Als charakteristische Reaktion der freien Weinsteins?re

Ohne Zusammenfassung     

On projective spaces PG(r, q) with r ≥ 4

In this paper a characterization of PG(r, q), r ≥ 4, in terms of planar spaces is given. Domenico Olanda: This research was carried out within the activity of INdAM-GNSAGA and supported by the Italian Ministry M.I.U.R.     

Y-junction of superconducting Josephson chains

We show that, for pertinent values of the fabrication and control parameters, an attractive finite coupling fixed point emerges in the phase diagram of a Y-junction of superconducting Josephson chains. The new fixed point arises only when the dimensionless flux f piercing the central loop of the network equals π   and, thus, does not break time-reversal invariance; for f≠π$f\ne \pi$, only the strongly coupled fixed point survives as a stable attractive fixed point. Phase slips (instantons) have a crucial role in establishing this transition: we show indeed that, at f=π$f=\pi$, a new set of instantons—the W-instantons—comes into play to destabilize the strongly coupled fixed point. Finally, we provide a detailed account of the Josephson current–phase relationship along the arms of the network, near each one of the allowed fixed points. Our results evidence remarkable similarities between the phase diagram accessible to a Y-junction of superconducting Josephson chains and the one found in the analysis of quantum Brownian motion on frustrated planar lattices.     

A large sample study of spin relaxation and magnetometric sensitivity of paraffin-coated Cs vapor cells

We have manufactured more than 250 nominally identical paraffin-coated Cs vapor cells (28 mm inner diameter bulbs) for multi-channel atomic magnetometer applications. We describe our dedicated cell characterization apparatus. For each cell we have determined the intrinsic longitudinal, Γ ₀₁, and transverse, Γ ₀₂, relaxation rates. Our best cell shows Γ ₀₁/2π≈0.5 Hz, and Γ ₀₂/2π≈2 Hz. We find a strong correlation of both relaxation rates which we explain in terms of reservoir and spin exchange relaxation. For each cell we have determined the optimal combination of rf and laser powers which yield the highest sensitivity to magnetic field changes. Out of all produced cells, 90% are found to have magnetometric sensitivities in the range of 9 to 30 fT . Noise analysis shows that the magnetometers operated with such cells have a sensitivity close to the fundamental photon shot noise limit.     

A Note on Strong Ellipticity in Two-Dimensional Isotropic Elasticity

Based on the choice of two physically meaningful strain measures, we study necessary and sufficient conditions for strong ellipticity of the equilibrium equations for two-dimensional isotropic hyperelastic bodies. Specifically, we show, depending on the values of the derivatives of the energy function, that strong ellipticity is equivalent to a single condition with a clear physical interpretation.     

An investigation on microscopic and macroscopic stability phenomena of composite solids with periodic microstructure

An analysis of the effects of microscopic instabilities on the homogenized response of heterogeneous solids with periodic microstructure and incrementally linear constitutive law is here carried out. In order to investigate the possibility to obtain a conservative prediction of microscopic primary instability in terms of homogenized properties, novel macroscopic constitutive stability measures are introduced, corresponding to the positive definiteness of the homogenized moduli tensors relative to a class of conjugate stress–strain pairs.Numerical simulations, addressed to hyperelastic microstructural models representing cellular solids and reinforced composites, are worked out through the implementation of an innovative one-way coupled finite element formulation able to determine sequentially the principal equilibrium solution, the incremental equilibrium solutions providing homogenized moduli and the stability eigenvalue problem solution, for a given monotonic macrostrain path. Both uniaxial and equibiaxial loading conditions are considered.The exact microscopic stability region in the macrostrain space, obtained by taking into account microstructural details, is compared with the macroscopic stability regions determined by means of the introduced macroscopic constitutive measures. These results highlight how the conservativeness of the adopted macroscopic constitutive stability measure with respect to microscopic primary instability, strictly depends on the type of loading condition (tensile or compressive) and the kind of microstructure.     

Water Diffusion in Glassy Polymers and their Silica Hybrids: an Analysis of State of Water Molecules and of the Effect of Tensile Stress

In-situ, time-resolved FTIR spectroscopy along with gravimetric analysis have been used to investigate water sorption and transport in several glassy polymeric matrices, characterized by different levels of interaction with water, as well as on polymer-silica hybrids. This technique has also been coupled to a dynamical-mechanical analyser to gather information on the water sorption kinetics and thermodynamics in a polymer sample submitted to stretching deformation and load. Results have been modelled by coupling the mass balance and momentum balance, using a theoretical approach developed for elastic matrices and low sorbed amounts by Larché and Cahn.     

Halogen Free Flame Retardant Agents for Polypropylene in Wire Coating Process

the processing behaviour and physical properties of polypropylene/flame retardant blends were investigated in order to evaluate their use in the wire-coating process. In particular, the need of flame retardancy, suitable melt processability and good mechanical properties of blends was taken into account. Three types of halogen free flame retardants were chosen and were melt blended to the polypropylene matrix. Blends properties were analysed by rheological, mechanical, and thermal characterization including flame retardancy tests. The wire coating process was also performed by a laboratory wire coating apparatus. The results demonstrated that some of the blends are suitable for the purpose of flame retardancy of electrical household wires as an alternative to PVC.