• Journal of Korea Water Resources Association
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• v.38 no.8 s.157
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• pp.631-643
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• 2005

The objective of this study is to perform hydraulic and numerical model experiments of the flows in circulation-water-pump(CWP) chambers of combined cycle power plants (CCPP) to be built and to suggest improvement plans if the flows might cause a serious problem on the operation of CWPs. Hydraulic model was constructed in a scale of 1 to 20 using acrylic sheets and a two dimensional numerical model used was RMA2. To evaluate results of Hydraulic and numerical model experiments, evaluation criteria of flow conditions in the intake canal and CWP chambers were determined. Vertical vorticities obtained from numerical simulations for the initial plan of CCPPs were qualitatively compared with results of hydraulic model experiments and the formation possibility of a large scale vortex, one of the flow evaluation criteria, was evaluated. The initial plan was found not to satisfy the flow evaluation. Nine improvement plans were devised and numerically simulated. Four alternative plans among nine improvement plans were selected and hydraulically experimented. On the ground of the results of hydraulic model experiments, a final improvement plan, one of four improvement plants, was suggested. When CWP chambers and intake canals were designed with spatial constraints, flow separating wall and guide walls were found to improve flow conditions in CWP chambers.

• Korean Journal of Materials Research
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• v.3 no.3
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• pp.261-271
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• 1993

Functionally Gradient Materials(FGM) of 4.5Pb($Ni_{1/3}Nb_{2/3})O_3$-55PZT and PLZT(lO/70 /30, 11/60/40) were prepared. Its dielectric and piezoelectric strain properties were investigated. The FGM were pressed into A/B/ A configuration using two kinds of films, one layer(A) was eliminated from FGM by polishing after sintering at $l250^{\circ}C$, 2 hrs. The acrylic binder system was successfully applied for crack free film through doctor blade method. The thickness of gradent layer in FGM was about 30${\mu}$m. Dielectric properties of FGM show the average value of each side layer. The strain-electric field characteristics of FGM were significantly improved comparison with the other single compositions. The prepared FGM piezoelectric actuator shows about 3${\mu}$m/IOOV displacement.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.4
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• pp.437-443
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• 2015

Purpose: This study evaluated the optical and physical and characteristics of soft contact lens polymerized with addition of 3-chloropyridine-4-carboxylic acid and 3-fluoropyridine-4-carboxylic acid in the basic hydrogel contact lens material. In particular, the utility of 3-chloropyridine-4-carboxylic acid and 3-fluoropyridine- 4-carboxylic acid as a hydrogel contact lens material was investigated. Methods: In this study, 3-chloropyridine-4-carboxylic acid and 3-fluoropyridine-4-carboxylic acid were used as additives. Also, 2-hydroxyethyl methacrylate, acrylic acid, methyl methacrylate and a cross-linker EGDMA were co-polymerized in the presence of AIBN as an initiator. Results: The physical properties of the produced polymers were measured as followings. The water content of 34.54~37.15%, refractive index of 1.4320~1.4342, tensile strength of 0.2872~0.3608 kgf and contact angle of $57.82{\sim}79.57^{\circ}$, UV-B transmittance of 76.8~82.4% and UV-A transmittance of 84.6~86.6% were obtained respectively. Conclusions: Based on the results of this study, contact lens material containing 3-chloropyridine-4-carboxylic acid and 3-fluoropyridine-4-carboxylic acid is expected to be able to used as a material for high wettability and UV-block hydrogel contact lens.

