3,595 research outputs found
Optical radar measurements of the atmosphere
Optical radar investigations of atmosphere, and Mie scattering intensity functions for backscatte
A proposal for the coherent propagation studies portion of the 10.6-micrometer laser communications experiment Advanced Technology Satellite-F technical proposal
Coherent propagation study proposal for ATS-F 10.6 micrometer laser communications experimen
A direct image of the obscuring disk surrounding an active galactic nucleus
Active galactic nuclei (AGN) are generally accepted to be powered by the
release of gravitational energy in a compact accretion disk surrounding a
massive black hole. Such disks are also necessary to collimate powerful radio
jets seen in some AGN. The unifying classification schemes for AGN further
propose that differences in their appearance can be attributed to the opacity
of the accreting material, which may obstruct our view of the central region of
some systems. The popular model for the obscuring medium is a parsec-scale disk
of dense molecular gas, although evidence for such disks has been mostly
indirect, as their angular size is much smaller than the resolution of
conventional telescopes. Here we report the first direct images of a pc-scale
disk of ionised gas within the nucleus of NGC 1068, the archetype of obscured
AGN. The disk is viewed nearly edge-on, and individual clouds within the
ionised disk are opaque to high-energy radiation, consistent with the unifying
classification scheme. In projection, the disk and AGN axes align, from which
we infer that the ionised gas disk traces the outer regions of the long-sought
inner accretion disk.Comment: 14 pages, LaTeX, PSfig, to appear in Nature. also available at
http://hethp.mpe-garching.mpg.de/Preprint
Review of the effectiveness of current community ownership mechanisms and of options for supporting the expansion of community ownership in Scotland
This report presents the findings of research commissioned by the Scottish Land Commission to review the effectiveness of community ownership mechanisms and options for simplifying or improving these mechanisms to enable and support the expansion of community ownership in Scotland. This included reviewing processes relating to negotiated sales or transfers of land and/or assets to communities, as well as legislative mechanisms including the Community Right to Buy (CRtB), Crofting Community Right to Buy, the Transfer of Crofting Estates (Scotland) Act 1997 and Asset Transfer measures under the Community Empowerment (Scotland) Act 2015
Extending the Arctic Sea Ice Freeboard and Sea Level Record with the Sentinel-3 Radar Altimeters
In February 2016 and April 2018 the European Space Agency launched the Sentinel-3A and 3B satellites respectively, as part of the European Commission’s multi-satellite Copernicus Programme. Here we process Sentinel-3A waveform data to estimate Arctic sea level anomaly and radar freeboard from November 2017 to April 2018. We compare our results to those from the CryoSat-2 satellite, and find an intermission bias on sea-level anomaly of 2 cm. We also find a mean radar freeboard difference of 1 cm, which we attribute to the use of empirical retrackers to retrieve lead and floe elevations. Ahead of Sentinel-3B waveform data being made available, we use orbit files to estimate the improvement in sampling resolution afforded by the addition of Sentinel-3A and 3B data to the CryoSat-2 dataset. By combining data from the three satellites, grid resolution or time-sampling can be almost tripled compared with using CryoSat-2 data alone
Neural correlates of enhanced visual short-term memory for angry faces: An fMRI study
Copyright: © 2008 Jackson et al.Background: Fluid and effective social communication requires that both face identity and emotional expression information are encoded and maintained in visual short-term memory (VSTM) to enable a coherent, ongoing picture of the world and its players. This appears to be of particular evolutionary importance when confronted with potentially threatening displays of emotion - previous research has shown better VSTM for angry versus happy or neutral face identities.Methodology/Principal Findings: Using functional magnetic resonance imaging, here we investigated the neural correlates of this angry face benefit in VSTM. Participants were shown between one and four to-be-remembered angry, happy, or neutral faces, and after a short retention delay they stated whether a single probe face had been present or not in the previous display. All faces in any one display expressed the same emotion, and the task required memory for face identity. We find enhanced VSTM for angry face identities and describe the right hemisphere brain network underpinning this effect, which involves the globus pallidus, superior temporal sulcus, and frontal lobe. Increased activity in the globus pallidus was significantly correlated with the angry benefit in VSTM. Areas modulated by emotion were distinct from those modulated by memory load.Conclusions/Significance: Our results provide evidence for a key role of the basal ganglia as an interface between emotion and cognition, supported by a frontal, temporal, and occipital network.The authors were supported by a Wellcome Trust grant (grant number 077185/Z/05/Z) and by BBSRC (UK) grant BBS/B/16178
