Parallel implementation of the non-smooth contact dynamics method for large particle systems

In numerous industrial applications there is the need to realistically model granular material. For instance, simulating the interaction of vehicles and tools with soil is of great importance for the design of earth moving machinery. The Discrete Element Method (DEM) has been successfully applied to this task [1, 2]. Large scale problems require a lot of computational resources. Hence, for the application in the industrial engineering process, the computational effort is an issue. In DEM parallelization is straight forward, since each contact between adjacent particles is resolved locally without regard of the other contacts. However, modelling a contact as a stiff spring imposes strong limitations on the time step size to maintain a stable simulation. The Non–Smooth Contact Dynamics Method (NSCD), on the other hand, models contacts globally as a set of inequality constraints on a system of perfectly rigid bodies [3]. At the end of every time step, all inequality constraints must be satisfied simultaneously, which can be achieved by solving a complementarity problem. This leads to a numerically stable method that is robust with respect to much larger time steps in comparison to DEM. Since a global problem must be solved, parallelization now strongly depends on the numerical solver that is used for the complementarity problem. We present our first massively parallel implementation of NSCD based on the projected Gauß-Jacobi (PGJ) iterative scheme presented in [4]. Focusing on one-sided asynchronous communication patterns with double buffering for data exchange, global synchronizations can be avoided. Only weak synchronization due to data dependencies of neighboring domains remains. The implementation is based on the Global address space Programming Interface (GPI), supplemented by the Multi Core Threading Package (MCTP) [5] on the processor level. This allows to efficiently overlap calculation and communication between processors

The interface of gravity and quantum mechanics illuminated by Wigner phase space

We provide an introduction into the formulation of non-relativistic quantum mechanics using the Wigner phase-space distribution function and apply this concept to two physical situations at the interface of quantum theory and general relativity: (i) the motion of an ensemble of cold atoms relevant to tests of the weak equivalence principle, and (ii) the Kasevich-Chu interferometer. In order to lay the foundations for this analysis we first present a representation-free description of the Kasevich-Chu interferometer based on unitary operators.Comment: 69 pages, 6 figures, minor changes to match the published version. The original publication is available at http://en.sif.it/books/series/proceedings_fermi or http://ebooks.iospress.nl/volumearticle/3809

Heme Oxygenase-1 Induction and Organic Nitrate Therapy: Beneficial Effects on Endothelial Dysfunction, Nitrate Tolerance, and Vascular Oxidative Stress

Organic nitrates are a group of very effective anti-ischemic drugs. They are used for the treatment of patients with stable angina, acute myocardial infarction, and chronic congestive heart failure. A major therapeutic limitation inherent to organic nitrates is the development of tolerance, which occurs during chronic treatment with these agents, and this phenomenon is largely based on induction of oxidative stress with subsequent endothelial dysfunction. We therefore speculated that induction of heme oxygenase-1 (HO-1) could be an efficient strategy to overcome nitrate tolerance and the associated side effects. Indeed, we found that hemin cotreatment prevented the development of nitrate tolerance and vascular oxidative stress in response to chronic nitroglycerin therapy. Vice versa, pentaerithrityl tetranitrate (PETN), a nitrate that was previously reported to be devoid of adverse side effects, displayed tolerance and oxidative stress when the HO-1 pathway was blocked pharmacologically or genetically by using HO-1+/– mice. Recently, we identified activation of Nrf2 and HuR as a principle mechanism of HO-1 induction by PETN. With the present paper, we present and discuss our recent and previous findings on the role of HO-1 for the prevention of nitroglycerin-induced nitrate tolerance and for the beneficial effects of PETN therapy