Towards Efficient Verification of Population Protocols

Population protocols are a well established model of computation by anonymous, identical finite state agents. A protocol is well-specified if from every initial configuration, all fair executions reach a common consensus. The central verification question for population protocols is the well-specification problem: deciding if a given protocol is well-specified. Esparza et al. have recently shown that this problem is decidable, but with very high complexity: it is at least as hard as the Petri net reachability problem, which is EXPSPACE-hard, and for which only algorithms of non-primitive recursive complexity are currently known. In this paper we introduce the class WS3 of well-specified strongly-silent protocols and we prove that it is suitable for automatic verification. More precisely, we show that WS3 has the same computational power as general well-specified protocols, and captures standard protocols from the literature. Moreover, we show that the membership problem for WS3 reduces to solving boolean combinations of linear constraints over N. This allowed us to develop the first software able to automatically prove well-specification for all of the infinitely many possible inputs.Comment: 29 pages, 1 figur

Computing in the RAIN: a reliable array of independent nodes

The RAIN project is a research collaboration between Caltech and NASA-JPL on distributed computing and data-storage systems for future spaceborne missions. The goal of the project is to identify and develop key building blocks for reliable distributed systems built with inexpensive off-the-shelf components. The RAIN platform consists of a heterogeneous cluster of computing and/or storage nodes connected via multiple interfaces to networks configured in fault-tolerant topologies. The RAIN software components run in conjunction with operating system services and standard network protocols. Through software-implemented fault tolerance, the system tolerates multiple node, link, and switch failures, with no single point of failure. The RAIN-technology has been transferred to Rainfinity, a start-up company focusing on creating clustered solutions for improving the performance and availability of Internet data centers. In this paper, we describe the following contributions: 1) fault-tolerant interconnect topologies and communication protocols providing consistent error reporting of link failures, 2) fault management techniques based on group membership, and 3) data storage schemes based on computationally efficient error-control codes. We present several proof-of-concept applications: a highly-available video server, a highly-available Web server, and a distributed checkpointing system. Also, we describe a commercial product, Rainwall, built with the RAIN technology

The European Union and the Cyprus problem: a story of limited impetus

This article discusses the role of the European Union (EU) in the Cyprus problem before and after accession in 2004. It is argued that, before 2004, Brussels provided limited incentives to the Greek Cypriots to contribute to resolution but, on the other hand, triggered a pro-solution/ EU trend amongst the Turkish Cypriots. On the contrary, in the post-accession era, the EU’s aptitude to contribute to a solution has further decreased: Greek Cypriots remain with inadequate EU-induced motivation to pursue resolution, while the pro-solution/ EU feelings of the Turkish Cypriots have receded, also due to Brussels’ failure to fulfill their expectations. While most of the literature on Cyprus has focused on the pre-accession period, the article offers a much needed insight into the EU’s role before and after Cyprus’ EU entry. The article draws on a variety of data, including a series of elite interviews conducted in Belgium and Cyprus

The Awkward New Member: Poland's Changing European Identity

Like those in other post-communist Central and East European countries, successive Polish governments were consistently eager to join the European Union although popular enthusiasm for membership took a notable dip in the late 1990s and two vociferous 'Eurosceptic' parties were elected to parliament in 2001. Since joining, however, public opinion has been very much in favour of the country's new European status and the considerable economic benefits it has brought. It seemed rather strange, then, that in September 2005 a parliament was elected distinguished by the nationalist sentiments of several major parties which fed into the adoption of what was seen as a strongly Eurosceptic stance on the part of Polish representatives in the European arena. Polish interests were pursued aggressively and in a manner that many thought was fundamentally un-European throughout much of 2007 at the several summits critically concerned with relaunching the constitutional project and formulating what has become the Reform Treaty. This behaviour played a significant part in the defeat of the incumbent government in the October 2007 and the subsequent installation of a new leadership generally perceived to be significantly more EU-friendly. Ironically for a government that promulgated the principle of 'Nice or death', it secured an agreement for the Nice provisions to stay in force until 2014 but then itself expired at the polls. It should not be assumed, however, that the new Civic Platform/Peasant Party coalition will not be an equally energetic proponent of the Polish national interest. 'Poland' has therefore had several identities in recent years, and seen considerable variation both among and between the different areas of public opinion, political parties and government policy. It will probably see several more in coming years

Autonomous Vehicle Coordination with Wireless Sensor and Actuator Networks

A coordinated team of mobile wireless sensor and actuator nodes can bring numerous benefits for various applications in the field of cooperative surveillance, mapping unknown areas, disaster management, automated highway and space exploration. This article explores the idea of mobile nodes using vehicles on wheels, augmented with wireless, sensing, and control capabilities. One of the vehicles acts as a leader, being remotely driven by the user, the others represent the followers. Each vehicle has a low-power wireless sensor node attached, featuring a 3D accelerometer and a magnetic compass. Speed and orientation are computed in real time using inertial navigation techniques. The leader periodically transmits these measures to the followers, which implement a lightweight fuzzy logic controller for imitating the leader's movement pattern. We report in detail on all development phases, covering design, simulation, controller tuning, inertial sensor evaluation, calibration, scheduling, fixed-point computation, debugging, benchmarking, field experiments, and lessons learned