We consider the Widom–Rowlinson model of two types of interacting particles on d-regular graphs. We prove a tight upper bound on the occupancy fraction, the expected fraction of vertices occupied by a particle under a random configuration from the model. The upper bound is achieved uniquely by unions of complete graphs on d + 1 vertices, K d+1. As a corollary we find that K d+1 also maximizes the normalized partition function of the Widom–Rowlinson model over the class of d-regular graphs. A special case of this shows that the normalized number of homomorphisms from any d-regular graph G to the graph HWR , a path on three vertices with a loop on each vertex, is maximized by K d+1. This proves a conjecture of Galvin.

A logical constant is weakly disharmonious if its elimination rules are weaker than its introduction rules. Substructural weak disharmony is the weak disharmony generated by structural restrictions on the eliminations. I argue that substructural weak disharmony is not a defect of the constants which exhibit it. To the extent that it is problematic, it calls into question the structural properties of the derivability relation. This prompts us to rethink the issue of controlling the structural properties of a logic by means of harmony. I argue that such a control is possible and desirable. Moreover, it is best achieved by global tests of harmony.

This work presents a novel command strategy developed to improve operator performance and minimize difficulties in teleoperation tasks for mobile-manipulator systems with a holonomic base. Aimed specifically at novice operators, virtual fixtures are introduced as a means to minimize collisions and assist in navigation. Using the 6-degree-of-freedom (DOF) Omnibot mobile-manipulator system (MMS), a command strategy is implemented such that the operator need only control a 3-DOF haptic joystick to achieve full control of the Omnibot MMS. The command strategy is used to coordinate control between the arm and the base of the system, prevent collisions with known obstacles, and alert the operator of proximity to those obstacles with haptic forces. Through experimental testing it is shown that operator performance improved with the use of virtual fixtures.

This paper describes the motivation for the development of the HuroCupcompetition and follows the rule development from its inaugural competition from2002 to 2015. The history of HuroCup is broken down into its growing phase(2002–2006), a time of explosive growth (2007–2011), and currenttimes. This paper describes the main research focus of HuroCup, the multi-eventhumanoid robot competition: (a) active balancing, (b) complex motion planning,and (c) human–robot interaction and shows how the various HuroCup eventsrelate to those research topics. This paper concludes with some medium- andlong-term goals of the rule development for HuroCup.

We correct two typos and an error in The Arithmetic of the Even and the Odd, and provide an axiom system for a weak arithmetic in which the fact that a square root of an integer is either irrational or an integer can be proved.

Logicians and philosophers of science have proposed various formal criteria for theoretical equivalence. In this paper, we examine two such proposals: definitional equivalence and categorical equivalence. In order to show precisely how these two well-known criteria are related to one another, we investigate an intermediate criterion called Morita equivalence.

In this study of affordances for second language (L2) learning in World of Warcraft (WoW) group play, we compared three gameplay episodes spanning a semester-long course. Applying multimodal analysis framed by ecological, dialogical and distributed (EDD) views (Zheng and Newgarden, forthcoming), we explored four English as a second language learners’ verbalizations and avatar actions. Players learned to take skilled linguistic action as they coordinated recurrent WoW gameplay activities (questing, planning next moves, traveling, learning a skill, etc.). Frequent activities matched Common European Framework of Reference (CEFR) speaking proficiency descriptors, used widely in L2 teaching and learning (L2TL), providing evidence that players engaged in the types of communicative activities interaction-oriented classroom approaches develop. However, in the WoW context, interactions were not planned, but emerged as players dynamically directed the course of play. Furthermore, modalities of avatar-embodiment and conversing over Skype allowed players to flexibly integrate language and actions to co-act toward game goals, discuss non-game topics during play, or demonstrate comprehension with avatar actions alone, an affordance for less verbal players. This research builds on previous work (Zheng, Newgarden & Young, 2012) relating WoW’s multiplayer activities and L2 learners’ skilled linguistic actions. We refer to Chemero’s (2009) model of the animal-environment system to explain how L2 learners develop abilities to take skilled linguistic action by acting on affordances in WoW. The EDD framework presented may enable other researchers to account for more of the complexities involved in L2 learning in multimodal, multiplayer virtual environments.

We propose and investigate a semantics for peer data exchange systems where different peers are related by data exchange constraints and trust relationships. These two elements plus the data at the peers' sites and their local integrity constraints are made compatible via a semantics that characterizes sets of solution instances for the peers. They are the intended – possibly virtual – instances for a peer that are obtained through a data repair semantics that we introduce and investigate. The semantically correct answers from a peer to a query, the so-called peer consistent answers, are defined as those answers that are invariant under all its different solution instances. We show that solution instances can be specified as the models of logic programs with a stable model semantics. The repair semantics is based on null values as used in SQL databases, and is also of independent interest for repairs of single databases with respect to integrity constraints.

Online language learning and teaching in multimodal contexts has been identified as one of the key research areas in computer-aided learning (CALL) (Lamy, 2013; White, 2014).1 This paper aims to explore meaning-making in online language learner interactions via desktop videoconferencing (DVC) and in doing so illustrate multimodal transcription and analysis as well as the application of theoretical frameworks from other fields. Recordings of learner DVC interactions and interviews are qualitatively analysed within a case study methodology. The analysis focuses on how semiotic resources available in DVC are used for meaning-making, drawing on semiotics, interactional sociolinguistics, nonverbal communication, multimodal interaction analysis and conversation analysis. The findings demonstrate the use of contextualization cues, five codes of the body, paralinguistic elements for emotional expression, gestures and overlapping speech in meaning-making. The paper concludes with recommendations for teachers and researchers using and investigating language learning and teaching in multimodal contexts.

Generative type abstractions – present in Haskell, OCaml, and other languages – are useful concepts to help prevent programmer errors. They serve to create new types that are distinct at compile time but share a run-time representation with some base type. We present a new mechanism that allows for zero-cost conversions between generative type abstractions and their representations, even when such types are deeply nested. We prove type safety in the presence of these conversions and have implemented our work in GHC.

The last years have seen an increasing interest in classifying (existence claims in) classical mathematical theorems according to their strength. We pursue this goal from the refined perspective of computational complexity. Specifically, we establish that rigorously solving the Dirichlet Problem for Poisson's Equation is in a precise sense ‘complete’ for the complexity class ${\#\mathcal{P}}$ and thus as hard or easy as parametric Riemann integration (Friedman 1984; Ko 1991. Complexity Theory of Real Functions).