407 research outputs found
Diet of dingoes and other wild dogs in peri-urban areas of north-eastern Australia
Knowledge of the resource requirements of urban predators can improve our understanding of their ecology and assist town planners and wildlife management agencies in developing management approaches that alleviate human-wildlife conflicts. Here we examine food and dietary items identified in scats of dingoes in peri-urban areas of north-eastern Australia to better understand their resource requirements and the potential for dingoes to threaten locally fragmented populations of native fauna. Our primary aim was to determine what peri-urban dingoes eat, and whether or not this differs between regions. We identified over 40 different food items in dingo scats, almost all of which were mammals. Individual species commonly observed in dingo scats included agile wallabies, northern brown bandicoots and swamp wallabies. Birds were relatively common in some areas but not others, as were invertebrates. Dingoes were identified as a significant potential threat to fragmented populations of koalas. Dietary overlap was typically very high or near-identical between regions, indicating that peri-urban dingoes ate the same types or sizes of prey in different areas. Future studies should seek to quantify actual and perceived impacts of, and human attitudes towards, peri-urban dingoes, and to develop management strategies with a greater chance of reducing human-wildlife conflicts
Direct generation of optical vortices
A detailed scheme is established for the direct generation of optical vortices, signifying light endowed with orbital angular momentum. In contrast to common techniques based on the tailored conversion of the wave front in a conventional beam, this method provides for the direct spontaneous emission of photons with the requisite field structure. This form of optical emission results directly from the electronic relaxation of a delocalized exciton state that is supported by a ringlike array of three or more nanoscale chromophores. An analysis of the conditions leads to a general formulation revealing a requirement for the array structure to adhere to one of a restricted set of permissible symmetry groups. It is shown that the coupling between chromophores within each array leads to an energy level splitting of the exciton structure, thus providing for a specific linking of exciton phase and emission wavelength. For emission, arrays conforming to one of the given point-group familiesâ doubly degenerate excitons exhibit the specific phase characteristics necessary to support vortex emission. The highest order of exciton symmetry, corresponding to the maximum magnitude of electronic orbital angular momentum supported by the ring, provides for the most favored emission. The phase properties of the emission produced by the relaxation of such excitons are exhibited on plots which reveal the azimuthal phase progression around the ring, consistent with vortex emission. It is proven that emission of this kind produces electromagnetic fields that map with complete fidelity onto the phase structure of a Laguerre-Gaussian optical mode with the corresponding topological charge. The prospect of direct generation paves the way for practicable devices that need no longer rely on the modification of a conventional laser beam by a secondary optical element. Moreover, these principles hold promise for the development of a vortex laser, also based on nanoscale exciton decay, enabling the production of coherent radiation with a tailor-made helical wave front
The SAMI Galaxy Survey: Shocks and Outflows in a normal star-forming galaxy
We demonstrate the feasibility and potential of using large integral field
spectroscopic surveys to investigate the prevalence of galactic-scale outflows
in the local Universe. Using integral field data from SAMI and the Wide Field
Spectrograph, we study the nature of an isolated disk galaxy, SDSS
J090005.05+000446.7 (z = 0.05386). In the integral field datasets, the galaxy
presents skewed line profiles changing with position in the galaxy. The skewed
line profiles are caused by different kinematic components overlapping in the
line-of-sight direction. We perform spectral decomposition to separate the line
profiles in each spatial pixel as combinations of (1) a narrow kinematic
component consistent with HII regions, (2) a broad kinematic component
consistent with shock excitation, and (3) an intermediate component consistent
with shock excitation and photoionisation mixing. The three kinematic
components have distinctly different velocity fields, velocity dispersions,
line ratios, and electron densities. We model the line ratios, velocity
dispersions, and electron densities with our MAPPINGS IV shock and
photoionisation models, and we reach remarkable agreement between the data and
the models. The models demonstrate that the different emission line properties
are caused by major galactic outflows that introduce shock excitation in
addition to photoionisation by star-forming activities. Interstellar shocks
embedded in the outflows shock-excite and compress the gas, causing the
elevated line ratios, velocity dispersions, and electron densities observed in
the broad kinematic component. We argue from energy considerations that, with
the lack of a powerful active galactic nucleus, the outflows are likely to be
driven by starburst activities. Our results set a benchmark of the type of
analysis that can be achieved by the SAMI Galaxy Survey on large numbers of
galaxies.Comment: 17 pages, 15 figures. Accepted to MNRAS. References update
Testing current synthesis models of the X-ray background
We present synthesis models of the X-ray background where the available X-ray
observational constraints are used to derive information on the AGN population
properties. We show the need for luminous X-ray absorbed AGNs, the QSO2s, in
reproducing the 2-10 keV source counts at relatively bright fluxes. We compare
a model where the evolution of absorbed AGNs is faster than that of unabsorbed
ones, with a standard model where absorbed and unabsorbed AGNs evolve at the
same rate. It is found that an increase by a factor of ~2 from z=0 to z~1.3 in
the ratio between absorbed and unabsorbed AGNs would provide a significant
improvement in the data description. Finally, we make predictions on the AGNs
to be observed in deep X-ray surveys which contain information on the AGN space
density at high redshift.Comment: 11 pages with 8 figures, A&A accepte
Rosat, Asca and Osse Observations of the Broad Line Radio Galaxy 3C120
We present simultaneous observations of the superluminal radio galaxy 3C120
performed with the ASCA and GRO (OSSE) satellites on February-March 1994, as
well as an analysis of all the ROSAT archival data. The ASCA spectrum of this
object can be described by an absorbed (N_H=1.6e^21 cm^-2) power law with
photon index Gamma_ASCA=2 and a very broad sigma>0.8 keV intense iron line
(EW>400 eV) at ~ 6 keV. The combined ASCA--OSSE data do not exclude the
presence of a narrower (sigma=0.4 keV) and less intense (EW<300 eV) iron line
plus a hard component, corresponding either to reflection from an accretion
disk or to a flatter power law from a jet. However a single power law plus
broad Fe line is preferred from a statistical point of view by the ASCA data.
