• Journal of Korea Foundry Society
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• v.25 no.5
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• pp.203-208
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• 2005

The main emphasis of this study is to optimize the process variables for manufacturing aluminum foam materials by direct foaming of remelted aluminum scraps. Aluminum foams were fabricated from two different raw materials, pure aluminum and used beverage cans. For both cases, $TiH_{2}$ was used as a foaming agent. Calcium was added as a thickener for the foaming of pure aluminum and no thickener was added for that of used beverage Cans because the pre-existing oxides of the used beverage cans are used as a thickener. Calcium and $TiH_{2}$ content varies from 0.5wt.% to 2.0wt.% and from 0.5wt.% to 1.5wt.%, respectively. The processing conditions, such as the effect of calcium on the melt viscosity, foaming temperature, and the optimum amount of the foaming agent with regard to the melt viscosity were discussed.

• Journal of the Korean Society of Physical Medicine
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• v.15 no.4
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• pp.1-9
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• 2020

PURPOSE: The current generation has shortened hamstrings due to a sedentary lifestyle, resulting in reduced flexibility of the hamstring and dysfunction. This study was undertaken to compare effects of three different release exercises on hamstring flexibility, in participants with short hamstrings. METHODS: Totally, 20 subjects having short hamstrings were involved in this study. The inclusion criterion for study participation was active knee extension test (AKET) less than 60°. All participants were subjected to 3 methods: hamstring foam roller release (HFRR), sitting self myofascial release (sitting SMR), and standing self myofascial release (Standing SMR). All participants randomly performed all three methods to avoid bias caused by learning or fatigue. Passive knee extension test (PKET), AKET, finger to floor distance test (FTFT), and pelvic tilting angle test (PTAT) were measured pre- and post-exercises. RESULTS: The PKET, AKET and FTFT were significantly increased after HFRR, sitting SMR, and standing SMR exercise (p < .05). However, PTAT was not significantly increased after the three exercises (p > .05). Furthermore, no significant differences were observed between PKET, AKET, FTFT and PTAT subsequent to HFRR, sitting SMR, and standing SMR (p > .05). CONCLUSION: Our results indicate that HFRR, sitting SMR and standing SMR were immediately effective in improving hamstring flexibility in participants with short hamstrings.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.2
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• pp.42-52
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• 2015

In this study, cellulose nanofibrils (CNF) were modified through carboxymethylation or TEMPO-mediated oxidation and their effects on ionicity and characteristics of sheet, film, and foam were investigated. Carboxymethylation was carried out on pulp fibers as a pre-treatment before preparation of CNF. The gel-like and translucent CNF hydrogel was obtained by grinding of carboxymethylated cellulose fibers. Carboxymethylated CNF film and freeze dried sheet showed higher transparency than that of untreated CNF. The CNF sheet with high strength and the CNF foam without large ice crystals were obtained by using the carboxymethylated CNF. TEMPO-mediated oxidation was carried out as a post-treatment of CNF. The zeta potential and charge demand of TEMPO-oxidized CNF were increased with an increase in oxidation time and addition amount of NaClO. The density of sheet made of TEMPO oxidized CNF was increased with the amount of oxidizing agent. The TEMPO oxidized cellulose nanofiber (TOCN) which was obtained from supernatant after centrifugation could be converted to transparent film.

• Physical Therapy Rehabilitation Science
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• v.7 no.1
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• pp.35-40
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• 2018

Objective: The purpose of this study was to investigate the immediate effect of applying self-myofascial release (SMR) to the plantar fascia using a foam roller on hamstring and lumbar spine superficial back line (SBL). Design: Randomized controlled trial. Methods: Thirty-one healthy adults agreed to the method and purpose of the study. Selection and exclusion criteria were screened, and baseline measurements for the Toe Touch test and passive straight leg raise (PSLR) test were obtained. The participants were then randomly assigned to the SMR group or the sham group. After group assignment, the SMR group rolled the surface of the foot from the heel to the metatarsal head using a foam roller for 5 minutes. The sham group received passive mobilization of the ankle joint in the supine position. Afterwards, the Toe Touch test and the passive straight leg-raise test were re-assessed. Results: In the SMR group, the Toe Touch test results showed significant improvement (p<0.05). Left and right PSLR test results showed a significant increase (p<0.05). In the sham group, there was no significant difference between pre and post-test results. The SMR group showed a significant difference in the PSLR test and Toe Touch test compared to the sham group (p<0.05). Conclusions: The results of this study showed that SMR on the plantar fascia was immediately effective for improving the flexibility of the SBL of the lumbar spine and hamstring.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6B
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• pp.695-701
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• 2006

