http://www.maths.qmul.ac.uk/%7Elatora/report_06.pdf

Complex networks: Structure and dynamics

J. Appl. Cryst.の発刊に際して

https://deim.urv.cat/~alexandre.arenas/publicacions/pdf/review.pdf

Synchronization in complex networks

The origin of large but rare cascades that are triggered by small initial shocks is a phenomenon that manifests itself as diversely as cultural fads, collective action, the diffusion of norms and innovations, and cascading failures in infrastructure and organizational networks. This paper presents a possible explanation of this phenomenon in terms of a sparse, random network of interacting agents whose decisions are determined by the actions of their neighbors according to a simple threshold rule. Two regimes are identified in which the network is susceptible to very large cascades—herein called global cascades—that occur very rarely. When cascade propagation is limited by the connectivity of the network, a power law distribution of cascade sizes is observed, analogous to the cluster size distribution in standard percolation theory and avalanches in self-organized criticality. But when the network is highly connected, cascade propagation is limited instead by the local stability of the nodes themselves, and the size distribution of cascades is bimodal, implying a more extreme kind of instability that is correspondingly harder to anticipate. In the first regime, where the distribution of network neighbors is highly skewed, it is found that the most connected nodes are far more likely than average nodes to trigger cascades, but not in the second regime. Finally, it is shown that heterogeneity plays an ambiguous role in determining a system's stability: increasingly heterogeneous thresholds make the system more vulnerable to global cascades; but an increasingly heterogeneous degree distribution makes it less vulnerable.

/pdf/a-simple-model-of-global-cascades-on-random-networks-zv4xfy8ajb.pdf

A simple model of global cascades on random networks

Stable non-Gaussian random processes , by G. Samorodnitsky and M. S. Taqqu. Pp. 632. £49.50. 1994. ISBN 0-412-05171-0 (Chapman and Hall).

The construction and development of a new ideal MHD 3D-equilibrium solver, capable of dealing with magnetic islands and stochastic regions in a fast, accurate and scalable manner will be described. The SIESTA code will complement other existent 3D MHD island solvers and is particularly suited for applications that require not only accuracy but speed of evaluation as well, such as experimental 3D equilibrium reconstruction or stellarator design. SIESTA will also be useful to calculate MHD equilibria at very high spatial resolutions, such as those that might be required for the investigation of NTMs at ITER-relevant temperature and resistivity conditions. SIESTA is based on a preconditioned, iterative algorithm that takes advantage of a pre-existent VMEC solution to provide both a background coordinate system that guarantees a compact representation as well as a good initial guess for the iterative procedure. Details of the algorithm implementation, its performance on some simple test problems and initial steps towards its porting to a massively parallel environment will be discussed.

http://absimage.aps.org/image/DPP07/MWS_DPP07-2007-001418.pdf

SIESTA: an Scalable Island Equilibrium Solver for Toroidal Applications

Quiet-time statistics is an approach to the analysis of fluctuation time series that, by measuring the duration of successive transport events and the quiet times between them, allows the extraction of information on the long-range correlations in the system. It provides information similar to that obtained from rescaled adjusted range (R∕S) statistics. However, when the data are contaminated by extraneous oscillations, it is difficult to effectively use R∕S statistics or standard quiet-time analysis. In this paper, quiet-time analysis is generalized so that time series contaminated by oscillations can be treated. This new technique is effective over a wide range of time scales.

Determination of long-range correlations by quiet-time statistics

Particles and field lines outside the ATF plasma

This presentation will review developments on the integration of advanced modeling and simulation techniques into the analysis step of experimental data obtained at the Spallation Neutron Source A workflow framework for the purpose of refining molecular mechanics force-fields against quasi-elastic neutron scattering data is presented The workflow combines software components to submit model simulations to remote high performance computers, a message broker interface for communications between the optimizer engine and the simulation production step, and tools to convolve the simulated data with the experimental resolution A test application shows the correction to a popular fixed-charge water model in order to account polarization effects due to the presence of solvated ions Future enhancements to the refinement workflow are discussed This work is funded through the DOE Center for Accelerating Materials Modeling

Integrating Advanced Materials Simulation Techniques into an Automated Data Analysis Workflow at the Spallation Neutron Source

Significant improvements in real-time efficiency have been obtained for plasma fluid turbulence calculations by microtasking the nonlinear fluid code KITE in which they are implemented on the CRAY Y-MP C90 at the National Energy Research Supercomputer Center (NERSC). The number of processors accessed concurrently scales linearly with problem size. Close to six concurrent processors have so far been obtained with a three-dimensional nonlinear production calculation at the currently allowed memory size of 80 Mword. With a calculation size corresponding to the maximum allowed memory of 200 Mword in the next system configuration, the authors expect to be able to access close to ten processors of the C90 concurrently with a commensurate improvement in real-time efficiency. These improvements in performance are comparable to those expected from a massively parallel implementation of the same calculations on the Intel Paragon.

/pdf/multi-cpu-plasma-fluid-turbulence-calculations-on-a-cray-y-1aypnzaven.pdf

Vickie E. Lynch

Papers

SIESTA: an Scalable Island Equilibrium Solver for Toroidal Applications

Determination of long-range correlations by quiet-time statistics

Particles and field lines outside the ATF plasma

Integrating Advanced Materials Simulation Techniques into an Automated Data Analysis Workflow at the Spallation Neutron Source

Multi-CPU plasma fluid turbulence calculations on a CRAY Y-MP C90