• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.6
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• pp.706-715
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• 2012

Electro-optical sigma-delta modulators are the core module of digital receiver to digitize wideband radio-frequency signals directly at an antenna. Electro-optical sigma-delta modulators use a pulsed laser to oversample an input radio-frequency signals at two Mach-Zehnder Interferometer(MZI) and shape the quantization noise using a fiber-lattice accumulator. Decimation filtering is applied to the quantizer output to construct the input signal with high resolution. The jitter affects greatly on reconstructing the original input signal of modulator. This paper analyzes the performance of first order single bit electro-optical sigma-delta modulator in the time domain and the frequency domain. The performance of modulator is analyzed by using asynchronous spectral averaging of the reconstructed signal's spectrum in the frequency domain. The reference value of time jitter is presented by analyzing the performance of jitter effects. This kind of jitter value can be used as a reference value on the design of modulators.

• Steel and Composite Structures
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• v.18 no.1
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• pp.51-69
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• 2015

In recent years, the use of fiber reinforced polymer composites has increased because of their unique features. They have been used widely in the aircraft and space industries, medical and sporting goods and automotive industries. Thanks to their beneficial and various advantages over traditional materials such as high strength, high rigidity, low weight, corrosion resistance, low maintenance cost, aesthetic appearance and easy demountable or moveable construction. In this paper, it is aimed to determine and compare the geometrically nonlinear static and dynamic analysis results of footbridges using steel and glass fiber reinforced polymer composite (GFRP) materials. For this purpose, Halgavor suspension footbridge is selected as numerical examples. The analyses are performed using three identical footbridges, first constructed from steel, second built only with GFRP material and third made of steel- GFRP material, under static and dynamic loadings using finite element method. In the finite element modeling and analyses, SAP2000 program is used. Geometric nonlinearities are taken into consideration in the analysis using P-Delta criterion. The numerical results have indicated that the responses of the three bridges are different and that the response values obtained for the GFRP composite bridge are quite less compared to the steel bridge. It is understood that GFRP material is more useful than the steel for the footbridges.

• Fibers and Polymers
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• v.3 no.1
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• pp.18-23
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• 2002

The structure development and dynamic properties of fibers produced by high-speed spinning of P(EN-ET) random copolymers were investigated. The as-spun fibers were found to remain amorphous up to the spinning speed of 1500 m/min, and subsequent increases in speed resulted in the crystalline domains containing primarily $\alpha$ crystalline modification of PEN. The f modification was not found up to spinning speeds of 4500 m/min. On the other hand, annealing of constrained fibers spun at the 2100 m/min at 180,200, and 240^{\circ}C$ exhibited $\beta$-form crystalline structure, while the annealed fibers spun in 600-1500 m/min range exhibited dominantly $\alpha$-form. However $\beta$-form crystals disappeared above the spinning speed of 3000 m/min. With increasing spinning speeds from 600 to 4500 m/min, the storage modulus of as-spun fibers increased continuously and reached a value of about 10.4 spa at room temperature. The tan $\delta$curves showed the $\alpha$-relaxation peak at about 155-165^{\circ}C$, which is considered to correspond to the glass transition. The $\alpha$-relaxation peaks became smaller and broader, and shift to higher temperatures as the spinning speed increases, meaning that molecular mobility in the amorphous region is restricted by increased crystalline domain.

• Fibers and Polymers
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• v.7 no.4
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• pp.333-338
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• 2006

