• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.88-91
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• 2002

The two dimensional size effect of specimen gauge section (length x width) was investigated on the compressive behavior of a T300/924 [45/-45/0/90]3s, carbon fiber-epoxy laminate. A modified ICSTM compression test fixture was used together with an anti-buckling device to test 3mm thick specimens with a 30$\times$30, 50$\times$50, 70$\times$70, and 90mm$\times$90mm gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post failure examination suggests that $0^{\circ}$ fiber microbuckling is the critical damage mechanism that causes final failure. This is the matrix dominated failure mode and its triggering depends very much on initial fiber waviness. It is suggested that manufacturing process and quality may play a significant role in determining the compressive strength. When the anti-buckling device was used on specimens, it was showed that the compressive strength with the device was slightly greater than that without the device due to surface friction between the specimen and the device by pretoque in bolts of the device. In the analysis result on influence of the anti-buckling device using the finite element method, it was found that the compressive strength with the anti-buckling device by loaded bolts was about 7% higher than actual compressive strength. Additionally, compressive tests on specimen with an open hole were performed. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of fiber microbuckling and delamination initiates at the edge of the hole at approximately 80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3mm (depends on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of unnotched compressive strength and in-plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1015-1021
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• 2010

In this study, the effect of the C/SiC composition ratio on the impact damage of a reaction sintered SiC (RS-SiC) plates was evaluated. An impact test was conducted by using an air gun. The impacter used was a steel ball with a diameter of 2 mm, and the impact velocities were 113, 122, and 180 m/s. The RS-SiC plates were $20\times20\times3$ mm with different C/SiC composition ratios. The ring crack diameters damaged by a steel ball were determined using SEM images. It was observed that the maximum diameter increased with increasing impact velocity, and it rapidly changed with increasing C/SiC composition ratio because of the effect of residual Si and the variation flexural strength. Cone cracks were formed in the case of C/SiC composition ratios of 0.4~0.5, this indicated that the impact damage changed from a ring crack to a cone crack in this critical range of C/SiC composition ratios. The C/SiC composition ratio of 0.3 was determined to be the optimal ratio for the RS-SiC manufacturing process.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.3
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• pp.303-312
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• 2008

Multi-axial compression tests have been frequently adopted for the evaluation of material properties of rock cores and rock fracture model tests. Special care has to be applied on the boundary condition between the specimen and loading platen to draw the precise test results of the multi-axial compression tests. With the use of dry steel platen, the stress rotation will occur, due to the frictional restraint from the boundary between the specimen and loading platen. The restraint will deviate the expected test results under the conditions of the given external pressures. Various methods have been applied to reduce the side restraint along the specimen/loading platen interface. The steel brush type loading platen is one example of the attempts. In this paper, a new type of loading platen is introduced to overcome the limitation caused by the use of the brush type loading platen, which requires some internal space for the installation of the brushes. The new type of loading platen, roller supported steel piston type loading platen. is constituted of shot steel pistons which have sufficient stiffness to deliver the external pressure and the shaft type roller installed at the rear of the pistons. The pistons are designed to follow the local deformation of the specimens. In this paper, structural details of the loading platen are presented and frictional and biaxial compression tests results are shown to verify the required functions of the loading platen. Furthermore, calibration process is followed by a comparison between the test results and numerical analyses.

• Journal of the Korean Society of Food Science and Nutrition
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• v.35 no.4
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• pp.499-506
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• 2006

Response surface methodology was used to investigate the cookie manufacturing process with black rice flour. A three- variable, three-level central composite design was employed where the independent variables were the amount of black rice flour ($0{\sim}20%$), baking time ($10{\sim}14 min$), and sugar type (sucrose, aspartame and oligosaccarides). pHs of dough and cookie tended to increase with the addition of black rice flour. Moisture content of dough slightly increased with tile addition of black rice flour but nearly affected by baking time. Spread factor increased with the addition of black rice flour and it was more evident in the samples prepared with sucrose. L*-value decreased but a*-value increased significantly with the addition of black rice flour. Generally the amount of black rice flour in the sample did not affect the textural characteristics of cookie. As the amount of black rice and baking time increased, sensory flavor became stronger. Sensory sweetness as well as hardness increased but sensory color became darker with the addition of black rice flour. In addition, the response surface models developed in this study for most of physicochemical and sensory characteristics of black rice cookie were adequate.

