Realization theory of discrete-time linear switched systems

The paper presents realization theory of discrete-time linear switched systems. We present necessary and sufficient conditions for an input–output map to admit a discrete-time linear switched system realization. In addition, we present a characterization of minimality of discrete-time linear switched systems in terms of reachability and observability. Further, we prove that minimal realizations are unique up to isomorphism. We also discuss algorithms for converting a linear switched system to a minimal one and for constructing a state-space representation from input–output data. The paper uses the theory of rational formal power series in non-commutative variables.     

Formal methods integration in software engineering

This paper presents an extract from our works on a software engineering method for avionic real-time systems [3], the C-Method, which covers the whole software lifecycle thanks to a seamless process, and integrates formal methods in its process. Because distributed, real-time and embedded (DRE) systems have safety critical concerns, they require the use of formal languages (that allow non-ambiguous and rigorous specifications) in order to be able to prove their non-functional properties. Therefore, the “C-Method” relies on the use of formal languages in the earliest steps of the system specification and on the use of semi-formal languages in the analysis, design and programming steps. The fundamental question is how to integrate several languages with different levels of formalization and abstraction. The previous software engineering methods were based on a single language or notation, so they did not address this issue. In order to make the transitions more continuous between semi-formal and formal specifications, we have introduced in the development process what we call “intermediate” languages (+CAL and Why), that are easy to manipulate but directly linked to a formal language (TLA+ for +CAL, Why for PVS).     

Fluid dynamic behavior of dispensing small droplets through a thin liquid film

This paper presents a technology for dispensing droplets through thin liquid layers. The system consists of a free liquid film, which is suspended in a frame and positioned in front of a piezoelectric printhead. A droplet, generated by the printhead, merges with the film, but due to its momentum, passes through and forms a droplet that separates on the other side and continues its flight. The technology allows the dispensing, mixing and ejecting of picolitre liquid samples in a single step. This paper overviews the concept, potential applications, experiments, results and a numerical model. The experimental work includes studying the flight of ink droplets, which ejected from an inkjet print head, fly through a free ink film, suspended in a frame and positioned in front of the printhead. We experimentally observed that the minimum velocity required for the 80 pl droplets to fly through the 75 ± 24 μm thick ink film was of 6.6 m s^?1. We also present a numerical simulation of the passage of liquid droplets through a liquid film. The numerical results for different initial speeds of droplets and their shapes are taken into account. We observed that during the droplet–film interaction, the surface energy is partially converted to kinetic energy, and this, together with the impact time, helps the droplets penetrate the film. The model includes the Navier–Stokes equations with continuum-surface-tension force derived from the phase-field/Cahn–Hilliard equation. This system allows us to simulate the motion of a free surface in the presence of surface tension during merging, mixing and ejection of droplets. The influence of dispensing conditions was studied and it was found that the residual velocity of droplets after their passage through the thin liquid film well matches the measured velocity from the experiment.     

Molecular weight between physical entanglements in natural rubber: A critical parameter during strain-induced crystallization

The purpose of this paper is to clarify the role of crosslink density of natural rubber on its strain-induced crystallization. A series of new in situ synchrotron X-ray diffraction experiments were performed during the stretching process of weakly and highly vulcanized natural rubber samples. The experimental data have been analysed in terms of both crystallite size and crystallization rate. Moreover, a careful treatment of previously published data that might appear contradictory has been done. The comparison between all these data, coming from NR of different origins and with different crosslinking states, demonstrates that the molecular weight between physical entanglements in natural rubber appears as a key parameter for strain-induced crystallization (SIC).     

DEPAS: a decentralized probabilistic algorithm for auto-scaling

The dynamic provisioning of virtualized resources offered by cloud computing infrastructures allows applications deployed in a cloud environment to automatically increase and decrease the amount of used resources. This capability is called auto-scaling and its main purpose is to automatically adjust the scale of the system that is running the application to satisfy the varying workload with minimum resource utilization. The need for auto-scaling is particularly important during workload peaks, in which applications may need to scale up to extremely large-scale systems. Both the research community and the main cloud providers have already developed auto-scaling solutions. However, most research solutions are centralized and not suitable for managing large-scale systems, moreover cloud providers’ solutions are bound to the limitations of a specific provider in terms of resource prices, availability, reliability, and connectivity. In this paper we propose DEPAS, a decentralized probabilistic auto-scaling algorithm integrated into a P2P architecture that is cloud provider independent, thus allowing the auto-scaling of services over multiple cloud infrastructures at the same time. Our experiments (simulations and real deployments), which are based on real service traces, show that our approach is capable of: (i) keeping the overall utilization of all the instantiated cloud resources in a target range, (ii) maintaining service response times close to the ones obtained using optimal centralized auto-scaling approaches.     

