734 research outputs found
The BMW Deep X-ray Cluster Survey
We briefly describe the main features of the Brera Multi-Wavelet (BMW) survey
of serendipitous X-ray clusters, based on the still unexploited ROSAT-HRI
archival observations. Cluster candidates are selected from the general BMW
catalogue of 20,000 sources based exclusively on their X-ray extension.
Contrary to common wisdom, a clever selection of the HRI energy channels allows
us to significantly reduce the background noise, thus greatly improving the
ability to detect low surface-brightness sources as clusters. The resulting
sample of ~250 candidates shows a very good sky coverage down to a flux
\~3x10^-14 erg/s/cm^2 ([0.5-2.0] keV band), i.e comparable to existing
PSPC-based deep survey, with a particularly interesting area of ~100 sq.deg.
around fluxes ~10^-13 erg/s/cm^2, i.e. where highly-luminous, rare systems at
z~0.6-1 can be detected. At the same time, the superior angular resolution of
the instrument should avoid biases against intrinsically small systems, while
easing the identification process (e.g. by spotting blends and AGN
contaminants). While about 20% of the candidates are already identified with
groups/clusters at z<0.3 on the DSS2 images, we have started a deep CCD imaging
campaign to observe all sources associated to "blank fields". First results
from these observations reveal a distant (z>0.5) bonafide cluster counterpart
for ~80% of the targets.Comment: 3 pages, 2 figures; to appear in Proc. of the ESO/ECF/STSCI workshop
on "Deep Fields", Garching Oct 2000, (Publ: Springer
Web-based randomised controlled trials in orthodontics
Randomised controlled trials (RCT) are considered the best source of scientific evidence--the gold standard--when evaluating the efficacy of orthodontic treatments. Frequently, RCT are planned as multicentre trials, with the intention of increasing statistical power and raising the precision of outcome estimates. The management of large-scale RCT, however, requires even more thorough organisation than conventional RCT. Indeed, the need for high accuracy and standardisation in data collection, research aids, secretarial skills, staff and patient training, and organisational meetings, make these studies time-consuming, expensive and, in general, relatively complex to carry out well. A website was developed to support a large scale-orthodontic RCT which aimed to evaluate the efficacy of a functional appliance(www.ortodonzia.unina.it). Websites such as this can increase the quality of data collection, simplify the randomisation process, speed up data collection, and improve trial monitoring. Web-based RCT have the potential to help globalise orthodontic research and also increase our rate of acquisition of evidence in orthodontics
On the influence of the mean-free-path parameter on intranuclear cascade calculations
In a recent letter GINOCCHIO and BLANN (2) compared results of intranuclear cascade model (ICM) calculations obtained either with a nucleon mean-free-path (mfp) in nuclear matter corresponding to free 3~-2C scattering cross-sections, or with a four times longer mfp. The latter assumption was reported to give far poorer agreement with the experimental data; and this conclusion was reported as evidence in favour of the use of the shorter mfp values in pre-equilibrium decay models, whose alternate formulations have been lately discussed at some length (2.6). We maintain tha t ICI~[ calculations performed with the free ~ ~ scatter mfp in general do not afford an accurate reproduction of the excitation functions of reactions induced by protons of some tens of MeV, and of the energy integrated spectra of the emitted particles. In fact, published results of ICM calculations have shown a systematic tendency to underestimate the emission of high-energy particles, and to overestimate compound-nucleus production. We made this statement, which agrees with an opinion already expressed by MILLER (D, on the basis of the findings of several works cited in ref. (2). Our belief is further supported by other results of BERTINI et al. (S) (e l . Specifically fig. 4 thereof), and even by the figures reported by the authors of ref. (1). However, in spite of such inadequacies of the ICM calculations, the model seems to retain a good measure of appeal as an intui t ive tool much in use for practical purposes
The 0.1-200 keV spectrum of the blazar PKS 2005-489 during an active state
The bright BL Lac object PKS 2005-489 was observed by BeppoSAX on November
1-2, 1998, following an active X-ray state detected by RossiXTE. The source,
detected between 0.1 and 200 keV, was in a very high state with a continuum
well fitted by a steepening spectrum due to synchrotron emission only. Our
X-ray spectrum is the flattest ever observed for this source. The different
X-ray spectral slopes and fluxes, as measured by various satellites, are
consistent with relatively little changes of the peak frequency of the
synchrotron emission, always located below 10^{17} Hz. We discuss these results
in the framework of synchrotron self-Compton models. We found that for the
BeppoSAX observation, the synchrotron peak frequency is between 10^{15} and
2.5x10^{16} Hz, depending on the model assumptions.Comment: 7 pages, 4 figures, accepted for publication in A&
Liquefied natural gas for the UK: a life cycle assessment
PURPOSE: Liquefied natural gas (LNG) is expected to become an important component of the UK’s energy supply because the national hydrocarbon reserves on the continental shelf have started diminishing. However, use of any carbon-based fuel runs counter to mitigation of greenhouse gas emissions (GHGs). Hence, a broad environmental assessment to analyse the import of LNG to the UK is required.
