Chonbuk National University

About: Chonbuk National University is a education organization based out in Jeonju, South Korea. It is known for research contribution in the topics: Apoptosis & Graphene. The organization has 14820 authors who have published 28884 publications receiving 554131 citations.

Marginal and internal fit of all-ceramic crowns fabricated with two different CAD/CAM systems.

Abstract: This study evaluated the accuracy of marginal and internal fit between the all-ceramic crowns manufactured by a conventional double-layer computer-aided design/computer-aided manufacturing (CAD/CAM) system and a single-layer system. Ten standardized crowns were fabricated from each of these two systems: conventional double-layer CAD/CAM system (Procera) and a single-layer system (Cerec 3D). The copings and completed crowns were seated on the abutments by a special device that facilitated uniform loading, and the marginal discrepancies were measured. Internal gaps were also measured using a low-viscosity silicone material. Marginal discrepancies of Procera copings were significantly smaller than those of Procera crowns and Cerec 3D crowns (p 0.05). On internal gaps, Cerec 3D crowns showed significantly larger internal gaps than Procera copings and crowns (p < 0.05). Within the limitations of this study, the single-layer system demonstrated acceptable marginal and internal fit.

Ovicidal and adulticidal effects of Eugenia caryophyllata bud and leaf oil compounds on Pediculus capitis.

Abstract: The toxicity of Eugenia caryophyllata bud and leaf oil-derived compounds (acetyleugenol, beta-caryophyllene, eugenol, alpha-humulene, and methyl salicylate) and congeners of eugenol (isoeugenol and methyleugenol) against eggs and females of Pediculus capitis was examined using direct contact application and fumigation methods and compared with those of the widely used delta-phenothrin and pyrethrum. In a filter paper diffusion bioassay with female P. capitis, the pediculicidal activity of the Eugenia bud and leaf oils was comparable to those of delta-phenothrin and pyrethrum on the basis of LT(50) values at 0.25 mg/cm(2). At 0.25 mg/cm(2), the compound most toxic to female P. capitis was eugenol followed by methyl salicylate. Acetyleugenol, beta-caryophyllene, alpha-humulene, isoeugenol, and methyleugenol were not effective. Eugenol at 0.25 mg/cm(2) was as potent as delta-phenothrin and pyrethrum but was slightly less effective than the pyrethroids at 0.125 mg/cm(2). Against P. capitis eggs, methyl salicylate and eugenol were highly effective at 0.25 and 1.0 mg/cm(2), respectively, whereas little or no activity at 5 mg/cm(2) was observed with the other test compounds as well as with delta-phenothrin and pyrethrum. In fumigation tests with female P. capitis at 0.25 mg/cm(2), eugenol and methyl salicylate were more effective in closed cups than in open ones, indicating that the effect of the compounds was largely due to action in the vapor phase. Neither delta-phenothrin nor pyrethrum exhibited fumigant toxicity. The Eugenia bud and leaf essential oils, particularly eugenol and methyl salicylate, merit further study as potential P. capitis control agents or lead compounds.

Sulfonated graphene oxide/Nafion composite membranes for high temperature and low humidity proton exchange membrane fuel cells

Abstract: Iron oxide (Fe3O4) nanoparticles anchored over sulfonated graphene oxide (SGO) and Nafion/Fe3O4–SGO composites were fabricated and applied as potential proton exchange membranes in proton exchange membrane fuel cells (PEMFCs) operated at high temperature and low humidity. Fe3O4 nanoparticles bridge SGO and Nafion through electrostatic interaction/hydrogen bonding and increased the intrinsic thermal and mechanical stabilities of Nafion/Fe3O4–SGO composite membranes. Nafion/Fe3O4–SGO composite membranes increased the compactness of ionic domains and enhanced the water absorption and proton conductivity while restricting hydrogen permeability across the membranes. The proton conductivity of Nafion/Fe3O4–SGO (3 wt%) composite membrane at 120 °C under 20% relative humidity (RH) was 11.62 mS cm−1, which is 4.74 fold higher than that of a pristine recast Nafion membrane. PEMFC containing the Nafion/Fe3O4–SGO composite membrane delivered a peak power density of 258.82 mW cm−2 at a load current density of 640.73 mA cm−2 while operating at 120 °C under 25% RH and ambient pressure. In contrast, under identical operating conditions, a peak power density of only 144.89 mW cm−2 was achieved with the pristine recast Nafion membrane at a load current density of 431.36 mA cm−2. Thus, Nafion/Fe3O4–SGO composite membranes can be used to address various critical problems associated with commercial Nafion membranes in PEMFC applications.

Red-to-Ultraviolet Emission Tuning of Two-Dimensional Gallium Sulfide/Selenide.

Abstract: Graphene-like two-dimensional (2D) nanostructures have attracted significant attention because of their unique quantum confinement effect at the 2D limit. Multilayer nanosheets of GaS-GaSe alloy are found to have a band gap (Eg) of 2.0-2.5 eV that linearly tunes the emission in red-to-green. However, the epitaxial growth of monolayers produces a drastic increase in this Eg to 3.3-3.4 eV, which blue-shifts the emission to the UV region. First-principles calculations predict that the Eg of these GaS and GaSe monolayers should be 3.325 and 3.001 eV, respectively. As the number of layers is increased to three, both the direct/indirect Eg decrease significantly; the indirect Eg approaches that of the multilayers. Oxygen adsorption can cause the direct/indirect Eg of GaS to converge, resulting in monolayers with a strong emission. This wide Eg tuning over the visible-to-UV range could provide an insight for the realization of full-colored flexible and transparent light emitters and displays.