• Fire Science and Engineering
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• v.26 no.4
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• pp.42-47
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• 2012

In the study, fire extinguishing concentration of $K_2CO_3$-Zeolite composite was measured. Zeolite composite is a porous adsorbent which has small particle size, low density and anti-catalytic effect. Scanning Electron Microscopy, X-Ray diffraction and thermal analysis were also conducted to investigate the structural properties of composite. The result showed that despite of weight ratio, the extinguishing concentration of the composite was lower than pure $K_2CO_3$. The extinguishing concentration of $K_2CO_3$-Zeolite composite which has weight ratio of 7 : 3 was 5.72 times lower than that of pure $K_2CO_3$ and 1.1 times lower than that of ABC powder. The SEM and XRD patterns showed that $K_2CO_3$ was adsorbed on the Zeolite properly, and through the thermal analysis, it was founded that the composite is more effective extinguishing agent than pure $K_2CO_3$.

• Korean Journal of Food Science and Technology
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• v.16 no.3
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• pp.329-335
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• 1984

The effect of peeling methods, spherecity and weight of potatoes and carrots on the peeling efficiency were investigated. The changes in the surface texture by peeling were estimated by Rheometer and were related to the changes in the microstructure. The optimum mechanical peeling conditions using abrasion type rotary peeler were 90 sec. at 300 rpm for potatoes, 70 sec. at 300 rpm for sweet potatoes and 60 sec. at 300 rpm for carrots. The peeling loss was influenced by the sphericity and weight of the sample. The optimum conditions for alkali peeling were 90 sec. immersion in boiling 10% NaOH solution for potatoes, 300 sec. in boiling 10% NaOH solution for sweet potatoes and 60 sec. in boiling 6% NaOH solution for carrots. Severe damage of surface structure was noticed by alkali peeling, demonstrated by denaturation of starch granules in the cell. The structural damage observed by microscope was related to the reduction of cutting force after peeling.

• Journal of Physiology & Pathology in Korean Medicine
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• v.33 no.2
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• pp.123-130
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• 2019

In this study, we investigated the effects of MOK pharmacopuncture at high-doses which are increased 10 to 100-fold in clinics, on propylthiouracil (PTU)-induced hypothyroidism in rats and the safety. We measured the changes of body weight, food and water intake, body temperature, the serum levels of thyroid hormones (TSH, T3, and T4), AST and ALT, glucose, lipid metabolites (total cholesterol, HDL-cholesterol, LDL-cholesterol, and triglyceride) and observed histopathological changes of thyroid tissues by H&E staining. We also analyzed the peaks of constituents of MOK using HPLC. In the results, the treatment of MOK pharmacopuncture at high-dose (30 mg/kg) in hypothyroidism-induced rats for 2 weeks was shown the improvement effects on the decrease of body weight, food intake, and body temperature, The MOK pharmacopunture at high dose regulated the imbalance of thyroid hormones, glucose, and lipid metabolites and also inhibited the structural damages of thyroid tissues. In liver damage, the MOK pharmacopuncture at high dose reduced the increase of AST and ALT levels in hypothyroid rats. We identified the MOK constituents in HPLC analysis. In conclusion, the treatment of MOK pharmacopuncture at high dose has a therapeutic effect on hypothyroidism without liver toxicity, suggesting that the MOK pharmacopuncture be usefully applicable to treat with hypothyroidism in clinics.

