3,307 research outputs found
Chandra and XMM-Newton Observations of the Double Cluster Abell 1758
Abell 1758 was classified as a single rich cluster of galaxies by Abell, but
a ROSAT observation showed that this system consists of two distinct clusters
(A1758N and A1758S) separated by approximately 8\arcmin (a projected
separation of 2 Mpc in the rest frame of the clusters). Only a few galaxy
redshifts have been published for these two clusters, but the redshift of the
Fe lines in the Chandra and XMM-Newton spectra shows that the recessional
velocities of A1758N and A1758S are within 2,100 km s. Thus, these two
clusters most likely form a gravitationally bound system, but our imaging and
spectroscopic analyses of the X-ray data do not reveal any sign of interaction
between the two clusters. The Chandra and XMM-Newton observations show that
A1758N and A1758S are both undergoing major mergers.
A1758N is in the late stages of a large impact parameter merger between two 7
keV clusters. The two remnant cores have a projected separation of 800 kpc.
Based on the measured pressure jumps preceding the two cores, they are receding
from one another at less than 1,600 km s. The two cores are surrounded
by hotter gas (--12 keV) that was probably shock heated during
the early stages of the merger. The gas entropy in the two remnant cores is
comparable with the central entropy observed in dynamically relaxed clusters,
indicating that the merger-induced shocks stalled as they tried to penetrate
the high pressure cores of the two merging systems.Each core also has a wake of
low entropy gas indicating that this gas was ram pressure stripped without
being strongly shocked (abridged). (A copy of the paper with higher resolution
images is available at http://asc.harvard.edu/~lpd/a1758.ps).Comment: paper plus 13 figure
Bad Religion as False Religion : An Empirical Study of UK Religious Education Teachers’ Essentialist Religious Discourse
Peer reviewedPublisher PD
Information and Timing in Repeated Partnerships
In a repeated partnership game with imperfect monitoring, we distinguish among the effects of (1) shortening the period over which actions are held fixed, (2) increasing the frequency with which accumulated information is reported, and (3) reducing the amount of discounting of payoffs between successive periods. While reducing the amount of discounting generally improves incentives for cooperation, the other two changes can have the reverse effect. When the game is specified in the customary way with information reported at the end of each period of fixed action, the net effect of shortening the period length can be to destroy all incentives for cooperation, reversing the usual conclusion associated with the Folk Theorem for repeated games. Moreover, when interest rates are low, reducing the frequency of information reporting can greatly enhance the efficiency of equilibrium
Boninite and Harzburgite from Leg 125 (Bonin-Mariana Forearc): A Case Study of Magma Genesis during the Initial Stages of Subduction
Holes drilled into the volcanic and ultrabasic basement of the Izu-Ogasawara and Mariana forearc terranes during Leg 125 provide data on some of the earliest lithosphere created after the start of Eocene subduction in the Western Pacific. The volcanic basement contains three boninite series and one tholeiite series. (1) Eocene low-Ca boninite and low-Ca bronzite andesite pillow lavas and dikes dominate the lowermost part of the deep crustal section through the outer-arc high at Site 786. (2) Eocene intermediate-Ca boninite and its fractionation products (bronzite andesite, andesite, dacite, and rhyolite) make up the main part of the boninitic edifice at Site 786. (3) Early Oligocene intermediate-Ca to high-Ca boninite sills or dikes intrude the edifice and perhaps feed an uppermost breccia unit at Site 786. (4) Eocene or Early Oligocene tholeiitic andesite, dacite, and rhyolite form the uppermost part of the outer-arc high at Site 782. All four groups can be explained by remelting above a subduction zone of oceanic mantle lithosphere that has been depleted by its previous episode of partial melting at an ocean ridge. We estimate that the average boninite source had lost 10-15 wt% of melt at the ridge before undergoing further melting (5-10%) shortly after subduction started. The composition of the harzburgite (<2% clinopyroxene, Fo content of about 92%) indicates that it underwent a total of about 25% melting with respect to a fertile MORB mantle. The low concentration of Nb in the boninite indicates that the oceanic lithosphere prior to subduction was not enriched by any asthenospheric (OIB) component.
