Quantum Monte Carlo Simulation of the two-dimensional ionic Hubbard model

The Quantum Monte Carlo simulations of the ionic Hubbard model on a two-dimensional square lattice at half filling were performed. The method based on the direct-space, proposed by Suzuki and al., Hirsch and al., was used. Cycles of increasing and decreasing values of the Coulomb interaction $U$ were performed for fixed temperature ($kT=0.01$). Results indicate that, at low temperature, the two insulator phases are separated by a metallic phase for weak to intermediate values of the staggered potential $\Delta$. For large Coulomb repulsion the system is in a Mott insulator with an antiferromagnetism order. On increasing and decreasing the Coulomb interaction $U$ the metal-Mott insulator transition shows an hysteresis phenomenon while the metal-band insulator transition is continue. For large $\Delta$ it seems that the metallic region shrinks to a single metallic point. However, the band insulator to the Mott insulator transition is not direct for the studied model. A phase diagram is drawn for the temperature $kT=0.01$. For $\Delta =0.5$ cycles of increasing and decreasing temperature were programmed for different values of the Coulomb interaction $U$ . A behaviour change appears for $U\simeq 1.75$. This suggests that a crossover line divides the metallic region of the phase diagram

Simulation Monte-Carlo du Modèle de Hubbard à deux dimensions

14 pagesThe Quantum Monte-Carlo simulations of the two-dimensional Hubbard model are presented for the half filling. The method based on the direct-space proposed by Suzuki and al., and Hirsch and al. was used. The states generated by this method are basis states in occupation number representation built with Wannier states localised on each site of the square array. The configurations of fermions can be observed on the real 2D array. An antiferromagnetic factor is defined and calculated for each temperature. The curves of energy, specific heat, conducivity and antiferromagnetic factor are presented for different values of the repulsive coulombian on site interaction U. There is a metal-insulator transition at low temperature for small values of U. This transition corresponds with a paramagnetic-ferromagnetic first order transition. Indeed, for these interaction values, the energy curves show a gap which is a characteristic of a first order transition. An hysteresis phenomenon appears on the conductivity curves. There is a behaviour change for U/t=3.5. For the values U>3.5 there is ferromagnetic-paramagnetic change without observable effect on the energy and the specific heat. The metal-insulator transition does not exist any more, the conductivity stays very small. Isotherms of the physical quantities versus U/t show a transition which seems to be the metal-insulator Mott transition. These results allow to draw a phase diagram with two first order transition lines

Game Jam 4 Investigating Design Issues with (partly) autonomous systems

International audienceAutonomous behavior like collecting resources is a key element in a variety of games. Managing autonomous behavior in games does not seem to pose problems when playing a game. The area of safety-critical systems has a variety of autonomous behaviors that have to be managed in their user interfaces. Carrying on with previous work about design and engineering critical interactive systems using contributions from gaming research and practice [7][8] this proposal aims to investigate the ability to use a Game Jam as a research method in the area of safety-critical systems, especially on new design issues encountered with (partly) autonomous systems

Quantum Monte Carlo simulation of two-dimensional Emery model

The Quantum Monte Carlo simulation of the two-dimensional Emery model of the CuO2 plane of hight Tc superconductors were performed. The method based on the direct-space proposed by Suzuki and Hirsch was used. Contrary to the method based on the Hubbard-Stratonovich transformation, the states generated by this method are basis states in occupation number representation, i. e. configurations of fermions can be observed on real two-dimensional array.Energy and specific heat were computed for different dopings. Specific heat curves show peaks at low temperature which could be assigned to electronic transitions. Quantity similar to current-current correlation function were computed. The static electric conductivity curves obtained by this way show metal-insulator transitions and two different metallic behaviours. On the direct-space states generated at low temperature and zero doping, the fermions form antiferromagnetic loops while they form antiferromagnetic chains for other dopings. The loops seem to appear when the conductivity becomes zero while yhe conductivity increases with the numbers of chains but superconductivity is not unambiguously evident

Designing and Assessing Interactive Systems Using Task Models (2015)

International audienceThis two-part course takes a practical approach to introduce the principles, methods and tools in task modelling. Part 1: A non-technical introduction demonstrates that task models support successful design of interactive systems. Part 2: A more technical interactive hands-on exercise of how to "do it right", such as: How to go from task analysis to task models? How to assess (through analysis and simulation) that a task model is correct? How to identify complexity of user tasks

