• Journal of Korean Society on Water Environment
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• v.24 no.4
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• pp.415-422
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• 2008

Drinking water treatment is enhanced by coagulant dosages and chlorine injection because of pH increase in raw water in droughty seasons such as spring and fall. But water quality deterioration is occurred by increase in residual aluminium and disinfection by-products. Coagulation process can be used to control natural organic matter (NOM) during water treatment. The effect of coagulation process appeared to depend on the pH of water rather than coagulant dosages. In this study, for water treatment in high pH season $H_2SO_4$ was applied for pH adjustment at full scale. Before and after pH adjustment by $H_2SO_4$ injection, water quality of drinking water was evaluate. In the result of investigation of total organic carbon (TOC) removal in high pH season, TOC was removed approximately 30~40%, which showed decrease in water treatment efficiency. Also, it is increased both particle numbers and residual Al concentration in the water. After $H_2SO_4$ injection for adjustment to pH<7.5 in settled water, treated water turbidity decreased in 0.047 NTU from 0.059 NTU, and particle numbers of filtered water decreased in 20/mL from 90/mL. On the other side, TOC removal efficiency increased in approximately 10% after adjustment of pH. In the result of decrease in pH in raw water through more coagulants and prechlorine without $H_2SO_4$ injection, trihalomethanes (THMs) concentration increased in $16{\mu}g/L$ from $8{\mu}g/L$.

• Microbiology and Biotechnology Letters
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• v.31 no.4
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• pp.400-407
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• 2003

In microbial coal desulfurization process (MCDP) by using Acidithiobacillus ferrooxidans, the effect of process variables on pyritic sulfur removal efficiency has been investigated. The inhibitory effect of toxic materials contained in coal matrix on the activity of desulfurizing bacteria have been evaluated in coal extracts, and the results showed that the method was useful to evaluate the applicability of a coal which is to be desulfurization to MCDP. The removal efficiency increased with decreasing particle size and decreases with increasing pulp density, but has no significant influence of particle size and pup densities at high pulp densities over 20 wt%. The mass transfers of gaseous nutrients such as oxygen and carbon dioxide into coal slurry with various pulp densities and coal particle size has been studied in an airlift bioreactor. Mass transfer coefficient was independent of pulp density in coal slurry with fine particle below 175 $\mu\textrm{m}$, but significantly decreased with increasing pulp density over 225 $\mu\textrm{m}$. The coal particles over 575 $\mu\textrm{m}$ were significantly settled to the bottom of bioreactor resulting in poor mixing. Considering mass transfer, pulp density and coal mixing, an optimal size of coal particle for the microbial coal desulfurization process seems to be about 500 $\mu\textrm{m}$.

• Analytical Science and Technology
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• v.11 no.4
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• pp.260-265
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• 1998

Spherical, ${\mu}m$-sized particles of barium titanyl oxalate were prepared by thermal decomposition of dimethyl oxalate in acidic barium and titanium solutions. Precipitation was carried out in the presence of several supporting anions. Spherical particles having a specific type of particle size distribution. i.e., unimodal or bimodal distribution, with mean size in the range of $0.2{\sim}3{\mu}m$, were formed depending on the supporting anions, oxalate ion generation rate and aging time. Particles of barium titanyl oxalate settled on the bottom of the beaker at the aging time of 120 min grew to the critical monosize of about $1.5{\sim}3{\mu}m$. XRD spectra and chemical analyses of barium titanate showed that barium titanyl oxalate with high qualities could be synthesized by choosing chloride ion as a supporting anion and increasing the reaction temperatures.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.4
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• pp.67-82
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• 2003

A 2-dimensional hydrodynamic model has been applied to understand water circulation pattern in Lake Deacheong. The simulation results have been used in sediment transport modeling. A sediment transport model using a particle tracking method has been developed to simulate sediment transport in the ocean, river and reservoir. The model was applied to estimate transport track of particulate pollutants in the lake. The hydrodynamic model was verified for water level variations and showed good agreements. Through the results we found out that water velocity is less than 5 cnysec for mean yearly flow and more than 120 cnysec at some points for the simulated flood flow. The incoming sediment particles in flood season reached into the Daecheong Dam. But the incoming sediment particles in the mean flow were settled down at riverbed and didn't move into the dam. These results can be used in setting up water quality management plan in the lake.

• Journal of Biosystems Engineering
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• v.28 no.4
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• pp.351-360
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• 2003

This study was carried out to settle the plugging problem which occurs frequently when agricultural wettable powder is used in pest control work using the crushing and the dispersing effects caused by irradiation of ultrasonic wave. Sonication was applied to the wettable powder suspension in a beaker for 30 seconds using a 28 kHz, 200 W PZT BLT, and the image of suspension before and after sonication was observed using a microscope and a SEM. The image of tow commercial wettable powder suspensions in water observed using an optics microscope showed that the agglomerated particles were irregularly distributed over the whole observed region when stirred mechanically, while showing more uniform distribution composed of comparatively single particles in the whole observed region after sonication. Concerning the above, the projected areas of particles in the four suspensions after sonication were decreased distinctively in the observed range of the microscope and the atomization of crystals was much developed. Over the measured range of 5.6∼4,157 ${\mu}$m particle size, the overall projected area of particles was decreased to 58.3∼89.6% on the average after sonication. When the SEM images of sonicated wettable powder suspensions dissolved in water and CH$_3$OH were compared to the suspensions before sonication, such phenomena as the atomization of particles, the expansion of voids between particles, the reduction and the decrease of agglomerated particle groups, and the progress of crack developments on the surface of flake-shaped particles were observed. It seemed possible that the plugging problem that occurs frequently in pest control machine when using wettable powder would be settled by the use of sonication.

