E. P. Stoll

A new filtering algorithm for medical magnetic resonance and computer tomography images

Inner views of tubular structures based on computer tomography (CT) and magnetic resonance (MR) data sets may be created by virtual endoscopy. After a preliminary segmentation procedure for selecting the organ to be represented, the virtual endoscopy is a new postprocessing technique using surface or volume rendering of the data sets. In the case of surface rendering, the segmentation is based on a grey level thresholding technique. To avoid artifacts owing to the noise created in the imaging process, and to restore spurious resolution degradations, a robust Wiener filter was applied. This filter working in Fourier space approximates the noise spectrum by a simple function that is proportional to the square root of the signal amplitude. Thus, only points with tiny amplitudes consisting mostly of noise are suppressed. Further artifacts are avoided by the correct selection of the threshold range. Afterwards, the lumen and the inner walls of the tubular structures are well represented and allow one to distinguish between harmless fluctuations and medically significant structures.

First-principles calculation of electric field gradients and hyperfine couplings in YBa2Cu3O7

Abstract:The local electronic structure of YBa2Cu3O7 has been calculated using first-principles cluster methods. Several clusters embedded in an appropriate background potential have been investigated. The electric field gradients at the copper and oxygen sites are determined and compared to previous theoretical calculations and experiments. Spin polarized calculations with different spin multiplicities have enabled a detailed study of the spin density distribution to be made and a simultaneous determination of magnetic hyperfine coupling parameters. The contributions from on-site and transferred hyperfine fields have been disentangled with the conclusion that the transferred spin densities essentially are due to nearest neighbour copper ions only with marginal influence of ions further away. This implies that the variant temperature dependencies of the planar copper and oxygen NMR spin-lattice relaxation rates are only compatible with commensurate antiferromagnetic correlations. The theoretical hyperfine parameters are compared with those derived from experimental data.

FRACTALS IN ISOTROPIC SYSTEMS GENERATED WITH ATTRACTING SPHERES

Isotropic non-crystal fractal systems are simulated. Lennard-Jones fluids are heated up to very high temperatures and annealed to frozen glassy or amorphous states. From the set of all connections between next neighbors separated by less than 1.15σ, a subset is selected randomly with the probability p≈pc. With these bonds the percolation cluster is determined, and all particles not belonging to this cluster are removed. A fractal dimension D≈2.58 is determined using the box-counting method. Considering the slope of the statis structure factor S(q), D is ≈2.40. Both values are close to the ones of a fractal system on a three-dimensional lattice but larger than the fractal dimension D = 1.7 of a recent small angle neutron scattering experiment of base-catalyzed silica aerogels.

Charge and spin density distributions around Zn impurities in cuprates

The effect of zinc substitution on the local electronic structure of several cuprates is investigated using first-principles cluster calculations. Clusters comprising 5, 9, and 13 copper atoms in the cuprate plane of La

First Principles Investigation of Local Distortions in Doped La2CuO4

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Influence of Spin-Orbit Couplings to Nuclear Spin-Lattice Relaxation Rates in Sr-Doped La2CuO4

CuO

On the distribution of intrinsic holes in cuprates

_4

Comparison of the Electronic Structures of La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2

, YBa

A TOOLKIT FOR INTERACTIVE MOLECULAR DYNAMICS SIMULATION AND VISUALIZATION

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Doping high Tc superconductors with oxygen and metallic atoms: a molecular dynamics study

Cu