Silk fibroin (SF) fiber from the Antheraea pernyi silkworm was treated with a 1.23 N iodine-potassium iodide ($I_2-KI$) aqueous solution, and the structure and physical properties were investigated to clarify the effects of the iodine treatment. The noticeably high weight gain value of SF fiber, about 25 wt% was attributed to the absorption of polyiodide ions in the form of $I_3{^-}\;and\;I_5{^-}$. Fourier transform infrared spectroscopy and X-ray diffraction measurements suggested that polyiodide ions mainly entered the amorphous region. In addition, a new sharp reflection on the meridional direction, corresponding to a period of $7.0{\AA}$, was observed and indicated the possibility of the formation of mesophase structure of ${\beta}$-conformation chains. Dynamic viscoelastic measurements showed that the damping tan ${\delta}$ peak at $270^{\circ}C$ gradually shifted to lower temperature in the iodinated SF fibers, suggesting an enhancement of the molecular motion of the fibroin chains induced by the presence of polyiodide ions. With heating above $254^{\circ}C$, the iodine component introduced intermolecular cross-linking of SF, and the melt flow of the sample was inhibited. The thermal decomposition stability of fibroin molecules was greatly enhanced by iodine treatment.

• Composites Research
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• v.29 no.5
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• pp.269-275
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• 2016

Multiscale hybrid composites, which consist of polymeric resins, microscale fibers and nanoscale reinforcements, have drawn significant attention in the field of advanced, high-performance materials. Despite their advantages, multiscale hybrid composites show challenges associated with nanomaterial dispersion, viscosity, interfacial bonding and load transfer, and orientation control. In this paper, carbon nanotube(CNT)/carbon fiber(CF)/polycarbonate(PC) multiscale hybrid composite were fabricated by a solution process to overcome the difficulties associated with controlling the melt viscosity of thermoplastic resins. The dependence of CNT loading was studied by varying the method to add CNTs, i.e., impregnation of CF with CNT/PC/solvent solution and impregnation of CNT-coated CF with PC/solvent solution. In addition, hybrid composites were fabricated through surfactant-aided CNT dispersion followed by vacuum filtration. The morphologies of the surfaces of hybrid composites, as analyzed by scanning electron microscopy, revealed the quality of PC impregnation depends on the processing method. Dynamic mechanical analysis was performed to evaluate their mechanical performance. It was analyzed that if the position of the value of tan ${\delta}$ is closer to the ideal line, the adhesion between polymer and carbon fiber is stronger. The effect of mechanical interlocking has a great influence on the dynamic mechanical properties of the composites with CNT-coated CF, which indicates that coating CF with CNTs is a suitable method to fabricate CNT/CF/PC hybrid composites.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.8
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• pp.149-154
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• 1999

FRMLs(Fiber Reinforced Metal Laminates) is a new type of hybrid materials. FRMLs consists of high strength metal and fiber which are laminated using a structural adhesive bond(epoxy resin). The effect of resin mixture ratios on the fatigue crack propagation behavior and mechanical property of Aramid fiber reinforced aluminum composites was investigated. The epoxy, diglycidylether of bisphenol A(DGEBA) was cured with methylene dianiline(MDA) with or without accelerator(K-54). Eight kinds of resin mixture ratio were tested for the experiment ; five kinds of FRMLs(1))epoxy & curing agent) and three kinds of FRMLs(2)(epoxy & curing agent & accelerator). FRMLs(2) have a more effective characteristics on the fatigue crack propagation behavior and mechanical property than FRMLs(1)

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.623-631
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• 2003

It is considered that the application of advanced composite materials to the prostheses for the disables is important to improve their bio-mechanical performance. Particularly, energy storing foot prosthesis is mostly important to restore gait ability of the disables with low-extremity amputation since it could provide propulsion at terminal stance enhancing the disables ability to walk long distance even run and jump. Therefore, the energy storing spring of Prosthetic foot keel under cyclic bending moment use mainly of high strength glass fiber reinforced plastic. The main objective of this study was to evaluate the stacking sequence effect using the delamination growth rate(dA$_{D}$/dN) of energy storing spring in glass fiber reinforced plastic under cyclic bending moment. The test results indicated that the shape of delamination zone depends on stacking sequence in GFRP laminates. Delamination area(A$_{D}$) turns out that variable types with the contour increased non-linearly toward the damage zones.nes.

