On the slow decay ofO(2) correlations in the absence of topological excitations: Remark on the Patrascioiu-Seiler model

For spin models withO(2)-invariant ferromagnetic interactions, the Patrascioiu-Seiler constraint is |arg(S(x))–arg(S(y))|₀ for all |x–y|=1. It is shown that in two-dimensional systems of two-component spins the imposition of such contraints with ₀ small enough indeed results in the suppression of exponential clustering. More explicitly, it is shown that in such systems on every scale the spin-spin correlation function obeys S(x)·S(y)1/(2|x–y|²) at any temperature, includingT=. The derivation is along the lines proposed by A. Patrascioiu and E. Seiler, with the yet unproven conjectures invoked there replaced by another geometric argument.Dedicated to Oliver Penrose on the occasion of his 65th birthday.     

Nuclear probes in life sciences

The nuclear quadrupole interaction at metal sites in macromolecules monitored by time differential perturbed angular correlation provides information on the local environment of metal ions residing at these sites. This information is obtained in the ultra-trace regime and is, therefore, extremely valuable for research on reaction pathways of enzymatic heavy metal detoxification, for the development of radiopharmaceuticals, for investigations into protein architectures on surfaces, and for environmental research. This revised version was published online in August 2006 with corrections to the Cover Date.     

Unforeseen properties of MnAs epilayers grown on GaAs semiconductor

This paper reviews some recent works performed on MnAs/GaAs thin films and other related structures grown by molecular beam epitaxy. The impact of epitaxy on the magneto-structural properties of MnAs and possible applications of MnAs epilayers are discussed. A brief account of recent results obtained on the magneto-transport in MnAs/GaAs/MnAs magnetic tunnel junctions is also given, highlighting several appealing and promising properties of this system for spintronics applications.     

Magnetically assisted gas-solid fluidization in a tapered vessel:Part II Dimensionless bed expansion scaling

The article presents an effort to create dimensionless scaling correlations of the overall bed porosity in the case of magnetically assisted fluidization in a tapered vessel with external transverse magnetic field. This is a stand of portion of new branch in the magnetically assisted fluidization recently created concerning employment of tapered vessels. Dimensional analysis based on "pressure transform" of the initial set of variables and involving the magnetic granular Bond number has been applied to deve...     

Witten Laplacian Method for The Decay of Correlations

The aim of this paper is to apply direct methods to the study of integrals that appear naturally in Statistical Mechanics and Euclidean Field Theory. We provide weighted estimates leading to the exponential decay of the two-point correlation functions for certain classical convex unbounded models. The methods involve the study of the solutions of the Witten Laplacian equations associated with the Hamiltonian of the system.     

Slow Rates of Mixing for Dynamical Systems with Hyperbolic Structures

We consider invertible discrete-time dynamical systems having a hyperbolic product structure in some region of the phase space with infinitely many branches and variable return time. We show that the decay of correlations of the SRB measure associated to that hyperbolic structure is related to the tail of the recurrence times. We also give sufficient conditions for the validity of the Central Limit Theorem. This extends previous results by Young in (Ann. Math. 147: 585–650, [1998]; Israel J. Math. 110: 153–188, [1999]). Work carried out at the Federal University of Bahia, University of Porto and IMPA. J.F.A. was partially supported by FCT through CMUP and POCI/MAT/61237/2004. V.P. was partially supported by PADCT/CNPq and POCI/MAT/61237/2004.     

Normal and superconducting state in the presence of forward electron-phonon and impurity scattering

By assuming that the superconducting pairing is due to the forward E-P scattering (FEP pairing) it is shown that the critical temperature of clean systems depends linearly on the E-P coupling constant and the isotope effect is very small. Impurities with the pronounced forward scattering (FS impurities) change analytical properties of the quasiparticle Green's function substantially compared to the case of the isotropic scattering. The FS impurities are pair-breaking and affect in the same way s- and d-wave FEP pairing making in the dirty limit.The usual isotropic impurity scattering is pair-weakening for s-wave and pair-breaking for the d-wave FEP pairing. Received 1st July 1998     

$ \Phi$ -variable calculated for the mixture of thermal sources

The -variable, a measure of statistical correlation of particle momenta, introduced by Mrówczyński and Gaździcki, has been calculated for the events simulated with a simple thermal toy model. It is shown that mixing two thermal sources of unequal temperature can result in negative values of .