855 research outputs found
An MHD study of SN 1006 and determination of the ambient magnetic field direction
In this work we employ an MHD numerical code to reproduce the morphology
observed for SN 1006 in radio synchrotron and thermal X-ray emission. We
introduce a density discontinuity, in the form of a flat cloud parallel to the
Galactic Plane, in order to explain the NW filament observed in optical
wavelengths and in thermal X-rays. We compare our models with observations. We
also perform a test that contrasts the radio emitting bright limbs of the SNR
against the central region, finding additional support to our results. Our main
conclusion is that the most probable direction of the ambient magnetic field is
on average perpendicular to the Galactic Plane.Comment: 7 pages, 5 figures, accepted by MNRA
3D MHD simulation of polarized emission in SN 1006
We use three dimensional magnetohydrodynamic (MHD) simulations to model the
supernova remnant SN 1006. From our numerical results, we have carried out a
polarization study, obtaining synthetic maps of the polarized intensity, the
Stokes parameter , and the polar-referenced angle, which can be compared
with observational results. Synthetic maps were computed considering two
possible particle acceleration mechanisms: quasi-parallel and
quasi-perpendicular. The comparison of synthetic maps of the Stokes parameter
maps with observations proves to be a valuable tool to discern
unambiguously which mechanism is taking place in the remnant of SN 1006, giving
strong support to the quasi-parallel model.Comment: 6 pages, 4 figures, accepted by MNRA
Power consumption evaluation of circuit-switched versus packet-switched optical backbone networks
While telecommunication networks have historically been dominated by a circuit-switched paradigm, the last decades have seen a clear trend towards packet-switched networks. In this paper we evaluate how both paradigms perform in optical backbone networks from a power consumption point of view, and whether the general agreement of circuit switching being more power-efficient holds. We consider artificially generated topologies of various sizes, mesh degrees and not yet previously explored in this context transport linerates. We cross-validate our findings with a number of realistic topologies. Our results show that, as a generalization, packet switching can become preferable when the traffic demands are lower than half the transport linerate. We find that an increase in the network node count does not consistently increase the energy savings of circuit switching over packet switching, but is heavily influenced by the mesh degree and (to a minor extent) by the average link length
Diversity Of Short Gamma-Ray Burst Afterglows From Compact Binary Mergers Hosting Pulsars
Short gamma-ray bursts (sGRBs) are widely believed to result from the mergers
of compact binaries. This model predicts an afterglow that bears the
characteristic signatures of a constant, low density medium, including a smooth
prompt-afterglow transition, and a simple temporal evolution. However, these
expectations are in conflict with observations for a non-negligible fraction of
sGRB afterglows. In particular, the onset of the afterglow phase for some of
these events appears to be delayed and, in addition, a few of them exhibit
late- time rapid fading in their lightcurves. We show that these peculiar
observations can be explained independently of ongoing central engine activity
if some sGRB progenitors are compact binaries hosting at least one pulsar. The
Poynting flux emanating from the pulsar companion can excavate a bow-shock
cavity surround- ing the binary. If this cavity is larger than the shock
deceleration length scale in the undisturbed interstellar medium, then the
onset of the afterglow will be delayed. Should the deceleration occur entirely
within the swept-up thin shell, a rapid fade in the lightcurve will ensue. We
identify two types of pulsar that can achieve the conditions necessary for
altering the afterglow: low field, long lived pulsars, and high field pulsars.
We find that a sizable fraction (~20-50%) of low field pulsars are likely to
reside in neutron star binaries based on observations, while their high field
counterparts are not. Hydrodynamical calculations motivated by this model are
shown to be in good agreement with observations of sGRB afterglow lightcurves.Comment: Accepted to ApjL. Direct comparison to observed X-Ray afterglows now
included. 5 Figure
Localization of the UsProtein Kinase of Equine Herpesvirus Type 1 Is Affected by the Cytoplasmic Structures Formed by the Novel IR6 Protein
AbstractPrevious work revealed that the Us(unique short) segment of equine herpesvirus type-1 (EHV-1), like that of other alphaherpesviruses, encodes a serine/threonine protein kinase (PK). Experiments were carried out to identify the PK encoded by the EHV-1 EUS2 gene (ORF 69) and to ascertain its time course of synthesis and cellular localization. Western blot and immunoprecipitation analyses of EHV-1-infected cell extracts using a PK-specific polyclonal antibody generated against a bacterially expressed TrpE/PK fusion protein identified the UsPK as a 42- to 45-kDa phosphoprotein. The PK protein is first synthesized at 3 hr postinfection, is produced throughout the infection cycle, and is incorporated into EHV-1 virions. Interestingly, immunoprecipitation analyses revealed that the PK protein within the cytoplasm is associated with the 33-kDa IR6 novel protein of EHV-1, is expressed abundantly as an early protein, and is present in the large rod-like structures formed by the IR6 protein (ORF67 protein) within the cytoplasm of infected cells. Confocal microscopic examination of cells stained with fluorescein-labeled antibody clearly showed that the PK protein colocalized with the cytoplasmic IR6 rod-like structures and remained associated with these unique structures during infection. In contrast, in cells infected with the EHV-1 RacM strain in which the IR6 protein harbors four amino acid substitutions that prevent formation of the rod-like structures (Osterriederet al.,1996,Virology217, 442–451), the PK protein localized predominantly to the nucleus. The possible significance of the association of the IR6 and PK proteins in EHV-1 replication is discussed
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