Brief Announcement: Lower Bounds for Asymptotic Consensus in Dynamic Networks

In this work we study the performance of asymptotic and approximate consensus algorithms in dynamic networks. The asymptotic consensus problem requires a set of agents to repeatedly set their outputs such that the outputs converge to a common value within the convex hull of initial values. This problem, and the related approximate consensus problem, are fundamental building blocks in distributed systems where exact consensus among agents is not required, e.g., man-made distributed control systems, and have applications in the analysis of natural distributed systems, such as flocking and opinion dynamics. We prove new nontrivial lower bounds on the contraction rates of asymptotic consensus algorithms, from which we deduce lower bounds on the time complexity of approximate consensus algorithms. In particular, the obtained bounds show optimality of asymptotic and approximate consensus algorithms presented in [Charron-Bost et al., ICALP\u2716] for certain classes of networks that include classical failure assumptions, and confine the search for optimal bounds in the general case. Central to our lower bound proofs is an extended notion of valency, the set of reachable limits of an asymptotic consensus algorithm starting from a given configuration. We further relate topological properties of valencies to the solvability of exact consensus, shedding some light on the relation of these three fundamental problems in dynamic networks

The column density towards LMC X-1

We measure the neutral absorption towards the black hole X-ray binary system LMC X-1 from six archival soft X-ray spectra obtained with the gratings and/or CCD detectors on Chandra, XMM-Newton, and Swift. Four spectral models for the soft continuum have been investigated. While the powerlaw model may overestimate NH considerably, the others give consistent results. Taking the lower metalicity of the Large Magellanic Cloud into account, we find equivalent hydrogen column densities of N_H = (1.0-1.3)*10^22 cm^-2, with a systematic dependence on the orbital phase. This variation of the neutral absorption can nearly explain the orbital modulation of the soft X-ray flux recently detected with the All Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE).Comment: 4 pages, accepted for publication as a Letter in Astronomy and Astrophysic

United Nations global study on children deprived of liberty

The UN Global Study on Children Deprived of Liberty, published in 2019, is a comprehensive Study conducted by Manfred Nowak, a large team of experts from all over the world and 274 children who were interviewed. The findings of the Study concern six thematic areas in which children live deprived of liberty: juvenile justice, detention with their primary caregivers, for migration-related reasons, in institutions, in the context of armed conflict or on national security grounds. The Study also focuses on the gender dimension, the impact on the health of the children and children with disabilities, as well the views and perspectives of children themselves. According to the research more than 7 million children are currently living in deprivation of liberty. In addition to other findings related to the specific thematic areas, this comprehensive publication also contains a large set of recommendations

Spectroscopy of the stellar wind in the Cygnus X-1 system

The X-ray luminosity of black holes is produced through the accretion of material from their companion stars. Depending on the mass of the donor star, accretion of the material falling onto the black hole through the inner Lagrange point of the system or accretion by the strong stellar wind can occur. Cygnus X-1 is a high mass X-ray binary system, where the black hole is powered by accretion of the stellar wind of its supergiant companion star HDE226868. As the companion is close to filling its Roche lobe, the wind is not symmetric, but strongly focused towards the black hole. Chandra-HETGS observations allow for an investigation of this focused stellar wind, which is essential to understand the physics of the accretion flow. We compare observations at the distinct orbital phases of 0.0, 0.2, 0.5 and 0.75. These correspond to different lines of sights towards the source, allowing us to probe the structure and the dynamics of the wind.Comment: conference proceeding from Integral/Bart Workshop Karlsbad, CZ, 14.4-18.4 201

The 17th Kilbrandon Lecture (University of Strathclyde, 30 January 2020) : The UN Global Study on Children Deprived of Liberty - Deprivation of liberty is deprivation of childhood

I am very honoured to deliver the 17th Kilbrandon Lecture in paying tribute to the achievements of Lord Kilbrandon and the Scottish Children's Hearing System today in this beautiful lecture hall. My lecture will deal with one of the most important human rights of children, their right to personal liberty. Since children are in their formative years, they need freedom to develop their talents, skills and their personality. That is the main reason why Article 37(b) of the UN Convention on the Rights of the Child (CRC) established for the right to personal liberty a much higher standard than for adults. While adults may be arrested and detained for various reasons under the sole condition that such deprivation of liberty is in conformity with domestic law and non-arbitrary, the CRC adds that the arrest and detention of children shall be used only as a measure of last resort and for the shortest appropriate period of time. This means that children shall only be detained in truly exceptional circumstances, when non-custodial solutions are definitely not appropriate