Imaging of Hepatocellular Carcinoma by Computed Tomography and Magnetic Resonance Imaging: State of the Art

Hepatocellular carcinoma (HCC) is a very frequent tumor worldwide. Its incidence is linked to the distribution of liver cirrhosis and viral hepatitis, which are the main risk factors for the development of HCC. For the evaluation of the cirrhotic liver and for the diagnosis of HCC, multidetector computed tomography (MDCT) proved to be a robust and reliable tool. In MDCT the diagnosis of HCC can be made based on neovascularization with increased arterial and decreased portal venous supply. With modern magnetic resonance imaging (MRI), spatial resolution and robustness increased dramatically. Beside the evaluation of neovascularization by means of gadolinium-enhanced early dynamic MRI, the main advantages of MRI are additional information on tissue composition and liver-specific function. With diffusion-weighted imaging or plain T(1)- and T(2)-weighted sequences, different tissue elements like fat, hemorrhage, glycogen, edema and cellular density can be evaluated. Liver-specific contrast agents give insight into the Kupffer cell density or the hepatocellular function. The integration of all these parts into the MR examination allows for a very high detection rate for overt HCC nowadays, although very small HCCs are still a challenge. Moreover, insight into the different stages of hepatocarcinogenesis can be possible with MRI. Despite its limited availability in some countries, it has to be rendered to be the modality of choice for the distinct evaluation of the cirrhotic liver. Copyright (C) 2009 S. Karger AG, Base

Laboratory Bounds on Electron Lorentz Violation

Violations of Lorentz boost symmetry in the electron and photon sectors can be constrained by studying several different high-energy phenomenon. Although they may not lead to the strongest bounds numerically, measurements made in terrestrial laboratories produce the most reliable results. Laboratory bounds can be based on observations of synchrotron radiation, as well as the observed absences of vacuum Cerenkov radiation. Using measurements of synchrotron energy losses at LEP and the survival of TeV photons, we place new bounds on the three electron Lorentz violation coefficients c_(TJ), at the 3 x 10^(-13) to 6 x 10^(-15) levels.Comment: 18 page

Coupled DEM-LBM method for the free-surface simulation of heterogeneous suspensions

The complexity of the interactions between the constituent granular and liquid phases of a suspension requires an adequate treatment of the constituents themselves. A promising way for numerical simulations of such systems is given by hybrid computational frameworks. This is naturally done, when the Lagrangian description of particle dynamics of the granular phase finds a correspondence in the fluid description. In this work we employ extensions of the Lattice-Boltzmann Method for non-Newtonian rheology, free surfaces, and moving boundaries. The models allows for a full coupling of the phases, but in a simplified way. An experimental validation is given by an example of gravity driven flow of a particle suspension

Analysis of the velocity field of granular hopper flow

We report the analysis of radial characteristics of the flow of granular material through a conical hopper. The discharge is simulated for various orifice sizes and hopper opening angles. Velocity profiles are measured along two radial lines from the hopper cone vertex: along the main axis of the cone and along its wall. An approximate power law dependence on the distance from the orifice is observed for both profiles, although differences between them can be noted. In order to quantify these differences, we propose a Local Mass Flow index that is a promising tool in the direction of a more reliable classification of the flow regimes in hoppers

Computer simulation of fatigue under diametrical compression

We study the fatigue fracture of disordered materials by means of computer simulations of a discrete element model. We extend a two-dimensional fracture model to capture the microscopic mechanisms relevant for fatigue, and we simulate the diametric compression of a disc shape specimen under a constant external force. The model allows to follow the development of the fracture process on the macro- and micro-level varying the relative influence of the mechanisms of damage accumulation over the load history and healing of microcracks. As a specific example we consider recent experimental results on the fatigue fracture of asphalt. Our numerical simulations show that for intermediate applied loads the lifetime of the specimen presents a power law behavior. Under the effect of healing, more prominent for small loads compared to the tensile strength of the material, the lifetime of the sample increases and a fatigue limit emerges below which no macroscopic failure occurs. The numerical results are in a good qualitative agreement with the experimental findings.Comment: 7 pages, 8 figures, RevTex forma

Magnetic models on Apollonian networks

Thermodynamic and magnetic properties of Ising models defined on the triangular Apollonian network are investigated. This and other similar networks are inspired by the problem of covering an Euclidian domain with circles of maximal radii. Maps for the thermodynamic functions in two subsequent generations of the construction of the network are obtained by formulating the problem in terms of transfer matrices. Numerical iteration of this set of maps leads to exact values for the thermodynamic properties of the model. Different choices for the coupling constants between only nearest neighbors along the lattice are taken into account. For both ferromagnetic and anti-ferromagnetic constants, long range magnetic ordering is obtained. With exception of a size dependent effective critical behavior of the correlation length, no evidence of asymptotic criticality was detected.Comment: 21 pages, 5 figure

Riemann solvers and undercompressive shocks of convex FPU chains

We consider FPU-type atomic chains with general convex potentials. The naive continuum limit in the hyperbolic space-time scaling is the p-system of mass and momentum conservation. We systematically compare Riemann solutions to the p-system with numerical solutions to discrete Riemann problems in FPU chains, and argue that the latter can be described by modified p-system Riemann solvers. We allow the flux to have a turning point, and observe a third type of elementary wave (conservative shocks) in the atomistic simulations. These waves are heteroclinic travelling waves and correspond to non-classical, undercompressive shocks of the p-system. We analyse such shocks for fluxes with one or more turning points. Depending on the convexity properties of the flux we propose FPU-Riemann solvers. Our numerical simulations confirm that Lax-shocks are replaced by so called dispersive shocks. For convex-concave flux we provide numerical evidence that convex FPU chains follow the p-system in generating conservative shocks that are supersonic. For concave-convex flux, however, the conservative shocks of the p-system are subsonic and do not appear in FPU-Riemann solutions