1,230 research outputs found
The End of the Lines for OX 169: No Binary Broad-Line Region
We show that unusual Balmer emission line profiles of the quasar OX 169,
frequently described as either self-absorbed or double peaked, are actually
neither. The effect is an illusion resulting from two coincidences. First, the
forbidden lines are quite strong and broad. Consequently, the [N II]6583 line
and the associated narrow-line component of H-alpha present the appearance of
twin H-alpha peaks. Second, the redshift of 0.2110 brings H-beta into
coincidence with Na I D at zero redshift, and ISM absorption in Na I D divides
the H-beta emission line. In spectra obtained over the past decade, we see no
substantial change in the character of the line profiles, and no indication of
intrinsic double-peaked structure. The H-gamma, Mg II, and Ly-alpha emission
lines are single peaked, and all of the emission-line redshifts are consistent
once they are correctly attributed to their permitted and forbidden-line
identifications. A systematic shift of up to 700 km/s between broad and narrow
lines is seen, but such differences are common, and could be due to
gravitational and transverse redshift in a low-inclination disk. Stockton &
Farnham (1991) had called attention to an apparent tidal tail in the host
galaxy of OX 169, and speculated that a recent merger had supplied the nucleus
with a coalescing pair of black holes which was now revealing its existence in
the form of two physically distinct broad-line regions. Although there is no
longer any evidence for two broad emission-line regions in OX 169, binary black
holes should form frequently in galaxy mergers, and it is still worthwhile to
monitor the radial velocities of emission lines which could supply evidence of
their existence in certain objects.Comment: 19 pages, 5 figures, accepted for publication in Ap.
Farmers in Côte d'Ivoire value integrating tree diversity in cocoa for the provision of ecosystem services
Côte d'Ivoire produces 40 % of the world supply of cocoa but much of the plantation area is aging and declining in productivity, while opportunities for land expansion into new forest land are quickly disappearing. Rejuvenation strategies for cocoa presently coalesce either around improved varieties and greater use of agro-chemical inputs in full sun systems or eco-certification that requires trees to be integrated with cocoa. Here, we explore the possibility of uniting these approaches through building on current farmer practice of incorporating trees in their cocoa fields to improve cocoa productivity and diversify their livelihoods. We interviewed 355 farmers about trees integrated in their cocoa fields across four locations in the South-West of Côte d'Ivoire in 2012, stratified by whether or not farmers were eco-certified. Despite the massive deforestation, a rich diversity of trees was found in cocoa fields and an overwhelming majority of farmers (95 %) wanted more trees and/or more tree species, regardless of their certification status or ethnic origin. There was a consensus that most trees were compatible with cocoa, but farmers also traded off negative impacts of some species against their productive contribution to their livelihood. Farmers valued tree diversity on their cocoa plots and provided detailed information on how 32 tree species interacted with cocoa in terms of soil moisture retention, soil fertility improvement and pest and disease interactions but also had key gaps in knowledge about alternative hosts of mirids and mistletoe. The majority of farmers were not aware of the certification requirements for tree species and shade cover but a much higher proportion of certified farmers (76 %) had received information about shade trees than non-certified farmers (15 %), although advice only related to eight tree species. Scope for building on local knowledge and practice to sustainably increase cocoa productivity through promoting tree diversity while enhancing other ecosystem service provision was identified and the next steps required to realize this set out. (Résumé d'auteur
The Circumstellar Disk of HD 141569 Imaged with NICMOS
Coronagraphic imaging with the Near Infrared Camera and Multi Object
Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4'')
radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected
light image at 1.1 micron shows the disk oriented at a position angle of 356
+/- 5 deg and inclined to our line of sight by 51 +/- 3 deg; the intrinsic
scattering function of the dust in the disk makes the side inclined toward us,
the eastern side, brighter. The disk flux density peaks 185 AU (1.''85) from
the star and falls off to both larger and smaller radii. A region of depleted
material, or a gap, in the disk is centered 250 AU from the star. The dynamical
effect of one or more planets may be necessary to explain this morphology.Comment: 4 pages, LaTeX with emulateapj.sty and epsfig.sty, 4 postscript
figures, Accepted to ApJ Letter
Heat and fluid flow in a scraped-surface heat exchanger containing a fluid with temperature-dependent viscosity
Scraped-surface heat exchangers (SSHEs) are extensively used in a wide variety of industrial settings where the continuous processing of fluids and fluid-like materials is involved. The steady non-isothermal flow of a Newtonian fluid with temperature-dependent viscosity in a narrow-gap SSHE when a constant temperature difference is imposed across the gap between the rotor and the stator is investigated. The mathematical model is formulated and the exact analytical solutions for the heat and fluid flow of a fluid with a general dependence of viscosity on temperature for a general blade shape are obtained. These solutions are then presented for the specific case of an exponential dependence of viscosity on temperature. Asymptotic methods are employed to investigate the behaviour of the solutions in several special limiting geometries and in the limits of weak and strong thermoviscosity. In particular, in the limit of strong thermoviscosity (i.e., strong heating or cooling and/or strong dependence of viscosity on temperature) the transverse and axial velocities become uniform in the bulk of the flow with boundary layers forming either just below the blade and just below the stationary upper wall or just above the blade and just above the moving lower wall. Results are presented for the most realistic case of a linear blade which illustrate the effect of varying the thermoviscosity of the fluid and the geometry of the SSHE on the flow
Contribution of a Disk Component to Single Peaked Broad Lines of Active Galactic Nuclei
We study the disk emission component hidden in the single-peaked Broad
Emission Lines (BELs) of Active Galactic Nuclei (AGN). We compare the observed
broad lines from a sample of 90 Seyfert 1 spectra taken from the Sloan Digital
Sky Survey with simulated line profiles. We consider a two-component Broad Line
Region (BLR) model where an accretion disk and a surrounding non-disk region
with isotropic cloud velocities generate the simulated BEL profiles. The
analysis is mainly based in measurements of the full widths (at 10%, 20% and
30% of the maximum intensity) and of the asymmetries of the line profiles.