Satisfaction with democracy and voter turnout
Numerous studies conclude that countries in which citizens express higher levels of satisfaction with democracy also tend to display higher levels of voter turnout in national elections. Yet it is difficult to draw causal inferences from this positive cross-sectional relationship, because democracies feature many historical, cultural, and institutional differences that are not easily controlled for in cross-sectional comparisons. We apply an alternative, temporal approach to this issue by asking the question: Are over-time declines (increases) in aggregate levels of satisfaction within democracies associated with increases (declines) in levels of voter turnout within these democracies? Our temporal analysis of this relationship in 12 democracies over the period 1976–2011 reveals a pattern that is the opposite of that suggested by previous cross-sectional studies: namely, we find that over-time increases in citizens’ satisfaction with democracy are associated with significant decreases in voter turnout in national elections in these countries. </jats:p
The characteristic blue spectra of accretion disks in quasars as uncovered in the infrared
Quasars are thought to be powered by supermassive black holes accreting
surrounding gas. Central to this picture is a putative accretion disk which is
believed to be the source of the majority of the radiative output. It is well
known, however, that the most extensively studied disk model -- an optically
thick disk which is heated locally by the dissipation of gravitational binding
energy -- is apparently contradicted by observations in a few major respects.
In particular, the model predicts a specific blue spectral shape asymptotically
from the visible to the near-infrared, but this is not generally seen in the
visible wavelength region where the disk spectrum is observable. A crucial
difficulty was that, toward the infrared, the disk spectrum starts to be hidden
under strong hot dust emission from much larger but hitherto unresolved scales,
and thus has essentially been impossible to observe. Here we report
observations of polarized light interior to the dust-emiting region that enable
us to uncover this near-infrared disk spectrum in several quasars. The revealed
spectra show that the near-infrared disk spectrum is indeed as blue as
predicted. This indicates that, at least for the outer near-infrared-emitting
radii, the standard picture of the locally heated disk is approximately
correct. The model problems at shorter wavelengths should then be directed
toward a better understanding of the inner parts of the revealed disk. The
newly uncovered disk emission at large radii, with more future measurements,
will also shed totally new light on the unanswered critical question of how and
where the disk ends.Comment: published in Nature, 24 July 2008 issue. Supplementary Information
can be found at
http://www.mpifr-bonn.mpg.de/div/ir-interferometry/suppl_info.pdf Published
version can be accessed from
http://www.nature.com/nature/journal/v454/n7203/pdf/nature07114.pd
Grand Challenges: Improving HIV Treatment Outcomes by Integrating Interventions for Co-Morbid Mental Illness.
In the fourth article of a five-part series providing a global perspective on integrating mental health, Sylvia Kaaya and colleagues discuss the importance of integrating mental health interventions into HIV prevention and treatment platforms. Please see later in the article for the Editors' Summary
The Formation of the First Massive Black Holes
Supermassive black holes (SMBHs) are common in local galactic nuclei, and
SMBHs as massive as several billion solar masses already exist at redshift z=6.
These earliest SMBHs may grow by the combination of radiation-pressure-limited
accretion and mergers of stellar-mass seed BHs, left behind by the first
generation of metal-free stars, or may be formed by more rapid direct collapse
of gas in rare special environments where dense gas can accumulate without
first fragmenting into stars. This chapter offers a review of these two
competing scenarios, as well as some more exotic alternative ideas. It also
briefly discusses how the different models may be distinguished in the future
by observations with JWST, (e)LISA and other instruments.Comment: 47 pages with 306 references; this review is a chapter in "The First
Galaxies - Theoretical Predictions and Observational Clues", Springer
Astrophysics and Space Science Library, Eds. T. Wiklind, V. Bromm & B.
Mobasher, in pres
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