3,064 research outputs found
A survey of stellar X-ray flares from the XMM-Newton serendipitous source catalogue: Hipparcos-Tycho cool stars
The X-ray emission from flares on cool (i.e. spectral-type F-M) stars is
indicative of very energetic, transient phenomena, associated with energy
release via magnetic reconnection. We present a uniform, large-scale survey of
X-ray flare emission. The XMM-Newton Serendipitous Source Catalogue and its
associated data products provide an excellent basis for a comprehensive and
sensitive survey of stellar flares - both from targeted active stars and from
those observed serendipitously in the half-degree diameter field-of-view of
each observation. The 2XMM Catalogue and the associated time-series
(`light-curve') data products have been used as the basis for a survey of X-ray
flares from cool stars in the Hipparcos Tycho-2 catalogue. In addition, we have
generated and analysed spectrally-resolved (i.e. hardness-ratio), X-ray
light-curves. Where available, we have compared XMM OM UV/optical data with the
X-ray light-curves. Our sample contains ~130 flares with well-observed
profiles; they originate from ~70 stars. The flares range in duration from ~1e3
to ~1e4 s, have peak X-ray fluxes from ~1e-13 to ~1e-11 erg/cm2/s, peak X-ray
luminosities from ~1e29 to ~1e32 erg/s, and X-ray energy output from ~1e32 to
~1e35 erg. Most of the ~30 serendipitously-observed stars have little
previously reported information. The hardness-ratio plots clearly illustrate
the spectral (and hence inferred temperature) variations characteristic of many
flares, and provide an easily accessible overview of the data. We present flare
frequency distributions from both target and serendipitous observations. The
latter provide an unbiased (with respect to stellar activity) study of flare
energetics; in addition, they allow us to predict numbers of stellar flares
that may be detected in future X-ray wide-field surveys. The serendipitous
sample demonstrates the need for care when calculating flaring rates.Comment: 26 pages, 24 figures. Additional tables and figures available as 4
ancillary files. To be published in Astronomy and Astrophysic
Combination of gastric atrophy, reflux symptoms and histological subtype indicates two distinct aetiologies of gatric cardia cancer.
<b>INTRODUCTION</b>
Atrophic gastritis is a risk factor for non-cardia gastric cancer, and gastro-oesophageal reflux
disease (GORD) for oesophageal adenocarcinoma. The role of atrophic gastritis and GORD in the
aetiology of adenocarcinoma of the cardia remains unclear. We have investigated the association
between adenocarcinoma of the different regions of the upper gastrointestinal tract and atrophic
gastritis and GORD symptoms.
<b>METHODS</b>
138 patients with upper GI adenocarcinoma and age and sex matched controls were studied.
Serum pepsinogen I/II was used as a marker of atrophic gastritis and categorised to five quintiles.
History of GORD symptoms, smoking and H.pylori infection was incorporated in logistic regression
analysis. Lauren classification of gastric cancer was used to subtype gastric and oesophageal
adenocarcinoma.
<b>RESULTS</b>
Non-cardia cancer was associated with atrophic gastritis but not with GORD symptoms; 55% of
these cancers were intestinal subtype. Oesophageal adenocarcinoma was associated with GORD
symptoms, but not with atrophic gastritis; 84% were intestinal subtype. Cardia cancer was positively
associated with both severe gastric atrophy [OR, 95% CI: 3.92 (1.77 – 8.67)] and with frequent
GORD symptoms [OR, 95% CI: 10.08 (2.29 – 44.36)] though the latter was only apparent in the nonatrophic
subgroup and in the intestinal subtype. The association of cardia cancer with atrophy was
stronger for the diffuse versus intestinal subtype and this was the converse of the association
observed with non-cardia cancer.
