• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.129-136
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• 2018

The estimation of the fatigue design life for large welded structures is usually performed using the liner cumulative damage method such as Palmgren-Miner rule or the equivalent damage method. When a fatigue crack is detected in a welded steel structure, the residual service life has to be estimated base on S-N curve method and liner elastic fracture mechanics. In this study, to examine the 3D fatigue crack behavior and estimate the fatigue life of out-of-plane gusset fillet welded joint, the fatigue tests were carried out on the model specimens. Investigations of three-dimensional fatigue crack propagation on gusset welded joint was used the finite element analysis of FEMAP with NX NASTRAN and FRANC3D. Fatigue crack growth analysis was carried out to demonstrate the effects of aspect ratio, initial crack length and stress ratio on out-of-plane gusset welded joints. In addition, the crack behaviors of fatigue tests were compared with those of the 3D crack propagation analysis in terms of changes in crack length and aspect ratio. From this analysis result, SIFs behaviors and crack propagation rate of gusset welded joint were shown to be similar fatigue test results and the fatigue life can also be predicted.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.23-26
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• 1995

The objectives of the present study are 1)to find the effect of the diameter of transpedicular screws on their fixational strength in pedicles under static pull-out loading, 2)to determine the biomechanical correlation between the pedicle diameter and the screw diameter, and 3)to find the effects of other factors in the screw design, such as materials, screw pitch, thread height and shape on their fixational strength. Biomechanical tests (Test I) were performed to evaluate the effect of the screw diameter on pull-out strength by using 60 porcine pedicls and six groups of custom-made pedicle screws with different diameters (the major and the minor diameter of the screws used in the testing varied from 4mm upto 9mm and from 3mm upto 8mm, respectively) while all other factors (materials, screw pitch, thread height and shape etc.) were fixed. In Test II, by using 61 porcine pedicles, the relationship between the ratio of the pedicle diameter and the screw diameter(=aspect ratio) of the custum-made screw and the pull-out strength of the screw was investigated. Test III was performed with 94 porcine pedicles and 8 different types of the commercial screws from 6 major productors in order to determine the effect of the screw diameter, pitch and the thread shape on the pull-out strength of the screw, respectively. The results of Test I showed that the axial pull-out resistance of the screw could be increased prportionaly to the screw diameter(P<0.05). But this increase in the pull-out resistance did not found when the screws of 4mm or 9mm in the diameter were employed. It was found from the results of Test II that the screws had its maximum pull-out resistant force when the aspect ratio ranging 40 - 69% (P<0.05). based on the results for the major diameter against the minor diameter of screw, the maximal pull-out resistance was found at 60-65% (P<0.05). According to these biomechanical testing results, it seems that the screw with a moderately large pitch is more desirable and the buttress-shaped screw can provide stronger fixation than the V-shape one can, if other designal factor and conditions were fixed.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.3
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• pp.313-319
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• 2017

Cylindrical shells are often used in ship structures at deck plating with a camber, side shell plating at fore and aft parts, and bilge structure part. It has been believed that such curved shells can be modelled fundamentally by a part of a cylinder under axial compression. From the estimations with the usage of cylinder models, it is known that, in general, curvature increases the buckling strength of a curved shell subjected to axial compression, and that curvature is also expected to increase the ultimate strength. We conduct series of elasto-plastic large deflection analyses in order to clarify the fundamentals in buckling and plastic collapse behaviour of cylindrical shells under axial compression. From the numerical results, we derive design formula for predicting the ultimate strength of cylindrical shell, based on a series of the nonlinear finite element calculations for all edges, simply supporting plating, varying the slenderness ratio, curvature and aspect ratio, as well as the following design formulae for predicting the ultimate strength of cylindrical shell. From a number of analysis results, fitting curve can be developed to use parameter of slenderness ratio with implementation of the method of least squares. The accuracy of design formulae for evaluating ultimate strength has been confirmed by comparing the calculated results with the FE-analysis results and it has a good agreement to predict their ultimate strength.

