Unified Analysis of Collapsible and Ordered Pushdown Automata via Term Rewriting

We model collapsible and ordered pushdown systems with term rewriting, by encoding higher-order stacks and multiple stacks into trees. We show a uniform inverse preservation of recognizability result for the resulting class of term rewriting systems, which is obtained by extending the classic saturation-based approach. This result subsumes and unifies similar analyses on collapsible and ordered pushdown systems. Despite the rich literature on inverse preservation of recognizability for term rewrite systems, our result does not seem to follow from any previous study.Comment: in Proc. of FRE

Necessary and sufficient conditions for macroscopic realism from quantum mechanics

Macroscopic realism, the classical world view that macroscopic objects exist independently of and are not influenced by measurements, is usually tested using Leggett-Garg inequalities. Recently, another necessary condition called no-signaling in time (NSIT) has been proposed as a witness for non-classical behavior. In this paper, we show that a combination of NSIT conditions is not only necessary but also sufficient for a macrorealistic description of a physical system. Any violation of macroscopic realism must therefore be witnessed by a suitable NSIT condition. Subsequently, we derive an operational formulation for NSIT in terms of positive operator-valued measurements and the system Hamiltonian. We argue that this leads to a suitable definition of "classical" measurements and Hamiltonians, and apply our formalism to some generic coarse-grained quantum measurements.Comment: 10 pages, published versio

‘Interrupted’ landscapes: post-earthquake reconstruction in between urban renewal and social identity of local communities

Il presente saggio vuole affrontare il tema della ricostruzione postsismica con un'attenzione alla questione del paesaggio, termine che lega in maniera indissolubile la realtà fisica del territorio a quei valori immateriali (storici, culturali, produttivi, enogastronomici, ecc.) che costituiscono l'identità dei luoghi. In questo senso si intendono “paesaggi interrotti” i luoghi distrutti dal sisma, perchè sono state interrotte le storie che legano gli abitanti al luogo, è stato interrotto quel processo di narrazione continua e di attribuzione di senso e significati che avviene tra una collettività e il suo territorio. La ricerca parte dall'analisi delle recenti ricostruzioni post-sistmiche, che hanno oscillato tra le due idee opposte di new town, poco distanti dalle città distrutte e ricostruzione “dov'era, com'era”. Il saggio indaga la dimensione sociale e semiologica del paesaggio, riflettendo sul tema dell'identità sociale, sull'attaccamento al luogo da parte degli abitanti, anche con l'obiettivo di definire linee guida e strategie progettuali per la ricostruzione sostenibile dei paesi distrutti dal sisma e da altri eventi disastrosi. In particolare vengono definite azioni di governance, strategie resilienti a partire dal coinvolgimento delle comunità locali e buone pratiche per la ricostruzione secondo un approccio paesaggistico al progetto urbano

Compelled to control: conflicting visions of the future of cyberspace

This report looks at the desire among states for greater control over the digital domain. It considers the convergence of controlling desires among the major cyberpowers and examines some of the main dynamics of the Russian and Chinese positions. Their positions are examined relative to each other and to the Western consensus. The paper analyses the potential implications for the global internet and the impact that developing countries may have on the dialogue

Federal Asbestos Legislation: The Winners Are ...

Under the guise of providing aid to victims of asbestos-related illnesses, a small group of companies has lobbied for and won relief from their liability worth tens of billions of dollars in the Senate's asbestos trust fund bill, according to this Public Citizen report.Their success in protecting their corporate interests, however, will sharply reduce the funds under the legislation that will be available to asbestos victims, the report finds. Meanwhile, some of the nation's largest financial investment firms have spent millions of dollars in lobbying and campaign contributions to position themselves to score big rewards should the legislation pass.The big winners in the legislation, S. 852, include a handful of Fortune 500 companies -- Dow Chemical, Ford, General Electric, General Motors, Honeywell, Pfizer and Viacom -- and at least 10 asbestos makers that have filed for bankruptcy.Public Citizen found an intense Capitol Hill lobbying campaign on behalf of the Fortune 500 companies to win the financial concession was spearheaded by a relatively unknown entity called the Asbestos Study Group (ASG), which refuses to make its full membership list public

Reachability analysis of first-order definable pushdown systems

We study pushdown systems where control states, stack alphabet, and transition relation, instead of being finite, are first-order definable in a fixed countably-infinite structure. We show that the reachability analysis can be addressed with the well-known saturation technique for the wide class of oligomorphic structures. Moreover, for the more restrictive homogeneous structures, we are able to give concrete complexity upper bounds. We show ample applicability of our technique by presenting several concrete examples of homogeneous structures, subsuming, with optimal complexity, known results from the literature. We show that infinitely many such examples of homogeneous structures can be obtained with the classical wreath product construction.Comment: to appear in CSL'1

Spectrum of the Laplace-Beltrami Operator and the Phase Structure of Causal Dynamical Triangulation

We propose a new method to characterize the different phases observed in the non-perturbative numerical approach to quantum gravity known as Causal Dynamical Triangulation. The method is based on the analysis of the eigenvalues and the eigenvectors of the Laplace-Beltrami operator computed on the triangulations: it generalizes previous works based on the analysis of diffusive processes and proves capable of providing more detailed information on the geometric properties of the triangulations. In particular, we apply the method to the analysis of spatial slices, showing that the different phases can be characterized by a new order parameter related to the presence or absence of a gap in the spectrum of the Laplace-Beltrami operator, and deriving an effective dimensionality of the slices at the different scales. We also propose quantities derived from the spectrum that could be used to monitor the running to the continuum limit around a suitable critical point in the phase diagram, if any is found.Comment: 21 pages, 26 figures, 2 table

Timed pushdown automata revisited

This paper contains two results on timed extensions of pushdown automata (PDA). As our first result we prove that the model of dense-timed PDA of Abdulla et al. collapses: it is expressively equivalent to dense-timed PDA with timeless stack. Motivated by this result, we advocate the framework of first-order definable PDA, a specialization of PDA in sets with atoms, as the right setting to define and investigate timed extensions of PDA. The general model obtained in this way is Turing complete. As our second result we prove NEXPTIME upper complexity bound for the non-emptiness problem for an expressive subclass. As a byproduct, we obtain a tight EXPTIME complexity bound for a more restrictive subclass of PDA with timeless stack, thus subsuming the complexity bound known for dense-timed PDA.Comment: full technical report of LICS'15 pape