• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.879-884
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• 2012

In this present study, Aspergillus niger NRRL 567 was cultivated on an inert support material and the effects of various fermentation parameters including temperature, nutrient solution pH, inoculation level, and moisture content were observed and optimized by one-factor-at-a-time (OFAT) and response surface methodology (RSM), sequentially. It was found that the incubation temperature of $30^{\circ}C$ with 75% moisture content, nutrient solution pH of 7.1 and inoculation level of $4.0{\times}10^6$ spores/ml were the most favorable. Again, fermentation parameters were optimized using RSM. The determined optimum condition is $26.5^{\circ}C$, pH 9.9, 75.1%, and $6.0{\times}10^6$ spores/ml. Under this optimized condition, A. niger NRRL 567 produced 118.8 g citric acid/kg dry peat moss at 72 hr. Maximum citric acid production of optimized condition by RSM represented a 1.6-fold increase compared to that obtained from control experiment.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.193-200
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• 1988

The starting materials were aluminum hydroxide prepared by precipitation method at the conditions of pH values; 7, 9, 10 and 11. The properties of alumina powder on heat-treatment were studied. After dehydrating structural water from amorphous aluminum hydroxide, the first formed phase was amorphous alumina and its specific surface are was decreased. The specific surface area was increased by dehydration of structural water from aluminum hydroxides except amorphous aluminum hydroxide. The specific surface area was increased with increase of the ratio of A1OOH to $A1(OH)_3$ in the region of transition aluminas. The rate of transition from aluminum hydroxide to alpha alumina occurred in the order of 7, 10, 9 and 11 of pH values. The morphology of alpha alumina powders was skeleton particles remaining outer shape of aluminum hydroxide. Both the elevation of heat-treatment temperature and the transition toalpha alumina decreased specific surface area and brought about the growth of particles.

• Journal of the Korean Vacuum Society
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• v.12 no.S1
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• pp.79-82
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• 2003

We present the investigation on P- and As-desorption process from the (001) InP surface in metal organic chemical vapor deposition using surface photoabsorption (SPA). The monochromatic SPA signal showed rapid initial increase to reach In-stabilized surface value after $PH_3$ was turned off, but in case of As-desorption, the signal showed clear existence of a metastable state after the $AsH_3$ was turned off. The SPA spectra at each stable surfaces were taken to confirm the interpretation. This result indicates that the As-desorption process should be understood as a two-step process, in contrast to P-desorption of one-step process.

• The Korean Journal of Zoology
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• v.19 no.1
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• pp.25-32
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• 1976

To observe the changes of mucosubstances of the mucous secreting cells, stomach tissues in frog tadpoles at each stage of metamorphosis were fixed in 10% buffered formalin at $4^{\circ}C$, embedded in paraffin, sectioned to 4 $\mu$m thickness and stained with periodic acid-Schiff(PAS) and alcian blue (AB) of pH 2.5 and pH 1.0. The results obtained were as follows: 1. The reactivities of the surface mucous cells, which exhibited strong PAS-positivity and weak alcianophilia at both pH 2.5 and 1.0, were not changed in metamorphosis stages and the intracellular contents of neutral mucosubstances in the surface mucous cells increased significantly in XXIV and XXV stages of metamorphosis. 2. In the foveolar mucous cells, which appear after metamorphosis XXI, the staining reactivities to PAS, AB of pH 2.5 and 1.0 were the same as that of surface mucous cells during metamorphosis and the alcianophilia were stronger at pH 1.0 than at pH 2.5. 3. THe mucous neck cells, which appear after metamorphosis XXIV, exhibited a strong PAS-positive reaction and weak alcianophilia at metamorphosis XXIV but at metamorphosis XXV weak reactivity to PAS and strong alcianophilia at pH 1.0.

• Journal of Aquaculture
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• v.16 no.2
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• pp.76-83
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• 2003

To improve the efficiency of removal of bacteria and virus with DynaSand Filters used for treatment of recycling wastewater from aquaculture, effect of biofilm formation on bacterial transport through coated sand was estimated. At the neutral pH (pH 7.0), the coated sand was positive of zeta potential (surface charge). Column experiments were also carried out to test the effect of uncoated sand as well as coated sand with Al and Fe. The coated sand influenced more significantly the surface properties, adsorption and transport than the uncoated sand. The leaching batch system investigated for synthetic water showed concentrations of 7.47, 4.80, 20.89 and 7.23 mg/L for the uncoated sand, coated sand with Al, Fe and Al+Fe, respectively. Hence there are significant differences among the tested coatings with reference to bacterial transport and surface properties.

• Microbiology and Biotechnology Letters
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• v.32 no.4
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• pp.317-321
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• 2004

We selected a solvent for producing antioxidants from sporophyll of Undaria pinnatOptimum extraction condition for antioxidant ability(Y) of sporophyll of U. pinnatifida was investigated using response surface methodology(RSM). A compound central design was used with variables ($X_1$)temperature($^{\circ}C$) (3.4; 20; 60; 100; 116.6); ($X_2$) pH(1.8; 3; 6; 9; 10.2) and ($X_3$) treatment time(min) (1.7; 10; 30; 50; 58.3). Antioxidant activities were increased with decreasing pH and increasing temperature. The optimal extraction conditions for antioxidant ability(Y) of sporophyll of U. pinnatifida were found to be temperature $51.55^{\circ}C$, pH 4.2 and treatment time 28.2 min. Among the variables tested, pH showed greater significant facin extraction of antioxidants from sporophyll of U. pinnatifida.

