13,021 research outputs found
Hidden torsion, 3-manifolds, and homology cobordism
This paper continues our exploration of homology cobordism of 3-manifolds
using our recent results on Cheeger-Gromov rho-invariants associated to
amenable representations. We introduce a new type of torsion in 3-manifold
groups we call hidden torsion, and an algebraic approximation we call local
hidden torsion. We construct infinitely many hyperbolic 3-manifolds which have
local hidden torsion in the transfinite lower central subgroup. By realizing
Cheeger-Gromov invariants over amenable groups, we show that our hyperbolic
3-manifolds are not pairwise homology cobordant, yet remain indistinguishable
by any prior known homology cobordism invariants. Additionally we give an
answer to a question about transfinite lower central series of homology
cobordant 3-manifold groups, asked by T. D. Cochran and M. H. Freedman.Comment: 24 pages; a new theorem answering a question of Cochran and Freedman
(Kirby List 3.78) added; referee's comments incorporated; to appear in J.
Topolog
On the isomorphism question for complete Pick multiplier algebras
Every multiplier algebra of an irreducible complete Pick kernel arises as the
restriction algebra \mv = \{f\big|_V : f \in \cM_d\}, where is some
integer or , \cM_d is the multiplier algebra of the Drury-Arveson
space , and is a subvariety of the unit ball. For finite it is
known that, under mild assumptions, every isomorphism between two such algebras
\mv and \mw is induced by a biholomorphism between and . In this
paper we consider the converse, and obtain positive results in two directions.
The first deals with the case where is the proper image of a finite Riemann
surface. The second deals with the case where is a disjoint union of
varieties.Comment: 17 pages. Final version, to appear in Integral Equations and Operator
Theor
Analytic design of a 2.0 GHz space borne linear injected beam crossed field amplifier Final report
High efficiency design for crossed field amplifier for application in synchronous satellite
Heat transfer to a gas containing a cloud of particles Final report, 1 Jun. 1962 - 31 May 1968
Radiant heat transfer to particle cloud
A Simple Non-equilibrium Feedback Model for Galaxy-Scale Star Formation: Delayed Feedback and SFR Scatter
We explore a class of simple non-equilibrium star formation models within the
framework of a feedback-regulated model of the ISM, applicable to
kiloparsec-scale resolved star formation relations (e.g. Kennicutt-Schmidt).
Combining a Toomre-Q-dependent local star formation efficiency per free-fall
time with a model for delayed feedback, we are able to match the normalization
and scatter of resolved star formation scaling relations. In particular, this
simple model suggests that large (dex) variations in star formation rates
(SFRs) on kiloparsec scales may be due to the fact that supernova feedback is
not instantaneous following star formation. The scatter in SFRs at constant gas
surface density in a galaxy then depends on the properties of feedback and when
we observe its star-forming regions at various points throughout their
collapse/star formation "cycles". This has the following important
observational consequences: (1) the scatter and normalization of the
Kennicutt-Schmidt relation are relatively insensitive to the local
(small-scale) star formation efficiency, (2) but gas depletion times and
velocity dispersions are; (3) the scatter in and normalization of the
Kennicutt-Schmidt relation is a sensitive probe of the feedback timescale and
strength; (4) even in a model where deterministically
dictates star formation locally, time evolution, variation in local conditions
(e.g., gas fractions and dynamical times), and variations between galaxies can
destroy much of the observable correlation between SFR and
in resolved galaxy surveys. Additionally, this model exhibits large scatter in
SFRs at low gas surface densities, in agreement with observations of flat outer
HI disk velocity dispersion profiles.Comment: 15 pages, 6 figures, accepted by MNRAS (04/25/2019
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