• Journal of the Optical Society of Korea
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• v.7 no.2
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• pp.89-96
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• 2003

A new method to control the free spectral range of a long period fiber grating is proposed and theoretically analyzed. As the refractive index decreases radially outward in the silica cladding due to graded doping of fluorine, waveguide dispersion in the cladding modes was modified to result in the effective indices change and subsequently the phase matching conditions for coupling with the core mode in a long period fiber grating. Enlargement of the free spectral range in a long period fiber grating was theoretically confirmed.

• Current Optics and Photonics
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• v.3 no.4
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• pp.298-303
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• 2019

We propose a photonic quasi-crystal fiber (PQF) for supporting up to 14 orbital angular momentum (OAM) modes with low and ultra-flat dispersion characteristics over the C+L bands. The designed PQF which consists of a large hollow center and quasi structural small air holes in the clad region exhibits low confinement losses and a large effective index separation (>$10^{-4}$) between the vector modes. This proposed fiber could potentially be exploited for mode division multiplexing and other OAM mode applications in fibers.

• Journal of Animal Science and Technology
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• v.61 no.1
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• pp.18-27
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• 2019

With South Korea's limited capability of feed production because of its relatively small cultivable area, the country is pushed to depend on foreign feed imports despite the immensely fluctuating price of corn. Hence, intensive efforts to increase the total cultivable area in Korea like extending of farming to mountainous area is being practiced. Corn was planted in Goesan County, a mountainous area in the country. Grain and stover were harvested separately in three harvest periods: early-harvest (Aug 8), mid-harvest (Aug 18), and late-harvest (Aug 28). The nutrient composition such as dry matter (DM), crude protein (CP), crude fat (EE), organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF), and non-fibrous carbohydrates (NFC) was determined after harvest. Effective degradability (ED) of the major nutrients (DM, NDF, ADF, and CP) were measured through in vitro fermentation of rumen fluid from Hanwoo (Korean cattle). pH, ammonia-N concentration, volatile fatty acid (VFA) concentration, and gas production were periodically measured at 0, 3, 6, 12, 24, 48, and 72 h. Corn grain showed higher nutrient content and ED than stover. It also had higher gas production but its pH, ammonia-N, and total VFA concentration were lower than corn stover. The best nutrient composition of corn grain was observed in early-harvest (high CP, EE, NDF, OM, NFC, and low ADF). Early-harvest of corn grain also had high effective degradability of dry matter (EDDM), effective degradability of neutral detergent fiber (EDNDF), effective degradability of acid detergent fiber (EDADF), and total VFA concentration. On the other hand, the best nutrient composition of stover was observed in mid-harvest (high DM, CP, NDF, and low ADF). EDDM, EDNDF, and EDADF were pronounced in early-harvest and mid-harvest of stover but the latter showed high total VFA concentration. Hence, early and mid-harvested corn stover and grain in a mountainous area preserved their nutrients, which led to the effective degradation of major nutrients and high VFA production.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.209-220
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• 1999

This paper is aimed to evaluate the effectiveness of flexural toughness of slab panel structures($60{\times}60{\times}10$) reinforced by steel fiber instead of wire mesh. Steel fiber used in this study is double hooked Dramix type fiber. And the fiber length is 60mm, diameter is 0.8mm, Various assessment methods of toughness index are used to estimate the proper effectiveness. In this experimental study, we find that Johnston, JCI-SF4 and EFNARC method are more effective to assess the flexural toughness of slab panels than the others. And the steel fiber is very effective alternative material to reinforce slab panel structures instead of wire mesh. Fiber volume fraction of 0.5~0.75% is more useful than the others in enhancing the post-peak energy absorption and toughness index by Johnston's $I_{5.5}$ assessment method. And the slab panels reinforcing with steel fiber are more resistant to crack propagation than wire mesh reinforcing slabs.

• International Journal of Highway Engineering
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• v.17 no.3
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• pp.77-83
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• 2015

PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS : A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS : The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.

