The Discovery of a Second Luminous Low Mass X-ray Binary in the Globular Cluster M15

We report an observation by the Chandra X-ray Observatory of 4U2127+119, the X-ray source identified with the globular cluster M15. The Chandra observation reveals that 4U2127+119 is in fact two bright sources, separated by 2.7". One source is associated with AC211, the previously identified optical counterpart to 4U2127+119, a low mass X-ray binary (LMXB). The second source, M15-X2, is coincident with a 19th U magnitude blue star that is 3.3" from the cluster core. The Chandra count rate of M15-X2 is 2.5 times higher than that of AC211. Prior to the 0.5" imaging capability of Chandra the presence of two so closely separated bright sources would not have been resolved. The optical counterpart, X-ray luminosity and spectrum of M15-X2 are consistent with it also being an LMXB system. This is the first time that two LMXBs have been seen to be simultaneously active in a globular cluster. The discovery of a second active LMXB in M15 solves a long standing puzzle where the properties of AC211 appear consistent with it being dominated by an extended accretion disk corona, and yet 4U2127+119 also shows luminous X-ray bursts requiring that the neutron star be directly visible. The resolution of 4U2127+119 into two sources suggests that the X-ray bursts did not come from AC211, but rather from M15-X2. We discuss the implications of this discovery for understanding the origin and evolution of LMXBs in GCs as well as X-ray observations of globular clusters in nearby galaxies.Comment: 18 pages, 4 figures, Accepted for publication in Ap J Letter

Resisting globalization: voting power indices and the national interest in EU decision making

The European integration process can be regarded as an aspect of the overall process of globalization and at the same time as an attempt to reconcile the move towards standardization with the defence of national diversity. A central role in the effort to exploit the benefits of integration without hampering the national interest is the collective decision-making process in the EU shared by the Council and the Parliament, where national representatives struggle for the conquest of the \u201clion\u2019s share\u201d in the division of the surplus stemming from the compromise on common policies. The paper focuses on the rationale behind the various Indices of Voting Power (Penrose, Banzhaf, Shapley and Shubik, and Holler) which are the formal tools meant to understanding the coalition formation and assessing the probability of reaching an agreement. In the EU Council, although ministers tend to reach a broad consensus and explicit voting is rare, decision may be taken by qualified majority voting where countries are assigned weights reflecting their size. This practice has often been objected on the grounds that the potential emergence of permanent coalitions would prevent countries from being adequately represented, and eventually a different rule was proposed. The pros and cons of the newly proposed system are analysed through the computation of the Indices of Voting Power for the EU Council and Parliament

Hierarchical Partial Planarity

In this paper we consider graphs whose edges are associated with a degree of {\em importance}, which may depend on the type of connections they represent or on how recently they appeared in the scene, in a streaming setting. The goal is to construct layouts of these graphs in which the readability of an edge is proportional to its importance, that is, more important edges have fewer crossings. We formalize this problem and study the case in which there exist three different degrees of importance. We give a polynomial-time testing algorithm when the graph induced by the two most important sets of edges is biconnected. We also discuss interesting relationships with other constrained-planarity problems.Comment: Conference version appeared in WG201

Using artificial intelligence in fungal lung disease: CPA CT imaging as an example

This positioning paper aims to discuss current challenges and opportunities for artificial intelligence (AI) in fungal lung disease, with a focus on chronic pulmonary aspergillosis and some supporting proof-of-concept results using lung imaging. Given the high uncertainty in fungal infection diagnosis and analyzing treatment response, AI could potentially have an impactful role; however, developing imaging-based machine learning raises several specific challenges. We discuss recommendations to engage the medical community in essential first steps towards fungal infection AI with gathering dedicated imaging registries, linking with non-imaging data and harmonizing image-finding annotations

Natural clustering: the modularity approach

We show that modularity, a quantity introduced in the study of networked systems, can be generalized and used in the clustering problem as an indicator for the quality of the solution. The introduction of this measure arises very naturally in the case of clustering algorithms that are rooted in Statistical Mechanics and use the analogy with a physical system.Comment: 11 pages, 5 figure enlarged versio

The discovery of 12min X-ray pulsations from 1WGA J1958.2+3232

During a systematic search for periodic signals in a sample of ROSAT PSPC (0.1-2.4 keV) light curves, we discovered 12min large amplitude X-ray pulsations in 1WGA J1958.2+3232, an X-ray source which lies close to the galactic plane. The energy spectrum is well fit by a power law with a photon index of 0.8, corresponding to an X-ray flux of about 10E-12 ergs cmE-2 sE-1. The source is probably a long period, low luminosity X-ray pulsar, similar to X Per, or an intermediate polar.Comment: 5 pages (figures included). Accepted for publication on MNRA

Technological choices under institutional constraints: measuring the impact on earnings dispersion

The paper investigates the relationship between labour market and redistributive institutions in Europe. The hypothesis is put forward of a changing balance between decreasing labour market regulation and increasing income redistribution. Econometric estimates conducted in the paper show that more redistribution has been traded off for regulation thus allowing for higher wage inequality