A systematic calculation of magnetization and specific heat contributions due to fluctuations of vortex lattice in strongly type II superconductors to precision of 1% is presented. We complete the calculation of the two loop low temperature perturbation theory by including the umklapp processes. Then the gaussian variational method is adapted to calculation of thermodynamic characteristics of t...

We propose a quantitative estimate of the charge gap that opens in the onedimensional dimerized Hubbard model at quarter-filling due to dimerization, which makes the system effectively half–filled, and to repulsion, which induces umklapp scattering processes. Our estimate is expected to be valid for any value of the repulsion and of the parameter describing the dimerization. It is based on anal...

We present analytic results for ground-state properties of Hubbard-type models in terms of the Gutzwiller variational wave function with nonzero values of the magnetization m. In dimension D51 approximation-free evaluations are made possible by appropriate canonical transformations and an analysis of umklapp processes. We calculate the double occupation and the momentum distribution, as well as...

Making use of the classical second-moment sum rule, it is possible to convert a series of constant-Q x-ray Brillouin scattering scans (Q momentum transfer) into a series of constant frequency scans over the measured Q range. The method is applied to literature results for the longitudinal phonon dispersion in several glass formers. The constant frequency scans are well fitted in terms of a Q-in...

Thermal transport measurements in multi-wall carbon nanotube (MWCNT) bundles at elevated temperatures up to 830 K are reported using a novel generalized electrothermal technique. Compared with individual CNTs, the thermal conductivity (k) of MWCNT bundles is two to three orders of magnitude lower, suggesting the thermal transport in MWCNT bundles is dominated by the tube-to-tube thermal contact...

Angular momentum conservation is a physical law that must be obeyed in any closed system. However, it is well known from standard textbooks that in the case of interactions with phonons a part of the total momentum and of the total angular momentum can be absorbed by the whole crystal and is then no longer considered (cf. e.g. the Mössbauer effect[1] and the Umklapp process[2]). Therefore, ther...

The role of non polar optic phonon scatterin g and of umklapp acoustic phonon scattering is analy zed for a delocali zed p ositroni um atom in ionic crystals at elev ated temp eratures. A t temp eratures above w hich they become essential both of these scattering mechanisms contribute to the imagina ry self-energy of p ositroni um renormalizi ng its acoustic deformation potential constant. I t ...