Darwinian Data Structure Selection

Data structure selection and tuning is laborious but can vastly improve an application's performance and memory footprint. Some data structures share a common interface and enjoy multiple implementations. We call them Darwinian Data Structures (DDS), since we can subject their implementations to survival of the fittest. We introduce ARTEMIS a multi-objective, cloud-based search-based optimisation framework that automatically finds optimal, tuned DDS modulo a test suite, then changes an application to use that DDS. ARTEMIS achieves substantial performance improvements for \emph{every} project in $5$ Java projects from DaCapo benchmark, $8$ popular projects and $30$ uniformly sampled projects from GitHub. For execution time, CPU usage, and memory consumption, ARTEMIS finds at least one solution that improves \emph{all} measures for $86\%$ ($37/43$) of the projects. The median improvement across the best solutions is $4.8\%$, $10.1\%$, $5.1\%$ for runtime, memory and CPU usage. These aggregate results understate ARTEMIS's potential impact. Some of the benchmarks it improves are libraries or utility functions. Two examples are gson, a ubiquitous Java serialization framework, and xalan, Apache's XML transformation tool. ARTEMIS improves gson by $16.5$\%, $1\%$ and $2.2\%$ for memory, runtime, and CPU; ARTEMIS improves xalan's memory consumption by $23.5$\%. \emph{Every} client of these projects will benefit from these performance improvements.Comment: 11 page

Measurement of turbulent flame speed of natural gas/air mixtures at elevated pressure

Turbulent flame speeds were measured over a range of pressures to 0.8 MPa using a jet flow apparatus fired with a synthetic mixture representing a mid-European natural gas. The equivalence ratio empty set was 0.9. The gas contained significant proportions of ballast gases and higher hydrocarbons. The method adopted was the 'flame angle' technique, using schlieren imaging to obtain the flame vertex angle from the peak density gradient. Image analysis techniques were developed to reduce interpretation errors and give an unbiased result. The data show higher flame speeds than those obtained with pure methane at elevated pressures, using similar methodology, and has an application in numerical modelling of combustors

Asymptotically Universal Crossover in Perturbation Theory with a Field Cutoff

We discuss the crossover between the small and large field cutoff (denoted x_{max}) limits of the perturbative coefficients for a simple integral and the anharmonic oscillator. We show that in the limit where the order k of the perturbative coefficient a_k(x_{max}) becomes large and for x_{max} in the crossover region, a_k(x_{max}) is proportional to the integral from -infinity to x_{max} of e^{-A(x-x_0(k))^2}dx. The constant A and the function x_0(k) are determined empirically and compared with exact (for the integral) and approximate (for the anharmonic oscillator) calculations. We discuss how this approach could be relevant for the question of interpolation between renormalization group fixed points.Comment: 15 pages, 11 figs., improved and expanded version of hep-th/050304

The Effect of Scattering on Pulsar Polarization Angle

The low-frequency profiles of some pulsars manifest temporal broadening due to scattering, usually accompanied by flat polarization position angle (PA) curves. Assuming that the scattering works on the 4 Stokes parameters in the same way, we have simulated the effect of scattering on polarization profiles and find that the scattering can indeed flatten the PA curves. Since the higher-frequency profiles suffer less from scattering, they are convolved with scattering models to fit the observed low-frequency profiles. The calculated flat PA curves exactly reproduce the corresponding observations.Comment: 4 pages. Accepted by A&

Chiral expansion of the π0→γγ\pi^0\rightarrow\gamma\gamma decay width

A chiral field theory of mesons has been applied to study the contribution of the current quark masses to the $\pi^0\rightarrow\gamma\gamma$ decay width at the next leading order. $2\%$ enhancement has been predicted and there is no new parameter.Comment: 9 page