• Polymer(Korea)
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• v.26 no.2
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• pp.260-269
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• 2002

The fire resistance of particulate polypropylene composite systems were investigated by using various reinforced particles such as zeolite, talc, $CaCO_3$ particles. In this study, The effect of particle size on the thermal properties of composite and the effect of reinforced particles on the fire resistance were studied. The inorganic reinforced particles used in this study were recycled zeolite(average particle diameter=85.34 $mu extrm{m}$), $CaCO_3$ (33.93 $mu extrm{m}$), and talc (18.51 $mu extrm{m}$). The fire resistance of composite systems was thoroughly examined by measuring limited oxygen index (LOI, ASTM D2863) and cone calorimetry (ASTM E1354, ISO 5660). Thermal stability of composite systems was thoroughly examined by measuring TGA. The flame retardants (DBDPO) and reinforced particles reduce the maximum heat release rate (M-HRR) in the order of Talc > $CaCO_3$ > recycled Zeolite. Comparing the cone calorimetry experimental results of the particle reinforced polymer composite system exhibited twice higher efficiency than DBDPO in polypropylene systems, and the LOI also showed similar trends to the cone calorimetry experiments. The optical and scanning electron microscopy techniques were used to investigate the composites ash layer and the core fracture surfaces in the burning process. The reinforcing inorganic particles seemed to accumulate at the surface of ash layer, and subsequently intercept the oxygen transport and heat transfer into the core area.

• Applied Microscopy
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• v.19 no.2
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• pp.119-137
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• 1989

It has been shown in this and earlier investigation that the turtle bladder mucosa has three main cell types on their mucosal surface. They are the granular cells, ${\alpha}$ CA cells, and ${\beta}$ CA cells. The three major transport mechanisms that occurs in the turtle bladder are sodium reabsorption, proton secretion, and bicarbonate secretion. In the present work the trans-port mechanisms by bladder epithelial cells of freshwater turtle, Pseudemys scripta, are summarized as follows. 1. The granular cells play an important role in sodium transport, while the ${\alpha}$ and ${\beta}$ CA cells do not appear to play a determining role in sodium transport. 2. It appears that the active sodium transport in the granular cells occurs in two-step process, implying that first, sodium diffuses into the cells, followed by an energy-dependent efflux step, which is catalyzed by the ouabain-sensitive Na-K ATPase. 3. The ${\alpha}$ type of CA cells are responsible for the proton secretion using the proton pump on the apical plasma membrane, while the ${\beta}$ type of CA cells are believed to be responsible for bicarbonate secretion. 4. When looked at under freeze-fracture electron microscopy, the apical plasma membrane of ${\alpha}$ cells have a characteristic population of rod-shaped intramembranous particles which are believed to be components of the proton pumps. Conversely, ${\beta}$ type of CA cells show rod-shaped particles in their basolateral plasma membranes, which is consistent with the proton absorptive, bicarbonate secretory mechanism. 5. In the turtle bladder, the ${\alpha}$ and ${\beta}$ type of cells are believed to be both responsible for proton transport, but in opposite directions.

• Journal of Adhesion and Interface
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• v.2 no.1
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• pp.9-17
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• 2001

Curing behavior and interfacial properties were evaluated using electrical resistance measurement and tensile/compressive fragmentation test. Electrical resistivity difference (${\Delta}R$) during curing process was not observed in a bare carbon fiber. On the other hand, ${\Delta}R$ appeared due to the matrix contraction in single-carbon fiber/epoxy composite. Logarithmic electrical resistivity of the untreated single-carbon fiber composite increased suddenly to the infinity when the fiber fracture occurred under tensile loading, whereas that of the ED composite reached relatively broadly up to the infinity. Comparing to the untreated case, interfacial shear strength (IFSS) of the ED treated composite increased significantly in both tensile fragmentation and compressive Broutman test. Microfailure modes of the untreated and the ED treated fiber composite showed the debonding and the cone shapes in tensile test, respectively. For compressive test, fractures of diagonal slippage were observed in both untreated and the ED treated composite. Sharp-end shape fractures exhibited in the untreated composite, whereas relatively dull fractures showed in the ED Heated composite. It is proved that ED treatments affected differently on the interfacial adhesion and microfailure mechanism under tensile/compressive tests.

