• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.1
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• pp.55-77
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• 2012

A Modern Rock TBM is a tunnel excavation method combining the conventional tunnelling method with the mechanized tunnelling method. It is a hybrid system that excavates a tunnel with TBM and supports the ground by ring beam, wire mesh, rock bolt, shotcrete, i.e., conventional tunnelling method. In the Modern Rock TBM, a ring beam is similar to a steel rib in NATM in the way that uses H-beam. But using a ring beam is more effective than a steel rib because it is installed in a closed-circle. Therefore, improving the performance of the ring beam is a key factor for achieving tunnel stability. In this respect, this study introduces a pressurized ring beam that might be functioning more effectively by confining convergence during tunnel excavation. In order to verify the effect of the pressurized ring beam, a three-dimensional numerical analysis was conducted. The numerical analysis confirms an increase in the minimum principal stress and reduction in the plastic strain that triggers excessive displacement. The analysis result also indicates a decrease in the relative displacement occurring after installing the ring beam, and expansion in spacing between the ring beams.

• Tunnel and Underground Space
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• v.14 no.4
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• pp.248-260
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• 2004

Damage in brittle rock due to stress increase starts from initiation of microcracks, and then results in failure by forming macro failure planes due to propagation and coalescence of these discrete cracks. Conventionally, continuum approaches using macro-failure criteria or a number of elasto-plastic models have been major solution to implement rock damage and failure. However, actual brittle failure processes can be better described in phenomenological approach if initiation and propagation of discrete fractures are explicitly considered. This study presents damage and failure process of rock using a boundary element code, FRACOD, which has been developed to model fracturing process of rocks. Through a series of numerical uniaxial compressive tests, the feasibility of the developed model was verified, and realistic rock failure process was reproduced considering scale effects in rocks. In addition, the fracturing process and the corresponding rock damage in the vicinity of deep shaft in rock mass were presented as an application of this approach. This approach will be expected to contribute to finding better engineering solutions for the analysis of stability problems in brittle rock masses.

• Journal of Hydrogen and New Energy
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• v.26 no.3
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• pp.212-220
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• 2015

The engineering plastic of sulfonated polyether ether ketone (SPEEK) as a polymer matrix has been developed in this lab to replace Nafion, solid polymer electrolytes of perfluorosulfonic acid membrane which has several flaws such as high cost, and limited operational temperature above $80^{\circ}C$. The SPEEK was prepared in the sulfonation reaction of polyether ether ketone (PEEK). The organic-inorganic blended composite membranes were prepared by sol-gel casting method with loading the highly dispersed ceria and cesium-substituted tungstosilicic acid (Cs-TSiA) with cross-linking agent contents of 0.01 mL. In conclusion, CL-SPEEK/Cs-TSiA/ceria 1% membrane showed the optimum results such as 0.1882 S/cm of proton conductivity at $80^{\circ}C$, and 99.61 MPa of tensile strength which were better than Nafion 117 membrane.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.314-316
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• 2006

In this paper, the plastic organic thin-film transistors (OTFTs) with $32{\ast}32$ array are presented. Flexible organic light emitting diodes (OLEDs) operated by OTFTs are fabricated with a novel lamination method and the results are also presented. OTFT pixels defined by photolithography, and pentacene deposited by thermal evaporation. Fabrication method and the performances of green PHOLEDs with high efficiency, stability, and electrical performance are discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1489-1498
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• 2013

The monolithically coupled finite element analysis for a deformable unsaturated soil slope is performed to investigate the effect of antecedent rainfall which is assumed by initial conditions varying degree of saturation (36, 51, 77%) in finite element analysis. The distributions of matric suction and deformation on slope surface obtained from numerical simulation show the instability of antecedent rainfall-induced unsaturated soil slope. Moreover, the numerical analysis using Drucker-Prager model can be checked if a soil slope has reached failure (trial failure criterion $f^{tr}$ >0, plastic behavior) or not (trial failure criterion $f^{tr}$ < 0, elastic behavior). It is found that displacement of slope surface layer increases and the matric suction on soil slope decreases with an increase of initial degree of saturation by antecedent rainfall. Especially, the matric suction of the soil slope in dry condition (S=36%) rapidly decreases rather than that in wet condition (S=51%) at the same rainfall duration. The results of the trial failure criterion ($f^{tr}$ > 0) show slope instability in the toe region and surface of the slopes.

• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.395-402
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• 2010

This study reports a portable and precision photonic biosensor reader that can measure the concentration of a particular antigen using an optical resonant reflection biosensor (ORRB). To create a compact biosensor reader, a compact tunable vertical-cavity surface-emitting laser (VCSEL) and a compact built-in wavelength meter were manufactured. The wavelength stability and accuracy of the compact built-in wavelength meter were measured to be less than 0.02 nm and 0.06 nm, respectively. The tunable VCSEL emission wavelength was measured with the compact built-in wavelength meter, it has a fast sweep time (~ 10 seconds) and a wide tuning range (> 4 nm) that are sufficient for biosensor applications based on ORRB. The reflection spectrum of a plastic based ORRB chip was measured by the fabricated portable photonic biosensor reader using the VCSEL and wavelength meter. Although the reader is the size of a palmtop device, it could make a precise measurement of the peak wavelength on equal terms with a conventional bulky optical spectrometer.

