Non-uniform circle formation algorithm for oblivious mobile robots with convergence toward uniformity

AbstractThis paper presents a distributed algorithm whereby a group of mobile robots self-organize and position themselves into forming a circle in a loosely synchronized environment. In spite of its apparent simplicity, the difficulty of the problem comes from the weak assumptions made on the system. In particular, robots are anonymous, oblivious (i.e., stateless), unable to communicate directly, and disoriented in the sense that they share no knowledge of a common coordinate system. Furthermore, robots’ activations are not synchronized. More specifically, the proposed algorithm ensures that robots deterministically form a non-uniform circle in a finite number of steps and converges to a situation in which all robots are located evenly on the boundary of the circle

Facial cellulitis revealing choreo-acanthocytosis: A case report

We report a 62 year-old-man with facial cellulitis revealing choreo-acanthocytosis (ChAc). He showed chorea that started 20 years ago. The orofacial dyskinisia with tongue and cheek biting resulted in facial cellulitis. The peripheral blood smear revealed acanthocytosis of 25%. The overall of chorea, orofacial dyskinetic disorder, peripheral neuropathy, disturbed behavior, acanthocytosis and the atrophy of caudate nuclei was suggestive of a diagnosis of ChAc. To our knowledge no similar cases of facial cellulitis revealing choreo-acanthocytosis  (ChAc) were found in a review of the literature.Key words: Choreo-acanthocytosis, facial cellulitis, dyskinetic movement

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

On Distributed Cooperative Mobile Robotics: Decomposition of Basic Problems and Study of a Self-stabilizing Circle Formation Algorithm

Enabling mobile robots to work in cooperating teams holds great promises as an efficient and reliable way to solving tasks autonomously. However, addressing the coordination and control of autonomous mobile robots within a team remains a difficult task. Many people have addressed this issue by studying how a complex global behavior can emerge from the interactions of many robots exhibiting a simple local behavior. This approach, called behavior-based, can provide us with an interesting insight on these issues, but it also gives the wrong impression that they are solved. This is however very far from reality, since these heuristics can provide no assurance that a given problem will actually be solved, let alone any proof of correctness. In contrast, we look at the problem from a computational standpoint, in the sense that we try to determine the local behavior of robots, given a desired global behavior. In particular, our work focuses on basic recurring problems of cooperation. The main contributions of this dissertation are as follows. First, we outline a specification framework to define basic problems for cooperative autonomous mobile robots. The framework consists of four generic properties that can be combined to define various different problems

Fault-Resilient Cooperation of Autonomous Mobile Robots with Unreliable Compass Sensors

Supervisor:Defago Xavier情報科学研究科博

On Distributed Cooperative Mobile Robotics:Decomposition of Basic Problems and Study of a Self-stabilizing Circle Formation Algorithm

Supervisor:Takuya Katayama情報科学研究科修

Self-stabilizing algorithm for circle formation by disoriented oblivious mobile robots

This paper presents a distributed algorithm whereby a group of mobile robots self-organize and position themselves into forming a circle. The difficulty of the problem results from the fact that robots are anonymous, oblivious, unable to communicate directly, and also disoriented, i.e, share no knowledge of a common coordinate system. More precisely, the proposed algorithm ensures that the robots deterministically form a circle in a finite number ofsteps and converges to a situation in which all robots are located evenly on the boundary of the circle. In addition, thanks to the nature of the assumed model (i.e., oblivious robots), the algorithm is also self-stabilizing.リサーチレポート（北陸先端科学技術大学院大学情報科学研究科

Tight bound on the gathering of two oblivious mobile robots with inconsistent compasses

We consider a system of autonomous mobile robots that can move in the two dimensional space. These robots must gather, in finite time, at a single point in the plane, not predetermined (gathering problem). We consider that the robots are equipped with compasses, although these compasses can be inconsistent. In our previous work, we proposed an algorithm that gathers two oblivious mobile robots in finite time when the compasses diverge by at most 45°. In this paper, we extend this work by proving a tight bound on the degree of divergence of robots' compasses for solving the gathering problem. More specifically, we present a self-stabilizing algorithm to gather, in a finite time, two oblivious robots equipped with compasses that can differ by an angle strictly smaller than 180°, and we show that it is a tight bound.リサーチレポート（北陸先端科学技術大学院大学情報科学研究科