338 research outputs found
Understanding possible electromagnetic counterparts to loud gravitational wave events: Binary black hole effects on electromagnetic fields
In addition to producing loud gravitational waves (GW), the dynamics of a
binary black hole system could induce emission of electromagnetic (EM)
radiation by affecting the behavior of plasmas and electromagnetic fields in
their vicinity. We here study how the electromagnetic fields are affected by a
pair of orbiting black holes through the merger. In particular, we show how the
binary's dynamics induce a variability in possible electromagnetically induced
emissions as well as an enhancement of electromagnetic fields during the
late-merge and merger epochs. These time dependent features will likely leave
their imprint in processes generating detectable emissions and can be exploited
in the detection of electromagnetic counterparts of gravitational waves.Comment: 12 page
Are gauge shocks really shocks?
The existence of gauge pathologies associated with the Bona-Masso family of
generalized harmonic slicing conditions is proven for the case of simple 1+1
relativity. It is shown that these gauge pathologies are true shocks in the
sense that the characteristic lines associated with the propagation of the
gauge cross, which implies that the name ``gauge shock'' usually given to such
pathologies is indeed correct. These gauge shocks are associated with places
where the spatial hypersurfaces that determine the foliation of spacetime
become non-smooth.Comment: 7 pages, 5 figures, REVTEX 4. Revised version, including corrections
suggested by referee
Robustness of the Blandford-Znajek mechanism
The Blandford-Znajek mechanism has long been regarded as a key ingredient in
models attempting to explain powerful jets in AGNs, quasars, blazzars etc. In
such mechanism, energy is extracted from a rotating black hole and dissipated
at a load at far distances. In the current work we examine the behaviour of the
BZ mechanism with respect to different boundary conditions, revealing the
mechanism robustness upon variation of these conditions. Consequently, this
work closes a gap in our understanding of this important scenario.Comment: 7 pages, accepted in CQ
Coherence Resonance in Chaotic Systems
We show that it is possible for chaotic systems to display the main features
of coherence resonance. In particular, we show that a Chua model, operating in
a chaotic regime and in the presence of noise, can exhibit oscillations whose
regularity is optimal for some intermediate value of the noise intensity. We
find that the power spectrum of the signal develops a peak at finite frequency
at intermediate values of the noise. These are all signatures of coherence
resonance. We also experimentally study a Chua circuit and corroborate the
above simulation results. Finally, we analyze a simple model composed of two
separate limit cycles which still exhibits coherence resonance, and show that
its behavior is qualitatively similar to that of the chaotic Chua systemComment: 4 pages (including 4 figures) LaTeX fil
Global high-order numerical schemes for the time evolution of the general relativistic radiation magneto-hydrodynamics equations
Modeling correctly the transport of neutrinos is crucial in some
astrophysical scenarios such as core-collapse supernovae and binary neutron
star mergers. In this paper, we focus on the truncated-moment formalism,
considering only the first two moments (M1 scheme) within the grey
approximation, which reduces Boltzmann seven-dimensional equation to a system
of equations closely resembling the hydrodynamic ones. Solving the M1
scheme is still mathematically challenging, since it is necessary to model the
radiation-matter interaction in regimes where the evolution equations become
stiff and behave as an advection-diffusion problem. Here, we present different
global, high-order time integration schemes based on Implicit-Explicit
Runge-Kutta (IMEX) methods designed to overcome the time-step restriction
caused by such behavior while allowing us to use the explicit RK commonly
employed for the MHD and Einstein equations. Finally, we analyze their
performance in several numerical tests.Comment: 18 + 6. Updated manuscript matching published version + additional
appendix "Comparing the convergence order of IMEX and semi-implicit schemes
Effect of different digestates derived from anaerobic co-digestion of Olive Mill Solid Waste (OMSW) and various microalgae as fertilizers for the cultivation of ryegrass
Aims
The aim of this work was to evaluate the fertilizing effect of three anaerobic co-digestates on the growth of the herbaceous plant Lolium rigidum.
