Significant progress was made in recent years in the understanding of the proton spin kinetics in polymer melts. Generally, the proton spin kinetics is determined by intramolecular and intermolecular magnetic dipole-dipole contributions of proton spi
ns. During many decades it was postulated that the main contribution is a result of intramolecular magnetic dipole-dipole interactions of protons belonging to the same polymer segment. It appears that this postulate is far from reality. The relative weights of intra- and intermolecular contributions are time dependent and sensitive to details of polymer chain dynamics. It is shown that for isotropic models of polymer dynamics the influence of the intermolecular magnetic dipole-dipole interactions increases faster with increasing evolution time (i.e. decreasing frequency) than the corresponding influence of the intramolecular counterpart. On the other hand, an inverted situation is predicted by the tube-reptation model: here the influence of the intramolecular magnetic dipole-dipole interactions increases faster with time than the contribution from intermolecular interactions. The intermolecular contribution in the proton relaxation of polymer melts can experimentally be isolated using the isotope dilution technique and this opens a new perspective for experimental investigations of polymer dynamics by proton NMR.
A systematic connection between QCD and nuclear few- and many-body properties in the form of the Effective Field Theory without pions is applied to $Ale 6$ nuclei to determine its range of applicability. We present results at next-to-leading order fo
r the Tjon correlation and for a correlation between the singlet S-wave $^3$He-neutron scattering length and the triton binding energy. In the A=6 sector we performed leading order calculations for the binding energy and the charge and matter radii of the halo nucleus $^6$He. Also at leading order, the doublet S-wave 4-He-neutron phase shifts are compared with R-matrix data. These analysis provide evidence for a sufficiently fast convergence of the effective field theory, in particular, our results in $Ale 4$ predict an expansion parameter of about 1/3, and they converge to data within the predicted uncertainty band at this order. A properly adjusted three-body contact force which we include together with the Coulomb interaction in all calculations is found to correctly renormalize the pion-less theory at leading- and next-to-leading order, i.e. the power counting does not require four-body forces at the respective order.
