316 research outputs found
Evolution of Supermassive Black Holes from Cosmological Simulations
The correlations between the mass of supermassive black holes and properties
of their host galaxies are investigated through cosmological simulations. Black
holes grow from seeds of 100 solar masses inserted into density peaks present
in the redshift range 12-15. Seeds grow essentially by accreting matter from a
nuclear disk and also by coalescences resulting from merger episodes. At z=0,
our simulations reproduce the black hole mass function and the correlations of
the black hole mass both with stellar velocity dispersion and host dark halo
mass. Moreover, the evolution of the black hole mass density derived from the
present simulations agrees with that derived from the bolometric luminosity
function of quasars, indicating that the average accretion history of seeds is
adequately reproduced . However, our simulations are unable to form black holes
with masses above at , whose existence is inferred
from the bright quasars detected by the Sloan survey in this redshift range.Comment: Talk given at the International Workshop on Astronomy and
Relativistic Astrophysics (IWARA 2009), Maresias, Brazil. to be published in
the International Journal of Modern Physics
Coalescence Rate of Supermassive Black Hole Binaries Derived from Cosmological Simulations: Detection Rates for LISA and ET
The coalescence history of massive black holes has been derived from
cosmological simulations, in which the evolution of those objects and that of
the host galaxies are followed in a consistent way. The present study indicates
that supermassive black holes having masses greater than underwent up to 500 merger events along their history. The derived
coalescence rate per comoving volume and per mass interval permitted to obtain
an estimate of the expected detection rate distribution of gravitational wave
signals ("ring-down") along frequencies accessible by the planned
interferometers either in space (LISA) or in the ground (Einstein). For LISA,
in its original configuration, a total detection rate of about is
predicted for events having a signal-to-noise ratio equal to 10, expected to
occur mainly in the frequency range . For the Einstein gravitational
wave telescope, one event each 14 months down to one event each 4 years is
expected with a signal-to-noise ratio of 5, occurring mainly in the frequency
interval . The detection of these gravitational signals and their
distribution in frequency would be in the future an important tool able to
discriminate among different scenarios explaining the origin of supermassive
black holes.Comment: 18 pages, 7 figures, to appear in the IJMP
Cyclic di-GMP inactivates T6SS and T4SS activity in Agrobacterium tumefaciens
© 2019 The Authors. The Type VI secretion system (T6SS) is a bacterial nanomachine that delivers effector proteins into prokaryotic and eukaryotic preys. This secretion system has emerged as a key player in regulating the microbial diversity in a population. In the plant pathogen Agrobacterium tumefaciens, the signalling cascades regulating the activity of this secretion system are poorly understood. Here, we outline how the universal eubacterial second messenger cyclic diâGMP impacts the production of T6SS toxins and T6SS structural components. We demonstrate that this has a significant impact on the ability of the phytopathogen to compete with other bacterial species in vitro and in planta. Our results suggest that, as opposed to other bacteria, câdiâGMP turns down the T6SS in A. tumefaciens thus impacting its ability to compete with other bacterial species within the rhizosphere. We also demonstrate that elevated levels of câdiâGMP within the cell decrease the activity of the Type IV secretion system (T4SS) and subsequently the capacity of A. tumefaciens to transform plant cells. We propose that such peculiar control reflects on câdiâGMP being a key second messenger that silences energyâcosting systems during early colonization phase and biofilm formation, while low câdiâGMP levels unleash T6SS and T4SS to advance plant colonization.Biotechnology and Biological Sciences Research Council. Grant Numbers: BB/L007959/1, BB/M02735X/1
Ministry of Science and Technology, Taiwan. Grant Number: 104-2311-B-001-025-MY
Appearances can be deceptive: Revealing a hidden viral infection with deep sequencing in a plant quarantine context
Comprehensive inventories of plant viral diversity are essential for effective quarantine and sanitation efforts. The safety of
regulated plant material exchanges presently relies heavily on techniques such as PCR or nucleic acid hybridisation, which
are only suited to the detection and characterisation of specific, well characterised pathogens. Here, we demonstrate the
utility of sequence-independent next generation sequencing (NGS) of both virus-derived small interfering RNAs (siRNAs)
