Anomalous isomeric shifts in Mössbauer spectra of substituted leucites (K,Rb, Cs)(Al,B, Fe)Si2O6

Summary A systematic investigation on the properties of synthetic iron-substituted leucite-like silicates has been performed by M?ssbauer spectroscopy. The obtained data on the isomeric shifts indicate that along the chains of tetrahedra present in the anionic framework of these silicates a readjustement of the bond lengths takes place, due to the large ionic radius of iron which exceeds those of silicon and aluminum.     

Investigation of cordierite lattice defects by thermoluminescence experiments

Summary The thermoluminescence of α- and μ-cordierite samples has been recordedvs. temperature and wavelength. Arguments ascribing the observed emission to the easy ion exchanges characterizing cordierite lattices are advanced.     

A study of lattice defects in solids belonging to Al2O3−B2O3 and Al2O3−SiO2 systems by thermoluminescence experiments

Summary Spectrally resolved thermoluminescent emission has been investigated in solids belonging to Al₂O₃−B₂O₃ and Al₂O₃−SiO₂ systems. These solids, which are characterized by a structure like that of alumino-silicate mullite, contain a high density of oxygen and aluminum or boron lacunae. This fact favours the occurrence of both-sign interstitial ions acting as carrier traps. The results show a close similarity with those obtained when studying, with the same experimental method, the thermoluminescent emission of alumina. The overall analysis of data allows for reliable conclusions on the nature of crystal defects in these materials.     

Parallel simulated annealing

This article introduces the notion of restricted parallelism for networks, a generalization of the unlimited parallelism for Boltzmann machines. The convergence of the annealing algorithm in the restricted parallel form is established, for an arbitrary network.     

Wilson fermions and axion electrodynamics in optical lattices

We show that ultracold Fermi gases in optical superlattices can be used as quantum simulators of relativistic lattice fermions in 3+1 dimensions. By exploiting laser-assisted tunneling, we find an analogue of the so-called naive Dirac fermions, and thus provide a realization of the fermion doubling problem. Moreover, we show how to implement Wilson fermions, and discuss how their mass can be inverted by tuning the laser intensities. In this regime, our atomic gas corresponds to a phase of matter where Maxwell electrodynamics is replaced by axion electrodynamics: a 3D topological insulator.     

Experimental investigation of ovine intervertebral disc units in longitudinal loading

The assessment of the predictive power of material models for soft biological tissues is an important issue when it comes to realistic simulations for medical applications. The determination of the model parameters needs sound experimental data. In our case we want to test the viscoelastic properties of ovine lumbar intervertebral discs (IVD's) in longitudinal loading. The complex geometry as well as the small imposed displacements combined with rather high forces are to be treated. The two vertebrae adjacent to the IVD are mounted using custom made clampings where attention is paid not to prestress the tissue. First tests were done with steel springs in order to check the suitability of the used materials testing machine. No significant compliance of the machine could be detected but a negative hysteresis that might origin from the data acquisition process. Experiments on IVD's gave us an in-depth insight into the underlying mechanics such that we can now define appropriate protocols for future experiments. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Image deblurring by sparsity constraint on the Fourier coefficients

This paper is concerned with the image deconvolution problem. For the basic model, where the convolution matrix can be diagonalized by discrete Fourier transform, the Tikhonov regularization method is computationally attractive since the associated linear system can be easily solved by fast Fourier transforms. On the other hand, the provided solutions are usually oversmoothed and other regularization terms are often employed to improve the quality of the restoration. Of course, this weighs down on the computational cost of the regularization method. Starting from the fact that images have sparse representations in the Fourier and wavelet domains, many deconvolution methods have been recently proposed with the aim of minimizing the ?₁-norm of these transformed coefficients. This paper uses the iteratively reweighted least squares strategy to introduce a diagonal weighting matrix in the Fourier domain. The resulting linear system is diagonal and hence the regularization parameter can be easily estimated, for instance by the generalized cross validation. The method benefits from a proper initial approximation that can be the observed image or the Tikhonov approximation. Therefore, embedding this method in an outer iteration may yield further improvement of the solution. Finally, since some properties of the observed image, like continuity or sparsity, are obviously changed when working in the Fourier domain, we introduce a filtering factor which keeps unchanged the large singular values and preserves the jumps in the Fourier coefficients related to the low frequencies. Numerical examples are given in order to show the effectiveness of the proposed method.