• Journal of Nutrition and Health
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• v.26 no.3
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• pp.231-247
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• 1993

This study was designed to confirm the effect of dietary protein level and oral administration of tryptophan on brain serotonin metabolism. Two animal experiments were conducted. The objectives and results of research were as follows : In the first experiment, it was investigated whether administration of reserpine to Sprague-Dawley rats fed 6% or 20% casein diet induced decrease in serum tryptophan and large neutral amino acid(LNAA) concentrations, tryptophan/LNAA concentration ratio, brain tryptophan, serotonin and 5-hydroxyindoleacetic acid(5-HIAA) contents. Brain serotonin content of 6% casein diet group was lower than those of 20% casein diet group. Both 6% and 20% casein diet groups administered with reserpine to induce the analogous depression, showed the notable decrease in brain serotonin content when they were compared with 20% casein diet group not administered with reserpine. Serum tryptophan/LNAA ration and brain 5-HIAA content showed a tendency similar to the change of serotonin content, but the mean difference among all groups was not significant. From these results, it could be said that when the dietary protein level was low, brain serotonin content was decrease. The second experimnt was to see the change in serum tryptophan concentration and tryptophan/LNAA ratio and brain tryptophan, serotonin and 5-HIAA content when tryptophan was administered orally to the animals treated with reserpine. Serum tryptophan concentration tended to increase in both reserpine-treated 6% and 20% casein diet groups administered with tryptophan, especially in the 6% casein diet group. Serum tryptophan/LNAA concentration ratio tended to incrase in reserpine-tteated 6% casein diet group, while decrease in reserpine-treated 20% casein diet group. Brain tryptophan content was increased in both reserpine-treated 6% and 20% casein diet groups. However, brain serotonin content of reserpine-treated 6% casein diet group showed a tendency to decrease, while that of reserpine-treated 20% casein group increase. Consequently, the effect of tryptophan administration on increase of brain tryptophan and serotonin content in animals treated with reserpine was far more excellent in 20% casein diet groups. It was concluded that dietary protein intake and tryptophan administration increase brain serotonin level. Accordingly, it was possible to confirm that brain function, particularly in aspect of behavior related to the serotonin, was changed with manipulation of dietary composition.

• Journal of Korean Society of Steel Construction
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• v.10 no.2 s.35
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• pp.201-209
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• 1998

The presence of elevated temperature can alter significantly the structural response of fibre-reinforced laminated composites. A thermal environment causes degradation in both strength and constitutive properties, particularly in the case of fibre-reinforced polymeric composites. Furthermore, associated thermal expansion, either alone or in combination with mechanically induced deformation, can result in buckling, large deflections, and excessively high stress levels. Consequently, it is often imperative to consider environmental effects in the analysis and design of laminated systems. Exact analytical solutions of higher-order shear deformation theory is developed to study the thermal buckling of cross-ply and antisymmetric angle-ply rectangular plates. The buckling behavior of moderately thick cross-ply and antisymmetric angle-ply laminates that are simply supported and subject to a uniform temperature rise is analyzed. Numerical results are presented for fiber-reinforced laminates and show the effects of ply orientation, number of layers, plate thickness, and aspects ratio on the critical buckling temperature and compared with those obtained using the classical and first-order shear deformation theory.

• Applied Chemistry for Engineering
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• v.17 no.6
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• pp.619-624
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• 2006

This study was performed to investigate the formation process of calcium sulfate ${\alpha}$-hemihydrate from FGD gypsum produced at thermal power plant burning bituminous coal. The experimental results showed that calcium sulfate $\alpha$-hemihydrate with a large aspect ratio was produced in the temperature range of $120^{\circ}C$ and $140^{\circ}C$ in the absence of additives through dissolution-recrystallization mechanism. It was also observed that addition of Na-succinate as a catalyst changed crystal shape from acicular to prismatic, resulting in decreased water/powder ratio down to 33%. Optimum concentration of Na-succinate was 20mM. It was confirmed that the optimum moulding pressure and moisture content of moulded body from FGD gypsum were $30kg_f/cm^2$ and between 10% and 15% respectively, which prevent moulded body from collapsing and maximize the capillary effect by given pore volume while autoclaving.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.235-241
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• 2006