and virion-associated nucleic acids (VANA) for the detailed identification and characterisation of viruses infecting two
quarantined sugarcane plants. Both plants originated from Egypt and were known to be infected with Sugarcane streak
Egypt Virus (SSEV; Genus Mastrevirus, Family Geminiviridae), but were revealed by the NGS approaches to also be infected by
a second highly divergent mastrevirus, here named Sugarcane white streak Virus (SWSV). This novel virus had escaped
detection by all routine quarantine detection assays and was found to also be present in sugarcane plants originating from
Sudan. Complete SWSV genomes were cloned and sequenced from six plants and all were found to share .91% genomewide
identity. With the exception of two SWSV variants, which potentially express unusually large RepA proteins, the SWSV
isolates display genome characteristics very typical to those of all other previously described mastreviruses. An analysis of
virus-derived siRNAs for SWSV and SSEV showed them to be strongly influenced by secondary structures within both
genomic single stranded DNA and mRNA transcripts. In addition, the distribution of siRNA size frequencies indicates that
these mastreviruses are likely subject to both transcriptional and post-transcriptional gene silencing. Our study stresses the
potential advantages of NGS-based virus metagenomic screening in a plant quarantine setting and indicates that such
techniques could dramatically reduce the numbers of non-intercepted virus pathogens passing through plant quarantine
stations
Appearances can be deceptive: revealing a hidden viral infection with deep sequencing in a plant quarantine context
Comprehensive inventories of plant viral diversity are essential for effective quarantine and sanitation efforts. The safety of regulated plant material exchanges presently relies heavily on techniques such as PCR or nucleic acid hybridisation, which are only suited to the detection and characterisation of specific, well characterised pathogens. Here, we demonstrate the utility of sequence-independent next generation sequencing (NGS) of both virus-derived small interfering RNAs (siRNAs) and virion-associated nucleic acids (VANA) for the detailed identification and characterisation of viruses infecting two quarantined sugarcane plants. Both plants originated from Egypt and were known to be infected with Sugarcane streak Egypt Virus (SSEV; Genus Mastrevirus, Family Geminiviridae), but were revealed by the NGS approaches to also be infected by a second highly divergent mastrevirus, here named Sugarcane white streak Virus (SWSV). This novel virus had escaped detection by all routine quarantine detection assays and was found to also be present in sugarcane plants originating from Sudan. Complete SWSV genomes were cloned and sequenced from six plants and all were found to share .91% genomewide identity. With the exception of two SWSV variants, which potentially express unusually large RepA proteins, the SWSV isolates display genome characteristics very typical to those of all other previously described mastreviruses. An analysis of virus-derived siRNAs for SWSV and SSEV showed them to be strongly influenced by secondary structures within both genomic single stranded DNA and mRNA transcripts. In addition, the distribution of siRNA size frequencies indicates that these mastreviruses are likely subject to both transcriptional and post-transcriptional gene silencing. Our study stresses the potential advantages of NGS-based virus metagenomic screening in a plant quarantine setting and indicates that such techniques could dramatically reduce the numbers of non-intercepted virus pathogens passing through plant quarantine stations
Report of a workshop on technical approaches to construction of a seafloor geomagnetic observatory
This report considers the technical issues on sensors, data recording and transmission, control and timing, power, and
packaging associated with constricting a seafloor geomagnetic observatory. Existing technologies either already in use for
oceanographic purposes or adapted from terrestral geomagnetic observatories could be applied to measure the vector
magnetic field components and absolute intensity with minimal development. The major technical challenge arises in
measuring absolute direction on the seafloor because terrestral techniques are not transferrable to the deep ocean. Two
solutions to this problem were identified. The first requires the development of an instrument which measures the
instantaneous declination and inclination of the magnetic field relative to a north-seeking gyroscope and the local vertical.
The second is a straightforward extension of a precision acoustic method for determining absolute position on the seafloor.Funding was provided by the National Science Foundation under grant EAR94-21712 and the
National Aeronautics and Space Administration
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