Aging and Non Linear Glassy Dynamics in a Mean-Field Model

The mean-field dynamics of a particle in a random, but short range correlated potential, offers the opportunity of observing both aging and driven stationary regimes. Using a geometrical approach previously introduced by the author, we study here the relation between these two situations, in the pure relaxational limit, i.e. the zero temperature case. In the stationary regime, the velocity(v) -force(f) characteristics is a power law, while the characteristic times scale like powers of v, in agreement with an early proposal by Horner. The cross-over between the aging, linear-response regime and the non linear stationary regime is smooth, and we propose a parametrisation of the correlation functions valid in both cases, by means of an "effective time". We conclude that aging and non linear response are dual manifestations of a single out-of-equilibrium state, which might be a generic situation.Comment: 15 pages, 7 figures, submitted to European Journal of Physics

Geometrical Approach for the Mean-Field Dynamics of a Particle in a Short Range Correlated Random Potential

The zero temperature relaxational dynamics of a particle in a short range correlated random potential is addressed. We derive a set of "two-times" mean-field dynamical equations, accounting for a possible mean displacement of the particle when subject to an external force. We show first detailed results from the numerical integration of the above mentionned equations. We mainly pay attention to the exponentially decreasing spatial correlations case, for which simple analytical arguments provide valuable results about the hessian of the energy landscape, and we propose a geometrical description of the "mean-field aging". Our numerical results and further analytical arguments give access to the waiting time dependence of the main characteristic time scales.Comment: 22 pages, 7 figures, submitted to European Journal of Physics

Equity and Neutrality in Housing Taxation

Equity and neutrality are distinct concepts in housing taxation and weak and strong tenure neutrality should be distinguished. When a tax system is tested for those criteria, the taxes paid by landlords must be included, as they affect the rents renters pay. This paper defines appropriate tests, applies them to a stylised tax system and simulates tax changes designed to restore equity and/or neutrality. It shows how the homeowner's implicit income should be computed for taxes to be fundamentally tenure neutral or equitable or both. And it shows the key role played by the differential in producing housing services under owner-occupation and renting.Housing taxation; tenure choice; tax equity; tax neutrality

Assessing Sustainability at Farm Level using RISE Tool: Results from Armenia

Environmental Economics and Policy, Farm Management,

Virtual humans: thirty years of research, what next?

In this paper, we present research results and future challenges in creating realistic and believable Virtual Humans. To realize these modeling goals, real-time realistic representation is essential, but we also need interactive and perceptive Virtual Humans to populate the Virtual Worlds. Three levels of modeling should be considered to create these believable Virtual Humans: 1) realistic appearance modeling, 2) realistic, smooth and flexible motion modeling, and 3) realistic high-level behaviors modeling. At first, the issues of creating virtual humans with better skeleton and realistic deformable bodies are illustrated. To give a level of believable behavior, challenges are laid on generating on the fly flexible motion and complex behaviours of Virtual Humans inside their environments using a realistic perception of the environment. Interactivity and group behaviours are also important parameters to create believable Virtual Humans which have challenges in creating believable relationship between real and virtual humans based on emotion and personality, and simulating realistic and believable behaviors of groups and crowds. Finally, issues in generating realistic virtual clothed and haired people are presente

Trotter Derivation of Algorithms for Brownian and Dissipative Particle Dynamics

This paper focuses on the temporal discretization of the Langevin dynamics, and on different resulting numerical integration schemes. Using a method based on the exponentiation of time dependent operators, we carefully derive a numerical scheme for the Langevin dynamics, that we found equivalent to the proposal of Ermak, and not simply to the stochastic version of the velocity-Verlet algorithm. However, we checked on numerical simulations that both algorithms give similar results, and share the same ``weak order two'' accuracy. We then apply the same strategy to derive and test two numerical schemes for the dissipative particle dynamics (DPD). The first one of them was found to compare well, in terms of speed and accuracy, with the best currently available algorithms.Comment: to be published in J.Chem.Phy

Piercing the Glare: Direct Imaging Search for Planets in the Sirius System

Astrometric monitoring of the Sirius binary system over the past century has yielded several predictions for an unseen third system component, the most recent one suggesting a \leq50 MJup object in a ~6.3-year orbit around Sirius A. Here we present two epochs of high-contrast imaging observations performed with Subaru IRCS and AO188 in the 4.05 \mum narrow-band Br alpha filter. These data surpass previous observations by an order of magnitude in detectable companion mass, allowing us to probe the relevant separation range down to the planetary mass regime (6-12 M_Jup at 1", 2-4 M_Jup at 2", and 1.6 M_Jup beyond 4"). We complement these data with one epoch of M-band observations from MMT/AO Clio, which reach comparable performance. No dataset reveals any companion candidates above the 5-sigma level, allowing us to refute the existence of Sirius C as suggested by the previous astrometric analysis. Furthermore, our Br alpha photometry of Sirius B confirms the lack of an infrared excess beyond the white dwarf's blackbody spectrum.Comment: 6 pages, 5 figures, accepted for publication in ApJ Letter