167 research outputs found
A weakly stable algorithm for general Toeplitz systems
We show that a fast algorithm for the QR factorization of a Toeplitz or
Hankel matrix A is weakly stable in the sense that R^T.R is close to A^T.A.
Thus, when the algorithm is used to solve the semi-normal equations R^T.Rx =
A^Tb, we obtain a weakly stable method for the solution of a nonsingular
Toeplitz or Hankel linear system Ax = b. The algorithm also applies to the
solution of the full-rank Toeplitz or Hankel least squares problem.Comment: 17 pages. An old Technical Report with postscript added. For further
details, see http://wwwmaths.anu.edu.au/~brent/pub/pub143.htm
Massive binary black holes in galactic nuclei and their path to coalescence
Massive binary black holes form at the centre of galaxies that experience a
merger episode. They are expected to coalesce into a larger black hole,
following the emission of gravitational waves. Coalescing massive binary black
holes are among the loudest sources of gravitational waves in the Universe, and
the detection of these events is at the frontier of contemporary astrophysics.
Understanding the black hole binary formation path and dynamics in galaxy
mergers is therefore mandatory. A key question poses: during a merger, will the
black holes descend over time on closer orbits, form a Keplerian binary and
coalesce shortly after? Here we review progress on the fate of black holes in
both major and minor mergers of galaxies, either gas-free or gas-rich, in
smooth and clumpy circum-nuclear discs after a galactic merger, and in
circum-binary discs present on the smallest scales inside the relic nucleus.Comment: Accepted for publication in Space Science Reviews. To appear in hard
cover in the Space Sciences Series of ISSI "The Physics of Accretion onto
Black Holes" (Springer Publisher
Sport, genetics and the `natural athlete': The resurgence of racial science
This article explores the ethical implications of recent discussions that naturalize the relationship between race, the body and sport within the frame of genetic science. Many suggestions of a racially distributed genetic basis for athletic ability and performance are strategically posited as a resounding critique of the `politically correct' meta-narratives of established sociological and anthropological forms of explanation that emphasize the social and cultural construction of race. I argue that this use of genetic science in order to describe and explain common-sense impressions of racial physiology and sporting ability is founded on erroneous premises of objectivity and disinterest, and inflates the analytical efficacy of scientific truth claims. I suggest that assertions of a value-free science of racial athletic ability reify race as inherited permanent biological characteristics that produce social hierarchies and are more characteristic of a longer history of `racial science'
Genetic, abiotic and social influences on sex differentiation in cichlid fishes and the evolution of sequential hermaphroditism
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73799/1/j.1467-2979.2005.00184.x.pd
Implications of H.E.S.S. observations of pulsar wind nebulae
In this review paper on pulsar wind nebulae (PWN) we discuss the properties
of such nebulae within the context of containment against cross-field diffusion
(versus normal advection), the effect of reverse shocks on the evolution of
offset ``Vela-like'' PWN, constraints on maximum particle energetics, magnetic
field strength estimates based on spectral and spatial properties, and the
implication of such field estimates on the composition of the wind. A
significant part of the discussion is based on the High Energy Stereoscopic
System ({\it H.E.S.S.} or {\it HESS}) detection of the two evolved pulsar wind
nebulae Vela X (cocoon) and HESS J1825-137. In the case of Vela X (cocoon) we
also review evidence of a hadronic versus a leptonic interpretation, showing
that a leptonic interpretation is favored for the {\it HESS} signal. The
constraints discussed in this review paper sets a general framework for the
interpretation of a number of offset, filled-center nebulae seen by {\it HESS}.
These sources are found along the galactic plane with galactic latitudes
, where significant amounts of molecular gas is found. In these
regions, we find that the interstellar medium is inhomogeneous, which has an
effect on the morphology of supernova shock expansion. One consequence of this
effect is the formation of offset pulsar wind nebulae as observed.Comment: to appear in Springer Lecture Notes on Neutron Stars and Pulsars: 40
years after their discovery, eds. W. Becke
Size Doesn't Matter: Towards a More Inclusive Philosophy of Biology
notes: As the primary author, OâMalley drafted the paper, and gathered and analysed data (scientific papers and talks). Conceptual analysis was conducted by both authors.publication-status: Publishedtypes: ArticlePhilosophers of biology, along with everyone else, generally perceive life to fall into two broad categories, the microbes and macrobes, and then pay most of their attention to the latter. âMacrobeâ is the word we propose for larger life forms, and we use it as part of an argument for microbial equality. We suggest that taking more notice of microbes â the dominant life form on the planet, both now and throughout evolutionary history â will transform some of the philosophy of biologyâs standard ideas on ontology, evolution, taxonomy and biodiversity. We set out a number of recent developments in microbiology â including biofilm formation, chemotaxis, quorum sensing and gene transfer â that highlight microbial capacities for cooperation and communication and break down conventional thinking that microbes are solely or primarily single-celled organisms. These insights also bring new perspectives to the levels of selection debate, as well as to discussions of the evolution and nature of multicellularity, and to neo-Darwinian understandings of evolutionary mechanisms. We show how these revisions lead to further complications for microbial classification and the philosophies of systematics and biodiversity. Incorporating microbial insights into the philosophy of biology will challenge many of its assumptions, but also give greater scope and depth to its investigations
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