22,199 research outputs found
Early black-hole seeds in the first billion years
Supermassive black holes with billion solar masses are in place already
within the first Gyr, however, their origin and growth in such a short lapse of
time is extremely challenging to understand. Here, we discuss the formation
paths of early black-hole seeds, showing the limits of light black-hole seeds
from stellar origin and the expected characteristics of heavy/massive
black-hole seeds originated by gas direct collapse in peculiar primordial
conditions. To draw conclusions on the possible candidates and the role of the
ambient medium, we use results from N-body hydrodynamic simulations including
atomic and molecular non-equilibrium abundance calculations, cooling, star
formation, feedback mechanisms, stellar evolution, metal spreading of several
heavy elements from SNII, AGB and SNIa, and multifrequency radiative transfer
over 150 frequencies coupled to chemistry and SED emission for popII-I and
popIII stellar sources. Standard stellar-origin light black holes are unlikely
to be reliable seeds of early supermassive black holes, because, under
realistic assumptions, they cannot grow significantly in less than a billion
years. Alternatively, massive black-hole seeds might originate from direct
collapse of pristine gas in primordial quiescent mini-haloes that are exposed
to stellar radiation from nearby star forming regions. The necessary conditions
required to form these heavy seeds must be complemented with information on the
complex features of local environments and the fine balance between chemistry
evolution and radiative transfer.Comment: minor revisio
Common vocabularies for collective intelligence - work in progress
Web based applications and tools offer a great potential to increase the efficiency of information flow and communication among different agents during emergencies. Among the different factors, technical and non technical, that hinder the integration of an information model in emergency management sector, is a lack of a common, shared vocabulary. This paper furthers previous work in the area of ontology development, and presents a summary and overview of the goal, process and methodology to construct a shared set of metadata that can be used to map existing vocabulary. This paper is a work in progress report
Neuronal oxidative injury in the development of the epileptic disease : a potential target for novel therapeutic approaches
Epileptic diseases affect about 50 million people in the world and approximately 30% of patients diagnosed with epilepsy are unresponsive to current medications. For these reasons, primary prevention of epilepsy represents one of the priorities in epilepsy research. Intracellular oxido-reductive (redox) state is well known to play a crucial role, contributing to the maintenance of the proper function of biomolecules. Therefore, oxidative stress results in functional cellular disruption and cellular damage and may cause subsequent cell death via oxidation of proteins, lipids, and nucleotides. Recently, the role of oxidative stress in the early stage and in the progression of epileptic disorders has begun to be recognized. The early molecular response to oxidative stress represents a short-term reversible phenomenon that precedes higher and irreversible forms of oxidation. This article reviews the current understanding of the epileptogenic phenomena related to seizure-induced oxidative injury as potential âcritical periodâ therapeutic targets for the prevention of chronic epileptic disorder.peer-reviewe
Hydrodynamical chemistry simulations of the SZ effect and the impacts from primordial non-Gaussianities
The impacts of Compton scattering of hot cosmic gas with the cosmic microwave
background radiation (Sunyaev-Zel'dovich effect, SZ) are consistently
quantified in Gaussian and non-Gaussian scenarios, by means of 3D numerical,
N-body, hydrodynamic simulations, including cooling, star formation, stellar
evolution and metal pollution (He, C, O, Si, Fe, S, Mg, etc.) from different
stellar phases, according to proper yields for individual metal species and
mass-dependent stellar lifetimes. Light cones are built through the simulation
outputs and samples of one hundred maps for the resulting temperature
fluctuations are derived for both Gaussian and non-Gaussian primordial
perturbations. From them, we estimate the possible changes due to early
non-Gaussianities on: SZ maps, probability distribution functions, angular
power spectra and corresponding bispectra. We find that the different growth of
structures in the different cases induces significant spectral distortions only
in models with large non-Gaussian parameters, . In general, the
overall trends are covered by the non-linear, baryonic evolution, whose
feedback mechanisms tend to randomize the gas behaviour and homogenize its
statistical features, quite independently from the background matter
distribution. Deviations due to non-Gaussianity are almost undistinguishable
for , remaining always at few-per-cent level, within
the error bars of the Gaussian scenario. Rather extreme models with present more substantial deviations from the Gaussian case,
overcoming baryon contaminations and showing discrepancies up to a factor of a
few in the spectral properties.Comment: 10 pages, 4 figures, accepted for publication on MNRA
The imprint of cosmological non-Gaussianities on primordial structure formation
We study via numerical N-body/SPH chemistry simulations the effects of
primordial non-Gaussianities on the formation of the first stars and galaxies,
and investigate the impact of supernova feedback in cosmologies with different
fnl. Density distributions are biased to higher values, so star formation and
the consequent feedback processes take place earlier in high-fnl models and
later in low-fnl ones. Mechanical feedback is responsible for shocking and
evacuating the gas from star forming sites earlier in the highly non-Gaussian
cases, because of the larger bias at high densities. Chemical feedback
translates into high-redshift metal filling factors that are larger by some
orders of magnitude for larger fnl, but that converge within one Gyr, for both
population III and population II-I stellar regimes. The efficient enrichment
process, though, leads to metallicities > 0.01 Zsun by redshift ~9, almost
independently from fnl. The impact of non-Gaussianities on the formation of
dark-matter haloes at high redshift is directly reflected in the properties of
the gas in these haloes, as models with larger fnl show more concentrated gas
profiles at early times. Non-Gaussian signatures in the gas behaviour are lost
after the first feedback takes place and introduces a significant degree of
turbulence and chaotic motions.Comment: 10 pages, 9 figures - accepted for publication in MNRA
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