The ROSAT data yield a column density in excess of the Galactic value. The
spectral slopes, ranging from Gamma_ROSAT=2.5 to 3.3, are steeper than that
measured by ASCA, suggesting the presence of a soft excess. The 0.1-2 keV
power-law slope is variable and softer at higher intensity. These results show
that the combined soft and hard X-ray spectrum of 3C120 is rather complex. The
intrinsic absorption, the soft excess, and the iron line indicate that the
X-ray emission from this blazar-like radio galaxy is dominated by a
Seyfert-like component, at least in the 0.1-10keV energy band. The jet
contribution, if present, becomes important only at higher energies.Comment: 25 pages, Latex, 8 PostScript figures, to appear in The Astrophysical
Journa
VFR-into-IMC Accident Trends: Perceptions of Deficiencies in Training
Pilots who operate under visual flight rules (VFR) and in visual meteorological conditions, who then continue flight into instrument meteorological conditions (IMC), remain as one of the leading causes of fatal aircraft accidents in general aviation. This paper examines past and current research initiatives, in seeking to identify causal factors and gaps in training that lead to VFR-into-IMC aircraft accidents, using a mixed methods approach. The Aircraft Owners and Pilots Association Air Safety Institute database and the National Transportation Safety Board database search engines were used to identify accident reports associated with VFR flight into IMC/deteriorating weather conditions for a 10-year time period (2003 to 2012). A national survey was also conducted to gain deeper insight into the self-identified training deficiencies of pilots. There is evidence that situational awareness is linked to decision-making, and there is a lack of proper training with regards to weather and weather technology concepts, making it difficult for pilots to gain these knowledge areas, skills, and abilities throughout their initial flight training and subsequent experience
The ASCA X-Ray Spectrum Of The Broad-Line Radio Galaxy Pictor A: A Simple Power Law With No Fe K-alpha Line
We present the X-ray spectrum of the broad-line radio galaxy Pictor A as
observed by ASCA in 1996. The main objective of the observation was to detect
and study the profiles of the Fe~K lines. The motivation was the fact
that the Balmer lines of this object show well-separated displaced peaks,
suggesting an origin in an accretion disk. The 0.5-10 keV X-ray spectrum is
described very well by a model consisting of a power law of photon index 1.77
modified by interstellar photoelectric absorption. We find evidence for neither
a soft nor a hard (Compton reflection) excess. More importantly, we do not
detect an Fe K-alpha line, in marked contrast with the spectra of typical
Seyfert galaxies and other broad-line radio galaxies observed by ASCA. The
99%-confidence upper limit on the equivalent width of an unresolved line at a
rest energy of 6.4 keV is 100 eV, while for a broad line (FWHM of approximately
60,000 km/s) the corresponding upper limit is 135 eV. We discuss several
possible explanations for the weakness of the Fe K-alpha line in Pictor~A
paying attention to the currently available data on the properties of Fe
K-alpha lines in other broad-line radio galaxies observed by ASCA. We speculate
that the absence of a hard excess (Compton reflection) or an Fe K-alpha line is
an indication of an accretion disk structure that is different from that of
typical Seyfert galaxies, e.g., the inner disk may be an ion torus.Comment: To appear in the Astrophysical Journal (18 pages, including 8
postscript figures; uses psfig.tex
The peatland vegetation burning debate: keep scientific critique in perspective. A response to Brownet al. and Douglaset al.
Invited reply
The role of fire in UK peatland and moorland management: the need for informed, unbiased debate
Fire has been used for centuries to generate and manage some of the UK's cultural landscapes. Despite its complex role in the ecology of UK peatlands and moorlands, there has been a trend of simplifying the narrative around burning to present it as an only ecologically damaging practice. That fire modifies peatland characteristics at a range of scales is clearly understood. Whether these changes are perceived as positive or negative depends upon how trade-offs are made between ecosystem services and the spatial and temporal scales of concern. Here we explore the complex interactions and trade-offs in peatland fire management, evaluating the benefits and costs of managed fire as they are currently understood. We highlight the need for (i) distinguishing between the impacts of fires occurring with differing severity and frequency, and (ii) improved characterization of ecosystem health that incorporates the response and recovery of peatlands to fire. We also explore how recent research has been contextualized within both scientific publications and the wider media and how this can influence non-specialist perceptions. We emphasize the need for an informed, unbiased debate on fire as an ecological management tool that is separated from other aspects of moorland management and from political and economic opinions
Cosmodynamics: Energy conditions, Hubble bounds, density bounds, time and distance bounds
We refine and extend a programme initiated by one of the current authors
[Science 276 (1997) 88; Phys. Rev. D56 (1997) 7578] advocating the use of the
classical energy conditions of general relativity in a cosmological setting to
place very general bounds on various cosmological parameters. We show how the
energy conditions can be used to bound the Hubble parameter H(z), Omega
parameter Omega(z), density rho(z), distance d(z), and lookback time T(z) as
(relatively) simple functions of the redshift z, present-epoch Hubble parameter
H_0, and present-epoch Omega parameter Omega_0. We compare these results with
related observations in the literature, and confront the bounds with the recent
supernova data.Comment: 21 pages, 2 figure
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