749 research outputs found
The Black Hole to Bulge Mass Relation in Active Galactic Nuclei
The masses of the central black holes in Active Galactic Nuclei (AGNs) can be
estimated using the broad emission-lines as a probe of the virial mass. Using
reverberation mapping to determine the size of the Broad Line Region (BLR) and
the width of the variable component of the line profile H line it is
possible to find quite accurate virial mass estimates for AGNs with adequate
data. Compiling a sample of AGNs with reliable central masses and bulge
magnitudes we find an average black-hole-to-bulge mass ratio of 0.0003, a
factor of 20 less than the value found for normal galaxies and for bright
quasars. This lower ratio is more consistent with the back hole mass density
predicted from quasar light, and is similar to the central black hole/bulge
mass ratio in our Galaxy. We argue that the black hole/bulge mass ratio
actually has a significantly larger range than indicated by mssive black holes
detected in normal galaxies (using stellar dynamics) and in bright quasars,
which may be biased towards large black holes. We derive a scenario of black
hole growth that explains the observed distribution.Comment: 12 pages LaTeX, including 2 revised figures, revised table. Revised
version to be published in the Astrophysical Journal (Letters) Ap.J.Lett. 51
Improving Access to Medicines in Poor Countries: The Role of Universities
Universities Allied for Essential Medicines, a coalition of students and faculty across North America, focuses on how academic research institutions can help to improve access to essential medicines
Spins of the supermassive black hole in M87: new constraints from TeV observations
The rapid TeV ray variability detected in the well-known nearby
radio galaxy M87 implies an extremely compact emission region (5-10
Schwarzschild radii) near the horizon of the supermassive black hole in the
galactic center. TeV photons are affected by dilution due to interaction with
the radiation field of the advection-dominated accretion flow (ADAF) around the
black hole, and can thus be used to probe the innermost regions around the
black hole. We calculate the optical depth of the ADAF radiation field to the
TeV photons and find it strongly depends on the spin of the black hole. We find
that transparent radii of 10 TeV photons are of and
for the maximally rotating and non-rotating black holes, respectively. With the
observations, the calculated transparent radii strongly suggest the black hole
is spinning fast in the galaxy. TeV photons could be used as a powerful
diagnostic for estimating black hole spins in galaxies in the future.Comment: 4 pages, 4 figures. to appear in ApJ
QSO's from Galaxy Collisions with Naked Black Holes
In the now well established conventional view (see Rees [1] and references
therein), quasi-stellar objects (QSOs) and related active galactic nuclei (AGN)
phenomena are explained as the result of accretion of plasma onto giant black
holes which are postulated to form via gravitational collapse of the high
density regions in the centers of massive host galaxies. This model is
supported by a wide variety of indirect evidence and seems quite likely to
apply at least to some observed AGN phenomena. However, one surprising set of
new Hubble Space Telescope (HST) observations [2-4] directly challenges the
conventional model, and the well known evolution of the QSO population raises
some additional, though not widely recognized, difficulties. We propose here an
alternative possibility: the Universe contains a substantial independent
population of super-massive black holes, and QSO's are a phenomenon that occurs
due to their collisions with galaxies or gas clouds in the intergalactic medium
(IGM). This hypothesis would naturally explain why the QSO population declines
very rapidly towards low redshift, as well as the new HST data.Comment: plain TeX file, no figures, submitted to Natur
Artificial Intelligence as an Enabler of Quick and Effective Production Repurposing Manufactur-ing: An Exploratory Review and Future Research Propositions
The outbreak of Covid-19 created disruptions in manufacturing operations. One of the most serious negative impacts is the shortage of critical medical supplies. Manufacturing firms faced pressure from governments to use their manufacturing capacity to repurpose their production for meeting the critical demand for necessary products. For this purpose, recent advancements in technology and artificial intelligence (AI) could act as response solutions to conquer the threats linked with repurposing manufacturing (RM). The studyâs purpose is to investigate the significance of AI in RM through a systematic literature review (SLR). This study gathered around 453 articles from the SCOPUS database in the selected research field. Structural Topic Modeling (STM) was utilized to generate emerging research themes from the selected documents on AI in RM. In addition, to study the research trends in the field of AI in RM, a bibliometric analysis was undertaken using the R-package. The findings of the study showed that there is a vast scope for research in this area as the yearly global production of articles in this field is limited. However, it is an evolving field and many research collaborations were identified. The study proposes a comprehensive research framework and propositions for future research development
Closing the access gap for health innovations: an open licensing proposal for universities
BACKGROUND: This article centers around a proposal outlining how research universities could leverage their intellectual property to help close the access gap for health innovations in poor countries. A recent deal between Emory University, Gilead Sciences, and Royalty Pharma is used as an example to illustrate how 'equitable access licensing' could be put into practice. DISCUSSION: While the crisis of access to medicines in poor countries has multiple determinants, intellectual property protection leading to high prices is well-established as one critical element of the access gap. Given the current international political climate, systemic, government-driven reform of intellectual property protection seems unlikely in the near term. Therefore, we propose that public sector institutions, universities chief among them, adopt a modest intervention â an Equitable Access License (EAL) â that works within existing trade-law and drug-development paradigms in order to proactively circumvent both national and international obstacles to generic medicine production. Our proposal has three key features: (1) it is prospective in scope, (2) it facilitates unfettered generic competition in poor countries, and (3) it centers around universities and their role in the biomedical research enterprise. Two characteristics make universities ideal agents of the type of open licensing proposal described. First, universities, because they are upstream in the development pipeline, are likely to hold rights to the key components of a wide variety of end products. Second, universities acting collectively have a strong negotiating position with respect to other players in the biomedical research arena. Finally, counterarguments are anticipated and addressed and conclusions are drawn based on how application of the Equitable Access License would have changed the effects of the licensing deal between Emory and Gilead
Young stars and non-stellar emission in the aligned radio galaxy 3C 256
We present ground-based images of the z=1.824 radio galaxy 3C 256 in the
standard BVRIJHK filters and an interference filter centered at 8800A, a Hubble
Space Telescope image in a filter dominated by Ly-alpha emission (F336W), and
spectra covering rest-frame wavelengths from Ly-alpha to [O III] 5007. Together
with published polarimetry observations, we use these to decompose the overall
spectral energy distribution into nebular continuum emission, scattered quasar
light, and stellar emission. The nebular continuum and scattered light together
comprise half (one third) of the V-band (K-band) light within a 4-arcsec
aperture, and are responsible for the strong alignment between the
optical/near-infrared light and the radio emission. The stellar emission is
dominated by a population estimated to be 100-200 Myr old (assuming a Salpeter
IMF), and formed in a short burst with a peak star formation rate of 1-4x10^3
Msun/yr. The total stellar mass is estimated to be no more than 2x10^{11} Msun,
which is far less than other luminous radio galaxies at similar redshifts, and
suggests that 3C 256 will undergo further star formation or mergers.Comment: 35 pages including 10 figures; to appear in Nov 10 Ap
The black hole mass distribution in early-type galaxies: cusps in HST photometry interpreted through adiabatic black hole growth
The surface brightness profiles of early-type galaxies have central cusps.
