Poisson ratio and excess low-frequency vibrational states in glasses

In glass, starting from a dependence of the Angell's fragility on the Poisson ratio [V. N. Novikov and A. P. Sokolov, Nature 431, 961 (2004)], and a dependence of the Poisson ratio on the atomic packing density [G. N. Greaves et al., Nat. Mater. 10, 823 (2011)], we propose that the heterogeneities are predominantly density fluctuations in strong glasses (lower Poisson ratio) and shear elasticity fluctuations in fragile glasses (higher Poisson ratio). Because the excess of low-frequency vibration modes in comparison with the Debye regime (boson peak) is strongly connected to these fluctuations, we propose that they are breathing-like (with change of volume) in strong glasses and shear-like (without change of volume) in fragile glasses. As a verification, it is confirmed that the excess modes in the strong silica glass are predominantly breathing-like. Moreover, it is shown that the excess breathing-like modes in a strong polymeric glass are replaced by shear-like modes under hydrostatic pressure as the glass becomes more compact

Using GASP for Collaborative Interaction within 3D Virtual Worlds

International audienceIn this paper, we present Gasp, a General Animation and Simulation Platform, whose purpose is to animate autonomous or userdriven agents, and we explain how it can be used for Collaborative Virtual Reality. First, we explain its architecture, based on the notion of simulation objects (or agents) associated with a calculation part (the behavior). Then we describe how it is possible to distribute eciently our agents upon a network in order to share the amount of calculation between several computers. Finally, as the visualisation of a simulation is also a simulation object, we show that our architecture allows us to distribute several visualisations upon a network to share a 3D interactive simulation between several users

Modèle de caractérisation des visualisations de données complexes en grandes quantités

International audienceVisualizing large and complex datasets is an issue that must be tackled more and more often in the domain of professional systems, given the increasing capacity of data providers. In this paper, we introduce a model supporting the characterization of all the dimensions that have an impact on big and/or complex data representation solutions, which enables us to highlightthe limits of existing visualization solutions.La visualisation de grandes quantités données complexes est un problème de plus en plus courant dans le domaine des systèmes professionnels, en raison des capacités de création et de stockage de données qui augmentent sans cesse. Dans cet article nous présentons un modèle permettant de caractériser l'ensemble des dimensions qui ont un impact sur la représentation de données complexes et/ou en grandes quantités, ce qui nous permet de mettre en avant les limites des solutions de visualisation existantes

Collaborative Virtual Environments for Ergonomics: Embedding the Design Engineer Role in the Loop

International audienceThe aim of this paper is to define the role and duties of a design engineer involved in a collaborative ergonomic design session supported by a 3D collaborative virtual environment. For example, such a session can be used to adapt the manual task an operator must achieve in the context of an industrial assembly line. We first present the interest of such collaborative sessions. Then we present a related work explaining the need of proper 3DCVE and metaphors to obtain efficient collaborative ergonomic design sessions. Then, after a short definition of the role of the engineer in such sessions, we propose a use case highlighting the type of metaphor such engineers need to have to be efficient in such a framework. Discussion and future works ends the paper

Efficient validation and construction of border arrays

In this article we present an on-line linear time and space algorithm to check if an integer array f is the border array of at least one string w built on a bounded or unbounded size alphabet Σ. We first show some relations between the border array of some string w and the skeleton of the DFA recognizing Σ ∗ · w, independently of the explicit knowledge of w. This enables us to design algorithms for validating and generating border arrays that outperform existing ones [4, 3]. The validating algorithm lowers the delay (time spent on one element of the array) from O(|w|) to O(min{|Σ|, |w|}) comparing to algorithms in [4, 3]. Finally we give some results on the numbers of distinct border arrays on some alphabet sizes.

Expert evaluation of the usability of HeloVis: a 3D Immersive Helical Visualization for SIGINT Analysis

International audienceThis paper presents an evaluation of HeloVis: a 3D interactive visualization that relies on immersive properties to improve user performance during SIGnal INTelligence (SIGINT) analysis. HeloVis draws on perceptive biases, highlighted by Gestalt laws, and on depth perception to enhance the recurrence properties contained in the data. In this paper, we briefly recall what is SIGINT, the challenges that it brings to visual analytics, and the limitations of state of the art SIGINT tools. Then, we present HeloVis, and we evaluate its efficiency through the results of an evaluation that we have made with civil and military operators who are the expert end-users of SIGINT analysis

Visualisation de nuages de points 3D acquis par un laser : impact de la vision stéréoscopique et du suivi de la tête sur une recherche de cible

International audienceIn military context, we study the visualization of 3D point clouds sense by a drone flying around a battlefield area equipped with a 3D laser. We propose a user experiment protocol in order to study the effect of stereo and head tracking rendering on a target research task with a virtual reality headset. Our first results show a clear advantage when stereo and head tracking rendering are activated.Nous étudions dans un contexte militaire la visualisation de nuages de points 3D acquis par un laser embarqué sur un drone tournant autour d’une zone de combat. Nous proposons un protocole expérimental permettant d’évaluer l’impact de la vision stéréoscopique et du suivi de la tête sur une recherche de cible avec un casque de réalité virtuelle. Les premiers résultats montrent un avantage lorsque la vision stéréoscopique et le suivi de la tête sont activés

Enabling Collaboration between Heterogeneous 3D Viewers through a PAC-C3D Modeling of the Shared Virtual Environment

International audienceWe propose to illustrate how the PAC-C3D software model makes it possible to share networked 3D Virtual Environments (VE) between heterogeneous 3D viewers written in Java3D and jReality

PAC-C3D: A New Software Architectural Model for Designing 3D Collaborative Virtual Environments

International audienceWe propose PAC-C3D as a new software model for 3D Collaborative Virtual Environments (CVE). This model merges the results from two research fields: distribution models for CVE and HCI design for computer-supported cooperative work. PAC-C3D proposes to describe each part of a shared virtual object through explicit interfaces to ensure a strong separation between the core functions of a virtual environment, its (visual) representations, and its collaborative features such as synchronization and consistency maintenance between remote users. PAC-C3D makes it possible to design a CVE with low dependency between the core functions, the distribution mode and the 3D graphics API used. It explicitly deals with the main distribution modes encountered in CVE. It makes it easy to use different 3D graphics API for different nodes involved in the same collaborative session, providing interoperability between these 3D graphics API. It also makes it possible to integrate other kinds of 3D representations such as physics engines into the CVE

Evaluation of a Reconfigurable Tangible Device for Collaborative Manipulation of Objects in Virtual Reality

International audienceIn this paper we introduce an evaluation of a Reconfigurable Tangible Device (RTD) for collaborative manipulation of objects in virtual environments. The considered RTD, called RTD-3, has a triangular shape that naturally provides three points of manipulation. The shape of the tangible triangle can be reconfigured at any time as its branches can be shrunk or stretched by users at will. Thanks to this simple shape the RTD-3 can be easily attached to any 3D virtual object and fully defines its virtual motion in 6~Degrees of Freedom. We have conducted an experiment to assess the potential of the RTD-3 and compare it with classical techniques used for collaborative virtual manipulation. Participants were asked to manipulate and assemble, in a collaborative manner, virtual parts. Our results suggest that the physical manipulation proposed by the tangible device is significantly preferred by participants in terms of immersion, realism of interaction and preparation to the real task. Although our approach is slightly slower than the other tested methods, it produces the fewest collisions