Some results on the limits of thought

Generalizing on some arguments due to Arthur Prior and Dmitry Mirimanoff, we provide some further limitative results on what can be thought.PostprintPeer reviewe

Equatorial mass loss from Be stars

Be stars are thought to be fast rotating stars surrounded by an equatorial disc. The formation, structure and evolution of the disc are still not well understood. In the frame of single star models, it is expected that the surface of an initially fast rotating star can reach its keplerian velocity (critical velocity). The Geneva stellar evolution code has been recently improved, in order to obtain some estimates of the total mass loss and of the mechanical mass loss rates in the equatorial disc during the whole critical rotation phase. We present here the first results of the computation of a grid of fast rotating B stars evolving towards the Be phase, and discuss the first estimates we obtained.Comment: 2 pages, 2 figures To appear in the proceedings of the IAUS 272 on "Active OB stars: structure, evolution, mass loss and critical limits

Fermi-LAT upper limits on gamma-ray emission from colliding wind binaries

Context: Colliding wind binaries (CWBs) are thought to give rise to a plethora of physical processes including acceleration and interaction of relativistic particles. Observation of synchrotron radiation in the radio band confirms there is a relativistic electron population in CWBs. Accordingly, CWBs have been suspected sources of high-energy gamma-ray emission since the COS-B era. Theoretical models exist that characterize the underlying physical processes leading to particle acceleration and quantitatively predict the non-thermal energy emission observable at Earth. Aims: We strive to find evidence of gamma-ray emission from a sample of seven CWB systems: WR 11, WR 70, WR 125, WR 137, WR 140, WR 146, and WR 147. Theoretical modelling identified these systems as the most favourable candidates for emitting gamma-rays. We make a comparison with existing gamma-ray flux predictions and investigate possible constraints. Methods: We used 24 months of data from the Large Area Telescope (LAT) on-board the Fermi Gamma Ray Space Telescope to perform a dedicated likelihood analysis of CWBs in the LAT energy range. Results: We find no evidence of gamma-ray emission from any of the studied CWB systems and determine corresponding flux upper limits. For some CWBs the interplay of orbital and stellar parameters renders the Fermi-LAT data not sensitive enough to constrain the parameter space of the emission models. In the cases of WR140 and WR147, the Fermi-LAT upper limits appear to rule out some model predictions entirely and constrain theoretical models over a significant parameter space. A comparison of our findings to the CWB eta Car is made.Comment: 9 pages, 3 figure

Random structures for partially ordered sets

This thesis is presented in two parts. In the first part, we study a family of models of random partial orders, called classical sequential growth models, introduced by Rideout and Sorkin as possible models of discrete space-time. We analyse a particular model, called a random binary growth model, and show that the random partial order produced by this model almost surely has infinite dimension. We also give estimates on the size of the largest vertex incomparable to a particular element of the partial order. We show that there is some positive probability that the random partial order does not contain a particular subposet. This contrasts with other existing models of partial orders. We also study "continuum limits" of sequences of classical sequential growth models. We prove results on the structure of these limits when they exist, highlighting a deficiency of these models as models of space-time. In the second part of the thesis, we prove some correlation inequalities for mappings of rooted trees into complete trees. For T a rooted tree we can define the proportion of the total number of embeddings of T into a complete binary tree that map the root of T to the root of the complete binary tree. A theorem of Kubicki, Lehel and Morayne states that, for two binary trees with one a subposet of the other, this proportion is larger for the larger tree. They conjecture that the same is true for two arbitrary trees with one a subposet of the other. We disprove this conjecture by analysing the asymptotics of this proportion for large complete binary trees. We show that the theorem of Kubicki, Lehel and Morayne can be thought of as a correlation inequality which enables us to generalise their result in other directions

Particle systems with quasi-homogeneous initial states and their occupation time fluctuations

Occupation time fluctuation limits of particle systems in R^d with independent motions (symmetric stable Levy process, with or without critical branching) have been studied assuming initial distributions given by Poisson random measures (homogeneous and some inhomogeneous cases). In this paper, with d=1 for simplicity, we extend previous results to a wide class of initial measures obeying a quasi-homogeneity property, which includes as special cases homogeneous Poisson measures and many deterministic measures (simple example: one atom at each point of Z), by means of a new unified approach. In previous papers, in the homogeneous Poisson case, for the branching system in "low" dimensions, the limit was characterized by a long-range dependent Gaussian process called sub-fractional Brownian motion (sub-fBm), and this effect was attributed to the branching because it had appeared only in that case. An unexpected finding in this paper is that sub-fBm is more prevalent than previously thought. Namely, it is a natural ingredient of the limit process in the non-branching case (for "low" dimension), as well. On the other hand, fractional Brownian motion is not only related to systems in equilibrium (e.g., non-branching system with initial homogeneous Poisson measure), but it also appears here for a wider class of initial measures of quasi-homogeneous type

The 2017 Vermont Opioid Prescribing Rules: Prescriber Attitudes

Introduction. In July of 2017, Vermont enacted new rules on acute opioid pre- scribing to reduce misuse, addiction, and overdose associated with prescription opioids. The new rules include requirements of non-opioid therapy use when possible, querying VPMS, patient education and informed consent, and co-prescription of naloxone. Our study objective was to gain insight into the perspectives of opioid prescribers on the new rules. Methods. The 17-item survey included closed and open-ended questions addressing prescriber perceptions about the new rules as well as demographic information about respondents. The survey was sent to Vermont-based opioid prescribers via email, to multiple healthcare organizations and professional societies, and through personal contacts. Open-ended responses were categorized using paired reviewers and group consensus, using a grounded theory approach. Results. A total of 431 responses were obtained, with MD/DOs accounting for 65%, APRNs- 14%, DDS/DMD- 7%, PAs-13%, and NDs- 1%. Of the respondents, 75% thought that more restrictive opioid prescribing rules were necessary, 74% felt the new rules would have some positive effect on the opioid crisis, but only 48% were in favor of the new rules. Barriers to implementation included co-prescribing naloxone (50% were unsuccessful), justifying exceptions to rules in medical record (46% unsuc- cessful), considering non-pharmacologic therapies (39% unsuccessful), and adhering to prescription limits (31% unsuccessful). Conclusions. Roll-out of the new rules has been criticized for implementation issues, overall reducing favorability among prescribers. Feedback obtained may be utilized by the Vermont Health Department and by other states to improve current models of opioid prescribing.https://scholarworks.uvm.edu/comphp_gallery/1264/thumbnail.jp

Resource speed limits: Maximal rate of resource variation

Recent advances in quantum resource theories have been driven by the fact that many quantum information protocols make use of different facets of the same physical features, e.g. entanglement, coherence, etc. Resource theories formalise the role of these important physical features in a given protocol. One question that remains open until now is: How quickly can a resource be generated or degraded? Using the toolkit of quantum speed limits we construct bounds on the minimum time required for a given resource to change by a fixed increment, which might be thought of as the power of said resource, i.e., rate of resource variation. We show that the derived bounds are tight by considering several examples. Finally, we discuss some applications of our results, which include bounds on thermodynamic power, generalised resource power, and estimating the coupling strength with the environment.Comment: 6 pages, 2 figure