Biomedical subjects

Jae Chang Kim

Publications and source records attributed to Jae Chang Kim.

8 recordsLinked to original sources

PubMed2006

Optical configuration of a horizontal-switching liquid-crystal cell for improvement of the viewing angle.

We propose an optical configuration of a horizontal-switching liquid-crystal cell, consisting of a splayed liquid-crystal cell and uniaxial films, to improve the viewing angle characteristics by compensating for the phase dispersion in a diagonal direction. The optical design of the proposed configuration was performed on a Poincaré sphere with geometric calculations. By fabricating in-plane switching cells with the introduced configuration, we demonstrated their optical performances. As a result, we found that the diagonal viewing angle of the proposed horizontal-switching cell could be increased by 80% compared to a symmetrical viewing cone.

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PubMed2006

Transflective liquid-crystal display using low-twisted vertically aligned mode.

We present the design of a transflective and low-power LCD using a low-twist vertically aligned liquid crystal (LC) cell, achieved by blending a chiral additive with a patterned reflector in a single-domain configuration. Unlike the conventional single-domain transflective LCD, in which it is possible to optimize only one of the transmissive and reflective regions, the device suggests that it is possible to optimize both the transmission and reflection design to obtain favorable results in both reflective and transmissive light conditions by optimizing the chiral pitch and twist angle. From the parameter space diagram (PSD) method, which does not include the information on chiral pitch and the nonuniform LC director tilt angle, optimization focused on the transmissive region is performed. By analyzing the relation between the transmittance and the chiral pitch under the applied voltage, the optimized twist angle and chiral pitch are proposed. It is described that the optimized twist angle is also available for the reflective region by the dynamic PSD method by considering the average tilt angle under applied voltage.

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PubMed2005

Determination of azimuthal anchoring energy in a twisted nematic liquid crystal.

On the basis of the torque balance equation between the twisting elastic power and the torsional anchoring energy and the Jones matrix equation of twisted nematic liquid crystals (TNLCs), an improved optical method for measuring the azimuthal anchoring strength of NLCs is proposed. In the given experimental setup, the rotation of the LC layer under fixing the transmission axis of the analyzer presents optical transmission curves to give information of the real twist angle. By rotating the analyzer with the obtained real twist angle in any rotation angle of the LC layer, cell thickness is calculated. From the obtained real twist angle and cell thickness, the azimuthal anchoring strength of nematic liquid crystals (NLCs) is easily determined.

Journal Article↗

PubMed2005

Improvement of the desulfurization and regeneration properties through the control of pore structures of the Zn-Ti-based H2S removal sorbents.

To improve the sulfur removing capacity of the conventional Zn-Ti-based H2S removal sorbents, a new Zn-Ti based sorbent (ZT-cp) was prepared by the coprecipitation method and tested in a packed bed reactor at middle temperature conditions (H2S absorption at 480 degrees C, regeneration at 580 degrees C). The new Zn-Ti-based sorbent showed excellent sulfur removing capacity without deactivation, even after 10 cycles of absorption and regeneration. The conventional Zn-Ti-based sorbents (ZT-700, ZT-1000), however, that were prepared by physical mixing, were continuously deactivated. In particular, the initial sulfur removing capacity of the ZT-cp sorbent showed a very high absorption value (0.22 g S/g sorbent), which corresponded to 91.6% of theoretical absorption amount. These results can be explained by the difference in physical properties such as pore volume, surface area, and particle size. It was also found that the sulfides formed from the ZT-cp and ZT-1000 sorbents with spinel structure were easily regenerated even at 580 degrees C. Those from the ZT-700 sorbent, with separated ZnO and TiO2 structures, needed a temperature higher than 610 degrees C for regeneration.

Hydrogen Sulfide↗

PubMed2005

Surface-anchoring properties related to the distribution of polyimide chains in a twisted nematic liquid-crystal cell.

On the basis of a general Rapini and Papoular equation and the unified surface-anchoring energy, surface-anchoring strength is newly defined theoretically as a function of the azimuthal deviation angle of the surface liquid-crystal directors and the statistical distribution of polyimide chains in a typical twisted nematic liquid-crystal cell. Then these are determined experimentally by the surface second-harmonic generation method, which is nonlinear optics, and the optical phase retardation method. We assume that the anisotropy distribution of polyimide chains induced by the rubbing strength is dominated by a Gaussian distribution around the rubbing direction.

Journal Article↗

PubMed2005

Relationship of cataract symptoms of preoperative patients and vision-related quality of life.

BACKGROUND: This study was conducted in an attempt to describe the status of cataract symptoms of preoperative cataract patients, as well as to determine the relationship between cataract symptom and vision-related quality of life measures. RESEARCH DESIGN: A cross-sectional study design was used. Study subjects were selected using non-probabilistic methods. The study sample consisted of 132 patients scheduled for cataract surgery in one eye. Information was obtained from study subjects by conducting face-to-face interviews. PARTICIPANTS: Study subjects were adult cataract patients at Samsung and Kunyang General Hospitals in Seoul, Korea, and Tulane University Hospital and Clinics in New Orleans, Louisiana, United States of America. MEASUREMENTS: Degree to which study subjects were "bothered" by cataract symptoms was measured by using the 5-item Cataract Symptom Scores (CSS). The number of symptoms, highest scored symptom among the five, number of symptoms extremely bothering, and the mean of cataract symptom score were created based on the CSS measure. Vision-related quality of life was assessed by using the Visual Function 14 Items (VF-14) and Global Measure of Vision (GMV) for trouble and satisfaction. RESULTS: The symptoms "blurry vision" and "worsening of vision" were most frequently reported. The symptom "colors looking different" was rarely reported among preoperative cataract patients. The degree to which study subjects were bothered by "blurry vision" and "seeing glare, halo, or rings" was highly associated with visual function, visual trouble, and visual satisfaction. Multiple regression analysis revealed that the newly developed cataract symptom-related scales, as well as total amount of degree to which study subjects were "bothered" by symptoms were highly related to vision-related quality of life measures. These relationships were persistent after controlling for major socio-demographic variables. CONCLUSIONS: The results indicate that cataract symptoms are highly associated with vision-related quality of life. The results also suggest that the number of symptoms, highest scored symptom among the five, number of symptoms extremely bothering, and the mean cataract symptom scores should be considered an important cataract symptom-related scale when analyzing quality of life, including cataract symptom.

Aged↗

PubMed2004

Effect of azimuthal anchoring strength on stability in a bistable chiral splay nematic liquid crystal device.

The stabilization of the metastable 180 degrees twist state in a bistable chiral splay nematic liquid crystal device is studied. The stability of the metastable 180 degrees twist state is explained using the azimuthal anchoring strength, which is a function of the twist elastic constant and the cell gap. A stable 180 degrees twist state as well as the permanent retention time can be obtained by increasing the anchoring energy above a certain threshold.

Journal Article↗

PubMed2004

Dependence of threshold behavior upon surface distribution of polymer chains in a twisted nematic liquid crystal.

On the basis of a general Rapini and Papoular equation and a unified surface anchoring energy theory, dependence of the threshold behavior of the liquid crystal director upon the statistical distribution of polyimide chains is theoretically investigated for a twisted nematic liquid crystal cell. We assumed that the anisotropy distribution of polyimide chains induced by the rubbing can be dominated by a Gaussian distribution around the rubbing direction. Our results show that the threshold behavior of a twisted nematic liquid crystal is affected strongly by the surface distribution of polymer chains.

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