Fine Grain Modeling of Task Deviations for Assessing Qualitatively the Impact of Both System Failures and Human Error on Operator Performance

International audienceOperators of critical interactive systems are trained and qualified before being allowed to operate critical systems in “real” contexts. However, during operation, things might happen differently from during training sessions as system failures may occur and operators may make errors when interacting with the system. Both events may also be cross-related as a misunderstanding of a system failure can lead to an erroneous subsequent operation.The proposed approach focuses on assessing the impact that potential failures and/or human errors may have on human performance. This analysis targets the design and development phases of the system, when user tasks are analyzed in order to build the right system (i.e. corresponding to the users’ needs and activities they have to perform on the system). We use a task modeling notation for describing precisely operators’ activities as well as information, knowledge and objects required for performing these activities. These task models are then augmented into several variants through integration of potential system failure patterns (with associated recovery tasks) and human error patterns. The produced deviated task models are used to assess the impact of the task deviation on the operators’ performance

Enhanced Task Modelling for Systematic Identification and Explicit Representation of Human Errors

International audienceTask models produced from task analysis, are a very important element of UCD approaches as they provide support for describing users goals and users activities, allowing human factors specialists to ensure and assess the effectiveness of interactive applications. As user errors are not part of a user goal they are usually omitted from tasks descriptions. However, in the field of Human Reliability Assessment, task descriptions (including task models) are central artefacts for the analysis of human errors. Several methods (such as HET, CREAM and HERT) require task models in order to systematically analyze all the potential errors and deviations that may occur. However, during this systematic analysis, potential human errors are gathered and recorded separately and not connected to the task models. Such non integration brings issues such as completeness (i.e. ensuring that all the potential human errors have been identified) or combined errors identification (i.e. identifying deviations resulting from a combination of errors). We argue that representing human errors explicitly and systematically within task models contributes to the design and evaluation of error-tolerant interactive system. However, as demonstrated in the paper, existing task modeling notations, even those used in the methods mentioned above, do not have a sufficient expressive power to allow systematic and precise description of potential human errors. Based on the analysis of existing human error classifications, we propose several extensions to existing task modelling techniques to represent explicitly all the types of human error and to support their systematic task-based identification. These extensions are integrated within the tool-supported notation called HAMSTERS and are illustrated on a case study from the avionics domain

A multi-formalism approach for model-based dynamic distribution of user interfaces of critical interactive systems.

International audienceEvolution in the context of use requires evolutions in the user interfaces even when they are currently used by operators. User Centered Development promotes reactive answers to this kind of evolutions either by software evolutions through iterative development approaches or at runtime by providing additional information to the operators such as contextual help for instance. This paper proposes a model-based approach to support proactive management of context of use evolutions. By proactive management we mean mechanisms in place to plan and implement evolutions and adaptations of the entire user interface (including behaviour) in a generic way. The approach proposed handles both concentration and distribution of user interfaces requiring both fusion of information into a single UI or fission of information into several ones. This generic model-based approach is exemplified on a safety critical system from space domain. It presents how the new user interfaces can be generated at runtime to provide a new user interface gathering in a single place all the information required to perform the task. These user interfaces have to be generated at runtime as new procedures (i.e. sequences of operations to be executed in a semi-autonomous way) can be defined by operators at any time in order to react to adverse events and to keep the space system in operation. Such contextual, activity-related user interfaces complement the original user interfaces designed for operating the command and control system. The resulting user interface thus corresponds to a distribution of user interfaces in a focus+context way improving usability by increasing both efficiency and effectiveness

HAMSTERS : un environnement d’édition et de simulation de modèles de tâches

National audienceCet article décrit une démonstration concernant l’outil logiciel HAMSTERS (Human-centered Assessment and Modeling to Support Task Engineering for Resilient Systems). HAMSTERS est un outil logiciel de modélisation permettant d’éditer, de simuler et d’analyser des modèles de tâches basés sur la notation éponyme. HAMSTERS a été conçu et développé pour les besoins de projets de recherche industriels principalement dans les domaines de l’aéronautique et de l’espace