44,104 research outputs found
Mobile Agents Rendezvous in spite of a Malicious Agent.
No full textWe examine the problem of rendezvous, i.e., having multiple mobile agents gather in a single node of the network. Unlike previous studies, we need to achieve rendezvous in presence of a very powerful adversary, a malicious agent that moves through the network and tries to block the honest agents and prevents them from gathering. The malicious agent can be thought of as a mobile fault in the network. The malicious agent is assumed to be arbitrarily fast, has full knowledge of the network and it cannot be exterminated by the honest agents. On the other hand, the honest agents are assumed to be quite weak: They are asynchronous and anonymous, they have only finite memory, they have no prior knowledge of the network and they can communicate with the other agents only when they meet at a node. Can the honest agents achieve rendezvous starting from an arbitrary configuration in spite of the malicious agent? We present some neces- sary conditions for solving rendezvous in spite of the malicious agent in arbitrary networks. We then focus on the ring and mesh topologies and provide algorithms to solve rendezvous. For ring networks, our algorithms solve rendezvous in all feasible instances of the problem, while we show that rendezvous is impossible for an even number of agents in unoriented rings. For the oriented mesh networks, we prove that the problem can be solved when the honest agents initially form a connected configuration without holes if and only if they can see which are the occupied nodes within a two-hops distance. To the best of our knowledge, this is the first attempt to study such a powerful and mobile fault model, in the con- text of mobile agents. Our model lies between the more powerful but static fault model of black holes (which can even destroy the agents), and the less powerful but mobile fault model of Byzantine agents (which can only imitate the honest agents but can neither harm nor stop them)
Leader election and compaction for asynchronous silent programmable matter
No full textWe study models and algorithms for Programmable Matter (PM, shortly), that is matter with the ability to change its physical properties (e.g., shape or optical properties) in a programmable fashion. PM can be implemented by assembling a system of weak self-organizing computational elements, called particles, that can be programmed via distributed algorithms to collectively achieve some global task. We first introduce SILBOT, a new and weak modeling approach that, unlike previous ones, does not require: i) any synchronization mechanism nor explicit communication between particles; ii) atomicity for the performed actions; iii) activation of one particle at the time within a finite neighborhood. Second, we present a distributed algorithm to solve, in the SILBOT model, a foundational primitive for PM, namely Leader Election. This algorithm manages initial configurations that are both connected (i.e. particles induce a connected graph) and compact (i.e. without holes). Third, we show that, if the initial configuration contains holes, it is impossible to achieve leader election while preserving connectivity. Finally, we design an algorithm to handle configurations admitting holes. Specifically, the algorithm achieves compaction, i.e. stabilizes the system into a compact connected configuration, while at the same time accomplishing leader election, provided that particles are able to sense holes
Seminário sobre aquacultura 14 a 16 de dezembro de 1983
No full textA necessidade de desenvolver a aquacultura em Portugal obriga à escolha das espécies mais indicadas para tal finalidade. A propósito o autor chama a atenção para as graves consequências que podem advir das introduções e/ou transferências de animais aquáticos, quer para as espécies locais e meio ambiente, como para a para a saúde pública.Concerning the need to choose the most convenient species to cultivate in order to implement aquaculture in Portugal, the author draws the attention to the deleterious consequences of introductions and transfers of aquatic animals.Caixa Geral de Depósito
A Queuing and Statistical Analysis of Freeway Bottleneck Formation
