• Macromolecular Research
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• v.12 no.3
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• pp.322-324
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• 2004

Poly(1-dodecyl-2,5-pyrrylene vinylene) (PDPV) has an extended 1t-conjugated structure and exhibits characteristic spectroscopic features. The PDPV we prepared has an absorption maximum at 510nm and its long absorption tail at ca. 750nm in methylene chloride is due to the long 1t-conjugated system connected to vinyl group. The large red-shift of emission was 625nm upon excitation at 480nm, which suggests the existence of a low emissive state. The emission of PDPV in less-polar solvents decreased markedly relative to that in the more-polar solvents; this observation was ascribed possibly to quenching by a strong vibrational mode of the dodecyl groups of PDPV in less-polar solvents. Furthermore, the emission from the high-energy side had a single decay component (0.1㎱, 49.96%), while that from the low-energy side had two components (0.6㎱, 27.1 %; 2.7㎱, 22.87%). We characterized the redox properties of PDPV by cyclic voltammetry. Every redox peak showed irreversible behavior; the oxidation peaks appeared at 1.7,0.8, and 0.6V and the reduction peak at -0.5V.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.2
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• pp.102-107
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• 2003

This study puts focus on the optimization of growth temperature of CIGS absorber layer which affects severely the performance of solar cells. The CIGS absorber layers were prepared by three-stage co-evaporation of metal elements in the order of In-Ga-Se. The effect of the growth temperature of 1st stage was found not to be so important, and 350$^{\circ}C$ to be the lowest optimum temperature. In the case of growth temperature at 2nd/3rd stage, the optimum temperature was revealed to be 550$^{\circ}C$. The XRD results of CIGS films showed a strong (112) preferred orientation and the Raman spectra of CIGS films showed only the Al mode peak at 173cm$\^$-1/. Scanning electron microscopy results revealed very small grains at 2nd/3rd stage growth temperature of 480$^{\circ}C$. At higher temperatures, the grain size increased together with a reduction in the number of the voids. The optimization of experimental parameters above mentioned, through the repeated fabrication and characterization of unit layers and devices, led to the highest conversion efficiency of 15.4% from CIGS-based thin film solar cell with a structure of Al/ZnO/CdS/CIGS/Mo/glass.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.12
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• pp.639-647
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• 2001

We present an integrated optical microswitch, composed of silicon waveguides, gold-coaled silicon micromirrors, and electrostatic contact actuators, for applications to the optical signal transceivers. For a low switching voltage, we modify the conventional curled electrode microactuator into a electrostatic microactuator with touch-down beams. We fabricate the silicon waveguides and the electrostatically actuated micromirrors using the ICP etching process of SOI wafers. We observe the single mode wave propagation through the silicon waveguide with the measured micromirror loss of $4.18\pm0.25dB$. We analyze major source of the micromirror loss, thereby presenting guidelines for low-loss micromirror designs. From the fabricated microswitch, we measure the switching voltage of 31.74V at the resonant frequency of 6.89kHz. Compared to the conventional microactuator, the present contact microactuator achieves 77.4% reduction of the switching voltage. We also discuss a feasible method to reduce the switching voltage to 10V level by using the electrode insulation layers having the residual stress less than 30MPa.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.8
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• pp.431-439
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• 1999

Among the variable-speed AC motor drive systems, the static slip power recovery system has been widely adopted in large power drives because a high efficiency drive can be obtained by recovering the slip power to the AC line. Although many improvements have been made in this system, several problems also remain such as the need of transformer in inverter AC side, which results in limiting speed control range and increasing the losses, production of reactive power by the control of inverter firing angle, harmonics in line currents, and so on. This paper presents the novel high performance slip power recovery system using the boost converter and small size filter in the rotor circuit, which recovers slip power of a wound rotor induction machine to AC supply efficiently with the aid of the boost converter, in which most of the problems in conventional system can be solved. The speed can be controlled by the duty ratio of the converter switch, not by inverter firing angle. As a results, the proposed system can operate in high power factor and the harmonic currents caused by the inverter and rectifier can be considerably suppressed. The validity of the proposed system verified by demonstrating the good agreement in the simulation and experimental results.

• Journal of Microbiology and Biotechnology
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• v.25 no.8
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• pp.1299-1306
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• 2015

This study aims to investigate the mechanism of action of the cinnamon bark essential oil (CB), when used singly and also in combination with piperacillin, for its antimicrobial and synergistic activity against beta-lactamase TEM-1 plasmid-conferred Escherichia coli J53 R1. Viable count of bacteria for this combination of essential oil and antibiotic showed a complete killing profile at 20 h and further confirmed its synergistic effect by reducing the bacteria cell numbers. Analysis on the stability of treated cultures for cell membrane permeability by CB when tested against sodium dodecyl sulfate revealed that the bacterial cell membrane was disrupted by the essential oil. Scanning electron microscopy observation and bacterial surface charge measurement also revealed that CB causes irreversible membrane damage and reduces the bacterial surface charge. In addition, bioluminescence expression of Escherichia coli [pSB1075] and E. coli [pSB401] by CB showed reduction, indicating the possibility of the presence of quorum sensing (QS) inhibitors. Gas-chromatography and mass spectrometry of the essential oil of Cinnamomum verum showed that trans-cinnamaldehyde (72.81%), benzyl alcohol (12.5%), and eugenol (6.57%) were the major components in the essential oil. From this study, CB has the potential to reverse E. coli J53 R1 resistance to piperacillin through two pathways; modification in the permeability of the outer membrane or bacterial QS inhibition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.2
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• pp.56-67
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• 2006

