106,520 research outputs found
Thermonuclear explosions of rapidly rotating white dwarfs - II. Detonations
Context: Superluminous type Ia supernovae (SNe Ia) may be explained by
super-Chandrasekhar-mass explosions of rapidly rotating white dwarfs (WDs). In
a preceding paper, we showed that the deflagration scenario applied to rapidly
rotating WDs generates explosions that cannot explain the majority of SNe Ia.
Aims: Rotation of the progenitor star allows super-Chandrasekhar-mass WDs to
form that have a shallower density stratification. We use simple estimates of
the production of intermediate and iron group elements in pure detonations of
rapidly rotating WDs to assess their viability in explaining rare SNe Ia.
Methods: We numerically construct WDs in hydrostatic equilibrium that rotate
according to a variety of rotation laws. The explosion products are estimated
by considering the density stratification and by evaluating the result of
hydrodynamics simulations. Results: We show that a significant amount of
intermediate mass elements is produced for theoretically motivated rotation
laws, even for prompt detonations of WDs. Conclusions: Rapidly rotating WDs
that detonate may provide an explanation of rare superluminous SNe Ia in terms
of both burning species and explosion kinematics.Comment: 7 pages, 5 figures, accepted for publication by A&
Context unification is in PSPACE
Contexts are terms with one `hole', i.e. a place in which we can substitute
an argument. In context unification we are given an equation over terms with
variables representing contexts and ask about the satisfiability of this
equation. Context unification is a natural subvariant of second-order
unification, which is undecidable, and a generalization of word equations,
which are decidable, at the same time. It is the unique problem between those
two whose decidability is uncertain (for already almost two decades). In this
paper we show that the context unification is in PSPACE. The result holds under
a (usual) assumption that the first-order signature is finite.
This result is obtained by an extension of the recompression technique,
recently developed by the author and used in particular to obtain a new PSPACE
algorithm for satisfiability of word equations, to context unification. The
recompression is based on performing simple compression rules (replacing pairs
of neighbouring function symbols), which are (conceptually) applied on the
solution of the context equation and modifying the equation in a way so that
such compression steps can be in fact performed directly on the equation,
without the knowledge of the actual solution.Comment: 27 pages, submitted, small notation changes and small improvements
over the previous tex
Data processing plan for orbiting solar observatory /OSO-B2/
Scheduling, analog-to-digital conversion, and quality control of data processing for Orbiting Solar Observatory /OSO-B2
Approximating parabolas as natural bounds of Heisenberg spectra: Reply on the comment of O. Waldmann
O. Waldmann has shown that some spin systems, which fulfill the condition of
a weakly homogeneous coupling matrix, have a spectrum whose minimal or maximal
energies are rather poorly approximated by a quadratic dependence on the total
spin quantum number. We comment on this observation and provide the new
argument that, under certain conditions, the approximating parabolas appear as
natural bounds of the spectrum generated by spin coherent states.Comment: 2 pages, accepted for Europhysics Letter
New technique for replica symmetry breaking with application to the SK-model at and near T=0
We describe a novel method which allows the treatment of high orders of
replica-symmetry-breaking (RSB) at low temperatures as well as at T=0 directly,
without a need for approximations or scaling assumptions. It yields the low
temperature order function q(a,T) in the full range and is
complete in the sense that all observables can be calculated from it. The
behavior of some observables and the finite RSB theory itself is analyzed as
one approaches continuous RSB. The validity and applicability of the
traditional continuous formulation is then scrutinized and a new continuous RSB
formulation is proposed
Thermonuclear explosions of rapidly rotating white dwarfs - I. Deflagrations
Context: Turbulent deflagrations of Chandrasekhar mass White Dwarfs are
commonly used to model Type Ia Supernova explosions. In this context, rapid
rotation of the progenitor star is plausible but has so far been neglected.
Aims: The aim of this work is to explore the influence of rapid rotation on the
deflagration scenario. Methods: We use three dimensional hydrodynamical
simulations to model turbulent deflagrations ignited within a variety of
rapidly rotating CO WDs obeying rotation laws suggested by accretion studies.
Results: We find that rotation has a significant impact on the explosion. The
flame develops a strong anisotropy with a preferred direction towards the
stellar poles, leaving great amounts of unburnt matter along the equatorial
plane. Conclusions: The large amount of unburnt matter is contrary to observed
spectral features of SNe Ia. Thus, rapid rotation of the progenitor star and
the deflagration scenario are incompatible in order to explain SNe Ia.Comment: 13 pages, 10 figures, accepted for publication by A&
Old Remedies in the Biotechnology Age: Moore v. Regents
The California Supreme Court, by excluding a potential remedy, has eliminated many concerns generated by a lower court decision resolving rights to the cell line derived from John Moore\u27s spleen. Yet, the Supreme Court gave little attention to remedies that remain. The authors argue that a constructive trust, a remedy of considerable vintage and great flexibility, could be applied to achieve a just result in such circumstances without affecting the biotechnology world at large
A two-dimensional representation of four-dimensional gravitational waves
The Einstein equation in D dimensions, if restricted to the class of
space-times possessing n = D - 2 commuting hypersurface-orthogonal Killing
vectors, can be equivalently written as metric-dilaton gravity in 2 dimensions
with n scalar fields. For n = 2, this results reduces to the known reduction of
certain 4-dimensional metrics which include gravitational waves. Here, we give
such a representation which leads to a new proof of the Birkhoff theorem for
plane-symmetric space--times, and which leads to an explanation, in which sense
two (spin zero-) scalar fields in 2 dimensions may incorporate the (spin two-)
gravitational waves in 4 dimensions. (This result should not be mixed up with
well--known analogous statements where, however, the 4-dimensional space-time
is supposed to be spherically symmetric, and then, of course, the equivalent
2-dimensional picture cannot mimic any gravitational waves.) Finally, remarks
on hidden symmetries in 2 dimensions are made.Comment: 12 pages, LaTeX, no figures, Int. J. Mod. Phys. D in prin
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