Picrites from Nuussuaq Peninsula and Qeqertarssuaq (Disko) Island, West Greenland, preserve trace element and isotopic signatures reflecting the composition of the Icelandic plume head. Os isotope ...ratios are low (187Os/188Os(i)=0.1272–0.1371) in terms of global plume related magmatism, and this is coupled with anomalously high Os abundances and radiogenic 143Nd/144Nd(i) isotopes. Crustally contaminated basalts within the West Greenland sequences possess Os and Nd isotopic signatures consistent with mixing between initial plume head compositions and two discrete types of West Greenland continental crust. One crustal component is of a local sedimentary origin, and the other is typical of ancient felsic crust. The low Os isotopic signatures of the picritic units are considered to be those of the initial mantle plume. The fact that such low Os isotope ratios occur in sequences with high 3He/4He, and the non-systematic variation in Os isotopes with indices of fractionation/accumulation and Pb isotopes, argue against mixing with depleted MORB mantle or ancient subcontinental lithospheric mantle. The high Os concentrations in the picrites are attributed to high degrees of partial melting (>25%) of mantle containing no residual sulphide. This is consistent with models for plume heads in which anomalous mantle temperatures initiate melting at high pressures generating large degrees of partial melting. Unradiogenic Os and radiogenic Nd components in plume-related CFB magmatism may preserve contributions from a reservoir which is sampled only occasionally in young oceanic basalts. Such a reservoir shares Os isotopic features with the primitive upper mantle (PUM), which may also be manifest in the ‘Kea’ component of Hawaiian magmatism. Therefore, portions of the West Greenland continental flood basalt province arguably represent the first direct sampling of unmodified plume head material derived from the lower mantle or lower portions of the upper mantle.
'Deliberative democracy' is often dismissed as a set of small-scale, academic experiments. This volume seeks to demonstrate how the deliberative ideal can work as a theory of democracy on a larger ...scale. It provides a new way of thinking about democratic engagement across the spectrum of political action, from towns and villages to nation states, and from local networks to transnational, even global systems. Written by a team of the world's leading deliberative theorists, Deliberative Systems explains the principles of this new approach, which seeks ways of ensuring that a division of deliberative labour in a system nonetheless meets both deliberative and democratic norms. Rather than simply elaborating the theory, the contributors examine the problems of implementation in a real world of competing norms, competing institutions and competing powerful interests. This pioneering book will inspire an exciting new phase of deliberative research, both theoretical and empirical.
The Lherz peridotite massif, in the French Pyrenees, is intruded by a number of hornblendite and garnet-amphibole-pyroxenite (GAP) veins. New, high quality, elemental and isotopic data are presented ...for veins and their adjacent harzburgite wallrocks in order to evaluate the extent of reaction and the ability of fluids to permeate clinopyroxene-poor peridotites.
Hornblendite and GAP veins have convex upward rare earth element (REE) profiles consistent with an origin as crystal segregates from alkali basalts. In all of the traverses Mg# increases away from the veins and MnO, TiO
2, Zr, and the REE decrease away from the veins within a zone < 50 cm from the veins. Calculated melts in equilibrium with hornblendite veins have strong LREE enrichment similar to many alkali basalts. Metasomatism adjacent to these veins is consistent with small-scale outward movement of alkali basalt, equilibration with wallrock minerals and precipitation of amphibole and phlogopite. Increase in
Ce
Sm
ratios and decrease in Ce contents away from the veins is consistent with equilibration of the calculated melt from the vein with the preexisting harzburgites. A region with high
Ce
Sm
on the right of one vein may be the result of chromatographic fractionation of melt during percolation from the amphibole-bearing veins. However, this is not observed on the opposite side of the vein and ratios are variable within the zone, so an asymmetrical and irregular chromatographic front would be required. The high
Ce
Sm
ratios, therefore, most likely reflect pre-vein REE heterogeneity in the harzburgites.
Data for the Lherz massif suggest that dramatic variations in incompatible element concentrations can develop metasomatically in the continental lithospheric mantle over a relatively short length scale.
