Vienna University of Technology

About: Vienna University of Technology is a education organization based out in Vienna, Austria. It is known for research contribution in the topics: Laser & Cloud computing. The organization has 16723 authors who have published 49341 publications receiving 1302168 citations.

CPR - curved planar reformation

Abstract: Visualization of tubular structures such as blood vessels is an important topic in medical imaging. One way to display tubular structures for diagnostic purposes is to generate longitudinal cross-sections in order to show their lumen, wall, and surrounding tissue in a curved plane. This process is called curved planar reformation (CPR). We present three different methods to generate CPR images. A tube-phantom was scanned with computed tomography (CT) to illustrate the properties of the different CPR methods. Furthermore we introduce enhancements to these methods: thick-CPR, rotating-CPR and multi-path-CPR.

Quantum Theory of Attosecond XUV Pulse Measurement by Laser Dressed Photoionization

Abstract: The first reported measurements of single attosecond pulses use laser dressed single-photon extreme ultraviolet (XUV) ionization of gas atoms. The determination of XUV pulse duration from the electron spectrum is based on a classical theory. Although classical models are known to give a qualitatively correct description of strong laser atom interaction, the validity must be scrutinized by a quantum-mechanical analysis. We establish a theoretical framework for the accurate temporal characterization of attosecond XUV pulses. Our analysis reveals an improved scheme that allows for direct experimental discrimination between single and multiple attosecond pulses.

Electronic structure and transport in type-I and type-VIII clathrates containing strontium, barium, and europium

Abstract: The thermoelectric properties of filled gallium-germanium clathrates are analyzed from a band-structure point of view. Using the virtual crystal approximation the undoped clathrates are calculated to be semiconductors with band gaps around 0.6--0.9 eV. The conduction bands hybridize with the unoccupied d states of the guest atoms. This means that the thermoelectric properties of n-doped type-I clathrates depend strongly on the guest atom while p doped clathrates are relatively unaffected. The type-VIII structures have disperse bands centered around the voids in the framework structure. This explains the low effective masses observed for n-doped type-VIII structures. It also means that the electronic structure and thermoelectric properties are relatively independent of the guest atom and that p-doped should have favorable thermoelectric properties while n-doped type-VIII structures have poor properties. We estimate a figure of merit of 1.2 at 400 K for an optimally p-doped europium-VIII clathrate. In addition we predict that the strontium-VIII clathrate should be stable.

Physical weathering of marbles caused by anisotropic thermal expansion

Abstract: Marbles as building stones as well as in their natural environments show complex weathering phenomena. The most important damage scenario is based on the highly anisotropic thermal expansion coefficient α of calcite, i.e. extreme expansion parallel and contraction normal to the crystallographic c-axis. Therefore, the rock fabric and especially the lattice-preferred orientation (texture) of calcite and/or dolomite as the predominant mineral phases in marbles have a significant influence on the mechanical weathering. The textures of marbles from five different locations vary from a more or less perfect prolate to moderate oblate shape of the [006] pole figure tensor. Accordingly, the texture-derived bulk thermal dilatation anisotropy covers a broad range from –0.048 to 0.680. The modelled thermal dilatations correlate with those obtained from experimental measurements. The difference in magnitude is basically explained by the microcrack fabrics which was not considered in the computations. All samples show a deterioration due to thermal treatment regardless of the strength of texture. The directional dependence of (a) the total magnitude of the thermal dilatation coefficient and (b) of the residual strain is highest in marbles with a strong texture, whereas the Carrara marble with a weak texture exhibits a uniform crack formation. The progressive loss of cohesion along grain boundaries due to dilatancy may serve as an example for the initial stage of physical weathering.