148 research outputs found
The first five percent of neural contrast spikes from a visual scene robustly computes the gravity vector
Wave Propagation Through Non-Uniform Plasma
Increased energy demand has led to plans for building many new dams in the western Amazon, mostly in the Andean region. Historical data and mechanistic scenarios are used to examine potential impacts above and below six of the largest dams planned for the region, including reductions in downstream sediment and nutrient supplies, changes in downstream flood pulse, changes in upstream and downstream fish yields, reservoir siltation, greenhouse gas emissions and mercury contamination. Together, these six dams are predicted to reduce the supply of sediments, phosphorus and nitrogen from the Andean region by 69, 67 and 57% and to the entire Amazon basin by 64, 51 and 23%, respectively. These large reductions in sediment and nutrient supplies will have major impacts on channel geomorphology, floodplain fertility and aquatic productivity. These effects will be greatest near the dams and extend to the lowland floodplains. Attenuation of the downstream flood pulse is expected to alter the survival, phenology and growth of floodplain vegetation and reduce fish yields below the dams. Reservoir filling times due to siltation are predicted to vary from 106-6240 years, affecting the storage performance of some dams. Total CO2 equivalent carbon emission from 4 Andean dams was expected to average 10 Tg y-1 during the first 30 years of operation, resulting in a MegaWatt weighted Carbon Emission Factor of 0.139 tons C MWhr-1. Mercury contamination in fish and local human populations is expected to increase both above and below the dams creating significant health risks. Reservoir fish yields will compensate some downstream losses, but increased mercury contamination could offset these benefits
JWST UNCOVER: Discovery of Galaxy Candidates Behind the Lensing Cluster Abell 2744
We present the results of a search for high-redshift () galaxy
candidates in the JWST UNCOVER survey, using deep NIRCam and NIRISS imaging in
7 bands over arcmin and ancillary HST observations. The NIRCam
observations reach a limiting magnitude of AB. The
identification of high candidates relies on a combination of a dropout
selection and photometric redshifts. We find 16 candidates at and 3
candidates at , eight candidates are deemed very robust. Their lensing
amplification ranges from to 11.5. Candidates have a wide range of
(lensing-corrected) luminosities and young ages, with low stellar masses
( log(M/M) ) and low star formation rates
(SFR=0.2-7 M yr), confirming previous findings in early JWST
observations of . A few galaxies at appear to show a clear
Balmer break between the F356W and F444W/F410M bands, which helps constrain
their stellar mass. We estimate blue UV continuum slopes between
and , typical for early galaxies at but not as extreme as the
bluest recently discovered sources. We also find evidence for a rapid
redshift-evolution of the mass-luminosity relation and a redshift-evolution of
the UV continuum slope for a given range of intrinsic magnitude, in line with
theoretical predictions. These findings suggest that deeper JWST observations
are needed to reach the fainter galaxy population at those early epochs, and
follow-up spectroscopy will help better constrain the physical properties and
star formation histories of a larger sample of galaxies.Comment: Submitted to MNRA
Anti-Allergic Cromones Inhibit Histamine and Eicosanoid Release from Activated Human and Murine Mast Cells by Releasing Annexin A1
PMCID: PMC3601088This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Progress on improving Agricultural Nitrogen use efficiency: UK-China viortual joint centers on Nitrogen Agronomy
Two virtual joint centers for nitrogen agronomy were established between the UK and China to facilitate collaborative research aimed at improving nitrogen use efficiency (NUE) in agricultural production systems and reducing losses of reactive N to the environment. Major focus areas were improving fertilizer NUE, use of livestock manures, soil health, and policy development and knowledge exchange. Improvements to fertilizer NUE included attention to application rate in the context of yield potential and economic considerations and the potential of improved practices including enhanced efficiency fertilizers, plastic film mulching and cropping design. Improved utilization of livestock manures requires knowledge of the available nutrient content, appropriate manure processing technologies and integrated nutrient management practices. Soil carbon, acidification and biodiversity were considered as important aspects of soil health. Both centers identified a range of potential actions that could be taken to improve N management, and the research conducted has highlighted the importance of developing a systemslevel approach to assessing improvement in the overall efficiency of N management and avoiding unintended secondary effects from individual interventions. Within this context, the management of fertilizer emissions and
livestock manure at the farm and regional scales appear to be particularly important targets for mitigation
UNCOVER: Illuminating the Early Universe -- JWST/NIRSpec Confirmation of Galaxies
Observations of high-redshift galaxies provide a critical direct test to the
theories of early galaxy formation, yet to date, only four have been
spectroscopically confirmed at . Due to strong gravitational lensing over
a wide area, the galaxy cluster field Abell~2744 is ideal for searching for the
earliest galaxies. Here we present JWST/NIRSpec observations of two galaxies: a
robust detection at , and a plausible
candidate at . The galaxies are
discovered in JWST/NIRCam imaging and their distances are inferred with
JWST/NIRSpec spectroscopy, all from the JWST Cycle 1 UNCOVER Treasury survey.
