2,456 research outputs found
Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland
This is the final version of the article. Available from Springer Verlag via the DOI in this record.Two occurrences of platinum-group elements (PGEs) along the northern margin of the Skaergaard intrusion include a sulfide-bearing gabbro with slightly less than 1 ppm PGE + Au and a clinopyroxene-actinolite-plagioclase-biotite-ilmenite schist with 16 vol% sulfide and 1.8 ppm PGE + Au. Both have assemblages of pyrrhotite, pentlandite, and chalcopyrite typical for orthomagmatic sulfides. Matching platinum-group mineral assemblages with sperrylite (PtAs2), kotulskite (Pd(Bi,Te)1â2), froodite (PdBi2), michenerite (PdBiTe), and electrum (Au,Ag) suggest a common origin. Petrological and geochemical similarities suggest that the occurrences are related to the Skaergaard intrusion. The Marginal Border Series locally displays Ni depletion consistent with sulfide fractionation, and the PGE fractionation trends of the occurrences are systematically enriched by 10â50 times over the chilled margin. The PGE can be explained by sulfide-silicate immiscibility in the Skaergaard magma with R factors of 110â220. Nickel depletion in olivine suggests that the process occurred within the host cumulate, and the low R factors require little sulfide mobility. The sulfide assemblages are different to the chalcopyrite-bornite-digenite assemblage found in the Skaergaard Layered Series and Platinova Reef. These differences can be explained by the early formation of sulfide melt, while magmatic differentiation or sulfur loss caused the unusual sulfide assemblage within the Layered Series. The PGEs indicate that the sulfides formed from the Skaergaard magma. The sulfides and PGEs could not have formed from the nearby Watkins Fjord wehrlite intrusion, which is nearly barren in sulfide. We suggest that silicate-sulfide immiscibility led to PGE concentration where the Skaergaard magma became contaminated with material from the Archean basement.The authors are grateful for logistical support from Platina Resources Ltd., Geological Survey of Denmark and Greenland, and members of the 2011 Skaergaard field team. JCĂA was supported by grants from Helford Geoscience LLP and the Camborne School of Mines Trust. CT was supported by the Danish Natural Research Council and the Carlsberg Foundation, and CEL was supported by the US National Science Foundation (EAR-1019887). Samples were sectioned and prepared by Steve Pendray at Camborne School of Mines. The QEMSCAN is a registered trade mark of FEI Corporation
Recommended from our members
GABAergic neurons comprise a major cell type in rodent visual relay nuclei: an immunocytochemical study of pretectal and accessory optic nuclei.
The enzyme glutamic acid decarboxylase (GAD) has been localized in sections of rodent brains (gerbil, rat) using conventional immunocytochemical techniques. Our findings demonstrate that large numbers of GAD-positive neurons and axon terminals (puncta) are present in the visual relay nuclei of the pretectum and the accessory optic system. The areas of highest density of these neurons are in the nucleus of the optic tract (NOT) of the pretectum, the dorsal and lateral terminal accessory optic nuclei (DTN, LTN), the ventral and dorsal subdivisions of the medial terminal accessory optic nucleus (MTNv, MTNd), and the interstitial nucleus of the posterior fibers of the superior fasciculus (inSFp). The findings indicate that 27% of the NOT neurons are GAD-positive and that these neurons are distributed over all of the NOT except the most superficial portion of the NOT caudally. The GAD-positive neurons of the NOT are statistically smaller (65.9 microns2) than the total population of neurons of the NOT (84.3 microns2) but are otherwise indistinguishable in shape from the total neuron population. The other visual relay nuclei that have been analyzed (DTN, LTN, MTNv, MTNd, inSFp) are similar in that from 21% to 31% of their neurons are GAD-positive; these neurons are smaller in diameter and are more spherical than the total populations of neurons. The data further show that a large proportion of the neurons in these visual relay nuclei are contacted by GAD-positive axon terminals. It is estimated that approximately one-half of the neurons of the NOT and the terminal accessory optic nuclei receive a strong GABAergic input and have been called "GAD-recipient neurons". Further, the morphology of the GAD-positive neurons combined with their similar distribution to the GAD-recipient neurons suggest that many of these neurons are acting as GABAergic, local circuit neurons. On the other hand, the large number of GAD-positive neurons in the NOT and MTN (20-30%) in relation to estimates of projection neurons (75%) presents the possibility that some may in fact be projection neurons. The overall findings provide morphological evidence which supports the general conclusion that GABAergic neurons play a significant role in modulating the output of the visually related NOT and terminal accessory optic nuclei
Determinants of Perinatal Outcomes in Dialyzed and Transplanted Women in Australia.
