Driven waves in a two-fluid plasma

We study the physics of wave propagation in a weakly ionised plasma, as it applies to the formation of multifluid, MHD shock waves. We model the plasma as separate charged and neutral fluids which are coupled by ion-neutral friction. At times much less than the ion-neutral drag time, the fluids are decoupled and so evolve independently. At later times, the evolution is determined by the large inertial mismatch between the charged and neutral particles. The neutral flow continues to evolve independently; the charged flow is driven by and slaved to the neutral flow by friction. We calculate this driven flow analytically by considering the special but realistic case where the charged fluid obeys linearized equations of motion. We carry out an extensive analysis of linear, driven, MHD waves. The physics of driven MHD waves is embodied in certain Green functions which describe wave propagation on short time scales, ambipolar diffusion on long time scales, and transitional behavior at intermediate times. By way of illustration, we give an approximate solution for the formation of a multifluid shock during the collision of two identical interstellar clouds. The collision produces forward- and reverse J shocks in the neutral fluid and a transient in the charged fluid. The latter rapidly evolves into a pair of magnetic precursors on the J shocks, wherein the ions undergo force free motion and the magnetic field grows monotonically with time. The flow appears to be self similar at the time when linear analysis ceases to be valid.Comment: 18 pages including 24 figures, accepted by MNRA

The development of a resource-efficient photovoltaic system

This paper presents the measures taken in the demonstration of the photovoltaic case study developed within the European project ‘Towards zero waste in industrial networks’ (Zerowin), integrating the D4R (Design for recycling, repair, refurbishment and reuse) criteria at both system and industrial network level. The demonstration is divided into three phases. The first phase concerns the development of a D4R photovoltaic concept, the second phase focused on the development of a specific component of photovoltaic systems and the third phase was the demonstration of the D4R design in two complete photovoltaic systems (grid-connected and stand-alone). This paper includes a description of the installed photovoltaic systems, including a brief summary at component level of the lithium ion battery system and the D4R power conditioning system developed for the pilot installations. Additionally, industrial symbioses within the network associated with the photovoltaic systems and the production model for the network are described

Quantitative optical and near-infrared spectroscopy of molecular hydrogen towards HH91A

Integral-field spectroscopy of molecular hydrogen in the optical wavelength region and complementary long-slit near-infrared spectroscopy are presented towards HH91A.The detection of some 200 H_2 lines arising from ro-vibrational levels up to v'=8 ranging between 7700A and 2.3 microns is reported. The emission arises from thermally excited gas where the bulk of the material is at 2750 K and where 1% is at 6000 K. The total column density of shocked gas is N(H_2) = 10^{18} cm^{-2}. Non-thermal excitation scenarios such as UV-fluorescence do not contribute to the excitation of H_2 towards HH91A. The emission is explained in terms of a slow non-dissociative J-shock which propagates into a low-density medium which has been swept-up by previous episodes of outflows which have occurred in the evolved HH90/91 complex.Comment: A&A accepte

Extended Far-Infrared CO Emission in the Orion OMC-1 Core

We report on sensitive far-infrared observations of $^{12}$CO pure rotational transitions in the OMC-1 core of Orion. The lines were observed with the Long Wavelength Spectrometer (LWS) in the grating mode on board the Infrared Space Observatory (ISO), covering the 43-197 $\mu$m wavelength range. The transitions from $J_{up}=14$ up to $J_{up}=19$ have been identified across the whole OMC-1 core and lines up to $J_{up}= 43$ have been detected towards the central region, KL/IRc2. In addition, we have taken high-quality spectra in the Fabry-Perot mode of some of the CO lines. In KL/IRc2 the lines are satisfactorily accounted for by a three-temperature model describing the plateau and ridge emission. The fluxes detected in the high-$J$ transitions ($J_{up} > 34$) reveal the presence of a very hot and dense gas component ($T=1500-2500$ K; $\rm N(CO)$=2\times 10^{17}\cmmd$), probably originating from some of the embedded sources previously observed in the$\rm H_2$near-infrared lines. At all other positions in the OMC-1 core, we estimate kinetic temperatures$\geq 80$ K and as high as 150 K at some positions around IRc2, from a simple Large-Velocity Gradient model.Comment: 10 pages, 3 figure

EFFEX : a tool to model the consequences of dust explosions

International audienceSome accidents, such as the explosion of the silo in Blaye in August 1997, remind us that explosions of combustible dust can have serious consequences, not only for the industrial installations concerned but also for the environment. The necessity of being able to estimate the effects of an explosion of this type became apparent at the beginning of the 1990s. Owing to the complexity of this subject which involves the mechanical resistance of structures, flame propagation and fluid mechanics, etc., a simulation tool clearly had to be developed. It was in these circumstances that EFFEX was developed. EFFEX is not a software based on the discretization of space but it solves differential equations, each variable of which is considered to be a time function. This is therefore an "integral" type of software code. It is made up of a set of eight modules covering the characterisation of the explosion conditions, the estimation of the mechanical behaviour of the containment and the evaluation of the consequences. Comparison of the results for each of the main modules shows satisfactory consistency with available experimental results. Trials using EFFEX to simulate past accidents, including the transmission and reinforcement of the explosion between subsequent volumes, in order to verify the satisfactory linking of the various modules gave results that were similar to the actual consequences. Several tens of calculation were made so far on silo type of equipments and a synthesis is proposed in addition to a general description of the software

J.-P. Boutinet, N. Denoyel, G. Pineau, & J.-Y. Robin. (dir.). Penser l’accompagnement adulte

Publié sous la direction de J-P Boutinet, N. Denoyel, G. Pineau et J.-Y. Robin, Penser l’accompagnement adulte correspond à la suite (et non aux actes) du colloque international qui s’est tenu en mai 2003 sur le thème de « l’accompagnement et ses paradoxes ». Depuis, l’actualité autour de ce sujet n’a pas faibli et les auteurs ont souhaité faire le point sur les pratiques d'accompagnement et les façons dont elles sont théorisées dans le but de fournir des éléments de réponse destinés à mieux ..