Time-dependent ejection velocity model for the outflow of Hen 3--1475

We present 2D axisymmetric and 3D numerical simulations of the proto-planetary nebula Hen 3-1475, which is characterized by a remarkably highly collimated optical jet, formed by a string of shock-excited knots along the axis of the nebula. It has recently been suggested that the kinematical and morphological properties of the Hen 3-1475 jet could be the result of an ejection variability of the central source (Riera et al. 2003). The observations suggest a periodic variability of the ejection velocity superimposed on a smoothly increasing ejection velocity ramp. From our numerical simulations, we have obtained intensity maps (for different optical emission lines) and position-velocity diagrams, in order to make a direct comparison with the HST observations of this object. Our numerical study allows us to conclude that a model of a precessing jet with a time-dependent ejection velocity, which is propagating into an ISM previously perturbed by an AGB wind, can succesfully explain both the morphological and the kinematical characteristics of this proto-planetary nebula.Comment: Astronomy and Astrophysics (accepted) (8 figures

Body Size Evolution in Extant Oryzomyini Rodents: Cope's Rule or Miniaturization?

At the macroevolutionary level, one of the first and most important hypotheses that proposes an evolutionary tendency in the evolution of body sizes is “Cope's rule". This rule has considerable empirical support in the fossil record and predicts that the size of species within a lineage increases over evolutionary time. Nevertheless, there is also a large amount of evidence indicating the opposite pattern of miniaturization over evolutionary time. A recent analysis using a single phylogenetic tree approach and a Bayesian based model of evolution found no evidence for Cope's rule in extant mammal species. Here we utilize a likelihood-based phylogenetic method, to test the evolutionary trend in body size, which considers phylogenetic uncertainty, to discern between Cope's rule and miniaturization, using extant Oryzomyini rodents as a study model. We evaluated body size trends using two principal predictions: (a) phylogenetically related species are more similar in their body size, than expected by chance; (b) body size increased (Cope's rule)/decreased (miniaturization) over time. Consequently the distribution of forces and/or constraints that affect the tendency are homogenous and generate this directional process from a small/large sized ancestor. Results showed that body size in the Oryzomyini tribe evolved according to phylogenetic relationships, with a positive trend, from a small sized ancestor. Our results support that the high diversity and specialization currently observed in the Oryzomyini tribe is a consequence of the evolutionary trend of increased body size, following and supporting Cope's rule

Thickening agents used for dysphagia management: effect on bioavailability of water, medication and feelings of satiety

Dysphagia is the medical term for difficulty swallowing. Thickened liquids are often used in the management of dysphagia to improve bolus control and to help prevent aspiration. A range of starches and gums has historically been used to thicken liquids. Although thickened liquids improve swallow safety, they appear to have a great potential for unintended physiological consequences. Initial concerns were raised about the impact of thickeners on water binding due to the high prevalence of dehydration amongst individuals with dysphagia. Thankfully, regardless of thickening agent, thickeners do not affect water bioavailability. This effect holds true even for extremely thick fluids. However, bioavailability of medication is impaired with viscous substances. Liquids thickened to as little as 150 mPa.s retards drug release. In addition, feelings of satiety and thirst increase with increasingly viscous fluids. Flavour deteriorates with increasing thickness regardless of thickening agent. Therapeutically clinicians often prescribe small volumes of thickened liquids, consumed often. Yet small volumes of thick substances consumed with a long oral processing time, which is common for individuals with dysphagia, reduces the amount consumed. A combination of poor flavour, and increasing feelings of fullness result in little motivation and poor physiologic drive to consume thickened liquids.This review provides evidence from the dysphagia, pharmaceutical and food technology literature to show unintended side effects of thickened liquids that contribute to dehydration and potential sub-theraputic medication levels for individuals with dysphagia. The physical property of viscosity rather than a particular thickening agent appears to be key. Provision of "spoon-thick" or "extremely thick liquids" is particularly likely to contribute to dehydration and poor bioavailability of solid dose medication. Clinicians are encouraged to prescribe the minimal level of thickness needed for swallowing safety. Consultation with pharmacy and dietetic staff is essential for optimum management of individuals with dysphagia. Given the aged population forecasts for the year 2050, improved dysphagia management should be a high priority