4,973 research outputs found
New Two-Dimensional Models of Supernova Explosions by the Neutrino-Heating Mechanism: Evidence for Different Instability Regimes in Collapsing Stellar Cores
The neutrino-driven explosion mechanism for core-collapse supernovae in its
modern flavor relies on the additional support of hydrodynamical instabilities
in achieving shock revival. Two possible candidates, convection and the
so-called standing accretion shock instability (SASI), have been proposed for
this role. In this paper, we discuss new successful simulations of supernova
explosions that shed light on the relative importance of these two
instabilities. While convection has so far been observed to grow first in
self-consistent hydrodynamical models with multi-group neutrino transport, we
here present the first such simulation in which the SASI grows faster while the
development of convection is initially inhibited. We illustrate the features of
this SASI-dominated regime using an explosion model of a 27 solar mass
progenitor, which is contrasted with a convectively-dominated model of an 8.1
solar mass progenitor with subsolar metallicity, whose early post-bounce
behavior is more in line with previous 11.2 and 15 solar mass explosion models.
We analyze the conditions discriminating between the two different regimes,
showing that a high mass-accretion rate and a short advection time-scale are
conducive for strong SASI activity. We also briefly discuss some important
factors for capturing the SASI-driven regime, such as general relativity, the
progenitor structure, a nuclear equation of state leading to a compact
proto-neutron star, and the neutrino treatment. Finally, we evaluate possible
implications of our findings for 2D and 3D supernova simulations. Our results
show that a better understanding of the SASI and convection in the non-linear
regime is required.Comment: 12 pages, 13 figures; revised version accepted for publication in Ap
Predictions of the pseudo-complex theory of Gravity for EHT observations- II. Theory and predictions
We present a resum\'e on the modified theory of gravity, called
pseudo-complex General Relativity (pc-GR). It is the second in a series of
papers, where the first one (Boller et al. 2019, referred to as paper I)
discussed the observational consequences of pc-GR. In this paper, we
concentrate on the underlying theory. PC-GR involves an algebraic extension of
the standard theory of GR and it depends on two phenomenological parameters. An
element included in pc-GR that is not present in standard GR is the
energy-momentum tensor corresponding to an anisotropic ideal fluid, which we
call dark energy. The two parameters are related to the coupling of mass to the
dark energy and its fall-off as a function of r. The consequences and
predictions of this theory will be discussed in the context of the
observational results of the Even Horizon Telescope, expected soon. Our main
result is that due to the accumulation of dark energy near a large mass, the
modified theory predicts a dark ring followed by a bright ring in the emission
profile of the accretion disc. We also discuss the light ring in the equatorial
plane.Comment: 2 figure
Light curve analysis of ordinary type IIP supernovae based on neutrino-driven explosion simulations in three dimensions
Type II-plateau supernovae (SNe IIP) are the most numerous subclass of
core-collapse SNe originating from massive stars. In the framework of the
neutrino-driven explosion mechanism, we study the SN outburst properties for a
red supergiant progenitor model and compare the corresponding light curves with
observations of the ordinary Type IIP SN 1999em. Three-dimensional (3D)
simulations of (parametrically triggered) neutrino-driven explosions are
performed with the (explicit, finite-volume, Eulerian, multifluid
hydrodynamics) code PROMETHEUS, using a presupernova model of a 15 Msun star as
initial data. At approaching homologous expansion, the hydrodynamical and
composition variables of the 3D models are mapped to a spherically symmetric
configuration, and the simulations are continued with the (implicit, Lagrangian
radiation-hydrodynamics) code CRAB to follow the blast-wave evolution during
the SN outburst. Our 3D neutrino-driven explosion model with an explosion
energy of about 0.5x10^51 erg produces Ni-56 in rough agreement with the amount
deduced from fitting the radioactively powered light-curve tail of SN 1999em.
The considered presupernova model, 3D explosion simulations, and light-curve
calculations can explain the basic observational features of SN 1999em, except
for those connected to the presupernova structure of the outer stellar layers.
Our 3D simulations show that the distribution of Ni-rich matter in velocity
space is asymmetric with a strong dipole component that is consistent with the
observations of SN 1999em. The monotonic luminosity decline from the plateau to
the radioactive tail in ordinary SNe IIP is a manifestation of the intense
turbulent mixing at the He/H composition interface.Comment: 16 pages, 13 figures, 2 tables; added figure, discussions, and
references; accepted for publication in Ap
Use of a single bipolar electrode in the posterior arytenoid muscles for bilateral monitoring of the recurrent laryngeal nerves in thyroid surgery
The aims were to assess the technical feasibility of using a single electrode in the posterior arytenoid muscles (PAM) for intraoperative monitoring of the recurrent laryngeal nerve (RLN) in thyroid surgery, to validate the new method against the insertion of electrodes placed in the vocal cord muscle, and to report the results of the clinical application of the new concept. A total of 52 patients were enrolled. The handling and safety of RLN monitoring was tested by simultaneous registration of the EMG response from vocal fold electrodes and PAM electrodes. Acoustically and electromyographically we found nearly the same values for the arytenoid muscles as for the vocal folds, although the signals taken from the vocal folds were slightly stronger. PAM recording using a single bipolar electrode is technically feasible and as reliable compared to the standard vocal cord monitorin
Elektronen-Energieverlust-Spektroskopie an A 15-Supraleitern
Student newspaper includes campus, local and national news stories and photographs. For additional information about this collection see http://digitalcommons.wou.edu/.https://digitalcommons.wou.edu/ocelamron_volume25/1029/thumbnail.jp
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