• The Journal of Korean Academy of Prosthodontics
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• v.47 no.2
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• pp.125-135
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• 2009

Statement of problem: Loosening or fracture of the abutment screw is one of the common problems related to the dental implant. Generally, in order to make the screw joint stable, the preload generated by tightening torque needs to be increased within the elastic limit of the screw. However, additional tensile forces can produce the plastic deformation of abutment screw when functional loads are superimposed on preload stresses, and they can elicit loosening or fracture of the abutment screw. Therefore, it is necessary to find the optimum tightening torque that maximizes a fatigue life and simultaneously offer a reasonable degree of protection against loosening. Purpose: The purpose of this study was to present the influence of tightening torque on the implant-abutment screw joint stability with the 3 dimensional finite element analysis. Material and methods: In this study, the finite element model of the implant system with external butt joint connection was designed and verified by comparison with additional theoretical and experimental results. Four different amount of tightening torques(10, 20, 30 and 40 Ncm) and the external loading(250 N, $30^{\circ}$) were applied to the model, and the equivalent stress distributions and the gap distances were calculated according to each tightening torque and the result was analyzed. Results: Within the limitation of this study, the following results were drawn; 1) There was the proportional relation between the tightening torque and the preload. 2) In case of applying only the tightening torque, the maximum stress was found at the screw neck. 3) The maximum stress was also shown at the screw neck under the external loading condition. However in case of applying 10 Ncm tightening torque, it was found at the undersurface of the screw head. 4) The joint opening was observed under the external loading in case of applying 10 Ncm and 20 Ncm of tightening torque. 5) When the tightening torque was applied at 40 Ncm, under the external loading the maximum stress exceeded the allowable stress value of the titanium alloy. Conclusion: Implant abutment screw must have a proper tightening torque that will be able to maintain joint stability of fixture and abutment.

• Journal of Life Science
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• v.26 no.11
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• pp.1275-1281
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• 2016

The principal objective of this fundamental research was to analyze the physicochemical properties the and antioxidative activity of Napa cabbage pickle (NCP) for development of low-salt pickles. NCP-1 was a smaller than NCP at amount soy sauce (10%). The pH of NCP and NCP-1 were $4.51{\pm}0.15$, $4.85{\pm}0.08$ immediately after preparation. The pH of NCP and NCP-1 was reduced to $4.08{\pm}0.05$ and $4.31{\pm}0.12$ over time during 60 days of storage. The acidity of the NCP and NCP-1 immediately after preparation were 0.51% and 0.38% and increased to 0.67% and 0.56% after 60 days of storage. The salinity for the NCP ranged from 1.71-2.22% and NCP-1 ranged from 1.18-1.63%. The L value, which indicates the lightness, was the highest at day 0 and the lowest at 60 day. The tensile strength value of NCP was $10.9{\pm}0.05kgf/cm^2$ and NCP-1 in $11.84{\pm}0.11kgf/cm^2$ at day 0 and then significantly decreased with time in storage. The cutting force of NCP was $1004{\pm}7.12gf/cm^2$ and NCP-1 in $845{\pm}5.27gf/cm^2$ at day 0, which increased over time in storage. The overall acceptability of NCP was the highest at day 30, but the overall acceptability of NCP-1 was the highest at day 45. NCP-1 extracts at day 60 showed the highest antioxidant activity of 66.04%, whereas the NCP extract at day 0 showed the lowest antioxidant activity of 45.41%. These results showed that depending on the content of the seasoning pickle difference in the antioxidant activity. Thus, the best pickled Napa cabbage is determined by a smaller amount soy sauce in NCP-1, and the results could provide a basis for improving the availability and quality of Napa cabbage.

• Journal of Korean Society of Forest Science
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• v.16 no.1
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• pp.33-62
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• 1972

