Characterization of fibril reinforced membranes for fuel cells

Characteristics of fibril reinforced membranes developed by Asahi Glass Company are reviewed. PTFE-fibrils <1 μm in diameter are dispersed in ion-exchange membranes uniformly. Mechanical properties, such as tensile strength, tear strength, creep property and compressive property were examined and compared with non-reinforced membranes. Fibril reinforced membranes, even by the addition of a small amount of PTFE-fibrils (2.7 wt.%), show excellent mechanical strength, especially in creep and tear strength. Cell performance is nearly equal to the one using a non-reinforced membrane and cell voltage stays about the same during the cell operation at 80 °C for 3000 h.     

Output and picosecond amplification characteristics of an efficient and high-power discharge excimer laser

Improvements in output pulse energy and efficiency of a conventional capacitor-transfer-type discharge excimer laser with automatic preionization have been achieved by extending the discharge volume and resulting moderate pumping of the active medium. The discharge laser produces a pulse energy of more than 1 J for XeCl, KrF, and ArF lasers in square beams of about 2×2 cm², and the maximum overall efficiency observed is 2.9% for XeCl, 3.2% for KrF and 1.8% for ArF. The laser device has been involved in a picosecond ( 32 ps) XeCl laser amplification system, and was operated as an amplifier at a repetitive frequency of 10 Hz. Saturation fluence for XeCl laser was measured to be 1.4 mJ/cm², and the picosecond pulse energy of 40 mJ was extracted from the amplifier.On leave from Ebara Corp., 6-6-7, Ginza, Chuo-ku, Tokyo 104, JapanOn leave from Mitsubishi Heavy Industries, LTD., 4-6-22, Kan-on shinmachi, Nishi-ku, Hiroshima 733, Japan     

Tunneling conductance of a Bi2Sr2CaCu2O8-SnO2 junction along the c-axis

fine structure was observed in the conductance curve of a tunneling junction composed of a single crystalline Bi2212 and an evaporated SnO₂ film. It is similar to those of Bi2212-GaAs mechanical junctions and there is a certain correspondence between the structure and the phonon density of states. Thus the previous conclusion that the structure is due to phonons has been complemented by this work. The energy gap 2 was 57 meV at 13 K and T _c was 78 K. 2(0)/k _B T _c is then 8.3. (T) showed the BCS-like temperature dependence.     

Photodynamic Efficiency of Protoporphyrin IX: Comparison of Endogenous Protoporphyrin IX Induced by 5-Aminolevulinic Acid and Exogenous Porphyrin IX

Abstract— Photodynamic efficiency of protoporphyrin IX (PP) accumulated in HeLa cells by the incubation of PP with HeLa cells was compared with that of accumulated PP formed from 5-aminolevulinic acid (ALA) as a precursor. The ALA-induced PP was photodynamically more efficient than exogenous PP. The difference is caused by monomelic PP concentration and PP localization site in HeLa cells. Exogenous PP was accumulated mainly in plasma membrane, and the membrane was strongly damaged by irradiation. The ALA-induced PP was selectively accumulated in mitochondria and inactivated the mitochondrial function by irradiation.     

Energy transfer reaction of cationic porphyrin complexes on the clay surface: effect of sample preparation method

Photochemical energy transfer of non-aggregated cationic porphyrins on an anionic-type clay (Smecton SA) surface was investigated. The efficiency of energy transfer and excited-state quenching in the absence of energy transfer were evaluated at various loading levels of porphyrin on the clay surface and were found to be significantly affected by the loading level. As the latter increased, both energy transfer efficiency and excited-state quenching increased. Judging from the dependency of energy-transfer efficiency on the porphyrin loading level, a partially clustered structure, but without aggregation, of porphyrins on the clay surface is proposed.     

Palladium-catalyzed preparation of α-allyl esters and α,β-unsaturated esters from saturated esters via their silyl acetals

Reaction of ketene silyl acetals with allylic carbonates in the presence of palladium-phosphine catalyst in dioxane gives α-allyl esters in high yields. When the reaction is carried out with phosphine-free palladium catalyst in nitriles, α,β-unsaturated esters are obtained in good yields.     

Energy Dissipation Processes of singlet‐excited 1‐Hydroxyfluorenone and its Hydrogen‐bonded Complex with N‐methylimidazole¶

Effects of solvent, pH and hydrogen bonding with N‐methylimidazole (MIm) on the photophysical properties of 1‐hydroxyfluorenone (1HOF) have been studied. Fluorescence lifetime, fluorescence quantum yield and triplet yield measurements demonstrated that intersystem crossing was the dominant process in apolar media and its rate constant significantly diminished with increasing solvent polarity. The acceleration of internal conversion in alcohols paralleled the strength of intermolecular hydrogen bonding. The faster energy dissipation from the singlet‐excited state in cyclohexane was attributed to intramolecular hydrogen bonding. The pK_a of 1HOF decreased from 10.06 to 5.0 on light absorption, and H₃O⁺ quenched the singletexcited molecules in a practically diffusion‐controlled reaction. On addition of MIm in toluene, dual fluorescence was observed, which was attributed to reversible formation of excited hydrogen‐bonded ion pair. Rate constants for the various deactivation pathways were derived from the combined analysis of the steady‐state and the time‐resolved fluorescence results.     

Determination of selenium in human serum by liquid chromatography/electron capture atmospheric pressure chemical ionization mass spectrometry after acid digestion and derivatization using 2,3-diaminonaphthalene

Analysis of selenium in biological samples is very important and numerous analytical methods for the element have been developed. One of the most convenient and widely used methods for routine determination of serum selenium is a fluorometric method using 2,3-diaminonaphthalene (DAN); however, this method lacks specificity. We observed that 4,5-benzopiazselenol (BPS), a selenium derivative of DAN, is ionized with electron capture in an atmospheric pressure chemical ionization (APCI) interface, and subsequently established a method for determining total human serum selenium by means of liquid chromatography/atmospheric pressure chemical ionization mass spectrometry. All pretreatment procedures were carried out in a single test tube to minimize selenium loss. The recovery of organic or inorganic selenium spiked to human serum was 97-103%.The detection limit of BPS was equivalent to 0.2 ng of selenium and the lower quantitative limit of serum selenium was 10 ng mL(-1). The coefficient of variation of standard concentrations in control serum samples was 4.5%. The purity of the observed peak obtained from serum samples was confirmed using the ion cluster technique.     

Ruthenium‐Catalyzed Cycloisomerization of 2,2′‐Diethynyl‐ biphenyls Involving Cleavage of a Carbon–Carbon Triple Bond

A ruthenium complex catalyzes a new cycloisomerization reaction of 2,2′‐diethynylbiphenyls to form 9‐ethynylphenanthrenes, thereby cleaving the carbon–carbon triple bond of the original ethynyl group. A metal–vinylidene complex is generated from one of the two ethynyl groups, and its carbon–carbon double bond undergoes a [2+2] cycloaddition with the other ethynyl group to form a cyclobutene. The phenanthrene skeleton is constructed by the subsequent electrocyclic ring opening of the cyclobutene moiety.