• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.1
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• pp.71-82
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• 2011

This paper presents the tensile strength of shotcrete steel fibers depending on the shape of steel fiber. The experimental and numerical analyses are performed in this study. In experimental study, a series of laboratory pullout tests are carried out by changing both the angle and the length of the embedded steel fiber according to the corresponding type of steel fiber in order to derive the optimal type of steel fiber. Results obtained from the experimental work are evaluated and compared with the numerical analysis results. The results clearly show that the pull-out strength of the steel fiber are increased with increasing the hook angle and embedded angle of steel fiber. It is also found that the pull-out strength of the steel fiber is larger in case of the short steel fiber body length.

• Current Optics and Photonics
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• v.4 no.2
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• pp.141-147
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• 2020

To understand the cause of the high light transmittance of the human eye, the optical effects of the collagen fibers of the stroma layer, which constitute the majority of the cornea, were analyzed. These collagen fibers, approximately 20 nm in diameter, have a regular arrangement. Accordingly, the optical properties of the collagen fibers and the fiber layer were analyzed by simulation. A standing wave was formed in the incident space by the overlapping incident light and the light reflected by the plate. In addition, it was confirmed that when the collagen fibers are arranged in a layer, the light transmittance periodically changes, depending on the number of fiber layers. The standing wave was formed in the incident space, and the light's intensity distribution was changed by the nanoscale collagen fibers in the section with the collagen layer, which affected the transmittance. To explain this phenomenon, the collagen fiber was defined as a second light source, and an attempt was made to describe the simulation results in terms of overlap of the incident light with the light emitted from the collagen fiber.

• Earthquakes and Structures
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• v.10 no.1
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• pp.91-104
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• 2016

In this paper we investigate the existence of SH-waves in fiber-reinforced layer placed over a heterogeneous elastic half-space. The heterogeneity of the elastic half-space is caused by the exponential variations of density and rigidity. As a special case when both the layers are homogeneous, our derived equation is in agreement with the general equation of Love wave. Numerically, it is observed that the velocity of SH-waves decreases with the increase of heterogeneity and reinforced parameters. The dimensionless phase velocity of SH-waves increases with the decreases of dimensionless wave number and shown through figures.

• Korean Journal of Optics and Photonics
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• v.17 no.5
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• pp.396-400
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• 2006

We present a weather-insensitive optical free-space communication method supporting optical packet channels. It operates optical fiber amplifiers in gain-saturation regions. When the propagation loss gets too high, it decreases the average packet rate, or the average packet length, or both, to increase the optical power level launched into the free-space. As a demonstration, we transmit $8{\times}10$ Gigabit Ethernet channels over a terrestrial distance of 2.4 km. One gain-saturated free-space optical repeater is used at the halfway point.

• The Journal of Natural Sciences
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• v.8 no.2
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• pp.17-20
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• 1996

We show Equivariant Serre Problem in real algebraic category is true when dimension of the fiber is one i.e., we show an equivariant line bundle over a real representation space is isomorphic to a product bundle of a real representation space and some G-module.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.282-295
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• 2012

Fiber reinforced polymer matrix composites are widely used to provide protection against ballistic impact and blast events. There are several factors that govern the structural response and mechanical properties of a textile composite structure, of which the fiber-matrix interfacial behavior is a crucial determinant. This paper reviews the microbond or microdroplet test methodology that is used to characterize the fiber-matrix interfacial behavior, particularly the interface shear strength (IFSS). The various analytical, experimental, and numerical approaches applied to the microbond test are reviewed in detail.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.771-777
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• 2007

In this paper, thermal expansion coefficients of fiber-reinforced composite materials are predicted by direct numerical simulation. From comparing the predicted results with experimental results, it is confirmed that direct numerical simulation gives similar results to the previously proposed methods while minimizing artificial assumptions. Additionally trend of variation in thermal expansion coefficients is investigated according to the fiber volume fraction.

• Journal of the Korean Institute of Rural Architecture
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• v.6 no.3
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• pp.106-115
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• 2004

In this paper, the compressive strength and ductility enhancement of concrete by lateral confinement of carbon-fiber sheets(CFS) have been studied experimentaly with cylinder specimens and square short columns reinforced externally by CFS. Test variables were amount of lateral reinforcement by CFS and space of hoop bars. Test results showed that lateral reinforcements by carbon-fiber sheets provided lateral confinement successfully for the concrete specimens and were more effective for ductility enhancement than for strength increase, and that the lateral confinement coefficient of cabon-fiber sheets increased according to narrowing the space of hoop bars in the double lateral confinement made by CFS and hoop bars.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.2
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• pp.18-33
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• 2008

This paper presents design optimization of a new Active Twist Rotor (ATR) blade and conducts its aeroelastic analysis in forward flight condition. In order to improve a twist actuation performance, the present ATR blade utilizes a single crystal piezoelectric fiber composite actuator and the blade cross-sectional layout is designed through an optimization procedure. The single crystal piezoelectric fiber composite actuator has excellent piezoelectric strain performance when compared with the previous piezoelectric fiber composites such as Active Fiber Composites (AFC) and Macro Fiber Composites (MFC). Further design optimization gives a cross-sectional layout that maximizes the static twist actuation while satisfying various blade design requirements. After the design optimization is completed successfully, an aeroelastic analysis of the present ATR blade in forward flight is conducted to confirm the efficiency in reducing the vibratory loads at both fixed- and rotating-systems. Numerical simulation shows that the present ATR blade utilizing single crystal piezoelectric fiber composites may reduce the vibratory loads significantly even with much lower input-voltage when compared with that used in the previous ATR blade. However, for an application of the present single crystal piezoelectric actuator to a full scaled rotor blade, several issues exist. Difficulty of manufacturing in a large size and severe brittleness in its material characteristics will need to be examined.

• Tunnel and Underground Space
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• v.14 no.4
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• pp.241-247
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• 2004

In this study, new polypropylene fiber was developed for shotcrete and concrete reinforcement, by treating the surface of the polypropylene by maleic anhydride grafted polypropylene(mPP). Dispersiveness of the fiber was tested. Mechanical properties of fiber reinforced shotcrete was tested.