1,940 research outputs found
The central parsecs of M87: jet emission and an elusive accretion disc
We present the first simultaneous spectral energy distribution (SED) of M87
core at a scale of 0.4 arcsec () across the electromagnetic
spectrum. Two separate, quiescent, and active states are sampled that are
characterized by a similar featureless SED of power-law form, and that are thus
remarkably different from that of a canonical active galactic nuclei (AGN) or a
radiatively inefficient accretion source. We show that the emission from a jet
gives an excellent representation of the core of M87 core covering ten orders
of magnitude in frequency for both the active and the quiescent phases. The
inferred total jet power is, however, one to two orders of magnitude lower than
the jet mechanical power reported in the literature. The maximum luminosity of
a thin accretion disc allowed by the data yields an accretion rate of , assuming 10% efficiency. This power
suffices to explain M87 radiative luminosity at the jet-frame, it is however
two to three order of magnitude below that required to account for the jet's
kinetic power. The simplest explanation is variability, which requires the core
power of M87 to have been two to three orders of magnitude higher in the last
200 yr. Alternatively, an extra source of power may derive from black hole
spin. Based on the strict upper limit on the accretion rate, such spin power
extraction requires an efficiency an order of magnitude higher than predicted
from magnetohydrodynamic simulations, currently in the few hundred per cent
range.Comment: 18 pages, 6 figures. Accepted for publication in MNRA
Soil P and cation availability and crop uptake in a forage rotation under conventional and reduced tillage
Long-term conservation tillage can modify vertical distribution of nutrients in soil profiles and alter nutrient availability and yields of crops
Effects of fire and three fire-fighting chemicals on main soil properties, plant nutrient content and vegetation growth and cover after 10 years.
The study addresses a knowledge-gap in the long-term ecological consequences of fire and fire-fighting
chemicals. Ten years after a prescribed fire and the application of three fire-fighting chemicals, their effects
on the soil-plant system were evaluated. Five treatments were established: unburnt soils (US) and burnt
soils treated with water alone (BS), foaming agent (BS+Fo), Firesorb (BS+Fi) and ammonium polyphosphate
(BS+Ap). Soils (0-2 cm depth) and foliar material of shrubs (Erica umbellata, Pterospartum tridentatum and
Ulex micranthus) and trees (Pinus pinaster) were analysed for total N, 15N, and soil-available and plant total
macronutrients and trace elements. Soil pH, NH4
+-N and NO3
--N; pine basal diameter and height; and shrub
cover and height were also measured. Compared with US plots, burnt soils had less nitrates and more Mo.
Although differences were not always significant, BS+Ap had the highest levels of soil available P, Na and
Al. Plants from BS+Ap plots had higher values of 15N (P. pinaster and E. umbellata), P (all species), Na (P.
tridentatum and U. micranthus) and Mg (E. umbellata and P. tridentatum) than other treatments; while K in
plants from BS+Ap plots was the highest among treatments for P. pinaster and the lowest for the shrubs.
Pines in US plots were higher and wider than in burnt treatments, except for BS+Ap, where the tallest and
widest trees were found, although half of them were either death (the second highest mortality after BS+Fi)
or had a distorted trunk. BS+Ap was the treatment with strongest effects on plants, showing E. umbellata
the lowest coverage and height, P. tridentatum the highest coverage, U. micranthus one of the lowest
coverages and being the only treatment where Genista triacanthos was absent. Consequently, it is concluded
that both fire and ammonium polyphosphate application had significant effects on the soil-plant system
after 10 years.Peer reviewe
Indicadores clave de sostenibilidad en sistemas de montaña. El caso del corredor seco guatemalteco
Las zonas de montaña tienen particularidades únicas que han de ser tenidas en cuenta para elaborar cualquier plan de desarrollo sostenible. En estas áreas, la falta de accesos,la fragilidad de los suelos, la marginalidad de las tierras y la heterogeneidad de sus condiciones KÃsicas, hacen que las estrategias de adaptación de sus habitantes sean aún más
dinámicas y variadas de las que pudiera tener cualquier sistema campesino de noFaltura, lo que plantea un desafÃo añadido
Blockchain-based architecture for the control of logistics activities: Pharmaceutical utilities case study
Logistics services involve a wide range of transport operations between distributors and clients. Currently, the large number of
intermediaries are a challenge for this sector, as it makes all the processes more complicated. To face that problem, we propose
a system that uses smart contracts to remove intermediaries and speed up logistics activities. Our new model combines smart
contracts and a multi-agent system in a single platform to improve the current logistics system by increasing organization,
security and getting rid of several human intermediaries to automate its processes, making distribution times significantly
faster. Also, with this kind of approach, it is possible to apply penalties to parties that do not comply with the terms of using
this platform.This work was developed as part of ‘Virtual Ledger Technologies DLT/Blockchain y Cripto-IOT sobre organizaciones virtuales de agentes ligeros y su aplicación en la eficiencia en el transporte de última milla’, ID SA267P18, project cofinanced by Junta Castilla y León, ConsejerÃa de Educación and FEDER funds. Also, the research work carried out by Yeray Mezquita is supported by the pre-doctoral fellowship from the University of Salamanca and Banco Santander
Synthesis of optimal digital shapers with arbitrary noise using a genetic algorithm
This paper presents structure, design and implementation of a novel technique for determining the optimal shaping, in time-domain, for spectrometers by means of a Genetic Algorithm (GA) specifically designed for this purpose. The proposed algorithm is able to adjust automatically the coefficients for shaping an input signal. Results of this experiment have been compared to a previous simulated annealingalgorithm. Finally, its performance and capabilities were tested using simulation data and a real particle detector, as a scintillator.Ministerio de Ciencia e Innovació
Impact of converter losses on the optimal power flow solution of hybrid networks based on VSC-MTDC
This paper studies the impact of voltage source converter (VSC) losses on the solution of the optimal power flow (OPF) of hybrid AC/DC systems with a multi-terminal configuration. The motivation of this analysis is that the expected development of high voltage direct current (HVDC) systems will entail an increase of the number of converter stations, and consequently, converter losses might not be negligible when compared with conventional transmission losses of AC and DC lines. Towards this end, an extended OPF model is proposed considering a combination of VSC based multi-terminal HVDC grids (VSC-MTDC) and AC systems. The OPF model represents converter losses according to the state-of-the art modeling where different expressions are used when the converter functions as an inverter or as a rectifier. Three simpler alternative approaches are also implemented and the obtained OPF solutions are assessed. In order to compare the OPF solutions, a comparison metric is proposed. Obtained results show that modeling the converter losses in a simplified way could lead to very different power flow solutions, especially for the DC branches.Postprint (author's final draft
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