Side-entrainment in a jet embedded in a sidewind

Numerical simulations of HH jets never show side-entrainment of environmental material into the jet beam. This is because the bow shock associated with the jet head pushes the surrounding environment into a dense shell, which is never in direct contact with the sides of the jet beam. We present 3D simulations in which a side-streaming motion (representing the motion of the outflow source through the surrounding medium) pushes the post-bow shock shell into direct contact with the jet beam. This is a possible mechanism for modelling well collimated "molecular jets" as an atomic/ionic flow which entrains molecules initially present only in the surrounding environment.Comment: 8 pages, 12 figures, 1 table, accepted for publication in Ap

Diffusive shock acceleration in extragalactic jets

We calculate the temporal evolution of distributions of relativistic electrons subject to synchrotron and adiabatic processes and Fermi-like acceleration in shocks. The shocks result from Kelvin-Helmholtz instabilities in the jet. Shock formation and particle acceleration are treated in a self-consistent way by means of a numerical hydrocode. We show that in our model the number of relativistic particles is conserved during the evolution, with no need of further injections of supra-thermal particles after the initial one. From our calculations, we derive predictions for values and trends of quantities like the spectral index and the cutoff frequency that can be compared with observations.Comment: 12 pages containing 7 postscript figures; uses A&A macros. Accepted for publication in Astronomy and Astrophysic

Time-Dependent MHD Shocks and Line Emission: The Case of the DG Tau Jet

The line emission from a growing number of Herbig-Haro jets can be observed and resolved at angular distances smaller than a few arcseconds from the central source. The interpretation of this emission is problematic, since the simplest model of a cooling jet cannot sustain it. It has been suggested that what one actually observes are shocked regions with a filling factor of $\sim 1$. In this framework, up to now, comparisons with observations have been based on stationary shock models. Here we introduce for the first time the self-consistent dynamics of such shocks and we show that considering their properties at different times, i.e. locations, we can reproduce observational data of the DG Tau microjet. In particular, we can interpret the spatial behavior of the [SII]6716/6731 and [NII]/[OI]6583/6300 line intensity ratios adopting a set of physical parameters that yield values of mass loss rates and magnetic fields consistent with previous estimates. We also obtain the values of the mean ionization fraction and electron density along the jet, compare these values with the ones derived from observations using the sulfur doublet to constrain the electron density (e.g. Bacciotti et al. 1995).Comment: 6 pages, 3 figure

Simulations of Nonthermal Electron Transport in Multidimensional Flows: Application to Radio Galaxies

We have developed an economical, effective numerical scheme for cosmic-ray transport suitable for treatment of electrons up to a few hundreds of GeV in multidimensional simulations of radio galaxies. The method follows the electron population in sufficient detail to allow computation of synthetic radio and X-ray observations of the simulated sources, including spectral properties (see the companion paper by Tregillis et al. 1999). The cosmic-ray particle simulations can follow the effects of shock acceleration, second-order Fermi acceleration as well as radiative and adiabatic energy losses. We have applied this scheme to 2-D and 3-D MHD simulations of jet-driven flows and have begun to explore links between dynamics and the properties of high energy electron populations in radio lobes. The key initial discovery is the great importance to the high energy particle population of the very unsteady and inhomogeneous flows, especially near the end of the jet. Because of this, in particular, our simulations show that a large fraction of the particle population flowing from the jet into the cocoon never passes through strong shocks. The shock strengths encountered are not simply predicted by 1-D models, and are quite varied. Consequently, the emergent electron spectra are highly heterogeneous. Rates of synchrotron aging in "hot-spots" seem similarly to be very uneven, enhancing complexity in the spectral properties of electrons as they emerge into the lobes and making more difficult the task of comparing dynamical and radiative ages.Comment: 7 pages, 1 figure; to appear in Life Cycles of Radio Galaxies, ed. J. Biretta et al., New Astronomy Review

Embodied energy and operational energy evaluation in tall buildings according to different typologies of façade

Abstract Although recent studies demonstrate the importance of including the Embodied Energy (EE) in building analysis, only the Operational Energy (OE) is currently taken into account in building energy demand calculation method. In particular, the EE plays an important role in tall buildings evaluation, because the energy demand increases with building height. Aim of this study was to assess the Embodied Energy in evaluation of different types of tall building facade systems performances along with the Operational Energy, pointing out the importance of taking into account both these aspects. Within the research activity here presented, 8 glazed envelope typologies, in 5 different climate zones, have been evaluated

Shading dynamically. Observation, feedback and design

The dynamic building envelope able to vary the performances in relation to the climatic stresses and to the user’s needs, represents one of the main technological trends of the last decades, aimed at implementing the energy efficiency of the buildings and the internal environmental comfort. In this scenario, a challenge that is still open is the creation of dynamic systems that are easy to use, manage and maintain with reduced manufacturing and management costs. The article intends to describe the research process that led to the design of an innovative external shielding system that can be orientated and moved automatically, at low cost and easily produced, thus allowing simple and economic management over time

The effect of a stellar magnetic variation on the jet velocity

Stellar jets are normally constituted by chains of knots with some periodicity in their spatial distribution, corresponding to a variability of order of several years in the ejection from the protostar/disk system. A widely accepted theory for the presence of knots is related to the generation of internal working surfaces due to variations in the jet ejection velocity. In this paper we study the effect of variations in the inner disk-wind radius on the jet ejection velocity. We show that a small variation in the inner disk-wind radius produce a variation in the jet velocity large enough to generate the observed knots. We also show that the variation in the inner radius may be related to a variation of the stellar magnetic field.Comment: 5 pages, 3 figures, accepted for publication in Ap