• Tunnel and Underground Space
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• v.20 no.5
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• pp.344-351
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• 2010

Slip along a frictional fracture can be approached as initiation and propagation of a mode II crack along its own plane. Fracture mechanics theories predict that under pure mode II loading initiation will occur when the energy release rate of the fracture attains a critical value ($G_{IIC}$), which is generally taken as a material property. For the past few years the rock mechanics group at Purdue University has investigated experimentally the dependence of $G_{IIC}$ on normal stress and on the frictional characteristics of a fracture. A number of experiments has been conducted first on acrylic, a material that, using photoelastic methods, allows visualization of the stress field ahead of the fracture tip; and later on gypsum, a rock model material with relatively low unconfined compression strength. The experimental investigation has been expanded to include other frictional materials with higher unconfined compression strength. Direct shear tests have been conducted on specimens made with cement paste. New observations together with previous experiments indicate that $G_{IIC}$ can only be considered a material property when the peak friction angle of the discontinuity is similar to the residual friction angle; otherwise the critical energy release rate increases with normal stress.

• Horticultural Science & Technology
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• v.34 no.1
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• pp.84-93
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• 2016

Plant factories with artificial lights require a large amount of electrical energy for lighting; therefore, enhancement of light use efficiency will decrease the cost of plant production. The objective of this study was to enhance the light use efficiency by using filters to diffuse the light from LED sources in plant factory conditions. The two treatments used diffuse glasses with haze factors of 40% and 80%, and a control without the filter. For each treatment, canopy light distribution was evaluated by a 3-D ray tracing method and canopy photosynthesis was measured with a sealed acrylic chamber. Sixteen lettuces for each treatment were cultivated hydroponically in a plant factory for 28 days after transplanting and their growth was compared. Simulation results showed that the light absorption was concentrated on the upper part of the lettuce canopy in treatments and control. The control showed particularly poor canopy light distribution with hotspots of light intensity; thus the light use efficiency decreased compared to the treatments. Total light absorption was the highest in the control; however, the amount of effective light absorption was higher in treatments than the control, and was highest in treatment using filters with a haze factor of 80%. Canopy photosynthesis and plant growth were significantly higher in all the treatments. In conclusion, application of the diffuse glass filters enhanced the canopy light distribution, photosynthesis, and growth of the plants under LED lighting, resulting in enhanced the light use efficiency in plant factory conditions.

• Restorative Dentistry and Endodontics
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• v.12 no.2
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• pp.45-53
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• 1987

The purpose of this study was to evaluate the tensile bond strength between composite resin and the human enamel. Three composite resin systems, two chemical (Clearfil Posterior, and Clearfil Posterior-3) and one light cure (Photo Clearfil-A), used with and without an intermediate resin (clearfil bonding agent), were evaluated under different amounts of load (10g, 200g and 200g for a moment) for in vitro tensile bond strength to acid-eched human enamel. Clinically intact buccal or lingual surfaces of 144 freshly extracted human permanent molars, embedded in acrylic were flattened with No #600 carborundum discs. Samples were randomly assigned to the different materials and treatments using a table of random numbers. Eight samples were thus prepared for each group(Table 2) these surfaces were etched with an acid etchant (Kurarey Co. Japan) in a mode of etching for 30 seconds, washing for 15 seconds, and drying for 30-seconds. During the polymerization of composite resin on the acid-etched enamel surfaces with and without bonding agent 10-gram, 200 gram and temporary 200 gram of load were applied. The specimens were stored in 50% relation humidity at $37^{\circ}C$ for 24 hours before testing. An universal Testing machine (Intesco model No. 2010, Tokyo, Japan) was used to apply tensile loads in the vertical directed (fig 5), and the force required for separation was recorded with a cross head speed of 0.25 mm/min and 20 kg in full scale. The results were as follow: 1. The tensile bond strength was much greater in applying a bonding agent than in not doing that. 2. The tensile bond strength of chemical cure composite resin was higher than that of light cure composite resin with applying on bonding agent on the acid-etched enamel. 3. In case of not applying a bonding agents on the acid-etching enamel, the highest tensile bond strength under 200 gram of load was measured in light cure composite resin. 4. The tensile bond strength under 200-gram of load has no relation with applying the bonding agent. 5. Under the load of 10-gram, There was significant difference in tensile bond strength as applying the bonding agent.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.401-412
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• 1998

