Results from FOPI on strangeness production and propagation at SIS energies

Heavy ion collisions at SIS energies (1-2 AGeV) offer an unique tool to probe the properties of hot and dense nuclear matter. In particular, the partial restoration of chiral symmetry is predicted to lead in this energy range to in-medium modifications of hadron properties. Strange particle production below or close to the threshold energy is a useful probe to investigate these in-medium effects. The FOPI collaboration has recently measured the production and the propagation of charged and neutral strange particles. The K+ production probability is investigated as a function of the system size at a beam energy of 1.5 AGeV. Results on K0 production in Ru+Ru collisions at 1.69 AGeV are presented, as well as K-/K+ ratio as a function of rapidity. In addition, the sideward flow of charged and neutral strange particles has been measured. Results are compared to predictions of transport calculations (BUU and IQMD).Comment: 8 pages, 6 figures, talk presented at SQM2001 in Frankfurt, Sept.2001, submitted to Journal of Physics

Silent Self-stabilizing BFS Tree Algorithms Revised

In this paper, we revisit two fundamental results of the self-stabilizing literature about silent BFS spanning tree constructions: the Dolev et al algorithm and the Huang and Chen's algorithm. More precisely, we propose in the composite atomicity model three straightforward adaptations inspired from those algorithms. We then present a deep study of these three algorithms. Our results are related to both correctness (convergence and closure, assuming a distributed unfair daemon) and complexity (analysis of the stabilization time in terms of rounds and steps)

Optimal Probabilistic Ring Exploration by Asynchronous Oblivious Robots

We consider a team of $k$ identical, oblivious, asynchronous mobile robots that are able to sense (\emph{i.e.}, view) their environment, yet are unable to communicate, and evolve on a constrained path. Previous results in this weak scenario show that initial symmetry yields high lower bounds when problems are to be solved by \emph{deterministic} robots. In this paper, we initiate research on probabilistic bounds and solutions in this context, and focus on the \emph{exploration} problem of anonymous unoriented rings of any size. It is known that $\Theta(\log n)$ robots are necessary and sufficient to solve the problem with $k$ deterministic robots, provided that $k$ and $n$ are coprime. By contrast, we show that \emph{four} identical probabilistic robots are necessary and sufficient to solve the same problem, also removing the coprime constraint. Our positive results are constructive

I got 40 million in my pocket: A functional idea analysis on a selection of President Donald J. Trump’s Tweets in relation to political populist theories

Through a functional idea analysis, this study explores and discuss what possible strategies President Donald J. Trump has on Twitter based on a selection of Mr. Trump’s tweets. The material is based on six tweets within three policy categories (Healthcare, the U.S./Mexican Border Wall and the Media) with two tweets in each category. The tweets were selected from the highest respectively lowest amount of retweets. The methods for the functional idea analysis are based on Evert Vedung’s theories and the theoretical framework is based on theories on political populism. The assumption was that President Trump uses populist rhetorical strategies in the tweets with the highest amount of retweets. In the least retweeted messages, the assumption was to find less populist strategies. The purpose of this study was to explore the functions of the tweets through the lens of populism in order to examine what can be said on Mr. Trump’s rhetorical approaches on Twitter. The findings show that Trump uses rhetorical populism throughout the material, regardless how many retweets the message had. Through the functional idea analysis and political populist theories, this study finds that the selected material consists of classic populist rhetorics which are strategically outlined in order to cover facts behind often antiestablishment arguments

Bounds for self-stabilization in unidirectional networks

A distributed algorithm is self-stabilizing if after faults and attacks hit the system and place it in some arbitrary global state, the systems recovers from this catastrophic situation without external intervention in finite time. Unidirectional networks preclude many common techniques in self-stabilization from being used, such as preserving local predicates. In this paper, we investigate the intrinsic complexity of achieving self-stabilization in unidirectional networks, and focus on the classical vertex coloring problem. When deterministic solutions are considered, we prove a lower bound of $n$ states per process (where $n$ is the network size) and a recovery time of at least $n(n-1)/2$ actions in total. We present a deterministic algorithm with matching upper bounds that performs in arbitrary graphs. When probabilistic solutions are considered, we observe that at least $\Delta + 1$ states per process and a recovery time of $\Omega(n)$ actions in total are required (where $\Delta$ denotes the maximal degree of the underlying simple undirected graph). We present a probabilistically self-stabilizing algorithm that uses $\mathtt{k}$ states per process, where $\mathtt{k}$ is a parameter of the algorithm. When $\mathtt{k}=\Delta+1$, the algorithm recovers in expected $O(\Delta n)$ actions. When $\mathtt{k}$ may grow arbitrarily, the algorithm recovers in expected O(n) actions in total. Thus, our algorithm can be made optimal with respect to space or time complexity

