Molecular dynamics simulations of complex shaped particles using Minkowski operators

The Minkowski operators (addition and substraction of sets in vectorial spaces) has been extensively used for Computer Graphics and Image Processing to represent complex shapes. Here we propose to apply those mathematical concepts to extend the Molecular Dynamics (MD) Methods for simulations with complex-shaped particles. A new concept of Voronoi-Minkowski diagrams is introduced to generate random packings of complex-shaped particles with tunable particle roundness. By extending the classical concept of Verlet list we achieve numerical efficiencies that do not grow quadratically with the body number of sides. Simulations of dissipative granular materials under shear demonstrate that the method complies with the first law of thermodynamics for energy balance.Comment: Submitted to Phys. Rev.

The entropic origin of disassortativity in complex networks

Why are most empirical networks, with the prominent exception of social ones, generically degree-degree anticorrelated, i.e. disassortative? With a view to answering this long-standing question, we define a general class of degree-degree correlated networks and obtain the associated Shannon entropy as a function of parameters. It turns out that the maximum entropy does not typically correspond to uncorrelated networks, but to either assortative (correlated) or disassortative (anticorrelated) ones. More specifically, for highly heterogeneous (scale-free) networks, the maximum entropy principle usually leads to disassortativity, providing a parsimonious explanation to the question above. Furthermore, by comparing the correlations measured in some real-world networks with those yielding maximum entropy for the same degree sequence, we find a remarkable agreement in various cases. Our approach provides a neutral model from which, in the absence of further knowledge regarding network evolution, one can obtain the expected value of correlations. In cases in which empirical observations deviate from the neutral predictions -- as happens in social networks -- one can then infer that there are specific correlating mechanisms at work.Comment: 4 pages, 4 figures. Accepted in Phys. Rev. Lett. (2010

SN 2018bsz: A Type I superluminous supernova with aspherical circumstellar material

