High efficiency discharge-pumped XeCl laser

Received: 19 March 1997/Revised version: 7 August 1997     

Electrochemical pressure impedance spectroscopy for investigation of mass transfer in polymer electrolyte membrane fuel cells

Mass transfer phenomena in membrane fuel cells are complex and diversified because of the presence of complex transport pathways including porous media of very different pore sizes and possible formation of liquid water. Electrochemical impedance spectroscopy, although allowing valuable information on ohmic phenomena, charge transfer and mass transfer phenomena, may nevertheless appear insufficient below 1 Hz. Use of another variable, that is, back pressure, as an excitation variable for electrochemical pressure impedance spectroscopy is shown here a promising tool for investigations and diagnosis of fuel cells.     

Zigzag lines in a (001)Si low-angle twist boundary

A low angle twist boundary formed by bonding an ultrathin (001) silicon film onto a (001) silicon wafer is investigated using two-beam transmission electron microscopy to identify positively zigzag lines which separate large interfacial regions formed by square networks of 1/2? 110 ? screw misfit dislocations. An approach to the elastic field of a zigzag line is proposed from the repetitive use of angular dislocations added to a ribbon-like uniform distribution of infinitesimal dislocations parallel to a family of pure screw misfit dislocations. Theoretical and experimental images of successive triple nodes are compared to derive the unique set of Burgers vectors attached to a zigzag line. In principle, this approach can be applied to any elongated hexagonal mesh of a dislocation network.     

Continuous-wave tunnel ring fiber laser

The continuous-wave oscillation of a tunnel ring fiber laser is demonstrated. The high losses encountered in tunneling systems are compensated for by a high-gain amplifying medium from barrier widths for 0 to lambda/2. The experimental observations are in good agreement with a simple theoretical model. This near-field probe system allows one to detect small displacements in the picometer range.     

A new behaviour of the interstitial element H or D in solution in rare-earth metal

The study of the resistivity of the Lu-(H or D) system makes clear certain characteristics of the α phase and indicates a change for the interstitial element in the transition range 170–400°C. On both sides of this domain an appreciable difference is observed in the properties of the solid solution. The α1 phase of the domain below 170°C has a higher resistivity and a maximum hydrogen concentration independent of the temperature. For the phase α of the domain above 400°C, the expansions both with the concentration growth and with the rise in temperature are isotropic contrary to the α1 phase.The resistivity and X-ray diffraction studies, taking into account the lattice symmetry, allow us to conclude that a change may occur in the type of interstices filled by the hydrogen atoms, tetrahedral for the α phase and octahedral with H atoms associating in pairs for the α1 phase. Among the lanthanide metals, we find that only lutetium and thulium, in uniting with H or D, have the low temperature α1 phase.