Introduction: Drivers of adverse perinatal outcomes in pregnancies of women receiving chronic kidney replacement therapy (KRT) remain poorly understood. Methods: Births ℠20 weeks of gestation in Australian women receiving KRT were analyzed for perinatal outcomes stratified by maternal KRT exposure (dialysis or transplant, analyzed separately), by linking the Australia and New Zealand Dialysis and Transplant Registry (ANZDATA) and perinatal data sets (1991-2013). Results: Of 2,948,084 babies (1,628,181 mothers), 248 were born to mothers receiving KRT (transplant, n = 211; dialysis, n = 37), with live birth rates ℠94%. The perinatal death rate was 162, 62, and 9 per 1000 births in the dialysis, transplant, and non-KRT cohorts, respectively. Babies exposed to KRT had increased odds of prematurity, small-for-gestational age (SGA), poor birth condition, resuscitation, intensive care admission, and longer hospitalization, with the dialysis cohort having worse outcomes. Preterm babies of dialyzed and transplanted mothers (compared with preterm babies with no KRT exposure) experienced 1.6- to 2.7-fold higher odds for all adverse outcomes, except birthweight 10-fold higher odds of preterm birth and low birthweight and 1.8- to 4.6-fold increased odds of other adverse outcomes. In transplanted women, mediation analysis revealed that pregnancy-induced hypertension contributed only a modest proportional effect (2.5%-11.2%) on adverse outcomes. Conclusion: Maternal dialysis and transplantation conferred excess perinatal morbidity, particularly for preterm babies, and even in women with good preconception allograft function. Pregnancy-induced hypertension is not the predominant determinant of perinatal morbidity. Preconception counseling of women with kidney disease should encompass discussion of perinatal complications
Parenthood and pregnancy in Australians receiving treatment for end-stage kidney disease: protocol of a national study of perinatal and parental outcomes through population record linkage.
INTRODUCTION:Achieving parenthood is challenging in individuals receiving renal replacement therapy (RRT; dialysis or kidney transplantation) for end-stage kidney disease. Decision-making regarding parenthood in RRT recipients should be underpinned by robust data, yet there is limited data on parental factors that drive adverse health outcomes. Therefore, we aim to investigate the perinatal risks and outcomes in parents receiving RRT. METHODS AND ANALYSIS:This is a multijurisdictional probabilistic data linkage study of perinatal, hospital, birth, death and renal registers from 1991 to 2013 from New South Wales, Western Australia, South Australia and the Australian Capital Territory. This study includes all babies born â„20 weeks' gestation or 400 g birth weight captured through mandated data collection in the perinatal data sets. Through linkage with the Australian and New Zealand Dialysis and Transplant (ANZDATA) registry, babies exposed to RRT (and their parents) will be compared with babies who have not been exposed to RRT (and their parents) to determine obstetric and fetal outcomes, birth rates and fertility rates. One of the novel aspects of this study is the method that will be used to link fathers receiving RRT to the mothers and their babies within the perinatal data sets, using the birth register, enabling the identification of family units. The linked data set will be used to validate the parenthood events directly reported to ANZDATA. ETHICS AND DISSEMINATION:Ethics approval was obtained from Human Research Ethics Committees (HREC) and Aboriginal HREC in each jurisdiction. Findings of this study will be disseminated at scientific conferences and in peer-reviewed journals in tabular and aggregated forms. De-identified data will be presented and individual patients will not be identified. We will aim to present findings to relevant stakeholders (eg, patients, clinicians and policymakers) to maximise translational impact of research findings
The singlet scalar as FIMP dark matter
The singlet scalar model is a minimal extension of the Standard Model that
can explain the dark matter. We point out that in this model the dark matter
constraint can be satisfied not only in the already considered WIMP regime but
also, for much smaller couplings, in the Feebly Interacting Massive Particle
(FIMP) regime. In it, dark matter particles are slowly produced in the early
Universe but are never abundant enough to reach thermal equilibrium or
annihilate among themselves. This alternative framework is as simple and
predictive as the WIMP scenario but it gives rise to a completely different
dark matter phenomenology. After reviewing the calculation of the dark matter
relic density in the FIMP regime, we study in detail the evolution of the dark
matter abundance in the early Universe and the predicted relic density as a
function of the parameters of the model. A new dark matter compatible region of
the singlet model is identified, featuring couplings of order 10^-11 to 10^-12
for singlet masses in the GeV to TeV range. As a consequence, no signals at
direct or indirect detection experiments are expected. The relevance of this
new viable region for the correct interpretation of recent experimental bounds
is emphasized.Comment: 12 pages, 6 figure
Elementary processes governing the evolution of road networks
Urbanisation is a fundamental phenomenon whose quantitative characterisation
is still inadequate. We report here the empirical analysis of a unique data set
regarding almost 200 years of evolution of the road network in a large area
located north of Milan (Italy). We find that urbanisation is characterised by
the homogenisation of cell shapes, and by the stability throughout time of
high-centrality roads which constitute the backbone of the urban structure,
confirming the importance of historical paths. We show quantitatively that the
growth of the network is governed by two elementary processes: (i)
