4,645 research outputs found
Non-thermal radio emission from O-type stars. V. 9 Sgr
The colliding winds in a massive binary system generate synchrotron emission
due to a fraction of electrons that have been accelerated to relativistic
speeds around the shocks in the colliding-wind region. We studied the radio
light curve of 9 Sgr = HD 164794, a massive O-type binary with a 9.1-yr period.
We investigated whether the radio emission varies consistently with orbital
phase and we determined some parameters of the colliding-wind region. We
reduced a large set of archive data from the Very Large Array (VLA) to
determine the radio light curve of 9 Sgr at 2, 3.6, 6 and 20 cm. We also
constructed a simple model that solves the radiative transfer in the
colliding-wind region and both stellar winds. The 2-cm radio flux shows clear
phase-locked variability with the orbit. The behaviour at other wavelengths is
less clear, mainly due to a lack of observations centred on 9 Sgr around
periastron passage. The high fluxes and nearly flat spectral shape of the radio
emission show that synchrotron radiation dominates the radio light curve at all
orbital phases. The model provides a good fit to the 2-cm observations,
allowing us to estimate that the brightness temperature of the synchrotron
radiation emitted in the colliding-wind region at 2 cm is at least 4 x 10^8 K.
The simple model used here already allows us to derive important information
about the colliding-wind region. We propose that 9 Sgr is a good candidate for
more detailed modelling, as the colliding-wind region remains adiabatic during
the whole orbit thus simplifying the hydrodynamics.Comment: 10 pages, 3 figures, accepted for publication in A&
Massive non-thermal radio emitters: new data and their modelling
During recent years some non-thermal radio emitting OB stars have been
discovered to be binary, or multiple systems. The non-thermal emission is due
to synchrotron radiation that is emitted by electrons accelerated up to high
energies. The electron acceleration occurs at the strong shocks created by the
collision of radiatively-driven winds. Here we summarize the available radio
data and more recent observations for the binary Cyg OB2 No. 9. We also show a
new emission model which is being developed to compare the theoretical total
radio flux and the spectral index with the observed radio light curves. This
comparison will be useful in order to solve fundamental questions, such as the
determination of the stellar mass loss rates, which are perturbed by clumping.Comment: 3 pages, 1 figure, poster at Four Decades of Research on Massive
Stars-A Scientific Meeting in Honour of Anthony F.J.Moffa
Manganese-56 coincidence-counting facility precisely measures neutron-source strength
Precise measurement of neutron-source strength is provided by a manganese 56 coincidence-counting facility using the manganese-bath technique. This facility combines nuclear instrumentation with coincidence-counting techniques to handle a wide variety of radioisotope-counting requirements
The 2.35 year itch of Cyg OB2 #9. II. Radio monitoring
Cyg OB2 #9 is one of a small set of non-thermal radio emitting massive O-star
binaries. The non-thermal radiation is due to synchrotron emission in the
colliding-wind region. Cyg OB2 #9 was only recently discovered to be a binary
system and a multi-wavelength campaign was organized to study its 2011
periastron passage. We report here on the results of the radio observations
obtained in this monitoring campaign. We used the Expanded Very Large Array
(EVLA) radio interferometer to obtain 6 and 20 cm continuum fluxes. The
observed radio light curve shows a steep drop in flux sometime before
periastron. The fluxes drop to a level that is comparable to the expected
free-free emission from the stellar winds, suggesting that the non-thermal
emitting region is completely hidden at that time. After periastron passage,
the fluxes slowly increase. We introduce a simple model to solve the radiative
transfer in the stellar winds and the colliding-wind region, and thus determine
the expected behaviour of the radio light curve. From the asymmetry of the
light curve, we show that the primary has the stronger wind. This is somewhat
unexpected if we use the astrophysical parameters based on theoretical
calibrations. But it becomes entirely feasible if we take into account that a
given spectral type - luminosity class combination covers a range of
astrophysical parameters. The colliding-wind region also contributes to the
free-free emission, which can help to explain the high values of the spectral
index seen after periastron passage. Combining our data with older Very Large
Array (VLA) data allows us to derive a period P = 860.0 +- 3.7 days for this
system. With this period, we update the orbital parameters that were derived in
the first paper of this series.Comment: 10 pages, 4 figures, accepted for publication in A&
