6,178 research outputs found
Small deviations for fractional stable processes
Let R be a symmetric a-stable Riemann-Liouville process with Hurst parameter
H > 0. Consider ||.|| a translation invariant, b-self-similar, and
p-pseudo-additive functional semi-norm. We show that if H > (b + 1/p) and c =
(H - b - 1/p), then x log P [ log ||R|| - k 0,
with k finite in the Gaussian case a = 2. If a < 2, we prove that k is finite
when R is continuous and H > (b + 1/p + 1/a). We also show that under the above
assumptions, x log P [ log ||X|| - k 0, where k is
finite and X is the linear a-stable fractional motion with Hurst parameter 0 <
H < 1 (if a = 2, then X is the classical fractional Brownian motion). These
general results recover many cases previously studied in the literature, and
also prove the existence of new small deviation constants, both in Gaussian and
Non-Gaussian frameworks.Comment: 30 page
On finite generation of the Johnson filtrations
We prove that every term of the lower central series and Johnson filtrations
of the Torelli subgroups of the mapping class group and the automorphism group
of a free group is finitely generated in a linear stable range. This was
originally proved for the second terms by Ershov and He.Comment: 32 pages. v2: very minor edits. Weaker versions of the results of
this paper previously appeared in arXiv:1704.01529 and arXiv:1703.04190v
The Miura Map on the Line
The Miura map (introduced by Miura) is a nonlinear map between function
spaces which transforms smooth solutions of the modified Korteweg - de Vries
equation (mKdV) to solutions of the Korteweg - de Vries equation (KdV). In this
paper we study relations between the Miura map and Schroedinger operators with
real-valued distributional potentials (possibly not decaying at infinity) from
various spaces. We also investigate mapping properties of the Miura map in
these spaces. As an application we prove existence of solutions of the Korteweg
- de Vries equation in the negative Sobolev space H^{-1} for the initial data
in the range of the Miura map.Comment: 33 page
Simulating the Formation of Massive Protostars: I. Radiative Feedback and Accretion Disks
We present radiation hydrodynamic simulations of collapsing protostellar
cores with initial masses of 30, 100, and 200 M. We follow their
gravitational collapse and the formation of a massive protostar and
protostellar accretion disk. We employ a new hybrid radiative feedback method
blending raytracing techniques with flux-limited diffusion for a more accurate
treatment of the temperature and radiative force. In each case, the disk that
forms becomes Toomre-unstable and develops spiral arms. This occurs between
0.35 and 0.55 freefall times and is accompanied by an increase in the accretion
rate by a factor of 2-10. Although the disk becomes unstable, no other stars
are formed. In the case of our 100 and 200 M simulation, the star
becomes highly super-Eddington and begins to drive bipolar outflow cavities
that expand outwards. These radiatively-driven bubbles appear stable, and
appear to be channeling gas back onto the protostellar accretion disk.
Accretion proceeds strongly through the disk. After 81.4 kyr of evolution, our
30 M simulation shows a star with a mass of 5.48 M and a
disk of mass 3.3 M, while our 100 M simulation forms a 28.8
M mass star with a 15.8 M disk over the course of 41.6 kyr,
and our 200 M simulation forms a 43.7 M star with an 18
M disk in 21.9 kyr. In the absence of magnetic fields or other forms
of feedback, the masses of the stars in our simulation do not appear limited by
their own luminosities.Comment: 24 pages, 14 figures. Accepted to The Astrophysical Journa
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