3,641 research outputs found
The effect of early dark matter halos on reionization
The annihilation of dark matter particles releases energy, ionizing some of
the gas in the Universe. We investigate the effect of dark matter halos on
reionization. We show that the effect depends on the assumed density profile,
the particle mass, and the assumed minimum halo mass. For NFW halos and typical
WIMPs, we find the effect to be quite small. However, light dark matter
candidates in the MeV range can contribute significantly to reionization and
can make an important contribution to the measured optical depth. This effect
may be used to constrain light dark matter models. We also study the effect of
varying the halo density profile on reionization.Comment: Minor changes from v2. Accepted for publication in Phys. Rev.
Black-hole remnants from black-hole-neutron-star mergers
Observations of gravitational waves and their electromagnetic counterparts may soon uncover the existence of coalescing compact binary systems formed by a stellar-mass black hole and a neutron star. These mergers result in a remnant black hole, possibly surrounded by an accretion disk. The mass and spin of the remnant black hole depend on the properties of the coalescing binary. We construct a map from the binary components to the remnant black hole using a sample of numerical-relativity simulations of different mass ratios q, (anti)aligned dimensionless spins of the black hole aBH, and several neutron star equations of state. Given the binary total mass, the mass and spin of the remnant black hole can therefore be determined from the three parameters (q,aBH,Λ), where Λ is the tidal deformability of the neutron star. Our models also incorporate the binary black hole and test-mass limit cases and we discuss a simple extension for generic black-hole spins. We combine the remnant characterization with recent population synthesis simulations for various metallicities of the progenitor stars that generated the binary system. We predict that black-hole-neutron-star mergers produce a population of remnant black holes with masses distributed around 7 M and 9 M. For isotropic spin distributions, nonmassive accretion disks are favored: no bright electromagnetic counterparts are expected in such mergers
A disrupted bulgeless satellite galaxy as counterpart of the ultraluminous X-ray source ESO 243-49 HLX-1
The point-like X-ray source HLX-1, close to the S0 galaxy ESO 243-49, is one the strongest intermediate-mass black hole candidates, but the nature of its counterpart is still puzzling. By means of N-body/smoothed particle hydrodynamics simulations, we investigate the hypothesis that the HLX-1 counterpart is the nucleus of a bulgeless satellite galaxy, which undergoes a minor merger with the S0galaxy.We derived synthetic surface brightness profiles for the simulated counterpart of HLX-1 in six Hubble Space Telescope (HST) filters, ranging from far ultraviolet (FUV) to infrared wavelengths, and we compared them with the observed profiles. Our model matches the emission associated with the HLX-1 counterpart in all considered filters, including the bluer ones, even without requiring the contribution of an irradiated disc. The simulation can also account for an extended FUV emission, which is hinted at by the analysis of the F140LP HST filter. This matching is impossible to achieve by assuming either a bulgy satellite, a young star cluster, or an irradiated disc component
The optogenetic revolution in cerebellar investigations
The cerebellum is most renowned for its role in sensorimotor control and coordination, but a growing number of anatomical and physiological studies are demonstrating its deep involvement in cognitive and emotional functions. Recently, the development and refinement of optogenetic techniques boosted research in the cerebellar field and, impressively, revolutionized the methodological approach and endowed the investigations with entirely new capabilities. This translated into a significant improvement in the data acquired for sensorimotor tests, allowing one to correlate single-cell activity with motor behavior to the extent of determining the role of single neuronal types and single connection pathways in controlling precise aspects of movement kinematics. These levels of specificity in correlating neuronal activity to behavior could not be achieved in the past, when electrical and pharmacological stimulations were the only available experimental tools. The application of optogenetics to the investigation of the cerebellar role in higher-order and cognitive functions, which involves a high degree of connectivity with multiple brain areas, has been even more significant. It is possible that, in this field, optogenetics has changed the game, and the number of investigations using optogenetics to study the cerebellar role in non-sensorimotor functions in awake animals is growing. The main issues addressed by these studies are the cerebellar role in epilepsy (through connections to the hippocampus and the temporal lobe), schizophrenia and cognition, working memory for decision making, and social behavior. It is also worth noting that optogenetics opened a new perspective for cerebellar neurostimulation in patients (e.g., for epilepsy treatment and stroke rehabilitation), promising unprecedented specificity in the targeted pathways that could be either activated or inhibited
Microbial assisted phytodepuration for water reclamation: Environmental benefits and threats
Climate changes push for water reuse as a priority to counteract water scarcity and minimize water footprint especially in agriculture, one of the highest water consuming human activities. Phytodepuration is indicated as a promising technology for water reclamation, also in the light of its economic and ecological sustainability, and the use of specific bacterial inocula for microbial assisted phytodepuration has been proposed as a further advance for its implementation. Here we provided an overview on the selection and use of plant growth promoting bacteria in Constructed Wetland (CW) systems, showing their advantages in terms of plant growth support and pollutant degradation abilities. Moreover, CWs are also proposed for the removal of emerging organic pollutants like antibiotics from urban wastewaters. We focused on this issue, still debated in the literature, revealing the necessity to deepen the knowledge on the antibiotic resistance spread into the environment in relation to treated wastewater release and reuse. In addition, given the presence in the plant system of microhabitats (e.g. rhizosphere) that are hot spot for Horizontal Gene Transfer, we highlighted the importance of gene exchange to understand if these events can promote the diffusion of antibiotic resistance genes and antibiotic resistant bacteria, possibly entering in the food production chain when treated wastewater is used for irrigation. Ideally, this new knowledge will lead to improve the design of phytodepuration systems to maximize the quality and safety of the treated effluents in compliance with the 'One Health' concept
A Panchromatic Study of the Globular Cluster NGC 1904. I: The Blue Straggler Population
By combining high-resolution (HST-WFPC2) and wide-field ground based (2.2m
ESO-WFI) and space (GALEX) observations, we have collected a multi-wavelength
photometric data base (ranging from the far UV to the near infrared) of the
galactic globular cluster NGC1904 (M79). The sample covers the entire cluster
extension, from the very central regions up to the tidal radius. In the present
paper such a data set is used to study the BSS population and its radial
distribution. A total number of 39 bright () BSS has been
detected, and they have been found to be highly segregated in the cluster core.