Detailed stellar population modeling using JWST NIRCam and NIRSpec data
corroborates the primeval characteristics of these galaxies: low mass (), young, rapidly-assembling, metal-poor, and star-forming.
Interestingly, both galaxies are spatially resolved, having lensing-corrected
rest-UV effective radii on the order of 300-400 pc, which are notably larger
than other spectroscopically confirmed systems. The observed
dynamic range of size spans over an order of magnitude, implying
a significant scatter in the size-mass relation at early times. Deep into the
epoch of reionization, these discoveries elucidate the emergence of the first
galaxies.Comment: submitted to ApJL; 13 pages, 4 figures, 2 table
UNCOVER: The growth of the first massive black holes from JWST/NIRSpec -- spectroscopic confirmation of an X-ray luminous AGN at z=10.1
The James Webb Space Telescope is now detecting early black holes (BHs) as
they transition from "seeds" to supermassive BHs. Recently Bogdan et al. (2023)
reported the detection of an X-ray luminous supermassive BH, UHZ-1, with a
photometric redshift at . Such an extreme source at this very high
redshift provides new insights on seeding and growth models for BHs given the
short time available for formation and growth. Harnessing the exquisite
sensitivity of JWST/NIRSpec, here we report the spectroscopic confirmation of
UHZ-1 at . We find that the NIRSpec/Prism spectrum is
typical of recently discovered z~10 galaxies, characterized primarily by
star-formation features. We see no clear evidence of the powerful X-ray source
in the rest-frame UV/optical spectrum, which may suggest heavy obscuration of
the central BH, in line with the Compton-thick column density measured in the
X-rays. We perform a stellar population fit simultaneously to the new NIRSpec
spectroscopy and previously available photometry. The fit yields a stellar mass
estimate for the host galaxy that is significantly better constrained than
prior photometric estimates ().
Given the predicted BH mass (), the resulting
ratio of remains two to three orders of magnitude higher than
local values, thus lending support to the heavy seeding channel for the
formation of supermassive BHs within the first billion years of cosmic
evolution.Comment: 9 pages, 4 figures, submitted to ApJL. Minor text correction
UNCOVER: A NIRSpec Identification of a Broad-line AGN at z = 8.50
Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at z = 8.50 displaying a clear broad-line component as inferred from the Hβ line with FWHM = 3439 ± 413 km s−1, typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of
and a bolometric luminosity of Lbol ∼ 6.6 × 1045 erg s−1. These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of , which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high-z faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy–black hole coevolution in the early Universe
UNCOVER:A NIRSpec Identification of a Broad-line AGN at z = 8.50
Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at z = 8.50 displaying a clear broad-line component as inferred from the Hβ line with FWHM = 3439 ± 413 km s−1, typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of log 10 ( M BH / M ⊙ ) = 8.17 ± 0.42 and a bolometric luminosity of L bol ∼ 6.6 × 1045 erg s−1. These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of log 10 ( M * / M ⊙ ) < 8.7 , which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high-z faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy-black hole coevolution in the early Universe.</p
UNCOVER: A NIRSpec Identification of a Broad Line AGN at z = 8.50
Deep observations with JWST have revealed an emerging population of red
point-like sources that could provide a link between the postulated
supermassive black hole seeds and observed quasars. In this work we present a
JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey, of a
massive accreting black hole at , displaying a clear broad-line
component as inferred from the H line with FWHM = km
s, typical of the broad line region of an active galactic nucleus (AGN).
The AGN nature of this object is further supported by high ionization, as
inferred from emission lines, and a point-source morphology. We compute the
black hole mass of log, and a bolometric
luminosity of erg s. These values
imply that our object is accreting at of the Eddington limit.
Detailed modeling of the spectral energy distribution in the optical and
near-infrared, together with constraints from ALMA, indicate an upper limit on
the stellar mass of log, which would lead to an
unprecedented ratio of black hole to host mass of at least . This
is orders of magnitude higher compared to the local QSOs, but is consistent
with recent AGN studies at high redshift with JWST. This finding suggests that
a non-negligible fraction of supermassive black holes either started out from
massive seeds and/or grew at a super-Eddington rate at high redshift. Given the
predicted number densities of high- faint AGN, future NIRSpec observations
of larger samples will allow us to further investigate the galaxy-black hole
co-evolution in the early Universe.Comment: 14 pages, 6 figures, 2 tables. Submitted to ApJ
- …