Influence of Crystallization on the Conversion of Sm3+→Sm2+ in SrO–Bi2O3–K2O–B2O3 Glass‐Ceramics

Sm³⁺‐doped glass 13SrO–2Bi₂O₃–5K₂O–80B₂O₃ was fabricated by the conventional melt‐quenching technique. The glass‐ceramics were obtained by heating the as‐prepared glasses in air atmosphere at selected temperatures 550°C, 600°C, 615°C, and 650°C, respectively. The luminescence spectra of both Sm³⁺ and Sm²⁺ were detected in the ceramic heated at 650°C where crystalline phase is formed. The as‐prepared glass and the ceramics heated at 550°C, 600°C, and 615°C show only the emission due to Sm³⁺. In the sample heated at 650°C in air atmosphere, however, part of Sm³⁺ ions was converted to Sm²⁺, giving rise to sharp emission lines which are characteristic of Sm²⁺ in crystalline state. It is suggested that Sm²⁺ ions are located at Sr²⁺ site in the ceramic while Sm³⁺ ions are located at Bi³⁺ sites. The Sm²⁺‐doped glass‐ceramic has a high optical stability because the fluorescence intensity decreases by only about 8% of its initial value upon excitation at 488 nm Ar⁺ laser.     

Rapid dye adsorption for dye-sensitized solar cells using a simple ultrasonication method

The dye adsorption process for dye-sensitized solar cells (DSSCs) is the most rate limiting step, usually consuming up to 24 h depending on the film thickness and particle size. In this study, we propose a simple and effective method to reduce the dye adsorption time using a general bath-type ultrasonic device. Applying the ultrasonication method, the dye adsorption time was much reduced compared to the conventional dipping method for the full uptake of dye molecules. For further studies, the sole effect of solution temperature on the dye adsorption was also investigated due to the solution temperature increase during the ultrasonication process. The UV and IR absorbance analyses were performed to detect the possible structural changes of dye molecules during the ultrasonication process.     

Effect of Repetitive Lysine-Tryptophan Motifs on the Eukaryotic Membrane

In a previous study, we synthesized a series of peptides containing simple sequence repeats, (KW)_n–NH₂ (n = 2,3,4 and 5) and determined their antimicrobial and hemolytic activities, as well as their mechanism of antimicrobial action. However, (KW)₅ showed undesirable cytotoxicity against RBC cells. In order to identify the mechanisms behind the hemolytic and cytotoxic activities of (KW)₅, we measured the ability of these peptides to induce aggregation of liposomes. In addition, their binding and permeation activities were assessed by Trp fluorescence, calcein leakage and circular dichrorism using artificial phospholipids that mimic eukaryotic liposomes, including phosphatidylcholine (PC), PC/sphingomyelin (SM) (2:1, w/w) and PC/cholesterol (CH) (2:1, w/w). Experiments confirmed that only (KW)₅ induced aggregation of all liposomes; it formed much larger aggregates with PC:CH (2:1, w/w) than with PC or PC:SM (2:1, w/w). Longer peptide (KW)₅, but not (KW)₃ or (KW)₄, strongly bound and partially inserted into PC:CH compared to PC or PC:SM (2:1, w/w). Calcein release experiments showed that (KW)₅ induced calcein leakage from the eukaryotic membrane. Greater calcein leakage was induced by (KW)₅ from PC:CH than from PC:SM (2:1, w/w) or PC, whereas (KW)₄ did not induce calcein leakage from any of the liposomes. Circular dichroism measurements indicated that (KW)₅ showed higher conformational transition compared to (KW)₄ due to peptide-liposome interactions. Taken together, our results suggest that (KW)₅ reasonably mediates the aggregation and permeabilization of eukaryotic membranes, which could in turn explain why (KW)₅ displays efficient hemolytic activity.     

