A Protocol for the Atomic Capture of Multiple Molecules at Large Scale

With the rise of service-oriented computing, applications are more and more based on coordination of autonomous services. Envisioned over largely distributed and highly dynamic platforms, expressing this coordination calls for alternative programming models. The chemical programming paradigm, which models applications as chemical solutions where molecules representing digital entities involved in the computation, react together to produce a result, has been recently shown to provide the needed abstractions for autonomic coordination of services. However, the execution of such programs over large scale platforms raises several problems hindering this paradigm to be actually leveraged. Among them, the atomic capture of molecules participating in concur- rent reactions is one of the most significant. In this paper, we propose a protocol for the atomic capture of these molecules distributed and evolving over a large scale platform. As the density of possible reactions is crucial for the liveness and efficiency of such a capture, the protocol proposed is made up of two sub-protocols, each of them aimed at addressing different levels of densities of potential reactions in the solution. While the decision to choose one or the other is local to each node participating in a program's execution, a global coherent behaviour is obtained. Proof of liveness, as well as intensive simulation results showing the efficiency and limited overhead of the protocol are given.Comment: 13th International Conference on Distributed Computing and Networking (2012

Study of fault-tolerant software technology

Presented is an overview of the current state of the art of fault-tolerant software and an analysis of quantitative techniques and models developed to assess its impact. It examines research efforts as well as experience gained from commercial application of these techniques. The paper also addresses the computer architecture and design implications on hardware, operating systems and programming languages (including Ada) of using fault-tolerant software in real-time aerospace applications. It concludes that fault-tolerant software has progressed beyond the pure research state. The paper also finds that, although not perfectly matched, newer architectural and language capabilities provide many of the notations and functions needed to effectively and efficiently implement software fault-tolerance

A Byzantine Fault Tolerant Distributed Commit Protocol

In this paper, we present a Byzantine fault tolerant distributed commit protocol for transactions running over untrusted networks. The traditional two-phase commit protocol is enhanced by replicating the coordinator and by running a Byzantine agreement algorithm among the coordinator replicas. Our protocol can tolerate Byzantine faults at the coordinator replicas and a subset of malicious faults at the participants. A decision certificate, which includes a set of registration records and a set of votes from participants, is used to facilitate the coordinator replicas to reach a Byzantine agreement on the outcome of each transaction. The certificate also limits the ways a faulty replica can use towards non-atomic termination of transactions, or semantically incorrect transaction outcomes.Comment: To appear in the proceedings of the 3rd IEEE International Symposium on Dependable, Autonomic and Secure Computing, 200

The Fault Is Not in Our Stars: Avoiding an Arms Race in Outer Space

The world is on the precipice of a new arms race in outer space, as China, Russia, the United States, and others undertake dramatic new initiatives in anti-satellite weaponry. These accelerated competitive efforts at space control are highly destabilizing because developed societies have come to depend so heavily upon satellite services to support the entire civilian economy and the modern military apparatus; any significant threat or disruption in the availability of space assets would be massively, and possibly permanently, disruptive. International law regarding outer space developed with remarkable rapidity in the early years of the Space Age, but the process of formulating additional treaties and norms for space has broken down over the past several decades; no additional legal instruments have emerged that could cope with today’s rising threats. This Article therefore proposes three initiatives. Although none of them can suffice to solve the emerging problems, they could, perhaps, provide additional diplomacy, reinvigorating the prospects for rapprochement in space. Importantly, each of these three ideas has deep roots in other sectors of arms control, where they have served both to restore a measure of stability and to catalyze even more ambitious agreements in the longer term. The first proposal is for a declaratory regime of “no first use” of specified space weapons; this would do little to directly alter states’ capabilities for space warfare, but could serve as a “confidence-building measure,” to temper their most provocative rhetoric and practices. The second concept is a “limited test ban,” to interdict the most dangerous debris-creating developmental tests of new space weapons. Third is a suggestion for shared “space situational awareness,” which would create an international apparatus enabling all participants to enjoy the benefits of greater transparency, reducing the possibilities for secret malign or negligent behavior. In each instance, the Article describes the proposal and its variations, assesses its possible contributions to space security, and displays the key precedents from other arms-control successes. The Article concludes by calling for additional, further-reaching space diplomacy, in the hope that these relatively modest initial measures could provoke more robust subsequent negotiations

Comparing nuclear power trajectories in Germany and the UK: from ‘regimes' to ‘democracies’ in sociotechnical transitions and Discontinuities

