• Applied Chemistry for Engineering
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• v.19 no.2
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• pp.173-178
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• 2008

Calcium lactate was prepared by reacting lactic acid with precipitated calcium carbonate (PCC) which was prepared by carbonation process (calcite) and solution process (aragonite). Effects of PCC morphology (calcite and aragonite) on calcium lactate by the solution process were investigated experimentally. Despite the slow forming rate at the initial stage, the final yield of calcium lactate appeared higher when calcite was used. Therefore, the maximum yield of calcium lactate using aragonite was 85.0% and that using calcite was 88.7%, respectively. For both cases, the optimum temperature for the preparation appeared at around $60^{\circ}C$. Furthermore, the increase in lactic acid concentration over 2.0 mol% increased slurry viscosity and deteriorated mass transfer, which resulted in low yield of calcium lactate for both cases. SEM analyses showed that the prepared calcium lactate appeared as plate-like crystal form, irrespective of PCC morphologies, reaction temperatures, and concentrations of lactic acid.

• The Korean Journal of Pharmacology
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• v.26 no.2
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• pp.113-120
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• 1990

Influences of trigger calcium on myocardial contraction from several sources were investigated on the frequency reduction-induced changes of contraction in rat left atria driven by electrical field stimulation. Rat atria elicited characteristic three phase-changes according to frequency reduction: the first rapid rise in twitch tension, the second transient fast decrease in tension and the third maintenance of twitch tension at about 200% of resting tension during high frequency. Caffeine treatment enormously suppressed the frequency reduction-induced twitch tension increase. The atrial contraction during high frequency vanished after verapamil treatment. But, during low frequency, atrial contraction revived in the presence of verapamil. Ouabain treatment and sodium depletion in superfusing solution abolished the characteristic second phase with slow frequency. These results suggest that slow calcium channel is an indispensable calcium entry route and calcium release from sarcoplasmic reticulum is an major source for trigger calcium in cardiac contraction. And sodium-calcium exchange has a modulatory roles in the regualtion of trigger calcium according to the changes of intracellular sodium concentration.

• Journal of Nutrition and Health
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• v.25 no.5
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• pp.360-378
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• 1992

This study was performed to investigate effect of dietary protein and calcium levels on cad-mium intoxication in rats. Adult Sprague-Dawley male rate(245$\pm$21g) were blocked into 18 groups of 7 animals according to body weight Nine experimental diets different with protein(40%, 15%, 7%) and calcium (1.3%, 0.6%, 0.1%) levels were prepared. Nine groups of animals were fed each diet with 50ppm cadmium in drinking water and the other 9 groups without cadmium for 30days. Results were summarized as follows: 1) Body weight gain F. E. R(Food Efficiency Ratio) and weights of liver kidney and femur were higher in high protein groups among cadmium exposed groups. 2) Cadmium contents in liver and intestine were higher in rats fed high protein diet or low calcium diet among cadmium exposed groups. Fecal cadmium excretion was highest in high protein-high calcium diet group among cadmium exposed animals. Metallothionein contents in liver kidney and intestine were higher in animals exposed to cadmium and fed high protein diets. 3) Gel filtration chromatography of cytosolic solution showed that the higher dietary protein and calcium levels were the more cadmium was found in metallothionein fractions. 4) No gross histopathological change was seen in liver kidney and intestine of cadmium exposed rats. However a significant increase of smooth endoplasmic reticulum which was alleveated by high protein-high calcium diet was observed. Results obtained indicated that not only high protein diet but also high calcium diet showed preventive effect on cadmium intoxication by increasing the induction of metallothionein syn-thesis and decreasing the cadmium absorption.

• Journal of Chest Surgery
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• v.21 no.2
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• pp.291-298
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• 1988

The effect of Vanadate on the isometric contraction, membrane potential and intracellular calcium ion activities of rabbit myocardial cells were investigated, using calcium selective microelectrode, filled with neutral calcium ion carrier, ETH-1001. The resting tension, the membrane potential and the intracellular calcium ion activities were recorded in normal Tyrode solution and compared with those in the contracture induced by 10 mM Vanadate. The following results were obtained: 1. The dose-response relationship between the contraction of Vanadate and twitch tension showed near-maximum response in 5mM with no corresponding changes in action potential. 2. The resting tension increased up to the amplitude of a control twitch in 10mM Vanadate with resting membrane potential, hyperpolarized. 3. Increase in intracellular calcium ion activities proceeded the contracture by 10mM Vanadate which were restored to the control level in accordance with a decrease of intracellular calcium ion activities. 4. The amplitude of contractures by 10mM Vanadate were 90-120% of the control twitch tension in which the intracellular calcium ion activities were increased about 70 times from p Ca, 7.1 in the control to p Ca, 5.8 in contractures.

