than that of uncoated MgO, after the treatment by the hydration-dehydration.

• Resources Recycling
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• v.10 no.6
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• pp.43-52
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• 2001

This study was conducted to obtain granular crystalline gypsum that can be used as raw material for Plaster boards or cements from waste Plaster board. Gypsum could be Preferentially disintegrated to gypsum needle in $10\mu\textrm{m}$ or less size by hydration after the dehydration of crushed waste Plaster board. The finer the gypsum needle, it is easier to remove coarse impurities and to recover the gypsum needle. The optimum conditions for obtain the finer gypsum size were dehydration rate of 75~85%, solid concentration at hydration of 10~15%, agitation speed of 250~400 rpm, crushing size before dehydration of 2 cm or less. Gypsum of 98.21% grade was recovered with 99.0% yield as the undersize of 325 mesh wet screening followed by the dehydration-hydration process performed at the conditions of dehydration rate of 80%, solid concentration at hydration of 15%, agitation speed of 300 rpm, crushing size before dehydration of 2 cm or less. After the recrystallization of recovered gypsum, Plate-like gypsum of $151\mu\textrm{m}$ size with 99.49% grade was obtained as the oversize of 270 mesh in a wet screening.

• Journal of Oral Medicine and Pain
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• v.46 no.4
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• pp.117-124
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• 2021

Purpose: Salivation is considered to be an important factor in the control of halitosis, and the amount of salivation has been shown to be closely related to the level of hydration. The purpose of our study was to evaluate the relationship between dehydration and halitosis. Methods: Twenty healthy young females with no dental problems were recruited. All participants were induced to become dehydrated and then over-hydrated. After inducing each hydration state, the severity of hydration and halitosis factor (organoleptic scores, amounts of resting and functional saliva, gas examinations, and tongue coatings) were measured. Hydration statuses were graded as dehydration, normal, or over-hydration according to urine osmolality. This was a cross sectional study with a cross over design. Results: The dehydrated status was associated with higher organoleptic scores than the normal or over-hydrated status (1.75±0.75 vs. 0.87±0.63, and 0.65±0.53, respectively. p<0.05). Mean values of CH₃SH, (CH₃)₂S in portable gas chromatography for the dehydrated, normal, and over-hydrated status were 11.70±37.00, 6.75±13.50, and 2.80±5.87 nmol/mol, 10.50±15.59, 7.25±10.87, and 1.50±2.55 nmol/mol, respectively. p>0.05). (CH₃)₂S (r=0.410, p=0.009) showed a moderate positive correlation with dehydration status. The resting salivation rates were relatively lower for the dehydrated status than for the normal or overhydrated status (p>0.05), and tongue coating results were also higher for the dehydrated status (p>0.05). Conclusions: Dehydration status appears to be positively correlated with a low resting salivation rate and high portable gas chromatography results. This shows that dehydration might be an etiologic factor of halitosis.

• Resources Recycling
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• v.15 no.3 s.71
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• pp.46-57
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• 2006

This study was carried out for the purpose of recovering the refined gypsum from waste phosphogypsum. The refined gypsum was recovered as a under product of 325 mesh wet screening followed by dehydration and hydration stage. The influence of dehydration temperature and time, dehydration rate, aging time, slurry density of hydration and sonication time on the yield and grade of gypsum were investigated. The refined gypsum of $94{\sim}96%$ grade is recovered in 95% yield by wet screening after selective dehydration and hydration process, from the phosphogypsum. For the better separation efficiency of gypsum, it is recommended to treat the phosphogypsum at the conditions of as follows; 6hr's dehydration at $140^{\circ}C$, hydration slury density of $3{\sim}10%$, hydration temperature of $20{\sim}30^{\circ}C$, hydration time of 2hr. In additions, addition of sodium citrate 0.005M and sonication of $5{\sim}10min.$ are effective for increase the recovery of gypsum. On the other hand, aging the dehydrated gypsum 16 hours or longer make decrease the recovery of gypsum remarkably.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.342-348
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• 2001

This study was conducted to obtain granular crystalline gypsum that can be used as raw material for plaster boards or cements from waste Plaster board. We could disintegrate preferentially gypsum to gypsum needle in 10${\mu}{\textrm}{m}$ or less size among the contents of waste plaster board (gypsum, paper, fiber, and inorganic material .etc.) by hydration afterwards the dehydration of crushed waste plaster board. In this case, the optimum conditions for minimizing the size of gypsum were dehydration rate of 75%~ 85%, hydration concentration of 10~20%, agitation speed of 250~400rpm, crushing size of 2cm or less. Gypsum of 98.21% grade was recovered with 99.0% yield from under screenings of 325mesh wet screening which followed by the dehydration-hydration process performed in the conditions of dehydration rate of 80%, hydration concentration of 15%, agitation speed of 300rpm, crushing size of 2cm or less. Subsequently, Plate-like Crystalline gypsum of is 151${\mu}{\textrm}{m}$ size and the grade of 99.49% with the Yield of 98.0% from the upper screenings of 270mesh wet screening carried out after the re-crystallization of the recovered gypsum needle slurry.

