7,031 research outputs found
Setting goals and choosing appropriate reference sites for restoring mine pit lakes as aquatic ecosystems: Case study from south west Australia
Pit lakes may form when open cut mining leaves a pit void behind that fills with ground and surface water. Often replacing terrestrial ecosystems that existed prior to mining, the pit lake may offer an alternative ecosystem with aquatic biodiversity values that can be realised through planned restoration. Restoration theory and mine closure regulatory requirements guides us toward restoring disturbed systems towards landscapes that are of regional value and relevance. However, how do we identify a restoration target for a novel aquatic habitat that did not exist prior to the new post-mining landscape? This paper presents a process of first identifying and then surveying local analogue aquatic systems to provide a direction for pit lake restoration efforts and achievement criteria for pit lake relinquishment. We illustrate this process using a case study from a sand mining operation located amongst wetlands in south western Australia. The company mines silica sands following mechanical removal of topsoil and then extraction of the ore from below the water table by dredging. Assessment of wetland and riparian vegetation in the surrounding area was completed through the establishment and measurement of temporary monitoring transects across five natural wetlands in the Kemerton area with several more visited and observations made. Distinct zonation of vegetation was found across each wetland, although typically wetland basins were unvegetated or filled with younger woody plants with patchy distributions. Fringing riparian vegetation consisted of few species (commonly Melaleuca rhaphiophylla and Lepidosperma longitudinale) but community composition and structure were variable between wetlands. The pattern of vegetation seen across natural wetlands was best explained by topography and soil chemistry with low lying areas more likely to experience regular flooding and accumulate organic matter and nutrients. We consider that, with good planning, rehabilitation, monitoring and management interventions to achieve a restoration trajectory, these new mining pit lakes can positively contribute to regional ecological values
Shear Modulus of an Elastic Solid under External Pressure as a function of Temperature: The case of Helium
The energy of a dislocation loop in a continuum elastic solid under pressure
is considered within the framework of classical mechanics. For a circular loop,
this is a function with a maximum at pressures that are well within reach of
experimental conditions for solid helium suggesting, in this case, that
dislocation loops can be generated by a pressure-assisted thermally activated
process. It is also pointed out that pinned dislocations segments can alter the
shear response of solid helium, by an amount consistent with current
measurements, without any unpinning.Comment: 5 pages, 3 figure
The optical/near-IR spectral energy distribution of the GRB 000210 host galaxy
We report on UBVRIZJsHKs-band photometry of the dark GRB 000210 host galaxy.
Fitting a grid of spectral templates to its Spectral Energy Distribution (SED),
we derived a photometric redshift (z=0.842\+0.0540.042) which is in excellent
agreement with the spectroscopic one (z=0.8463+/-0.0002; Piro et al. 2002). The
best fit to the SED is obtained with a blue starburst template with an age of
0.181\+0.0370.026 Gyr. We discuss the implications of the inferred low value of
Av and the age of the dominant stellar population for the non detection of the
GRB 000210 optical afterglow.Comment: 4 pages, 1 figure, contribution to the Rome 2002 GRB worksho
First INTEGRAL Observations of Eight Persistent Neutron Star Low Mass X-ray Binaries
Early results from the INTEGRAL Core Program, for a sample of eight
persistently bright neutron star low mass X-ray binaries in the energy range
from 5 keV to 200 keV are presented. It is shown that INTEGRAL efficiently
detects sources and that spectra may be obtained up to several hundreds of keV
by combining data from three of the four INTEGRAL instruments: JEM-X, IBIS and
SPI. For the source GX 17+2 it is shown that the spectrum extends well above
100 keV with a flattening of the spectrum above 30 keV. This might suggest a
non-thermal comptonisation emission, but uncertainties in the current data
reduction and background determination do not allow firm conclusions to be
drawn.Comment: 5 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Cygnus X-3 transition from the ultrasoft to the hard state
Aims: The nature of Cygnus X-3 is still not understood well. This binary
system might host a black hole or a neutron star. Recent observations by
INTEGRAL have shown that Cygnus X-3 was again in an extremely ultrasoft state.
Here we present our analysis of the transition from the ultrasoft state,
dominated by blackbody radiation at soft X-rays plus non-thermal emission in
the hard X-rays, to the low hard state.
Methods: INTEGRAL observed Cyg X-3 six times during three weeks in late May
and early June 2007. Data from IBIS/ISGRI and JEM-X1 were analysed to show the
spectral transition.
Results: During the ultrasoft state, the soft X-ray spectrum is
well-described by an absorbed (NH = 1.5E22 1/cm**2) black body model, whereas
the X-ray spectrum above 20 keV appears to be extremely low and hard (Gamma =
1.7). During the transition, the radio flux rises to a level of >1 Jy, and the
soft X-ray emission drops by a factor of 3, while the hard X-ray emission rises
by a factor of 14 and becomes steeper (up to Gamma = 4).
