• Macromolecular Research
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• v.15 no.1
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• pp.74-81
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• 2007

A series of photoreactive mesogens based on chalcone were prepared and their morphological behavior and reactivity were studied according to a variable number of alkyloxy tail carbons. The linear ester compounds 3a-h comprised two chalcone units connected to a benzene ring through ester linkages. All linear ester compounds showed enantiotropic liquid crystalline phases. The X-ray diffractograms for the mesophases of compounds 3a-h showed a set of reflections in the small-angle region which consisted of more than three sharp diffraction peaks with d spacings in the ratio of 1:1/2:1/3, confirming the well defined smectic A structures of the compounds. Compounds 3a-h were considered to be bifunctional monomers due to the presence of two photoreactive chalcone groups. Upon UV irradiation, its polymerization proceeded through the [2+2] addition reaction between chalcone units in a stepwise manner. An image pattern was obtained by the photopolymerization of the liquid crystal of the compound (3h) with decyloxy tails through a photomask. The irradiated part became dark while the masked part remained birefringent under polarized optical microscopy, which was ascribed to the production via the UV irradiation of a polymer or a dimer having cyclobutane rings by [2+2] addition, which thereby disrupted the alignment of the molecules.

• Transactions on Electrical and Electronic Materials
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• v.12 no.5
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• pp.218-221
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• 2011

We modified the optical properties of the $CuInS_2$ nanocrystal (NC) by alloying. Nanocrystals (NCs) with alloyed cores were synthesized by refluxing the as-synthesized $CuInS_2$ NCs with a mixture of cadmium acetate, zinc acetate and palmitic acid. The shift in emission wavelength of the NCs after shell layer formation was minimized by alloying. The photoluminescence (PL) spectra showed significant reduction of emission intensity. A detailed study on the emission process of NCs implies that the formation of shell layers with small lattice mismatch minimized the mismatch strain generated from the shell layers in contrast to core alloyed NCs. In particular, time-resolved PL spectra of the NCs showed a significant increase in the lifetime of excited carriers by modifying the band alignment of the NCs by modifying the shell composition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.10
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• pp.803-810
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• 2009

Micromirrors have a wide range of applications such as optical switches, laser scanners, and digital projection displays. Due to their low performances and high costs, however, practical applications of micromirrors are quite limited. At present micromirrors demand not only a better design but also a simple fabrication process. In this study a twisting-type micromirror that can be driven by two thermal bimorph actuators bending in opposite directions is designed from electro-thermo-mechanical theories and fabricated through a simple MEMS process. Each actuator consists of $SiO_2$ and gold thin-film layers. Simplified analytical model has been built to optimize the performance of micromirror. Due to unexpected resistance increase of metal film and alignment mismatch during fabrication process, experimental rotation angles of micromirrors are about $11^{\circ}$ at applied voltages less than 0.6V. From numerical simulation and analytical studies, however, the next design can provide rotation angles over $20^{\circ}$ at the same applied voltage.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.56-62
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• 2004

We present a diffraction grating interferometer of large equivalent wavelength specially designed for flatness testing of rough surfaces. Two transmission diffraction gratings are illuminated on the object under test by use of two measurement beams with different angles of incidence, which yields a large equivalent wavelength. This interferometer design minimizes unnecessary diffraction rays and the systematic error caused by the diffraction gratings, and provides a large working distance and easy alignment. To improve the measurement accuracy, phase shifting technique is applied and the equivalent wavelength error caused by defocus is calibrated. Test results obtained from mirror surfaces and machined rough surfaces are discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1070-1073
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• 2004

In this study, Tri(1-phenylpyrazolato)iridium $(Ir(ppz)_3)$ was prepared for the pure blue phosphorescent dopant and various host materials were used for the appropriate energy alignment. Although the luminance was pure blue with the CIE coordinates of x = 0.158, y = 0.139, device efficiencies didn't improve yet. Instead of finding the proper host materials, the alteration of structure of OLEDs affected the improvement of electrical and optical characteristics of the devices. It was worthy that insertion the exciton formation zone with the host material between the emitting zone and the exciton blocking layer. The device with a structure of ITO/NPB/Ir(ppz)3 doped in CBP/CBP for the exciton formation zone/BCP/Liq/Al was fabricated and the characteristics were observed compared with the devices without the exciton formation zone. When CBP was used for the exciton formation zone, the device efficiency reached to over 0.25 cd/A. While the device used CBP only for the host showed the luminous efficiency of under 0.11 cd/A

