1,319 research outputs found
X-ray observations of the Ultraluminous infrared galaxy IRAS19254-7245 (The Superantennae)
We present ROSAT HRI and ASCA observations of the well known ULIRG
IRAS19254-7245 (the Superantennae). The object is not detected by ROSAT
yielding a 3\sigma upper limit of L_x ~8x10^{41} erg/s in the 0.1-2 keV band.
However, we obtain a clear detection by ASCA yielding a luminosity in the 2-10
keV band of 2 \times 10^{42}erg/s. Its X-ray spectrum is very hard, equivalent
to a photon index of Gamma=1.0+-0.35.
We therefore, attempt to model the X-ray data with a "scatterer" model in
which the intrinsic X-ray emission along our line of sight is obscured by an
absorbing screen while some fraction, f, is scattered into our line of sight by
an ionized medium; this is the standard model for the X-ray emission in
obscured (but non Compton-thick)
Seyfert galaxies. We obtain an absorbing column of 2x10^{23}cm^{-2} for a
power-law photon index of Gamma=1.9, an order of magnitude above the column
estimated on the basis of optical observations; the percentage of the scattered
emission is high (~20%). Alternatively, a model where most of the X-ray
emission comes from reflection on a Compton thick torus (N_H>10^{24} cm^{-2})
cannot be ruled out.
We do not detect an Fe line at 6.4 keV; however, the upper limit (90%) to the
equivalent width of the 6.4 keV line is high (~3 keV).
All the above suggest that most of the X-ray emission originates in an highly
obscured Seyfert-2 nucleus.Comment: 5 pages, 1 figure, 1 table, To appear in MNRA
Dealing with natural language interfaces in a geolocation context
In the geolocation field where high-level programs and low-level devices
coexist, it is often difficult to find a friendly user inter- face to configure
all the parameters. The challenge addressed in this paper is to propose
intuitive and simple, thus natural lan- guage interfaces to interact with
low-level devices. Such inter- faces contain natural language processing and
fuzzy represen- tations of words that facilitate the elicitation of
business-level objectives in our context
Nitrogen transfer between clover and wheat in an intercropping experiment
A novel approach to the problem of improving nitrogen supply in organic farming is to use intercropping of cereals with a legume to provide nitrogen transfer within a season and/or to following crops. The affects of intercropping were studied in a column experiment using mixtures of winter wheat (Triticum aestivum cv. Claire), with white clover (w.c.) (Trifolium repens cv. Barblanca) and with red clover (r.c.) (Trifolium pratense cv. Britta). The effects of cutting and removal above ground clover material with and without additional soil disturbance were compared to leaving clover plants in situ and intercropped with wheat in a split root design. Wheat and clover plants, as monocultures, were used for the controls. 15N ammonium nitrate solution was applied. The wheat seeds were sown into the column without nitrogen. We found that the cutting treatment produced the highest yield of wheat. Available ammonium-N in the soil was greatest in the clover control treatment for the column with only red clover roots and in the cutting+soil disturbance treatment for the column with only white clover roots. Available nitrate-N was greatest in the soil disturbance treatment in the column with clover and wheat roots for both red and white clover. The cutting treatment produced the highest yield of wheat
Short time-scale optical variability of the dwarf Seyfert nucleus in NGC 4395
We present optical spectroscopic observations of the least-luminous known
Seyfert 1 galaxy, NGC 4395, which was monitored every half-hour over the course
of 3 nights. The continuum emission varied by ~35 per cent over the course of 3
nights, and we find marginal evidence for greater variability in the blue
continuum than the red. A number of diagnostic checks were performed on the
data in order to constrain any systematic or aperture effects. No correlations
were found that adequately explained the observed variability, hence we
conclude that we have observed real intrinsic variability of the nuclear
source. No simultaneous variability was measured in the broad H-beta line,
although given the difficulty in deblending the broad and narrow components it
is difficult to comment on the significance of this result. The observed short
time-scale continuum variability is consistent with NGC 4395 having an
intermediate-mass (~10^5 solar masses) central supermassive black hole, rather
than a very low accretion rate. Comparison with the Seyfert 1 galaxy NGC 5548
shows that the observed variability seems to scale with black hole mass in
roughly the manner expected in accretion models. However the absolute
time-scale of variability differs by several orders of magnitude from that
expected in simple accretion disc models in both cases.Comment: 16 pages, 14 figures, 5 tables, accepted for publication in MNRA
Local partnerships and urban governance: The case of Lisbon
Collaborative forms of governance in urban regeneration are increasingly gaining ground in
cities around the world, contributing to the active engagement of citizens in decision-making
processes that affect their neighbourhoods and lives. In some cases, municipalities embrace
local grassroot initiatives, as for example with the implementation of participatory budgets,
enabling active citizens to creatively invent ways to regain and co-manage the urban commons.
