Two Decades of Maude

This paper is a tribute to José Meseguer, from the rest of us in the Maude team, reviewing the past, the present, and the future of the language and system with which we have been working for around two decades under his leadership. After reviewing the origins and the language's main features, we present the latest additions to the language and some features currently under development. This paper is not an introduction to Maude, and some familiarity with it and with rewriting logic are indeed assumed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The Challenge of Unifying Semantic and Syntactic Inference Restrictions

While syntactic inference restrictions don't play an important role for SAT, they are an essential reasoning technique for more expressive logics, such as first-order logic, or fragments thereof. In particular, they can result in short proofs or model representations. On the other hand, semantically guided inference systems enjoy important properties, such as the generation of solely non-redundant clauses. I discuss to what extend the two paradigms may be unifiable

Improved Methodologies in Modeling and Predicting Failure in AASHTO M-180 Guardrail Steel Using Finite Element Analysis - Phase I

Steel guardrail systems have historic and widespread applications throughout the nation’s highways and roadways. However, catastrophic system failure can occur if the guardrail element ruptures, thus allowing an errant vehicle to pass uncontrolled through the system and potentially allow fractured ends to pierce the occupant compartment. To aid in the analysis and design of guardrail systems, further efforts are needed to develop and implement more reliable material failure criteria to predict and model guardrail steel rupture under all vehicle impact loading scenarios within impact simulation finite element method (FEM) software, such as LS-DYNA. This Phase I study accomplished a number of tasks to aid in this objective. First, historical and state-of-the-art failure criteria with emphasis on stress state dependent failure criteria were reviewed. Next, various failure surface methods that provide estimations on the triaxiality and Lode parameter vs. effective plastic strain at failure were review and analyzed. It was determined that more flexible failure surface fitting methods may provide better estimations, and larger more diverse testing programs are required to estimate the failure surface through all stress states. A failure surface method using a Smoothed, Thin-Plate Spline was also proposed to overcome short comings in existing failure surface estimation methods. Based on the review of the existing failure surfaces’ performance, a steel material testing program was developed, and testing was performed on 21 different specimen configurations that represent a range of stress states. The specimens were prepared using ASTM A572 Grade 50 steel with similar material properties as AASHTO M-180 guardrail steel. Test results and calculated material properties were presented herein. Lastly, a preliminary FEM modeling effort was conducted. Various modeling parameters were examined, including the effects from hourglass controls, mesh-size effects, inertial effects from load rate, and solid vs. shell behavior. Based on this analysis, preliminary models of the testing specimen were developed. Also, a preliminary material model was calibrated and presented herein. Conclusions were made, and recommendations were provided for continuing a Phase II effort. Advisor: Ronald K. Falle

Asynchronous Multiparty Session Type Implementability is Decidable - Lessons Learned from Message Sequence Charts

Multiparty session types (MSTs) provide efficient means to specify and verify asynchronous message-passing systems. For a global type, which specifies all interactions between roles in a system, the implementability problem asks whether there are local specifications for all roles such that their composition is deadlock-free and generates precisely the specified executions. Decidability of the implementability problem is an open question. We answer it positively for global types with sender-driven choice, which allow a sender to send to different receivers upon branching and a receiver to receive from different senders. To achieve this, we generalise results from the domain of high-level message sequence charts (HMSCs). This connection also allows us to comprehensively investigate how HMSC techniques can be adapted to the MST setting. This comprises techniques to make the problem algorithmically more tractable as well as a variant of implementability that may open new design space for MSTs. Inspired by potential performance benefits, we introduce a generalisation of the implementability problem that we, unfortunately, prove to be undecidable