• The Korean Journal of Physiology
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• v.19 no.2
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• pp.227-232
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• 1985

Previously, we had reported that the electrical stimulation of peripheral nerve with stimlatory parameters of 20 V strength and 2 Hz frequency for 60 min resulted in reducing the pain reaction. The present study was performed to evaluate if the pain reaction was affected by the peripheral nerve stimulation with different stimulatory parameters in the decerebrated cat. The flexion reflex was used as an index of the pain reaction. The reflex was elicited by stimulating the sural nerve (stimulus strength of 20 $V\;\times\;0.5$msec) and recorded as a compound action potential from the motor nerve innervated to the posterior biceps femoris muscle. The common perneal nerve was selected as a peripheral nerve on which the electrical stimulation of various intensities and frequencies was applied. The results are summarized as follows : 1) The peripheral nerve stimulation with 100 mV strength, regardless of frequencies, did not affect the pain reaction induced by the sural nerve stimulation. 2) When the stimulus of 1V intensity and slow frequency (2 Hz) was applied to the peripheral nerve for 30 min or 60 min, the pain reaction was significantly reduced comparing to the control. However, this reduced pain reaction by the peripheral nerve stimulation was not reversed by the injection of naloxone (0.02 mg/kg) 3) High frequency stimulus (60 Hz) of 1V intensity for 30 or 60 min did not show any effects of affecting the pain reaction. These results suggest that the stimulus of relatively high intensity (at least 1V) and low frequency (2 Hz) is needed to elicite the analgesic effect by the peripheral nerve stimulation. By the 1V stimulus, $A\delta$ nerve fiber is activated. Therefore, an $A\delta$ or smaller nerve fibers must be activated for showing analgesia by the peripheral nerve stimulation. However, the mechanism of analgesia by the $A\delta$ nerve activation alone was not related to the endogeneous morphine system since the reduced pain reaction by the $A\delta$ fiber activation alone was not reversed by the treatment of naloxone.

• Polymer(Korea)
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• v.30 no.1
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• pp.70-74
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• 2006

Plasticized cellulose diacetate(CDA) was prepared by homogenizing cellulose diacetate(CDA), triacetin(TA) and epoxidized soybean oil (ESO) in a high-speed mixer, then the CDA mixture was mixed with ramie fiber to produce a green composite material. In DMA analysis, the glass transition temperature of plasticized CDA and the composite was observed at $85\;^{\circ}C\;and\;140\;^{\circ}C$, respectively. A composite reinforced with alkali treated ramie fiber exhibited significantly higher mechanical properties, such as $15\;^{\circ}C$ increase in tensile strength as well as $41\;^{\circ}C$ increase in Young's modulus when compared with commercial polypropylene. In the SEM image analysis, much enhanced adhesion between plasticized CDA and alkali treated ramie fiber (AIRa) was observed.

• Fashion & Textile Research Journal
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• v.14 no.4
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• pp.641-647
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• 2012

This study investigates the sound properties of fabric frictional sound (SPL, ${\Delta}L$, ${\Delta}f$) according to the film type of PTFE laminated vapor-permeable water-repellent fabrics in order to understand the relationship between SPL and the basic properties of fabrics such as layer, yarn type, and thickness of fiber. This study accesses their mechanical properties and determines how to control them to minimize SPL. Eight PTFE laminated water-repellent fabrics, composed of four different film types (A, B, C, D) and with two different fabrics, were used as test specimens. Frictional sounds generated at 1.21m/s were recorded by using a fabric sound generator and SPLs were analyzed through Fast Fourier Transformation (FFT). The mechanical properties of fabrics were measured by KES-FB. The SPL value was lowest at 74.4dB in film type A and highest as 85.5dB in type D. Based on ANOVA and post-hoc test, specimens were classified into less Loud Group (A, B) and Loud Group (C, D). It was shown that SPL was lower when 2 layer (instead of 3 layer), filament yarn than staple, and thin fiber than thick were used. In Group I, shearing properties (G, 2HG5), geometrical roughness (SMD), compressional properties (LC, RC) and weight (W) showed high correlation with SPL however, elongation (EM) and shear stiffness (G) did with SPL in Group II.