• Journal of Korean Society of Environmental Engineers
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• v.31 no.9
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• pp.743-748
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• 2009

Chemical sludge conditioning is widely used to improve the dewatering efficiency. It is treated with commonly used conditioners, and then thickened and dewatered with a mechanical device. This paper aims to examine the flotation and thickening efficiencies of sewage sludge for conditioning conditions, such as unaerobic storage time, kinds of coagulant and dosages, and flotation conditions, such as sludge concentration and A/S ratio, using an dissolved air flotation apparatus. Experimental results showed that the specific surface area and specific resistance to filtration (SRF) were significantly increased and the flotation and thickening efficiencies were decreased with anaerobic storage time. However, the flotation and thickening efficiencies faintly decreased in sewage sludges conditioned as $Al_2(SO_4)_3$, $Fe_2(SO_4)_3$, and PSO-M. Flotation and thickening efficiencies in conditioned sewage sludge could be sustained up to 96% at A/S ratio of 0.01 mL/mg or over.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.2
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• pp.80-84
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• 2003

The mechanical and electrical properties of the hot-pressed and pressureless annealed SiC-Ti $B_2$electroconductive ceramic composites were investigated as functions of the liquid additives of $Al_2$ $O_3$+ $Y_2$ $O_3$. The result of phase analysis for the SiC-Ti $B_2$ composites by XRD revealed $\alpha$-SiC(6H), Ti $B_2$, and YAG(A $l_{5}$ $Y_3$ $O_{12}$ ) crystal phase. The relative density of SiC-Ti $B_2$ composites was increased with increased $Al_2$ $O_3$+ $Y_2$ $O_3$ contents. The fracture toughness showed the highest value of 6.04 Mpa $m^{\frac{1}{2}}$ for composites added with l2wt% A1$_2$ $O_3$+ $Y_2$ $O_3$ additives at room temperature. The electrical resistivity showed the lowest value of 6.2$\times$10$^{-3}$ $\Omega$ㆍcm for composite added with l6wt% $Al_2$ $O_3$+ $Y_2$ $O_3$ additives at room temperature. The electrical resistivity of the SiC-Ti $B_2$ composites was all positive temperature cofficient resistance(PTCR) in the temperature ranges from $25^{\circ}C$ to $700^{\circ}C$.

• Journal of the korean academy of Pediatric Dentistry
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• v.26 no.3
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• pp.479-485
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• 1999

Materials for posterior teeth includes amalgam, gold inlay and composite resin inlay. Amalgam and gold inlay have unsatisfyine esthetics. And because they simply obturate the cavity preparation, they do not strengthen the remaining tooth structure. Posterior composite resin has become established in recent years. However, its polymerization shrinkage and insufficient wear resistance were the most undesirable characteristic. The physical and mechanical properties of the composite resin inlay are further improved through heat treatment in an oven. The major part of polymerization contraction of the resin inlay takes place be fore cementation, and possible gap formation is only due to shrinkage of the thin layer of resin cement. With the semidirect technique, the inlay material is placed directly in the prepared tooth, and the primary polymerization is made by light activation with a handhold curing unit. Additional curing may take place extraorally with use of different curing ovens. It provides the patient with the benefits of luted restorations without the procedure of indirect lab-made inlay. I report three successfully treated cases by semidirect resin inlay technique. Entire clinical steps are described in detail with some discussions on the outcome.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.100-105
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• 2003

25Cr-20Ni series strainless steel have an excellent high temperature strength, high oxidation and high corrosion resistance. However, further improvement can be creep strength by work hardening prior creep. In the present study, the effect of prestraining at room temperature on the creep behavior of a Class M(STS310S) and a Class A(STS310J1TB) alloy containing precipitates have been examined. Prestraining was carried out at room temperature and range of prestrain was $0.5{\sim}2.5$ % at STS310J1TB and $2.0{\sim}7.0$ % at STS310S. Creep behavior and creep rate of pre-strained specimens were compared with that of virgin specimens. Room temperature prestraining produced the creep life that is longer than that of a virgin specimen both for STS310J1TB and STS310S when creep test carried out at the temperature lower than recrystallization temperature. The reason for this improvement of creep life was ascribable to the interaction between dislocations and precipitates in addition to the dislocation-dislocation interaction in STS310J1TB and the dislocation-dislocation interaction in STS310S. The beneficial effect of prestraining in STS310J1TB was larger than that of STS310S.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.948-954
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• 2002

Porous reaction bonded SiC with high fracture strength was developed using Si melt infiltration method for use of the support layer in high temperature gas filter that is essential to develop the next generation power system such as integrated gasification combined cycle system. The porosity and pore size of porous RBSC developed in this study were in the range of 32∼36% and 37∼90 ${\mu}m$ respectively and the maximum fracture strength of porous RBSC fabricated was 120 MPa. The fracture strength and thermal shock resistance of porous RBSC fabricated by Si melt infiltration were much improved compared to those of commercially available porous clay bonded SiC due to the formation of the strong SiC/Si interface between SiC particles. The characteristics of pore structure of porous RBSC was varied depending on the amounts of residual Si as Well as the size of SiC particle used in green body.