• Composites Research
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• v.32 no.4
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• pp.171-176
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• 2019

In this paper, the strength of the composite securement device was characterised by FE analysis. Preliminary frontal crash analysis for the vehicle, equipped with the conventional steel securement device, was carried out according to the ISO 10542 for special transportation to obtain loading data, which were applied to securement device during crash. The securement device consists of block, guide and rail and the weight fraction of rail was the highest among them, therefore, it is desirable to reduce weight of rail by applying carbon/epoxy composite. Also, it was found that 27% of lightweight effect was obtained by hybrid rail that bottom part was replaced by a composite compared to the conventional rail, i.e., made of SAPH 440, without sacrificing the structural strength.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.39-45
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• 2022

Normal strategy of structure optimization procedure has been minimum cost or weight design. Minimum weight design satisfying an allowable stress has been used for the ship and offshore structure, but minimum cost design could be used for the case of high human cost. Natural frequency analysis and forced vibration one have been used for the strength estimation of marine structures. For the case of high precision experiment facilities in marine field, the structure has normally enough margin in allowable stress aspect and sometimes needs high natural frequency of structure to obtain very high precise experiment results. It is not easy to obtain a structure design with high natural frequency, since the natural frequency depend on the stiffness to mass ratio of the structure and increase of structural stiffness ordinary accompanies the increase of mass. It is further difficult at the grillage structure design using the profiles, because the properties of profiles are not continuous but discrete, and resource of profiles are limited at the design of grillage structure. In this paper, the grillage structure design system under the constraint of high natural frequency is introduced. The design system adopted genetic algorithm to realize optimization procedure and can be used at the design of the experimental facilities of marine field such as a towing carriage, PMM, test frame, measuring frame and rotating arm.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.5
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• pp.85-95
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• 2021

Structure design sensitivity was evaluated using the orthogonal array experimental method for passive-type deck support frame (DSF) developed for float-over installation of the offshore plant. Moreover, approximation characteristics were also reviewed based on various meta-models. The minimum weight design of the DSF is significantly important for securing both maneuvering performance and buoyancy of a ship equipped with the DSF and guaranteeing structural design safety. The performance strength of the passive type DSF was evaluated through structure analysis based on the finite element method. The thickness of main structure members was applied to design factors, and output responses were considered structure weight and strength performances. Quantitative effects on the output responses for each design factor were evaluated using the orthogonal array experimental method and analysis of variance. The optimum design case was also identified from the orthogonal array experiment results. Various meta-models, such as Chebyshev orthogonal polynomial, Kriging, response surface method, and radial basis function-based neural network, were generated from the orthogonal array experiment results. The results of the orthogonal array experiment were validated using the meta-modeling results. It was found that the radial basis function-based neural network among the meta-models could approximate the design space of the passive type DSF with the highest accuracy.

• Structural Engineering and Mechanics
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• v.78 no.2
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• pp.125-134
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• 2021

In this paper, the effects of Tuned Mass dampers (TMDs) on the reduction of the vertical vibrations of a real horizontally curved steel box-girder bridge due to different traffic loads are numerically investigated. The performance of TMDs to reduce the bridge vibrations can be affected by the parameters such as dynamic characteristics of TMDs, the location of TMDs, the speed and weight of vehicles. In the first part of this study, the effects of mass ratio, damping percentage, frequency ratio, and location of TMDs on the performance of TMDs to decrease vertical vibrations of different sections of bridge deck are evaluated. In the second part, the performance of TMD is investigated for different speeds and weights of traffic loads. Results show that the mass ratio of TMDs is the more effective parameter in reducing imposed vertical vibration in comparison with the damping ratio. Furthermore, it is found that TMD is very sensitive to its tuned frequency, i.e., with a little deviation from a suitable frequency, the expected performance of TMD significantly decreased. TMDs have a positive and considerable performance at certain vehicle speeds and this performance declines when the weight of traffic loads is increased. Besides, the results reveal that the highest impact of TMD on the reduction of the vertical vibrations is when free vibrations occur for the bridge deck. In that case, maximum reductions of 24% and 59% are reported in the vertical acceleration of the bridge deck for the forced and free vibration amplitudes, respectively. The maximum reduction of 13% is also obtained for the maximum displacement of the bridge deck. The results are mainly related to the resonance condition.