METHODS: A cradle to gate life cycle assessment has been carried out of a specific but representative case: LNG imported to the UK from Qatar. The analysis covers the supply chain, from gas extraction through to distribution to the end-user, assuming state-of-the-art facilities and ships. A sensitivity analysis was also conducted on key parameters including the energy requirements of the liquefaction and vaporisation processes, fuel for propulsion, shipping distance, tanker volume and composition of raw gas.
RESULTS AND DISCUSSION: All environmental indicators of the CML methodology were analysed. The processes of liquefaction, LNG transport and evaporation determine more than 50% of the cradle to gate global warming potential (GWP). When 1% of the total gas delivered is vented as methane emissions leakage throughout the supply chain, the GWP increases by 15% compared to the GWP of the base scenario. The variation of the GWP increases to 78% compared to the base scenario when 5% of the delivered gas is considered to be lost as vented emissions. For all the scenarios analysed, more than 75% of the total acidification potential (AP) is due to the sweetening of the natural gas before liquefaction. Direct emissions from transport always determine between 25 and 49% of the total eutrophication potential (EP) whereas the operation and maintenance of the sending ports strongly influences the fresh water aquatic ecotoxicity potential (FAETP).
CONCLUSIONS: The study highlights long-distance transport of LNG and natural gas processing, including sweetening, liquefaction and vaporisation, as the key operations that strongly affect the life cycle impacts. Those cannot be considered negligible when the environmental burdens of the LNG supply chain are considered. Furthermore, the effect of possible fugitive methane emissions along the supply chain are critical for the impact of operations such as extraction, liquefaction, storage before transport, transport itself and evaporation
The resolved fraction of the Cosmic X-ray Background
We present the X-ray source number counts in two energy bands (0.5-2 and 2-10
keV) from a very large source sample: we combine data of six different surveys,
both shallow wide field and deep pencil beam, performed with three different
satellites (ROSAT, Chandra and XMM-Newton). The sample covers with good
statistics the largest possible flux range so far: [2.4*10^-17 - 10^-11] cgs in
the soft band and [2.1*10^-16 - 8*10^{-12}]cgs in the hard band. Integrating
the flux distributions over this range and taking into account the (small)
contribution of the brightest sources we derive the flux density generated by
discrete sources in both bands. After a critical review of the literature
values of the total Cosmic X--Ray Background (CXB) we conclude that, with the
present data, the 94.3%, and 88.8% of the soft and hard CXB can be ascribed to
discrete source emission. If we extrapolate the analytical form of the Log
N--Log S distribution beyond the flux limit of our catalog in the soft band we
find that the flux from discrete sources at ~3*10^-18 cgs is consistent with
the entire CXB, whereas in the hard band it accounts for only 93% of the total
CXB at most, hinting for a faint and obscured population to arise at even
fainter fluxes.Comment: Accepted for publication in Ap
HPC-REDItools: A novel HPC-aware tool for improved large scale RNA-editing analysis
Background: RNA editing is a widespread co-/post-transcriptional mechanism that alters primary RNA sequences through the modification of specific nucleotides and it can increase both the transcriptome and proteome diversity. The automatic detection of RNA-editing from RNA-seq data is computational intensive and limited to small data sets, thus preventing a reliable genome-wide characterisation of such process. Results: In this work we introduce HPC-REDItools, an upgraded tool for accurate RNA-editing events discovery from large dataset repositories. Availability: https://github.com/BioinfoUNIBA/REDItools2. Conclusions: HPC-REDItools is dramatically faster than the previous version, REDItools, enabling big-data analysis by means of a MPI-based implementation and scaling almost linearly with the number of available cores
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