Pulsar Timing Array Based Search for Supermassive Black Hole Binaries in the Square Kilometer Array Era

The advent of next generation radio telescope facilities, such as the Square Kilometer Array (SKA), will usher in an era where a pulsar timing array (PTA) based search for gravitational waves (GWs) will be able to use hundreds of well timed millisecond pulsars rather than the few dozens in existing PTAs. A realistic assessment of the performance of such an extremely large PTA must take into account the data analysis challenge posed by an exponential increase in the parameter space volume due to the large number of so-called pulsar phase parameters. We address this problem and present such an assessment for isolated supermassive black hole binary (SMBHB) searches using a SKA era PTA containing 10^{3} pulsars. We find that an all-sky search will be able to confidently detect nonevolving sources with a redshifted chirp mass of 10^{10}  M_{⊙} out to a redshift of about 28 (corresponding to a rest-frame chirp mass of 3.4×10^{8}  M_{⊙}). We discuss the important implications that the large distance reach of a SKA era PTA has on GW observations from optically identified SMBHB candidates. If no SMBHB detections occur, a highly unlikely scenario in the light of our results, the sky-averaged upper limit on strain amplitude will be improved by about 3 orders of magnitude over existing limits.

A Multi-State Optimization Framework for Parameter Estimation in Biological Systems

Parameter estimation is a key concern for reliable and predictive models of biological systems. In this paper, we propose a multi-objective, multi-state optimization framework that allows multiple data sources to be incorporated into the parameter estimation process. This enables the model to better represent a diverse range of data from both within and outwith the training set; and to determine more biologically relevant parameter values for the model parameters. The framework is based on a multi-objective PSwarm implementation (MoPSwarm) and is validated via a case study on the ERK signalling pathway, in which significant advantages over the conventional single-state approach are demonstrated. Several variants of the framework are analyzed to determine the optimal configuration for convergence and solution quality.