The CBE Hardware Accelerator for Numerical Relativity: A Simple Approach

Hardware accelerators (such as the Cell Broadband Engine) have recently received a significant amount of attention from the computational science community because they can provide significant gains in the overall performance of many numerical simulations at a low cost. However, such accelerators usually employ a rather unfamiliar and specialized programming model that often requires advanced knowledge of their hardware design. In this article, we demonstrate an alternate and simpler approach towards managing the main complexities in the programming of the Cell processor, called software caching. We apply this technique to a numerical relativity application: a time-domain, finite-difference Kerr black hole perturbation evolver, and present the performance results. We obtain gains in the overall performance of generic simulations that are close to the theoretical maximum that can be obtained through our parallelization approach.Comment: 5 pages, 2 figures; Accepted for publication in the International Journal of Modeling, Simulation, and Scientific Computing (IJMSSC

Performance Evaluation of Video Communications over 4G Network

With exponential increase in the volumes of video traffic in cellular net-works, there is an increasing need for optimizing the quality of video delivery. 4G networks (Long Term Evolution Advanced or LTE A) are being introduced in many countries worldwide, which allow a downlink speed of upto 1 Gbps and uplink of 100 Mbps over a single base station. In this paper, we characterize the performance of LTE A physical layer in terms of transmitted video quality when the channel condi-tions and LTE settings are varied. We test the performance achieved as the channel quality is changed and HARQ features are enabled in physical layer. Blocking and blurring metrics were used to model image quality.Comment: Accepted in ICACNI 2013. arXiv admin note: substantial text overlap with arXiv:1304.375

Signs and Stability in Higher-Derivative Gravity

Perturbatively renormalizable higher-derivative gravity in four space-time dimensions with arbitrary signs of couplings has been considered. Systematic analysis of the action with arbitrary signs of couplings in lorentzian flat space-time for no-tachyons, fixes the signs. Feynman $+i\epsilon$ prescription for these sign further grants necessary convergence in path-integral, suppressing the field modes with large action. This also leads to a sensible wick rotation where quantum computation can be performed. Running couplings for these sign of parameters makes the massive tensor ghost innocuous leading to a stable and ghost-free renormalizable theory in four space-time dimensions. The theory has a transition point arising from renormalisation group (RG) equations, where the coefficient of $R^2$ diverges without affecting the perturbative quantum field theory. Redefining this coefficient gives a better handle over the theory around the transition point. The flow equations pushes the flow of parameters across the transition point. The flow beyond the transition point is analysed using the one-loop RG equations which shows that the regime beyond the transition point has unphysical properties: there are tachyons, the path-integral loses positive definiteness, Newton's constant $G$ becomes negative and large, and perturbative parameters become large. These shortcomings indicate a lack of completeness beyond the transition point and need of a non-perturbative treatment of the theory beyond the transition point.Comment: 13 pages, 0 figures. V2: minor text modification, references added, minor typos and affiliation edited. Published in IJMP