Intersegmental interaction and critical concentrations in PET–HFIP solutions

Spectroscopic determinations of the concentrations associated with the onset of intermolecular interaction in solutions of poly(ethylene terephthalate) (PET) are described. The intersegment forces perturb the electronic spectra and induce ground-state aggregation. These phenomena become observable at different chain densities, reflecting the influence of concentration on the coil dimensions, as well as the dynamical nature of the interactions. An estimate of the equilibrium constant for PET dimer formation in hexafluoroisopropanol is reported.     

A new interpretation of quantum mechanics and its consequences in epistemology

A rather recent interpretation of quantum mechanics, known under the various names of consistent histories, decohering histories, or logical interpretation, has brought interpretation into a standard deductive theory and is now investigated in many places. A key difference with the Copenhagen interpretation is the status of classical physics, now derived completely from quantum principles in both its dynamical and logical aspects. After describing briefly this new interpretation in its essentials, leaving aside technical details, it is shown how its consequences in epistemology differ drastically from the familiar outcomes of the Copenhagen interpretation, leading in particular to a well-defined theory of knowledge. Some more speculative philosophical consequences associated with the unsolved problem of actuality are also mentioned.     

Superconductivity-induced phonon self-energy effects in high-T c superconductors

The superconductivity-induced self-energy of phonons has been calculated in the lowest-order conserving approximation using conventional strong-coupling theory and also including scattering at nonmagnetic impurities. Results for the dependence of the shift and the width of phonons on temperature and scattering rates are presented and their sensitivity on the strength of the electron-phonon coupling and on impurities is pointed out. The theory is applied to optical data in YBa₂Cu₃O₇ using the experimental one-phonon density, the value ofT _c and [^*=0.25 as inputs. Neglecting anisotropies and the momentum dependence of the electron-phonon coupling the resulting strong-coupling model with 2.9 yields results which are in good agreement with the data, in particular, if impurity scattering is taken into account.