Diffusion-weighted imaging of the brain at 7 T with echo-planar and turbo spin echo sequences: preliminary results

Ultra-high-field clinical MRI scanners (e.g., 7 T and above) are becoming increasingly prevalent and can potentially enhance diagnostic ability through higher contrast, resolution and/or sensitivity. Diffusion-weighted MRI is a highly valued component in today's radiological exam and may benefit from the enhanced signal-to-noise ratio provided by high field with the appropriate imaging strategy. The most common diffusion pulse sequence readout (echo-planar imaging (EPI)) has been widely employed for in vivo human 7 T diffusion tensor imaging (DTI). In this article, we present results of brain DTI at 7 T with two diffusion-weighted imaging pulse sequence readouts: echo-planar imaging (EPI-DTI) and turbo spin echo (TSE-DTI). Results indicate that analogous coverage, quality and resolution typical of lower field (2 mm) can be obtained by properly processed EPI-DTI at 7 T, and, with some reduction in efficiency and sharpness, TSE-DTI at 7 T. Furthermore, 7 T TSE-DTI shows promise in obtaining higher-resolution results in targeted acquisitions of specific brain areas.     

Electronic inhomogeneities,electron-lattice and pairing interactions in high-T c superconductors

The presence of electronic inhomogeneities strongly reduces the screening of the electron-ion interaction in high-temperature superconductors. This implies the existence of an non-totally screened long-range contribution to the electron-lattice coupling and opens an additional channel for the formation of copper pairs. We calculate the superconducting order parameter taking into account a) the longrange and the short-range parts of the electron-lattice interaction and b) the Coulomb repulsion between charge-carriers. We show that whereas the long-range electron-lattice coupling determines the anisotropy of the order parameter, the Coulomb repulsion and the short-range interactions determine its symmetry. Thus, different high-T _c superconductors may have s- or d-wave symmetry, depending on the relative strength of the interactions involved in the pairing.     

On the importance of anisotropic exchange coupling on to the structure of spin-polarized clusters in layered cuprates

The low energy spectrum of spin-polarized clusters in layered cuprates is examined. Two types of clusters confining the motion of oxygen holes are discussed. The ground state of the pentanuclear copper cluster has a total spin S = 2, whereas the one of the tetranuclear copper cluster is characterised by S= 3/2. Anisotropic exchange coupling splits the magnetic ground state into a sequence of state, which in a natural way provide e.g. an explanation of EPR data for La₂CuO_4+δ compounds.     

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On the prevalence of zero entropy

For a residual subset of the space of discrete stationary stochastic processes (under the weak topology for measures) the entropy is 0. The processes with arbitrarily large entropy are dense. For a residual subset of subshifts of the shift on a finite alphabet, the topological entropy is 0.     

Inactivation of bacterial endospores by photocatalytic nanocomposites

A novel biocidal photocatalytic nanocomposite, composed of TiO(2) and multi-walled carbon nanotubes (MWNTs), was synthesized via wet chemistry followed by a heat treatment. Uniform anatase coatings on MWNTs were successfully obtained with a thickness of a few nanometers. The nanostructure of the composite was determined by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The needle-like shape of the nanocomposite provided more than three times higher photocatalytic specific surface area than commercial TiO(2) nanoparticles (Degussa P25) when dispersed in water. Moreover, under ultraviolet (UV) radiation the excited electrons can be trapped at the interface between the TiO(2) layer and MWNTs and they can also be scavenged through the conductive graphitic layers. Thus, an intense photochemical reaction yielding a powerful biocide can be expected. Irradiating bacterial endospores (Bacillus cereus) with solar UV lamps in presence of the novel photocatalyst successfully inactivated the spores while solar UV lamps only or solar UV Lamps with Degussa P25 showed no significant inactivating behavior. Performance of photocatalytic nanocomposites was assessed based on time to achieve 90% inactivation of spores (LD(90)) and also in terms of time required to achieve a 1.0 log(10) reduction of spores in the tail region of the inactivation curve.     

Magnetismus des freien Elektronengases

A perturbation series for the free energy of independent electrons is presented and applied to the problem of dia- and paramagnetism of the free electron gas. By using a periodic magnetic field the boundary conditions can be exactly satisfied. The results agree with those of other authors using approximate boundary conditions.