• Korean Journal of Exercise Nutrition
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• v.25 no.4
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• pp.10-16
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• 2021

[Purpose] The purpose of this study was to (i) assess hydration levels in elite male football players during a national team training camp before and during qualifying matches, (ii) evaluate the effect of coaching strategies for hydration based on feedback from hydration monitoring, and (iii) assess possible relationships between hydration status and training load or wellness markers. [Methods] Thirty-one male players (age 27±4 yrs; height 185±6 cm; weight 82.9±6.7 kg; body fat 10.4±2.3%) representing a national team from the Union of European Football Associations (UEFA) participated. The players were studied during three different national team training camps related to the UEFA Nations League tournament. Urine specific gravity (U_SG) was measured to assess hydration status. During all camps, the players were actively coached on improving strategies for hydration and given individual feedback on their test results. The training load was measured using GPS technology, and wellness questionnaires were completed. [Results] U_SG decreased progressively and significantly (p<0.005) during camp 1 and hydration status improved over the three camps, with fewer dehydrated and more well-hydrated players identified during the last part of camp 3. Significantly (p<0.05) higher U_SG values were observed 2 days prior to a match (MD-2) than on match day (MD); consequently, 52% of the players were dehydrated on MD-2 and only 6% on MD. No correlations were observed between hydration status and training load or wellness markers. [Conclusion] Dehydration is a challenge in elite male football, but continuous monitoring of hydration status and coaching on hydration strategies can lead to major improvements and reduce the degree of dehydration.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.1
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• pp.34-41
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• 2004

The chemical heat pump based on the Dehydration/Hydration process with a MgO/$H_2O$ system has been researched. The reactor bed could be expected to store the heat around 200∼37$0^{\circ}C$ by the dehydration reaction and to release the heat around 100∼16$0^{\circ}C$ by the hydration reaction under the heat amplification mode operation. The heat output rate of the heat pump system was evaluated using the experimentally determined parameters. The results show that 6∼50 W/kg of heat output and 0.5∼0.8 of heat recovery ratio are attainable. The heat pump will be applicable for a load leveling in a co-generation system by chemical storage of surplus heat at low heat demand and by supplying heat in the peak load period.

• Clinical and Experimental Pediatrics
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• v.45 no.6
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• pp.790-795
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• 2002

Sporadic reports of hypernatremic dehydration in breastfed newborn infants have appeared in medical literature for at least 3 decades. We report the first case of hypernatremic dehydration resulting from inadequate breast-feeding in Korea. A 14-day old baby, born to a mentally retarded mother, was transferred to our hospital with a body weight loss of 460 g since birth(17%) and a serum sodium(Na) level of 179 mEq/L, after initial hydration at another hospital. On admission, a cardiac murmur was heard and an enlarged liver was palpated. Cardiac ultrasonogram revealed ventricular septal defect and ostium secundum atrial septal defect. During hydration, a seizure-like attack developed. Serum Na decreased to 135 mEq/L on the 5th day of admission. Brain ultrasonography and brain magnetic resonance image revealed no remarkable abnormalities. Electroencephalography was normal. She suffered from prerenal azotemia, hyperglycemia and disseminated intravascular coagulation at admission but was treated successfully. Heart failure was also controlled with dobutamine, diuretics and digoxin.

• Journal of the Korean Society of Industry Convergence
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• v.8 no.4
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• pp.191-196
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• 2005

This study was carried out to investigate the heat storage/release characteristics of the thermochemical reaction of the calcined dolomite with the packed bed shape experimental apparatus for development of chemical heat pump system. In the present study, it was found that MgO of the calcined dolomite was not hydrated during the hydration process under the experimental conditions. Therefore, the MgO of the calcined dolomite can be regard as an inert material. As a result, it was found that all of CaO packed kept the reaction temperature of about $510^{\circ}C$ through the entire part of the bed. The dehydration reaction was incurred first at the wall side area as the supplied heat was transferred through the wall side into the packed bed. As a result of the temperature and concentration spread, the reaction was completed at the wall side progressed into the center.

• Journal of Pharmaceutical Investigation
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• v.26 no.2
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• pp.99-103
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• 1996

Effects of glycerin and PEG 400 in donor and receptor solutions upon skin permeation of drug were investigated. Deoxycortisone was used as a model compound. In vitro skin permeation study with freshly excised hairless mouse skin was performed and the steady-state skin permeation rates of the drug were determined in different fractions of glycerin or PEG 400 in donor and receptor solutions. Glycerin in donor solution didn't show any effect on the skin permeation rate of deoxycortisone. However glycerin in receptor solution showed significant effect on the skin permeation rate of the drug. In glycerin, there's a critical concentration for balancing hydration and dehydration of skin. At low concentration, less than 20 %, glycerin showed the enhancement of the flux due to the hydration effect of skin. At high concentration, more than 30 %, glycerin retard the permeation rate which might be due to the dehydration effect on the dermis layer. Since dermis has more water content than the stratum corneum, the steady state skin permeation rates were more influenced when glycerin was in receptor solution than that of in donor solution. PEG 400 aqueous solutions doesn't affect the steady state permeation rate of deoxycortisone significantly.