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.275-287
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• 2023

The use of environmental-friendly building materials is becoming increasingly popular worldwide. Compared to the normal concrete, rubber-based concrete is considered more durable, environmentally friendly, socially and economically viable. In this investigation, M20 grade concrete was designed and the fine aggregates were replaced with crumb rubber of two different micron sizes (0.221 mm and 0.350 mm). Fly ash (FA) and silica fume (SF) replaces the binder as supplementary cementitious materials at a rate of 0, 5, 10, 15, and 20% by weight. The mechanical properties of concrete including compressive strength, tensile, and flexural strength were determined. The polynomial work expectation validates the response surface approach (RSM) concept for optimizing SF and FA substitution. The maximum compressive strength (22.53 MPa) can be observed for the concrete containing 10% crumb rubber, 15% fly ash and 15% silica fume. The reduced unit weight of the rubberized concrete may be attributed to the lower specific gravity of the rubber particles. Two-way ANOVA with a significance criterion of less than 0.001 has been utilized with modest residual error from the lack of fit and the pure error. The predictive model accurately forecasts the variable-response relationship. Since, the crumb rubber is obtained from wasted tires incorporating FA and SF as a cementitious ingredient, it helps to significantly improve mechanical properties of concrete and reduce environmental degradation.

• Structural Engineering and Mechanics
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• v.82 no.3
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• pp.295-312
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• 2022

This study investigates the effects of nano silica (NS) and micro steel fiber on the properties of ultra-high-performance concrete (UHPC). The experimental consists of three groups, each one with five percentages of NS content (0%, 2%, 4%, 6% and 8%) in addition to the 20% silica fume and 20% quartz powder proportioned according to the weight of cement added to the mixtures. In addition, three percentages of micro steel fibers (0%, 1% and 2%) were considered. Different mixtures with varying percentages of NS and micro steel fibers were prepared to set the water-to-binder ratio, such as 0.16% and 1.8% superplasticizer proportioned according the weight of the binder materials. The fresh properties, mechanical properties and elevated temperatures of the mixtures were calculated. Then, the results from the microstructure analyses were compared with that of the reference mixtureand it was found that 6% replacement of cement with NS was optimum replacement level. When the NS content was increased from 0% to 6%, the air content and permeability of the mixture decreased by 35% and 39%, the compressive and tensile strength improved by 21% and 18% and the flexural strength and modulus of elasticity increased by 20% and 11.5%, respectively. However, the effect of micro steel fibres on the compressive strength was inconclusive. The overall results indicate that micro steel fibres have the potential to improve the tensile strength, flexure strength and modulus of elasticity of the UHPC. The use of 6% NS together with 1% micro-steel fiber increased the concrete strength and reduce the cost of concrete mix.

• Advances in aircraft and spacecraft science
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• v.10 no.2
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• pp.107-125
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• 2023

Drag reduction is significant research in aircraft design due to its effect on the cost of operation and carbon footprint reduction. Aircraft currently use conventional solid winglets to reduce the induced drag, adding extra structural weight. Fluidic on-demand winglets can effectively reduce drag for low-speed flight regimes without adding any extra weight. These utilize the spanwise airflow from the wingtips using hydraulic actuators to create jets that negate tip vortices. This study develops a computational model to investigate fluidic on-demand winglets. The well-validated computational model is applied to investigate the effect of injection velocity and angle on the aerodynamic coefficients of a rectangular wing. Further, the turbulence parameters such as turbulent kinetic energy (TKE) and turbulent dissipation rate are studied in detail at various velocity injections and at an angle of 30°. The results show that the increase in injection velocity shifted the vortex core away from the wing tip and the increase in injection angle shifted the vortex core in the vertical direction. Further, it was found that a 30° injection is efficient among all injection velocities and highly efficient at a velocity ratio of 3. This technology can be adopted in any aircraft, effectively working at various angles of attack. The culmination of this study is that the implementation of fluidic winglets leads to a significant reduction in drag at low speeds for low aspect ratio wings.