Light-front versus Bethe-Salpeter forms of two nucleon amplitudes

We discuss the relation between the two nucleon Bethe-Salpeter amplitude and the light front wave functions. Both approaches provide a covariant description for the deuteron bound state and the two nucleon scattering state. A comparison is done for the spin-orbit functions as well explicit integrals are given on the basis of the Nakanishi integral representation method.Comment: 13 pages, Few Body Systems format needs fbsart11.sty, fbsedit2.st

Systematic study of effect of cross-drafts and nozzle diameter on shield gas coverage

A shield gas flow rate of 15–20 L min21 is typically specified in metal inert gas welding, but is often adjusted to as high as 36 L min21 by welders in practice. Not only is this overuse of shield gas wasteful, but uncontrolled high gas flows can lead to significant turbulence induced porosity in the final weld. There is therefore a need to understand and control the minimum shield gas flow rate used in practical welding where cross-drafts may affect the coverage. Very low gas coverage or no shielding leads to porosity and spatter development in the weld region. A systematic study is reported of the weld quality achieved for a range of shield gas flow rates, cross-draft speeds and nozzle diameters using optical visualisation and numerical modelling to determine the shield gas coverage. As a consequence of the study, the shield gas flow has been reduced to 12 L min21 in production welding, representing a significant process cost saving and reduced environmental impact with no compromise to the final weld quality

Photoinduced melting of superconductivity in the high-Tc superconductor La2-xSrxCuO4 probed by time-resolved optical and THz techniques

Dynamics of depletion and recovery of superconducting state in La2-xSrxCuO_4 thin films is investigated utilizing optical pump-probe and optical pump - THz probe techniques as a function of temperature and excitation fluence. The absorbed energy density required to suppress superconductivity is found to be about 8 times higher than the thermodynamically determined condensation energy density and nearly temperature independent between 4 and 25 K. These findings indicate that during the time when superconducting state suppression takes place (~0.7 ps), a large part (nearly 90%) of the energy is transferred to the phonons with energy lower than twice the maximum value of of the SC gap and only 10% is spent on Cooper pair breaking.Comment: 8 pages, 5 figure