• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.1017-1025
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• 2013

The monolithically coupled finite element analysis for a deformable unsaturated soil slope is performed to investigate matric suction distribution on a soil slope subjected to rainfall infiltration, which can consider the hydraulic-mechanical characteristics for the analysis. The soil-water characteristic curves (SWCC) are experimentally determined to estimate three types of hydraulic properties of domestic areas. Based on the physical properties, the distribution of matric suction is investigated by considering the major factors, such as soil conditions, rainfall intensities, and slope angles. It is found from the results of this study that the matric suction rapidly decreases with an increase in rainfall intensity, regardless a slope angle. The slope surface is more easily saturated when its saturated hydraulic conductivity is smaller than rainfall intensity, and for the case of multi-layered soil slope, hydraulic characteristics of slope surface has a significant influence on matric suction distribution.

• Polymer(Korea)
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• v.37 no.4
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• pp.507-512
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• 2013

A graphene/waterborne polyurethane (WPU) nano composite was prepared by in-situ polymerization of PU and graphene having isocyanate (iGO) group in order to improve physicochemical/electrical characteristics. The properties of the graphene/WPU nanocomposite can effectively be enhanced as compared pristine WPU; up to 57% of tensile strength and $10^2$ fold of electrical conductivity with introduction of 2 wt% graphene. In addition, mechanical/electrical properties of the graphene/WPU nanocompsite were higher than those of graphene/WPU composite prepared by a simple physical blend method. It might attribute to homogeneous dispersion of iGO in the WPU matrix via covalent bonds and hydrogen bonds between WPU and iGO from the results of morphological analysis by scanning electron microscopy (SEM).

• 한국체육학회지인문사회과학편
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• v.55 no.3
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• pp.543-551
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• 2016

The study was aimed at investigating the relationship between biomechanical properties of cervical muscles and smartphone addiction score in fifty healthy males using smartphone more than 60 minutes each day. The usage of smartphone was evaluated by smartphone addiction survey developed from Korean International Society Agency. Biomechanical properties of three major cervical muscles; splenius capitis, sternocleidomastoid and upper trapezius, were measured by Myoton, and conducted five parameters; frequency, decrement, stiffness, creep, and relaxation time. As results, all parameters had less than 2% of coefficient of variation(CV) between measurement intervals. Also, intra-class correlation coefficient(ICC) indicated a high reliability(ICC>.9, p<.01). Moreover, the smartphone addiction score was significantly different in frequency(r=.353, p<.05) and stiffness(r=.346, p<.05) on upper trapezius; in addition, in decrement(r=-.284, p<.05) and creep(r=.288, p<.05) on sternocleidomastoid. Especially, splenius capitis was closely related with the overuse of smartphone(frequency, r=-.368, p<.01; decrement, r=-.405, p<.01; stiffness, r=-.424, p<.01). In conclusion, this study implied that the overuse of smartphone is significantly related with the damage of cervical muscles, cervical pain, and headache; furthermore, Myoton can be used as an effective device to assess mechanical properties of cervical muscles.

• Polymer(Korea)
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• v.33 no.1
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• pp.91-95
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• 2009

We fabricated the electromagnetic (EM) noise absorber films for high temperature use by blending a soft magnetic powder with poly(amide imide) (PAI). The EM noise absorber films of PAI/soft magnet composite were prepared by casting the solution of poly(amide amic acid)/soft magnet powder into glass substrate with casting applicator device and then thermal imidization. The obtained films were fully characterized and their physical properties including thermal behavior, thermal stability and mechanical properties were studied. The EM noise absorption ability was also investigated using micro-strip line method. At 1 GHz, the power loss of composite film with 150 ${\mu}m$ thickness was about 25%.

