Mixmaster chaos

The significant discussion about the possible chaotic behavior of the mixmaster cosmological model due to Cornish and Levin [J.N. Cornish and J.J. Levin, Phys. Rev. Lett. 78 (1997) 998; Phys. Rev. D 55 (1997) 7489] is revisited. We improve their method by correcting nontrivial oversights that make their work inconclusive to precisely confirm their result: ``The mixmaster universe is indeed chaotic''.Comment: 9 pages, 4 figure

Actors, decision-making, and institutions in quantitative system modelling

Increasing realism in quantitative system modelling with respect to the representation of actors, decision-making, and institutions is critical to better understand the transition towards a low-carbon sustainable society. Yet, studies using quantitative system models, which have become a key analytical tool to support sustainability and decarbonization policies, focus on outcomes, therefore overlooking the dynamics of the drivers of change. We explore opportunities that arise from a deeper engagement of quantitative systems modelling with social science. We argue that several opportunities for enriching the realism in model-based scenario analysis can arise through model refinements oriented towards a more detailed approach in terms of actor heterogeneity, as well as through integration across different analytical and disciplinary approaches. Several opportunities that do not require major changes in model structure are ready to be seized. Promising ones include combining different types of models and enriching model-based scenarios with evidence from applied economics and transition studies

An Indication of Anisotropy in Arrival Directions of Ultra-high-energy Cosmic Rays through Comparison to the Flux Pattern of Extragalactic Gamma-Ray Sources

A new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above 20 EeV with zenith angles up to 80 degrees. recorded before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies from a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies from the Swift-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0 sigma, the highest value of the test statistic being for energies above 39 EeV. The three alternative models are favored against isotropy with 2.7 sigma-3.2 sigma significance. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed

Inferences on mass composition and tests of hadronic interactions from 0.3 to 100 EeV using the water-Cherenkov detectors of the Pierre Auger Observatory

We present a new method for probing the hadronic interaction models at ultrahigh energy and extracting details about mass composition. This is done using the time profiles of the signals recorded with the water-Cherenkov detectors of the Pierre Auger Observatory. The profiles arise from a mix of the muon and electromagnetic components of air showers. Using the risetimes of the recorded signals, we define a new parameter, which we use to compare our observations with predictions from simulations. We find, first, inconsistencies between our data and predictions over a greater energy range and with substantially more events than in previous studies. Second, by calibrating the new parameter with fluorescence measurements from observations made at the Auger Observatory, we can infer the depth of shower maximum Xmax for a sample of over 81,000 events extending from 0.3 to over 100 EeV. Above 30 EeV, the sample is nearly 14 times larger than what is currently available from fluorescence measurements and extending the covered energy range by half a decade. The energy dependence of ?Xmaxcopyright is compared to simulations and interpreted in terms of the mean of the logarithmic mass. We find good agreement with previous work and extend the measurement of the mean depth of shower maximum to greater energies than before, reducing significantly the statistical uncertainty associated with the inferences about mass composition

High resolution profile of radiocaesium deposition in Loch Lomond sediments - a failure of ¹³⁷Cs dating

A sediment core from the southern basin of freshwater Loch Lomond, Scotland, was thinly sectioned at 3mm intervals and analysed for radiocaesium, present as a result of fallout from the atmospheric nuclear weapons' testing programme of the 1950s and 1960s and from the Chernobyl reactor accident of April 1986. The high-resolution sampling enabled much improved resolution of peaks from weapons testing fallout and Chernobyl and led to the estimation of a sedimentation rate (30.9mgcm-2y-1) for which the uncertainty was a factor of five times less than that of a previous study based on a 1cm sampling frequency. Further potential advantages of high-resolution sampling in distinguishing possible influences upon the vertical distribution of radiocaesium in sediments are discussed

Manganese behaviour in the sediments of diverse Scottish freshwater lochs

Mn concentrations were determined in sediments and pore waters of five freshwater lochs in Scotland. The aim was to establish whether the geochemical behavior of Mn differed in a range of limnological conditions: oligotrophic/mesotrophic Loch Lomond; eutrophic unstratified Loch Leven; seasonally stratified eutrophic Balgavies Loch; oligotrophic, acidified Round Loch of Glenhead; and oligotrophic, acid-sensitive Loch Coire nan Arr. Although redox-driven diagenesis of Mn was evident in all lochs, the diversity of conditions in the lochs resulted in some cases in modifications to behavior predicted by conceptual models for transport of Mn at a redox boundary. These differences were reflected in the chemical associations and trends in concentration of Mn. A classic example of Mn redox cycling in the sediments of Loch Lomond provided a basis for comparison with other systems. Higher inventories of Mn in sediment collected from eutrophic Loch Leven during the summer, compared with sediment from autumn and winter sampling, were explained by the effects of enhanced primary productivity (high pH and dissolved oxygen concentrations) during a summer algal bloom. In Balgavies Loch, where the bottom water was hypoxic, at the time of sampling, previous diagenetic enrichment of Mn in the surface sediment was subject to modification by dissolution and release from the solid phase to pore water, which was elevated in Mn. The increase in solid-phase Mn concentration with depth and lack of significant surface enhancement of Mn in Round Loch contrasted markedly with results from other lochs. This was attributed mainly to acidification, producing a pH-related decrease in Mn sedimentation. Mn partitioning and porewater data for Loch Coire nan Arr were in some respects similar to those at Round Loch, with both lochs having peaty sediment. However, Mn concentration patterns attributed to acidification effects at Round Loch were not found in Loch Coire nan Arr