The High Altitude Water Cherenkov (HAWC) gamma-ray observatory observes atmospheric showers produced by incident gamma rays and cosmic rays with energy from 300 GeV to more than 100 TeV. A crucial ...phase in analyzing gamma-ray sources using ground-based gamma-ray detectors like HAWC is to identify the showers produced by gamma rays or hadrons. The HAWC observatory records roughly 25,000 events per second, with hadrons representing the vast majority (\(>99.9\%\)) of these events. The standard gamma/hadron separation technique in HAWC uses a simple rectangular cut involving only two parameters. This work describes the implementation of more sophisticated gamma/hadron separation techniques, via machine learning methods (boosted decision trees and neural networks), and summarizes the resulting improvements in gamma/hadron separation obtained in HAWC.
This is a short report on the preliminary findings of the gamma ray burst (GRB) working group for the white paper on the status and future of very high energy (VHE; > 50 GeV) gamma-ray astronomy. The ...white paper discusses the status of past and current attempts to observe GRBs at GeV-TeV energies, including a handful of low-significance, possible detections. The white paper concentrates on the potential of future ground-based gamma-ray experiments to observe the highest energy emission ever recorded for GRBs, particularly for those that are nearby and have high Lorentz factors in the GRB jet. It is clear that the detection of VHE emission would have strong implications for GRB models, as well as cosmic ray origin. In particular, the extended emission phase (including both afterglow emission and possible flaring) of nearby long GRBs could provide the best possibility for detection. The difficult-to-obtain observations during the prompt phase of nearby long GRBs and short GRBs could also provide particularly strong constraints on the opacity and bulk Lorentz factors surrounding the acceleration site. The synergy with upcoming and existing observatories will, of course, be critical for both identification of GRBs and for multiwavelength/multimessenger studies.
Ultramafic lamprophyre (UML) dykes from the Ferrar Province (Pensacola Mountains) of Antarctica preserve trace element and isotope signatures similar to Bouvet volcanic rocks, which are considered to ...reflect the palaeo composition of the Bouvet mantle plume. We report Sr, Nd, Pb, and Os isotope compositions for three ultramafic lamprophyre dykes emplaced at 183.2±2.2 Ma, coincident with the main Karoo–Ferrar magmatic event. The ultramafic lamprophyre dykes are characterized by high Ti, Cr, Ni, Nb/La, La
N/Yb
N, and Mg# values, and are the most primitive rocks of the Ferrar Province. The dykes have initial (183 Ma)
87Sr/
86Sr ratios of 0.7044–0.7055,
εNd of 4.6–4.8,
208Pb/
204Pb of 39.6–40.3, and
187Os/
188Os of 0.120–0.146 and contrast markedly with even the most primitive rocks of the Ferrar and Karoo provinces. The trace element and isotope characteristics have affinities to ocean island basalt (OIB) and the highly radiogenic character of
208Pb/
204Pb and
206Pb/
204Pb bear closest resemblance to Bouvet, which has previously been postulated as the plume responsible for the Ferrar Province. The ultramafic lamprophyres are believed to be the result of melting enriched Bouvet mantle plume material and represent one of the mantle end members in the Karoo–Ferrar province.
More than 800 published genetic association studies have implicated dozens of potential risk loci in Parkinson's disease (PD). To facilitate the interpretation of these findings, we have created a ...dedicated online resource, PDGene, that comprehensively collects and meta-analyzes all published studies in the field. A systematic literature screen of -27,000 articles yielded 828 eligible articles from which relevant data were extracted. In addition, individual-level data from three publicly available genome-wide association studies (GWAS) were obtained and subjected to genotype imputation and analysis. Overall, we performed meta-analyses on more than seven million polymorphisms originating either from GWAS datasets and/or from smaller scale PD association studies. Meta-analyses on 147 SNPs were supplemented by unpublished GWAS data from up to 16,452 PD cases and 48,810 controls. Eleven loci showed genome-wide significant (P < 5 × 10(-8)) association with disease risk: BST1, CCDC62/HIP1R, DGKQ/GAK, GBA, LRRK2, MAPT, MCCC1/LAMP3, PARK16, SNCA, STK39, and SYT11/RAB25. In addition, we identified novel evidence for genome-wide significant association with a polymorphism in ITGA8 (rs7077361, OR 0.88, P = 1.3 × 10(-8)). All meta-analysis results are freely available on a dedicated online database (www.pdgene.org), which is cross-linked with a customized track on the UCSC Genome Browser. Our study provides an exhaustive and up-to-date summary of the status of PD genetics research that can be readily scaled to include the results of future large-scale genetics projects, including next-generation sequencing studies.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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