`densification', corresponding to an increase in the local density of roads
around existing urban centres and (ii) `exploration', whereby new roads trigger
the spatial evolution of the urbanisation front. The empirical identification
of such simple elementary mechanisms suggests the existence of general, simple
properties of urbanisation and opens new directions for its modelling and
quantitative description.Comment: 10 pages, 6 figure
Multi-Scalar-Singlet Extension of the Standard Model - the Case for Dark Matter and an Invisible Higgs Boson
We consider a simple extension of the Standard Model by the addition of N
real scalar gauge singlets \vp that are candidates for Dark Matter. By
collecting theoretical and experimental constraints we determine the space of
allowed parameters of the model. The possibility of ameliorating the little
hierarchy problem within the multi-singlet model is discussed. The
Spergel-Steinhardt solution of the Dark Matter density cusp problem is
revisited. It is shown that fitting the recent CRESST-II data for Dark Matter
nucleus scattering implies that the standard Higgs boson decays predominantly
into pairs of Dark Matter scalars. It that case discovery of the Higgs boson at
LHC and Tevatron is impossible. The most likely mass of the dark scalars is in
the range 15 GeV \lsim \mvp \lsim 50 GeV with BR(h \to \vp\vp) up to 96%.Comment: 18 pages, 15 figure
A neurogenetic model for the study of schizophrenia spectrum disorders: The International 22q11.2 Deletion Syndrome Brain Behavior Consortium
Rare copy number variants contribute significantly to the risk for schizophrenia, with the
22q11.2 locus consistently implicated. Individuals with the 22q11.2 deletion syndrome
(22q11DS) have an estimated 25-fold increased risk for schizophrenia spectrum disorders,
compared to individuals in the general population. The International 22q11DS Brain Behavior
Consortium is examining this highly informative neurogenetic syndrome phenotypically and
genomically. Here we detail the procedures of the effort to characterize the neuropsychiatric and
neurobehavioral phenotypes associated with 22q11DS, focusing on schizophrenia and
subthreshold expression of psychosis. The genomic approach includes a combination of whole
genome sequencing and genome-wide microarray technologies, allowing the investigation of all
possible DNA variation and gene pathways influencing the schizophrenia-relevant phenotypic
expression. A phenotypically rich data set provides a psychiatrically well-characterized sample
of unprecedented size (n=1,616) that informs the neurobehavioral developmental course of
22q11DS. This combined set of phenotypic and genomic data will enable hypothesis testing to
elucidate the mechanisms underlying the pathogenesis of schizophrenia spectrum disorders
Building development and roads: implications for the distribution of stone curlews across the Brecks
Background: Substantial new housing and infrastructure development planned within England has the potential to conflict with the nature conservation interests of protected sites. The Breckland area of eastern England (the Brecks) is designated as a Special Protection Area for a number of bird species, including the stone curlew (for which it holds more than 60% of the UK total population). We explore the effect of buildings and roads on the spatial distribution of stone curlew nests across the Brecks in order to inform strategic development plans to avoid adverse effects on such European protected sites. Methodology: Using data across all years (and subsets of years) over the period 1988 â 2006 but restricted to habitat areas of arable land with suitable soils, we assessed nest density in relation to the distances to nearest settlements and to major roads. Measures of the local density of nearby buildings, roads and traffic levels were assessed using normal kernel distance-weighting functions. Quasi-Poisson generalised linear mixed models allowing for spatial auto-correlation were fitted. Results: Significantly lower densities of stone curlew nests were found at distances up to 1500m from settlements, and distances up to 1000m or more from major (trunk) roads. The best fitting models involved optimally distance-weighted variables for the extent of nearby buildings and the trunk road traffic levels. Significance : The results and predictions from this study of past data suggests there is cause for concern that future housing development and associated road infrastructure within the Breckland area could have negative impacts on the nesting stone curlew population. Given the strict legal protection afforded to the SPA the planning and conservation bodies have subsequently agreed precautionary restrictions on building development within the distances identified and used the modelling predictions to agree mitigation measures for proposed trunk road developments
Secluded Dark Matter Coupled to a Hidden CFT
Models of secluded dark matter offer a variant on the standard WIMP picture
and can modify our expectations for hidden sector phenomenology and detection.
In this work we extend a minimal model of secluded dark matter, comprised of a
U(1)'-charged dark matter candidate, to include a confining hidden-sector CFT.
This provides a technically natural explanation for the hierarchically small
mediator-scale, with hidden-sector confinement generating m_{gamma'}>0.
Furthermore, the thermal history of the universe can differ markedly from the
WIMP picture due to (i) new annihilation channels, (ii) a (potentially) large
number of hidden-sector degrees of freedom, and (iii) a hidden-sector phase
transition at temperatures T << M_{dm} after freeze out. The mediator allows
both the dark matter and the Standard Model to communicate with the CFT, thus
modifying the low-energy phenomenology and cosmic-ray signals from the secluded
sector.Comment: ~50p, 8 figs; v2 JHEP versio
- âŠ