The development of Integrated Real Time Control to optimise storm water management for the combined sewer system of Rome
Increasing urbanisation and intensification of human activities are common
trends all over the world. The higher portion of impermeable urban surfaces
often leads to well known effects on storm water runoff and its polluting
potential for receiving waters. Despite the variety of structural solutions and
management practices proposed to mitigate the operational and environmental
impact of urban runoff, their application on existing drainage systems can often
be either ineffective at a metropolitan scale or unfeasible for a densely urbanised
territory. Among all the proposed alternatives, the real time control (RTC) of
drainage systems is proving more and more promising to dynamically regulate
the system capacity in response to intense rainfall. The combined sewer network
of Rome, historically built with high-capacity pipes to collect storm water from
both urban and natural catchments, holds significant potential for RTC of online
storage and combined sewer overflows, to optimise the global drainage capacity
and reduce the impact of discharges on local river quality. To assess the real
benefits, the potential limits and the feasibility of such a system for the city
sewers, a pilot study has been conducted on a 3,000 hectare sub-catchment. It
involved the development of a fast-response hydrodynamic simulation tool for
the sewer network, the definition and evaluation of RTC strategies and the
implementation of an environmental integrated telemetry system. As described
here, the study has highlighted significant margins for the optimisation of the
global network capacity without any major interventions on the physical assets,
as well as some critical issues to solve for a fully operational RTC application
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Full-field and anomaly initialization using a low-order climate model: a comparison and proposals for advanced formulations
Initialization techniques for seasonal-to-decadal climate predictions fall into two main categories; namely full-field initialization (FFI) and anomaly initialization (AI). In the FFI case the initial model state is replaced by the best possible available estimate of the real state. By doing so the initial error is efficiently reduced but, due to the unavoidable presence of model deficiencies, once the model is let free to run a prediction, its trajectory drifts away from the observations no matter how small the initial error is. This problem is partly overcome with AI where the aim is to forecast future anomalies by assimilating observed anomalies on an estimate of the model climate.
The large variety of experimental setups, models and observational networks adopted worldwide make it difficult to draw firm conclusions on the respective advantages and drawbacks of FFI and AI, or to identify distinctive lines for improvement. The lack of a unified mathematical framework adds an additional difficulty toward the design of adequate initialization strategies that fit the desired forecast horizon, observational network and model at hand.
Here we compare FFI and AI using a low-order climate model of nine ordinary differential equations and use the notation and concepts of data assimilation theory to highlight their error scaling properties. This analysis suggests better performances using FFI when a good observational network is available and reveals the direct relation of its skill with the observational accuracy. The skill of AI appears, however, mostly related to the model quality and clear increases of skill can only be expected in coincidence with model upgrades.
We have compared FFI and AI in experiments in which either the full system or the atmosphere and ocean were independently initialized. In the former case FFI shows better and longer-lasting improvements, with skillful predictions until month 30. In the initialization of single compartments, the best performance is obtained when the stabler component of the model (the ocean) is initialized, but with FFI it is possible to have some predictive skill even when the most unstable compartment (the extratropical atmosphere) is observed.
Two advanced formulations, least-square initialization (LSI) and exploring parameter uncertainty (EPU), are introduced. Using LSI the initialization makes use of model statistics to propagate information from observation locations to the entire model domain. Numerical results show that LSI improves the performance of FFI in all the situations when only a portion of the system's state is observed. EPU is an online drift correction method in which the drift caused by the parametric error is estimated using a short-time evolution law and is then removed during the forecast run. Its implementation in conjunction with FFI allows us to improve the prediction skill within the first forecast year.