• Journal of the Korean Society for Precision Engineering
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• v.15 no.5
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• pp.93-99
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• 1998

Although laser interferometer measurement system has advantages of measurement range and accuracy, it has some disadvantages when measurement of multi degrees of freedom of motion are required. Because the traditional error measurement methods for geometric errors (two straightness and three angular errors) of a slide of machine tools measures error components one at a time. It may also create an optical path difference and affect the measurement accuracy. In order to identify and compensate for geometric errors of a moving rigid body in real time processes, an on-line error measurement system for simultaneous detection of the five error components of a moving object is required. Using laser alignment technique and some optoelectronic components, an on-line measurement system with 5 degrees of freedom was developed for the geometric error detection in this study Performance verification of the system has been performed on an error generating mechanism. Experimental results show the feasibility of this system for identifying geometric errors of a slide of machine tools.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.10
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• pp.559-563
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• 2009

Performance of refrigerant oil at the thrust-bearing and at the journal-bearing of a scroll compressor is a significant factor. This paper presents the friction and anti-wear characteristics of nano oil with a mixture of a refrigerant oil and carbon nano particles. The characteristics of friction and anti-wear using nano-oil is evaluated using the disk on disk tester for measuring friction surface temperature and the coefficient of friction. The average friction coefficient of nano-oil was reduced by 60% compared to raw oil under 600 N and 1,000 rpm. It is believed that the interaction of nano particles between surfaces can be improved the lubrication in the friction surfaces. Worn surfaces of frictional specimen were also investigated by the optical and atomic force microscopy. Conclusively, it is expected that wear and friction coefficient of compressor can be reduced by alignment applying nano-oil as refrigerant oil.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.258-263
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• 1998

Quasi-elastic light scattering is utilized to measure the mean diameter of the 0.3 $\mu\textrm{m}$-dimeter polystyrene sphere. The mean diameter of the polystyrene sphere is required to be known within the uncertainty of a few per centages. The systematic error has been considerably reduced by improving the system for the angle alignment and temperature measurement of cell. NIST SRM 1691 (0.269$\pm$0.007 $\mu\textrm{m}$: TEM; 0.275$\pm$0.007 $\mu\textrm{m}$: QELS) is measured to be 0.273 $\mu\textrm{m}$$\pm$0.006 $\mu\textrm{m}$ in mean diameter. Detailed description is given of the improved method and the resultant uncertainty, and the comparison of results with NIST is followed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.183-187
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• 2011

The polymer-stabilized blue phase liquid crystal (BPLC) cell has advantages such as sub-millisecond response time, wide viewing angle and no rubbing process for the alignment of liquid crystals. However, high operating voltage and low kerr constant of the polymer-stabilized blue phase liquid crystal deteriorate the electro-optical characteristic of the polymer-stabilized BPLC cell. In this paper, we proposed novel zig-zag electrode in cell layout and confirmed that proposed electrode shape could reduce an over 25 percent of operating voltage for BPLC cell without degradation of tranmittance by using Kerr constant simulation.

• Journal of Fashion Business
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• v.7 no.3
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• pp.60-70
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• 2003

Textile scientists have regarded the material appearance of natural fibers, especially that of silk or wool fibers, as the benchmark for reinventing the look and feel of the long term, friendly companion of mankind. The appearances or textures of the materials surrounding us in everyday life have long been interesting topics to many people.from scholars to painters. Even the simplest questions may require careful pondering. Why is the silk fabric so lustrous with subtlety? Recently, appearance models have become increasingly important in textile products. They are needed to model and simulate different models. In this study, the optical characteristics of filament yarns and knitted fabrics were investigated using images taken at various angles and illumination conditions. Then the images were analyzed using some image analysis techniques, such as thresholding and measuring luster blobs. The anisotropic nature of the filamentous specimens was studied based on the images acquired at different incident illumination and observing angles with several alignment positions of the fabric specimens. A few cylindrical models were generated using commercially available software, Rhinoceros, and then on the models, a ray-tracing algorithm based on a software, POV-Ray, was applied to simulate the appearance or lustrous images of the monofilament models.