1,483 research outputs found
On the Post-linear Quadrupole-Quadrupole Metric
The Hartle-Thorne metric defines a reliable spacetime for most astrophysical
purposes, for instance for the simulation of slowly rotating stars. Solving the
Einstein field equations, we added terms of second order in the quadrupole
moment to its post-linear version in order to compare it with solutions found
by Blanchet in the frame of the multi-polar post-Minkowskian framework. We
first derived the extended Hartle-Thorne metric in harmonic coordinates and
then showed agreement with the corresponding post-linear metric from Blanchet.
We also found a coordinate transformation from the post-linear Erez-Rosen
metric to our extended Hartle-Thorne spacetime. It is well known that the
Hartle-Thorne solution can be smoothly matched with an interior perfect fluid
solution with physically appropriate properties. A comparison among these
solutions provides a validation of them. It is clear that in order to represent
realistic solutions of self-gravitating (axially symmetric) matter
distributions of perfect fluid, the quadrupole moment has to be included as a
physical parameter
A phylogenomic perspective on the radiation of ray-finned fishes based upon targeted sequencing of ultraconserved elements
Ray-finned fishes constitute the dominant radiation of vertebrates with over
30,000 species. Although molecular phylogenetics has begun to disentangle major
evolutionary relationships within this vast section of the Tree of Life, there
is no widely available approach for efficiently collecting phylogenomic data
within fishes, leaving much of the enormous potential of massively parallel
sequencing technologies for resolving major radiations in ray-finned fishes
unrealized. Here, we provide a genomic perspective on longstanding questions
regarding the diversification of major groups of ray-finned fishes through
targeted enrichment of ultraconserved nuclear DNA elements (UCEs) and their
flanking sequence. Our workflow efficiently and economically generates data
sets that are orders of magnitude larger than those produced by traditional
approaches and is well-suited to working with museum specimens. Analysis of the
UCE data set recovers a well-supported phylogeny at both shallow and deep
time-scales that supports a monophyletic relationship between Amia and
Lepisosteus (Holostei) and reveals elopomorphs and then osteoglossomorphs to be
the earliest diverging teleost lineages. Divergence time estimation based upon
14 fossil calibrations reveals that crown teleosts appeared ~270 Ma at the end
of the Permian and that elopomorphs, osteoglossomorphs, ostarioclupeomorphs,
and euteleosts diverged from one another by 205 Ma during the Triassic. Our
approach additionally reveals that sequence capture of UCE regions and their
flanking sequence offers enormous potential for resolving phylogenetic
relationships within ray-finned fishes
Free Variables and the Two Matrix Model
We study the full set of planar Green's functions for a two-matrix model
using the language of functions of non-commuting variables. Both the standard
Schwinger-Dyson equations and equations determining connected Green's functions
can be efficiently discussed and solved. This solution determines the master
field for the model in the `-representation.'Comment: 8 pages, harvma
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