Effect of Nanoencapsulated Vitamin B1 Derivative on Inhibition of Both Mycelial Growth and Spore Germination of Fusarium oxysporum f. sp. raphani

Nanoencapsulation of thiamine dilauryl sulfate (TDS), a vitamin B1 derivative, was proved to effectively inhibit the spore germination of Fusarium oxysporum f. sp. raphani (F. oxysporum), as well as mycelial growth. The average diameter of nanoparticles was measured as 136 nm by being encapsulated with an edible encapsulant, lecithin, whose encapsulation efficiency was about 55% in containing 200 ppm of TDS concentration: the 100 ppm TDS nanoparticle solution showed a mycelial growth inhibition rate of 59%. These results were about similar or even better than the cases of treating 100 ppm of dazomet, a positive antifungal control (64%). Moreover, kinetic analysis of inhibiting spore germination were estimated as 6.6% reduction of spore germination rates after 24 h treatment, which were 3.3% similar to the case of treating 100 ppm of a positive control (dazomet) for the same treatment time. It was also found that TDS itself could work as an antifungal agent by inhibiting both mycelial growth and spore germination, even though its efficacy was lower than those of nanoparticles. Nanoparticles especially played a more efficient role in limiting the spore germination, due to their easy penetration into hard cell membranes and long resident time on the surface of the spore shell walls. In this work, it was first demonstrated that the nanoparticle of TDS not a harmful chemical can control the growth of F. oxysporum by using a lower dosage than commercial herbicides, as well as the inhibiting mechanism of the TDS. However, field trials of the TDS nanoparticles encapsulated with lecithin should be further studied to be effectively used for field applications.     

PG-2, a Potent AMP against Pathogenic Microbial Strains,from Potato (Solanum tuberosum L cv. Gogu Valley) Tubers Not Cytotoxic against Human Cells

In an earlier study, we isolated potamin-1 (PT-1), a 5.6-kDa trypsin-chymotrypsin protease inhibitor, from the tubers of a potato strain (Solanum tuberosum L cv. Gogu Valley). We established that PT-1 strongly inhibits pathogenic microbial strains, but not human bacterial strains, and that its sequence shows 62% homology with a serine protease inhibitor. In the present study, we isolated an antifungal and antibacterial peptide with no cytotoxicity from tubers of the same potato strain. The peptide (peptide-G2, PG-2) was isolated using salt-extraction, ultrafiltration and reverse-phase high performance liquid chromatography (RP-HPLC). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) showed the protein to have a molecular mass of 3228.5 Da, while automated Edman degradation showed the N-terminal sequence of PG-2 to be LVKDNPLDISPKQVQALCTDLVIRCMCCC-. PG-2 exhibited antimicrobial activity against Candida albicans, a human pathogenic yeast strain, and Clavibacter michiganensis subsp. michiganensis, a plant late blight strain. PG-2 also showed antibacterial activity against Staphylococcus aureus, but did not lyse human red blood cells and was thermostable. Overall, these results suggest PG-2 may be a good candidate to serve as a natural antimicrobial agent, agricultural pesticide and/or food additive.     

Electrical conductivity and thermoelectric power studies of solution-combustion-processed Ca2.76Cu0.24Co4O9

Nanocrystalline Ca_2.76Cu_0.24Co₄O₉ powders (25 nm in crystallite size) are synthesized by the solution combustion method, using aspartic acid as the combustion fuel. In this study, we discuss the effect of sintering temperature on the microstructure and thermoelectric properties of Ca_2.76Cu_0.24Co₄O₉. The density and grain size increase with an increase in sintering temperature. The Ca_2.76Cu_0.24Co₄O₉ sintered at 900 °C shows the largest value of electrical conductivity and Seebeck coefficient, resulting in the largest power factor (3.8×10^?4 W m^?1 K^?2 at 800 °C). This value is more than 22 times larger than that of the Ca_2.76Cu_0.24Co₄O₉ sintered at 940 °C (1.7×10^?5 W m^?1 K^?2 at 800 °C).     