The subduction component is characterized by (1) high Zr and Hf contents relative to Sm, Ti, Y, and middle-heavy REE, (2) light REE-enrichment, (3) low contents of Nb and Ta relative to Th, Rb, or La, (4) high contents of Na and Al, and (5) Pb isotopes on the Northern Hemisphere Reference Line. This component is unlike any subduction component from active arc volcanoes in the Izu-Mariana region or elsewhere. Modeling suggests that these characteristics fit a trondhjemitic melt from slab fusion in amphibolite facies. The resulting metasomatized mantle may have contained about 0.15 wt% water. The overall melting regime is constrained by experimental data to shallow depths and high temperatures (1250°C and 1.5 kb for an average boninite) of boninite segregation. We thus envisage that boninites were generated by decompression melting of a diapir of metasomatized residual MORB mantle leaving the harzburgites as the uppermost, most depleted residue from this second stage of melting. Thermal constraints require that both subducted lithosphere and overlying oceanic lithosphere of the mantle wedge be very young at the time of boninite genesis. This conclusion is consistent with models in which an active transform fault offsetting two ridge axes is placed under compression or transpression following the Eocene plate reorganization in the Pacific. Comparison between Leg 125 boninites and boninites and related rocks elsewhere in the Western Pacific highlights large regional differences in petrogenesis in terms of mantle mineralogy, degree of partial melting, composition of subduction components, and the nature of pre-subduction lithosphere. It is likely that, on a regional scale, the initiation of subduction involved subducted crust and lithospheric mantle wedge of a range of ages and compositions, as might be expected in this type of tectonic setting
A Bio-Logical Theory of Animal Learning
This article provides the foundation for a new predictive theory of animal learning that is based upon a simple logical model. The knowledge of experimental subjects at a given time is described using logical equations. These logical equations are then used to predict a subject’s response when presented with a known or a previously unknown situation. This new theory suc- cessfully anticipates phenomena that existing theories predict, as well as phenomena that they cannot. It provides a theoretical account for phenomena that are beyond the domain of existing models, such as extinction and the detection of novelty, from which “external inhibition” can be explained. Examples of the methods applied to make predictions are given using previously published results. The present theory proposes a new way to envision the minimal functions of the nervous system, and provides possible new insights into the way that brains ultimately create and use knowledge about the world
The response of Li and Mg isotopes to rain events in a highly-weathered catchment
Storms are responsible for up to ~50% of total annual rainfall on tropical islands and result in rapid increases in discharge from rivers. Storm events are, however, notoriously under-sampled and their effects on weathering rates and processes are poorly constrained. To address this, we have undertaken high-frequency sampling of Quiock Creek catchment, a Critical Zone Observatory located in Guadeloupe, over a period of 21 days, encompassing several storm events. Chemical and isotopic (Li and Mg) analyses of different critical zone reservoirs (throughfall, soil pore water, groundwater and river water) were used to assess the interactions between rock, water and secondary minerals. The Li concentrations and δ7Li values of these different reservoirs range from 14 to 95 nmol/kg and 1.8 to 16.8‰, respectively. After several rain events, the average δ7Li value (13.3‰) of soil solutions from the lower part of the soil profile (>~150 cm below the surface) was unchanged, whereas in the upper part of the profile δ7Li values increased by ~2–4‰ due to increased contribution from throughfall. By contrast, the δ26Mg value of soil waters in the upper part of the soil profile were not significantly affected by the rain events with an average value of −0.90‰. The δ26Mg values of the different fluid reservoirs were generally close to the value of throughfall (~−0.90‰), but higher δ26Mg values (up to −0.58‰) were measured in the deeper parts of the soil profile, whereas groundwaters that have a long residence time had lower δ26Mg values (down to −1.48‰). These higher and lower values are attributed to, respectively, adsorption/desorption of light Mg isotopes on/from the surface of clay minerals. The δ7Li value of the river waters was ~9.3‰, with a Li concentration of 60 μmol/kg, but during a storm these values decreased to, respectively, 7.8‰ and 40 μmol/kg. This change in δ7Li is consistent with an increased contribution of Li from the soil solution. Thus, even in highly weathered catchments, changes in hydrological conditions can have a significant impact on weathering processes and therefore the composition of river waters delivered to the ocean
