1,546 research outputs found
Biodiversity Conservation in Urbanising Forested Landscapes
Unprecedented human population growth combined with rapid
urbanisation of forest ecosystems highlight an urgent need to
plan for biodiversity conservation in forested landscapes. To
provide scientific evidence to guide management strategies and
urban planning, I studied the distribution and/or abundance of
amphibians and mammals and vegetation structure in a
forest-dominated landscape in south-eastern Australia. In five
scientific papers in three sections, I tackled important gaps of
knowledge on: (1) the distribution of pond-breeding frogs (Paper
I); (2) the distribution and abundance of mammals and vegetation
structure across forest-urban interfaces (Papers II-IV); and (3)
the fate of mammals under future scenarios of compact versus
dispersed urban growth (Paper V).
In the first section, I studied the influence of aquatic and
terrestrial variables on species richness and individual species
occurrence of pond-breeding frogs in an urbanising landscape. I
found the occurrence of common frogs depended on characteristics
of the local aquatic habitat. In contrast, the terrestrial
habitat was important for rare frogs: rare species richness
declined with small increases in road cover as far as 1 km from
the breeding habitat. While provision of aquatic habitat within
urban areas may increase the occurrence of common species, I
identified the need to preserve aquatic habitats within large
forest reserves to conserve urban-sensitive amphibians.
In the second section, I studied the distribution and abundance
of mammals and vegetation structure across forest-urban
interfaces of high and low housing density. For forest-dwelling
mammal species, I found low-density housing developments provided
suitable habitat, whereas high-density housing developments had
low species richness and species abundance. The lower abundance
of forest-dwelling mammals in high-density housing developments
was likely due to a stronger decline of forest vegetation
structures across the forest-urban interface. In addition, I
found the distribution of ground-dwelling mammals was better
explained by local habitat structure (e.g. understorey cover)
than by housing density or distance to an urban boundary. Based
on my findings, I argued for the local-scale management of
vegetation to improve habitat quality for mammals (e.g. to
maintain/provide mature trees and understorey cover). Because a
forest-dwelling species reduced its abundance at long distances
from urban boundaries, I recommended limiting the amount of
forest-urban interfaces when planning for urban development.
In the third section, I quantified the changes in mammal
distribution and abundance at a landscape scale under future
scenarios of compact (i.e. high-density housing) versus dispersed
(i.e. low-density housing) urban growth. Although I previously
found that dispersed development maintained biodiversity, I
discovered that the occurrence and abundance of urban-sensitive
species had a greater decrease under dispersed rather than
compact development. I concluded compact urban growth is less
damaging in landscapes with urban-sensitive fauna than dispersed
development.
Taken together as a connected body of work, my PhD research
demonstrates that positive conservation outcomes will be best
achieved by integrating: local-scale management of habitat to
improve habitat condition for fauna, with land use planning and
urban growth policies. Land planning and urban growth policies
should aim to limit forest clearing and fragmentation, the amount
of forest-urban interfaces, and the sprawl of low-density housing
development
Measured supersonic flame properties - Heat-release patterns, pressure losses, thermal choking limits
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76611/1/AIAA-24093-582.pd
WASP-4b Arrived Early for the TESS Mission
The Transiting Exoplanet Survey Satellite (TESS) recently observed 18
transits of the hot Jupiter WASP-4b. The sequence of transits occurred 81.6
11.7 seconds earlier than had been predicted, based on data stretching
back to 2007. This is unlikely to be the result of a clock error, because TESS
observations of other hot Jupiters (WASP-6b, 18b, and 46b) are compatible with
a constant period, ruling out an 81.6-second offset at the 6.4 level.
The 1.3-day orbital period of WASP-4b appears to be decreasing at a rate of
milliseconds per year. The apparent period change
might be caused by tidal orbital decay or apsidal precession, although both
interpretations have shortcomings. The gravitational influence of a third body
is another possibility, though at present there is minimal evidence for such a
body. Further observations are needed to confirm and understand the timing
variation.Comment: AJ accepte
HETE-II and the Interplanetary Network
The FREGATE experiment aboard HETE-II has been successfully integrated into
the Third Interplanetary Network (IPN) of gamma-ray burst detectors. We show
how HETE's timing has been verified in flight, and discuss what HETE can do for
the IPN and vice-versa.Comment: To appear in the proceedings of the conference on Gamma-Ray Burst and
Afterglow Astronomy 2001: A Workshop Celebrating the First Year of the HETE
Mission, to be published by AIP. Figures must be downloaded and printed
separatel
GRB970228 and a class of GRBs with an initial spikelike emission
(Shortened) The Swift and HETE-2 discovery of an afterglow associated
possibly with short GRBs opened the new problematic of their nature and
classification. This has been further enhanced by the GRB060614 observation and
by a re-analysis of the BATSE catalog leading to the identification of a new
GRB class with "an occasional softer extended emission lasting tenths of
seconds after an initial spikelike emission". We plan: a) to fit this new class
of "hybrid" sources within our "canonical GRB" scenario, where all GRBs are
generated by a "common engine" (i.e. the gravitational collapse to a black
hole); b) to propose GRB970228 as the prototype of the such a class. We analyze
BeppoSAX data on GRB970228 in the 40-700 keV and 2-26 keV energy bands within
the "fireshell" model. We find that GRB970228 is a "canonical GRB", like e.g.
