Average luminosity distance in inhomogeneous universes

The paper studies the correction to the distance modulus induced by inhomogeneities and averaged over all directions from a given observer. The inhomogeneities are modeled as mass-compensated voids in random or regular lattices within Swiss-cheese universes. Void radii below 300 Mpc are considered, which are supported by current redshift surveys and limited by the recently observed imprint such voids leave on CMB. The averaging over all directions, performed by numerical ray tracing, is non-perturbative and includes the supernovas inside the voids. Voids aligning along a certain direction produce a cumulative gravitational lensing correction that increases with their number. Such corrections are destroyed by the averaging over all directions, even in non-randomized simple cubic void lattices. At low redshifts, the average correction is not zero but decays with the peculiar velocities and redshift. Its upper bound is provided by the maximal average correction which assumes no random cancelations between different voids. It is described well by a linear perturbation formula and, for the voids considered, is 20% of the correction corresponding to the maximal peculiar velocity. The average correction calculated in random and simple cubic void lattices is severely damped below the predicted maximal one after a single void diameter. That is traced to cancellations between the corrections from the fronts and backs of different voids. All that implies that voids cannot imitate the effect of dark energy unless they have radii and peculiar velocities much larger than the currently observed. The results obtained allow one to readily predict the redshift above which the direction-averaged fluctuation in the Hubble diagram falls below a required precision and suggest a method to extract the background Hubble constant from low redshift data without the need to correct for peculiar velocities.Comment: 34 pages, 21 figures, matches the version accepted in JCA

The Evolution of Compact Binary Star Systems

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure

Tenure, gender and household structure

Starting with a review of recent literature on gender and housing, this paper goes on to develop a new theory of household structure, in which concepts of gender and generation play a key role. The utility of this theory is then demonstrated in the analysis of data from a survey of households in the City of Salford

Food, feeding and the material everyday geographies of infants: possibilities and potentials

This is an Accepted Manuscript of an article published by Taylor & Francis in Social and Cultural Geography on 16 Jun 2016, available online: http://dx.doi.org/10.1080/14649365.2016.1193889This paper forges an agenda for researching geographies of infants. Scholars have tended to overlook the everyday geographies of very young children. However, outside of geography, infancy is seen as a specifically dynamic period of life, and is subject to sustained research and policy intervention. In particular, early childhood is viewed as a key point in which to intervene to transform enduring, interconnected, societal, educational, and health based inequalities (Department of Health and Department for Education, 2013; US Early Head Start Act, 2007). Food and feeding are seen as critical both to the health of infants now and of the children and adults they become (NHS Start 4 Life, 2010). However, much policy and research under-theorises the importance of socio-spatial contexts and the subjectivity/agency of infants. There is, then, an urgent need for geographers to put infants onto the agenda, to inform and challenge these dominant accounts. Researching with infants necessitates not just critiquing modern, liberal notions of an autonomous subject/agent, but developing a new way of understanding subjectivity and agency. Drawing upon Lupton’s (2013) notion of infant-carer interembodiment, I suggest a way forward with reference to the material geographies of infant feeding