Methods
Nine treatments, combining different nutritional solutions (organic and inorganic) and number of fertilizations (one or two) were evaluated. Organic nutritive solution: plants grown with different olive mill solid waste (OMSW) -microalgae co-digestates: 75% OMSW-25% Raphidocelis subcapitata, volatile solids (VS) basis (OMSW-Rs); 50% OMSW- 50% Chlamydomonas Reinhardtii, VS basis (OMSW-Chl); and 75% OMSW-25% Secenedesmus quadricauda, VS basis (OMSW-Sq). Inorganic nutritive solution (INS): plants grown with inorganic Hoagland nutrient solution at 50%. After 60 days of experimentation, biometric and nutritional characteristics and photosynthetic activity were measured.
Results
The results showed a favourable growth, development and nutritional quality of L. rigidum plants when digestates obtained from the anaerobic co-digestion of OMSW-microalgae are used as organic nutritional solutions as opposed to INS ones. The highest total biomass of L. rigidum was obtained with the treatments that involved two fertilizations. No inhibition due to excess nutrients was observed. A higher root/shoot ratio was achieved with the digestates of OMSW-Rs and OMSW-Ch as compared to that obtained with OMSW-Sq (F = 17.23 p ≤ 0.001). The nitrogen shoot biomass obtained after the organic treatments with the above-mentioned co-digestates was higher than that obtained after the inorganic treatment. Net photosynthesis rates did not present differences in the co-digestates treatments, being equal or superior to the INS treatments.
Conclusions
The use of the anaerobic co-digestates from OMSW-microalgae can be considered a viable and promising alternative to inorganic fertilization
Intense Electromagnetic Outbursts from Collapsing Hypermassive Neutron Stars
We study the gravitational collapse of a magnetized neutron star using a
novel numerical approach able to capture both the dynamics of the star and the
behavior of the surrounding plasma. In this approach, a fully general
relativistic magnetohydrodynamics implementation models the collapse of the
star and provides appropriate boundary conditions to a force-free model which
describes the stellar exterior. We validate this strategy by comparing with
known results for the rotating monopole and aligned rotator solutions and then
apply it to study both rotating and non-rotating stellar collapse scenarios,
and contrast the behavior with what is obtained when employing the
electrovacuum approximation outside the star. The non-rotating electrovacuum
collapse is shown to agree qualitatively with a Newtonian model of the
electromagnetic field outside a collapsing star. We illustrate and discuss a
fundamental difference between the force-free and electrovacuum solutions,
involving the appearance of large zones of electric-dominated field in the
vacuum case. This provides a clear demonstration of how dissipative
singularities appear generically in the non-linear time-evolution of force-free
fluids. In both the rotating and non-rotating cases, our simulations indicate
that the collapse induces a strong electromagnetic transient. In the case of
sub-millisecond rotation, the magnetic field experiences strong winding and the
transient carries much more energy. This result has important implications for
models of gamma-ray bursts.Comment: 28 pages, 20 figures (quality lowered to reduce sizes). Improved
initial data and matching condition results in a lower, but still important,
energy emission. Added appendix with a discussion on effects of transition
laye
Opinions and beliefs held by Spanish teenagers regarding tobacco and alcohol consumption: A descriptive study
Background: Preventive strategies are the most effective approach for dealing with issues of substance abuse, particularly in teenagers. Such strategies adapt well to this target population. Our objective was to reveal the opinions and beliefs held by teenagers about tobacco and alcohol as types of drugs, and their effects on health.
Methods: In this cross-sectional study, participants completed a self-administered questionnaire based on the World Health Organization “Health Behaviour of School-aged Children” study. Our sample included 1,005 schoolchildren aged between 11 and 13 years, resident in the province of Co´rdoba in Spain. Descriptive and univariate analyses were performed using a chi-squared test.
Results: Of respondents, 25% (95% confidence interval [CI]: 22.2–27.6%) and 61% (95% CI: 58.0–64.1%), respectively, did not consider tobacco or alcohol to be drugs. No relationship was found between tobacco and alcohol use, and the belief that these are drugs (p = 0.477 and p = 0.217, respectively). A total 98.2% of adolescents surveyed (95% CI: 97.3–99.1%) believed that tobacco causes physical damage, mainly to the lungs, heart, and to the developing fetus. Additionally, 92.4% (95% CI: 90.6–94.0%) believed that alcohol is detrimental to health and identified the liver as the organ most frequently damaged by alcohol consumption. The media was identified as the main source of information about these substances by 78.0% of respondents (95% CI: 75.4–80.6%).