GRB050315, with the main peculiarity of a particularly low CircumBurst Medium
(CBM) average density n_{cbm}~10^{-3} #/cm^3. We also simulate the light curve
corresponding to a rescaled CBM density profile with n_{cbm}=1 #/cm^3. From
such a comparison it follows that the total time-integrated luminosity is a
faithful indicator of the GRB nature, contrary to the peak luminosity which is
merely a function of the CBM density. We call attention on discriminating the
short GRBs between the "genuine" and the "fake" ones. The "genuine" ones are
intrinsically short, with baryon loading B \la 10^{-5}, as stated in our
original classification. The "fake" ones, characterized by an initial spikelike
emission followed by an extended emission lasting tenths of seconds, have a
baryon loading 10^{-4} \la B \leq 10^{-2}. They are observed as such only due
to an underdense CBM consistent with a galactic halo environment which deflates
the afterglow intensity.Comment: 4 pages, 4 figures, to appear on A&A Letter
The origin of the late rebrightening in GRB 080503
GRB 080503, detected by Swift, belongs to the class of bursts whose prompt
phase consists of an initial short spike followed by a longer soft tail. It did
not show any transition to a regular afterglow at the end of the prompt
emission but exhibited a surprising rebrightening after one day. We aim to
explain this rebrightening with two different scenarios - refreshed shocks or a
density clump in the circumburst medium - and two models for the origin of the
afterglow, the standard one where it comes from the forward shock, and an
alternative one where it results from a long-lived reverse shock. We computed
afterglow light curves either using a single-zone approximation for the shocked
region or a detailed multizone method that more accurately accounts for the
compression of the material. We find that in several of the considered cases
the detailed model must be used to obtain a reliable description of the shock
dynamics. The density clump scenario is not favored. We confirm previous
results that the presence of the clump has little effect on the forward shock
emission, except if the microphysics parameters evolve when the shock enters
the clump. Moreover, we find that the rebrightening from the reverse shock is
also too weak when it is calculated with the multi-zone method. On the other
hand, in the refreshed-shock scenario both the forward and reverse shock models
provide satisfactory fits of the data under some additional conditions on the
distribution of the Lorentz factor in the ejecta and the beaming angle of the
relativistic outflow.Comment: 8 pages, 4 figures, accepted for publication in A&
A Comprehensive Study of Short Bursts from SGR 1806-20 and SGR 1900+14 Detected by HETE-2
We present the results of temporal and spectral studies of the short burst
(less than a few hundred milliseconds) from the soft gamma repeaters (SGRs)
1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005,
HETE-2 detected 50 bursts which were localized to SGR 1806-20 and 5 bursts
which were localized to SGR 1900+14. Especially SGR 1806-20 was active in 2004,
and HETE-2 localized 33 bursts in that year. The cumulative number-intensity
distribution of SGR 1806-20 in 2004 is well described by a power law model with
an index of -1.1+/-0.6. It is consistent with previous studies but burst data
taken in other years clearly give a steeper distribution. This may suggest that
more energetic bursts could occur more frequently in periods of greater
activity. A power law cumulative number-intensity distribution is also known
for earthquakes and solar flares. It may imply analogous triggering mechanisms.
Although spectral evolution during bursts with a time scale of > 20 ms is not
common in the HETE-2 sample, spectral softening due to the very rapid (< a few
milliseconds) energy reinjection and cooling may not be excluded. The spectra
of all short bursts are well reproduced by a two blackbody function (2BB) with
temperatures ~4 and ~11 keV. From the timing analysis of the SGR 1806-20 data,
a time lag of 2.2+/-0.4 ms is found between the 30-100 keV and 2-10 keV
radiation bands. This may imply (1) a very rapid spectral softening and energy
reinjection, (2) diffused (elongated) emission plasma along the magnetic field
lines in pseudo equilibrium with multi-temperatures, or (3) a separate (located
at < 700 km) emission region of softer component (say, ~4 keV) which could be
reprocessed X-rays by higher energy (> 11 keV) photons from an emission region
near the stellar surface.Comment: 50 pages, 14 figures, accepted for publication in PAS
HETE Observations of the Gamma-Ray Burst GRB030329: Evidence for an Underlying Soft X-ray Component
An exceptionally intense gamma-ray burst, GRB030329, was detected and
localized by the instruments on board the High Energy Transient Explorer
satellite (HETE) at 11:37:14 UT on 29 March 2003. The burst consisted of two
\~10s pulses of roughly equal brightness and an X-ray tail lasting >100s. The
energy fluence in the 30-400 keV energy band was 1.08e-4 erg/cm2, making
GRB030329 one of the brightest GRBs ever detected. Communication of a 2 arcmin
error box 73 minutes after the burst allowed the rapid detection of a
counterpart in the optical, X-ray, radio and the ensuing discovery of a
supernova with most unusual characteristics. Analyses of the burst lightcurves
reveal the presence of a distinct, bright, soft X-ray component underlying the
main GRB: the 2-10 keV fluence of this component is ~7e-6 erg/cm2. The main
pulses of GRB030329 were preceded by two soft, faint, non-thermal bumps. We
present details of the HETE observations of GRB030329.Comment: 22 pages, 5 figures, to be published in ApJ 617, no. 2 (10 December
2004). Referee comments have been incorporated; results of improved spectral
analysis are include
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