The reliability and failure mode effect analysis are effective means to achieve efficient and cost-reduction design for satellite development. The failure rate of COTS (Commercial-Off-The-Shelf) parts required for reliability analysis is not usually provided from the manufacturer. Space environment factors based on empirical data obtained from MIL-HDBK-217F can be applicable to the reliability calculation. As a radiation environment factor, the occurrence rate of SEL (Single Event Latch-up) is additionally incorporated for the failure rate prediction. In this paper, the statistical reliability analysis method for low-cost small satellite using COTS parts is suggested. This statistical reliability analysis was applied to HAUSAT-2 small satellite whose electronic boxes are consisted of many COTS parts to calculate the system reliability at the end of design mission life.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.73-83
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• 1998

Considering dynamic behaviors according to initial tension forces, geometric nonlinearity and the effect of higher eigen modes to participate in dynamic behaviors increase as initial tension forces decrease, and from phase portrait we can realize that period attractors are produced in many area with complexity. If initial tension forxes increase, difference between linear and nonlinear solutions will decrease and the first eigen mode dominate the dynamic behaviors and observing phase portrait, period attractors appear in certain area regularly. These results may offer meaningful informations to nonlinear dynamic analysis using modal reduction methods such as Lanczos modal analysis. And actually nonlinear dynamic analysis needs very large computational efforts. So, if we determine the number of eigen modes to take part in modal analysis corresponding to initial tension forces we will get more accurate data close to exact nonlinear dynamic solutions.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.11
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• pp.561-572
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• 2001

Since energy consumption of CMOS circuits has a quadratic dependency on the supply voltage, lowering the supply voltage is the most effective way of reducing energy consumption. We propose an intra-task voltage scheduling algorithm for low-energy hard real-time applications. Based on a static timing analysis technique, the proposed algorithm controls the supply voltage within an individual task boundary. By fully exploiting all the slack times, as scheduled program by the proposed algorithm always complete its execution near the deadline, thus achieving a high energy reduction ratio. In order to validate the effectiveness of the proposed algorithm, we built a software tool that automatically converts a DVS-unaware program into an equivalent low-energy program. Experimental results show that the low-energy version of an MPEG-4 encoder/decoder (converted by the software tool) consumes less than 7~25% of the original program running on a fixed-voltage system with a power-down mode.

• Journal of Navigation and Port Research
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• v.32 no.6
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• pp.481-487
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• 2008

Ship's wireless LAN was in the limelight as equipment of ease, cost reduction, various func tion al i ty. In the paper, a dual-bandpass filter for wireless LAN has proposed, which was designed by using dual-mode square loop resonator with square patch in compliance with 2.4 GHz and 5 GHz band of wireless LAN. The dual-bandpass filter could be designed by adjusting sizes of one perturbation element and three of reference elements in compliance with the frequency bands of 2.4 GHz and 5.8 GHz, Furthermore, new dual-bandpass filter was also designed by adjusting stopband of using open stubs in compliance with the frequency bands of 2.4 GHz and 5.2 GHz. The measured results for the fabricated dual-bandpass filters agreed well with the simulated ones, and hence, it was confirmed that the proposed design method is valid.

• Steel and Composite Structures
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• v.29 no.4
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• pp.557-567
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• 2018

Cylindrical shell structures buckle at service loads which are much lower than their associated theoretical buckling loads. The main source of this discrepancy is the presence of various imperfections which are created on the cylinder body during different processes as manufacturing, handling, assembling and machining. Many cylindrical shell structures are still designed against buckling based on the experimental data introduced by NASA SP-8007 as conservative lower bound curves. This study employed the numerical based Linear Buckling mode shape Imperfection (LBMI) method and modified it using a stochastic method to assess the effect of geometrical imperfections in more details on the buckling of cylindrical shells with and without the cutout. The comparison of results with those obtained from the numerical Simcple Perturbation Load Imperfection (SPLI) method for cylinders with and without cutout revealed a good correlation. The effect of two parameters of size and number of cutouts on the buckling load was investigated using the linear buckling and Modified LBMI methods. Results confirmed that in cylinders with a small cutout inserting geometrical imperfection using either SPLI or modified LBMI methods significantly reduced the value of the predicted buckling load. However, in cylinders with larger cutouts, the effect of the cutout is dominant, thus considering geometrical imperfection had a minor effect on the buckling loads predicted by both SPLI and modified LBMI methods. Furthermore, the modified LBMI method was employed to evaluate the combination effect of cutout numbers and size on the buckling load. It is shown that in small cutouts, an increasing in the cutout size up to a certain value resulted in a remarkable reduction of the buckling load, and beyond that limit, the buckling loads were constant against D/R ratios. In addition, the cutout number shows a more significant effect on decreasing the buckling load at small D/R ratios than large D/R ratios.