• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.4
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• pp.241-245
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• 2015

Energy Distribution Function in pure $CH_4$, $CF_4$ and mixtures of $CF_4$ and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for $CH_4$, $CF_4$ and Ar, were used. The differences of the transport coefficients of electrons in $CH_4$, mixtures of $CH_4$ and Ar, have been explained by the deduced energy distribution functions for electrons and the complete collision cross-sections for electrons. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in $CF_4$-Ar mixtures shows the Maxwellian distribution for energy. That is, $f({\varepsilon})$ has the symmetrical shape whose axis of symmetry is a most probably energy.

• Composites Research
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• v.12 no.4
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• pp.62-70
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• 1999

It was well recognized that damages associated mainly with the aging of civil infrastructrues were one of very serious problems for assurance of safety and reliability. In recent, carbon fiber sheet(CFS) has been widely used for reinforcement and rehabitation of damaged concrete beam. However, the fundamental mechanism of load transfer and its load-resistant for carbon fiber sheet reinforced concrete are not fully understood. In this study, three point bend test has been carried out to understand the damage progress and micro-failure mechanism of CFS reinforced concretes. For these purposes, four kinds of specimens are used, that is, concrete, respectively. Acoustic Emission(AE) technique was used to evaluate the characteristics of damage progress and failure mechanism of specimens. In addititon, two-dimensional AE source location was also performed to monitor crack initiation and propagation processes for four types of these specimens.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.3
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• pp.56-61
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• 2010

Recently, UV pulse laser is widely used in micro machining of the research, development and industry field of IT, NT and BT products because the laser short wavelength provides not only micro drilling, micro cutting and micro grooving which has a very fine line width, but also high absorption coefficient which allows a lot of type of materials to be machined more easily. To analyze the dynamic deformation during a very short processing time, which is nearly about several tens nanoseconds, the commercial Finite Element Analysis (FEA) code, LS-DYNA 3D, was employed for the computitional simulation of the UV laser micro machining behavior for thin copper material in this paper. A finite element model considering high strain rate effect is especially suggested to investigate the micro phenomena which are only dominated by mechanically pressure impact in disregard of thermally heat transfer. From these computational results, some of dynamic deformation behaviors such as dent deformation shapes, strains and stresses distributions were observed and compared with previous experimental works. These will help us to understand micro interaction between UV laser beam and material.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.662-662
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• 2013

Over the last several decades, innovative light-harvesting devices have evolved to achieve high efficiency in solar energy transfer. Research on the mechanisms for plasmon resonance is very desirable to overcome the conventional efficiency limits of photovoltaics. The influence of localized surface plasmon resonance on hot electron flow at a metal-semiconductor interface was observed with a Schottky diode composed of a thin silver layer on $TiO_2$. The photocurrent is generated by absorption of photons when electrons have enough energy to travel over the Schottky barrier and into the titanium oxide conduction band. The correlation between the hot electrons and the surface plasmon is confirmed by matching the range of peaks between the incident photons to current conversion efficiency (IPCE, flux of collected electrons per flux of incident photons) and UV-Vis spectra. The photocurrent measured on Ag/$TiO_2$ exhibited surface plasmon peaks; whereas, in contrast to the Au/$TiO_2$, a continuous Au thin film doesn't exhibit surface plasmon peaks. We modified the thickness and morphology of a continuous Ag layer by electron beam evaporation deposition and heating under gas conditions and found that the morphological change and thickness of the Ag film are key factors in controlling the peak position of light absorption.

• Structural Engineering and Mechanics
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• v.38 no.4
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• pp.385-403
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• 2011

Continuous deep girders which transmit the gravity load from the upper wall to the lower columns have frequently long end shear spans between the boundary of the upper wall and the face of the lower column. This paper presents the results of tests and analyses performed on three 1:2.5 scale specimens with long end shear spans, (the ratios of shear-span/total depth: 1.8 < a/h < 2.5): one designed by the conventional approach using the beam theory and two by the strut-and-tie approach. The conclusions are as follows: (1) the yielding strength of the continuous RC deep girders is controlled by the tensile yielding of the bottom longitudinal reinforcements, being much larger than the nominal strength predicted by using the section analysis of the girder section only or using the strut-and-tie model based on elastic-analysis stress distribution. (2) The ultimate strengths are 22% to 26% larger than the yielding strength. This additional strength derives from the strain hardening of yielded reinforcements and the shear resistance due to continuity with the adjacent span. (3) The pattern of shear force flow and failure mode in shear zone varies depending on the amount of vertical shear reinforcement. And (4) it is necessary to take into account the existence of the upper wall in the analysis and design of the deep continuous transfer girders that support the upper wall with a long end shear span.

