• Transactions on Electrical and Electronic Materials
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• v.18 no.4
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• pp.229-236
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• 2017

This paper deals with the design and implementation of an efficient topology for cascaded multilevel inverters with reduced part counts. In the proposed design, a well-established basic unit is first developed. The series extension of this unit results in the formation of the proposed multilevel inverter. The proposed design minimizes the number of power electronic components including insulated-gate bipolar transistors and gate driver circuits, which in turn cuts down the size of the inverter assembly and reduces the operating power losses. An explicit control strategy with enhanced device efficiency is also acquired. Thus, the part count reductions enhance not only the economical merits but also the technical features of the entire system. In order to accomplish the desired operational aspects, three algorithms are considered to determine the magnitudes of the dc voltage sources effectively. The proposed topology is compared with the conventional cascaded H-bridge multilevel inverter topology, to reflect the merits of the presented structure. In continue, both the analytical and experimental results of a cascaded 31-level structure are analyzed. The obtained results are discussed in depth, and the exemplary performance of the proposed structure is corroborated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.25-37
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• 2008

The capacity spectrum method (CSM) is a simple and graphical seismic analysis procedure. Originally, it has been developed for buildings, but now its applicability has been extended to bridge structures. It is based on the capacity curve estimated by pushover analysis and demand spectrum reduced from linear elastic design spectrum by using effective damping or strength reduction factor. In this paper, the inelastic demand spectrum as the reduced demand spectrum is calculated from the linear elastic design spectrum by using the several formulas for the strength reduction factor. The effects of the strength reduction factor for the capacity spectrum analysis are evaluated for 3 types of symmetric and asymmetric bridge structures. To investigate an accuracy of the CSM which several formulas for strength reduction factor were applied, the maximum displacements estimated by the CSM are compared with the results obtained by nonlinear time history analysis for 8 artificially generated earthquakes. The maximum displacements estimated by the CSM using the SJ formula among the several strength reduction factors provide the most accurate agreement with those calculated by the inelastic time history analysis.

• Earthquakes and Structures
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• v.8 no.2
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• pp.443-462
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• 2015

Some model building codes stipulate that the design displacement of a building can be computed using the elastic static analysis results multiplied by the deflection amplification factor, $C_d$. This approach for estimating the design displacement is essential and appealing in structural engineering practice when nonlinear response history analysis (NRHA) is not required. Furthermore, building codes stipulate the consideration of accidental torsion effects using accidental eccentricity, whether the buildings are symmetric-plan, or asymmetric-plan. In some model building codes, the accidental eccentricity is further amplified by the torsional amplification factor $A_x$ in order to minimize the discrepancy between statically and dynamically estimated responses. Therefore, this warrants exploration of the reliability of statically estimated design displacements in accordance with the building code requirements. This study uses the discrepancy curves as a way of assessing the reliability of the design displacement estimates resulting from the factors $C_d$ and $A_x$. The discrepancy curves show the exceedance probabilities of the differences between the statically estimated design displacements and NRHA results. The discrepancy curves of 3-story, 9-story, and 20-story example buildings are investigated in this study. The example buildings are steel special moment frames with frequency ratios equal to 0.7, 1.0, 1.3, and 1.6, as well as existing eccentricity ratios ranging from 0% to 30%.

• Steel and Composite Structures
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• v.19 no.3
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• pp.635-659
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• 2015

In this study, natural frequency analysis of a large deflected cantilever laminated composite beam fixed at both ends, which forms the case of a pre-stressed curved beam, is investigated. The laminated beam is considered to have symmetric and asymmetric lay-ups and the effective flexural modulus of the beam is used in the analysis. In order to obtain the pre-stressed composite curved beam case, an external vertical concentrated load is applied at the free end of a cantilever laminated composite beam and then the loading point of the deflected beam is fixed. The non-linear deflection curve of the flexible beam undergoing large deflection is obtained by the Reversion Method. The curved laminated composite beam is modeled by using the Finite Element Method with a straight-beam element approach. The effects of orientation angle and vertical load on the natural frequency parameter for the first four modes are examined and the results obtained are given in graphics. It has been found that the effect of the load parameter, which forms the curved laminated beam, on the natural frequency parameter, almost disappears after a certain value of the load parameter. This certain value differs for each laminated curved beam and each vibration mode.

• Earthquakes and Structures
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• v.9 no.5
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• pp.1091-1114
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• 2015

The adequacy of a number of advanced earthquake Intensity Measures (IMs) to predict the structural damage of earthquake resistant 3D R/C buildings is investigated in the present paper. To achieve this purpose three symmetric in plan and three asymmetric 5-storey R/C buildings are analyzed by nonlinear time history analysis using 74 bidirectional earthquake records. The two horizontal accelerograms of each ground motion are applied along the structural axes of the buildings and the structural damage is expressed in terms of the maximum and average interstorey drift as well as the overall structural damage index. For each individual pair of accelerograms the values of the aforementioned seismic damage measures are determined. Then, they are correlated with several strong motion scalar IMs that take into account both earthquake and structural characteristics. The research identified certain IMs which exhibit strong correlation with the seismic damage measures of the studied buildings. However, the degree of correlation between IMs and the seismic damage depends on the damage measure adopted. Furthermore, it is confirmed that the widely used spectral acceleration at the fundamental period of the structure is a relatively good IM for medium rise R/C buildings that possess small structural eccentricity.