In a similar vision, the Department of Housing and Local Development of the Municipality of
Lisbon launched in 2011 a participatory budget program, namely BIP/ZIP, to annually fund
bottom-up initiatives led by local partnerships in priority neighbourhoods that enable responses
to social and territorial emergencies.
The aim of this research is to investigate the matrix of local partnerships that have been
formulated throughout the eleven years of BIP/ZIP and understand their dynamic role in the
transformation of the urban governance in the city of Lisbon.info:eu-repo/semantics/publishedVersio
Quantum network routing and local complementation
Quantum communication between distant parties is based on suitable instances of shared entanglement. For efficiency reasons, in an anticipated quantum network beyond point-to-point communication, it is preferable that many parties can communicate simultaneously over the underlying infrastructure; however, bottlenecks in the network may cause delays. Sharing of multi-partite entangled states between parties offers a solution, allowing for parallel quantum communication. Specifically for the two-pair problem, the butterfly network provides the first instance of such an advantage in a bottleneck scenario. In this paper, we propose a more general method for establishing EPR pairs in arbitrary networks. The main difference from standard repeater network approaches is that we use a graph state instead of maximally entangled pairs to achieve long-distance simultaneous communication. We demonstrate how graph-theoretic tools, and specifically local complementation, help decrease the number of required measurements compared to usual methods applied in repeater schemes. We examine other examples of network architectures, where deploying local complementation techniques provides an advantage. We finally consider the problem of extracting graph states for quantum communication via local Clifford operations and Pauli measurements, and discuss that while the general problem is known to be NP-complete, interestingly, for specific classes of structured resources, polynomial time algorithms can be identified
Cosmological Evolution in a Type-0 String Theory
We study the cosmological evolution of a type-0 string theory by employing
non-criticality, which may be induced by fluctuations of the D3 brane worlds.
We check the consistency of the approach to O(alpha ') in the corresponding
sigma-model. The ten-dimensional theory is reduced to an effective
four-dimensional model, with only time dependent fields. We show that the
four-dimensional universe has an inflationary phase and graceful exit from it,
while the other extra dimensions are stabilized to a constant value, with the
fifth dimension much larger than the others. We pay particular attention to
demonstrating the role of tachyonic matter in inducing these features. The
Universe asymptotes, for large times, to a non-accelerating linearly-expanding
Universe with a time-dependent dilaton and a relaxing to zero vacuum energy a
la quintessence.Comment: 33 pages LATEX, seven eps figures incorporate
The X-ray spectra of optically selected Seyfert 2 galaxies. Are there any Sy2 galaxies with no absorption?
We present an X-ray spectral analysis of a sample of 8 bona-fide Seyfert 2
galaxies, selected on the basis of their high flux, from
the Ho et al. (1997) spectroscopic sample of nearby galaxies. We find that, in
general, the X-ray spectra of our Seyfert 2 galaxies are complex, with some our
objects having spectra different from the 'typical' spectrum of X-ray selected
Seyfert 2 galaxies. Two (NGC3147 and NGC4698) show no evidence for intrinsic
absorption. We suggest this is due to the fact that when the torus suppresses
the intrinsic medium and hard energy flux, underlying emission from the host
galaxy, originating in circumnuclear starbursts, and scattering from warm
absorbers contributes in these energy bands more significantly. Our asca data
alone cannot discriminate whether low absorption objects are Compton-thick AGN
with a strong scattered component or lack an obscuring torus. The most striking
example of our low absorption Seyfert 2 is NGC4698. Its spectrum could be
explained by either a dusty warm absorber or a lack of broad line clouds so
that its appearance as a Seyfert 2 is intrinsic and not due to absorption.Comment: 12 pages, to be published in MNRA
- …