Comparing these parameters for the simulated and observed H broad
lines, we {found} that the hidden disk emission {may} be present in BELs even
if the characteristic {of two peaked line profiles is} absent. For the
available sample of objects (Seyfert 1 galaxies with single-peaked BELs), our
study indicates that, {in the case of the hidden disk emission in single peaked
broad line profiles}, the disk inclination tends to be small (mostly
) and that the contribution of the disk emission to the total flux
should be smaller than the contribution of the surrounding region.Comment: 18 Figures, 1 Table, MNRAS-accepted. MNRAS-accepte
The all-sky GEOS RR Lyr survey with the TAROT telescopes. Analysis of the Blazhko effect
We used the GEOS database to study the Blazhko effect of galactic RRab stars.
The database is continuously enriched by maxima supplied by amateur astronomers
and by a dedicated survey by means of the two TAROT robotic telescopes. The
same value of the Blazhko period is observed at different values of the
pulsation periods and different values of the Blazhko periods are observed at
the same value of the pulsation period. There are clues suggesting that the
Blazhko effect is changing from one cycle to the next. The secular changes in
the pulsation and Blazhko periods of Z CVn are anticorrelated. The diagrams of
magnitudes against phases of the maxima clearly show that the light curves of
Blazhko variables can be explained as modulated signals, both in amplitude and
in frequency. The closed curves describing the Blazhko cycles in such diagrams
have different shapes, reflecting the phase shifts between the epochs of the
brightest maximum and the maximum O-C. Our sample shows that both clockwise and
anticlockwise directions are possible for similar shapes. The improved
observational knowledge of the Blazhko effect, in addition to some
peculiarities of the light curves, have still to be explained by a satisfactory
physical mechanism.Comment: 13 pages, 12 figures, accepted for publication in Astronomical
Journa
Recapitulation of the EEF1A2 D252H neurodevelopmental disorder-causing missense mutation in mice reveals a toxic gain of function
The Social and Political Dimensions of the Ebola Response: Global Inequality, Climate Change, and Infectious Disease
The 2014 Ebola crisis has highlighted public-health vulnerabilities in Liberia, Sierra
Leone, and Guinea – countries ravaged by extreme poverty, deforestation and
mining-related disruption of livelihoods and ecosystems, and bloody civil wars in
the cases of Liberia and Sierra Leone. Ebola’s emergence and impact are grounded
in the legacy of colonialism and its creation of enduring inequalities within African
nations and globally, via neoliberalism and the Washington Consensus. Recent
experiences with new and emerging diseases such as SARS and various strains of
HN influenzas have demonstrated the effectiveness of a coordinated local and
global public health and education-oriented response to contain epidemics. To what
extent is international assistance to fight Ebola strengthening local public health and
medical capacity in a sustainable way, so that other emerging disease threats, which
are accelerating with climate change, may be met successfully? This chapter
considers the wide-ranging socio-political, medical, legal and environmental factors
that have contributed to the rapid spread of Ebola, with particular emphasis on the
politics of the global and public health response and the role of gender, social
inequality, colonialism and racism as they relate to the mobilization and
establishment of the public health infrastructure required to combat Ebola and other
emerging diseases in times of climate change
On the Origin of Broad Fe K alpha and Hi H alpha Lines in AGN
We examine the properties of the Fe emission lines that arise near 6.4 keV in
the ASCA spectra of AGN. Our emphasis is on the Seyfert 1 galaxies where broad
and apparently complex Fe K alpha emission is observed. We consider various
origins for the line but focus on the pros and cons for line emitting accretion
disk models. We develop a simple model of an illuminated disk capable of
producing both X-ray and optical lines from a disk. The model is able to
reproduce the observed Fe K alpha FWHM ratio as well as the radii of maximum
emissivity implied by the profile redshifts. The overall profile shapes however
do not fit well the predictions of our disk illumination model nor do we derive
always consistent disk inclinations for the two lines. We conclude that the
evidence for and against an accretion disk origin for the Fe K alpha emission
is equal at best. The bulk of the data requires a very disparate set of line
fits which shed little light on a coherent physical model. We briefly consider
alternatives to disk emission models and show that a simple bicone model can
reproduce the FE line profiles equally well.Comment: 29 pages, 6 tables, 6 figures. Submitted for publication in the
Astrophysical Journal part
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