• Korean Journal of Materials Research
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• v.29 no.12
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• pp.804-811
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• 2019

As the importance of three-dimensiona (3D) nano patterns and structures has recently emerged, interest in the study of 3D structures of block copolymers has increased. However, most existing studies on block copolymer 3D patterns on substrates are limited to simple 3D structures such as a multi-layered forms. In this study, we propose an experimental method for realizing free-standing 3D block copolymer patterns on substrates using an e-beam lithographic template and film transfer method. The block copolymer 3D structure formed in wide hole templates are similar to simple multi-layered structures; however, as the width of the hole template become narrower, more complex block copolymer 3D structures are formed in which the upper and lower layer structures are interconnected. Furthermore, we introduce a method to fabricate novel block copolymer structures in which the 2D planar structures are connected to 3D complex structures. Proposed 3D block copolymer fabrication method provides a framework for generation of unconventional 3D structures of block copolymer, which can be useful for next generation 3D devices.

• Korean Journal of Optics and Photonics
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• v.15 no.2
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• pp.158-170
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• 2004

Wireless optical communication is expected for high-speed optical communication in the areas of saturated optical fiber communication and low population density. In this paper, we present an optical transmitter system for wireless optical communication with new design concepts different from the usual optical imaging system. The specifications are the following: the source is a laser diode(LD) of wavelength 830 nm in which the divergent angle from the tangential plane differs from that from the sagittal plane. Here, the requested transmission distances are very long range such as 500 m to 1500 m and beam diameter is 3 m at the receiver with symmetrical energy distribution. For the evaluation characteristics of this kind of non-imaging system, two optical quantities, the relative illumination distribution and energy transfer efficiency, are numerically calculated through lots of ray tracing.

• International Journal of Control, Automation, and Systems
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• v.5 no.1
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• pp.24-34
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• 2007

Closed-loop active twist control of integral helicopter rotor blades is investigated in this paper for reducing hub vibration induced in forward flight. A four-bladed fully articulated integral twist-actuated rotor system has been designed and tested successfully in wind tunnel in open-loop actuation. The integral twist deformation of the blades is generated using active fiber composite actuators embedded in the composite blade construction. An analytical framework is developed to examine integrally twisted helicopter blades and their aeroelastic behavior during different flight conditions. This aeroelastic model stems from a three-dimensional electroelastic beam formulation with geometrical-exactness, and is coupled with finite-state dynamic inflow aerodynamics. A system identification methodology that assumes a linear periodic system is adopted to estimate the harmonic transfer function of the rotor system. A vibration minimizing controller is designed based on this result, which implements a classical disturbance rejection algorithm with some modifications. Using the established analytical framework, the closed-loop controller is numerically simulated and the hub vibratory load reduction capability is demonstrated.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.2
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• pp.22-27
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• 2000

We present a sequential stereoscopic display system using volume holographic storage. Multiple angular multiplexed stereoscopic image pairs are recorded into a photorefractive crystal that can store data with high density, transfer them with high speed, and select a randomly chosen data element. The reference beam with Bragg selectivity is scattered by the index grating and the diffracted beams are propagating along the directions of the stereoscopic image pairs. The images are to be suitably projected on the left and right display plane sequentially for stereoscopic video viewing.

• Computers and Concrete
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• v.3 no.1
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• pp.65-77
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• 2006

This study reports the details of the finite element analysis of eleven shear critical partially prestressed concrete T-beams having steel fibers over partial or full depth. Prestressed concrete T-beams having a shear span to depth ratio of 2.65 and 1.59 and failing in the shear have been analyzed using 'ANSYS'. The 'ANSYS' model accounts for the nonlinear phenomenon, such as, bond-slip of longitudinal reinforcements, post-cracking tensile stiffness of the concrete, stress transfer across the cracked blocks of the concrete and load sustenance through the bridging of steel fibers at crack interface. The concrete is modeled using 'SOLID65'-eight-node brick element, which is capable of simulating the cracking and crushing behavior of brittle materials. The reinforcements such as deformed bars, prestressing wires and steel fibers have been modeled discretely using 'LINK8' - 3D spar element. The slip between the reinforcement (rebar, fibers) and the concrete has been modeled using a 'COMBIN39'-non-linear spring element connecting the nodes of the 'LINK8' element representing the reinforcement and nodes of the 'SOLID65' elements representing the concrete. The 'ANSYS' model correctly predicted the diagonal tension failure and shear compression failure of prestressed concrete beams observed in the experiment. The capability of the model to capture the critical crack regions, loads and deflections for various types of shear failures in prestressed concrete beam has been illustrated.