The aim of this study was to measure the regional micro-shear bond strength of dentin bonding agents to dentin, and to investigate the relationship between the micro-shear bond strength and two dentinal characteristics ; Vickers hardness and remaining dentin thickness. Twenty-four freshly extracted, noncarious human molars were selected for this study. The materials tested in this study consisted of two commercially available dentin bonding agents (MAC-BOND, ONE-STEP) and two restorative light-cured composite resins (AELITEFIL, Z100). The occlusal or side surface of tooth crown was sectioned to expose dentin, and the exposed surface was finally polished with # 600 sandpaper. Four groups of application methods were used combining the filling materials and the dentin bonding agents. The composite resin-attached tooth specimens were embeded in a cold cure acrylic resin, and were cut with a low speed diamond saw to the dimension of 1mm $\times$ 1mm. Nine specimens were obtained from each tooth. The cut specimens were divided into three groups depending on the position of the dentin bonding surface. The micro-shear bond strength, remaining dentin thickness, and dentinal hardness were measured. Experimental results were then statistically analyzed with ANOVA. t-test, Scheffe test, and regression analysis. From this experiment, the following results were obtained : 1. In the case of occlusal surface bonding, the pooled micro-shear bond strength of ONST-AELIT group (16.62 MPa) was significantly higher than that of MACB-AELIT group (9.91 MPa) (p<0.05). However, there was no significant difference in the micro-shear bond strength depending on the dentin position (p>0.05). 2. In the case of side surface bonding of crown, the pooled micro-shear bond strength of four different bonding groups was not significantly different among each other (p>0.05). However, in three of the test groups (ONST-AELIT, MACB-Z100, ONST-Z100), the micro-shear bond strength to the lower 1/3(III) position was significantly lower than that to middle 1/3(II) position of surface (p<0.05). 3. In the ONST-AELIT bonding group, the pooled micro-shear bond strength to the occlusal surface was significantly lower than that to the side surface of crown (p<0.05). 4. There was no significant correlation between the micro-shear bond strength and dentin hardness / remaining dentin thickness (p>0.05).

• Restorative Dentistry and Endodontics
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• v.35 no.6
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• pp.479-485
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• 2010

Objectives: The aim of this study was to compare the push-out bond strengths of resin cement/fiber post systems to post space dentin using different application methods of resin cement. Materials and Methods: Thirty extracted human premolars were selected and randomly divided into 3 groups according to the technique used to place the cement into root canal: using lentulo-spiral instrument (group Lentulo), applying the cement onto the post surface (group Direct), and injecting the material using a specific elongation tip (group Elongation tip). After shaping and filling of the root canal, post space was drilled using Rely-X post drill. Rely-X fiber post was seated using Rely-X Unicem and resin cement was light polymerized. The root specimens were embedded in an acrylic resin and the specimens were sectioned perpendicularly to the long axis using a low-speed saw. Three slices per each root containing cross-sections of coronal, middle and apical part of the bonded fiber posts were obtained by sectioning. The push-out bond strength was measured using Universal Testing Machine. Specimens after bond failure were examined using operating microscope to evaluate the failure modes. Results: Push-out bond strengths were statistically influenced by the root regions. Group using the elongation tip showed significantly higher bond strength than other ways. Most failures occurred at the cement/dentin interface or in a mixed mode. Conclusions: The use of an elongation tip seems to reduce the number of imperfections within the selfadhesive cement interface compared to the techniques such as direct applying with the post and lentulospiral technique.