Pitch pine (Pinus rigida Miller) in Korea has become one of the major silvicultural species for many years since it was introduced from the United States of America in 1907. To attain the more rational wood utilization basical researches on wood properties are primarily needed, since large scale of timber production from Pitch Pine trees has now been accomplishing in the forested areast hroughout the country. Under the circumustances, this experiment was carried out to study the wood anatomical, physical and mechanical properties of Pitch Pine grown in the country. Materials used in this study had been prepared by cutting the selected pitch pine trees from the Seoul National University Forests located in Suwon. To obtain and compare the anatomical and physical properties of the different parts of tree such as stem, branch, top and rootwood, this study had been divided into two categories (anatomical and physical). For the anatomical study macroscopical and microscopical features such as annual ring, intercellular cannal, ray, tracheid, ray trachid, ray parenchyma cell and pit etc. were observed and measured by the different parts (stem, branch, root and topwood) of tree. For the physical and mechanical properties the moisture content of geen wood, wood specific gravity, shrinkage, compression parallel to the grain, tension parallel and perpendicular to the grain, radial and tangential shear, bending, cleavage and hardness wree tested. According to the results this study may be concluded as follows: 1. The most important comparable features in general properties of wood among the different parts of tree were distinctness and width of annual ring, transition from spring to summerwood, wood color, odor and grain etc. In microscopical features the sizes of structural elements of wood were comparable features among the parts of tree. Among their features, length, width and thickness of tracheids, resin ducts and ray structures were most important. 2. In microscopical features among the different parts of tree stem and topwood were shown simillar reults in tissues. However in rootwood compared with other parts on the tangential surface distinctly larger ray structures were observed and measured. The maximum size of unseriate ray was attained to 27 cell ($550{\mu}$) height in length and 35 microns in width. Fusiform rays were formed occasionally the connected ray which contain one or several horizontal cannals. Branchwood was shown the same features like stemwood but the measured values were very low in comparing with other parts of tree. 3. Trachid length measured among the different parts of tree were shown largest in stem and shortest in branchwood. In comparing the tracheid length among the parts the differences were not shown only between stem and rootwood, but shown between all other parts of tree. Trachid diameters were shown widest in rootwood and narrowest in branchwood, and the differences among the different parts were not realized. Wall thickness were shown largest value in rootwood and smallest in branchwood, and the differences were shown between root and top or branchwood, and between stem and branch or top wood, but not shown between other parts of tree. 4. Moisture contents of green wood were shown highest in topwood and lowest in heartwood of stem. The differences among the different parts were recognized between top or heartwood and other parts of tree, but not between root and branchwood or root and sapwood. 5. Wood specific gravities were shown highest in stem and next order root and branchwood, but lowest in topwood. The differences were shown clearly between stemwood and other parts of tree, but not root and branchwood. However the significant difference is realized as most lowest value in topwood. 6. In compression strength parallel to the grain compared among the different parts of tree at the 14 percent of moisture content, highest strength was appeared in stem, next order branch and rootwood, but lowest in topwood. 7. In bending strength compared among the different parts of tree at the 14 percent of moisture content clearly highest strength was shown in branchwood, next order stem and root, but lowest in topwood. Though the branchwood has lower specific gravity than stemwood it was shown clearly high bending strength.

• Polymer(Korea)
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• v.28 no.1
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• pp.77-85
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• 2004

It has been widely used ultra high molecular weight polyethylene (UHMWPE) for the biomaterials due to its excellent mechanical properties and biocompatibility. In the case of blend of UHMPE with another polymeric biomaterials, however, UHMWPE might have low blend compatibility due to surface inertness. In this study, in order to improve the mechanical properties of poly(methyl methacrylate) (PMMA) bone cement by means of the impregnation of UHMWPE powder, we developed the novel surface modification method by the mixture of methyl methacrylate (MMA) and xylene. We investigated the variation of composition of MMA/xylene. It was confirmed by the analysis of Fourier transform infrared-attenuated total reflectance, scanning electron microscope, universal transverse mercator, and digital thermometer. The maximum mechanical strength of surface modified UHMWPE powder impregnated PMMA bone cement compound was observed the ratio of 1 : 1 (v/v％) MMA/xylene. Also its curing temperature decreased from 103 $^{\circ}C$ to 58 ∼ 73 $^{\circ}C$ The mechanism of surface modification of UHMWPE powder by the mixture of MMA/xylene has been proposed.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.773-783
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• 2007

A simple unbonded-type shear strengthening technique for reinforced concrete beams using wire rope units is developed. Six two-span continuous T-beams externally strengthened with wire rope units and an unstrengthened control beam were tested. The main variables investigated were the amount and prestressing force of wire rope units. All specimens had the same geometrical dimension and arrangement of internal reinforcement. Influence of the distribution of vertical stresses in beam web owing to the prestressing force of wire rope units on the diagonal shear cracking load and the ultimate shear capacity of beams tested is presented. Based on the current study, it can be concluded that the amount and initial prestress of wire rope should be limited to be above 2.5 times the minimum shear reinforcement ratio specified in ACI 318-05 and below 0.6 times its own tensile strength, respectively, to ensure the enhancement of shear capacity and ductile failure mode of the strengthened beams. A numerical analysis based on the upper-bound theorem is developed to assess the shear capacity of continuous T-beams strengthened with wire rope units. From the comparisons of measured and predicted shear capacities, a better agreement is achieved in the proposed numerical analysis than in empirical equations recommended by ACI 318-05.