• Elastomers and Composites
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• v.44 no.2
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• pp.164-174
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• 2009

PA66/EPDM/PP-g-MA and PA66/EPDM-g-MA/PP-g-MA composites were manufactured by a modular intermeshing twin screw extruder for enhanced low temperature impact resistance with different content of PP-g-MA. The results showed that composite containing 90 wt% of PA66, 8 wt% of EPDM-g-MA, and 2 wt% of PP-g-MA has a optimum value in the thermal and mechanical properties. The characteristics of the composites were analyzed by TGA, DSC, and SEM. From above results, we established that the low interfacial strength and the impact resistance at low temperature shown in a pre-existing PP/EPDM composite were enhanced by grafting with compatibilizer such as maleic anhydride. These results show the possibility of local manufacturing process and cost down with optimum screw configuration for best mixing quality in the twin screw extruder.

• Journal of Dental Anesthesia and Pain Medicine
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• v.16 no.1
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• pp.39-47
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• 2016

Background: Oxidative stress occurs during the aging process and other conditions such as bone fracture, bone diseases, and osteoporosis, but the role of oxidative stress in bone remodeling is unknown. Propofol exerts antioxidant effects, but the mechanisms of propofol preconditioning on oxidative stress have not been fully explained. Therefore, the aim of this study was to evaluate the protective effects of propofol against $H_2O_2$-induced oxidative stress on a human fetal osteoblast (hFOB) cell line via activation of autophagy. Methods: Cells were randomly divided into the following groups: control cells were incubated in normoxia (5% $CO_2$, 21% $O_2$, and 74% $N_2$) without propofol. Hydrogen peroxide ($H_2O_2$) group cells were exposed to $H_2O_2\;(200{\mu}M)$ for 2 h, propofol preconditioning (PPC)/$H_2O_2$ group cells were pretreated with propofol then exposed to $H_2O_2$, 3-methyladenine (3-MA)/PPC/$H_2O_2$ cells were pretreated with 3-MA (1 mM) and propofol, then were exposed to $H_2O_2$. Cell viability and apoptosis were evaluated. Osteoblast maturation was determined by assaying bone nodular mineralization. Expression levels of bone related proteins were determined by western blot. Results: Cell viability and bone nodular mineralization were decreased significantly by $H_2O_2$, and this effect was rescued by propofol preconditioning. Propofol preconditioning effectively decreased $H_2O_2$-induced hFOB cell apoptosis. However, pretreatment with 3-MA inhibited the protective effect of propofol. In western blot analysis, propofol preconditioning increased protein levels of collagen type I, BMP-2, osterix, and TGF-${\beta}1$. Conclusions: This study suggests that propofol preconditioning has a protective effect on $H_2O_2$-induced hFOB cell death, which is mediated by autophagy activation.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.4
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• pp.283-290
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• 2011

Purpose: This study compared the marginal bone loss around dental implant that were placed in the canine areas of the mandibles and finded the survival rate of implants, marginal bone loss around implants and prosthetic complications in 10 patients treated with overdentures retained with Locator attachments. Materials and methods: Ten patients who had received implant retained overdentures in the mandibules using two implants and Locator attachments at Daegu Catholic University Medical Center from 2004 to 2010 were included in this study. Evaluations of the survival rate of implants, marginal bone loss and prosthetic complications were performed. Results: Implants placed in this study showed a 100% survival rate and the average annual bone loss was 1.03 mm ${\pm}$ 0.20 mm in the first year. The patients have verbally indicated that they are comfortable and that their overdentures function well. But, implant retained overdentures had various prosthetic complications such as male change, relining, rebasing and denture fracture. Conclusion: Implant retained overdentures using two implant and Locator attachments in the fully edentulous mandibles is considered as a stable way for long terms because of minimal invasive operation, simple prosthetic process and easy repair.