The interaction between a linear polymer and an interface is studied for three types of surfaces: reflective, attractive, and repulsive. The freely jointed chain model is assumed in the equation of diffusion approach, with volume exclusion effects neglected. In this case, the distribution function of the polymer is derived with the assumption that one or both ends of the polymer are bound to the interface. We evaluate the mean thickness of the polymer layer, the average number of adsorbed monomers, and the mean distance of the monomers from the surface. When one end of the polymer is bound to the interface, the results are qualitatively compatible with those of the previous lattice models. When both ends are bound, the polymer stays nearer to the interface but the macroscopic mean values stay qualitatively the same.

We present an analysis based on the extrapolation of finite-size results to the infinite onedimensional spin-2 dimerized isotropic Heisenberg system for the whole range of the dimerization parameter 5 (I 5 I &1) at zero temperature. This system undergoes a transition at 5=0, and a gap opens in the spectrum of elementary excitations. The exponent v, which characterizes the opening of the gap, is estimated with use of the finite-size results (with size up to N =18). We investigate two finite-size-scaling hypotheses, assuming a pure power-1aw behavior [case (1)], or taking into account logarithmic corrections [case (2)]. To estimate v, we use the derivative cf the reciprocal of the gap, the derivative of the gap, and the Callan-Symanzik function. We show that the first of these is less affected by finite-size corrections than are the other two. Using it, we have obtained, in case (1), v=0. 71+0.01, in agreement with previous estimates, and in case (2), v=0. 668+0.001, in very good agreement with the value v= -, conjectured by den Nijs. We also show that, far from criticality, the ground-state energy per site may be described by the form I 5 I" with x =1.34+0.02. However, results for the derivative of this quantity show a different functional dependence upon 5, at least for 5 & 0.4. In fact, both the values of the ground-state energy and its derivative agree with the third-order perturbation theory of Harris, with agreement improving as 5 approaches 1.

No abstract

No abstract

A high-resolution infrared spectroscopic investigation of structure related to the 0-H dipole stretching mode (around 3500 cm ') was carried out in SrTi03. We discuss various models for the position of the hydrogen impurity in the matrix and justify the position that we have suggested in a previous paper. With this new assignment, we discuss the 16 highest intensity peaks observed at low temperature.The high-energy satellites are interpreted as arising from the absorption of hydrogen impurities located on inequivalent sites. These sites are made inequivalent by a combination of the antiferrodistortive transition at 105 K and the ferroelectric fluctuations that become important when the temperature decreases.