Communication Efficiency in Self-stabilizing Silent Protocols

Self-stabilization is a general paradigm to provide forward recovery capabilities to distributed systems and networks. Intuitively, a protocol is self-stabilizing if it is able to recover without external intervention from any catastrophic transient failure. In this paper, our focus is to lower the communication complexity of self-stabilizing protocols \emph{below} the need of checking every neighbor forever. In more details, the contribution of the paper is threefold: (i) We provide new complexity measures for communication efficiency of self-stabilizing protocols, especially in the stabilized phase or when there are no faults, (ii) On the negative side, we show that for non-trivial problems such as coloring, maximal matching, and maximal independent set, it is impossible to get (deterministic or probabilistic) self-stabilizing solutions where every participant communicates with less than every neighbor in the stabilized phase, and (iii) On the positive side, we present protocols for coloring, maximal matching, and maximal independent set such that a fraction of the participants communicates with exactly one neighbor in the stabilized phase

Self-stabilizing K-out-of-L exclusion on tree network

In this paper, we address the problem of K-out-of-L exclusion, a generalization of the mutual exclusion problem, in which there are $\ell$ units of a shared resource, and any process can request up to $\mathtt k$ units ($1\leq\mathtt k\leq\ell$). We propose the first deterministic self-stabilizing distributed K-out-of-L exclusion protocol in message-passing systems for asynchronous oriented tree networks which assumes bounded local memory for each process.Comment: 15 page

Self-Stabilizing Distributed Cooperative Reset

Self-stabilization is a versatile fault-tolerance approach that characterizes the ability of a system to eventually resume a correct behavior after any finite number of transient faults. In this paper, we propose a self-stabilizing reset algorithm working in anonymous networks. This algorithm resets the network in a distributed non-centralized manner, i.e., it is multi-initiator, as each process detecting an inconsistency may initiate a reset. It is also cooperative in the sense that it coordinates concurrent reset executions in order to gain efficiency. Our approach is general since our reset algorithm allows to build self-stabilizing solutions for various problems and settings. As a matter of facts, we show that it applies to both static and dynamic specifications since we propose efficient self-stabilizing reset-based algorithms for the (1-minimal) (f, g)-alliance (a generalization of the dominating set problem) in identified networks and the unison problem in anonymous networks. Notice that these two latter instantiations enhance the state of the art. Indeed, in the former case, our solution is more general than the previous ones, while in the latter case, the complexity of our unison algorithm is better than that of previous solutions of the literature

Stabilisation Instantanée Probabiliste

International audienceNous introduisons la stabilisation instantanée probabiliste. Cette propriété nous permet, en particulier, de concevoir des algorithmes distribués pour réseaux anonymes ayant de fortes propriétés de tolérance aux pannes transitoires. Un algorithme instantanément stabilisant probabiliste satisfait la sûreté de sa spécification immédiatement après que les pannes transitoires aient cessé; cependant il n'assure la vivacité de sa spécification que presque sûrement. Nous illustrons cette nouvelle propriété en proposant deux algorithmes instantanément stabilisants probabilistes d'élection avec garantie de service pour réseaux anonymes, ce problème n'ayant pas de solution déterministe

Concurrence et allocation de ressources locales instantanément stabilisante

International audienceCet article est un résumé de (Altisen et al., 2015) où nous étudions la notion de concurrence dans les problèmes d'allocation de ressources. Nous proposons des propriétés générales permettant d'exprimer la qualité de concurrence d'une solution à un problème d'allocation de ressources et établissons quelle qualité de concurrence peut être atteinte par un algorithme résolvant le problème d'allocation de ressources locales. Enfin, nous proposons un algorithme d'allocation de ressources locales instantanément stabilisant qui réalise cette qualité de concurrence