• Journal of the Korean institute of surface engineering
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• v.48 no.3
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• pp.73-81
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• 2015

Chloride plating solution was fabricated by dissolving metal Ni powders in solution with HCl and deionized water. Effects of deposition conditions on the properties of Ni films electrodeposited from chloride baths were studied. Current efficiency of Ni films electrodeposited from the baths containing saccharin was decreased with increasing the current density. Residual stress of Ni thin films ware measured to be about 230 ~ 435 MPa in the range of current density of $10{\sim}25mA/cm^2$. Cathode current efficiency in baths without saccharin was initially increased with increasing pH, while it was decreased with increasing pH further. Cathode current efficiency in baths with saccharin (except at pH 2) exhibited less 10 ~ 20% than that in baths without saccharin. Residual stress of Ni films electrodeposited from baths without saccharin was measured to be 388 ~ 473 MPa in the range of pH 2 ~ pH 5 and then was increased to 551 MPa at pH 6. On the other hand, residual stress of Ni films electrodeposited from baths with saccharin was increased with increasing pH. Surface morphology was strongly affected by the change of current density, but slightly by solution pH and addition of saccharin.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.8
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• pp.583-590
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• 2011

The effect of the physical parameters in the reactor (aeration depth, bubble size, and surface area) and the alkalinity of the solution on the ammonia stripping by bubbling were evaluated. When an airflow of 30 L/min was bubbled below the solution surface in the range 6-53 cm, the ammonia removal rate were observed to be the same regardless of the bubbling depths. At pH 10.0 and a temperature of $30^{\circ}C$, the average rate constant and the standard deviation were $0.178h^{-1}$ and 0.004. No appreciable changes in the ammonia removal rate were also observed with varying the bubble size and the air-contacting surface area. Alkalinity of the solution was found to affect the ammonia removal rate indirectly. This is expected because the pH of the solution would vary with dissolution of gaseous $CO_2$ by air bubbling. The real wastewaters from landfill site and domestic wastewater treatment plant were tested. In the case of domestic wastewater (pH = 7.1, alkalinity = 75 mg/L), the ammonia removal rate was poor even with the control of pH to 9.3. The raw landfill leachate (pH = 8.0, alkalinity = 6,525 mg/L), however, showed the appreciable removal rate with increasing pH during aeration. When the initial pH of the leachate was adjusted 9.4, the removal rate was significantly increased without changing the pH during aeration.

• Korean Journal of Materials Research
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• v.32 no.9
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• pp.361-368
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• 2022

The overall process, from the pre-treatment of aluminum substrates to the eco-friendly neutral electroless Ni-P plating process, was observed, compared, and analysed. To remove the surface oxide layer on the aluminum substrate and aid Ni-P plating, a zincation process was carried out. After the second zincation treatment, it was confirmed that a mostly uniform Zn layer was formed and the surface oxide of aluminum was also removed. The Ni-P electroless plating films were formed on the secondary zincated aluminum substrate using electroless plating solutions of pH 4.5 and neutral pH 7.0, respectively, while changing the plating bath temperature. When a neutral pH7.0 electroless solution was used, the Ni-P plating layer was uniformly formed even at the plating bath temperature of 50 ℃, and the plating speed was remarkably increased as the bath temperature was increased. On the other hand, when a pH 4.5 Ni-P electroless solution was used, a Ni-P plating film was not formed at a plating bath temperature of 50 ℃, and the plating speed was very slow compared to pH 7.0, although plating speed increased with increasing bath temperature. In the P contents, the P concentration of the neutral pH 7.0 Ni-P electroless plating layer was reduced by ~ 42.3 % compared to pH 4.5. Structurally, all of the Ni-P electroless plating layers formed in the pH 4.5 solution and the neutral (pH 7.0) solution had an amorphous crystal structure, as a Ni-P compound, regardless of the plating bath temperature.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.4
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• pp.210-217
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• 2003

An alternative method to the empirical approach such as Langmuir and Freundlich model, surface complexation model using thermodynamic database is used to simulate adsorption behavior of cadmium for oxide minerals. Sorption of cadmium onto amorphous silica ($SiO_2$) and synthetic goethite (${\alpha}$-FeOOH) at various conditions of pH, initial cadmium loading, oxide concentration, and ionic strength, were investigated. For both oxide minerals, increasing cadmium concentration resulted in right shifting of the sorption curve of cadmium as the function of pH. The $pH_{50}$, where 50% of cadmium sorbed, of goethite (pH 5.25) was much smaller than that of the silica (pH 7.83). The sorption of cadmium onto both minerals were not affected by the background ion strength from $10^{-1}$ to $10^{-2}$ M of $KNO_3$. It indicated that the binding affinity of goethite surface for cadmium is much stronger than that of silica. The strong affinity of oxide mineral for cadmium can be explained by the existence of coordination or covalent bond between cadmium and surface of it.