• Advances in concrete construction
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• v.6 no.5
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• pp.423-463
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• 2018

This paper investigates the behavior of normal and self-compacted steel fiber reinforced concrete (SCC-SFRC) corbels rehabilitated by Basalt Fiber Mesh (BFM) and Basalt Fiber Fabric (BFF) for the first time in literature. The research objective is to study the effectiveness of BFM and BFF in the rehabilitation of damaged reinforced concrete corbels with and without epoxy injection. The experimental program includes two types of concrete: normal concrete, and self-compacted concrete. For normal concrete, 12 corbels were rehabilitated by BFM without injection epoxy in cracks, with two values of compressive strength, three ratios of steel fiber (SF), and two values of shear span. For self-compacted concrete, 48 corbels were rehabilitated with different parameters where 12 corbels were rehabilitated by BFM with and without epoxy injection, 18 heated corbels with three different high-temperature level were rehabilitated by repairing cracks only by epoxy injection, and 18 heated corbels with three different high-temperature level were rehabilitated by repairing cracks by epoxy and wrapping by BFF. All 48 corbels have two values of compressive strength, three values volumetric ratios of SF, and two values of the shear span. Test results indicate that RC corbels rehabilitated by BFM only without injection did not show any increase in the ultimate load capacity. Moreover, For RC corbels that were repaired by epoxy without basalt wrapping, the ultimate load capacities showed an increase depending on the mode of failure of corbels before the rehabilitation. However, the rehabilitation with only crack repairing by epoxy injection is more effective on medium strength corbels as compared to high strength ones. Finally, it can be concluded that use of BFF is an effective and powerful technique for the strengthening of damaged RC corbels.

• Journal of the Korean Graphic Arts Communication Society
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• v.16 no.3
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• pp.157-170
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• 1998

To investigate the most effective way of cellulase utilization on paper making process and the systematic way of how to combine its components for better use, purified two major cellulase were applied to bleached kraft pulp at various dosage in the refining process and estimated the synergism effect of each components in the characteristics of papermaking fiber. freeness was not changed by $C_1$ Component dosage but strongly increased by Cx Component dosage. Drop in fiber viscosity, increase in WQV, fiber shortening and fine generation was strongly influenced by Cx Component, it seems to be that Cx Component works a hydrogenate that breaks hydrogen bonding in fiber and enhances pooling effect of fiber. $C_1$ Component was little influenced these characteristics of fiber but considered to help to make fiber surface smooth.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.747-752
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• 2008

Fiber-guided sensor system using a generator and a receiver can detect the amplitude of load or pressure. However, this type of sensor can show some difficulties in detecting the location of damages and pressure loadings. To overcome this weakness of this type, the ultrasonic active fiber sensor, which has an integrated ultrasonic generator and sensing part, was developed in this study. By using this sensor system, the location of mechanical loads can be exactly detected. Moreover, the ultrasonic active fiber sensor is more cost-effective than an ultrasonic fiber sensor using two piezoelectric transducers which are used as a generator and a receiver, respectively. Two applications of the ultrasonic active fiber sensor are demonstrated: cure monitoring of lead and measurement of liquid level. Present results showed that the active fiber sensor can be applied for various environmental sensing.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.88-89
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• 2017

Due to the increase in the usage of explosive materials and terrorism, the interest towards the superior explosion protective HPFRCC has risen. In existing research, the optimum ratio for solving the problematic problems such as the optimum fiber incorporation rate and the self-shrinkage crack of HPFRCC had been derived. However, there had been few or even no research upon how effective HPFRCC would perform protective explosion-proof in actual explosion. Therefore, this research compared the explosion-proof performance of HPFRCC according to fiber commination and mixing ratio. As a result, the combination of steel fiber and organic fiber showed excellent flow and strength, and it also improved the explosion resistance.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.5
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• pp.93-98
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• 1999

The results of an experimental investigation on the characteristics of compaction and compressive strength of polypropylene fiber reinforced soil are presented in this paper. This study has been performed to obtain the physical properties of PFRS(polypropylene fiber reinforced soil) such as strain-stress relationships, OMC(optimum moisture contents) and ${\gamma}$dmax (maximum dry unit weight), with four different contents (i.e., 0.1%, 0.3%, 0.5% and 1.0% weights ) of mono-filament and fibrillated polypropylene fibers. From the compaction test results, it is found that OMC increased with the contents ratio of fiber, but ${\gamma}$dmax decreased. It means that the improvement of the workability and the reduction of the weight of embankment structures by the asddtion of the polypropylene fiber. And, from the compression test results, it is found that the additon of the polypropylene fiber remarkably improved the compressive strength of PFRS. And it was observed in the viewpoint of strength that the fibrillated polypropylene fiber reinforced soil is more effective than the mono-filament polypropylene fiber reinforced soil.