Conclusions: Teenagers possess an acceptable level of knowledge and information about the negative effects of tobacco and alcohol on health; however, many of them do not consider these substances to be drug
PELIGROSIDAD A LOS MOVIMIENTOS DE LADERA EN LA VERTIENTE MERIDIONAL DE SIERRA NEVADA (GRANADA) A PARTIR DE LA ESTIMACIÓN MULTI-TÉCNICA DE LA ACTIVIDAD
El presente trabajo aborda la cartografía de la susceptibilidad y la peligrosidad a los movimientos de
ladera, en un ambiente montañoso, con información limitada sobre su actividad. El análisis y validación
de la susceptibilidad se realizada mediante un modelo elaborado a partir del ModelBuilder™ de ArcGIS
basado en el Método de la Matriz en un SIG. Dicho modelo necesita una cartografía previa de los
movimientos, un MDE y un análisis discriminante de los factores determinantes de la estabilidad.
Los datos del análisis reflejan que el 15% de la zona estudiada muestra una susceptibilidad a los
movimientos de moderada a muy alta que, a su vez, coincide con lugares donde se encuentran la mayoría
de las infraestructuras públicas de la región. Además, los valores registrados en la validación mediante el
grado de ajuste están por encima del 83% para las zonas de susceptibilidad alta y muy alta.
Estas zonas que presentan un mayor grado de susceptibilidad y, por tanto, una mayor exposición potencial
al riesgo, son las seleccionadas para el análisis detallado de la peligrosidad. El principal problema, que,
por otra parte, suele ser generalizado en este tipo de áreas para la estimación de la frecuencia con la que
se suceden movimientos de ladera, es la falta de información sobre su ocurrencia.
Por tanto, y con el objetivo de obtener la mayor información posible, los datos relativos a la actividad de
los movimientos se extraen de diversas fuentes y técnicas, de forma que interactivamente solventen sus
correspondientes limitaciones. Estos datos se extraen de una documentación previa, tanto en prensa como
bibliografía específica, donde se presentan trabajos sobre DInSAR, fotogrametría aérea y LIDAR, y TLS.
Además, se realiza de forma específica un análisis dendrogeomorfológico de árboles en movimientos de
ladera y se revisa la ortofotografía aérea histórica de la zona de estudio.
Posteriormente, con los datos de actividad, se realiza un análisis de los factores desencadenantes, que
refleja que los movimientos de ladera están relacionados con episodios de precipitaciones intensas y
prolongadas, y no tanto con la actividad sísmica del área.
Por último, de forma indirecta, se estima la peligrosidad de la zona de estudio a los movimientos de
ladera, asociando los resultados obtenidos de actividad con los factores desencadenantes; esto es, con
periodos de precipitaciones intensas. Así, se establece un periodo de retorno que se extrapola a toda el
área, con la asunción de que los grandes deslizamientos se generan o reactivan, conjuntamente con
movimientos superficiales, tras periodos lluviosos intensos y prolongados, y que las lluvias torrenciales
generan movimientos de ladera superficiales tipo flujo y desprendimientos.
Los resultados obtenidos indican que la frecuencia con la que se generan los movimientos es de 5 años
para los flujos superficiales y desprendimientos (F=0,2), y de 18 años para los deslizamientos y
movimientos complejos (F=0,06). La zona, en términos generales, presenta determinados sectores con
susceptibilidad moderada a muy alta, sin embargo la peligrosidad a los movimientos de ladera es de
moderada a muy baja. En términos de probabilidad temporal, los flujos y desprendimientos son los
movimientos con mayor peligrosidad
Relativistic MHD with Adaptive Mesh Refinement
This paper presents a new computer code to solve the general relativistic
magnetohydrodynamics (GRMHD) equations using distributed parallel adaptive mesh
refinement (AMR). The fluid equations are solved using a finite difference
Convex ENO method (CENO) in 3+1 dimensions, and the AMR is Berger-Oliger.
Hyperbolic divergence cleaning is used to control the
constraint. We present results from three flat space tests, and examine the
accretion of a fluid onto a Schwarzschild black hole, reproducing the Michel
solution. The AMR simulations substantially improve performance while
reproducing the resolution equivalent unigrid simulation results. Finally, we
discuss strong scaling results for parallel unigrid and AMR runs.Comment: 24 pages, 14 figures, 3 table
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