No full textA modified approach to treat traffic flow parameters (flow, density and speed) has been introduced in this paper. A queuing analysis has been conducted on traffic flow data on Interstate 94 in the Minneapolis-St. Paul metro area. A methodology has been developed to calibrate loop detector count data. Corrected flow data has been subjected to analysis using queuing analysis to compute densities and speeds on freeway sections. Statistical analysis identifies 'active bottleneck' locations on freeways and sections where bottlenecks occur because of disturbances caused by downstream bottlenecks propagating backwards in the form of shockwaves. A sample of six days on Interstate 94 was considered for the analysis. Our analysis reveals that the same section cannot always be characterized as a 'bottleneck' location; at some times it is active and at others, it is subject to downstream bottlenecks. Traffic flow characteristics change and that leads to changing situations on each freeway section.Minnesota Department of TransportationDas, Shantanu; Levinson, David M. (2004). A Queuing and Statistical Analysis of Freeway Bottleneck Formation. Retrieved from the University Digital Conservancy, http://dx.doi.org/doi:10.1061/(ASCE)0733-947X(2004)130:6(787)
Improved Distributed Algorithms for Coloring Interval Graphs with Application to Multicoloring Trees
No full textWe give a distributed (1+)-approximation algorithm for the minimum vertex coloring problem on interval graphs, which runs in the LOCAL model and operates in O(1 log∗ n) rounds. If nodes are aware of their interval representations, then the algorithm can be adapted to the CONGEST model using the same number of rounds. Prior to this work, only constant factor approximations using O(log∗ n) rounds were known [12]. Linial’s ring coloring lower bound implies that the dependency on log∗ n cannot be improved. We further prove that the dependency on 1 is also optimal. To obtain our CONGEST model algorithm, we develop a color rotation technique that may be of independent interest. We demonstrate that color rotations can also be applied to obtain a (1 + )-approximate multicoloring of directed trees in O(1 log∗ n) rounds.<br/
FIG. 1. — A in Contributions to the taxonomic status and molecular phylogeny of Asian Bronzeback Snakes (Colubridae, Ahaetuliinae, Dendrelaphis Boulenger, 1890), from Mizoram State, Northeast India
No full textFIG. 1. — A, sub-adult Dendrelaphis proarchos Wall, 1909 from Mizoram, NE India; B, everted hemipenial sulcal side (right) and asulcal side (left) of Dendrelaphis proarchos from Mizoram, NE India; C, Adult Dendrelaphis cyanochloris (Wall, 1921) from Mizoram, NE India. Scale bar: B, 5 mm.Published as part of Biakzuala, Lal, Lalremsanga, Hmar Tlawmte, Tariang, Angshuman Das, Vabeiryureilai, Mathipi, Muansanga, Lal, Hrima, Vanlal, Kumar, Vikas, Kundu, Shantanu, Purkayastha, Jayaditya & Vogel, Gernot, 2022, Contributions to the taxonomic status and molecular phylogeny of Asian Bronzeback Snakes (Colubridae, Ahaetuliinae, Dendrelaphis Boulenger, 1890), from Mizoram State, Northeast India, pp. 177-196 in Zoosystema 44 (7) on page 181, DOI: 10.5252/zoosystema2022v44a7, http://zenodo.org/record/642194
Functional Fractional Calculus
No full textWhen a new extraordinary and outstanding theory is stated, it has to face criticism and skeptism, because it is beyond the usual concept. The fractional calculus though not new, was not discussed or developed for a long time, particularly for lack of its application to real life problems. It is extraordinary because it does not deal with 'ordinary' differential calculus. It is outstanding because it can now be applied to situations where existing theories fail to give satisfactory results. In this book not only mathematical abstractions are discussed in a lucid manner, with physical mathemati
Graph Explorations with Mobile Agents
No full textInternational audienceThe basic primitive for a mobile agent is the ability to visit all the nodes of the graph in a systematic manner. This chapter considers the exploration of unknown graphs in full detail, for the specific mobile agent model considered in this book. The graph is considered to be finite, undirected and connected. Other than this fact, no prior knowledge of the graph is assumed. Several exploration techniques are introduced and explained for either a single agent, or multiple agents, exploring either labelled or unlabelled graphs. We focus on the efficiency of exploration and consider three different complexity measures, the time taken, the amount of memory used by the agents and the storage needed at each node of the graph. For exploration by multiple agents, we consider collaborative exploration by a team of colocated agents as well as distributed exploration by agents scattered in a graph. The concluding section presents some brief ideas and references on more advanced topics on graph exploration that are not covered in this chapter
- …
