The influence of the conduction electrons on the EFG in amorphous intermetallic alloys

The quadrupole splitting in alloys is determined by the structural and electronic properties of the alloy. Only in cases where the density of states at the Fermi level is constant or known as a function of the concentration, relevant structural information can be obtained from the quadrupole splitting.     

Local symmetry in some quasicrystalline AlTFe alloys

Mössbauer spectra of AlTFe-alloys with T=Cr or Mn, show a quadrupole splitting QS≈0.4 mm/s. This shows that the iron atom is not in an icosahedral site. In order to investigate the local symmetry further, we applied an external magnetic field H_ext≈5T, so that the asymmetry parameter ν can be obtained. Using a one site approximation the results are: ν=0.7 for decagonal Al₇(Mn_0.7Fe_0.3)₂ and ν=0.8 for icosahedral Al₆Cr_0.7Fe_0.3. This means that the iron atoms are in sites with a symmetry lower than axially symmetric. Most of the vertices in a Penrose lattice show such a symmetry.     

A note on the projecton of Gibbs measures

We give an example of a projection which maps two Gibbs measures for the same interaction into Gibbs measures for different interactions. As a corollary we find a case where by decimation a non-Gibbsian measure is transformed into a Gibbs measure.     

Giant resonances in exotic nuclear systems: What we expect and what we know

The characteristic features of γ-rays resulting from the decay of the Giant Dipole Resonance in very deformed, hot systems and in systems with a large isospin are discussed. For both cases there are recent theoretical predictions but very few if any data. With respect to hot, deformed systems it is argued that the discrepancy which exists between the measured and calculated asymmetry of the GDR γ-rays emitted in the fusion-fission process of hot actinide nuclei, might well be due to γ-emission during the saddle-to-scission stage of the fission process, that is from very deformed hot nuclear systems. The prospect of studying experimentally the behavior of Giant Resonances in systems with large isospin (=large neutron excess) is also discussed. Experiments on the GDR are feasible and will give information on the deformation of the emitting system.     

Systematics of the isoscalar giant monopole resonance from 60 MeV inelastic proton scattering

Evidence for an isoscalar giant monopole resonance is provided for seven nuclei with A ? 58. The resonance excitation energy is $\text{≈ 80 × A}{}^{\mathrm{<mtext>?1</mtext><mtext>3</mtext>}}\text{MeV}$. For nuclei with A ? 0, nearly 100% of the L = 0, T = 0 energy-weighted sum rule is depleted in the resonance, in agreement with earlier work on ²⁰⁸Pb and ¹⁴⁴Sm. Only ≈30% is found in ⁵⁸Ni, and no clear evidence is found for localized monopole strength in ⁴⁰Ca.     

Study of negative thermal expansion and shift in phase transition temperature in Ti4+- and Sn4+-substituted ZrW2O8 materials

The negative-thermal-expansion material ZrW(2)O(8) is known to undergo an order-disorder phase transition which affects its expansion behavior. In this study, Ti(4+) and Sn(4+) are examined as possible substituting ions for the Zr(4+) position in ZrW(2)O(8). This substitution leads to a decrease in cell parameters, as the ionic radii of the substituents are smaller than the Zr(4+) ionic radius. A remarkable decrease in transition temperature is noticed. DSC is used to quantify the enthalpy and entropy changes during the phase transition in order to reveal the mechanisms behind this decrease. It is shown that the strength of the M-O bond plays an important role, as it is a partner in the rigid unit mode motion and the order-disorder transition mechanism.     

Error control in the perfectly matched layer based multilevel fast multipole algorithm

The development of efficient algorithms to analyze complex electromagnetic structures is of topical interest. Application of these algorithms in commercial solvers requires rigorous error controllability. In this paper we focus on the perfectly matched layer based multilevel fast multipole algorithm (PML-MLFMA), a dedicated technique constructed to efficiently analyze large planar structures. More specifically the crux of the algorithm, viz. the pertinent layered medium Green functions, is under investigation. Therefore, particular attention is paid to the plane wave decomposition for 2-D homogeneous space Green functions in very lossy media, as needed in the PML-MLFMA. The result of the investigations is twofold. First, upper bounds expressing the required number of samples in the plane wave decomposition as a function of a preset accuracy are rigorously derived. These formulas can be used in 2-D homogeneous (lossy) media MLFMAs. Second, a more heuristic approach to control the error of the PML-MLFMA’s Green functions is presented. The theory is verified by means of several numerical experiments.     

Transformations of Gibbs measures

We study local transformations of Gibbs measures. We establish sufficient conditions for the quasilocality of the images and obtain results on the existence and continuity properties of their relative energies. General results are illustrated by simple examples. Received: 11 November 1997 / Revised version: 20 February 1998