C. Meyers

Adsorption of line segments on a square lattice.

We study the deposition of line segments on a two-dimensional square lattice. The estimates for the coverage at jamming obtained by Monte Carlo simulations and by seventh-order time-series expansion are successfully compared. The nontrivial limit of adsorption of infinitely long segments is studied, and the lattice coverage is consistently obtained using these two approaches.

Magnetic and thermal properties of 4 f − 3 d ladder-type molecular compounds

We report on the low-temperature magnetic susceptibilities and specific heats of the isostructural spin-ladder molecular complexes L 2 [M(opba)] 3 .xDMSO. y H 2 O, hereafter abbreviated by L 2 M 3 (where L=La, Gd, Tb, Dy, Ho and M=Cu. Zn). The results show that the Cu containing complexes (with the exception of La 2 Cu 3 ) undergo long-range magnetic order at temperatures below 2 K, and that for Gd 2 Cu 3 this ordering is ferromagnetic, whereas for Tb 2 Cu 3 and Dy 2 Cu 3 it is probably antiferromagnetic. The susceptibilities and specific heats of Tb 2 Cu 3 and Dy 2 Cu 3 above T C have been explained by means of a model taking into account nearest-as well as next-nearest-neighbor magnetic interactions. We show that the intraladder L-Cu interaction is the predominant one and that it is ferromagnetic for L=Gd, Tb, and Dy. For the cases of Tb, Dy, and Ho containing complexes, strong crystal field effects on the magnetic and thermal properties have to be taken into account. The magnetic coupling between the (ferromagnetic) ladders is found to be very weak and is probably of dipolar origin.

Exchanged naturality contributions from high-energy polarization measurements in two-body inclusive and exclusive reactions

In this paper, dealing with high-energy quasi-two-body of multiparticle production, we focus on what can be learned about exchanged naturality amplitudes from final polarization measurements with polarized or unpolarized beam and/or target. The separation of t-channel (boson exchange) and u-channel (baryon exchange) exchanges into components of natural and unnatural parity and the measure of naturality interferences are extensively studied in all cases which are now or wiil be soon available with present experimental techniques. Special attention is paid to the transversity amplitudes which are shown to be always naturality conserving.

Model-independent analysis of density-matrix element measurements in multiparticle reactions

Abstract We present a general study of polarization measurement in multiparticle production processes, including a definition of experimentally observable quantities, the splitting into natural- and unnatural parity exchanges and a study of their relative phase, and information concerning the quantum numbers of a packet of particles. When only one single particle is detected in the final state (inclusive reactions for instance) we prove that the usual formalism for two-body reactions is applicable. Very interesting new information on multi-particle production can be reached when it can be asserted that another particle has been emitted above or below a given plane, parallel or perpendicular to the scattering plane.

On the random filling of Rd by non-overlapping d-dimensional cubes

Abstract We compute the time-dependent coverage in the random sequential adsorption of aligned d-dimensional cubes in R d using time-series expansions. The seventh-order series in 2,3 and 4 dimensions is resummed in order to predict the coverage at jamming. The result is in agreement with Monte Carlo simulations. A simple argument, based on a property of the pertubative expansion valid at arbitrary orders, allows us to analytically derive some generalizations of the Palasti approximation.

Experimental determination of parity-doublet contributions in baryon-exchange reactions

Very simple relations between differential cross sections and polarizations in backward scattering (baryon exchange) which allow an experimental separation of parity-doublet contributions are pointed out. We show, for instance, that in πN elastic scattering, the cross sections with nucleon polarization parallel or antiparallel to the normal of the scattering plane are, respectively, proportional to unnatural or natural parity exchange. A rapid survey of available experimental data in πN elastic scattering and π−p→K0Λ exhibits unexpected features.

General features of low energy Kπ scattering from physical region method

Abstract We derive a dispersive method valid for low energy Kπ scattering which allows us to analyse the implications of crossing, unitarity and K ∗ existence. To provide accurate predictions for the s waves, this framework would have to be supplemented by other information.

Exchange degeneracy, absorption and loops in KN and KN scattering

Abstract We show that exchange degeneracy is fully compatible with all present high-energy experimental data and even, in most cases, at surprsingly we energy. We discuss the implications of the necessary absorptive corrections. At the end we obtain loops for partial waves corresponding to a set of exchange degenerate Y o ∗ all lying on a straight-line trajectory.

Surface superconducting states and paramagnetism in mesoscopic superconductors

In the framework of the Ginzburg-Landau equation, the temperature dependence of the upper critical field of small thin ringlike superconductors is studied. At equilibrium small parts of the phase diagram show paramagnetism for small hole sizes (larger than 15%). Their number and extension increase with the size of the hole. In these regions, only the inner part of the ring shows a positive magnetic moment. The order parameter density profile appears to change when crossing a first order transition line which separates different angular momentum values. We clarify the relationship between the localization of superconductivity nucleation and paramagnetism of these samples.

IS s-channel helicity really conserved in ϱ0 photoproduction?

Abstract We discuss problems related to helicity conservation and show that it is difficult to conclude that s -channel helicity is conserved from our present knowledge of ϱ meson photoproduction.