• Applied Chemistry for Engineering
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• v.28 no.6
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• pp.626-631
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• 2017

Transparent plastic substrates require an improvement in properties such as surface hardness and thermal stability for optical applications. In this study, UV-curable organic/inorganic hybrids were synthesized to improve those properties. In order to make the optimum dispersion of inorganic component into the organic matrix, an in situ synthetic method was applied based on sol-gel reaction. Dispersion of the inorganic component in the organic urethane acrylate matrix was improved by using a proper combination of sol-gel reaction and fast UV-curing resulting in the formation of the transparent coating layer. Various alkoxy silanes were employed to vary both the degree of curing and coating properties of UV-curable organic/inorganic hybrids. UV-cured organic/inorganic hybrid coatings showed an improved surface hardness and thermal resistance depending on the content of inorganic component.

• The Journal of the Korean dental association
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• v.53 no.9
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• pp.602-609
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• 2015

The aim of this document is to evaluate the effect of bite balance on physical fitness and motor capacity to determine the importance of the occlusal stability as a possible action mechanism of occlusal appliance including mouthguards on physical performances. We all remember that day when the prominent athlete was in the news wearing a mouthguard to improve human athletic performance. I once had investigated the determinants of athletic performance in all sorts of sports. Most of the studies had overinterpretation of results and lack of evidence to support the information. However, I discovered great expectations for new possibility in this field and settled for a more academic approach to this intriguing subject. The followings are some examples of the subject 1. Archers who wore occlusal appliances to increase the vertical dimension of occlusion by 2~3mm increased their ability to focus and to maintain good sense of balance. Their accuracy rate has been improved. The appliance was made of acrylic resin (a type of plastic). 2. Canoe players who wore occlusal appliances to increase the vertical dimension of occlusion by 5mm surpassed longtime competitor and won the race with 10 seconds gap. 3. A cycle rider who wore an occlusal appliance to treat his malocclusion surpassed his old record from 10.8 seconds to 10.3 seconds. His muscle reflexes (anaerobic exercise) and endurance (aerobic exercise) has been enhanced. 4. Occlusal appliances had a good effect on athletic performance in most sports such as swimming, diving, and weightlifting. As for the clenching on dentition, people clench their teeth when they push their physical and mental limits during sports activities. Clenching can be induced by physical exertion when maximum muscle strength is retained and this is similarly found in different types of exercises. In addition, restraint of respiratory function is observed. Therefore, creating a occlusal balance with occlusal appliance or mouthguard promoted a favorable influence when an athlete clenches.

• Journal of the Korean GEO-environmental Society
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• v.18 no.8
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• pp.5-15
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• 2017

To perform an integrated load analysis carried out to evaluate the stability evaluation of wind turbine generators, the six degree-of-freedom stiffness matrix of foundation, which describes relationships between loads and displacement, is needed. Since the foundation stiffness should accurately reflect the shape of foundation and the condition of soil, it is necessary to calculate the stiffness of the bucket foundation that considers the elasto-plastic behavior of the soil. In this study, finite element analyses were performed for a range of soils and shapes of bucket foundations to estimate the foundation stiffness. Normalized stiffness curves are developed from respective numerical simulations. Proposed results are considered to be useful because they can be directly applied in the design.

• Structural Engineering and Mechanics
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• v.65 no.3
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• pp.303-314
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• 2018

Shear walls are a typical member under a complex stress state and have complicated mechanical properties and failure modes. The separated-elements model Genetic Evolutionary Structural Optimization (GESO), which is a combination of an elastic-plastic stress method and an optimization method, has been introduced in the literature for designing such members. Although the separated-elements model GESO method is well recognized due to its stability, feasibility, and economy, its adequacy has not been experimentally verified. This paper seeks to validate the adequacy of the separated-elements model GESO method against experimental data and demonstrate its feasibility and advantages over the traditional elastic stress method. Two types of reinforced concrete shear wall specimens, which had the location of an opening in the middle bottom and the center region, respectively, were utilized for this study. For each type, two specimens were designed using the separated-elements model GESO method and elastic stress method, respectively. All specimens were subjected to a constant vertical load and an incremental lateral load until failure. Test results indicated that the ultimate bearing capacity, failure modes, and main crack types of the shear walls designed using the two methods were similar, but the ductility indexes including the stiffness degradation, deformability, reinforcement yielding, and crack development of the specimens designed using the separated-elements model GESO method were superior to those using the elastic stress method. Additionally, the shear walls designed using the separated-elements model GESO method, had a reinforcement layout which could closely resist the actual critical stress, and thus a reduced amount of steel bars were required for such shear walls.