Novel UV‐induced photografting process for preparing poly(tetrafluoroethylene)‐based proton‐conducting membranes

A novel process comprising the UV‐induced photografting of styrene into poly(tetrafluoroethylene) (PTFE) films and subsequent sulfonation has been developed for preparing proton‐conducting membranes. Although under UV irradiation the initial radicals were mainly generated on the surface of the PTFE films by the action of photosensitizers such as xanthone and benzoyl peroxide, the graft chains were readily propagated into the PTFE films. The sulfonation of the grafted films was performed in a chlorosulfonic acid solution. Fourier transform infrared and scanning electron microscopy were used to characterize the grafted and sulfonated membranes. With a view to use in fuel cells, the proton conductivity, water uptake, and mechanical properties of the prepared membranes were measured. Even through the degree of grafting was lower than 10%, the proton conductivity in the thickness direction of the newly prepared membranes could reach a value similar to that of a Nafion membrane. In comparison with γ‐ray radiation grafting, UV‐induced photografting is very simple and safe and is less damaging to the membranes because significant degradation of the PTFE main chains can be avoided. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2624–2637, 2007     

A characterization of certain irreducible symplectic 4-folds

 We give a characterization of irreducible symplectic fourfolds which are given as Hilbert scheme of points on a K3 surface. Received: 26 June 2002 / Revised version: 9 September 2002 Published online: 14 February 2003 Mathematics Subject Classification (2000): Primary 14J32, Secondary 32Q20     

Wiener's test for space-time random walks and its applications

This paper establishes a criterion for whether a -dimensional random walk on the integer lattice visits a space-time subset infinitely often or not. It is a precise analogue of Wiener's test for regularity of a boundary point with respect to the classical Dirichlet problem. The test obtained is applied to strengthen the harder half of Kolmogorov's test for the random walk.

     

Pd/C-Et3N-mediated catalytic hydrodechlorination of aromatic chlorides under mild conditions

A mild and efficient one-pot procedure for the hydrodechlorination of aromatic chlorides using a Pd/C-Et₃N system was developed. A variety of aromatic chlorides could be dechlorinated at room temperature and under ambient hydrogen pressure. Et₃N activates the catalysis and is likely to work as a single electron donor in this system.     

Efficient partial hydrogenation of trichloromethyl to gem-dichloromethyl groups in platinum on carbon-catalyzed system

While gem-dichloromethyl groups can be directly synthesized by the mono-dechlorination of the corresponding trichloromethyl groups, the suppression control of the over-reduction to form chloromethyl or methyl functionalities is quite difficult. We have established the efficient and widely applicable mono-dechlorination method of the trichloromethyl groups to form the corresponding gem-dichloromethyl groups using platinum on carbon in dimethylacetamide as a specific solvent at 25 °C under a hydrogen atmosphere. The mono-dechlorination of the α,α,α-trichloromethylcarbonyl groups smoothly proceeded by the use of platinum on carbon as a catalyst in a highly chemoselective manner, while the efficient mono-dechlorination of the alkyl- and aryl-trichloromethyl groups required the combined use of Bu₃SnH.     

Rotation rate of a three-wing rotor illuminated by upward-directed focused beam in optical tweezers

The optical torque and the trapping position (focal point) in optical tweezers are analyzed for upward-directed focused laser illumination using a ray optics model, considering that laser light is incident at not only the lower surface but also the side surface of a 3-wing rotor. The viscous drag force due to the pressure and the shearing stress on all surfaces of the rotor is evaluated using computational fluid dynamics. The rotation rate is simulated in water by balancing the optical torque with the drag force, resulting in 500 rpm for an SU-8 rotor with 20 μm diameter at a laser power of 200 mW. The trapping position is estimated to be 7.6 μm in the rotor with an upward-directed laser at 200 mW via an objective lens having a numerical aperture of 1.4. Both the rotation rate and the trapping position agree well with the values obtained in the experiment.     

Hitting time of a half-line by two-dimensional random walk

We consider the probability that a two-dimensional random walk starting from the origin never returns to the half-line {(x₁,x₂)|x₁0,x₂=0} before time n. It is proved that for aperiodic random walk with mean zero and finite 2+(>2)-th absolute moment, this probability times n^1/4 converges to some positive constant c^* as . We show that c^* is expressed by using the characteristic function of the increment of the random walk. For the simple random walk, this expression gives Mathematics Subject Classification (2000):60G50, 60E10     

Pyrimidine-pyrimidine base pairs stabilized by silver(I) ions

In the presence of Ag(I) ions, the C-T and m(5)iC (5-methylisocytosine)-T base pairs showed comparable stability to the C-Ag(I)-C base pair, and the m(5)iC-C base pair was highly stabilized by the synergetic effect of Ag(I) coordination and possible hydrogen bonding.     

Electromagnetic Properties of Lanthanum Manganese Oxides Doped with Iron

The mechanism of GMR effects in La(Mn_1–x Fe _x )O₃ (x=0, 0.01, 0.03) oxides has been investigated by means of magnetic measurements, resistivity measurements in magnetic field and Mössbauer spectroscopy. For the x=0.01 sample, the GMR behavior is similar to that of the conventional (La, A)MnO₃ (A: divalent cations) oxides. For the x=0.03 sample, even though the temperature dependence of the Mössbauer spectra was similar to that of the x=0.01 sample, the mechanism for the occurrence of the GMR effect seems to be different. The x=0 sample shows a similar behavior to the x=0.03 sample. A thermal stabilization of spin fluctuation is proposed for the x=0 and x=0.03 sample.     

Impossibility of embedding the left-right symmetric GUT in an extended Supergravity

We show the impossibility of embedding left-right symmetric grand unified models in an extended supergravity a la Ellis, Gaillard, Miani, Zumino, or Derendinger, Ferrara, Savoy.