Statistical Laws and Mechanics of Voronoi Random Lattices

We investigate random lattices where the connectivities are determined by the Voronoi construction, while the location of the points are the dynamic degrees of freedom. The Voronoi random lattices with an associated energy are immersed in a heat bath and investigated using a Monte Carlo simulation algorithm. In thermodynamic equilibrium we measure coordination number distributions and test the Aboav-Weaire and Lewis laws.Comment: 14 pages (figures not included), LaTeX, HLRZ-26/9

Discrete Fracture Model with Anisotropic Load Sharing

A two-dimensional fracture model where the interaction among elements is modeled by an anisotropic stress-transfer function is presented. The influence of anisotropy on the macroscopic properties of the samples is clarified, by interpolating between several limiting cases of load sharing. Furthermore, the critical stress and the distribution of failure avalanches are obtained numerically for different values of the anisotropy parameter $\alpha$ and as a function of the interaction exponent $\gamma$. From numerical results, one can certainly conclude that the anisotropy does not change the crossover point $\gamma_c=2$ in 2D. Hence, in the limit of infinite system size, the crossover value $\gamma_c=2$ between local and global load sharing is the same as the one obtained in the isotropic case. In the case of finite systems, however, for $\gamma\le2$, the global load sharing behavior is approached very slowly

Lattice Boltzmann scheme for relativistic fluids

A Lattice Boltzmann formulation for relativistic fluids is presented and numerically verified through quantitative comparison with recent hydrodynamic simulations of relativistic shock-wave propagation in viscous quark-gluon plasmas. This formulation opens up the possibility of exporting the main advantages of Lattice Boltzmann methods to the relativistic context, which seems particularly useful for the simulation of relativistic fluids in complicated geometries.Comment: Submitted to PR

Facilitated event-related power modulations during transcranial alternating current stimulation (tACS) revealed by concurrent tACS-MEG

Non-invasive approaches to modulate oscillatory activity in the brain are increasingly popular in the scientific community. Transcranial alternating current stimulation (tACS) has been shown to modulate neural oscillations in a frequency-specific manner. However, due to a massive stimulation artifact at the targeted frequency, little is known about effects of tACS during stimulation. It remains unclear how the continuous application of tACS affects event-related oscillations during cognitive tasks. Depending on whether tACS influences pre- or post-stimulus oscillations, or both, the endogenous, event-related oscillatory dynamics could be pushed in various directions or not at all. A better understanding of these effects is crucial to plan, predict, and understand outcomes of solely behavioral tACS experiments. In the present study, a recently proposed procedure to suppress tACS artifacts by projecting MEG data into source-space using spatial filtering was utilized to recover event-related power modulations in the alpha-band during a mental rotation task. MEG data of 25 human subjects was continuously recorded. After 10-minute baseline measurement, participants received either 20 minutes of tACS at their individual alpha frequency or sham stimulation. Another 40 minutes of MEG data were acquired thereafter. Data were projected into source-space and carefully examined for residual artifacts. Results revealed strong facilitation of event-related power modulations in the alpha-band during tACS application. These results provide first direct evidence that tACS does not counteract top-down suppression of intrinsic oscillations, but rather enhances pre-existent power modulations within the range of the individual alpha (= stimulation) frequency

Derivation of the Lattice Boltzmann Model for Relativistic Hydrodynamics

A detailed derivation of the Lattice Boltzmann (LB) scheme for relativistic fluids recently proposed in Ref. [1], is presented. The method is numerically validated and applied to the case of two quite different relativistic fluid dynamic problems, namely shock-wave propagation in quark-gluon plasmas and the impact of a supernova blast-wave on massive interstellar clouds. Close to second order convergence with the grid resolution, as well as linear dependence of computational time on the number of grid points and time-steps, are reported

Shot noise in carbon nanotube based Fabry-Perot interferometers

We report on shot noise measurements in carbon nanotube based Fabry-Perot electronic interferometers. As a consequence of quantum interferences, the noise power spectral density oscillates as a function of the voltage applied to the gate electrode. The quantum shot noise theory accounts for the data quantitatively. It allows to confirm the existence of two nearly degenerate orbitals. At resonance, the transmission of the nanotube approaches unity, and the nanotube becomes noiseless, as observed in quantum point contacts. In this weak backscattering regime, the dependence of the noise on the backscattering current is found weaker than expected, pointing either to electron-electron interactions or to weak decoherence

Effectiveness of the Combination of Memantine Plus Vitamin D on Cognition in Patients With Alzheimer Disease: A Pre-Post Pilot Study

Objective: To determine whether treatment with memantine plus vitamin D is more effective than memantine or vitamin D alone in improving cognition among patients with Alzheimer disease (AD). Methods: We studied 43 white outpatients (mean 84.7±6.3 years; 65.1% women) with a new diagnosis of AD, who had not taken anti-dementia drugs or vitamin D supplements. We prescribed memantine alone (n=18), vitamin D alone (n=17), or memantine plus vitamin D (n=8) for an average of 6 months. We assessed cognitive change with the Mini-Mental State Examination (MMSE). We used age, sex, pre-treatment MMSE score, and duration of treatment as covariables. Results: Before treatment, the 3 groups had comparable MMSE scores. At 6 months, participants taking memantine plus vitamin D increased their MMSE score by 4.0±3.7 points (P=0.034), while participants taking memantine alone remained stable (change of 0.0±1.8 points; P=0.891), as did those taking vitamin D alone (−0.6±3.1 points; P=0.504). Treatment with memantine plus vitamin D was associated with improvement in the MMSE score compared to memantine or vitamin D alone after adjustment for covariables (P<0.01). Mixed regression analysis showed that the visit by combined treatments (memantine plus vitamin D) interaction was significant (P=0.001), while memantine or vitamin D alone showed no effect. Conclusions: Patients with AD who took memantine plus vitamin D for 6 months had a statistically and clinically relevant gain in cognition, underlining possible synergistic and potentiating benefits of the combination