5,818 research outputs found
Indigenous vegetation types of Hamilton Ecological District
The following descriptions of indigenous vegetation types and lists of the most characteristic species have been compiled for the major landform units of the Hamilton Ecological District, which lies within the Waikato Ecological Region (McEwen 1987). The boundaries of the Hamilton Ecological District correspond approximately to those of the Hamilton basin, with the addition of parts of hills and foothills at the margins of the basin. The vegetation descriptions and species lists are based on knowledge of the flora of vegetation remnants in the ecological district, historical records (e.g., Gudex 1954), and extrapolation of data from other North Island sites with similar environmental profiles
M-Branes on k-center Instantons
We present analytic solutions for membrane metric function based on
transverse -center instanton geometries. The membrane metric functions
depend on more than two transverse coordinates and the solutions provide
realizations of fully localized type IIA D2/D6 and NS5/D6 brane intersections.
All solutions have partial preserved supersymmetries.Comment: 22 pages, 5 figure
Locally extracting scalar, vector and tensor modes in cosmological perturbation theory
Cosmological perturbation theory relies on the decomposition of perturbations
into so-called scalar, vector and tensor modes. This decomposition is non-local
and depends on unknowable boundary conditions. The non-locality is particularly
important at second- and higher-order because perturbative modes are sourced by
products of lower-oder modes, which must be integrated over all space in order
to isolate each mode. However, given a trace-free rank-2 tensor, a locally
defined scalar mode may be trivially derived by taking two divergences, which
knocks out the vector and tensor degrees of freedom. A similar local
differential operation will return a pure vector mode. This means that scalar
and vector degrees of freedom have local descriptions. The corresponding local
extraction of the tensor mode is unknown however. We give it here. The
operators we define are useful for defining gauge-invariant quantities at
second-order. We perform much of our analysis using an index-free
`vector-calculus' approach which makes manipulating tensor equations
considerably simpler.Comment: 13 pages. Final version to appear in CQ
Eguchi-Hanson Solitons in Odd Dimensions
We present a new class of solutions in odd dimensions to Einstein's equations
containing either a positive or negative cosmological constant. These solutions
resemble the even-dimensional Eguchi-Hanson-(A)dS metrics, with the added
feature of having Lorentzian signatures. They are asymptotic to
(A)dS. In the AdS case their energy is negative relative to that of
pure AdS. We present perturbative evidence in 5 dimensions that such metrics
are the states of lowest energy in their asymptotic class, and present a
conjecture that this is generally true for all such metrics. In the dS case
these solutions have a cosmological horizon. We show that their mass at future
infinity is less than that of pure dS.Comment: 26 pages, Late
A gravitational wave window on extra dimensions
We report on the possibility of detecting a submillimetre-sized extra
dimension by observing gravitational waves (GWs) emitted by pointlike objects
orbiting a braneworld black hole. Matter in the `visible' universe can generate
a discrete spectrum of high frequency GWs with amplitudes moderately weaker
than the predictions of general relativity (GR), while GW signals generated by
matter on a `shadow' brane hidden in the bulk are potentially strong enough to
be detected using current technology. We know of no other astrophysical
phenomena that produces GWs with a similar spectrum, which stresses the need to
develop detectors capable of measuring this high-frequency signature of large
extra dimensions.Comment: 9 pages, 5 figure
What does a primary care annual review for RA include? A national GP survey
Letter to the edito
The Arches Cluster: Extended Structure and Tidal Radius
At a projected distance of ~26 pc from Sgr A*, the Arches cluster provides
insight to star formation in the extreme Galactic Center (GC) environment.
Despite its importance, many key properties such as the cluster's internal
structure and orbital history are not well known. We present an astrometric and
photometric study of the outer region of the Arches cluster (R > 6.25") using
HST WFC3IR. Using proper motions we calculate membership probabilities for
stars down to F153M = 20 mag (~2.5 M_sun) over a 120" x 120" field of view, an
area 144 times larger than previous astrometric studies of the cluster. We
construct the radial profile of the Arches to a radius of 75" (~3 pc at 8 kpc),
which can be well described by a single power law. From this profile we place a
3-sigma lower limit of 2.8 pc on the observed tidal radius, which is larger
than the predicted tidal radius (1 - 2.5 pc). Evidence of mass segregation is
observed throughout the cluster and no tidal tail structures are apparent along
the orbital path. The absence of breaks in the profile suggests that the Arches
has not likely experienced its closest approach to the GC between ~0.2 - 1 Myr
ago. If accurate, this constraint indicates that the cluster is on a prograde
orbit and is located front of the sky plane that intersects Sgr A*. However,
further simulations of clusters in the GC potential are required to interpret
the observed profile with more confidence.Comment: 24 pages (17-page main text, 7-page appendix), 24 figures, accepted
to Ap
Recent Results and Perspectives for Precision Astrometry and Photometry with Adaptive Optics
Large ground-based telescopes equipped with adaptive optics (AO) systems have
ushered in a new era of high-resolution infrared photometry and astrometry.
Relative astrometric accuracies of <0.2 mas have already been demonstrated from
infrared images with spatial resolutions of 55-95 mas resolution over 10-20''
fields of view. Relative photometric accuracies of 3% and absolute photometric
accuracies of 5%-20% are also possible. I will review improvements and current
limitations in astrometry and photometry with adaptive optics of crowded
stellar fields. These capabilities enable experiments such as measuring orbits
for brown dwarfs and exoplanets, studying our Galaxy's supermassive black hole
and its environment, and identifying individual stars in young star clusters,
which can be used test the universality of the initial mass function.Comment: SPIE Conference Proceedin
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