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  • 1
    Publication Date: 2015-06-07
    Description: We present the identification of potential members of nearby Galactic globular clusters using radial velocities from the RAdial Velocity Experiment Data Release 4 (RAVE-DR4) survey data base. Our identifications are based on three globular clusters – NGC 3201, NGC 5139 ( Cen) and NGC 362 – all of which are shown to have |RV| 〉 100 km s –1 . The high radial velocity of cluster members compared to the bulk of surrounding disc stars enables us to identify members using their measured radial velocities, supplemented by proper motion information and location relative to the tidal radius of each cluster. The identification of globular cluster stars in RAVE DR4 data offers a unique opportunity to test the precision and accuracy of the stellar parameters determined with the currently available Stellar Parameter Pipelines used in the survey, as globular clusters are ideal test-beds for the validation of stellar atmospheric parameters, abundances, distances and ages. For both NGC 3201 and Cen, there is compelling evidence for numerous members (〉10) in the RAVE data base; in the case of NGC 362 the evidence is more ambiguous, and there may be significant foreground and/or background contamination in our kinematically selected sample. A comparison of the RAVE-derived stellar parameters and abundances with published values for each cluster and with BASTI isochrones for ages and metallicities from the literature reveals overall good agreement, with the exception of the apparent underestimation of surface gravities for giants, in particular for the most metal-poor stars. Moreover, if the selected members are part of the main body of each cluster our results would also suggest that the distances from Binney et al., where only isochrones more metal rich than –0.9 dex were used, are typically underestimated by ~40 per cent with respect to the published distances for the clusters, while the distances from Zwitter et al. show stars ranging from 1 to ~6.5 kpc – with indications of a trend towards higher distances at lower metallicities – for the three clusters analysed in this study.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 2
    Publication Date: 2015-06-12
    Description: We present the identification of potential members of nearby Galactic globular clusters using radial velocities from the RAdial Velocity Experiment Data Release 4 (RAVE-DR4) survey data base. Our identifications are based on three globular clusters – NGC 3201, NGC 5139 ( Cen) and NGC 362 – all of which are shown to have |RV| 〉 100 km s –1 . The high radial velocity of cluster members compared to the bulk of surrounding disc stars enables us to identify members using their measured radial velocities, supplemented by proper motion information and location relative to the tidal radius of each cluster. The identification of globular cluster stars in RAVE DR4 data offers a unique opportunity to test the precision and accuracy of the stellar parameters determined with the currently available Stellar Parameter Pipelines used in the survey, as globular clusters are ideal test-beds for the validation of stellar atmospheric parameters, abundances, distances and ages. For both NGC 3201 and Cen, there is compelling evidence for numerous members (〉10) in the RAVE data base; in the case of NGC 362 the evidence is more ambiguous, and there may be significant foreground and/or background contamination in our kinematically selected sample. A comparison of the RAVE-derived stellar parameters and abundances with published values for each cluster and with BASTI isochrones for ages and metallicities from the literature reveals overall good agreement, with the exception of the apparent underestimation of surface gravities for giants, in particular for the most metal-poor stars. Moreover, if the selected members are part of the main body of each cluster our results would also suggest that the distances from Binney et al., where only isochrones more metal rich than –0.9 dex were used, are typically underestimated by ~40 per cent with respect to the published distances for the clusters, while the distances from Zwitter et al. show stars ranging from 1 to ~6.5 kpc – with indications of a trend towards higher distances at lower metallicities – for the three clusters analysed in this study.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
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  • 3
    Publication Date: 2015-01-07