Two characteristic profile types are observed with HST: `core' profiles have a
break at a resolved radius and logarithmic cusp slope gamma < 0.3 inside that
radius; `power-law' profiles have no clear break and gamma > 0.3. With few
exceptions, galaxies with M_V
-20.5 have power-law profiles. Both profile types occur in galaxies with -22 <
M_V < -20.5. We show that these results are consistent with the hypothesis
that: (i) all early-type galaxies have black holes (BHs) that grew
adiabatically in homogeneous isothermal cores; and (ii) these `progenitor'
cores followed scaling relations similar to those of the fundamental plane.
The models studied here are the ones first proposed by Young. Models with BH
masses and progenitor cores that obey established scaling relations predict (at
Virgo) that galaxies with M_V < -21.2 have core profiles and galaxies with M_V
> -21.2 have power-law profiles. This reproduces both the sense and the
absolute magnitude of the observed transition. Intrinsic scatter in BH and
galaxy properties can explain why both types of galaxies are observed around
the transition magnitude. The observed bimodality in cusp slopes may be due to
a bimodality in M_bh/L, with rapidly rotating disky galaxies having larger
M_bh/L than slowly rotating boxy galaxies.
Application to individual galaxies with HST photometry yields a roughly
linear correlation between BH mass and V-band galaxy luminosity, log M_bh =
-1.83 + log L (solar units). This agrees with the average relation for nearby
galaxies with kinematically determined BH masses, and also with predictions
from quasar statistics (shortened abstract).Comment: 41 pages, LaTeX, with 11 PostScript figures. Submitted to the
Astronomical Journal. Postscript version also available from
http://sol.stsci.edu/~marel/abstracts/abs_R23.htm
Priority setting for collaborative health systems research in India: a method and the way forward
A comprehensive and collaborative knowledge translation and decision-making approach can help reduce the longstanding barriers to using research in policy and practice. Regular interaction between researchers and decision-makers increases the likelihood of using research knowledge. This interaction continuing over the entire research cycle is critical for developing research directions and potential use of the research outputs that benefit the health system. The India Health Systems Collaborative and ACCESS Health International have conducted a rigorous exercise to arrive at the priority research topics. A consensus-based method customised to the existing need was created, adapting from the Child Health and Nutrition Research Initiative (CHNRI) method for research priority setting. In this method, conducting literature reviews, key informant interviews and survey-based stakeholder consultations are critical steps for identifying policy-relevant research topics that demand utmost attention in the Indian setting. This article documents the processes followed to develop a preliminary list of core research priorities requiring urgent attention to facilitate policy development. Additionally, the article is about the essential and immediate next steps and the critical actions taken to undertake collaborative research on the identified research topics. The special issue of the Journal for Health Management dedicated to strengthening the Indian health system sets the foundation for promoting collaborative research, its dissemination for broader use by researchers and ensuing policy dialogues
The mass density in black holes inferred from the X-ray background
The X-ray Background (XRB) probably originates from the integrated X-ray
emission of active galactic nuclei (AGN). Modelling of its flat spectrum
implies considerable absorption in most AGN. Compton down-scattering means that
sources in which the absorption is Compton thick are unlikely to be major
contributors to the background intensity so the observed spectral intensity at
about 30 keV is little affected by photoelectric absorption. Assuming that the
intrinsic photon index of AGN is 2, we then use the 30 keV intensity of the XRB
to infer the absorption-corrected energy density of the background. Soltan's
argument then enables us to convert this to a mean local density in black
holes, assuming an accretion efficiency of 0.1 and a mean AGN redshift of 2.
The result is within a factor of two of that estimated by Haehnelt et al from
the optically-determined black hole masses of Magorrian et al. We conclude that
there is no strong need for any radiatively inefficient mode of accretion for
building the masses of black holes. Furthermore we show that the absorption
model for the XRB implies that about 85 per cent of accretion power in the
Universe is absorbed. This power probably emerges in the infrared bands where
it can be several tens per cent of the recently inferred backgrounds there. The
total power emitted by accretion is then about one fifth that of stars.Comment: 4 pages, accepted for publication in MNRA
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