195 research outputs found
Radiometric dates of uplifted marine fauna in Greece:Implications for the interpretation of recent earthquake and tectonic histories using lithophagid dates
n AD 365 a great (Mw N 8) earthquake lifted up western Crete, exposing a shoreline encrusted by marine
organisms, and up to 10 m of marine substrate beneath it. Radiocarbon ages determined for corals and
bryozoans exposed between the paleo-shoreline and present sea level are consistent, within measurement
error, with each other and with the date of the earthquake. But radiocarbon ages determined for the boring
bivalve Lithophaga lithophaga found on the same substrate are at least 350 years, and up to 2000 years, older
than the date of the earthquake that lifted them above sea level. These observations reveal two important
effects that limit the use of radiocarbon lithophagid ages in tectonic and paleoseismological studies. The first
is that the exceptional preservation potential of lithophagids allows them to remain intact and in situ long
after natural death, while the substrate continues to be colonised until eventual uplift. The second, which we
confirm with radiocarbon analysis of museum specimens of known age, is the incorporation of old (14C-free)
carbon into lithophagid shells from the limestone host rock into which the lithophagids bored. The two
effects are both significant in Crete and central Greece, and can cause the radiocarbon lithophagid ages to be
up to 2000 years older than the uplift event which exposed them. Understanding these effects is important
because lithophagids are far more abundantly preserved, and used to date uplift, than most other marine
organisms. This study shows that they can rarely be used to distinguish uplift events, or date them to better
than 1000 years, or even to distinguish whether observed uplift occurred in a single or in multiple events.
After taking account of these uncertainties, the ages of the lithophagids are, however, consistent with the
hypothesis that the highest prominent marine notches and exposed lithophagid holes within a few metres of
sea level in Greece formed when sea level became relatively stable ~ 6000 years ago, following rapid rise after
the last glacial maximum
The validity and reliability of the exposure index as a metric for estimating the radiation dose to the patient
Introduction
With the introduction of digital radiography, the feedback between image quality and over-exposure has been partly lost which in some cases has led to a steady increase in dose. Over the years the introduction of exposure index (EI) has been used to resolve this phenomenon referred to as âdose creepâ. Even though EI is often vendor specific it is always a related of the radiation exposure to the detector. Due to the nature of this relationship EI can also be used as a patient dose indicator, however this is not widely investigated in literature.
Methods
A total of 420 dose-area-product (DAP) and EI measurements were taken whilst varying kVp, mAs and body habitus on two different anthropomorphic phantoms (pelvis and chest). Using linear regression, the correlation between EI and DAP were examined. Additionally, two separate region of interest (ROI) placements/per phantom where examined in order to research any effect on EI.
Results
When dividing the data into subsets, a strong correlation between EI and DAP was shown with all R-squared values > 0.987. Comparison between the ROI placements showed a significant difference between EIs for both placements.
Conclusion
This research shows a clear relationship between EI and radiation dose which is dependent on a wide variety of factors such as ROI placement, body habitus. In addition, pathology and manufacturer specific EIâs are likely to be of influence as well.
Implications for practice
The combination of DAP and EI might be used as a patient dose indicator. However, the influencing factors as mentioned in the conclusion should be considered and examined before implementation
Mass Composition of Cosmic Rays in the Range 2 x 10^17 - 3 x 10^18 Measured with Haverah Park Array
At the Haverah Park Array a number of air shower observables were measured
that are relevant to the determination of the mass composition of cosmic rays.
In this paper we discuss measurements of the risetime of signals in large area
water-Cherenkov detectors and of the lateral distribution function of the
water-Cherenkov signal. The former are used to demonstrate that the CORSIKA
code, using the QGSJET98 model, gives an adequate description of the data with
a low sensitivity, in this energy range, to assumptions about primary mass. By
contrast the lateral distribution is sufficiently well measured that there is
mass sensitivity. We argue that in the range 0.2-1.0 EeV the data are well
represented with a bi-modal composition of 34+-2 % protons and the rest iron.
We also discuss the systematic errors induced by the choice of hadronic model.Comment: 16 pages, 13 figures. Accepted for publication in Astroparticle
Physic
Obliquity-driven expansion of North Atlantic sea ice during the last glacial
Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 10,382â10,390, doi:10.1002/2015GL066344.North Atlantic late Pleistocene climate (60,000 to 11,650âyears ago) was characterized by abrupt and extreme millennial duration oscillations known as Dansgaard-Oeschger (D-O) events. However, during the Last Glacial Maximum (LGM) 23,000 to 19,000âcal years ago (23 to 19âka), no D-O events are observed in the Greenland ice cores. Our new analysis of the Greenland ÎŽ18O record reveals a switch in the stability of the climate system around 30âka, suggesting that a critical threshold was passed. Climate system modeling suggests that low axial obliquity at this time caused vastly expanded sea ice in the Labrador Sea, shifting Northern Hemisphere westerly winds south and reducing the strength of meridional overturning circulation. The results suggest that these feedbacks tipped the climate system into full glacial conditions, leading to maximum continental ice growth during the LGM.Australian Research Council2016-06-1
Acute Conjunctivitis with Episcleritis and Anterior Uveitis Linked to Adiaspiromycosis and Freshwater Sponges, Amazon Region, Brazil, 2005
An epidemiologic investigation of an ocular disease outbreak among children was linked to the unusual fungus Emmonsia sp., an agent of adiaspiromycosis
Landscape genomics and biased FST approaches reveal single nucleotide polymorphisms under selection in goat breeds of North-East Mediterranean
<p>Abstract</p> <p>Background</p> <p>In this study we compare outlier loci detected using a <it>F<smcaps>ST </smcaps></it>based method with those identified by a recently described method based on spatial analysis (SAM). We tested a panel of single nucleotide polymorphisms (SNPs) previously genotyped in individuals of goat breeds of southern areas of the Mediterranean basin (Italy, Greece and Albania). We evaluate how the SAM method performs with SNPs, which are increasingly employed due to their high number, low cost and easy of scoring.</p> <p>Results</p> <p>The combined use of the two outlier detection approaches, never tested before using SNP polymorphisms, resulted in the identification of the same three loci involved in milk and meat quality data by using the two methods, while the <it>F<smcaps>ST </smcaps></it>based method identified 3 more loci as under selection sweep in the breeds examined.</p> <p>Conclusion</p> <p>Data appear congruent by using the two methods for <it>F<smcaps>ST </smcaps></it>values exceeding the 99% confidence limits. The methods of <it>F<smcaps>ST </smcaps></it>and SAM can independently detect signatures of selection and therefore can reduce the probability of finding false positives if employed together. The outlier loci identified in this study could indicate adaptive variation in the analysed species, characterized by a large range of climatic conditions in the rearing areas and by a history of intense trade, that implies plasticity in adapting to new environments.</p
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