Simulations of ferrite-dielectric-wire composite negative index materials

We perform extensive finite difference time domain simulations of ferrite based negative index of refraction composites. A wire grid is employed to provide negative permittivity. The ferrite and wire grid interact to provide both negative and positive index of refraction transmission peaks in the vicinity of the ferrite resonance. Notwithstanding the extreme anisotropy in the index of refraction of the composite, negative refraction is seen at the composite air interface allowing the construction of a focusing concave lens with a magnetically tunable focal length.     

Particle tunneling and scattering in a three-dimensional potential with a barrier

The particle tunneling through a 3-D rectangular potential barrier has been studied. The simplest model for multiple internal reflections has been assumed. The explicit expression for all the transmission and reflection probability amplitudes have been derived, as well as the tunneling and reflection phase times.      

Time dependence of mechanical and transport properties of drawn and annealed linear polyethylene

Linear polyethylene both as drawn, or drawn and subsequently annealed with free ends, changes its length, density, crystallinity, elastic modulus, sorption, and diffusivity as the sample stands completely unrestrained at room temperature. Most of these changes occur during the first few hours. But they are important on a molecular scale since they suggest strongly that drawn, and drawn and annealed samples are far from equilibrium. As a consequence of the tendency of each mobile tie molecule in the amorphous conformation to retract and to crystallize, the specimen approaches but does not reach complete equilibrium. The transient seems to be caused by slow crystallization of tie molecules which creates crystalline bridges across the amorphous layers.     

Mechanical and transport properties of drawn crosslinked low-density polyethylene

The values of drawing dependence of the density ρ, axial elastic modulus E, and maximum draw ratio λ of crosslinked low-density polyethylene (CLPE) rather similar to those obtained with un-crosslinked branched material of similarly low density. Very much the same applies to the equilibrium concentration of sorbed methylene chloride in the amorphous component and the zero-concentration diffusion coefficient D₀. The exponential concentration coefficient γD , however, even at the maximum draw ratio, shows no indication of the rapid increase so characteristic of the completed transformation from the lamellar to the fibrous structure. On the basis of this finding, one can understand the small deviations in the dependence of the mechanical properties between the crosslinked and uncrosslinked branched material. The segments between the crosslinks, much shorter than the free molecules, favor the formation of the interfibrillar tie molecules that limit the drawability of the sample. But since they cannot be extended to the same length as the free molecules, they contribute less to the total fraction of tie molecules per amorphous layer and hence yield a smaller axial elastic modulus.     

O- radical ions on MgO: a tool for a structural description of the surface

The present contribution aims to show that detailed information on structure and location of surface defective sites (surface vacancies, low co-ordination sites) can be obtained by combining data on the chemical reactivity of polycrystalline surfaces and EPR data. The use of nitrous oxide for bleaching trapped electron centres at the surface of MgO produces a remarkable variety of O^- species, which differ in their values of the energy splitting (δE) term between the p_z and the other two p orbitals of the radical ion. This indicates the existence of a corresponding variety of surface traps having different structural features.     

Mechanical and transport properties of highly drawn isotactic polypropylene

Quenched films of isotactic polypropylene were drawn at 110°C up to draw ratio λ = 18. The axial elastic modulus was measured as function of λ up to the highest achieved λ. The sorption and diffusion of CH₂Cl₂ at 25°C in the undrawn and drawn samples were studied. Exclusively transparent samples were used for the measurement of the density and transport properties. This reduces the maximum usable draw ratio to 15. The drawing process is inhomogeneous with neck propagation. In the neck the draw ratio increases by about 6. As a consequence of the increasing fraction of taut tie molecules the axial elastic modulus increases faster than the draw ratio. The transport parameters D, S, and λ indicate that the original lamellar morphology is completely transformed into the microfibrillar structure.     

Formation of Superoxo Species by Interaction of O2 with Na Atoms Deposited on MgO Powders: A Combined Continuous‐Wave EPR (CW‐EPR), Hyperfine Sublevel Correlation (HYSCORE) and DFT Study

The formation of O₂^? radical anions by contact of O₂ molecules with a Na pre‐covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O₂. The typical EPR signal of isolated Na atoms disappears when the reaction with O₂ takes place and new paramagnetic species are observed, which are attributed to different surface‐stabilised O₂^? radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O₂^?Na⁺ species to be determined, demonstrating the direct coordination of the O₂^? adsorbate to surface Na⁺ cations. DFT calculations enable the structural details of the formed species to be determined. Matrix‐isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface‐stabilised Na⁺? O₂^? complexes.     

A general framework for the construction of piecewise-polynomial local interpolants of minimum degree

In this paper we consider the problem of designing piecewise polynomial local interpolants of non-uniformly spaced data. We provide a constructive approach that, for any assigned degree of polynomial reproduction, continuity order, and support width, allows for generating the fundamental spline functions of minimum degree having the desired properties. Finally, the proposed construction is extended to handle open sets of data and to the case of multiple knots.