A radiation-hydrodynamics scheme valid from the transport to the diffusion limit

We present in this paper the numerical treatment of the coupling between hydrodynamics and radiative transfer. The fluid is modeled by classical conservation laws (mass, momentum and energy) and the radiation by the grey moment $M_1$ system. The scheme introduced is able to compute accurate numerical solution over a broad class of regimes from the transport to the diffusive limits. We propose an asymptotic preserving modification of the HLLE scheme in order to treat correctly the diffusion limit. Several numerical results are presented, which show that this approach is robust and have the correct behavior in both the diffusive and free-streaming limits. In the last numerical example we test this approach on a complex physical case by considering the collapse of a gas cloud leading to a proto-stellar structure which, among other features, exhibits very steep opacity gradients.Comment: 29 pages, submitted to Journal of Computational physic

Virtual Compton scattering off nuclei in the Δ\Delta-resonance region

Virtual Compton scattering in the $\Delta$-resonance region is considered in the case of a target nucleus. The discussion involves generalized polarizabilities and is developed for zero-spin nuclei, focusing on the new information coming from virtual Compton scattering in comparison with real Compton scattering.Comment: 8 pages, LaTeX, 3 figures available from the author

Mechanical Sensing of Living Systems — From Statics to Dynamics

Living systems are fascinating sensing machines that outmatch all artificial machines. Our aim is to put a focus on the dynamics of mechanosensing in cellular systems through concepts and experimental approaches that have been developed during the past decades. By recognizing that a cellular system is not simply the intricate assembly of active and passive macromolecular actors but that it can also manifest scale-invariant and/or highly nonlinear global dynamics, biophysicists have opened a new domain of investigation of living systems. In this chapter, we review methods and techniques that have been implemented to decipher the cascade of temporal events which enable a cell to sense a mechanical stimulus and to elaborate a response to adapt or to counteract this perturbation. We mainly describe intrusive (mechanical probes) and nonintrusive (optical devices) experimental methods that have proved to be efficient for real-time characterization of stationary and nonstationary cellular dynamics. Finally, we discuss whether thermal fluctuations, which are inherent to living systems, are a source of coordination (e.g., synchronization) or randomization of the global dynamics of a cell

Photon electroproduction off nuclei in the Δ\Delta-resonance region

The cross section for the $A(e,e'\gamma)A$ reaction is calculated, investigating the contribution from the nuclear target with respect to the radiative corrections from the electron. The reaction mechanism is studied for photon emission in the $\Delta$-resonance region, varying the scattering geometry and analyzing the most favourable kinematical conditions to extract information on the nuclear system.Comment: 10 pages, LaTeX, 6 figures available from the autho

On Local Approximations to the Nonlinear Evolution of Large-Scale Structure

We present a comparative analysis of several methods, known as local Lagrangian approximations, which are aimed to the description of the nonlinear evolution of large-scale structure. We have investigated various aspects of these approximations, such as the evolution of a homogeneous ellipsoid, collapse time as a function of initial conditions, and asymptotic behavior. As one of the common features of the local approximations, we found that the calculated collapse time decreases asymptotically with the inverse of the initial shear. Using these approximations, we have computed the cosmological mass function, finding reasonable agreement with N-body simulations and the Press-Schechter formula.Comment: revised version with color figures, minor changes, accepted for publication in the Astrophysical Journal, 30 pages, 13 figure

From a fossil-fuel to a biobased economy : the politics of industrial biotechnology

Industrial biotechnology involves the replacement of petrochemical processes and inputs with more energy-efficient and renewable biological ones. It is already being used in the production of biofuels and bioplastics and has been touted as a means by which modern economies can be shifted toward a more competitive, low-carbon growth model. This paper does two things. First, it outlines the policy framework established in the European Union and the narrative of a knowledge-based bioeconomy (KBBE) underpinning this. Second, it argues that the ‘win – win’ rhetoric contained within the KBBE narrative is misleading. Among the different groups commenting on the use of industrial biotechnology, the paper locates cleavages between farmers and agribusiness, between those convinced and those sceptical of environmental technofixes, and between procorporate and anticorporate NGOs. Taken together, they show the purported transition from a fossil-fuel to a bio-based economy to be a resolutely political one

Anisotropic elasticity in confocal studies of colloidal crystals

We consider the theory of fluctuations of a colloidal solid observed in a confocal slice. For a cubic crystal we study the evolution of the projected elastic properties as a function of the anisotropy of the crystal using numerical methods based on the fast Fourier transform. In certain situations of high symmetry we find exact analytic results for the projected fluctuations.Comment: 6 pages, 7 figure