Superconductivity in the Two-Band Hubbard Model in Infinite Dimensions

We study a two-band Hubbard model in the limit of infinite dimensions, using a combination of analytical methods and Monte-Carlo techniques. The normal state is found to display various metal to insulators transitions as a function of doping and interaction strength. We derive self-consistent equations for the local Green's functions in the presence of superconducting long-range order, and extend previous algorithms to this case. We present direct numerical evidence that in a specific range of parameter space, the normal state is unstable against a superconducting state characterized by a strongly frequency dependent order-parameter.Comment: 12 pages (14 figures not included, available upon request), Latex, LPTENS Preprint 93/1

On the appearance of internal wave attractors due to an initial or parametrically excited disturbance

In this paper we solve two initial value problems for two-dimensional internal gravity waves. The waves are contained in a uniformly stratified, square-shaped domain whose sidewalls are tilted with respect to the direction of gravity. We consider several disturbances of the initial stream function field and solve both for its free evolution and for its evolution under parametric excitation. We do this by developing a structure-preserving numerical method for internal gravity waves in a two-dimensional stratified fluid domain. We recall the linearized, inviscid Euler–Boussinesq model, identify its Hamiltonian structure, and derive a staggered finite difference scheme that preserves this structure. For the discretized model, the initial condition can be projected onto normal modes whose dynamics is described by independent harmonic oscillators. This fact is used to explain the persistence of various classes of wave attractors in a freely evolving (i.e. unforced) flow. Under parametric forcing, the discrete dynamics can likewise be decoupled into Mathieu equations. The most unstable resonant modes dominate the solution, forming wave attractors

Building consensus in strategic decision-making : system dynamics as a group support system

Contains fulltext : 28724.pdf (publisher's version ) (Open Access)System dynamics was originally founded as a method for modeling and simulating the behavior of industrial systems. In recent years it is increasingly employed as a Group Support System for strategic decision-making groups. The model is constructed in direct interaction with a management team, and the procedure is generally referred to as group model-building. The model can be conceptual (qualitative) or a full-blown (quantitative) computer simulation model. In this article, a case is described in which a qualitative system dynamics model was built to support strategic decision making in a Dutch government agency. Since people from different departments held strongly opposite viewpoints on the strategy, the agency had discussed its strategic problem for more than a year, but was obviously not able to reach consensus. The application of group model-building was successful in integrating opposite points of view, as well as in fostering consensus and creating commitment. The purpose of the article is twofold: first, to illustrate the process of group model-building with system dynamics; second, to evaluate why it was successful. Evaluation results reveal the importance of both systemic thinking through model-building and the role of the facilitator in catalyzing the strategic decision-making process

Staying Focused: Highlighting-on-Demand as Situational Awareness Support for Groups in Multidisplay Environments

User interfaces and visualisations are part of group problem solving. Technology is already a part of daily decision-making in multidisplay environments, both as communication tools and information devices. As these devices, such as large displays and visualisation tools become more accessible, there is an increasing opportunity to develop applications that enhance group decision-making abilities, rather than restrict them. This chapter presents the results of the empirical user study on the effect of the Highlighting-on-Demand concept on situational awareness and satisfaction with the group decision-making process in a real multidisplay environment. Highlighting-on-Demand interface enables a team member who is currently controlling the shared large display to draw attention of the other team members by highlighting certain visualisation. Displaying all alternatives on a shared large display fosters information sharing and the Highlighting-on-Demand interface enables group members to draw attention to certain visualisation, while keeping the other alternatives still in view. The results suggest that when group members use the Highlightingon-Demand interface during the discussion, the satisfaction with the final group decision increases. Participants expressed willingness to use the Highlighting awareness support for visualising real data (e.g., biomedical, omics experiments) and manipulating how the data is visualised to discuss the experiment results with other team members in real project discussions