Characterisation of forces exerted by the entire hand during the power grip: effect of the handle diameter

The objective of this study was to analyse the effect of the handle diameter on the grip forces exerted by the hand during a maximal power grip task. A handle ergometer, combining six instrumented beams and a pressure map, was used to determine the forces exerted by the palm side of the hand regrouping data from 10 anatomical sites (fingertips, phalanges, thumb, palm…). This methodology provided results giving new insight into the effect of the handle diameter on the forces exerted by the hand. First, it appeared that the relationship between the hand length/handle diameter ratio and the maximal grip force fit a U-inverted curve with maximal values observed for a handle diameter measuring 17.9% of the hand length. Second, it was showed that the handle diameter influenced the forces exerted on the anatomical sites of the hand. Finally, it was showed that the handle diameter influenced the finger force sharing particularly for the index and the little fingers. Practitioner Summary: This study analysed the effect of the handle diameter on the grip forces exerted by the hand during a maximal power grip force. This study showed that measurement of the totality of the forces exerted at the hand/handle interface is needed to better understand the ergonomics of handle tools. Our results could be re-used by designers and clinicians in order to develop handle tools which prevent hand pathologies.     

Qualitative and quantitative conditions for the transitivity of perceived causation:

If A caused B and B caused C, did A cause C? Although laypersons commonly perceive causality as being transitive, some philosophers have questioned this assumption, and models of causality in artificial intelligence are often agnostic with respect to transitivity. We consider two formal models of causation that differ in the way they represent uncertainty. The quantitative model uses a crude probabilistic definition, arguably the common core of more sophisticated quantitative definitions; the qualitative model uses a definition based on nonmonotonic consequence relations. Different sufficient conditions for the transitivity of causation are laid bare by the two models: The Markov condition on events for the quantitative model, and a so-called saliency condition (A is perceived as a typical cause of B) for the qualitative model. We explore the formal and empirical relations between these sufficient conditions, and between the underlying definitions of perceived causation. These connections shed light on the range of applicability of each model, contrasting commonsense causal reasoning (supposedly qualitative) and scientific causation (more naturally quantitative). These speculations are supported by a series of three behavioral experiments.     

Integrality and separability of multitouch interaction techniques in 3D manipulation tasks

Multitouch displays represent a promising technology for the display and manipulation of data. While the manipulation of 2D data has been widely explored, 3D manipulation with multitouch displays remains largely unexplored. Based on an analysis of the integration and separation of degrees of freedom, we propose a taxonomy for 3D manipulation techniques with multitouch displays. Using that taxonomy, we introduce Depth-Separated Screen-Space (DS3), a new 3D manipulation technique based on the separation of translation and rotation. In a controlled experiment, we compared DS3 with Sticky Tools and Screen-Space. Results show that separating the control of translation and rotation significantly affects performance for 3D manipulation, with DS3 performing faster than the two other techniques.     

Reasoning about ignorance and contradiction: many-valued logics versus epistemic logic

This paper tries to reinterpret three- and four-valued logics of partial ignorance and contradiction in the light of epistemic logic. First, we try to cast Kleene three-valued logic in the setting of a simplified form of epistemic logic. It is a two-tiered logic that embeds propositional logic into another propositional setting. The use of modalities enables Kleene truth values to be expressed at the syntactic level. Kleene logic is then a fragment of the simplified epistemic logic where modalities are in front of literals only. Kleene truth-tables can then be retrieved, while preserving tautologies of classical logic. Kleene logic connectives can be seen as set-valued extensions of Boolean logic ones, but the compositionality of Kleene logic leads to a lack of expressiveness and inferential power compared to the proposed epistemic logic. This methodology is then extended to Belnap four-valued logic, which is tailored to the handling of inconsistent information from various sources. A non-regular modal setting for reasoning about contradiction is obtained, where the adjunction law does not hold. It is a special case of a fragment of the monotonic modal logic EMN.