• The Journal of Engineering Geology
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• v.31 no.3
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• pp.381-393
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• 2021

Physical, mechanical, hydraulic, and geophysical tests were applied to validate methods of inspecting the effectiveness of grouting on an agricultural reservoir dam. Data obtained from series of in situ and laboratory tests considered four stages: before grouting; during grouting; immediately after grouting; and after aging the grouting for 28 days. The results of SPT and triaxial tests, including the unit weight, compressive strength, friction angle, cohesion, and N-value, indicated the extent of ground improvement with respect to grout injection. However, they sometimes contained errors caused by ground heterogeneity. Hydraulic conductivity obtained from in situ variable head permeability testing is most suitable for identifying the effectiveness of grouting because the impermeability of the ground increased immediately after grouting. Electric resistivity surveying is useful for finding a saturated zone and a seepage pathway, and multichannel analysis of surface waves (MASW) is suitable for analyzing the effectiveness of grouting, as elastic velocity increases distinctly after grouting injection. MASW also allows calculation from the P- and S- wave velocities of dynamic properties (e.g., dynamic elastic modulus and dynamic Poisson's ratio), which can be used in the seismic design of dam structures.

• Korean Journal of Materials Research
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• v.4 no.3
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• pp.287-294
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• 1994

PAN-based carbon fiber roving and fabric were heat treated at the temperature of $2170^{\circ}C$. Using non-heat treated and heat treated fabric, greenbodies of CFRP and GFRP were manufactured in the Autoclave. After the analysis of heat treated and non-heat treated carbon fiber roving and two types of greenbodies, the variations of physical and mechanical properties of carbon fibers and greenbodies with heat treatment were studied. Observing the cross-section of carbon fiber with SEM, we knew the diameter of carbon fiber was decreased from 6.8gm to 6.4p1. The results of TGA showed that the oxidation resistence was enhanced after heat treatment. The tensile strength of carbon fiber was decreased from (3.11$\pm 0.32)\times 10^3$ MPa to (1.87$\pm 0.26)\times 10^3$MPa, but tensile modulus was increased from (1.94$\pm 0.06)\times 10^5$ MPa to (2.02$\pm 0.11)\times 10^5$MPa after heat treatment. The interlaminar shear strengths of CFRP and GFRP were 148.8$\pm$1.6Mpa and 82.2$\pm$1.1Mpa, respectively. Torch test showed that CFRP was abraded smoothly but GFRP was delaminated.

• Geomechanics and Engineering
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• v.15 no.4
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• pp.1017-1027
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• 2018

To explore the influence of coal thickness on the mechanical behavior and the failure characteristics of rock-coal-rock (RCR) mass, the experimental investigation of uniaxial compressive tests was conducted first and then a systematic numerical simulation by particle flow code (PFC2D) was performed to deeply analyze the failure mechanical behavior of RCR specimens with different coal thicknesses in conventional compression tests. The overall elastic modulus and peak stress of RCR specimens lie between the rock and the coal. Inter-particle properties were calibrated to match the physical sample strength and the stiffness response. Numerical simulation results show that the deformation and strength behaviors of RCR specimens depend not only on the coal thickness, but also on the confining pressure. Under low confining pressures, the overall failure mechanism of RCR specimen is the serious damage of coal section when the coal thickness is smaller than 30 mm, but it is shear failure of coal section when the coal thickness is larger than 30 mm. Whereas under high confining pressures, obvious shear bands exist in both the coal section and the rock section when the coal thickness is larger than 30 mm, but when the coal thickness is smaller than 30mm, the failure mechanism is serious damage of coal section and shear failure of rock section.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.68-93
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• 1998

