Preparation of hydrophilic plasma–polymers derived from oxygen-containing organic monomers

Plasma polymerization of nine oxygen-containing organic monomers was surveyed for producing hydrophilic films on solid substrates on due consideration of chemical structures of the monomers, operative conditions for plasma polymerization, and resultant film characters. The wettability of the polymer films were evaluated by measuring the contact angles of water on the film surfaces while the power consumption was compared as the lowest wattage needed for sustaining normal deposition rates of the polymer films. It has been found that the monomers involving the triple bond in the chemical structure conducted plasma polymerization under very low wattage of radiofrequency power, and at the same time the deposition rate was relatively high. With respect to the chemical structures of the monomers, the hydroxyl group tended to initiate and sustain the electric discharge at somewhat lower power than other functional groups. Highly hydrophilic polymer films could, thus, be obtained under a soft plasma condition by using propargyl alcohol (2-propyn-1-ol) as a monomer having the triple bond and the hydroxyl group. X-Ray photoelectron spectra of the polymers suggested that the wettability was not simply dependent upon oxygen atom content of the polymers, but also dependent upon spatial arrangement of the oxygen atoms within the polymer molecules. © 1996 John Wiley & Sons, Inc.     

Ex vivo evidence for asymmetric tyrosine phosphorylation of ZAP-70 on double-positive thymocytes in the positive selection process

Antigen stimulation via TCR in mature T cells provides rapid induction of tyrosine phosphorylation of intracellular substrates including ZAP-70. To study the potential involvement of tyrosine phosphorylation in CD4+CD8+ [double-positive (DP)] thymocytes in the positive selection process in vivo, we isolated and analyzed them in the presence of phosphatase inhibitor. DP thymocytes were obtained from TCR transgenic mice (TCR-Tg) expressing MHC class I- or class II-restricted TCR in selecting and non-selecting MHC backgrounds respectively. The phosphorylation of ZAP-70 in DP thymocytes of class I-restricted TCR-Tg was significantly higher in the positively selecting background than in the non-selecting one. However, such a phosphorylation difference between selecting and non-selecting TCR-Tg was found to be considerably less in class II-restricted TCR-Tg. A similar bias for ZAP-70 phosphorylation was also observed on selecting DP thymocytes when I-A(beta) deficient- and beta2-microglobulin-deficient mice were compared. These ex vivo studies suggest that TCR-mediated signaling on DP thymocytes induces ZAP-70 phosphorylation under a different manner of engagement of TCR to class I and class II molecules in the positive selection process.     

Applying path‐counting methods for measuring the robustness of the network‐structured system

We consider the path‐counting problem that asks how many paths exist between any two different nodes in a network after deleting an arbitrary number of edges or nodes from the original network. Using path‐counting methods, we propose a quantitative method for measuring the robustness of the network‐structured system. First we define the connectivity function and attempt to obtain the expected connectivity function for the network. Applying the Monte Carlo method, we estimate expected edge deletion and node deletion connectivity functions when an arbitrary number of edges or nodes are deleted from the original network. We attempt to approximate the expected edge deletion connectivity function using an appropriate nonlinear function with two parameters. We also show the numerical results of applying the path‐counting method with their analysis in order to quantitatively evaluate the connectivity for some special types of networks.     

Carrier mobility in ethylene-vinylacetate copolymer estimated bytransient space charge

Carrier mobility in an ethylene vinyl acetate (EVA) copolymer film was measured by a new technique. The time-dependent charge distribution was monitored by the pulsed-electroacoustic method when a pulse voltage was superposed on a dc bias voltage. A positive charge packet was injected from the anode soon after the pulse application, and moved towards the cathode. It was suggested from the movement of the charge packet that the mobility of the positive carrier at 10 to 60 MV/m was in the order of 10^-13 m²/Vs at room temperature. When the pulse voltage was very high, a charge packet appeared within the bulk, suggesting that carrier dissociation takes place     

Laying season and egg shell cracks on the growth of Salmonella enteritidis in the egg albumen during storage

We studied the effects of laying seasons and egg shell cracks on the ability of egg albumen to support the growth of Salmonella Enteritidis (SE) in eggs. Hens eggs used were those laid in February, June, and October in a farm in Japan and stored at 10, 20, and 30 degrees C, and at 30 degrees C after storage at 10 degrees C, immediately after receipt or after cracking the shell. At several-day intervals during storage, the egg contents were poured into a dish, SE was inoculated into albumen, and then the growth of SE during 3 days incubation at 18 degrees C was measured. The results demonstrated that storage temperature and laying season affected the growth of SE in the egg albumen. The proportion of eggs upon which albumen allowed the growth of SE was higher in the eggs stored at 30 degrees C than those stored at 10 degrees C. The growth of SE in eggs was lowest in the following order of laying: February, October, and June. SE grew preferably in albumen of cracked eggs than intact eggs.     

Single Crystal Growth and Effect of Doping on Structural, Transport and Magnetic Properties of A1?xKxFe2As2 (A = Ba, Sr)

We demonstrate the preparation of large, free-standing iron pnictide single crystals with a size up to 20×10×1 mm³ using solvents in zirconia crucibles under argon atmosphere. Transport and magnetic properties have been investigated to study the effect of potassium doping on the structural and superconducting property of the compounds. The spin density wave (SDW) anomaly at T _s ∼138 K in BaFe₂As₂ single crystals from self-flux shifts to T _s ∼85 K due to Sn solvent growth. We show evidence for an incorporation of Sn on the Fe site. The electrical resistivity data show a sharp superconducting transition temperature T _c ∼38.5 K for a single crystal of Ba_0.68K_0.32Fe₂As₂. A nearly 100% shielding fraction and the bulk nature of the superconductivity for the single crystal are confirmed by magnetic susceptibility data. A sharp transition T _c ∼25 K occurs for the single crystal of Sr_0.85K_0.15Fe₂As₂. There is direct evidence for a coexistence of the SDW and superconductivity in the low doping regime of Sr_1−x K _x Fe₂As₂ single crystals. Structural implications of the doping effects as well as the coexistence of the two order parameters are discussed.     

Highly loaded silicone nanocomposite exhibiting quick thermoresponsive optical behavior

Bulk silicone nanocomposites with thermoresponsive optical behavior were fabricated using silica nanoparticle fillers within a cross-linked silicone matrix. Silica nanoparticles (25 nm diameter) were surface-modified, allowing for even distribution at 6-24 wt % within and covalent bonding to the silicone matrix. Utilizing the temperature-dependent match/mismatching of the refractive indices of the silica nanoparticle filler and the silicone matrix, bulk nanocomposites are highly transparent at room temperature and demonstrate significant increases in opacity with increasing temperature up to 100-150 °C. Such a response could be cycled quickly and repeatedly with no detrimental effect on the material.     

Lamination of alumina membranes to polymer surfaces: thick, hard, transparent, crack-free alumina films on polymers with excellent adhesion

Hard and transparent alumina (Al(2)O(3)) films with thicknesses in the range of 500 nm to 5 μm were successfully formed on polymethylmethacrylate (PMMA) and polystyrene (PS) surfaces. Our process is based on a lamination of anodized aluminum membranes (AAMs) to the polymer surfaces, followed by chemical etching. Because of capillary force, molten PS and liquid PMMA precursor were successfully pulled into the nanopores (10 nm diameter) within the Al(2)O(3) layers and solidified by cooling or polymerization, respectively. Our resulting AAM-laminated surfaces exhibited excellent adhesion and surface mechanical properties similar to those of fused silica, remaining crack-free and transparent even with Al(2)O(3) thicknesses exceeding 1 μm.