• Journal of the Korean Society of Food Science and Nutrition
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• v.39 no.5
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• pp.737-744
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• 2010

In order to provide fundamental data on development of rice noodles, the quality characteristics of 10 kinds of commercial rice noodles were evaluated. Rice noodles were categorized into 3 groups for examination: 100% rice noodles with different shapes; round shape noodles with different rice contents; and noodles with different rice contents but smilar cooking method. Cooking properties, texture measurement, and sensory characteristics were evaluated. Frozen rice noodles and instant type of noodles made from composite flour of rice and wheat flour exhibited higher scores in overall acceptance. As for the form of noodle, round-shaped noodles seemed to be preferred in comparison to flat-shaped noodles. Generally, noodles with high texture scores of cohesiveness, adhesiveness, chewiness, resilience but not high score of hardness having smooth surface were preferred affecting overall acceptance scores. It appears that cooking methods and cooking time recommended by manufactures, noodle thickness and shape, packaging types such as frozen, refrigerated, and dried noodles were more influential than rice contents in aspects to the quality characteristics of the commercial rice noodle products in this study.

• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1042-1047
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• 2002

The sedimentation characteristics of ceramic fiber were analyzed when viscosity of the slurry for ceramic paper formation was varied and zeta potential change and degree of dispersion with pH were studied as well. The proper viscosity of the slurry for dispersion of fibers was between 28 and 31 cps. Zeta potential of the slurry was sensitively changed with pH adjustment and showed maximum value of -35~-36 mV at ph 7.5~9.5, which indicated better dispersion of ceramic fiber as zeta potential of the slurry was increased. The sedimentation rate of ceramic fiber in a slurry was reported minimum at the maximum zeta potential. Water content of the casted paper should be lower than 83% after vacuum dehydration for retention of binder and lower than 62% after press rolling for wet paper handling. The obtained ceramic paper had tensile strength and basis weight, $102 kgf/cm^2$ and $98 g/m^2$, respectively.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.129-140
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• 2007

A major purpose of this study is to develop a drainage system that can quickly drain water penetrated into pavement layers to mitigate pot holes which is one of the major distress types in bridge deck pavements. This system can be established by applying a thin drainage layer between waterproof and pavement layers. The most important elements for this system are the performance of waterproof layer and construction technique for the thin drainage layer. The porous asphalt mix with the maximum aggregate size of 10mm is first developed based on the porous asphalt mix design guide proposed by NCAT, and various physical and mechanical tests are performed to confirm that the porous mix satisfies all the specification requirements. In addition, a series of laboratory tests including low-temperature bending and bonding strength tests for the MMA(Methyl Methacrylate) type of waterproofing material. It is observed from the tests that the MMA material satisfies all the specification requirements. To evaluate the Reld performance of the drainage system, a field study has been conducted on a relatively small size bridge. The QC/QA tests are conducted on the both waterproofing and pavement materials. It has been found that the drainage system works well to drain the water penetrated into the pavement layers.

• Membrane Journal
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• v.25 no.1
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• pp.48-59
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• 2015

This paper reports a fabrication of poly(L-lactic acid) (PLLA) scaffold membranes through phase separation process using pure and mixed solvents. Chloroform and 1,4-dioxane were used as pure solvents and mixed solvents were obtained by mixing the pure solvents together. Morphologies, mechanical properties and mass transfer characteristics of the scaffold membranes were investigated through SEM, stress-strain test and glucose diffusion test. Scaffold membranes from the solution with pure chloroform showed solid-wall pore structure. In contrast, nano-fibrous membranes were fabricated from the solution with pure 1,4-dioxane. In case of mixed solvents, the scaffold membranes showed various structures with changing composition of the solvents. When 1,4-dioxane content was lower than 20 wt% in the solvent, scaffold membrane showed solid-wall pore structure. When the content was 20 wt%, scaffold membranes with macropores with the maximum size of $100{\mu}m$ was obtained. In the concentration range of 1,4-dioxane over 25 wt%, the scaffold membranes showed nano-fibrous structures. In this range, the fibers showed different diameters with changing composition of the solvent. The minimum fiber diameter was about $15{\mu}m$, when 1,4-dioxane composition was 80 wt%. These results indicate that the composition of the solvent showed a significant effect on the structure of scaffold membrane.

• International Journal of Highway Engineering
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• v.7 no.4 s.26
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• pp.49-56
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• 2005

The effect of modified asphalts is evaluated by simple comparison of a single parameter (i.e., tensile strength, stiffness, etc.) between modified asphalt mixture and unmodified mixture. The use of a single parameter to evaluate the effect of modified asphalt must be questioned. Rather, a single unified framework that accounts for changes in key mixture properties is needed to effectively evaluate the modified asphalt mixtures. This study used a new performance-based fracture parameter as a single unified framework, the Energy Ratio (ER), for quantifying the effect of modified asphalts oil the fracture resistance of mixtures. The Energy Ratio was then used as a performance criterion for calculating the construction cost of two modified asphalt pavements (SBS and Crumb Rubber) and unmodified asphalt pavement. The results showed that the Energy Ratio of SBS modified asphalt was higher than those of crumb rubber and unmodified asphalt. Cost analyses indicated that the construction cost of the AC layer would be reduced by up to 24% by SBS modification. Based on the results, the Energy Ratio is capable of evaluating the effect of modified mixtures, and may form the basis of a promising fracture criterion for performance-based thickness design in asphalt pavements.