How to avoid a local epidemic becoming a global pandemic

Here, we combine international air travel passenger data with a standard epidemiological model of the initial 3 mo of the COVID-19 pandemic (January through March 2020; toward the end of which the entire world locked down). Using the information available during this initial phase of the pandemic, our model accurately describes the main features of the actual global development of the pandemic demonstrated by the high degree of coherence between the model and global data. The validated model allows for an exploration of alternative policy efficacies (reducing air travel and/or introducing different degrees of compulsory immigration quarantine upon arrival to a country) in delaying the global spread of SARS-CoV-2 and thus is suggestive of similar efficacy in anticipating the spread of future global disease outbreaks. We show that a lesson from the recent pandemic is that reducing air travel globally is more effective in reducing the global spread than adopting immigration quarantine. Reducing air travel out of a source country has the most important effect regarding the spreading of the disease to the rest of the world. Based upon our results, we propose a digital twin as a further developed tool to inform future pandemic decision-making to inform measures intended to control the spread of disease agents of potential future pandemics. We discuss the design criteria for such a digital twin model as well as the feasibility of obtaining access to the necessary online data on international air travel

Inseguendo fagiani selvatici: Partial order reduction for guarded command languages

This paper presents a method for testing whether objects in actor languages and active object languages exhibit locally deterministic behavior. We investigate such a method for a class of guarded command programs, abstracting from object-oriented features like method calls but focusing on cooperative scheduling of dynamically spawned processes executing in parallel. The proposed method can answer questions such as whether all permutations of an execution trace are equivalent, by generating candidate traces for testing which may lead to different final states. To prune the set of candidate traces, we employ partial order reduction. To further reduce the set, we introduce an analysis technique to decide whether a generated trace is schedulable. Schedulability cannot be decided for guarded commands using standard dependence and interference relations because guard enabledness is non-monotonic. To solve this problem, we use concolic execution to produce linearized symbolic traces of the executed program, which allows a weakest precondition computation to decide on the satisfiability of guards

ABS: A core language for abstract behavioral specification

This paper presents ABS, an abstract behavioral specification language for designing executable models of distributed object-oriented systems. The language combines advanced concurrency and synchronization mechanisms for concurrent object groups with a functional language for modeling data. ABS uses asynchronous method calls, interfaces for encapsulation, and cooperative scheduling of method activations inside concurrent objects. This feature combination results in a concurrent object-oriented model which is inherently compositional. We discuss central design issues for ABS and formalize the type system and semantics of Core ABS, a calculus with the main features of ABS. For Core ABS, we prove a subject reduction property which shows that well-typedness is preserved during execution; in particular, "method not understood" errors do not occur at runtime for well-typed ABS models. Finally, we briefly discuss the tool support developed for ABS

Enabling multimedia metadata interoperability by defining formal semantics of MPEG-7 profiles

MPEG-7 can be used to create complex and comprehensive metadata descriptions of multimedia content. Since MPEG-7 is defined in terms of an XML schema, the semantics of its elements have no formal grounding. In addition, certain features can be described in multiple ways. MPEG-7 profiles are subsets of the standard that apply to specific application