• Journal of the Korean GEO-environmental Society
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• v.17 no.10
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• pp.55-62
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• 2016

The frequency slope over a year due to climate collapse is connected with huge casualties and property damage, but the situation rarely reduce the damage that gradually increases in size. In order to suppress this, engineers are improved better reinforcement and continued efforts to improve the shear force or withdrawal force. In this study, the GangWhaGu attached to the nail tip that improves the soil nail pullout resistance, and a method to increase the nail integral GangWhaGu maximize the contact area soil - by increasing the friction of the grout seems to increase the effect of slope stability. In order to validate the experiment to determine the effect of reinforcing the soil nail pullout tests of indoor and Behavior GangWhaGu nail and through field tests were conducted and applicability. Experimental results, the case of a pull-out test compared to the GangWhaGu nail through the tensile force of the nail were to increase by approximately 20%.

• CELLMED
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• v.4 no.1
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• pp.3.1-3.8
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• 2014

Spa represents a treatment widely used in many rheumatic diseases (RD). The mechanisms by which immersion in mineral or thermal water ameliorates RD are not fully understood. The net benefit is probably the result of a combination of factors, among which the mechanical, thermal and chemical effects are most prominent. Buoyancy, immersion, resistance and temperature play important roles. According to the gate theory, pain relief may be due to the pressure and temperature of the water on skin; heat may reduce muscle spasm and increase the pain threshold. Mud-bath therapy increases plasma ${\beta}$-endorphin levels and secretion of corticotrophin, cortisol, growth hormone and prolactin. It has recently been demonstrated that thermal mud-bath therapy induces a reduction in circulating levels of prostaglandin E2, leukotriene B4, interleukin-$1{\beta}$ and tumour necrosis factor-${\alpha}$, important mediators of inflammation and pain. Furthermore, balneotherapy has been found to cause an increase in insulin-like growth factor-1, which stimulates cartilage metabolism, and transforming growth factor-${\beta}$. Beneficial anti-inflammatory and anti-degenerative effects of mineral water were confirmed in chondrocytes cultures, too. Various studies in vitro and in humans have highlighted the positive action of mud-packs and thermal baths, especially sulphurous ones, on the oxidant/antioxidant system. Overall, thermal stress has an immunosuppressive effect. Many other non-specific factors may also contribute to the beneficial effects observed after spa therapy in some RD, including effects on cardiovascular risk factors (e.g. adipokines) and changes in the environment, pleasant surroundings and the absence of work duties.

• Journal of the Korean Geotechnical Society
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• v.30 no.10
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• pp.55-65
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• 2014

Recent researches on debris flow is focused on understanding its movement mechanism and building a numerical simulator to predict its behavior. However, previous simulators emulating fluid-like debris flow have limitations in numerical stability, geometric modeling and application of various boundary conditions. In this study, depth integration is applied to continuity equation and force equilibrium for debris flow. Thickness of sediment, and average velocities in x and y flow direction are chosen for main variables in the analysis, which improve numerical stability in the area with zero thickness. Petrov-Galerkin formulation uses a discontinuous test function of the weighted matrix from DG scheme. Presented mechanical constitutive model combines fluid and granular behaviors for debris flow. Effects on slope angle, inducing debris height, and bottom friction resistance are investigated for a simple slope. Numerical results also show the effect of embankment at the bottom of the slope. Developed numerical simulator can assess various risk factors for the expected area of debris flow, and facilitate embankment design in order to minimize damage.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.111-117
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• 2003

In the design of the split type free displacer Stilting cryocooler the motion of the displacer is very important to decide the cooling capacity, which depends upon the working gas pressure, the swept volume in the compression space and the expansion space, operating frequency, the phase shift between piston and displacer, etc. In this study, Stirling cryocooler actuated by the electric farce of the dual linear motor is designed and manufactured. Cool down characteristics of the cold end with laser displacement sensor in the expander of the Stilting cryocooler is evaluated. The charging pressure was 15kg$_{f}$/$\textrm{cm}^2$ and operating frequency was 50Hz. Input power and the lowest temperature were about 32W and 67K, respectively. And, displacement of the piston is measured by LVDTs (Linear Variable Differential Transformers), displacement of thedisplacer is measured by laser optic method, and phase shift between piston and displacer is discussed. As the peak-to-peak pressure of the compressor was increased, peak-to-peak displacement of the displacer was increased. The peak-to-peak displacement of the displacer increases in the range of 0 - 64.5Hz(resonant frequency of the displacer), but decreases steeply when the operating frequency is bigger than the resonant frequency. Finally when the phase shift between displacements of the Piston and displacer is 45。, operating frequency is optimum and is decided by resonant frequency of the expander, mass and cross section area of the displacer and constant by friction and flow resistance.e.

• Journal of the Korea Institute of Building Construction
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• v.19 no.6
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• pp.495-501
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• 2019

Recently, research has been carried out into the use of carbon fiber reinforced polymer (CFRP), which has good tensile strength and corrosion resistance, as an alternative to rebar. But as of yet, the research into fatigue failure of CFRP is insufficient. In this paper, an analysis was performed of the mechanical behavior and failure patterns of CFRP reinforced concrete beams according to static and cyclic loads, in order to evaluate the safety and validity of CFRP rebar as an alternative material for rebar. The cyclic load ranged from 10 % to 70% of the ultimate load, and was loaded at a speed of 3Hz using a sine wave in the form of a three-point loading method. Through the static load test, the maximum load or stiffness of the beam was found to increase remarkably with the increase of the reinforcement, but the fatigue test showed that the number of repetitions decreased and the amount of deflection increased with the increase of the reinforcement.