We present a spectroscopic analysis of the most nearby Type I superluminous supernova (SLSN-I), SN 2018bsz. The photometric evolution of SN 2018bsz has several surprising features, including an unusual pre-peak plateau and evidence for rapid formation of dust greater than or similar to 200 d post-peak. We show here that the spectroscopic and polarimetric properties of SN 2018bsz are also unique. While its spectroscopic evolution closely resembles SLSNe-I, with early O II absorption and C II P Cygni profiles followed by Ca, Mg, Fe, and other O features, a multi-component H alpha profile appearing at similar to 30 d post-maximum is the most atypical. The H alpha is at first characterised by two emission components, one at similar to+3000 km s(-1) and a second at similar to - 7500 km s(-1), with a third, near-zero-velocity component appearing after a delay. The blue and central components can be described by Gaussian profiles of intermediate width (FWHM similar to 2000-6000 km s(-1)), but the red component is significantly broader (FWHM greater than or similar to 10000 km s(-1)) and Lorentzian. The blue H alpha component evolves towards a lower-velocity offset before abruptly fading at similar to + 100 d post-maximum brightness, concurrently with a light curve break. Multi-component profiles are observed in other hydrogen lines, including Pa beta, and in lines of Ca II and He I. Spectropolarimetry obtained before (10.2 d) and after (38.4 d) the appearance of the H lines shows a large shift on the Stokes Q - U plane consistent with SN 2018bsz undergoing radical changes in its projected geometry. Assuming the supernova is almost unpolarised at 10.2 d, the continuum polarisation at 38.4 d reaches P similar to 1.8%, implying an aspherical configuration. We propose that the observed evolution of SN 2018bsz can be explained by highly aspherical, possibly disk-like, circumstellar material (CSM) with several emitting regions. After the supernova explosion, the CSM is quickly overtaken by the ejecta, but as the photosphere starts to recede, the different CSM regions re-emerge, producing the peculiar line profiles. Based on the first appearance of H alpha, we can constrain the distance of the CSM to be less than similar to 6.5 x 10(15) cm (430 AU), or even lower (less than or similar to 87 AU) if the pre-peak plateau is related to an eruption that created the CSM. The presence of CSM has been inferred previously for other SLSNe-I, both directly and indirectly. However, it is not clear whether the rare properties of SN 2018bsz can be generalised for SLSNe-I, for example in the context of pulsational pair instability, or whether they are the result of an uncommon evolutionary path, possibly involving a binary companion.European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 2101.D-5023Villum Fonden 19054Science Foundation IrelandEuropean CommissionRoyal Society of LondonEuropean Commission RS-EA/3471Swedish Research CouncilEuropean Commission 2020-03330National Agency for Research and Development (ANID)/Scholarship Program/Doctorado Nacional 2021 - 21211203European Commission H2020-MSCA-IF-2018-842471Science Foundation IrelandMinistry of Science and Innovation, Spain (MICINN)Agencia Estatal de Investigacion (AEI)European Social Fund (ESF) "Investing in your future" under the 2019 Ramon y Cajal program RYC2019-027683-ICentro Superior de Investigaciones Cientificas (CSIC) 20215AT016program Unidad de Excelencia Maria de Maeztu CEX2020-001058-MEU Horizon 2020 research and innovation programme 101004719European Research Council (ERC)European Commission 948381Alan Turing InstituteGRAWITA/PRIN-MIUR project: "The new frontier of the Multi-Messenger Astrophysics: follow-up of electromagnetic transient counterparts of gravitational wave sources"HORIZON2020: AHEAD2020 871158 1103.D-0328 PID2020-115253GA-I00 HOSTFLOWS Swedish Research CouncilEuropean Commission 2020-03330National Agency for Research and Development (ANID)/Scholarship Program/Doctorado Nacional 2021 - 21211203European Commission H2020-MSCA-IF-2018-842471Science Foundation IrelandMinistry of Science and Innovation, Spain (MICINN)Agencia Estatal de Investigacion (AEI)European Social Fund (ESF) "Investing in your future" under the 2019 Ramon y Cajal program RYC2019-027683-ICentro Superior de Investigaciones Cientificas (CSIC) 20215AT016program Unidad de Excelencia Maria de Maeztu CEX2020-001058-MEU Horizon 2020 research and innovation programme 101004719European Research Council (ERC) European Commission 948381Alan Turing InstituteGRAWITA/PRIN-MIUR project: "The new frontier of the Multi-Messenger Astrophysics: follow-up of electromagnetic transient counterparts of gravitational wave sources"HORIZON2020: AHEAD2020 871158 1103.D-0328 PID2020-115253GA-I00 HOSTFLOW

Astronomical site selection: On the use of satellite data for aerosol content monitoring

The main goal of this work is the analysis of new approaches to the study of the properties of astronomical sites. In particular, satellite data measuring aerosols have recently been proposed as a useful technique for site characterization and searching for new sites to host future very large telescopes. Nevertheless, these data need to be critically considered and interpreted in accordance with the spatial resolution and spectroscopic channels used. In this paper we have explored and retrieved measurements from satellites with high spatial and temporal resolutions and concentrated on channels of astronomical interest. The selected datasets are OMI on board the NASA Aura satellite and MODIS on board the NASA Terra and Aqua satellites. A comparison of remote sensing and in situ techniques is discussed. As a result, we find that aerosol data provided by satellites up to now are not reliable enough for aerosol site characterization, and in situ data are required.Comment: LaTeX2e MN v2.2, 16 pages with 13 figures. Accepted for Mon. Not. R. Astron. Soc.(2008

The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence

We present an optical (gri) study during quiescence of the accreting millisecond X-ray pulsar IGR J00291+5934 performed with the 10.4m Gran Telescopio Canarias (GTC) in August 2014. Despite the source being in quiescence at the time of our observations, it showed a strong optical flaring activity, more pronounced at higher frequencies (i.e. the g band). Once the flares were subtracted, we tentatively recovered a sinusoidal modulation at the system orbital period in all bands, even if a significant phase shift with respect to an irradiated star, typical of accreting millisecond X-ray pulsars is detected. We conclude that the observed flaring could be a manifestation of the presence of an accretion disc in the system. The observed light curve variability could be explained by the presence of a superhump, which might be another proof of the formation of an accretion disc. In particular, the disc at the time of our observations was probably preparing to the new outburst of the source, that happened just a few months later, in 2015.Comment: 6 pages, 2 figures, 1 table. Accepted for publication in A&