Conclusions: The ultrasoft state apparently precedes the emission of a jet,
which is apparent in the radio and hard X-ray domain.Comment: 4 pages, 3 figures, accepted for publication as A&A Research Not
k-NN Embedding Stability for word2vec Hyper-Parametrisation in Scientific Text
Word embeddings are increasingly attracting the attention of researchers dealing with semantic similarity and analogy tasks. However, finding the optimal hyper-parameters remains an important challenge due to the resulting impact on the revealed analogies mainly for domain-specific corpora. While analogies are highly used for hypotheses synthesis, it is crucial to optimise word embedding hyper-parameters for precise hypothesis synthesis. Therefore, we propose, in this paper, a methodological approach for tuning word embedding hyper-parameters by using the stability of k-nearest neighbors of word vectors within scientific corpora and more specifically Computer Science corpora with Machine learning adopted as a case study. This approach is tested on a dataset created from NIPS (Conference on Neural Information Processing Systems) publications, and evaluated with a curated ACM hierarchy and Wikipedia Machine Learning outline as the gold standard. Our quantitative and qualitative analysis indicate that our approach not only reliably captures interesting patterns like ``unsupervised_learning is to kmeans as supervised_learning is to knn'', but also captures the analogical hierarchy structure of Machine Learning and consistently outperforms the 61%sate-of-the-art embeddings on syntactic accuracy with 68%
Comment on Vortex Mass and Quantum Tunneling of Vortices
Vortex mass in Fermi superfluids and superconductors and its influence on
quantum tunneling of vortices are discussed. The vortex mass is essentially
enhanced due to the fermion zero modes in the core of the vortex: the bound
states of the Bogoliubov qiasiparticles localized in the core. These bound
states form the normal component which is nonzero even in the low temperature
limit. In the collisionless regime , the normal component
trapped by the vortex is unbound from the normal component in the bulk
superfluid/superconductors and adds to the inertial mass of the moving vortex.
In the d-wave superconductors, the vortex mass has an additional factor
due to the gap nodes.Comment: 10 pages, no figures, version accepted in JETP Letter
Two-phase X-ray burst from GX 3+1 observed by INTEGRAL
INTEGRAL detected on August 31, 2004, an unusual thermonuclear X-ray burst
from the low-mass X-ray binary GX 3+1. Its duration was 30 min, which is
between the normal burst durations for this source (<~10 s) and the superburst
observed in 1998 (several hours). We see emission up to 30 keV energy during
the first few seconds of the burst where the bolometric peak luminosity
approaches the Eddington limit. This peculiar burst is characterized by two
distinct phases: an initial short spike of ~6 s consistent with being similar
to a normal type I X-ray burst, followed by a remarkable extended decay of
cooling emission. We discuss three alternative schemes to explain its twofold
nature: 1) unstable burning of a hydrogen/helium layer involving an unusually
large amount of hydrogen, 2) pure helium ignition at an unusually large depth
(unlikely in the present case), and 3) limited carbon burning at an unusually
shallow depth triggered by unstable helium ignition. Though none of these
provide a satisfactory description of this uncommon event, the former one seems
the most probable.Comment: A&A class LateX file, 5 pages, 4 postscript figures. Accepted in
Astronomy & Astrophysics Letters. One co-author added, modified abstract and
improved conclusion
Poster CS20.5 - Weakened magnetic braking supported by asteroseismic rotation
Studies using asteroseismic ages and rotation rates from star-spot rotation have indicated that standard age-rotation relations may break down roughly half-way through the main sequence lifetime, a phenomenon referred to as weakened magnetic braking. While rotation rates from spots can be difficult to determine for older, less active stars, rotational splitting of asteroseismic oscillation frequencies can provide rotation rates for both active and quiescent stars, and so can confirm whether this effect really takes place on the main sequence. In this talk, I’ll show how we obtained asteroseismic rotation rates of 91 main sequence stars showing high signal-to-noise modes of oscillation. Using these new rotation rates, along with effective temperatures, metallicities and seismic masses and ages, we built a hierarchical Bayesian mixture model that showed that our new ensemble more closely agreed with weakened magnetic braking, over a standard rotational evolution scenario
Integral results on GRB030320: a long gamma-ray burst detected at the edge of the field of view
GRB030320 is the 5th Gamma-ray burst (GRB) detected by INTEGRAL in the field
of view (FoV). It is so far the GRB with the largest off-axis angle with
respect to the INTEGRAL pointing direction, near to the edge of the FoV of both
main instruments, IBIS and SPI. Nevertheless, it was possible to determine its
position and to extract spectra and fluxes. The GRB nature of the event was
confirmed by an IPN triangulation. It is a ~ 60 s long GRB with two prominent
peaks separated by ~ 35 s. The spectral shape of the GRB is best represented by
a single power law with a photon index Gamma ~ 1.7. The peak flux in the 20 -
200 keV band is determined to ~ 5.7 photons cm-2 s-1 and the GRB fluence to 1.1
x 10-5 erg cm-2. Analysing the spectral evolution of the GRB, a
``hard-to-soft'' behaviour emerges. A search for an optical counterpart has
been carried out, but none was found.Comment: 5 pages, 3 figures. Accepted for publication in A&AL (INTEGRAL issue
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