Variational description of multi-fluid hydrodynamics: Uncharged fluids

We present a formalism for Newtonian multi-fluid hydrodynamics derived from an unconstrained variational principle. This approach provides a natural way of obtaining the general equations of motion for a wide range of hydrodynamic systems containing an arbitrary number of interacting fluids and superfluids. In addition to spatial variations we use ``time shifts'' in the variational principle, which allows us to describe dissipative processes with entropy creation, such as chemical reactions, friction or the effects of external non-conservative forces. The resulting framework incorporates the generalization of the entrainment effect originally discussed in the case of the mixture of two superfluids by Andreev and Bashkin. In addition to the conservation of energy and momentum, we derive the generalized conservation laws of vorticity and helicity, and the special case of Ertel's theorem for the single perfect fluid. We explicitly discuss the application of this framework to thermally conducting fluids, superfluids, and superfluid neutron star matter. The equations governing thermally conducting fluids are found to be more general than the standard description, as the effect of entrainment usually seems to be overlooked in this context. In the case of superfluid He4 we recover the Landau--Khalatnikov equations of the two-fluid model via a translation to the ``orthodox'' framework of superfluidity, which is based on a rather awkward choice of variables. Our two-fluid model for superfluid neutron star matter allows for dissipation via mutual friction and also ``transfusion'' via beta-reactions between the neutron fluid and the proton-electron fluid.Comment: uses RevTeX 4; 20 pages. To appear in PRD. v2: removed discussion of charged fluids and coupling to electromagnetic fields, which are submitted as a separate paper for a clearer presentation v3: fixed typo in Eq.(9), updated some reference

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

Parent communication and child pain and distress during painful pediatric cancer treatments

Children with cancer often consider treatment procedures to be more traumatic and painful than cancer itself. Previous research indicates that parents' behavior before and during painful medical procedures influences children's distress level. Understanding parents' naturally occurring communication patterns is essential to identifying families in need of an intervention to enhance coping and emotional well-being. Using the concept of definition of the situation from a symbolic interactionism theoretical framework, this study developed a typology of parent communication patterns and tested relationships between those patterns and children's responses to potentially painful treatment procedures. Analyses are based on video-recorded observations of 31 children and their primary parents (individuals functioning in a parenting role and serving as the primary familial caregivers during the observed procedure) in the USA during clinic visits for potentially painful pediatric oncology treatments. Four communication patterns emerged: normalizing, invalidating, supportive, and distancing. The most common communication patterns differed by clinic visit phase: normalizing during pre-procedure, supportive during procedure, and both distancing and supportive during post-procedure. Parents' communication also varied by procedure type. Supportive communication was most common during lumbar punctures; normalizing and distancing communication were most common during port starts. Six children (19.4%) experienced invalidation during at least one clinic visit phase. Analyses indicated that invalidated children experienced significantly more pain and distress than children whose parents used other communication patterns. This typology provides a theoretical approach to understanding previous research and offers a framework for the continuing investigation of the influence of parents' communication during potentially painful pediatric oncology procedures.Cancer Pediatric Communication Parent Distress Pain USA