Irradiation Pressure Effects in Close Binary Systems

We present a method for the calculation of the effects of external irradiation on the geometrical shape of the secondary in a close binary containing a compact star, the source of the radiation, and a normal companion star, where we include the possibility of shadowing by an accretion disc. The model is based on a simple modification of the standard Roche binary potential in which the radiation-pressure force is parameterised using the ratio of the radiation to the gravitational force. We have constructed numerical solutions of approximate 3-dimensional irradiated equipotential surfaces to demonstrate the main geometrical effects of external radiation pressure. For systems in which the inner Lagrangian point is irradiated directly and for sufficiently high irradiation fluxes, the critical condition for which the secondary fills its tidal lobe changes from an inner to an outer critical configuration, where the critical equipotential surface connects to one of the outer rather than the inner Lagrangian point. Such a situation may apply to evaporating binary pulsar systems (e.g. PSR 1957+20), stars orbiting supermassive black holes in AGN and some high-mass X-ray binaries (including Centaurus X-3). For systems containing an accretion disc, which shadows the inner Lagrangian point from the external irradiation, the presence of significant radiation pressure causes a non-axisymmetric deformation of the stellar surface. We have calculated modified Roche potentials to determine the main effects on the optical lightcurves and radial velocity curves for typical binary parameters. Compared to previous studies, the inclusion of irradiation-pressure effects results in changes in the derived system parameters (e.g. component masses, radial velocities) that may be as high as 30 per cent.Comment: 16 pages, 6 figures, submitted to MNRA

Magnetic Field Generation in Stars

Enormous progress has been made on observing stellar magnetism in stars from the main sequence through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence,in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Thus we maybe at the dawn of a new era of exciting discoveries in compact star magnetism driven by the opening of a new, non-electromagnetic observational window. We also review recent advances in the theory and computation of magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo theory. These advances offer insight into the action of stellar dynamos as well as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field generation in stars to appear in Space Science Reviews, Springe

A comparative study of mothers of infants hospitalized in an open ward neonatal intensive care unit and a combined pod and single-family room design

Abstract Background The well-being of mothers of infants requiring Neonatal Intensive Care Unit (NICU) hospitalization may be affected by the architectural design of the unit. A few recent studies suggest there may be some drawbacks of single-family rooms (SFRs) for infants and their mothers, such as isolation of mothers and reduced exposure to auditory stimulation for infants. Purpose To compare NICU-stress, symptoms of depression, perceptions of nurse-parent support and family-centered care, sleep disturbances, breastfeeding self-efficacy and readiness for discharge in mothers of infants cared for in an open ward (OW) to those cared for in a unit that includes both pods and SFRs. Methods A pre-post quasi-experimental study was conducted in a Canadian level 3 unit before and after transitioning to a new unit of 6-bed pods and SFRs. OW data were collected in 2014 and pod/SFR data 1 year after the transition in 2017 to 2018. Mothers of infants hospitalized for at least 2 weeks completed questionnaires about stress, depressive symptoms, support, family-centered care, and sleep disturbances. In the week prior to discharge, they responded to breastfeeding self-efficacy and readiness for discharge questionnaires. They described their presence in the NICU at enrollment and again prior to discharge. Results Pod/SFR mothers reported significantly less NICU-stress compared to OW mothers. OW mothers had greater sights and sounds stress and felt more restricted in their parental role. Pod/SFR mothers reported greater respect from staff. Controlling for maternal education, pod/SFR mothers perceived their infant’s readiness for discharge to be greater than OW mothers. There were no significant differences between groups in depressive symptoms, nurse-parent support, sleep disturbances, and breastfeeding self-efficacy. At enrollment and again in the weeks preceding discharge, pod/SFR mothers were present significantly more hours per week than OW mothers, controlling for maternal education. Conclusions Further study of small pods is indicated as these units may be less stressful for parents, and enhance family-centered care, as well as maternal presence, compared to OWs

The Power of the Weak: How Informal Power-Sharing Shapes the Work of the UN Security Council

To what extent is the work of international organizations shaped by their most powerful members? Can minor powers influence the decisions taken by these organizations? This dissertation presents the argument that great powers engage in power-sharing in order to attain unanimity inside international organizations, which enhances compliance and increases the effect of the signals these organizations convey to the public. The pursuit of unanimity lends weight even to votes that are not needed for the adoption of a proposal under the formal rules. It enables minor powers to exert more influence inside international organizations than they could if the formal rules and/or the balance of material power between member states determined the outcome of decision-making in international organizations. An analysis of the UN Security Council tests this argument. The dissertation identifies a series of informal power-sharing practices in the Security Council, which systematically depart from the organization's formal rules, and which promote consensus and augment minor powers' influence far beyond what one would expect on the basis of the material capabilities and voting power of these states. In turn, these informal power-sharing practices are motivated by great powers' desire to attain unanimous support for the policies enacted in the Security Council, irrespective of the body's formal voting rules. Survey experiments demonstrate the rationale behind great powers' pursuit of unanimity. They show that a policy's endorsement by a united Security Council has a much larger signaling effect on public opinion than the policy's approval by a divided Council. Qualitative case studies and novel design-based causal inference that exploits natural experiments show that minor powers strongly influence the deployment of UN peace operations and UN counter-terrorism sanctions, and that minor powers also use their influence in the Council to attain side-payments. Minor powers' influence is particularly strong during crises, when great powers are most eager to secure small states' votes through power-sharing. Interviews with diplomats in seven countries and quantitative analyses of exogenous variation in minor powers' representation on the Security Council under pre-determined rotation rules trace minor powers' influence to informal power-sharing practices in the Council