The physical properties of polymer are greatly influenced by the extent to which a resin cures. The presence of un reacted monomer can, have a plasticizing effect on the polymer, thereby altering the physical and mechanical properties of dentin bonding agent (DBA). If the DBA does not polymerize sufficiently, it will leave a weak bonding layer and lead to lower bond strength. The purpose of this study was to evaluate the shear bond strengths(SBS) and the degree of conversion (DC) of 4 commercialy avilable dentin bonding systems which are composed of 2 multi-bottle systems [Scotchbond Multi-Purpose (SMP), AeliteBond(AB)] and 2 onebottle systems [SingleBond(SB), One-Step(OS)]. For shear bond strength measurement, labial surfaces of freshly extracted bovine incisors were ground with # 600 grit SiC paper to expose dentin. Four different groups of samples were formed, with 10 samples. being made for each of the 4 commercial DBA in each group according to the curing sequences of DBA and overlayer thickness of composites: Group I (standard cure and 1mm thick composites) : The DBA was light cured and the composites of 1mm thickness was applied ; Group II (standard cure and 2mm thick composites) : The DBA was light cured and the composites of 2mm thickness was applied; Group III (simultaneous cure and 1mm thick composites) : The DBA was not light-cured and simultaneously cured with composites of 1mm thickness; Group N (simultaneous cure and 2mm thick composites) : The DBA was. not light-cured and simultaneously cured with composites of 2mm thickness. The SBS was measured immediately after the composites was bonded to the bovine dentin using an Instron machine. The DC of the DBA was examined in a thin film under simulated conditions of the experimental groups according to the curing sequences and overlayer thickness of composites in the SBS test. using a Fourier transform Infrared(FTIR) spectrometer. The following results were obtained from SBS tests and DC measurements 1. In SBS tests, the multi-bottle DBA(SMP, AB) had a generally higher bond strength values than the one bottle DBA(SB, OS). In DC measurements, the one bottle DBA(SB, OS) had a significantly higher DC than the multi-bottle DBA(SMP, AB). 2. In all DBAs except OS, there was no significant difference between the bond strength of group I (standard cure and 1mm thick composites) and that of group III (simultaneous cure and 1mm thick composites). SMP, SB in Group I had a significantly higher DC than those in group III, but AB, OS in group I had a significantly lower DC than those in group III 3. All DBAs in Goup II (standard cure and 2mm thick composites) had significantly higher bond strength and DC than those in Group N (simultaneous cure and 2mm thick composites). 4. In all DBAs, there was no significantly different SBS and DC between Group I and Group II, but all DBAs in Group III had significantly higher SBS and DC than those in Group IV.

• Membrane Journal
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• v.26 no.4
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• pp.239-252
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• 2016

Two-dimensional materials offer unique characteristics for membrane applications to water technology. With its atomic thickness, availability and stackability, graphene in particular is attracting attention in the research and industrial communities. Here, we present a brief overview of the recent research activities in this rising topic with bringing two membrane architecture into focus. Pristine graphene in single- and polycrystallinity poses a unique diffusion barrier property for most of chemical species at broad ambient conditions. If well designed and controlled, physical and chemical perforation can turn this barrier layer to a thinnest feasible membrane that permits ultimate permeation at given pore sizes. For subcontinuum pores, both molecular dynamics simulations and experiments predict potential salt rejection to envisage a seawater desalination application. Another novel membrane architecture is a stack of individual layers of 2D materials. When graphene-based platelets are chemically modified and stacked, the interplanar spacing forms a narrow transport pathway capable of separation of solvated ions from pure water. Bearing unbeknownst permeance and selectivity, both membrane architecture - ultrathin porous graphene and stacked platelets - offer a promising prospect for new extraordinary membranes for water technology applications.

• Journal of the Korean Society of Food Science and Nutrition
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• v.43 no.11
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• pp.1716-1723
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• 2014

This study was designed to examine the change in physical properties of extruded brown rice-vegetable mix at different pregelatinized brown rice contents and $CO_2$ gas injection. Moisture content, screw speed and die temperature were fixed to 30%, 100 rpm and 60, respectively. $CO_2$ gas injection was adjusted to 0, 300, 600, and 800 mL/min. The content of vegetables (carrot, pumpkin, kale and Angelica keiskei) mix was fixed 5%. Pregelatinized and raw brown rice powder were blended as the ratio of 0/95, 30/65 and 50/45. Specific mechanical energy input decreased as pregelatinized brown rice ratio increased. Expansion index increased and the size and number of pores increased but density decreased with the increasing in $CO_2$ gas injection. Gelatinization degree increased as $CO_2$ gas injection increased. In conclusion, cold extrusion with $CO_2$ gas injection at $60^{\circ}C$ die temperature could be applied for Saengsik (uncooked food) making.