Adenosine-mono-phosphate-activated protein kinase-independent effects of metformin in T cells
The anti-diabetic drug metformin regulates T-cell responses to immune activation and is proposed to function by regulating the energy-stress-sensing adenosine-monophosphate-activated protein kinase (AMPK). However, the molecular details of how metformin controls T cell immune responses have not been studied nor is there any direct evidence that metformin acts on T cells via AMPK. Here, we report that metformin regulates cell growth and proliferation of antigen-activated T cells by modulating the metabolic reprogramming that is required for effector T cell differentiation. Metformin thus inhibits the mammalian target of rapamycin complex I signalling pathway and prevents the expression of the transcription factors c-Myc and hypoxia-inducible factor 1 alpha. However, the inhibitory effects of metformin on T cells did not depend on the expression of AMPK in T cells. Accordingly, experiments with metformin inform about the importance of metabolic reprogramming for T cell immune responses but do not inform about the importance of AMPK
Evaluation of the Physical Activity and Public Health Course for Practitioners
From 1996–2013, a 6-day Physical Activity and Public Health Course for Practitioners has been offered yearly in the United States. An evaluation was conducted to assess the impact of the course on building public health capacity for physical activity and on shaping the physical activity and public health careers of fellows since taking the courses
Pole-to-Pole Connections : Similarities between Arctic and Antarctic Microbiomes and Their Vulnerability to Environmental Change
Acknowledgments JK acknowledges the Carl Zeiss foundation for PhD funding, the Marie-Curie COFUND-BEIPD PostDoc fellowship for PostDoc funding, FNRS travel funding and the logistical and financial support by UNIS. JK and FK acknowledge the Natural Environment Research Council (NERC) Antarctic Funding Initiative AFI-CGS-70 (collaborative gearing scheme) and logistic support from the British Antarctic Survey (BAS) for field work in Antarctica. JK and CZ acknowledge the Excellence Initiative at the University of Tübingen funded by the German Federal Ministry of Education and Research and the German Research Foundation (DFG). FH, AV, and PB received funding from MetaHIT (HEALTH-F4-2007-201052), Microbios (ERC-AdG-502 669830) and the European Molecular Biology Laboratory (EMBL). We thank members of the Bork group at EMBL for helpful discussions. We acknowledge the EMBL Genomics Core Facility for sequencing support and Y. P. Yuan and the EMBL Information Technology Core Facility for support with high-performance computing and EMBL for financial support. PC is supported by NERC core funding to the BAS “Biodiversity, Evolution and Adaptation” Team. MB was funded by Helge Ax:son Johnsons Stiftelse and PUT1317. DRD acknowledges the DFG funded project DI698/18-1 Dietrich and the Marie Curie International Research Staff Exchange Scheme Fellowship (PIRSES-GA-2011-295223). Operations in the Canadian High Arctic were supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), ArcticNet and the Polar Continental Shelf Program (PCSP). We are also grateful to the TOTAL Foundation (Paris) and the UK NERC (WP 4.3 of Oceans 2025 core funding to FCK at the Scottish Association for Marine Science) for funding the expedition to Baffin Island and within this context Olivier Dargent and Dr. Pieter van West for sample collection, and the Spanish Ministry of Science and Technology through project LIMNOPOLAR (POL200606635 and CGL2005-06549-C02-01/ANT to AQ as well as CGL2005-06549-C02-02/ANT to AC, the last of these co-financed by European FEDER funds). We are grateful for funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland), funded by the Scottish Funding Council (HR09011) and contributing institutions. Supplementary Material The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fevo.2017.00137/full#supplementary-materialPeer reviewedPublisher PD
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