A toluene-degrading bacterial strain was isolated from a mixed culture that was maintained using toluene as a sole carbon and energy source. The isolated bacterium was classified as Pseudomonas sp. TBD4 based on the close relationship to bacteria belonging to this genus. A bottle study to determine biodegradation rates of individual aromatic compounds showed that the biodegradation was faster in the order of toluene, benzene, styrene, and p-xylene. However, when various mixtures were subjected to TDB4, styrene was degraded at the highest rate, indicating that both toluene and p-xylene could stimulate the degradation of other substrates whereas styrene played as an inhibitor. In addition, the mixed culture and TDB4 were inoculated to the bioactive foam reactor (BFR), and the reactor performance and the corresponding change of microbial community were monitored using the fluorescent in situ hybridization (FISH) method. When an inlet concentration of the VOC mixture increased to greater than 250 ppm, the overall removal efficiency dropped significantly. The FISH measurement demonstrated that the ratio of TDB4 to the total bacteria also decreased to less than 20% along with the decline in removal efficiency in the BFR. As a result, the periodic addition of the pre-grown TDB4 might have been beneficial to achieve a stable performance in the BFR operated over an extended period.

• Magazine of the Korean Society of Agricultural Engineers
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• v.30 no.3
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• pp.106-113
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• 1988

This study was performed to obtain the basic data which can be applied to use of foamihg mortars. 1. At the mixing ratio 1:1, the highest strengths were showed by foaming mortam, respec - tively. But, it. gradually was decreased in poorer mixing ratio and more addition of foam- ing agent. The decreasing rates of strengths were incresed in poorer mixing ratio and more addition of foaming agent. 2. The strengths were decreased up to 77.0-92.8% by mix-foaming type and 36.7-74.4% by pre-foamed type than cement mortar. 3. At the mixing ratio of 1:1, the lowest air contents were showed by foaming mortars, respectively. But, it gradually was increased in poorer mixing ratio and more addition of foaming agent. The increasing rates of air contents were increased in richer mixing ratio and more addition of foaming agent. 4. Air contents were showed up to 26.0-63.8 times by mix-foaming type and 5.8-17.7 times by pre-foamed type than cement mortar, respectively. 5. The correlations between compressive strength and air content were highly significant, respectively. The multiple regression equations of strengths and air content were computed depending on a fuction of mixing ratio and addition of foarning agent. It was highly significant, respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.473-485
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• 2010

Lightweight materials using in-situ clay soil contain large amounts of fine grain and cement for increasing the strength, lighter weight to increase liquidity for the foam and the bulk of the material is conducted by the water. Domestic cases, Light weight soil to improve cementation and lightness using demountable mixing device is defined Smartsoil. Typical features are their self-leveling, self-compaction, folwability. By adjusting the amount of cement, the strength can be controlled artificially. And re-excavation is easy. In this paper, pre-loading method using the road due to the displacement of adjacent structures under construction as an alternative SmartSoil introduces the design and construction practices. Is to discuss and improve.

• Steel and Composite Structures
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• v.49 no.3
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• pp.281-291
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• 2023

Due to the fact that the nonlinear low-velocity impact response of graphene platelets reinforced metal foams (GPLRMF) doubly curved shells have not been investigated in the existing works, this paper aims to solve this issue. Using Reddy's high-order shear deformation theory (HSDT), the nonlinear governing equations of GPLRMF doubly curved shells are obtained by Euler-Lagrange method, discretized by Galerkin principle, and solved by the fourth-order Runge-Kutta method to obtain the impact force and central deflection. The nonlinear Hertz contact law is applied to determine the contact force. Finally, the impacts of graphene platelets (GPLs) distribution pattern, porosity distribution form, porosity coefficient, damping coefficient, impact parameters (radius and initial velocity), GPLs weight fraction, pre-stressing force and different shell types on the low-velocity impact curves are analyzed. It can be found that, among the four shell structures, the impact resistance of spherical shell is the best, while that of cylindrical shell is the worst.

• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.3
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• pp.141-148
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• 2022

A hybrid turbulence model has developed by combining a sub-grid scale model using dynamic k equation in LES with k-𝜔 SST model of RANS equation. To ascertain potential applicability of the hybrid turbulence model, fully developed turbulent channel flows at Re_𝜏=180 have been simulated of which computational domain has a top wall with coarse cells and a bottom wall with fine cells. The streamwise mean velocity and turbulent intensity profiles showed a good agreement with DNS data when using the hybrid model rather than using a single model in k-𝜔 SST or dynamic k equation models. Computational simulations of turbulent flows around KVLCC2 with a pre-swirl duct have been mainly performed using the hybrid turbulence model. Compared to the results obtained from RANS simulation with k-𝜔 SST model as well as LES with dynamic k equation SGS model, turbulent wakes of the duct in the present simulation using the hybrid turbulence model were very similar to that of LES. Also, the resistances acting on hull, rudder and duct in hybrid turbulence model were similar to those in RANS simulation whereas the viscous forces acting on the hull in LES had a significant error due to coarse cells inappropriate to the sub-grid scale model.