Jeong Kim

In-Situ Preparation of Highly Crystallized ZnO Nanopowders by Ultrasonic Spraying Combustion Method

To obtain a mass production of nanocrystalline ZnO powders, equipment that combines the conventional self-sustaining combustion process (SCP) with the ultrasonic spraying combustion method (USCM) were applied. The droplet was sprayed into the reaction zone of the furnace to carry out USCM that produces softly agglomerated crystalline ZnO particle with spherical shape. It was confirmed that the ZnO powder was prepared from ultrasonic spraying combustion method having smaller primary particle size, spherical shape with weak agglomeration and larger specific surface area than from conventional self-sustaining combustion method. Synthesized nanocrystalline ZnO powders have primary particle size in a range of 20∼30 nm, and specific surface area of about 20 m2/g under the optimum ultrasonic spray conditions.

Shiga Toxins Induce Apoptosis and ER Stress in Human Retinal Pigment Epithelial Cells

Shiga toxins (Stxs) produced by Shiga toxin-producing bacteria Shigella dysenteriae serotype 1 and select serotypes of Escherichia coli are the most potent known virulence factors in the pathogenesis of hemorrhagic colitis progressing to potentially fatal systemic complications such as acute renal failure, blindness and neurological abnormalities. Although numerous studies have defined apoptotic responses to Shiga toxin type 1 (Stx1) or Shiga toxin type 2 (Stx2) in a variety of cell types, the potential significance of Stx-induced apoptosis of photoreceptor and pigmented cells of the eye following intoxication is unknown. We explored the use of immortalized human retinal pigment epithelial (RPE) cells as an in vitro model of Stx-induced retinal damage. To the best of our knowledge, this study is the first report that intoxication of RPE cells with Stxs activates both apoptotic cell death signaling and the endoplasmic reticulum (ER) stress response. Using live-cell imaging analysis, fluorescently labeled Stx1 or Stx2 were internalized and routed to the RPE cell endoplasmic reticulum. RPE cells were significantly sensitive to wild type Stxs by 72 h, while the cells survived challenge with enzymatically deficient mutant toxins (Stx1A− or Stx2A−). Upon exposure to purified Stxs, RPE cells showed activation of a caspase-dependent apoptotic program involving a reduction of mitochondrial transmembrane potential (Δψm), increased activation of ER stress sensors IRE1, PERK and ATF6, and overexpression CHOP and DR5. Finally, we demonstrated that treatment of RPE cells with Stxs resulted in the activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38MAPK), suggesting that the ribotoxic stress response may be triggered. Collectively, these data support the involvement of Stx-induced apoptosis in ocular complications of intoxication. The evaluation of apoptotic responses to Stxs by cells isolated from multiple organs may reveal unique functional patterns of the cytotoxic actions of these toxins in the systemic complications that follow ingestion of toxin-producing bacteria.

Preparation of Electronic Ink Using TiO2 Particles Dispersed in Low Dielectric Solvent

An electrophoretic display using Ti0 2 particles is the most promising candidate because it offers various advantages such as ink-on-paper appearance, good contrast ratio, wide viewing angle, image stability in the off-state and extremely low power consumption. The core technology of electrophoretic display is dispersion controlling of TiO 2 nano particles in nonaqueous solution. To prepare an ink for electronic paper using TiO 2 nano particles, cyclohexane with low dielectric constant and transparency, polyethylene for producing polymer coating layer which reduces apparent density of Ti0 2 , and TiO 2 nano powders were intermixed using planetary-mill. The zeta-potential value of Ti0 2 particles in cyclohexane was measured about -40 mV, but was measured over -110 mV by dispersant attached to polyethylene-coated TiO 2 surface. Prepared electronic ink was filled in cross patterned micro-wall with 200 μm in width and 40 μm in height on ITO glass designed by photolithography. The response time of electronic paper evaluated by mobility of TiO 2 particle between micro-walls was measured 0.067sec, but the drift velocity from reflectance wave form during reverse turn of electronic ink was measured 0.07cm/sec.

Porous Silicon Layer by Electrochemical Etching for Silicon Solar Cell

An Electrochemical etching was used to form the porous silicon (PS) layer on the surface of the crystalline silicon wafer. The PS layer, in this study, will act as an antireflection coating to reduce the reflection of the incident light into the solar cell. The etching solution (electrolyte) was prepared by mixing HF (50%) and ethanol which was introduced for efficient bubble elimination on the silicon surface during etching process. The anodization of the silicon surface was performed under a constant current (galvanostat mode of the power supply), and process parameters, such as current density and etching time, were carefully tuned to minimize the surface reflectance of the heavily-doped wafer with sheet resistance between 20-30 / .