Abstract
Museums promote cultural experiences through exhibits and the stories behind them. Nevertheless, museums are not always designed to engage and interest young audiences, especially teenagers. Throughout this paper, we discuss teenagers as an important group to be considered within the Children-Computer Interaction field, and we report some techniques on designing with teens, in particular, arguing that participatory design methods can involve teenagers in the design process of technology for museums. For this purpose, we conceptualized, designed and deployed a co-design activity for teenagers (aged 15–17), where teenagers together with a researcher jointly created and designed a medium fidelity prototype. For this case study, participants were divided into groups and invited to think and create games and story plots for a selected museum. All the prototypes were made by the participants with the support and guidance of the researcher and the Aurasma software, an augmented reality tool. © 2019, ICST Institute for Computer Sciences, Social Informatics and Telecommunications Engineering.

Abstract
Navigation through immersive virtual environments is a key concept for virtual reality as it allows users to explore those environments. Therefore, it is important to understand virtual reality navigation interfaces and their impact on the users' experience. This paper presents an objective performance evaluation of two types of navigation: natural (real walking and walk-in-place) vs. unnatural (gamepad). Steering Law was the objective performance metric chosen since it captures the relationship between the time to travel a path and the difficulty of that path. In addition to performance, subjective metrics were also considered, namely the feeling of presence, cybersickness and user satisfaction. The experiments consisted of having participants complete a series of paths with different indexes of difficulty and the time that a participant took to walk each path was measured. Overall results show that the navigation through real walking yielded better results when it comes to performance, cybersickness, and user satisfaction than the walk-in-place and gamepad navigation interfaces.

Abstract
Developing robust and universal methods for unsupervised segmentation of moving objects in video sequences has proved to be a hard and challenging task that has attracted the attention of many researchers over the last decades. State-of-the-art methods are, in general, computationally heavy preventing their use in real-time applications. This research addresses this problem by proposing a robust and computationally efficient method, coined BMOG, that significantly boosts the performance of a widely used method based on a Mixture of Gaussians. The proposed solution explores a novel classification mechanism that combines color space discrimination capabilities with hysteresis and a dynamic learning rate for background model update. The complexity of BMOG is kept low, proving its suitability for real-time applications. BMOG was objectively evaluated using the ChangeDetection.net 2014 benchmark. An exhaustive set of experiments was conducted, and a detailed analysis of the results, using two complementary types of metrics, revealed that BMOG achieves an excellent compromise in performance versus complexity.

Abstract

Abstract
We introduce HHL, a hierarchical variant of hybrid logic. We study first order correspondence results and prove a Hennessy-Milner like theorem relating (hierarchical) bisimulation and modal equivalence for HHL. Combining hierarchical transition structures with the ability to refer to specific states at different levels, this logic seems suitable to express and verify properties of hierarchical transition systems, a pervasive semantic structure in Computer Science.

Abstract
Conflict-free Replicated Data Types (CRDTs) are distributed data types that make eventual consistency of a distributed object possible and non ad-hoc. Specifically, state-based CRDTs ensure convergence through disseminating the entire state, that may be large, and merging it to other replicas. We introduce Delta State Conflict-Free Replicated Data Types (delta-CRDT) that can achieve the best of both operation-based and state-based CRDTs: small messages with an incremental nature, as in operation-based CRDTs, disseminated over unreliable communication channels, as in traditional state-based CRDTs. This is achieved by defining delta-mutators to return a delta-state, typically with a much smaller size than the full state, that to be joined with both local and remote states. We introduce the delta-CRDT framework, and we explain it through establishing a correspondence to current state-based CRDTs. In addition, we present an anti-entropy algorithm for eventual convergence, and another one that ensures causal consistency. Finally, we introduce several delta-CRDT specifications of both well-known replicated datatypes and novel datatypes, including a generic map composition.