2,156 research outputs found
A precessing jet model for the PN K 3-35: simulated radio-continuum emission
The bipolar morphology of the planetary nebula (PN) K 3-35 observed in
radio-continuum images was modelled with 3D hydrodynamic simulations with the
adaptive grid code yguazu-a. We find that the observed morphology of this PN
can be reproduced considering a precessing jet evolving in a dense AGB
circumstellar medium, given by a mass loss rate
\dot{M}_{csm}=5x10^{-5}M_{\odot}/yr and a terminal velocity v_{w}=10 km/s.
Synthetic thermal radio-continuum maps were generated from numerical results
for several frequencies. Comparing the maps and the total fluxes obtained from
the simulations with the observational results, we find that a model of
precessing dense jets, where each jet injects material into the surrounding CSM
at a rate \dot{M}_j=2.8x10^{-4} {M_{\odot}/yr (equivalent to a density of
8x10^{4} {cm}^{-3}, a velocity of 1500 km/s, a precession period of 100 yr, and
a semi-aperture precession angle of 20 degrees agrees well with the
observations.Comment: 6 pages, 4 figures, accepted to MNRA
Asymmetric supernova remnants generated by Galactic, massive runaway stars
After the death of a runaway massive star, its supernova shock wave interacts
with the bow shocks produced by its defunct progenitor, and may lose energy,
momentum, and its spherical symmetry before expanding into the local
interstellar medium (ISM). We investigate whether the initial mass and space
velocity of these progenitors can be associated with asymmetric supernova
remnants. We run hydrodynamical models of supernovae exploding in the
pre-shaped medium of moving Galactic core-collapse progenitors. We find that
bow shocks that accumulate more than about 1.5 Mo generate asymmetric remnants.
The shock wave first collides with these bow shocks 160-750 yr after the
supernova, and the collision lasts until 830-4900 yr. The shock wave is then
located 1.35-5 pc from the center of the explosion, and it expands freely into
the ISM, whereas in the opposite direction it is channelled into the region of
undisturbed wind material. This applies to an initially 20 Mo progenitor moving
with velocity 20 km/s and to our initially 40 Mo progenitor. These remnants
generate mixing of ISM gas, stellar wind and supernova ejecta that is
particularly important upstream from the center of the explosion. Their
lightcurves are dominated by emission from optically-thin cooling and by X-ray
emission of the shocked ISM gas. We find that these remnants are likely to be
observed in the [OIII] lambda 5007 spectral line emission or in the soft
energy-band of X-rays. Finally, we discuss our results in the context of
observed Galactic supernova remnants such as 3C391 and the Cygnus Loop.Comment: 21 pages, 16 figure
Geometrical aspects and connections of the energy-temperature fluctuation relation
Recently, we have derived a generalization of the known canonical fluctuation
relation between heat capacity and
energy fluctuations, which can account for the existence of macrostates with
negative heat capacities . In this work, we presented a panoramic overview
of direct implications and connections of this fluctuation theorem with other
developments of statistical mechanics, such as the extension of canonical Monte
Carlo methods, the geometric formulations of fluctuation theory and the
relevance of a geometric extension of the Gibbs canonical ensemble that has
been recently proposed in the literature.Comment: Version accepted for publication in J. Phys. A: Math and The
Photo-ionization of planetary winds: case study HD209458b
Close-in hot Jupiters are exposed to a tremendous photon flux that ionizes
the neutral escaping material from the planet leaving an observable imprint
that makes them an interesting laboratory for testing theoretical models. In
this work we present 3D hydrodynamic simulations with radiation transfer
calculations of a close-in exoplanet in a blow-off state. We calculate the
Ly- absorption and compare it with observations of HD 209458b an
previous simplified model results.Our results show that the hydrodynamic
interaction together with a proper calculation of the photoionization proccess
are able to reproduce the main features of the observed Ly- absorption,
in particular at the blue-shifted wings of the line. We found that the ionizing
stellar flux produce an almost linear effect on the amount of absorption in the
wake. Varying the planetary mass loss rate and the radiation flux, we were able
to reproduce the absorption observed at .Comment: 9 pages, 6 figure
Waste-to-fuel opportunities for British quick service restaurants: A case study
The fast food supply chain is facing increasing operating costs due to volatile food and energy prices. Based on a case study of a major fast food logistics operator, this paper quantifies the potential for fuel generation from the waste generated by quick-service restaurants in Britain. Several fuel pathways and supply chains were mapped to understand the carbon intensity of the various waste-to-fuel opportunities, the number of heavy goods vehicles that might be powered and the key factors that could help companies make better informed decisions related to fuel generation from waste. The research suggested that depending on the scenarios considered, between 13.9 and 17.2 million GJ of energy could be obtained from fuels made from the waste arisings of British quick service restaurants and their distribution centres (DCs), representing between 4.4 and 5.8% of the national energy consumption from heavy goods vehicles (HGVs) and well-to-wheel (WTW) greenhouse gases (GHG) savings of between 652 and 898 thousand tonnes of CO2 equivalent annually. Used cooking oil and burger fat arising from British quick-service restaurants could generate enough energy to power up to 3891 HGVs with FAME diesel (B100), 1622 with HVO diesel (B100) or 1943 with biomethane annually. The paper and card generated by these same establishments could also power an additional 4623 biomethane vehicles, wood pallets could power an additional 73 bioethanol trucks and plastics could also power 341 vehicles running with synthetic diesel. The results showed that collections of separate waste fractions by logistics operators could make a relevant contribution towards the decarbonisation of the supply chain while reducing disposal fees and fuel costs. The carbon emissions resulting from this approach depend greatly on the footprint of the collection and transportation systems used to move waste from the restaurants to the processing plants and return the converted fuel back to the distribution centres where the vehicles are refuelled. Logistics firms are in a privileged position to manage these flows as they can use empty back-haul trips to collect and consolidate waste in distribution centres
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