This paper focuses on arguably the single most striking contrast in contemporary major energy politics in Europe (and even the developed world as a whole): the starkly differing civil nuclear policies of Germany and the UK. Germany is seeking entirely to phase out nuclear power by 2022. Yet the UK advocates a ‘nuclear renaissance’, promoting the most ambitious new nuclear construction programme in Western Europe.Here,this paper poses a simple yet quite fundamental question: what are the particular divergent conditions most strongly implicated in the contrasting developments in these two countries. With nuclear playing such an iconic role in historical discussions over technological continuity and transformation, answering this may assist in wider understandings of sociotechnical incumbency and discontinuity in the burgeoning field of‘sustainability transitions’. To this end, an ‘abductive’ approach is taken: deploying nine potentially relevant criteria for understanding the different directions pursued in Germany and the UK. Together constituted by 30 parameters spanning literatures related to socio-technical regimes in general as well as nuclear technology in particular, the criteria are divided into those that are ‘internal’ and ‘external’ to the ‘focal regime configuration’ of nuclear power and associated ‘challenger technologies’ like renewables. It is ‘internal’ criteria that are emphasised in conventional sociotechnical regime theory, with ‘external’ criteria relatively less well explored. Asking under each criterion whether attempted discontinuation of nuclear power would be more likely in Germany or the UK, a clear picture emerges. ‘Internal’ criteria suggest attempted nuclear discontinuation should be more likely in the UK than in Germany– the reverse of what is occurring. ‘External’ criteria are more aligned with observed dynamics –especially those relating to military nuclear commitments and broader ‘qualities of democracy’. Despite many differences of framing concerning exactly what constitutes ‘democracy’, a rich political science literature on this point is unanimous in characterising Germany more positively than the UK. Although based only on a single case,a potentially important question is nonetheless raised as to whether sociotechnical regime theory might usefully give greater attention to the general importance of various aspects of democracy in constituting conditions for significant technological discontinuities and transformations. If so, the policy implications are significant. A number of important areas are identified for future research, including the roles of diverse understandings and specific aspects of democracy and the particular relevance of military nuclear commitments– whose under-discussion in civil nuclear policy literatures raises its own questions of democratic accountability

The Communication Complexity of Atomic Commitment and of Gossiping

We consider the problem of atomic commitment of a transaction in a distributed database. This is a variant of the famous gossiping problem (see [HHL] for a survey). Given a set of communication costs between pairs of participant sites, we establish that the necessary communication cost for any atomic commitment algorithm is twice the cost of a certain minimum spanning tree. We also establish the necessary communication time for any atomic commitment algorithm, given a set of communication delays between pairs of participant sites, and the time at which each participant completes its subtransaction. Then we determine that both lower bounds are also upper bounds in the following sense. There is an efficient (i.e. polynomial-time) algorithm that, in the absence of failures, has a minimum communication cost. There is another efficient algorithm that, in the absence of failures, has a minimum communication time. However, unless P=NP, there is no efficient algorithm which has a minimum communication complexity, namely, for which the product of communication cost and communication time is minimum. Then we present a simple, linear time, distributed algorithm, called TREE-COMMIT, whose communication complexity is not worse than p times the minimum complexity, where p is the number of participants. Finally, we demonstrate that TREE-COMMIT is superior to the existing variants of the two-phase commit protocol

What Would Zero Look Like? A Treaty for the Abolition of Nuclear Weapons

Nuclear disarmament-the comprehensive, universal, and permanent abolition of all nuclear weapons, pursuant to a verifiable, legally binding international agreement-has long been one of the most ambitious, controversial, and urgent items on the agenda for arms control. To date, however, most of the discussion of getting to zero has highlighted the political, military, technical and diplomatic dimensions of this complex problem, and there has been relatively little attention to the legal requirements for drafting such a novel treaty. This Article fills that gap by offering two proposed agreements. The first, a non-legally-bindingfr amework accord, would be designedf or signature relatively soon (e.g., in 2015) to re-commit states to the goal of nuclear elimination and to energize their concerted individual and collective action on a set of prescribed steps in pursuit of it. The second, a legally-binding document, would be concluded at some point in the more distant future, when states had accomplished great reductions in their current nuclear arsenals and were ready, at last, to plunge forward to true abolition. The Article describes the conditions necessary for the further articulation of these two novel agreements, and the text of each instrument carries numerous annotations that identify competing options, describe the negotiating range, and illuminate the drafter\u27s choices. The hope is that something novel can be gained-fresh insights can be suggested, and new questions can be raised (even if answering them remains elusive)-by advancing the dialogue about nuclear disarmament to the concrete stage of treaty drafting