• Earthquakes and Structures
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• v.12 no.1
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• pp.1-12
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• 2017

Historical earthquakes have shown that successive seismic events may occur in regions of high seismicity. Such a sequence of earthquakes has the potential to increase the damage level of the structures, since any rehabilitation between the successive ground motions is practically impossible due to lack of time. Few studies about this issue can be found in literature, most of which focused their attention on the seismic response of SDOF systems or planar frame structures. The aim of the present study is to examine the impact of seismic sequences on the damage level of 3D multistorey R/C buildings with various structural systems. For the purposes of the above investigation a comprehensive assessment is conducted using three double-symmetric and three asymmetric in plan medium-rise R/C buildings, which are designed on the basis of the current seismic codes. The buildings are analyzed by nonlinear time response analysis using 80 bidirectional seismic sequences. In order to account for the variable orientation of the seismic motion, the two horizontal accelerograms of each earthquake record are applied along horizontal orthogonal axes forming 12 different angles with the structural axes. The assessment of the results revealed that successive ground motions can lead to significant increase of the structural damage compared to the damage caused by the corresponding single seismic events. Furthermore, the incident angle can radically alter the successive earthquake phenomenon depending on the special characteristics of the structure, the number of the sequential earthquakes, as well as the distance of the record from the fault.

• Journal of the Korean Society of Combustion
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• v.17 no.3
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• pp.17-29
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• 2012

The effects of strain rate and preferential diffusion of $H_2$ on flame extinction are numerically studied in interacting premixed syngas-air flames with fuel compositions of 50% $H_2$ + 50% CO and 30% $H_2$ + 70% CO. Flame stability diagrams mapping lower and upper limit fuel concentrations at flame extinction as a function of strain rate are examined. Increasing strain rate reduces the boundaries of both flammable lean and rich fuel concentrations and produces a flammable island and subsequently even a point, implying that there exists a limit strain rate over which interacting flame cannot be sustained anymore. Even if effective Lewis numbers are slightly larger than unity on extinction boundaries, the shape of the lean extinction boundary is slanted even at low strain rate, i.e. $a_g=30s^{-1}$ and is more slanted in further increase of strain rate, implying that flame interaction on lean extinction boundary is strong and thus hydrogen (as a deficient reactant) Lewis number much less than unity plays an important role of flame interaction. It is also shown that effects of preferential diffusion of $H_2$ cause flame interaction to be stronger on lean extinction boundaries and weaker on rich extinction boundaries. Detailed analyses are made through the comparison between flame structures with and without the restriction of the diffusivities of $H_2$ and H in symmetric and asymmetric fuel compositions. The reduction of flammable fuel compositions in increase of strain rate suggests that the mechanism of flame extinction is significant conductive heat loss from the stronger flame to ambience.

• Journal of Korea Multimedia Society
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• v.11 no.8
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• pp.1093-1100
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• 2008

Feistel and SPN are the two main structures in designing a block cipher algorithm. Unlike Feistel, an SPN has an asymmetric structure in encryption and decryption. In this paper we propose an SPN algorithm which has a symmetric structure in encryption and decryption. The whole operations in our SPN algorithm are composed of the even numbers of N rounds where the first half of them, 1 to N/2, applies function and the last half of them, (N+1)/2 to N, employs inverse function. Symmetry layer is executed to create a symmetry block in between function layer and inverse function layer. AES encryption and decryption algorithm, whose safety is already proved, are exploited for function and inverse function, respectively. In order to be secure enough against the byte or word unit-based attacks, 32bit rotation and simple logical operations are performed in symmetry layer. Due to the simplicity of the proposed encryption and decryption algorithm in hardware configuration, the proposed algorithm is believed to construct a safe and efficient cipher in Smart Card and RFID environments where electronic chips are built in.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.2 s.117
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• pp.177-182
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• 2007

This paper presents the InGaP/GaAs HBT differential LC VCO with low phase noise performance for adaptive feedback interference cancellation system(AF-lCS). The VCO is verified with enhanced tank structure including filtering technique. The output tuning range for proposed VCO using asymmetric inductor and symmetric capacitors withlow pass filtering technique is 207 MHz. The output powers are -6.68 including balun and cable loss. The phase noise of this VCO at 10 kHz, 100 kHz and 1 MHz are -102.02 dBc/Hz, -112.04 dBc/Hz and -130.40 dBc/Hz. The VCO is designed within total size of $0.9{\times}0.9mm^2$.

• Smart Structures and Systems
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• v.20 no.3
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• pp.329-342
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• 2017

In this paper, the dispersion characteristics of elastic waves propagation in sandwich nano-beams with functionally graded (FG) face-sheets reinforced with carbon nanotubes (CNTs) is investigated based on various high order shear deformation beam theories (HOSDBTs) as well as nonlocal strain gradient theory (NSGT). In order to align CNTs as symmetric and asymmetric in top and bottom face-sheets with respect to neutral geometric axis of the sandwich nano-beam, various patterns are employed in this analysis. The sandwich nano-beam resting on Pasternak foundation is subjected to thermal, magnetic and electrical fields. In order to involve small scale parameter in governing equations, the NSGT is employed for this analysis. The governing equations of motion are derived using Hamilton's principle based on various HSDBTs. Then the governing equations are solved using analytical method. A detailed parametric study is conducted to study the effects of length scale parameter, different HSDBTs, the nonlocal parameter, various aligning of CNTs in thickness direction of face-sheets, different volume fraction of CNTs, foundation stiffness, applied voltage, magnetic intensity field and temperature change on the wave propagation characteristics of sandwich nano-beam. Also cut-off frequency and phase velocity are investigated in detail. According to results obtained, UU and VA patterns have the same cut-off frequency value but AV pattern has the lower value with respect to them.