Diffusive approximation of a time-fractional Burger's equation in nonlinear acoustics

A fractional time derivative is introduced into the Burger's equation to model losses of nonlinear waves. This term amounts to a time convolution product, which greatly penalizes the numerical modeling. A diffusive representation of the fractional derivative is adopted here, replacing this nonlocal operator by a continuum of memory variables that satisfy local-in-time ordinary differential equations. Then a quadrature formula yields a system of local partial differential equations, well-suited to numerical integration. The determination of the quadrature coefficients is crucial to ensure both the well-posedness of the system and the computational efficiency of the diffusive approximation. For this purpose, optimization with constraint is shown to be a very efficient strategy. Strang splitting is used to solve successively the hyperbolic part by a shock-capturing scheme, and the diffusive part exactly. Numerical experiments are proposed to assess the efficiency of the numerical modeling, and to illustrate the effect of the fractional attenuation on the wave propagation.Comment: submitted to Siam SIA

Psychological Traits and Trading Strategies

This paper analyzes experimentally if psychological traits and cognitive biases affect trading behaviour and performance. Based on the answers of 67 subjects to a psychological questionnaire we measured their degree of overconfidence, impulsiveness and self-monitoring, and their availability, representativeness and confirmation biases. The 67 subjects also participated in an experimental financial market, in the spirit of Plott and Sunder (1988). We find that impulsive subjects tend to place more orders but do not incur larger losses. We also find that overconfident subjects and subjects prone to the confirmation and representativeness biases have a greater tendency to place unprofitable orders. This negative impact of cognitive biases on trading performance is sronger when subjects have acquired some experience of the game. This suggests that biased subjects engage in improper learning.

Numerical modeling of a time-fractional Burgers equation

A fractional time derivative is introduced into Burgers equation to model losses of nonlinear waves arising in acoustics. A diffusive representation of the fractional derivative replaces the non-local operator by a continuum of memory variables that satisfy local ordinary differential equations. A quadrature formula yields a system of local partial differential equations. The quadrature coefficients are computed by optimization with a positivity constraint. One resolves the hyperbolic part by a shock-capturing scheme, and the diffusive part exactly. Extensive details can be found in [3]

Description languages for multimodal interaction: a set ofguidelines and its illustration with SMUIML

This article introduces the problem of modeling multimodal interaction, in the form of markup languages. After an analysis of the current state of the art in multimodal interaction description languages, nine guidelines for languages dedicated at multimodal interaction description are introduced, as well as four different roles that such language should target: communication, configuration, teaching and modeling. The article further presents the SMUIML language, our proposed solution to improve the time synchronicity aspect while still fulfilling other guidelines. SMUIML is finally mapped to these guidelines as a way to evaluate their spectrum and to sketch future work

Une étude internationale sur la contingence de l'efficacité perçue des politiques de rémunération

On peut concevoir l'éclatement des pratiques de GRH comme étant la conséquence d'un alignement des choix opérés sur les autres variables de gestion en fonction des contingences internes. A partir de données collectées auprès de 602 grandes entreprises de trois pays (Angleterre, France,Canada) la recherche présentée ici met en évidence que l'existence d'un alignement des politiques de rémunération avec les autres politiques de GRH (contingence horizontale) donne une plus grande perception d'efficacité aux DRH que les alignements avec les autres variables de gestion (contingence verticale et transversale). Cependant, l'éclatement des pratiques ne nous est pas apparu total. Notre recherche empirique montre aussi qu'il existe des pratiques qui, quel que soit le contexte organisationnel, ont un impact positif sur la perception d'efficacité. C'est le cas, en particulier des politiques orientées vers la performance individuelle et la transparence des systèmes de rémunération.We might attribute the expanding scope of HRM to the alignment of choices made on other management variables relative to internal contingencies. The data were collected from 602 large organizations in three countries (Great Britain, France, Canada). The study shows that the relationship between compensation policies and other HRM practices (horizontal contingencies) leads to a higher perception of efficiency of the HRM director than the alignment with other management variables (vertical and transversal contingencies). However, the expanding scope of HRM practices did not appear complete. Our empirical results also show that such practices oriented toward individual performance and the openness of the compensation system, regardless of the organizational context, have a positive impact on perceptions of efficienc

First results from SAM-FP: Fabry-Perot observations with ground-layer adaptive optics - the structure and kinematics of the core of 30 Doradus

The aim of this paper is to present the first data set obtained with SOAR Adaptive Module-Fabry-Parot (SAM-FP), a Fabry-Perot instrument mounted inside the SOAR telescope Adaptive-Optics Module. This is the only existing imaging Fabry-Perot interferometer using laser-assisted ground-layer adaptive optics. SAM-FP was used to observe the ionized gas, traced by Halpha, in the centre of the 30 Doradus starburst (the Tarantula Nebula) in the Large Magellanic Cloud, with high spatial (~0.6" or 0.15 pc) and spectral (R=11200) resolution. Radial velocity, velocity dispersion and monochromatic maps were derived. The region displays a mix of narrow, sigma ~ 20 km/s profiles and multiple broader profiles with sigma ~ 70-80 km/s, indicating the complex nature of the nebula kinematics. A comparison with previously obtained VLT/FLAMES spectroscopy demonstrates that the data agree well in the regions of overlap, but the Fabry-Perot data are superior in spatial coverage. A preliminary analysis of the observations finds a new expanding bubble south of R136, with a projected radius of r=5.6 pc and an expansion velocity of 29 +/- 4 km/s. In addition, the first-time detailed kinematic maps derived here for several complexes and filaments of 30 Doradus allow identification of kinematically independent structures. These data exemplify the power of the combination of a high-order Fabry-Perot with a wide-field imager (3' x 3' GLAO-corrected field of view) for high-resolution spatial and spectral studies. In particular, SAM-FP data cubes are highly advantageous over multifibre or long-slit data sets for nebula structure studies and to search for small-scale bubbles, given their greatly improved spatial coverage. For reference, this paper also presents two appendices with detailed descriptions of the usage of Fabry-Perot devices, including formulae and explanations for understanding Fabry-Perot observations.Comment: 22 pages, 9 figures, 1 tabl