Numerical analysis on reaction injection molding of polyurethane foam by using a finite volume method

Foam reaction injection molding (FRIM) is one of the most popular and useful processes for producing polyurethane foam with a complex geometry. A theoretical model which includes chemical reactions, foaming, and mold filling was developed to analyze FRIM. Energy balance equation was derived by considering polyurethane reaction, water-isocyanate reaction, and evaporation of physical blowing agents. Density and viscosity model was proposed for the bubble suspension, which was assumed to be a homogeneous phase. Based on the theoretical model, three-dimensional numerical simulation for mold filling of the polyurethane foam was carried out to predict flow field, flow front advancement, and density distribution during mold filling. Mold filling of a refrigerator cavity was investigated numerically. The density and thermal conductivity of the foam in the flow front was higher than those in the initially filled region.     

Effects of the Weak Absorption Tail on the Transmission Loss of Ge–Sb–Se Optical Fibers

Selenide glass optical fibers were fabricated for Ge₃₀Sb₁₀Se₅₈S₂ and Ge₂₀Sb₁₀Se₇₀ glasses. Their transmission loss has been measured and compared with the theoretical attenuation loss that was calculated taking into account the electronic transition absorption, Rayleigh scattering, and multiphonon absorption. A low attenuation loss of the Ge₂₀Sb₁₀Se₇₀ glass composition in 1.2–1.7 μm range has been expected due to its high optical band gap energy compared with the Ge₃₀Sb₁₀Se₅₈S₂ glass. However, the measured attenuation loss of the Ge₃₀Sb₁₀Se₅₈S₂ glass fiber was ∼13 dB/m at 1.5 μm while Ge₂₀Sb₁₀Se₇₀ glass showed ∼82 dB/m. An enhanced weak absorption tail due to the localized states of the Ge₂₀Sb₁₀Se₇₀ glass was responsible for this behavior. Structural defects are related to the localized states and discussed for the present glass compositions.     

Complete benzene oxidation over Pt-Pd bimetal catalyst supported on γ-alumina: influence of Pt-Pd ratio on the catalytic activity

Pt-Pd bimetal catalysts were prepared in order to develop and investigate catalysts with excellent activity and stability for benzene destruction. In the reaction results, the addition of Pt to Pd/γ-Al₂O₃ catalyst brought about the increase of catalytic activity. Moreover, it was effective in preventing the deactivation of the catalysts in benzene combustion. The addition of some amount of Pt made Pd particles available for better benzene combustion. On the contrary, the addition of Pt beyond a certain amount decreases activity because of the Pd active sites overlapped with the Pt active sites. The activity of the catalysts is related to oxidation state of metal, Pd/Al ratio and particle size on γ-Al₂O₃. These effects of Pt addition to Pd catalysts were studied by XPS, XRD, and TEM analyses.     

Surface modification of silicone rubber by ion beam assisted deposition (IBAD) for improved biocompatibility

We studied the preparation of antimicrobial silicone rubbers of improved interfacial strength, which could be formed with the ion beam assisted deposition (IBAD) technique for coating metallic or inorganic materials (silver (Ag), Copper (Cu), and Hydroxyapatite(HAp)/TiO₂) on the silicone surface. Those coating materials provide high product safety as well as outstanding antimicrobial activity. The deposition methodology is composed of pre‐etching with oxygen gas, vaporizing the coating materials, and post‐treatment with Ar ion. With the evaporation of the coating materials, the Ar beam was focused on the substrate to assist deposition. It was found out that the ion assisting depositions in the IBAD process give a prominent enhancement in adhesion between silicone rubbers and coatings of Ag and Cu. The HAp/TiO₂ coating layer was easily dissolved in aqueous saline solution. All deposited layers display high antimicrobial activities against Staphlococcus aureus (ATCC 6538) and Escherichia coil (ATCC 25,922), showing 99.9% reduction of bacteria, respectively. In a cytotoxicity test, the Ag and HAp/TiO₂ coated silicone shows a decrease of cytotoxicity, while the Cu coating leads to a slight increase of cytotoxicity. The result on the surface modifications of silicone rubber will be employed in further study for applications of medical or rehabilitation devices. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1095–1101, 2005