<b>CONCLUSION</b>
These findings indicate two distinct aetiologies of cardia cancer, one arising from severe atrophic
gastritis and being of intestinal or diffuse subtype similar to non-cardia cancer, and one related to
GORD and intestinal in subtype, similar to oesophageal adenocarcinoma. Gastric atrophy, GORD
symptoms and histological subtype may distinguish between gastric versus oesophageal origin of
cardia cancer
Dynamic variation of supernatant quality in a dairy shed waste stabilisation pond system
An intensive monitoring program of a standard two-stage dairy shed waste stabilisation pond system was undertaken to determine the incidence and extent of spatial and temporal variation of basic physio-chemical parameters, and to shed light on the longer term dynamic nature of in-pond conditions. The anaerobicâfacultative pond system, located in a remote rural area, treats wastewater from the hosing down and hydraulic flushing of the milking parlour and holding yard at the farm dairy shed. A number of multi-parameter water quality field monitoring probes were permanently deployed at various locations within the two ponds to enable continuous measurement of temperature, pH, conductivity and dissolved oxygen. In addition, profiling of the supernatant of both ponds was undertaken at different times of the year to examine vertical variation of the same parameters. Continuous monitoring revealed spatial homogeneity in EC and pH levels in the upper metre of both ponds. Physio-chemical parameters also appear to change uniformly across the ponds in response to external stimuli such as rainfall. Neither pond, however, exhibits homogeneity down the profile of the supernatant. Seasonal stratification is prevalent in the facultative pond suggesting poor vertical mixing, while the anaerobic pond is notably affected by sludge accumulation. A long-term pattern of rising conductivity in both ponds indicated accumulation of dissolved salt species in the system due to recirculation of reclaimed effluent for hydraulic flushing of the dairy shed. In the facultative pond, diurnal fluctuations in dissolved oxygen, oxidation-reduction potential and turbidity during warmer months of the year closely followed temperature swings. The extensive data collected in this study provides a detailed picture of the physio-chemical dynamics of two-stage stabilisation pond systems treating dairy shed wastewater
The effect of temperature and strain rate on the tensile properties of some new textile yarns
The tensile properties of some new textile yarns have been studied with particular reference to the effect of temperature and rate of strain application on the stress-strain behaviour. The work has been split into two parts covering different types of material. In part 1, an Instron tensile tester was used to investigate the effect of strain rate and temperature on the stress-strain properties of two samples of polypropylene yarn. Differences in behaviour occurring between the samples were explained by measurements 6f structural properties such as isotactic index and average .molecular weight. Results were compared with data from the literature on an isotactic polypropylene yam. The method of reduced variables has been used to apply time- temperature superposition and obtain composite curves reduced to a standard reference temperature. This was done for the ultimate stress and strain values and values of stress at lower strains expressed as the tensile modulus. A similar superposition was obtained from stress relaxation data. In part 2, five samples of synthetic poly-urethane elastomeric yarns and one sample of natural rubber yarn have been studied under different conditions. The stress-strain curve, toughness, Schwartz value, elastic recovery and stress relaxation properties have been measured and compared. The stress-strain curve of one of the synthetic yams was studied at different temperatures and initial strain rates. Unlike polypropylene, the same superposition could not be applied to all the data in this case. The equivalence of changes in time and temperature alters with increasing strain as the molecular orientation alters. Yarns of completely different structure have been studied and it has been shown that time-temperature superposition can be applied, in a restricted form, to a non-linear semi-crystalline material. It is therefore possible to obtain data necessary to characterise the behaviour of a material over several decades of logarithmic time using a single instrument of a type used in normal tensile testing procedure
Plural policing in Europe:relationships and governance in contemporary security system
References to ‘plural policing’, ‘policing beyond the police’ and the ‘extended policing family’ are now commonplace in many discussions of policing in late modern societies. There is a danger that claims about the dynamic and changing nature of plural policing themselves become a new orthodoxy and begin to lose a sense of local nuance and recognition of the importance of place-based specificity and context in understanding the particularities of policing. It is this need to unpack the complex ways in which contemporary plural policing is now configured at a local level within different national political environments that provides the underpinning rationale for this Special Issue. Focussing on aspects of relationships and governance in six jurisdictions across northern and western Europe, it provides important insights into how the policies, practices and narratives around plural policing reflect the influence of particular histories and geographies. The first three articles are focused primarily on the relationships which have emerged in the public sector through its own processes of pluralisation, in particular, through the introduction of policing auxiliaries or municipal policing in Scotland, England and The Netherlands. The fourth article considers both relationships and governance in pluralised policing in Paris, France. A detailed analysis of the governance of safety and security is taken up in the final two articles, examining the cases of Austria and Belgium. These articles clearly demonstrate that experiences of pluralised policing vary widely within Europe and call into question the assumed dominance of neo-liberal forces in this area
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