Effects of Interplanetary Dust on the LISA drag-free Constellation

The analysis of non-radiative sources of static or time-dependent gravitational fields in the Solar System is crucial to accurately estimate the free-fall orbits of the LISA space mission. In particular, we take into account the gravitational effects of Interplanetary Dust (ID) on the spacecraft trajectories. The perturbing gravitational field has been calculated for some ID density distributions that fit the observed zodiacal light. Then we integrated the Gauss planetary equations to get the deviations from the LISA keplerian orbits around the Sun. This analysis can be eventually extended to Local Dark Matter (LDM), as gravitational fields are expected to be similar for ID and LDM distributions. Under some strong assumptions on the displacement noise at very low frequency, the Doppler data collected during the whole LISA mission could provide upper limits on ID and LDM densities.Comment: 11 pages, 6 figures, to be published on the special issue of "Celestial Mechanics and Dynamical Astronomy" on the CELMEC V conferenc

Wired communities in the city: Sydney, Australia

Questions relating to the ability of particular groups in society to access information and communications technologies (ICTs) have become a growing part of the academic and policy literature. The issues raised in this literature have revolved around a number of themes, many of which can be subsumed under concerns about a growing digital divide whereby society is being divided into information rich and information poor sectors. This differentiation can be between particular social groups irrespective of place, or between people in particular places be these large regional areas (e.g. metropolitan versus non-metropolitan) or localities and communities within an urban area. This paper focuses on the existence of a ‘digital divide’ across the Sydney metropolitan area. Using ABS 2001 census data the paper presents an analysis of computer and internet access and use for clusters of local communities and focuses on how usage differs across communities as differentiated by socio-economic status, household and family status and ethnic background