Finally, the application of these results in the context of realistic climate models is discussed
Sediment Transport in Sewers: The Cesarina Combined Sewer Network
The polluting effects of storm water runoff on the receiving waterbodies
represent an increasingly relevant problem in developing urban areas. In
combined sewer pipes, transiting flood waves cause the alternation of sediment
erosion and deposition of the solid material transported by the flow. Combined
sewer deposit, mainly generated as an effect of such phenomena during the dry
weather period between two rain events, is generally a mix of sand and highly
polluting materials. Accumulation of sediments along a combined sewer network
is often the cause of dysfunctions in the drainage system itself and negative
impacts on the quality of receiving waters, due to the resuspension and overflow
of pollutants. Both aspects have been investigated for the combined sewer of
Rome thanks to an experimental catchment of about 2800 ha in the Cesarina –
S. Basilio area. Based on the simulations conducted, structural solutions were
proposed and evaluated, aimed at reducing the operational and environmental
problems related to sewer sediment. The results show noticeable margins for the
optimisation of the whole sewer system and for the reduction of its
environmental impact
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The pgip family in soybean and three other legume species: evidence for a birth-and-death model of evolution
Polygalacturonase-inhibiting proteins (PGIPs) are leucine-rich repeat (LRR) plant cell wall glycoproteins involved in plant immunity. They are typically encoded by gene families with a small number of gene copies whose evolutionary origin has been poorly investigated. Here we report the complete characterization of the full complement of the pgip family in soybean (Glycine max [L.] Merr.) and the characterization of the genomic region surrounding the pgip family in four legume species. Results: BAC clone and genome sequence analyses showed that the soybean genome contains two pgip loci. Each locus is composed of three clustered genes that are induced following infection with the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, and remnant sequences of pgip genes. The analyzed homeologous soybean genomic regions (about 126 Kb) that include the pgip loci are strongly conserved and this conservation extends also to the genomes of the legume species Phaseolus vulgaris L., Medicago truncatula Gaertn. and Cicer arietinum L., each containing a single pgip locus. Maximum likelihood-based gene trees suggest that the genes within the pgip clusters have independently undergone tandem duplication in each species. Conclusions: The paleopolyploid soybean genome contains two pgip loci comprised in large and highly conserved duplicated regions, which are also conserved in bean, M. truncatula and C. arietinum. The genomic features of these legume pgip families suggest that the forces driving the evolution of pgip genes follow the birth-and-death model, similar to that proposed for the evolution of resistance (R) genes of NBS-LRR-type
Intraluminal recanalization of long infrainguinal chronic total occlusions using the Crosser system
Purpose: To assess the safety and efficacy of a device for vibrational angioplasty in the
percutaneous intraluminal recanalization of long infrainguinal chronic total occlusions (CTO).
Technique: The Crosser CTO Recanalization System is a mechanical recanalization device
that uses high-frequency vibrational energy to disrupt and channel through fibrocalcific
plaque without harming the vessel wall, thus assisting in the recanalization of an occluded
artery. In 12 diabetic patients (7 men; median age 71 years, range 58–80) with critical limb
ischemia owing to long (median length 26 cm, range 21–32) infrainguinal CTOs resistant to
conventional guidewire techniques, the Crosser CTO Recanalization System was
successful in intraluminally crossing the occlusion in 9 (75%) patients in ,5 minutes
(mean 4:03 minutes). The safety endpoint (distal lumen guidewire position with no vessel
perforation or dissection) was achieved in all successful cases.
Conclusion: In our preliminary experience, the Crosser CTO Recanalization Catheter
decreased crossing time, was safe, and achieved a high rate of intraluminal recanalization
of long infrainguinal CTOs.
J Endovasc Ther. 2009;16:23–27
Key words: critical limb ischemia, chronic total occlusion, percutaneous interventions,
infrainguinal occlusion, intraluminal recanalization, vibrational energ
Dipyridylmethane ethers as ligands for luminescent Ir complexes
This work reports two new cationic heteroleptic cyclometalated iridium complexes, containing ether derivatives of di(pyridin-2-yl)methanol. The new ligands are based on dipyridin-2-ylmethane and are designed to obtain ether-based intermediates with extended electronic conjugation by insertion of π system such as phenyl, allyl and ethynyl. Different synthetic strategies were employed to introduce these units, as molecular wires, between the dipyridin-2-ylmethane chelating portion and the terminal N-containing functional group, such as amine and carbamide. The corresponding complexes show luminescence in the blue region of the spectrum, lifetimes between 0.6 and 2.1 μs, high quantum yield and good electrochemical behavior. The computational description (DFT) of the electronic structure highlights the key role of the conjugated π systems on optical and electrochemical properties of the final products
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