• Korean Journal of Materials Research
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• v.16 no.3
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• pp.173-177
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• 2006

Porous surfaced Ti implant compacts were fabricated by electro-discharging-sintering (EDS) of atomized spherical Ti powders. Powders of $50-100{\mu}m$ in diameter were vibratarily settled into a quarts tube and subject to a high voltage and high density current pulse in Ar atmosphere. Single pulse of 0.7 to 2.0 kJ/0.7 gpowder, from 150, 300, and $450{\mu}F$ capacitors was applied in less than $400{\mu}sec$ to produce twelve different porous-surfaced Ti implant compacts. The solid core formed in the center of the compact shows similar microstructure of cp Ti which was annealed and quenched in water. Hardness value at the solid core was much higher than that at the particle interface and particles in the porous layer, which can be attributed to both heat treatment and work hardening effects induced by EDS. Compression tests were made to evaluate the mechanical properties of the EDS compacts. The compressive yield strength was in a range of 12 to 304MPa which significantly depends on input energy. Selected porous-surfaced Ti-6Al-4V dental implant compacts with a solid core have much higher compressive strengths compared to the human teeth and sintered Ti dental implants fabricated by conventional sintering process.

• Ocean and Polar Research
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• v.22 no.2
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• pp.69-80
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• 2000

A 3-D particle tracking model with normalized characteristic equations has been developed to predict the variation of near-field mixing characteristics and the far-field transport of the effluent plumes discharged from sea outfalls. The model was applied to the case study on the Masan sea outfall plumes discharged through a submerged multiport-diffuser. Numerical simulations of the effluent transport for 15 days which cover neap and spring tidal cycles in Masan Bay were conducted using fall velocities of the solid wastes and the initial plume characteristics obtained from normalized near-field characteristic equations. The results showed that time variations in near-field minimum dilutions with tidal ambient flow conditions are about $45{\sim}49$. Most of the heavy particles in the effluent plumes were settled and deposited in the vicinity of the outfalls immediately, and the finer particles were transported eastwards 3 km away from the outfalls for 15 days. A similar depositional trend of contaminated sediment was also found during a recent field survey.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.301-310
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• 2006

A series of laboratory tests was carried out for analyzing compaction characteristics of hydraulic fill soils(or hydraulically filled soils). Hydraulic fill soils were settled down by the weight of soil particle itself in water and consolidated by the extraction of water from the soil structures. Water content and dry unit weight were observed as the depth of sedimentation and consolidation soil. It was found from the result that the optimum water content $(W_{cpt})$ of the maximum unit weight$(\gamma_{dmax})$ is higher than that of laboratory compaction test(KS F 2312 A method). It was due to difference in compaction energy and compaction effect between two methods. And the maximum dry unit of hydraulic fill soil is smaller than that of laboratory compaction test. Especially in terms of compaction effect, the maximum relative compaction degrees$(R_{cmax})$ of Seamangum dredged sand, river sand and mixed sand, half and half of dredged and river sands, were 85%, 91% and 86%, respectively. It means that the compaction effect can be $85\sim91%$ of the maximum unit weight in laboratory compaction test.

• Membrane Journal
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• v.19 no.4
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• pp.268-276
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• 2009

In this study the basic data were settled down to establish theory of membrane module and apparatus for measuring suspended solid per particle size. The theory and technique were different with the conventional weight method and light scattering method. For this purpose silica, dextran, kaolin, and PEG (polyethylene glycol) suspended solutions were filtrated through glass fiber membranes GF/C and GF/A on membrane module for measuring TMP (Trans-membrane pressure) changes using digital pressure gages. And the related equation between modified solution concentration and TMP change slope was derived from the TMP change experiments, and then suspended solid concentration of samples could be expected by the equation.

• Journal of Sensor Science and Technology
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• v.22 no.6
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• pp.400-403
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• 2013

The piezoelectric composite film of ferroelectric PZT ceramic ($PbZr_xTi_{1-x}O_3$) and polymer (PDMS, Polydimethylsiloxane) was prepared to improve the flexibility of piezoelectric material. The bar coating method was applied to fabricate flexible nanocomposite film with large surface area by low cost process. In the case of using metal electrode on the composite film, although there is no problem by bending process, the electrode is usually broken away from the film by stretching process. However, the well-attached, flexible CNT electrode on PZT/PDMS film improved flexibility, especially stretchability. PZT particles was usually settled down into polymer matrix due to gravity of the weighty particle, so to improve the dispersion of PZT powder in polymer matrix, small amount of additives (CNT powder, Carbon nanotube powder) was physically mixed with the matrix. By stretching the film, an output voltage of PZT(70 wt%)/PDMS with CNT (0.5 wt%) was measured.