1,896 research outputs found
Microjansky sources at 1.4 GHz
We present a deep 1.4 GHz survey made with the Australia Telescope Compact
Array (ATCA), having a background RMS of 9 microJy near the image phase centre,
up to 25 microJy at the edge of a 50' field of view. Over 770 radio sources
brighter than 45 microJy have been catalogued in the field. The differential
source counts in the deep field provide tentative support for the growing
evidence that the microjansky radio population exhibits significantly higher
clustering than found at higher flux density cutoffs. The optical
identification rate on CCD images is approximately 50% to R=22.5, and the
optical counterparts of the faintest radio sources appear to be mainly single
galaxies close to this optical magnitude limit.Comment: 6 pages, 4 figures, accepted by ApJ Letters 4 May 199
Use of neural networks for the identification of new z>=3.6 QSOs from FIRST-SDSS DR5
We aim to obtain a complete sample of redshift > 3.6 radio QSOs from FIRST
sources having star-like counterparts in the SDSS DR5 photometric survey
(r<=20.2). We found that simple supervised neural networks, trained on sources
with SDSS spectra, and using optical photometry and radio data, are very
effective for identifying high-z QSOs without spectra. The technique yields a
completeness of 96 per cent and an efficiency of 62 per cent. Applying the
trained networks to 4415 sources without DR5 spectra we found 58 z>=3.6 QSO
candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z
QSOs. Spectra of 13 additional candidates from the literature and from SDSS DR6
revealed 7 more z>=3.6 QSOs, giving and overall efficiency of 60 per cent. None
of the non-candidates with spectra from NED or DR6 is a z>=3.6 QSO,
consistently with a high completeness. The initial sample of z>=3.6 QSOs is
increased from 52 to 76, i.e. by a factor 1.46. From the new identifications
and candidates we estimate an incompleteness of SDSS for the spectroscopic
classification of FIRST 3.6<=z<=4.6 QSOs of 15 percent for r<=20.2.Comment: 16 pages, 9 figures accepted for publication in MNRA
Role of the gut microbiota as a natural adjuvant for vaccine
Vaccines have provided the most beneficial contribution to public health. Generating antigen specific antibody responses and long lasting memory are crucial for the protective immunity offered by vaccination. Unfortunately, not all individuals respond in the same manner to vaccine formulations. The microbiota is established during postnatal development and remains relatively stable for long periods. Our understanding that the microbiota can have beneficial effects on human health has led immunologists to investigate how these organisms may shape the innate and adaptive immune responses of the host. In this review we examine the impact of the microbiota on the host immune responses to vaccines and explore the possibility of how the commensal bacteria may act as natural adjuvants to enhance systemic immune responses to vaccines
Impact of astronomical research from different countries
The impact of astronomical research carried out by different countries has
been compared by analysing the 1000 most-cited astronomy papers published
1991-8 (125 from each year). 61% of the citations are to papers with first
authors at institutions in the USA, 11% in the UK, 5% in Germany, 4% in Canada,
3% in Italy and 3% in France. 17% are to papers with first authors in ESO
countries. The number of citations is approximately proportional to the number
of IAU members in a given country. The number of citations per IAU astronomer
is highest in the USA, Switzerland and the UK. Within continental Europe, the
number of citations per IAU astronomer varies little from country to country,
but is slightly higher in the north than in the south. The sample of 1000
papers maps regional subject preferences. 62% of the extragalactic papers in
the sample were published from the USA, 15% from the UK, 23% from other
countries (mainly in continental Europe). 62% of the papers on stars were also
published from the USA, but the fractions from the UK and from other countries
are 2% and 36% respectively.Comment: 6 pages, 3 fig. Accepted for publishing in A
The merging/AGN connection: A case for 3D spectroscopy
We discuss an ongoing study of the connection between galaxy
merging/interaction and AGN activity, based on integral field spectroscopy. We
focus on the search for AGN ionization in the central regions of mergers,
previously not classified as AGNs. We present here the science case, the
current status of the project, and plans for future observations.Comment: 4 pages, 3 figure, Euro3D Science Workshop, Cambridge, May 2003, AN,
accepte
Calving rates at tidewater glaciers vary strongly with ocean temperature
TerraSAR-X data were provided by DLR (project OCE1503), and funded by the Conoco Phillips-Lundin Northern Area Program through the CRIOS project (Calving Rates and Impact on Sea level). A.L. and S.B. are affiliated to the Climate Change Consortium of Wales (C3W). Mooring work is supported by the UK Natural Environment Research Council (Oceans 2025 and Northern Sea Program) and the Research Council of Norway (projects Cleopatra: 178766, Cleopatra II: 216537, and Circa: 214271/F20). Contribution by F.C. was undertaken through the Scottish Alliance for Geoscience Environment and Society (SAGES).Rates of ice mass loss at the calving margins of tidewater glaciers (frontal ablation rates) are a key uncertainty in sea level rise projections. Measurements are difficult because mass lost is replaced by ice flow at variable rates, and frontal ablation incorporates sub-aerial calving, and submarine melt and calving. Here we derive frontal ablation rates for three dynamically contrasting glaciers in Svalbard from an unusually dense series of satellite images. We combine ocean data, ice-front position and terminus velocity to investigate controls on frontal ablation. We find that frontal ablation is not dependent on ice dynamics, nor reduced by glacier surface freeze-up, but varies strongly with sub-surface water temperature. We conclude that calving proceeds by melt undercutting and ice-front collapse, a process that may dominate frontal ablation where submarine melt can outpace ice flow. Our findings illustrate the potential for deriving simple models of tidewater glacier response to oceanographic forcing.Publisher PDFPeer reviewe
