Meaningful characterisation of perturbative theoretical uncertainties

We consider the problem of assigning a meaningful degree of belief to uncertainty estimates of perturbative series. We analyse the assumptions which are implicit in the conventional estimates made using renormalisation scale variations. We then formulate a Bayesian model that, given equivalent initial hypotheses, allows one to characterise a perturbative theoretical uncertainty in a rigorous way in terms of a credibility interval for the remainder of the series. We compare its outcome to the conventional uncertainty estimates in the simple case of the calculation of QCD corrections to the e+e- -> hadrons process. We find comparable results, but with important conceptual differences. This work represents a first step in the direction of a more comprehensive and rigorous handling of theoretical uncertainties in perturbative calculations used in high energy phenomenology.Comment: 28 pages, 5 figures. Language modified in order to make it more 'bayesian'. No change in results. Version published in JHE

Reconnection surgery in adult post-operative short bowel syndrome < 100 cm: is colonic continuity sufficient to achieve enteral autonomy without autologous gastrointestinal reconstruction? Report from a single center and systematic review of literature

A systematic bibliographic research concerning patients operated on for SBS was performed: inclusion criteria were adult age, reconnection surgery and SBS &lt; 100 cm. Autologous gastrointestinal reconstruction represented an exclusion criteria. The outcomes of interest were the rate of total parenteral nutrition (TPN) independence and the length of follow-up (minimum 1 year) after surgery. We reviewed our experience from 2003 to 2013 with minimum 1-year follow-up, dealing with reconnection surgery in 13 adults affected by &lt; 100 cm SBS after massive small bowel resection: autologous gastrointestinal reconstruction was not feasible. Three (out of 5168 screened papers) non randomized controlled trials with 116 adult patients were analysed showing weaning from TPN (40%, 50% and 90% respectively) after reconnection surgery without autologous gastrointestinal reconstruction. Among our 13 adults, mean age was 54.1 years (53.8 % ASA III): 69.2 % had a high stomal output (&gt; 500 cc/day) and TPN dependence was 100%. We performed a jejuno-colonic anastomosis (SBS type II) in 53.8%, in 46.1% of cases without ileo-cecal valve, leaving a mean residual small bowel length of 75.7 cm. In-hospital mortality was 0%. After a minimum period of 1 year of intestinal rehabilitation, all our patients (100%) went back to oral intake and 69.2% were off TPN (9 patients). No one was listed for transplantation. A residual small bowel length of minimum 75 cm, even if reconnected to part of the colon, seems able to produce a TPN independence without autologous gastrointestinal reconstruction after a minimum period of 1 year of intestinal rehabilitation

In Situ X-ray Raman Scattering Spectroscopy of the Formation of Cobalt Carbides in a Co/TiO2 Fischer–Tropsch Synthesis Catalyst

We present in situ experiments to study the possible formation of cobalt carbides during Fischer–Tropsch synthesis (FTS) in a Co/TiO2 catalyst at relevant conditions of pressure and temperature. The experiments were performed by a combination of X-ray Raman scattering (XRS) spectroscopy and X-ray diffraction (XRD). Two different experiments were performed: (1) a Fischer–Tropsch Synthesis (FTS) reaction of an ∼14 wt % Co/TiO2 catalyst at 523 K and 5 bar under H2 lean conditions (i.e., a H2:CO ratio of 0.5) and (2) carburization of pure cobalt (as reference experiment). In both experiments, the Co L3-edge XRS spectra reveal a change in the oxidation state of the cobalt nanoparticles, which we assign to the formation of cobalt carbide (Co2C). The C K edge XRS spectra were used to quantify the formation of different carbon species in both experiments.Peer reviewe

A population of luminous accreting black holes with hidden mergers

Major galaxy mergers are thought to play an important part in fuelling the growth of supermassive black holes. However, observational support for this hypothesis is mixed, with some studies showing a correlation between merging galaxies and luminous quasars and others showing no such association. Recent observations have shown that a black hole is likely to become heavily obscured behind merger-driven gas and dust, even in the early stages of the merger, when the galaxies are well separated (5 to 40 kiloparsecs). Merger simulations further suggest that such obscuration and black-hole accretion peaks in the final merger stage, when the two galactic nuclei are closely separated (less than 3 kiloparsecs). Resolving this final stage requires a combination of high-spatial-resolution infrared imaging and high-sensitivity hard-X-ray observations to detect highly obscured sources. However, large numbers of obscured luminous accreting supermassive black holes have been recently detected nearby (distances below 250 megaparsecs) in X-ray observations. Here we report high-resolution infrared observations of hard-X-ray-selected black holes and the discovery of obscured nuclear mergers, the parent populations of supermassive-black-hole mergers. We find that obscured luminous black holes (bolometric luminosity higher than 2x10^44 ergs per second) show a significant (P<0.001) excess of late-stage nuclear mergers (17.6 per cent) compared to a sample of inactive galaxies with matching stellar masses and star formation rates (1.1 per cent), in agreement with theoretical predictions. Using hydrodynamic simulations, we confirm that the excess of nuclear mergers is indeed strongest for gas-rich major-merger hosts of obscured luminous black holes in this final stage.Comment: To appear in the 8 November 2018 issue of Nature. This is the authors' version of the wor

The Hubbard model within the equations of motion approach

The Hubbard model has a special role in Condensed Matter Theory as it is considered as the simplest Hamiltonian model one can write in order to describe anomalous physical properties of some class of real materials. Unfortunately, this model is not exactly solved except for some limits and therefore one should resort to analytical methods, like the Equations of Motion Approach, or to numerical techniques in order to attain a description of its relevant features in the whole range of physical parameters (interaction, filling and temperature). In this manuscript, the Composite Operator Method, which exploits the above mentioned analytical technique, is presented and systematically applied in order to get information about the behavior of all relevant properties of the model (local, thermodynamic, single- and two- particle ones) in comparison with many other analytical techniques, the above cited known limits and numerical simulations. Within this approach, the Hubbard model is shown to be also capable to describe some anomalous behaviors of the cuprate superconductors.Comment: 232 pages, more than 300 figures, more than 500 reference

Clusters of galaxies : observational properties of the diffuse radio emission

Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures...(abridged)... Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution. We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes.Comment: Accepted for the publication in The Astronomy and Astrophysics Review. 58 pages, 26 figure