No significant upturn in the BSS frequency has been observed in the outskirts
of NGC 1904, in contrast to other clusters (M 3, 47 Tuc, NGC 6752, M 5) studied
with the same technique. Such evidences, coupled with the large radius of
avoidance estimated for NGC 1904 ( core radii), indicate that
the vast majority of the cluster heavy stars (binaries) has already sunk to the
core. Accordingly, extensive dynamical simulations suggest that BSS formed by
mass transfer activity in primordial binaries evolving in isolation in the
cluster outskirts represent only a negligible (0--10%) fraction of the overall
population.Comment: ApJ accepte
Dynamical age differences among coeval star clusters as revealed by blue stragglers
Globular star clusters that formed at the same cosmic time may have evolved
rather differently from a dynamical point of view (because that evolution
depends on the internal environment) through a variety of processes that tend
progressively to segregate stars more massive than the average towards the
cluster centre. Therefore clusters with the same chronological age may have
reached quite different stages of their dynamical history (that is, they may
have different dynamical ages). Blue straggler stars have masses greater than
those at the turn-off point on the main sequence and therefore must be the
result of either a collision or a mass-transfer event. Because they are among
the most massive and luminous objects in old clusters, they can be used as test
particles with which to probe dynamical evolution. Here we report that globular
clusters can be grouped into a few distinct families on the basis of the radial
distribution of blue stragglers. This grouping corresponds well to an effective
ranking of the dynamical stage reached by stellar systems, thereby permitting a
direct measure of the cluster dynamical age purely from observed properties.Comment: Published on the 20 December 2012 issue of Natur
Novel PCB-degrading Rhodococcus strains able to promote plant growth for assisted rhizoremediation of historically polluted soils
Extended soil contamination by polychlorinated biphenyls (PCBs) represents a global environmental issue that can hardly be addressed with the conventional remediation treatments. Rhizoremediation is a sustainable alternative, exploiting plants to stimulate in situ the degradative bacterial communities naturally occurring in historically polluted areas. This approach can be enhanced by the use of bacterial strains that combine PCB degradation potential with the ability to promote plant and root development. With this aim, we established a collection of aerobic bacteria isolated from the soil of the highly PCB-polluted site \u201cSIN Brescia-Caffaro\u201d (Italy) biostimulated by the plant Phalaris arundinacea. The strains, selected on biphenyl and plant secondary metabolites provided as unique carbon source, were largely dominated by Actinobacteria and a significant number showed traits of interest for remediation, harbouring genes homologous to bphA, involved in the PCB oxidation pathway, and displaying 2,3-catechol dioxygenase activity and emulsification properties. Several strains also showed the potential to alleviate plant stress through 1-aminocyclopropane-1-carboxyl-ate deaminase activity. In particular, we identified three Rhodococcus strains able to degrade in vitro several PCB congeners and to promote lateral root emergence in the model plant Arabidopsis thaliana in vivo. In addition, these strains showed the capacity to colonize the root system and to increase the plant biomass in PCB contaminated soil, making them ideal candidates to sustain microbial-assisted PCB rhizoremediation through a bioaugmentation approach
Retention of arsenic and selenium compounds present in coal combustion and gasification flue gases using activated carbons
7 pages, 7 figures, 6 tables.-- Printed version published Aug 2007.The emission of potentially toxic compounds of arsenic and selenium present in flue gases from coal combustion and gasification processes has led to the need for gas cleaning systems capable of reducing their content. This work is focused on the capture of these elements in activated carbons which have proven to have good retention capacities for mercury compounds in gas phase. Two commercial activated carbons (Norit RBHG3 and Norit RB3) and a carbon prepared via activation of a pyrolysed coal (CA) were tested in simulated coal combustion and gasification atmospheres in a laboratory scale reactor. Arsenic and selenium compounds were retained to different extents on these carbons, retention efficiency depending mainly on the speciation of the element, which in turn depends on the gas atmosphere. Arsenic retention was similar in both combustion and gasification atmospheres unlike selenium retention. Moreover the retention of arsenic was lower than that of selenium.This work was carried out with the financial support of ECSC (7220-ED/095). We are also grateful to our colleagues in ICB (CSIC) R. Juan and C. Ruiz who prepared the CA activated carbon and Amelia Martínez Alonso of INCAR who assisted us in the textural characterization.Peer reviewe
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