Juwoon Park

Ginsenoside-Rs4, a new type of ginseng saponin concurrently induces apoptosis and selectively elevates protein levels of p53 and p21WAF1 in human hepatoma SK-HEP-1 cells

In this paper, we present evidence that ginsenoside-Rs4 (G-Rs4; an acetylated analogue of ginsenoside-Rg5), a new ginseng saponin isolated from Panax ginseng C. A. Meyer, elevates protein levels of p53 and p21WAF1, which are associated with the induction of apoptosis in SK-HEP-1 cells. Flow cytometric analyses showed that G-Rs4 initially arrested the cell cycle at the G1/S boundary, but consequently induced apoptosis as evidenced by generating an apoptotic peak. The induction of apoptosis was confirmed by the results of DNA fragmentation assays and alterations in cell morphology after treatment of the cells with G-Rs4. Immunoblot assays showed that G-Rs4 significantly elevated protein levels of p53 and p21WAF1, concurrently with the downregulation of both cyclins E- and A-dependent kinase activities and induction of apoptosis. We suggest that G-Rs4 induces apoptosis, the effect of which is closely related to the downregulation of both cyclins E- and A-dependent kinase activity as a consequence of selectively elevating protein levels of p53 and p21WAF1 in SK-HEP-1 cells.

A 35-60 GHz single-pole double-throw(SPDT) switching circuit using direct contact MEMS switches and double resonance technique

In this paper, a single-pole double-throw(SPDT) switching circuit was demonstrated using direct contact MEMS switches and double resonance technique for Q-band and V-band applications. The size of the fabricated SPDT switching circuit is about 1 mm/spl times/2 mm. The direct contact MEMS switches are formed on the CPW transmission lines and actuated with electrostatic force. The fabricated single-pole single-throw(SPST) MEMS switch shows the insertion loss of 0.34 dB and the isolation of 15.5 dB at 50 GHz, respectively. The responses of the fabricated SPDT switching circuit were measured with the frequencies from 0 to 100 GHz. The insertion loss is below 1 dB and isolation is better than 19 dB from 35 GHz to 60 GHz. At the center frequency of 47 GHz, the insertion loss is measured 0.45 dB and isolation is 22 dB. The actuation voltage of the switch is 35V.

Thermoresponsive Microcarriers for Smart Release of Hydrate Inhibitors under Shear Flow

The hydrate formation in subsea pipelines can cause oil and gas well blowout. To avoid disasters, various chemical inhibitors have been developed to prevent or delay the hydrate formation and growth. Nevertheless, direct injection of the inhibitors results in environmental contamination and cross-suppression of inhibition performance in the presence of other inhibitors against corrosion and/or formation of scale, paraffin, and asphaltene. Here, we suggest a new class of microcarriers that encapsulate hydrate inhibitors at high concentration and release them on demand without active external triggering. The key to the success in microcarrier design lies in the temperature dependence of polymer brittleness. The microcarriers are microfluidically created to have an inhibitor-laden water core and polymer shell by employing water-in-oil-in-water (W/O/W) double-emulsion drops as a template. As the polymeric shell becomes more brittle at a lower temperature, there is an optimum range of shell thickness that renders the shell unstable at temperature responsible for hydrate formation under a constant shear flow. We precisely control the shell thickness relative to the radius by microfluidics and figure out the optimum range. The microcarriers with the optimum shell thickness are selectively ruptured by shear flow only at hydrate formation temperature and release the hydrate inhibitors. We prove that the released inhibitors effectively retard the hydrate formation without reduction of their performance. The microcarriers that do not experience the hydration formation temperature retain the inhibitors, which can be easily separated from ruptured ones for recycling by exploiting the density difference. Therefore, the use of microcarriers potentially minimizes the environmental damages.

Hydrate formation in water-laden microcapsules for temperature-sensitive release of encapsulants

Microcapsules have been widely used to store and release active materials for various purposes. In this work, we design microcapsules that separate an inner water phase from guest molecules in the surrounding medium with a polymeric shell. The water and guest molecules are brought into contact within the shell, where a hydrate is formed when the temperature is lower than the hydrate formation condition. A steady supply of water and guest molecules through the shell matrix into the hydrates yields local cracks in the shell. As the hydrates continue to grow in the absence of external shear flow, the cracks slowly propagate along the whole shell. In contrast, in the presence of external shear, the cracks formed by the hydrate formation are rapidly widened by the shear. This is the first direct evidence presenting the effects of hydrate formation on water-laden microcapsules. We believe that the microcapsules can be further engineered to produce temperature-sensitive microcarriers for controlled delivery of specialty chemicals.