The group structure associated with lattice systems without constraints is extended to systems with constraints and some of its physical consequences are investigated. In particular low- and high-temperature expansions, equilibrium equations and duality transformations are analyzed within this...

We illustrate how a condensed boson system may be treated in the framework of the canonical ensemble retaining the condensate operators as operators. It is easy to obtain from this method the results of what one might call the modified grand canonical ensemble in which one has a fixed μ and...

The equilibrium properties of the classical f.c.c. Heisenberg ferromagnet are studied by Monte- Carlo techniques for small finite systems. Using the asymptotic dependence on the system size the results are extrapolated to the infinite system. The critical temperature is found to be Tc = 3.18 ±...

For Ising models with general interactions correlation-function identities of the form ΣBλB〈σB〉〈σBσA〉 = 0 are studied. It is shown that each identity of this form is equivalent to a set of special identities, in which the coefficients λB take only the values -1,0,1. A necessary and...

Using the optic-acoustic effect, measurements of the relaxation time were made after exciting the v4 mode of CD4. This was done for pure CD4 and for mixtures of CD4 with He, Ne, Ar and Kr, the results being 3.9±0.2, 1.8±0.2, 18±2, 70±15 and ≳ 100 μs at 1 atm, respectively. From the...

The Heisenberg ferromagnet with dipole-dipole interactions was studied. It was shown that the presence of dipole-dipole interactions changes the direction of the quantization axis, gives the anharmonical correction to the low temperature magnetization proportional to the square of the...

The notion of a critical exponent was first used by Van der Waals in 1893 for describing the critical behavior of the surface tension. He also noticed in the early 1890's that experimental data on capillarity indicated a nonclassical value for the surface tension exponent. Verschaffelt found...

A simple variational approach to the eigenvalue problem of the transfer operator is proposed. After reducing the transfer operator according to the symmetries of the Hamiltonian, the leading eigenvalues of the irreducible blocks can be evaluated by elementary variational principles. Hence the...

The density gradient correction to kinetic energy (nine times smaller than the original von Weizsäcker correction) has been used within local density formalism to calculate the cold compression curve of metals. Numerical results are reported for Li, Be, Al and Cu. The modifications to the...

The information theoretic surprisal analysis is employed to characterise the recent quantal close-coupling computations of rotational excitation rates by Green. The analysis is based on comparing the actual rates to the priors k0 which depend only on the temperature and the reduced “energy...