• Polymer(Korea)
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• v.36 no.1
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• pp.76-87
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• 2012

Three kinds of hydroxypropyl cellulose (HPC) derivatives, [6-{4-(4-cyanophenylazo)phenoxy}]hexyloxypropyl celluloses (CAHPCs) with degree of etherification (DET) ranging from 0.4 to 3, fully substituted acrylic acid esters of HPC (HPCA) and CAHPCs (CAHPCAs) were synthesized. The crosslinked HPCA (HPCAG) and CAHPCAs (CAHPCAGs) were also prepared by exposing thermotropic mesophases of HPCA and CAHPCAs to UV light. Both CAHPCs and CAHPCAs with DET ${\leq}$ 1.2, as well as HPC and HPCA, formed enantiotropic cholesteric phases whose optical pitches(${\lambda}_m$'s) increase with temperature, wheras both CAHPCs and CAHPCAs with DET ${\geq}$ 1.4 showed monotropic nematic phases. CAHPCAGs with DET ${\leq}$ 1.2, as well as CAHPCAs with DET ${\leq}$ 1.2, exhibited reflection colors in a wide temperature range. On the other hand, CAHPCAGs with DET ${\geq}$ 1.4, as well as CAHPCAs with DET ${\geq}$ 1.4, showed Schileren textures typical of nematic phase, indicating that the liquid crystalline structure is virtually locked upon photocrosslinking. The isotropization temperatures($T_i$'s) of both CAHPCAs and CAHPCAGs decreased with increasing DET. The $T_i$ of CAHPCAG, however, was higher than that of CAHPCA at the same DET. Moreover, the temperature dependence of ${\lambda}_m$ of CAHPCAGs was much weaker than that of CAHPCAs.

• Bulletin of the Korean Chemical Society
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• v.7 no.2
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• pp.137-142
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• 1986

The luminescence spectra of $Ru(bpy)_3^{2+}$ in poly(methacrylic acid) (PMA) solutions varied sensitively with pH. At pH < 5.5, the emission intensity increased with pH up to 4 times, while it decreased with pH beyond the pH. The enhanced emission intensity was accompanied by blue-shift of the emission maxima as much as 15 nm. The enhancement of emission intensity was attributed to the restricted rotational mobility of ligand of the cation bound to densely coiled PMA molecules at pH < 5.5. The sharp decrease in emission intensity with increasing pH near pH 5.6 was accounted for conformational transition of the polymer to more extended structure, which was also revealed in viscosity measurement. The enhancement of emission intensity became higher as NaCl concentration of the solution increased. The binding constant of $Ru(bpy)_3^{2+}$ with two carboxylate groups of PMA was calculated as $2{\times}10^5\;M^{-1}$ in 0.1 M NaCl at pH 5.2. The pH dependence of luminescence quenching rate of $Ru(bpy)_3^{2+}$ by $Cu^{++}$ also showed maximum near pH 5, and the rate was more than $10^3$ times higher than that in water, whereas the maximum enhancement of quenching rate (about 20 times) in poly(acrylic acid) (PAA) solution occurred at pH 4.5. On the other hand, the pH dependence for neutral water soluble nitrobenzene (NB) exhibited opposite trend to that of $Cu^{++}$. The quenching constant vs pH curve for $MV^{++}$ was composite of those for $Cu^{++}$ and NB. The anomalous high quenching rate for $Cu^{++}$ in PMA solution at pH < 5.5 was attributed to the binding of $Ru(bpy)_3^{2+}$ and $Cu^{++}$ to the same region of PMA, when it conforms densely coiled structure in the pH range. The observation of mininium quenching rate for NB near pH 5.5 indicated that the $Ru(bpy)_3^{2+}$ bound to the densely coiled PMA is not accessible by NB, which is in bulk water phase. The composite nature of the pH dependence of quenching rate for $MV^{++}$ in PMA solution was attributed to the smaller binding affinity of the cation to PMA, compared to that of $Cu^{++}$. The sharp, cooperative conformational transition with pH observed in PMA was not revealed in PAA. But, the pH dependence of quenching rates in this polymer reflected increased charge density and, thus, binding of cations to the polymer, and expansion of the polymer chain with pH.