• Korean Journal of Metals and Materials
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• v.49 no.5
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• pp.362-366
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• 2011

Aluminosilicate inorganic polymer binder has been studied as an alternative to ordinary Portland cement due to its higher physical properties, chemical resistance and thermal resistance. This study has been carried out in an attempt to understand the hardening characteristics of aluminosilicate binder by varying the content of calcium. Samples with four different ratios of Al, Si, and Ca were synthesized in this study with the Al:Si:Ca mol ratio being 1.00:1.85~1.98:0.29~2.12. Furthermore, an alkali silicate solution was prepared with the sodium hydroxide (NaOH) and sodium silicate (NaSi). The hardening characteristics of the specimens were analyzed using XRD, SEM, and TG/DTA. In addition, compressive strength and sintering time of specimens were measured as a function of calcium content. The results showed that the specimen containing 2.12 mol% calcium offered the highest compressive strength. However, the compressive strength of the specimen containing 0.26 mol% calcium was lower relative to the other specimens. The results displayed a distinct tendency that as more calcium was added to the inorganic polymer, setting time became shorter. When calcium was added to the inorganic polymer structure, a second phase was not formed, indicating that the addition of calcium does not affect the crystalline structure.

• Journal of Sericultural and Entomological Science
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• v.40 no.1
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• pp.70-77
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• 1998

This study was carried out in order to find out the relationship between physical and chemical properties of silk fiber treated by concentrated calcium nitrate solution. The tensile, thermal and dynamic mechanical properties are also examined on Ca(NO3)2 treated silk fibers. The tensile properties of silk fibers treated by calcium nitrate changed with a concentration. The thermal behavior were also affected by the concentration of calcium nitrate. The degradation temperature (endotherms) and glass transition temperature shifted to lower temperature as the treated concentration increased. It is thought that the physical properties are strongly related to the structure and morphology of Ca(NO3)2 treated silk fibers. As a result, these give property changes with a concentration dependence.

• Journal of Sericultural and Entomological Science
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• v.39 no.1
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• pp.12-16
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• 1997

Effects of calcium on mulberry growth and freezing tolerance were examined by water culture. Calcium was supplied by folar spray with the levels of 0, 5, and 40 ppm. Muberry stems developed by 130 cm at Ca2+ 40ppm, 82 cm at Ca2+ 5 ppm and 23 cm at Ca2+ 0 ppm. Muberry roots also developed vigorously at Ca2+ 40 ppm, but did poorly at Ca2+ 5 ppm and changed to brown in color, and died becoming necrosis at Ca2+ 0 ppm. Content of calcium in leaves and barks were increased at Ca2+ 40 ppm compared with at Ca2+ 5 ppm. Total sugar, RNA, proline and phospholipid at Ca2+ 40 ppm were also more increased than those at Ca2+ 5 ppm. Mulberry stems grown at Ca2+ 40 ppm showed a sufficient tolerance at -10 for 24 hours while stems grown at Ca2+ 5 ppm did a weak tolerance at the same conditions.

• Journal of Korean Society on Water Environment
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• v.26 no.3
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• pp.525-531
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• 2010

To figure out the importance of temperature on electrochemical properties in water environment, calcium carbonate, one of important substances in water chemistry, was chosen to make suspensions. The result of electrokinetic potential of calcium carbonate suspensions revealed that it tended to increase as temperature increased. In addition, electrokinetic potential was negatively increased as suspensions became more basic. Its isoelectric point was ca. 7 regardless of temperature. The adsorption of hydrogen ions on calcium carbonate particles followed endothermic reaction. This result was verified by continuously measuring pH as adding HCl solution in calcium carbonate suspension. It explained that suspensions' potential was determined by DLVO theory which calculated total interaction energy between particles. Suspensions' total interaction energy was proportional to the value of electrokinetic potential. Furthermore, total interaction energy between particles increased as suspensions' temperature was increased.

• Journal of the Korean Ceramic Society
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• v.13 no.1
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• pp.20-24
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• 1976

These are many kinds of self-hardening methods for sand mold using sodium silicate. When sodium silicate solution is mixed with calcium-orthosilicate powder hardening reaction occurs, which is based for self-hardening method at high temperature. The high temperature strength and resicual strength of mold are related to the mole ratio of sodium silicate and the contents of calcium-orthosilicate powder. The results obtained in this study were as follows: 1) The high temperature strength of mold was maximum at about $600^{\circ}C$, and at higher temperature showed lower value on the contrary. 2) The high temperature strength of mold was increased by increasing the amount of sodium silicate having lower mole ratio and high concentration. 3) The residual strength of mold was reduced by increasing the mole ratio of sodium silicate and increasing the concentration of calcium-orthosilicate.

• Journal of the Korean Ceramic Society
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• v.50 no.4
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• pp.275-279
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• 2013

The purpose of this study was to prepare calcium phosphate cement [CPC] for use in artificial bone. Nano-crystalline calcium phosphate [CaP] was precipitated at $37^{\circ}C$ using highly active $Ca(OH)_2$ in DI water and an aqueous solution of $H_3PO_4$. From the XRD measurements, the nano-CaP powder was close to apatitic TCP phase and the powders fired at $800^{\circ}C$ showed a critical ${\beta}$-TCP phase. A mixture of one mole $CaCO_3$ and two moles di-calcium phosphate was calcined at $1100^{\circ}C$ to make a reference ${\beta}$-TCP material. The nano-CaP powders were added to the normal ${\beta}$-TCP matrix and fired at $900^{\circ}C$ to make a ${\beta}$-TCP block. The sintered block showed improved mechanical strength, which was caused by the solid state interaction between nano-CaP and normal ${\beta}$-TCP.