Mullite short fibers have been fabricated by adapting the Kneading-Drying-Calcination (KDC) process and characterized. The effect of the addition of foaming agent and calcination temperature on the formation of mullite fibers from coal fly ash, was examined. In the present work, ammonium alum $NH_4Al(SO_4)_2\;12H_2O$ synthesized trom coal fly ash and sodium phosphate $Na_2HPO_4\;2H_2O$ were used as foaming agents. After calcination at $1300^{\circ}C$ for 10 h and then etching with 20% HF solution at $50^{\circ}C$ for 5 h using a microwave heating source, the alumina-deficient $(AI_2O_3/SiO_2$ = 1.13, molar ratio) orthorhombic mullite fibers with a width of ${\sim}0.8mm$ (aspect ratio >30), were prepared from the coal fly ash with $AI_2O_3/SiO_2$ = 0.32, molar ratio by the addition of $NH_4AI(SO_4)_2\;12H_2O$, and with further addition of 2 wt% sodium phosphate. The excessive addition of sodium phosphate rather decreased the formation of mullite fibers, possibly due to the large amount of liquid phase prior to mullitization reaction.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1-4
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• 2008

Flat plate slab has been widely used in high rise building for its remarkable advantages. However, Flat plate structures under lateral load are susceptible to punching shear of the slab-column connection. Exterior slab-column connections has an unsymmetrical critical section for eccentric shear of which perimeter is less than that of interior connection, and hence, around the connection, unbalanced moment and eccentric shear are developed by both gravity load and lateral loads. Therefore, exterior connections is susceptible to punching shear failure. For that reason, this study compare ACI 318-05 to CEB-FIP MC 90 that is based on experiment results and existing data of flat plate exterior connections. This study shows that compared to CEB-FIP MC 90 is more exact about eccentric shear stress, unbalanced moment and Both of all are not suitable in large column aspect ratio. Considering gravity shear ratio, These are suitable but design condition only consider gravity shear ratio. So these should be considered differences from change of design condition

• Journal of Korean Vacuum Science & Technology
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• v.4 no.4
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• pp.93-96
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• 2000

Microchannel plates (MCPs) have been developed by introducing new materials and process technologies. Main body was made of alumina by programmable punching, laminating, and firing. The channel walls of pore arrays of an MCP were deposited with thin films by electroless copper plating and sol-gel process. Our MCP has advantages such as easy fabrication, durability, high temperature endurance, and applicability to the large size comparing with the conventional MCPs. Experiments on the brightness of an MCP incorporated FED revealed that the FED with a MCP is three to four times brighter than a conventional FED. Moreover, the focusing in a FED is improved. Incorporating an MCP into a FED is one of promising methods to enhance the characteristics of the FED. In addition, amplification yield of the MCP is measured for varying the aspect ratio and the input current.

• Journal of Powder Materials
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• v.20 no.2
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• pp.125-128
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• 2013

Magnetic and dielectric properties of rubber composites are controlled by using two kinds of high-permeability metal particles with different electrical conductivity (Sendust, Permalloy), and their effect on microwave absorbance has been investigated, focusing on the quasi-microwave frequency band (0.8-2 GHz). Noise absorbing sheets are composite materials of magnetic flake particles of high aspect ratio dispersed in polymer matrix with various filler amount of 80-90 wt.%. The frequency dispersion and magnitude of complex permeability is almost the same for Sendust and Permalloy composite specimens. However, the complex permittivity of the Permalloy composite (${{\varepsilon}_r}^{\prime}{\simeq}250$, ${{\varepsilon}_r}^{{\prime}{\prime}}{\simeq}50$) is much greater than that of Sendust composite (${{\varepsilon}_r}^{\prime}{\simeq}70$, ${{\varepsilon}_r}^{{\prime}{\prime}}{\simeq}0$). Due to the large dielectric permittivity of Permalloy composite, the absorbing band is shifted to lower frequency region. However, the investigation of impedance matching reveals that the magnetic permeability is still small to satisfy the zero-reflected condition at the quasi-microwave frequency band, resulting in a small microwave absorbance lower than 10 dB.