A search for evidence of irradiation in Centaurus X-4 during quiescence

We present a study of the neutron star X-Ray Transient Cen X-4. Our aim is to look for any evidence of irradiation of the companion with a detailed analysis of its radial velocity curve, relative contribution of the donor star and Doppler tomography of the main emission lines. To improve our study all our data are compared with a set of simulations that consider different physical parameters of the system, like the disc aperture angle and the mass ratio. We conclude that neither the radial velocity curve nor the orbital variation of the relative donor's contribution to the total flux are affected by irradiation. On the other hand, we do see emission from the donor star at H${\alpha}$ and HeI 5876 which we tentatively attribute to irradiation effects. In particular, the H${\alpha}$ emission from the companion is clearly asymmetric and we suggest is produced by irradiation from the hot-spot. Finally, from the velocity of the HeI 5876 spot we constrain the disc opening angle to alpha=7-14 deg.Comment: 4 pages, 5 figures, accepted for publication in A&A as a R

C-GOALS II. Chandra Observations of the Lower Luminosity Sample of Nearby Luminous Infrared Galaxies in GOALS

We analyze Chandra X-ray observatory data for a sample of 63 luminous infrared galaxies (LIRGs), sampling the lower-infrared luminosity range of the Great Observatories All-Sky LIRG survey (GOALS), which includes the most luminous infrared selected galaxies in the local universe. X-rays are detected for 84 individual galaxies within the 63 systems, for which arcsecond resolution X-ray images, fluxes, infrared and X-ray luminosities, spectra and radial profiles are presented. Using X-ray and MIR selection criteria, we find AGN in (31$\pm$5)% of the galaxy sample, compared to the (38$\pm$6)% previously found for GOALS galaxies with higher infrared luminosities (C-GOALS I). Using mid-infrared data, we find that (59$\pm$9)% of the X-ray selected AGN in the full C-GOALS sample do not contribute significantly to the bolometric luminosity of the host galaxy. Dual AGN are detected in two systems, implying a dual AGN fraction in systems that contain at least one AGN of (29$\pm$14)%, compared to the (11$\pm$10)% found for the C-GOALS I sample. Through analysis of radial profiles, we derive that most sources, and almost all AGN, in the sample are compact, with half of the soft X-ray emission generated within the inner $\sim 1$ kpc. For most galaxies, the soft X-ray sizes of the sources are comparable to those of the MIR emission. We also find that the hard X-ray faintness previously reported for the bright C-GOALS I sources is also observed in the brightest LIRGs within the sample, with $L_{\rm FIR}>8\times10^{10}$ L$_{\odot}$.Comment: 24 pages, 13 figures, 11 tables, accepted for publication in A&

Development of a new tool for assessing Health-Related Quality of Life in patients with primary hyperparathyroidism

Background: Several studies in recent years have evaluated Health Related Quality of Life (HRQoL) of patients with primary hyperparathyroidism (PHPT). No disease specific questionnaires are available to assess the impact of the disease. The aim of this research is to describe the development of a new disease specific Quality of Life (QoL) questionnaire for use specifically with PHPT patients. Methods: A conceptual model was developed describing the impact of the disease and its symptoms on QoL domains. A literature review was conducted to identify the most relevant domains. A focus group with experts was used to validate the domains; 24 patients were also interviewed to complement the information from the patient's perspective. A content analysis of the interviews was performed to identify items related with the impact of the disease, leading to PHPQoL-V.1 which was presented to a sample of 67 patients. Reliability was assessed by Cronbach's coefficient alpha and item-total score correlations. Validity was assessed by a factor analysis performed to determine the number of domains. Rasch analysis was carried out in order to refine the questionnaire items. Results: 259 items were extracted from the interviews that were subsequently reduced to 34 items. Cronbach's coefficient alpha was 0.92. The factor analysis extracted two domains (physical and emotional). After Rasch analysis the questionnaire PHPQoL-V.2 kept 16 items (9 physical and 7 emotional). The questionnaire was developed in a Spanish population and the final version was translated to English through translation and back-translation. Conclusion: The first disease specific HRQoL questionnaire for PHPT patients (PHPQoL-16) has been developed. Validation studies designed to assess measurement properties of this tool are currently underway