Infant mortality in South Africa - distribution, associations and policy implications, 2007: an ecological spatial analysis
<p>Abstract</p> <p>Background</p> <p>Many sub-Saharan countries are confronted with persistently high levels of infant mortality because of the impact of a range of biological and social determinants. In particular, infant mortality has increased in sub-Saharan Africa in recent decades due to the HIV/AIDS epidemic. The geographic distribution of health problems and their relationship to potential risk factors can be invaluable for cost effective intervention planning. The objective of this paper is to determine and map the spatial nature of infant mortality in South Africa at a sub district level in order to inform policy intervention. In particular, the paper identifies and maps high risk clusters of infant mortality, as well as examines the impact of a range of determinants on infant mortality. A Bayesian approach is used to quantify the spatial risk of infant mortality, as well as significant associations (given spatial correlation between neighbouring areas) between infant mortality and a range of determinants. The most attributable determinants in each sub-district are calculated based on a combination of prevalence and model risk factor coefficient estimates. This integrated small area approach can be adapted and applied in other high burden settings to assist intervention planning and targeting.</p> <p>Results</p> <p>Infant mortality remains high in South Africa with seemingly little reduction since previous estimates in the early 2000's. Results showed marked geographical differences in infant mortality risk between provinces as well as within provinces as well as significantly higher risk in specific sub-districts and provinces. A number of determinants were found to have a significant adverse influence on infant mortality at the sub-district level. Following multivariable adjustment increasing maternal mortality, antenatal HIV prevalence, previous sibling mortality and male infant gender remained significantly associated with increased infant mortality risk. Of these antenatal HIV sero-prevalence, previous sibling mortality and maternal mortality were found to be the most attributable respectively.</p> <p>Conclusions</p> <p>This study demonstrates the usefulness of advanced spatial analysis to both quantify excess infant mortality risk at the lowest administrative unit, as well as the use of Bayesian modelling to quantify determinant significance given spatial correlation. The "novel" integration of determinant prevalence at the sub-district and coefficient estimates to estimate attributable fractions further elucidates the "high impact" factors in particular areas and has considerable potential to be applied in other locations. The usefulness of the paper, therefore, not only suggests where to intervene geographically, but also what specific interventions policy makers should prioritize in order to reduce the infant mortality burden in specific administration areas.</p
Classical field theory. Advanced mathematical formulation
In contrast with QFT, classical field theory can be formulated in strict
mathematical terms of fibre bundles, graded manifolds and jet manifolds. Second
Noether theorems provide BRST extension of this classical field theory by means
of ghosts and antifields for the purpose of its quantization.Comment: 30 p
Model Management Systems: Proposed Model Representations and Future Designs
The availability of microcomputers, modeling langauges and general purpose spreadsheets has resulted in an increase in the use of models for decision making within organizatons. Decision makers with microcomputers on their desks and spreadsheet and modeling software can create models rapidly. Problems with model redundancy, consistency, integrity and security have prompted an increased interest in the design of model management systems (MMS). Several model management designs have been discussed in the literature. Different model representation techniques have been proposed. These include formal logic, semantic inheritance networks, frames, and relational representations. The approaches to model management are evaluated in respect to their model manipulation and model storage functions. A framework for the design of MMS is proposed based on the system design objectives and the system domain complexity. Advantages and disadvantages of each model representation method are identified. Application domains for the classifications are proposed which focus on the strengths and weaknesses of the model representation for supporting model storage and model manipulation functions. An example of the design of a MMS using the classification is presented
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