Collective Construction of 2D Block Structures with Holes

In this paper we present algorithms for collective construction systems in which a large number of autonomous mobile robots trans- port modular building elements to construct a desired structure. We focus on building block structures subject to some physical constraints that restrict the order in which the blocks may be attached to the structure. Specifically, we determine a partial ordering on the blocks such that if they are attached in accordance with this ordering, then (i) the structure is a single, connected piece at all intermediate stages of construction, and (ii) no block is attached between two other previously attached blocks, since such a space is too narrow for a robot to maneuver a block into it. Previous work has consider this problem for building 2D structures without holes. Here we extend this work to 2D structures with holes. We accomplish this by modeling the problem as a graph orientation problem and describe an O(n^2) algorithm for solving it. We also describe how this partial ordering may be used in a distributed fashion by the robots to coordinate their actions during the building process.Comment: 13 pages, 3 figure

A dwarf planet class object in the 21:5 resonance with Neptune

We report the discovery of an Hr = 3.4 ± 0.1 dwarf planet candidate by the Pan-STARRS Outer Solar System Survey. 2010 JO179 is red with (g − r) = 0.88 ± 0.21, roughly round, and slowly rotating, with a period of 30.6 hr. Estimates of its albedo imply a diameter of 600–900 km. Observations sampling the span between 2005 and 2016 provide an exceptionally well determined orbit for 2010 JO179, with a semimajor axis of 78.307 ± 0.009 au; distant orbits known to this precision are rare. We find that 2010 JO179 librates securely within the 21:5 mean-motion resonance with Neptune on 100 Myr timescales, joining the small but growing set of known distant dwarf planets on metastable resonant orbits. These imply a substantial trans-Neptunian population that shifts between stability in high-order resonances, the detached population, and the eroding population of the scattering disk

Hidradenitis suppurativa.

Contains fulltext : 80512.pdf (publisher's version ) (Closed access)BACKGROUND: Hidradenitis suppurativa is a chronic, recurrent, suppurative cutaneous disease. Despite its incidence, optimal medical or surgical treatment remains unclear. This review describes the disease, ranging from pathogenesis to treatment and prognosis. METHODS: Articles were sourced from PubMed and Medline, using the MeSH terms 'hidradenitis suppurativa' and 'acne inversa'. Selection of articles was based on peer review, journal, relevance and English language. RESULTS AND CONCLUSION: On the basis of histological findings, the disease is now considered inflammatory and originating from the hair follicle; therefore, the term 'acne inversa' is favoured by some experts. The exact aetiology remains obscure but smoking seems to be a major triggering factor. Treatment should be individualized according to the site and extent of the disease. Absolute cessation of smoking is essential in the treatment of hidradenitis. Management with antibiotics or other medications may relieve early symptoms, but radical surgery may be necessary for control and to prevent recurrence