    Description: We aim to characterize high-velocity (HiVel) stars in the solar vicinity both chemically and kinematically using the fourth data release of the RAdial Velocity Experiment (RAVE). We used a sample of 57 HiVel stars with Galactic rest-frame velocities larger than 275 km s –1 . With 6D position and velocity information, we integrated the orbits of the HiVel stars and found that, on average, they reach out to 13 kpc from the Galactic plane and have relatively eccentric orbits consistent with the Galactic halo. Using the stellar parameters and [α/Fe] estimates from RAVE, we found the metallicity distribution of the HiVel stars peak at [ M /H] = –1.2 dex and is chemically consistent with the inner halo. There are a few notable exceptions that include a hypervelocity star candidate, an extremely HiVel bound halo star, and one star that is kinematically consistent with the halo but chemically consistent with the disc. High-resolution spectra were obtained for the metal-rich HiVel star candidate and the second highest velocity star in the sample. Using these high-resolution data, we report the discovery of a metal-rich halo star that has likely been dynamically ejected into the halo from the Galactic thick disc. This discovery could aid in explaining the assembly of the most metal-rich component of the Galactic halo.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 4
    Publication Date: 2016-02-09
    Description: We report the identification of extended tidal debris potentially associated with the globular cluster NGC 3201, using the RAdial Velocity Experiment (RAVE) catalogue. We find the debris stars are located at a distance range of 1–7 kpc based on the forthcoming RAVE distance estimates. The derived space velocities and integrals of motion show interesting connections to NGC 3201, modulo uncertainties in the proper motions. Three stars, which are among the four most likely candidates for NGC 3201 tidal debris, are separated by 80° on the sky yet are well matched by the 12 Gyr, [Fe/H] = –1.5 isochrone appropriate for the cluster. This is the first time tidal debris around this cluster has been reported over such a large spatial extent, with implications for the cluster's origin and dynamical evolution.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 5
    Publication Date: 2014-03-29
    Description: We experience the visual world through a series of saccadic eye movements, each one shifting our gaze to bring objects of interest to the fovea for further processing. Although such movements lead to frequent and substantial displacements of the retinal image, these displacements go unnoticed. It is widely assumed that a primary mechanism underlying this apparent stability is an anticipatory shifting of visual receptive fields (RFs) from their presaccadic to their postsaccadic locations before movement onset. Evidence of this predictive 'remapping' of RFs has been particularly apparent within brain structures involved in gaze control. However, critically absent among that evidence are detailed measurements of visual RFs before movement onset. Here we show that during saccade preparation, rather than remap, RFs of neurons in a prefrontal gaze control area massively converge towards the saccadic target. We mapped the visual RFs of prefrontal neurons during stable fixation and immediately before the onset of eye movements, using multi-electrode recordings in monkeys. Following movements from an initial fixation point to a target, RFs remained stationary in retinocentric space. However, in the period immediately before movement onset, RFs shifted by as much as 18 degrees of visual angle, and converged towards the target location. This convergence resulted in a threefold increase in the proportion of RFs responding to stimuli near the target region. In addition, like in human observers, the population of prefrontal neurons grossly mislocalized presaccadic stimuli as being closer to the target. Our results show that RF shifts do not predict the retinal displacements due to saccades, but instead reflect the overriding perception of target space during eye movements.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4064801/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4064801/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zirnsak, Marc -- Steinmetz, Nicholas A -- Noudoost, Behrad -- Xu, Kitty Z -- Moore, Tirin -- EY014924/EY/NEI NIH HHS/ -- R01 EY014924/EY/NEI NIH HHS/ -- T32 MH020016/MH/NIMH NIH HHS/ -- Howard Hughes Medical Institute/ -- England -- Nature. 2014 Mar 27;507(7493):504-7. doi: 10.1038/nature13149.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Department of Neurobiology, Stanford University School of Medicine, Stanford, California 94305, USA [2] Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California 94305, USA. ; Department of Neurobiology, Stanford University School of Medicine, Stanford, California 94305, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24670771" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Electrodes ; Fixation, Ocular/physiology ; Humans ; Macaca mulatta ; Male ; Models, Neurological ; Neurons/physiology ; Prefrontal Cortex/cytology/*physiology ; Retina/physiology ; Saccades/*physiology ; Visual Acuity/physiology ; Visual Fields/physiology ; Visual Perception/*physiology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 1996-08-16
