A Bayesian Method for Oscillator Stability Analysis

The power spectral density of frequency fluctuations of an oscillator is generally modeled as a sum of power laws with integer exponents (from-2 to +2). However, a power law with a fractional exponent may exist. We propose a method for measuring the level of such a noise process and determining the probability density of the exponent. This yields a criterion for compatibility with an integer exponent. This method is based upon a Bayesian approach called the reference analysis of Bernardo-Berger. The application to a sequence of frequency measurement from a quartz oscillator illustrates this paper. Index Terms oscillator characterization, time stability, noise analysis, Bayesian analysis I

Search of a gravitational wave background in timing residuals of PSR 1937 21: minimal model and upper limits on Omega_gr

International audienceAlthough many phenomena can account for pulsar timing residuals, previous upper limits on the amplitude Omega_gr of a gravitational wave background were all obtained with the same decomposition into a measurement noise with known variance and a gravitational noise parametrized by Omega_gr. The justification of this minimal model (MM) is its ability to provide, on average over an infinite set of measurements, the highest upper limits on Omega_gr compared with other models. Keeping with this model, and using free-access Arecibo data concerning PSR 1937 21, we derive a set of 157 estimators of Omega_gr and obtain the 95 per cent confidence upper limit of 1.7x10^-7 using a Bayesian method. We also show evidence of a third term in the residuals (97 per cent confidence), which questions the adequacy of the MM

Overview on the Clean Sky Technology Evaluator assessments

Cross-positioned within the Clean Sky Programme, the Technology Evaluator (TE) is a dedicated evaluation platform. It has the key role of assessing the environmental impact of the technologies developed in Clean Sky and their level of success towards the ACARE environmental goals. TE assessments consider all promising green technologies selected by Clean Sky´s ITDs (Integrated Technology Demonstrator platforms) in which these technologies are developed and clustered in coherent and mutually compatible solution sets, identifying optimized new future aircraft solutions. The ITDs are: • Smart Fixed Wing Aircraft (SFWA) addressing large aircraft technologies • Green Regional Aircraft (GRA) addressing regional aircraft technologies • Green Rotorcraft (GRC) addressing rotorcraft technologies • Sustainable And Green Engines (SAGE) addressing engine technologies • Systems for Green Operations (SGO) addressing aircraft systems The ITD technologies are integrated into simplified conceptual aircraft performance models in order to evaluate the Clean Sky technology solution sets at aircraft level. These aircraft are named Clean Sky concept aircraft. Using these Clean Sky concept aircraft as a basis the TE conducts assessments at three levels: • Aircraft level At aircraft level the environmental evaluation of a single flight is performed. To this end a Clean Sky concept aircraft and its reference technology aircraft are compared along the same reference trajectory in order to determine the environmental benefit of the Clean Sky technologies. The main environmental indicators considered are noise on ground, fuel burn and emissions (CO2 and NOX). • Airport level At airport level the environmental impact on local communities around an airport is assessed. To this end a year 2020 airport traffic scenario with reference technology aircraft is compared with the same traffic scenario but in which Clean Sky concept aircraft replace their reference technology counterpart. The main metrics at airport level are noise on the ground, population impacted by certain noise levels, and emissions (CO2 and NOX). • Air transport system (ATS) level At ATS level the environmental impact of Clean Sky technologies is quantified at global scale. To this end a year 2020 fleet traffic scenario with reference technology aircraft is compared with the same traffic scenario but in which Clean Sky concept aircraft replace their reference technology counterpart. Fuel burn and emissions (CO2 and NOX) are the main indicators of interest at ATS level. The present paper will give an overview on the TE methodology and present the latest results at the three assessment levels