A Process Calculus for Dynamic Networks

In this paper we propose a process calculus framework for dynamic networks in which the network topology may change as computation proceeds. The proposed calculus allows one to abstract away from neighborhood-discovery computations and it contains features for broadcasting at multiple transmission ranges and for viewing networks at different levels of abstraction. We develop a theory of confluence for the calculus and we use the machinery developed towards the verification of a leader-election algorithm for mobile ad hoc networks

Dwelling or duelling in possibilities: how (Ir)relevant are African feminisms?

In its four decades of rebirth, the world has debated (enough) the relevance of feminism, but there is, surprisingly, refreshingly emergent dimensions at the turn of the twenty-first century: feminisms from feminism flowing from Africa. The theories or models of Womanism, Stiwanism, Motherism, and Nego-feminism, with their underlying assumptions and values,were all born at various end times of the twentieth century with a common objective of seeking gender justice. This paper examines the crucial question of how relevant these models are to the global practice of woman as human. What propels their separateness, and why didn‘t they combine to make a more solid stance on the plight of the African woman? In fact, why can‘t they simply identify with the general feminism? Put differently, are they dwelling in the same terrain or are they separable and easily recognisable discourses duelling in possibilities for the woman in Africa in particular and the woman of the globe in general? More specifically, how (ir)relevant are African feminisms?In trying to answer these questions, the paper presents a critical review of the afore-mentioned theories of African feminisms with the goal of providing readers an understanding of what is new in each model, and what is similar or different between the various strands of African feminisms. The paper concludes with the author‘s analysis of the model that holds the best promise or possibilities for African feminism to achieve its seemingly elusive goal of gender equality

Probabilistic Mobility Models for Mobile and Wireless Networks

International audienceIn this paper we present a probabilistic broadcast calculus for mobile and wireless networks whose connections are unreliable. In our calculus, broadcasted messages can be lost with a certain probability, and due to mobility the connection probabilities may change. If a network broadcasts a message from a location, it will evolve to a network distribution depending on whether nodes at other locations receive the message or not. Mobility of nodes is not arbitrary but guarded by a probabilistic mobility function (PMF), and we also define the notion of a weak bisimulation given a PMF. It is possible to have weak bisimular networks which have different probabilistic connectivity information. We furthermore examine the relation between our weak bisimulation and a minor variant of PCTL* [1]. Finally, we apply our calculus on a small example called the Zeroconf protocol [2]

A Calculus for Orchestration of Web Services

We introduce COWS (Calculus for Orchestration of Web Services), a new foundational language for SOC whose design has been influenced by WS-BPEL, the de facto standard language for orchestration of web services. COWS combines in an original way a number of ingredients borrowed from well-known process calculi, e.g. asynchronous communication, polyadic synchronization, pattern matching, protection, delimited receiving and killing activities, while resulting different from any of them. Several examples illustrates COWS peculiarities and show its expressiveness both for modelling imperative and orchestration constructs, e.g. web services, flow graphs, fault and compensation handlers, and for encoding other process and orchestration languages

Regulating Data Exchange in Service Oriented Applications

We define a type system for COWS, a formalism for specifying and combining services, while modelling their dynamic behaviour. Our types permit to express policies constraining data exchanges in terms of sets of service partner names attachable to each single datum. Service programmers explicitly write only the annotations necessary to specify the wanted policies for communicable data, while a type inference system (statically) derives the minimal additional annotations that ensure consistency of services initial configuration. Then, the language dynamic semantics only performs very simple checks to authorize or block communication. We prove that the type system and the operational semantics are sound. As a consequence, we have the following data protection property: services always comply with the policies regulating the exchange of data among interacting services. We illustrate our approach through a simplified but realistic scenario for a service-based electronic marketplace

Parameterized Verification of Safety Properties in Ad Hoc Network Protocols

We summarize the main results proved in recent work on the parameterized verification of safety properties for ad hoc network protocols. We consider a model in which the communication topology of a network is represented as a graph. Nodes represent states of individual processes. Adjacent nodes represent single-hop neighbors. Processes are finite state automata that communicate via selective broadcast messages. Reception of a broadcast is restricted to single-hop neighbors. For this model we consider a decision problem that can be expressed as the verification of the existence of an initial topology in which the execution of the protocol can lead to a configuration with at least one node in a certain state. The decision problem is parametric both on the size and on the form of the communication topology of the initial configurations. We draw a complete picture of the decidability and complexity boundaries of this problem according to various assumptions on the possible topologies.Comment: In Proceedings PACO 2011, arXiv:1108.145

Sudden Cardiac Death in Athletes: Facts and Fallacies.

The benefits of exercise for cardiovascular and general health are many. However, sudden cardiac death (SCD) may occur in apparently healthy athletes who perform at the highest levels. A diverse spectrum of diseases is implicated in SCD in athletes, and while atherosclerotic coronary artery disease predominates in individuals of >35 years of age, primary cardiomyopathies and ion channelopathies are prevalent in young individuals. Prevention of SCD in athletes relies on the implementation of health policies aimed at the early identification of arrhythmogenic diseases (such as cardiac screening) and successful resuscitation (such as widespread utilization of automatic external defibrillators and training members of the public on cardiopulmonary resuscitation). This review will focus on the epidemiology and aetiologies of SCD in athletes, and examine fallacies in the approach to this controversial field. Furthermore, potential strategies to prevent these tragic events will be discussed, analysing current practice, gaps in knowledge and future directions

Distributed Consensus, Revisited

We provide a novel model to formalize a well-known algorithm, by Chandra and Toueg, that solves Consensus among asynchronous distributed processes in the presence of a particular class of failure detectors (Diamond S or, equivalently, Omega), under the hypothesis that only a minority of processes may crash. The model is defined as a global transition system that is unambigously generated by local transition rules. The model is syntax-free in that it does not refer to any form of programming language or pseudo code. We use our model to formally prove that the algorithm is correct

Compiling Pattern Matching in Join-Patterns

We propose an extension of the join-calculus with pattern matching on algebraic data types. Our initial motivation is twofold: to provide an intuitive semantics of the interaction between concurrency and pattern matching; to define a practical compilation scheme from extended join-definitions into ordinary ones plus (ML) pattern matching. To assess the correctness of our compilation scheme, we develop a theory of the applied join-calculus, a calculus with value-passing and value matching

Connectivity and energy-aware preorders for mobile ad-hoc networks

Network connectivity and energy conservation are two major goals in mobile ad-hoc networks (MANETs). In this paper we propose a probabilistic, energy-aware, broadcast calculus for the analysis of both such aspects of MANETs. We first present a probabilistic behavioural congruence together with a co-inductive proof technique based on the notion of bisimulation. Then we define an energy-aware preorder over networks. The behavioural congruence allows us to verify whether two networks exhibit the same (probabilistic) connectivity behaviour, while the preorder makes it possible to evaluate the energy consumption of different, but behaviourally equivalent, networks. In practice, the quantitative evaluation of the models is carried out by resorting to the statistical model checking implemented in the PRISM tool, i.e., a simulation of the probabilistic model. We consider two case studies: first we evaluate the performance of the Location Aided Routing protocol, then we compare the energy efficiency of the Go-Back-N protocol with that of the Stop-And-Wait in a network with mobility