    Description: Apolipoproteins are protein constituents of plasma lipid transport particles. Human apolipoprotein A-IV (apoA-IV) was expressed in the liver of C57BL/6 mice and mice deficient in apoE, both of which are prone to atherosclerosis, to investigate whether apoA-IV protects against this disease. In transgenic C57BL/6 mice on an atherogenic diet, the serum concentration of high density lipoprotein (HDL) cholesterol increased by 35 percent, whereas the concentration of endogenous apoA-I decreased by 29 percent, relative to those in transgenic mice on a normal diet. Expression of human apoA-IV in apoE-deficient mice on a normal diet resulted in an even more severe atherogenic lipoprotein profile, without affecting the concentration of HDL cholesterol, than that in nontransgenic apoE-deficient mice. However, transgenic mice of both backgrounds showed a substantial reduction in the size of atherosclerotic lesions. Thus, apoA-IV appears to protect against atherosclerosis by a mechanism that does not involve an increase in HDL cholesterol concentration.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Duverger, N -- Tremp, G -- Caillaud, J M -- Emmanuel, F -- Castro, G -- Fruchart, J C -- Steinmetz, A -- Denefle, P -- New York, N.Y. -- Science. 1996 Aug 16;273(5277):966-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Rhone-Poulenc Rorer, Gencell Division, Atherosclerosis Department, Centre de Recherches de Vitry-Alfortville, 94403 Vitry sur Seine Cedex, France. G. C.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8688083" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Apolipoprotein A-I/blood ; Apolipoproteins A/blood/*physiology ; Apolipoproteins E/blood/deficiency ; Arteriosclerosis/*prevention & control ; Cholesterol/blood ; Cholesterol, HDL/blood ; Diet, Atherogenic ; Female ; Humans ; Mice ; Mice, Inbred C57BL ; Mice, Transgenic
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
    Publication Date: 2015-04-08
    Description: A large population of neurons can, in principle, produce an astronomical number of distinct firing patterns. In cortex, however, these patterns lie in a space of lower dimension, as if individual neurons were "obedient members of a huge orchestra". Here we use recordings from the visual cortex of mouse (Mus musculus) and monkey (Macaca mulatta) to investigate the relationship between individual neurons and the population, and to establish the underlying circuit mechanisms. We show that neighbouring neurons can differ in their coupling to the overall firing of the population, ranging from strongly coupled 'choristers' to weakly coupled 'soloists'. Population coupling is largely independent of sensory preferences, and it is a fixed cellular attribute, invariant to stimulus conditions. Neurons with high population coupling are more strongly affected by non-sensory behavioural variables such as motor intention. Population coupling reflects a causal relationship, predicting the response of a neuron to optogenetically driven increases in local activity. Moreover, population coupling indicates synaptic connectivity; the population coupling of a neuron, measured in vivo, predicted subsequent in vitro estimates of the number of synapses received from its neighbours. Finally, population coupling provides a compact summary of population activity; knowledge of the population couplings of n neurons predicts a substantial portion of their n(2) pairwise correlations. Population coupling therefore represents a novel, simple measure that characterizes the relationship of each neuron to a larger population, explaining seemingly complex network firing patterns in terms of basic circuit variables.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4449271/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4449271/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Okun, Michael -- Steinmetz, Nicholas A -- Cossell, Lee -- Iacaruso, M Florencia -- Ko, Ho -- Bartho, Peter -- Moore, Tirin -- Hofer, Sonja B -- Mrsic-Flogel, Thomas D -- Carandini, Matteo -- Harris, Kenneth D -- 095668/Wellcome Trust/United Kingdom -- 095669/Wellcome Trust/United Kingdom -- 095853/Wellcome Trust/United Kingdom -- EY014924/EY/NEI NIH HHS/ -- R01 EY014924/EY/NEI NIH HHS/ -- T32 MH020016/MH/NIMH NIH HHS/ -- Howard Hughes Medical Institute/ -- Medical Research Council/United Kingdom -- Wellcome Trust/United Kingdom -- England -- Nature. 2015 May 28;521(7553):511-5. doi: 10.1038/nature14273. Epub 2015 Apr 6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] UCL Institute of Neurology, University College London, London WC1N 3BG, UK [2] Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6DE, UK [3] UCL Institute of Ophthalmology, University College London, London EC1V 9EL, UK. ; 1] UCL Institute of Neurology, University College London, London WC1N 3BG, UK [2] Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6DE, UK [3] UCL Institute of Ophthalmology, University College London, London EC1V 9EL, UK [4] Howard Hughes Medical Institute and Department of Neurobiology, Stanford University, Stanford, California 94305-5125, USA. ; 1] Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6DE, UK [2] Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland. ; Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6DE, UK. ; Center for Molecular and Behavioral Neuroscience, Rutgers University, 197 University Avenue, Newark, New Jersey 07102, USA. ; Howard Hughes Medical Institute and Department of Neurobiology, Stanford University, Stanford, California 94305-5125, USA. ; UCL Institute of Ophthalmology, University College London, London EC1V 9EL, UK. ; 1] UCL Institute of Neurology, University College London, London WC1N 3BG, UK [2] Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6DE, UK [3] Center for Molecular and Behavioral Neuroscience, Rutgers University, 197 University Avenue, Newark, New Jersey 07102, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25849776" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Female ; Macaca mulatta ; Male ; Mice ; Models, Neurological ; Neurons/*cytology/*physiology ; Optogenetics ; Synapses/physiology ; Visual Cortex/*cytology/*physiology
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    Electronic ISSN: 1476-4687
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  • 8
    Publication Date: 2017-05-06
    Description: Meiotic crossover frequencies show wide variation among organisms. But most organisms maintain at least one crossover per homolog pair (obligate crossover). In Saccharomyces cerevisiae , previous studies have shown crossover frequencies are reduced in the mismatch repair related mutant mlh3 and enhanced in a meiotic checkpoint mutant pch2 by up to twofold at specific chromosomal loci, but both mutants maintain high spore viability. We analyzed meiotic recombination events genome-wide in mlh3 , pch2 , and mlh3 pch2 mutants to test the effect of variation in crossover frequency on obligate crossovers. mlh3 showed ~30% genome-wide reduction in crossovers (64 crossovers per meiosis) and loss of the obligate crossover, but nonexchange chromosomes were efficiently segregated. pch2 showed ~50% genome-wide increase in crossover frequency (137 crossovers per meiosis), elevated noncrossovers as well as loss of chromosome size dependent double-strand break formation. Meiotic defects associated with pch2 did not cause significant increase in nonexchange chromosome frequency. Crossovers were restored to wild-type frequency in the double mutant mlh3 pch2 (100 crossovers per meiosis), but obligate crossovers were compromised. Genetic interference was reduced in mlh3 , pch2 , and mlh3 pch2 . Triple mutant analysis of mlh3 pch2 with other resolvase mutants showed that most of the crossovers in mlh3 pch2 are made through the Mus81 - Mms4 pathway. These results are consistent with a requirement for increased crossover frequencies in the absence of genetic interference for obligate crossovers. In conclusion, these data suggest crossover frequencies and the strength of genetic interference in an organism are mutually optimized to ensure obligate crossovers.
    Electronic ISSN: 2160-1836
    Topics: Biology
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  • 9
    Publication Date: 2016-10-16
    Description: SPIDERS (The SPectroscopic IDentification of eROSITA Sources) is a programme dedicated to the homogeneous and complete spectroscopic follow-up of X-ray active galactic nuclei and galaxy clusters over a large area (~7500 deg 2 ) of the extragalactic sky. SPIDERS is part of the Sloan Digital Sky Survey (SDSS)-IV project, together with the Extended Baryon Oscillation Spectroscopic Survey and the Time-Domain Spectroscopic Survey. This paper describes the largest project within SPIDERS before the launch of eROSITA : an optical spectroscopic survey of X-ray-selected, massive (~10 14 –10 15 M ) galaxy clusters discovered in ROSAT and XMM–Newton imaging. The immediate aim is to determine precise ( z  ~ 0.001) redshifts for 4000–5000 of these systems out to z  ~ 0.6. The scientific goal of the program is precision cosmology, using clusters as probes of large-scale structure in the expanding Universe. We present the cluster samples, target selection algorithms and observation strategies. We demonstrate the efficiency of selecting targets using a combination of SDSS imaging data, a robust red-sequence finder and a dedicated prioritization scheme. We describe a set of algorithms and work-flow developed to collate spectra and assign cluster membership, and to deliver catalogues of spectroscopically confirmed clusters. We discuss the relevance of line-of-sight velocity dispersion estimators for the richer systems. We illustrate our techniques by constructing a catalogue of 230 spectroscopically validated clusters (0.031 〈  z  〈 0.658), found in pilot observations. We discuss two potential science applications of the SPIDERS sample: the study of the X-ray luminosity-velocity dispersion ( L X –) relation and the building of stacked phase-space diagrams.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 10
    Publication Date: 2019
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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